Trace elements at the intersection of marine biological and geochemical evolution

USGS Publications Warehouse

Robbins, Leslie J.; Lalonde, Stefan V.; Planavsky, Noah J.; Partin, Camille A.; Reinhard, Christopher T.; Kendall, Brian; Scott, Clinton T.; Hardisty, Dalton S.; Gill, Benjamin C.; Alessi, Daniel S.; Dupont, Christopher L.; Saito, Mak A.; Crowe, Sean A.; Poulton, Simon W.; Bekker, Andrey; Lyons, Timothy W.; Konhauser, Kurt O.

2016-01-01

Life requires a wide variety of bioessential trace elements to act as structural components and reactive centers in metalloenzymes. These requirements differ between organisms and have evolved over geological time, likely guided in some part by environmental conditions. Until recently, most of what was understood regarding trace element concentrations in the Precambrian oceans was inferred by extrapolation, geochemical modeling, and/or genomic studies. However, in the past decade, the increasing availability of trace element and isotopic data for sedimentary rocks of all ages has yielded new, and potentially more direct, insights into secular changes in seawater composition – and ultimately the evolution of the marine biosphere. Compiled records of many bioessential trace elements (including Ni, Mo, P, Zn, Co, Cr, Se, and I) provide new insight into how trace element abundance in Earth's ancient oceans may have been linked to biological evolution. Several of these trace elements display redox-sensitive behavior, while others are redox-sensitive but not bioessential (e.g., Cr, U). Their temporal trends in sedimentary archives provide useful constraints on changes in atmosphere-ocean redox conditions that are linked to biological evolution, for example, the activity of oxygen-producing, photosynthetic cyanobacteria. In this review, we summarize available Precambrian trace element proxy data, and discuss how temporal trends in the seawater concentrations of specific trace elements may be linked to the evolution of both simple and complex life. We also examine several biologically relevant and/or redox-sensitive trace elements that have yet to be fully examined in the sedimentary rock record (e.g., Cu, Cd, W) and suggest several directions for future studies.

Rare Earth Element and Trace Element Data Associated with Hydrothermal Spring Reservoir Rock, Idaho

DOE Data Explorer

Quillinan, Scott; Bagdonas, Davin

2017-06-22

These data represent rock samples collected in Idaho that correspond with naturally occurring hydrothermal samples that were collected and analyzed by INL (Idaho Falls, ID). Representative samples of type rocks were selected to best represent the various regions of Idaho in which naturally occurring hydrothermal waters occur. This includes the Snake River Plain (SRP), Basin and Range type structures east of the SRP, and large scale/deep seated orogenic uplift of the Sawtooth Mountains, ID. Analysis includes ICP-OES and ICP-MS methods for Major, Trace, and REE concentrations.

Trace element content of gossans at four mines in the West Shasta massive sulfide district.

USGS Publications Warehouse

Sanzolone, R.F.; Domenico, J.A.

1985-01-01

Paired analyses of the spongy whole-rock gossan and its botryoidal crust ("chipped rock rind') show little differences, whereas duplicate samples of each at individual sites show such extreme differences as to preclude the use of the data in areal mapping. Gossans from disseminated sulphides have lower and less variable trace-element contents than gossans from massive sulphides, due in part to dilution by rock silicates. Computer reduction of the data by a regionalizing algorithm enables determination of pattern differences among the four mines.-G.J.N.

Different origins of garnet in high pressure to ultrahigh pressure metamorphic rocks

NASA Astrophysics Data System (ADS)

Xia, Qiong-Xia; Zhou, Li-Gang

2017-09-01

Garnet in high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in subduction zone commonly shows considerable zonation in major and trace elements as well as mineral inclusions, which bears information on its growth mechanism via metamorphic or peritectic reactions in coexistence with relic minerals and metamorphic fluids or anatectic melts at subduction-zone conditions. It provides an important target to retrieve physicochemical changes in subduction-zone processes, including those not only in pressure and temperature but also in the durations of metamorphism and anatexis. Garnet from different compositions of HP to UHP metamorphic rocks may show different types of major and trace element zonation, as well as mineral inclusions. Discrimination between the different origins of garnet provides important constraints on pressure and temperature and the evolution history for the HP to UHP metamorphic rocks. Magmatic garnet may occur as relics in granitic gneisses despite metamorphic modification at subduction-zone conditions, with spessartine-increasing or flat major element profiles from inner to outer core and exceptionally higher contents of trace elements than metamorphic mantle and rim. Metamorphic garnet can grow at different metamorphic stages during prograde subduction and retrograde exhumation, with spessartine-decreasing from core to rim if the intracrystalline diffusion is not too fast. The compositional profiles of metamorphic garnet in the abundances of grossular, almandine and pyrope are variable depending on the composition of host rocks and co-existing minerals. Peritectic garnet grows through peritectic reactions during partial melting of HP to UHP rocks, with the composition of major elements to be controlled by anatectic P-T conditions and the compositions of parental rocks and anatectic melts. Trace element profiles in garnet with different origins are also variable depending on the coexisting mineral assemblages, the garnet-forming reactions and the property of metamorphic fluids or anatectic melts. Mineral inclusions not only present key clues to identify the different origins of garnet, but also serve as sound candidates for the temporal constraint on garnet growth.

Trace elements in Zn Pb Ag deposits and related stream sediments, Brooks Range Alaska, with implications for Tl as a pathfinder element

USGS Publications Warehouse

Graham, G.E.; Kelley, K.D.; Slack, J.F.; Koenig, A.E.

2009-01-01

The Zn-Pb-Ag metallogenic province of the western and central Brooks Range, Alaska, contains two distinct but mineralogically similar deposit types: shale-hosted massive sulphide (SHMS) and smaller vein-breccia occurrences. Recent investigations of the Red Dog and Anarraaq SHMS deposits demonstrated that these deposits are characterized by high trace-element concentrations of As, Ge, Sb and Tl. This paper examines geochemistry of additional SHMS deposits (Drenchwater and Su-Lik) to determine which trace elements are ubiquitously elevated in all SHMS deposits. Data from several vein-breccia occurrences are also presented to see if trace-element concentrations can distinguish SHMS deposits from vein-breccia occurrences. Whole-rock geochemical data indicate that Tl is the most consistently and highly concentrated characteristic trace element in SHMS deposits relative to regional unmineralized rock samples. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of pyrite and sphalerite indicate that Tl is concentrated in pyrite in SHMS. Stream sediment data from the Drenchwater and Su-Lik SHMS show that high Tl concentrations are more broadly distributed proximal to known or suspected mineralization than As, Sb, Zn and Pb anomalies. This broader distribution of Tl in whole-rock and particularly stream sediment samples increases the footprint of exposed and shallowly buried SHMS mineralization. High Tl concentrations also distinguish SHMS mineralization from the vein-breccia deposits, as the latter lack high concentrations of Tl but can otherwise have similar trace-element signatures to SHMS deposits. ?? 2009 AAG/Geological Society of London.

Quantitative analysis of major and trace elements in NH4HF2-modified silicate rock powders by laser ablation - inductively coupled plasma mass spectrometry.

PubMed

Zhang, Wen; Hu, Zhaochu; Liu, Yongsheng; Yang, Wenwu; Chen, Haihong; Hu, Shenghong; Xiao, Hongyan

2017-08-29

In this paper, we described a NH 4 HF 2 digestion method as sample preparation for the rapid determination of major and trace elements in silicate rocks using laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS). Sample powders digested by NH 4 HF 2 at 230 °C for 3 h form ultrafine powders with a typical grain size d 80  < 8.5 μm, and various silicate rocks have a consistent grain morphology and size, allowing us to produce pressed powder pellets that have excellent cohesion and homogeneity suitable for laser ablation micro-analysis without the addition of binder. The influences of the digestion parameters were investigated and optimized, including the evaporation stage of removing residual NH 4 HF 2 , sample homogenization, selection of the digestion vessel and calibration strategy of quantitative analysis. The optimized NH 4 HF 2 digestion method was applied to dissolve six silicate rock reference materials (BCR-2, BHVO-2, AGV-2, RGM-2, GSP-2, GSR-1) covering a wide range of rock types. Ten major elements and thirty-five trace elements were simultaneously analyzed by LA-ICP-MS. The analytical results of the six reference materials generally agreed with the recommended values, with discrepancies of less than 10% for most elements. The analytical precision is within 5% for most major elements and within 10% for most trace elements. Compared with previous methods of LA-ICP-MS bulk analysis, our method enables the complete dissolution of refractory minerals, such as zircon, in intermediate-acidic intrusive rocks and limits contamination as well as the loss of volatile elements. Moreover, there are many advantages for the new technique, including reducing matrix effects between reference materials and samples, spiking the internal standard simply and feasibly and sample batch processing. The applicability filed of the new technique in this study was focused on the whole-rock analysis of igneous rock samples, which are from basic rocks to acid rocks (45% < SiO 2  < 73%). However, we thought that the NH 4 HF 2 digestion method can be used as a new alternative in LA-ICP-MS for a wider range of geological samples, and will significantly accelerate the application of LA-ICP-MS for the whole-rock analysis. Copyright © 2017 Elsevier B.V. All rights reserved.

Characterization of frictional melting processes in subduction zone faults by trace element and isotope analyses

NASA Astrophysics Data System (ADS)

Ishikawa, T.; Ujiie, K.

2017-12-01

Pseudotachylytes found in exhumed accretionary complexes, which are considered to be formed originally at seismogenic depths, are of great importance for elucidating frictional melting and concomitant dynamic weakening of the fault during earthquake in subduction zones. However, fluid-rich environment of the subduction zone faults tends to cause extensive alteration of the pseudotachylyte glass matrix in later stages, and thus it has been controversial that pseudotachylytes are rarely formed or rarely preserved. Chemical analysis of the fault rocks, especially on fluid-immobile trace elements and isotopes, can be a useful means to identify and quantify the frictional melting occurred in subduction zone faults. In this paper, we report major and trace element and Sr isotope compositions for pseudotachylyte-bearing dark veins and surrounding host rocks from the Mugi area of the Shimanto accretionary complex (Ujiie et al., J. Struct. Geol. 2007). Samples were collected from a rock chip along the microstructure using a micro-drilling technique, and then analyzed by ICP-MS and TIMS. Major element compositions of the dark veins showed a clear shift from the host rock composition toward the illite composition. The dark veins, either unaltered or completely altered, were also characterized by extreme enrichment in some of the trace elements such as Ti, Zr, Nb and Th. These results are consistent with disequilibrium melting of the fault zone. Model calculations revealed that the compositions of the dark veins can be produced by total melting of clay-rich matrix in the source rock, leaving plagioclase and quartz grains almost unmolten. The calculations also showed that the dark veins are far more enriched in melt component than that expected from the source rock compositions, suggesting migration and concentration of frictional melt during the earthquake faulting. Furthermore, Sr isotope data of the dark veins implied the occurrence of frictional melting in multiple stages. These results demonstrate that trace element and isotope analyses are useful not only to detect preexistence of pseudotachylytes but also to evaluate the frictional melting in subduction zone faults quantitatively.

Determination of major elements by wavelength-dispersive X-ray fluorescence spectrometry and trace elements by inductively coupled plasma mass spectrometry in igneous rocks from the same fused sample (110 mg)

NASA Astrophysics Data System (ADS)

Amosova, Alena A.; Panteeva, Svetlana V.; Chubarov, Victor M.; Finkelshtein, Alexandr L.

2016-08-01

The fusion technique is proposed for simultaneous determination of 35 elements from the same sample. Only 110 mg of rock sample was used to obtain fused glasses for quantitative determination of 10 major elements by wavelength dispersive X-ray fluorescence analysis, 16 rare earth elements and some other trace elements by inductively coupled plasma mass spectrometry analysis. Fusion was performed with 1.1 g of lithium metaborate and LiBr solution as the releasing agent in platinum crucible in electric furnace at 1100 °C. The certified reference materials of ultramafic, mafic, intermediate and felsic igneous rocks have been applied to obtain the calibration curves for rock-forming oxides (Na2O, MgO, Al2O3, SiO2, P2O5, K2O, CaO, TiO2, MnO, Fe2O3) and some trace elements (Ba, Sr, Zr) determination by X-ray fluorescence analysis. The repeatability does not exceed the allowable standard deviation for a wide range of concentrations. In the most cases the relative standard deviation was less than 5%. Obtained glasses were utilized for the further determination of rare earth (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and some other (Ba, Sr, Zr, Rb, Cs, Y, Nb, Hf, Ta, Th and U) trace elements by inductively coupled plasma mass spectrometry analysis with the same certified reference materials employed. The results could mostly be accepted as satisfactory. The proposed procedure essentially reduces the expenses in comparison with separate sample preparation for inductively coupled plasma mass spectrometry and X-ray fluorescence analysis.

Leaching of boron, arsenic and selenium from sedimentary rocks: I. Effects of contact time, mixing speed and liquid-to-solid ratio.

PubMed

Tabelin, Carlito Baltazar; Hashimoto, Ayaka; Igarashi, Toshifumi; Yoneda, Tetsuro

2014-02-15

Sedimentary rocks of marine origin excavated in tunnel projects were recently identified as potentially hazardous because they could release significant amounts of toxic trace elements when exposed to the environment. This study investigated the leaching characteristics of B, As, Se and the major coexisting ions under various conditions to identify the factors and processes controlling their evolution in the leachate. In addition, we evaluated whether the parameters of the currently used leachability test for excavated rocks were adequate. Although the leachabilities of B, As and Se similarly increased at longer contact times, only those of B and As were influenced by the mixing speed and/or liquid-to-solid ratio (L/S). The majority of trace elements dissolved in the leachate originated from the dissolution of soluble salts formed from seawater of the Cretaceous trapped during the formation of the sedimentary rocks. Moreover, the alkaline pH of the leachates could be attributed to the simultaneous dissolutions at varying degrees of the mineral components of the rocks as well as the precipitation of clay minerals. In the leaching test of excavated rocks for regulatory purposes, the best values of contact time and mixing speed should represent conditions of the highest trace element extractabilities, which in this study were found at longer contact times (>48 h) and the fastest mixing speed (200 rpm). The most appropriate L/S for the leaching test is 10 because it was around this L/S that the extractabilities and leaching concentrations of the trace elements were simultaneously observed at their highest values. Copyright © 2013 Elsevier B.V. All rights reserved.

Leaching of boron, arsenic and selenium from sedimentary rocks: II. pH dependence, speciation and mechanisms of release.

PubMed

Tabelin, Carlito Baltazar; Hashimoto, Ayaka; Igarashi, Toshifumi; Yoneda, Tetsuro

2014-03-01

Sedimentary rocks excavated in Japan from road- and railway-tunnel projects contain relatively low concentrations of hazardous trace elements like boron (B), arsenic (As) and selenium (Se). However, these seemingly harmless waste rocks often produced leachates with concentrations of hazardous trace elements that exceeded the environmental standards. In this study, the leaching behaviors and release mechanisms of B, As and Se were evaluated using batch leaching experiments, sequential extraction and geochemical modeling calculations. The results showed that B was mostly partitioned with the residual/crystalline phase that is relatively stable under normal environmental conditions. In contrast, the majority of As and Se were associated with the exchangeable and organics/sulfides phases that are unstable under oxidizing conditions. Dissolution of water-soluble phases controlled the leaching of B, As and Se from these rocks in the short term, but pyrite oxidation, calcite dissolution and adsorption/desorption reactions became more important in the long term. The mobilities of these trace elements were also strongly influenced by the pH of the rock-water system. Although the leaching of Se only increased in the acidic region, those of B and As were enhanced under both acidic and alkaline conditions. Under strongly acidic conditions, the primarily release mechanism of B, As and Se was the dissolution of mineral phases that incorporated and/or adsorbed these elements. Lower concentrations of these trace elements in the circumneutral pH range could be attributed to their strong adsorption onto minerals like Al-/Fe-oxyhydroxides and clays, which are inherently present and/or precipitated in the rock-water system. The leaching of As and B increased under strongly alkaline conditions because of enhanced desorption and pyrite oxidation while that of Se remained minimal due to its adsorption onto Fe-oxyhydroxides and co-precipitation with calcite. Copyright © 2013 Elsevier B.V. All rights reserved.

Green and Fast Laser Fusion Technique for Bulk Silicate Rock Analysis by Laser Ablation-Inductively Coupled Plasma Mass Spectrometry.

PubMed

Zhang, Chenxi; Hu, Zhaochu; Zhang, Wen; Liu, Yongsheng; Zong, Keqing; Li, Ming; Chen, Haihong; Hu, Shenghong

2016-10-18

Sample preparation of whole-rock powders is the major limitation for their accurate and precise elemental analysis by laser ablation inductively-coupled plasma mass spectrometry (ICPMS). In this study, a green, efficient, and simplified fusion technique using a high energy infrared laser was developed for major and trace elemental analysis. Fusion takes only tens of milliseconds for each sample. Compared to the pressed pellet sample preparation, the analytical precision of the developed laser fusion technique is higher by an order of magnitude for most elements in granodiorite GSP-2. Analytical results obtained for five USGS reference materials (ranging from mafic to intermediate to felsic) using the laser fusion technique generally agree with recommended values with discrepancies of less than 10% for most elements. However, high losses (20-70%) of highly volatile elements (Zn and Pb) and the transition metal Cu are observed. The achieved precision is within 5% for major elements and within 15% for most trace elements. Direct laser fusion of rock powders is a green and notably simple method to obtain homogeneous samples, which will significantly accelerate the application of laser ablation ICPMS for whole-rock sample analysis.

Trace-element evidence for the origin of desert varnish by direct aqueous atmospheric deposition

NASA Astrophysics Data System (ADS)

Thiagarajan, Nivedita; Aeolus Lee, Cin-Ty

2004-07-01

Smooth rock surfaces in arid environments are often covered with a thin coating of Fe-Mn oxyhydroxides known as desert varnish. It is debated whether such varnish is formed (a) by slow diagenesis of dust particles deposited on rock surfaces, (b) by leaching from the underlying rock substrate, or (c) by direct deposition of dissolved constituents in the atmosphere. Varnishes collected from smooth rock surfaces in the Mojave Desert and Death Valley, California are shown here to have highly enriched and fractionated trace-element abundances relative to upper continental crust (UCC). They are highly enriched in Co, Ni, Pb and the rare-earth elements (REEs). In particular, they have anomalously high Ce/La and low Y/Ho ratios. These features can only be explained by preferential scavenging of Co, Ni, Pb and the REEs by Fe-Mn oxyhydroxides in an aqueous environment. High field strength elements (HFSEs: Zr, Hf, Ta, Nb, Th), however, show only small enrichments despite the fact that these elements should also be strongly scavenged by Fe-Mn oxyhydroxides. This suggests that their lack of enrichment is a feature inherited from a solution initially poor in HFSEs. The first two scenarios for varnish formation can be ruled out as follows. The high enrichment factors of Fe, Mn and many trace elements cannot be generated by mass loss associated with post-depositional diagenesis of dust particles because such a process predicts only a small increase in concentration. In addition, the highly fractionated abundance patterns of particle reactive element pairs (e.g., Ce/La and Y/Ho) rules out leaching of the rock substrate. This is because if leaching were to occur, varnishes would grow from the inside to the outside, and thus any particle-reactive trace element leached from the substrate would be quantitatively sequestered in the Fe-Mn oxyhydroxide layers, prohibiting any significant elemental fractionations. One remaining possibility is that the Fe, Mn and trace metals in varnish are derived from leaching of dust particles entrained in rain or fog droplets either in the atmosphere or during wet atmospheric deposition. The high trace metal enrichment factors require that most of the dust was physically removed before or during varnish formation. The remaining aqueous counterpart would be depleted in HFSEs and Th relative to the REEs, Co, Ni and Pb because the former are more insoluble and hence largely retained in the removed dust fraction. The high Ce/La ratios suggest that precipitation of trace metals may have been governed by equilibrium partitioning in an excess of wet atmospheric deposition. If varnishes are indeed derived from wet atmospheric deposition, they may provide a record of the aqueous component of atmospheric dust inputs to various environments.

No Martian soil component in shergottite meteorites

NASA Astrophysics Data System (ADS)

Barrat, J. A.; Jambon, A.; Ferrière, L.; Bollinger, C.; Langlade, J. A.; Liorzou, C.; Boudouma, O.; Fialin, M.

2014-01-01

We report on the major and trace element geochemistry of the impact melts contained in some shergottite meteorites. It has been previously proposed that some of these impact melts formed from a mixture of the host rock and a Martian soil component (e.g., Rao et al., 1999) or from partially weathered portions of the host rock (Chennaoui Aoudjehane et al., 2012). Our results contradict both of these theories. Trace element abundances of a glass pod from the EETA 79001A meteorite are identical to those of the host lithology, and indicate that no additional component is required in this case. The impact melts in Tissint share the same trace element features as the host rock, and no secondary phases produced by Martian secondary processes are involved. The light rare earth enrichments displayed by two small samples of Tissint (Chennaoui Aoudjehane et al., 2012) are possibly the result of some contamination of small stones on desert soil before the recovery of the meteorites.

Geochemistry of continental subduction-zone fluids

NASA Astrophysics Data System (ADS)

Zheng, Yong-Fei; Hermann, Joerg

2014-12-01

The composition of continental subduction-zone fluids varies dramatically from dilute aqueous solutions at subsolidus conditions to hydrous silicate melts at supersolidus conditions, with variable concentrations of fluid-mobile incompatible trace elements. At ultrahigh-pressure (UHP) metamorphic conditions, supercritical fluids may occur with variable compositions. The water component of these fluids primarily derives from structural hydroxyl and molecular water in hydrous and nominally anhydrous minerals at UHP conditions. While the breakdown of hydrous minerals is the predominant water source for fluid activity in the subduction factory, water released from nominally anhydrous minerals provides an additional water source. These different sources of water may accumulate to induce partial melting of UHP metamorphic rocks on and above their wet solidii. Silica is the dominant solute in the deep fluids, followed by aluminum and alkalis. Trace element abundances are low in metamorphic fluids at subsolidus conditions, but become significantly elevated in anatectic melts at supersolidus conditions. The compositions of dissolved and residual minerals are a function of pressure-temperature and whole-rock composition, which exert a strong control on the trace element signature of liberated fluids. The trace element patterns of migmatic leucosomes in UHP rocks and multiphase solid inclusions in UHP minerals exhibit strong enrichment of large ion lithophile elements (LILE) and moderate enrichment of light rare earth elements (LREE) but depletion of high field strength elements (HFSE) and heavy rare earth elements (HREE), demonstrating their crystallization from anatectic melts of crustal protoliths. Interaction of the anatectic melts with the mantle wedge peridotite leads to modal metasomatism with the generation of new mineral phases as well as cryptic metasomatism that is only manifested by the enrichment of fluid-mobile incompatible trace elements in orogenic peridotites. Partial melting of the metasomatic mantle domains gives rise to a variety of mafic igneous rocks in collisional orogens and their adjacent active continental margins. The study of such metasomatic processes and products is of great importance to understanding of the mass transfer at the slab-mantle interface in subduction channels. Therefore, the property and behavior of subduction-zone fluids are a key for understanding of the crust-mantle interaction at convergent plate margins.

Trace element evaluation of a suite of rocks from Reunion Island, Indian Ocean

USGS Publications Warehouse

Zielinski, R.A.

1975-01-01

Reunion Island consists of an olivine-basalt shield capped by a series of flows and intrusives ranging from hawaiite through trachyte. Eleven rocks representing the total compositional sequence have been analyzed for U, Th and REE. Eight of the rocks (group 1) have positive-slope, parallel, chondrite-normalized REE fractionation patterns. Using a computer model, the major element compositions of group 1 whole rocks and observed phenocrysts were used to predict the crystallization histories of increasingly residual liquids, and allowed semi-quantitative verification of origin by fractional crystallization of the olivine-basalt parent magma. Results were combined with mineral-liquid distribution coefficient data to predict trace element abundances, and existing data on Cr, Ni, Sr and Ba were also successfully incorporated in the model. The remaining three rocks (group 2) have nonuniform positive-slope REE fractionation patterns not parallel to group 1 patterns. Rare earth fractionation in a syenite is explained by partial melting of a source rich in clinopyroxene and/or hornblende. The other two rocks of group 2 are explained as hybrids resulting from mixing of syenite and magmas of group 1. ?? 1975.

Accessory minerals and subduction zone metasomatism: a geochemical comparison of two mélanges (Washington and California, U.S.A.)

USGS Publications Warehouse

Sorensen, Sorena S.; Grossman, Jeffrey N.

1993-01-01

Data from the Gee Point and Catalina mélanges suggest that the accessory minerals titanite, rutile, apatite, zircon and REE-rich epidote play a significant role in the enrichment of trace elements in both mafic and ultramafic rocks during subduction-related fluid-rock interaction. Mobilization of incompatible elements, and deposition of such elements in the accessory minerals of mafic and ultramafic rocks may be fairly common in fluid-rich metamorphic environments in subduction zones.

Mineral chemistry of magnetite from magnetite-apatite mineralization and their host rocks: examples from Kiruna, Sweden, and El Laco, Chile

NASA Astrophysics Data System (ADS)

Broughm, Shannon G.; Hanchar, John M.; Tornos, Fernando; Westhues, Anne; Attersley, Samuel

2017-12-01

Interpretation of the mineralizing environment of magnetite-apatite deposits remains controversial with theories that include a hydrothermal or magmatic origin or a combination of those two processes. To address this controversy, we have analyzed the trace element content of magnetite from precisely known geographic locations and geologic environments from the Precambrian magnetite-apatite ore and host rocks in Kiruna, Sweden, and the Pliocene-Holocene El Laco volcano in the Atacama desert of Chile. Magnetite samples from Kiruna have low trace element concentrations with little chemical variation between the ore, host, and related intrusive rocks. Magnetite from andesite at El Laco, and dacite from the nearby Láscar volcano, has high trace element concentrations typical of magmatic magnetite. El Laco ore magnetite have low trace element concentrations and displays growth zoning in incompatible elements (Si, Ca, and Ce), compatible elements (Mg, Al, and Mn), large-ion lithophile element (Sr), and high field strength element (Y, Nb, and Th). The El Laco ore magnetite are similar in composition to magnetite that has been previously interpreted to have crystallized from hydrothermal fluids; however, there is a significant difference in the internal zoning patterns. At El Laco, each zoned element is either enriched or depleted in the same layers, suggesting the magnetite crystallized from a volatile-rich, iron-oxide melt. In general, the compositions of magnetite from these two deposits plot in very wide fields that are not restricted to the proposed fields in published discriminant diagrams. This suggests that the use of these diagrams and genetic models based on them should be used with caution.

Trace Elements in River Waters

NASA Astrophysics Data System (ADS)

Gaillardet, J.; Viers, J.; Dupré, B.

2003-12-01

Trace elements are characterized by concentrations lower than 1 mg L-1 in natural waters. This means that trace elements are not considered when "total dissolved solids" are calculated in rivers, lakes, or groundwaters, because their combined mass is not significant compared to the sum of Na+, K+, Ca2+, Mg2+, H4SiO4, HCO3-, CO32-, SO42-, Cl-, and NO3-. Therefore, most of the elements, except about ten of them, occur at trace levels in natural waters. Being trace elements in natural waters does not necessarily qualify them as trace elements in rocks. For example, aluminum, iron, and titanium are major elements in rocks, but they occur as trace elements in waters, due to their low mobility at the Earth's surface. Conversely, trace elements in rocks such as chlorine and carbon are major elements in waters.The geochemistry of trace elements in river waters, like that of groundwater and seawater, is receiving increasing attention. This growing interest is clearly triggered by the technical advances made in the determination of concentrations at lower levels in water. In particular, the development of inductively coupled plasma mass spectrometry (ICP-MS) has considerably improved our knowledge of trace-element levels in waters since the early 1990s. ICP-MS provides the capability of determining trace elements having isotopes of interest for geochemical dating or tracing, even where their dissolved concentrations are extremely low.The determination of trace elements in natural waters is motivated by a number of issues. Although rare, trace elements in natural systems can play a major role in hydrosystems. This is particularly evident for toxic elements such as aluminum, whose concentrations are related to the abundance of fish in rivers. Many trace elements have been exploited from natural accumulation sites and used over thousands of years by human activities. Trace elements are therefore highly sensitive indexes of human impact from local to global scale. Pollution impact studies require knowledge of the natural background concentrations and knowledge of pollutant behavior. For example, it is generally accepted that rare earth elements (REEs) in waters behave as good analogues for the actinides, whose natural levels are quite low and rarely measured. Water quality investigations have clearly been a stimulus for measurement of toxic heavy metals in order to understand their behavior in natural systems.From a more fundamental point of view, it is crucial to understand the behavior of trace elements in geological processes, in particular during chemical weathering and transport by waters. Trace elements are much more fractionated by weathering and transport processes than major elements, and these fractionations give clues for understanding the nature and intensity of the weathering+transport processes. This has not only applications for weathering studies or for the past mobilization and transport of elements to the ocean (potentially recorded in the sediments), but also for the possibility of better utilization of trace elements in the aqueous environment as an exploration tool.In this chapter, we have tried to review the recent literature on trace elements in rivers, in particular by incorporating the results derived from recent ICP-MS measurements. We have favored a "field approach" by focusing on studies of natural hydrosystems. The basic questions which we want to address are the following: What are the trace element levels in river waters? What controls their abundance in rivers and fractionation in the weathering+transport system? Are trace elements, like major elements in rivers, essentially controlled by source-rock abundances? What do we know about the chemical speciation of trace elements in water? To what extent do colloids and interaction with solids regulate processes of trace elements in river waters? Can we relate the geochemistry of trace elements in aquatic systems to the periodic table? And finally, are we able to satisfactorily model and predict the behavior of most of the trace elements in hydrosystems?An impressive literature has dealt with experimental works on aqueous complexation, uptake of trace elements by surface complexation (inorganic and organic), uptake by living organisms (bioaccumulation) that we have not reported here, except when the results of such studies directly explain natural data. As continental waters encompass a greater range of physical and chemical conditions, we focus on river waters and do not discuss trace elements in groundwaters, lakes, and the ocean. In lakes and in the ocean, the great importance of life processes in regulating trace elements is probably the major difference from rivers.Section 5.09.2 of this chapter reports data. We will review the present-day literature on trace elements in rivers to show that our knowledge is still poor. By comparing with the continental abundances, a global mobility index is calculated for each trace element. The spatial and temporal variability of trace-element concentrations in rivers will be shown to be important. In Section 5.09.3, sources of trace elements in river waters are indicated. We will point out the great diversity of sources and the importance of global anthropogenic contamination for a number of elements. The question of inorganic and organic speciation of trace elements in river water will then be addressed in Section 5.09.4, considering some general relationships between speciation and placement in the periodic table. In Section 5.09.5, we will show that studies on organic-rich rivers have led to an exploration of the "colloidal world" in rivers. Colloids are small particles, passing through the conventional filters used to separate dissolved and suspended loads in rivers. They appear as major carriers of trace elements in rivers and considerably complicate aqueous-speciation calculation. Finally, in Section 5.09.6, the significance of interactions between solutes and solid surfaces in river waters will be reviewed. Regulation by surfaces is of major importance for a great range of elements. Although for both colloids and surface interactions, some progress has been made, we are still far from a unified model that can accurately predict trace-element concentrations in natural water systems. This is mainly due to our poor physical description of natural colloids, surface site complexation, and their interaction with solutes.

A new method for automated discontinuity trace mapping on rock mass 3D surface model

NASA Astrophysics Data System (ADS)

Li, Xiaojun; Chen, Jianqin; Zhu, Hehua

2016-04-01

This paper presents an automated discontinuity trace mapping method on a 3D surface model of rock mass. Feature points of discontinuity traces are first detected using the Normal Tensor Voting Theory, which is robust to noisy point cloud data. Discontinuity traces are then extracted from feature points in four steps: (1) trace feature point grouping, (2) trace segment growth, (3) trace segment connection, and (4) redundant trace segment removal. A sensitivity analysis is conducted to identify optimal values for the parameters used in the proposed method. The optimal triangular mesh element size is between 5 cm and 6 cm; the angle threshold in the trace segment growth step is between 70° and 90°; the angle threshold in the trace segment connection step is between 50° and 70°, and the distance threshold should be at least 15 times the mean triangular mesh element size. The method is applied to the excavation face trace mapping of a drill-and-blast tunnel. The results show that the proposed discontinuity trace mapping method is fast and effective and could be used as a supplement to traditional direct measurement of discontinuity traces.

Lu-Hf, in-situ Sr and Pb isotope and trace element systematics for mantle eclogites from the Diavik diamond mine: Evidence for Paleoproterozoic subduction beneath the Slave craton, Canada

NASA Astrophysics Data System (ADS)

Schmidberger, Stefanie S.; Simonetti, Antonio; Heaman, Larry M.; Creaser, Robert A.; Whiteford, Sean

2007-02-01

Lu-Hf, Sm-Nd and in-situ clinopyroxene Sr and Pb isotope systematics, and mineral major and in-situ trace element compositions were obtained for a suite of non-diamond and diamond-bearing eclogites from the Diavik kimberlites (A154; 55 Ma old), Slave craton (Canada). Temperature estimates of last equilibration in the lithosphere for the non-diamond-bearing Diavik eclogites define two groups; low-temperature (800-1050 °C) and high-temperature eclogites (1100-1300 °C). Most diamond-eclogites indicate temperatures similar to those of the high-temperature eclogites. Isotopic and major and trace element systematics for the non-diamond- and diamond-bearing eclogites indicate overlapping chemical compositions suggesting similar rock formational histories. Calculated whole rock major and trace element abundances using chemical and modal abundances for constituent minerals exhibit broad similarities with mafic cumulates from ophiolite sequences. Most importantly the calculated whole rock eclogite compositions display positive Sr and Eu anomalies, typically interpreted as the result of plagioclase accumulation in cumulate rocks of oceanic crust sequences. Initial whole rock Hf isotopic values and in-situ Sr isotope data from clinopyroxene grains provide evidence that the eclogites were derived from precursor rocks with depleted mantle isotope characteristics. These combined results support the interpretation that the eclogites from Diavik represent remnants of subducted oceanic crust. Lu-Hf isotope systematics indicate that the oceanic protolith for the eclogites formed in the Paleoproterozoic at ˜ 2.1 Ga, which is in agreement with the in-situ Pb isotope data from clinopyroxene. This result also corroborates the ˜ 2.1 Ga Lu-Hf model ages recorded by mantle zircons from eclogite found within the Jericho kimberlite in the northern Slave Province (˜ 200 km northwest of Diavik). The results from both studies indicate a link between eclogite formation and Paleoproterozoic subduction of oceanic lithosphere along the present-day western margin of the Archean Slave craton.

Stages of weathering mantle formation from carbonate rocks in the light of rare earth elements (REE) and Sr-Nd-Pb isotopes

NASA Astrophysics Data System (ADS)

Hissler, Christophe; Stille, Peter

2015-04-01

Weathering mantles are widespread and include lateritic, sandy and kaolinite-rich saprolites and residuals of partially dissolved rocks. These old regolith systems have a complex history of formation and may present a polycyclic evolution due to successive geological and pedogenetic processes that affected the profile. Until now, only few studies highlighted the unusual high content of associated trace elements in weathering mantles originating from carbonate rocks, which have been poorly studied, compared to those developing on magmatic bedrocks. For instance, these enrichments can be up to five times the content of the underlying carbonate rocks. However, these studies also showed that the carbonate bedrock content only partially explains the soil enrichment for all the considered major and trace elements. Up to now, neither soil, nor saprolite formation has to our knowledge been geochemically elucidated. Therefore, the aim of this study was to examine more closely the soil forming dynamics and the relationship of the chemical soil composition to potential sources. REE distribution patterns and Sr-Nd-Pb isotope ratios have been used because they are particularly well suited to identify trace element migration, to recognize origin and mixing processes and, in addition, to decipher possible anthropogenic and/or "natural" atmosphere-derived contributions to the soil. Moreover, leaching experiments have been applied to identify mobile phases in the soil system and to yield information on the stability of trace elements and especially on their behaviour in these Fe-enriched carbonate systems. All these geochemical informations indicate that the cambisol developing on such a typical weathering mantle ("terra fusca") has been formed through weathering of a condensed Bajocian limestone-marl facies. This facies shows compared to average world carbonates important trace element enrichments. Their trace element distribution patterns are similar to those of the soil suggesting their close genetic relationships. Sr-Nd-Pb isotope data allow to identify four principal components in the soil: a silicate-rich pool at close to the surface, a leachable REE enriched pool at the bottom of the soil profile, the limestone facies on which the weathering profile developed and an anthropogenic, atmosphere-derived component detected in the soil leachates of the uppermost soil horizon. The leachable phases are mainly secondary carbonate-bearing REE phases such as bastnaesite. The isotope data and trace element distribution patterns indicate that at least four geological and environmental events impacted the chemical and isotopical compositions of the soil system since the Cretaceous.

Magma Chamber of the 26.5 ka Oruanui Eruption, Taupo Volcano, New Zealand

NASA Astrophysics Data System (ADS)

Liu, Y.; Anderson, A. T.; Wilson, C. J.; Davis, A. M.

2004-12-01

We have investigated melt inclusions and their host quartz crystals from the Bishop-Tuff-sized 26.5 ka Oruanui eruption at Taupo volcano, New Zealand. Compositions (major and trace elements, H2O and CO2) of melt inclusions and cathodoluminescence (CL) images of quartz were obtained for eight individual pumices from early, middle and late depositional units. All melt inclusions are high-silica weakly peraluminous rhyolites. Melt inclusions for different eruptive phases have similar ranges of H2O contents (3.8-5.2 wt %), but late-erupted samples have higher CO2 contents (mostly > 140 ppm). A positive correlation between CO2 and compatible trace elements such as Sr suggests that crystallization and melt entrapment occurred under gas-saturated conditions. Trace elements variations in melt inclusions are consistent with fractionation of 30-40 wt % crystals (plagioclase+quartz+pyroxene+amphibole). Crystal contents in pumices, trace-element contents in melt inclusions, and CL zoning patterns of quartz show no correlation with eruptive phases, suggesting that the Oruanui magma was well mixed before eruption. Some Oruanui quartz crystals contain distinctive CL zonings with a jagged ('restitic') core mantled by a black CL zone. Trace element variations in melt inclusions in the 'restitic' cores are consistent with fractionation of Ba-bearing minerals such as sanidine and/or biotite, both of which are rare or absent in rocks erupted from Taupo volcanic center. The above evidence suggests that Oruanui rhyolite is generated by assimilation of previous intruded rocks or country rocks, differentiated by crystal fractionation, and then mixed prior to eruption. Despite the differences in trace element and volatile contents, and crystal assemblages, both Bishop Tuff and Oruanui magmas involve crystal fractionation as one of the main differentiation mechanisms during their evolution. However, there are pronounced differences in the pre-eruptive stratification of the two chambers, which may reflect the tectonic settings, eruption rates, and ages of the systems.

Distribution of siderophile and other trace elements in melt rock at the Chicxulub impact structure

NASA Technical Reports Server (NTRS)

Schuraytz, B. C.; Lindstrom, D. J.; Martinez, R. R.; Sharpton, V. L.; Marin, L. E.

1994-01-01

Recent isotopic and mineralogical studies have demonstrated a temporal and chemical link between the Chicxulub multiring impact basin and ejecta at the Cretaceous-Tertiary boundary. A fundamental problem yet to be resolved, however, is identification of the projectile responsible for this cataclysmic event. Drill core samples of impact melt rock from the Chichxulub structure contain Ir and Os abundances and Re-Os isotopic ratios indicating the presence of up to approx. 3 percent meteoritic material. We have used a technique involving microdrilling and high sensitivity instrumental neutron activation analysis (INAA) in conjunction with electron microprobe analysis to characterize further the distribution of siderophile and other trace elements among phases within the C1-N10 melt rock.

Granulite-facies rocks in the Whatley Mill gneiss, Pine Mountain basement massif, Eastern Alabama

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daniell, N.; Salpas, P.A.

1993-03-01

The Pine Mountain basement massif is a granulite terrane exposed in a tectonic window through the Inner Piedmont of western Georgia and eastern Alabama. Investigations of the westernmost extent of the massif, the Whatley Mill Gneiss, have revealed four distinct lithologies: (1) an augen gneiss, the type lithology; (2) mylonite that develops in the shear zones cutting the unit; (3) a phaneritic rock showing weak to no foliation; (4) enclaves of biotite gneiss within the weakly-foliated rock. Additionally, the weakly-foliated rock comprises two distinct phases which are in sharp contact along curved and undulating boundaries: phase 1 is a coarser-grainedmore » rock; phase 2 is a finer-grained rock of the same mineralogy as phase 1 except it contains rare hypersthene. This first recorded observation of hypersthene unequivocally confirms the granulite-facies origin of the unit. Major and trace element compositions of the phase 1 rock are identical to those of the augen gneiss. The phase 2 rock, has a distinct composition with higher SiO[sub 2] and lower incompatible trace elements than the phase 1 rock. The enclaves display a range in major elements but higher incompatible elements than the other lithologies. Geochemical and petrologic relationships leads one to interpret: (1) the weakly-foliated rock retains many of its primary igneous features including its two phases and enclaves; (2) the two phases of the weakly-foliated rock arose as a result of injection of one magma (phase 2) into a cooler, crystal mush solidifying from another magma (phase 1); (3) the enclaves represent either autoliths of xenoliths; (4) the augen gneiss arose by isochemical deformation of the phase 1 rock.« less

Bioturbating animals control the mobility of redox-sensitive trace elements in organic-rich mudstone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harazim, Dario; McIlroy, Duncan; Edwards, Nicholas P.

Bioturbating animals modify the original mineralogy, porosity, organic content, and fabric of mud, thus affecting the burial diagenetic pathways of potential hydrocarbon source, seal, and reservoir rocks. High-sensitivity, synchrotron rapid scanning X-ray fluorescence elemental mapping reveals that producers of phycosiphoniform burrows systematically partition redox-sensitive trace elements (i.e., Fe, V, Cr, Mn, Co, Ni, Cu, and As) in fine-grained siliciclastic rocks. Systematic differences in organic carbon content (total organic carbon >1.5 wt%) and quality (Δ 13C org~0.6‰) are measured between the burrow core and host sediment. The relative enrichment of redox-sensitive elements in the burrow core does not correlate with significantmore » neo-formation of early diagenetic pyrite (via trace metal pyritization), but is best explained by physical concentration of clay- and silt-sized components. A measured loss (~–15%) of the large-ionic-radius elements Sr and Ba from both burrow halo and core is most likely associated with the release of Sr and Ba to pore waters during biological ( in vivo) weathering of silt- to clay-sized lithic components and feldspar. In conclusion, this newly documented effect has significant potential to inform the interpretation of geochemical proxy and rock property data, particularly from shales, where elemental analyses are commonly employed to predict reservoir quality and support paleoenvironmental analysis.« less

Bioturbating animals control the mobility of redox-sensitive trace elements in organic-rich mudstone

DOE PAGES

Harazim, Dario; McIlroy, Duncan; Edwards, Nicholas P.; ...

2015-10-07

Bioturbating animals modify the original mineralogy, porosity, organic content, and fabric of mud, thus affecting the burial diagenetic pathways of potential hydrocarbon source, seal, and reservoir rocks. High-sensitivity, synchrotron rapid scanning X-ray fluorescence elemental mapping reveals that producers of phycosiphoniform burrows systematically partition redox-sensitive trace elements (i.e., Fe, V, Cr, Mn, Co, Ni, Cu, and As) in fine-grained siliciclastic rocks. Systematic differences in organic carbon content (total organic carbon >1.5 wt%) and quality (Δ 13C org~0.6‰) are measured between the burrow core and host sediment. The relative enrichment of redox-sensitive elements in the burrow core does not correlate with significantmore » neo-formation of early diagenetic pyrite (via trace metal pyritization), but is best explained by physical concentration of clay- and silt-sized components. A measured loss (~–15%) of the large-ionic-radius elements Sr and Ba from both burrow halo and core is most likely associated with the release of Sr and Ba to pore waters during biological ( in vivo) weathering of silt- to clay-sized lithic components and feldspar. In conclusion, this newly documented effect has significant potential to inform the interpretation of geochemical proxy and rock property data, particularly from shales, where elemental analyses are commonly employed to predict reservoir quality and support paleoenvironmental analysis.« less

Chemical Analyses of Pre-Holocene Rocks from Medicine Lake Volcano and Vicinity, Northern California

USGS Publications Warehouse

Donnelly-Nolan, Julie M.

2008-01-01

Chemical analyses are presented in an accompanying table (Table 1) for more than 600 pre-Holocene rocks collected at and near Medicine Lake Volcano, northern California. The data include major-element X-ray fluorescence (XRF) analyses for all of the rocks plus XRF trace element data for most samples, and instrumental neutron activation analysis (INAA) trace element data for many samples. In addition, a limited number of analyses of Na2O and K2O by flame photometry (FP) are included as well assome wet chemical analyses of FeO, H2O+/-, and CO2. Latitude and longitude location information is provided for all samples. This data set is intended to accompany the geologic map of Medicine Lake Volcano (Donnelly-Nolan, in press); map unit designations are given for each sample collected from the map area.

Major and trace element concentrations in samples from 72275 and 72255. [chemical composition of lunar rocks

NASA Technical Reports Server (NTRS)

Haskin, L. A.; Blanchard, D. P.; Korotev, R.; Jacobs, J. W.; Brannon, J. A.; Herrmann, A. G.

1974-01-01

Analytical data have been obtained for Co, Sc, Hf, Zn, Cr, Ga, Rb, Cs, Ni, major elements, and rare earth elements in eight samples from boulder 1. The data for trace elements were obtained by radiochemical neutron activation analysis. Major elements, except Na and Mn, were obtained by atomic absorption spectral photometry. Values for Na and Mn were obtained by neutron activation analysis of the same powder that was later dissolved to provide the atomic absorption analyses.

Publications - RDF 2005-5 | Alaska Division of Geological & Geophysical

Science.gov Websites

content DGGS RDF 2005-5 Publication Details Title: Major-oxide, minor-oxide, and trace-element geochemical ., and Lessard, R.R., 2005, Major-oxide, minor-oxide, and trace-element geochemical data from rocks ; Zinc; Zirconium Top of Page Department of Natural Resources, Division of Geological & Geophysical

Publications - GMC 264 | Alaska Division of Geological & Geophysical

Science.gov Websites

DGGS GMC 264 Publication Details Title: X-ray fluorescence trace element data of the following U.S for more information. Bibliographic Reference Werdon, M.B., 1996, X-ray fluorescence trace element . Bureau of Mines hard rock mineral pulp samples from the Colville mining district: West Kivliktort

Isotopic and trace element variability in altered and unaltered tuffs at Yucca Mountain, Nevada

USGS Publications Warehouse

Peterman, Z.E.; Spengler, R.W.; Singer, F.R.; Dickerson, R.P.

1993-01-01

Reference stratigraphic sections near Yucca Mountain, Nevada were established and sampled in outcrop areas where the volcanic rocks have been minimally altered. Isotopic and trace element analyses obtained for these reference sections are baseline data for assessing the degree and extent of element mobility attendant with past zonal alteration of the rock mass. In agreement with earlier studies, zeolitization is shown to have occurred under wholesale open-system conditions. Calcium was increased by two three times the baseline values and strontium up to twenty times. In contrast, barium displays less variability, and the high-field strength elements zirconium and titanium were the least mobile during zeolitization. The data reported here establish the usefulness of reference sections of assessing past elements mobility. The information gained will be helpful in predicting possible future element mobility induced by thermally activated fluids in the near field of a potential repository.

Publications - RDF 2015-14 | Alaska Division of Geological & Geophysical

Science.gov Websites

content DGGS RDF 2015-14 Publication Details Title: Jumbo Dome, interior Alaska: Whole-rock, major- and , 2015, Jumbo Dome, interior Alaska: Whole-rock, major- and trace-element analyses: Alaska Division of

Earth's first stable continents did not form by subduction

NASA Astrophysics Data System (ADS)

Johnson, Tim; Brown, Michael; Gardiner, Nicholas; Kirkland, Christopher; Smithies, Hugh

2017-04-01

The geodynamic setting in which Earth's first stable cratonic nuclei formed remains controversial. Most exposed Archaean continental crust comprises rocks of the tonalite-trondhjemite-granodiorite (TTGs) series that were produced from partial melting of low magnesium basaltic source rocks and have 'arc-like' trace element signatures that resemble continental crust produced in modern supra-subduction zone settings. The East Pilbara Terrane, Western Australia, is amongst the oldest fragments of preserved continental crust of Earth. Low magnesium basalts of the Paleoarchaean Coucal Formation, at the base of the Pilbara Supergroup, have trace element compositions consistent with the putative source rocks for TTGs. These basalts may be remnants of the ≥35 km-thick pre-3.5 Ga plateau-like basaltic crust that is predicted to have formed if mantle temperatures were much hotter than today. Using phase equilibria modelling of an average uncontaminated Coucal basalt, we confirm their suitability as TTG source rocks. The results suggest that TTGs formed by 20-30% melting along high geothermal gradients (≥700 °C/GPa), which accord with apparent geotherms recorded by >95% of Archaean rocks worldwide. Moreover, the trace element composition of the Coucal basalts demonstrates that they were derived from an earlier generation of mafic/ultramafic rocks, and that the arc-like signature in Archaean TTGs was inherited through an ancestral source lineage. The protracted multistage process required for production and stabilisation of Earth's first continents, coupled with the high geothermal gradients, are incompatible with modern-style subduction and favour a stagnant lid regime in the early Archaean.

Trace elements and radon in groundwater across the United States, 1992-2003

USGS Publications Warehouse

Ayotte, Joseph D.; Gronberg, Jo Ann M.; Apodaca, Lori E.

2011-01-01

Trace-element concentrations in groundwater were evaluated for samples collected between 1992 and 2003 from aquifers across the United States as part of the U.S. Geological Survey National Water-Quality Assessment Program. This study describes the first comprehensive analysis of those data by assessing occurrence (concentrations above analytical reporting levels) and by comparing concentrations to human-health benchmarks (HHBs). Data from 5,183 monitoring and drinking-water wells representing more than 40 principal and other aquifers in humid and dry regions and in various land-use settings were used in the analysis. Trace elements measured include aluminum (Al), antimony (Sb), arsenic (As), barium (Ba), beryllium (Be), boron (B), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), lithium (Li), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se), silver (Ag), strontium (Sr), thallium (Tl), uranium (U), vanadium (V), and zinc (Zn). Radon (Rn) gas also was measured and is included in the data analysis. Climate influenced the occurrence and distribution of trace elements in groundwater whereby more trace elements occurred and were found at greater concentrations in wells in drier regions of the United States than in humid regions. In particular, the concentrations of As, Ba, B, Cr, Cu, Mo, Ni, Se, Sr, U, V, and Zn were greater in the drier regions, where processes such as chemical evolution, ion complexation, evaporative concentration, and redox (oxidation-reduction) controls act to varying degrees to mobilize these elements. Al, Co, Fe, Pb, and Mn concentrations in groundwater were greater in humid regions of the United States than in dry regions, partly in response to lower groundwater pH and (or) more frequent anoxic conditions. In groundwater from humid regions, concentrations of Cu, Pb, Rn, and Zn were significantly greater in drinking-water wells than in monitoring wells. Samples from drinking-water wells in dry regions had greater concentrations of As, Ba, Pb, Li, Sr, V, and Zn, than samples from monitoring wells. In humid regions, however, concentrations of most trace elements were greater in monitoring wells than in drinking-water wells; the exceptions were Cu, Pb, Zn, and Rn. Cu, Pb, and Zn are common trace elements in pumps and pipes used in the construction of drinking-water wells, and contamination from these sources may have contributed to their concentrations. Al, Sb, Ba, B, Cr, Co, Fe, Mn, Mo, Ni, Se, Sr, and U concentrations were all greater in monitoring wells than in drinking-water wells in humid regions. Groundwater from wells in agricultural settings had greater concentrations of As, Mo, and U than groundwater from wells in urban settings, possibly owing to greater pH in the agricultural wells. Significantly greater concentrations of B, Cr, Se, Ag, Sr, and V also were found in agricultural wells in dry regions. Groundwater from dry-region urban wells had greater concentrations of Co, Fe, Pb, Li, Mn, and specific conductance than groundwater from agricultural wells. The geologic composition of aquifers and aquifer geochemistry are among the major factors affecting trace-element occurrence. Trace-element concentrations in groundwater were characterized in aquifers from eight major groups based on geologic material, including (1) unconsolidated sand and gravel; (2) glacial unconsolidated sand and gravel; (3) semiconsolidated sand; (4) sandstone; (5) sandstone and carbonate rock; (6) carbonate rock; (7) basaltic and other volcanic rock; and (8) crystalline rock. The majority of groundwater samples and the largest percentages of exceedences of HHBs were in the glacial and nonglacial unconsolidated sand and gravel aquifers; in these aquifers, As, Mn, and U are the most common trace elements exceeding HHBs. Overall, 19 percent of wells (962 of 5,097) exceeded an HHB for at least one trace element. The trace elements with HHBs included in this summary were Sb, As, Ba, Be, B, Cd, Cr,

Metasomatic Reaction Zones as Monitors of Trace Element Transfer at the Slab-Mantle Interface: the Case of the Hochwart Peridotite (Ulten Zone, Italy)

NASA Astrophysics Data System (ADS)

Marocchi, M.; Hermann, J.; Bargossi, G. M.; Mair, V.; Morten, L.

2006-12-01

Ultramafic blocks belonging to the Hochwart peridotite outcrop (Ulten Zone, Italian Alps) preserve a series of metasomatic mineral zones generated by infiltration of Si-rich hydrous fluids which occurred at the gneiss- peridotite interface. The age of the high pressure metamorphism for the Hochwart complex has been constrained at 330 Ma (Tumiati et al., 2003, EPSL, 210, 509-526). The country rocks are stromatic gneisses consisting mainly of quartz, K-feldspar, garnet, kyanite, biotite and muscovite. The ultramafic body consists of strongly serpentinized metaperidotites which are exposed as a hectometre-size lens along a steep gully, associated to monomineralic zones that developed at the contact between the peridotite body and the garnet gneiss country rocks. The composition of the metasomatic zones has been investigated in detail and records an order of metasomatic zoning formed by phlogopite-rich to tremolite-anthophyllite-rich rocks going from the host gneiss towards the peridotite. In some cases, the ultramafics fade into the gneisses developing serpentine and talc which has replaced, presumably at lower temperatures, the serpentine matrix and occurs in association with chlorite. Phlogopite aggregates (phlogopitite) with accessory minerals (quartz + zircon + apatite) and metabasic pods (phlogopite and hornblende) also occur. Black tourmaline (schorl-dravite solid solution) has been found for the first time in the contact near the phlogopite zone, suggesting an external addition of elements (boron and fluorine) to the system at high temperature. The formation of the metasomatic zones composed exclusively of hydrous phases must have involved extensive H2O-metasomatism as already documented for the Ulten peridotites. The source for these fluids can be a system of trondhjemitic-pegmatitic dikes cutting the peridotite that would have channelled aqueous fluids into the ultramafic rocks. Whole-rock geochemistry and trace element (LA ICP-MS) composition of hydrous phases (phlogopite and amphibole) in different metasomatic zones indicate mobility of many elements, including elements such as Ta which are considered to have scarce mobility in fluids. Trace element composition of accessory minerals in the phlogopite-rich zone suggests that the trace element signature of subduction zone fluids may be fractionated in this zone. The progressive depletion in some trace elements (LREE) and enrichment in LILE and Li from the peridotite towards the gneiss suggests a strong influence of bulk composition on the trace element budget of hydrous minerals. Since the ultramafic blocks can be representative of metasomatic processes occurring at the slab-mantle interface, we can infer that metasomatic reactions between slab-derived fluids and ultramafic mantle wedge will follow a specific series of reactions, creating mineral zonation similar to those observed in this study. Our results further favour the evidence that the primary composition of subduction zone fluids is modified substantially by metasomatic reactions occurring in the mantle wedge.

Along and Across Arc Variation of the Central Andes by Single Crystal Trace Element Analaysis

NASA Astrophysics Data System (ADS)

Michelfelder, G.; Sundell, T.; Wilder, A.; Salings, E. E.

2017-12-01

Along arc and across arc geochemical variations at continental volcanic arcs are influenced by a number of factors including the composition and thickness of the continental crust, mantle heterogeneity, and fluids from the subducted slab. Whole rock geochemical trends along and across the arc front of the Central Volcanic Zone (CVZ) have been suggested to be primarily influenced by the composition and thickness of the crust. In the CVZ, Pb isotopic domains relate volcanic rock compositions to the crustal basement and systematically varies with crustal age. It has been shown repeatedly that incompatible trace element trends and trace element ratios can be used to infer systematic geochemical changes. However, there is no rule linking magmatic process or chemical heterogeneity/ homogeneity as a result of large crustal magma storage reservoirs such as MASH zones to the observed variation. Here we present a combination of whole rock major- and trace element data, isotopic data and in situ single crystal data from plagioclase, pyroxene and olivine for six stratovolcanoes along the arc front and in the back arc of the CVZ. We compare geochemical trends at the whole and single crystal scale. These volcanoes include lava flows and domes from Cerro Uturuncu in the back-arc, Aucanquilcha, Ollagüe, San Pedro-San Pablo, Lascar, and Lazufre from the arc front. On an arc-wide scale, whole rock samples of silicic lavas from these six composite volcanoes display systematically higher K2O, LILE, REE and HFSE contents and 87Sr/86Sr ratios with increasing distance from the arc-front. In contrast, the lavas have systematically lower Na2O, Sr, and Ba contents; LILE/HFSE ratios; 143Nd/144Nd ratios; and more negative Eu anomalies. Silicic magmas along the arc-front reflecting melting of young, mafic composition source rocks with the continental crust becoming increasingly older and more felsic toward the east. These trends are paralleled in the trace element compositions of plagioclase cores which systematically become less diverse in composition in younger lava flows from each center. We suggest these trends result from progressively smaller degrees of mantle partial melting, primary melt generation, and crustal hybridization with distance from the arc-front and varying influence of MASH zone processes.

Trace and minor element variations and sulfur isotopes in crystalline and colloform ZnS: Incorporation mechanisms and implications for their genesis

USGS Publications Warehouse

Pfaff, Katharina; Koenig, Alan; Wenzel, Thomas; Ridley, Ian; Hildebrandt, Ludwig H.; Leach, David L.; Markl, Gregor

2011-01-01

Various models have been proposed to explain the formation mechanism of colloform sphalerite, but the origin is still under debate. In order to decipher influences on trace element incorporation and sulfur isotope composition, crystalline and colloform sphalerite from the carbonate-hosted Mississippi-Valley Type (MVT) deposit near Wiesloch, SW Germany, were investigated and compared to sphalerite samples from 52 hydrothermal vein-type deposits in the Schwarzwald ore district, SW Germany to study the influence of different host rocks, formation mechanisms and fluid origin on trace element incorporation. Trace and minor element incorporation in sphalerite shows some correlation to their host rock and/or origin of fluid, gangue, paragenetic minerals and precipitation mechanisms (e.g., diagenetic processes, fluid cooling or fluid mixing). Furthermore, crystalline sphalerite is generally enriched in elements like Cd, Cu, Sb and Ag compared to colloform sphalerite that mainly incorporates elements like As, Pb and Tl. In addition, sulfur isotopes are characterized by positive values for crystalline and strongly negative values for colloform sphalerite. The combination of trace element contents, typical minerals associated with colloform sphalerite from Wiesloch, sulfur isotopes and thermodynamic considerations helped to evaluate the involvement of sulfate-reducing bacteria in water-filled karst cavities. Sulfate-reducing bacteria cause a sulfide-rich environment that leads in case of a metal-rich fluid supply to a sudden oversaturation of the fluid with respect to galena, sphalerite and pyrite. This, however, exactly coincides with the observed crystallization sequence of samples involving colloform sphalerite from the Wiesloch MVT deposit.

Petrographic and petrological study of lunar rock materials

NASA Technical Reports Server (NTRS)

Winzer, S. R.

1977-01-01

Impact melts and breccias from the Apollo 15 and 16 landing sites were examined optically and by electron microscope/microprobe. Major and trace element abundances were determined for selected samples. Apollo 16 breccias contained impact melts, metamorphic and primary igneous rocks. Metamorphic rocks may be the equivalents of the impact melts. Apollo 15 breccias studied were fragment-laden melts derived from gabbro and more basalt target rocks.

Pristine nonmare rocks and the nature of the lunar crust

NASA Technical Reports Server (NTRS)

Warren, P. H.; Wasson, J. T.

1977-01-01

It is shown that the interdisciplinary study of the nonmare lunar rocks based on trace element, major element, and isotopic data plus petrographic evidence can succeed in amassing a large suite of demonstrably pristine rocks, and that the relative numbers of these rocks are not in accord with statistics amassed on soil fragments and glasses. The term 'pristine' is taken to mean rocks with primary compositions (albeit not necessarily textures) produced by lunar endogenous igneous processes. Melt rocks and crystalline matrix breccias produced by impact processes are excluded. A petrographic synonym for pristine would be 'unremelted, monomict'. It is found that anorthositic norites and noritic anorthosites were rare as primary nonmare rocks. Mechanical mixing appears to have been the dominant petrogenetic process on the highlands.

Alkali trace elements in Gale crater, Mars, with ChemCam: Calibration update and geological implications

NASA Astrophysics Data System (ADS)

Payré, V.; Fabre, C.; Cousin, A.; Sautter, V.; Wiens, R. C.; Forni, O.; Gasnault, O.; Mangold, N.; Meslin, P.-Y.; Lasue, J.; Ollila, A.; Rapin, W.; Maurice, S.; Nachon, M.; Le Deit, L.; Lanza, N.; Clegg, S.

2017-03-01

The Chemistry Camera (ChemCam) instrument onboard Curiosity can detect minor and trace elements such as lithium, strontium, rubidium, and barium. Their abundances can provide some insights about Mars' magmatic history and sedimentary processes. We focus on developing new quantitative models for these elements by using a new laboratory database (more than 400 samples) that displays diverse compositions that are more relevant for Gale crater than the previous ChemCam database. These models are based on univariate calibration curves. For each element, the best model is selected depending on the results obtained by using the ChemCam calibration targets onboard Curiosity. New quantifications of Li, Sr, Rb, and Ba in Gale samples have been obtained for the first 1000 Martian days. Comparing these data in alkaline and magnesian rocks with the felsic and mafic clasts from the Martian meteorite NWA7533—from approximately the same geologic period—we observe a similar behavior: Sr, Rb, and Ba are more concentrated in soluble- and incompatible-element-rich mineral phases (Si, Al, and alkali-rich). Correlations between these trace elements and potassium in materials analyzed by ChemCam reveal a strong affinity with K-bearing phases such as feldspars, K-phyllosilicates, and potentially micas in igneous and sedimentary rocks. However, lithium is found in comparable abundances in alkali-rich and magnesium-rich Gale rocks. This very soluble element can be associated with both alkali and Mg-Fe phases such as pyroxene and feldspar. These observations of Li, Sr, Rb, and Ba mineralogical associations highlight their substitution with potassium and their incompatibility in magmatic melts.

Hyperacid volcano-hydrothermal fluids from Copahue volcano, Argentina: Analogs for "subduction zone fluids"?

NASA Astrophysics Data System (ADS)

Varekamp, J. C.

2007-12-01

Hyperacid concentrated Chlorine-Sulfate brines occur in many young arc volcanoes, with pH values <1, high concentrations of volcanogenic elements (S, Cl, F, As, B) and the main rock forming elements (Ca, Al, Mg, K, Na, P). Sulfur isotope data and Silica thermometry from such fluids sampled over a ten year period from the Copahue volcanic system (Argentina) suggest reservoir temperatures of 175-300 oC, whereas the surface fluids do not exceed local boiling temperatures. These fluids are generated at much lower P-T conditions than fluids associated with a dehydrating subducted sediment complex below arc volcanoes, but their fundamental chemical compositions may have similarities. Incompatible trace element, major element concentrations and Pb isotope compositions of the fluids were used to determine the most likely rock protoliths for these fluids. Mean rock- normalized trace element diagrams then indicate which elements are quantitatively extracted from the rocks and which are left behind or precipitated in secondary phases. Most LILE show flat rock-normalized patterns, indicating close to congruent dissolution, whereas Ta-Nb-Ti show strong depletions in the rock-normalized diagrams. These HFSE are either left behind in the altered rock protolith or were precipitated along the way up. The behavior of U and Th is almost identical, suggesting that in these low pH fluids with abundant ligands Th is just as easily transported as U, which is not the case in more dilute, neutral fluids. Most analyzed fluids have steeper LREE patterns than the rocks and have negative Eu anomalies similar to the rocks. Fluids that interacted with newly intruded magma e.g., during the 2000 eruption, have much less pronounced Eu anomalies, which was most likely caused by the preferential dissolution of plagioclase when newly intruded magma interacted with the acid fluids. The fluids show a strong positive correlation between Y and Cd (similar to MORB basalts, Yi et al., JGR, 2000), suggesting that Cd is mainly a rock-derived element that may not show chalcophilic behavior. The fluids are strongly enriched (relative to rock) in As, Zn and Pb, suggesting that these elements were carried with the volcanic gas phase into the system. In summary, if these fluids are broadly similar to fluids from dehydrating subducted sediments, they tend to transport preferently the LILE, LREE, U as well as Th, while the HFSE are left behind.

Volatile trace elements and the characterization of the Cayley Formation and the primitive lunar crust

NASA Technical Reports Server (NTRS)

Jovanovic, S.; Reed, G. W., Jr.

1973-01-01

Two types of highland terrain appear to be present at the Apollo 16 landing site. The Plains Formation called Cayley is ubiquitous and blankets even those regions that were presumably a part of the mountainous Descartes Formation. The second type of terrain is that associated with the ejectae from North and South Ray craters. The stratigraphy sampled by the ejectae underlays the Cayley layer as characterized above and may permit a redefinition of Descartes Formation as that which underlays the smooth Plains deposits. These conclusions are based on the concentrations and chemical coherence between elements such as Cl-F-P2O5 and Ru-Os. The primitive lunar crust may be characterized by the type of feldspathic rocks which are enriched in trace elements, such as Cl, Br, U, Te, Ru, and Os, as found in 'rusty' rock 66095 and in 61016; other feldspathic rocks are depleted and may be of secondary origin.

Enhanced identification of trace element fingerprint of prehistoric pigments by PIXE mapping

NASA Astrophysics Data System (ADS)

Lebon, M.; Pichon, L.; Beck, L.

2018-02-01

The elemental composition of Fe rich rocks used as pigment during prehistoric periods can provide valuable information about the type of material used and their geological origin. However, these materials present several analytical constraints since their patrimonial value involve using non-invasive techniques maintaining a high sensitivity of the detection and the quantification of trace elements. Micro-beam techniques also require to take into account the heterogeneity of these geomaterials from the macroscopic to microscopic scales. Several previous studies have demonstrated that PIXE analysis satisfies these analytical conditions. However, application of micro-PIXE analysis is still complex when thin and discontinuous layer of pigment is deposed on the surface of other materials such as rocks or bones. In such case, PIXE imaging could improve the ability to take into account the high heterogeneity of such archaeological objects. In study, we used PIXE imaging system developed at the NewAGLAE facility in order to visualize distribution of elements associated with iron-rich pigment phase. The results obtained show that PIXE maps can improve the identification of the main trace elements specific to the iron mineral phase. By grouping pixels of iron-rich areas and performing quantitative treatment, it was possible to reveal additional trace elements associated to pigment. This study highlights the contribution of PIXE imaging to the identification of elements associated with mineral phases of interest and to use them as proxies to discriminate different geological materials used in archaeological context.

Imprints of an "Arc" Signature onto Subduction Zone Eclogites from Central Guatemala

NASA Astrophysics Data System (ADS)

Simons, K. K.; Sorensen, S. S.; Harlow, G. E.; Brueckner, H. K.; Goldstein, S. L.; Hemming, N. G.; Langmuir, C. H.

2007-12-01

High-pressure, low-temperature (HP-LT) rocks associated with the Motagua fault zone in central Guatemala occur as tectonic blocks in serpentinite mélange. Dismembered jadeitite and albitite veins within the melange are crystallization products of subduction fluids at <400° C and 0.4-1.4 GPa. Lawsonite eclogites represent the deepest, coldest rocks, with peak metamorphic conditions of approx. 2.6 GPa and 480°C. They contain a subduction fluid overprint acquired during retrogression to blue- and green-schist-facies conditions, seen mostly as hydrous phases (e.g. phengite, glaucophane) in veins and overgrowths. The low temperatures recorded in these rocks indicate they have only seen an aqueous fluid, not a melt, and therefore, could provide a window into the acquisition of an arc signature at a cold margin. Trace-element patterns for both eclogite and jadeitite resemble arc lavas, with large enrichments in the most fluid mobile elements (e.g. Cs, Tl, Ba, Pb), moderate enrichments in U, Th, Be and LREE and generally little to no enrichment in HFSE and HREE, although enriched Nb in jadeitite indicates some HFSE mobility. Trace-element patterns also have similarities to average subducting sediment (GLOSS), with enrichments in Th, Be, Ba and Li that suggest a sediment contribution. Nd versus Sr isotopes lie to the right of the mantle array, indicating a hydrous fluid contribution from altered ocean crust or sediment. Overall, Guatemalan eclogites resemble counterparts from the Franciscan Complex (CA) and the Dominican Republic. Guatemalan and Franciscan eclogites are interpreted to have had a MORB protolith despite the arc trace element signature because of: 1) similarities in major elements to MORB; 2) HREE and HFSE abundances similar to MORB; and 3) high 143Nd/144Nd that overlap MORB values. The modifications that transformed these eclogites from a MORB trace element pattern to an arc one can be attributed to an aqueous subduction fluid at moderate depths (<75km). This transformation may be due to the increased solubilities of some minerals (e.g., jadeite, albite, clays, sulfates) at high pressure, high water/rock ratios from dehydration reactions, and an abundance of alkali-aluminosilicate components in subduction fluids. Together these may act to dissolve and transport trace elements (including elements considered insoluble like Nb) out of the slab and into the mantle wedge. The Guatemala data thus indicate that the arc geochemical fingerprint may be achieved at cold margins without the need for melting.

Enrichment of trace elements in garnet amphibolites from a paleo-subduction zone: Catalina Schist, southern California

USGS Publications Warehouse

Sorensen, Sorena S.; Grossman, J.N.

1989-01-01

The abundance, P-T stability, solubility, and element-partitioning behavior of minerals such as rutile, garnet, sphene, apatite, zircon, zoisite, and allanite are critical variables in models for mass transfer from the slab to the mantle wedge in deep regions of subduction zones. The influence of these minerals on the composition of subduction-related magmas has been inferred (and disputed) from inverse modelling of the geochemistry of island-arc basalt, or by experiment. Although direct samples of the dehydration + partial-melting region of a mature subduction zone have not been reported from subduction complexes, garnet amphibolites from melanges of circumpacific and Caribbean blueschist terranes reflect high T (>600??C) conditions in shallower regions. Such rocks record geochemical processes that affected deep-seated, high-T portions of paleo-subduction zones. In the Catalina Schist, a subduction-zone metamorphic terrane of southern California, metasomatized and migmatitic garnet amphibolites occur as blocks in a matrix of meta-ultramafic rocks. This mafic and ultramafic complex may represent either slab-derived material accreted to the mantle wedge of a nascent subduction zone or a portion of a shear zone closely related to the slab-mantle wedge contact, or both. The trace-element geochemistry of the complex and the distribution of trace elements among the minerals of garnet amphibolites were studied by INAA, XRF, electron microprobe, and SEM. In order of increasing alteration from a probable metabasalt protolith, three common types of garnet amphibolite blocks in the Catalina Schist are: (1) non-migmatitic, clinopyroxene-bearing blocks, which are compositionally similar to MORB that has lost an albite component; (2) garnet-amphibolite blocks, which have rinds that reflect local interaction between metabasite, metaperidotite, and fluid; and (3) migmatites that are extremely enriched in Th, HFSE, LREE, and other trace elements. These trace-element enrichments are mineralogically controlled by rutile, garnet, sphene, apatite, zircon, zoisite, and allanite. Alkali and alkaline earth elements are much less enriched in the solid assemblage, and thus appear to be decoupled from the other elements in the inferred metasomatic process(es). The compositions of migmatitic garnet amphibolite blocks seem to complement that of "average" island-arc tholeiite. Trace-element metasomatism reflects fluid-solid, rather than melt-solid, interaction. The metasomatic effects indicate that H2O-rich fluid, perhaps with a significant component of Na-Al silicate and alkalis, carried Th, U, Sr, REE, and HFSE. Fractionations of LREE in migmatites resemble those of migmatitic metasedimentary rocks underlying the mafic and ultramafic complex. "Exotic" LREE deposited in allanite in migmatites could have been derived from fluids in equilibrium with subducted sediment. If the paleo-subduction zone represented by the mafic and ultramafic complex of the Catalina Schist had continued its thermal and fluid evolution, a selvage of similarly enriched rocks might have been generated along the slab-mantle wedge contact between ~30 and 85 km depth. Rocks affected by "subduction-zone metasomatism," although rarely recognized at the surface, could be volumetrically significant products of the initiation of subduction and may prove to be geochemical probes of convergent margins that approach the significance of xenoliths in the study of other magmatic environments. ?? 1989.

Trace Element Study of MORB Glasses from 14¡ã-16¡ãN along Mid-Atlantic Ridge by LA-ICP- MS

NASA Astrophysics Data System (ADS)

Barzoi, C. A.; Casey, J. F.; Gao, Y.; Lapen, T.

2007-12-01

A comparison of 20 MORB glasses from 14°-16° N along the Mid-Atlantic Ridge using both solution-based and in situ laser ablation-based ICP-MS trace element analyses on the same samples was conducted. Li, Be, Sc, Ti, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Ba, La, Ce, Pr, Nd, Sm, Eu, Tb, Gd, Dy, Ho, Er, Tm, Yb,Lu, Hf, Ta, Pb, Th, and U were analyzed using the Varian 810 quadrupole ICP-MS. The instrument features a 90 degree ion mirror and low noise double-off-axis quadrupole that allows high sensitivity and low backgrounds. Precision in term of relative standard deviation (RSD) of the measurements for both methods based on repeated analyses of USGS BIR-1G and BHVO-2G glass standards and Max Planck KL-2G glass standard is within 5 % for all trace elements with the exception of Pb, which averaged 12 %. Measured trace element abundances are within 2% of recommended standard values using both solution and laser ablation methods. Comparison between the analyte concentrations obtained by solution-based ICP-MS and in situ microanalysis by laser ablation reveals little systematic differences in abundances(<5% for all elements). The two-method correlation and strong repeatability of the results indicate that rapid in situ trace element analysis by laser ablation ICP-MS is likely to become a preferred method of trace element analysis for MORB glasses. Our geochemical results and previous studies of MORB glasses in the region of the MAR between 14°-16°N show that basalts are characterized isotopic and incompatible element enrichment.The nature of the enrichment has been the topic of significant discussion and speculation because a specific mantle plume is not well defined in the region. Likewise the magma supply is probably small in the region as the magmatic crust is interpreted to be very thin in most of the area studied. Integrated studies of major element, trace element, and isotopic variations among basalts, gabbroic rocks and igneous and residual ultramafic rocks in the region indicate that 1) the enriched basalts have positive Ta-Nb anomalies, enriched relative to U, Th, and La 2) basalts have relatively high SiO2 abundances compared to the global average, 3) basalts show a HIMU isotopic signature, and 4) bulk major element abundances and mineral chemistry in mantle rocks indicate that they are among the most depleted,although variably refertilized, residual mantle assemblages sampled to date along MORs.We suggest that much of the regional variation in major and trace element data, as well as isotopic data and the unusual regional geology (multiple core complexes) can be explained by melting of a sub-axial mantle that contains two end members, one highly depleted and the other enriched. These components appear to involve ancient recycled ocean crust and lithospheric mantle.

Feasibility of estimating cementation rates in a brittle fault zone using Sr/Ca partition coefficients for sedimentary diagenesis

NASA Astrophysics Data System (ADS)

Hadizadeh, Jafar; Foit, Franklin F.

2000-04-01

Cement phases such as calcite or quartz often incorporate trace elements from the parent fluids as they crystallize. Experimental sedimentary diagenesis indicates that trace element partition coefficients reflect rates of cementation. The applicability of these findings to fault zone cementation is examined as we make a preliminary attempt to estimate calcite cementation rate in a brittle fault zone directly from the fault-rock composition data. Samples for this study were collected from the Knoxville outcrop of the Saltville fault in Tennessee. The cementation rates for the fault rock samples range from 1×10 -12 to 3×10 -13 m3/ h per m, in agreement with some experimental rates and the rates reported for samples from the DSDP sites. When applied to a non-responsive pore-system model, these rates result in rapid precipitation sealing indicating the influence exerted by the surface-area/volume ratio of the pore network. We find it feasible to obtain a reasonable range of values for the cementation rate using the trace element partition method. However, the study also indicates the need for relatively accurate values for the trace/carrier element ratio in the fault zone syntectonic pore fluid, and exhumed cement.

Geologic setting and petrology of Apollo 15 anorthosite /15415/.

NASA Technical Reports Server (NTRS)

Wilshire, H. G.; Schaber, G. G.; Jackson, E. D.; Silver, L. T.; Phinney, W. C.

1972-01-01

The geological setting, petrography and history of this Apollo 15 lunar rock sample are discussed, characterizing the sample as coarse-grained anorthosite composed largely of calcic plagioclase with small amounts of three pyroxene phases. The presence of shattered and granulated minerals in the texture of the rock is traced to two or more fragmentation events, and the presence of irregular bands of coarsely recrystallized plagioclase and minor pyroxene crossing larger plagioclase grains is traced to an earlier thermal metamorphic event. It is pointed out that any of these events may have affected apparent radiometric ages of elements in this rock. A comparative summarization of data suggests that this rock is the least-deformed member of a suite of similar rocks ejected from beneath the regolith at Spur crater.

Volatile transfer and recycling at convergent margins: Mass-balance and insights from high-P/T metamorphic rocks

NASA Astrophysics Data System (ADS)

Bebout, Gray E.

The efficiency with which volatiles are deeply subducted is governed by devolatilization histories and the geometries and mechanisms of fluid transport deep in subduction zones. Metamorphism along the forearc slab-mantle interface may prevent the deep subduction of many volatile components (e.g., H2O, Cs, B, N, perhaps As, Sb, and U) and result in their transport in fluids toward shallower reservoirs. The release, by devolatilization, and transport of such components toward the seafloor or into the forearc mantle wedge, could in part explain the imbalances between the estimated amounts of subducted volatiles and the amounts returned to Earth's surface. The proportion of the initially subducted volatile component that is retained in rocks subducted to depths greater than those beneath magmatic arcs (>100 km) is largely unknown, complicating assessments of deep mantle volatile budgets. Isotopic and trace element data and volatile contents for the Catalina Schist, the Franciscan Complex, and eclogite-facies complexes in the Alps (and elsewhere) provide insight into the nature and magnitude of fluid production and transport deep in subduction zones and into the possible effects of metamorphism on the compositions of subducting rocks. Compatibilities of the compositions of the subduction-related rocks and fluids with the isotopic and trace element compositions of various mantle-derived materials (igneous rocks, xenoliths, serpentinite seamounts) indicate the potential to trace the recycling of rock and fluid reservoirs chemically and isotopically fractionated during subduction-zone metamorphism.

Whole-rock and sulfide-mineral geochemical data for samples from volcanogenic massive sulfide deposits of the Bonnifield district, east-central Alaska

USGS Publications Warehouse

Dusel-Bacon, Cynthia; Slack, John F.; Koenig, Alan E.; Foley, Nora K.; Oscarson, Robert L.; Gans, Kathleen D.

2011-01-01

This Open-File Report presents geochemical data for outcrop and drill-core samples from volcanogenic massive sulfide deposits and associated metaigneous and metasedimentary rocks in the Wood River area of the Bonnifield mining district, northern Alaska Range, east-central Alaska. The data consist of major- and trace-element whole-rock geochemical analyses, and major- and trace-element analyses of sulfide minerals determined by electron microprobe and laser ablation—inductively coupled plasma—mass spectrometry (LA-ICP-MS) techniques. The PDF consists of text, appendix explaining the analytical methods used for the analyses presented in the data tables, a sample location map, and seven data tables. The seven tables are also available as spreadsheets in several file formats. Descriptions and discussions of the Bonnifield deposits are given in Dusel-Bacon and others (2004, 2005, 2006, 2007, 2010).

Trace elements in streambed sediments of small subtropical streams on O'ahu, Hawai'i: Results from the USGS NAWQA program

USGS Publications Warehouse

De Carlo, E. H.; Tomlinson, M.S.; Anthony, S.S.

2005-01-01

Data are presented for trace element concentrations determined in the <63 ??m fraction of streambed sediment samples collected at 24 sites on the island of O'ahu, Hawai'i. Sampling sites were classified as urban, agricultural, mixed (urban/agricultural), or forested based on their dominant land use, although the mixed land use at selected sampling sites consisted of either urban and agricultural or forested and agricultural land uses. Forest dominated sites were used as reference sites for calculating enrichment factors. Trace element concentrations were compared to concentrations from studies conducted in the conterminous United States using identical methods and to aquatic-life guidelines provided by the Canadian Council of Ministers of the Environment. A variety of elements including Pb, Cr, Cu and Zn exceeded the aquatic-life guidelines in selected samples. All of the Cr and Zn values and 16 of 24 Cu values exceeded their respective guidelines. The potential toxicity of elements exceeding guidelines, however, should be considered in the context of strong enrichments of selected trace elements attributable to source rocks in Hawai'i, as well as in the context of the abundance of fine-grained sediment in the streambed of O'ahu streams. Statistical methods including cluster analysis, Kruskal-Wallis non-parametric test, correlation analysis, and principal component analysis (PCA) were used to evaluate differences and elucidate relationships between trace elements and sites. Overall, trace element distributions and abundances can be correlated to three principal sources of elements. These include basaltic rocks of the volcanic edifice (Fe, Al, Ni, Co, Cr, V and Cu), carbonate/seawater derived elements (Mg, Ca, Na and Sr), and elements enriched owing to anthropogenic activity (P, Sn, Cd, Sn, Ba and Pb). Anthropogenic enrichment gradients were observed for Ba, Cd, Pb, Sn and Zn in the four streams in which sediments were collected upstream and downstream. The findings of this study are generally similar to but differ slightly from previous work on sediments and suspended particulate matter in streams, from two urban watersheds of O'ahu, Hawai'i. Inter-element associations in the latter were often stronger and indicated a mixture of anthropogenic, agricultural and basaltic sources of trace elements. Some elements fell into different statistical categories in the two studies, owing in part to differences in study design and the hydrogeological constraints on the respective study areas.

Rare earth element abundances in rocks and minerals from the Fiskenaesset Complex, West Greenland. [comparison with lunar anorthosites

NASA Technical Reports Server (NTRS)

Henderson, P.; Fishlock, S. J.; Laul, J. C.; Cooper, T. D.; Conard, R. L.; Boynton, W. V.; Schmitt, R. A.

1976-01-01

The paper reports activation-analysis determinations of rare-earth-element (REE) and other trace-element concentrations in selected rocks, plagioclase, and mafic separates from the Fiskenaesset Complex. The REE abundances are found to be very low and atypical in comparison with other terrestrial anorthosites. The plagioclases are shown to be characterized by a deficiency in heavy RE elements relative to light ones and a positive Eu anomaly, while the mafic separates are enriched in heavy rare earths and have no Eu anomaly, except in one sample. It is found that the bulk and trace-element abundances of the plagioclases are similar to those observed in some lunar anorthosites, but the degree of Eu anomaly is less in the plagioclases. The data are taken as confirmation of the idea that fractionation processes were involved in the origin of the Complex, and it is concluded that the Complex may have been produced from a magma generated by partial melting of a garnet-bearing source.

Composition of the lithospheric mantle in the Siberian craton : New constraints from fresh peridotites from the Udachnaya-East Kimberlite

NASA Astrophysics Data System (ADS)

Doucet, Luc-Serge; Ionov, Dmitri A.; Ashchepkov, Igor

2010-05-01

Peridotite xenoliths from the Udachnaya kimberlite pipe represent the major source of lithospheric mantle samples beneath central Siberian craton. An important problem with the availble data [1], however, is that the Udachnaya xenoliths, like many other kimberlite-hosted peridotite suites worldwide, are extensively altered due to interaction with host magma and post-eruption alteration. This alteration causes particular dificulties for whole-rock studies including microstructures, modal estimates and chemical compositions. We report petrographic data and major and trace element compositions for whole-rocks and minerals of some 30 unusually fresh peridotite xenolith from the Udachnaya-East kimberlite. Our study has two goals. The first is to present and discuss trace element data on rocks and minerals from Udachnaya, whose composition remains little known. The other one is to explore how the availability of the fresh peridotites improves our knowledge of petrology and geochemistry of cratonic mantle in relation to published data on altered samples [1]. The xenoliths are spinel, garnet-spinel and garnet facies peridotites including garnet- and cpx-rich lherzolites, garnet and spinel harzburgites and dunites. Thermobarometric estimates for garnet bearing rocks yield T = 800-1350°C and P = 20-70 kbar, low-T spinel facies rocks may originate from shallower levels. Thus, the suite represents a lithospheric profile from the sub-Moho mantle down to ~210 km. The deeper peridotites commonly have porphyroclastic microstructures with mainly neoblast olivine, opx porphyroclasts and cpx and garnet with broadly variable morphologies whereas rocks of shallow origin are commonly protogranular. Trace element compositions in bulk rocks appear to be affected by host magma contamination with enrichments in highly to moderately incompatible elements as well as in alkalis. Nevertheless, the kimberlite-related contamination cannot explain a combination of low Th and U and high Sr contents. The broad range of heavy REE appears to be controlled by the presence and the abundance of garnet and is also related to microstructures such that granular spinel harzburgites have lower HREE contents than "fertile" porphyroclastic garnet lherzolites. Trace elements in cpx and garnet have equilibrated patterns in porphyroclastic peridotites and complex sinusoidal shapes in granular peridotites. Bulk-rock major element compositions show important variations in Mg# (0.89 - 0.93), SiO2 (41.5 - 46.6%), Al2O3 (0.3 - 4%) and CaO (0.3 - 4%). As for compatible trace elements, the major element compositions appear to be related to microstructures. Calculated modal compositions show highly variable opx contents (4.5 - 24%), which are generally lower than in Kaapvaal peridotites but are similar to those from the North Atlantic craton [3]. Overall, modal compositions and the contents of low-mobility elements, are consistent with an origin by variable degrees of partial melting of fertile mantle [1-3]. The range in FeO contents (6-8.5%) may indicate either variable melting depths [2] or post-melting enrichments. Enrichments in SiO2 show some similarities to those in supra-subduction xenoliths [4]; enrichments in highly incompatible elements can be explained by metasomatism with possible involvement of subduction-related fluids. Strong correlations between chemical compositions and microstructures indicate the involvement of tectonic processes in melt percolation and metasomatism. We suggest that the cratonic lithosphere in Siberia was formed in three stages: (1) formation of proto-cratonic mantle by high-degree melting at variable depth, (2) accretion of the proto-craton domains in subduction-related settings, (3) metasomatism commonly accompanied by deformation. [1] Boyd et al (1997) Contrib. Mineral. Petrol. 128, 228-246. [2] Herzberg (2004) J. Petrol. 45, 2507-2530. [3] Wittig et al (2008) Lithos 71, 289-322. [4] Ionov (2009) J. Petrol. In press

Alkali trace elements in Gale crater, Mars, with ChemCam: Calibration update and geological implications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Payre, Valerie; Fabre, Cecile; Cousin, Agnes

The Chemistry Camera (ChemCam) instrument onboard Curiosity can detect minor and trace elements such as lithium, strontium, rubidium, and barium. Their abundances can provide some insights about Mars' magmatic history and sedimentary processes. We focus on developing new quantitative models for these elements by using a new laboratory database (more than 400 samples) that displays diverse compositions that are more relevant for Gale crater than the previous ChemCam database. These models are based on univariate calibration curves. For each element, the best model is selected depending on the results obtained by using the ChemCam calibration targets onboard Curiosity. New quantificationsmore » of Li, Sr, Rb, and Ba in Gale samples have been obtained for the first 1000 Martian days. Comparing these data in alkaline and magnesian rocks with the felsic and mafic clasts from the Martian meteorite NWA7533—from approximately the same geologic period—we observe a similar behavior: Sr, Rb, and Ba are more concentrated in soluble- and incompatible-element-rich mineral phases (Si, Al, and alkali-rich). Correlations between these trace elements and potassium in materials analyzed by ChemCam reveal a strong affinity with K-bearing phases such as feldspars, K-phyllosilicates, and potentially micas in igneous and sedimentary rocks. However, lithium is found in comparable abundances in alkali-rich and magnesium-rich Gale rocks. This very soluble element can be associated with both alkali and Mg-Fe phases such as pyroxene and feldspar. Here, these observations of Li, Sr, Rb, and Ba mineralogical associations highlight their substitution with potassium and their incompatibility in magmatic melts.« less

Alkali trace elements in Gale crater, Mars, with ChemCam: Calibration update and geological implications

DOE PAGES

Payre, Valerie; Fabre, Cecile; Cousin, Agnes; ...

2017-03-20

The Chemistry Camera (ChemCam) instrument onboard Curiosity can detect minor and trace elements such as lithium, strontium, rubidium, and barium. Their abundances can provide some insights about Mars' magmatic history and sedimentary processes. We focus on developing new quantitative models for these elements by using a new laboratory database (more than 400 samples) that displays diverse compositions that are more relevant for Gale crater than the previous ChemCam database. These models are based on univariate calibration curves. For each element, the best model is selected depending on the results obtained by using the ChemCam calibration targets onboard Curiosity. New quantificationsmore » of Li, Sr, Rb, and Ba in Gale samples have been obtained for the first 1000 Martian days. Comparing these data in alkaline and magnesian rocks with the felsic and mafic clasts from the Martian meteorite NWA7533—from approximately the same geologic period—we observe a similar behavior: Sr, Rb, and Ba are more concentrated in soluble- and incompatible-element-rich mineral phases (Si, Al, and alkali-rich). Correlations between these trace elements and potassium in materials analyzed by ChemCam reveal a strong affinity with K-bearing phases such as feldspars, K-phyllosilicates, and potentially micas in igneous and sedimentary rocks. However, lithium is found in comparable abundances in alkali-rich and magnesium-rich Gale rocks. This very soluble element can be associated with both alkali and Mg-Fe phases such as pyroxene and feldspar. Here, these observations of Li, Sr, Rb, and Ba mineralogical associations highlight their substitution with potassium and their incompatibility in magmatic melts.« less

Back arc basalts from Patagonia: sediment input in a distal subduction domain

NASA Astrophysics Data System (ADS)

Hesse, A.; Mandeville, C.; Varekamp, J. C.

2007-12-01

Cinder cones and lava flows from the Loncopue graben in N Patagonia (37 S) were sampled over a 180 km N-S transect. These mainly basaltic and trachybasaltic lava flows carry olivine with Cr-Al-rich spinel inclusions, while some more evolved flows carry clinopyroxene and plagioclase. Most of these rocks have between 5-8 percent MgO, and show highly variable K and LIL trace element concentrations. The rocks have up to 180 ppm Ni and 250 ppm Cr. Relative trace element abundance diagrams show negative Ta-Nb anomalies in most rocks, although their depths vary strongly. The REE patterns show LREE enrichment and most rocks have no Eu anomalies, indicating the absence of significant plagioclase fractionation. The basalts have constant U/Th values (~0.25) that are similar to those found in the nearby Copahue-Caviahue arc volcanics. Microprobe analyses of the main phases show olivine with Mg # of 80-87 and up to 2600 ppm Ni. Simulations with the Melts-pMelts programs and application of mineral-melt geothermometers suggest that most olivine phenocrysts crystallized at ~8-10 kbar pressure at temperatures of 1170-1220 oC and with 1-3 percent H2O in the melt. The Sr isotope compositions of 9 samples show a range from 0.7033 - 0.7043, which are negatively correlated with Nd isotope ratios (0.51273- 0.51292). Surprisingly, the most MgO-rich basalt has the most radiogenic Sr isotope ratio. The Pb isotope ratios, well outside the DMM range, correlate very poorly with either Sr isotope ratios or in Pb-Pb isotope graphs. The lack of correlation between degree of evolution and Sr isotope ratios as well as the primitive nature of the rocks and crystals suggest that crustal assimilation was not a major process impacting the composition of these small magma volumes. Incompatible trace element patterns of several samples resemble those of detrital sediment samples from the Pacific, which together with the isotopic data suggest that these magmas may carry a subducted sediment component. Trace element concentrations and ratios do not correlate with radiogenic isotope ratios, suggesting that more than one contaminant source impacted the mantle domain, e.g., fluids as well as sediment melts. Isotope and trace element ratios vary considerably between cinder cones that are only 10-15 km apart, suggesting that the underlying mantle is highly heterogeneous, enriched in subducted components in thin veins and patches. The Loncopue basalts seem to be transitional in composition between the very voluminous S-Patagonia back-arc basalts and the Copahue-Caviahue arc rocks to the north.

Major to ultra trace element bulk rock analysis of nanoparticulate pressed powder pellets by LA-ICP-MS

NASA Astrophysics Data System (ADS)

Peters, Daniel; Pettke, Thomas

2016-04-01

An efficient, clean procedure for bulk rock major to trace element analysis by 193 nm Excimer LA-ICP-MS analysis of nanoparticulate pressed powder pellets (PPPs) employing a binder is presented. Sample powders are milled in water suspension in a planetary ball mill, reducing average grain size by about one order of magnitude compared to common dry milling protocols. Microcrystalline cellulose (MCC) is employed as a binder, improving the mechanical strength of the PPP and the ablation behaviour, because MCC absorbs 193 nm laser light well. Use of MCC binder allows for producing cohesive pellets of materials that cannot be pelletized in their pure forms, such as quartz powder. Rigorous blank quantification was performed on synthetic quartz treated like rock samples, demonstrating that procedural blanks are irrelevant except for a few elements at the 10 ng g-1 concentration level. The LA-ICP-MS PPP analytical procedure was optimised and evaluated using six different SRM powders (JP-1, UB-N, BCR-2, GSP-2, OKUM, and MUH-1). Calibration based on external standardization using SRM 610, SRM 612, BCR-2G, and GSD-1G glasses allows for evaluation of possible matrix effects during LA-ICP-MS analysis. The data accuracy of the PPP LA-ICP-MS analytical procedure compares well to that achieved for liquid ICP-MS and LA-ICP-MS glass analysis, except for element concentrations below ˜30 ng g-1, where liquid ICP-MS offers more precise data and in part lower limits of detection. Uncertainties on the external reproducibility of LA-ICP-MS PPP element concentrations are of the order of 0.5 to 2 % (1σ standard deviation) for concentrations exceeding ˜1 μg g-1. For lower element concentrations these uncertainties increase to 5-10% or higher when analyte-depending limits of detection (LOD) are approached, and LODs do not significantly differ from glass analysis. Sample homogeneity is demonstrated by the high analytical precision, except for very few elements where grain size effects can rarely still be resolved analytically. Matrix effects are demonstrated for PPP analysis of diverse rock compositions and basalt glass analysis when externally calibrated based on SRM 610 and SRM 612 glasses; employing basalt glass GSD-1G or BCR-2G for external standardisation basically eliminates these problems. Perhaps the most prominent progress of the LA-ICP-MS PPP analytical procedure presented here is the fact that trace elements not commonly analysed, i.e. new, unconventional geochemical tracers, can be measured straightforwardly, including volatile elements, the flux elements Li and B, the chalcophile elements As, Sb, Tl, Bi, and elements that alloy with metal containers employed in conventional glass production approaches. The method presented here thus overcomes many common problems and limitations in analytical geochemistry and is shown to be an efficient alternative for bulk rock trace elements analysis.

Critical elements in sediment-hosted deposits (clastic-dominated Zn-Pb-Ag, Mississippi Valley-type Zn-Pb, sedimentary rock-hosted Stratiform Cu, and carbonate-hosted Polymetallic Deposits): A review: Chapter 12

USGS Publications Warehouse

Marsh, Erin; Hitzman, Murray W.; Leach, David L.

2016-01-01

Some sediment-hosted base metal deposits, specifically the clastic-dominated (CD) Zn-Pb deposits, carbonate-hosted Mississippi Valley-type (MVT) deposits, sedimentary-rock hosted stratiform copper deposits, and carbonate-hosted polymetallic (“Kipushi type”) deposits, are or have been important sources of critical elements including Co, Ga, Ge, and Re. The generally poor data concerning trace element concentrations in these types of sediment-hosted ores suggest that there may be economically important concentrations of critical elements yet to be recognized.

Nickel-iron spherules in tektites - Non-meteoritic in origin

NASA Technical Reports Server (NTRS)

Ganapathy, R.; Larimer, J. W.

1983-01-01

The concentrations of several diagnostic trace elements were determined in two comparatively large NiFe spherules extracted from tektites. The purpose of the study was to obtain some clues about the chemistry of the projectile that is presumed responsible for the formation of these tektites. However, the trace element pattern is distinctly terrestrial implying that the spherules are the result of in-situ reduction of the host rock and are not meteoritic in origin.

Trace element partitioning between coexisting biotite and muscovite from metamorphic rocks, western Labrador: Structural, compositional and thermal controls

NASA Astrophysics Data System (ADS)

Yang, Panseok; Rivers, Toby

2000-04-01

Coexisting biotite and muscovite in ten metapelitic and quartzofeldspathic rocks from western Labrador have been analyzed by electron microprobe for major and minor elements and by a laser ablation microprobe coupled to ICP-MS (LAM-ICP-MS) for selected trace elements - Li, Sc, V, Cr, Mn, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Cs, Ba, REE, Hf and Ta. The samples have experienced a single prograde Grenvillian metamorphism ranging from 490 to 680°C and from 7 to 12 kbar. The trace element compositions of coexisting micas in the metamorphic rocks are used to assess the effects of crystal structure, major element composition and temperature on the partitioning of each element between biotite and muscovite. Overall, trace element distributions are systematic across the range of metamorphic grade and bulk composition, suggesting that chemical equilibrium was approached. Most distribution coefficients (biotite/muscovite) show good agreement with published data. However, distribution coefficients for Co and Sr are significantly different from previous determinations, probably because of contamination associated with older data obtained by bulk analysis techniques. The sequence of distribution coefficients is governed mainly by the ionic radii and charges of substituting cations compared to the optimum ionic radius of each crystallographic site in the micas. In particular, distribution coefficients exhibit the sequence Cr 3+ (0.615 Å) > V 3+ (0.64 Å) > Sc 3+ (0.745 Å) in VI-sites, and Ba 2+ (1.61 Å) > Sr 2+ (1.44 Å) and Cs + (1.88 Å) > K + (1.64 Å) > Rb + (1.72 Å) > Na + (1.39 Å) in XII-sites. The distributions of Li, Sc, Sr and Ba appear to be thermally sensitive but are also controlled by major element compositions of micas. V and Zr partitioning is dependent on T and may be used to cross-check thermometry calculations where the latter suffer from retrograde re-equilibration and/or high concentrations of Fe 3+. The ranges and dependence of distribution coefficients on major element compositions provide important constraints on the values that can be used in geochemical modeling.

Net Acid Production, Acid Neutralizing Capacity, and Associated Mineralogical and Geochemical Characteristics of Animas River Watershed Igneous Rocks Near Silverton, Colorado

USGS Publications Warehouse

Yager, Douglas B.; Choate, LaDonna; Stanton, Mark R.

2008-01-01

This report presents results from laboratory and field studies involving the net acid production (NAP), acid neutralizing capacity (ANC), and magnetic mineralogy of 27 samples collected in altered volcanic terrain in the upper Animas River watershed near Silverton, Colo., during the summer of 2005. Sampling focused mainly on the volumetrically important, Tertiary-age volcanic and plutonic rocks that host base- and precious-metal mineralization in the study area. These rocks were analyzed to determine their potential for neutralization of acid-rock drainage. Rocks in the study area have been subjected to a regional propylitic alteration event, which introduced calcite, chlorite (clinochlore), and epidote that have varying amounts and rates of acid neutralizing capacity (ANC). Locally, hydrothermal alteration has consumed any ANC and introduced minerals, mainly pyrite, that have a high net acid production (NAP). Laboratory studies included hydrogen pyroxide (H2O2) acid digestion and subsequent sodium hydroxide (NaOH) titration to determine NAP, and sulfuric acid (H2SO4) acid titration experiments to determine ANC. In addition to these environmental rock-property determinations, mineralogical, chemical, and petrographic characteristics of each sample were determined through semiquantitative X-ray diffractometry (Rietveld method), optical mineralogy, wavelength dispersive X-ray fluorescence, total carbon-carbonate, and inductively coupled plasma?mass spectrometric analysis. An ANC ranking was assigned to rock samples based on calculated ANC quantity in kilograms/ton (kg/t) calcium carbonate equivalent and ratios of ANC to NAP. Results show that talus near the southeast Silverton caldera margin, composed of andesite clasts of the Burns Member of the Silverton Volcanics, has the highest ANC (>100 kg/t calcium carbonate equivalent) with little to no NAP. The other units found to have moderate to high ANC include (a) andesite lavas and volcaniclastic rocks of the San Juan Formation, west and northwest of the Silverton caldera, and (b) the Picayune Megabreccia Member of Sapinero Mesa Tuff along the western San Juan caldera margin. Sultan Mountain stock, composed of granitoid intrusive rocks, was shown to have low ANC and moderate NAP. Sequential leachate analyses on a suite of whole-rock samples from the current and a previous study indicate that host rock composition and mineralogy control leachate compositions. The most mafic volcanic samples had high leachate concentrations for Mg, Fe, and Ca, whereas silicic volcanic samples had lower ferromagnesiun compositions. Samples with high chlorite abundance also had high leachable Mg concentrations. Trace-element substitution, such as Sr for Ca in plagioclase, controls high Sr concentrations in those samples with high plagioclase abundance. High Ti abundance in leachate was observed in those samples with high magnetite concentrations. This is likely due to samples containing intergrown magnetite-ilmenite. Whole rocks having high trace-element concentrations have relatively high leachate trace-element abundances. Some lavas of the San Juan Formation and Burns Member of the Silverton Volcanics had elevated Zn-, Cd-, and Pb-leachate concentrations. Manganese was also elevated in one San Juan Formation sample. Other San Juan Formation and Burns Member lavas had low to moderate trace-element abundances. One sample of the pyroxene andesite member of the Silverton Volcanics had elevated concentrations for As and Mo. Most other pyroxene andesite member samples had low leachate trace-element abundances. Mine-waste-leachate analyses indicated that one mine-waste sample had elevated concentrations of Cu (1.5 orders of magnitude), Zn (1 order of magnitude), As (1 order of magnitude), Mo (1.5 to 2 orders of magnitude), Cd (1 to 2 orders of magnitude), and Pb (2 to 3 orders of magnitude) compared to whole rocks. These data indicate the importance of whole-rock geochemistry or leachate analys

Trace element abundances in megacrysts and their host basalts - Constraints on partition coefficients and megacryst genesis

NASA Technical Reports Server (NTRS)

Irving, A. J.; Frey, F. A.

1984-01-01

Rare earth and other trace element abundances are determined in megacrysts of clinopyroxene, orthopyroxene, amphibole, mica, anorthoclase, apatite and zircon, as well as their host basalts, in an effort to gather data on mineral/melt trace element partitioning during the high pressure petrogenesis of basic rocks. Phase equilibria, major element partitioning and isotopic ratio considerations indicate that while most of the pyroxene and amphibole megacrysts may have been in equilibrium with their host magmas at high pressures, mica, anorthoclase, apatite, and zircon megacrysts are unlikely to have formed in equilibrium with their host basalts. It is instead concluded that they were precipitated from more evolved magmas, and have been mixed into their present hosts.

Major- and Trace-Element Concentrations in Rock Samples Collected in 2005 from the Taylor Mountains 1:250,000-scale Quadrangle, Alaska

USGS Publications Warehouse

Klimasauskas, Edward P.; Miller, Marti L.; Bradley, Dwight C.; Bundtzen, Tom K.; Hudson, Travis L.

2006-01-01

The data consist of major- and minor-element concentrations for rock samples collected during 2005 by the U.S. Geological Survey. Samples were analyzed by fire assay (Au, Pd, Pt), cold vapor atomic absorption spectroscopy (Hg), and the inductively coupled plasma mass spectrometry (ICPMS) 10 and 42 element methods. For details of sample preparation and analytical techniques see USGS Open File Report 02-0223 (Analytical methods for chemical analysis of geologic and other materials, U.S. Geological Survey), available at .

Fluid-related inclusions in Alpine high-pressure peridotite reveal trace element recycling during subduction-zone dehydration of serpentinized mantle (Cima di Gagnone, Swiss Alps)

NASA Astrophysics Data System (ADS)

Scambelluri, Marco; Pettke, Thomas; Cannaò, Enrico

2015-11-01

Serpentinites release at sub-arc depths volatiles and several fluid-mobile trace elements found in arc magmas. Constraining element uptake in these rocks and defining the trace element composition of fluids released upon serpentinite dehydration can improve our understanding of mass transfer across subduction zones and to volcanic arcs. The eclogite-facies garnet metaperidotite and chlorite harzburgite bodies embedded in paragneiss of the subduction melange from Cima di Gagnone derive from serpentinized peridotite protoliths and are unique examples of ultramafic rocks that experienced subduction metasomatism and devolatilization. In these rocks, metamorphic olivine and garnet trap polyphase inclusions representing the fluid released during high-pressure breakdown of antigorite and chlorite. Combining major element mapping and laser-ablation ICP-MS bulk inclusion analysis, we characterize the mineral content of polyphase inclusions and quantify the fluid composition. Silicates, Cl-bearing phases, sulphides, carbonates, and oxides document post-entrapment mineral growth in the inclusions starting immediately after fluid entrapment. Compositional data reveal the presence of two different fluid types. The first (type A) records a fluid prominently enriched in fluid-mobile elements, with Cl, Cs, Pb, As, Sb concentrations up to 103 PM (primitive mantle), ∼102 PM Tl, Ba, while Rb, B, Sr, Li, U concentrations are of the order of 101 PM, and alkalis are ∼2 PM. The second fluid (type B) has considerably lower fluid-mobile element enrichments, but its enrichment patterns are comparable to type A fluid. Our data reveal multistage fluid uptake in these peridotite bodies, including selective element enrichment during seafloor alteration, followed by fluid-rock interaction along with subduction metamorphism in the plate interface melange. Here, infiltration of sediment-equilibrated fluid produced significant enrichment of the serpentinites in As, Sb, B, Pb, an enriched trace element pattern that was then transferred to the fluid released at greater depth upon serpentine dehydration (type A fluid). The type B fluid hosted by garnet may record the composition of the chlorite breakdown fluid released at even greater depth. The Gagnone study-case demonstrates that serpentinized peridotites acquire water and fluid-mobile elements during ocean floor hydration and through exchange with sediment-equilibrated fluids in the early subduction stages. Subsequent antigorite devolatilization at subarc depths delivers aqueous fluids to the mantle wedge that can be prominently enriched in sediment-derived components, potentially triggering arc magmatism without the need of concomitant dehydration/melting of metasediments or altered oceanic crust.

Laser-ablation ICP-MS as a tool for whole rock trace element analyses on fused powders

NASA Astrophysics Data System (ADS)

Girard, G.; Rooney, T. O.

2013-12-01

Here we present an accurate and precise technique for routine trace element analysis of geologic materials by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We focus on rock powders previously prepared for X-ray fluorescence by fusion in a Li2B4O7 flux, and subsequently quenched in a Pt mold to form a glass disk. Our method allows for the analysis up to 30 trace elements by LA-ICP-MS using a Photon-Machines Analyte G2 193 nm excimer laser coupled to a Thermo-Fisher Scientific ICAP Q quadrupole ICP-MS. Analyses are run as scans on the surface of the disks. Laser ablation conditions for which trace element fractionation effects are minimal have been empirically determined to be ~ 4 J m-2 fluence, at 10 Hz , and 10 μm s-1 scan speed, using a 110 μm laser beam size. Ablated material is carried into the ICP-MS by a He carrier at a rate of 0.75 L min-1. Following pre-ablation to remove surface particles, samples are ablated for 200 s, of which 140 s are used for data acquisition. At the end of each scan, a gas blank is collected for 30 s. Dwell times for each element vary between 15 and 60 μs, depending on abundance and instrument sensitivity, allowing 120 readings of each element during the data acquisition time window. To correct for variations in the total volume of material extracted by the laser, three internal standards are used, Ca, Fe and Zr. These elements are routinely analyzed by X-ray fluorescence by the Geoanalytical laboratory at Michigan State University with precision and accuracy of <5%. The availability of several internal standards allows for better correction of possible persisting laser ablation fractionation effects; for a particular trace element, we correct using the internal standard that best reproduces its ablation behavior. Our calibration is based on a combination of fused powders of US Geological Survey and Geological Survey of Japan rock standards, NIST SRM 612 glass, and US Geological Survey natural and synthetic basalt glasses. Instrumental drift is monitored during each run using two fused standards analyzed multiple times as unknowns. We routinely achieve an external precision of <5% on multiple replicates of standards run as unknowns, which are also within <5% of certified values. Elements analyzed include most first row transition metals, large ion lithophile elements, high field strength elements, lanthanide and actinide rare earth elements.

Earth’s first stable continents did not form by subduction

NASA Astrophysics Data System (ADS)

Johnson, Tim E.; Brown, Michael; Gardiner, Nicholas J.; Kirkland, Christopher L.; Smithies, R. Hugh

2017-02-01

The geodynamic environment in which Earth’s first continents formed and were stabilized remains controversial. Most exposed continental crust that can be dated back to the Archaean eon (4 billion to 2.5 billion years ago) comprises tonalite-trondhjemite-granodiorite rocks (TTGs) that were formed through partial melting of hydrated low-magnesium basaltic rocks; notably, these TTGs have ‘arc-like’ signatures of trace elements and thus resemble the continental crust produced in modern subduction settings. In the East Pilbara Terrane, Western Australia, low-magnesium basalts of the Coucal Formation at the base of the Pilbara Supergroup have trace-element compositions that are consistent with these being source rocks for TTGs. These basalts may be the remnants of a thick (more than 35 kilometres thick), ancient (more than 3.5 billion years old) basaltic crust that is predicted to have existed if Archaean mantle temperatures were much hotter than today’s. Here, using phase equilibria modelling of the Coucal basalts, we confirm their suitability as TTG ‘parents’, and suggest that TTGs were produced by around 20 per cent to 30 per cent melting of the Coucal basalts along high geothermal gradients (of more than 700 degrees Celsius per gigapascal). We also analyse the trace-element composition of the Coucal basalts, and propose that these rocks were themselves derived from an earlier generation of high-magnesium basaltic rocks, suggesting that the arc-like signature in Archaean TTGs was inherited from an ancestral source lineage. This protracted, multistage process for the production and stabilization of the first continents—coupled with the high geothermal gradients—is incompatible with modern-style plate tectonics, and favours instead the formation of TTGs near the base of thick, plateau-like basaltic crust. Thus subduction was not required to produce TTGs in the early Archaean eon.

Fluid-rock interaction during a large earthquake recorded in fault gouge: A case study of the Nojima fault, Japan

NASA Astrophysics Data System (ADS)

Bian, D.; Lin, A.

2016-12-01

Distinguishing the seismic ruptures during the earthquake from a lot of fractures in borehole core is very important to understand rupture processes and seismic efficiency. In particular, a great earthquake like the 1995 Mw 7.2 Kobe earthquake, but again, evidence has been limited to the grain size analysis and the color of fault gouge. In the past two decades, increasing geological evidence has emerged that seismic faults and shear zones within the middle to upper crust play a crucial role in controlling the architectures of crustal fluid migration. Rock-fluid interactions along seismogenic faults give us a chance to find the seismic ruptures from the same event. Recently, a new project of "Drilling into Fault Damage Zone" has being conducted by Kyoto University on the Nojima Fault again after 20 years of the 1995 Kobe earthquake for an integrated multidisciplinary study on the assessment of activity of active faults involving active tectonics, geochemistry and geochronology of active fault zones. In this work, we report on the signature of slip plane inside the Nojima Fault associated with individual earthquakes on the basis of trace element and isotope analyses. Trace element concentrations and 87Sr/86Sr ratios of fault gouge and host rocks were determined by an inductively coupled plasma mass spectrometer (ICP-MS) and thermal ionization mass spectrometry (TIMS). Samples were collected from two trenches and an outcrop of Nojima Fault which. Based on the geochemical result, we interpret these geochemical results in terms of fluid-rock interactions recorded in fault friction during earthquake. The trace-element enrichment pattern of the slip plane can be explained by fluid-rock interactions at high temperature. It also can help us find the main coseismic fault slipping plane inside the thick fault gouge zone.

Earth's first stable continents did not form by subduction.

PubMed

Johnson, Tim E; Brown, Michael; Gardiner, Nicholas J; Kirkland, Christopher L; Smithies, R Hugh

2017-03-09

The geodynamic environment in which Earth's first continents formed and were stabilized remains controversial. Most exposed continental crust that can be dated back to the Archaean eon (4 billion to 2.5 billion years ago) comprises tonalite-trondhjemite-granodiorite rocks (TTGs) that were formed through partial melting of hydrated low-magnesium basaltic rocks; notably, these TTGs have 'arc-like' signatures of trace elements and thus resemble the continental crust produced in modern subduction settings. In the East Pilbara Terrane, Western Australia, low-magnesium basalts of the Coucal Formation at the base of the Pilbara Supergroup have trace-element compositions that are consistent with these being source rocks for TTGs. These basalts may be the remnants of a thick (more than 35 kilometres thick), ancient (more than 3.5 billion years old) basaltic crust that is predicted to have existed if Archaean mantle temperatures were much hotter than today's. Here, using phase equilibria modelling of the Coucal basalts, we confirm their suitability as TTG 'parents', and suggest that TTGs were produced by around 20 per cent to 30 per cent melting of the Coucal basalts along high geothermal gradients (of more than 700 degrees Celsius per gigapascal). We also analyse the trace-element composition of the Coucal basalts, and propose that these rocks were themselves derived from an earlier generation of high-magnesium basaltic rocks, suggesting that the arc-like signature in Archaean TTGs was inherited from an ancestral source lineage. This protracted, multistage process for the production and stabilization of the first continents-coupled with the high geothermal gradients-is incompatible with modern-style plate tectonics, and favours instead the formation of TTGs near the base of thick, plateau-like basaltic crust. Thus subduction was not required to produce TTGs in the early Archaean eon.

Major and trace element chemistry of Boulder 1 at Station 2, Apollo 17

NASA Technical Reports Server (NTRS)

Blanchard, D. P.; Haskin, L. A.; Jacobs, J. W.; Brannon, J. C.; Korotev, R. L.

1975-01-01

Twenty-seven samples from Boulder 1 at Station 2 are analyzed for major and trace elements by atomic absorption spectrophotometry and neutron activation analysis. Two types of matrix and several types of clast materials are characterized on the basis of their chemistry. It is shown that one matrix type is a common material at the Apollo 17 site, while the other is probably exotic to that site. The most unusual clast materials found are coarse norite (an old rock no longer found in millimeter fragments at the site) and pigeonite basalt (possibly a highland volcanic rock). It is concluded that the boulder-forming process combined materials from at least two different localities or vertical strata.

SilMush: A procedure for modeling of the geochemical evolution of silicic magmas and granitic rocks

NASA Astrophysics Data System (ADS)

Hertogen, Jan; Mareels, Joyce

2016-07-01

A boundary layer crystallization modeling program is presented that specifically addresses the chemical fractionation in silicic magma systems and the solidification of plutonic bodies. The model is a Langmuir (1989) type approach and does not invoke crystal settling in high-viscosity silicic melts. The primary aim is to model a granitic rock as a congealed crystal-liquid mush, and to integrate major element and trace element modeling. The procedure allows for some exploratory investigation of the exsolution of H2O-fluids and of the fluid/melt partitioning of trace elements. The procedure is implemented as a collection of subroutines for the MS Excel spreadsheet environment and is coded in the Visual Basic for Applications (VBA) language. To increase the flexibility of the modeling, the procedure is based on discrete numeric process simulation rather than on solution of continuous differential equations. The program is applied to a study of the geochemical variation within and among three granitic units (Senones, Natzwiller, Kagenfels) from the Variscan Northern Vosges Massif, France. The three units cover the compositional range from monzogranite, over syenogranite to alkali-feldspar granite. An extensive set of new major element and trace element data is presented. Special attention is paid to the essential role of accessory minerals in the fractionation of the Rare Earth Elements. The crystallization model is able to reproduce the essential major and trace element variation trends in the data sets of the three separate granitic plutons. The Kagenfels alkali-feldspar leucogranite couples very limited variation in major element composition to a considerable and complex variation of trace elements. The modeling results can serve as a guide for the reconstruction of the emplacement sequence of petrographically distinct units. Although the modeling procedure essentially deals with geochemical fractionation within a single pluton, the modeling results bring up a number of questions about the petrogenetic relationships among parental magmas of nearly coeval granitic units emplaced in close proximity.

Determination of elemental content off rocks by laser ablation inductively coupled plasma mass spectrometry

USGS Publications Warehouse

Lichte, F.E.

1995-01-01

A new method of analysis for rocks and soils is presented using laser ablation inductively coupled plasma mass spectrometry. It is based on a lithium borate fusion and the free-running mode of a Nd/YAG laser. An Ar/N2 sample gas improves sensitivity 7 ?? for most elements. Sixty-three elements are characterized for the fusion, and 49 elements can be quantified. Internal standards and isotopic spikes ensure accurate results. Limits of detection are 0.01 ??g/g for many trace elements. Accuracy approaches 5% for all elements. A new quality assurance procedure is presented that uses fundamental parameters to test relative response factors for the calibration.

Trace element composition and cathodoluminescence of kyanite and its petrogenetic implications

NASA Astrophysics Data System (ADS)

Müller, Axel; van den Kerkhof, Alfons M.; Selbekk, Rune S.; Broekmans, Maarten A. T. M.

2016-09-01

Kyanite crystals from fourteen localities worldwide were analysed for their abundances of the trace elements Na, Mg, K, Ca, Ti, V, Cr, Mn, and Fe and cathodoluminescence (CL) properties. Based on protolith type, metamorphic setting, and distinctive trace element fingerprints, a genetic classification of kyanite-bearing rocks is suggested: (A) Al-rich metasediments which commonly contain coarse-grained quartz-kyanite segregations; (B) metamorphosed granitic rocks, specifically granulites; (C) metamorphosed argillic alteration zones hosted originally in felsic igneous rocks; (D) metamorphosed argillic alteration zones hosted originally in mafic igneous rocks; and (E) metamorphosed mafic to ultramafic rocks, specifically eclogites. Vanadium and Cr concentrations reflect both protolith and host rock compositions and therefore may provide a geochemical fingerprint for the nature of the protolith. The incorporation of Fe into kyanite is largely controlled by oxygen fugacity during kyanite formation, and therefore, in most cases, its concentration cannot be related to that of the protolith. From our results, Ti concentration appears to be related to metamorphic grade, particularly formation temperature. If proven by further studies, Ti-in-kyanite may provide a useful geothermometer. Correlation of trace element abundances with CL spectra confirms that common red CL, which is composed of the spectral bands centred at 1.69 eV (734 nm), 1.75 eV (708 nm), and 1.80 eV (689 nm), is related to Cr3+ defects. CL spectra of most kyanites show in addition a low-intensity blue emission centred at 2.56 eV (485 nm). Correlation of the intensity of the blue emission with Ti suggests that it is related to or sensitized by Ti4+ or Ti3+ defects. Kyanites with >3200 µgg-1 Fe show generally no detectable CL due to the CL-quenching effect of Fe2+. Our findings provide new criteria in the exploration for and quality assessment of new kyanite deposits. The Ti content, one of the critical contaminants of kyanite products, besides Fe, Ca, and Mg, appears predictable from the observed correlation of Ti with formation temperature. Iron will be hard to predict because its incorporation is mainly controlled by the oxidizing conditions during kyanite formation and the estimation of these conditions requires advanced analytical methods. Magnesium and Ca are consistently low in all investigated samples. From a regional exploration viewpoint, group C and D kyanites have the lowest Ti and relative low Fe and, therefore, will be most refractory. Due to their attractive blue colour, kyanite-bearing rocks of group C have potential as ornamental or dimension stone.

Trace elements geochemistry of fractured basement aquifer in southern Malawi: A case of Blantyre rural

NASA Astrophysics Data System (ADS)

Mapoma, Harold Wilson Tumwitike; Xie, Xianjun; Nyirenda, Mathews Tananga; Zhang, Liping; Kaonga, Chikumbusko Chiziwa; Mbewe, Rex

2017-07-01

In this study, twenty one (21) trace elements in the basement complex groundwater of Blantyre district, Malawi were analyzed. The majority of the analyzed trace elements in the water were within the standards set by World Health Organization (WHO) and Malawi Standards Board (MSB). But, iron (Fe) (BH16 and 21), manganese (Mn) (BH01) and selenium (Se) (BH02, 13, 18, 19 and 20) were higher than the WHO and MSB standards. Factor analysis (FA) revealed up to five significant factors which accounted for 87.4% of the variance. Factor 1, 2 and 3 suggest evaporite dissolution and silicate weathering processes while the fourth factor may explain carbonate dissolution and pH influence on trace element geochemistry of the studied groundwater samples. According to PHREEQC computed saturation indices, dissolution, precipitation and rock-water-interaction control the levels of trace elements in this aquifer. Elevated concentrations of Fe, Mn and Se in certain boreholes are due to the geology of the aquifer and probable redox status of groundwater. From PHREEQC speciation results, variations in trace element species were observed. Based on this study, boreholes need constant monitoring and assessment for human consumption to avoid health related issues.

Hydrothermal Links Between the Caribbean Plateau and OAE2

NASA Astrophysics Data System (ADS)

Duncan, R. A.; Snow, L. J.

2003-12-01

A popular current model for the sporadic occurrence of ocean anoxic events (OAEs) in the Cretaceous ties hydrothermally-induced changes in ocean chemistry (bio-limiting trace metals) during ocean plateau (LIP) volcanism to increased surface productivity, followed by mid-to-deep water oxygen depletion and accumulation of organic-rich sediments. This proposed connection is far from accepted, and important unresolved aspects include the timing of events and yet-to-be-proved synchroneity of volcanism and OAEs, the sensitivity of phytoplankton to bio-limiting (and toxic) trace metals, the difference in biotic responses at various OAEs, and the source of the hydrothermal inputs (sea floor spreading centers or ocean plateaus). To test this hypothesis we have measured the distribution of major, minor and trace element abundances in five pelagic carbonate and black shale sequences that bracket the OAE2, defined by a prominent positive excursion in the global seawater d13C record. Sedimentary sections at Rock Creek Canyon (Pueblo, CO), ODP Site 1138 (Kerguelen Plateau), Bass River (NJ), Totuma well (Venezuela) and Baranca el Canyon (Mexico) were chosen to examine potential trace metal patterns and gradients around the proposed source of hydrothermal inputs - the Caribbean Plateau, whose initial volcanic activity has been dated at 93-89 Ma. ICP-AES and ICP-MS elemental abundances from whole rock samples are normalized to Zr to remove the effect of terrestrial inputs. We find prominent trace metal "spikes" (up to 50 times background) for elements known to be concentrated in volatile degassing of magmas and in hydrothermal plumes resulting from seawater-rock reactions. These anomalies begin at the onset and continue well into the d13C excusion at all five sites. Furthermore, the magnitude of the anomalies decreases with distance from the Caribbean region, and the pattern of elements shifts from a wide range of metals near-source to predominantly long residence time metals far "downstream".

Critical Elements in Reservoir Rocks of Produced Fluids Nevada and Utah August 2017

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simmons, Stuart

Critical and trace element data for drill cuttings from Beowawe, Dixie Valley, and Roosevelt Hot Springs-Blundell geothermal production fields, for drill cuttings from Uinta basin producing oil-gas wells, and from outcrops in the Sevier Thermal Anomaly-Utah.

Mineralogy and petrogenesis of lunar magnesian granulitic meteorite Northwest Africa 5744

NASA Astrophysics Data System (ADS)

Kent, Jeremy J.; Brandon, Alan D.; Joy, Katherine H.; Peslier, Anne H.; Lapen, Thomas J.; Irving, Anthony J.; Coleff, Daniel M.

2017-09-01

Lunar meteorite Northwest Africa (NWA) 5744 is a granulitic breccia with an anorthositic troctolite composition that may represent a distinct crustal lithology not previously described. This meteorite is the namesake and first-discovered stone of its pairing group. Bulk rock major element abundances show the greatest affinity to Mg-suite rocks, yet trace element abundances are more consistent with those of ferroan anorthosites. The relatively low abundances of incompatible trace elements (including K, P, Th, U, and rare earth elements) in NWA 5744 could indicate derivation from a highlands crustal lithology or mixture of lithologies that are distinct from the Procellarum KREEP terrane on the lunar nearside. Impact-related thermal and shock metamorphism of NWA 5744 was intense enough to recrystallize mafic minerals in the matrix, but not intense enough to chemically equilibrate the constituent minerals. Thus, we infer that NWA 5744 was likely metamorphosed near the lunar surface, either as a lithic component within an impact melt sheet or from impact-induced shock.

Tectonic Origin of Serpentinites on Syros, Greece: Geochemical Signatures of Seafloor Serpentinization Preserved in the HP/LT Subduction Complex

NASA Astrophysics Data System (ADS)

Raia, N. H.; Cooperdock, E. H. G.; Barnes, J.; Stockli, D. F.; Schwarzenbach, E. M.

2016-12-01

Serpentinized ultramafic rocks are commonly found in exhumed HP/LT subduction complexes, but their tectonic origins (i.e., setting of serpentinization) are difficult to decipher due to extensive alteration. Growing literature and geochemical datasets demonstrate that immobile elements (REE, HFSE) in serpentinites can retain magmatic signatures indicative of the tectonic setting of parent peridotite, while fluid-mobile elements and stable isotopic signatures shed light on the fluids causing serpentinization. This study combines whole-rock trace and major element geochemistry, stable isotope (δD and δO) analyses with petrographic observation to determine the tectonic origin of ultramafic rocks in the HP/LT Aegean subduction complex. The best-preserved HP rocks of the Cycladic Blueschist Unit (CBU) are found on Syros, Greece, where serpentinized ultramafic rocks within the CBU are closely associated with metamorphosed remnants of subducted oceanic crust. All samples are completely serpentinized, lacking relict pyroxene or spinel grains, with typical assemblages consisting of serpentine, talc, chlorite, magnetite, and minor carbonate. The serpentinizing fluid was characterized using stable isotopes. δD and δO values of bulk-rock serpentinite powders and chips, respectively, suggest seafloor serpentinites hydrated by seawater at low T, typical of alteration at mid-ocean ridges and hyper-extended margins (δD = -64 to -33‰ and δO = 5.2 to 9.0‰). To fingerprint a tectonic origin, whole rock serpentinite REE patterns are compared to a global database of whole rock serpentinite analyses from fore-arc mantle wedge, mid-ocean ridge, and hyper-extended margin tectonic settings. Whole rock major element, trace element, and REE analyses are consistent with limited melt extraction, flat REE patterns (LaN/SmN = 0.2-2.6, SmN/YbN = 0.3-3.5; N= C1 normalized), and do not show pronounced Eu anomalies. These data are consistent with abyssal peridotites derived from hyper-extended margin settings, although some overlap with mid-ocean ridge serpentinites makes it difficult to rule out. In any case, the geochemical signatures retained in these serpentinites indicate they are unlikely sourced from the mantle wedge, as has been historically speculated.

Lead isotope evolution across the Neoproterozoic boundary between craton and juvenile crust, Bayuda Desert, Sudan

NASA Astrophysics Data System (ADS)

Evuk, David; Lucassen, Friedrich; Franz, Gerhard

2017-11-01

Metaigneous mafic and ultramafic rocks from the juvenile Neoproterozoic Arabian Nubian Shield (ANS) and the Proterozoic, reworked Saharan Metacraton (SMC) have been analysed for major- and trace elements and Sr, Nd, and Pb isotopes. Most of the rocks are amphibolites metamorphosed at amphibolite facies conditions, some with relicts of a granulite facies stage. The other rocks are metapyroxenites, metagabbros, and some ultramafic rocks. Trace element compositions of the metabasaltic (dominantly tholeiitic) rocks resemble the patterns of island arcs and primitive lavas from continental arcs. Variable Sr and Nd isotope ratios indicate depleted mantle dominance for most of the samples. 207Pb/204Pb signatures distinguish between the influence of high 207Pb/204Pb old SMC crust and depleted mantle signatures of the juvenile ANS crust. The Pb isotope signatures for most metabasaltic rocks, metapyroxenites and metagabbros from SMC indicate an autochthonous formation. The interpretation of the new data together with published evidence from mafic xenoliths on SMC and ophiolite from ANS allows an extrapolation of mantle evolution in time. There are two lines of evolution in the regional mantle, one, which incorporates potential upper crust material during Neoproterozoic, and a second one with a depleted mantle signature since pre-Neoproterozoic that still is present in the Red Sea and Gulf of Aden spreading centres.

Descartes Mountains and Cayley Plains - Composition and provenance

NASA Technical Reports Server (NTRS)

Drake, M. J.; Taylor, G. J.; Goles, G. G.

1974-01-01

Trace element compositions of petrographically characterized 2-4 mm lithic fragments from Apollo 16 soil samples are used to calculate initial REE concentrations in liquids in equilibrium with lunar anorthosites and to discuss the provenance of the Cayley Formation. Lithic fragments may be subdivided into four groups: (1) ANT rocks, (2) K- and SiO2-rich mesostasis-bearing rocks, (3) poikiloblastic rocks, and (4) (spinel) troctolites. Model liquids in equilibrium with essentially monominerallic anorthosites have initial REE concentrations 5-8 times those of chondrites. The REE contents of K- and SiO2-rich mesostasis-bearing rocks and poikiloblastic rocks are dominated by the mesostasis phases. ANT rocks appear to be more abundant in the Descartes Mountains, while poikiloblastic rocks appear to be more abundant in the Cayley Plains. Poikiloblastic rocks have intermediate to high LIL-element concentrations yet the low gamma-ray activity of Mare Orientale implies low LIL-element concentrations. Consequently, it is unlikely that the Cayley Formation is Orientale ejecta. A local origin as ejecta from smaller impacts is a more plausible model for the deposition of the Cayley Formation.

Tracking hydrothermal alteration and mineralization in rock-forming and accessory minerals from the Lyon Mountain Granite and related iron oxide apatite (IOA) ores from the Adirondack Mountains, New York State

NASA Astrophysics Data System (ADS)

Buchanan, A.; Hanchar, J. M.; Steele-MacInnis, M. J.; Crowley, J. L.; Valley, P. M.; Fisher, C. M.; Fedo, C.; Piccoli, P. M.; Fournelle, J.

2012-12-01

The Lyon Mountain granite (LMG) is located in the northeastern Adirondack Mountains in New York State and hosts several low-titanium iron oxide apatite (IOA) ore deposits. The ores are predominately hosted by perthite bearing granite, which has been extensively altered to albite and microcline granite by Na and K metasomatism. This alteration results in several distinct groups of rocks that are dominated by either K or Na addition and a group composed of mixed Na and K addition. The different groups of altered perthite also lie on a trend suggestive of addition of Fe to each, consistent with a secondary mineralization origin. Previous work showed that the host rocks of the IOA ores have zircon with ~1150 Ma cores and 1060-1050 Ma rims and whole grains. This study aims to further constrain the timing of LMG emplacement, subsequent hydrothermal alteration, and Fe mineralization through geochemical analysis of the major, minor, and accessory phases and geochronology of accessory phases. SIMS analyses of zircon from several of the IOA ores reveal at least two periods of growth after LMG magmatism, at 1039 +/- 4.4 Ma and 1016 +/- 7 Ma to 1000 +/- 9 Ma. In situ EMPA and LA-ICPMS trace element analyses of the zircon rims and cores reveal that in two samples the zircon rims are enriched in rare earth elements (REE) compared to their cores, potentially pointing to a hydrothermal origin. Apatite has unusually high REE and Y concentrations (some total REE2O3 > 20 wt. % oxide and up to 8 wt. % oxide Y2O3), as does titanite, which allowed for the in situ analysis of Sm-Nd in apatite and titanite by LA-MC-ICP-MS. Initial Nd isotopic composition of both ore and host rock apatite and host rock titanite are consistent with published Adirondack initial Nd whole rock data, suggesting a local source for REE in these ores. EMPA and LA-ICPMS trace-element analyses of the major rock-forming minerals indicate that the feldspar have undergone Na-metasomatism and are depleted in REEs, perhaps signifying the "local source" and the mechanism of the REE enrichment in the LMG apatite in the IOA ores and host rocks. In contrast, the minor- and trace-element compositions of the other major rock-forming minerals (e.g., clinopyroxene and fayalite) as well as the zircon, and fluorite in the LMG have average igneous granitic trace- and minor-element compositions. To better understand the timing and origin of these post ~1050 Ma events, U-Pb ID-TIMS dating of apatite and titanite, and in situ LA-MC-ICPMS Sm-Nd analysis were done on the ore and host rock samples. Apatite dates range from 1050 to 850 Ma and titanite dates range from ~1015 to 970 Ma. There is significant age variation within samples and within grains. Titanite does not have sufficient spread for accurate Sm-Nd isochron dating and two ore-apatite samples have homogenous initial Nd isotopic and Sm-Nd elemental ratios, precluding calculation of Sm-Nd dates. A third ore sample shows a large spread in Sm-Nd and yields a Sm-Nd isochron date of ~850 Ma, in close agreement with U-Pb apatite dates. The Sm-Nd isochron and U-Pb apatite dates may reflect cooling recorded in these minerals or a younger hydrothermal mineralization event.

Geochemistry of Rock Samples Collected from the Iron Hill Carbonatite Complex, Gunnison County, Colorado

USGS Publications Warehouse

Van Gosen, Bradley S.

2008-01-01

A study conducted in 2006 by the U.S. Geological Survey collected 57 surface rock samples from nine types of intrusive rock in the Iron Hill carbonatite complex. This intrusive complex, located in Gunnison County of southwestern Colorado, is known for its classic carbonatite-alkaline igneous geology and petrology. The Iron Hill complex is also noteworthy for its diverse mineral resources, including enrichments in titanium, rare earth elements, thorium, niobium (columbium), and vanadium. This study was performed to reexamine the chemistry and metallic content of the major rock units of the Iron Hill complex by using modern analytical techniques, while providing a broader suite of elements than the earlier published studies. The report contains the geochemical analyses of the samples in tabular and digital spreadsheet format, providing the analytical results for 55 major and trace elements.

Across and along arc geochemical variations in altered volcanic rocks: Evidence from mineral chemistry of Jurassic lavas in northern Chile, and tectonic implications

NASA Astrophysics Data System (ADS)

Rossel, Pablo; Oliveros, Verónica; Ducea, Mihai N.; Hernandez, Laura

2015-12-01

Postmagmatic processes mask the original whole-rock chemistry of most Mesozoic igneous rocks from the Andean arc and back-arc units preserved in Chile. Mineral assemblages corresponding to subgreenschist metamorphic facies and/or propylitic hydrothermal alteration are ubiquitous in volcanic and plutonic rocks, suggesting element mobility at macroscopic and microscopic scale. However, fresh primary phenocrysts of clinopyroxene and plagioclase do occur in some of the altered rocks. We use major and trace element chemistry of such mineral phases to infer the geochemical variations of four Jurassic arc and four back-arc units from northern Chile. Clinopyroxene belonging to rocks of the main arc and two units of the bark-arc are augites with low contents of HFSE and REE; they originated from melting of an asthenospheric mantle source. Clinopyroxenes from a third back-arc unit show typical OIB affinities, with high Ti and trace element contents and low Si. Trace elemental variations in clinopyroxenes from these arc and back-arc units suggest that olivine and clinopyroxene were the main fractionating phases during early stages of magma evolution. The last back-arc unit shows a broad spectrum of clinopyroxene compositions that includes depleted arc-like augite, high Al and high Sr-Ca diopside (adakite-like signature). The origin of these lavas is the result of melting of a mixture of depleted mantle plus Sr-rich sediments and subsequent high pressure fractionation of garnet. Thermobarometric calculations suggest that the Jurassic arc and back-arc magmatism had at least one crustal stagnation level where crystallization and fractionation took place, located at ca. ~ 8-15 km. The depth of this stagnation level is consistent with lower-middle crust boundary in extensional settings. Crystallization conditions calculated for high Al diopsides suggest a deeper stagnation level that is not consistent with a thinned back-arc continental crust. Thus minor garnet fractionation occurred before these magmas reached the base of the crust. The presented data support the existence of a heterogeneous sub arc mantle and complex magmatic processes in the early stages of the Andean subduction.

Comparison between PGAA and ID-AMS analysis for determining chlorine content in whole rock basalt

NASA Astrophysics Data System (ADS)

di Nicola, L.; Schnabel, C.; Wilcken, K. M.; Gméling, K.

2009-04-01

Accurate determination of chlorine concentrations in terrestrial rocks is of importance for the interpretation of terrestrial in-situ cosmogenic 36Cl. Neutron capture by 35Cl, together with production from Ca and K, is one of the three major production pathways of 36Cl in rocks. Here, we present an inter-comparison of chlorine determinations by two procedures. The first approach is an independent Cl determination by prompt gamma (neutron) activation analysis (PGAA). The second method is isotope dilution based on isotopically-enriched stable chlorine carrier added during chemical sample preparation for accelerator mass spectrometry (ID-AMS). Twenty six (26) whole rock samples have been processed for PGAA and ID-AMS analyses. Elemental analysis by PGAA provides concentrations of major, minor and trace elements including the target elements for 36Cl production (K, Ca, Ti, and Fe), as well as of neutron absorbers and neutron moderators (H, B, Cl, Sm and Gd). The Cl concentrations determined during this study constitute the first inter-comparison for concentrations below 100 μCl/g. Our results show no significant difference in Cl concentrations between methods, and comparable uncertainties. This agreement guarantees that during the procedure we employ for whole rock sample no significant loss of stable chlorine from either the spike or the sample occurs before isotopic equilibration, prior to AgCl precipitation. Furthermore, we show that the elemental analysis by PGAA offers anadvance for the interpretation of 36Cl measurements. It allows simultaneous measurement of major and most trace element concentrations with a precision necessary for calculating the relative contributions to 36Cl production rates of the different mechanisms. Finally, the Cl concentration can be used to optimize the amount of isotopically-enriched spike for AMS-ID sample preparation for 36Cl.

Inception and Early Evolution of the Aleutian Arc

NASA Astrophysics Data System (ADS)

Bezard, R.; Hoernle, K.; Hauff, F.; Portnyagin, M.; Werner, R.; Yogodzinski, G.; Jicha, B.; Garbe-Schönberg, D.; Turner, S.; Schaefer, B. F.

2017-12-01

Constraining the timing and style of subduction initiation in the Aleutian system is critical to model the Cenozoic geodynamic evolution of the Pacific. Until now, the oldest ages for the Aleutian arc suggest a subduction inception at c.a. 46-47 Ma. However, the compositions of these samples (arc tholeiites and calc-alkaline rocks) are different from those of typical early-arc sequences found at extensively studied subduction systems (Izu-Bonin-Mariana), dominated by FABs and boninites. Thus, if the FAB/boninite model applies to the Aleutian, the oldest units might not have been recovered yet and the arc inception could have occurred earlier than 47 Ma. To test this hypothesis, we have sampled the lowermost submarine Aleutian sequences at ten forearc and rear-arc localities during the R/V SONNE Cruise 249. We present preliminary whole-rock major and trace element concentrations, Sr-Nd-Hf-Pb isotopes as well as U-Pb zircon dating on the recovered igneous rocks. The sample compositions range from tholeiitic to calc-alkaline. No boninites were found. Most of the samples show strong subduction signatures. However, the remaining rocks present no or minor arc-type trace element features. These samples are either depleted tholeiites with similar trace element characteristics to FABs or enriched calc-alkaline rocks. Preliminary zircon dating suggests an age of 47.2 ± 1.2 Ma for one of the samples with strong arc signatures, consistent with the oldest published ages for the Aleutian so far. However, based on their compositional similarities to FABs, the depleted tholeiites should be older than the arc-type rocks, suggesting that subduction initiation could have occurred earlier than the above-mentioned age. The absence of boninite could either reflect an incomplete sampling of the early-arc sequences or a different initiation style compared to other Pacific subduction zones. Further ages and radiogenic isotope data should refine these interpretations.

The vernon supersuite: Mesoproterozoic A-type granitoid rocks in the New Jersey highlands

USGS Publications Warehouse

Volkert, R.A.; Drake, Avery A.

1998-01-01

Abundant Mesoproterozoic A-type granitoid rocks of two intrusive suites underlie approximately 50 percent of the New Jersey Highlands. These rocks, the Byram Intrusive and Lake Hopatcong Intrusive Suites, consist of granite, alaskite, quartz monzonite, monzonite, and minor pegmatite. Byram and Lake Hopatcong rocks, although different mineralogically, are similar geochemically and contain overlapping abundances of most major and trace elements. Petrographic relationships, geochronology, field relationships, and geochemical similarities support a comagmatic origin for both suites. They constitute the here named Vernon Supersuite.

Trace elements quantified by the APXS on Mars

NASA Astrophysics Data System (ADS)

Gellert, R.; Berger, J. A.; Boyd, N.; O'Connell-Cooper, C.; Desouza, E.; Thompson, L. M.; VanBommel, S.; Yen, A.

2017-12-01

The APXS accurately quantifies many trace elements within the dime-sized sample: Ni, Cu, Zn, Ga, Ge, Pb, Br, Se, As, and Y with 20 ppm detection limit (DL) and Rb, Sr, Zr, Co, Cr, and Mn with 200 ppm DL. Together with the major and minor elements, this gives important constraints for a variety of formation processes of the investigated soils, floats or extensive bedrock on Mars. The global soil, found at all rover landing sites, was used to define an average Mars value for Ni, Zn, Cr and Mn, with a consistent value of Fe/Mn 50 for soils and igneous rocks. All other APXS trace elements are below DL. Strong enrichments or depletions can both give evidence for the formation processes and link together groups of rocks and indicate their common diagenetic origin. Felsic rocks at Gale and Gusev have Cr, Ni and Zn far below soil, indicating their likely igneous origin. Further, similarly low values are found in elevated silica samples in the Murray Fm. at Gale where these elements have been mobilized and leached by fluids. High Sr and Ga was found in the host rock surrounding the Garden City vein system, which contains also high Ge, Mn and Cu, indicating mobilization in high temperature and/or acidic fluids after the Murray was lithified. The fracture fill sample Stephen at Windjana is high in Zn, Co and Cu. Germanium is enriched in the Murray Fm with very consistent values of about 100 ppm over many kilometers and 200 meters elevation, similar to perviously found bedrock at Yellowknife Bay and Windjana in Gale. Zinc is highly elevated but changes significantly with elevation in Murray, often correlated with Fe/Mn, possibly indicating changing redox conditions. Pb and Se are highly enriched at Pahrump (150, 75 ppm, resp.), drop first to low values and increase again uphill towards HematiteRidge. Nodules found at Pahrump show striking evidence for (Mg, Ni)-sulfates with Nickel up to 4% in the sulfates. All together these trends might indicate hydrothermal activity. The MER APXS instruments with somewhat higher DL found similar patterns. Elevated Ge was found at Home plate, Gusev crater, and at the rim of Endeavour crater at Meridiani Planum. Together with detailed investigations of SNC meteorites, the APXS detected trace elements supplement the bulk chemistry significantly and allow new insights into the formation processes encountered on Mars

Ion microprobe mass analysis of lunar samples. Lunar sample program

NASA Technical Reports Server (NTRS)

Anderson, C. A.; Hinthorne, J. R.

1971-01-01

Mass analyses of selected minerals, glasses and soil particles of lunar, meteoritic and terrestrial rocks have been made with the ion microprobe mass analyzer. Major, minor and trace element concentrations have been determined in situ in major and accessory mineral phases in polished rock thin sections. The Pb isotope ratios have been measured in U and Th bearing accessory minerals to yield radiometric age dates and heavy volatile elements have been sought on the surfaces of free particles from Apollo soil samples.

Tectonic origin of serpentinites on Syros, Greece: Geochemical signatures of abyssal origin preserved in a HP/LT subduction complex

NASA Astrophysics Data System (ADS)

Cooperdock, Emily H. G.; Raia, Natalie H.; Barnes, Jaime D.; Stockli, Daniel F.; Schwarzenbach, Esther M.

2018-01-01

This study combines whole rock trace and major element geochemistry, and stable isotope (δD and δ18O) analyses with petrographic observations to deduce the origin and tectonic setting of serpentinization of ultramafic blocks from the exhumed HP/LT Aegean subduction complex on Syros, Greece. Samples are completely serpentinized and are characterized by mineral assemblages that consist of variable amounts of serpentine, talc, chlorite, and magnetite. δD and δ18O values of bulk rock serpentinite powders and chips (δD = - 64 to - 33‰ and δ18O = + 5.2 to + 9.0‰) reflect hydration by seawater at temperatures < 250 °C in an oceanic setting pre-subduction, or by fluids derived from dehydrating altered oceanic crust during subduction. Fluid-mobile elements corroborate the possibility of initial serpentinization by seawater, followed by secondary fluid-rock interactions with a sedimentary source pre- or syn-subduction. Whole rock major element, trace element, and REE analyses record limited melt extraction, exhibit flat REE patterns, and do not show pronounced Eu anomalies. The geochemical signatures preserved in these serpentinites argue against a mantle wedge source, as has been previously speculated for ultramafic rocks on Syros. Rather, the data are consistent with derivation from abyssal peridotites in a hyper-extended margin setting or mid-ocean ridge and fracture zone environment. In either case, the data suggest an extensional and/or oceanic origin associated with the Cretaceous opening of the Pindos Ocean and not a subduction-related derivation from the mantle wedge.

Origin Of Extreme 3He/4He Signatures In Icelandic Lavas: Insights From Melt Inclusion Studies

NASA Astrophysics Data System (ADS)

Harlou, R.; Kent, A. J.; Breddam, K.; Davidson, J. P.; Pearson, D. G.

2003-12-01

Helium isotopes are considered a powerful tool for tracking different mantle domains. Yet, the origin of He isotope variations in many basaltic suites remains enigmatic and often difficult to link with more lithophile chemical and isotopic tracers. One problem is that He isotope ratios are measured from crushed olivines and thus reflect prior fluid and melt fluxes trapped in inclusions within the olivine grains, whereas the lithophile elements mainly reflect the host lava. In an attempt to link He and lithophile element variations, we have characterized the major and trace element composition including volatile elements, of olivine-hosted melt inclusions from three ankaramitic lavas from Vestfirdir, NW-Iceland. Previous studies have reported extreme 3He/4He ratios from NW-Iceland and one ankaramite (SEL97) has been suggested to provide the most precise estimate of the radiogenic (Sr-Nd-Pb) isotopic composition of a relatively undegassed (high 3He/4He) mantle component (C or FOZO) common to several ocean islands (Hilton et al. 1999, EPSL 173, 53-60). The samples investigated here exhibit amongst the highest 3He/4He ratios observed in terrestrial rocks (42.9 and 34.8 R/Ra). A detailed account of the trace element signature of melt inclusions in these samples may thus help explain the origin of FOZO. One sample of similar composition to these, has a lower He content and a relatively poorly defined He isotope composition of 8.15 +/- 5.1 R/Ra (Breddam & Kurz, 2001, EOS, 82, F1315). In terms of major elements, the whole rock data reflect olivine accumulation, whereas the melt inclusion data reflect ol + cpx fractionation. The melt inclusions are generally basaltic (Mg#: 52-62), with primitive mantle normalised trace element concentrations that are broadly parallel the host lavas. There is little compositional difference between melt inclusion populations from high and low 3He/4He lavas, although inclusions of the low 3He/4He lava have lower S and moderately lower Cl. The observed range of trace element ratios: [La/Sm]N 1-4, [La/Yb]N 1-5, Sr/Nd 14-24, Ba/Rb 9-23, and Ce/Pb 5-46, covers much of the range observed in Icelandic alkali basalts. The compositional similarities between inclusions and host lavas suggests that bulk rock compositions are petrogenetically related to the melts sampled by melt inclusions. If He predominantly resides in these inclusions, it suggests that the whole rock composition is an aggregate derived from the same melts that contain the measured He.

Trace elements record complex histories in diogenites

NASA Astrophysics Data System (ADS)

Balta, J. B.; Beck, A. W.; McSween, H. Y.

2012-12-01

Diogenite meteorites are cumulate rocks composed mostly of orthopyroxene and chemically linked to eucrites (basaltic) and howardites (brecciated mixtures of diogenites and eucrites). Together, they represent the largest single family of achondrite meteorites delivered to Earth, and have been spectrally linked to the asteroid 4 Vesta, the largest remaining basaltic protoplanet. However, this spectral link is non-unique as many basaltic asteroids likely formed and were destroyed in the early solar system. Recent work suggested that Vesta may be an unlikely parent body for the diogenites based on correlations between trace elements and short-lived isotope decay products, which would be unlikely to survive on a body as large as Vesta due to its long cooling history [1]. Recent analyses of terrestrial and martian olivines have demonstrated that trace element spatial distributions can preserve evidence of their crystallization history even when major elements have been homogenized [2]. We have mapped minor elements including Cr, Al, and Ti in seemingly homogeneous diogenite orthopyroxenes and found a variety of previously unobserved textures. The pyroxenes in one sample (GRA 98108) are seemingly large grains of variable shapes and sizes, but the trace elements reveal internal grain boundaries between roughly-equal sized original subgrains, with equilibrated metamorphic triple junctions between them and trace element depletions at the boundaries. These trends suggest extraction of trace elements by a magma along those relict grain boundaries during a reheating event. Two other samples show evidence of fracturing and annealing, with trace element mobility within grains. One sample appears to have remained a closed system during annealing (MET 01084), while the other has interacted with a fluid or magma to move elements along annealed cracks (LEW 88679). These relict features establish that the history of diogenite pyroxenes is more complex than their homogeneous major element compositions imply. Many trace element analyses are performed using either bulk rock techniques or spot analyses, and these maps suggest those types of analyses likely sample variable trace element abundances even within otherwise homogeneous grains, rendering their results difficult to interpret. Consequently, the correlation discussed previously between trace elements and short lived isotopes has likely been impacted by post-magmatic alteration and cannot solely be used to argue that HED's cannot be derived from Vesta. Furthermore, these maps strengthen the HED-Vesta link by suggesting that the diogenites underwent an extended history of cooling, reheating, partial melting, impact fragmentation, fluid/melt migration, and finally re-annealing. These complicated steps are particularly noteworthy as the pyroxene cumulate layer on the asteroid Vesta should lie beneath the eucritic crust, implying that early impacts were able to penetrate that crust and affect the diogenite layers early in Vesta's history, most likely while the asteroid was still hot enough to allow for annealing and regrowth of fractured grains. [1] Schiller et al. (2011) [2] Milman-Barris et al. (2008)

Publications - RDF 2002-3 | Alaska Division of Geological & Geophysical

Science.gov Websites

geochemical data from the rocks collected in the Big Delta Quadrangle, Alaska in 2001 Authors: Athey, J.E or please see our publication sales page for more information. Quadrangle(s): Big Delta Bibliographic , minor-oxide, trace-element, and geochemical data from the rocks collected in the Big Delta Quadrangle

Major and EDXRF Trace Element Chemical Analyses of Volcanic Rocks from Lassen Volcanic National Park and Vicinity, California

USGS Publications Warehouse

Clynne, Michael A.; Muffler, L.J.P.; Siems, D.F.; Taggart, J.E.; Bruggman, Peggy

2008-01-01

This open-file report presents WDXRF major-element chemical data for late Pliocene to Holocene volcanic rocks collected from Lassen Volcanic National Park and vicinity, California. Data for Rb, Sr, Ba, Y, Zr, Nb, Ni, Cr, Zn and Cu obtained by EDXRF are included for many samples. Data are presented in an EXCEL spreadsheet and are keyed to rock units as displayed on the Geologic Map of Lassen Volcanic National Park and vicinity (Clynne and Muffler, in press). Location of the samples is given in latitude and longitude in degrees and decimal minutes and in decimal degrees.

Alteration and geochemical zoning in Bodie Bluff, Bodie mining district, eastern California

USGS Publications Warehouse

Herrera, P.A.; Closs, L.G.; Silberman, M.L.

1993-01-01

Banded, epithermal quartz-adularia veins have produced about 1.5 million ounces of gold and 7 million ounces of silver from the Bodie mining district, eastern California. The veins cut dacitic lava flows, pyroclastic rocks and intrusions. Sinter boulders occur in a graben structure at the top of Bodie Bluff and fragments of sinter and mineralized quartz veins occur in hydrothermal breccias nearby. Explosive venting evidently was part of the evolution of the ore-forming geothermal systems which, at one time, must had reached the paleosurface. Previous reconnaissance studies at Bodie Bluff suggested that the geometry of alteration mineral assemblages and distribution of some of the major and trace elements throughout the system correspond to those predicted by models of hot-spring, volcanic rock hosted precious metal deposits (Silberman, 1982; Silberman and Berger, 1985). The current study was undertaken to evaluate these sugestions further. About 500 samples of quartz veins and altered rocks, including sinter, collected over a vertical extent of 200 meters within Bodie Bluff were petrographically examined and chemically analyzed for trace elements by emission spectrographic and atomic absorption methods. Sixty-five samples were analyzed for major elements by X-ray fluorescence methods. The results of these analyses showed that, in general, alteration mineral assemblage and vertical geochemical zoning patterns follow those predicted for hot-spring deposits, but that geochemical zoning patterns for sinter and quartz veins (siliceous deposits), and altered wall rocks are not always similar. The predicted depth-concentration patterns for some elements, notably Au, Ag, Hg, and Tl in quartz veins, and Hg, As and Ag in wall rocks were not as expected, or were perturbed by the main ore producing zone. For both quartz veins and altered wall rocks, the main ore zone had elevated metal contents. Increased concentration of many of these elements could indicate proximity to this zone. However, irregularities in the distribution of some key elements, such as Au and Ag, relative to the predictive models suggest that a larger suite of elements be considered for exploration for ore zones within the district. ?? 1993.

Geochemistry, petrography, and zircon U-Pb geochronology of Paleozoic metaigneous rocks in the Mount Veta area of east-central Alaska: implications for the evolution of the westernmost part of the Yukon-Tanana terrane

USGS Publications Warehouse

Dusel-Bacon, Cynthia; Day, Warren C.; Aleinikoff, John N.

2013-01-01

We report the results of new mapping, whole-rock major, minor, and trace-element geochemistry, and petrography for metaigneous rocks from the Mount Veta area in the westernmost part of the allochthonous Yukon–Tanana terrane (YTT) in east-central Alaska. These rocks include tonalitic mylonite gneiss and mafic metaigneous rocks from the Chicken metamorphic complex and the Nasina and Fortymile River assemblages. Whole-rock trace-element data from the tonalitic gneiss, whose igneous protolith was dated by SHRIMP U–Pb zircon geochronology at 332.6 ± 5.6 Ma, indicate derivation from tholeiitic arc basalt. Whole-rock analyses of the mafic rocks suggest that greenschist-facies rocks from the Chicken metamorphic complex, a mafic metavolcanic rock from the Nasina assemblage, and an amphibolite from the Fortymile River assemblage formed as island-arc tholeiite in a back-arc setting; another Nasina assemblage greenschist has MORB geochemical characteristics, and another mafic metaigneous rock from the Fortymile River assemblage has geochemical characteristics of calc-alkaline basalt. Our geochemical results imply derivation in an arc and back-arc spreading region within the allochthonous YTT crustal fragment, as previously proposed for correlative units in other parts of the terrane. We also describe the petrography and geochemistry of a newly discovered tectonic lens of Alpine-type metaharzburgite. The metaharzburgite is interpreted to be a sliver of lithospheric mantle from beneath the Seventymile ocean basin or from sub-continental mantle lithosphere of the allochthonous YTT or the western margin of Laurentia that was tectonically emplaced within crustal rocks during closure of the Seventymile ocean basin and subsequently displaced and fragmented by faults.

Trace-element composition of Chicxulub crater melt rock, K/T tektites and Yucatan basement

NASA Technical Reports Server (NTRS)

Hildebrand, A. R.; Gregoire, D. C.; Attrep, M., Jr.; Claeys, P.; Thompson, C. M.; Boynton, W. V.

1993-01-01

The Cretaceous/Tertiary (K/T) boundary Chicxulub impact is the best preserved large impact in the geologic record. The Chicxulub crater has been buried with no apparent erosion of its intracrater deposits, and its ejecta blanket is known and is well preserved at hundreds of localities globally. Although most of the molten material ejected from the crater has been largely altered, a few localities still preserve tektite glass. Availability of intra- and extracrater impact products as well as plausible matches to the targeted rocks allows the comparison of compositions of the different classes of impact products to those of the impacted lithologies. Determination of trace-element compositions of the K/T tektites, Chicxulub melt rock, and the targeted Yucatan silicate basement and carbonate/evaporite lithologies have been made using instrumental neutron activation analysis (INAA) and inductively coupled plasma mass spectrometry (ICP-MS). Some sample splits were studied with both techniques to ensure that inter-laboratory variation was not significant or could be corrected. The concentration of a few major and minor elements was also checked against microprobe results. Radiochemical neutron activation analysis (RNAA) was used to determine Ir abundances in some samples.

Tectonic setting and metallogenesis of volcanogenic massive sulfide deposits in the Bonnifield Mining District, Northern Alaska Range: Chapter B in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

USGS Publications Warehouse

Dusel-Bacon, Cynthia; Aleinikoff, John N.; Premo, Wayne R.; Paradis, Suzanne; Lohr-Schmidt, Ilana; Gough, Larry P.; Day, Warren C.

2007-01-01

This paper summarizes the results of field and laboratory investigations, including whole-rock geochemistry and radiogenic isotopes, of outcrop and drill core samples from volcanogenic massive sulfide (VMS) deposits and associated metaigneous rocks in the Wood River area of the Bonnifield mining district, northern Alaska Range (see fig. 1 of Editors’ Preface and Overview). U-Pb zircon igneous crystallization ages from felsic rocks indicate a prolonged period of Late Devonian to Early Mississippian (373±3 to 357±4 million years before present, or Ma) magmatism. This magmatism occurred in a basinal setting along the ancient Pacific margin of North America. The siliceous and carbonaceous compositions of metasedimentary rocks, Precambrian model ages based on U-Pb dating of zircon and neodymium ages, and for some units, radiogenic neodymium isotopic compositions and whole-rock trace-element ratios similar to those of continental crust are evidence for this setting. Red Mountain (also known as Dry Creek) and WTF, two of the largest VMS deposits, are hosted in peralkaline metarhyolite of the Mystic Creek Member of the Totatlanika Schist. The Mystic Creek Member is distinctive in having high concentrations of high-field-strength elements (HFSE) and rare-earth elements (REE), indicative of formation in a within-plate (extensional) setting. Mystic Creek metarhyolite is associated with alkalic, within-plate basalt of the Chute Creek Member; neodymium isotopic data indicate an enriched mantle component for both members of this bimodal (rhyolite-basalt) suite. Anderson Mountain, the other significant VMS deposit, is hosted by the Wood River assemblage. Metaigneous rocks in the Wood River assemblage span a wide compositional range, including andesitic rocks, which are characteristic of arc volcanism. Our data suggest that the Mystic Creek Member likely formed in an extensional, back-arc basin that was associated with an outboard continental-margin volcanic arc that included rocks of the Wood River assemblage. We suggest that elevated HFSE and REE trace-element contents of metavolcanic rocks, whose major-element composition may have been altered, are an important prospecting tool for rocks of VMS deposit potential in east-central Alaska.

Content and distribution of arsenic, bismuth, lithium and selenium in mineral and synthetic fertilizers and their contribution to soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Senesi, N.; Polemio, M.; Lorusso, L.

1979-01-01

Concentrations of arsenic, bismuth, lithium and selenium were determined by atomic absorption spectrophotometry in 32 samples of commercial fertilizers from various manufacturers and distributors. Arsenic and lithium were detected in all investigated samples, bismuth in 50% of samples and selenium only in two samples. Arsenic content ranged from 2 to 321 ppM; lithium varied from 5 to 0.1 ppM; bismuth was always lower than 0.5 ppM; selenium was detectable at the levels of 10 and 13 ppM. Fertilizers made from rock phosphates contained trace element amounts generally higher than those derived from rock carbonates, synthetic nitrogen fertilizers and potassium sulphate.more » Additions of trace elements from fertilizers applied at common rates to cultivated soils are tabulated and discussed on the basis of the natural soil reserves and toxicity levels for plants. Whereas applications of bismuth resulted always very low to influence the usual soil content and plant uptakes and selenium was only rarely present in fertilizers, lithium and moreover arsenic additions by fertilizers could influence the trace element status in soil, overcoming occasionally the toxicity levels for more sensitive crops.« less

Heterogeneous hydrogen distribution in orthopyroxene from veined mantle peridotite (San Carlos, Arizona): Impact of melt-rock interactions

NASA Astrophysics Data System (ADS)

Denis, Carole M. M.; Demouchy, Sylvie; Alard, Olivier

2018-03-01

Experimental studies have shown that hydrogen embedded as a trace element in mantle mineral structures affects the physical properties of mantle minerals and rocks. Nevertheless, hydrogen concentrations in mantle minerals are much lower than predicted by hydrogen solubilities obtained experimentally at high pressure and temperature. Here, we report textural analyses and major and trace element concentrations (including hydrogen) in upper mantle minerals from a spinel-bearing composite xenolith (dunite and pyroxenite) transported by silica-undersaturated mafic alkaline lavas from the San Carlos volcanic field (Arizona, USA). Our results suggest that the composite xenolith results from the percolation-reaction of a basaltic liquid within dunite channels, and is equilibrated with respect to trace elements. Equilibrium temperatures range between 1011 and 1023 °C. Hydrogen concentrations (expressed in ppm H2O by weight) obtained from unpolarized and polarized Fourier transform infrared spectroscopy are low, with average values <2 ppm H2O, 24 ppm H2O, and 53 ppm H2O for olivine, orthopyroxene, and clinopyroxene, respectively; hydrogen concentrations in olivine are below the detection limit. These low hydrogen concentrations are consistent with depletion by high melt-rock ratio interactions. Clinopyroxene hydrogen concentrations are homogeneous, whereas polarized infrared profile measurements across single-crystals of orthopyroxene reveal hydrogen-depleted rims, which are interpreted as the result of dehydration by ionic diffusion, possibly triggered by melt-rock interactions. We conclude that pyroxenes, like olivine, are unreliable hydrogen proxies, and that the remaining hydrogen concentrations observed in peridotites might only represent the 'tip of the iceberg' of the water stored in the Earth's upper mantle.

Geochemistry of the Serifos calc-alkaline granodiorite pluton, Greece: constraining the crust and mantle contributions to I-type granitoids

NASA Astrophysics Data System (ADS)

Stouraiti, C.; Baziotis, I.; Asimow, P. D.; Downes, H.

2017-11-01

The Late Miocene (11.6-9.5 Ma) granitoid intrusion on the island of Serifos (Western Cyclades, Aegean Sea) is composed of syn- to post-tectonic granodiorite with quartz monzodiorite enclaves, cut by dacitic and aplitic dikes. The granitoid, a typical I-type metaluminous calcic amphibole-bearing calc-alkaline pluton, intruded the Cycladic Blueschists during thinning of the Aegean plate. Combining field, textural, geochemical and new Sr-Nd-O isotope data presented in this paper, we postulate that the Serifos intrusion is a single-zoned pluton. The central facies has initial 87Sr/86Sr = 0.70906 to 0.7106, ɛNd(t) = - 5.9 to - 7.5 and δ18Οqtz = + 10 to + 10.6‰, whereas the marginal zone (or border facies) has higher initial 87Sr/86Sr = 0.711 to 0.7112, lower ɛ Nd(t) = - 7.3 to - 8.3, and higher δ18Οqtz = + 10.6 to + 11.9‰. The small range in initial Sr and Nd isotopic values throughout the pluton is paired with a remarkable uniformity in trace element patterns, despite a large range in silica contents (58.8 to 72 wt% SiO2). Assimilation of a crustally derived partial melt into the mafic parental magma would progressively add incompatible trace elements and SiO2 to the evolving mafic starting liquid, but the opposite trend, of trace element depletion during magma evolution, is observed in the Serifos granodiorites. Thermodynamic modeling of whole-rock compositions during simple fractional crystallization (FC) or assimilation-fractional crystallization (AFC) processes of major rock-forming minerals—at a variety of pressure, oxidation state, and water activity conditions—fails to reproduce simultaneously the major element and trace element variations among the Serifos granitoids, implying a critical role for minor phases in controlling trace element fractionation. Both saturation of accessory phases such as allanite and titanite (at SiO2 ≥ 71 wt%)(to satisfy trace element constraints) and assimilation of partial melts from a metasedimentary component (to match isotopic data) must have accompanied fractional crystallization of the major phases.

Major and minor oxide and trace element determination in silicate rocks by direct current plasma optical emission echelle spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bankston, D.C.; Humphris, S.E.; Thompson, G.

1979-07-01

A technique for the determination of major concentrations of SiO/sub 2/, Al/sub 2/O/sub 3/, Fe/sub 2/O/sub 3/, MgO, CaO, Na/sub 2/O, and K/sub 2/O, minor levels of TiO/sub 2/, P/sub 2/O/sub 5/, and MnO, and trace concentrations of Ba, Cr, Cu, Ni, Sr, V, and Zn, in semi-microsamples 200 mg) of powdered whole rock, is described. Chemically diverse standard reference rocks are used both for calibration and assessment of accuracy. A lithium metaborate fusion melt of each standard or sample is dissolved in dilute HNO/sub 3/ containing Cs/sup +/ at a level of 0.2% (w/v). The resulting solution is usedmore » to perform all analyses except those for Na/sub 2/O and K/sub 2/O, which are determined in a portion of the original sample solution wherein the Cs/sup +/ concentration has been raised to 0.32% (w/v). Analyses of both portions of each sample solution are performed using an optical emission spectrometer/spectrograph equipped with an echelle monochromator and a dc argon plasma excitation source. Trace element detection limits ranged from 2 ppM for Cu to 15 ppM for Zn. A study of precision based on replicate determinations in three splits of the proposed USGS reference basalt BHVO-1 yielded the following results: (1) For analyses of the major and minor oxide constituents, values of the percent relative standard deviation (RSD) ranged from 1 for CaO, to 21 for P/sub 2/O/sub 5/. 2) For trace element determinations, values of the RSD ranged from 2 for Cu, to 19 for Zn. 2 figures, 11 tables.« less

Rare Earth Geochemistry of Rock Core form WY Reservoirs

DOE Data Explorer

Quillinan, Scott; Bagdonnas, Davin; McLaughlin, J. Fred; Nye, Charles

2016-10-01

These data include major, minor, trace and rare earth element concentration of geologic formations in Wyoming oil and gas fields. *Note - Link below contains updated version of spreadsheet (6/14/2017)

Chronology and petrogenesis of a 1.8 g lunar granitic clast:14321,1062

NASA Technical Reports Server (NTRS)

Shih, C.-Y.; Bansal, B. M.; Wiesmann, H.; Nyquist, L. E.; Bogard, D. D.; Wooden, J. L.

1985-01-01

Geochronological, isotopic, and trace element data for a pristine granite clast from Apollo 14 breccia 14321 obtained using Rb-Sr, Sm-Nd, and (Ar-39)-(Ar-40) methods are presented. Trace element data for a possibly related evolved rock, the quartz-monodiorite clast from breccia 15404 are also presented, and the relationship between these two rock types is discussed. The concordancy of the Rb-Sr and Sm-Nd internal isochron ages and especially the Rb-Sr model age strongly suggest that the granite clast formed 4.1 AE ago. It probably crystallized slowly in the crust and was later excavated and brecciated about 3.88 AE ago, as indicated by the Ar-Ar age. A two-stage model involving crystal fractionation followed by silicate liquid immiscibility is proposed for the lunar granite genesis.

Modelling the petrogenesis of high Rb/Sr silicic magmas

USGS Publications Warehouse

Halliday, A.N.; Davidson, J.P.; Hildreth, W.; Holden, P.

1991-01-01

Rhyolites can be highly evolved with Sr contents as low as 0.1 ppm and Rb Sr > 2,000. In contrast, granite batholiths are commonly comprised of rocks with Rb Sr 100. Mass-balance modelling of source compositions, differentiation and contamination using the trace-element geochemistry of granites are therefore commonly in error because of the failure to account for evolved differentiates that may have been erupted from the system. Rhyolitic magmas with very low Sr concentrations (???1 ppm) cannot be explained by any partial melting models involving typical crustal source compositions. The only plausible mechanism for the production of such rhyolites is Rayleigh fractional crystallization involving substantial volumes of cumulates. A variety of methods for modelling the differentiation of magmas with extremely high Rb/Sr is discussed. In each case it is concluded that the bulk partition coefficients for Sr have to be large. In the simplest models, the bulk DSr of the most evolved types is modelled as > 50. Evidence from phenocryst/glass/whole-rock concentrations supports high Sr partition coefficients in feldspars from high silica rhyolites. However, the low modal abundance of plagioclase commonly observed in such rocks is difficult to reconcile with such simple fractionation models of the observed trace-element trends. In certain cases, this may be because the apparent trace-element trend defined by the suite of cognetic rhyolites is the product of different batches of magma with separate differentiation histories accumulating in the magma chamber roof zone. ?? 1991.

Geochemical characterization of slags, other mines wastes, and their leachates from the Elizabeth and Ely mines (Vermont), the Ducktown mining district (Tennessee), and the Clayton smelter site (Idaho)

USGS Publications Warehouse

Piatak, Nadine M.; Seal, Robert R.; Hammarstrom, Jane M.; Meier, Allen L.; Briggs, Paul H.

2003-01-01

Waste-rock material produced at historic metal mines contains elevated concentrations of potentially toxic trace elements. Two types of mine waste were examined in this study: sintered waste rock and slag. The samples were collected from the Elizabeth and Ely mines in the Vermont copper belt (Besshi-type massive sulfide deposits), from the Copper Basin mining district near Ducktown, Tennessee (Besshi-type massive sulfide deposits), and from the Clayton silver mine in the Bayhorse mining district, Idaho (polymetallic vein and replacement deposits). The data in this report are presented as a compilation with minimal interpretation or discussion. A detailed discussion and interpretation of the slag data are presented in a companion paper. Data collected from sintered waste rock and slag include: (1) bulk rock chemistry, (2) mineralogy, (3) and the distribution of trace elements among phases for the slag samples. In addition, the reactivity of the waste material under surficial conditions was assessed by examining secondary minerals formed on slag and by laboratory leaching tests using deionized water and a synthetic solution approximating precipitation in the eastern United States.

Trace geochemistry of lunar material

NASA Technical Reports Server (NTRS)

Morrison, G. H.

1974-01-01

The lunar samples from the Apollo 16 and 17 flights which were analyzed include soil, igneous rock, anorthositic gabbro, orange soil, subfloor basalt, and norite breccia. Up to 57 elements including majors, minors, rare earths and other trace elements were determined in the lunar samples. The analytical techniques used were spark source mass spectrometry and neutron activation analysis. The latter was done either instrumentally or with group radiochemical separations. The differences in abundances of the elements in lunar soils at the various sites are discussed. With regard to the major elements only Si is about the same at all the sites. A detailed analysis which was performed on a sample of the Allende meteorite is summarized.

Geochemistry and tectonic setting of the Paleoproterozoic metavolcanic rocks from the Chirano Gold District, Sefwi belt, Ghana

NASA Astrophysics Data System (ADS)

Senyah, Gloria A.; Dampare, Samuel B.; Asiedu, Daniel K.

2016-10-01

Major and trace elements, including rare earth elements (REEs) data are presented for metavolcanic rocks of the Paleoproterozoic Birimian Sefwi belt to determine the geochemical characteristics as well as the possible tectonic setting of emplacement of these rocks. In order to accomplish the aim of the study, the petrographical characteristics of the rocks were examined coupled with analysis of the rocks for their whole-rock major and trace elements contents by ICP-AES and ICP-MS methods respectively. The rocks have been classified as basalt/basaltic andesites and dolerites based on their textural and mineralogical compositions. It is observed that the rocks have suffered various degrees of alteration evident in the overprinting of primary minerals such as pyroxenes and plagioclase by chlorite, epidote, sericite and others. Generally, the rocks are moderately deformed and may have experienced at least greenschist metamorphism. The basalt/basaltic andesites are derivative magmas [Mg# (20-51), Cr (10-220 ppm) and Ni (5-137 ppm)], and show flat REE to fractionated REE patterns with (La/Sm)N = 1.36-3.90, (La/Yb)N = 1.17-5.32 and strong negative to non-existent Eu anomalies (Eu/Eu* = 0.51-1.03). N-MORB-normalised multi-element diagrams show that the rocks have geochemical patterns characterised by enrichment in LILE relative to HFSE and in LREE relative to HREE. The basalt/basaltic andesites exhibit characteristics of subduction zone-related magmas, such as pronounced negative Nb-Ta anomalies, slightly negative Hf and variable negative Ti anomalies. The dolerites do not vary much from the basalts and basaltic andesites. The MgO and Fe2O3 values of the dolerite range from 2.97 to 6.93 and 5.98 to 14.35 wt.% respectively, corresponding to Mg#s of 38-62. LREEs enrichment over HREEs with (La/Sm)N ranging from 0.61 to 4.61 and (Gd/Yb)N ranging from 0.99 to 2.91 is also typical of these rocks. The dolerites also exhibit quite invariable Eu anomalies (Eu/Eu* = 0.81-1.00) and display a pronounced Nb-Ta trough and a minor negative Ti anomaly, suggesting arc characteristics. The metavolcanic rocks from the study area generally exhibit subduction-related setting characteristics with evidence of a sub-lithospheric contamination.

On nutrients and trace metals: Effects from Enhanced Weathering

NASA Astrophysics Data System (ADS)

Amann, T.; Hartmann, J.

2015-12-01

The application of rock flour on suitable land ("Enhanced Weathering") is one proposed strategy to reduce the increase of atmospheric CO2 concentrations. At the same time it is an old and established method to add fertiliser and influence soil properties. Investigations of this method focused on the impact on the carbonate system, as well as on engineering aspects of a large-scale application, but potential side effects were never discussed quantitatively. We analysed about 120,000 geochemically characterised volcanic rock samples from the literature. Applying basic statistics, theoretical release rates of nutrients and potential contaminants by Enhanced Weathering were evaluated for typical rock types. Applied rock material can contain significant amounts of essential or beneficial nutrients (potassium, phosphorus, micronutrients). Their release can partly cover the demand of major crops like wheat, rice or corn, thereby increasing crop yield on degraded soils. However, the concentrations of considered elements are variable within a specific rock type, depending on the geological setting. High heavy metal concentrations are found in (ultra-) basic rocks, the class with the highest CO2 drawdown potential. More acidic rocks contain less or no critical amounts, but sequester less CO2. Findings show that the rock selection determines the capability to supply significant amounts of nutrients, which could partly substitute industrial mineral fertiliser usage. At the same time, the release of harmful trace element has to be considered. Through careful selection of regionally available rocks, benefits could be maximised and drawbacks reduced. The deployment of Enhanced Weathering to sequester CO2 and to ameliorate soils necessitates an ecosystem management, considering the release and fate of weathered elements in plants, soils and water. Cropland with degraded soils would benefit while having a net negative CO2 effect, while other carbon dioxide removal strategies, like afforestation, biofuel production, and biochar application could benefit from Enhanced Weathering side effects, as organic carbon pools are positively influenced.

Major and trace element investigation of the Pine Mountain massif--The southernmost exposure of Grenville age crust in North America

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salpas, P.A.; Daniell, N.

1992-01-01

The Pine Mountain massif is a 1.1 Ga basement massif exposed in Alabama and Georgia. The Whatley Mill Gneiss (WMG) constitutes a major exposure of rock in the Pine Mountain massif of eastern Alabama. Based on appearance in outcrop, the WMG can be divided into three distinct lithologies. The first is a massive augen gneiss (AG) consisting of K-spar augen in a finer grained matrix of biotite, K-spar, plagioclase, and quartz. The second lithology is a fine-grained gneiss (FG) composed predominantly of quartz with minor muscovite. The FG occurs sporadically as band of mylonite within the AG. The third lithologymore » is generally accepted to be the protolith of the AG. It is a relatively unfoliated and undeformed rock (UN) of sparse occurrence whose mineralogy is similar to that of the AG but also contains hornblende and rounded mafic inclusions of biotite gneiss. AG and FG samples were collected along a traverse through over 220 meters of stratigraphic thickness of the WMG and were analyzed for major element compositions by XRF and for trace element compositions by INAA. Relative to the AG samples, the FG samples are enriched in SiO[sub 2] and depleted in FeO and ferromagnesian trace elements such as Sc. REE concentrations are generally higher in the AG than in the FG but the sizes of the ranges in concentrations among both groups of rocks are similar. REE systematics indicate that the silica-rich fluid introduced into the AG during shearing appears to have made negligible contributions to the absolute and relative whole-rock REE concentrations but, instead, simply diluted the REE in the parent AG. Based upon the limited sampling of UN so far, deformation to produce the foliated AG, including augen formation, appears to have occurred isochemically.« less

Fluid-rock interaction recorded in fault rocks of the Nobeoka Thrust, fossilized megasplay fault in an ancient accretionary complex

NASA Astrophysics Data System (ADS)

Hasegawa, R.; Yamaguchi, A.; Fukuchi, R.; Kitamura, Y.; Kimura, G.; Hamada, Y.; Ashi, J.; Ishikawa, T.

2017-12-01

The relationship between faulting and fluid behavior has been in debate. In this study, we clarify the fluid-rock interaction in the Nobeoka Thrust by major/trace element composition analysis using the boring core of the Nobeoka Thrust, an exhumed analogue of an ancient megasplay fault in Shimanto accretionary complex, southwest Japan. The hanging wall and the footwall of the Nobeoka Thrust show difference in lithology and metamorphic grade, and their maximum burial temperature is estimated from vitrinite reflectance analysis to be 320 330°C and 250 270°C, respectively (Kondo et al., 2005). The fault zone was formed in a fluid-rich condition, as evidenced by warm fluid migration suggested by fluid inclusion analysis (Kondo et al., 2005), implosion brecciation accompanied by carbonate precipitation followed by formation of pseudotachylyte (Okamoto et al., 2006), ankerite veins coseismically formed under reducing conditions (Yamaguchi et al., 2011), and quartz veins recording stress rotation in seismic cycles (Otsubo et al., 2016). In this study, first we analyzed the major/trace element composition across the principal slip zone (PSZ) of the Nobeoka Thrust by using fragments of borehole cores penetrated through the Nobeoka Thrust. Many elements fluctuated just above the PSZ, whereas K increase and Na, Si decrease suggesting illitization of plagioclase, as well as positive anomalies in Li and Cs were found within the PSZ. For more detail understanding, we observed polished slabs and thin sections of the PSZ. Although grain size reduction of deformed clast and weak development of foliation were observed entirely in the PSZ by macroscopic observation, remarkable development of composite planar fabric nor evidence of friction melting were absent. In this presentation, we show the result of major/trace element composition corresponding to the internal structure of PSZ, and discuss fluid-rock interaction and its impact to megasplay fault activity in subduction zones.

Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos spreading center: role of crystal fractionation and mantle heterogeneity.

USGS Publications Warehouse

Clague, D.A.; Frey, F.A.; Thompson, G.; Rindge, S.

1981-01-01

A wide range of rock types (abyssal tholeiite, Fe-Ti-rich basalt, andesite, and rhyodacite) were dredged from near 95oW and 85oW on the Galapagos spreading center. Computer modeling of major element compositions has shown that these rocks could be derived from common parental magmas by successive degrees of fractional crystallization. However, the P2O5/K2O ratio implies distinct mantle source compositions for the two areas. These source regions also have different rare earth element (REE) abundance patterns. The sequence of fractionated lavas differs for the two areas and indicates earlier fractionation of apatite and titanomagnetite in the lavas from 95oW. The mantle source regions for these two areas are interpreted to be depleted in incompatible (and volatile?) elements, although the source region beneath 95oW is less severely depleted in La and K. -Authors

Webinar on the Removal of Uranium from Drinking Water by Small System Treatment Technology

EPA Science Inventory

Abstract: Radionuclides, such as uranium (U), occur naturally as trace elements in rocks and soils and thus can be found in dissolved forms in ground waters. Uranium has four oxidation states (+3, +4, +5, and +6) and is a very reactive element forming a variety of stable complexe...

The role of sample preparation in interpretation of trace element concentration variability in moss bioindication studies

USGS Publications Warehouse

Migaszewski, Z.M.; Lamothe, P.J.; Crock, J.G.; Galuszka, A.; Dolegowska, S.

2011-01-01

Trace element concentrations in plant bioindicators are often determined to assess the quality of the environment. Instrumental methods used for trace element determination require digestion of samples. There are different methods of sample preparation for trace element analysis, and the selection of the best method should be fitted for the purpose of a study. Our hypothesis is that the method of sample preparation is important for interpretation of the results. Here we compare the results of 36 element determinations performed by ICP-MS on ashed and on acid-digested (HNO3, H2O2) samples of two moss species (Hylocomium splendens and Pleurozium schreberi) collected in Alaska and in south-central Poland. We found that dry ashing of the moss samples prior to analysis resulted in considerably lower detection limits of all the elements examined. We also show that this sample preparation technique facilitated the determination of interregional and interspecies differences in the chemistry of trace elements. Compared to the Polish mosses, the Alaskan mosses displayed more positive correlations of the major rock-forming elements with ash content, reflecting those elements' geogenic origin. Of the two moss species, P. schreberi from both Alaska and Poland was also highlighted by a larger number of positive element pair correlations. The cluster analysis suggests that the more uniform element distribution pattern of the Polish mosses primarily reflects regional air pollution sources. Our study has shown that the method of sample preparation is an important factor in statistical interpretation of the results of trace element determinations. ?? 2010 Springer-Verlag.

Publications - RDF 2008-1 v. 1.0.1 | Alaska Division of Geological &

Science.gov Websites

main content DGGS RDF 2008-1 v. 1.0.1 Publication Details Title: Major-oxide, minor-oxide, and trace , S.E., and Jing, L., 2008, Major-oxide, minor-oxide, and trace-element geochemical data from rocks and Birch Creek; Hope Creek; Idaho Creek; Major Oxides; McManus Creek; Montana Creek; Polar Creek; Pool

Trace element geochemistry (Li, Ba, Sr, and Rb) using Curiosity's ChemCam: early results for Gale crater from Bradbury Landing Site to Rocknest

USGS Publications Warehouse

Ollila, Ann M.; Newsom, Horton E.; Clark, Benton; Wiens, Roger C.; Cousin, Agnes; Blank, Jen G.; Mangold, Nicolas; Sautter, Violaine; Maurice, Sylvestre; Clegg, Samuel M.; Gasnault, Olivier; Forni, Olivier; Tokar, Robert; Lewin, Eric; Dyar, M. Darby; Lasue, Jeremie; Anderson, Ryan; McLennan, Scott M.; Bridges, John; Vaniman, Dave; Lanza, Nina; Fabre, Cecile; Melikechi, Noureddine; Perett, Glynis M.; Campbell, John L.; King, Penelope L.; Barraclough, Bruce; Delapp, Dorothea; Johnstone, Stephen; Meslin, Pierre-Yves; Rosen-Gooding, Anya; Williams, Josh

2014-01-01

The ChemCam instrument package on the Mars rover, Curiosity, provides new capabilities to probe the abundances of certain trace elements in the rocks and soils on Mars using the laser-induced breakdown spectroscopy technique. We focus on detecting and quantifying Li, Ba, Rb, and Sr in targets analyzed during the first 100 sols, from Bradbury Landing Site to Rocknest. Univariate peak area models and multivariate partial least squares models are presented. Li, detected for the first time directly on Mars, is generally low (100 ppm and >1000 ppm, respectively. These analysis locations tend to have high Si and alkali abundances, consistent with a feldspar composition. Together, these trace element observations provide possible evidence of magma differentiation and aqueous alteration.

Trace element and isotopic composition of apatite in carbonatites from the Blue River area (British Columbia, Canada) and mineralogy of associated silicate rocks

NASA Astrophysics Data System (ADS)

Mitchell, Roger; Chudy, Thomas; McFarlane, Christopher R. M.; Wu, Fu-Yuan

2017-08-01

Apatites from the Verity, Fir, Gum, Howard Creek and Felix carbonatites of the Blue River (British Columbia, Canada) area have been investigated with respect to their paragenesis, cathodoluminescence, trace element and Sr-Nd isotopic composition. Although all of the Blue River carbonatites were emplaced as sills prior to amphibolite grade metamorphism and have undergone deformation, in many instances magmatic textures and mineralogy are retained. Attempts to constrain the U-Pb age of the carbonatites by SIMS, TIMS and LA-ICP-MS studies of zircon and titanite were inconclusive as all samples investigated have experienced significant Pb loss during metamorphism. The carbonatites are associated with undersaturated calcite-titanite amphibole nepheline syenite only at Howard Creek although most contain clasts of disaggregated phoscorite-like rocks. Apatite from each intrusion is characterized by distinct, but wide ranges, in trace element composition. The Sr and Nd isotopic compositions define an array on a 87Sr/86Sr vs²Nd diagram at 350 Ma indicating derivation from depleted sub-lithospheric mantle. This array could reflect mixing of Sr and Nd derived from HIMU and EM1 mantle sources, and implies that depleted mantle underlies the Canadian Cordillera. Although individual occurrences of carbonatites in the Blue River region are mineralogically and geochemically similar they are not identical and thus cannot be considered as rocks formed from a single batch of parental magma at the same stage of magmatic evolution. However, a common origin is highly probable. The variations in the trace element content and isotopic composition of apatite from each occurrence suggest that each carbonatite represents a combination of derivation of the parental magma(s) from mineralogically and isotopically heterogeneous depleted mantle sources coupled with different stages of limited differentiation and mixing of these magmas. We do not consider these carbonatites as primary direct partial melts of the sub-lithospheric mantle which have ascended from the asthenosphere without modification of their composition.

Laser ablation ICP-MS and traditional micromorphological techniques applied to the study of different genetic horizons in thin sections: soil genesis and trace element distribution

NASA Astrophysics Data System (ADS)

Scarciglia, Fabio; Barca, Donatella; de Rosa, Rosanna; Pulice, Iolanda; Vacca, Andrea

2010-05-01

This work focuses on an innovative methodological approach to investigate in situ chemical composition of trace and rare earth (REE) elements in discrete soil features from different soil horizons: laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied to clay coatings, pedogenic matrix and skeletal parent rock fragments in thin sections, coupled with traditional pedological investigations, specially clay mineralogy and micromorphology. Analyses were performed on 80 μm-thick sections obtained from undisturbed soil samples, which represent three reddish argillic (Bt) horizons from an Alfisol developed on late Pleistocene slope deposits and three brown organic-mineral (A) horizons from an Entisol formed on Holocene aggrading fluvial sediments in the Muravera area (southeast Sardinia, Italy). Validation of the LA-ICP-MS technique provides in situ accurate and reproducible (RSD 13-18%) analysis of low concentration trace elements in the studied soil samples (0.001-0.1 ppm). Our results showed a high reliability of this method on soil thin sections and revealed that concentrations of trace and rare earth elements in the different portions of a soil profile can be used to investigate their distribution, as a response to soil-forming processes. A general trend of increase of most trace elements from rock fragments to (both clayey and organic-rich) soil matrix, to clay coatings in argillic horizons is clearly highlighted. On this basis a prominent role of pedogenetic processes in element fractionation and distribution during weathering can be supposed. In particular, element adsorption onto reactive sites of organic matter and clay particles (and possibly Fe-oxyhydroxides) and clay illuviation appear the main pedogenetic processes able to promote element enrichment after their release from the weathering of primary minerals. As clay coatings exhibit the highest concentration of trace elements, and specifically of REEs, and represent the most mobile solid phase in the soil profile, this tool can be used as a reliable indicator of soil weathering after a preliminary assessment of illuvial clay pedofeatures. This feature is consistent with a progressively increasing time of soil development, testified by the older age of the Alfisol than the Entisol profile. Such a result is also supported by a comparison of trace element concentrations between the clay and the fine earth fractions of the bulk soil horizons performed with ICP-MS in solution, showing REE enrichment in the clays from the former soil. Moreover, trace element patterns show some discontinuous trends among soil features of different horizons, coherently with erosive and/or depositional discontinuities described in the field.

Simultaneous thermodynamic and geochemical analyses for P-T-time and mass transport toward comprehensive understanding of metamorphism

NASA Astrophysics Data System (ADS)

Uno, M.; Nakamura, H.; Iwamori, H.

2011-12-01

Individual parcel of regional metamorphic rock records physico-chemical conditions such as P-T path, mass transfer and deformation with the Lagrangian specification. On the other hand, a metamorphic belt as an ensemble of such parcels may provide a large-scale flow field of energy (e.g., temperature, entropy) and mass (including both solid and fluid phases with elements and isotopes) with the Eulerian specification. However, there is so far few model that integrates all the variables stated above. Phase petrology provides mostly the intensive variables (e.g., P-T path), whereas geochemistry provides mostly the extensive variables (time-integrated mass transfer), and these two have been treated separately. Here we combine phase petrology and geochemistry from a scale of mineral grain, and solve them under a simultaneous and consistent set of thermodynamic and mass balance equation. For this sake, the Sanbagawa metamorphic belt in Japan has been surveyed. To understand the nature of fluid during rehydration, we analyzed both basic rocks and pelitic rocks that record retrograde reactions. Major and trace element compositions of each mineral, and bulk rock chemistry have been analyzed with EPMA, LA-ICP-MS, XRF and ICP-MS, respectively. Retrograde P-T path and the extent of rehydration of each rock have been obtained by applying the Gibbs' method (e.g. Spear, 1993; Okamoto&Toriumi, 2001) to amphiboles. Trace element budget along a specific P-T path were calculated by equating differential mass balance equation for major and trace elements as follows; XfluiddMfluid = ⊙MsolidXsolid + ⊙XsoliddMsolid Where the X and M denotes compositions and modes of minerals and dX and dM are their changes along a specific P-T change. The mineral compositions (Xsolid), mineral modes (Msolid), mineral growths (dMsolid) for zoned minerals (amphibole and/or garnet) and fluid compositions (Xfluid) were derived from the results of Gibbs' method, X-ray map and fluid/mineral partition coefficients, respectively. Thus, the unknowns are dMs, and the equations are solved for them. As a result, the mass transfer during the specific P-T change (Xfluid dMfluid) can be specified. It is revealed that fluid mobile elements such as LIL elements, Sr and Pb are mostly proportional to LOI (loss on ignition). LOI and extent of rehydration is proportional in the Sanbagawa belt (Okamoto&Toriumi, 2005), thus the observed enrichment of LILE, Sr and Pb are interpreted to be associated with rehydration. The Sr isotope ratios of the basic shists also increase with LOI, implying that the differences in bulk rock chemistry are not attributed to differences in mineral modes,but addition and/or reaction with external source of fluids with high 87Sr/86Sr. The estimated fluid composition is similar to calculated compositions of slab-derived fluids (Nakamura et al., 2008). From mass balance calculation, trace element budget associated with rehydration reactions and their spatial distribution will be presented, and the mechanisms of mass and fluid transfer will be discussed.

Trace element zoning as a record of chemical disequilibrium during garnet growth

NASA Astrophysics Data System (ADS)

Chernoff, Carlotta B.; Carlson, William D.

1999-06-01

Trace element concentrations in pelitic garnets from the Picuris Range of New Mexico display precipitous changes coincident with abrupt variations in Ca concentration. These patterns probably arise from the transitory participation of different trace element enriched phases in the garnet forming reaction. Changes in the reactant and product assemblages occur at different times during the reaction history for crystals of different size, so they cannot be the result of any event affecting the entire rock, such as a change in pressure, temperature, or fluid composition. Instead, they reflect kinetic factors that cause Ca, Y, Yb, P, Ti, Sc, Zr, Hf, Sr, Na, and Li to fail to achieve chemical equilibrium during garnet growth. Caution is needed to avoid misinterpreting excursions in the concentration of these elements as event markers recording simultaneous rockwide changes in intensive parameters, when in fact they may record transient disequilibrium states that are local in scope, and not contemporaneous.

Behavior of major and trace elements upon weathering of peridotites in New Caledonia : A possible site on ultramafic rocks for the Critical Zone Exploration Network (CZEN) ?

NASA Astrophysics Data System (ADS)

Juillot, Farid; Fandeur, D.; Fritsch, E.; Morin, G.; Ambrosi, J. P.; Olivi, L.; Cognigni, A.; Hazemann, J. L.; Proux, O.; Webb, S.; Brown, G. E., Jr.

2010-05-01

Ultramafic rocks cover about 1% of the continental surfaces and are related to ophiolitic bodies formed near convergent plate boundaries (Coleman, 1977). The most typical ultramafic rocks are dunite and harzburgite, which are composed of easily weatherable ferromagnesian mineral species (olivines and pyroxenes), but also of more resistant spinels (chromite and magnetite). Oceanic serpentinization of these ultramafic rocks usually lead to partial transformation of these initial mineral assemblages by forming hydrous layer silicates such as serpentine (lizardite, chrysotile and antigorite) talc, chlorite and actinolite (Malpas, 1992). It also lead to the formation of highly sheared textures, which favor meteoric weathering through preferential water flows. Compared to their crystalline rock counterpart that covers most of the continental surfaces, these ultramafic rocks mainly differ by their lower SiO2, Al2O3 and K2O contents (less than 50%, 10% and 1%, respectively) and, on the opposite, much higher MgO content (more than 18%). Moreover, they commonly have higher concentrations in FeO and other trace elements, such as Ni, Cr, Mn and Co. Weathering of these rocks is then at the origin of major geochemical anomalies on continental surfaces, especially when they occur in tropical and subtropical regions. Such conditions are encountered in New Caledonia where one third of the surface is covered with peridotites (mainly harzburgite with small amounts of dunite) obducted about 35 millions years ago during large tectonic events in the Southwest Pacific at the Late Eocene (Cluzel et al., 2001). Tropical weathering of these ultramafic rocks lead to the development of thick lateritic regoliths where almost all Mg and Si have been leached out and Fe, Mn, Ni, Cr and Co have been relatively concentrated. In these oxisols, Ni, Cr and Co can exhibit concentration up to several wt%, which make them good candidates for ore mining (New Caledonia is the third Ni producer in the world). However, these high concentration of potentially toxic elements can represent a serious hazard for the environmental quality of the Caledonian ecosystem which is a '' biodiversity hotspot' (Myers, 2000), which emphasize the strong need for characterizing the natural cycling of these elements upon weathering of ultramafic rocks. To reach this goal, we have studied the mineralogical distribution, crystal-chemistry and mass balance modelling of major (Si, Mg, Al, Fe, Mn) and trace elements (Ni, Cr and Co) in the freely-drained weathering profile developed in the serpentinized harzburgites of Mt Koniambo (West Coast of New Caledonia). Results show that both hydrothermal and meteoric processes contributed to the vertical differentiation of this freely drained weathering profiles in serpentinized ultramafic rocks. Finally, they also emphasize the importance of both redox reactions and interactions with Mn- and Fe-oxyhydroxydes (Fandeur et al., 2009a; 2009b) to explain the opposite behavior observed between very mobile Ni and almost immobile Cr (Fandeur et al., 2010). These results bring new insights on the geochemical behavior of trace elements upon weathering of ultramafic rocks under tropical conditions leading to the formation of supergene ore deposits. They also emphasize the interest of such a weathering site on ultramafic rocks under tropical climate to complemente the reference sites of the Critical Zone Exploration Network (CZEN). References Cluzel D., Aitchinson J.C. and Picard C. (2001) Tectonic accretion and underplating of mafic terranes in the Late Eocene intraoceanic fore-arc of New-Caledonia (Southwest Pacific): geodynamic implications. Tectonophysics, 340, 23-59. Coleman, R.G. (1977) Ophiolites: Ancient oceanic lithosphere?: Berlin, Germany, Springer-Verlag, 229p. Fandeur D., Juillot F., Morin G., Olivi L., Cognigni A., Fialin M., Coufignal F., Ambrosi J.P., Guyot F. and Fritsch E. (2009a). Synchrotron-based speciation of chromium in an Oxisol from New-Caledonia : Importance of secondary Fe-oxyhydroxydes. American Mineralogist, 94, 710-719. Fandeur D., Juillot F., Morin G., Olivi L., Cognigni A., Webb S., Ambrosi J.P., Fritsch E. and Brown Jr. G.E. (2009b). XANES evidence for oxidation of Cr(III) to Cr(VI) by Mn-oxides in a lateritic regolith developed on serpentinized ultramafic rocks in New Caledonia. Environmental Science and Technology, 43, 7384-7390. Fandeur D., Fritsch E., Juillot F., Morin G., and Ambrosi J.P. (2010). Influence of mineralization and weathering on the distribution and mobility of major and trace elements along a freely-drained lateritic regolith developed in ultramafic rocks in New-Caledonia. Chemical Geology, submitted. Malpas J. (1992) Serpentine and the geology of serpentinized rocks. In The ecology of aeras with serpentinized rocks, Roberts B.A. and Proctor J (eds), Kluwer Academic Publishers, Netherland. Myers, N., R. A. Mittermeier, C. G. Mittermeier, G. A. B. da Fonseca, J. Kent (2000) Biodiversity hotspots for conservation priorities. Nature, 403, 853-858.

Petrogenesis of voluminous mid-Tertiary ignimbrites of the Sierra Madre Occidental, Chihuahua, Mexico

NASA Astrophysics Data System (ADS)

Cameron, Maryellen; Bagby, William C.; Cameron, Kenneth L.

1980-10-01

The mid-Tertiary ignimbrites of the Sierra Madre Occidental of western Mexico constitute the largest continuous rhyolitic province in the world. The rhyolites appear to represent part of a continental magmatic arc that was emplaced when an eastward-dipping subduction zone was located beneath western Mexico. In the Batopilas region of the northern Sierra Madre Occidental the mid-Tertiary Upper Volcanic sequence is composed predominantly of rhyolitic ignimbrites, but volumetrically minor lava flows as mafic as basaltic andesite are also present. The basaltic andesite to rhyolite series is calc-alkalic and contains ˜1% K2O at 60% SiO2. Trace element abundances of a typical ignimbrite with 73% SiO2 are Sr ˜ 225 ppm, Rb ˜130 ppm, Y ˜32 ppm, Th ˜12 ppm, Zr ˜200 ppm, and Nb ˜15 ppm. The entire series plots as coherent and continuous trends on variation diagrams involving major and trace elements, and the trends are distinct from those of geographicallyassociated rocks of other suites. We interpret these and other geochemical variations to indicate that the rocks are comagmatic. Mineral chemistry, Sr isotopic data, and REE modelling support this interpretation. Least squares calculations show that the major element variations are consistent with formation of the basaltic andesite to rhyolite series by crystal fractionation of observed phenocryst phases in approximate modal proportions. In addition, calculations modelling the behavior of Sr with the incompatible trace element Th favor a fractional crystallization origin over a crustal anatexis origin for the rock series. The fractionating minerals included plagioclase (> 50%), and lesser amounts of Fe-Ti oxides, pyroxenes, and/or hornblende. The voluminous ignimbrites represent no more than 20% of the original mass of a mantle-derived mafic parental magma.

Trace element and Nd, Sr, Pb isotope geochemistry of Kilauea Volcano, Hawai'i, near-vent eruptive products: 1983-2001

USGS Publications Warehouse

Thornber, Carl R.; Budahn, James R.; Ridley, W. Ian; Unruh, Daniel M.

2003-01-01

This open-file report serves as a repository for geochemical data referred to in U.S. Geological Survey Professional Paper 1676 (Heliker, Swanson, and Takahashi, eds., 2003), which includes multidisciplinary research papers pertaining to the first twenty years of Puu Oo Kupaianaha eruption activity. Details of eruption characteristics and nomenclature are provided in the introductory chapter of that volume (Heliker and Mattox, 2003). Geochemical relations of this data are depicted and interpreted by Thornber (2003), Thornber and others (2003a) and Thornber (2001). This report supplements Thornber and others (2003b) in which whole-rock and glass major-element data on ~1000 near-vent lava samples collected during the 1983 to 2001 eruptive interval of Kilauea Volcano, Hawai'i, are presented. Herein, we present whole-rock trace element compositions of 85 representative samples collected from January 1983 to May 2001; glass trace-element compositions of 39 Pele’s Tear (tephra) samples collected from September 1995 to September 1996, and whole-rock Nd, Sr and Pb isotopic analyses of 10 representative samples collected from September 1983 to September 1993. Thornber and others (2003b) provide a specific record of sample characteristics, location, etc., for each of the samples reported here. Spreadsheets of both reports may be integrated and sorted based upon time of formation or sample numbers. General information pertaining to the selectivity and petrologic significance of this sample suite is presented by Thornber and others (2003b). As justified in that report, this select suite of time-constrained geochemical data is suitable for constructing petrologic models of pre-eruptive magmatic processes associated with prolonged rift zone eruption of Hawaiian shield volcanoes.

A Geochemical Study of Postshield Volcanism and the Generation of Trachyte on West Maui, HI

NASA Astrophysics Data System (ADS)

Trenkler, M. L.; Cousens, B.

2016-12-01

The West Maui Volcano provides a complete evolutionary history of a fully developed Hawaiian volcano described by three main phases: (1) the tholeiitic shield-building stage of the Wailuku Basalts; (2) the postshield alkalic stage Honolua Volcanics; and (3) the rejuvenated stage Lahaina Volcanics of silica-undersaturated rocks. On West Maui, the postshield Honolua Volcanics erupted highly differentiated rocks (benmoreite to trachyte), with little to no intermediate alkalic rocks, upon cessation of tholeiitic shield building. Utilizing K-Ar dated samples, we present 35 new major and trace element analyses of shield, postshield, and rejuvenated stage lavas on West Maui in an attempt to identify the mechanisms present during evolution from basalt to trachyte over a defined temporal and spatial range. Wailuku basalts are dominated by olivine fractionation, whereas decreasing Sc and CaO/Al2O3 with increasing degree of differentiation indicate Honolua benmoreites and trachytes heavily fractionated clinopyroxene. Major element trends are consistent with crystallization of titano-magnetite, potassium feldspar, and minor apatite. Trace element patterns of the Honolua Volcanics are uniform with strong enrichments in LILE and the LREEs indicating fractionation and lower degrees of partial melting compared to Wailuku basalts. The HREEs are enriched relative to shield basalts with Gd/Yb values of 2.0-2.8 as a result of high degrees of fractionation and the presence of crystalizing apatite. Major and trace element trends follow the evolution of the postshield Hawi Volcanics of Kohala, where alkalic basalts differentiate up to trachyte. Compared to shield lavas, the Honolua Volcanics represent a drastic decrease in magma supply rates, infrequent eruptions, and magma residence times long enough to produce highly differentiated magmas with no significant mafic magma input.

Implications of Eocene-age Philippine Sea and forearc basalts for initiation and early history of the Izu-Bonin-Mariana arc

NASA Astrophysics Data System (ADS)

Yogodzinski, Gene M.; Bizimis, Michael; Hickey-Vargas, Rosemary; McCarthy, Anders; Hocking, Benjamin D.; Savov, Ivan P.; Ishizuka, Osamu; Arculus, Richard

2018-05-01

Whole-rock isotope ratio (Hf, Nd, Pb, Sr) and trace element data for basement rocks at ocean drilling Sites U1438, 1201 and 447 immediately west of the KPR (Kyushu-Palau Ridge) are compared to those of FAB (forearc basalts) previously interpreted to be the initial products of IBM subduction volcanism. West-of-KPR basement basalts (drill sites U1438, 1201, 447) and FAB occupy the same Hf-Nd and Pb-Pb isotopic space and share distinctive source characteristics with εHf mostly > 16.5 and up to εHf = 19.8, which is more radiogenic than most Indian mid-ocean ridge basalts (MORB). Lead isotopic ratios are depleted, with 206Pb/204Pb = 17.8-18.8 accompanying relatively high 208Pb/204Pb, indicating an Indian-MORB source unlike that of West Philippine Basin plume basalts. Some Sr isotopes show affects of seawater alteration, but samples with 87Sr/86Sr < 0.7034 and εNd > 8.0 appear to preserve magmatic compositions and also indicate a common source for west-of-KPR basement and FAB. Trace element ratios resistant to seawater alteration (La/Yb, Lu/Hf, Zr/Nb, Sm/Nd) in west-of-KPR basement are generally more depleted than normal MORB and so also appear similar to FAB. At Site U1438, only andesite sills intruding sedimentary rocks overlying the basement have subduction-influenced geochemical characteristics (εNd ∼ 6.6, εHf ∼ 13.8, La/Yb > 2.5, Nd/Hf ∼ 9). The key characteristic that unites drill site basement rocks west of KPR and FAB is the nature of their source, which is more depleted in lithophile trace elements than average MORB but with Hf, Nd, and Pb isotope ratios that are common in MORB. The lithophile element-depleted nature of FAB has been linked to initiation of IBM subduction in the Eocene, but Sm-Nd model ages and errorchron relationships in Site U1438 basement indicate that the depleted character of the rocks is a regional characteristic that was produced well prior to the time of subduction initiation and persists today in the source of modern IBM arc volcanic rocks with Sm/Nd > 0.34 and εNd ∼ 9.0.

Trace-element fingerprints of chromite, magnetite and sulfides from the 3.1 Ga ultramafic-mafic rocks of the Nuggihalli greenstone belt, Western Dharwar craton (India)

NASA Astrophysics Data System (ADS)

Mukherjee, Ria; Mondal, Sisir K.; González-Jiménez, José M.; Griffin, William L.; Pearson, Norman J.; O'Reilly, Suzanne Y.

2015-06-01

The 3.1 Ga Nuggihalli greenstone belt in the Western Dharwar craton is comprised of chromitite-bearing sill-like ultramafic-mafic rocks that are surrounded by metavolcanic schists (compositionally komatiitic to komatiitic basalts) and a suite of tonalite-trondhjemite-granodiorite gneissic rocks. The sill-like plutonic unit consists of a succession of serpentinite (after dunite)-peridotite-pyroxenite and gabbro with bands of titaniferous magnetite ore. The chromitite ore-bodies (length ≈30-500 m; width ≈2-15 m) are hosted by the serpentinite-peridotite unit. Unaltered chromites from massive chromitites (>80 % modal chromite) of the Byrapur and Bhaktarhalli chromite mines in the greenstone belt are characterized by high Cr# (100Cr/(Cr + Al)) of 78-86 and moderate Mg# (100 Mg/(Mg + Fe2+)) of 45-55. In situ trace-element analysis (LA-ICPMS) of unaltered chromites indicates that the parental magma of the chromitite ore-bodies was a komatiite lacking nickel-sulfide mineralization. In the Ga/Fe3+# versus Ti/Fe3+# diagram, the Byrapur chromites plot in the field of suprasubduction zone (SSZ) chromites while those from Bhaktarhalli lie in the MOR field. The above results corroborate our previous results based on major-element characteristics of the chromites, where the calculated parental melt of the Byrapur chromites was komatiitic to komatiitic basalt, and the Bhaktarhalli chromite was derived from Archean high-Mg basalt. The major-element chromite data hinted at the possibility of a SSZ environment existing in the Archean. Altered and compositionally zoned chromite grains in our study show a decrease in Ga, V, Co, Zn, Mn and enrichments of Ni and Ti in the ferritchromit rims. Trace-element heterogeneity in the altered chromites is attributed to serpentinization. The trace-element patterns of magnetite from the massive magnetite bands in the greenstone belt are similar to those from magmatic Fe-Ti-V-rich magnetite bands in layered intrusions, and magnetites from andesitic melts, suggesting that magnetite crystallized from an evolved gabbroic melt. Enrichments of Ni, Co, Te, As and Bi in disseminated millerite and niccolite occurring within chromitites, and in disseminated bravoite within magnetites, reflect element mobility during serpentinization. Monosulfide solid solution inclusions within pyroxenes (altered to actinolite) in pyroxenite, and interstitial pyrites and chalcopyrites in magnetite, retain primary characteristics except for Fe-enrichment in chalcopyrite, probably due to sub-solidus re-equilibration with magnetite. Disseminated sulfides are depleted in platinum-group elements (PGE) due to late sulfide saturation and the PGE-depleted nature of the mantle source of the sill-like ultramafic-mafic plutonic rocks in the Nuggihalli greenstone belt.

A simple model for closure temperature of a trace element in cooling bi-mineralic systems

NASA Astrophysics Data System (ADS)

Liang, Yan

2015-09-01

Closure temperature is defined as the lower temperature limit at which the element of interest effectively ceases diffusive exchange with its surrounding medium during cooling. Here we generalize the classic equation of Dodson (1973) for cooling mono-mineralic systems to cooling bi-mineralic aggregates by considering diffusive exchange of a trace element between the two minerals in a closed system. We present a simple analytical model that includes key parameters affecting the closure temperature of a trace element in cooling bi-mineralic systems: cooling rate, temperature-dependent diffusion coefficients for the trace element in the two minerals, temperature-dependent partition coefficient of the trace element between the two minerals, effective grain sizes of the two minerals, and volume proportions of the minerals in the system. We show that closure temperatures of a trace element in cooling bi-mineralic systems are bounded by the closure temperatures of the trace element in the two mono-mineralic systems and that our generalized model reduces to Dodson's equation when one of the mineral serves as "an effective infinite" reservoir to the other mineral. Application to closure temperatures of REE in orthopyroxene and clinopyroxene bi-mineralic systems highlights the importance of REE diffusion and partitioning in the pyroxenes as well as clinopyroxene modal abundance and grain size in the systems. Closure temperatures for REE in two-pyroxene bearing equigranular rocks are controlled primarily by diffusion in orthopyroxene unless the modal abundance of clinopyroxene is very small. This has important bearings on the interpretation of temperatures derived from the REE-in-two-pyroxene thermometer.

Elemental analysis using a handheld X-Ray fluorescence spectrometer

USGS Publications Warehouse

Groover, Krishangi D.; Izbicki, John

2016-06-24

The U.S. Geological Survey is collecting geologic samples from local stream channels, aquifer materials, and rock outcrops for studies of trace elements in the Mojave Desert, southern California. These samples are collected because geologic materials can release a variety of elements to the environment when exposed to water. The samples are to be analyzed with a handheld X-ray fluorescence (XRF) spectrometer to determine the concentrations of up to 27 elements, including chromium.

Major, trace element and isotope geochemistry (Sr-Nd-Pb) of interplinian magmas from Mt. Somma-Vesuvius (Southern Italy)

USGS Publications Warehouse

Somma, R.; Ayuso, R.A.; de Vivo, B.; Rolandi, G.

2001-01-01

Major, trace element and isotopic (Sr, Nd, Pb) data are reported for representative samples of interplinian (Protohistoric, Ancient Historic and Medieval Formations) activity of Mt. Somma-Vesuvius volcano during the last 3500 years. Tephra and lavas exhibit significant major, trace element and isotopic variations. Integration of these data with those obtained by previous studies on the older Somma suites and on the latest activity, allows to better trace a complete petrological and geochemical evolution of the Mt. Somma-Vesuvius magmatism. Three main groups of rocks are recognized. A first group is older than 12.000 yrs, and includes effusive-explosive activity of Mt. Somma. The second group (8000-2700 yrs B.P.) includes the products emitted by the Ottaviano (8000 yrs. B.P.) and Avellino (3550 yrs B.P.) plinian eruptions and the interplinian activity associated with the Protohistoric Formation. Ancient Historic Formation (79-472 A.D.), Medieval Formation (472-1139 A.D.) and Recent interplinian activity (1631-1944 A.D.) belong to the third group of activity (79-1944 A.D.). The three groups of rocks display distinct positive trends of alkalis vs. silica, which become increasingly steeper with age. In the first group there is an increase in silica and alkalis with time, whereas an opposite tendency is observed in the two younger groups. Systematic variations are also evident among the incompatible (Pb, Zr, Hf, Ta, Th, U, Nb, Rb, Cs, Ba) and compatible elements (Sr, Co, Cr). REE document variable degrees of fractionation, with recent activity displaying higher La/Yb ratios than Medieval and Ancient Historic products with the same degree of evolution. N-MORB normalized multi-element diagrams for interplinian rocks show enrichment in Rb, Th, Nb, Zr and Sm (> *10 N-MORB). Sr isotope ratios are variable, with Protohistoric rocks displaying 87Sr/86Sr= 0.70711-0.70810, Ancient Historic 87Sr/86Sr=0.70665-0.70729, and Medieval 87Sr/86Sr=0.70685-0.70803. Neodymium isotopic compositions in the interplinian rocks show a tendency to become slightly more radiogenic with age, from the Protohistoric (143Nd/144Nd=0.51240-0.51247) to Ancient Historic (143Nd/144Nd=0.51245-0.51251). Medieval interplinian activity (143Nd/144Nd: 0.51250-0.51241) lacks meaningful internal trends. All the interplinian rocks have virtually homogeneous compositions of 207Pb/204Pb and 208Pb/204Pb in acid-leached residues (207Pb/204Pb ???15.633 to 15.687, 208Pb/204Pb ???38.947 to 39.181). Values of 206Pb/204Pb are very distinctive, however, and discriminate among the three interplinian cycles of activity (Protohistoric: 18.929-18.971, Ancient Historic: 19.018-19.088, Medieval: 18.964-19.053). Compositional trends of major, trace element and isotopic compositions clearly demonstrate strong temporal variations of the magma types feeding the Somma-Vesuvius activity. These different trends are unlikely to be related only to low pressure evolutionary processes, and reveal variations of parental melt composition. Geochemical data suggest a three component mixing scheme for the interplinian activity. These involve HIMU-type and DMM-type mantle and Calabrian-type lower crust. Interaction between these components has taken place in the source; however, additional quantitative constraints must be acquired in order to better discriminate between magma characteristics inherited from the sources and those acquired during shallow level evolution.

Petrogenesis of the ∼500 Ma Fushui mafic intrusion and Early Paleozoic tectonic evolution of the Northern Qinling Belt, Central China

NASA Astrophysics Data System (ADS)

Shi, Yu; Pei, Xiaoli; Castillo, Paterno R.; Liu, Xijun; Ding, Haihong; Guo, Zhichao

2017-06-01

The Fushui mafic intrusion in the Qinling orogenic belt (QOB) is composed of meta-gabbro, meta-gabbro-diorite, diorite, and syenite. Most of these rocks are metamorphosed under the upper greenschist facies to lower amphibolite facies metamorphism. Zircon separates from eight samples have LA-ICP-MS U-Pb ages of 497-501 Ma which are taken to be the emplacement age of magmas that formed the Fushui intrusion. Most of the zircon grains exhibit negative εHf values, correspond to TDM2 model ages of late Paleoproterozoic-early Mesoproterozoic or Neoproterozoic and suggest that the mafic rocks were most probably derived from mafic melts produced by partial melting of a previously metasomatized lithospheric mantle. The intrusion is not extensively contaminated by crustal materials and most chemical compositions of rocks are not modified during the greenschist to amphibolite-facies metamorhism. Rocks from the intrusion have primitive mantle-normalized trace element patterns with significant enrichment in light-REE and large ion lithophile elements (LILE) and depletion in high field-strength elements (HFSE). On the basis of the trace element contents, the Fushui intrusion was derived from parental magmas generated by <10% partial melting of both phlogopite-lherzolite and garnet-lherzolite mantle sources. These sources are best interpreted to be in a subduction-related arc environment and have been modified by fluids released from a subducting slab. The formation of the Fushui intrusion was related to the subduction of the Paleotethyan Shangdan oceanic lithosphere at ∼500 Ma.

Solar wind radiation damage effects in lunar material

NASA Technical Reports Server (NTRS)

Hapke, B.; Cohen, A. J.; Cassidy, W. A.

1971-01-01

The research on solar wind radiation damage and other effects in lunar samples which was conducted to understand the optical properties of lunar materials is reported. Papers presented include: solar radiation effects in lunar samples, albedo of the moon, radiation effects in lunar crystalline rocks, valence states of 3rd transition elements in Apollo 11 and 12 rocks, and trace ferric iron in lunar and meteoritic titanaugites.

A process for reducing rocks and concentrating heavy minerals

USGS Publications Warehouse

Strong, Thomas R.; Driscoll, Rhonda L.

2016-03-30

Once the rock is reduced to grains, it is necessary to separate the grains into paramagnetic and nonparamagnetic and heavy and light mineral fractions. In separating grains by property, those minerals chemically suited for radiometric dating are abundantly concentrated. Grams of mineralogical material can then be analyzed and characterized by multiple methods including trace element chemistry, laser ablation, and in particular, ion geochronology.

Development of a mixed seawater-hydrothermal fluid geochemical signature during alteration of volcanic rocks in the Archean (∼2.7 Ga) Abitibi Greenstone Belt, Canada

NASA Astrophysics Data System (ADS)

Brengman, Latisha A.; Fedo, Christopher M.

2018-04-01

We investigated a group of silicified volcanic rocks from the ∼2.72 Ga Hunter Mine Group (HMG), Abitibi Greenstone Belt, Canada, in order to document progressive compositional change associated with alteration in a subaqueous caldera system. Rocks of the HMG divide into three groups based on mineralogy and texture for petrographic and geochemical analyses. Volcanic features (phenocrysts, pseudomorphs after primary glass shards, lapilli, volcanic clasts) are preserved in all groups, despite changing mineralogy from primarily quartz, feldspar, chlorite (Groups 1 and 2), to quartz, hematite and carbonate (Groups 2 and 3). Compositionally, Group 1 rocks resemble volcanic rocks in the region, while Group 2 and 3 rocks show a change in mineralogy to iron, silica, and carbonate minerals, which is associated with depletion of many major and trace elements associated with volcanic rocks (Al2O3, Na2O, K2O, Zr). In addition, rare earth elements display a clear progression from volcanic signatures in Group 1 (PrSN/YbSN = 1.7-2.96, EuSN/EuSN∗ = 0.84-1.72, Y/Ho = 25.20-27.41, LaSN/LaSN∗ = 0.97-1.29, and Zr/Hf = 38.38-42.09) to transitional mixed volcanic, hydrothermal, and seawater signatures in Group 2 (PrSN/YbSN 1.33-2.89, EuSN/EuSN∗ 1.33-2.5, Y/Ho = 23.94-30, LaSN/LaSN∗ 0.93-1.34, and Zr/Hf = 40-70), to mixed hydrothermal and seawater signatures in Group 3 (PrSN/YbSN 0.62-2.88, EuSN/EuSN∗ 1.30-7.15, LaSN/LaSN∗ 1.02-1.86, Y/Ho = 25.56-55, and Zr/Hf = 35-50). We interpret that silicification of volcanic rocks (Group 1) produced transitional altered volcanic rocks (Group 2), and siliceous and jaspilitic rocks (Group 3), based on preservation of delicate volcanic features. Building on this explanation, we interpret that major, trace- and rare-earth element mobility occurred during the process of silicification, during which siliceous and jaspilitic rocks (Group 3) acquired aspects of the rare-earth element geochemical signatures of marine chemical precipitates. We conclude that seafloor silicification in hydrothermal depositional settings is capable of producing rocks that resemble marine chemical precipitates such as banded iron formation, and could be a process that is widespread in the Archean. Consequently, because silicified volcanic rocks from the HMG possess mixed seawater and hydrothermal rare-earth element characteristics similar to Archean iron formations and cherts, we suggest caution must be exercised when interpreting the geochemical information preserved in metamorphosed rocks where original genesis is unknown.

The chemical and isotopic differentiation of an epizonal magma body: Organ Needle pluton, New Mexico

USGS Publications Warehouse

Verplanck, P.L.; Farmer, G.L.; McCurry, M.; Mertzman, S.A.

1999-01-01

Major and trace element, and Nd and Sr isotopic compositions of whole rocks and mineral separates from the Oligocene, alkaline Organ Needle pluton (ONP), southern New Mexico, constrain models for the differentiation of the magma body parental to this compositionally zoned and layered epizonal intrusive body. The data reveal that the pluton is rimmed by lower ??(Nd) (~-5) and higher 87Sr/86Sr (~0.7085) syenitic rocks than those in its interior (??(Nd) ~ 2, 87Sr/86Sr ~0.7060) and that the bulk compositions of the marginal rocks become more felsic with decreasing structural depth. At the deepest exposed levels of the pluton, the ??(Nd)~-5 lithology is a compositionally heterogeneous inequigranular syenite. Modal, compositional and isotopic data from separates of rare earth element (REE)-bearing major and accesory mineral phases (hornblende, titanite, apatite, zircon) demonstrate that this decoupling of trace and major elements in the inequigranular syenite results from accumulation of light REE (LREE)-bearing minerals that were evidently separated from silicic magmas as the latter rose along the sides of the magma chamber. Chemical and isotopic data for microgranular mafic enclaves, as well as for restite xenoliths of Precambrian granite wall rock, indicate that the isotopic distinction between the marginal and interior facies of the ONP probably reflects assimilation of the wall rock by ??(Nd) ~-2 mafic magmas near the base of the magma system. Fractional crystallization and crystal liquid separation of the crystally contaminated magma at the base and along the margins of the chamber generated the highly silicic magmas that ultimately pooled at the chamber top.

Further foraging for pristine nonmare rocks - Correlations between geochemistry and longitude

NASA Technical Reports Server (NTRS)

Warren, P. H.; Wasson, J. T.

1980-01-01

The most recent results from a project to find and describe pristine (that is, compositionally endogenous) nonmare rocks are reported. Sixteen nonmare samples are characterized petrographically and by composition, among them numerous key trace elements (siderophiles, incompatibles). Current knowledge about nonmare lunar rocks is surveyed, with emphasis placed on correlations between geochemistry and longitude. Several systematic differences between western ANT (that is, nonKREEPy, nonmare) rocks and the much more thoroughly studied eastern ANT rocks are noted. It is noted that western ANT rocks, whether pristine or nonpristine, tend to have higher Eu/Sm than their eastern counterparts. Pristine western ANT rocks, however, tend to have lower Sc/Sm and Ti/Sm than pristine eastern ANT rocks.

Mapping age and trace elements using laser ablation split-stream (LASS) ICPMS

NASA Astrophysics Data System (ADS)

Kylander-Clark, A. R.; Hacker, B. R.; Cottle, J. M.

2012-12-01

One of the biggest challenges in the determination of the timing and rates of metamorphic processes is tying the age of a particular mineral to the conditions (i.e., pressure, temperature, fluid composition) at which that phase grew. Conventional microbeam techniques increase our understanding of crustal evolution by enabling this linkage; e.g., x-ray maps of monazite allow us to pinpoint grain segments that grew under a different set of conditions, cathodoluminescence images of zircon reveal zoning patterns and hence targets for dating different metamorphic and/or igneous events, and rare-earth element (REE) transects across garnet reveal the budget of a variety of trace elements during a metamorphic episode, to name but a few. More recent advances in LA-ICPMS and SIMS have allowed the ability to produce age maps or trace element maps—thus further our understanding of crystallization processes—but not both. Here we employ laser ablation split-stream (LASS) to quantitatively image the age, and trace element signature of datable phases such as zircon, monazite, titanite, and rutile in metamorphic rocks on the micron scale. By mapping the age and TE signature of a metamorphic phase, we can better interpret the metamorphic stage at which all portions of that phase grew, and relate it to other phases/portions of phases within that rock, such as garnet. For example, zircons and monazites from from eclogites reveal complex zoning in REEs indicating growth prior to, during, and post eclogite-facies metamorphism; those zones correspond to distinct age domains. Metamorphosed titanite reveals differences in diffusivities of TEs in inherited portions of the grain; e.g., Pb-loss is more prominent than diffusion of REEs, which in turn diffuse faster than higher charged ions, such as Th.

Provenance and tectonic settings of sands from Puerto Peñasco, Desemboque and Bahia Kino beaches, Gulf of California, Sonora, México

NASA Astrophysics Data System (ADS)

Madhavaraju, J.; Tom, Milu; Lee, Yong IL; Balaram, V.; Ramasamy, S.; Carranza-Edwards, A.; Ramachandran, A.

2016-11-01

Textural, heavy minerals and geochemical (major, trace and rare earth elements) studies were undertaken on the sands from Puerto Peñasco, Desemboque and Bahia Kino beaches to determine the provenance and tectonic settings. Puerto Peñasco and Bahia Kino sands are coarse grained to fine grained, while Desemboque sands are fine grained. Geochemically, these sands are classified as arkose. The sands are depleted in most of the trace elements relative to upper continental crust (UCC), except for few trace elements (Sr, Rb and Ba), which are slightly enriched. High ΣREE content are observed in the Desemboque sands (94.43 ± 6.9) than in the Puerto Peñasco and Bahia Kino sands (51.58 ± 17.06; 72.38 ± 9.27; respectively). The chemical index of alteration (CIA) values of Puerto Peñasco, Desemboque and Bahia Kino sands (PP: 42 to 50; DE: 48 to 50; BK: 44 to 50: respectively) indicate the low intensity of chemical weathering in the source rocks. The tectonic discriminant-function-based multidimensional diagram shows arc and rift settings for Puerto Peñasco sands whereas rift setting for both Desemboque and Bahia Kino sands. The heavy mineral assemblage, immobile trace elements, REE patterns, elemental ratios such Eu/Eu*, (La/Lu)cn, La/Sc, Th/Sc, La/Co, Th/Co, and Cr/Th, various bivariate and ternary plots indicate the contribution of sediments from felsic composition. This interpretation is supported by the comparison of REE patterns of the Puerto Peñasco, Desemboque and Bahia Kino sands with the potential source rocks exposed nearby the study areas.

The Variscan calc-alkalic plutonism of western Corsica: mineralogy and major and trace element geochemistry

NASA Astrophysics Data System (ADS)

Cocherie, A.; Rossi, Ph.; Le Bel, L.

1984-10-01

Petrographic and structural observations on the calc-alkalic plutonism of western Corsica revealed the existence of several successively emplaced units associated with large basic bodies. The present mineralogical and geochemical study deals with the genesis, evolution and relationships of these different units. Basic plutonism is represented by three genetically linked types of rock: norites and troctolites with cumulate textures characterized by low REE contents and either no Eu anomaly or a positive Eu anomaly; gabbros with enriched LREE relatively to HREE patterns, probably close to an initial basaltic liquid; and diorites ranging up to charnockites which represent liquids evolved to varying degrees, mainly by fractional crystallization. Trace element data and studies on the evolution of pyroxene pairs demonstrate the consanguinity of these calc-alkaline basic rocks which are derived from a high alumina basaltic melt. The various granitoids (granodiorites, monzogranites and leucocratic monzogranites, i.e., adamellites) have distinct evolution trends as shown by the composition of their mafic minerals and by trace element distributions. They cannot be considered as being derivatives of the basic suite and they cannot be related by a common fractionation sequence. Rather, they represent distinctive batches of crustal anatexis. In addition, hybridization phenomena with the basic melt are noticed in granodiorites. The particular problem of the low La/Yb, Eu/Eu∗ and the high U, Th, Cs leucocratic monzogranites is discussed in detail. In addition to more conventional trace element diagrams, the simultaneous statistical treatment of all the geochemical data by correspondence factor analysis is shown to be a very use tool in distinguishing between the different units and to classify the elements according to their geochemical properties.

Petrogenesis of basaltic volcanic rocks from the Pribilof Islands, Alaska, by melting of metasomatically enriched depleted lithosphere, crystallization differentiation, and magma mixing

USGS Publications Warehouse

Chang, J.M.; Feeley, T.C.; Deraps, M.R.

2009-01-01

The Pribilof Islands, Alaska, are located in the Bering Sea in a continental intraplate setting. In this study we examine the petrology and geochemistry of volcanic rocks from St. Paul (0??54-0??003 Ma) and St. George (2??8-1??4 Ma) Islands, the two largest Pribilof Islands. Rocks from St. George can be divided into three groups: group 1 is a high-MgO, low-SiO. 2 suite composed primarily of basanites; group 2 is a high-MgO, high-SiO 2 suite consisting predominantly of alkali basalts; group 3 is an intermediate- to low-MgO suite that includes plagioclase-phyric subalkali basalts and hawaiites. Major and trace element geochemistry suggests that groups 1 and 2 formed by small-degree partial melting of amphibole-bearing to amphibole-free garnet peridotite. Group 1 rocks were the earliest melts produced from the most hydrous parts of the mantle, as they show the strongest geochemical signature of amphibole in their source. The suite of rocks from St. Paul ranges from 14??4 to 4??2 wt % MgO at relatively constant SiO 2 contents (43??1-47??3 wt %). The most primitive St. Paul rocks are modeled as mixtures between magmas with compositions similar to groups 1 and 2 from St. George Island, which subsequently fractionated olivine, clinopyroxene, and spinel to form more evolved rocks. Plagioclase-phyric group 3 rocks from St. George are modeled as mixtures between an evolved melt similar to the evolved magmas on St. Paul and a fractionated group 2 end-member from St. George. Mantle potential temperatures estimated for primitive basanites and alkali basalts are ???1400??C and are similar to those of mid-ocean ridge basalts (MORB). Similarly, 87Sr/. 86Sr and 143Nd/. 144Nd values for all rocks are MORB-like, in the range of 0??702704-0??703035 and 0??513026-0??513109, respectively. 208Pb/. 204Pb vs 206Pb/. 204Pb values lie near the MORB end-member but show a linear trend towards HIMU (high time-integrated 238U/. 204Pb). Despite isotopic similarities to MORB, many of the major and trace element characteristics are similar to those of ocean island basalts (OIB), including enrichment in alkalis and incompatible trace elements. These characteristics are interpreted to indicate that their mantle source experienced an ancient melt-removal event that is reflected in depleted radiogenic isotopic compositions and was then re-enriched by metasomatism that elevated incompatible trace element contents, but was too young to produce a time-integrated change in radiogenic isotopic ratios. Evidence suggests that the Pribilof Island basalts did not form in either a plume or a back-arc basin tectonic setting. Rather, they were produced by melting of metasomatically hydrated upper mantle peridotite at relatively low temperatures and were able to erupt at the surface through extensional or transtensional faults that served as conduits for the magmas. ?? The Author 2009. Published by Oxford University Press.

Mineralogy and Geochemistry of Granitic rocks within Lichen Hills, Outback Nunatak, Northern Victoria Land, Antarctica

NASA Astrophysics Data System (ADS)

KIM, T.; KIM, Y.; Lee, I.; Lee, J.; Woo, J.

2015-12-01

The study areas, Lichen Hills and Outback Nunatak are located in the Northern Victoria Land which is close to Pacific Ocean side of Transantarctic Mountain (TAM), Antarctica. According to the study of Zeller and Dreschoff (1990), the radioactivity values of Lichen hills and Frontier Mt. area in the Victoria Land were very high. To identify the geochemical characteristics of granitic rocks in these areas, 13 samples of Lichen Hills rocks and 4 samples of Outback Nunatak rocks are analyzed. For mineralogical study, samples were observed in macroscale as well as microscale including microscope electron probe analysis. Rock samples of Lichen Hills, Outback Nunatak are mainly leucogranite and granitic pegmatite. These rock samples are composed of quartz, k-feldspar, plagioclase, muscovite, garnet, tourmaline like granite. In SEM-EDS analysis, the observed light colored minerals show relatively high Th, U, Dy, Ce, Nb concentration. This suggests that rock samples may contain minerals such as fergusonite, monazite, thorite, allanite, karnasurtite which are considered to be REE-bearing minerals. Samples of related rocks have been analyzed in terms of major, trace and rare earth element (REE) concentrations using X-ray fluorescence (XRF) spectrometer and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). As concentration of SiO2 increase, Al2O3, TiO2, Fe2O3, MgO, P2O5 concentration decrease and Na2O, K2O, MnO concentration increase. Analyzed trace elements and REE are normalized using CI Chondrite, Primitive mantle. The normalized data show that LREE are enriched compared to HREE. The distinct negative anomalies of Eu, Sr are observed, indicating that rock-forming melts are fairly processed state of fractional crystallization. It means that Th, U, Nb, Ta are much enriched in the melts.

Rare earth element selenochemistry of immiscible liquids and zircon at Apollo 14 - An ion probe study of evolved rocks on the moon

NASA Technical Reports Server (NTRS)

Snyder, Gregory A.; Taylor, Lawrence A.; Crozaz, Ghislaine

1993-01-01

Results are presented of trace-element analyses of three lunar zircons. The major-element and REE compositions were determined using electron microprobes, and a correction was made for zircon for Zr-Si-O molecular interferences in the La to Pr mass region. The three zircons were found to exhibit similar REE abundances and patterns. Results of the analyses confirm earlier studies (Hess et al., 1975; Watson, 1976; Neal and Taylor, 1989) on the partitioning behavior of trace elements in immiscible liquid-liquid pairs. The results also support the postulated importance of silicate liquid immiscibility in the differentiation of the upper mantle and crust of the moon.

Preliminary examination of the Yamato-86032 lunar meteorite. II - Major and trace element chemistry

NASA Technical Reports Server (NTRS)

Koeberl, Christian; Warren, Paul H.; Lindstrom, Marilyn M.; Spettel, Bernhard; Fukuoka, Takaaki

1989-01-01

Results of the chemical composition analysis of Yamato-86032, found in Antarctica in 1986, are summarized. The meteorite may be classified as an anorthositic breccia, but its trace element composition is different from the composition of the other known lunar meteorites. The major element chemistry of Y-86032 is similar to the other lunar meteorites, except for the iron content, which is lower by a factor of about 1.4. The abundances of incompatible and lithophile elements such as Zr, Hf, Ta, Th, or the REEs are very low and comparable to Y-82192/3. Other elements, in particular Fe, Ti, Sc, Cr, Mn, and Co, have lower abundances in Y-86032 than in Y-82192/3. Variations between individual analysis demonstrate that the rock itself is heterogeneous.

Igneous Complexes of the Orochenka Caldera of the East Sikhote-Alin Belt: U-Pb (SHRIMP) Age, Trace and Rare Earth Element Composition, and Au-Ag Mineralization

NASA Astrophysics Data System (ADS)

Sakhno, V. G.; Kovalenko, S. V.

2018-04-01

New data are presented on the geology and composition of volcanic and intrusive rocks of the Orochenka caldera, which is located in the western part of the East Sikhote Alin volcanic belt. The SHRIMP and ICP MS age of zircons of volcanic and intrusive rocks, respectively, and the composition of the volcanic rocks allow comparison of these complexes with volcanic rocks of the eastern part of the volcanic structure. New data indicate the period of transition between subduction to transform regimes.

Factor analysis of rock, soil and water geochemical data from Salem magnesite mines and surrounding area, Salem, southern India

NASA Astrophysics Data System (ADS)

Satyanarayanan, M.; Eswaramoorthi, S.; Subramanian, S.; Periakali, P.

2017-09-01

Geochemical analytical data of 15 representative rock samples, 34 soil samples and 55 groundwater samples collected from Salem magnesite mines and surrounding area in Salem, southern India, were subjected to R-mode factor analysis. A maximum of three factors account for 93.8 % variance in rock data, six factors for 84 % variance in soil data, five factors for 71.2 % in groundwater data during summer and six factors for 73.7 % during winter. Total dissolved solids are predominantly contributed by Mg, Na, Cl and SO4 ions in both seasons and are derived from the country rock and mining waste by dissolution of minerals like magnesite, gypsum, halite. The results also show that groundwater is enriched in considerable amount of minor and trace elements (Fe, Mn, Ni, Cr and Co). Nickel, chromium and cobalt in groundwater and soil are derived from leaching of huge mine dumps deposited by selective magnesite mining activity. The factor analysis on trivalent, hexavalent and total Cr in groundwater indicates that most of the Cr in summer is trivalent and in winter hexavalent. The gradational decrease in topographical elevation from northern mine area to the southern residential area, combined regional hydrogeological factors and distribution of ultramafic rocks in the northern part of the study area indicate that these toxic trace elements in water were derived from mine dumps.

Accessory mineral records of tectonic environments? (Invited)

NASA Astrophysics Data System (ADS)

Storey, C.; Marschall, H. R.; Enea, F.; Taylor, J.; Jennings, E. S.

2010-12-01

Accessory mineral research continues to gather momentum as we seek to unleash their full potential. It is now widely recognised that robust accessory minerals, such as zircon, rutile, titanite, allanite and monazite, are archives of important trace elements that can help deduce metamorphic reaction history in metapelites, metabasites and other rock types. Moreover, they are important carriers of certain trace elements and govern or influence the products of partial melting and of fluid-rock interaction (e.g. magmas and mineralisation) in settings like subduction zones and hydrothermal systems. Perhaps most importantly, they can often be dated using the U-Th-Pb system. More recently, radiogenic (Lu-Hf, Sm-Nd, Rb-Sr) and stable (O) isotope systems have been applied and have further pushed the utility of accessory mineral research. In this talk I will discuss some of these advances towards one particular aim: the use of detrital accessory minerals for fingerprinting tectonic environments. This is a particularly laudable aim in Precambrian rocks, for which the preservation potential of orogenic belts and fossil subduction zones and their diagnostic metamorphic rocks is low. The implication is that our understanding of plate tectonics, particularly in the Archaean, is biased by the preserved in-tact rock record. An analogy is that Jack Hills zircons record evidence of Earth’s crust some 400 Ma before the preserved rock record begins. I will focus on some recent advances and new data from rutile and also the mineral inclusion record within zircon, which shows great promise for petrologic interpretation.

Lead isotopes and trace metals in dust at Yucca Mountain

USGS Publications Warehouse

Kwak, Loretta; Neymark, Leonid A.; Peterman, Zell E.

2008-01-01

Lead (Pb)-isotope compositions and trace-metal concentrations were determined for samples of dust collected from underground and surface locations at and near the proposed radioactive waste repository at Yucca Mountain, Nevada. Rare earth element concentrations in the dust samples from the underground tunnels are similar to those in wholerock samples of the repository host rocks (Miocene Tiva Canyon Tuff and Topopah Spring Tuff), supporting interpretation that the subsurface dust is mainly composed of rock comminuted during tunnel construction. Other trace metals (arsenic, cadmium, cobalt, chromium, copper, manganese, nickel, lead, antimony, thallium, and zinc) are variably enriched in the subsurface dust samples relative to the average concentrations in the host rocks. Average concentrations of arsenic and lead in dust samples, high concentrations of which can cause corrosion of waste canisters, have enrichment factors from 1.2 to 1.6 and are insignificant relative to the range of concentrations for these metals observed in the host rock samples. Most dust samples from surface sites also are enriched in many of these trace metals relative to average repository host rocks. At least some of these enrichments may be artifacts of sampling. Plotted on a 208Pb/206Pb-207Pb/206Pb graph, Pb-isotope compositions of dust samples from underground sites form a mixing line extending from host-rock Pb-isotope compositions towards compositions of many of the dust samples from surface sites; however, combined Pb concentration and isotope data indicate the presence of a Pbenriched component in the subsurface dust that is not derived from host rock or surface dust and may derive from anthropogenic materials introduced into the underground environment.

Textural and Mineralogical Analysis of Volcanic Rocks by µ-XRF Mapping.

PubMed

Germinario, Luigi; Cossio, Roberto; Maritan, Lara; Borghi, Alessandro; Mazzoli, Claudio

2016-06-01

In this study, µ-XRF was applied as a novel surface technique for quick acquisition of elemental X-ray maps of rocks, image analysis of which provides quantitative information on texture and rock-forming minerals. Bench-top µ-XRF is cost-effective, fast, and non-destructive, can be applied to both large (up to a few tens of cm) and fragile samples, and yields major and trace element analysis with good sensitivity. Here, X-ray mapping was performed with a resolution of 103.5 µm and spot size of 30 µm over sample areas of about 5×4 cm of Euganean trachyte, a volcanic porphyritic rock from the Euganean Hills (NE Italy) traditionally used in cultural heritage. The relative abundance of phenocrysts and groundmass, as well as the size and shape of the various mineral phases, were obtained from image analysis of the elemental maps. The quantified petrographic features allowed identification of various extraction sites, revealing an objective method for archaeometric provenance studies exploiting µ-XRF imaging.

Soil fertility status and spatial distribution of selected trace elements in south-western Serbia

NASA Astrophysics Data System (ADS)

Mrvic, Vesna; Kostic-Kravljanac, Ljiljana; Cakmak, Dragan; Pivic, Radmila; Saljnikov, Elmira; Nikoloski, Mile; Perovic, Veljko

2010-05-01

Soil fertility status and spatial distribution of selected trace elements in south-western Serbia V. Mrvic, Lj. Kostic-Kravljanac, D. Čakmak, R. Pivić, E. Saljnikov, M. Nikoloski, V. Perović Institute of Soil Science, 11000 Belgrade, Serbia (vesnavmrvic@yahoo.com) Main characteristic of surface soil layer (pH in KCl, humus, available P and K), and content of trace elements (Ni, Cr, Cu, Zn, Pb, Cd, As, Hg) were analysed on area of southwestern Serbia, covering total 959 000 ha (one sample represents 1000 ha) . About 30 % of samples have very acid reaction. Main portion of soil samples (86%) is poorly suplied with available phosphorus (<8 mg/100g), and these are located under forests, meadows, pastures and orchards. Supplies of available potasium and humus are well. On the other hand, in small number of soil samples (4%), mostly on fertile alluvial soils, there are high P and K concentration, which are consequence of inadequate usage of mineral fertilizers. Content of trace elements in 70 % of soil samples is bellow maximum allowed concentration (MAC). The most frequente potential pollutants are Cr and Ni, which is assosiated with mafic and ultramafic rocks, which are common in this region (mountains naerby river Ibar - Troglav, Stolovi, Čemerno, Željin, Golija, Kopaonik; near Sjenica- peridotites of mn. Ozren). There are dominace of Eutric Leptosols soil type, with Ni content above 100 mg/kg, and in some samples above 1000 mg/kg. In smaller number of samples arsenic and lead exceed MAC, while other elements exceed MAD very rarelly. There are elevated Pb content in Kopaonik mountain area, and elevated As content besides this region, are in mine zone of Golija and Cemerno. These are mountain soils formed on acid igneous and metamorphic rocks, which are enriched with ores of Pb, Zn and other elements. Eventually negative influences of these elements on plants and other components of ecosystem may be esstimated only after detalied investigation.

Chemical composition of rocks and soils at Taurus-Littrow

NASA Technical Reports Server (NTRS)

Rose, H. J., Jr.; Cuttitta, F.; Berman, S.; Brown, F. W.; Carron, M. K.; Christian, R. P.; Dwornik, E. J.; Greenland, L. P.

1974-01-01

Seventeen soils and seven rock samples were analyzed for major elements, minor elements, and trace elements. Unlike the soils at previous Apollo sites, which showed little difference in composition at each collection area, the soils at Taurus-Littrow vary widely. Three soil types are evident, representative of (1) the light mantle at the South Massif, (2) the dark mantle in the valley, and (3) the surface material at the North Massif. The dark-mantle soils are chemically similar to those at Tranquillitatis. Basalt samples from the dark mantle are chemically similar although they range from fine to coarse grained. It is suggested that they originated from the same source but crystallized at varying depths from the surface.

Redox Sensitive Trace Element Enrichments of Organic Matter Rich Rocks (Kürnüç-Göynük/Bolu, Turkey)

NASA Astrophysics Data System (ADS)

Engin, H.; Sarı, A.; Koç, Ş.

2012-04-01

The oil shale deposits of Himmetoğlu and Hatıldağ nearby Göynük (Bolu/Türkiye) are well known oil shale deposits in Turkey. However, there is no detailed study about shale and marl type organic matter rich rocks of Kürnüç (Göynük (Bolu/Türkiye) currently available in the literature. This study aims to determine the enrichment of redox sensitive trace elements of organic matter rich rocks deposited at Kürnüç. The Kızılçay formation which outcrops in the vicinity of Kürnüç contains organic matter-rich rocks of marl and shale type. TOC %wt contents of Kürnüç vicinity rocks varies between 2,52-8,38 with an average of 6,13. The enrichments of S and Fe in these rocks and S% vs Fe% plot indicate the presence of pyrite and/or marcasite occurrences (r = 0,56). Also C-Fe-S relationship for the Kürnüç vicinity organic rich rocks suggest oxic and partially suboxic conditions. Some information about redox conditions of depositional environment of organic-rich rocks are obtained using redox sensitive element ratios such as V/(V+Ni), Ni/Co, U/Th and V/Sc. V/(V+Ni) ratios came out to be between 0,44-0,67, indicating suboxic-anoxic conditions; Ni/Co values are between 4,08-11,76, which indicates oxic-suboxic conditions; U/Th values are between 0,46-6,00, indicating suboxic-anoxic conditions; V/Sc values are between 5,53-24,50, pointing out oxic-suboxic condition. According to these values, Kürnüç vicinity organic matter-rich rocks are generally deposited in oxic to anoxic redox conditions. The redox sensitive elements Ni (20 - 129 ppm, with an average of 51,73 ppm), Co (0,2 - 20,6 ppm, with an average of 10,29 ppm), Cr (0,002 - 0,068%, with an average of 0,01%), Th (0,5 - 7,1 ppm, with an average of 4,02 ppm), Sc (1 - 13 ppm, with an average of 7,51 ppm), V (8 - 153 ppm, with an average of 70,55 ppm), U (0,6 - 35 ppm, with an average of 3,49 ppm) are obtained from the organic matter rich rocks. These elements are enriched 1-10 times relative to Average Shale, Coast of Peru, UCC (Upper Continental Crust), PAAS (Post Archean Average Shale), NASC (North American Shale Composit).

The effects of trace element content on pyrite oxidation rates

NASA Astrophysics Data System (ADS)

Gregory, D. D.; Lyons, T.; Cliff, J. B.; Perea, D. E.; Johnson, A.; Romaniello, S. J.; Large, R. R.

2017-12-01

Pyrite acts as both an important source and sink for many different metals and metalloids in the environment, including many that are toxic. Oxidation of pyrite can release these elements while at the same time producing significant amounts of sulfuric acid. Such issues are common in the vicinity of abandoned mines and smelters, but, as pyrite is a common accessory mineral in many different lithologies, significant pyrite oxidation can occur whenever pyritic rocks are exposed to oxygenated water or the atmosphere. Accelerated exposure to oxygen can occur during deforestation, fracking for petroleum, and construction projects. Geochemical models for pyrite oxidation can help us develop strategies to mitigate these deleterious effects. An important component of these models is an accurate pyrite oxidation rate; however, current pyrite oxidation rates have been determined using relatively pure pyrite. Natural pyrite is rarely pure and has a wide range of trace element concentrations that may affect the oxidation rate. Furthermore, the position of trace elements within the mineral lattice can also affect the oxidation rate. For example, elements such as Ni and Co, which substitute into the pyrite lattice, are thought to stabilize the lattice and thus prevent pyrite oxidation. Alternatively, trace elements that are held within inclusions of other minerals could form a galvanic cell with the surrounding pyrite, thus enhancing pyrite oxidation rates. In this study, we present preliminary analyses from three different pyrite oxidation experiments each using natural pyrite with different trace element compositions. These results show that the pyrite with the highest trace element concentration has approximately an order of magnitude higher oxidation rate compared to the lowest trace element sample. To further elucidate the mechanisms, we employed microanalytical techniques to investigate how the trace elements are held within the pyrite. LA-ICPMS was used to determine the variability of trace element content from the pyrite samples. These data were then used to select areas of interest for NanoSIMS analyses, which in turn was used to select areas for TEM and APT. These analyses show that the trace element content of pyrite can be highly variable, which may significantly affect the rate of pyrite oxidation.

South-to-north pyroxenite-peridotite source variation correlated with an OIB-type to arc-type enrichment of magmas from the Payenia backarc of the Andean Southern Volcanic Zone (SVZ)

NASA Astrophysics Data System (ADS)

Brandt, Frederik Ejvang; Holm, Paul Martin; Søager, Nina

2017-01-01

New high-precision minor element analysis of the most magnesian olivine cores (Fo85-88) in fifteen high-MgO (Mg#66-74) alkali basalts or trachybasalts from the Quaternary backarc volcanic province, Payenia, of the Andean Southern Volcanic Zone in Argentina displays a clear north-to-south decrease in Mn/Feol. This is interpreted as the transition from mainly peridotite-derived melts in the north to mainly pyroxenite-derived melts in the south. The peridotite-pyroxenite source variation correlates with a transition of rock compositions from arc-type to OIB-type trace element signatures, where samples from the central part of the province are intermediate. The southernmost rocks have, e.g., relatively low La/Nb, Th/Nb and Th/La ratios as well as high Nb/U, Ce/Pb, Ba/Th and Eu/Eu* = 1.08. The northern samples are characterized by the opposite and have Eu/Eu* down to 0.86. Several incompatible trace element ratios in the rocks correlate with Mn/Feol and also reflect mixing of two geochemically distinct mantle sources. The peridotite melt end-member carries an arc signature that cannot solely be explained by fluid enrichment since these melts have relatively low Eu/Eu*, Ba/Th and high Th/La ratios, which suggest a component of upper continental crust (UCC) in the metasomatizing agent of the northern mantle. However, the addition to the mantle source of crustal materials or varying oxidation state cannot explain the variation in Mn and Mn/Fe of the melts and olivines along Payenia. Instead, the correlation between Mn/Feol and whole-rock (wr) trace element compositions is evidence of two-component mixing of melts derived from peridotite mantle source enriched by slab fluids and UCC melts and a pyroxenite mantle source with an EM1-type trace element signature. Very low Ca/Fe ratios ( 1.1) in the olivines of the peridotite melt component and lower calculated partition coefficients for Ca in olivine for these samples are suggested to be caused by higher H2O contents in the magmas derived from subduction zone enriched mantle. Well-correlated Mn/Fe ratios in the wr and primitive olivines demonstrate that the Mn/Fewr of these basalts that only fractionated olivine and chromite reflects the Mn/Fe of the primitive melts and can be used as a proxy for the amount of pyroxenite melt in the magmas. Using Mn/Fewr for a large dataset of primitive Payenia rocks, we show that decreasing Mn/Fewr is correlated with decreasing Mn and increasing Zn/Mn as expected for pyroxenite melts.

Compositional gradients in large reservoirs of silicic magma as evidenced by ignimbrites versus Taylor Creek Rhyolite lava domes

NASA Astrophysics Data System (ADS)

Duffield, Wendell A.; Ruiz, Joaquin

1992-04-01

The Taylor Creek Rhyolite of southwest New Mexico consists of 20 lava domes and flows that were emplaced during a period of a few thousand years or less in late Oligocene time. Including genetically associated pyroclastic deposits, which are about as voluminous as the lava domes and flows, the Taylor Creek Rhyolite represents roughly 100 km3 of magma erupted from vents distributed throughout an area of several hundred square kilometers. Major-element composition is metaluminous to weakly peraluminous high-silica rhyolite and is nearly constant throughout the lava field. The magma reservoir for the Taylor Creek Rhyolite was vertically zoned in trace elements, 87Sr/86Sr, and phenocryst abundance and size. Mean trace-element concentrations, ranges in concentrations, and element-pair correlations are similar to many subalkaline silicic ignimbrites. However, the polarity of the zonation was opposite that in reservoirs for ignimbrites, for most constituents. For example, compared to the Bishop Tuff, only 87Sr/86Sr and Sc increased upward in both reservoirs. Quite likely, a dominant but nonerupted volume of the magma reservoir for the Taylor Creek Rhyolite was zoned like that for the Bishop Tuff, whereas an erupted, few-hundred-meter-thick cap on the magma body was variably contaminated by roof rocks whose contribution to this part of the magma system moderated relatively extreme trace-element concentrations of uncontaminated Taylor Creek Rhyolite but did not change the sense of correlation for most element pairs. The contaminant probably was a Precambrian rock of broadly granitic composition and with very high 87Sr/86Sr. Although examples apparently are not yet reported in the literature, evidence for a similar thin contaminated cap on reservoirs for large-volume silicic ignimbrites may exist in the bottom few meters of ignimbrites or perhaps only in the pumice fallout that normally immediately precedes ignimbrite emplacement. 87Sr/86Sr in sanidine phenocrysts of the Taylor Creek Rhyolite is higher than that of their host whole rocks. Covariation of this isotope ratio with sanidine abundance and size indicates positive correlations for all three features with decreasing distance to the roof of the magma reservoir. The sanidine probably is more radiogenic than host whole rock because growing phenocrysts partly incorporated Sr from the first partial melt of roof rocks, which contained the highly radiogenic Sr of Precambrian biotite ± hornblende, whereas diffusion was too slow for sanidine to incorporate much of the Sr from subsequently produced less radiogenic partial melt of roof rocks, before eruption quenched the magma system. Disequilibrium between feldspar phenocrysts and host groundmass is fairly common for ignimbrites, and a process of contamination similar to that for the Taylor Creek Rhyolite may help explain some of these situations.

Compositional gradients in large reservoirs of silicic magma as evidenced by ignimbrites versus Taylor Creek Rhyolite lava domes

USGS Publications Warehouse

Duffield, W.A.; Ruiz, J.

1992-01-01

The Taylor Creek Rhyolite of southwest New Mexico consists of 20 lava domes and flows that were emplaced during a period of a few thousand years or less in late Oligocene time. Including genetically associated pyroclastic deposits, which are about as voluminous as the lava domes and flows, the Taylor Creek Rhyolite represents roughly 100 km3 of magma erupted from vents distributed throughout an area of several hundred square kilometers. Major-element composition is metaluminous to weakly peraluminous high-silica rhyolite and is nearly constant throughout the lava field. The magma reservoir for the Taylor Creek Rhyolite was vertically zoned in trace elements, 87Sr/86Sr, and phenocryst abundance and size. Mean trace-element concentrations, ranges in concentrations, and element-pair correlations are similar to many subalkaline silicic ignimbrites. However, the polarity of the zonation was opposite that in reservoirs for ignimbrites, for most constituents. For example, compared to the Bishop Tuff, only 87Sr/86Sr and Sc increased upward in both reservoirs. Quite likely, a dominant but nonerupted volume of the magma reservoir for the Taylor Creek Rhyolite was zoned like that for the Bishop Tuff, whereas an erupted, few-hundred-meter-thick cap on the magma body was variably contaminated by roof rocks whose contribution to this part of the magma system moderated relatively extreme trace-element concentrations of uncontaminated Taylor Creek Rhyolite but did not change the sense of correlation for most element pairs. The contaminant probably was a Precambrian rock of broadly granitic composition and with very high 87Sr/86Sr. Although examples apparently are not yet reported in the literature, evidence for a similar thin contaminated cap on reservoirs for large-volume silicic ignimbrites may exist in the bottom few meters of ignimbrites or perhaps only in the pumice fallout that normally immediately precedes ignimbrite emplacement. 87Sr/86Sr in sanidine phenocrysts of the Taylor Creek Rhyolite is higher than that of their host whole rocks. Covariation of this isotope ratio with sanidine abundance and size indicates positive correlations for all three features with decreasing distance to the roof of the magma reservoir. The sanidine probably is more radiogenic than host whole rock because growing phenocrysts partly incorporated Sr from the first partial melt of roof rocks, which contained the highly radiogenic Sr of Precambrian biotite ?? hornblende, whereas diffusion was too slow for sanidine to incorporate much of the Sr from subsequently produced less radiogenic partial melt of roof rocks, before eruption quenched the magma system. Disequilibrium between feldspar phenocrysts and host groundmass is fairly common for ignimbrites, and a process of contamination similar to that for the Taylor Creek Rhyolite may help explain some of these situations. ?? 1992 Springer-Verlag.

A reconnaissance for signs of a Mississippi Valley-type lead-zinc mineralizing system on the eastern flank of the Rutbah Uplift, Anbar Province, Iraq

USGS Publications Warehouse

Hayes, Timothy S.; Mustafa, Mazin; Bennet, Thair

2014-01-01

Reconnaissance field visits and rock sampling were conducted at eight geologically selected locations within Mesozoic rocks on the eastern flank of the Rutbah Uplift, Anbar Province, western Iraq, in an attempt to determine if these rocks have been affected by a Mississippi Valley-Type (MVT) lead-zinc mineralizing system. Samples subsequently were studied by carbonate mineral staining, transmitted and reflected light petrology, and scanning electron microscopy with semi-quantitative energy dispersive elemental analyses. Single samples were studied by each, inductively coupled plasma mass spectrometry analyses of trace elements and fluid inclusion microthermometry. Permissive evidence indicates that there has been a MVT system present, but none of the evidence is considered definitive.

Publications - PDF 97-29I | Alaska Division of Geological & Geophysical

Science.gov Websites

igneous rocks of the Tanana B-1 Quadrangle and vicinity Authors: Newberry, R.J., and Haug, S.A , and Sr isotopic data for igneous rocks of the Tanana B-1 Quadrangle and vicinity: Alaska Division of ; Isotopes; Plutonic; STATEMAP Project; Trace Elements; Volcanic Top of Page Department of Natural Resources

Geochemistry of the Neoproterozoic metabasic rocks from the Negele area, southern Ethiopia: Tectonomagmatic implications

NASA Astrophysics Data System (ADS)

Yihunie, Tadesse; Adachi, Mamoru; Yamamoto, Koshi

2006-03-01

Neoproterozoic metabasic rocks along with metasediments and ultramafic rocks constitute the Kenticha and Bulbul lithotectonic domains in the Negele area. They occur as amphibolite and amphibole schist in the Kenticha, and amphibole schist and metabasalt in the Bulbul domains. These rocks are dominantly basaltic in composition and exhibit low-K tholeiitic characteristics. They are slightly enriched in large ion lithophile (LIL) and light rare earth (LRE) elements and depleted in high field strength (HFS) and heavy rare earth (HRE) elements. They exhibit chemical characteristics similar to back-arc basin and island-arc basalts, but include a few samples with slightly higher Y, Zr and Nb contents. Initial Sr isotopic ratios and ɛNd values for the Kenticha metabasic rocks range from 0.7048 to 0.7051 and from 4.7 to 9.6 whereas for the Bulbul metabasic rocks they range from 0.7032 to 0.7055 and from -0.1 to 5.5, respectively. The trace elements and Sr-Nd isotope compositions of samples from the Kenticha and Bulbul domains suggest similar, but isotopically heterogeneous magma sources. The magma is inferred to have derived from depleted source with a contribution from an enriched mantle source component.

The Geochemical Databases GEOROC and GeoReM - What's New?

NASA Astrophysics Data System (ADS)

Sarbas, B.; Jochum, K. P.; Nohl, U.; Weis, U.

2017-12-01

The geochemical databases GEOROC (http: georoc.mpch-mainz.gwdg.de) and GeoReM (http: georem.mpch-mainz.gwdg.de) are maintained by the Max Planck Institute for Chemistry in Mainz, Germany. Both online databases became crucial tools for geoscientists from different research areas. They are regularly upgraded by new tools and new data from recent publications obtained from a wide range of international journals. GEOROC is a collection of published analyses of volcanic rocks and mantle xenoliths. Since recently, data for plutonic rocks are added. The analyses include major and trace element concentrations, radiogenic and non-radiogenic isotope ratios as well as analytical ages for whole rocks, glasses, minerals and inclusions. Samples come from eleven geological settings and span the whole geological age scale from Archean to Recent. Metadata include, among others, geographic location, rock class and rock type, geological age, degree of alteration, analytical method, laboratory, and reference. The GEOROC web page allows selection of samples by geological setting, geography, chemical criteria, rock or sample name, and bibliographic criteria. In addition, it provides a large number of precompiled files for individual locations, minerals and rock classes. GeoReM is a database collecting information about reference materials of geological and environmental interest, such as rock powders, synthetic and natural glasses as well as mineral, isotopic, biological, river water and seawater reference materials. It contains published data and compilation values (major and trace element concentrations and mass fractions, radiogenic and stable isotope ratios). Metadata comprise, among others, uncertainty, analytical method and laboratory. Reference materials are important for calibration, method validation, quality control and to establish metrological traceability. GeoReM offers six different search strategies: samples or materials (published values), samples (GeoReM preferred values), chemical criteria, chemical criteria based on bibliography, bibliography, as well as methods and institutions.

Volatile, Trace Element and Isotopic Variations of Mafic Arc Volcanic Rocks from Nicaragua and Costa Rica

NASA Astrophysics Data System (ADS)

Hoernle, K.; Sadofsky, S.; Nichols, H.; Portnyagin, M.; van den Bogaard, P.; Alvarado, G.

2003-12-01

Quaternary volcanic rocks from the Central American Volcanic Arc in central Nicaragua and central Costa Rica exhibit major differences in their volatile, trace element and isotopic compositions. Olivine-hosted melt inclusions in Nicaraguan volcanic rocks with high Fo contents (>73) extend to high H2O (up to 5.3%), S (10-6860 ppm) and Cl (490-2340 ppm) contents. The volcanic rocks have high ratios of fluid mobile to fluid immobile elements such as Ba/La (65-122), Ba/Th (484-1304) and U/La (0.08-0.17). Additionally, they have 143Nd/144Nd (0.51300-0.51307) similar to normal mid-ocean-ridge basalts (N-MORB) from the East Pacific Rise (EPR), but 87Sr/86Sr (0.7035-0.7042) ratios are much higher than those found in fresh EPR glasses. Pb isotopic compositions of the samples (e.g. 206Pb/204Pb = 18.5-19.0, 207Pb/204Pb = 15.52-15.58) form an array between EPR basalts and subducted sediments. The volatile, trace element and isotope data are consistent with mixing of fluids highly enriched in fluid-mobile elements from subducted sediments with a N-MORB-type mantle wedge to produce the Nicaraguan volcanic rocks. In contrast, olivine-hosted melt inclusions (Fo >82) in Costa Rican volcanic rocks show a similar range in H2O (up to 5.1%) to Nicaraguan inclusions but overall have lower S (0-1340 ppm) and Cl (10-790 ppm) contents. Costa Rican lavas also have lower Ba/La (7-35), Ba/Th (55-338), U/La (0.02-0.12), 87Sr/86Sr (0.7035-0.7038) and 143Nd/144Nd (0.51292-0.51301) than Nicaraguan lavas, but 87Sr/86Sr and Pb isotope ratios (e.g. 206Pb/204Pb = 19.02-19.32) are more radiogenic than in Nicaragua and than usually found in fresh EPR MORB. Our data are consistent with the presence of Galapagos Hotspot-type components in the source of the central Costa Rican volcanic rocks, derived from the subducting Galapagos Hotspot Track and from Galapagos-type material entering the mantle wedge through a slab tear or window (Abratis and Worner, 2000; Geology). The estimated volume of volcanic rocks erupted in the last 100,000 years (Carr et al., 1990, Contrib. Min. Pet.; in press, AGU Spec. Pub.) are substantially higher in central Costa Rica than in Nicaragua, suggesting greater productivity of melting beneath Costa Rica. Since the flux of hydrous fluids appears to be similar beneath both arc segments, higher melt productivity beneath Costa Rica could reflect the presence of larger volumes of more fertile, hotter Galapagos-type mantle upwelling through a slab tear or window into the Costa Rican mantle wedge.

Mantle sources and magma evolution of the Rooiberg lavas, Bushveld Large Igneous Province, South Africa

NASA Astrophysics Data System (ADS)

Günther, T.; Haase, K. M.; Klemd, R.; Teschner, C.

2018-06-01

We report a new whole-rock dataset of major and trace element abundances and 87Sr/86Sr-143Nd/144Nd isotope ratios for basaltic to rhyolitic lavas from the Rooiberg continental large igneous province (LIP). The formation of the Paleoproterozoic Rooiberg Group is contemporaneous with and spatially related to the layered intrusion of the Bushveld Complex, which stratigraphically separates the volcanic succession. Our new data confirm the presence of low- and high-Ti mafic and intermediate lavas (basaltic—andesitic compositions) with > 4 wt% MgO, as well as evolved rocks (andesitic—rhyolitic compositions), characterized by MgO contents of < 4 wt%. The high- and low-Ti basaltic lavas have different incompatible trace element ratios (e.g. (La/Sm)N, Nb/Y and Ti/Y), indicating a different petrogenesis. MELTS modelling shows that the evolved lavas are formed by fractional crystallization from the mafic low-Ti lavas at low-to-moderate pressures ( 4 kbar). Primitive mantle-normalized trace element patterns of the Rooiberg rocks show an enrichment of large ion lithophile elements (LILE), rare-earth elements (REE) and pronounced negative anomalies of Nb, Ta, P, Ti and a positive Pb anomaly. Unaltered Rooiberg lavas have negative ɛNdi (- 5.2 to - 9.4) and radiogenic ɛSri (6.6 to 105) ratios (at 2061 Ma). These data overlap with isotope and trace element compositions of purported parental melts to the Bushveld Complex, especially for the lower zone. We suggest that the Rooiberg suite originated from a source similar to the composition of the B1-magma suggested as parental to the Bushveld Lower Zone, or that the lavas represent eruptive successions of fractional crystallization products related to the ultramafic cumulates that were forming at depth. The Rooiberg magmas may have formed by 10-20% crustal assimilation by the fractionation of a very primitive mantle-derived melt within the upper crust of the Kaapvaal Craton. Alternatively, the magmas represent mixtures of melts from a primitive, sub-lithospheric mantle plume and an enriched sub-continental lithospheric mantle (SCLM) component with harzburgitic composition. Regardless of which of the two scenarios is invoked, the lavas of the Rooiberg Group show geochemical similarities to the Jurassic Karoo flood basalts, implying that the Archean lithosphere strongly affected both of these large-scale melting events.

Petrographic and geochemical data for Cenozoic volcanic rocks of the Bodie Hills, California and Nevada

USGS Publications Warehouse

du Bray, Edward A.; John, David A.; Box, Stephen E.; Vikre, Peter G.; Fleck, Robert J.; Cousens, Brian L.

2013-04-23

Petrographic and geochemical data for Cenozoic volcanic rocks of the Bodie Hills, California and Nevada // // This report presents petrographic and geochemical data for samples collected during investigations of Tertiary volcanism in the Bodie Hills of California and Nevada. Igneous rocks in the area are principally 15–6 Ma subduction-related volcanic rocks of the Bodie Hills volcanic field but also include 3.9–0.1 Ma rocks of the bimodal, post-subduction Aurora volcanic field. Limited petrographic results for local basement rocks, including Mesozoic granitoid rocks and their metamorphic host rocks, are also included in the compilation. The petrographic data include visual estimates of phenocryst abundances as well as other diagnostic petrographic criteria. The geochemical data include whole-rock major oxide and trace element data, as well as limited whole-rock isotopic data.

Geological and Petrological Characteristics of Oligocene Magmatic Rocks in The Biga Peninsula, NW Turkey

NASA Astrophysics Data System (ADS)

Erenoglu, Oya

2016-04-01

Oligocene magmatic activity in the Biga Peninsula (NW-Anatolia) produced widespread volcano-plutonic complexes. The study region, where in north of the Evciler village in the middle of Biga Peninsula includes these igneous assemblages. In this study, the petrographic and geochemical characteristics of igneous rocks in the region were investigated as well as the geological locations. The magmatic rocks are classified as 6 different units using their lithostratigraphical properties. The volcanism in the region starts with basaltic andesite lava including basalt dykes in the Lower Oligocene. In the Upper Oligocene, the evolved magma by crustal contamination produced commonly dacitic and andesitic lavas. The volcanism continued with andesitic lavas which had significant alterations in the region during this period. Evciler pluton including granite and granodiorite composition with shallow intrusive, was located with the related volcanism at the same time. The volcanic products, i.e. andesitic and trachydacitic lavas, was completed in the interval between Upper Oligocene and Lower Miocene. The post-collisional Oligocene sequence is associated with calc-alkaline composition and it has middle, high-K. Trace and rare earth elements (REE) diagrams show the enrichment in both large-ion lithophile elements (LILE) and light rare earth elements (LREE) with respect to the high field strength elements (HFSE), and a significant increment in heavy rare earth element consumption (HREE). The features of major, trace and rare earth elements of plutonic and volcanic rocks and the compositional variations of Oligocene volcanic group indicate increasing amounts of partial melting, crustal contamination and/or assimilation. The Oligocene post-collisional volcanism in Biga Peninsula points out the lithospheric mantle source enriched by subduction which controlled by slab break-off and lithospheric delamination. Acknowledgement. This study was supported by Canakkale Onsekiz Mart University Scientific Research Project Coordination Unit (Project no: FBA-2015-566) Keywords: Biga Peninsula, oligocene, post-collisional volcanism, petrology

Geological-hydrogeochemical characteristics of a “silver spring” water source (the Lozovy ridge)

NASA Astrophysics Data System (ADS)

Ivanova, I. S.; Bragin, I. V.; Chelnokov, G. A.; Bushkareva, K. Yu; Shvagrukova, E. V.

2016-03-01

Geological and hydrogeological characteristics of the Lozovy ridge (Southern Primorye) are studied, as far as karst phenomena are widely distributed within its boundaries. Water-bearing rocks of the karst water source “Silver Spring” (“Serebryany Klyuch”), which is located near the bottom of the “Bear’s fang” (“Medvezhiy klyk”) cave, are investigated. It is found that karst rocks are presented by calcite (CaCO3), and an accessory mineral is barite (BaSO4). It is determined that among the trace elements forming the composition of carbonate water-bearing rocks the maximum concentrations are typical for Sr, Ba, Fe, Al, Za, Mn, Cu, and Ni. Also, the chemical composition of the waters taken from the “Silver Spring” water source is studied. These waters are fresh, hydrocarbonate, calcium, and weakly alkaline. Among the elements of the spring, such elements as Sr, Ba, Fe, Al, Zn, Mn, Cu, and Ni have the maximum concentration. The other elements have concentrations less than 1 µg/l.

Diogenites: Cumulates from Asteroid 4 Vesta: Insights from Orthopyroxene and Spinel Chemistry

NASA Technical Reports Server (NTRS)

Papike, James J.; Bowman, L. E.; Spilde, M. N.; Fowler, G. W.; Shearer, C. K.

1996-01-01

Cumulate rocks are important planetary lithologies, but they can be difficult to interpret. Important clues to the nature of their parental melts may still be present in the interiors of cumulus phases. However, in some cases, even the cores of the cumulus grains may have been modified by postcrystallization reactions with trapped melt and other cumulus phases. We have previously studied the major-, minor-, and trace-element chemistry of orthopyroxene from a suite of diogenites and concluded that their chemical attributes can best be explained by crystallization from parental melts that were derived from a depleted mantle source that had already experienced eucrite removal. However, we and others have had difficulty explaining the great range in concentration of minor elements (Al, Ti) and trace elements (REE, Y, Zr) if all diogenites were derived from a single magmatic system. Therefore, we have investigated the chemistry of diogenitic spinels to see if they still held clues to the diogenite parental melt compositions. Although spinel is low in abundance in diogenites (<5 vol%) it still may hold clues to the maomatic and metamorphic history of these rocks.

Rare earths and other trace elements in Apollo 14 samples.

NASA Technical Reports Server (NTRS)

Helmke, P. A.; Haskin, L. A.; Korotev, R. L.; Ziege, K. E.

1972-01-01

REE and other trace elements have been determined in igneous rocks 14053, 14072, and 14310, in breccias 14063 and 14313, and in fines 14163. All materials analyzed have typical depletions of Eu except for feldspar fragments from the breccias and igneous fragments from 14063. Igneous rocks 14072 and 14053 have REE concentrations very similar to Apollo 12 basalts; 14310 has the highest REE concentrations yet observed for a large fragment of lunar basalt. The effects of crystallization of a basaltic liquid as a closed system on the concentrations of Sm and Eu in feldspar are considered. Small anorthositic fragments may have originated by simple crystallization from very highly differentiated basalt (KREEP) or by closed-system crystallization in a less differentiated starting material. Application of independent models of igneous differentiation to Sm and Eu in massive anorthosite 15415 and to Sm and Eu in lunar basalts suggests a common starting material with a ratio of concentrations of Sm and Eu about the same as that in chondrites and with concentrations of those elements about 15 times enriched over chondrites.

The zonal distribution of selected elements above the Kalamazoo porphyry copper deposit, San Manuel district, Pinal County, Arizona

USGS Publications Warehouse

Chaffee, M.A.

1976-01-01

There may be many as-yet-undiscovered porphyry copper deposits that exist as blind deposits deep within exposed rock bodies. The Kalamazoo porphyry copper-molybdenum deposit is a blind deposit present at depths up to at least 1,000 m (about 3,200 ft) that contains zoning features common to many of the known porphyry copper deposits found in western North and South America. As the preliminary phase in a geochemical study of the Kalamazoo deposit, whole-rock samples of core and cuttings from two drill holes have been analyzed for 60 different elements. Each hole represents a different major rock unit and each has penetrated completely through all the existing alteration zones and the ore zone. Plots of concentration vs. depth for 17 selected elements show distinct high- or low-concentration zones that are spatially related to the ore zone. For most of the ore-related elements no significant correlation with the two lithologies is apparent. The spatial distribution and abundance of elements such as Co, Cu, S, Se, Mn, Tl, Rb, Zn, B, and Li may be useful in determining the direction for exploration to proceed to locate a blind deposit. Trace element studies should be valuable in evaluating areas containing extensive outcrops of rocks with disseminated pyrite. Elemental zoning should be at least as useful as alteration-mineralization zoning for evaluating rock bodies thought to contain blind deposits similar to the Kalamazoo deposit. ?? 1976.

Prevention of sulfide oxidation in sulfide-rich waste rock

NASA Astrophysics Data System (ADS)

Nyström, Elsa; Alakangas, Lena

2015-04-01

The ability to reduce sulfide oxidation in waste rock after mine closure is a widely researched area, but to reduce and/or inhibit the oxidation during operation is less common. Sulfide-rich (ca 30 % sulfur) waste rock, partially oxidized, was leached during unsaturated laboratory condition. Trace elements such as As and Sb were relatively high in the waste rock while other sulfide-associated elements such as Cu, Pb and Zn were low compared to common sulfide-rich waste rock. Leaching of unsaturated waste rock lowered the pH, from around six down to two, resulting in continuously increasing element concentrations during the leaching period of 272 days. The concentrations of As (65 mg/L), Cu (6.9 mg/L), Sb (1.2 mg/L), Zn (149 mg/L) and S (43 g/L) were strongly elevated at the end of the leaching period. Different alkaline industrial residues such as slag, lime kiln dust and cement kiln dust were added as solid or as liquid to the waste rock in an attempt to inhibit sulfide oxidation through neo-formed phases on sulfide surfaces in order to decrease the mobility of metals and metalloids over longer time scale. This will result in a lower cost and efforts of measures after mine closure. Results from the experiments will be presented.

[Variation characteristics and environmental significant of trace elements under rainfall condition in karst groundwater].

PubMed

Chen, Xue-Bin; Yang, Ping-Heng; Lan, Jia-Cheng; Mo, Xue; Shi, Yang

2014-01-01

Chemical dynamics of Qingmuguan karst groundwater system were continuously monitored during the rainfall events. A series of high-resolution concentrations data on trace elements, such as barium, strontium, iron, manganese, aluminum, and other major elements were acquired. Correlation analysis and analysis of concentration curve were employed to identify the sources and migration path of the trace elements. And the formation process of trace elements in groundwater was discussed with the geological background of underground river basin. Research shows that barium and strontium derived from carbonate dissolution appeared to be stored in features such as fissures and pores. These two ions were recharged into the underground river by diffusion during precipitation, which resulted in small changes in the their concentration. However total iron, total manganese and aluminum derived from soil erosion varied relatively widely with strong response to rainfall, attributing to the migration of total iron and aluminum with overland flow to recharge the subterranean river directly via sinkholes while total manganese via soil-rock porous media. The results showed that concentrations of all the five trace elements were below 1 mg x L(-1), and the highest concentrations of total iron, total manganese and aluminum exceeded the limit of drinking water. To some extent, the concentrations of total iron and aluminum may be an indicator for soil erosion and water quality.

Geochemical compositions of Neoproterozoic to Lower Palaeozoic (?) shales and siltstones in the Volta Basin (Ghana): Constraints on provenance and tectonic setting

NASA Astrophysics Data System (ADS)

Amedjoe, Chiri G.; Gawu, S. K. Y.; Ali, B.; Aseidu, D. K.; Nude, P. M.

2018-06-01

Many researchers have investigated the provenance and tectonic setting of the Voltaian sediments using the geochemistry of sandstones in the basin. The shales and siltstones in the basin have not been used much in the provenance studies. In this paper, the geochemistry of shales and siltstones in the Kwahu Group and Oti Group of the Voltaian Supergroup from Agogo and environs in the southeastern section of the basin has constrained the provenance and tectonic setting. Trace element ratios La/Sc, Th/Sc and Cr/Th and REEs sensitive to average source compositions revealed sediments in the shales and siltstones may mainly be from felsic rocks, though contributions from old recycled sediments and some andesitic rock sediments were identified. The felsic rocks may be granites and/or granodiorites. Some intermediate rocks of andesitic composition are also identified, while the recycled sediments were probably derived from the basement metasedimentary rocks. The enrichment of light REE (LaN/YbN c. 7.47), negative Eu anomalies (Eu/Eu* c. 0.59), and flat heavy REE chondrite-normalized patterns, denote an upper-continental-crustal granitic source materials for the sediments. Trace-element ternary discriminant diagrams reveal passive margin settings for sediments, though some continental island arc settings sediments were also depicted. Mixing calculations based on REE concentrations and modeled chondrite-normalized REE patterns suggest that the Birimian basement complex may be the source of detritus in the Voltaian Basin. REEs are more associated with shales than siltstones. On this basis chondrite-normalized REE patterns show that shale lithostratigraphic units may be distinguished from siltstone lithostratigraphic units. The significant variability in shales elemental ratios can therefore be used to distinguish between shales of the Oti Group from that of the Kwahu Group.

Origin and geodynamic setting of Late Cenozoic granitoids in Sulawesi, Indonesia

NASA Astrophysics Data System (ADS)

Maulana, Adi; Imai, Akira; Van Leeuwen, Theo; Watanabe, Koichiro; Yonezu, Kotaro; Nakano, Takanori; Boyce, Adrian; Page, Laurence; Schersten, Anders

2016-07-01

Late Cenozoic granitoids are widespread in a 1600 km long belt forming the Western and Northern Sulawesi tectono-magmatic provinces. They can be divided into three rock series: shoshonitic (HK), high-K felsic calc-alkaline (CAK), and normal calc-alkaline to tholeiitic (CA-TH). Representative samples collected from eleven plutons, which were subjected to petrography, major element, trace element, Sr, Nd, Pb isotope and whole-rock δ18O analyses, are all I-type and metaluminous to weakly peraluminous. The occurrence of the two K-rich series is restricted to Western Sulawesi, where they formed in an extensional, post-subduction tectonic setting with astenospheric upwelling providing thermal perturbation and adiabatic decompression. Two parental magma sources are proposed: enriched mantle or lower crustal equivalent for HK magmas, and Triassic igneous rocks in a Gondwana-derived fragment thrust beneath the cental and northern parts of Western Sulawesi for CAK magmas. The latter interpretation is based on striking similarities in radiogenic isotope and trace element signatures. CA-TH granitoids are found mostly in Northern Sulawesi. Partial melting of lower-middle crust amphibolites in an active subduction environment is the proposed origin of these rocks. Fractional crystallization and crustal contamination have played a significant role in magma petrogenesis, particularly in the case of the HK and CAK series. Contamination by organic carbon-bearing sedimentary rocks of the HK and CAK granitoids in the central part of Western Sulawesi is suggested by their ilmenite-series (reduced) character. The CAK granitoids further to the north and CA-TH granitoids in Northern Sulawesi are typical magnetite-series (oxidized). This may explain differences in mineralization styles in the two regions.

Geochemical signature of provenance, tectonics and chemical weathering in the Quaternary flood plain sediments of the Hindon River, Gangetic plain, India

NASA Astrophysics Data System (ADS)

Mondal, M. E. A.; Wani, H.; Mondal, Bulbul

2012-09-01

The Ganga basin in the Himalayan foreland is a part of the world's largest area of modern alluvial sedimentation. Flood plain sediments of the Hindon River of the Gangetic plain have been analyzed for sediment texture, major and trace elements including rare earth elements (REEs). The results have been used to characterize the source rock composition and to understand the intensity of chemical weathering, tectonics and their interplay in the Hindon flood plain. The sediments of the Hindon flood plain dominantly consist of sand sized particles with little silt and clay. The geochemistry of the Hindon sediments has been compared to the Siwalik mudstone of the Siwalik Group (Siwaliks). The Siwalik sedimentary rocks like sandstones, mudstones and conglomerates are the known source rocks for the Hindon flood plain sediments. Mudstone geochemistry has been considered best to represent the source rock characteristics. The UCC (Upper Continental Crust) normalized major and trace elements of the Hindon flood plain sediments are very similar to the Siwalik mudstone except for Th and Cr. Furthermore, the average chondrite normalized REE pattern of the Hindon flood plain sediments is similar to the Siwalik mudstone. Textural immaturity, K/Rb ratios and the average CIA (Chemical Index of Alteration) and PIA (Plagioclase Index of Alteration) values of the Hindon flood plain sediments indicate that the sediments have not been affected by chemical weathering. Our study suggests that the active tectonics of the Himalayas and monsoon climate enhances only physical erosion of the source rocks (Siwaliks) rather than the chemical alteration. These factors help the Hindon sediments to retain their parental and tectonic signature even after recycling.

Magmatic evolution of lunar highland rocks estimated from trace elements in plagioclase: A new bulk silicate Moon model with sub-chondritic Ti/Ba, Sr/Ba, and Sr/Al ratios

NASA Astrophysics Data System (ADS)

Togashi, Shigeko; Kita, Noriko T.; Tomiya, Akihiko; Morishita, Yuichi

2017-08-01

The compositions of host magmas of ferroan anorthosites (FAN-host magmas) were estimated from secondary ion mass spectrometry analyses of plagioclase in lunar highland rocks. The evolution of the magmas was investigated by considering phase relations based on the MELTS algorithm and by re-examining partition coefficients for trace elements between plagioclase and melts. Data little affected by post-magmatic processes were selected by using plagioclase with relatively primitive Sc and Co contents. The FAN-host magma contained 90-174 ppm Sr, 40-119 ppm Ba and 0.5-1.3% TiO2, and had sub-chondritic Sr/Ba and Ti/Ba ratios. It is difficult to account for the formation of FAN-host magma on the basis of magma evolution processes of previously proposed bulk silicate Moon models with chondritic ratios for refractory elements at global scale. Therefore, the source of the FAN-host magma must have had primordial sub-chondritic Sr/Ba and Ti/Ba ratios. The FAN-host magmas were consistent in refractory elements with the estimated host mafic magma for feldspathic crust based on lunar meteorites, and some very-low-Ti mare rocks from lunar meteorites. Here, we propose an alternative bulk silicate Moon model (the cBSM model), which is enriched in crustal components of proto-bodies relative to the present whole Earth-Moon system.

Biogeochemical sampling in the Mahd Adh Dhahab District, Kingdom of Saudi Arabia

USGS Publications Warehouse

Ebens, Richard J.; Shacklette, Hansford T.; Worl, Ronald G.

1983-01-01

A biogeochemical reconnaissance of the Mahd adh Dhahab district, Kingdom of Saudi Arabia, confirms the ability of deep-rooted Acacia trees to reflect bedrock concentrations of some trace elements. The analytical values for lead, zinc, selenium, and cadmium in ash of tree branches are significantly higher in samples from areas of known mineralization (13 sites) than in samples from areas of no known mineralization (12 sites). Geometric mean concentrations of these elements in the two areas (mineralized; nonmineralized), quoted as parts per million in ash, are lead (122; 28), zinc (713; 443), selenium (1.2; 0.6), and cadmium (1.4; 0.5). The range of molybdenum values in ash from the two areas is similar, but a cluster of four sites in an area classified as nonmineralized corresponds to an area where the U.S. Geological Survey reported anomalous molybdenum values in rock in 1965. Results for other elements were either equivocal (mercury, tellurium, silver) or showed no correspondence to the two areas. Mean values for barium, manganese, potassium, and sodium are significantly higher in areas of no known mineralization, but we conclude that this reflects a difference in country rock major-element chemistry rather than the effect of ore-forming processes. The pattern of trace-metal values in Acacia ash is present whether the sampled tree grows on bedrock, on talus, or on residual or modern alluvium. This fact suggests that the trace-element chemistry of the trees reflects bedrock geochemistry and implies that Acacia biogeochemistry could be applied as a prospecting tool in areas where bedrock is not well exposed.

The magmatic evolution and genesis of the Quaternary basanite-trachyphonolite suite of Itasy (Madagascar) as inferred by geochemistry, Sr-Nd-Pb isotopes and trace element distribution in coexisting phases

NASA Astrophysics Data System (ADS)

Melluso, L.; Tucker, R. D.; Cucciniello, C.; le Roex, A. P.; Morra, V.; Zanetti, A.; Rakotoson, R. L.

2018-06-01

The Itasy is a Pleistocene-Holocene volcanic field in central Madagascar, located to the west of the Ankaratra volcanic complex. It comprises scoria cones and lava domes (>120), with associated pyroclastic fall and mafic lava flows, covering an area of ab. 400 km2. The last volcanic episodes probably dated ca. 6000-7100 y BP; warm springs and geysers are active. The juvenile samples comprise a peculiar, almost bimodal, rock suite ranging from potassic leucite-kaersutite-bearing basanites, tephrites and phonotephrites, to benmoreites and titanite-haüyne-bearing trachyphonolites (MgO from 9-10 wt% to 0.1 wt%). These rocks show continuous and overlapping variations in the bulk-rock and phase composition (olivine, clinopyroxene, amphibole, feldspar, leucite, haüyne, nepheline, oxides, apatite, titanite, glass and other accessories). The basanites have homogeneous isotopic composition (87Sr/86Sr = 0.70366-0.70378, 143Nd/144Nd = 0.51274-0.51277, 206Pb/204Pb = 18.7-18.9, 207Pb/204Pb = 15.53-15.56; 208Pb/204Pb = 38.89-39.01), and a marked enrichment in the most incompatible elements (LILE and HFSE reach 100-215 times primitive mantle). These features are consistent with low degrees of partial melting of a volatile-, LILE- and HFSE-rich, amphibole-bearing peridotitic mantle induced by uplift during an E-W-directed extensional regime, as is found in central Madagascar. The marked changes in the geochemical composition, and small variations of the Sr-Nd-Pb isotopes in the trachyphonolites (87Sr/86Sr = 0.70425-0.70446, 143Nd/144Nd = 0.51266-0.51269, 206Pb/204Pb = 18.18-18.39, 207Pb/204Pb = 15.49-15.51; 208Pb/204Pb = 38.38-39.57) with respect to basanites and tephrites point to a limited amount of crustal contamination by the relatively low-206Pb/204Pb, low-143Nd/144Nd, high-87Sr/86Sr Precambrian basement rocks (of Middle Archean to Late Proterozoic age), and highlight the geochemical effects of titanite and anorthoclase removal on the trace element fractionation trends, a feature also shown in the trace element composition of the phenocrysts in trachyphonolites. Supplementary Table S2: synopsis of the mineral assemblages of the main lithotypes of the Itasy complex. Supplementary Table S3: composition of olivine of the Itasy rocks. Supplementary Table S4: composition of oxides of the Itasy rocks. Supplementary Table S5: composition of pyroxene of the Itasy rocks. Supplementary Table S6: composition of amphibole, biotite and rhönite of the Itasy rocks. Supplementary Table S7: composition of feldspar and glass of the Itasy rocks. Supplementary Table S8: composition of feldspathoids of the Itasy rocks. Supplementary Table S9: composition of titanite, apatite, other accessories of the Itasy rocks. Supplementary Table S10: Recapitulation of mass balance calculations between rocks of different degree of magmatic evolution, and detailed results. The composition of the phases is reported in the supplementary tables. Supplementary Table S11: average REE mineral/bulk rock ratios for titanite, amphibole and clinopyroxene. The partition coefficients of titanite, clinopyroxene, apatite and amphibole are taken from Olin and Wolff (2012), Fedele et al. (2009, 2015) and Tiepolo et al. (2007). Note that amphibole of RT-06I-355 could not be considered in equilibrium with the host rock (cf. Supplementary Figs. S1a, S1b, S1c).

Abraded Target on Rock 'Champagne' in Gusev Crater

NASA Technical Reports Server (NTRS)

2005-01-01

NASA's Mars Exploration Rover Spirit took this microscopic image of a target called 'Bubbles' on a rock called 'Champagne' after using its rock abrasion tool to grind a hole through the rock's outer surface. The circular area where the rock's interior is exposed is about 5 centimeters (2 inches) across. This rock is different from rocks out on the plains of Gusev Crater but is similar to other rocks in this area of the 'Columbia Hills' in that it rich in phosphorus. Plagioclase, a mineral commonly found in igneous rocks, is also present in these rocks, according to analysis with Spirit's miniature thermal emission spectrometer. By using the rover's alpha particle X-ray spectrometer to collect data for multiple martian days, or sols, scientists are also beginning to get measurements of trace elements in the rocks. Spirit took the images that are combined into this mosaic on sol 358 (Jan. 3, 2005).

Multivariate statistical analysis to characterize/discriminate between anthropogenic and geogenic trace elements occurrence in the Campania Plain, Southern Italy.

PubMed

Busico, Gianluigi; Cuoco, Emilio; Kazakis, Nerantzis; Colombani, Nicolò; Mastrocicco, Micòl; Tedesco, Dario; Voudouris, Konstantinos

2018-03-01

Shallow aquifers are the most accessible reservoirs of potable groundwater; nevertheless, they are also prone to various sources of pollution and it is usually difficult to distinguish between human and natural sources at the watershed scale. The area chosen for this study (the Campania Plain) is characterized by high spatial heterogeneities both in geochemical features and in hydraulic properties. Groundwater mineralization is driven by many processes such as, geothermal activity, weathering of volcanic products and intense human activities. In such a landscape, multivariate statistical analysis has been used to differentiate among the main hydrochemical processes occurring in the area, using three different approaches of factor analysis: (i) major elements, (ii) trace elements, (iii) both major and trace elements. The elaboration of the factor analysis approaches has revealed seven distinct hydrogeochemical processes: i) Salinization (Cl - , Na + ); ii) Carbonate rocks dissolution; iii) Anthropogenic inputs (NO 3 - , SO 4 2- , U, V); iv) Reducing conditions (Fe 2+ , Mn 2+ ); v) Heavy metals contamination (Cr and Ni); vi) Geothermal fluids influence (Li + ); and vii) Volcanic products contribution (As, Rb). Results from this study highlight the need to separately apply factor analysis when a large data set of trace elements is available. In fact, the impact of geothermal fluids in the shallow aquifer was identified from the application of the factor analysis using only trace elements. This study also reveals that the factor analysis of major and trace elements can differentiate between anthropogenic and geogenic sources of pollution in intensively exploited aquifers. Copyright © 2017 Elsevier Ltd. All rights reserved.

Petrology of lunar rocks and implication to lunar evolution

NASA Technical Reports Server (NTRS)

Ridley, W. I.

1976-01-01

Recent advances in lunar petrology, based on studies of lunar rock samples available through the Apollo program, are reviewed. Samples of bedrock from both maria and terra have been collected where micrometeorite impact penetrated the regolith and brought bedrock to the surface, but no in situ cores have been taken. Lunar petrogenesis and lunar thermal history supported by studies of the rock sample are discussed and a tentative evolutionary scenario is constructed. Mare basalts, terra assemblages of breccias, soils, rocks, and regolith are subjected to elemental analysis, mineralogical analysis, trace content analysis, with studies of texture, ages and isotopic composition. Probable sources of mare basalts are indicated.

Spatial and temporal variability of trace element concentrations in an urban subtropical watershed, Honolulu, Hawaii

USGS Publications Warehouse

Heinen, De Carlo E.; Anthony, S.S.

2002-01-01

Trace metal concentrations in soils and in stream and estuarine sediments from a subtropical urban watershed in Hawaii are presented. The results are placed in the context of historical studies of environmental quality (water, soils, and sediment) in Hawaii to elucidate sources of trace elements and the processes responsible for their distribution. This work builds on earlier studies on sediments of Ala Wai Canal of urban Honolulu by examining spatial and temporal variations in the trace elements throughout the watershed. Natural processes and anthropogenic activity in urban Honolulu contribute to spatial and temporal variations of trace element concentrations throughout the watershed. Enrichment of trace elements in watershed soils result, in some cases, from contributions attributed to the weathering of volcanic rocks, as well as to a more variable anthropogenic input that reflects changes in land use in Honolulu. Varying concentrations of As, Cd, Cu, Pb and Zn in sediments reflect about 60 a of anthropogenic activity in Honolulu. Land use has a strong impact on the spatial distribution and abundance of selected trace elements in soils and stream sediments. As noted in continental US settings, the phasing out of Pb-alkyl fuel additives has decreased Pb inputs to recently deposited estuarine sediments. Yet, a substantial historical anthropogenic Pb inventory remains in soils of the watershed and erosion of surface soils continues to contribute to its enrichment in estuarine sediments. Concentrations of other elements (e.g., Cu, Zn, Cd), however, have not decreased with time, suggesting continued active inputs. Concentrations of Ba, Co, Cr, Ni, V and U, although elevated in some cases, typically reflect greater proportions attributed to natural sources rather than anthropogenic input. ?? 2002 Elsevier Science Ltd. All rights reserved.

Trace element distribution in peridotite xenoliths from Tok, SE Siberian craton: A record of pervasive, multi-stage metasomatism in shallow refractory mantle

NASA Astrophysics Data System (ADS)

Ionov, Dmitri A.; Chazot, Gilles; Chauvel, Catherine; Merlet, Claude; Bodinier, Jean-Louis

2006-03-01

Spinel peridotite xenoliths in alkali basalts at Tok, SE Siberian craton range from fertile lherzolites to harzburgites and wehrlites; olivine-rich (70-84%) rocks are dominant. REE patterns in the lherzolites range from nearly flat for fertile rocks (14-17% cpx) to LREE-enriched; the enrichments are positively correlated with modal olivine, consistent with high-permeability of olivine-rich rocks during melt percolation. Clinopyroxene in olivine-rich Tok peridotites typically has convex-upward trace element patterns (La/Nd PM < 1 and Nd/Yb PM ≫ 1), which we consider as evidence for equilibration with evolved silicate liquids (with higher REE and lower Ti contents than in host basalts). Whole-rock patterns of the olivine-rich xenoliths range from convex-upward to LREE-enriched (La/Nd PM > 1); the LREE-enrichments are positively correlated with phosphorus abundances and are mainly hosted by accessory phosphates and P-rich cryptocrystalline materials. In addition to apatite, some Tok xenoliths contain whitlockite (an anhydrous, halogen-poor and Na-Mg-rich phosphate), which is common in meteorites and lunar rocks, but has not been reported from any terrestrial mantle samples. Some olivine-rich peridotites have generations of clinopyroxene with distinct abundances of Na, LREE, Sr and Zr. The mineralogical and trace element data indicate that the lithospheric mantle section represented by the xenoliths experienced a large-scale metasomatic event produced by upward migration of mafic silicate melts followed by percolation of low- T, alkali-rich melts and fluids. Chromatographic fractionation and fractional crystallisation of the melts close to the percolation front produced strong LREE-enrichments, which are most common in the uppermost mantle and are related to carbonate- and P 2O 5-rich derivatives of the initial melt. Reversal and gradual retreat of the percolation front during thermal relaxation to ambient geotherm ("retrograde" metasomatism) caused local migration and entrapment of small-volume residual fluids and precipitation of volatile-rich accessory minerals. A distinct metasomatic episode, which mainly produced "anhydrous" late-stage interstitial materials was concomitant with the alkali basaltic magmatism, which brought the xenoliths to the surface.

La Isla de Gorgona, Colombia: A petrological enigma?

NASA Astrophysics Data System (ADS)

Kerr, Andrew C.

2005-09-01

A wide range of intrusive (wehrlite, dunite, gabbro and olivine gabbro) and extrusive (komatiites picrites and basalts) igneous rocks are found on the small pacific island of Gorgona. The island is best known for its ˜90 Ma spinifex-textured komatiites: the only true Phanerozoic komatiites yet discovered. Early work led to suggestions that the rocks of the island formed at a mid-ocean ridge, however more recent research supports an origin as part of a hot mantle plume-derived oceanic plateau. One of the main lines of evidence for this origin stems from the inferred high mantle source temperatures required to form the high-MgO (> 15 wt.%) komatiites and picrites. Another remarkable feature of the island, considering its small size (8 × 2.5 km), is the degree of chemical and radiogenic isotopic heterogeneity shown by the rocks. This heterogeneity requires a mantle source region with at least three isotopically distinctive source regions (two depleted and one enriched). Although these mantle source regions appear to be derived in significant part from recycled oceanic crust and lithosphere, enrichments in 187Os, 186Os and 3He in Gorgona lavas and intrusive rocks, suggest some degree of transfer of material from the outer core to the plume source region at D″. Modelling reveals that the komatiites probably formed by dynamic melting at an average pressure of 3-4 GPa leaving residual harzburgite. Trace element depletion in Gorgona ultramafic rocks appears to be the result of earlier, deeper melting which produced high-MgO trace element-enriched magmas. The discovery of a trace-element enriched picrite on the island has confirmed this model. Gorgona accreted onto the palaeocontinental margin of northwestern South America in the Eocene and palaeomagnetic work reveals that it was formed at ˜26 °S. It has been proposed that Gorgona is a part of the Caribbean-Colombian Oceanic Plateau (CCOP), however, the CCOP accreted in the Late Cretaceous and was derived from a more equatorial palaeolatitude. This evidence, and differing geochemical signatures, strongly suggests that Gorgona and probably other coastal oceanic plateau sequences in Colombia and Ecuador, belong to a completely different oceanic plateau to the CCOP.

Martian Igneous Geochemistry: The Nature of the Martian Mantle

NASA Technical Reports Server (NTRS)

Mittlefehldt, D. W.; Elkins-Tanton, L. T.; Peng, Z. X.; Herrin, J. S.

2012-01-01

Mafic igneous rocks probe the interiors of their parent objects, reflecting the compositions and mineralogies of their source regions, and the magmatic processes that engendered them. Incompatible trace element contents of mafic igneous rocks are widely used to constrain the petrologic evolution of planets. We focus on incompatible element ratios of martian meteorites to constrain the petrologic evolution of Mars in the context of magma ocean/cumulate overturn models [1]. Most martian meteorites contain some cumulus grains, but regardless, their incompatible element ratios are close to those of their parent magmas. Martian meteorites form two main petrologic/ age groupings; a 1.3 Ga group composed of clinopyroxenites (nakhlites) and dunites (chassignites), and a <1 Ga group composed of basalts and lherzolites (shergottites).

The trace and Pb isotope chemistry of the Jan Mayen Fracture Zone and the extinct Aegir Ridge

NASA Astrophysics Data System (ADS)

Sayit, K.; Hanan, B. B.; Ito, G.; Howell, S. M.; Vogt, P. R.; Breivik, A. J.; Mjelde, R.; Pedersen, R.

2012-12-01

The extinct Aegir Ridge (AR) was active during the early opening of the N-Atlantic, 54 to 25 Ma, when spreading jumped to the Kolbeinsey Ridge. Crustal thickness produced by the AR is low (3.5 to 6 km), and the magmatically starved Norway Basin appears as a hole in the surrounding excess volcanism of the Iceland hotspot. Two possible alternatives are; either the lithospheric structure of the Jan Mayen micro-continent (JMMC) blocked the plume flow to the AR, and/or Iceland plume material reaching the ridge experienced a previous melt extraction, leading to relatively low melt production. We report the trace element and Pb isotope systematics of the mafic rocks dredged from the AR ~64-69° N and adjacent Jan Mayen FZ. On the basis of the immobile trace element chemistry, several groups are identified, with a large range of Zr/Nb (2.7-60.7). A very-depleted group ([Ce/Yb]N = 0.3) was found in the Jan Mayen FZ, while the most enriched, OIB-like group ([Ce/Yb]N = 12.4) was recovered from the ridge flank scarps. A notable feature of the Aegir samples is variable Th enrichment relative Nb (Th/Nb = 0.07-0.49), similar to subduction zone signatures. In terms of Pb isotopes, the samples show significant variations that correlate with trace element chemistry (206Pb/204Pb: 207Pb/204Pb: 208Pb/204Pb = 16.63-18.81:15.16-15.55:36.67-38.62). The Pb systematics of the Aegir rocks are compatible with a three-component mixing model with mixing trends between the C-like Iceland plume component and a mixture that is composed of EM-1-type material and depleted MORB asthenosphere. The presence of the C-like isotope compositions in the Aegir samples from the Jan Mayen FZ and ridge flank scarps suggests that Iceland plume material has been tapped. However, the very-depleted trace element signatures indicate that the plume component was previously melt depleted. Apparently, the JMMC impeaded flow of enriched plume material to the AR. The Aegir rocks Pb isotope signature may represent pollution of the NA MORB source, during early opening of the ocean basin, by material dispersed during interaction of the Iceland plume and the continental lithosphere.

Trace elements in olivine of ultramafic lamprophyres controlled by phlogopite-rich mineral assemblages in the mantle source

NASA Astrophysics Data System (ADS)

Veter, Marina; Foley, Stephen F.; Mertz-Kraus, Regina; Groschopf, Nora

2017-11-01

Carbonate-rich ultramafic lamprophyres (aillikites) and associated rocks characteristically occur during the early stages of thinning and rifting of cratonic mantle lithosphere, prior to the eruption of melilitites, nephelinites and alkali basalts. It is accepted that they require volatile-rich melting conditions, and the presence of phlogopite and carbonate in the source, but the exact source rock assemblages are debated. Melts similar to carbonate-rich ultramafic lamprophyres (aillikites) have been produced by melting of peridotites in the presence of CO2 and H2O, whereas isotopes and trace elements appear to favor distinct phlogopite-bearing rocks. Olivine macrocrysts in aillikites are usually rounded and abraded, so that it is debated whether they are phenocrysts or mantle xenocrysts. We have analyzed minor and trace element composition in olivines from the type aillikites from Aillik Bay in Labrador, Canada. We characterize five groups of olivines: [1] mantle xenocrysts, [2] the main phenocryst population, and [3] reversely zoned crystals interpreted as phenocrysts from earlier, more fractionated, magma batches, [4] rims on the phenocrysts, which delineate aillikite melt fractionation trends, and [5] rims around the reversely zoned olivines. The main phenocryst population is characterized by mantle-like Ni (averaging 3400 μg g- 1) and Ni/Mg at Mg# of 88-90, overlapping with phenocrysts in ocean island basalts and Mediterranean lamproites. However, they also have low 100 Mn/Fe of 0.9-1.3 and no correlation between Ni and other trace elements (Sc, Co, Li) that would indicate recycled oceanic or continental crust in their sources. The low Mn/Fe without high Ni/Mg, and the high V/Sc (2-5) are inherited from phlogopite in the source that originated by solidification of lamproitic melts at the base of the cratonic lithosphere in a previous stage of igneous activity. The olivine phenocryst compositions are interpreted to result from phlogopite and not high modal pyroxene in the source. The presence of kimberlites and ultramafic lamprophyres of Mesozoic age in Greenland indicates the persistence of a steep edge to the cratonic lithosphere at a time when this had been removed from the western flank in Labrador.

Rare earth elements upon assessment of reasons of the geophagy in Sikhote-Alin region (Russian Federation), Africa and other world regions.

PubMed

Panichev, Alexander M; Popov, Vladimir K; Chekryzhov, Igor Yu; Seryodkin, Ivan V; Stolyarova, Tatiana A; Zakusin, Sergey V; Sergievich, Alexandr A; Khoroshikh, Pavel P

2016-12-01

Rocks eaten by wild animals on the Bolshoy Shanduyskiy kudur in the Sikhote-Alin region (Russian Federation) are zeolite-clay mineral complexes-products of weathering of zeolitized vitric tuffs of rhyolite composition, deposited in aqueous medium within the volcanic caldera of about 55 million years ago. By composition of rock-forming oxides, the tuffs refer to high-potassium calc-alkaline series. In trace elements of most favorite kudurites of the Bolshoy Shanduyskiy kudur, there are significantly increased contents of most of rare earth elements (2-5 times in comparison with surrounding rocks). The results of our analysis of geological and geochemical data on kudurs and kudurites in another part of the Sikhote-Alin, as well as on other regions of the world (particularly, in Africa and Indonesia), taking into account new data on the prevalence of rare earth elements in living matter and their medical and biological properties, enable us to consider the version of causal connection of the geophagy with rare earth elements.

Some additional observations on inclusions in the granitic rocks of the Sierra Nevada

USGS Publications Warehouse

Dodge, F.C.W.; Kistler, R.W.

1990-01-01

Microgranular quartz diorite and diorite inclusions are widespread in central Sierra Nevada granitoid rocks and are almost exclusively restricted to hornblende-bearing rocks, most commonly felsic tonalites and mafic granodiorites. The Nd-Sm and Rb-Sr systematics indicate that most inclusions were in isotopic equilibrium with enclosing materials at the time of formation. Silica contents of inclusions and granitoids are contiguous, but inclusions generally contain less than, and granitoids more than, 60% SiO2. Ferric oxide and H2O+ trends relative to SiO2 suggests many inclusions formed as concentrations of hydrous mafic minerals. Variation of other major element oxides and trace elements support this inference. Most inclusions represent fragmented crystal accumulations of early-formed, near-liquidus minerals generated from these previously mixed magmas. -from Authors

Investigating Microbe-Mineral Interactions: Recent Advances in X-Ray and Electron Microscopy and Redox-Sensitive Methods

NASA Astrophysics Data System (ADS)

Miot, Jennyfer; Benzerara, Karim; Kappler, Andreas

2014-05-01

Microbe-mineral interactions occur in diverse modern environments, from the deep sea and subsurface rocks to soils and surface aquatic environments. They may have played a central role in the geochemical cycling of major (e.g., C, Fe, Ca, Mn, S, P) and trace (e.g., Ni, Mo, As, Cr) elements over Earth's history. Such interactions include electron transfer at the microbe-mineral interface that left traces in the rock record. Geomicrobiology consists in studying interactions at these organic-mineral interfaces in modern samples and looking for traces of past microbe-mineral interactions recorded in ancient rocks. Specific tools are required to probe these interfaces and to understand the mechanisms of interaction between microbes and minerals from the scale of the biofilm to the nanometer scale. In this review, we focus on recent advances in electron microscopy, in particular in cryoelectron microscopy, and on a panel of electrochemical and synchrotron-based methods that have recently provided new understanding and imaging of the microbe-mineral interface, ultimately opening new fields to be explored.

Albari granodiorite - a typical calcalkaline diapir of volcanic arc stage from the Arabian Shield

NASA Astrophysics Data System (ADS)

Radain, Abdulaziz A.

Granodiorite rocks of the Arabian Shield are generally considered to be collision-related granitoids. However, there are some granodiorites that were formed during the volcanic arc stage. Major and trace elements studies are carried out on Albari diapiric granodiorite to reveal its tectonic environment. This intrusive rock type is common in the Taif arc province (Mahd adh Dhahab quadrangle) of the Asir microplate near the border of the southeast dipping subduction zone that ended up with arc-arc collision (Asir-Hijaz microplates) along the now known Bir Umq suture zone. The granodiorite exhibits a calcalkaline trend on ternary AFM and K 2ONa 2OCaO diagrams. Tectonic discrimination diagrams using multicationic parameters (R1 = 4Sill(Na+K)2(Fe+Ti); R2 = 6Ca+2Mg+Al), SiO 2-trace elements (Nb, Y, Rb), and Y versus Nb and Rb versus (Y+Nb) indicate a destructive active plate margin or volcanic arc stage tectonic environment. Albari calcalkaline granodiorite might have been derived directly from partial melting of subducted oceanic crust or overlying mantle contaminated with variable amounts of intermediate (quartz diorite, diorite, tonalite, trondhjemite) early and late volcanic arc-related plutonic country rocks.

Geochemical modeling of low melt-fraction anatexis in a peraluminous system: The Pena Negra complex (central Spain)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bea, F.

1991-07-01

A study was made of the chemical fractionation associated with four cases of anatectic segregation of low melt-fraction cordieritic granites from migmatized meta-greywackes. The aims of the study were to (1) reveal the fractionation patterns of major and trace elements, (2) compare the major element chemistry of leucogranites and the quantitative behavior of source minerals during anatexis - inferred by mass-balance adjustment - with available experimental data for peraluminous systems, and (3) discuss the behavior of trace elements in crustal melting by comparing the chemically determined composition of leucogranites with the results of three fractionation models. Two of these assumemore » a perfect diffusive behavior of trace elements within residual solids, but they use a different set of distribution coefficients. The third assumes a perfect nondiffusive behavior. In relation to their source rocks, the leucogranites are strongly depleted in Li, Transition Elements, and Light Rare Earth Elements, but enriched in K{sub 2}O, SiO{sub 2}, and Ba. Mass balance analysis using the Anatexis Mixing Model shows that the chemistry of cordierite leucogranites is compatible with its having originated by closed-system, water-undersaturated anatexis on previously migmatized meta-greywackes, leaving a residue enriched in cordierite plus biotite and exhausted in K-feldspar. Biotite melts congruently unless important amounts of sillimanite were also present in the source. Compared with experimental metals obtained from sources with the same chemical composition but with a different femic mineralogy (biotite + sillimanite, instead of cordierite + biotite), the Pena Negra leucogranites are richer in K{sub 2}O and MgO with a lower Fe/(Fe + Mg) ratio. The differences in magnesium are believed to result from the changes in the mineral assemblage of the source rocks.« less

Geochemical characteristics of the La Réunion mantle plume source inferred from olivine-hosted melt inclusions from the adventive cones of Piton de la Fournaise volcano (La Réunion Island)

NASA Astrophysics Data System (ADS)

Valer, Marina; Schiano, Pierre; Bachèlery, Patrick

2017-09-01

Major and trace element compositions were obtained for bulk rocks and melt inclusions hosted in olivine crystals (Fo > 85) from the adventive cones of the Piton de La Fournaise volcano (La Réunion Island). Ratios of highly incompatible trace elements for these magmas are used to identify the nature of the La Réunion mantle plume source. Although adventive cone lavas display unusual major element compositions compared to the historical lavas of the volcano (e.g., lower CaO/Al2O3), trace element data suggest that the magmas emitted by the adventive cones originate from a common chemical source. This source may correspond to either a homogeneous mixed source of different mantle components or a near-primitive less-differentiated mantle source. The melt inclusions display ratios of highly incompatible elements (e.g., Th/La, Nb/La) which are similar to primitive mantle values, and lower Nb/U ratios compared to most oceanic basalts. These results and previous isotopic and trace element data suggest that La Réunion plume samples a source which is intermediate between a primitive-like mantle domain and a slightly depleted one almost unaffected by the recycling processes. This source could have originated from early depletion of the primitive mantle. Assuming a depletion 4.45 Gyr ago, 10% melting of this slightly depleted source could explain the enriched trace element concentrations of the melt inclusions.

Health benefits of geologic materials and geologic processes

USGS Publications Warehouse

Finkelman, R.B.

2006-01-01

The reemerging field of Medical Geology is concerned with the impacts of geologic materials and geologic processes on animal and human health. Most medical geology research has been focused on health problems caused by excess or deficiency of trace elements, exposure to ambient dust, and on other geologically related health problems or health problems for which geoscience tools, techniques, or databases could be applied. Little, if any, attention has been focused on the beneficial health effects of rocks, minerals, and geologic processes. These beneficial effects may have been recognized as long as two million years ago and include emotional, mental, and physical health benefits. Some of the earliest known medicines were derived from rocks and minerals. For thousands of years various clays have been used as an antidote for poisons. "Terra sigillata," still in use today, may have been the first patented medicine. Many trace elements, rocks, and minerals are used today in a wide variety of pharmaceuticals and health care products. There is also a segment of society that believes in the curative and preventative properties of crystals (talismans and amulets). Metals and trace elements are being used in some of today's most sophisticated medical applications. Other recent examples of beneficial effects of geologic materials and processes include epidemiological studies in Japan that have identified a wide range of health problems (such as muscle and joint pain, hemorrhoids, burns, gout, etc.) that may be treated by one or more of nine chemically distinct types of hot springs, and a study in China indicating that residential coal combustion may be mobilizing sufficient iodine to prevent iodine deficiency disease. ?? 2006 MDPI. All rights reserved.

Comprehensive Pb-Sr-Nd-Hf isotopic, trace element, and mineralogical characterization of mafic to ultramafic rock reference materials

NASA Astrophysics Data System (ADS)

Fourny, Anaïs.; Weis, Dominique; Scoates, James S.

2016-03-01

Controlling the accuracy and precision of geochemical analyses requires the use of characterized reference materials with matrices similar to those of the unknown samples being analyzed. We report a comprehensive Pb-Sr-Nd-Hf isotopic and trace element concentration data set, combined with quantitative phase analysis by XRD Rietveld refinement, for a wide range of mafic to ultramafic rock reference materials analyzed at the Pacific Centre for Isotopic and Geochemical Research, University of British Columbia. The samples include a pyroxenite (NIM-P), five basalts (BHVO-2, BIR-1a, JB-3, BE-N, GSR-3), a diabase (W-2), a dolerite (DNC-1), a norite (NIM-N), and an anorthosite (AN-G); results from a leucogabbro (Stillwater) are also reported. Individual isotopic ratios determined by MC-ICP-MS and TIMS, and multielement analyses by HR-ICP-MS are reported with 4-12 complete analytical duplicates for each sample. The basaltic reference materials have coherent Sr and Nd isotopic ratios with external precision below 50 ppm (2SD) and below 100 ppm for Hf isotopes (except BIR-1a). For Pb isotopic reproducibility, several of the basalts (JB-3, BHVO-2) require acid leaching prior to dissolution. The plutonic reference materials also have coherent Sr and Nd isotopic ratios (<50 ppm), however, obtaining good reproducibility for Pb and Hf isotopic ratios is more challenging for NIM-P, NIM-N, and AN-G due to a variety of factors, including postcrystallization Pb mobility and the presence of accessory zircon. Collectively, these results form a comprehensive new database that can be used by the geochemical community for evaluating the radiogenic isotope and trace element compositions of volcanic and plutonic mafic-ultramafic rocks.

Preface to highly siderophile element constraints on Earth and planetary processes

NASA Astrophysics Data System (ADS)

Riches, Amy J. V.

2017-11-01

The geochemical properties of the highly siderophile elements (HSEs; Os, Ir, Ru, Rh, Pt, Pd, Re and Au) - being strongly iron-loving, but also chalcophile (i.e., having an affinity for sulphide), and generally occurring at ultra trace levels in silicate rocks, their weathered products, and oceanic waters - mean that this suite of elements and their isotopic compositions are useful in tracing a wide variety of processes. Thus, the HSEs are useful probes with which to tackle major research questions pertinent to past and present day change at a variety of scales and in a range of Earth and other-worldly environments by constraining reservoir compositions, chemical drivers, and the timing of key events and/or transformation rates.

Determination of rare earth elements in geological materials by inductively coupled argon plasma/atomic emission spectrometry

USGS Publications Warehouse

Crock, J.G.; Lichte, F.E.

1982-01-01

Inductively coupled argon plasma/optical emission spectrometery (ICAP/OES) is useful as a simultaneous, multielement analytical technique for the determination of trace elements in geological materials. A method for the determination of trace-level rare earth elements (REE) in geological materials using an ICAP 63-channel emission spectrometer is described. Separation and preconcentration of the REE and yttrium from a sample digest are achieved by a nitric acid gradient cation exchange and hydrochloric acid anion exchange. Precision of 1-4% relative standard deviation and comparable accuracy are demonstrated by the triplicate analysis of three splits of BCR-1 and BHVO-1. Analyses of other geological materials including coals, soils, and rocks show comparable precision and accuracy.

Provenance and geochemical behavior of fluorine in the soils of an endemic fluorosis belt, central Iran

NASA Astrophysics Data System (ADS)

Dehbandi, Reza; Moore, Farid; Keshavarzi, Behnam

2017-05-01

The concentration of fluorine, major, trace and rare earth elements (REEs) were used to estimate the probable sources and provenance of fluorine in the soils of an endemic fluorosis belt in central Iran. Total fluorine (TF) in soils varied from 146 to 406 mg/kg with a mean of 277.5 mg/kg. Calculated enrichment factor (EF) and single factor pollution index (SFPI) revealed that the majority of soil samples were moderately contaminated by fluorine. The very strong positive correlation of TF with weathering indices and soil's fine sized fractions indicated that chemical weathering and alteration of parent rocks/soils are the main controlling factors of fluorine behavior in soils. Fluorine affinity to immobile transition trace elements and REEs suggested the role of heavy minerals as the potential F host phases. Modal mineralogy along with SEM-EDX analysis indicated that apatite, fluorapophyllite, epidote, biotite, muscovite and chlorite, as well as, clay minerals are the main F-bearing minerals in the studied soils. Discriminant, bivariate and ternary diagrams of elemental compositions displayed similar geochemical signature of soils to intermediate-acidic rocks and local shales. Based on the weathering indices, soils were immature and showed a non-steady state weathering trend from upper continental crust (UCC), acidic and intermediate igneous source rocks towards shale composition possibly due to mixing of moderately weathered and un-weathered sources of different primary compositions.

Lunar Ferroan Anorthosite Petrogenesis: Clues from Trace Element Distributions in FAN Subgroups

NASA Astrophysics Data System (ADS)

Floss, Christine; James, Odette B.; McGee, James J.; Crozaz, Ghislaine

1998-04-01

The rare earth elements (REE) and selected other trace elements were measured in plagioclase and pyroxene from nine samples of the lunar ferroan anorthosite (FAN) suite of rocks. Samples were selected from each of four FAN subgroups previously defined by James et al. (1989). Plagioclase compositions are homogeneous within each sample, but high- and low-Ca pyroxenes from lithic clasts typically have different REE abundances from their counterparts in the surrounding granulated matrices. Measured plagioclase/low-Ca pyroxene concentration ratios for the REE have steeper patterns than experimentally determined plagioclase/low-Ca pyroxene partition coefficients in most samples. Textural and trace element evidence suggest that, although subsolidus equilibration may be responsible for some of the discrepancy, plagioclase compositions in most samples have been largely unaffected by intermineral redistribution of the REE. The REE systematics of plagioclase from the four subgroups are broadly consistent with their derivation through crystallization from a single evolving magma. However, samples from some of the subgroups exhibit a decoupling of plagioclase and pyroxene compositions that probably reflects the complexities inherent in crystallization from a large-scale magmatic system. For example, two anorthosites with very magnesian mafic minerals have highly evolved trace element compositions; major element compositions in plagioclase also do not reflect the evolutionary sequence recorded by their REE compositions. Finally, a noritic anorthosite breccia with relatively ferroan mafic minerals contains several clasts with high and variable REE and other trace element abundances. Although plagioclase REE compositions are consistent with their derivation from a magma with a KREEPy trace element signature, very shallow REE patterns in the pyroxenes suggest the addition of a component enriched in the light REE.

Petrology and Geochemistry of Unbrecciated Harzburgitic Diogenite MIL 07001: A Window Into Vestan Geological Evolution

NASA Technical Reports Server (NTRS)

Mittlefehldt, D. W.; Peng, Z. X.; Mertzman, S. A.; Mertzman, K. R.

2014-01-01

There is a strong case that asteroid 4 Vesta is the parent of the howardite, eucrite and diogenite (HED) meteorites. Models developed for the geological evolution of Vesta can satisfy the compositions of basaltic eucrites that dominate in the upper crust. The bulk compositional characteristics of diogenites - cumulate harzburgites and orthopyroxenites from the lower crust - do not fit into global magma ocean models that can describe the compositions of basaltic and cumulate eucrites. Recent more detailed formation models do make provision for a more complicated origin for diogenites, but this model has yet to be completely vetted. Compositional studies of bulk samples has led to the hypothesis that many diogenites were formed late by interaction of their parent melts with a eucritic crust, but those observations may alternatively be explained by subsolidus equilibration of trace elements between orthopyroxene and plagioclase and Ca-phosphate in the rocks. Differences in radiogenic Mg-26 content between diogenites and eucrites favors early formation of the former, not later formation. Understanding the origin of diogenites is crucial for understanding the petrologic evolution of Vesta. We have been doing coordinated studies of a suite of diogenites including petrologic investigations, bulk rock major and trace element studies, and in situ trace element analyses of orthopyroxene. Here we will focus on an especially unusual, and potentially key, diogenite, MIL 07001.

Trace element geochemistry of altered volcanic ash layers (tonsteins) in late Permian coal-bearing formations of eastern Yunnan and western Guizhou Provinces, China

USGS Publications Warehouse

Zhou, Y.; Bohor, B.F.; Ren, Y.

2000-01-01

Trace element compositions were determined (by instrumental neutron activation analysis; INAA) in 30 samples of synsedimentary volcanic ash-derived tonsteins and detrital claystones from coal seams within the late Permian coal-bearing formation of eastern Yunnan and western Guizhou Provinces, China. The characteristics of trace-element geochemistry in the tonsteins can be distinguished from those of detrital claystones because of the former's unique volcanic-ash origin. The detrital claystones are characterized by their relatively high content of V, Ti, Sc, Cr, Co and Ni, relatively low content of Th and U, Th/U ratio, and small negative Eu anomaly (Eu/Eu* 0.63-0.93). Overall, these trace element characteristics are consistent with a mafic source similar to the composition of basalt rocks in the erosional region on the western edge of the study area. In contrast, the tonsteins are low in V, Ti, Sc, Cr, Co and Ni contents and have a high Th/U ratio with a distinct negative Eu anomaly (Eu/Eu* normally in the range of 0.2-0.4), consistent with a silicic magmatic source. Within the group of tonsteins, those from the lower section (P2.1) of the coal-bearing formation are relatively high in Ti, Zr, Hf, Nb, Ta and rare earth elements (REE), as compared to those from the middle and upper sections (P2.2+3). In trace-element discrimination diagrams (scatter plots) of Hf-Ta, Ti-Ta, Ti-V, Hf-Sc, Lu-Hf and Lu-Th, tonsteins from the P2.1 horizon always fall in isolated distribution areas, separate from the tonsteins of the P2.2+3 horizon. These results suggest that the source materials of tonsteins from the two separate horizons were probably derived from volcanic ash falls of two distinctly different natures. Based on a comparison of the concentrations and assemblages of trace elements between various magmatic rocks, the source materials of tonsteins from P2.1 horizon were mostly composed of calc-alkalic, silica-poor volcanic ash (similar to rhyodacitic magma), whereas those from P2.+3 were apparently more siliceous and K-rich (rhyolitic magma). Thus, tonsteins from the two different horizons are characterized by unique geochemical properties, which remain constant over a wide lateral extent. Integration of trace-elemental compositions with mineralogical and textural observations makes possible the establishment of tonstein stratigraphy, thus, facilitating more precise and reliable coal-seam correlations. (C) 2000 Elsevier Science B.V. All rights reserved.Trace element compositions were determined in 30 samples of synsedimentary volcanic ash-derived tonsteins and detrital claystones from coal seams within the late Permian coal-bearing formation of eastern Yunnan and western Guizhou Provinces, China. The characteristics of trace-element geochemistry in the tonsteins can be distinguished from those of detrital claystones because of the former's unique volcanic-ash origin. The detrital claystones are characterized by their relatively high content of V, Ti, Sc, CR, Co and Ni, relatively low content of Th and U, Th/U ratio, and small negative Eu anomaly.

Stanford-USGS shrimp-RG ion microprobe: A new approach to determining the distribution of trace elements in coal

USGS Publications Warehouse

Kolker, A.; Wooden, J.L.; Persing, H.M.; Zielinski, R.A.

2000-01-01

The distribution of Cr and other trace metals of environmental interest in a range of widely used U.S. coals was investigated using the Stanford-USGS SHRIMP-RG ion microprobe . Using the oxygen ion source, concentrations of Cr (11 to 176 ppm), V (23 to 248 ppm), Mn (2 to 149 ppm), Ni (2 to 30 ppm), and 13 other elements were determined in illite/smectite, a group of clay minerals commonly present in coal. The results confirm previous indirect or semi-quantitative determinations indicating illite/smectite to be an important host of these metals. Calibration was achieved using doped aluminosilicate-glass synthetic standards and glasses prepared from USGS rock standards. Grains for analysis were identified optically, and confirmed by 1) precursory electron microprobe analysis and wavelength-dispersive compositional mapping, and 2) SHRIMP-RG major element data obtained concurrently with trace element results. Follow-up investigations will focus on the distribution of As and other elements that are more effectively ionized with the cesium primary beam currently being tested.

The earth's oldest known crust - A geochronological and geochemical study of 3900-4200 Ma old detrital zircons from Mt. Narryer and Jack Hills, Western Australia

NASA Astrophysics Data System (ADS)

Maas, Roland; Kinny, Peter D.; Williams, Ian S.; Froude, Derek O.; Compston, William

1992-03-01

Trace element characteristics were analyzed and inclusions were identified within a suite of pre-3.9 Ga detritral zircons from western Australia representing the earth's oldest-known minerals. A diversity of trace-element compositions was found, particularly in the REE compositions of the old Mt. Narryer zircons, implying a variety of source-rock compositions and hence, the presence of a differentiated crust in the earth 4.15-4.20 Ga ago. Comparisons drawn with data obtained from younger detrital zircons occurring within the same deposits indicate nothing unique about the chemical compositions of the old grains. A number of interelement covariations were observed among the analyzed grains which were independent of age and isotopic characteristics, most notably that occurring between Lu and Hf. A general positive correlation between total LREE and the U + Th contents is also apparent. The findings indicate an origin in felsic igneous rocks, which has implications for early-Archaean crustal evolution.

Origin, mode of emplacement, and trace element geochemistry of albertite at the type locality, Albert Mines, southeastern New Brunswick, Canada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farrell, K.P.J.; Mossman, D.J.

1995-07-01

Fracturing of oil shale was coeval with albertite vein formation at Albert Mines early in the diagenetic history of the Lower Carboniferous (Tourmasian) Albert Formation. Albertite of this type locality is a pre-oil bitumen produced as a result of overpressuring due to a high rate of hydrocarbon generation and, as such, is largely preserved in an immature source rock. Dolomite precipitated in albertite during emplacement of the latter, and was sourced from an accompanying CO{sub 2}-rich fluid phase. Trace element contents of albertite are within the range of selected other major bitumen occurrences and, except for nickel, are lower thanmore » those of the host rock. Ratios of Ni/V are elevated in comparison with the host oil shale and with other bitumen occurrences. Carbon isotope values for albertite range from 27.92 to 30.80 {per_thousand}, {delta} {sup 13}C, within the range of most conventional crudes.« less

Petrography and geochemistry of clastic sedimentary rocks as evidences for provenance of the Lower Cambrian Lalun Formation, Posht-e-badam block, Central Iran

NASA Astrophysics Data System (ADS)

Etemad-Saeed, N.; Hosseini-Barzi, M.; Armstrong-Altrin, John S.

2011-09-01

Petrography and geochemistry (major, trace and rare earth elements) of clastic rocks from the Lower Cambrian Lalun Formation, in the Posht-e-badam block, Central Iran, have been investigated to understand their provenance. Petrographical analysis suggests that the Lalun conglomerates are dominantly with chert clasts derived from a proximal source, probably chert bearing Precambrian Formations. Similarly, purple sandstones are classified as litharenite (chertarenite) and white sandstones as quartzarenite types. The detrital modes of purple and white sandstones indicate that they were derived from recycled orogen (uplifted shoulders of rift) and stable cratonic source. Most major and trace element contents of purple sandstones are generally similar to upper continental crust (UCC) values. However, white sandstones are depleted in major and trace elements (except SiO 2, Zr and Co) relative to UCC, which is mainly due to the presence of quartz and absence of other Al-bearing minerals. Shale samples have considerably lower content in most of the major and trace elements concentration than purple sandstones, which is possibly due to intense weathering and recycling. Modal composition (e.g., quartz, feldspar, lithic fragments) and geochemical indices (Th/Sc, La/Sc, Co/Th, Cr/Th, Cr/V and V/Ni ratios) of sandstones, and shales (La/Sc and La/Cr ratios) indicate that they were derived from felsic source rocks and deposited in a passive continental margin. The chondrite-normalized rare earth element (REE) patterns of the studied samples are characterized by LREE enrichment, negative Eu anomaly and flat HREE similar to an old upper continental crust composed chiefly of felsic components in the source area. The study of paleoweathering conditions based on modal composition, chemical index of alteration (CIA), plagioclase index of alteration (PIA) and A-CN-K (Al 2O 3 - CaO + Na 2O - K 2O) relationships indicate that probably chemical weathering in the source area and recycling processes have been more important in shale and white sandstones relative to purple sandstones. The results of this study suggest that the main source for the Lalun Formation was likely located in uplifted shoulders of a rifted basin (probably a pull-apart basin) in its post-rift stage (Pan-African basement of the Posht-e-badam block).

Petrogenesis of ultramafic rocks and olivine-rich troctolites from the East Taiwan Ophiolite in the Lichi mélange

NASA Astrophysics Data System (ADS)

Morishita, Tomoaki; Ghosh, Biswajit; Soda, Yusuke; Mizukami, Tomoyuki; Tani, Ken-ichiro; Ishizuka, Osamu; Tamura, Akihiro; Komaru, Chihiro; Aari, Shoji; Yang, Hsiao-Chin; Chen, Wen-Shan

2017-12-01

We examine ultramafic and olivine-rich troctolite blocks of the East Taiwan Ophiolite (ETO) in the Lichi Mélange. Although ultramafic rocks are extensively serpentinized, the primary minerals, such as olivine, orthopyroxene, clinopyroxene, spinel and plagioclase can be identified. The ultramafic rocks are classified into harzburgite (± clinopyroxene), dunite, and olivine websterite. Major and trace element compositions of the primary minerals in harzburgites, such as the Cr# [= Cr/(Cr + Al) atomic ratio] of chromian spinel (0.3-0.58) and incompatible elements-depleted trace element patterns of clinopyroxenes, indicate their residue origin after partial melting with less flux components. These compositions are similar to those from mid-ocean ridge peridotites as well as back-arc peridotites from the Philippine Sea Plate. The olivine websterite contains discrete as well as occasional locally concentrated plagioclase grains. Petrological characteristics coupled with similarity in trace element patterns of clinopyroxenes in the harzburgite and olivine websterite samples indicate that the olivine websterite is likely formed by clinopyroxene addition to a lherzolitic/harzburgitic peridotite from a pyroxene-saturated mafic melt. Dunite with medium Cr# spinels indicates cumulus or replacement by melt-peridotite reaction origins. Mineral composition of olivine-rich troctolite cannot be explained by simple crystallization from basaltic magmas, but shows a chemical trend expected for products after melt-peridotite interactions. Mineral compositions of the dunite and olivine-rich troctolite are also within chemical ranges of mid-ocean ridge samples, and are slightly different from back-arc samples from the Philippine Sea Plate. We conclude that peridotites in the ETO are not derived from the northern extension of the Luzon volcanic arc mantle. Further geochronological study is, however, required to constrain the origin of the ETO ophiolite, because peridotites are probably indistinguishable in petrology and mineralogy between the Philippine Sea and the South China Sea/Eurasian Plates.

Utilizing rare earth elements as tracers in high TDS reservoir brines in CCS applications

DOE PAGES

McLing, Travis; Smith, William; Smith, Robert

2014-12-31

In this paper we report the result of research associated with the testing of a procedures necessary for utilizing natural occurring trace elements, specifically the Rare Earth Elements (REE) as geochemical tracers in Carbon Capture and Storage (CCS) applications. Trace elements, particularly REE may be well suited to serve as in situ tracers for monitoring geochemical conditions and the migration of CO₂-charged waters within CCS storage systems. We have been conducting studies to determine the efficacy of using REE as a tracer and characterization tool in the laboratory, at a CCS analogue site in Soda Springs, Idaho, and at amore » proposed CCS reservoir at the Rock Springs Uplift, Wyoming. Results from field and laboratory studies have been encouraging and show that REE may be an effective tracer in CCS systems and overlying aquifers. In recent years, a series of studies using REE as a natural groundwater tracer have been conducted successfully at various locations around the globe. Additionally, REE and other trace elements have been successfully used as in situ tracers to describe the evolution of deep sedimentary Basins. Our goal has been to establish naturally occurring REE as a useful monitoring measuring and verification (MMV) tool in CCS research because formation brine chemistry will be particularly sensitive to changes in local equilibrium caused by the addition of large volumes of CO₂. Because brine within CCS target formations will have been in chemical equilibrium with the host rocks for millions of years, the addition of large volumes of CO₂ will cause reactions in the formation that will drive changes to the brine chemistry due to the pH change caused by the formation of carbonic acid. This CO₂ driven change in formation fluid chemistry will have a major impact on water rock reaction equilibrium in the formation, which will impart a change in the REE fingerprint of the brine that can measured and be used to monitor in situ reservoir conditions. Our research has shown that the REE signature imparted to the formation fluid by the introduction of CO₂ to the formation, can be measured and tracked as part of an MMV program. Additionally, this REE fingerprint may serve as an ideal tracer for fluid migration, both within the CCS target formation, and should formation fluids migrate into overlying aquifers. However application of REE and other trace elements to CCS system is complicated by the high salt content of the brines contained within the target formations. In the United States by regulation, in order for a geologic reservoir to be considered suitable for carbon storage, it must contain formation brine with total dissolved solids (TDS) > 10,000 ppm, and in most cases formation brines have TDS well in excess of that threshold. The high salinity of these brines creates analytical problems for elemental analysis, including element interference with trace metals in Inductively Coupled Plasma Mass Spectroscopy (ICP-MS) (i.e. element mass overlap due to oxide or plasma phenomenon). Additionally, instruments like the ICP-MS that are sensitive enough to measure trace elements down to the parts per trillion level are quickly oversaturated when water TDS exceeds much more than 1,000 ppm. Normally this problem is dealt with through dilution of the sample, bringing the water chemistry into the instruments working range. However, dilution is not an option when analyzing these formation brines for trace metals, because trace elements, specifically the REE, which occur in aqueous solutions at the parts per trillion levels. Any dilution of the sample would make REE detection impossible. Therefore, the ability to use trace metals as in situ natural tracers in high TDS brines environments requires the development of methods for pre-concentrating trace elements, while reducing the salinity and associated elemental interference such that the brines can be routinely analyzed by standard ICP-MS methods. As part of the Big Sky Carbon Sequestration Project the INL-CAES has developed a rapid, easy to use process that pre-concentrates trace metals, including REE, up to 100x while eliminating interfering ions (e.g. Ba, Cl). The process is straightforward, inexpensive, and requires little infrastructure, using only a single chromatography column with inexpensive, reusable, commercially available resins and wash chemicals. The procedure has been tested with synthetic brines (215,000 ppm or less TDS) and field water samples (up to 5,000 ppm TDS). Testing has produced data of high quality with REE capture efficiency exceeding 95%, while reducing interfering elements by > 99%.« less

Brushed Target on Rock 'Champagne' in Gusev Crater

NASA Technical Reports Server (NTRS)

2005-01-01

NASA's Mars Exploration Rover Spirit took this microscopic image of a target called 'Bubbles' on a rock called 'Champagne' after using its rock abrasion tool to brush away a coating of dust. The circular brushed area is about 5 centimeters (2 inches) across. This rock is different from rocks out on the plains of Gusev Crater but is similar to other rocks in this area of the 'Columbia Hills' in that it has higher levels of phosphorus. Plagioclase, a mineral commonly found in igneous rocks, is also present in these rocks, according to analysis with the minature thermal emission spectrometer. By using the alpha particle X-ray spectrometer to collect data over multiple martian days, or sols, scientists are also beginning to get measurements of trace elements in these rocks. Spirit took the images that are combined into this mosaic on sol 354 (Dec. 30, 2004).

Trace elements in winter snow of the Dolomites (Italy): a statistical study of natural and anthropogenic contributions.

PubMed

Gabrielli, P; Cozzi, G; Torcini, S; Cescon, P; Barbante, C

2008-08-01

Knowledge of the occurrence of trace elements deposited in fresh alpine snow is very limited. Although current sources of major ionic inorganic species have been well established, this is not the case for many trace elements. This manuscript attempts to reconstruct the origin of Ag, Ba, Bi, Cd, Co, Cr, Cu, Fe, Mo, Mn, Pb, Sb, Ti, U, V and Zn in winter surface snow, extensively collected in the Dolomites region (Eastern Alps, Italy). Sampling of surface snow was conducted weekly during the winter 1998 at 21 sites at altitudes ranging from approximately 1000 to approximately 3000 m. This led to a remarkable dataset of trace element concentrations in surface snow from low latitudes. Here we show a preliminary statistical investigation conducted on the 366 samples collected. It was found that V, Sb, Zn, Cd, Mo and Pb have a predominantly anthropogenic origin, linked to the road traffic in the alpine valleys and the nearby heavily industrialised area of the Po Valley. In addition, the occasionally strong Fe and Cr input may reflect the mechanical abrasion of ferrous components of the vehicles. However, much of the Fe along with Mn, U and Ti originates primarily from the geological background of the Dolomites. A marine contribution was found to be negligible for all the trace elements. The origin of other trace elements is less clear: Ag can be possibly attributed to a predominantly anthropogenic origin while Cr, Co, Cu and Ba are usually from crustal rocks but different than the Dolomites.

Characterisation of mineral deposition systems associated with rock art in the Kimberley region of northwest Australia.

PubMed

Green, Helen; Gleadow, Andrew; Finch, Damien

2017-10-01

This data article contains mineralogical and chemical data from mineral accretions sampled from rock art shelters in the Kimberley region of north west Australia. The accretions were collected both on and off pigment and engraved rock art of varying styles observed in the Kimberley with an aim of providing a thorough understanding of the formation and preservation of such materials in the context of dating [1]. This contribution includes processed powder X-ray Diffraction data, Scanning Electron Microscopy energy dispersive spectroscopy data, and Laser Ablation ICP-MS trace element mapping data.

Geochemical typification of kimberlite and related rocks of the North Anabar region, Yakutia

NASA Astrophysics Data System (ADS)

Kargin, A. V.; Golubeva, Yu. Yu.

2017-11-01

The results of geochemical typification of kimberlites and related rocks (alneites and carbonatites) of the North Anabar region are presented with consideration of the geochemical specification of their source and estimation of their potential for diamonds. The content of representative trace elements indicates the predominant contribution of an asthenospheric component (kimberlites and carbonatites) in their source, with a subordinate contribution of vein metasomatic formations containing Cr-diopside and ilmenite. A significant contribution of water-bearing potassium metasomatic parageneses is not recognized. According to the complex of geochemical data, the studied rocks are not industrially diamondiferous.

Paragneiss zircon geochronology and trace element geochemistry, North Qaidam HP/UHP terrane, western China

USGS Publications Warehouse

Mattinson, C.G.; Wooden, J.L.; Zhang, J.X.; Bird, D.K.

2009-01-01

In the southeastern part of the North Qaidam terrane, near Dulan, paragneiss hosts minor peridotite and UHP eclogite. Zircon geochronology and trace element geochemistry of three paragneiss samples (located within a ???3 km transect) indicates that eclogite-facies metamorphism resulted in variable degrees of zircon growth and recrystallization in the three samples. Inherited zircon core age groups at 1.8 and 2.5 Ga suggest that the protoliths of these rocks may have received sediments from the Yangtze or North China cratons. Mineral inclusions, depletion in HREE, and absence of negative Eu anomalies indicate that zircon U-Pb ages of 431 ?? 5 Ma and 426 ?? 4 Ma reflect eclogite-facies zircon growth in two of the samples. Ti-in-zircon thermometry results are tightly grouped at ???660 and ???600 ??C, respectively. Inclusions of metamorphic minerals, scarcity of inherited cores, and lack of isotopic or trace element inheritance demonstrate that significant new metamorphic zircon growth must have occurred. In contrast, zircon in the third sample is dominated by inherited grains, and rims show isotopic and trace element inheritance, suggesting solid-state recrystallization of detrital zircon with only minor new growth. ?? 2009 Elsevier Ltd.

Aqueous Alteration of Endeavour Crater Rim Apron Rocks

NASA Technical Reports Server (NTRS)

Mittlefehldt, David W.; Ming, Douglas W.; Gellert, Ralf; Clark, Benton C.; Morris, Richard V.; Yen, Albert S.; Arvidson, Raymond E.; Crumpler, Larry S.; Farrand, William H.; Grant, John A.;

Aqueous Alteration of Endeavour Crater Rim Apron Rocks

NASA Astrophysics Data System (ADS)

Ming, D. W.; Mittlefehldt, D. W.; Gellert, R.; Clark, B. C.; Morris, R. V.; Yen, A. S.; Arvidson, R. E.; Crumpler, L. S.; Farrand, W. H.; Grant, J. A., III; Jolliff, B. L.; Parker, T. J.; Peretyazhko, T.

2014-12-01

Mars Exploration Rover Opportunity is exploring Noachian age rocks of the rim of 22 km diameter Endeavour crater. Overlying the pre-impact lithologies and rim breccias is a thin apron of fine-grained sediments, the Grasberg fm, forming annuli on the lower slopes of rim segments. Hesperian Burns fm sandstones overly the Grasberg fm. Grasberg rocks have major element compositions that are distinct from Burns fm sandstones, especially when comparing interior compositions exposed by the Rock Abrasion Tool. Grasberg rocks are also different from Endeavour rim breccias, but have general compositional similarities to them. Grasberg sediments are plausibly fine-grained materials derived from the impact breccias. Veins of CaSO4 transect Grasberg fm rocks demonstrating post-formation aqueous alteration. Minor/trace elements show variations consistent with mobilization by aqueous fluids. Grasberg fm rocks have low Mn and high Fe/Mn ratios compared to the other lithologies. Manganese likely was mobilized and removed from the Grasberg host rock by redox reactions. We posit that Fe2+ from acidic solutions associated with formation of the Burns sulfate-rich sandstones acted as an electron donor to reduce more oxidized Mn to Mn2+. The Fe contents of Grasberg rocks are slightly higher than in other rocks suggesting precipitation of Fe phases in Grasberg materials. Pancam spectra show that Grasberg rocks have a higher fraction of ferric oxide minerals than other Endeavour rim rocks. Solutions transported Mn2+ into the Endeavour rim materials and oxidized and/or precipitated it in them. Grasberg has higher contents of the mobile elements K, Zn, Cl, and Br compared to the rim materials. Similar enrichments of mobile elements were measured by the Spirit APXS on West Spur and around Home Plate in Gusev crater. Enhancements in these elements are attributed to interactions of hydrothermal acidic fluids with the host rocks. Interactions of fluids with the Grasberg fm postdate the genesis of the Endeavour rim phyllosilicates. The aqueous alteration history of Endeavour rim rocks is complicated by different styles of alteration that have spanned the Noachian and Hesperian. Late stage acidic aqueous alteration of Grasberg fm materials is likely penecontemporaneous with the diagenesis of the sulfate-rich sediments of Meridiani Planum.

Copahue volcano and its regional magmatic setting

USGS Publications Warehouse

Varekamp, J C; Zareski, J E; Camfield, L M; Todd, Erin

2016-01-01

Copahue volcano (Province of Neuquen, Argentina) has produced lavas and strombolian deposits over several 100,000s of years, building a rounded volcano with a 3 km elevation. The products are mainly basaltic andesites, with the 2000–2012 eruptive products the most mafic. The geochemistry of Copahue products is compared with those of the main Andes arc (Llaima, Callaqui, Tolhuaca), the older Caviahue volcano directly east of Copahue, and the back arc volcanics of the Loncopue graben. The Caviahue rocks resemble the main Andes arc suite, whereas the Copahue rocks are characterized by lower Fe and Ti contents and higher incompatible element concentrations. The rocks have negative Nb-Ta anomalies, modest enrichments in radiogenic Sr and Pb isotope ratios and slightly depleted Nd isotope ratios. The combined trace element and isotopic data indicate that Copahue magmas formed in a relatively dry mantle environment, with melting of a subducted sediment residue. The back arc basalts show a wide variation in isotopic composition, have similar water contents as the Copahue magmas and show evidence for a subducted sedimentary component in their source regions. The low 206Pb/204Pb of some backarc lava flows suggests the presence of a second endmember with an EM1 flavor in its source. The overall magma genesis is explained within the context of a subducted slab with sediment that gradually looses water, water-mobile elements, and then switches to sediment melt extracts deeper down in the subduction zone. With the change in element extraction mechanism with depth comes a depletion and fractionation of the subducted complex that is reflected in the isotope and trace element signatures of the products from the main arc to Copahue to the back arc basalts.

Cryptic trace-element alteration of Anorthosite, Stillwater complex, Montana

USGS Publications Warehouse

Czamanske, G.K.; Loferski, P.J.

1996-01-01

Evidence of cryptic alteration and correlations among K, Ba, and LREE concentrations indicate that a post-cumulus, low-density aqueous fluid phase significantly modified the trace-element contents of samples from Anorthosite zones I and II of the Stillwater Complex, Montana. Concentrations of Ba, Ca, Co, Cr, Cu, Fe, Hf, K, Li, Mg, Mn, Na, Ni, Sc, Sr, Th, Zn, and the rare-earth elements (REE) were measured in whole rocks and plagioclase separates from five traverses across the two main plagioclase cumulate (anorthosite) zones and the contiguous cumulates of the Stillwater Complex in an attempt to better understand the origin and solidification of the anorthosites. However, nearly the entire observed compositional range for many trace elements can be duplicated at a single locality by discriminating between samples rich in oikocrystic pyroxene and those which are composed almost entirely of plagioclase and show anhedral-granular texture. Plagioclase separates with high trace-element contents were obtained from the pyroxene-poor samples, for which maps of K concentration show plagioclase grains to contain numerous fractures hosting a fine-grained, K-rich phase, presumed to be sericite. Secondary processes in layered intrusions have the potential to cause cryptic disturbance, and the utmost care must be taken to ensure that samples provide information about primary processes. Although plagioclase from Anorthosite zones I and II shows significant compositional variation, there are no systematic changes in the major- or trace-element compositions of plagioclase over as much as 630 m of anorthosite thickness or 18 km of strike length. Plagioclase in the two major anorthosite zones shows little distinction in trace-element concentrations from plagioclase in the cumulates immediately below, between, and above these zones.

Historical volcanic eruptions in the Canary Islands, tephra composition, and insights into the crystal cargo of basaltic magmas

NASA Astrophysics Data System (ADS)

Longpre, M. A.; Muller, J.; Beaudry, P.; Andronikides, A.; Felpeto, A.

2017-12-01

Since the 16th century, at least 13 volcanic eruptions have occurred in the Canary Islands that formed monogenetic cinder cones and lava flow fields: 2 on Lanzarote, 4 on Tenerife, 6 on La Palma, and 1 on the submarine flank of El Hierro. Here we present a comprehensive new dataset of tephra composition for all 13 eruptions, comprising major and trace element data for bulk rocks and matrix glasses, as well as vesicularity and crystallinity measurements. In addition, we compile available volcanological and petrological information for specific eruptions, including estimates of lava flow area and volume. All lapilli samples show a vesicularity of 40-50 vol% and a vesicle-free crystallinity (crystals ≥ 250 µm) of 5-15 vol%. Modal mineralogy varies significantly between samples, typically consisting of olivine ± clinopyroxene ± Fe-Ti oxide ± plagioclase ± amphibole in different proportions. All but 2 tephras have basanite-tephrite bulk rock compositions. Lapilli from vents of the AD 1730-1736 Timanfaya eruption, Lanzarote, largely are basaltic, whereas the AD 1798 Chahorra eruption, Tenerife, produced phonotephrite tephra. These results are in agreement with published bulk lava flow data. Unsurprisingly, glass compositions are more evolved than bulk rocks and MgOglass is weakly positively correlated to MgObulk (MgOglass = 0.30*MgObulk + 2.11, R2 = 0.54). Both bulk rocks and glasses show strikingly similar multi-element diagram patterns, with strong enrichment relative to the bulk-silicate Earth and marked positive Nb and Ta and negative Pb anomalies — typical for ocean island basalts. Glass/bulk rock elemental ratios reveal systematic differences between samples that relate to their mineralogy; for example, Lanzarote tephras that lack significant clinopyroxene and Fe-Ti oxide crystals have higher Scglass/Scbulk and Vglass/Vbulk than Tenerife, La Palma and El Hierro samples that typically contain these minerals. Among all elements, K and P display the greatest average glass/bulk rock enrichment factors (1.41 ± 0.18 and 1.47 ± 0.17, respectively). This work provides an internally consistent framework for the comparison of historical Canary Island eruptions and offers novel insights into the relationships between trace element signatures and the crystal cargo of basaltic magmas.

Trace element and strontium isotope characteristics of volcanic rocks from Isla Tortuga: a young seamount in the Gulf of California

USGS Publications Warehouse

Batiza, Rodey; Futa, K.; Hedge, C.E.

1979-01-01

Isla Tortuga is a small isolated central volcano which is located near an actively spreading trough in the Gulf of California. The basalt lavas from Tortuga which have the highest Mg/Fe and Ni contents have trace element abundances and ratios and 87Sr/86Sr which are similar to those of mid-ocean ridge tholeiite. The major element, rare earth element and Sr abundances of fractionated tholeiite (low Mg/Fe) and tholeiitic andesite of Tortuga are consistent with an origin by closed-system fractional crystallization. This hypothesis is not supported by K, Na, Rb and Ba abundances in the lavas nor by their variable 87Sr/86Sr (0.7024-0.7035). It is proposed that the apparent decoupling of light rare earth elements, other incompatible trace elements and 87Sr/86Sr is due to contamination of some Tortuga magmas while they are fractionated in a high-level crustal magma chamber. The mantle source of least-contaminated, high Mg/Fe basalt lavas of Tortuga is similar, although not identical to the source of normal mid-ocean ridge tholeiite; significant differences exist. The reasons for these differences are not yet known. ?? 1979.

Popping Rocks Revealed: Investigations from 14°N on the Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Wanless, V. D.; Jones, M.; Kurz, M. D.; Soule, S. A.; Fornari, D. J.; Bendana, S.; Mittelstaedt, E. L.

2017-12-01

The popping rock, recovered in dredge 2πD43 in 1985, is commonly considered to be one of the most representative samples of undegassed upper mantle, based on high volatile and noble gas abundances. While this basalt is used to reconstruct mantle volatile contents and CO2 fluxes from mid-ocean ridges (MOR), the origin of the popping rock has remained ambiguous due to a lack of geologic context. Here, we present results from the first combined geochemical, geophysical, and geologic investigation of popping rocks from 14N on the Mid-Atlantic Ridge. By combining lava compositions with high-resolution bathymetric maps, we show that the popping rocks are confined to a single geographic area, at the transition between magmatic and tectonic segments. Fifteen popping rocks were collected in situ using the Alvin submersible in 2016. X-ray microtomography indicates that these lavas have variable vesicle abundances; including the highest vesicularities (>19%) recorded for any MOR basalt. Dissolved CO2 contents (163-175 ppm) are similar to proximal non-popping rocks and are in equilibrium at their eruption depths (>3600 m); however, total CO2 contents (based on vesicularity, dissolved CO2, and vesicle gas contents) are higher than non-popping rocks, ranging from 2800-14150 ppm. The popping rocks have average 3He/4He ratios of 8.17 ± 0.1 Ra and 4He concentrations of 1.84e-5 to 7.67e-5 cc/g STP. Compared to non-popping lavas, the popping rocks have a narrow range of major and trace element concentrations, suggesting little to no crystallization occurred during ascent or eruption. REE patterns and trace element ratios are indistinguishable in the popping rocks (La/Sm = 2.89 ± 0.05), indicating similar mantle sources and extents of melting. Based on lava compositions and spatial distribution, we suggest that the popping rocks at 14N were produced under similar magmatic conditions and erupted over short timescales, perhaps during a series of closely timed eruptions.

Element distribution patterns in the ordovician Galena group, Southeastern Minnesota: Indicators of fluid flow and provenance of terrigenous material

USGS Publications Warehouse

Lively, R.S.; Morey, G.B.; Mossler, J.H.

1997-01-01

As part of a regional geochemical investigation of lower Paleozoic strata in the Hollandale embayment of southeastern Minnesota, elemental concentrations in acid-insoluble residues were determined for carbonate rock in the Middle Ordovician Galena Group. Elemental distribution patterns within the insoluble residues, particularly those of Ti, Al, and Zr, show that the Wisconsin dome and the Wisconsin arch, which contributed sediment to the embayment prior to Galena time, continued as weak sources of sediment during this period. In contrast, trace metals commonly associated with Mississippi Valley-type lead-zinc mineralization, including Pb, Zn, Cu, Ag, Ni, Co, As, and Mo, show dispersal patterns that are independent of those associated with primary depositional phenomena. These trace metals are concentrated in southern Minnesota in carbonate rocks near the interface between limestone- and dolostone-dominated strata. Dispersal patterns imply that the metals were carried by a north-flowing regional ground-water system. The results show that the geochemical attributes of insoluble residues can be used to distinguish provenance and transport directions of primary sediments within a depositional basin from effects of subsequent regional ground-water flow systems.

Ni/S/Cl systematics and the origin of impact-melt glasses in Martian meteorite Elephant Moraine 79001

NASA Astrophysics Data System (ADS)

Schrader, Christian M.; Cohen, Barbara A.; Donovan, John J.; Vicenzi, Edward P.

2016-04-01

Martian meteorite Elephant Moraine A79001 (EET 79001) has received considerable attention for the unusual composition of its shock melt glass, particularly its enrichment in sulfur relative to the host shergottite. It has been hypothesized that Martian regolith was incorporated into the melt or, conversely, that the S-enrichment stems from preferential melting of sulfide minerals in the host rock during shock. We present results from an electron microprobe study of EET 79001 including robust measurements of major and trace elements in the shock melt glass (S, Cl, Ni, Co, V, and Sc) and minerals in the host rock (Ni, Co, and V). We find that both S and major element abundances can be reconciled with previous hypotheses of regolith incorporation and/or excess sulfide melt. However, trace element characteristics of the shock melt glass, particularly Ni and Cl abundances relative to S, cannot be explained either by the incorporation of regolith or sulfide minerals. We therefore propose an alternative hypothesis whereby, prior to shock melting, portions of EET 79001 experienced acid-sulfate leaching of the mesostasis, possibly groundmass feldspar, and olivine, producing Al-sulfates that were later incorporated into the shock melt, which then quenched to glass. Such activity in the Martian near-surface is supported by observations from the Mars Exploration Rovers and laboratory experiments. Our preimpact alteration model, accompanied by the preferential survival of olivine and excess melting of feldspar during impact, explains the measured trace element abundances better than either the regolith incorporation or excess sulfide melting hypothesis does.

Zircon U-Pb dating of eclogite from the Qiangtang terrane, north-central Tibet: a case of metamorphic zircon with magmatic geochemical features

NASA Astrophysics Data System (ADS)

Zhai, Qing-guo; Jahn, Bor-ming; Li, Xian-hua; Zhang, Ru-yuan; Li, Qiu-li; Yang, Ya-nan; Wang, Jun; Liu, Tong; Hu, Pei-yuan; Tang, Suo-han

2017-06-01

Zircon is probably the most important mineral used in the dating formation of high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks. The origin of zircon, i.e., magmatic or metamorphic, is commonly assessed by its external morphology, internal structure, mineral inclusions, Th/U ratios and trace element composition. In this study, we present an unusual case of metamorphic zircon from the Qiangtang eclogite, north-central Tibet. The zircon grains contain numerous eclogite-facies mineral inclusions, including omphacite, phengite, garnet and rutile; hence, they are clearly of metamorphic origin. However, they display features similar to common magmatic zircon, including euhedral crystal habit, high Th/U ratios and enriched heavy rare earth elements pattern. We suggest that these zircon grains formed from a different reservoir from that for garnet where no trace elements was present and trace element equilibrium between zircon and garnet was achieved. U-Pb dating of zircon gave an age of 232-237 Ma for the eclogite, and that of rutile yielded a slightly younger age of ca. 217 Ma. These ages are consistent with the reported Lu-Hf mineral isochron and phengite Ar-Ar ages. The zircon U-Pb and mineral Lu-Hf isochron ages are interpreted as the time of the peak eclogite-facies metamorphism, whereas the rutile U-Pb and phengite Ar-Ar ages represent the time of exhumation to the middle crust. Thus, the distinction between metamorphic and magmatic zircons cannot be made using only Th/U ratios and heavy REE compositions for HP-UHP metamorphic rocks of oceanic derivation.

Synchrotron X-ray fluorescence analyses of stratospheric cosmic dust - New results for chondritic and low-nickel particles

NASA Technical Reports Server (NTRS)

Flynn, G. J.; Sutton, S. R.

1990-01-01

Trace element abundance determinations were performed using synchrotron X-ray fluorescence on nine particles collected from the stratosphere and classified as cosmic. Improvements to the Synchrotron Light Source allowed the detection of all elements between Cr and Mo, with the exceptions of Co and As, in our largest particle. The minor and trace element abundance patterns of three Ni-depleted particles were remarkably similar to those of extraterrestrial igneous rocks. Fe/Ni and Fe/Mn ratios suggest that one of these may be of lunar origin. All nine particles exhibited an enrichment in Br, ranging from 1.3 to 38 times the C1 concentration. Br concentrations were uncorrelated with particle size, as would be expected for a surface correlated component acquires from the stratosphere.

Geochemistry of volcanic rocks from the Wawa greenstone belt

NASA Technical Reports Server (NTRS)

Schulz, K. J.; Sylvester, P. J.; Attoh, K.

1983-01-01

The Wawa greenstone belt is located in the District of Algoma and extends east-northeast from Lake Superior to the western part of the Sudbury District in Ontario, Canada. Recent mapping by Attoh has shown that an unconformity at the base of the Dore' Formation and equivalent sedimentary rocks marks a significant stratigraphic break which can be traced throughout the volcanic belt. This break has been used to subdivide the volcanic-sedimentary into pre- and post-Dore' sequences. The pre-Dore' sequence includes at least two cycles of mafic-to-felsic volcanism, each capped by an iron-formation unit. The post-Dore' sequence includes an older mafic-to-felsic unit, which directly overlies sedimentary rocks correlated with the Dore' Formation, and a younger felsic breccia unit interpreted to have formed as debris flows from a felsic volcanic center. In the present study, samples of both the pre-and post-Dore' volcanic sequences were analyzed for major and trace elements, incuding rare earths (REE). This preliminary study is part of an ongoing program to assess the petrogenesis of the volcanic rocks of the Wawa greenstone belt.

Light rare earth element systematics as a tool for investigating the petrogenesis of phoscorite-carbonatite associations, as exemplified by the Phalaborwa Complex, South Africa

NASA Astrophysics Data System (ADS)

Milani, Lorenzo; Bolhar, Robert; Frei, Dirk; Harlov, Daniel E.; Samuel, Vinod O.

2017-12-01

In-situ trace element analyses of fluorapatite, calcite, dolomite, olivine, and phlogopite have been undertaken on representative phoscorite and carbonatite rocks of the Palaeoproterozoic Phalaborwa Complex. Textural and compositional characterization reveals uniformity of fluorapatite and calcite among most of the intrusions, and seems to favor a common genetic origin for the phoscorite-carbonatite association. Representing major repositories for rare earth elements (REE), fluorapatite and calcite exhibit tightly correlated light REE (LREE) abundances, suggesting that partitioning of LREE into these rock forming minerals was principally controlled by simple igneous differentiation. However, light rare earth element distribution in apatite and calcite cannot be adequately explained by equilibrium and fractional crystallization and instead favors a complex crystallization history involving mixing of compositionally distinct magma batches, in agreement with previously reported mineral isotope variability that requires open-system behaviour.

Apollo 16 returned lunar samples - Lithophile trace-element abundances

NASA Technical Reports Server (NTRS)

Philpotts, J. A.; Schuhmann, S.; Kouns, C. W.; Lum, R. K. L.; Bickel, A. L.; Schnetzler, C. C.

1973-01-01

Lithium, K, Rb, Sr, Ba, rare-earth, Zr, and Hf abundances have been determined by mass-spectrometric isotope-dilution for Apollo 16 soils, anorthosite 61016, and 'basalt' 68415 whole-rock and separated pyroxene and plagioclase. Our sample of 61016 is similar to some other lunar anorthosites in lithophile trace-element concentrations but at a slightly lower level. It was probably accumulated from a little differentiated basalt. Basalt 68415 might be a homogeneous mixture of KREEP and anorthosite material; it appears to have crystallized under conditions as reducing as those holding for mare-basalts. The soil fines cover only a limited compositional range. No obvious chemical differences were noted between the Descartes and Cayley formations. Most of the compositional variation of the soils can be accounted for in terms of the addition of plagioclase. The existence of very high alumina basalt as an independent magma-type appears debatable in view of its KREEP-like lithophile trace-element relative concentrations and the observed lunar radioactivity distribution.

Major- and trace-element concentrations in rock samples collected in 2004 from the Taylor Mountains 1:250,000-scale quadrangle, Alaska

USGS Publications Warehouse

Klimasauskas, Edward P.; Miller, Marti L.; Bradley, Dwight C.; Karl, Sue M.; Baichtal, James F.; Blodgett, Robert B.

2006-01-01

The Kuskokwim mineral belt of Bundtzen and Miller (1997) forms an important metallogenic region in southwestern Alaska that has yielded more than 3.22 million ounces of gold and 400,000 ounces of silver. Precious-metal and related deposits in this region associated with Late Cretaceous to early Tertiary igneous complexes extend into the Taylor Mountains 1:250,000-scale quadrangle. The U.S. Geological Survey is conducting geologic mapping and a mineral resource assessment of this area that will provide a better understanding of the geologic framework, regional geochemistry, and may provide targets for mineral exploration and development. During the 2004 field season 137 rock samples were collected for a variety of purposes. The 4 digital files accompanying this report reflect the type of analysis performed and its intended purpose and are available for download as an Excel workbook, comma delimited format (*.csv), dBase 4 files (*.dbf) or as point coverages in ArcInfo interchange format (*.e00). Data values are provided in percent, pct (1gram per 100grams), or parts per million, ppm (1gram per 1,000,000grams) per the column heading in the table. All samples were analyzed for a suite of 42 trace-elements (icp42.*) to provide data for use in geochemical exploration as well as some baseline data. Selected samples were analyzed by additional methods; 104 targeted geochemical exploration samples were analyzed for gold, arsenic, and mercury (auashg.*); 21 of these samples were also analyzed to obtain concentrations of 10 loosely bound metals (icp10.*); 33 rock samples were analyzed for major element oxides to support the regional mapping program (reg.*), of which 28 sedimentary rock samples were also analyzed for total carbon, and carbonate carbon.

The Northeast Kingdom batholith, Vermont: magmatic evolution and geochemical constraints on the origin of Acadian granitic rocks

USGS Publications Warehouse

Ayuso, R.A.; Arth, Joseph G.

1992-01-01

Five Devonian plutons (West Charleston, Echo Pond, Nulhegan, Derby, and Willoughby) that constitute the Northeast Kingdom batholith in Vermont show wide ranges in elemental abundances and ratios consistent with major crustal contributions during their evolution. The batholith consists of metaluminous quartz gabbro, diorite and quartz monzodiorite, peraluminous granodiorite and granite, and strongly peraluminous leucogranite. Contents of major elements vary systematically with increasingSiO40) and have small negative Eu anomalies. The strongly peraluminous Willoughby leucogranite has unique trace-element abundances and ratios relative to the rest of the batholith, including low contents of Hf, Zr, Sr, and Ba, low values of K/Rb (80-164), Th/Ta (<9), Rb/Cs (7-40), K/Cs (0.1-0.5), Ce/Pb (0.5-4), high values of Rb/Sr (1-18) low to moderate REE contents and light-REE enriched patterns (with small negative Eu anomalies). Flat REE patterns (with large negative Eu anomalies) are found in a small, hydrothermally-altered area characterized by high abundances of Sn (up to 26 ppm), Rb (up to 670 ppm), Li (up to 310 ppm), Ta (up to 13.1 ppm), and U (up to 10 ppm). There is no single mixing trend, fractional crystallization assemblage, or assimilationscheme that accounts for all trace elementvariations from quartz gabbro to granite in the Northeast Kingdom batholith. The plutons originated by mixing mantle-derived components and crustal melts generated at different levels in the heterogeneous lithosphere in a continental collisional environment. Hybrid rocks in the batholith evolved by fractional crystallization and assimilation of country rocks (<50% by mass), and some of the leucogranitic rocks were subsequently disturbed by a mild hydrothermal event that resulted in the deposition of small amounts of sulfide minerals. ?? 1992 Springer-Verlag.

Meter Scale Heterogeneities in the Oceanic Mantle Revealed in Ophiolites Peridotites

NASA Astrophysics Data System (ADS)

Haller, M. B.; Walker, R. J.; Day, J. M.; O'Driscoll, B.; Daly, J. S.

2016-12-01

Mid-ocean ridge basalts and other oceanic mantle-derived rocks do not capture the depleted endmember isotopic compositions present in oceanic peridotites. Ophiolites are especially useful in interrogating this issue as field-based observations can be paired with geochemical investigations over a wide range of geologic time. Grid sampling methods (3m x 3m) at the 497 Ma Leka Ophiolite Complex (LOC), Norway, and the 1.95 Ga Jormua Ophiolite Complex (JOC), Finland, offer an opportunity to study mantle domains at the meter and kilometer scale, and over a one billion year timespan. The lithology of each locality predominately comprises harzburgite, hosting layers and lenses of dunite and pyroxenite. Here, we combine highly siderophile elements (HSE) and Re-Os isotopic analysis of these rocks with major and trace element measurements. Harzburgites at individual LOC grid sites show variations in γOs(497 Ma) (-2.1 to +2.2) at the meter scale. Analyses of adjacent, more radiogenic dunites within the same LOC grid, reveal that dunites may either have similar γOs to their host harzburgite, or different, implying interactions between spatially associated rock types may differ at the meter scale. Averaged γOs values between the mantle sections of two LOC grid sites (+1.3 and -0.4) separated by 5 km indicate km-scale heterogeneity in the convecting upper mantle. Pd/Ir and Ru/Ir ratios are scattered and do not obviously correlate with γOs values. Analyses of pyroxenites within LOC grid sections, thin section observations of relict olivine grains, and whole rock major and trace element data are also examined to shed light on the causes of the isotopic heterogeneities in the LOC. Data from JOC grid sampling will be presented as well.

The role of sulfides in the fractionation of highly siderophile and chalcophile elements during the formation of martian shergottite meteorites

NASA Astrophysics Data System (ADS)

Baumgartner, Raphael J.; Fiorentini, Marco L.; Lorand, Jean-Pierre; Baratoux, David; Zaccarini, Federica; Ferrière, Ludovic; Prašek, Marko K.; Sener, Kerim

2017-08-01

The shergottite meteorites are ultramafic to mafic igneous rocks whose parental magmas formed from partial melting of the martian mantle. This study reports in-situ laser ablation inductively coupled plasma mass spectrometry analyses for siderophile and chalcophile major and trace elements (i.e., Co, Ni, Cu, As, Se, Ag, Sb, Te, Pb, Bi, and the highly siderophile platinum-group elements, PGE: Os, Ir, Ru, Rh, Pt and Pd) of magmatic Fe-Ni-Cu sulfide assemblages from four shergottite meteorites. They include three geochemically similar incompatible trace element- (ITE-) depleted olivine-phyric shergottites (Yamato-980459, Dar al Gani 476 and Dhofar 019) that presumably formed from similar mantle and magma sources, and one distinctively ITE-enriched basaltic shergottite (Zagami). The sulfides in the shergottites have been variably modified by alteration on Earth and Mars, as well as by impact shock-shock related melting/volatilization during meteorite ejection. However, they inherit and retain their magmatic PGE signatures. The CI chondrite-normalized PGE concentration patterns of sulfides reproduce the whole-rock signatures determined in previous studies. These similarities indicate that sulfides exerted a major control on the PGE during shergottite petrogenesis. However, depletions of Pt (and Ir) in sulfide relative to the other PGE suggest that additional phases such discrete Pt-Fe-Ir alloys have played an important role in the concentration of these elements. These alloys are expected to have enhanced stability in reduced and FeO-rich shergottite magmas, and could be a common feature in martian igneous systems. A Pt-rich PGM was found to occur in a sulfide assemblage in Dhofar 019. However, its origin may be related to impact shock-related sulfide melting and volatilisation during meteorite ejection. In the ITE-depleted olivine-phyric shergottites, positive relationships exist between petrogenetic indicators (e.g., whole-rock Mg-number) and most moderately to strongly siderophile and chalcophile elements in sulfides. These variations extend to incompatible elements like Te and Pd. The whole-rock concentrations of Pd derived from mass-balance calculations decrease by one order of magnitude in the order Y-980459, DaG 476 and Dhofar 019, and broadly overlap the trends in previously published whole-rock analyses. Mantle heterogeneities, and the timing of sulfide saturation as function of mantle melting and/or magma fractionation following ascent from the mantle, may have been the controlling factors of the siderophile and chalcophile element systematics in the analyzed shergottites.

Experimental Study of the Partitioning of Siderophile Elements in a Crystallizing Lunar Magma Ocean

NASA Technical Reports Server (NTRS)

Galenas, M.; Righter, K.; Danielson, L.; Pando, K.; Walker, R. J.

2012-01-01

The distributions of trace elements between the lunar interior and pristine crustal rocks were controlled by the composition of starting materials, lunar core formation, and crystallization of the lunar magma ocean (LMO) [1]. This study focuses on the partitioning of highly siderophile elements (HSE) including Re, Os, Ir, Ru, Pt, Rh, Pd and Au as well as the moderately siderophile elements Mo and W, and the lithophile elements of Hf and Sr. Our experiments also include Ga, which can be slightly siderophile, but is mostly considered to be chalcophile. Partitioning of these elements is not well known at the conditions of a crystallizing LMO. Previous studies of HSE partitioning in silicate systems have yielded highly variable results for differing oxygen fugacity (fO2) and pressure [2-4]. For example, under certain conditions Pt is compatible in clinopy-roxene [2] and Rh and Ru are compatible in olivine [3]. The silicate compositions used for these experiments were nominally basaltic. Ruthenium, Rh, and Pd are incompatible in plagioclase under these conditions[4]. However, this latter study was done at extremely oxidizing conditions and at atmospheric pressure, possibly limiting the applicability for consideration of conditions of a crystallizing LMO. In this study we address the effects of pressure and oxygen fugacity on the crystal/liquid partition coefficients of these trace elements. We are especially interested in the plagioclase/melt partition coefficients so that it may be possible to use reverse modeling to constrain the concentrations of these elements in the lunar mantle through their abundances in pristine crustal rocks.

Petrogenetic and geodynamic origin of the Neoarchean Doré Lake Complex, Abitibi subprovince, Superior Province, Canada

NASA Astrophysics Data System (ADS)

Polat, Ali; Frei, Robert; Longstaffe, Fred J.; Woods, Ryan

2018-04-01

The Neoarchean (ca. 2728 Ma) anorthosite-bearing Doré Lake Complex in the northeastern Abitibi subprovince, Quebec, was emplaced into an association of intra-oceanic tholeiitic basalts and gabbros known as the Obatogamau Formation. The Obatogamau Formation constitutes the lower part of the Roy Group, which is composed of two cycles of tholeiitic-to-calc-alkaline volcanic and volcaniclastic rocks, siliciclastic and chemical sedimentary rocks, and layered mafic-to-ultramafic sills. In this study, we report major and trace element results, and Nd, Sr, Pb and O isotope data for anorthosites, leucogabbros, gabbros and mafic dykes from the Doré Lake Complex and spatially associated basalts and gabbros of the Obatogamau Formation to assess their petrogenetic origin and geodynamic setting. Field and petrographic observations indicate that the Doré Lake Complex and associated volcanic rocks underwent extensive metamorphic alteration under greenschist facies conditions, resulting in widespread epidotization (20-40%) and chloritization (10-40%) of many rock types. Plagioclase recrystallized mainly to anorthite and albite endmembers, erasing intermediate compositions. Metamorphic alteration also led to the mobilization of many elements (e.g., LILE and transition metals) and to significant disturbance of the Rb-Sr and U-Pb isotope systems, resulting in 1935 ± 150 and 3326 ± 270 Ma errorchron ages, respectively. The Sm-Nd isotope system was less disturbed, yielding an errorchron age of 2624 ± 160 Ma. On many binary major and trace element diagrams, the least altered anorthosites and leucogabbros, and the gabbros and mafic dykes of the Doré Lake Complex plot in separate fields, signifying the presence of two distinct magma types in the complex. The gabbros and mafic dykes in the Doré Lake Complex share the geochemical characteristics of tholeiitic basalts and gabbros in the Obatogamau Formation, suggesting a possible genetic link between the two rock associations. Initial ɛNd (+2.6 to +5.0) and δ18O (+6.1 to +7.9‰) values for the Doré Lake Complex and gabbros of the Obatogamau Formation (ɛNd = +2.8 to +4.0; δ18O = +7.3 to 8.0‰) are consistent with depleted mantle sources. All rock types in the Doré Lake Complex and the Roy Group share the trace element characteristics of modern arc magmas, suggesting a suprasubduction zone setting for these two lithological associations. On the basis of regional geology and geochemical data, we suggest that the Doré Lake Complex and the Obatogamau Formation represent a dismembered fragment of a suture zone, like many Phanerozoic ophiolites, resulting from closure of a back-arc basin between 2703 and 2690 Ma.

Chemical and mineralogical analysis of devonian black-shale samples from Martin County, Kentucky; Carroll and Washington counties, Ohio; Wise County, Virginia; and Overton County, Tennessee, U.S.A.

USGS Publications Warehouse

Leventhal, J.S.; Hosterman, J.W.

1982-01-01

Core samples of Devonian shales from five localities in the Appalachian basin have been analyzed chemically and mineralogically. The amounts of major elements are similar; however, the minor constituents, organic C, S, phosphate and carbonate show ten-fold variations in amounts. Trace elements Mo, Ni, Cu, V, Co, U, Zn, Hg, As and Mn show variations in amounts that can be related to the minor constituents. All samples contain major amounts of quartz, illite, two types of mixed-layer clays, and chlorite in differing quantities. Pyrite, calcite, feldspar and kaolinite are also present in many samples in minor amounts. Dolomite, apatite, gypsum, barite, biotite and marcasite are present in a few samples in trace amounts. Trace elements listed above are strongly controlled by organic C with the exception of Mn which is associated with carbonate minerals. Amounts of organic C generally range from 3 to 6%, and S is in the range of 2-5%. Amounts of trace elements show the following general ranges in ppm (parts per million): Co, 20-40; Cu, 40-70; U, 10-40; As, 20-40; V, 150-300; Ni, 80-150; high values are as much as twice these values. The organic C was probably the concentrating agent, and the organic C and sulfide S together created an environment that immobilized and preserved these trace elements. Closely spaced samples showing an abrupt transition in color also show changes in organic C, S and trace-element contents. Several associations exist between mineral and chemical content. Pyrite and marcasite are the only minerals found to contain sulfide-S. In general, the illite-chlorite mixed-layer clay mineral shows covariation with organic C if calcite is not present. The enriched trace elements are not related to the clay types, although the clay and organic matter are intimately associated as the bulk fabric of the rock. ?? 1982.

Detrital Zircons From the Jack Hills and Mount Narryer, Western Australia: Geochronological, Morphological, and Geochemical Evidence for Diverse >4000 Ma Source Rocks

NASA Astrophysics Data System (ADS)

Crowley, J. L.; Myers, J. S.; Sylvester, P. J.; Cox, R. A.

2004-05-01

Detrital zircons from all major clastic units in the Jack Hills and Mount Narryer metasedimentary belts, Western Australia, were analyzed for morphology, internal zoning, inclusion mineralogy, age, and trace element concentrations (latter two obtained by laser-ablation microprobe ICPMS). The results show that zircons were derived from a wide diversity of rocks, including previously described, >4000 Ma grains that are older than any known terrestrial rocks. In three metaconglomerate samples from the western Jack Hills, 4200-3800 Ma zircons ("old grains") comprise 14% of the population, 3800-3600 Ma grains form only 2%, and 3550-3250 Ma zircons ("young grains") are dominant with a significant peak at 3380 Ma. Old and young grains are interpreted as being from similar rock types because they are indistinguishable in trace element concentrations, size (several hundred microns), morphology (subequant, typically fragmented), internal zoning (typically both oscillatory and sector), and U concentration (50-200 ppm). Many of these properties suggest an intermediate plutonic source, whereas an evolved granitic source was previously interpreted from rare-earth element and oxygen isotope data. Detrital zircons in quartzites and metaconglomerates at Mount Narryer differ significantly from zircons from the western Jack Hills. Old grains comprise only 3% (most of which are 4200-4100 Ma), 3800-3600 Ma zircons form 31%, and there are peaks at 3650, 3600, and 3500 Ma. Old and young grains have similar properties that suggest granitic sources, such as elongate prismatic morphology, oscillatory zoning, high U concentrations (100-600 ppm), and xenotime and monazite inclusions. Trace element concentrations are broadly similar to those in Jack Hills zircons, with notable exceptions being generally higher U, smaller Ce and Eu anomalies, and lower Nb/Ta. It is considered unlikely that Jack Hills zircons were derived from granitic gneisses that surround the metasedimentary belts because only a few detrital grains match gneiss zircons in age, morphology, and U concentration. The sources were probably distal, or perhaps destroyed or removed from the region during Neoarchean tectonism. In contrast, Mount Narryer zircons are similar to gneiss zircons, suggesting they were derived from the gneisses, which may include a minor, currently undiscovered 4200-4100 Ma granitic component. Such diversity in age and nature of Hadean detrital zircons is compelling evidence that Earth's crust was heterogeneous by 4200 Ma.

Trace-element geochemistry of metabasaltic rocks from the Yukon-Tanana Upland and implications for the origin of tectonic assemblages in east-central Alaska

USGS Publications Warehouse

Dusel-Bacon, C.; Cooper, K.M.

1999-01-01

We present major- and trace- element geochemical data for 27 amphibolites and six greenstones from three structural packages in the Yukon-Tanana Upland of east-central Alaska: the Lake George assemblage (LG) of Devono-Mississippian augen gneiss, quartz-mica schist, quartzite, and amphibolite; the Taylor Mountain assemblage (TM) of mafic schist and gneiss, marble, quartzite, and metachert; and the Seventymile terrane of greenstone, serpentinized peridotite, and Mississippian to Late Triassic metasedimentary rocks. Most LG amphibolites have relatively high Nb, TiO2, Zr, and light rare earth element contents, indicative of an alkalic to tholeiitic, within-plate basalt origin. The within-plate affinities of the LG amphibolites suggest that their basaltic parent magmas developed in an extensional setting and support a correlation of these metamorphosed continental-margin rocks with less metamorphosed counterparts across the Tintina fault in the Selwyn Basin of the Canadian Cordillera. TM amphibolites have a tholeiitic or calc-alkalic composition, low normalized abundances of Nb and Ta relative to Th and La, and Ti/V values of <20, all indicative of a volcanic-arc origin. Limited results from Seventymile greenstones indicate a tholeiitic or calc-alkalic composition and intermediate to high Ti/V values (27-48), consistent with either a within-plate or an ocean-floor basalt origin. Y-La-Nb proportions in both TM and Seventymile metabasalts indicate the proximity of the arc and marginal basin to continental crust. The arc geochemistry of TM amphibolites is consistent with a model in which the TM assemblage includes arc rocks generated above a west-dipping subduction zone outboard of the North American continental margin in mid-Paleozoic through Triassic time. The ocean-floor or within-plate basalt geochemistry of the Seventymile greenstones supports the correlation of the Seventymile terrane with the Slide Mountain terrane in Canada and the hypothesis that these oceanic rocks originated in a basin between the continental margin and an arc to the west.

Rare earth and trace element geochemistry of a fragment of Jurassic seafloor, Point Sal, California

NASA Technical Reports Server (NTRS)

Menzies, M.; Blanchard, D.; Brannon, J.; Korotev, R.

1977-01-01

Rocks from an ophiolite suite once on the seafloor were analyzed for rare earth elements (REE), Sc, Co, Na2O, Cr, Zn and FeO. Strontium isotope exchange noted in some of the lavas is attributed to basalt-seawater interaction; the Ce abundance in smectite- and zeolite-bearing lavas may also be due to prolonged exposure to seawater. The higher grades of metamorphic rock, however, show no variation from the usual flat or slightly light REE depleted profiles. Plutonic igneous rock, all light REE depleted, have total REE abundances varying by a factor of 100 between the dunites and diorites. In order of decreasing REE abundance are hornblende, clinopyroxene, plagioclase, orthopyroxene and olivine. Calculations of REE contents of liquids in equilibrium with early cumulative clinopyroxenes suggest that the parent to the stratiform sequence was more depleted in light REE than the parent to the lava pile.

Geochemistry of lunar crustal rocks from breccia 67016 and the composition of the moon

NASA Technical Reports Server (NTRS)

Norman, Marc D.; Taylor, Stuart R.

1992-01-01

The geochemistry of anorthositic clasts from an Apollo 16 breccia 67016 is studied in order to investigate the role of these rock types in lunar crustal evolution. The samples have aluminous, alkali-poor compositions and varied FeO and MgO contents. Three compositional groups are recognized. One group is poor in mafic constituents with low abundances of lithophile trace elements typical of lunar anorthosites, while the other two groups are more mafic and are distinguished from each other by FeO/MgO ratios greater than one in the case of ferroan noritic and less than one in the case of magnesian troctolitic. These mafic-enriched varieties have considerably higher lithophile element concentrations, at levels similar to that of the bulk lunar crust. The ferroan noritic clasts may represent a fundamental type of igneous rock in the lunar crust which has not been widely recognized.

Catalog of Mount St. Helens 2004-2007 Dome Samples with Major- and Trace-Element Chemistry

USGS Publications Warehouse

Thornber, Carl R.; Pallister, John S.; Rowe, Michael C.; McConnell, Siobhan; Herriott, Trystan M.; Eckberg, Alison; Stokes, Winston C.; Cornelius, Diane Johnson; Conrey, Richard M.; Hannah, Tammy; Taggart, Joseph E.; Adams, Monique; Lamothe, Paul J.; Budahn, James R.; Knaack, Charles M.

2008-01-01

Sampling and analysis of eruptive products at Mount St. Helens is an integral part of volcano monitoring efforts conducted by the U.S. Geological Survey?s Cascades Volcano Observatory (CVO). The objective of our eruption sampling program is to enable petrological assessments of pre-eruptive magmatic conditions, critical for ascertaining mechanisms for eruption triggering and forecasting potential changes in eruption behavior. This report provides a catalog of near-vent lithic debris and new dome-lava collected during 34 intra-crater sampling forays throughout the October 2004 to October 2007 (2004?7) eruptive interval at Mount St. Helens. In addition, we present comprehensive bulk-rock geochemistry for a time-series of representative (2004?7) eruption products. This data, along with that in a companion report on Mount St. Helens 2004 to 2006 tephra by Rowe and others (2008), are presented in support of the contents of the U.S. Geological Survey Professional Paper 1750 (Sherrod and others, eds., 2008). Readers are referred to appropriate chapters in USGS Professional Paper 1750 for detailed narratives of eruptive activity during this time period and for interpretations of sample characteristics and geochemical data. The suite of rock samples related to the 2004?7 eruption of Mount St. Helens and presented in this catalog are archived at the David A. Johnson Cascades Volcano Observatory, Vancouver, Wash. The Mount St. Helens 2004?7 Dome Sample Catalogue with major- and trace-element geochemistry is tabulated in 3 worksheets of the accompanying Microsoft Excel file, of2008-1130.xls. Table 1 provides location and sampling information. Table 2 presents sample descriptions. In table 3, bulk-rock major and trace-element geochemistry is listed for 44 eruption-related samples with intra-laboratory replicate analyses of 19 dacite lava samples. A brief overview of the collection methods and lithology of dome samples is given below as an aid to deciphering the dome sample catalog. This is followed by an explanation of the categories of sample information (column headers) in Tables 1 and 2. A summary of the analytical methods used to obtain the geochemical data in this report introduces the presentation of major- and trace-element geochemistry of 2004?7 Mount St. Helens dome samples in table 3. Intra-laboratory results for the USGS AGV-2 standard are presented (tables 4 and 5), which demonstrate the compatibility of chemical data from different sources.

Effect of ultramafic intrusions and associated mineralized rocks on the aqueous geochemistry of the Tangle Lakes Area, Alaska: Chapter C in Studies by the U.S. Geological Survey in Alaska, 2011

USGS Publications Warehouse

Wang, Bronwen; Gough, Larry P.; Wanty, Richard B.; Lee, Gregory K.; Vohden, James; O’Neill, J. Michael; Kerin, L. Jack

2013-01-01

Stream water was collected at 30 sites within the Tangle Lakes area of the Delta mineral belt in Alaska. Sampling focused on streams near the ultramafic rocks of the Fish Lake intrusive complex south of Eureka Creek and the Tangle Complex area east of Fourteen Mile Lake, as well as on those within the deformed metasedimentary, metavolcanic, and intrusive rocks of the Specimen Creek drainage and drainages east of Eureka Glacier. Major, minor, and trace elements were analyzed in aqueous samples for this reconnaissance aqueous geochemistry effort. The lithologic differences within the study area are reflected in the major-ion chemistry of the water. The dominant major cation in streams draining mafic and ultramafic rocks is Mg2+; abundant Mg and low Ca in these streams reflect the abundance of Mg-rich minerals in these intrusions. Nickel and Cu are detected in 84 percent and 87 percent of the filtered samples, respectively. Nickel and Cu concentrations ranged from Ni <0.4 to 10.1 micrograms per liter (mg/L), with a median of 4.2 mg/L, and Cu <0.5 to 27 mg/L, with a median of 1.2 mg/L. Trace-element concentrations in water are generally low relative to U.S. Environmental Protection Agency freshwater aquatic-life criteria; however, Cu concentrations exceed the hardness-based criteria for both chronic and acute exposure at some sites. The entire rare earth element (REE) suite is found in samples from the Specimen Creek sites MH5, MH4, and MH6 and, with the exception of Tb and Tm, at site MH14. These samples were all collected within drainages containing or downstream from Tertiary gabbro, diabase, and metagabbro (Trgb) exposures. Chondrite and source rock fractionation profiles for the aqueous samples were light rare earth element depleted, with negative Ce and Eu anomalies, indicating fractionation of the REE during weathering. Fractionation patterns indicate that the REE are primarily in the dissolved, as opposed to colloidal, phase.

Sandstone type uranium deposits in the Ordos Basin, Northwest China: A case study and an overview

NASA Astrophysics Data System (ADS)

Akhtar, Shamim; Yang, Xiaoyong; Pirajno, Franco

2017-09-01

This paper provides a comprehensive review on studies of sandstone type uranium deposits in the Ordos Basin, Northwest China. As the second largest sedimentary basin, the Ordos Basin has great potential for targeting sandstone type U mineralization. The newly found and explored Dongsheng and Diantou sandstone type uranium deposits are hosted in the Middle Jurassic Zhilou Formation. A large number of investigations have been conducted to trace the source rock compositions and relationship between lithic subarkose sandstone host rock and uranium mineralization. An optical microscopy study reveals two types of alteration associated with the U mineralization: chloritization and sericitization. Some unusual mineral structures, with compositional similarity to coffinite, have been identified in a secondary pyrite by SEM These mineral phases are proposed to be of bacterial origin, following high resolution mapping of uranium minerals and trace element determinations in situ. Moreover, geochemical studies of REE and trace elements constrained the mechanism of uranium enrichment, displaying LREE enrichment relative to HREE. Trace elements such as Pb, Mo and Ba have a direct relationship with uranium enrichment and can be used as index for mineralization. The source of uranium ore forming fluids and related geological processes have been studied using H, O and C isotope systematics of fluid inclusions in quartz veins and the calcite cement of sandstone rocks hosting U mineralization. Both H and O isotopic compositions of fluid inclusions reveal that ore forming fluids are a mixture of meteoric water and magmatic water. The C and S isotopes of the cementing material of sandstone suggest organic origin and bacterial sulfate reduction (BSR), providing an important clue for U mineralization. Discussion of the ore genesis shows that the greenish gray sandstone plays a crucial role during processes leading to uranium mineralization. Consequently, an oxidation-reduction model for sandstone-type uranium deposit is proposed, which can elucidate the source of uranium in the deposits of the Ordos Basin, based on the role of organic materials and sulfate reducing bacteria. We discuss the mechanism of uranium deposition responsible for the genesis of these large sandstone type uranium deposits in this unique sedimentary basin.

Trace elements and isotope data of the Um Garayat gold deposit, Wadi Allaqi district, Egypt

NASA Astrophysics Data System (ADS)

Zoheir, Basem; Emam, Ashraf; Pitcairn, Iain K.; Boskabadi, Arman; Lehaye, Yann; Cooper, Matthew J.

2018-04-01

Trace element composition of sulfides and O, C, Sr and S isotopic data are assessed to constrain the evolution and potential fluid and metal sources of the Um Garayat gold deposit. Ore microscopy and BSE investigations of quartz veins show blocky arsenopyrite and pyrite replaced in part by pyrrhotite, chalcopyrite, sphalerite, galena, and gersdorffite. Free-milling gold occurs commonly in close association with the late sulfides, and along fractures in pyrite. On the other hand, recrystallized pyrite is disseminated in host metavolcaniclastic/metasedimentary rocks that commonly contain carbonaceous material. In situ LA-ICP-MS analysis of sulfides shows the recrystallized pyrite enriched in most trace elements, while blocky pyrite contains only some traces of arsenic. Detected concentrations of gold (up to 17 ppm) were only reported in arsenopyrite disseminated in quartz veins. The δ34S values of blocky pyrite and pyrrhotite in quartz veins define a narrow range (1.6 to 3.7‰), suggesting a homogenous sulfur source which is consistent with the dominantly mafic host rocks. The recrystallized pyrite has a distinctive sulfur isotope composition (δ34S - 9.3 to - 10.6‰), which is rather comparable to diagenetic sulfides. Hydrothermal carbonate in quartz veins and wallrock have nearly constant values of δ18O (10.5 to 11.9‰) and δ13C (- 4.2 to - 5.5‰). Based on constraints from mineral assemblages and chlorite thermometry, data of six samples indicate that carbonate precipitation occurred at 280 °C from a homogenous hydrothermal fluid with δ18OH2O 4.4 ± 0.7‰ and δ13C = 3.7 ± 0.8‰. Strontium isotope values of two samples (87Sr/86Sr = 0.7024 and 0.7025) are similar to the initial 87Sr/86Sr ratios of island arc metabasalts ( 710 Ma) in the South Eastern Desert. The generally homogenous sulfur, C, O, Sr isotope data are suggestive of metamorphogenic fluids, likely produced from dominantly mafic volcanic rocks at the greenschist-amphibolite facies transition.

The Boring Billion, a slingshot for Complex Life on Earth.

PubMed

Mukherjee, Indrani; Large, Ross R; Corkrey, Ross; Danyushevsky, Leonid V

2018-03-13

The period 1800 to 800 Ma ("Boring Billion") is believed to mark a delay in the evolution of complex life, primarily due to low levels of oxygen in the atmosphere. Earlier studies highlight the remarkably flat C, Cr isotopes and low trace element trends during the so-called stasis, caused by prolonged nutrient, climatic, atmospheric and tectonic stability. In contrast, we suggest a first-order variability of bio-essential trace element availability in the oceans by combining systematic sampling of the Proterozoic rock record with sensitive geochemical analyses of marine pyrite by LA-ICP-MS technique. We also recall that several critical biological evolutionary events, such as the appearance of eukaryotes, origin of multicellularity & sexual reproduction, and the first major diversification of eukaryotes (crown group) occurred during this period. Therefore, it appears possible that the period of low nutrient trace elements (1800-1400 Ma) caused evolutionary pressures which became an essential trigger for promoting biological innovations in the eukaryotic domain. Later periods of stress-free conditions, with relatively high nutrient trace element concentration, facilitated diversification. We propose that the "Boring Billion" was a period of sequential stepwise evolution and diversification of complex eukaryotes, triggering evolutionary pathways that made possible the later rise of micro-metazoans and their macroscopic counterparts.

Turbidite geochemistry and evolution of the Izu-Bonin arc and continents

NASA Astrophysics Data System (ADS)

Gill, J. B.; Hiscott, R. N.; Vidal, Ph.

1994-10-01

The major and trace element and NdPb isotopic composition of Oligocene to Pleistocene volcaniclastic sands and sandstones derived from the Izu Bonin island arc has been determined. Many characteristics of the igneous sources are preserved and record the geochemical evolution of juvenile proto-continental crust in an island arc. After an initial boninitic phase, arc geochemistry has varied primarily as the result of backarc basin formation. The Izu arc source became depleted in incompatible trace elements during backarc basin formation, and re-enriched after spreading stopped in the basin. Renewed rifting during the Pliocene to Recent caused felsic magmatism as a result of easier eruption of differentiates rather than as a result of crustal melting. Four isotopically-distinct source components are recognized. Their combination in the sources of the Izu-Bonin and Mariana arcs initially was similar but diverged after backarc basin formation. The Izu arc turbidites are more similar to Archean than post-Archean sedimentary rocks, indicating that the production of new upper crust at subduction zones has changed little over time. The turbidites are similar in major element composition to average continental crust but are depleted in incompatible trace elements, especially Th and Nb. Consequently, the net effect of adding juvenile arc crust to continents is to reverse the trend of planetary trace element differentiation instead of continuing the process.

Publications - GMC 411 | Alaska Division of Geological & Geophysical

Science.gov Websites

outcrop samples from the 2001 DGGS Salcha River-Pogo project, Big Delta Quadrangle, Alaska Authors . Quadrangle(s): Big Delta Bibliographic Reference Newberry, R.J., 2012, Whole-rock and trace element analyses of two amphibolite outcrop samples from the 2001 DGGS Salcha River-Pogo project, Big Delta Quadrangle

Chemical analyses and K-Ar ages of samples from 13 drill holes, Medicine Lake volcano, California

USGS Publications Warehouse

Donnelly-Nolan, Julie M.

2006-01-01

Chemical analyses and K-Ar ages are presented for rocks sampled from drill holes at Medicine Lake volcano, northern California. A location map and a cross-section are included, as are separate tables for drill hole information, major and trace element data, and for K-Ar dates.

Carbonates of the Gunflint Banded Iron Formation as Analogs of Martian Carbonates

NASA Technical Reports Server (NTRS)

Pun, A.; Papike, J. J.; Shearer, C. K.

2001-01-01

Terrestrial iron formations preserve remnants of life on Earth and may serve as analogs for identifying evidence of biologic activity in martian rocks. We report on the petrography, mineralogy and trace-element abundances of carbonates of the Gunflint banded iron formation. Additional information is contained in the original extended abstract.

Germanium Isotopes - the Global Budget and Paleoceanographic Potential

NASA Astrophysics Data System (ADS)

Baronas, J. J.; Hammond, D. E.; Rouxel, O. J.

2017-12-01

The distribution of element isotope ratios in rocks, sediments, rivers, and seawater can provide key insights about the operation and coupling of various biogeochemical cycles that are directly or indirectly responsible for the climate and habitability of the Earth surface environment. Germanium (Ge) is a trace element that shares many chemical similarities with silicon (Si), in addition to some siderophilic, chalcophilic, and organophilic properties. As a result, Ge stable isotope ratios (δ74Ge) and Ge/Si ratios can be used to trace various biogeochemical processes. These include silicate rock weathering, which modulates atmospheric pCO2 and supplies nutrients to ecosystems, biogenic silica formation, which is coupled to ocean productivity, and marine sediment diagenesis, which ultimately controls the removal of material from the Earth's surface. I will present an overview of my dissertation research concerning the global Ge isotope cycle, with insights into Ge isotope fractionation during secondary mineral precipitation during weathering on continents and during authigenesis in marine sediments. I will also discuss the potential for the δ74Ge sedimentary record to be used as a paleoceanographic proxy, given the constraints on the global Ge isotope budget.

Petrographic and geochemical characterization of the granitic rocks of the Araguainha impact crater, Brazil

NASA Astrophysics Data System (ADS)

Silva, Dailto; Lana, Cristiano; Souza Filho, Carlos Roberto

2016-03-01

Petrographic and geochemical data obtained on the Araguainha impact crater (Goiás/Mato Grosso States, Brazil) indicate the existence of several molten products that originated during impact-induced congruent melting of an alkali-granite exposed in the inner part of the central uplift of the structure. Although previous studies have described these melts to some extent, there is no detailed discussion on the petrographic and geochemical variability in the granite and its impactogenic derivatives, and therefore, little is known about the geochemical behavior and mobility of trace elements during its fusion in the central part of the Araguainha crater. This paper demonstrates that the preserved granitoid exposed in the core of the structure is a magnesium-rich granite, similar to postcollisional, A-type granites, also found in terrains outside the Araguainha crater, in the Brasília orogenic belt. The molten products are texturally distinct and different from the original rock, but have very similar geochemical composition, making it difficult to separate these lithotypes based on concentrations of major and minor elements. This also applies for trace and rare earth elements (REE), thus indicating a high degree of homogenization during impact-induced congruent melting under high pressure and postshock temperature conditions. Petrographic observations, along with geochemical data, indicate that melting occurs selectively, where some of the elements are transported with the melt. Simultaneously, there is an effective dissolution of the rock (granite), which leads to entrainment of the most resistant solid phases (intact or partially molten minerals) into the melt. Minerals more resistant to melting, such as quartz and oxides, contribute substantially to a chemical balance between the preserved granite and the fusion products generated during the meteoritic impact.

The Easternmost Southwest Indian Ridge: A Laboratory to Study MORB and Oceanic Gabbro Petrogenesis in a Very Low Melt Supply Context

NASA Astrophysics Data System (ADS)

Paquet, M.; Cannat, M.; Hamelin, C.; Brunelli, D.

2014-12-01

Our study area is located at the ultra-slow Southwest Indian Ridge, east of the Melville Fracture Zone, between 61 and 67°E. The melt distribution in this area is very heterogeneous, with corridors of ultramafic seafloor where plate separation is accommodated by large offset normal faults [Sauter, Cannat et al., 2013]. These ultramafic corridors also expose rare gabbros and basalts. We use the major and trace elements composition of these magmatic rocks to document the petrogenesis of MORB in this exceptionnally low melt supply portion of the MOR system. Basalts from the easternmost SWIR represent a global MORB end-member for major element compositions [Meyzen et al., 2003], with higher Na2O and Al2O3 wt%, and lower CaO and FeO wt% at a given MgO. Within this group, basalts from the ultramafic corridors have particularly high Na2O, low CaO and FeO wt%. Best fitting calculated liquid lines of descent are obtained for crystallization pressures of ~8 kbar. Gabbroic rocks recovered in the ultramafic corridors include gabbros, oxide-gabbros and variably impregnated peridotites. This presentation focuses on these impregnated samples, where cpx have high Mg#, yet are in equilibrium with the nearby basalts in terms of their trace element compositions. Plagioclase An contents vary over a broad range, and there is evidence for opx resorption. These characteristics result from melt-mantle interactions in the axial lithosphere, which may explain several peculiar major element characteristics of the basalts. Similar interactions probably occur beneath ridges at intermediate to slow and ultraslow spreading rates. We propose that they are particularly significant in our study area due to its exceptionnally low integrated melt-rock ratio.

Hydrogeochemical survey of groundwater for selected areas in the Arabian Shield and in cover rocks, Kingdom of Saudi Arabia

USGS Publications Warehouse

McHugh, John B.; Miller, W. Roger

1989-01-01

In the spring of 1984, a hydrogeochemical survey was conducted in the Kingdom of Saudi Arabia to test ground water as a sampling medium in exploration for mineral deposits. Eighty-one water samples (mostly from wells) were collected. The samples were analysed for the presence and concentration of major cations and anions, as well as a suite of trace elements. Most of the water samples contained high concentrations of dissolved salts. The majority of the samples showed no significant amounts of the trace elements. A few well-water samples contained moderately anomalous concentrations of zinc, molybdenum, and uranium. These anomalies could be due to salinity effects, contamination, or the proximity of mineral sources. This survey has established some baseline water-chemistry data, especially for the trace metals, which to date have not been reported in ground water in the Kingdom of Saudi Arabia.

Magma genesis in the lesser Antilles island arc

NASA Astrophysics Data System (ADS)

Hawkesworth, C. J.; Powell, M.

1980-12-01

143Nd/ 144Nd, 87Sr/ 86Sr and REE results are reported on volcanic rocks from the islands of Dominica and St. Kitts in the Lesser Antilles. Particular attention is given to the lavas and xenoliths of the Foundland (basalt-andesite) and the Plat Pays (andesite-dacite) volcanic centres on Dominica. Combined major and trace element [ 2] and isotope results suggest that the bulk of the andesites and dacites on Dominica, and by analogy in the rest of the arc, are produced by fractional crystallisation of basaltic magma. The differences in the erupted products of the two volcanoes do not appear to be related to any significant differences in the source rocks of the magmas. Along the arc 87Sr/ 86Sr ratios range from 0.7037 on St. Kitts, to 0.7041-0.7047 on Dominica, and 0.7039-0.7058 on Grenada [ 5], and these are accompanied by a parallel increase in K, Sr, Ba and the light REE's. Moreover, compared with LIL-element-enriched and -depleted rocks from MOR and intraplate environments, the basic rocks from the Lesser Antilles are preferentially enriched in alkaline elements (K, Ba, Rb, Sr) relative to less mobile elements such as the rare earths. 143Nd/ 144Nd varies from 0.51308 on St. Kitts, to 0.51286 on Dominica, and 0.51264-0.51308 on Grenada [ 5], and all these samples have relatively high 87Sr/ 86Sr ratios compared with the main trend of Nd and Sr isotopes for most mantle-derived volcanic rocks. Alkaline elements and 87Sr appear to have been introduced from the subducted ocean crust, but the results on other, less mobile elements are more ambiguous — island arc tholeiites (as on St. Kitts) do not appear to contain significant amounts of REE's, Zr, Y, etc., from the subducted oceanic crust, but such a contribution may be present in more LIL-element-enriched calc-alkaline rock types.

Trace Elements in Manganese Minerals as Potential Biosignatures on Mars

NASA Astrophysics Data System (ADS)

Lanza, N.; Clegg, S. M.; Cousin, A.; Forni, O.; Kirk, M. F.; Lamm, S. N.; Ollila, A.; Wiens, R. C.

2017-12-01

Observations from the Curiosity rover in Gale crater, Mars have shown the presence of high abundances of manganese (>3 wt% MnO) within sedimentary rocks throughout the traverse. Such high Mn abundances point to the past presence of abundant liquid water and strongly oxidizing conditions. On Earth, these types of environments are almost always habitable and are frequently inhabited by microbes. Given its close association with life and habitable environments on Earth, manganese has long been considered a potential biosignature for Mars. However, high concentrations of martian Mn have only recently been observed. In addition to the observations in Gale crater, high abundances of Mn have also been observed in Endeavor crater by the Opportunity rover and in the paired martian meteorites NWA 7034 and 7533 (`Black Beauty'), suggesting that Mn deposits may be more widespread on Mars than previously thought. The goal of this work is to determine whether there are unique signatures from rover payload instruments that can distinguish Mn-rich deposits as biogenic in origin (i.e., produced by life) from abiogenic Mn deposits. Importantly, Mn-oxides are known to scavenge trace metals from water because of their surface charge properties. We hypothesize that the presence and abundance of specific trace elements are the critical, distinguishing evidence for identifying the biogenic origin of Mn-bearing materials. A suite of natural rocks containing Mn-rich minerals with a range of Mn redox states was selected for analysis with laser-induced breakdown spectroscopy (LIBS). Samples with a biogenic origin had mixed valence redox states between Mn3+ and Mn4+ as inferred by mineralogy. Trace elements Ba, Li, Sr, and Rb were quantified and the presence or absence of Zn and Cu was ascertained by examining key LIBS peaks. Results show that samples with a known microbial origin had moderate Mn abundances >30 wt% MnO and higher Li and Ba. These results suggest that high Mn abundance alone is not sufficient evidence of a biosignatures. However, the presence of trace elements may help to infer the redox state of Mn, which may in turn point to samples that are more likely to have a biogenic origin.

Linking Serpentinite Geochemistry with Possible Alteration and Evolution of Supra-Subduction Wedge Mantle

NASA Astrophysics Data System (ADS)

Scambelluri, M.; Cannaò, E.; Agostini, S.; Gilio, M.

2016-12-01

Serpentinites are able to transport and release volatiles and fluid-mobile elements (FME) found in arc magmas. Constraining the trace element compositions of these rocks and of fluids released by de-serpentinization improves our knowledge of mass transfer from subduction zones to volcanic arcs, and of the role of slab and wedge mantle in this global process. Studies of high-pressure ultramafic rocks exhumed from plate interface settings reveal the fluid/rock interactions atop the slab and the processes that can affect the mantle wedge. Alpine eclogite-facies antigorite serpentinite (Voltri Massif) and fully de-serpentinized meta-peridotite (Cima di Gagnone) are enriched in sediment-derived As, Sb, U, Pb before peak dehydration. Their Sr, Pb and B isotopic compositions are reset during prograde (forearc) interaction with slab fluids. The eclogitic garnet and olivine from the Cima di Gagnone metaperidotite trap primary inclusions of the fluid released during breakdown of antigorite and chlorite. The inclusions display FME enrichments (high Cl, S; variable Cs, Rb, Ba, B, Pb, As, Sb) indicating element release from rocks to fluids during dehydration under subarc conditions. Our studies show that serpentinized mantle rocks from subduction zones sequester FME from slab fluids and convey these components and radiogenic isotopes into the mantle wedge upon dehydration. The geochemical processes revealed by such plate-interface rocks can apply to the supra-subduction mantle. Shallow element release from slabs to mantle wedge, downdrag of this altered mantle and its subsequent (subarc) dehydration transfers crust-derived FMEs to the arc magma sources without the need of concomitant subarc dehydration/melting of metasedimentary slab components. The slab signature detected in arc lavas can thus result from geochemical mixing of sediment, oceanic crust and ultramafic reservoirs into altered wedge-mantle rocks, rather than being attributed to multiple fluids.

Provenance and depositional history of continental slope sediments in the Southwestern Gulf of Mexico unraveled by geochemical analysis

NASA Astrophysics Data System (ADS)

Armstrong-Altrin, John S.; Machain-Castillo, María Luisa; Rosales-Hoz, Leticia; Carranza-Edwards, Arturo; Sanchez-Cabeza, Joan-Albert; Ruíz-Fernández, Ana Carolina

2015-03-01

The aim of this work is to constrain the provenance and depositional history of continental slope sediments in the Southwestern Gulf of Mexico (~1089-1785 m water depth). To achieve this, 10 piston sediment cores (~5-5.5 m long) were studied for mineralogy, major, trace and rare earth element geochemistry. Samples were analyzed at three core sections, i.e. upper (0-1 cm), middle (30-31 cm) and lower (~300-391 cm). The textural study reveals that the core sediments are characterized by silt and clay fractions. Radiocarbon dating of sediments for the cores at different levels indicated a maximum of ~28,000 year BP. Sediments were classified as shale. The chemical index of alteration (CIA) values for the upper, middle, and lower sections revealed moderate weathering in the source region. The index of chemical maturity (ICV) and SiO2/Al2O3 ratio indicated low compositional maturity for the core sediments. A statistically significant correlation observed between total rare earth elements (∑REE) versus Al2O3 and Zr indicated that REE are mainly housed in detrital minerals. The North American Shale Composite (NASC) normalized REE patterns, trace element concentrations such as Cr, Ni and V, and the comparison of REE concentrations in sediments and source rocks indicated that the study area received sediments from rocks intermediate between felsic and mafic composition. The enrichment factor (EF) results indicated that the Cd and Zn contents of the upper section sediments were influenced by an anthropogenic source. The trace element ratios and authigenic U content of the core sediments indicated the existence of an oxic depositional environment.

Energy-Constrained Recharge, Assimilation, and Fractional Crystallization (EC-RAχFC): A Visual Basic computer code for calculating trace element and isotope variations of open-system magmatic systems

NASA Astrophysics Data System (ADS)

Bohrson, Wendy A.; Spera, Frank J.

2007-11-01

Volcanic and plutonic rocks provide abundant evidence for complex processes that occur in magma storage and transport systems. The fingerprint of these processes, which include fractional crystallization, assimilation, and magma recharge, is captured in petrologic and geochemical characteristics of suites of cogenetic rocks. Quantitatively evaluating the relative contributions of each process requires integration of mass, species, and energy constraints, applied in a self-consistent way. The energy-constrained model Energy-Constrained Recharge, Assimilation, and Fractional Crystallization (EC-RaχFC) tracks the trace element and isotopic evolution of a magmatic system (melt + solids) undergoing simultaneous fractional crystallization, recharge, and assimilation. Mass, thermal, and compositional (trace element and isotope) output is provided for melt in the magma body, cumulates, enclaves, and anatectic (i.e., country rock) melt. Theory of the EC computational method has been presented by Spera and Bohrson (2001, 2002, 2004), and applications to natural systems have been elucidated by Bohrson and Spera (2001, 2003) and Fowler et al. (2004). The purpose of this contribution is to make the final version of the EC-RAχFC computer code available and to provide instructions for code implementation, description of input and output parameters, and estimates of typical values for some input parameters. A brief discussion highlights measures by which the user may evaluate the quality of the output and also provides some guidelines for implementing nonlinear productivity functions. The EC-RAχFC computer code is written in Visual Basic, the programming language of Excel. The code therefore launches in Excel and is compatible with both PC and MAC platforms. The code is available on the authors' Web sites http://magma.geol.ucsb.edu/and http://www.geology.cwu.edu/ecrafc) as well as in the auxiliary material.

Contrasting sodic and mildly potassic magma differentiation lineages at The Pleaides volcanic complex, northern Victoria Land, Antarctica

NASA Astrophysics Data System (ADS)

Kim, J.; Park, J. W.; Lee, J.; Kyle, P. R.; Lee, M. J.

2017-12-01

The magma evolution of The Pleiades, a Quaternary alkaline volcanic complex in northern Victoria Land, Antarctica, is investigated using major and trace elements, and Sr, Nd and Pb isotopic data. The volcanic rocks can be subdivided into two distinct magmatic lineages based on petrography and whole-rock compositions: (1) a sodic silica-undersaturated alkaline lineage with abundant kaersutite phenocrysts, and (2) a mildly-potassic and mildly-alkaline, nearly silica-saturated lineage containing olivine but not kaersutite. The basanite and trachybasalt of both lineages exhibit similar degrees of negative K anomalies, moderately steep rare earth element patterns, and elevated trace element ratios such as Ce/Pb (> 20) and Nb/U (> 38), suggesting their primary magmas were generated by low degree (≤3%) of partial melting of amphibole and garnet-bearing mantle sources. The sodic lineage is characterized by elevated 206Pb/204Pb (>19.5) ratios and narrow ranges of 87Sr/86Sr (0.70313-0.70327) and 143Nd/144Nd (0.51289-0.51290) ratios consistent with a significant HIMU component typical of Neogene volcanic rocks in Antarctica. The mafic rocks of the potassic lineage have isotopic compositions similar to those of the sodic lineage, however the evolved lavas in the lineage have higher 87Sr/86Sr (> 0.7035) and lower 143Nd/144Nd (< 0.51285) and 206Pb/204Pb (< 19.3) ratios than the mafic rocks, suggesting significant amounts of crustal contamination. The pressure-temperature paths estimated by clinopyroxene-liquid thermobarometry are similar in each lineage. The mafic magmas were emplaced at Moho depths ( 1.2 GPa) and the evolved magmas pooled at middle-crustal depths ( 0.7 GPa). Mass-balance calculations based on whole-rock and mineral compositions show that kaersutite fractionation has played a major role in magma differentiation of the sodic lineage whereas the compositional variations of the potassic lineage can be ascribed to fractionation of a kaersutite-free mineral assemblage and a maximum of 17% crustal assimilation.

A new method for automatic discontinuity traces sampling on rock mass 3D model

NASA Astrophysics Data System (ADS)

Umili, G.; Ferrero, A.; Einstein, H. H.

2013-02-01

A new automatic method for discontinuity traces mapping and sampling on a rock mass digital model is described in this work. The implemented procedure allows one to automatically identify discontinuity traces on a Digital Surface Model: traces are detected directly as surface breaklines, by means of maximum and minimum principal curvature values of the vertices that constitute the model surface. Color influence and user errors, that usually characterize the trace mapping on images, are eliminated. Also trace sampling procedures based on circular windows and circular scanlines have been implemented: they are used to infer trace data and to calculate values of mean trace length, expected discontinuity diameter and intensity of rock discontinuities. The method is tested on a case study: results obtained applying the automatic procedure on the DSM of a rock face are compared to those obtained performing a manual sampling on the orthophotograph of the same rock face.

Trace-element patterns of fibrous and monocrystalline diamonds: Insights into mantle fluids

NASA Astrophysics Data System (ADS)

Rege, S.; Griffin, W. L.; Pearson, N. J.; Araujo, D.; Zedgenizov, D.; O'Reilly, S. Y.

2010-08-01

During their growth diamonds may trap micron-scale inclusions of the fluids from which they grew, and these "time capsules" provide insights into the metasomatic processes that have modified the subcontinental lithospheric mantle. LAM-ICPMS analysis of trace elements in > 500 fibrous and monocrystalline diamonds worldwide has been used to understand the nature of these fluids. Analyses of fibrous diamonds define two general types of pattern, a "fibrous-high" (FH) one with high contents of LREE, Ba and K, and a "fibrous-low" (FL) pattern characterized by depletion in LREE/MREE, Ba and K, negative anomalies in Sr and Y, and subchondritic Zr/Hf and Nb/Ta. Both types may be found in fibrous diamonds from single deposits, and in three Yakutian pipes some diamonds show abrupt transitions from inclusion-rich cores with FH patterns to clearer rims with FL patterns. Most monocrystalline diamonds show FL-type patterns, but some have patterns that resemble those of FH fibrous diamonds. Peridotitic and eclogitic monocrystalline diamonds may show either patterns with relatively flat REE, or patterns with more strongly depleted LREE. Kimberlites that contain peridotitic diamonds with "high" patterns also contain eclogitic diamonds with "high" patterns. Strong similarities in the patterns of these two groups of diamonds may suggest high fluid/rock ratios. Many diamonds of the "superdeep" paragenesis have trace-element patterns similar to those of other monocrystalline diamonds. This may be evidence that the trace-element compositions of deep-seated fluids are generally similar to those that form diamonds in the subcontinental lithospheric mantle. The element fractionations observed between the FH and FL patterns are consistent with the immiscible separation of a silicic fluid from a carbonatite-silicate fluid, leaving a residual carbonatitic fluid strongly enriched in LREE, Ba and alkalies. This model would suggest that most monocrystalline diamonds crystallized from the more silicic fraction. Comparison with studies of single fluid inclusions in fibrous diamonds suggests that the FH patterns reflect trapped inclusions of high-Mg and low-Mg carbonatitic high-density fluids. In terms of the rock-forming elements, the fluids that precipitated the rims of some fibrous diamonds (FL pattern) and most monocrystalline diamonds are broadly similar to some hydro-silicic high-density fluids found in fibrous diamonds. However, there are still significant differences between the trace-element patterns of most monocrystalline diamonds and known high-density fluids, and further research is required to understand the formation and growth of these diamonds.

Implications of Late Cretaceous U-Pb zircon ages of granitic intrusions cutting ophiolitic and volcanogenic rocks for the assembly of the Tauride allochthon in SE Anatolia (Helete area, Kahramanmaraş Region, SE Turkey)

NASA Astrophysics Data System (ADS)

Nurlu, Nusret; Parlak, Osman; Robertson, Alastair; von Quadt, Albrecht

2016-01-01

An assemblage of NE-SW-trending, imbricate thrust slices (c. 26 km E-W long × 6.3 km N-S) of granitic rocks, basic-felsic volcanogenic rocks (Helete volcanics), ophiolitic rocks (Meydan ophiolite) and melange (Meydan melange) is exposed near the Tauride thrust front in SE Anatolia. The volcanogenic rocks were previously assumed to be Eocene because of associated Nummulitic limestones. However, ion probe U-Pb dating of zircons extracted from the intrusive granitic rocks yielded ages of 92.9 ± 2.2-83.1 ± 1.5 Ma (Cenomanian-Campanian). The Helete volcanic unit and the overlying Meydan ophiolitic rocks both are intruded by granitic rocks of similar age and composition. Structurally underlying ophiolite-related melange includes similar-aged, but fragmented granitic intrusions. Major, trace element and rare earth element analyses coupled with electron microprobe analysis of the granitic rocks show that they are metaluminus to peraluminus and calc-alkaline in composition. A magmatic arc setting is inferred from a combination of tectonomagmatic discrimination, ocean ridge granite-normalized multi-element patterns and biotite geochemistry. Sr-Nd-Pb isotope data further suggest that the granitoid rocks were derived from variably mixed mantle and crustal sources. Granitic rocks cutting the intrusive rocks are inferred to have crystallized at ~5-16 km depth. The volcanogenic rocks and granitic rocks originated in a supra-subduction zone setting that was widely developed throughout SE Anatolia. Initial tectonic assembly took place during the Late Cretaceous probably related to northward subduction and accretion beneath the Tauride continent (Keban and Malatya platforms). Initial tectonic assembly was followed by exhumation and then transgression by shelf-depth Nummulitic limestones during Mid-Eocene, as documented in several key outcrops. Final emplacement onto the Arabian continental margin took place during the Early Miocene.

The Mesozoic metamorphic-magmatic events in the Medog area, the Eastern Himalayan Syntaxis: constraints from zircon U-Pb geochronology, trace elements and Hf isotope compositions in granitoids

NASA Astrophysics Data System (ADS)

Dong, Hanwen; Xu, Zhiqin; Li, Yuan; Liu, Zhao; Li, Huaqi

2015-01-01

Based on the regional geological mapping, several granitoid intrusions had been discovered in the Eastern Himalayan Syntaxis (EHS). In order to constrain their petrogenesis and discuss their relations with the regional tectonics, we carried out U-Pb dating, trace elements and Hf isotope geochemistry studies on zircons separated from the granitoid rocks, in the area of the EHS. In this contribution, the granitoid rocks are mainly composed of diorites (X20-1-6) and granitic gneissic rocks (X2-15-1). The U-Pb zircon dating of diorites yields a crystallization age of 193.8 ± 2.0 Ma. These zircon have ɛ Hf( t) values ranging from -6.48 to -0.05, indicating an involvement of ancient crustal materials in the generation of these igneous rocks. The zircons from the Medog granitic gneissic rock commonly show zoning structures. The REE patterns and abundances of the inherited cores are different from those of the oscillatory rims. The LA-ICP-MS U-Pb zircon in situ analyses indicate that: (1) the zircon cores give multi-stage magmatic event ages ranging from 516 to 1,826 Ma, of which six ages are converged on 1,330-911 Ma, it is considered that the migmatitic gneiss has been formed in this time, and (2) while the zircon rims yield 206Pb/238U weighted mean ages of 217.4 ± 3.0 Ma (MSWD = 3.2), which was interpreted to represent the ages of the Triassic anatexis. Their ɛ Hf( t) values range from -18.98 to -8.36 and -14.22 to 8.72, respectively. The timing of the anatexis in the Medog area is coeval with the widespread metamorphism in Lhasa terrane.

Chemistry of Diogenites and Evolution of their Parent Asteroid

NASA Technical Reports Server (NTRS)

Mittlefehldt, D.W.; Beck, A.W.; McSween, H.Y.; Lee, C-T A.

2009-01-01

Diogenites are orthopyroxenite meteorites [1]. Most are breccias, but remnant textures indicate they were originally coarse-grained rocks, with grain sizes of order of cm. Their petrography, and major and trace element chemistry support an origin as crustal cumulates from a differentiated asteroid. Diogenites are genetically related to the basaltic and cumulate-gabbro eucrites, and the polymict breccias known as howardites, collectively, the HED suite. Spectroscopic observations, orbit data and dynamical arguments strongly support the hypothesis that asteroid 4 Vesta is the parent object for HED meteorites [2]. Here we discuss our new trace element data for a suite of diogenites and integrate these into the body of literature data. We use the combined data set to discuss the petrologic evolution of diogenites and 4 Vesta.

Chemical interactions in the subduction factory: New insights from an in situ trace element and hydrogen study of the Ichinomegata and Oki-Dogo mantle xenoliths (Japan)

NASA Astrophysics Data System (ADS)

Satsukawa, Takako; Godard, Marguerite; Demouchy, Sylvie; Michibayashi, Katsuyoshi; Ildefonse, Benoit

2017-07-01

The uppermost mantle in back arc regions is the site of complex interactions between partial melting, melt percolation, and fluid migration. To constrain these interactions and evaluate their consequences on geochemical cycles, we carried out an in situ trace element and water study of a suite of spinel peridotite xenoliths from two regions of the Japan back arc system, Ichinomegata (NE Japan) and Oki-Dogo (SW Japan), using LA-ICPMS and FTIR spectrometry, respectively. This study provides the first full dataset of trace element and hydrogen compositions in peridotites including analyses of all their main constitutive silicate minerals: olivine, orthopyroxene and clinopyroxene. The Ichinomegata peridotites sample a LREE-depleted refractory mantle (Mg# olivine = 0.90; Cr# spinel = 0.07-0.23; Yb clinopyroxene = 7.8-13.3 × C1-chondrite, and La/Yb clinopyroxene = 0.003-0.086 × C1-chondrite), characterized by Th-U positive anomalies and constant values of Nb/Ta. The composition of the studied Ichinomegata samples is consistent with that of an oceanic mantle lithosphere affected by cryptic metasomatic interactions with hydrous/aqueous fluids (crypto-hydrous metasomatism). In contrast, the Oki-Dogo peridotites have low Mg# olivine (0.86-0.93) and a broad range of compositions with clinopyroxene showing "spoon-shaped" to flat, and LREE-enriched patterns. They are also characterized by their homogeneous compositions in the most incompatible LILE (e.g., Rb clinopyroxene = 0.01-0.05 × primitive mantle) and HFSE (e.g., Nb clinopyroxene = 0.01-2.16 × primitive mantle). This characteristic is interpreted as resulting from various degrees of melting and extensive melt-rock interactions. FTIR spectroscopy shows that olivine in both Ichinomegata and Oki-Dogo samples has low water contents ranging from 2 to 7 ppm wt. H2O. In contrast, the water contents of pyroxenes from Ichinomegata peridotites (113-271 ppm wt. H2O for orthopyroxene, and 292-347 ppm wt. H2O for clinopyroxene) are significantly higher than in Oki-Dogo peridotites (9-35 ppm wt. H2O for orthopyroxene, and 15-98 ppm wt. H2O for clinopyroxene). This indicates a relationship between melt-rock interaction and water concentrations in pyroxenes. Our study suggests that the water content of the Japan mantle wedge is controlled by the late melt/fluid/rock interactions evidenced by trace element geochemistry: a mechanism triggered by magma-rock interactions may have acted as an efficient dehydrating process in the Oki-Dogo region while the Ichinomegata mantle water content is controlled by slab-derived crypto-hydrous metasomatism.

Chemical and Sr isotopic characterization of North America uranium ores: Nuclear forensic applications

DOE PAGES

Balboni, Enrica; Jones, Nina; Spano, Tyler; ...

2016-08-31

This study reports major, minor, and trace element data and Sr isotope ratios for 11 uranium ore (uraninite, UO 2+x) samples and one processed uranium ore concentrate (UOC) from various U.S. deposits. The uraninite investigated represent ores formed via different modes of mineralization (e.g., high- and low-temperature) and within various geological contexts, which include magmatic pegmatites, metamorphic rocks, sandstone-hosted, and roll front deposits. In situ trace element data obtained by laser ablation-ICP-MS and bulk sample Sr isotopic ratios for uraninite samples investigated here indicate distinct signatures that are highly dependent on the mode of mineralization and host rock geology. Relativemore » to their high-temperature counterparts, low-temperature uranium ores record high U/Th ratios (>1000), low total rare earth element (REE) abundances (<1 wt%), high contents (>300 ppm) of first row transition metals (Sc, Ti, V, Cr, Mn, Co, Ni), and radiogenic 87Sr/ 86Sr ratios (>0.7200). Comparison of chondrite normalized REE patterns between uraninite and corresponding processed UOC from the same locality indicates identical patterns at different absolute concentrations. Lastly, this result ultimately confirms the importance of establishing geochemical signatures of raw, uranium ore materials for attribution purposes in the forensic analysis of intercepted nuclear materials.« less

Chemical and Sr isotopic characterization of North America uranium ores: Nuclear forensic applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balboni, Enrica; Jones, Nina; Spano, Tyler

This study reports major, minor, and trace element data and Sr isotope ratios for 11 uranium ore (uraninite, UO 2+x) samples and one processed uranium ore concentrate (UOC) from various U.S. deposits. The uraninite investigated represent ores formed via different modes of mineralization (e.g., high- and low-temperature) and within various geological contexts, which include magmatic pegmatites, metamorphic rocks, sandstone-hosted, and roll front deposits. In situ trace element data obtained by laser ablation-ICP-MS and bulk sample Sr isotopic ratios for uraninite samples investigated here indicate distinct signatures that are highly dependent on the mode of mineralization and host rock geology. Relativemore » to their high-temperature counterparts, low-temperature uranium ores record high U/Th ratios (>1000), low total rare earth element (REE) abundances (<1 wt%), high contents (>300 ppm) of first row transition metals (Sc, Ti, V, Cr, Mn, Co, Ni), and radiogenic 87Sr/ 86Sr ratios (>0.7200). Comparison of chondrite normalized REE patterns between uraninite and corresponding processed UOC from the same locality indicates identical patterns at different absolute concentrations. Lastly, this result ultimately confirms the importance of establishing geochemical signatures of raw, uranium ore materials for attribution purposes in the forensic analysis of intercepted nuclear materials.« less

Origin, speciation, and fluxes of trace-element gases at Augustine volcano, Alaska: Insights into magma degassing and fumarolic processes

NASA Astrophysics Data System (ADS)

Symonds, Robert B.; Reed, Mark H.; Rose, William I.

1992-02-01

Thermochemical modeling predicts that trace elements in the Augustine gas are transported from near-surface magma as simple chloride (NaCl, KCl, FeCl 2, ZnCl 2, PbCl 2, CuCl, SbCl 3, LiCl, MnCl 2, NiCl 2, BiCl, SrCl 2), oxychloride (MoO 2Cl 2), sulfide (AsS), and elemental (Cd) gas species. However, Si, Ca, Al, Mg, Ti, V, and Cr are actually more concentrated in solids, beta-quartz (SiO 2), wollastonite (CaSiO 3), anorthite (CaAl 2Si 2O 8), diopside (CaMgSi 2O 6), sphene (CaTiSiO 5), V 2O 3(c), and Cr 2O 3(c), respectively, than in their most abundant gaseous species, SiF 4, CaCl 2, AlF 2O, MgCl 2 TiCl 4, VOCl 3, and CrO 2Cl 2. These computed solids are not degassing products, but reflect contaminants in our gas condensates or possible problems with our modeling due to "missing" gas species in the thermochemical data base. Using the calculated distribution of gas species and the COSPEC SO 2 fluxes, we have estimated the emission rates for many species (e.g., COS, NaCl, KCl, HBr, AsS, CuCl). Such forecasts could be useful to evaluate the effects of these trace species on atmospheric chemistry. Because of the high volatility of metal chlorides (e.g., FeCl 2, NaCl, KCl, MnCl 2, CuCl), the extremely HCl-rich Augustine volcanic gases are favorable for transporting metals from magma. Thermochemical modeling shows that equilibrium degassing of magma near 870°C can account for the concentrations of Fe, Na, K, Mn, Cu, Ni and part of the Mg in the gases escaping from the dome fumaroles on the 1986 lava dome. These calculations also explain why gases escaping from the lower temperature but highly oxidized moat vents on the 1976 lava dome should transport less Fe, Na, K, Mn and Ni, but more Cu; oxidation may also account for the larger concentrations of Zn and Mo in the moat gases. Nonvolatile elements (e.g., Al, Ca, Ti, Si) in the gas condensates came from eroded rock particles that dissolved in our samples or, for Si, from contamination from the silica sampling tube. Only a very small amount of rock contamination occurred (water/rock ratios between 10 4 and 10 6). Erosion is more prevalent in the pyroclastic flow fumaroles than in the summit vents, reflecting physical differences in the fumarole walls: ash vs. lava. Trace element contents of volcanic gases show enormous variability because of differences in the intensive parameters of degassing magma and variable amounts of wall rock erosion in volcanic fumaroles.

Constraints on the magmatic evolution of the oceanic crust from plagiogranite intrusions in the Oman ophiolite

NASA Astrophysics Data System (ADS)

Haase, Karsten M.; Freund, Sarah; Beier, Christoph; Koepke, Jürgen; Erdmann, Martin; Hauff, Folkmar

2016-05-01

We present major and trace element as well as Sr, Nd, and Hf isotope data on a suite of 87 plutonic rock samples from 27 felsic crustal intrusions in seven blocks of the Oman ophiolite. The rock compositions of the sample suite including associated more mafic rocks range from 48 to 79 wt% SiO2, i.e. from gabbros to tonalites. The samples are grouped into a Ti-rich and relatively light rare earth element (LREE)-enriched P1 group [(Ce/Yb) N > 0.7] resembling the early V1 lavas, and a Ti-poor and LREE-depleted P2 group [(Ce/Yb) N < 0.7] resembling the late-stage V2 lavas. Based on the geochemical differences and in agreement with previous structural and petrographic models, we define phase 1 (P1) and phase 2 (P2) plutonic rocks. Felsic magmas in both groups formed by extensive fractional crystallization of olivine, clinopyroxene, plagioclase, apatite, and Ti-magnetite from mafic melts. The incompatible element compositions of P1 rocks overlap with those from mid-ocean ridges but have higher Ba/Nb and Th/Nb trending towards the P2 rock compositions and indicating an influence of a subducting slab. The P2 rocks formed from a more depleted mantle source but show a more pronounced slab signature. These rocks also occur in the southern blocks (with the exception of the Tayin block) of the Oman ophiolite implying that the entire ophiolite formed above a subducting slab. Initial Nd and Hf isotope compositions suggest an Indian-MORB-type mantle source for the Oman ophiolite magmas. Isotope compositions and high Th/Nb in some P2 rocks indicate mixing of a melt from subducted sediment into this mantle.

Fluorine, fluorite, and fluorspar in central Colorado

USGS Publications Warehouse

Wallace, Alan R.

2010-01-01

Fluorine (F) is a widespread element that was deposited in a variety of rocks, minerals, and geologic environments in central Colorado. It occurs as a trace element, as a major component of the mineral fluorite (CaFs), and as a major economic source of fluorine in fluorspar deposits, which are massive concentrations of fluorite. This study has compiled available geochemical analyses of rocks, both unmineralized and mineralized, to determine the distribution of fluorine in specific age-lithologic categories, ranging from 1.8-giga-annum (Ga) metamorphic rocks to modern soils, throughout central Colorado. It also draws upon field studies of fluorine-rich mineral deposits, including fluorspar deposits, to decipher the nearly two-billion-year-long geologic history of fluorine in the study area, with implications for mineral-resource evaluations and exploration. The resulting compilation provides an important inventory of the naturally occurring levels and sources of fluorine that ultimately weather, erode, and become part of surface waters that are used for domestic water supplies in densely populated areas along the Colorado Front Range. Most commonly, fluorine is a trace element in virtually all rocks in the region. In the 3,798 unmineralized rocks that were analyzed for fluorine in the study area, the average fluorine content was 1,550 parts per million (ppm). The median was 640 ppm, nearly identical to the average crustal abundance of 650 ppm, and some high-fluorine rocks in the Pikes Peak area skewed the average to a value much greater than the median. Most unmineralized age-lithologic rock suites, including Proterozoic metamorphic rocks, 1.7- and 1.4-Ga granitic batholiths, Cambrian igneous rocks, Phanerozoic sedimentary rocks, and Laramide and Tertiary igneous rocks, had median fluorine values of 400 to 740 ppm fluorine. In all suites, however, a small number of analyzed samples contained more than 1 percent (10,000 ppm) fluorine. The 1.1-Ga plutonic rocks related to the Pikes Peak batholith had a mean fluorine content of 1,700 ppm, and primary magmatic fluorite and fluorite-bearing pegmatites are common throughout that igneous mass. Fluorine was deposited in many types of economic mineral deposits in central Colorado, and it currently is a significant trace element in some thermal springs. In the fluorspar deposits, fluorine contents were as high as 37 percent. Some fluorine-rich porphyry systems, such as Jamestown, had fluorine values that ranged from 200 ppm to nearly 37 percent fluorine, and veins in other deposits contained hydrothermal fluorite, although it was not ubiquitous. For the 495 samples from non-fluorspar mining districts (and excluding Jamestown), however, the median fluorine content was 990 ppm. This is above the crustal average but still relatively modest compared to the fluorspar deposits, and it indicates that the majority of the mineralizing systems in central Colorado did not deposit large amounts of fluorine. Nevertheless, the fluorine- and fluorite-rich mineral deposits could be used as guides for the evaluation and discovery of related but concealed porphyry and epithermal base- and precious-metal deposits. The Cenozoic geologic history of central Colorado included multiple periods during which fluorine-bearing rocks and mineral deposits were exposed, weathered, and eroded. This protracted history has released fluorine into soils and regoliths, and modern rainfall and snowmelt interact with these substrates to add fluorine to the hydrosphere. This study did not evaluate the fluorine contents of water or make any predictions about what areas might be major sources for dissolved fluorine. However, the abundant data that are available on fluorine in surface water and ground water can be coupled with the results of this study to provide additional insight into natural sources of fluorine in domestic drinking water.

U–Pb, Rb–Sr, and U-series isotope geochemistry of rocks and fracture minerals from the Chalk River Laboratories site, Grenville Province, Ontario, Canada

USGS Publications Warehouse

Neymark, Leonid; Peterman, Zell E.; Moscati, Richard J.; Thivierge, R. H.

2013-01-01

As part of the Geologic Waste Management Facility feasibility study, Atomic Energy of Canada Ltd. (AECL) is evaluating the suitability of the Chalk River Laboratories (CRL) site in Ontario, situated in crystalline rock of the southwestern Grenville Province, for the possible development of an underground repository for low- and intermediate-level nuclear waste. This paper presents petrographic and trace element analyses, U–Pb zircon dating results, and Rb–Sr, U–Pb and U-series isotopic analyses of gneissic drill core samples from the deep CRG-series characterization boreholes at the CRL site. The main rock types intersected in the boreholes include hornblende–biotite (±pyroxene) gneisses of granitic to granodioritic composition, leucocratic granitic gneisses with sparse mafic minerals, and garnet-bearing gneisses with variable amounts of biotite and/or hornblende. The trace element data for whole-rock samples plot in the fields of within-plate, syn-collision, and volcanic arc-type granites in discrimination diagrams used for the tectonic interpretation of granitic rocks.Zircons separated from biotite gneiss and metagranite samples yielded SHRIMP-RG U–Pb ages of 1472 ± 14 (2σ) and 1045 ± 6 Ma, respectively, in very good agreement with widespread Early Mesoproterozoic plutonic ages and Ottawan orogeny ages in the Central Gneiss Belt. The Rb–Sr, U–Pb, and Pb–Pb whole-rock errorchron apparent ages of most of the CRL gneiss samples are consistent with zircon U–Pb age and do not indicate substantial large-scale preferential element mobility during superimposed metamorphic and water/rock interaction processes. This may confirm the integrity of the rock mass, which is a positive attribute for a potential nuclear waste repository. Most 234U/238U activity ratios (AR) in whole rock samples are within errors of the secular equilibrium value of one, indicating that the rocks have not experienced any appreciable U loss or gain within the past 1 Ma. However, 234U/238U AR in fracture mineral samples collected down to borehole lengths of about 740 m deviate from the secular equilibrium value and 234U/238U model ages calculated for fracture mineral samples showing excess 234U range from 593 to 1415 ka, thus providing evidence of fracture flow in the associated bedrock during the past 1.5 Ma. Rare earth element patterns are variable in fracture-filling calcites and Fe oxides/hydroxides but are similar to those observed in associated whole-rock samples. The observed Ce anomalies are very small (CeN/CeN∗≈1">CeN/CeN∗≈1), do not vary with depth, and, therefore, do not contain evidence that the studied fracture minerals precipitated from oxidizing waters at the conceptual depth of a repository.

Developing a trace element biosignature for modern and ancient (and extraterrestrial?) microbial life

NASA Astrophysics Data System (ADS)

Gangidine, A.; Czaja, A. D.; Havig, J. R.

2017-12-01

Positively identifying fossil microorganisms is often a challenge due to poor preservation. Thermal and geological alteration can lead to extreme distortion in ancient microbial fossils to the point that they may be morphologically unrecognizable, making it crucial to have a biosignature that can be used regardless of such conditions to help establish biogenicity. Through analysis of trace element sequestration by silicified microorganisms of various ages, a new biosignature may be developed with the potential to be robust and yield paleobiological information, even in the absence of morphological preservation. Biological materials preserved in modern silica-depositing hot springs from Yellowstone National Park have been shown to contain a higher concentration of certain trace elements relative to the surrounding non-biological material. BIO-SIMS analyses also have shown apparent co-localization of certain trace elements relative to recently silicified microbes (Figure 1). By measuring the abundances, ratios, and spatial distributions of major and trace elements (e.g., Si, C, N, Fe, Mn, Ga, As) in modern and ancient microorganisms, it will be possible to deduce what elements are preferentially concentrated by life, and if this signature is preserved in the rock record during and after the fossilization process. By evaluating trace element abundances and distributions in a suite of hot spring deposit samples of ages ranging from modern (Yellowstone National Park) to 3.5 Ga (Dresser Formation), this biosignature may be calibrated across all timescales. Such a biosignature would provide a strong tool for determining biogenicity by itself, or strengthen any argument for or against biogenicity when used in unison with other detection methods. As hydrothermal silica deposits are thought to be widespread on the Martian surface, the use of this trace element biosignature for the upcoming Mars 2020 mission would allow a robust analysis to aid in the determination of the biogenicity of collected samples. For a mission such as Mars 2020, with a primary mission objective of finding ancient life, the burden of proof for identifying putative life will be unprecedented.

Geochemistry of ocean floor serpentinites world-wide: constraints on the ultramafic input to subduction zones

NASA Astrophysics Data System (ADS)

Kodolányi, J.; Pettke, T.; Spandler, C.; Kamber, B.; Gméling, K.

2009-04-01

Serpentinite can be a major component of the upper part of the oceanic lithosphere and is a significant H2O-contributor to subduction zones (Scambelluri et al. 2004). Serpentinite dehydration releases large amounts of water through a very limited number of discontinuous reactions and it is therefore expected to have the potential of leaving a trace element chemical fingerprint in overlying rocks (Ulmer and Trommsdorff 1995; Scambelluri et al. 2004; see also Pettke et al. 2009). We present major and trace element whole rock (XRF, ICP-MS and PGAA) and in-situ mineral (EPMA and LA-ICP-MS) analyses of serpentinized peridotites sampled on DSDP/ODP drilling cruises, in order to chemically characterize the hydrated ultramafic input of subduction zones. The studied 39 samples cover all major geodynamic settings where serpentinites occur on recent ocean floors (fast and slow spreading mid-ocean ridges, passive margins and supra-subduction zones). All rock samples consist of one or two serpentine (srp) polymorphs, brucite (brc), magnetite (mag), and relic high-temperature mantle minerals: olivine (ol), orthopyroxene (opx), clinopyroxene (cpx) and spinel (spl). Serpentine + brc replace ol, forming a mesh-like network around relic crystal fragments. Magnetite usually forms strings of individual crystals along the srp mesh-network. Very rare iowaite (a H2O and Cl-bearing Fe-Mg oxy-hydroxide) remnants were found around the ol core of mesh srp and in the srp ± brc replacements after ol mesh cores. Orthopyroxene alters to bastitic pseudomorphs which consist of srp rarely accompanied by brc. Associated mag is generally absent. The degree of ol and opx alteration is variable, i.e., there are samples in which opx is completely whereas ol is only partially altered and vice versa, which suggests variable temperatures of alteration (alteration rate of opx is higher than that of ol above ca. 350 °C; Martin and Fyfe 1970). Clinopyroxene and spl appear to be weakly altered in thoroughly serpentinized samples. Where present, carbonate (cab) forms veins or fills former srp ± brc pseudomorphs after ol or opx. Major, minor and trace element chemistry of the serpentinites generally reflects that of their ultramafic precursor (Mg-rich and Si-poor rocks with low trace element contents). With respect to certain elements, however, we detect significant serpentinization-related changes. Besides their high H2O-contents (8.7-17.2 wt. %), the hydrated harzburgites and lherzolites also display high B and Cl concentrations (8-177 μg/g and 1160-5920 μg/g, respectively) relative to depleted mantle values (0.06 and 0.51 ppm, respectively; Salters and Stracke 2004). Supra-subduction zone serpentinites contain 10 to 100 times more Cs (0.04-1.2 μg/g) and Rb (0.1-7.1 μg/g) than samples from mid-ocean ridges and passive margins (Cs: below 0.07 μg/g; Rb: 0.004-1.17 μg/g). We often observe 100 to 1000-fold enrichments in U, Pb, Sr and Li relative to elements of similar compatibility in the mantle. In-situ mineral analyses suggest that B and Cl reside in serpentine minerals. Cesium and Rb whole rock and mineral chemical data correlate well, too. If carbonates are not present, the Sr budget of serpentinites is largely controlled by serpentine minerals that take up 0.36 to 21 μg/g Sr, i.e., orders of magnitude more than concentrations of precursor ol and opx. Bastites tend to have (about 1.5-4 times) higher trace-element concentrations than mesh rims, suggesting that precursor mineralogy (e.g. harzburgites vs. dunites) and alteration temperature (Martin and Fyfe 1970) can affect serpentinite chemistry. Enrichments of U, Pb and Li may have multiple origins, i.e., may be only partly related to serpentinization and low-temperature carbonate addition. Our study shows that serpentinites from representative geodynamic settings have variable, but generally depleted chemical character, inherited from precursor mantle rocks. However, notably B and Cl are enriched, but not uniformly so and independent of geodynamic setting. Supra-subduction zone serpentinites reveal additional enrichments in Cs, Rb, ±Sr, identifying an alteration fluid source that is not pure seawater. In conclusion, precursor mineralogy and magmatic history together with hydration temperature govern the trace element budget of ocean floor serpentinites, which, apart from supplying H2O to the subduction zone, may also be a significant source of B and Cl to the arc magma source and, depending on geodynamic setting, may even influence the element budget for Cs, Rb, Pb, U and .Sr. References: Martin B, Fyfe WS (1970) Some experimental and theoretical observations on the kinetics of hydration reactions with particular reference to serpentinization. Chem Geol 6: 185-202 Pettke T, Spandler C, Kodolányi J, Scambelluri M (2009) The chemical signatures of progressive dehydration stages in subducted serpentinites (this volume) Salters VJM, Stracke A (2004) Composition of the depleted mantle. Geochem Geophys Geosyst 5 Doi: 10.1029/2003GC000597 Scambelluri M, Fiebig J, Malaspina N, Müntener O, Pettke T (2004) Serpentinite Subduction: Implications for Fluid Processes and Trace-Element Recycling. Int Geol Rev 46: 595-613 Ulmer P, Trommsdorff V (1995) Serpentine stability to mantle depths and subduction-related magmatism. Science 268: 858-861

Simultaneous determination of macronutrients, micronutrients and trace elements in mineral fertilizers by inductively coupled plasma optical emission spectrometry

NASA Astrophysics Data System (ADS)

de Oliveira Souza, Sidnei; da Costa, Silvânio Silvério Lopes; Santos, Dayane Melo; dos Santos Pinto, Jéssica; Garcia, Carlos Alexandre Borges; Alves, José do Patrocínio Hora; Araujo, Rennan Geovanny Oliveira

2014-06-01

An analytical method for simultaneous determination of macronutrients (Ca, Mg, Na and P), micronutrients (Cu, Fe, Mn and Zn) and trace elements (Al, As, Cd, Pb and V) in mineral fertilizers was optimized. Two-level full factorial design was applied to evaluate the optimal proportions of reagents used in the sample digestion on hot plate. A Doehlert design for two variables was used to evaluate the operating conditions of the inductively coupled plasma optical emission spectrometer in order to accomplish the simultaneous determination of the analyte concentrations. The limits of quantification (LOQs) ranged from 2.0 mg kg- 1 for Mn to 77.3 mg kg- 1 for P. The accuracy and precision of the proposed method were evaluated by analysis of standard reference materials (SRMs) of Western phosphate rock (NIST 694), Florida phosphate rock (NIST 120C) and Trace elements in multi-nutrient fertilizer (NIST 695), considered to be adequate for simultaneous determination. Twenty-one samples of mineral fertilizers collected in Sergipe State, Brazil, were analyzed. For all samples, the As, Ca, Cd and Pb concentrations were below the LOQ values of the analytical method. For As, Cd and Pb the obtained LOQ values were below the maximum limit allowed by the Brazilian Ministry of Agriculture, Livestock and Food Supply (Ministério da Agricultura, Pecuária e Abastecimento - MAPA). The optimized method presented good accuracy and was effectively applied to quantitative simultaneous determination of the analytes in mineral fertilizers by inductively coupled plasma optical emission spectrometry (ICP OES).

Selection of superior salt/boron tolerant Stanleya pinnata genotypes and quantification of their selenium phytoremediation abilities in drainage sediment.

USDA-ARS?s Scientific Manuscript database

The semi-metallic mineral Se, a naturally-occurring trace element, is primarily found as selenate originating from sedimentary and shale rock formations, e.g., in the western side of the San Joaquin Valley of central California (WSJV). Because selenate-Se is water soluble, bioavailable and biomagnif...

Publications - RDF 2016-2 | Alaska Division of Geological & Geophysical

Science.gov Websites

, Major-oxide and trace-element geochemistry of mafic rocks in the Carboniferous Lisburne Group, Ivishak Surveys Skip to content State of Alaska myAlaska My Government Resident Business in Alaska Visiting Alaska State Employees DGGS State of Alaska search Alaska Division of Geological & Geophysical

Extraordinary trace-element accumulations in roadside cedars near Centerville, Missouri

DOE Office of Scientific and Technical Information (OSTI.GOV)

Connor, J.J.; Shacklette, H.T.; Erdman, J.A.

1971-01-01

Unusually high concentrations of lead, copper, zinc, and cadmium were found in samples of cedar (Juniperus virginiana L.) collected on the roadside of State Highway 21-72 about 4 miles northeast of Centerville, Mo. For 15 samples, geometric mean concentrations for these elements in cedar ash were, in parts per million: Pb, 5,800; Cu, 190; An, 940; and Cd, 12. The high concentrations are thought to reflect vehicular transport of lead-bearing ores from mine to smelter, rather than mineralized rock at depth.

A Crystal Stratigraphy Approach to Deciphering the Petrogenesis of the Detroit Seamount

NASA Astrophysics Data System (ADS)

Simonetti, A.; Davenport, J.; Neal, C. R.

2012-12-01

The Detroit Seamount (DSM) erupted ~76-81 Ma ago, and is the northwestern terminus of the Hawaiian-Emperor Seamount chain. The Hawaiian-Emperor Seamount chain has drastically furthered our understanding of how and where mantle plumes originate, the dynamics of interactions between plumes and mantle, and plate movement in the recent past. DSM Basalts from Site 1203 of Leg 197 of the Ocean Drilling Program (ODP) contain, by rock volume, a large quantity of plagioclase and olivine phenocrysts. Previous investigations into magma chamber processes via phenocryst analysis such as those occurring at the DSM have largely relied solely on major and trace element analyses. However, since both are easily susceptible to post-solidification alteration processes, in this study we are undertaking a multi-faceted approach to deciphering the petrogenetic history of the DSM basalts via crystal stratigraphy, crystal size distributions (CSDs), electron microprobe analysis (EPMA), laser ablation and multi-collector inductively coupled plasma mass spectrometry (LA- and MC-ICP-MS), microdilling and phase separation, and isotope analysis of whole-rock, olivine and plagioclase phenocrysts and their associated melt inclusions. A preliminary Sr isotope and trace element investigation of DSM whole rock basalts from Site 884 yielded a range of values between 0.70262 and 0.70276, as well as MORB-like trace element patterns. Notably, the plagioclase rims analyzed possessed a more radiogenic (87Sr/86Sr)I than the core (0.70361 ± 2 vs. 0.70347 ± 2). Our initial interpretation of this radiogenic increase from core-to-rim was crystal growth in an OIB-rich magma source that was not cogenetic with its matrix. Eight olivine phenocrysts from DSM basalts were analyzed for major elements using scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) techniques. Fosterite contents of the olivine phenocrysts range from 84-86. Olivines from basalt sample 10R-4 exhibit a well-defined correlation between Ni and Mn contents, whereas those from sample 10R-3 show a more limited range of Mn and Ni compositions. The trends defined by the data from the olivine phenocrysts clearly suggest that fractional crystallization was not the sole magma differentiation process to have occurred. Rare earth element (REE) abundances for the olivine phenocrysts are low, and generally range from 0.1 to 2 ppm, with those from basalt sample 10R-4 containing higher abundances than sample 10R-3. Melt inclusions from within plagioclase phenocrysts in DSM basalt sample 9R-2 from Site 884 were analyzed via laser ablation-ICP-MS. Results from the analyses indicate that the melt inclusions are LREE-enriched and negatively-sloped compared to the LREE-depleted basalt whole rock compositions from the DSM and the East Pacific Rise. Of interest, the La concentrations in the melt inclusions are notably similar to abundances found for the Manua Kea tholeiites. Trace element data and Sr isotope ratios for both melt inclusions and phenocrysts from the DSM basalts are all indicative of open system behavior and possibly consistent with magma mixing between at least two end-member mantle components.

Early Cretaceous bimodal volcanic rocks in the southern Lhasa terrane, south Tibet: Age, petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Wang, Chao; Ding, Lin; Liu, Zhi-Chao; Zhang, Li-Yun; Yue, Ya-Hui

2017-01-01

Limited geochronological and geochemical data from Early Cretaceous igneous rocks of the Gangdese Belt have resulted in a dispute regarding the subduction history of Neo-Tethyan Ocean. To approach this issue, we performed detailed in-situ zircon U-Pb and Hf isotopic, whole-rock elemental and Sr-Nd isotopic analyses on Late Mesozoic volcanic rocks exposed in the Liqiongda area, southern Lhasa terrane. These volcanic rocks are calc-alkaline series, dominated by basalts, basaltic andesites, and subordinate rhyolites, with a bimodal suite. The LA-ICPMS zircon U-Pb dating results of the basaltic andesites and rhyolites indicate that these volcanic rocks erupted during the Early Cretaceous (137-130 Ma). The basaltic rocks are high-alumina (average > 17 wt.%), enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs), showing subduction-related characteristics. They display highly positive zircon εHf(t) values (+ 10.0 to + 16.3) and whole-rock εNd(t) values (+ 5.38 to + 7.47). The silicic suite is characterized by low Al2O3 (< 15.4 wt.%), Mg# (< 40), and TiO2 (< 0.3 wt.%) abundances; enriched and variable concentrations of LILEs and REEs; and strongly negative Eu anomalies (Eu/Eu* = 0.08-0.19), as well as depleted Hf isotopic compositions (εHf(t) = + 4.9 to + 16.4) and Nd isotopic compositions (εNd(t) = + 5.26 to + 6.71). Consequently, we envision a process of basaltic magmas similar to that of MORB extracted from a source metasomatized by slab-derived components for the petrogenesis of mafic rocks, whereas the subsequent mafic magma underplating triggered partial melting of the juvenile crust to generate acidic magma. Our results confirm the presence of Early Cretaceous volcanism in the southern Lhasa terrane. Combined with the distribution of the contemporary magmatism, deformation style, and sedimentary characteristics in the Lhasa terrane, we favor the suggestion that the Neo-Tethyan oceanic lithosphere was flat-lying beneath the Lhasa terrane during the Early Cretaceous. Appendix Table A2. LA-MC-ICPMS zircon Hf isotopes of volcanic rocks from Liqiongda area. Appendix Table A3. Whole-rock major, trace element and Sr-Nd isotope data of the volcanic rocks from the Liqiongda area.

Emission spectrographic determination of volatile trace elements in geologic materials by a carrier distillation technique

USGS Publications Warehouse

Barton, H.N.

1986-01-01

Trace levels of chalcophile elements that form volatile sulfide minerals are determined in stream sediments and in the nonmagnetic fraction of a heavy-mineral concentrate of stream sediments by a carrier distillation emission spectrographic method. Photographically recorded spectra of samples are visually compared with those of synthetic standards for the two sample types. Rock and soil samples may also be analyzed by comparison with the stream-sediment standards. A gallium oxide spectrochemical carrier/buffer enhances the early emission of the volatile elements. Detection limits in parts per million attained are: Sb 5, As 20, Bi 0.1, Cd 1, Cu 1, Pb 2, Ag 0.1, Zn 2, and Sn 0.1. A comparison with other methods of analysis, total-burn emission and atomic absorption spectroscopy, shows good correlation for standard reference for materials and samples from a variety of geologic terranes. ?? 1986.

Age and geochemistry of the Newania dolomite carbonatites, India: implications for the source of primary carbonatite magma

NASA Astrophysics Data System (ADS)

Ray, Jyotiranjan S.; Pande, Kanchan; Bhutani, Rajneesh; Shukla, Anil D.; Rai, Vinai K.; Kumar, Alok; Awasthi, Neeraj; Smitha, R. S.; Panda, Dipak K.

2013-12-01

The Newania carbonatite complex of India is one of the few dolomite-dominated carbonatites of the world. Intruding into Archean basement gneisses, the rocks of the complex have undergone limited diversification and are not associated with any alkaline silicate rock. Although the magmatic nature of the complex was generally accepted, its age of emplacement had remained equivocal because of the disturbed nature of radioisotope systems. Many questions about the nature of its mantle source and mode of origin had remained unanswered because of lack of geochemical and isotopic data. Here, we present results of our effort to date the complex using 147Sm-143Nd, 207Pb-206Pb and 40Ar-39Ar dating techniques. We also present mineral chemistry, major and trace element geochemistry and Sr-Nd isotopic ratio data for these carbonatites. Our age data reveal that the complex was emplaced at ~1,473 Ma and parts of it were affected by a thermal event at ~904 Ma. The older 207Pb-206Pb ages reported here (~2.4 Ga) and by one earlier study (~2.3 Ga; Schleicher et al. Chem Geol 140:261-273, 1997) are deemed to be a result of heterogeneous incorporation of crustal Pb during the post-emplacement thermal event. The thermal event had little effect on many magmatic signatures of these rocks, such as its dolomite-magnesite-ankerite-Cr-rich magnetite-magnesio-arfvedsonite-pyrochlore assemblage, mantle like δ13C and δ18O and typical carbonatitic trace element patterns. Newania carbonatites show fractional crystallization trend from high-Mg to high-Fe through high-Ca compositions. The least fractionated dolomite carbonatites of the complex possess very high Mg# (≥80) and have similar major element oxide contents as that of primary carbonatite melts experimentally produced from peridotitic sources. In addition, lower rare earth element (and higher Sr) contents than a typical calcio-carbonatite and mantle like Nb/Ta ratios indicate that the primary magma for the complex was a magnesio-carbonatite melt and that it was derived from a carbonate bearing mantle. The Sr-Nd isotopic data suggest that the primary magma originated from a metasomatized lithospheric mantle. Trace element modelling confirms such an inference and suggests that the source was a phlogopite bearing mantle, located within the garnet stability zone.

Origin of cratonic lithospheric mantle roots: A geochemical study of peridotites from the North Atlantic Craton, West Greenland

NASA Astrophysics Data System (ADS)

Wittig, N.; Pearson, D. G.; Webb, M.; Ottley, C. J.; Irvine, G. J.; Kopylova, M.; Jensen, S. M.; Nowell, G. M.

2008-09-01

A critical examination of the extent to which geodynamic information on the initial mantle depletion and accretion event(s) is preserved in kimberlite-borne cratonic SCLM peridotite xenoliths is attempted by using new major and trace element data of whole-rock peridotites ( n = 55) sampled across the North Atlantic Craton (NAC; West Greenland). We also present additional whole-rock trace element data of mantle xenoliths from Somerset Island, the Slave and Kaapvaal cratons for comparison. Peridotites comprising the West Greenland SCLM are distinctly more olivine-rich and orthopyroxene-poor than most other cratonic peridotites, in particular those from the Kaapvaal craton. The West Greenland peridotites have higher Mg/Si but lower Al/Si, Al 2O 3 and CaO than cratonic mantle from the Kaapvaal Craton. We suggest that the more orthopyroxene depleted, harzburgite to dunite character of the NAC peridotites reflects more of the original melting history than peridotites from other cratons and in that sense may be more typical of cratonic lithosphere compositions prior to extensive modification. Despite this, some modal and cryptic metasomatism has clearly taken place in the West Greenland lithosphere. The insensitivity of major elements to pressure of melting at high degrees of melt extraction combined with the ease with which these elements may be changed by modal metasomatism mean that we cannot confidently constrain the depth of melting of peridotites using this approach. Mildly incompatible trace elements offer much more promise in terms of providing geodynamic information about the original Archean melting regime. The very low, systematically varying heavy REE abundances in NAC whole-rock peridotites and in peridotites from all other cratons where high-quality data are available provide ubiquitous evidence for a shallow melting regime in the absence of, or to the exhaustion of garnet. This finding explicitly excludes large extents of deep (iso- and polybaric) melting, which results in high initial garnet abundances and increasing heavy REE abundances. This evidence renders models that invoke large plume-like melting environments redundant in explaining SCLM formation and suggests broadly modern plate tectonic environments are responsible for the depletion of cratonic SCLM. A combination of the shallow melting environment and uniformly high levels of depletion indicate that melting to form the NAC lithosphere and that of other cratons probably took place in a subduction-zone environment.

Optimisation of flame parameters for simultaneous multi-element atomic absorption spectrometric determination of trace elements in rocks

USGS Publications Warehouse

Kane, J.S.

1988-01-01

A study is described that identifies the optimum operating conditions for the accurate determination of Co, Cu, Mn, Ni, Pb, Zn, Ag, Bi and Cd using simultaneous multi-element atomic absorption spectrometry. Accuracy was measured in terms of the percentage recoveries of the analytes based on certified values in nine standard reference materials. In addition to identifying optimum operating conditions for accurate analysis, conditions resulting in serious matrix interferences and the magnitude of the interferences were determined. The listed elements can be measured with acceptable accuracy in a lean to stoicheiometric flame at measurement heights ???5-10 mm above the burner.

Peralkaline- and calc-alkaline-hosted volcanogenic massive sulfide deposits of the Bonnifield District, East-Central Alaska

USGS Publications Warehouse

Dusel-Bacon, Cynthia; Foley, Nora K.; Slack, John E.; Koenig, Alan E.; Oscarson, Robert L.

2012-01-01

Volcanogenic massive sulfide (VMS) Zn-Pb-Cu-Ag-Au deposits of the Bonnifield mining district formed during Late Devonian-Early Mississippian magmatism along the western edge of Laurentia. The largest deposits, Dry Creek and WTF, have a combined resource of 5.7 million tonnes at 10% Zn, 4% Pb, 0.3% Cu, 300 grams per tonne (g/t) Ag, and 1.6 g/t Au. These polymetallic deposits are hosted in high field strength element (HFSE)- and rare-earth element (REE)-rich peralkaline (pantelleritic) metarhyolite, and interlayered pyritic argillite and mudstone of the Mystic Creek Member of the Totatlanika Schist Formation. Mystic Creek metarhyolite and alkali basalt (Chute Creek Member) constitute a bimodal pair that formed in an extensional environment. A synvolcanic peralkaline quartz porphyry containing veins of fluorite, sphalerite, pyrite, and quartz intrudes the central footwall at Dry Creek. The Anderson Mountain deposit, located ~32 km to the southwest, occurs within calc-alkaline felsic to intermediate-composition metavolcanic rocks and associated graphitic argillite of the Wood River assemblage. Felsic metavolcanic rocks there have only slightly elevated HFSEs and REEs. The association of abundant graphitic and siliceous argillite with the felsic volcanic rocks together with low Cu contents in the Bonnifield deposits suggests classification as a siliciclastic-felsic type of VMS deposit. Bonnifield massive sulfides and host rocks were metamorphosed and deformed under greenschist-facies conditions in the Mesozoic. Primary depositional textures, generally uncommon, consist of framboids, framboidal aggregates, and spongy masses of pyrite. Sphalerite, the predominant base metal sulfide, encloses early pyrite framboids. Galena and chalcopyrite accompanied early pyrite formation but primarily formed late in the paragenetic sequence. Silver-rich tetrahedrite is a minor late phase at the Dry Creek deposit. Gold and Ag are present in low to moderate amounts in pyrite from all of the deposits; electrum inclusions occur in Dry Creek sphalerite. Contents and ratios of trace elements in graphitic argillite that serve as proxies for the redox state of the bottom waters in the basin indicate that Dry Creek mineralization took place in suboxic to periodically anoxic bottom waters. Trace element data show higher contents of Tl-Mn-As in pyrite from the Anderson Mountain deposit compared to the Dry Creek or WTF deposits and thus suggest that Anderson Mountain may have formed at lower temperatures or under slightly more oxidizing conditions. No exact modern analogue for the tectonic setting of the Bonnifield VMS deposits is known, although the back-arc regions of the Okinawa Trough and Woodlark Basin satisfy the requirement for a submarine, extensional setting adjacent to a continental margin. Limited occurrences of peralkaline volcanic rocks occur in these two potential analogues, but the peralkalinity of those rocks is much less than that of the Mystic Creek Member metarhyolites in the Bonnifield district. The highly elevated trace element (e.g., Zr, Nb) contents of Mystic Creek metarhyolites suggest that a better analogue may be a submarine rifted continental margin. The calc-alkaline composition of the host rocks to the Anderson Mountain deposit suggests that mineralization there formed in a continental margin arc, outboard of the extended continental margin setting of the peralkaline-hosted Dry Creek and WTF deposits.

Rock weathering by indigenous heterotrophic bacteria of Bacillus spp. at different temperature: a laboratory experiment

NASA Astrophysics Data System (ADS)

Štyriaková, I.; Štyriak, I.; Oberhänsli, H.

2012-07-01

The bio-weathering of basalt, granite and gneiss was experimentally investigated in this study. These rock-forming minerals weathered more rapidly via the ubiquitous psychrotrophic heterotrophic bacteria . With indigenous bacteria of Bacillus spp. from sediments of Lake Baikal, we traced the degradation process of silicate minerals to understand the weathering processes occurring at the change temperature in the subsurface environment with organic input. The bacteria mediated dissolution of minerals was monitored with solution and solid chemistry, X-ray analyses as well as microscopic techniques. We determined the impact of the bacteria on the mineral surface and leaching of K, Ca, Mg, Si, Fe, and Al from silicate minerals. In the samples the release of major structural elements of silicates was used as an overall indicator of silicate mineral degradation at 4°C and 18°C from five medium exchanges over 255 days of rock bioleaching. The increase of temperature importantly affected the efficiency of Fe extraction from granite and basalt as well as Si extraction from granite and gneiss. In comparison with elemental extraction order at 4°C, Ca was substituted first by Fe or Si. It is evident that temperature influences rock microbial weathering and results in a change of elements extraction.

Bernard J. Wood Receives 2013 Harry H. Hess Medal: Citation

NASA Astrophysics Data System (ADS)

Hofmann, Albrecht W.

2014-01-01

As Harry Hess recognized over 50 years ago, mantle melting is the fundamental motor for planetary evolution and differentiation. Melting generates the major divisions of crust mantle and core. The distribution of chemical elements between solids, melts, and gaseous phases is fundamental to understanding these differentiation processes. Bernie Wood, together with Jon Blundy, has combined experimental petrology and physicochemical theory to revolutionize the understanding of the distribution of trace elements between melts and solids in the Earth. Knowledge of these distribution laws allows the reconstruction of the source compositions of the melts (deep in Earth's interior) from their abundances in volcanic rocks. Bernie's theoretical treatment relates the elastic strain of the lattice caused by the substitution of a trace element in a crystal to the ionic radius and charge of this element. This theory, and its experimental calibrations, brought order to a literature of badly scattered, rather chaotic experimental data that allowed no satisfactory quantitative modeling of melting processes in the mantle.

Isotopic and trace element geochemistry of the Seligdar magnesiocarbonatites (South Yakutia, Russia): Insights regarding the mantle evolution beneath the Aldan-Stanovoy shield

NASA Astrophysics Data System (ADS)

Doroshkevich, Anna G.; Prokopyev, Ilya R.; Izokh, Andrey E.; Klemd, Reiner; Ponomarchuk, Anton V.; Nikolaeva, Irina V.; Vladykin, Nikolay V.

2018-04-01

The Paleoproterozoic Seligdar magnesiocarbonatite intrusion of the Aldan-Stanovoy shield in Russia underwent extensive postmagmatic hydrothermal alteration and metamorphic events. This study comprises new isotopic (Sr, Nd, C and O) data, whole-rock major and trace element compositions and trace element characteristics of the major minerals to gain a better understanding of the source and the formation process of the carbonatites. The Seligdar carbonatites have high concentrations of P2O5 (up to 18 wt%) and low concentrations of Na, K, Sr and Ba. The chondrite-normalized REE patterns of these carbonatites display significant enrichments of LREE relative to HREE with an average La/Ybcn ratio of 95. Hydrothermal and metamorphic overprints changed the trace element characteristics of the carbonatites and their minerals. These alteration processes were responsible for Sr loss and the shifting of the Sr isotopic compositions towards more radiogenic values. The altered carbonatites are further characterized by distinct 18O- and 13C-enrichments compared to the primary igneous carbonatites. The alteration most likely resulted from both the percolation of crustal-derived hydrothermal fluids and subsequent metamorphic processes accompanied by interaction with limestone-derived CO2. The narrow range of negative εNd(T) values indicates that the Seligdar carbonatites are dominated by a homogenous enriched mantle source component that was separated from the depleted mantle during the Archean.

Diatremes of the Hopi Buttes, Arizona; chemical and statistical analyses

USGS Publications Warehouse

Wenrich, K.J.; Mascarenas, J.F.

1982-01-01

Lacustrine sediments deposited in maar lakes of the Hopi Buttes diatremes are hosts for uranium mineralization of as much as 1500 ppm. The monchiquites and limburgite turfs erupted from the diatremes are distinguished from normal alkalic basalts of the Colorado Plateau by their extreme silica undersaturation and high water, TiO2, and P2O5 contents. Many trace elements are also unusually abundant, including Ag, As, Ba, Be, Ce, Dy, Eu, F, Gd, Hf, La, Nd, Pb, Rb, Se, Sm, Sn, Sr, Ta, Tb, Th, U, V, Zn, and Zr. The lacustrine sediments, which consist predominantly of travertine and clastic rocks, are the hosts for syngenetic and epigenetic uranium mineralization of as much as 1500 ppm uranium. Fission track maps show the uranium to be disseminated within the travertine and clastic rocks, and although microprobe analyses have not, as yet, revealed discrete uranium-bearing phases, the clastic rocks show a correlation of high Fe, Ti, and P with areas of high U. Correlation coefficients show that for the travertines, clastics, and limburgite ruffs, Mo, As, Sr, Co, and V appear to have the most consistent and strongest correlations with uranium. Many elements, including many of the rare-earth elements, that are high in these three rocks are also high in the monchiquites, as compared to the average crustal abundance for the respective rock type. This similar suite of anomalous elements, which includes such immobile elements as the rare earths, suggests that Fluids which deposited the travertines were related to the monchiquitic magma. The similar age of about 5 m.y. for both the lake beds and the monchiquites also appears to support this source for the mineralizing fluids.

Apatite in carbonatitic rocks: Compositional variation, zoning, element partitioning and petrogenetic significance

NASA Astrophysics Data System (ADS)

Chakhmouradian, Anton R.; Reguir, Ekaterina P.; Zaitsev, Anatoly N.; Couëslan, Christopher; Xu, Cheng; Kynický, Jindřich; Mumin, A. Hamid; Yang, Panseok

2017-03-01

Apatite-group phosphates are nearly ubiquitous in carbonatites, but our understanding of these minerals is inadequate, particularly in the areas of element partitioning and petrogenetic interpretation of their compositional variation among spatially associated rocks and within individual crystals. In the present work, the mode of occurrence, and major- and trace-element chemistry of apatite (sensu lato) from calcite and dolomite carbonatites, their associated cumulate rocks (including phoscorites) and hydrothermal parageneses were studied using a set of 80 samples from 50 localities worldwide. The majority of this set represents material for which no analytical data are available in the literature. Electron-microprobe and laser-ablation mass-spectrometry data ( 600 and 400 analyses, respectively), accompanied by back-scattered-electron and cathodoluminescence images and Raman spectra, were used to identify the key compositional characteristics and zoning patterns of carbonatitic apatite. These data are placed in the context of phosphorus geochemistry in carbonatitic systems and carbonatite evolution, and compared to the models proposed by previous workers. The documented variations in apatite morphology and zoning represent a detailed record of a wide range of evolutionary processes, both magmatic and fluid-driven. The majority of igneous apatite from the examined rocks is Cl-poor fluorapatite or F-rich hydroxylapatite (≥ 0.3 apfu F) with 0.2-2.7 wt.% SrO, 0-4.5 wt.% LREE2O3, 0-0.8 wt.% Na2O, and low levels of other cations accommodated in the Ca site (up to 1000 ppm Mn, 2300 ppm Fe, 200 ppm Ba, 150 ppm Pb, 700 ppm Th and 150 ppm U), none of which show meaningful correlation with the host-rock type. Silicate, (SO4)2 - and (VO4)3 - anions, substituting for (PO4)3 -, tend to occur in greater abundance in crystals from calcite carbonatites (up to 4.2 wt.% SiO2, 1.5 wt.% SO3 and 660 ppm V). Although (CO3)2 - groups are very likely present in some samples, Raman micro-spectroscopy proved inconclusive for apatites with small P-site deficiencies and other substituent elements in this site. Indicator REE ratios sensitive to redox conditions (δCe, δEu) and hydrothermal overprint (δY) form a fairly tight cluster of values (0.8-1.3, 0.8-1.1 and 0.6-0.9, respectively) and may be used in combination with trace-element abundances for the development of geochemical exploration tools. Hydrothermal apatite forms in carbonatites as the product of replacement of primary apatite, or is deposited in fractures and interstices as euhedral crystals and aggregates associated with typical late-stage minerals (e.g., quartz and chlorite). Hydrothermal apatite is typically depleted in Sr, REE, Mn and Th, but enriched in F (up to 4.8 wt.%) relative to its igneous precursor, and also differs from the latter in at least some of key REE ratios [e.g., shows (La/Yb)cn ≤ 25, or a negative Ce anomaly]. The only significant exception is Sr(± REE,Na)-rich replacement zones and overgrowths on igneous apatite from some dolomite(-bearing) carbonatites. Their crystallization conditions and source fluid appear to be very different from the more common Sr-REE-depleted variety. Based on the new evidence presented in this work, trace-element partitioning between apatite and carbonatitic magmas, phosphate solubility in these magmas, and compositional variation of apatite-group minerals from spatially associated carbonatitic rocks are critically re-evaluated.

LA-ICP-MS analysis of trace elements in glass spherules of the El'gygytgyn impact structure, Siberia

NASA Astrophysics Data System (ADS)

Adolph, Leonie; Deutsch, Alex

2010-05-01

The 3.58±0.04 Ma old El'gygytgyn impact structure (Central Chukotka, NE Siberia) with a diameter of 18 km (Gurov and Gurova 1979, Layer 2000) is one of only two terrestrial craters with a volcanic target; therefore, analysis of its target and impact lithologies is of basic interest for comparative planetology. Lake El'gygytgyn is a very valuable climate archive in the Arctic as it was neither covered by glaciers (Melles et al. 2007) nor has the lake ever fallen dry. Climate and impact research were the rationale for the ICDP drilling project that finished successfully in spring 2009. Impactites like melt rocks and breccias are rarely found in outcrops yet are present in the 80 m terrace of Lake El'gygytgyn (Gurov and Gurova 1979). Numerous investigations on petrography, shock metamorphism, and geochemistry of impactites from El'gygytgyn have been published so far (e.g. Gurov et al. 2007). We report the first trace element data for seven 30- to 760-μm-sized impact glass spherules that have been collected about10 km off the crater center from a terrace deposit of the Enmyvaam River outside the crater rim. The spherules are translucent with colors ranging from amber, dark brown to nearly black; they contain a few circular bubbles, schlieren, and very rarely mineral clasts and breccia fragments. Major elements were measured with the JEOL JXA 8600 MX Superprobe, 31 trace elements were analyzed with the Finnigan Element2 LA-ICP-MS with 5 Hz, 8-9 J/cm2 at with Si as internal, and NIST612 as external standard (Institut f. Mineralogie, WWU Münster). The spot size was 60 μm. All spherules show a very homogeneous major and trace element distribution yet clear differences exist between the samples in the SiO2 content (in weight percent) 53-68: four of the glasses are dacitic, two andesitic, and one basaltic-andesitic in composition. In addition, MgO (2.1-9.2), K2O (0.6-3.3), and (in ppm) Ni (317-1096), Co (25-79), Zr (100-169), Rb (18-107), and Ba (459-1092) display wide ranges in concentration. The Ni/Co ratio is consistently high (11-14), the Zr/Hf ratio range between 36 and an anomalous high value of about 50, the Nb/Ta ratio vary from 17.6 to 14.9. The rare earth element distribution patterns are similar, yet samples with low SiO2 contents (53.1-58.4) have lower REE concentrations except for Eu. The new trace element data for impact glass lithologies from El'gygytgyn extent the range of known impactites (Gurov et al. 2007) into the field of more mafic compositions. Basalts to andesites are known to occur in the El'gygytgyn area, and obviously form the precursor lithologies for two of the spherules. All impact glass samples plot in the Zr-Ti-Y-diagram (in the tectonic setting for calc-alkaline rocks, as expected from the larger geological frame (Chekhovich et al. 1999), indicating that impact melting did not change the primary characteristics of the precursor rocks. In agreement with this setting are the Nb/Ta and Zr/Hf values although a Zr/Hf of 50 is remarkable. Origin and importance of the exceptional high Ni contents, in combination with high Ni/Co ratios are currently not understood. We exclude, however, technical reasons for these data as analyses of standard glass NIST 612 measured as unknown yielded satisfactory results.

Geochemistry, thermometry and isotope ratios on the same zircon crystals: the tandem use of quadrupole LA-ICPMS and CA-TIMS

NASA Astrophysics Data System (ADS)

Olin, P. H.; Schmitz, M. D.; Crowley, J. L.

2011-12-01

Current trends in igneous petrology include the extraction of diverse geochemical information from smaller sample targets by ever more efficient and cost effective means. Igneous zircons are repositories of several types of petrogenetic information, such as magmatic crystallization ages obtained using U-Pb geochronology, magmatic temperatures using Ti-in-zircon geothermometry, and magmatic differentiation and/or mixing trends using trace element contents. Here we demonstrate a tandem quadrupole LA-ICPMS and CA-TIMS approach on single zircon crystals and within domains in single crystals, which extracts all of these data from a single laser spot analysis and then guides the acquisition of CA-TIMS ages at precisions relevant to magmatic histories. We present data from zircon-bearing intrusive and extrusive rocks spanning the compositional spectrum, and highlight results from silicic volcanic rocks with different affinities. The utility of our approach is illustrated in zircons from the Temora diorite, a commonly used standard material which we analysed using 25-μm ablation spots placed on dozens of grains which had been previously annealed and chemically abraded prior to mounting in epoxy. Our LA-ICPMS results illustrate a 3- to 5-fold variation in trace element concentrations and trace element ratios over >150 degrees of cooling as estimated from Ti-in-zircon thermometry. Some geochemical parameters (e.g., Nb/Ta variations and Eu anomalies) are consistent with crystal fractionation during progressive crystallization, while others are bimodal (e.g., Hf and U contents), suggesting the mixing of crystal/magma batches prior to final solidification. LA-ICPMS U-Pb spot ages reproduce the accepted CA-TIMS age within 2% precision and accuracy, while our CA-TIMS results on the same grains constrain the development of the observed geochemical variability to within 100 ka. Other zircon standard materials to be presented include Plesovich syenite, FC1 gabbro, and R33 diorite. Analyses of zircons from selected western Snake River Plain silicic volcanic units further demonstrate the capability of our approach. These units are targeted with the overarching goal of better understanding magmatism in the region and to identify geochemical fingerprints to better distinguish among and to correlate between units. Several rhyolites distributed along the northern margin of the plain have LA-ICPMS ages of ca. 11 Ma, within error of each other and their CA-TIMS ages, and reveal differences in temperatures of crystallization and trace element contents and ratios. Individual units have crystallization temperatures that span 100 degrees or more, and show correlations with whole-rock major and trace element contents and ratios. In many cases, zircon geochemical parameters such as REE and Y contents, and Nb/Ta and Th/U ratios allow units proximal to each other to be distinguished from one another while also providing fingerprints to correlate to distal units on the south side of the plain or elsewhere in the province.

Chemical composition of crystalline rock fragments from Luna 16 and Luna 20 fines

NASA Technical Reports Server (NTRS)

Cimbalnikova, A.; Palivcova, M.; Frana, J.; Mastalka, A.

1977-01-01

The chemical composition (bulk, rare earth, and trace elements) of the Luna 16 mare regolith and luna 20 highland regolith is discussed. The rock samples considered are 14 basaltic rock fragments (Luna 16) and 13 rock fragments of the ANT suite (Luna 20). On the basis of bulk composition, two types of basaltic rocks have been differentiated and defined in the Luna 16 regolith: mare basalts (fundamental crystalline rocks of Mare Fecunditatis) and high-alumina basalts. The bulk analyses of rock fragments of the ANT suite also enabled distinction of two rock types: anorthositic norites and troctolites and/or spinal-troctolites (the most abundant crystalline rocks of the highland region, the landing site of luna 20), and anorthosites. The chemical compositions of Luna 16 and Luna 20 regolith samples are compared. Differences in the chemistry of the Luna 16 mare regolith and that of mare basalts are discussed. The chemical affinity between the Luna 20 highland regolith and (a) anorthositic norites and (b) troctolites and/or spinel-troctolites has been ascertained.

Arsenic in rocks and stream sediments of the central Appalachian Basin, Kentucky

USGS Publications Warehouse

Tuttle, Michele L.W.; Goldhaber, Martin B.; Ruppert, Leslie F.; Hower, James C.

2002-01-01

Arsenic (As) enrichment in coal and stream sediments has been documented in the southern Appalachian basin (see Goldhaber and others, submitted) and is attributed to interaction of rocks and coal with metamorphic fluids generated during the Allegheny Orogeny (late Paleozoic). Similarly derived fluids are expected to affect the coal and in the Kentucky Appalachian Basin to the north as well. In addition, similar processes may have influenced the Devonian oil shale on the western margin of the basin. The major goals of this study are to determine the effect such fluids had on rocks in the Kentucky Appalachian basin (fig. 1), and to understand the geochemical processes that control trace-metal source, residence, and mobility within the basin. This report includes data presented in a poster at the USGS workshop on arsenic (February 21 and 22, 2001), new NURE stream sediment data3 , and field data from a trip in April 2001. Although data for major and minor elements and all detectable trace metals are reported in the Appendices, the narrative of this report primarily focuses on arsenic.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sablock, J.

A trace element signature, a characteristic pattern of enrichment and depletion of trace elements, was determined for a group of siliciclastic-carbonate Oxfordian and Kimmeridgian sedimentary strata, collected from outcrops in western Montana, southeastern British Columbia and southern Alberta. The average values, by petrofacies, of 10 major and 18 trace elements were measured for 40 samples. These data were normalized to Upper Continental Crust (UCC), and plotted against averaged published values of graywackes from the same facies. The rare earth elements (REEs), as well as Ti, Zr, Nb and Y are considered immobile even through diagenesis, and at least low levelmore » metamorphism. So these elements should form a reliable part of the geochemical signature. Compared to UCC and average graywacke, Jurassic samples are very depleted in Zr, Nb and Y. Oxfordian samples have slightly higher rare earth element values, i.e. La, Ce and Nd, than either other Jurassic samples or average graywacke. The most likely source of REE values are garnets and tourmaline which occur as inclusions in monocrystalline quartz grains. This pattern, and petrological study, point to a sedimentary source area, deficient in feldspar, heavy minerals and rock fragments. The consistency of the signature throughout this time may indicate slow uplift of a widespread sedimentary source area, or could be an effect of greater mixing and shorter residence time of dissolved materials in an epeiric sea.« less

Age and whole rock glass compositions of proximal pyroclastics from the major explosive eruptions of Somma-Vesuvius: A review as a tool for distal tephrostratigraphy

NASA Astrophysics Data System (ADS)

Santacroce, Roberto; Cioni, Raffaello; Marianelli, Paola; Sbrana, Alessandro; Sulpizio, Roberto; Zanchetta, Giovanni; Donahue, Douglas J.; Joron, Jean Louis

2008-10-01

A review of compositional data of the major explosive eruptions of Vesuvius is presented, comparing compositions (major elements) of whole rock with glass shards from the proximal deposits, hopefully useful for long-distance correlation. A critical review of published and new geochronological data is also provided. All available 14C ages are calibrated to give calendar ages useful for the reconstruction of the volcanological evolution of the volcanic complex. The pyroclastic deposits of the four major Plinian eruptions (22,000 yr cal BP "Pomici di Base", 8900 yr cal BP "Mercato Pumice", 4300 yr cal BP "Avellino Pumice", and A.D. 79 "Pompeii Pumice") are widely dispersed and allow a four-folded, Plinian to Plinian, stratigraphic division: 1. B-M (between Pomici di Base and Mercato); 2. M-A (between Mercato and Avellino); 3. A-P (between Avellino and Pompeii); 4. P-XX (from the Pompeii Pumice to the last erupted products of the XXth century). Within each interval, the age, lithologic and compositional features of pyroclastic deposits of major eruptions, potentially useful for tephrostratigraphic purposes on distal areas, are briefly discussed. The Vesuvius rocks are mostly high Potassic products, widely variable in terms of their silica saturation. They form three groups, different for both composition and age: 1. slightly undersaturated, older than Mercato eruption; 2. mildly undersaturated, from Mercato to Pompeii eruptions; 3. highly undersaturated, younger than Pompeii eruption. For whole rock analyses, the peculiar variations in contents of some major and trace elements as well as different trends in element/element ratios, allow a clear, unequivocal, easy diagnosis of the group they belong. Glass analyses show large compositional overlap between different groups, but selected element vs. element plots are distinctive for the three groups. The comparative analysis of glass and whole rock major element compositions provides reliable geochemical criteria helping in the recognition, frequently not obvious, of distal products from the different single eruptions.

Petrogenesis of Western Cascades Silicic Volcanics Near Sweet Home, Oregon

NASA Astrophysics Data System (ADS)

Cook, G. W.; White, C. M.

2002-12-01

Silicic lavas in the Menagerie Wilderness east of Sweet Home, Oregon are Oligocene to Miocene in age and range in composition from dacite (low K) to trachydacite (high K) and rhyolite (medium K). Three distinct silicic centers have been distinguished through a combination of field observation, chemistry and petrography. Phenocryst assemblages in rocks of the centers are plagioclase-hornblende-magnetite (Rooster Rock rhyolite), plagioclase-quartz-magnetite (Soda Fork rhyolite) and quartz-plagioclase-biotite-hornblende-magnetite (Moose Mt. rhyolite). The silicic volcanics in the study area are similar in terms of mineral content and overall chemical composition. Despite this, chemical evidence suggests that the three centers are petrologically unrelated. REE variations and least squares modeling of major element compositions are consistent with fractionation of plagioclase and hornblende. The rhyolites have moderate Eu anomalies and have flat MREE and HREE signatures. Least squares models and bivariate plots of major and trace elements also suggest fractionation of the aforementioned phases for both the andesite to dacite, and dacite to rhyolite steps. Comparisons with similar silicic centers show the Menagerie rocks share affinities with High Cascades rocks thought to have been derived through fractional crystallization (Crater Lake and South Sister). Plots of ratios of incompatible trace elements were utilized to determine if assimilation played some role alongside fractional crystallization in differentiation. Plots of Ba/La vs. Ba, Rb/Zr vs. Rb and Rb/Th vs. Rb show systematic positive increases in the ratios between a plausible parent magma (icelandite) and the rhyolites. These increases are not easily explained by fractional crystallization but can be modeled by assimilation of silicic crust. Overall, it seems likely that the three centers evolved independently through similar petrogenetic processes from an andesitic parent. The most plausible petrogenetic scenario involves some combination of fractional crystallization and assimilation of partial melts of silicic crust.

Trace element analyses of fluid-bearing diamonds from Jwaneng, Botswana

NASA Astrophysics Data System (ADS)

Schrauder, Marcus; Koeberl, Christian; Navon, Oded

1996-12-01

Fibrous diamonds from Botswana contain abundant micro-inclusions, which represent syngenetic mantle fluids under high pressure. The major element composition of the fluids within individual diamonds was found to be uniform, but a significant compositional variation exists between different diamond specimens. The composition of the fluids varies between a carbonatitic and a hydrous endmember. To constrain the composition of fluids in the mantle, the trace element contents of thirteen micro-inclusion-bearing fibrous diamonds from Botswana was studied using neutron activation analysis. The concentrations of incompatible elements (including K, Na, Br, Rb, Sr, Zr, Cs, Ba, Hf, Ta, Th, U, and the LREEs) in the fluids are higher than those of mantle-derived rocks and melt inclusions. The compatible elements (e.g., Cr, Co, Ni) have abundances that are similar to those of the primitive mantle. The concentrations of most trace elements decrease by a factor of two from the carbonate-rich fluids to the hydrous fluids. Several models may explain the observed elemental variations. Minerals in equilibrium with the fluid were most likely enriched in incompatible elements, which does not agree with derivation of the fluids by partial melting of common peridotites or eclogites. Fractional crystallization of a kimberlite-like magma at depth may yield carbonatitic fluids with low mg numbers (atomic ratio [Mg/(Mg+Fe)]) and high trace element contents. Fractionation of carbonates and additional phases (e.g., rutile, apatite, zircon) may, in general, explain the concentrations of incompatible elements in the fluids, which preferably partition into these phases. Alternatively, mixing of fluids with compositions similar to those of the two endmembers may explain the observed variation of the elemental contents. The fluids in fibrous diamonds might have equilibrated with mineral inclusions in eclogitic diamonds, while peridotitic diamonds do not show evidence of interaction with these fluids. The chemical composition of the fluids in fibrous diamonds indicates that, at p, T conditions that are characteristic for diamond formation, carbonatitic and hydrous fluids are efficient carriers of incompatible elements.

Publications - PDF 98-36A | Alaska Division of Geological & Geophysical

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Provenance of Carboniferous sedimentary rocks in the northern margin of Dabie Mountains, central China and the tectonic significance: constraints from trace elements, mineral chemistry and SHRIMP dating of zircons

NASA Astrophysics Data System (ADS)

Li, Renwei; Li, Shuangying; Jin, Fuquan; Wan, Yusheng; Zhang, Shukun

2004-04-01

A suite of slightly metamorphosed Carboniferous sedimentary strata occurs in the northern margin of the Dabie Mountains, central China. It consists, in ascending order, of the upper Huayuanqiang Formation (C 1), the Yangshan Formation (C 1), the Daorenchong Formation (C 1-2), the most widely distributed Huyoufang Formation (C 2) and the Yangxiaozhuang Formation (C 2). The provenance of the Carboniferous sedimentary rocks is constrained by the integration of trace elements, detrital mineral chemistry and sensitive high resolution ion microprobe (SHRIMP) dating of detrital zircons, which can help to understand the connection between the provenance and the Paleozoic tectonic evolution of the Qinling-Dabie Orogen. The trace element compositions indicate that the source terrain was probably a continental island arc. Detrital tourmalines were mainly derived from aluminous and Al-poor metapelites and metapsammites, and some are sourced from Li-poor granitoids, pegmatites and aplites. Detrital garnets, found only in the uppermost Huyoufang Formation, are almandine and Mn-almandine garnets, indicating probable sources mainly from garnetiferous schists, and partly from granitoid rocks. The detrital white K-micas are muscovitic in the Huayuanqiang, Daorenchong and Huyoufang Formations, and phengitic with Si contents (p.f.u.) from 3.20 up to max. 3.47-3.53 in the uppermost Huyoufang and the Yangxiaozhuang Formations, a meta-sedimentary source. Major components in the detrital zircon age structure for the Huyoufang Formation range from 506 to 363 Ma, centering on ˜400 and ˜480 Ma, which is characteristic of the Qinling and Erlangping Groups in the Qinling and Tongbai Mountains, central China. Evidently, the major source of the Carboniferous sedimentary rocks in the northern margin of Dabie Mountains was from the southern margin of the Sino-Korean Craton represented by the Qinling and Erlangping Groups. The source area was an island-arc system during the Early Paleozoic that collided with the Sino-Korea plate towards the end of the Early Paleozoic or during the Devonian. A prominent feature in the detrital zircon age structure of the Huyoufang Formation is the Neoproterozoic detritus, which could be derived only from the Yangtze Craton. Reasonable interpretation of the two distinct source materials for the Huyoufang Formation is that the two plates were juxtaposed through collision before the late Carboniferous.

Abundance, distribution and bioavailability of major and trace elements in surface sediments from the Cai River estuary and Nha Trang Bay (South China Sea, Vietnam)

NASA Astrophysics Data System (ADS)

Koukina, S. E.; Lobus, N. V.; Peresypkin, V. I.; Dara, O. M.; Smurov, A. V.

2017-11-01

Major (Si, Al, Fe, Ti, Mg, Ca, Na, K, S, P), minor (Mn) and trace (Li, V, Cr, Co, Ni, Cu, Zn, As, Sr, Zr, Mo, Cd, Ag, Sn, Sb, Cs, Ba, Hg, Pb, Bi and U) elements, their chemical forms and the mineral composition, organic matter (TOC) and carbonates (TIC) in surface sediments from the Cai River estuary and Nha Trang Bay were first determined along the salinity gradient. The abundance and ratio of major and trace elements in surface sediments are discussed in relation to the mineralogy, grain size, depositional conditions, reference background and SQG values. Most trace-element contents are at natural levels and are derived from the composition of rocks and soils in the watershed. A severe enrichment of Ag is most likely derived from metal-rich detrital heavy minerals such as Ag-sulfosalts. Along the salinity gradient, several zones of metal enrichment occur in surface sediments because of the geochemical fractionation of the riverine material. The parts of actually and potentially bioavailable forms (isolated by four single chemical reagent extractions) are most elevated for Mn and Pb (up to 36% and 32% of total content, respectively). The possible anthropogenic input of Pb in the region requires further study. Overall, the most bioavailable parts of trace elements are associated with easily soluble amorphous Fe and Mn oxyhydroxides. The sediments are primarily enriched with bioavailable metal forms in the riverine part of the estuary. Natural (such as turbidities) and human-generated (such as urban and industrial activities) pressures are shown to influence the abundance and speciation of potential contaminants and therefore change their bioavailability in this estuarine system.

Tracking the source of the enriched martian meteorites in olivine-hosted melt inclusions of two depleted shergottites, Yamato 980459 and Tissint

NASA Astrophysics Data System (ADS)

Peters, T. J.; Simon, J. I.; Jones, J. H.; Usui, T.; Moriwaki, R.; Economos, R. C.; Schmitt, A. K.; McKeegan, K. D.

2015-05-01

The apparent lack of plate tectonics on all terrestrial planets other than Earth has been used to support the notion that for most planets, once a primitive crust forms, the crust and mantle evolve geochemically-independent through time. This view has had a particularly large impact on models for the evolution of Mars and its silicate interior. Recent data indicating a greater potential that there may have been exchange between the martian crust and mantle has led to a search for additional geochemical evidence to support the alternative hypothesis, that some mechanism of crustal recycling may have operated early in the history of Mars. In order to study the most juvenile melts available to investigate martian mantle source(s) and melting processes, the trace element compositions of olivine-hosted melt inclusions for two incompatible-element-depleted olivine-phyric shergottites, Yamato 980459 (Y98) and Tissint, and the interstitial glass of Y98, have been measured by Secondary Ionization Mass Spectrometry (SIMS). Chondrite-normalized Rare Earth Element (REE) patterns for both Y98 and Tissint melt inclusions, and the Y98 interstitial glass, are characteristically light-REE depleted and parallel those of their host rock. For Y98, a clear flattening and upward inflection of La and Ce, relative to predictions based on middle and heavier REE, provides evidence for involvement of an enriched component early in their magmatic history; either inherited from a metasomatized mantle or crustal source, early on and prior to extensive host crystallization. Comparing these melt inclusion and interstitial glass analyses to existing melt inclusion and whole-rock data sets for the shergottite meteorite suite, defines mixing relationships between depleted and enriched end members, analogous to mixing relationships between whole rock Sr and Nd isotopic measurements. When considered in light of their petrologic context, the origin of these trace element enriched and isotopically evolved signatures represents either (1) crustal assimilation during the final few km of melt ascent towards the martian surface, or (2) assimilation soon after melt segregation, through melt-rock interaction with a portion of the martian crust recycled back into the mantle.

Statistical tables and charts showing geochemical variation in the Mesoproterozoic Big Creek, Apple Creek, and Gunsight formations, Lemhi group, Salmon River Mountains and Lemhi Range, central Idaho

USGS Publications Warehouse

Lindsey, David A.; Tysdal, Russell G.; Taggart, Joseph E.

2002-01-01

The principal purpose of this report is to provide a reference archive for results of a statistical analysis of geochemical data for metasedimentary rocks of Mesoproterozoic age of the Salmon River Mountains and Lemhi Range, central Idaho. Descriptions of geochemical data sets, statistical methods, rationale for interpretations, and references to the literature are provided. Three methods of analysis are used: R-mode factor analysis of major oxide and trace element data for identifying petrochemical processes, analysis of variance for effects of rock type and stratigraphic position on chemical composition, and major-oxide ratio plots for comparison with the chemical composition of common clastic sedimentary rocks.

Aspects of the history of 66095 based on trace elements in clasts and whole rock

NASA Technical Reports Server (NTRS)

Jovanovic, S.; Reed, G. W., Jr.

1982-01-01

Halogens, P, U and Na are reported in anorthositic and basaltic clasts and matrix from rusty rock 66095. Large fractions of Cl and Br associated with the separated phases from 66095 are soluble in H2O. Up to two orders of magnitude variation in concentrations of these elements in the breccia components and varying H2O-soluble Cl/Br ratios indicate different sources of volatiles. An approximately constant ratio of the H2O- to 0.1 M HNO3-soluble Br in the various components suggests no appreciable alteration in the original distributions of this element in the breccia forming processes. Up to 50% or more of the phosphorus and of the non-H2O-soluble Cl was dissolved from most of the breccia components by 0.1 M HNO3. Clast and matrix residues from the leaching steps contain, in most cases, the Cl/P2O5 ratio found in 66095 whole rock and in a number of other Apollo 16 samples. Evidence that phosphates are the major P-phases in the breccia is based on the 0.1 M acid solubility of Cl and P in the matrix sample and on elemental concentrations which are consistent with those of KREEP.

Ancient and modern rhyolite: Using zircon trace element compositions to examine the origin of volcanic rocks

NASA Astrophysics Data System (ADS)

Klemetti, E. W.; Lackey, J.; Starnes, J.; Wooden, J. L.

2011-12-01

Volcanic rocks are an important marker for magmatism in the Earth's past and may be all that remains (or is exposed) to elucidate on magmagenesis in ancient terranes. Unlike plutonic rocks, which are likely aggregates of many pulses of magmatism over 104 to 106 year timescales, volcanic rocks are snapshots into specific moments in the development of a magmatic system, and in a larger sense, the tectonic setting in which the volcanoes reside. However, volcanic rocks from the rock record are commonly altered, preventing straightforward petrogenetic interpretation. In contrast, studies of refractory trace minerals such as zircon allow original petrogenesis to be recovered. In the south central Sierra Nevada batholith, Triassic to Cretaceous meta-rhyolites of the Mineral King roof pendant record snapshots of rhyolitic volcanism from key intervals of magmatism in the Sierra arc, however these rhyolites are highly altered and deformed, so little can be deduced about the original magmas or their tectonic settings. To resolve this, we recovered zircon from the four principle rhyolite units to date via SHRIMP-RG. Ages on rhyolites at Mineral King range from ˜196 Ma to 134 Ma, with three of the rhyolites being between 134 and 136 Ma. We also measured trace element composition (REE, Hf, Y and others) to explore the origins of the rhyolites. We can examine the processes at work in the development of these rhyolites along the western margin of North America during the Jurassic and Cretaceous by comparing them with modern volcanic arcs that produce abundant rhyolite eruptions, such as the Okataina Caldera Complex, New Zealand. Compared to zircon from the Okataina rhyolites, Mineral King rhyolites show a much more fractionation-dominated pattern of high Eu/Eu* (0.30-0.50) to low (<0.10) Eu/Eu* relative to increasing Hf, suggesting systems dominated by crystal fractionation or derived from a feldspar-rich source, unlike Okataina zircon that suggest abundance crystal recycling along with crystal fractionation. At a given Hf concentration, the Th/U of Mineral King rhyolites are lower than Okataina rhyolites. Yb/Sm are, on average, lower for Mineral King rhyolite at a given Hf than in the Okataina rhyolites. At high Hf concentrations (>12000 ppm), Mineral King rhyolites show a wide range of Yb/Sm (<100 to 500). A xenocrystic zircon with an age of ~1.63 Ga was found in one Mineral King rhyolite suggesting crustal melting/assimilation was also important during the evolution in the younger rhyolites in the pendant. Additionally, bulk zircon oxygen isotopic analyses from Mineral King rhyolites show a change from more mantle-like values δ18O at 196 Ma (+5.3%) to higher values at 136 Ma (+6.8%), evidence of increasing input of continental crust. In all, the differences in the trace element and isotopic compositions between the Okataina and Mineral King zircon likely reflect the difference in the crustal thickness and composition of their respective crustal settings, but also reflect the particular volcanic environment.

OIB signatures in basin-related lithosphere-derived alkaline basalts from the Batain basin (Oman) - Constraints from 40Ar/39Ar ages and Nd-Sr-Pb-Hf isotopes

NASA Astrophysics Data System (ADS)

Witte, M.; Jung, S.; Pfänder, J. A.; Romer, R. L.; Mayer, B.; Garbe-Schönberg, D.

2017-08-01

Tertiary rift-related intraplate basanites from the Batain basin of northeastern Oman have low SiO2 (< 45.6 wt.%), high MgO (> 9.73 wt.%) and moderate to high Cr and Ni contents (Cr > 261 ppm, Ni > 181 ppm), representing near primary magmas that have undergone fractionation of mainly olivine and magnetite. Rare earth element systematics and p-T estimates suggest that the alkaline rocks are generated by different degrees of partial melting (4-13%) of a spinel-peridotite lithospheric mantle containing residual amphibole. The alkaline rocks show restricted variations of 87Sr/86Sr and 143Nd/144Nd ranging from 0.70340 to 0.70405 and 0.51275 to 0.51284, respectively. Variations in Pb isotopes (206Pb/204Pb: 18.59-18.82, 207Pb/204Pb: 15.54-15.56, 208Pb/204Pb: 38.65-38.98) of the alkaline rocks fall in the range of most OIB. Trace element constraints together with Sr-Nd-Pb isotope composition indicate that assimilation through crustal material did not affect the lavas. Instead, trace element variations can be explained by melting of a lithospheric mantle source that was metasomatized by an OIB-type magma that was accumulated at the base of the lithosphere sometimes in the past. Although only an area of less than 1000 km2 was sampled, magmatic activity lasted for about 5.5 Ma with a virtually continuous activity from 40.7 ± 0.7 to 35.3 ± 0.6 Ma. During this period magma composition was nearly constant, i.e. the degree of melting and the nature of the tapped source did not change significantly over time.

Trace element determination of zircons from adakites and granitoids: implications for petrogenetic processes

NASA Astrophysics Data System (ADS)

Chen, T. W.; Chu, M. F.; Chung, S. L.; Iizuka, Y.

2017-12-01

Zircon has long been proposed as a time capsule of crustal formation. Concerning of its high capacity of lithophile elements, the dramatic change of crustal chemical composition in late Archean, i.e. from TTG suites to granitoids, may be recorded in zircon remnants. In this study, major- and trace element contents of zircons from adakites, a modern analogue of TTG suites, in southern Tibet were determined by EPMA and LA-ICPMS, respectively, and compared with those in Gangdese granitoids and Sumatra high/low ΣREE granitoids in order to examine the hypothesis. The REE patterns of zircons in this study show little inter-sample discrepancy though there is significant difference in whole-rock HREE contents between adakites and granitoids. Since none of geochemical feature, including REE contents, of zircons correlates with SiO2 content or ASI of corresponding host rocks, fractional crystallization shows insignificant impact on the compositional variation in zircons. In addition to the influence of lattice strain and charge balance requirements, zircons in these rock samples are proposed to crystallize from the magma mush, so they record the composition with least composition difference, not that of the bulk melt. More specifically, the pre-/co-existing mineral phases, e.g. apatite, play a critical role in preferentially taking the LREE and MREE from melt, and eliminating the HREE depletion in residual melt and thus zircons of Gangdese adakites. With the aim of objectively identifying geochemical discriminants of zircons from adakites and granitoids, statistical analysis was used and then 8 parameters were selected, i.e. Ti, V, Yb, Hf, Sc/Yb, U/Yb, Eu/Eu*, ΣHREE. Despite the zircon populations of adakites- and granitoids-origins overlapping in any bivariate plot, the linear combination of discriminants provides a potential way to distinguish zircons from these two groups.

Palaeoenvironment and Its Control on the Formation of Miocene Marine Source Rocks in the Qiongdongnan Basin, Northern South China Sea

PubMed Central

Li, Wenhao; Zhang, Zhihuan; Wang, Weiming; Lu, Shuangfang; Li, Youchuan; Fu, Ning

2014-01-01

The main factors of the developmental environment of marine source rocks in continental margin basins have their specificality. This realization, in return, has led to the recognition that the developmental environment and pattern of marine source rocks, especially for the source rocks in continental margin basins, are still controversial or poorly understood. Through the analysis of the trace elements and maceral data, the developmental environment of Miocene marine source rocks in the Qiongdongnan Basin is reconstructed, and the developmental patterns of the Miocene marine source rocks are established. This paper attempts to reveal the hydrocarbon potential of the Miocene marine source rocks in different environment and speculate the quality of source rocks in bathyal region of the continental slope without exploratory well. Our results highlight the palaeoenvironment and its control on the formation of Miocene marine source rocks in the Qiongdongnan Basin of the northern South China Sea and speculate the hydrocarbon potential of the source rocks in the bathyal region. This study provides a window for better understanding the main factors influencing the marine source rocks in the continental margin basins, including productivity, preservation conditions, and the input of terrestrial organic matter. PMID:25401132

Komatiites and nickel sulfide ores of the Black Swan area, Yilgarn Craton, Western Australia. 3: Komatiite geochemistry, and implications for ore forming processes

NASA Astrophysics Data System (ADS)

Barnes, Stephen J.; Hill, Robin E. T.; Evans, Noreen J.

2004-11-01

The Black Swan komatiite sequence is a package of dominantly olivine-rich cumulates with lesser volumes of spinifex textured rocks, interpreted as a section through an extensive komatiite lava flow field. The sequence hosts a number of nickel sulfide orebodies, including the Silver Swan massive shoot and the Cygnet and Black Swan disseminated orebodies. A large body of whole rock analyses on komatiitic rocks from the Black Swan area has been filtered for metasomatic effects. With the exception of mobile elements such as Ca and alkalis, most samples retain residual igneous geochemistry, and can be modelled predominantly by fractionation and accumulation of olivine. Whole rock MgO FeO relationships imply a relatively restricted range of olivine compositions, more primitive than the olivine which would have been in equilibrium with the transporting komatiite lavas, and together with textural data indicate that much of the cumulus olivine in the sequence was transported. Flow top compositions show evidence for chromite saturation, but the cumulates are deficient in accumulated chromite. Chromite compositions are typical of those found in compound flow-facies komatiites, and are distinct from those in komatiitic dunite bodies. Incompatible trace element abundances show three superimposed influences: control by the relative proportion of olivine to liquid; a signature of crustal contamination and an overprint of metasomatic introduction of LREE, Zr and Th. This overprint is most evident in cumulates, and relatively insignificant in the spinifex rocks. Platinum and palladium behaved as incompatible elements and are negatively correlated with MgO. They show no evidence for wholesale depletion due to sulfide extraction, which was evidently restricted to specific lava tubes or pathways. The lack of correspondence between PGE depletion and contamination by siliceous material implies that contamination alone is insufficient to generate S-saturation and ore formation in the absence of sulfide in the assimilant. Contamination signatures in spinifex-textured rocks may be a guide to Ni-sulfide mineralisation, but are not entirely reliable in the absence of other evidence. The widespread vesicularity of the sequence may be attributable to assimilated water rather than to primary mantle-derived volatiles, and cannot be taken as evidence for primary volatile-rich magmas. The characteristic signature of the Black Swan Succession is the presence of highly localised disseminated sulfide within a sequence showing more widespread evidence for crustal contamination and interaction with its immediate substrate. This has important implications for the applicability of trace element geochemistry in exploration for komatiite-hosted nickel deposits.

Review: Impacts of permafrost degradation on inorganic chemistry of surface fresh water

NASA Astrophysics Data System (ADS)

Colombo, Nicola; Salerno, Franco; Gruber, Stephan; Freppaz, Michele; Williams, Mark; Fratianni, Simona; Giardino, Marco

2018-03-01

Recent studies have shown that climate change is impacting the inorganic chemical characteristics of surface fresh water in permafrost areas and affecting aquatic ecosystems. Concentrations of major ions (e.g., Ca2 +, Mg2 +, SO42 -, NO3-) can increase following permafrost degradation with associated deepening of flow pathways and increased contributions of deep groundwater. In addition, thickening of the active layer and melting of near-surface ground ice can influence inorganic chemical fluxes from permafrost into surface water. Permafrost degradation has also the capability to modify trace element (e.g., Ni, Mn, Al, Hg, Pb) contents in surface water. Although several local and regional modifications of inorganic chemistry of surface fresh water have been attributed to permafrost degradation, a comprehensive review of the observed changes is lacking. The goal of this paper is to distil insight gained across differing permafrost settings through the identification of common patterns in previous studies, at global scale. In this review we focus on three typical permafrost configurations (pervasive permafrost degradation, thermokarst, and thawing rock glaciers) as examples and distinguish impacts on (i) major ions and (ii) trace elements. Consequences of warming climate have caused spatially-distributed progressive increases of major ion and trace element delivery to surface fresh water in both polar and mountain areas following pervasive permafrost degradation. Moreover, localised releases of major ions and trace elements to surface water due to the liberation of soluble materials sequestered in permafrost and ground ice have been found in ice-rich terrains both at high latitude (thermokarst features) and high elevation (rock glaciers). Further release of solutes and related transport to surface fresh water can be expected under warming climatic conditions. However, complex interactions among several factors able to influence the timing and magnitude of the impacts of permafrost degradation on inorganic chemistry of surface fresh water (e.g., permafrost sensitivity to thawing, modes of permafrost degradation, characteristics of watersheds) require further conceptual and mechanistic understanding together with quantitative diagnosis of the involved mechanisms in order to predict future changes with confidence.

Precambrian tholeiitic-dacitic rock-suites and Cambrian ultramafic rocks in the Pennine nappe system of the Alps: Evidence from Sm-Nd isotopes and rare earth elements

USGS Publications Warehouse

Stille, P.; Tatsumoto, M.

1985-01-01

Major element, trace element and Sm-Nd isotope analyses were made of polymetamorphic hornblendefelses, plagioclase amphibolites and banded amphibolites from the Berisal complex in the Simplon area (Italy, Switzerland) to determine their age, origin and genetic relationships. In light of major and rare earth element data, the hornblendefelses are inferred to have originally been pyroxene-rich cumulates, the plagioclase amphibolites and the dark layers of the banded amphibolites to have been tholeiitic basalts and the light layers dacites. The Sm-Nd isotope data yield isochron ages of 475??81 Ma for the hornblendefelses, 1,018??59 Ma for the plagioclase amphibolites and 1,071??43 Ma for the banded amphibolites. The 1 Ga magmatic event is the oldest one ever found in the crystalline basement of the Pennine nappes. The Sm -Nd isotope data support the consanguinity of the tholeiitic dark layers and the dacitic light layers of the banded amphibolites with the tholeiitic plagioclase amphibolites and the ultramafic hornblendefelses. The initial e{open}Nd values indicate that all three rock types originated from sources depleted in light rare earth elements. We suggest that plagioclase and banded amphibolites were a Proterozoic tholeiite-dacite sequence that was strongly deformed and flattened during subsequent folding. The hornblendefelses are thought to be Cambrian intrusions of pyroxene-rich material. ?? 1985 Springer-Verlag.

Precambrian tholeiitic-dacitic rock-suites and Cambrian ultramafic rocks in the Pennine nappe system of the Alps: Evidence from Sm-Nd isotopes and rare earth elements

NASA Astrophysics Data System (ADS)

Stille, P.; Tatsumoto, M.

1985-04-01

Major element, trace element and Sm-Nd isotope analyses were made of polymetamorphic hornblendefelses, plagioclase amphibolites and banded amphibolites from the Berisal complex in the Simplon area (Italy, Switzerland) to determine their age, origin and genetic relationships. In light of major and rare earth element data, the hornblendefelses are inferred to have originally been pyroxene-rich cumulates, the plagioclase amphibolites and the dark layers of the banded amphibolites to have been tholeiitic basalts and the light layers dacites. The Sm-Nd isotope data yield isochron ages of 475±81 Ma for the hornblendefelses, 1,018±59 Ma for the plagioclase amphibolites and 1,071±43 Ma for the banded amphibolites. The 1 Ga magmatic event is the oldest one ever found in the crystalline basement of the Pennine nappes. The Sm -Nd isotope data support the consanguinity of the tholeiitic dark layers and the dacitic light layers of the banded amphibolites with the tholeiitic plagioclase amphibolites and the ultramafic hornblendefelses. The initial ɛ Nd values indicate that all three rock types originated from sources depleted in light rare earth elements. We suggest that plagioclase and banded amphibolites were a Proterozoic tholeiite-dacite sequence that was strongly deformed and flattened during subsequent folding. The hornblendefelses are thought to be Cambrian intrusions of pyroxene-rich material.

Detrital rutile geochemistry and thermometry from the Dabie orogen: Implications for source-sediment links in a UHPM terrane

NASA Astrophysics Data System (ADS)

Liu, Lei; Xiao, Yilin; Wörner, G.; Kronz, A.; Simon, K.; Hou, Zhenhui

2014-08-01

This study explores the potential of detrital rutile geochemistry and thermometry as a provenance tracer in rocks from the Central Dabie ultrahigh-pressure metamorphic (UHPM) zone in east-central China that formed during Triassic continental collision. Trace element data of 176 detrital rutile grains selected from local river sediments and 91 rutile grains from distinct bedrocks in the Shuanghe and Bixiling areas, obtained by both electron microprobe (EMP) and in situ LA-ICP-MS analyses, suggest that geochemical compositions and thermometry of detrital rutiles are comparable to those from their potential source rocks. After certification of the Cr-Nb discrimination method for the Central Dabie UHPM zone, we show that 29% of the detrital rutiles in the Shuanghe area were derived from metamafic sources whereas in the Bixiling area that it is up to 76%. Furthermore, the proportion of distinct types of detrital rutiles combined with modal abundances of rutile in metapelites and metamafic bedrocks can be used to estimate the proportion of different source lithologies. Based on this method the proportion of mafic source rocks was estimated to ∼10% at Shuanghe and >60% at Bixiling, respectively, which is consistent with the proportions of eclogite (the major rutile-bearing metamafic rock) distribution in the field. Therefore, the investigation of detrital rutiles is a potential way to evaluate the proportion of metamafic rocks and even to prospect for metamafic bodies in UHPM terranes. Zr-in-rutile temperatures were calculated at different pressures and compared with temperatures derived from rock-in rutiles and garnet-clinopyroxene Fe-Mg thermometers. Temperatures calculated for detrital rutiles range from 606 °C to 707 °C and 566 °C to 752 °C in Shuanghe and Bixiling, respectively, at P = 3 GPa with an average temperatures of ca. 630 °C for both areas. These temperature averages and ranges are similar to those calculated for rutiles from surrounding source rocks. Combined with comparable Zr distribution characteristics between detrital and source rock rutiles, demonstrating a close source-sediment link for rutiles from clastic and rock in UHPM terranes. Thus rutiles can be accurate tracers of source rock lithologies in sedimentary provenance studies even at a small regional scale. In Bixiling, Nb/Ta ratios of metamafic and metapelitic detrital rutiles fall between 11.0 to 27.3 and 7.7 to 20.5, respectively. In contrast, in Shuanghe, these ratios are highly variable, ranging from 10.9 to 71.0 and 7.6 to 87.1, respectively. When ignoring four outlier compositions with extremely high Nb/Ta in Shuanghe, a distinct clustering of Nb/Ta ratios in rutiles is shown: metapelitic detrital rutiles have Nb/Ta of 7-40 vs. metamafic detrital rutiles with Nb/Ta = 11-25. The Nb/Ta characteristics in detrital rutiles from both areas may reflect the degree of fluid-rock interaction during metamorphism and/or different source lithologies. Therefore, the trace element compositions in detrital rutiles can accurately trace the lithology, proportion and fluid-rock interaction of different source rocks.

Petrology and trace element geochemistry of the Honolulu volcanics, Oahu: implications for the oceanic mantle below Hawaii.

USGS Publications Warehouse

Clague, D.A.; Frey, F.A.

1982-01-01

These volcanic rocks are the products of small-volume, late-stage vents along rifts cutting the older massive Koolan tholeiitic shield on Oahu. Most of the lavas and tuffs have the geochemical features expected of near-primary magmas derived from a peridotite source with olivine Fo87-89, e.g. 100 Mg/(Mg + Fe2+) > 65, Ni > 250 p.p.m. and the presence of ultramafic mantle xenoliths at 18 of the 37 vents. Thus the geochemistry of the alkali olivine basalt, basanite, nephelinite and nepheline melilitite lavas and tuffs of these Honolulu volcanic rocks has been used to deduce the composition of their mantle source and the conditions under which they were generated by partial melting in the mantle. New major- and trace-element analyses for 31 samples are tabulated and indicate derivation by partial melting of a garnet (<10%) lherzolite source which was isotopically homogeneous and compositionally uniform for most major and trace elements, though apparently heterogeneous in TiO2, Zr, Hf, Nb and Ta (due perhaps to the low inferred degrees of melting which failed to exhaust the source in minor residual phases). In comparison with estimates of a primordial mantle composition and the mantle source of MORB, the garnet peridotite source of these Honolulu volcanics was increasingly enriched in the sequence heavy REE, Y, Tb, Ti, Sm, Zr and Hf, for which a multi-stage history is required. This composition differs from the source of the previously erupted tholeiitic shield, nor is it represented in the upper-mantle xenoliths in the lavas and tuff of the unit.-R.A.H.

Chemical layering in the upper mantle of Mars: Evidence from olivine-hosted melt inclusions in Tissint

NASA Astrophysics Data System (ADS)

Basu Sarbadhikari, A.; Babu, E. V. S. S. K.; Vijaya Kumar, T.

2017-02-01

Melting of Martian mantle, formation, and evolution of primary magma from the depleted mantle were previously modeled from experimental petrology and geochemical studies of Martian meteorites. Based on in situ major and trace element study of a range of olivine-hosted melt inclusions in various stages of crystallization of Tissint, a depleted olivine-phyric shergottite, we further constrain different stages of depletion and enrichment in the depleted mantle source of the shergottite suite. Two types of melt inclusions were petrographically recognized. Type I melt inclusions occur in the megacrystic olivine core (Fo76-70), while type II melt inclusions are hosted by the outer mantle of the olivine (Fo66-55). REE-plot indicates type I melt inclusions, which are unique because they represent the most depleted trace element data from the parent magmas of all the depleted shergottites, are an order of magnitude depleted compared to the type II melt inclusions. The absolute REE content of type II displays parallel trend but somewhat lower value than the Tissint whole-rock. Model calculations indicate two-stage mantle melting events followed by enrichment through mixing with a hypothetical residual melt from solidifying magma ocean. This resulted in 10 times enrichment of incompatible trace elements from parent magma stage to the remaining melt after 45% crystallization, simulating the whole-rock of Tissint. We rule out any assimilation due to crustal recycling into the upper mantle, as proposed by a recent study. Rather, we propose the presence of Al, Ca, Na, P, and REE-rich layer at the shallower upper mantle above the depleted mantle source region during the geologic evolution of Mars.

Geochemical, oxygen, and neodymium isotope compositions of metasediments from the Abitibi greenstone belt and Pontiac Subprovince, Canada: Evidence for ancient crust and Archean terrane juxtaposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, R.; Kerrich, R.; Maas, R.

1993-02-01

The Abitibi greenstone belt (AGB) and Pontiac Subprovince (PS) in the southwestern Superior Province are adjacent greenstone-plutonic and metasedimentary-dominated terranes, respectively, separated by a major fault zone. Metasediments from these two contrasting terranes are compared in terms of major- and trace-element and O- and Nd-isotope compositions, and detrital zircon ages. The following two compositional populations of metasediments are present in the low-grade, Abitibi southern volcanic zone: (1) a mafic-element-enriched population (MEP) characterized by flat, depleted REE patterns; enhanced Mg, Cr, Co, Ni, and Sc; low-incompatible-element contents; and minor or absent normalized negative troughs at Nb, Ta, and Ti; and (2)more » a low-mafic-element population (LMEP) featuring LREE-enriched patterns; enhanced Rb, Cs, Ba, Th, and U contents; and pronounced normalized negative troughs at Nb, Ta, and Ti. These geochemical features are interpreted to indicate that the MEP sediments were derived from an ultramafic- and mafic-dominated oceanic provenance, whereas the LMEP sediments represent mixtures of mafic and felsic are source rocks. The PS metasediments are essentially indistinguishable from Abitibi LMEP on the basis of major-element and transition metal abundances, suggesting comparable types of source rocks and degrees of maturity, but are distinct in terms of some trace elements and O-isotope compositions. The Pontiac metasediments are depleted in [sup 18]O and enriched in Cs, Ba, Pb, Th, U, Nb, Ta, Hf, Zr, and total REE and also have higher ratios of Rb/K, Cs/Rb, Ba/Rb, Ta/Nb, Th/La, and Ba/La relative to the Abitibi LMEP. Two subtypes of REE patterns have been identified in PS metasediments. The first subtype is interpreted to be derived from provenances of mixed mafic and felsic volcanic rocks, whereas the Eu-depleted type has features that are typical of post-Archean sediments or Archean K-rich granites and volcanic equivalents. 100 refs., 9 figs., 4 tabs.« less

Petrology of the axial ridge of the Mariana Trough backarc spreading center

NASA Astrophysics Data System (ADS)

Hawkins, J. W.; Lonsdale, P. F.; Macdougall, J. D.; Volpe, A. M.

1990-10-01

The axial ridge of the Mariana Trough backarc basin, between 17°40'N and 18°30'N rises as much as 1 km above the floor of a 10-15 km wide rift valley. Physiographic segmentation, with minor ridge offsets and overlaps, coincides with a petrologic segmentation seen in trace element and isotope chemistry. Analyses of 239 glass and 40 aphyric basalt samples, collected with ALVIN and by dredging, show that the axial ridge is formed largely of (olivine) hypersthene-normative tholeiitic basalt. About half of these are enriched in both LIL elements and volatiles, but are depleted in HFS elements like other rocks found throughout much of the Mariana Trough. The LIL enrichments distinguish these rocks from N-MORB even though Nd and Sr isotope ratios indicate that much of the crust formed from a source similar to that for N-MORB. In addition to LIL-enriched basalt there is LIL depleted basalts even more closely resembling N-MORB in major and trace elements as well as Sr, Nd and Pb isotopes. Both basalt varieties have higher Al and lower total Fe than MORB at equivalent Mg level. Mg# ranges from relatively "primitive" (e.g. Mg# 65-70) to more highly fractionated (e.g. Mg# 45-50). Highest parts of the axial ridge are capped by pinnacles with elongated pillows of basaltic andesite (e.g. 52-56%) SiO 2. These are due to extreme fractional crystallization of basalts forming the axial ridge. Active hydrothermal vents with chimneys and mats of opaline silica, barite, sphalerite and lesser amounts of pyrite, chalcopyrite and galena formed near these silicic rocks. The vents are surrounded by distinctive vent animals, polychaete worms, crabs and barnacles. Isotope data indicate that the Mariana Trough crust was derived from a heterogeneous source including mantle resembling the MORB-source and an "arc-source" component. The latter was depleted in HFS elements in previous melting events and later modified by addition of H 2O and LIL elements.

An internally consistent inverse model to calculate ridge-axis hydrothermal fluxes

NASA Astrophysics Data System (ADS)

Coogan, L. A.; Dosso, S.

2010-12-01

Fluid and chemical fluxes from high-temperature, on-axis, hydrothermal systems at mid-ocean ridges have been estimated in a number of ways. These generally use simple mass balances based on either vent fluid compositions or the compositions of altered sheeted dikes. Here we combine these approaches in an internally consistent model. Seawater is assumed to enter the crust and react with the sheeted dike complex at high temperatures. Major element fluxes for both the rock and fluid are calculated from balanced stoichiometric reactions. These reactions include end-member components of the minerals plagioclase, pyroxene, amphibole, chlorite and epidote along with pure anhydrite, quartz, pyrite, pyrrhotite, titanite, magnetite, ilmenite and ulvospinel and the fluid species H2O, Mg2+, Ca2+, Fe2+, Na+, Si4+, H2S, H+ and H2. Trace element abundances (Li, B, K, Rb, Cs, Sr, Ba, U, Tl, Mn, Cu, Zn, Co, Ni, Pb and Os) and isotopic ratios (Li, B, O, Sr, Tl, Os) are calculated from simple mass balance of a fluid-rock reaction. A fraction of the Cu, Zn, Pb, Co, Ni, Os and Mn in the fluid after fluid-rock reaction is allowed to precipitate during discharge before the fluid reaches the seafloor. S-isotopes are tied to mineralogical reactions involving S-bearing phases. The free parameters in the model are the amounts of each mineralogical reaction that occurs, the amounts of the metals precipitated during discharge, and the water-to-rock ratio. These model parameters, and their uncertainties, are constrained by: (i) mineral abundances and mineral major element compositions in altered dikes from ODP Hole 504B and the Pito and Hess Deep tectonic windows (EPR crust); (ii) changes in dike bulk-rock trace element and isotopic compositions from these locations relative to fresh MORB glass compositions; and (iii) published vent fluid compositions from basalt-hosted high-temperature ridge axis hydrothermal systems. Using a numerical inversion algorithm, the probability density of different model parameter sets has been computed and thus the probability of different fluid and chemical fluxes. Most data can be fit by the model within their uncertainty. The entire dataset is best-fit with a water-to-rock mass ratio between 1.3 and 2.1 (~1 to 1.5 x10**13 kg yr-1) implying a substantial fraction of the magmatic (latent) heat available to drive the axial hydrothermal system is extracted by these systems. Many element fluxes are better constrained than in previous studies (e.g., Sr: 2 to 7 x10**8 moles yr-1; Ca: 2 to 7 x10**11 moles yr-1). Future developments will use experimental data to further constrain the model.

Lithospheric and Asthenospheric Contributions to Post-Collisional Volcanism in the Lesser Caucasus Mts (Armenia)

NASA Astrophysics Data System (ADS)

Sugden, P.; Savov, I. P.; Wilson, M.; Meliksetian, K.; Navasardyan, G.

2017-12-01

Continental collision zones remain the most enigmatic tectonic setting for volcanic activity on earth. The Lesser Caucasus Mts are host to widespread and unique intraplate volcanism, associated with the active Arabia-Eurasia continental collision. Volcanic products range from alkali basalts to rhyolites (including extensive ignimbrites), and occur as basaltic lava flow fields, large composite and shield volcanoes, and regions of distributed (mostly monogenetic) volcanism. Geomorphology, archaeology, and historical accounts suggest volcanic activity has extended in to the Holocene-historical period. The high quality of the exposures and the diversity of unaltered rock types makes Armenia an ideal natural laboratory for studying the sources of magmatism in an active continental collision zone. For the first time, we will present the mineral chemistry (ol, px, amph), whole rock major and trace element, and Sr-Nd isotope compositions of volcanic rocks from southernmost Armenia- namely the Gegham, Vardenis and Syunik volcanic highlands. We compare our dataset with the composition of post-collisional volcanic rocks elsewhere in the Arabia-Eurasia collision zone. Samples from S. Armenia are more mafic, more alkaline and more K2O rich. All volcanic rocks show negative HFSE anomalies and LILE and LREE enrichments reminiscent of continental volcanic arc settings. However, volcanic rocks in Southern Armenia are further enriched in some of the most incompatible trace elements, most notably LREE, Sr and P, and have higher La/Yb, Th/Yb, Ta/Yb, and more variable Th/Nb. Volcanic rocks from Eastern Anatolia and N. Armenia have Sr-Nd isotope compositions similar to those of the Mesozoic volcanic arc (87Sr/86Sr 0.7034-0.7045; 143Nd/144Nd 0.5128-0.5129), whereas samples from S. Armenia deviate towards more enriched compositions resembling a typical EM-I type reservoir (87Sr/86Sr 0.7041- 0.7047; 143Nd/144Nd 0.5127-0.5128). We argue that these distinctive geochemical characteristics result from the addition of an enriched lithospheric component to a ubiquitous subduction-modified baseline asthenospheric mantle. This EM-I like component may be characteristic for not only intraplate hotspot volcanoes but also to collisional and arc settings.

Resolving the potential mantle reservoirs that influence volcanism in the West Antarctic Rift System

NASA Astrophysics Data System (ADS)

Maletic, E. L.; Darrah, T.

2017-12-01

Lithospheric extension and magmatism are key characteristics of active continental rift zones and are often associated with long-lasting alkaline magmatic provinces. In these settings, a relationship between lithospheric extension and mantle plumes is often assumed for the forces leading to rift evolution and the existence of a plume is commonly inferred, but typically only extension is supported by geological evidence. A prime example of long-lasting magmatism associated with an extensive area of continental rifting is the West Antarctic Rift System (WARS), a 2000 km long zone of ongoing extension within the Antarctic plate. The WARS consists of high alkaline silica-undersaturated igneous rocks with enrichments in light rare earth elements (LREEs). The majority of previous geochemical work on WARS volcanism has focused on bulk classification, modal mineralogy, major element composition, trace element chemistry, and radiogenic isotopes (e.g., Sr, Nd, and Pb isotopes), but very few studies have evaluated volatile composition of volcanics from this region. Previous explanations for WARS volcanism have hypothesized a plume beneath Marie Byrd Land, decompression melting of a fossilized plume head, decompression melting of a stratified mantle source, and mixing of recycled oceanic crust with one or more enriched mantle sources from the deep mantle, though researchers are yet to reach a consensus. Unlike trace elements and radiogenic isotopes which can be recycled between the crust and mantle and which are commonly controlled by degrees of partial melting and prior melt differentiation, noble gases are present in low concentrations and chemically inert, allowing them to serve as reliable tracers of volatile sources and subsurface processes. Here, we present preliminary noble gas isotope (e.g., 3He/4He, CO2/3He, CH4/3He, 40Ar/36Ar, 40Ar*/4He) data for a suite of lava samples from across the WARS. By coupling major and trace element chemistry with noble gas elemental and isotopic composition and other volatiles from a suite of volcanic rocks in the WARS, we can better constrain a magmatic source and provide geological evidence that could support or oppose the existence of a mantle plume, HIMU plume, or deconvolve mantle-lithosphere interactions.

Continuous magma recharge at Mt. Etna during the 2011-2013 period controls the style of volcanic activity and compositions of erupted lavas

NASA Astrophysics Data System (ADS)

Viccaro, Marco; Calcagno, Rosario; Garozzo, Ileana; Giuffrida, Marisa; Nicotra, Eugenio

2015-02-01

Volcanic rocks erupted during the January 2011 - April 2013 paroxysmal sequence at Mt. Etna volcano have been investigated through in situ microanalysis of mineral phases and whole rock geochemistry. These products have been also considered within the framework of the post-2001 record, evidencing that magmas feeding the 2011-2013 paroxysmal activity inherited deep signature comparable to that of the 2007-2009 volcanic rocks for what concerns their trace element concentration. Analysis performed on plagioclase, clinopyroxene and olivine, which are sensitive to differentiation processes, show respectively fluctuations of the An, Mg# and Fo contents during the considered period. Also major and trace elements measured on the whole rock provide evidence of the evolutionary degree variations through time. Simulations by MELTS at fixed chemical-physical parameters allowed the definition of feeding system dynamics controlling the geochemical variability of magmas during the 2011-2013 period. Specifically, compositional changes have been interpreted as due to superimposition of fractional crystallization and mixing in variable proportions with more basic magma ascending from intermediate to shallower levels of the plumbing system. Composition of the recharging end-member is compatible with that of the most basic magmas emitted during the 2007 and the early paroxysmal eruptions of 2012. Analysis of the erupted volumes of magma combined with its petrologic evolution through time support the idea that large volumes of magma are continuously intruded and stored in the intermediate plumbing system after major recharging phases in the deepest levels of it. Transient recharge from the intermediate to the shallow levels is then responsible for the paroxysmal eruptions.

Chemical composition of core samples from Newark Basin, a potential carbon sequestration site

NASA Astrophysics Data System (ADS)

Seltzer, A. M.; Yang, Q.; Goldberg, D.

2012-12-01

Injection of carbon dioxide into deep saline aquifers has been identified as a promising mitigation option of greenhouse gases, the successful management of which is considered to be one of the most urgent and important challenges. Given the high energy production in the New York metropolitan area, the Newark Basin region is considered to be a potential future sequestration site. However, the risk of an upward leak of sequestered CO2, especially to a shallow drinking water aquifer, is a key concern facing geological sequestration as a safe and viable mitigation option. In this study, we measured the chemical composition of 25 cores from various depths throughout Newark Basin as a precursor for an ex situ incubation experiment using these rock samples and aquifer water to simulate a leak event. Inductively coupled plasma mass spectrometry analysis of microwave-assisted digested rock powders and X-ray fluorescence analysis of the rock powders were conducted to obtain the concentrations of major and trace elements. Most of the major and trace elements show wide concentration ranges at one to two orders of magnitude. Understanding the chemical composition of these Newark Basin core samples is important not only for characterizing materials used for the later lab incubation, but also for gaining a broader understanding of the chemistry of the Newark Basin and profiling the region according to the varying risks associated with a leak of sequestered CO2 to a drinking water aquifer.

A pristine eucrite-like gabbro from Descartes and its exotic kindred

NASA Technical Reports Server (NTRS)

Marvin, U. B.; Warren, P. H.

1980-01-01

A coarse-grained plagioclase-pyroxene gabbro (61224,6) with a cumulate texture suggestive of a slowly cooled plutonic rock was recovered from the 4-10 mm fraction of an Apollo 16 soil. The rock is uncommonly poor in feldspar and rich in Na for a lunar highlands lithology. Trace element analyses show extremely low siderophile element concentrations which confirm the pristine character indicated by the texture. The composition of 61224,6 is compared with those of 3 other pristine, exceptionally mafic, nonmare gabbros and of certain eucrites. 61224,6 and the three other gabbros have notable chemical differences but share relatively high ratios of Ti/Sm and Sc/Sm which suggest a possible genetic relationship. We conclude that 61224,6 represents a Na-rich cumulate from a layered intrusion within the highlands crust.

New bulk and in situ isotopic and elemental geochemistry of shallow drill core from Atlantis Massif: insights into the sources and paths of fluids and clasts

NASA Astrophysics Data System (ADS)

Bilenker, L.; Weis, D.; Scoates, J. S.

2017-12-01

We present stable Fe and radiogenic isotope and complementary trace element data for samples from Atlantis Massif. This oceanic core complex is located at 30°N where the Atlantis Transform Fault intersects the Mid-Atlantic Ridge (MAR) and is associated with the Lost City Hydrothermal Field (LCHF). It is a unique place to investigate the abiotic and biotic geochemical processes that play a role in the alteration of both crustal and mantle seafloor rocks. The samples analyzed represent a shallow (<15 m) survey of five drill sites (IODP Expedition 357) within Atlantis Massif, varying in distance from the LCHF and MAR. Analyses were performed on a sample set spanning a wide range in degree of alteration and lithology. Bulk measurements involved dissolving whole rock powders, whereas in situ analyses were performed on digested microdrilled samples or by laser ablation. Bulk rock Fe isotope values (n = 34) are correlated with loss-on-ignition (LOI) by sample lithology and location relative to LCHF. Using LOI as a proxy for degree of alteration, this observation indicates that the Fe isotope systematics of seafloor crustal and mantle rocks preserve indicators of fluid flow and source. The Hf and Nd isotope compositions for various lithologies form all analyzed sites are homogeneous, indicating minimal alteration of these isotopic systems. Bulk Sr values provide insight into elemental exchange between seawater and the surface of Atlantis Massif and bulk Pb isotopes allow for fingerprinting of the source of basalt breccias through comparison with published Pb isotope values of MAR basalts. The new results cluster around the Pb, Hf, Nd isotopic composition of mid-ocean ridge basalt from 30.68°N and do not match samples north or south of that location. In situ Fe isotope data within three altered samples reflect varying degrees of hydrothermal and seawater interaction, where the Fe isotope ratios within each sample are likely correlated with extent of exchange or redox. Laser trace element and Pb isotope data in progress will allow us to investigate this further. This study contributes to our understanding of element mobility and mass transfer during chemical reactions within the seafloor, provides insight into the source of the lithological units and fluid flow, and allows for quantification of alteration processes.

Elemental and Sr-Nd isotopic geochemistry of Cretaceous to Early Paleogene granites and volcanic rocks in the Sikhote-Alin Orogenic Belt (Russian Far East): implications for the regional tectonic evolution

NASA Astrophysics Data System (ADS)

Zhao, Pan; Jahn, Bor-ming; Xu, Bei

2017-09-01

The Sikhote-Alin Orogenic Belt in Russian Far East is an important Late Mesozoic to Early Cenozoic accretionary orogen related to the subduction of the Paleo-Pacific Plate. This belt was generated by successive accretion of terranes made of accretionary prisms, turbidite basins and island arcs to the continental margin of northeastern Asia (represented by the Bureya-Jiamusi-Khanka Block) from Jurassic to Late Cretaceous. In order to study the tectonic and crustal evolution of this orogenic belt, we carried out zircon U-Pb dating, and whole-rock elemental and Sr-Nd isotopic analyses on granites and volcanic rocks from the Primorye region of southern Sikhote-Alin. Zircon dating revealed three episodes of granitoid emplacement: Permian, Early Cretaceous and Late Cretaceous to Early Paleogene. Felsic volcanic rocks (mainly rhyolite, dacite and ignimbrite) that overlay all tectonostratigraphic terranes were erupted during 80-57 Ma, postdating the accretionary process in the Sikhote-Alin belt. The Cretaceous-Paleogene magmatism represents the most intense tectonothermal event in the Sikhote-Alin belt. Whole-rock major and trace elemental data show arc-like affinity for granitoids and volcanic rocks, indicating that they were likely generated in a supra-subduction setting. Their initial 87Sr/86Sr ratios range from 0.7048 to 0.7114, and εNd(t) values vary from +1.7 to -3.8 (mostly < 0). Thus, the elemental and Sr-Nd isotopic data suggest that the felsic magmas were generated by partial melting of source rocks comprising mantle-derived juvenile component and recycled crustal component. In addition to the occurrence in the Sikhote-Alin orogenic belt, Cretaceous to Early Paleogene magmatic rocks are also widespread in NE China, southern Korean peninsula, Japanese islands and other areas of Russian Far East, particularly along the coastal regions of the Okhotsk and Bering Seas. These rocks constitute an extended magmatic belt along the continental margin of NE Asia. The generation of this belt was ascribed to subduction of the Paleo-Pacific Plate.

Tectonic Setting and Bimodal Magmatic Evolution of Eocene Volcanic Rocks of the Bijgerd-Kuh-e Kharchin area, Uromieh-Dokhtar Zone, Iran

NASA Astrophysics Data System (ADS)

Davarpanah, A.; Khalatbari-Jafari, M.; Babaie, H. A.; Krogstad, E. J.; Mobasher, K.; La Tour, T. E.; Deocampo, D. M.

2008-12-01

Geochemical composition and texture of the Middle and Late Eocene volcanic, volcaniclastic, and volcanic- sedimentary rocks in the Bijgerd-Kuh-e Kharchin area, northwest of Saveh, provide significant geochemical and geological clues for the tectonic and magmatic evolution of the Uromieh-Dokhtar volcanic-plutonic zone of Iran. The Middle Eocene volcanic rocks have an intermediate composition and include green tuff and tuffaceous sandstone with intercalated sandstone, sandy tuff, and shale. The shale has lenses of nummulite- bearing limestone with a Middle Eocene detrital age. The time between the Middle and Late Eocene volcanic activities in this area is marked by the presence of andesite and rhyolitic tuff. The Late Eocene succession is distinguished by the presence of four alternating levels (horizons) of intermediate lava and ignimbrite which we designate as Eig. The ignimbrites of the Eig sequence have a rhyolitic composition and include ignimbrite- breccia, ignimbrite-tuff, and ignimbrite-lava pairs. The volume of the felsic volcanic rocks in this sequence far exceeds that of the intermediate rocks, which makes it unlikely that they evolved through the magmatic differentiation of a basaltic magma. The presence of the nummulite-bearing limestone lenses, and sandstone and conglomerate interbeds between the ignimbrites, suggests a shallow marine environment for the pyroclastic deposition and probably the eruptions. The tuff and siltstone of the Est unit that sits above the first ignimbrite may represent deep water, Late Eocene deposit. Oligo-Miocene limestone of the Qom Formation unconformably overlies the uppermost Late Eocene ignimbrite. Washings from red marls give microfossils with Late Eocene age for the Eig sequence, which is synchronous with other paleontological evidence that puts the peak volcanic activity as Late Eocene in the Bijgerd-Kuh-e Kharchin area. Field and petrographic evidence for magma mixing/mingling is given by the presence of mafic- intermediate enclaves in the ignimbrite, hybrid breccias with felsic and mafic clasts, felsic pseudo-flames filled with intermediate lava, heterogeneity in the ignimbrite texture, and sieve texture and oscillatory zoning of plagioclase and opacitization of olivine in the intermediate lava. Geochemical analyses of the major and trace elements (including the REE) and rock texture and assemblages indicate the bimodal magmatic characteristics of the mafic-intermediate lavas and ignimbrites. The tuff and the breccia show a hybrid elemental distribution between those of rhyolite and basalt. The ignimbrites show more enriched compositions than those of the mafic and intermediate rocks on the chondrite-normalized trace element distribution diagram. The higher enrichment of the LREE in the ignimbrites may be due to a crustal contribution. The primitive mantle-normalized elemental distributions show a distinct depletion of Nb and Ti, which suggests a subduction-related volcanism during Eocene.

Petrography and geochemistry of the primary ore zone of the Kenticha rare metal granite-pegmatite field, Adola Belt, Southern Ethiopia: Implications for ore genesis and tectonic setting

NASA Astrophysics Data System (ADS)

Mohammedyasin, Mohammed Seid; Desta, Zerihun; Getaneh, Worash

2017-10-01

The aim of this work is to evaluate the genesis and tectonic setting of the Kenticha rare metal granite-pegmatite deposit using petrography and whole-rock geochemical analysis. The samples were analysed for major elements, and trace and rare earth elements by ICP-AES and ICP-MS, respectively. The Kenticha rare metal granite-pegmatite deposit is controlled by the N-S deep-seated normal fault that allow the emplacement of the granite-pegmatite in the study area. Six main mineral assemblages have been identified: (a) alaskitic granite (quartz + microcline + albite with subordinate muscovite), (b) aplitic layer (quartz + albite), (c) muscovite-quartz-microcline-albite pegmatite, (d) spodumene-microcline-albite pegmatite, partly albitized or greisenized, (e) microcline-albite-green and pink spodumene pegmatite with quartz-microcline block, which is partly albitized and greisenized, and (f) quartz core. This mineralogical zonation is also accompanied by variation in Ta ore concentration and trace and rare earth elements content. The Kenticha granite-pegmatite is strongly differentiated with high SiO2 (72-84 wt %) and enriched with Rb (∼689 ppm), Be (∼196 ppm), Nb (∼129 ppm), Ta (∼92 ppm) and Cs (∼150 ppm) and depleted in Ba and Sr. The rare earth element (REE) patterns of the primary ore zone (below 60 m depth) shows moderate enrichment in light REE ((La/Yb)N = ∼8, and LREE/HREE = ∼9.96) and negative Eu-anomaly (Eu/Eu* = ∼0.4). The whole-rock geochemical data display the Within Plate Granite (WPG) and syn-Collisional Granite (syn-COLG) suites and interpret as its formation is crustal related melting. The mineralogical assemblage, tectonic setting and geochemical signatures implies that the Kenticha rare metal bearing granite pegmatite is formed by partial melting of metasedimentary rocks during post-Gondwana assembly and further tantalite enrichment through later hydrothermal-metasomatic processes.

Mantle xenoliths from Central Vietnam: evidence for at least Meso-Proterozoic formation of the lithospheric mantle

NASA Astrophysics Data System (ADS)

Proßegger, Peter; Ntaflos, Theodoros; Ackerman, Lukáš; Hauzenberger, Christoph; Tran, Tuan Anh

2016-04-01

Intraplate Cenozoic basalts that are widely dispersed along the continental margin of East Asia belong to the Western Pacific "diffuse" igneous province. They consist mainly of alkali basalts, basanites,rarely nephelinites, which are mantle xenolith-bearing, potassic rocks and quartz tholeiites. The volcanism in this area has been attributed to the continental extension caused by the collision of India with Asia and by the subduction of the Pacific Ocean below Asia. We studied a suite of 24 mantle xenoliths from La Bang Lake, Dak Doa district and Bien Ho, Pleiku city in the Gia Province, Central Vietnam. They are predominantly spinel lherzolites (19) but spinel harburgites (3) and two garnet pyroxenites are present as well. The sizes of the xenoliths range from 5 to 40 cm in diameter with medium to coarse-grained protogranular textures. Whole rock major and trace element analyses display a wide range of compositions. The MgO concentration varies from 36.0 to 45.8 wt% whereas Al2O3 and CaO range from 0.63 to 4.36 wt% and from 0.52 to 4.21 wt% (with one sample having CaO of 6.63 wt%) respectively. Both CaO and Al2O3 positively correlate with MgO most likely indicating that the sampled rocks were derived from a common mantle source experienced variable degrees of partial melting. Mineral analyses show that the rock forming minerals are chemically homogeneous. The Fo contents of olivine vary between 89.2 and 91.2 and the Mg# of orthopyroxene and clinopyroxene range from 89 to 92 and 89 to 94 respectively. The range of Cr# for spinel is 0.06-0.26. Model calculations in both whole rock and clinopyroxenes show that lithospheric mantle underneath Central Vietnam experienced melt extractions that vary between 2-7, 12-15 and 20-30%. The majority of the primitive mantle-normalized whole rock and clinopyroxene REE patterns are parallel to each other indicating that clinopyroxene is the main repository of the trace elements. Clinopyroxenes are divided into two groups: group A with concave upwards REE and (La/Yb)N < 1 suggesting various degrees of melt extraction and group B with (La/Yb)N ranging between 1 and 10. The group B in a mantle normalized trace element diagram shows negative Pb and Sr anomalies compared to their neighbour elements, which together with the general absence of hydrous phases, suggest variable interaction with percolating silicate melt(s). The primitive-mantle normalized highly siderophile element (HSE) concentration pattern show almost no fractionation among Ir, Ru and Pt with only slight depletion in Os suggesting very limited effect of metasomatism on the HSE contents. On the other hand, most of the samples display clear Re addition from the percolating melts preventing calculation of reliable rhenium depletion ages (TRD). However, one sample with depleted Pd and Re signature yield TRD of 1.0 Ga which can be interpreted as a minimum SCLM stabilization age in this area. Mantle xenoliths from Central Vietnam range from fertile to depleted compositions partly affected by metasomatic silicate melts. Re-Os isotopic composition reveals a Meso-Proterozoic minimum stabilization age of the lithospheric mantle.

Petrologic and chemical changes in ductile shear zones as a function of depth in the continental crust

NASA Astrophysics Data System (ADS)

Yang, Xin-Yue

Petrologic and geochemical changes in ductile shear zones are important for understanding deformational and geochemical processes of the continental crust. This study examines three shear zones that formed under conditions varying from lower greenschist facies to upper amphibolite facies in order to document the petrologic and geochemical changes of deformed rocks at various metamorphic grades. The studied shear zones include two greenschist facies shear zones in the southern Appalachians and an upper amphibolite facies shear zone in southern Ontario. The mylonitic gneisses and mylonites in the Roses Mill shear zone of central Virginia are derived from a ferrodiorite protolith and characterized by a lower greenschist facies mineral assemblage. Both pressure solution and recrystallization were operative deformation mechanisms during mylonitization in this shear zone. Strain-driven dissolution and solution transfer played an important role in the mobilization of felsic components (Si, Al, K, Na, and Ca). During mylonitization, 17% to 32% bulk rock volume losses of mylonites are mainly attributed to removal of these mobile felsic components by a fluid phase. Mafic components (Fe, Mg, Ti, Mn and P) and trace elements, REE, Y, V and Sc, were immobile. At Rosman, North Carolina, the Brevard shear zone (BSZ) shows a deformational transition from the coarse-grained Henderson augen gneiss (HAG) to proto-mylonite, mylonite and ultra-mylonite. The mylonites contain a retrograde mineral assemblage as a product of fluid-assisted chemical breakdown of K-feldspar and biotite at higher greenschist facies conditions. Recrystallization and intra-crystalline plastic deformation are major deformation mechanisms in the BSZ. Fluid-assisted mylonitization in the BSZ led to 6% to 23% bulk volume losses in mylonites. During mylonitization, both major felsic and mafic elements and trace elements, Rb, Sr, Zr, V, Sc, and LREE were mobile; however, the HREEs were likely immobile. A shear zone in the Parry Sound domain, Ontario, formed at upper amphibolite facies conditions. The deformation process of the shear zone involves fully plastic deformation and high-temperature dynamic recrystallization and annealing recovery of both quartz and plagioclase. Geochemical evidence indicates that the chemical changes in the deformed rocks resulted from mixing of mafic and felsic layers together with fluid-assisted mass transfer within the shear zone. A geochemical model that incorporates closed-system two-component mixing with open-system mass transfer can well explain the observed major and trace element data.

Search for a meteoritic component at the Beaverhead impact structure, Montana

NASA Technical Reports Server (NTRS)

Lee, Pascal; Kay, Robert W.

1992-01-01

The Beaverhead impact structure, in southwestern Montana, was identified recently by the presence of shatter cones and impactites in outcrops of Proterozoic sandstones of the Belt Supergroup. The cones occur over an area greater than 100 sq km. Because the geologic and tectonic history of this region is long and complex, the outline of the original impact crater is no longer identifiable. The extent of the area over which shatter cones occur suggests, however, that the feature may have been at least 60 km in diameter. The absence of shatter cones in younger sedimentary units suggests that the impact event occurred in late Precambrian or early Paleozoic time. We have collected samples of shocked sandstone from the so-called 'Main Site' of dark-matrix breccias, and of impact breccias and melts from the south end of Island Butte. The melts, occurring often as veins through brecciated sandstone, exhibit a distinctive fluidal texture, a greenish color, and a cryptocrystalline matrix, with small inclusions of deformed sandstone. Samples of the same type, along with country rock, were analyzed previously for major- and trace-element abundances. It was found that, although the major-element composition as relatively uniform, trace-element composition showed variations between the melt material and the adjacent sandstone. These variations were attributed to extensive weathering and hydrothermal alteration. In a more specific search for a possible meteoritic signature in the breccia and the melt material we have conducted a new series of trace-element analyses on powders of our own samples by thermal neutron activation analysis. Our results indicate that Ir abundances in the breccia, the melts, and the adjacent sandstone clasts are no greater than about 0.1 ppb, suggesting no Ir enrichment of the breccia or the melts relative to the country rock. However, both the breccia and the melt material exhibit notable enrichments in Cr (8- and 10-fold), in U (9- and 5-fold), and in the heavy REE's (1.5- and 3-fold), respectively.

Geochemistry of the Shuksan greenschists and blueschists, North Cascades, Washington: Variably fractionated and altered metabasalts of oceanic affinity

NASA Astrophysics Data System (ADS)

Dungan, M. A.; Vance, J. A.; Blanchard, D. P.

1983-06-01

The Shuksan schist comprises a structurally coherent, metabasaltic member of the Easton Formation, the uppermost allochthon (Shuksan thrust plate) in the thrust system of the western North Cascades of Washington State. Late Jurassic metamorphism at moderately high P/T produced interlayering of actinolite-bearing greenschist assemblages with blue amphibole-bearing rocks. Major and trace element analyses of twelve greenschist and blueschist samples have been used to establish similarities between the basaltic protolith and moderately to strongly fractionated Type I MORB, to distinguish the effects of seafloor alteration superimposed on the primary igneous chemistry, and to evaluate the origin and nature of the chemical controls which produced the two mineral assemblages. The twelve analyzed samples exhibit moderate to strong LREE depletion, and characteristically low concentrations of other non-labile trace elements such as Nb, Th and Hf. The highly to moderately incompatible elements Ti, P, Nb, Zr, Hf, Y, Sc, and the REE vary by factors of 1.5 to 3.5 within the suite in a systematic pattern, increasing smoothly with increasing total iron. The relative enrichments of these elements are inversely proportional to bulk partition coefficients estimated for fractionation of basaltic magmas. The magnitude of the negative europium anomaly increases with overall incompatible element enrichment. These variations are consistent with the production of a wide spectrum of compositions by different degrees of low pressure fractionation of similar Type I MORB parent magmas. The concentrations of Sr, Rb, Na, and K vary irregularly and do not correlate with the non-labile trace elements. K and Rb are substantially elevated over typical MORB values in most samples and exhibit a consistently lower ratio (K/Rb=400 vs 1000) than fresh MORB. Concentrations of these four elements are believed to have been modified by low temperature seafloor alteration (pre-metamorphic) characterized by the formation of K-rich celadonitic clays, palagonite and minor potassium feldspar. The critical chemical variables that control the occurrence of actinolite and blue amphibole in the Shuksan schists are total iron, Fe2O3-content and Na/Ca (all high in blueschists). The chemical features were largely established by magmatic processes and inherited from the igneous parent rocks; the chemically more evolved samples are blueschists. The Fe2O3-content and Na/Ca, however, may be modified during alteration, rendering initial bulk compositions near the chemical boundary susceptible to changes which may shift rock compositions from one compatibility field to the other. Heterogeneous alteration of pillow lavas and other fragmental deposits, followed by intense flattening during metamorphism, provides a mechanism for generating blueschists and greenschists interlayered on the cm scale.

Geochemistry of Martian Meteorites and the Petrologic Evolution of Mars

NASA Technical Reports Server (NTRS)

Mittlefehldt, D. W.

2002-01-01

Mafic igneous rocks serve as probes of the interiors of their parent bodies - the compositions of the magmas contain an imprint of the source region composition and mineralogy, the melting and crystallization processes, and mixing and assimilation. Although complicated by their multifarious history, it is possible to constrain the petrologic evolution of an igneous province through compositional study of the rocks. Incompatible trace elements provide one means of doing this. I will use incompatible element ratios of martian meteorites to constrain the early petrologic evolution of Mars. Incompatible elements are strongly partitioned into the melt phase during igneous processes. The degree of incompatibility will differ depending on the mineral phases in equilibrium with the melt. Most martian meteorites contain some cumulus grains, but nevertheless, incompatible element ratios of bulk meteorites will be close to those of their parent magmas. ALH 84001 is an exception, and it will not be discussed. The martian meteorites will be considered in two groups; a 1.3 Ga group composed of the clinopyroxenites and dunite, and a younger group composed of all others.

Petrogenesis of Pliocene Alkaline Volcanic Rocks from Southeastern Styrian Basin, Austria

NASA Astrophysics Data System (ADS)

Ali, Sh.; Ntaflos, Th.

2009-04-01

Petrogenesis of Pliocene Alkaline Volcanic Rocks from Southeastern Styrian Basin, Austria Sh. Ali and Th. Ntaflos Dept. of Lithospheric Research, University of Vienna, Austria Neogene volcanism in the Alpine Pannonian Transition Zone occurred in a complex geodynamic setting. It can be subdivided into a syn-extentional phase that comprises Middle Miocene dominantly potassic, intermediate to acidic volcanism and a post-extensional phase, which is characterized by eruption of alkaline basaltic magmas during the Pliocene to Quartenary in the Styrian Basin. These alkaline basaltic magmas occur as small eruptive centers dominating the geomorphology of the southeastern part of the Styrian Basin. The eruptive centers along the SE Styrian Basin from North to South are: Oberpullendorf, Pauliberg, Steinberg, Strandenerkogel, Waltrafelsen and Klöch. The suite collected volcanic rocks comprise alkali basalts, basanites and nephelinites. Pauliberg: consists of alkali basalts that exhibit a narrow range of SiO2 (44.66-47.70 wt %) and wide range of MgO (8.52-13.19-wt %), are enriched in TiO2 (3.74-4.18 wt %). They are enriched in incompatible trace elements such as Zr (317-483 ppm), Nb (72.4-138 ppm) and Y (30.7-42 ppm). They have Nb/La ratio of 1.89 (average) and Cen/Ybn=15.22-23.11. Oberpullendorf: it also consists of alkali basalts with higher SiO2 (50.39 wt %) and lower TiO2 (2.80 wt %) if compared with the Pauliberg suite. Incompatible trace elements are lower than in Pauliberg; Zr =217 ppm, Nb=49.8 ppm, Y=23.6 ppm and Nb/La=1.93. The Oberpullendorf alkalibasalts are relative to Pauliberg lavas more depleted in LREE (Cen/Ybn=12.78). Steinberg: it consists of basanites with SiO2=44.49-46.85 wt %, MgO=6.30-9.13-wt %, and TiO2 =2.09-2.26 wt %. They are enriched in incompatible trace elements such as Zr (250-333 ppm), Nb (94-130 ppm), Y (24.7-31.9 ppm) and Nb/La=1.59 (average). The Cen/Ybn ratio varies between 18.17 and 22.83 indicating relative steep REE chondrite normalized patterns. Strandenerkogel: it consists of nephelinites with narrow compositional ranges; SiO2 =40.99-42.44 wt %, MgO=6.63-6.92 wt % and TiO2=2.03-2.07 wt %. They are enriched in incompatible trace elements such as Zr (362-382 ppm), Nb (139-153 ppm) and Y (39.5-40.7 ppm). They have Nb/La ratio of 1.20 and are strongly enriched in LREE (Cen/Ybn=25.04-28.11). Waltrafelsen: there are like in Strandenerkogel and have SiO2=42.42 wt %, MgO=6.55 wt %, and TiO2=2.01 wt %. The incompatible trace elements such as Zr (362 ppm), Nb (145 ppm) and Y (38.3 ppm) are similar to that of Stranerkogel. They have Nb/La ratio of 1.27 and are strongly enriched in LREE (Cen/Ybn=24.92). Klöch: it consists of basanites with similar to Steinberg composition (SiO2=45.34-46.60 wt %, MgO=8.98-10.11 wt %, and TiO2= 2.28-2.37 wt %. Incompatible trace elements such as Zr (252-273 ppm), Nb (94.2-101 ppm) and Y (24.4-27.2 ppm) are high. They have Nb/La ratio of 1.71 (average). Their REE abundances compared to Steinberg are slightly lower (Cen/Ybn=18.19-20.17). The Nb/La ratio of all the studied rock varieties is greater than one indicates an OIB-like asthenospheric mantle source for the basaltic magma. All the studied rock varieties except alkali basalts of Pauliberg have Tbn/Ybn ratios which are comparable to those of the alkali basalts of Hawaii ((Tbn/Ybn range from 1.89 to 2.45); the Hawaiian basalts are considered to have been derived from a garnet-lherzolite mantle source (Frey et al. 1991; McKenzie & O'Nions, 1991). The chondrite normalized HREE abundances indicate the presence of garnet as a residual phase in the melt source region as can be inferred from the Dy/Yb ratio (average 2.93) which is greater than that of chondritic Dy/Yb ratio (1.57) All the studied rock varieties display alkaline affinity and negative K-anomaly. The negative K-anomaly suggests either a source character, (e.g. frozen HIMU-like veins or pockets in the depleted lherzolite)? or it is consistent with the presence of a K-bearing hydrous phase in the residual mantle. References FREY, F. A., GARCIA, M. O., WISE, W. S., KENNEDY, A., GURRIET, P. & ALBAREDE, F. 1991. The evolution of Mauna Kea volcano, Hawaii: Petrogenesis of tholeiitic and alkali basalts. Journal of Geophysical Research 96, 14347-75. MCKENZIE, D. P. & O'NIONS, R. K. 1991. Partial melting distributions from inversion of rare earth element concentrations. Journal of Petrology 32, 1021-91.

Geochemical and Nd isotopic constraints for the origin of Late Archean turbidites from the Yellowknife area, Northwest Territories, Canada

NASA Astrophysics Data System (ADS)

Yamashita, Katsuyuki; Creaser, Robert A.

1999-10-01

A detailed geochemical and isotopic study of Late Archean turbidites and volcanic rocks from the Yellowknife area, Slave province, was undertaken to constrain the nature of exposed crust at the time of 2.6 to 2.7 Ga crustal consolidation. The ɛNdT values of the volcanic rocks range from +1.7 to -4.4. This variation can be produced by assimilation of pre-2.8 Ga basement by a depleted mantle-derived magma, possibly followed by fractional crystallization. The turbidites are typically metamorphosed to greenschist to amphibolite facies, and where metamorphosed to greenschist facies, different units of Bouma sequence can be observed. The different units of Bouma sequence were sampled and analyzed separately to evaluate the possible differences in geochemical and isotopic signatures. The geochemical data presented here is in accord with the previously proposed model that argues for a mixture of 20% mafic-intermediate volcanic rocks, +55% felsic volcanic rocks, and +25% granitic rocks as a source of these turbidites. However, our revised calculation with the new data presented here argues for 1 to 2% input from an ultramafic source, as well as somewhat higher input from mafic-intermediate volcanic sources in the upper shale units compared to the lower sand units. The ɛNdT values of the turbidites generally are lower in the upper shale units compared to the lower sand units. Detailed inspection of trace-element data suggest that this is not an artifact of rare earth element-rich heavy minerals concentrating in the lower sand units of the turbidites, but rather is a result of “unmixing” of detritus with different ɛNdT values during sediment transportation and deposition. The upper shale units of the turbidites are isotopically compatible with a derivation mainly from crustally contaminated volcanic rocks, similar to those exposed in the Yellowknife area. The lower sand units contain a higher proportion of westerly derived plutonic rock detritus, characterized by higher ɛNdT, suggesting that there are area(s) west of Yellowknife not underlain by older (2.8-4.0 Ga) basement. The trace-element characteristics of these turbidites (i.e., Cr, Ni, La, Th, Sc, Eu/Eu∗, and GdN/YbN) are distinct from those of typical post-Archean turbidites. This observation is consistent with the models that predict that the chemical composition of the upper continental crust was slightly different in the Archean compared to post-Archean time.

Isotopic and elemental chemistry of sedimentary pyrite: A combined analytical and statistical approach to a novel planetary biosignature

NASA Astrophysics Data System (ADS)

Figueroa, M. C.; Gregory, D. D.; Lyons, T. W.; Williford, K. H.

2017-12-01

Life processes affect trace element abundances in pyrite such that sedimentary and hydrothermal pyrite have significantly different trace element signatures. Thus, we propose that these biogeochemical data could be used to identify pyrite that formed biogenetically either early in our planet's history or on other planets, particularly Mars. The potential for this approach is elevated because pyrite is common in diverse sedimentary settings, and its trace element content can be preserved despite secondary overprints up to greenschist facies, thus minimizing the concerns about remobilization that can plague traditional whole rock studies. We are also including in-situ sulfur isotope analysis to further refine our understanding of the complex signatures of ancient pyrite. Sulfur isotope data can point straightforwardly to the involvement of life, because pyrite in sediments is inextricably linked to bacterial sulfate reduction and its diagnostic isotopic expressions. In addition to analyzing pyrite of known biological origin formed in the modern and ancient oceans under a range of conditions, we are building a data set for pyrite formed by hydrothermal and metamorphic processes to minimize the risk of false positives in life detection. We have used Random Forests (RF), a machine learning statistical technique with proven efficiency for classifying large geological datasets, to classify pyrite into biotic and abiotic end members. Coupling the trace element and sulfur isotope data from our analyses with a large existing dataset from diverse settings has yielded 4500 analyses with 18 different variables. Our initial results reveal the promise of the RF approach, correctly identifying biogenic pyrite 97 percent of the time. We will continue to couple new in-situ S-isotope and trace element analyses of biogenic pyrite grains from modern and ancient environments, using cutting-edge microanalytical techniques, with new data from high temperature settings. Our ultimately goal is a refined search tool with straightforward application in the search for early life on Earth and distant life recorded in meteorites, returned samples, and in situ measurements.

Genesis of Cenozoic intraplate high Mg# andesites in Northeast China

NASA Astrophysics Data System (ADS)

Liu, J. Q.; Chen, L. H.; Zhong, Y.; Wang, X. J.

2017-12-01

High-Mg# andesites (HMAs) are usually generated in the converged plate boundary and have genetic relationships with slab subduction. However, it still remained controversial about the origin of those HMAs erupted in the intra-plate setting. Here we present major, trace element, and Sr-Nd-Pb-Hf isotopic compositions for the Cenozoic intra-plate HMAs from Northeast China to constrain their origin and formation process. Cenozoic Xunke volcanic rocks are located in the northern Lesser Khingan Range, covering an area of about 3, 000 km2. These volcanic rocks are mainly basaltic andesite and basaltic trachyandesite, with only several classified as trachyandesite and andesites. They have high SiO2 contents (54.3-57.4 wt%) and Mg# (49.6-57.8), falling into the scope of high Mg# andesites. The Xunke HMAs are enriched in large ion lithophile elements but depleted in high field strength elements, with positive Ba, K, Sr and negative Zr-Hf, and Ti anomalies. Their trace element absolute concentrations are between those of potassic basalts and Wuchagou HMAs. The Xunke HMAs have relatively enriched Sr-Nd-Hf isotopes (87Sr/86Sr = 0.705398-0.705764, ɛNd=-8.8-3.8, ɛHf=0.5-11.7), and low radiogenic Pb isotopes (206Pb/204Pb = 16.701-17.198), towards to the EM1 end-member, which indicates that they are ultimately derived from ancient, recycled crustal components. Primitive silica-rich melts were generated from higher degrees of partial melting of recycled crustal materials (relative to potassic basalts) and then interacted with the peridotite to produce the Xunke HMAs.

Trace element diffusion in minerals: the role of multiple diffusion mechanisms operating simultaneously

NASA Astrophysics Data System (ADS)

Dohmen, R.; Marschall, H.; Wiedenbeck, M.; Polednia, J.; Chakraborty, S.

2016-12-01

Diffusion of trace elements, often with ionic charge that differs from those of ions in the regular structural sites of a mineral, controls a number of important processes in rocks, such as: (i) Closure of radiogenic isotopic systems, (e.g. Pb diffusion in rutile; REE diffusion in garnet); (ii) Closure of trace element thermometers (e.g., Zr in rutile, Mg in plagioclase, Al in olivine); (iii) Closure of element exchange between melt inclusions and host minerals (e.g., H, REE in olivine). In addition, preserved trace element zoning profiles in minerals can be used for diffusion chronometry (e.g. Nb in rutile, Mg in plagioclase). However, experimentally determined diffusion coefficients of these trace elements are in many cases controversial (e.g., REE in olivine: [1] vs. [2]; Mg in plagioclase: [3] vs. [4]). We have carried out experiments to study the diffusion behavior in olivine, rutile, and plagioclase, and are able to show that two mechanisms of diffusion, differing in rates by up to four orders of magnitude, may operate simultaneously in a given crystal. The two mechanisms result in complex diffusion profile shapes. As a general rule, the incorporation of heterovalent substituting elements in relatively high concentrations is necessary to activate two diffusion mechanisms. This behavior is produced by the control of these elements on the point defect chemistry of a mineral - these impurities become a majority point defect when a threshold concentration limit is exceeded. In certain cases, e.g., for Li in olivine, the trace element can also be incorporated in different sites, resulting in interaction of the different species with other point defects (vacancies) during diffusion. Thus, depending on the diffusion couple used in the experiment, the associated concentration gradients within the mineral, and the analytical techniques used to measure the diffusion profile, only one diffusion mechanism may be activated or detected. These studies allow us to explain some of the differing results noted above and such considerations need to be taken into account when modelling diffusion in natural systems. [1] Cherniak 2010, Am Mineral 95:362-368; [2] Spandler and O'Neill 2010, Contrib Mineral Petrol 159:791-818; [3] Faak et al. 2013 Geochim Cosmochim Acta 123:195-217; [4] Van Orman et al. 2014 Earth Planet Sci Lett 385:79-88

Slab-derived metasomatism in the Carpathian-Pannonian mantle revealed by investigations of mantle xenoliths from the Bakony-Balaton Highland Volcanic Field

NASA Astrophysics Data System (ADS)

Créon, Laura; Delpech, Guillaume; Rouchon, Virgile; Guyot, François

2017-08-01

A suite of fifteen peridotite xenoliths from the Bakony-Balaton Highland Volcanic Field (BBHVF, Pannonian Basin, Central Europe) that show abundant petrographic evidence of fluid and melt percolation were studied in order to decipher the formation of their melt pockets and veins. The suite mainly consists of "fertile" lherzolites (5.8-19.9 vol.% clinopyroxene) and a few harzburgites (1.9-5.4 vol.% clinopyroxene) from well-known localities (Szentbékkálla, Szigliget) and two previously unreported localities (Füzes-tó and Mindszentkálla). Major and trace element data indicate that most of the peridotites record variable degrees of partial melt extraction, up to > 15% for the harzburgites. Subsequently, the xenoliths experienced at least two stages of metasomatic modification. The first stage was associated with percolation of a volatile-bearing silicate melt and resulted in crystallization of amphibole, enrichment in the most incompatible trace elements (Ba, Th, U, Sr), and development of negative Nb-Ta anomalies in clinopyroxene. The second and last metasomatic event, widespread beneath the BBHVF, is associated with the formation of silicate melt pockets, physically connected to a network of melt veins, with large and abundant CO2 vesicles. The glass in these veins has sub-alkaline trachy-andesitic composition and displays an OIB-like trace element signature. Its composition attests to the migration through a supra-subduction zone mantle wedge of silicic melt highly enriched in volatiles (CO2, H2O, Cl, F), LILE, REE and HFSE and consistent with compositions of natural and experimental examples of slab melting-derived magma. In the present case, however, melt was likely derived from melting of oceanic crust and carbonated sediments under conditions where Nb-rich mineral phases were not stable in the residue. A likely scenario for the origin such melts involves melting after subduction ceased as the slab thermally equilibrated with the asthenosphere. Melt-rock reactions due to ascent of hot, CO2-rich, siliceous melt to near-Moho depths triggered destabilization of amphibole and primary clinopyroxene, spinel, and possibly olivine. The resulting andesitic glass in melt pockets evolved to more mafic compositions due to mantle mineral assimilation but has heterogeneous trace element signatures mostly inherited from preexisting amphibole. The present example of melt-rock reactions between highly volatile-enriched siliceous slab-derived melt and peridotite from the upper part of the lithospheric mantle ultimately produced derivative melt with major element composition akin to calc-alkaline basaltic andesite, with generally low trace elements concentrations but selective pronounced enrichments in LILE's such as Ba, Sr, Pb.

The Quaternary calc-alkaline volcanism of the Patagonian Andes close to the Chile triple junction: geochemistry and petrogenesis of volcanic rocks from the Cay and Maca volcanoes (˜45°S, Chile)

NASA Astrophysics Data System (ADS)

D'Orazio, M.; Innocenti, F.; Manetti, P.; Tamponi, M.; Tonarini, S.; González-Ferrán, O.; Lahsen, A.; Omarini, R.

2003-08-01

Major- and trace-element, Sr-Nd isotopes, and mineral chemistry data were obtained for a collection of volcanic rock samples erupted by the Cay and Maca Quaternary volcanoes, Patagonian Andes (˜45°S, Chile). Cay and Maca are two large, adjacent stratovolcanoes that rise from the Chiloe block at the southern end of the southern volcanic zone (SVZ) of the Andes. Samples from the two volcanoes are typical medium-K, calc-alkaline rocks that form two roughly continuous, largely overlapping series from subalkaline basalt to dacite. The overall geochemistry of the samples studied is very similar to that observed for most volcanoes from the southern SVZ. The narrow range of Sr-Nd isotope compositions ( 87Sr/ 86Sr=0.70389-0.70431 and 143Nd/ 144Nd=0.51277-0.51284) and the major- and trace-element distributions indicate that the Cay and Maca magmas differentiated by crystal fractionation without significant contribution by crustal contamination. This is in accordance with the thin (<30 km), relatively young (Paleozoic or more recent) continental crust beneath the volcanoes. The nature of the subduction-derived materials involved in the genesis of the Cay and Maca magmas is investigated by means of the relative concentration of fluid mobile (e.g. Ba) and fluid immobile (e.g. Nb, Ta, Zr, Y) elements and other relevant trace-element ratios (e.g. Sr/Y). The results indicate that small amounts (<1 wt%) of both subducted sediments and slab-released fluids were added to the mantle sources of the Cay and Maca volcanoes and that, despite the very young age (<10 Ma) of the oceanic lithosphere subducted beneath the volcanoes, slab melts were not involved in the magma genesis. Notwithstanding the proximity of the Cay and Maca magma sources to the northern edge of the slab window generated by the subduction of the Chile ridge under the South American plate, we did not find any geochemical evidence for a contribution of a subslab asthenospheric mantle. However, this mantle has been used to explain the peculiar geochemical features (e.g. the mild alkalinity and relatively low ratios between large ion lithophile and high field strength elements) of the Hudson volcano, which is located even closer to the slab window than the Cay and Maca volcanoes are.

Actualistic models of mantle metasomatism documented in a composite xenolith from Dish Hill, California

USGS Publications Warehouse

Nielson, J.E.; Budahn, J.R.; Unruh, D.M.; Wilshire, H.G.

1993-01-01

Major and trace-element whole rock and mineral variations in composite hornblendite-peridotite xenolith Ba-2-1, from Dish Hill, CA, are due to a single event of metasomatism in the mantle. The hornblendite is the crystallized selvage of a dike conduit charged with incompatible-element-enriched hydrous mafic magma. The magma infiltrated the refractory peridotite wallrock, reacted with its constituent minerals, and simultaneously deposited amphibole. The systematic data from this study show considerable variation in isotopic values and trace elements. These data provide insight into a mantle process that was defined previously from samples without context, lacking evidence about the number or source of metasomatic events. In the contact zone of Ba-2-1, peridotite is enriched in Fe, Ti, CO2) and H2O; clinopyroxene and amphibole also are enriched in Fe and Ti, but clinopyroxene appears slightly depleted in CaO. Compared to chondrites, peridotite, clinopyroxene, and probably amphibole are enriched in light rare earth (LREEcn) and other incompatible trace elements. Values of 87Sr 86Sr and 143Nd 144Nd in the contact zone are close to isotopic equilibrium with the dike. Whole rock and constituent clinopyroxene compositions change to those of refractory peridotite with distance from the contact. These compositional variations were modelled using Gresens' equation for whole-rock major and minor elements, and calculations for isotopic ratios and REEs, which emulate the effects of Chromatographic fractionation. The choice of endmembers was restricted to compositions actually present in mantle samples from Dish Hill. Model results indicate that: 1. (1) the variations can be explained as the result of a single metasomatic event, probably a single pulse of previously fractionated liquid; 2. (2) the ratio of total interacting liquid to peridotite was at least 1:3 by weight in the contact zone; and 3. (3) the composition of the metasomatic liquid changed progressively as it infiltrated beyond that zone. The small distance over which variations occur is due to the small amount of liquid that infiltrated. Only in the contact zone was peridotite wallrock saturated by a liquid composition similar to the dike. Comparison of the Ba-2-1 data with those of another xenolith from Dish Hill suggests that the compositional variations of mantle metasomatism result from both the compositional contrast between the metasomatizing liquid and wallrock and the relative abundances of each. Compositional and volumetric variations of mantle partial melts and their fractionates, and repeated events of melting and reaction in contiguous mantle, can create broad ranges of metasomatic "signatures" from the same process. ?? 1993.

The chemical signatures of progressive dehydration stages in subducted serpentinites

NASA Astrophysics Data System (ADS)

Pettke, T.; Spandler, C.; Kodolanyi, J.; Scambelluri, M.

2009-04-01

Fluids mediate chemical cycling in subduction zones. Nonetheless, the chemistry of serpentinite-dehydration fluids from down-going slabs and their chemical effects on ascent are only very poorly constrained. We report new data on discontinuous dehydration reactions, including the measurement of individual fluid inclusions in prograde minerals from natural occurrences, and one case study tracing the infiltration of serpentinite-derived fluid in mafic eclogite. Together, these studies demonstrate that serpentinite-derived fluids are commonly dilute, but that there may be selected trace element abundances (and ratios ?) that characterize such fluid provenance. Brucite dehydration represents the first relevant liberation of crystal-bound water from serpentinites formed on the ocean floor (ocean floor mantle hydration chemistry is addressed in Kodolanyi et al., this session). Discordant olivine-Ti-clinohumite-antigorite-clinopyroxene-magnetite veins in ca. 2.3 GPa antigorite serpentinites of the Erro Tobbio in the Ligurian Alps, Italy, formed from aqueous, dilute fluids containing Li, Sr, Ba, Rb, Pb as determined on texturally-early fluid inclusions in olivine. This prograde olivine preserves high Ni (1500 - 3000 µg/g) and is identified most readily by elevated Li (1-20 µg/g), B (1-20 µg/g) and Mn contents. Aqueous fluid inclusions in some clinopyroxene (Cpx) of the same veins host variably (sometimes highly) saline fluid inclusions, interpreted to represent the "spent" fluid after formation of hydrous vein minerals (chlorite, antigorite). Vein bulk-rock trace-element concentrations show enrichment in Ti, Ba, Nb, Li, HREE and Cu relative to the wall rocks, accompanied by depletion in Cr. This mostly reflects the mineral transformations (sources / sinks) occurring at this stage of serpentinite dehydration. Antigorite-breakdown is arguably the most prominent water release from down-going slabs. Olivine-orthopyroxene-chlorite rocks at Cerro del Almirez (Spain), recording this dehydration event, contain olivine-hosted polyphase inclusions interpreted to represent fluid inclusions trapped during antigorite breakdown. Preliminary compositional data show enrichments in B, Cs, Pb, Li, Sr, Rb, K, Ba (decreasing order) and depletions in Ca, Ti, La relative to primitive mantle, closely corresponding to the incompatible element pattern of typical island arc lavas. Transfer of such fluids to the melting source of island arc magmas may be critical to developing their distinctive trace element signatures. Omphacite-rich (± garnet, rutile, talc and zircon) veins cutting eclogite (Fe-Ti gabbro protolith, Monviso, W Italian Alps) record serpentinite-derived fluid pathways though the subducted slab at ca. 70 km depth. Although these veins largely formed by local eclogite-derived fluids, they also preserve discrete generations of vein minerals enriched in Mg, Cr, Ni, B, As and Sb, and zircon with elevated Epsilon(Hf) compared to host-rock eclogite zircon. These chemical and isotopic characteristics suggest external fluid input, from serpentinite dehydration. Moreover, distinctive oscillatory or irregular Cr zonations observed in omphacite, garnet and rutile from the veins are interpreted to record episodic fracturing and fluid infiltration over >10 m along transient brittle fractures at high pressures. Our current data suggest that dehydration fluid pervades the rock at the site of liberation, and that episodic fluid escape from the dehydration site may be effectively channelized. This supports growing evidence for highly focused reactive fluid flow through slabs. Robust constraints on the chemical composition and nature of dehydration fluids from serpentinites and how they evolve during ascent may greatly aid in recognizing such features from outcrop to thin-section scales, in turn providing us with more comprehensive sample material to advance our understanding on fluid-mediated cycling in subduction zones. Reference Kodolanyi et al., this session

Geochemical characterization of the siliciclastic rocks of Chitravati Group, Cuddapah Supergroup: Implications for provenance and depositional environment

NASA Astrophysics Data System (ADS)

Somasekhar, V.; Ramanaiah, S.; Sarma, D. Srinivasa

2018-06-01

Petrological and geochemical studies have been carried out on Pulivendla and Gandikota Quartzite from Chitravati Group of Cuddapah Supergroup to decipher the provenance and depositional environment. Both the units are texturally mature with sub-rounded to well-rounded and moderately to well-sorted grains. Majority of the framework grains are quartz, in the form of monocrystalline quartz, followed by feldspars (K-feldspar and plagioclase), mica, rock fragments, heavy minerals, with minor proportion of the matrix and cement. Based on major element geochemical classification diagram, Pulivendla Quartzite is considered as quartz-arenite and arkose to sub-arkose, whereas Gandikota Quartzite falls in the field of lith-arenite and arkose to sub-arkose. Weathering indices like CIA, PIA, CIW, ICV, Th/U ratio and A-CN-K ternary diagram suggest moderate to intense chemical weathering of the source rocks of these quartzites. Whole rock geochemistry of quartzites indicate that they are primarily from the first-cycle sediments, along with some minor recycled components. Also their sources were mostly intermediate-felsic igneous rocks of Archean age. The tectonic discrimination plots, Th-Sc-Zr/10 of both these formations reflect active to passive continental margin setting. Chondrite-normalized rare earth element (REE) patterns, and various trace element ratios like Cr/Th, Th/Co, La/Sc and Th/Cr indicate dominantly felsic source with minor contribution from mafic source. Th/Sc ratios of Pulivendla and Gandikota Quartzite are in close proximity with average values of 2.83, 3.45 respectively, which is higher than AUCC (Th/Sc=0.97), demonstrating that the contributions from more alkali source rocks than those that contributed to AUCC.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Guohui; Qafoku, Nikolla; Lawter, Amanda R.

A series of batch and column experiments combined with solid phase characterization studies (i.e., quantitative x-ray diffraction and wet chemical extractions) were conducted to address a variety of scientific issues and evaluate the impacts of the potential leakage of carbon dioxide (CO2) from deep subsurface storage reservoirs. The main objective was to gain an understanding of how CO2 gas influences: 1) the aqueous phase pH; and 2) mobilization of major, minor, and trace elements from minerals present in an aquifer overlying potential CO2 sequestration subsurface repositories. Rocks and slightly weathered rocks representative of an unconfined, oxidizing carbonate aquifer within themore » continental US, i.e., the Edwards aquifer in Texas, were used in these studies. These materials were exposed to a CO2 gas stream or were leached with a CO2-saturated influent solution to simulate different CO2 gas leakage scenarios, and changes in aqueous phase pH and chemical composition were measured in the liquid samples collected at pre-determined experimental times (batch experiments) or continuously (column experiments). The results from the strong acid extraction tests confirmed that in addition to the usual elements present in most soils, rocks, and sediments, the Edward aquifer samples contain As, Cd, Pb, Cu, and occasionally Zn, which may potentially be mobilized from the solid to the aqueous phase during or after exposure to CO2. The results from the batch and column experiments confirmed the release of major chemical elements into the contacting aqueous phase (such as Ca, Mg, Ba, Sr, Si, Na, and K); the mobilization and possible rapid immobilization of minor elements (such as Fe, Al, and Mn), which are able to form highly reactive secondary phases; and sporadic mobilization of only low concentrations of trace elements (such as As, Cd, Pb, Cu, Zn, Mo, etc.). The results from this experimental research effort will help in developing a systematic understanding of how CO2 leakage is likely to influence pertinent geochemical processes (e.g., dissolution/precipitation, sorption/desorption) in the aquifer sediments and will support site selection, risk assessment, policy-making, and public education efforts associated with geologic carbon sequestration.« less

A relatively reduced Hadean continental crust

NASA Astrophysics Data System (ADS)

Yang, Xiaozhi; Gaillard, Fabrice; Scaillet, Bruno

2014-05-01

Among the physical and chemical parameters used to characterize the Earth, oxidation state, as reflected by its prevailing oxygen fugacity (fO2), is a particularly important one. It controls many physicochemical properties and geological processes of the Earth's different reservoirs, and affects the partitioning of elements between coexisting phases and the speciation of degassed volatiles in melts. In the past decades, numerous studies have been conducted to document the evolution of mantle and atmospheric oxidation state with time and in particular the possible transition from an early reduced state to the present oxidized conditions. So far, it has been established that the oxidation state of the uppermost mantle is within ±2 log units of the quartz-fayalite-magnetite (QFM) buffer, probably back to ~4.4 billion years ago (Ga) based on trace-elements studies of mantle-derived komatiites, kimberlites, basalts, volcanics and zircons, and that the O2 levels of atmosphere were initially low and rose markedly ~2.3 Ga known as the Great Oxidation Event (GOE), progressively reaching its present oxidation state of ~10 log units above QFM. In contrast, the secular evolution of oxidation state of the continental crust, an important boundary separating the underlying upper mantle from the surrounding atmosphere and buffering the exchanges and interactions between the Earth's interior and exterior, has rarely been addressed, although the presence of evolved crustal materials on the Earth can be traced back to ~4.4 Ga, e.g. by detrital zircons. Zircon is a common accessory mineral in nature, occurring in a wide variety of igneous, sedimentary and metamorphic rocks, and is almost ubiquitous in crustal rocks. The physical and chemical durability of zircons makes them widely used in geochemical studies in terms of trace-elements, isotopes, ages and melt/mineral inclusions; in particular, zircons are persistent under most crustal conditions and can survive many secondary processes such as metamorphism, weathering and erosion. Thus, zircons in granites of shallow crust may record the chemical/isotopic composition of the deep crust that is otherwise inaccessible, and offer robust records of the magmatic and crust-forming events preserved in the continental crust. In fact, due to the absence of suitable rock records (in particular for periods older than ~4.0 Ga), studies in recent years concerning the nature, composition, growth and evolution of the continental crust, and especially the Hadean crust, have heavily relied on inherited/detrital zircons. Natural igneous zircons incorporate rare-earth elements (REE) and other trace elements in their structure at concentrations controlled by the temperature, pressure, fO2 and composition of their crystallization environment. Petrological observations and recent experiments have shown that the concentration of Ce relative to other REE in igneous zircons can be used to constrain the fO2 during their growth. By combining available trace-elements data of igneous zircons of crustal origin, we show that the Hadean continental crust was significantly more reduced than its modern counterpart and experienced progressive oxidation till ~3.6 billions years ago. We suggest that the increase in the oxidation state of the Hadean continental crust is related to the progressive decline in the intensity of meteorite impacts during the late veneer. Impacts of carbon- and hydrogen-rich materials during the formation of Hadean granitic crust must have favoured strongly reduced magmatism. The conjunction of cold, wet and reduced granitic magmatism during the Hadean implies the degassing of methane and water. When impacts ended, magma produced by normal decompression melting of the mantle imparted more oxidizing conditions to erupted lavas and the related crust.

Forensic Excavation of Rock Masses: A Technique to Investigate Discontinuity Persistence

NASA Astrophysics Data System (ADS)

Shang, J.; Hencher, S. R.; West, L. J.; Handley, K.

2017-11-01

True persistence of rock discontinuities (areas with insignificant tensile strength) is an important factor controlling the engineering behaviour of fractured rock masses, but is extremely difficult to quantify using current geological survey methodologies, even where there is good rock exposure. Trace length as measured in the field or using remote measurement devices is actually only broadly indicative of persistence for rock engineering practice and numerical modelling. Visible traces of discontinuities are treated as if they were open fractures within rock mass classifications, despite many such traces being non-persistent and actually retaining considerable strength. The common assumption of 100% persistence, based on trace length, is generally extremely conservative in terms of strength and stiffness, but not always so and may lead to a wrong prediction of failure mechanism or of excavatability. Assuming full persistence would give hopelessly incorrect predictions of hydraulic conductivity. A new technique termed forensic excavation of rock masses is introduced, as a procedure for directly investigating discontinuity persistence. This technique involves non-explosive excavation of rock masses by injecting an expansive chemical splitter along incipient discontinuities. On expansion, the splitter causes the incipient traces to open as true joints. Experiments are described in which near-planar rock discontinuities, through siltstone and sandstone, were opened up by injecting the splitter into holes drilled along the lines of visible traces of the discontinuities in the laboratory and in the field. Once exposed the surfaces were examined to investigate the pre-existing persistence characteristics of the incipient discontinuities. One conclusion from this study is that visible trace length of a discontinuity can be a poor indicator of true persistence (defined for a fracture area with negligible tensile strength). An observation from this series of experiments was that freshly failed surfaces through pre-existing rock bridges were relatively rough compared to sections of pre-existing weaker areas of geologically developed (though still incipient) discontinuities. Fractographic features such as hackle and rib marks were typical of the freshly broken rock bridges, whereas opened-up areas of incipient discontinuity were smoother. Schmidt hammer rebound values were generally higher for the rock bridge areas, probably reflecting their lower degree of chemical and physical weathering.

Biologically mediated isotope fractionations - Biochemistry, geochemical significance and preservation in the earth's oldest sediments

NASA Technical Reports Server (NTRS)

Schidlowski, M.

1983-01-01

Preferential metabolization of isotopically light carbon and sulfur has resulted in a fractionation of the stable isotopes of these elements on a global scale, with the light species (C-12, S-32) markedly concentrated in biogenic materials. Since the biological effects are basically retained when carbon and sulfur are incorporated in sediments, the respective fractionations are propagated into the rock section of the geochemical cycle, this having consequently caused a characteristic bipartition of both elements between 'light' and 'heavy' crustal reservoirs. Preservation of the biological isotope effects in sedimentary rocks makes it possible to trace the underlying biochemical processes back over most of the geological record. According to the available evidence, biological (autotrophic) carbon fixation arose prior to 3.5(if not 3.8) billion years ago, while the emergence of dissimilatory sulfate reduction antedates the appearance of the oldest presumably bacteriogenic sulfur isotope patterns in rocks between 2.7 and 2.8 billion years old. Hence, biological control of the terrestrial carbon and sulfur cycles has been established very early in the earth's history.

Geochemistry of Archean shales from the Pilbara Supergroup, Western Australia

NASA Astrophysics Data System (ADS)

McLennan, Scott M.; Taylor, S. R.; Eriksson, K. A.

1983-07-01

Archean clastic sedimentary rocks are well exposed in the Pilbara Block of Western Australia. Shales from turbidites in the Gorge Creek Group ( ca. 3.4 Ae) and shales from the Whim Creek Group ( ca. 2.7 Ae) have been examined. The Gorge Creek Group samples, characterized by muscovite-quartzchlorite mineralogy, are enriched in incompatible elements (K, Th, U, LREE) by factors of about two, when compared to younger Archean shales from the Yilgarn Block. Alkali and alkaline earth elements are depleted in a systematic fashion, according to size, when compared with an estimate of Archean upper crust abundances. This depletion is less notable in the Whim Creek Group. Such a pattern indicates the source of these rocks underwent a rather severe episode of weathering. The Gorge Creek Group also has fairly high B content (85 ± 29 ppm) which may indicate normal marine conditions during deposition. Rare earth element (REE) patterns for the Pilbara samples are characterized by light REE enrichment ( La N/Yb N ≥ 7.5 ) and no or very slight Eu depletion ( Eu/Eu ∗ = 0.82 - 0.99 ). A source comprised of about 80% felsic igneous rocks without large negative Eu-anomalies (felsic volcanics, tonalites, trondhjemites) and 20% mafic-ultramafic volcanics is indicated by the trace element data. Very high abundances of Cr and Ni cannot be explained by any reasonable provenance model and a secondary enrichment process is called for.

Geochronology and geochemistry of the Early Jurassic Yeba Formation volcanic rocks in southern Tibet: Initiation of back-arc rifting and crustal accretion in the southern Lhasa Terrane

NASA Astrophysics Data System (ADS)

Wei, Youqing; Zhao, Zhidan; Niu, Yaoling; Zhu, Di-Cheng; Liu, Dong; Wang, Qing; Hou, Zengqian; Mo, Xuanxue; Wei, Jiuchuan

2017-05-01

Understanding the geological history of the Lhasa Terrane prior to the India-Asia collision ( 55 ± 10 Ma) is essential for improved models of syn-collisional and post-collisional processes in the southern Lhasa Terrane. The Miocene ( 18-10 Ma) adakitic magmatism with economically significant porphyry-type mineralization has been interpreted as resulting from partial melting of the Jurassic juvenile crust, but how this juvenile crust was accreted remains poorly known. For this reason, we carried out a detailed study on the volcanic rocks of the Yeba Formation (YF) with the results offering insights into the ways in which the juvenile crust may be accreted in the southern Lhasa Terrane in the Jurassic. The YF volcanic rocks are compositionally bimodal, comprising basalt/basaltic andesite and dacite/rhyolite dated at 183-174 Ma. All these rocks have an arc-like signature with enriched large ion lithophile elements (LILEs; e.g., Rb, Ba and U) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs; e.g., Nb, Ta, Ti). They also have depleted whole-rock Sr-Nd and zircon Hf isotopic compositions, pointing to significant mantle isotopic contributions. Modeling results of trace elements and isotopes are most consistent with the basalts being derived from a mantle source metasomatized by varying enrichment of subduction components. The silicic volcanic rocks show the characteristics of transitional I-S type granites, and are best interpreted as resulting from re-melting of a mixed source of juvenile amphibole-rich lower crust with reworked crustal materials resembling metagraywackes. Importantly, our results indicate northward Neo-Tethyan seafloor subduction beneath the Lhasa Terrane with the YF volcanism being caused by the initiation of back-arc rifting. The back-arc setting is a likely site for juvenile crustal accretion in the southern Lhasa Terrane.

A survey of the selenochemistry of major, minor and trace elements.

NASA Technical Reports Server (NTRS)

Schmitt, R. A.; Laul, J. C.

1973-01-01

Average data for igneous and/or metaigneous rocks and soils from seven lunar sites are presented. There are compositional similarities between Apollo 11 and Luna 16 eastern maria, Ap 12 and 15 western maria, and between Ap 16 and L 20 highlands. Subtle differences do exist between the paired mare sites and the two highland sites and striking differences between the eastern and western maria. Chondritic normalized REE (rare earth element) patterns for igneous rocks and soils from all sites range from 7-350 generally with negative Eu anomalies. Anorthositic gabbroes to anorthosites, presumably highland material, exhibit a positive Eu anomaly. The REE patterns or Sr isotopic ratios suggest two lava flows each for the L 16 and Ap 14 sites, at least four lava flows for the Ap 11 and 12 site and about six for the Ap 15 site.

Geologic Field Notes, Geochemical Analyses, and Field Photographs of Outcrops and Rock Samples from the Big Delta B-1 Quadrangle, East-Central Alaska

USGS Publications Warehouse

Day, Warren C.; O'Neill, J. Michael

2008-01-01

The U.S. Geological Survey, in cooperation with the Alaska Department of Natural Resources Division of Mining, Land, and Water, has released a geologic map of the Big Delta B-1 quadrangle of east-central Alaska (Day and others, 2007). This companion report presents the major element oxide and trace element geochemical analyses, including those for gold, silver, and base metals, for representative rock units and for grab samples from quartz veins and mineralized zones within the quadrangle. Also included are field station locations, field notes, structural data, and field photographs based primarily on observations by W.C. Day with additions by J.M. O'Neill and B.M. Gamble, all of the U.S. Geological Survey. The data are provided in both Microsoft Excel spread sheet format and as a Microsoft Access database.

Local equilibrium of mafic enclaves and granitoids of the Turtle pluton, southeast California: Mineral, chemical, and isotopic evidence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, C.M.

Major element and trace element compositions of whole rocks, mineral compositions, and Rb-Sr isotopic compositions of enclave and host granitoid pairs from the Early Cretaceous, calc-alkaline Turtle pluton of southeastern California suggest that the local environmental profoundly affects some enclave types. In the Turtle pluton, where the source of fine-grained, mafic enclaves can be deduced to be magmatic by the presence of partially disaggregated basaltic dikes, mineral chemistry suggests partial or complete local equilibrium among mineral species in the enclave and its host granitoid. Because of local Rb-Sr isotopic equilibration between fine-grained enclaves and host granitoid, one cannot use Srmore » isotopes to distinguish an enclave source independent of its host rocks from an enclave source related to the enclosing pluton. However, preliminary Nd isotopic data suggest an independent, mantle source for enclaves.« less

The Uitkomst intrusion and Nkomati Ni-Cu-Cr-PGE deposit, South Africa: trace element geochemistry, Nd isotopes and high-precision geochronology

NASA Astrophysics Data System (ADS)

Maier, W. D.; Prevec, S. A.; Scoates, J. S.; Wall, C. J.; Barnes, S.-J.; Gomwe, T.

2018-01-01

The Uitkomst intrusion is a tubular mafic-ultramafic layered body that hosts one of South Africa's largest Ni-Cu-Cr-PGE deposits, Nkomati. The sulphide ore occurs in the form of massive lenses in the immediate quartzitic footwall and as disseminations within peridotite. The chromite ore forms an up to ˜10-m-thick layer in the lower portion of the intrusion. Uitkomst has generally been interpreted as a magma conduit, possibly related to the Bushveld event. Here, we present a new high-precision U-Pb zircon date of 2057.64 ± 0.69 Ma that overlaps with the age of the Merensky Reef of the Bushveld Complex and thus demonstrates a coeval relationship between the intrusions. Based on incompatible trace elements as well as O- and Nd isotope data (ɛNd -4.5 to -6.2), we show that the Uitkomst parent magmas were contaminated with up to 20% Archean upper crust prior to emplacement, and with up to 15% dolomitic country rock during emplacement. Ore formation at Nkomati was critically aided by substantial devolatisation and removal of dolomitic floor rocks leading to hydrodynamic concentration of sulphide and chromite during slumping of crystal mushes into the trough-like centre of the subsiding intrusion and its footwall.

N-MORB crust beneath Fuerteventura in the easternmost part of the Canary Islands: evidence from gabbroic xenoliths

NASA Astrophysics Data System (ADS)

Neumann, Else-Ragnhild; Vannucci, Riccardo; Tiepolo, Massimo

2005-09-01

Gabbro xenoliths reported in this paper were collected in northern Fuerteventura, the Canary Island located closest to the coast of Africa. The xenoliths are very fresh and consist of Ti-Al-poor clinopyroxene + plagioclase (An87-67) + olivine (Fo72-86) ± orthopyroxene. Clinopyroxene and orthopyroxene are constantly and markedly depleted in light rare earth elements (LREE) relative to heavy REE (HREE), as expected for cumulus minerals formed from highly refractory N-MORB-type melts. In contrast, whole-rock Primordial Mantle-normalized trace element patterns range from mildly S-shaped (mildly depleted in Pr-Sm relative to both the strongly incompatible elements Rb-La and the HREE) to enriched. Estimates show that the trace element compositions of the rocks and their minerals are compatible with formation as N-MORB gabbro cumulates, which have been infiltrated at various extents (≤1% to >5%) by enriched alkali basaltic melts. The enriched material is mainly concentrated along grain boundaries and cracks through mineral grains, suggesting that the infiltration is relatively recent, and is thus associated with the Canary Islands magmatism. Our data contradict the hypothesis that a mantle plume was present in this area during the opening of the Atlantic Ocean. No evidence of continental material that might reflect attenuated continental crust in the area has been found. Gabbro xenoliths with REE and trace element compositions similar to those exhibited by the Fuerteventura gabbros are also found among gabbro xenoliths from the islands of La Palma (western Canary Islands) and Lanzarote. The compositions of the most depleted samples from these islands are closely similar, implying that there was no significant change in chemistry during the early stages of formation of the Atlantic oceanic crust in this area. Strongly depleted gabbros similar to those collected in Fuerteventura have also been retrieved in the MARK area along the central Mid-Atlantic Ridge. The presence of N-MORB oceanic crust beneath Fuerteventura implies that the continent-ocean transition in the Canary Islands area must be relatively sharp, in contrast to the situation both further north along the coast of Morocco, and along the Iberian peninsula.

Immature intra-oceanic arc-type volcanism on the Izanagi Plate revealed by the geochemistry of the Daimaruyama greenstones in the Hiroo Complex, southern Hidaka Belt, central Hokkaido, Japan

NASA Astrophysics Data System (ADS)

Yamasaki, Toru; Nanayama, Futoshi

2018-03-01

The Izanagi Plate is assumed to have underlain the western Panthalassa Ocean to the east of Eurasia, and to have been subducting under the Eurasian continent. Although the Izanagi Plate has been lost to subduction, the subduction complexes of the circum-Panthalassa continental margins provide evidence that subduction-related volcanism occurred within the Panthalassa Ocean, and not just along its margins. The Daimaruyama mass is a kilometer-sized allochthonous greenstone body in the Hiroo Complex in the southeastern part of the Nakanogawa Group in the southern Hidaka Belt, northern Japan. The Hiroo Complex is a subduction complex that formed within the Paleo-Kuril arc-trench system at 57-48 Ma. The Daimaruyama greenstones consist mainly of coarse volcaniclastic rocks with lesser amount of lava. Red bedded chert, red shale, and micritic limestone are also observed as blocks associated with the greenstones. The presence of Early Cretaceous (Aptian-Albian) radiolaria in red bedded cherts within the greenstones indicates that the Daimaruyama greenstones formed after this time. An integrated major and trace element geochemical dataset for whole-rocks and clinopyroxenes of the greenstones indicates a calc-alkaline magmatic trend with low TiO2 contents and increases in SiO2 and decreases in FeO* with increasing differentiation. Negative anomalies of Nb, Ta, and Ti in normal mid-ocean-ridge basalt type normalized patterns are interpreted as "arc-signatures". Using "rhyolite-MELTS", we conducted a numerical simulation of magmatic differentiation under conditions of 1.5 kbar and H2O = 3 wt% to reproduce the liquid line of descent of the Daimaruyama greenstones. Back-calculations of the equilibrium melt compositions from the trace element chemistry of the clinopyroxenes generally agree with the whole-rock rare earth element compositions of the Daimaruyama greenstones, therefore providing support for the conditions used for the rhyolite-MELTS calculations as well as the actual results. Clinopyroxene trace element compositions indicate substantial enrichment of Ba in the magma, reflecting the participation of shallow subduction components such as aqueous fluids. Geochemical investigations reveal that the Daimaruyama greenstones were probably submarine volcanic rocks that formed as a result of the subduction of the Izanagi Plate within the Thalassa Ocean (the Thalassa Ocean was the eastern realm of Panthalassa, and represents the proto-Pacific Ocean) after the Early Cretaceous (Aptian-Albian; 125-101 Ma), and they were eventually accreted onto the Paleo-Kuril arc-trench system at 57-48 Ma to form an allochthonous block as part of the mélange facies of the Hiroo Complex on the landward slope of the trench.

The geochemistry and petrogenesis of an ophiolitic sequence from Pindos, Greece

NASA Astrophysics Data System (ADS)

Capedri, S.; Venturelli, G.; Bocchi, G.; Dostal, J.; Garuti, G.; Rossi, A.

1980-06-01

The ophiolites of Northern Pindos have been studied in a section close to the village of Perivoli (Grevena District). The section comprises cumulus rocks ranging from ultramafics to gabbros, overlain by dolerites (non-cumulus microgabbro) capped by thick frequently pillowed lava flows. The sequence is cut by basaltic dykes. While the cumulus rocks and the dolerites are mostly fresh, the lavas and dykes are strongly transformed. Major and trace element (Ni, Cr, Sc, Y, Zr, Nb, Sr, Ba, Zn, Cu, V, Li) data are presented for selected samples from the sequence. For some elements, the volcanic/subvolcanic rocks (flows, dykes, dolerites) exhibit wide chemical characteristics which are considered to mainly reflect variations within the parent magmas. Some lavas appear to be closely comparable with the present-day ocean-floor basalts, while other flows and most of the dykes are strongly depleted in some “incompatible” elements and are similar to some rocks from immature island arcs. The dolerites have transitional chemical features. The Pindos lavas differ from Western Mediterranean ophiolites in that the former have lower Ti,P,Zr,Y, higher Fe tot. and normally higher Ti/Zr ratio. The volcanic/subvolcanic rocks from Pindos have been derived from separate magmas. Some lavas were possibly produced by variable partial melting of an already depleted mantle source, while the lavas exhibiting ocean-floor affinity were probably generated by partial melting of a less depleted source. The wide chemical variations of the Pindos lavas cannot be easily explained by an ocean-ridge system. An “island arc-marginal basin system” could better account for the observed chemical features.

Analytical performance of a versatile laboratory microscopic X-ray fluorescence system for metal uptake studies on argillaceous rocks

NASA Astrophysics Data System (ADS)

Gergely, Felicián; Osán, János; Szabó, B. Katalin; Török, Szabina

2016-02-01

Laboratory-scale microscopic X-ray fluorescence (micro-XRF) plays an increasingly important role in various fields where multielemental investigations of samples are indispensable. In case of geological samples, the reasonable detection limits (LOD) and spatial resolutions are necessary to identify the trace element content in microcrystalline level. The present study focuses on the analytical performance of a versatile laboratory-scale micro-XRF system with various options of X-ray sources and detectors to find the optimal experimental configuration in terms of sensitivities and LOD for selected elements in loaded petrographic thin sections. The method was tested for sorption studies involving thin sections prepared from cores of Boda Claystone Formation, which is a potential site for a high-level radioactive waste repository. Loaded ions in the sorption measurements were Cs(I) and Ni(II) chemically representing fission and corrosion products. Based on the collected elemental maps, the correlation between the elements representative of main rock components and the selected loaded ion was studied. For the elements of interest, Cs(I) and Ni(II) low-power iMOXS source with polycapillary and silicon drift detector was found to be the best configuration to reach the optimal LOD values. Laboratory micro-XRF was excellent to identify the responsible key minerals for the uptake of Cs(I). In case of nickel, careful corrections were needed because of the relatively high Ca content of the rock samples. The results were compared to synchrotron radiation micro-XRF.

The Mapping X-ray Fluorescence Spectrometer (MapX)

NASA Astrophysics Data System (ADS)

Sarrazin, P.; Blake, D. F.; Marchis, F.; Bristow, T.; Thompson, K.

2017-12-01

Many planetary surface processes leave traces of their actions as features in the size range 10s to 100s of microns. The Mapping X-ray Fluorescence Spectrometer (MapX) will provide elemental imaging at 100 micron spatial resolution, yielding elemental chemistry at a scale where many relict physical, chemical, or biological features can be imaged and interpreted in ancient rocks on planetary bodies and planetesimals. MapX is an arm-based instrument positioned on a rock or regolith with touch sensors. During an analysis, an X-ray source (tube or radioisotope) bombards the sample with X-rays or alpha-particles / gamma-rays, resulting in sample X-ray Fluorescence (XRF). X-rays emitted in the direction of an X-ray sensitive CCD imager pass through a 1:1 focusing lens (X-ray micro-pore Optic (MPO)) that projects a spatially resolved image of the X-rays onto the CCD. The CCD is operated in single photon counting mode so that the energies and positions of individual X-ray photons are recorded. In a single analysis, several thousand frames are both stored and processed in real-time. Higher level data products include single-element maps with a lateral spatial resolution of 100 microns and quantitative XRF spectra from ground- or instrument- selected Regions of Interest (ROI). XRF spectra from ROI are compared with known rock and mineral compositions to extrapolate the data to rock types and putative mineralogies. When applied to airless bodies and implemented with an appropriate radioisotope source for alpha-particle excitation, MapX will be able to analyze biogenic elements C, N, O, P, S, in addition to the cations of the rock-forming elements >Na, accessible with either X-ray or gamma-ray excitation. The MapX concept has been demonstrated with a series of lab-based prototypes and is currently under refinement and TRL maturation.

Composition of the earth's upper mantle. II - Volatile trace elements in ultramafic xenoliths

NASA Technical Reports Server (NTRS)

Morgan, J. W.; Wandless, G. A.; Petrie, R. K.; Irving, A. J.

1980-01-01

Radiochemical neutron activation analysis was used to determine the nine volatile elements Ag, Bi, Cd, In, Sb, Se, Te, Tl, and Zn in 19 ultramafic rocks, consisting mainly of spinel and garnet lherzolites. A sheared garnet lherzolite, PHN 1611, may approximate undepleted mantle material and tends to have a higher volatile element content than the depleted mantle material represented by spinel lherzolites. Comparisons of continental basalts with PHN 1611 and of oceanic ridge basalts with spinel lherzolites show similar basalt: source material partition factors for eight of the nine volatile elements, Sb being the exception. The strong depletion of Te and Se in the mantle, relative to lithophile elements of similar volatility, suggests that 97% of the earth's S, Se and Te may be in the outer core.

Geochemical and isotopic study of impact melts and spherules from the Lonar impact crater, India, indicate melting of the Precambrian basement beneath the 'target' Deccan basalts

NASA Astrophysics Data System (ADS)

Chakrabarti, R.; Goderis, S.; Banerjee, A.; Gupta, R. D.; Claeys, P.; Vanhaecke, F. F.

2016-12-01

The 1.88 km diameter Lonar impact Crater, with age estimates ranging from 52 -570 ka, is located in the Buldana district of Maharashtra, India. It is an almost circular depression hosted entirely in the 65Ma old basalt flows of the Deccan Traps and is the best-known terrestrial analogue for impact craters in the Inner Solar System. Isotopic studies indicate that the basalts around Lonar correlate with the Poladpur suite, one of the mid-section volcano-stratigraphic units of the Deccan traps. Recently collected samples of the host basalt and impact melts, were analyzed for major and trace element concentrations using ICPMS, as well as for Nd and Sr isotope ratios using TIMS. Relatively more radiogenic Sr and less radiogenic Nd isotopic composition of the melt rocks compared to earlier measurements of similar rocks from Lonar are consistent with melting of the Precambrian basement beneath the Deccan basalt. Spherules ranging in size from 100 mm to 1 mm, were hand-picked under a binocular microscope from unconsolidated soil samples, collected from the south-eastern rim of the crater. Thirty-five spherule samples, screened for surface alteration using SEM were analyzed for major and trace element concentrations including PGEs using LA-ICPMS. The spherules were further classified into two groups using the Chemical Index of Alteration(CIA). Iridium and Cr concentrations of the spherules are consistent with mixing of a chondritic impactor (with 2-8% contribution) with the target rock(s). On a Nb (fluid immobile) -normalized binary plot of Th versus Cr, the composition of the spherules can be explained by mixing between the host basalt and a chondritic impactor with a definite, but minor contribution of the basement beneath Lonar, the composition of which is approximated using the average composition of the upper continental crust (UCC). Variability in the light-REE fractionation of the spherules (La/Sm(N)) can also be explained by a similar three component mixing. Overall, our geochemical data for both the melt rocks and spherules suggest mixing between the chondritic impactor, the Deccan host basalt and the basement rocks at Lonar.

Petrogenesis of early Jurassic basalts in southern Jiangxi Province, South China: Implications for the thermal state of the Mesozoic mantle beneath South China

NASA Astrophysics Data System (ADS)

Cen, Tao; Li, Wu-xian; Wang, Xuan-ce; Pang, Chong-jin; Li, Zheng-xiang; Xing, Guang-fu; Zhao, Xi-lin; Tao, Jihua

2016-07-01

Early Jurassic bimodal volcanic and intrusive rocks in southern South China show distinct associations and distribution patterns in comparison with those of the Middle Jurassic and Cretaceous rocks in the area. It is widely accepted that these rocks formed in an extensional setting, although the timing of the onset and the tectonic driver for extension are debated. Here, we present systematic LA-ICP-MS zircon U-Pb ages, whole-rock geochemistry and Sr-Nd isotope data for bimodal volcanic rocks from the Changpu Formation in the Changpu-Baimianshi and Dongkeng-Linjiang basins in southern Jiangxi Province, South China. Zircon U-Pb ages indicate that the bimodal volcanic rocks erupted at ca. 190 Ma, contemporaneous with the Fankeng basalts ( 183 Ma). A compilation of geochronological results demonstrates that basin-scale basaltic eruptions occurred during the Early Jurassic within a relatively short interval (< 5 Ma). These Early Jurassic basalts have tholeiitic compositions and OIB-like trace element distribution patterns. Geochemical analyses show that the basalts were derived from depleted asthenospheric mantle, dominated by a volatile-free peridotite source. The calculated primary melt compositions suggest that the basalts formed at 1.9-2.1 GPa, with melting temperatures of 1378 °C-1405 °C and a mantle potential temperature (TP) ranging from 1383 °C to 1407 °C. The temperature range is somewhat hotter than normal mid-ocean-basalt (MORB) mantle but similar to an intra-plate continental mantle setting, such as the Basin and Range Province in western North America. This study provides an important constraint on the Early Jurassic mantle thermal state beneath South China. Reference: Raczek, I., Stoll, B., Hofmann, A.W., Jochum, K.P. 2001. High-precision trace element data for the USGS reference materials BCR-1, BCR-2, BHVO-1, BHVO-2, AGV-1, AGV-2, DTS-1, DTS-2, GSP-1 and GSP-2 by ID-TIMS and MIC-SSMS. Geostandards Newsletter 25(1), 77-86.

Isotopic and trace element compositions of upper mantle and lower crustal xenoliths, Cima volcanic field, California: Implications for evolution of the subcontinental lithospheric mantle

USGS Publications Warehouse

Mukasa, S.B.; Wilshire, H.G.

1997-01-01

Ultramafic and mafic xenoliths from the Cima volcanic field, southern California, provide evidence of episodic modification of the upper mantle and underplating of the crust beneath a portion of the southern Basin and Range province. The upper mantle xenoliths include spinel peridotite and anhydrous and hydrous pyroxenite, some cut by igneous-textured pyroxenite-gabbro veins and dikes and some by veins of amphibole ?? plagioclase. Igneous-textured pyroxenites and gabbros like the dike rocks also occur abundantly as isolated xenoliths inferred to represent underplated crust. Mineral and whole rock trace element compositions among and within the different groups of xenoliths are highly variable, reflecting multiple processes that include magma-mantle wall rock reactions, episodic intrusion and it filtration of basaltic melts of varied sources into the mantle wall rock, and fractionation. Nd, Sr, and Pb isotopic compositions mostly of clinopyroxene and plagioclase mineral separates show distinct differences between mantle xenoliths (??Nd = -5.7 to +3.4; 87Sr/86Sr = 0.7051 - 0.7073; 206Pb/204Pb = 19.045 - 19.195) and the igneous-textured xenoliths (??Nd = +7.7 to +11.7; 87Sr/86Sr = 0.7027 - 0.7036 with one carbonate-affected outlier at 0.7054; and 206Pb/204Pb = 18.751 - 19.068), so that they cannot be related. The igneous-textured pyroxenites and gabbros are similar in their isotopic compositions to the host basaltic rocks, which have ??Nd of+5.1 to +9.3; 87Sr/86Sr of 0.7028 - 0.7050, and 206Pb/204Pb of 18.685 - 21.050. The igneous-textured pyroxenites and gabbros are therefore inferred to be related to the host rocks as earlier cogenetic intrusions in the mantle and in the lower crust. Two samples of peridotite, one modally metasomatized by amphibole and the other by plagioclase, have isotopic compositions intermediate between the igneous-textured xenoliths and the mantle rock, suggesting mixing, but also derivation of the metasomatizing magmas from two separate and distinct sources. Sm-Nd two-mineral "isochrons" yield apparent ages for petrographically identical rocks believed to be coeval ranging from -0 to 113 ?? 26 Ma, indicating the unreliability of dating these rocks with this method. Amphibole and plagioclase megacrysts are isotopically like the host basalts and probably originate by mechanical breakup of veins comagmatic with the host basaltic rocks. Unlike other Basin and Range localities, Cima Cr-diopside group isotopic compositions do not overlap with those of the host basalts. Copyright 1997 by the American Geophysical Union.

Petrogenesis of Late Cretaceous lava flows from a Ceno-Tethyan island arc: The Raskoh arc, Balochistan, Pakistan

NASA Astrophysics Data System (ADS)

Siddiqui, Rehanul Haq; Qasim Jan, M.; Asif Khan, M.

2012-10-01

The Raskoh arc is about 250 km long, 40 km wide and trends in an ENE direction. The oldest rock unit in the Raskoh arc is an accretionary complex (Early to Late Jurassic), which is followed in age by Kuchakki Volcanic Group, the most wide spread unit of the Raskoh arc. The Volcanic Group is mainly composed of basaltic to andesitic lava flows and volcaniclastics, including agglomerate, volcanic conglomerate, breccia and tuff, with subordinate shale, sandstone, limestone and chert. The flows generally form 3-15 m thick lenticular bodies but rarely reach up to 300 m. They are mainly basaltic-andesites with minor basalts and andesites. The main textures exhibited by these rocks are hypocrystalline porphyritic, subcumulophyric and intergranular. The phenocrysts comprise mainly plagioclase (An30-54 in Nok Chah and An56-64 in Bunap). They are embedded in a micro-cryptocrystalline groundmass having the same minerals. Apatite, magnetite, titanomagnetite and hematite occur as accessory minerals. Major, trace and rare earth elements suggest that the volcanics are oceanic island arc tholeiites. Their low Mg # (42-56) and higher FeO (total)/MgO (1.24-2.67) ratios indicate that the parent magma of these rocks was not directly derived from a mantle source but fractionated in an upper level magma chamber. The trace element patterns show enrichment in LILE and depletion in HFSE relative to N-MORB. Their primordial mantle-normalized trace element patterns show marked negative Nb anomalies with positive spikes on K, Ba and Sr which confirm their island arc signatures. Slightly depleted LREE to flat chondrite normalized REE patterns further support this interpretation. The Zr versus Zr/Y and Cr versus Y studies show that their parent magma was generated by 20-30% melting of a depleted mantle source. The trace elements ratios including Zr/Y (1.73-3.10), Ti/Zr (81.59-101.83), Ti/V (12.39-30.34), La/YbN (0.74-2.69), Ta/Yb (0.02-0.05) and Th/Yb (0.11-0.75) of the volcanics are more consistent with oceanic island arcs rather than continental margin arcs. It is suggested that the Raskoh arc is an oceanic island arc which formed due to the intra-oceanic convergence in the Ceno-Tethys during the Late Cretaceous rather than constructed on the southern continental margin of the Afghan block, as claimed by previous workers. It is further suggested that the Semail, Zagros, Chagai-Raskoh, Muslim Bagh, and Waziristan island arcs were developed in a single but segmented Cretaceous Ceno-Tethyan convergence zone.

Petrogenesis of Tertiary continental intra-plate lavas between Siebengebirge and Westerwald, Germany: Constraints from trace element systematics and Nd, Sr and Pb isotopes

NASA Astrophysics Data System (ADS)

Schubert, S.; Jung, S.; Pfänder, J. A.; Hauff, F.; Garbe-Schönberg, D.

2015-10-01

New 39Ar/40Ar ages and major- and trace-element and radiogenic isotope data are presented for basanites and alkali basalts from the transition area between the Westerwald and Siebengebirge volcanic fields (Germany) that belongs to the Central European Volcanic Province (CEVP). The 39Ar/40Ar ages indicate ages of c. 24 and c. 5 Ma which are fully compatible with previous K/Ar ages indicating that the evolution of this volcanic field belongs to the Westerwald area (28-22 Ma and 5 Ma) rather than to the Siebengebirge area (26-23 Ma). Based on the occurrence of > 30 isolated volcanic plugs with a simple igneous history, this volcanic field can be viewed as a monogenetic volcanic field. Compositions of some basanites are primitive, whereas others and the alkali basalts show decreasing Cr and Ni contents and CaO/Al2O3 ratios. However, increasing TiO2, Al2O3 and incompatible elements (Sr, Zr, Y, Hf, Ta) concentrations with decreasing MgO indicating fractionation of mainly olivine with minor amounts of clinopyroxene and spinel can be noticed. Rare earth element systematics suggest that most of the alkaline rocks are generated by different degrees of melting (5%-10%) of a garnet-bearing peridotite containing some residual amphibole. Negative anomalies of Rb and K in primitive mantle-normalized diagrams and a lack of Ba/Rb fractionation suggest that amphibole was the major OH-bearing mineral phase in the mantle. The alkaline rocks have a restricted range in 87Sr/86Sr and 143Nd/144Nd ratios ranging from 0.7033 to 0.7044 and from 0.51275 to 0.51285, respectively. Lead isotope compositions (206Pb/204Pb: 19.21-19.65; 207Pb/204Pb: 15.62-15.67; 208Pb/204Pb: 39.10-39.46) of the alkaline rocks are within the range of most OIB in which the higher values approach the composition of the European Asthenospheric Reservoir (EAR). The correlation between Sr and Nd isotopes and trace element constraints (Ce/Pb; Nb/U) indicates that for some samples interaction with crustal rocks during fractionation has occurred. Miocene intraplate basaltic volcanism in the area probably occurred as a result of minor "baby plume" activity. Each volcanic plug records evidence of a specific stage of fractionation with or without assimilation; however, in summary the lavas plot on a single fractionation path. This implies that during evolution of the volcanic field initial melting took place in the asthenosphere or at the lithosphere-asthenosphere interface. The melts moved through the lithospheric mantle and stagnated at crustal levels, however the observed fractionation paths suggest that they were fed from a single reservoir. This model, which involves small-scale plume impact followed by asthenosphere-lithosphere interaction together with minor crustal contamination, should also be applicable to other intra-continental rift-related areas.

Trace-element record in zircons during exhumation from UHP conditions, North-East Greenland Caledonides

USGS Publications Warehouse

McClelland, W.C.; Gilotti, J.A.; Mazdab, F.K.; Wooden, J.L.

2009-01-01

Coesite-bearing zircon formed at ultrahigh-pressure (UHP) conditions share general characteristics of eclogite-facies zircon with trace-element signatures characterized by depleted heavy rare earth elements (HREE), lack of an Eu anomaly, and low Th/ U ratios. Trace-element signatures of zircons from the Caledonian UHP terrane in North-East Greenland were used to examine the possible changes in signature with age during exhumation. Collection and interpretation of age and trace-element analyses of zircon from three samples of quartzofeldspathic gneiss and two leucocratic intrusions were guided by core vs. rim zoning patterns as imaged by cathodoluminesence. Change from igneous to eclogite-facies metamorphic trace-element signature in protolith zircon is characterized by gradual depletion of HREE, whereas newly formed metamorphic rims have flat HREE patterns and REE concentrations that are distinct from the recrystallized inherited cores. The signature associated with eclogite-facies metamorphic zircon is observed in coesite-bearing zircon formed at 358 ?? 4 Ma, metamorphic rims formed at 348 ?? 5 Ma during the initial stages of exhumation, and metamorphic rims formed at 337 ?? 5 Ma. Zircons from a garnet-bearing granite emplaced in the neck of an eclogite boudin and a leucocratic dike that cross-cuts amphibolite-facies structural fabrics have steeply sloping HREE patterns, variably developed negative Eu anomalies, and low Th/U ratios. The granite records initial decompression melting and exhumation at 347 ?? 2 Ma and later zircon rim growth at 329 ?? 5. The leucocratic dike was likely emplaced at amphibolite-facies conditions at 330 ?? 2 Ma, but records additional growth of compositionally similar zircon at 321 ??2 Ma. The difference between the trace-element signature of metamorphic zircon in the gneisses and in part coeval leucocratic intrusions indicates that the zircon signature varies as a function of lithology and context, thus enhancing its ability to aid in the interpretation of U-Pb data and track the exhumation history of UHP terranes. The differences may reflect variation in elemental availability through breakdown reactions in quartzofeldpathic gneiss vs. availability during melt production and/or crystallization. UHP rocks in North-East Greenland began exhumation by 347 ?? 2 Ma, were still at HP eclogite-facies conditions at 337 ?? 5 Ma and were at amphibolite-facies conditions by 330 ?? 2 Ma. ?? 2009 E. Schweizerbart'sche Verlagsbuchhandlung.

Modeling groundwater flow and quality

USGS Publications Warehouse

Konikow, Leonard F.; Glynn, Pierre D.; Selinus, Olle

2013-01-01

In most areas, rocks in the subsurface are saturated with water at relatively shallow depths. The top of the saturated zone—the water table—typically occurs anywhere from just below land surface to hundreds of feet below the land surface. Groundwater generally fills all pore spaces below the water table and is part of a continuous dynamic flow system, in which the fluid is moving at velocities ranging from feet per millennia to feet per day (Fig. 33.1). While the water is in close contact with the surfaces of various minerals in the rock material, geochemical interactions between the water and the rock can affect the chemical quality of the water, including pH, dissolved solids composition, and trace-elements content. Thus, flowing groundwater is a major mechanism for the transport of chemicals from buried rocks to the accessible environment, as well as a major pathway from rocks to human exposure and consumption. Because the mineral composition of rocks is highly variable, as is the solubility of various minerals, the human-health effects of groundwater consumption will be highly variable.

Lunar Prospector: overview.

PubMed

Binder, A B

1998-09-04

Lunar Prospector is providing a global map of the composition of the moon and analyzing the moon's gravity and magnetic fields. It has been in a polar orbit around the moon since 16 January 1998. Neutron flux data show that there is abundant H, and hence probably abundant water ice, in the lunar polar regions. Gamma-ray and neutron data reveal the distribution of Fe, Ti, and other major and trace elements on the moon. The data delineate the global distributions of a key trace element-rich component of lunar materials called KREEP and of the major rock types. Magnetic mapping shows that the lunar magnetic fields are strong antipodal to Mare Imbrium and Mare Serenitatis and has discovered the smallest known magnetosphere, magnetosheath, and bow shock complex in the solar system. Gravity mapping has delineated seven new gravity anomalies and shown that the moon has a small Fe-rich core of about 300 km radius.

Use of olivine and plagioclase saturation surfaces for the petrogenetic modeling of recrystallized basic plutonic systems

NASA Technical Reports Server (NTRS)

Hanson, G. N.

1983-01-01

During petrogenetic studies of basic plutonic rocks, there are at least three major questions to be considered: (1) what were the relative proportions of cumulate crystals and intercumulus melt in a given sample? (2) what is the composition and variation in composition of the melts within the pluton? and (3) what is the original composition of the liquids, their source and evolution prior to the time of emplacement? Use of both saturation surfaces can place strong limits on the compositions of potential cumulate phases and intercumulus melts. Consideration of appropriate trace elements can indicate whether a sample is an orthocumulate, adcumulate or mesocumulate. Thus, when trace element and petrographic data are considered together with the saturation surfaces, it should be possible to begin to answer the three major questions given above, even for strongly recrystallized basic plutons.

Geochemical and isotopic (Nd-Pb-Sr-O) variations bearing on the genesis of volcanic rocks from Vesuvius, Italy

USGS Publications Warehouse

Ayuso, R.A.; de Vivo, B.; Rolandi, G.; Seal, R.R.; Paone, A.

1998-01-01

Alkaline volcanism produced by Monte Somma-Vesuvius volcano includes explosive plinian and subplinian activity in addition to effusive lava flows. Pumice, scoria, and lava (150 samples) exhibit major- and trace-element gradients as a function of SiO2 (58.9-47.2 wt%) and MgO (0-7.8 wt%); Mg value are ???50. Internally gradational chemical groups or cycles are distinguished by age: (1) 25 000 to 14 000 yr B.P.; (2) 8000 yr B.P. to A.D. 79; and (3) A.D. 79 to 1944. A small number of lavas, dikes and scora were also analysed from the Somma formation (~ 35 000 to 25 000 yr B.P.). Within each group, contents of Na2O + K2O increas with decreasing MgO along distinct rocks. Nb/Y values are variable from 0.66 to 3.14 (at SiO2 ??? 50 wt%) generally in the range of alkaline and ultra-alkaline rocks. Variations in contents of some majro elements (e.g., P and Ti), and trace elements (e.g., Th, Nb, Ta, Zr, Hf, Pb, La, and Sc), as well as contrasting trends in ratios of various elements (e.g., Ta/Yb, Hf/U, Th/Ta, Th/Hf, Th/Yb, etc.) are also generally consistent with the group subdivisions. For example, Th/Hf increases from ??? 5 to ??? 10 with decreasing age for the Vesuvius system as a whole, yielding similar compositions in the least evolved rocks (low-silica, high-MgO, imcompatible element-poor) erupted at the end of each cycle. Internal variations within individual eruptions also systematically changed generally towards a common mafic composition at the end of each cycle, thus reflecting the dominanit volume in the magma chamber. At the start of a new eruptive cycle, the rocks are relatively enriched in incompatible elements; younger groups also contain higher abundances than other groups. N-MORB-normalized multielement diagrams exhibit selective enrichments of Sr, K, Rb, Th, and the light rare-earth elements; deep Nb and Ta negative anomalies commonly seen in rocks generated at orogenic margins are absent in the light rare-earth elements; deep Nb and Ta netgative anomalies commonly seen in rocks generated at orogenic margins are absent in our samples. Sr isotopic compositions are known to be variable within some of the units, in agreement with our data (87Sr/86Sr ~ 0.70699 to 0.70803) and with contributions from several isotopic components. Isotopic compositions for ??18O (7.3 to 10.2%), Pb for mineral separates and whole rocks (206Pb/204Pb ~ 18.947 to 19.178, 207Pb/204/Pb ~ 15.617 to 15.769, 208Pb/204Pb ~38.915 to 39.345), and Nd (143Nd ~ 0.51228 to 0.51251) also show variability. Oxygen isotope data show that pumices have higher ??18O values than cogenetic lavas, and that ??18O values and SiO2 are correlated. Radiogenic and stable isotope data plot within range of isotopic compositions for the Roman comagmatic province. Fractional crystallization cannot account for the radiogenic isotopic compositions of the Vesuvius magmas. We favor instead the combined effects of heterogeneous magma sources, together with isotopic exchange near the roof of the magma chamber. We suggest that metasomatized continental mantle lithosphere is the principal source of the magmas. This kind of enriched mantle was melted and reactivated in an area of continental extension (incipient rift setting) without direct reliance on contemporaneous subduction processes but possibly with input from mantle sources that resemble those that produce ocean island basalts.

Water in Earth's mantle: Hydrogen analysis of mantle olivine, pyroxenes and garnet using the SIMS

NASA Technical Reports Server (NTRS)

Kurosawa, Masanori; Yurimoto, Hisayoshi; Sueno, Shigeho

1993-01-01

Hydrogen (or water) in the Earth's interior plays a key role in the evolution and dynamics of the planet. However, the abundance and the existence form of the hydrogen have scarcely been clear in practice. Hydrogen in the mantle was incorporated in the interior during the formation of the Earth. The incorporated hydrogen was hardly possible to concentrate locally inside the Earth considering its high mobility and high reactivity. The hydrogen, preferably, could be distributed homogeneously over the mantle and the core by the subsequent physical and chemical processes. Therefore, hydrogen in the mantle could be present in the form of trace hydrogen in nominally anhydrous mantle minerals. The hydrogen and the other trace elements in mantle olivines, orthopyroxenes, clinopyroxenes, and garnets were determined using secondary ion mass spectrometry (SIMS) for elucidating (1) the exact hydrogen contents, (2) the correlation between the hydrogen and the other trace elements, (3) the dependence of the hydrogen contents on the depth, and (4) the dependence of the whole rock water contents on the depth.

The Chemical Behavior of Fluids Released during Deep Subduction Based on Fluid Inclusions

NASA Astrophysics Data System (ADS)

Frezzotti, M. L.; Ferrando, S.

2014-12-01

We present a review of current research on fluid inclusions in (HP-) UHP metamorphic rocks that, combined with existing experimental research and thermodynamic models, allow us to investigate the chemical and physical properties of fluids released during deep subduction, their solvent and element transport capacity, and the subsequent implications for the element recycling in the mantle wedge. An impressive number of fluid inclusion studies indicate three main populations of fluid inclusions in HP and UHP metamorphic rocks: i) aqueous and/or non-polar gaseous fluid inclusions (FI), ii) multiphase solid inclusions (MSI), and iii) melt inclusions (MI). Chemical data from preserved fluid inclusions in rocks match with and implement "model" fluids by experiments and thermodynamics, revealing a continuity behind the extreme variations of physico-chemical properties of subduction-zone fluids. From fore-arc to sub-arc depths, fluids released by progressive devolatilization reactions from slab lithologies change from relatively diluted chloride-bearing aqueous solutions (± N2), mainly influenced by halide ligands, to (alkali) aluminosilicate-rich aqueous fluids, in which polymerization probably governs the solubility and transport of major (e.g., Si and Al) and trace elements (including C). Fluid inclusion data implement the petrological models explaining deep volatile liberation in subduction zones, and their flux into the mantle wedge.

Bunburra Rockhole: Exploring the geology of a new differentiated asteroid

NASA Astrophysics Data System (ADS)

Benedix, G. K.; Bland, P. A.; Friedrich, J. M.; Mittlefehldt, D. W.; Sanborn, M. E.; Yin, Q.-Z.; Greenwood, R. C.; Franchi, I. A.; Bevan, A. W. R.; Towner, M. C.; Perrotta, G. C.; Mertzman, S. A.

2017-07-01

Bunburra Rockhole is the first recovered meteorite of the Desert Fireball Network. We expanded a bulk chemical study of the Bunburra Rockhole meteorite to include major, minor and trace element analyses, as well as oxygen and chromium isotopes, in several different pieces of the meteorite. This was to determine the extent of chemical heterogeneity and constrain the origin of the meteorite. Minor and trace element analyses in all pieces are exactly on the basaltic eucrite trend. Major element analyses show a slight deviation from basaltic eucrite compositions, but not in any systematic pattern. New oxygen isotope analyses on 23 pieces of Bunburra Rockhole shows large variation in both δ17O and δ18O, and both are well outside the HED parent body fractionation line. We present the first Cr isotope results of this rock, which are also distinct from HEDs. Detailed computed tomographic scanning and back-scattered electron mapping do not indicate the presence of any other meteoritic contaminant (contamination is also unlikely based on trace element chemistry). We therefore conclude that Bunburra Rockhole represents a sample of a new differentiated asteroid, one that may have more variable oxygen isotopic compositions than 4 Vesta. The fact that Bunburra Rockhole chemistry falls on the eucrite trend perhaps suggests that multiple objects with basaltic crusts accreted in a similar region of the Solar System.

A Thorium-rich Mare Basalt Rock Fragment from the Apollo 12 Regolith: A Sample from a Young Procellarum Flow?

NASA Technical Reports Server (NTRS)

Jolliff, B. L.; Zeigler, R. A.; Korotev, R. L.; Barra, F.; Swindle, T. D.

2005-01-01

In this abstract, we report on the composition, mineralogy and petrography of a basaltic rock fragment, 12032,366-18, found in the Apollo 12 regolith. Age data, collected as part of an investigation by Barra et al., will be presented in detail in. Here, only the age dating result is summarized. This rock fragment garnered our attention because it is significantly enriched in incompatible elements, e.g., 7 ppm thorium, compared to other known lunar basalts. Its mineral- and trace-element chemistry set it apart from other Apollo 12 basalts and indeed from all Apollo and Luna basalts. What makes it potentially very significant is the possibility that it is a sample of a relatively young, thorium-rich basalt flow similar to those inferred to occur in the Procellarum region, especially northwestern Procellarum, on the basis of Lunar Prospector orbital data. Exploiting the lunar regolith for the diversity of rock types that have been delivered to a landing site by impact processes and correlating them to their likely site of origin using remote sensing will be an important part of future missions to the Moon. One such mission is Moonrise, which would collect regolith samples from the South Pole-Aitken Basin, concentrating thousands of rock fragments of 3-20 mm size from the regolith, and returning the samples to Earth.

Petrochemistry of Mafic Rocks Within the Northern Cache Creek Terrane, NW British Columbia, Canada

NASA Astrophysics Data System (ADS)

English, J. M.; Johnston, S. T.; Mihalynuk, M. G.

2002-12-01

The Cache Creek terrane is a belt of oceanic rocks that extend the length of the Cordillera in British Columbia. Fossil fauna in this belt are exotic with respect to the remainder of the Canadian Cordillera, as they are of equatorial Tethyan affinity, contrasting with coeval faunas in adjacent terranes that show closer linkages with ancestral North America. Preliminary results reported here from geochemical studies of mafic rocks within the Nakina area of NW British Columbia further constrain the origin of this enigmatic terrane. The terrane is typified by tectonically imbricated slices of chert, argillite, limestone, wacke and volcaniclastic rocks, as well as mafic and ultramafic rocks. These lithologies are believed to represent two separate lithotectonic elements: Upper Triassic to Lower Jurassic, subduction-related accretionary complexes, and dismembered basement assemblages emplaced during the closure of the Cache Creek ocean in the Middle Jurassic. Petrochemical analysis revealed four distinct mafic igneous assemblages that include: magmatic 'knockers' of the Nimbus serpentinite mélange, metabasalts of 'Blackcaps' Mountain, augite-phyric breccias of 'Laughing Moose' Creek, and volcanic pediments to the reef-forming carbonates of the Horsefeed Formation. Major and trace element analysis classifies the 'Laughing Moose' breccias and the carbonate-associated volcanics as alkaline in nature, whereas the rest are subalkaline. Tectonic discrimination diagrams show that the alkaline rocks are of within-plate affinity, while the 'Blackcaps' basalts and 'knockers' from within the mélange typically straddle the island-arc tholeiite and the mid-ocean ridge boundaries. However, primitive mantle normalized multi-element plots indicate that these subalkaline rocks have pronounced negative Nb anomalies, a characteristic arc signature. The spatial association of alkaline volcanic rocks with extensive carbonate domains points to the existence of seamounts within the Cache Creek ocean. However, the precise origin of the 'Laughing Moose' breccias remains somewhat uncertain and may be related to a subsequent rifting event. To conclude, preliminary data from the Nakina region show it to be dominated by two different petrogenetic components: alkaline volcanic rocks of within-plate affinity, and primitive arc-related, subalkaline mafic rocks. An accretionary complex/ oceanic arc origin may provide a mechanism to explain the lithological diversity within the Nakina area.

Geochemistry of basement rocks of incoming plate (Cocos Ridge) from Sites U1381 and 1414, IODP Expeditions 334 and 344

NASA Astrophysics Data System (ADS)

Yan, Q.; Shi, X.

2015-12-01

The drilling sites of IODP 334 and 344 lie in the being subducted part of Cocos Ridge, offshore Costa Rica. Some seamount clusters distributed in the northwest side of the sites. Most scientists accepted that the Cocos ridge is intimately related to the activity of Galapagos plume (e.g., Hoernle et al., 2000, 2004, 2008). In this study we have selected some basaltic samples from U1381A, U1381C and U1414A (IODP 334 and 344) (Harris et al., 2015a, b) to carry out petrogenetic study. Major element compositions show that these basaltic rocks belong to sub-alkaline rocks, which is consistent with previous study on basalts from northern side of Cocos ridge. The characteristics of trace element composition are similar to that of EMORB, and the compositional differences in trace elements among samples reflect the influence of fractional crystallization. Sr-Nd-Pb isotopic compositions of these basaltic rocks show that there exist mantle heterogeneity beneath the Cocos ridge, and they may be the product of mixing between DMM/GSC and EMII. The new data show more enriched source feature than those from Galapagos hotspot (and its tracks) in previous study (Hoernle et al., 2000,2004), and slightly more enriched than those Miocene to Pliocene arc volcanics from Central America (Gazel et al., 2009). Partial melting model show that the parental basalts for these basaltic rocks may be produced by 13 to 28% partial melting of garnet pyroxenite. ReferencesGazel et al., 2009. G-cubed.10, Q02S11, doi:10.1029/2008GC002246.//Harris, R.N., Sakaguchi, A., Petronotis, K., and the Expedition 344 Scientists. 2015a. Input Site U1381. Proceedings of the Integrated Ocean Drilling Program, Volume 344//Harris, R.N., Sakaguchi, A., Petronotis, K., and the Expedition 344 Scientists. 2015b. Input Site U1414.Proceedings of the Integrated Ocean Drilling Program, Volume 344//Hoernle et al., 2000. Geology, 28(5),435-438//Hoernle et al., 2004. Geology, 32,697-700//Hoernle et al., 2008. Nature, 451,1094-1098 (This study was supported by National Natural Science Foundation of China (NSFC nos. 41296030 and 41322036, and IODP-China.)

Serpentinite-driven Exhumation of the UHP Lago di Cignana Unit in the Fossil Alpine Plate Interface

NASA Astrophysics Data System (ADS)

Scambelluri, M.; Gilio, M.; Angiboust, S.; Godard, M.; Pettke, T.

2015-12-01

The Lago di Cignana Unit (LCU) is a coesite- [1] and diamond-bearing [2] slice of oceanic-derived eclogites and metasediments recording Alpine UHP metamorphism at 600 °C-3.2 GPa (~110 km depth) [3]. The LCU is tectonically sandwiched between the eclogitic Zermatt-Saas Zone (ZSZ; 540 °C-3.2 GPa) [4] and the blueschist Combin Zone (400 °C-0.9 GPa) [5] along a tectonic structure joining HP units recording a ~1.2 GPa (40 km) pressure difference. So far, the ZSZ has been attributed to normal HP conditions and the mechanism driving exhumation and accretion of the LCU in its present structural position is not fully understood.We performed petrography and bulk-rock trace element analyses of rocks from LCU and ZSZ serpentinites. We observed that, while serpentinites in the core of the ZSZ show normal subduction zone trace elements and REE's patterns, the Ol+Ti-chu+Chl veins and host serpentinites enveloping the LCU are strongly enriched in sediment-derived fluid-mobile elements (U, Th, Nb, Ta, Ce, Y, As, Sb) and REE's: their patterns well match those of the closely associated LCU-UHP rocks.The presence of extremely enriched Ol+Ti-chu+Chl veins in the serpentinites at direct contact with the UHP Lago di Cignana Unit suggests that fluid exchange between serpentinite and LCU crustal rocks occurred at peak metamorphic conditions. Their coupling therefore occurred during subduction burial and/or peak UHP conditions. As such, the buoyancy force originating from the relatively light serpentinites fuelled the exhumation of the Lago di Cignana Unit. In this contest, the tectonic contact between the Zermatt-Saas Zone and the Combin Zone evolved into a true tectonic plate interface surface.1. Reinecke (1998). Lithos 42(3), 147-189; 2. Frezzotti et al. (2011). Nat. Geosci. 4(10), 703-706; 3. Groppo et al. (2009). J. Metam. Geol. 27(3), 207-231; 4. Angiboust et al. (2009). Terra Nova 21(3), 171-180; 5. Reddy et al. (1999). J. Metam. Geol. 17, 573-590.

The carbonatite-marble dykes of Abyan Province, Yemen Republic: the mixing of mantle and crustal carbonate materials revealed by isotope and trace element analysis

NASA Astrophysics Data System (ADS)

Le Bas, M. J.; Ba-Bttat, M. A. O.; Taylor, R. N.; Milton, J. A.; Windley, B. F.; Evins, P. M.

2004-09-01

Dykes of carbonate rocks, that cut gneisses in the Lowder-Mudiah area of southern Yemen, consist of dolomite and/or calcite with or without apatite, barite and monazite. Petrographic observations, mineralogical, XRF and ICP-MS analyses reveal that some of the carbonate rocks are derived from sedimentary protoliths, whereas others are magmatic calcio- and magnesio-carbonatites some of which are mineralized with barite-monazite. The interbanded occurrence and apparent contemporary emplacement of these different rock types within individual dykes, backed by Sr Nd isotope evidence, are interpreted to show that intrusion of mantle-derived carbonatite magma was accompanied by mobilization of crustal marbles. That took place some 840 Ma ago but the REE-mineralization is dated at ca. 400 Ma.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dupre, B.; Rousseau, D.; Gaillardet, J.

The Congo river Basin is the second largest drainage basin in the world, after the Amazon. The materials carried by its main rivers provide the opportunity to study the products of denudation of a large fraction of the upper continental crust of the African continent. This paper presents the chemical composition of the different phases carried in the Congo rivers and is followed by a companion paper, devoted to the modelling of major and trace elements. The Congo river between Bangui and Brazzaville as well as its main tributaries, including a few organic-rich rivers, also called Black Rivers, were sampledmore » during the 1989 high water stage. The three main phases (suspended load, dissolved load, and bedload) were analysed for twenty-five major and trace elements. Concentrations normalized to the upper continental crust show that in each river, suspended sediments and dissolved load are chemical complements for the most soluble elements (Ca, Na, Sr, K, Ba, Rb, and U). While these elements are enriched in the dissolved loads, they are considerably depleted in the corresponding suspended sediments. This is consistent with their high mobility during weathering. Another type of complementarity is observed for Zr and Hf between suspended sediments and bedload, related to the differential velocity of suspended sediments and zircons which are concentrated in bedloads. Compared to other rivers, absolute dissolved concentrations of Ca, Na, Sr, K, Ba, Rb, and U are remarkably low. Surprisingly, high dissolved concentrations are found in the Congo waters for other trace elements (e.g., REEs), especially in the Black rivers. On a world scale, these concentrations are among the highest measured in rivers and are shown to be pH dependent for a number of dissolved trace elements. The dissolved loads are systematically normalized to the suspended loads for each river, in order to remove the variations of the element abundances owing to source rock variations.« less

Mid-to-Lower-level Plutonic Rocks From Crust of the Southern Mariana Forearc: Implications for Growth of Continental Crust

NASA Astrophysics Data System (ADS)

Fryer, P.; Reagan, M.

2006-12-01

Tonalitic plutonic rocks dredged from the southern Mariana forearc are similar in terms of major element composition to tonalitic plutonic rocks of the Tanzawa Mountains on the Izu Peninsula of Japan. The tonalites of the Tanzawa Mountains have been interpreted to represent mid-lower crustal plutonic rocks that make up the 6.0 to 6.3 km/s layer identified in seismic velocity profiles of the Izu arc at 32°N. The tonalities of the southern Mariana forearc may be analogous to the Tanzawa tonalities in terms of lithology and presumably seismic velocities, but have distinctive trace element and isotopic compositions. The exposure of these rocks on the southern Mariana forearc in a location where it is narrower by up to 80 km than elsewhere along its strike indicates a truncation of the arc lithosphere by tectonic erosion in the southern Mariana forearc. If tectonic processes in the forearc have exposed silicic plutonic rock of the arc lithosphere within 150 km of the volcanic front, then the structure of the Mariana arc and forearc is likely similar to that of the Izu arc, where seismic velocity structure suggests 25% of the arc/forearc lithosphere is comprised of a mid-crustal level tonalitic plutonic complex. The trace element and Sr isotopic compositions of the tonalities dredged from the Mariana forearc links them to a suprasubduction-zone environment. The Pb isotopic compositions, however, are consistent with crystallization ages that may be as old as Cretaceous. The compositions of these tonalites differ markedly from those of silicic volcanic rocks that have erupted throughout the history of the IBM arc and suggest that they represent a minor component of the arc. Nevertheless, the presence of Cretaceous tonalites in the Mariana forearc suggests that a portion of its crust may predate subduction initiation. The presence of silicic mid-to-lower crustal level plutonics beneath the Mariana arc as well as Eocene rhyolites on Saipan indicate that average major element composition of the arc crust may be comparable with average continental crust. This is consistent with estimates of the average composition of the Izu arc crust from seismic velocity studies and petrologic studies of exposures of the Izu arc crust in southern Japan's Izu peninsula. These data imply that the island arc that developed along the entire margin of the Philippine Sea plate may have had a generally similar structure and composition. Most components of the IBM arc crust, however, have relatively flat rare-earth patterns and low rare-earth concentrations compared with average continental crust. The averaged composition of the IBM crust, as a whole, differs markedly from that suggested by studies of the velocity structure of the central Aleutian arc. If the continental crust was generated in oceanic island arc settings throughout the history of the Earth, then its sources were significantly more enriched in LREE than the sources for the Cenozoic IBM arcs.

A petrologic comparison of Triassic plutonism in the San Gabriel and Mule Mountains, southern California

NASA Astrophysics Data System (ADS)

Barth, Andrew P.; Tosdal, R. M.; Wooden, J. L.

1990-11-01

Triassic magmatism in the southwest U.S. Cordillera forms a semicontinuous magmatic arc extending from northwestern Nevada to southeastern California. Quartz monzodioritic and quartz monzonitic rocks and associated diorites and granites are widespread in southeastern California, and we suggest that these rocks represent exposure of a structurally deeper part of the Triassic arc, where it was emplaced into comparatively thick Proterozoic crust. Elemental and isotopic data suggest that Triassic quartz monzodiorites and quartz monzonites in the Mule and San Gabriel Mountains were derived from a relatively undepleted, nonradiogenic mafic lithospheric source, with virtually no upper crustal interaction. Very limited data for associated Triassic(?) diorites indicate a wide range in composition and a surprisingly radiogenic isotopic signature. Younger Triassic(?) granites record a strong geochemical signature of interaction with continental crust, including inherited zircon and high initial Sr ratios but comparatively less radiogenic Pb isotopic compositions. The major and trace element geochemistry of Late Triassic plutonic rocks in southeastern California is similar in many respects to alkalic components of the Triassic arc in the Mojave Desert. However, contemporaneous rocks farther north have a calc-alkalic signature, perhaps reflecting the variation in age and composition of lithosphere across which the Triassic arc was constructed.

A petrologic comparison of Triassic plutonism in the San Gabriel and Mule Mountains, southern California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barth, A.P.; Tosdal, R.M.; Wooden, J.L.

1990-11-10

Triassic magmatism in the southwest US Cordillera forms a semicontinuous magmatic arc extending from northwestern Nevada to southeastern California. Quartz monzodioritic and quartz monzonitic rocks and associated diorites and granites are widespread in southeastern California, and the authors suggest that these rocks represent exposure of a structurally deeper part of the Triassic arc, where it was emplaced into comparatively thick Proterozoic crust. Elemental and isotopic data suggest that Triassic quartz monzodiorites and quartz monzonites in the Mule and San Gabriel Mountains were derived from a relatively undepleted, nonradiogenic mafic lithospheric source, with virtually no upper crustal interaction. Very limited datamore » for associated Triassic ( ) diorites indicate a wide range in composition and a surprisingly radiogenic isotopic signature. Younger Triassic( ) granites record a strong geochemical signature of interaction with continental crust, including inherited zircon and high initial Sr ratios but comparatively less radiogenic Pb isotopic compositions. The major and trace element geochemistry of Late Triassic plutonic rocks in southeastern California is similar in many respects to akalic components of the Triassic arc in the Mojave Desert. However, contemporaneous rocks farther north have a calc-alkalic signature, perhaps reflecting the variation in age and composition of lithosphere across which the Triassic arc was constructed.« less

Geochemical constraints on depth of origin of oceanic carbonatites: The Cape Verde case

NASA Astrophysics Data System (ADS)

Doucelance, Régis; Hammouda, Tahar; Moreira, Manuel; Martins, João C.

2010-12-01

We present new Sr-Nd isotope compositions together with major- and trace element concentrations measured for whole rocks and mineral separate phases (apatite, biotite and calcite) from fifteen Cape Verde oceanic carbonatites (Atlantic Ocean). Trace element patterns of calcio- and magnesio-carbonatites present a strong depletion in K, Hf, Zr and Ti and an overall enrichment in Sr and REE relative to Cape Verde basalts, arguing for distinct source components between carbonatites and basalts. Sr and Nd isotopic ratios show small, but significant variations defining a binary mixing between a depleted end-member with unradiogenic Sr and radiogenic Nd values and a ''enriched'' end-member compatible with old marine carbonates. We interpret the depleted end-member as the Cape Verde oceanic lithosphere by comparison with previous studies on Cape Verde basalts. We thus propose that oceanic carbonatites are resulting from the interaction of a deep rooted mantle plume carrying a lower 4He/ 3He signature from the lower mantle and a carbonated metasomatized lithosphere, which by low degree melting produced carbonatite magmas. Sr-Nd compositions and trace element patterns of carbonatites argue in favor of a metasomatic agent originating from partial melting of recycled, carbonated oceanic crust. We have successfully reproduced the main geochemical features of this model using a Monte-Carlo-type simulation.

Boron and strontium isotope ratios and major/trace elements concentrations in tea leaves at four major tea growing gardens in Taiwan.

PubMed

Chang, Cheng-Ta; You, Chen-Feng; Aggarwal, Suresh Kumar; Chung, Chuan-Hsiung; Chao, Hung-Chun; Liu, Hou-Chun

2016-06-01

Isotopic compositions of B and Sr in rocks and sediments can be used as tracers for plant provincial sources. This study aims to test whether tea leaf origin can be discriminated using (10)B/(11)B and Sr isotopic composition data, along with concentrations of major/trace elements, in tea specimens collected from major plantation gardens in Taiwan. The tea leaves were digested by microwave and analyzed by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS). The data showed significant variations in (87)Sr/(86)Sr ratios (from 0.70482 to 0.71462), which reflect changes in soil, groundwater or irrigation conditions. The most radiogenic tea leaves were found at the Taitung garden and the least radiogenic ones were from the Hualien garden. The δ (11)B was found to change appreciably (δ (11)B = 0.38-23.73 ‰) which could be due to fertilizers. The maximum δ (11)B was also observed in tea samples from the Hualien garden. Principal component analysis combining (87)Sr/(86)Sr, δ (11)B and major/trace elements results successfully discriminated different sources of major tea gardens in Taiwan, except the Hualien gardens, and this may be due to rather complicated local geological settings.

Alteration mineralogy and geochemistry as an exploration tool for detecting basement heat sources in sedimentary basins

NASA Astrophysics Data System (ADS)

Uysal, Tonguc; Gasparon, Massimo; van Zyl, Jacobus; Wyborn, Doone

2010-05-01

The Cooper Basin located in South Australia and Queensland hosts some of the hottest granites in the world at economic drilling depths (240°C at 3.5 km). Investigating the mechanism of heat-producing element enrichment in the Cooper Basin granite is crucial for understanding hot-dry rock geothermal systems and developing exploration strategies. Trace element (by ICP-MS) and stable isotope geochemistry of whole rock granite samples and hydrothermal phyllosilicate alteration minerals separated from the granite and overlying sandstones and mudstones of the Cooper Basin were examined in detail. Granite core samples from relatively shallow depths in Moomba 1 and Big Lake 1 are strongly altered with pervasive sericite (illite) and quartz precipitation, probably associated with intense micro-fracturing and veining. The intensity of hydrothermal alteration is less in deeper samples from Mcleod 1, Jolokia and Habanero 1. Highly altered granites from former holes are substantially enriched in lithophile elements, particularly in Cs, Rb, Be, Th, U and rare earth elements (REE) relative to the upper continental crust (UCC). U and Th contents with concentrations of up to 30 and 144 ppm, respectively, are 10 and 13 times higher than those of the UCC. Comparison of the trace element composition of the same samples dissolved by open beaker acid digestion and high-pressure acid bomb digestion (to dissolve zircon) shows that zircon is not the main repository of U and Th in the Cooper Basin granite. Instead, we propose that the enrichment of heat-producing elements was promoted by a regional hydrothermal event leading to the precipitation of U and Th- bearing minerals such as illite, K-feldspar and thorite. Crystallinity index (illite crystallinity) of the sericite indicates hydrothermal temperatures ranging from 250°C (in Moomba 1 and Big Lake 1) to 350°C (in McLeod 1 and Jolokia 1). In the overlying sedimentary rocks, crystallinity of authigenic illites translates to lower crystallisation temperatures (150-200°C). Normalised REE patterns of the mostly altered granite samples show a strong negative Ce anomaly, signifying oxidation of trivalent Ce to less soluble tetravalent Ce. Oxygen and hydrogen isotope compositions of illites from the granites and sedimentary rocks are very similar, with d18O = -1.8 per mill to +2.7 per mill; δD = -99 per mill to -121 per mill for granites and d18O = +2.3 per mill to +9.7 per mill, dD = -78 per mill to -119 per mill for sedimentary rocks. The calculated oxygen and hydrogen isotope compositions of fluids in equilibrium with the illites are depleted in 18O and deuterium, comparable to those of waters reported for most high-latitude sedimentary basins. Hence, stable isotope data of alteration minerals in the granite and the overlying sedimentary rocks suggest the operation of a hydrothermal system involving high latitude meteoric waters during extensional tectonism in the Cooper Basin region. Investigation of alteration mineralogy and geochemistry of relatively shallow sedimentary sections (generally intersected in previously drilled petroleum holes) represents a potentially strong tool to evaluate the presence of a geothermal heat source in the basement of sedimentary basins.

The formation and trace elements of garnet in the skarn zone from the Xinqiao Cu-S-Fe-Au deposit, Tongling ore district, Anhui Province, Eastern China

NASA Astrophysics Data System (ADS)

Xiao, Xin; Zhou, Tao-fa; White, Noel C.; Zhang, Le-jun; Fan, Yu; Wang, Fang-yue; Chen, Xue-feng

2018-03-01

Xinqiao is a large copper-gold deposit and consists of two major mineralization types: stratabound and skarn. The skarn occurs along the contact between a quartz diorite intrusion and Carboniferous-Triassic limestone. Xinqiao has a strongly developed skarn zone, including endoskarn and exoskarn; the exoskarn is divided into proximal and distal exoskarn. We present systematic major, trace and rare earth element (REE) concentrations for garnets from the skarn zone, discuss the factors controlling the incorporation of trace elements into the garnets, and constrain the formation and evolution of the garnet from skarn zone in Xinqiao deposit. Grossular (Adr20-44Grs56-80) mostly occurs in endoskarn and has typical HREE-enriched and LREE-depleted patterns, with small Eu anomalies and low ∑REE. Garnets from the exoskarn show complex textures and chemical compositions. The composition of garnets range from Al-rich andradite (Adr63-81Grs19-47) to andradite (Adr67-98Grs2-33). Garnet in endoskarn has typical HREE-enriched and LREE-depleted patterns. Al-rich andradite in proximal skarn has small Eu anomalies and moderate ∑REE. Andradite from distal exoskarn shows strong positive Eu anomalies and has variable ∑REE. The U, Y, Fe and Al relationship with ∑REE shows that two mechanisms controlled incorporation of REE into the garnets: crystal chemistry (substitution and interstitial solid solution) mainly controlled in the endoskarn garnet (grossular) and the proximal exoskarn (Al-rich andradite), and fluid and rock chemistry (surface adsorption and occlusion) controlled REEs in the distal exoskarn. Furthermore, Al has a negative relationship with ∑REE indicating that REE3+ did not follow a coupled, YAG-type substitution into the garnets. Variations in textures and trace and rare earth elements of garnets suggest that the garnets in the endoskarn formed by slow crystal growth at low W/R ratios and near-neutral pH in a closed system during periods of diffusive metasomatism. The garnets in the exoskarn formed rapidly from externally derived fluids during advective metasomatism, and adsorption had a major control on the REE patterns in distal exoskarn. With the end of water-rock reaction, the contents of REE decreased in the hydrothermal fluid, and the system became nearly closed.

Using X-ray Fluorescence to Date Petroglyphs

NASA Astrophysics Data System (ADS)

McNeil, James

2009-10-01

Petroglyphs were created by ancient peoples of the Colorado Plateau who pecked figures of cultural or religious significance into the desert varnish, the ubiquitous dark patina covering the rock surfaces of the region. Manganese (Mn) is a significant elemental component of desert varnish that is often at trace levels in the substrate rock. As such, F. Lytle has shown that under certain conditions, it may be possible to estimate the age of petroglpyhs using Mn levels. In this work we use x-ray fluorescence to measure Mn levels in the desert varnish of petroglyphs and then use dated graffiti to attempt to calibrate the Mn level with age. Preliminary results from petroglyph panels in eastern Utah will be presented.

Chemical composition of samples collected from waste rock dumps and other mining-related features at selected phosphate mines in southeastern Idaho, western Wyoming, and northern Utah

USGS Publications Warehouse

Moyle, Phillip R.; Causey, J. Douglas

2001-01-01

This report provides chemical analyses for 31 samples collected from various phosphate mine sites in southeastern Idaho (25), northern Utah (2), and western Wyoming (4). The sampling effort was undertaken as a reconnaissance and does not constitute a characterization of mine wastes. Twenty-five samples were collected from waste rock dumps, 2 from stockpiles, and 1 each from slag, tailings, mill shale, and an outcrop. All samples were analyzed for a suite of major, minor, and trace elements. Although the analytical data set for the 31 samples is too small for detailed statistical analysis, a summary of general observations is made.

Strontium Isotopic Composition of Paleozoic Carbonate Rocks in the Nevada Test Site Vicinity, Clark, Lincoln, and Nye Counties, Nevada and Inyo County, California.

DOE Office of Scientific and Technical Information (OSTI.GOV)

James B. Paces; Zell E. Peterman; Kiyoto Futa

2007-08-07

Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously aroundmore » the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared to values for Paleozoic seawater present at the time of deposition. Many of the samples have 87Sr/86Sr compositions that remain relatively unmodified from expected seawater values. However, rocks underlying the northern Nevada Test Site as well as rocks exposed at Bare Mountain commonly have elevated 87Sr/86Sr values derived from post-depositional addition of radiogenic Sr most likely from fluids circulating through rubidium-rich Paleozoic strata or Precambrian basement rocks.« less

Strontium Isotopic Composition of Paleozoic Carbonate Rocks in the Nevada Test Site Vicinity, Clark, Lincoln, and Nye Counties, Nevada, and Inyo County, California

USGS Publications Warehouse

Paces, James B.; Peterman, Zell E.; Futo, Kiyoto; Oliver, Thomas A.; Marshall, Brian D.

2007-01-01

Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously around the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared to values for Paleozoic seawater present at the time of deposition. Many of the samples have 87Sr/86Sr compositions that remain relatively unmodified from expected seawater values. However, rocks underlying the northern Nevada Test Site as well as rocks exposed at Bare Mountain commonly have elevated 87Sr/86Sr values derived from post-depositional addition of radiogenic Sr most likely from fluids circulating through rubidium-rich Paleozoic strata or Precambrian basement rocks.

Unravelling the effects of melt depletion and secondary infiltration on mantle Re-Os isotopes beneath the French Massif Central

NASA Astrophysics Data System (ADS)

Harvey, J.; Gannoun, A.; Burton, K. W.; Schiano, P.; Rogers, N. W.; Alard, O.

2010-01-01

Spinel lherzolite xenoliths from Mont Briançon, French Massif Central, retain evidence for multiple episodes of melt depletion and melt/fluid infiltration (metasomatism). Evidence for primary melt depletion is still preserved in the co-variation of bulk-rock major elements (MgO 38.7-46.1 wt.%; CaO 0.9-3.6 wt.%), and many samples yield unradiogenic bulk-rock Os isotope ratios ( 187Os/ 188Os = 0.11541-0.12626). However, many individual xenoliths contain interstitial glasses and melt inclusions that are not in equilibrium with the major primary minerals. Incompatible trace element mass balance calculations demonstrate that metasomatic components comprise a significant proportion of the bulk-rock budget for these elements in some rocks, ranging to as much as 25% of Nd and 40% of Sr Critically, for Re-Os geochronology, melt/fluid infiltration is accompanied by the mobilisation of sulfide. Consequently, bulk-rock isotope measurements, whether using lithophile (e.g. Rb-Sr, Sm-Nd) or siderophile (Re-Os) based isotope systems, may only yield a perturbed and/or homogenised average of these multiple events. Osmium mass balance calculations demonstrate that bulk-rock Os in peridotite is dominated by contributions from two populations of sulfide grain: (i) interstitial, metasomatic sulfide with low [Os] and radiogenic 187Os/ 188Os, and (ii) primary sulfides with high [Os] and unradiogenic 187Os/ 188Os, which have been preserved within host silicate grains and shielded from interaction with transient melts and fluid. The latter can account for >97% of bulk-rock Os and preserve geochronological information of the melt from which they originally precipitated as an immiscible liquid. The Re-depletion model ages of individual primary sulfide grains preserve evidence for melt depletion beneath the Massif Central from at least 1.8 Gyr ago despite the more recent metasomatic event(s).

Late Cretaceous (ca. 95 Ma) magnesian andesites in the Biluoco area, southern Qiangtang subterrane, central Tibet: Petrogenetic and tectonic implications

NASA Astrophysics Data System (ADS)

He, Haiyang; Li, Yalin; Wang, Chengshan; Zhou, Aorigele; Qian, Xinyu; Zhang, Jiawei; Du, Lintao; Bi, Wenjun

2018-03-01

The tectonic evolutionary history of the Lhasa and Qiangtang collision zones remains hotly debated because of the lack of pivotal magmatic records in the southern Qiangtang subterrane, central Tibet. We present zircon U-Pb dating, whole-rock major and trace-element geochemical analyses, and Sr-Nd isotopic data for the newly discovered Biluoco volcanic rocks from the southern Qiangtang subterrane, central Tibet. Zircon U-Pb dating reveals that the Biluoco volcanic rocks were crystallized at ca. 95 Ma. The samples are characterized by low SiO2 (50.26-54.53 wt%), high Cr (109.7-125.92 ppm) and Ni (57.4-71.58 ppm), and a high Mg# value (39-56), which plot in the magnesian andesites field on the rock classification diagram. They display highly fractionated rare earth element patterns with light rare earth element enrichment ([La/Yb]N = 21.04-25.24), high Sr/Y (63.97-78.79) and no negative Eu anomalies (Eu/Eu* = 0.98-1.04). The Biluoco volcanic rocks are depleted in Nb, Ta and Ti and enriched in Ba, Th, U and Pb. Moreover, the eight samples of Biluoco volcanic rocks display constant (87Sr/86Sr)i ratios (0.70514-0.70527), a positive εNd(t) value (2.16-2.68) and younger Nd model ages (0.56-0.62 Ga). These geochemical signatures indicate that the Biluoco volcanic rocks were most likely derived from partial melting of the mantle wedge peridotite metasomatized by melts of subducted slab and sediment in the subducted slab, invoked by asthenospheric upwelling resulting from the slab break-off of the northward subduction of the Bangong-Nujiang oceanic lithosphere. Identification of ca. 95 Ma Biluoco magnesian andesites suggests they were a delayed response of slab break-off of the northward subduction of the Bangong-Nujiang oceanic lithosphere at ca. 100 Ma.

Oxidative mobilization of cerium and uranium and enhanced release of "immobile" high field strength elements from igneous rocks in the presence of the biogenic siderophore desferrioxamine B

NASA Astrophysics Data System (ADS)

Kraemer, Dennis; Kopf, Sebastian; Bau, Michael

2015-09-01

Polyvalent trace elements such as the high field strength elements (HFSE) are commonly considered rather immobile during low-temperature water-rock interaction. Hence, they have become diagnostic tools that are widely applied in geochemical studies. We present results of batch leaching experiments focused on the mobilization of certain HFSE (Y, Zr, Hf, Th, U and rare earth elements) from mafic, intermediate and felsic igneous rocks in the presence and absence, respectively, of the siderophore desferrioxamine B (DFOB). Our data show that DFOB strongly enhances the mobility of these trace elements during low-temperature water-rock interaction. The presence of DFOB produces two distinct features in the Rare Earths and Yttrium (REY) patterns of leaching solutions, regardless of the mineralogical and chemical composition or the texture of the rock type studied. Bulk rock-normalized REY patterns of leaching solutions with DFOB show (i) a very distinct positive Ce anomaly and (ii) depletion of La and other light REY relative to the middle REY, with a concave downward pattern between La and Sm. These features are not observed in experiments with hydrochloric acid, acetic acid or deionized water. In DFOB-bearing leaching solutions Ce and U are decoupled from and selectively enriched relative to light REY and Th, respectively, due to oxidation to Ce(IV) and U(VI). Oxidation of Ce3+ and U4+ is promoted by the significantly higher stability of the Ce(IV) and U(VI) DFOB complexes as compared to the Ce(III) and U(IV) DFOB complexes. This is similar to the relationship between the Ce(IV)- and Ce(III)-pentacarbonate complexes that cause positive Ce anomalies in alkaline lakes. However, while formation of Ce(IV) carbonate complexes is confined to alkaline environments, Ce(IV) DFOB complexes may produce positive Ce anomalies even in mildly acidic and near-neutral natural waters. Siderophore-promoted dissolution processes also significantly enhance mobility of other 'immobile' HFSE and may not only cause or modify Ce anomalies and Th-U fractionation, but also mobilization of and fractionation between Zr, Hf, Th and redox-insensitive REY during weathering, pedogenesis, diagenesis and incongruent dissolution of particles in seawater and freshwater. Siderophores may significantly affect the use of HFSE as geochemical tools. Concave downward light REY patterns may be used as a biosignature for water-rock interaction in the presence of siderophores. Enhanced and preferential mobilization of U relative to Th in the presence of siderophores may produce Th-U signals comparable to those indicative of weathering under oxidized conditions, which might constrain the use of U concentrations and Th/U ratios as a paleoredox-proxy. The enhanced mobilization of Zr and especially Hf from igneous rocks in the presence of DFOB might have implications for the use of the latter as a tracer for the impact of continental weathering on seawater chemistry. Because siderophore complexes affect the particle-reactivity of Hf and Zr, they may prevent effective removal of terrigenous Hf and Zr during aggregation/coagulation of riverine particles in estuaries. Siderophore-promoted solubilization and stabilization might hence be an additional way to transport continental Hf and Zr to the oceans. Furthermore, siderophore-enhanced mobilization may also have implications for the remediation techniques employed to immobilize HFSE such as U, Th and REY, at nuclear waste and reprocessing sites and at REY ore processing plants, where soils are commonly contaminated with these (sometimes radioactive) heavy metals.

Petrology of basalts from Loihi Seamount, Hawaii

NASA Astrophysics Data System (ADS)

Hawkins, James; Melchior, John

1983-12-01

Loihi Seamount is the southeasternmost active volcano of the Emperor-Hawaii linear volcanic chain. It comprises a spectrum of basalt compositional varieties including basanite, alkali basalt, transitional basalt and tholeiite. Samples from four dredge collections made on Scripps Institution of Oceanography Benthic Expedition in October 1982 are tholeiite. The samples include highly vesicular, olivine-rich basalt and dense glass-rich pillow fragments containing olivine and augite phenocrysts. Both quartz-normative and olivine-normative tholeiites are present. Minor and trace element data indicate relatively high abundances of low partition coefficient elements (e.g., Ti, K, P. Rb, Ba, Zr) and suggest that the samples were derived by relatively small to moderate extent of partial melting, of an undepleted mantle source. Olivine composition, MgO, Cr and Ni abundances, and Mg/(Mg+Fe), are typical of moderately fractionated to relatively unfractionated "primary" magmas. The variations in chemistry between samples cannot be adequately explained by low-pressure fractional crystallization but can be satisfied by minor variations in extent of melting if a homogeneous source is postulated. Alternatively, a heterogeneous source with variable abundances of certain trace elements, or mixing of liquids, may have been involved. Data for 3He/ 4He, presented in a separate paper, implies a mantle plume origin for the helium composition of the Loihi samples. There is little variation in the helium isotope ratio for samples having different compositions and textures. The helium data are not distinctive enough to unequivocally separate the magma sources for the tholeiitic rocks from the other rock types such as Loihi alkalic basalts and the whole source region for Loihi may have a nearly uniform helium compositions even though other element abundances may be variable. Complex petrologic processes including variable melting, fractional crystallization and magma mixing may have blurred original helium isotopic signatures.

Multivariate analyses of Erzgebirge granite and rhyolite composition: Implications for classification of granites and their genetic relations

USGS Publications Warehouse

Forster, H.-J.; Davis, J.C.; Tischendorf, G.; Seltmann, R.

1999-01-01

High-precision major, minor and trace element analyses for 44 elements have been made of 329 Late Variscan granitic and rhyolitic rocks from the Erzgebirge metallogenic province of Germany. The intrusive histories of some of these granites are not completely understood and exposures of rock are not adequate to resolve relationships between what apparently are different plutons. Therefore, it is necessary to turn to chemical analyses to decipher the evolution of the plutons and their relationships. A new classification of Erzgebirge plutons into five major groups of granites, based on petrologic interpretations of geochemical and mineralogical relationships (low-F biotite granites; low-F two-mica granites; high-F, high-P2O5 Li-mica granites; high-F, low-P2O5 Li-mica granites; high-F, low-P2O5 biotite granites) was tested by multivariate techniques. Canonical analyses of major elements, minor elements, trace elements and ratio variables all distinguish the groups with differing amounts of success. Univariate ANOVA's, in combination with forward-stepwise and backward-elimination canonical analyses, were used to select ten variables which were most effective in distinguishing groups. In a biplot, groups form distinct clusters roughly arranged along a quadratic path. Within groups, individual plutons tend to be arranged in patterns possibly reflecting granitic evolution. Canonical functions were used to classify samples of rhyolites of unknown association into the five groups. Another canonical analysis was based on ten elements traditionally used in petrology and which were important in the new classification of granites. Their biplot pattern is similar to that from statistically chosen variables but less effective at distinguishing the five groups of granites. This study shows that multivariate statistical techniques can provide significant insight into problems of granitic petrogenesis and may be superior to conventional procedures for petrological interpretation.

Major and trace element geochemistry and background concentrations for soils in Connecticut

USGS Publications Warehouse

Brown, Craig; Thomas, Margaret A.

2014-01-01

Soil samples were collected throughout Connecticut (CT) to determine the relationship of soil chemistry with the underlying geology and to better understand background concentrations of major and trace elements in soils. Soil samples were collected (1) from the upper 5 cm of surficial soil at 100 sites, (2) from the A horizon at 86 of these sites, and (3) from the deeper horizon, typically the C horizon, at 79 of these sites. The <2-millimeter fraction of each sample was analyzed for 44 elements by methods that yield the total or near-total elemental content. Sample sites were characterized by glacial setting, underlying bedrock geology, and soil type. These spatial data were used with element concentrations in the C-horizon to relate geologic factors to soil chemistry. Concentrations of elements in C-horizon soils varied with grain size in surficial glacial materials and with underlying rock types, as determined using nonparametric statistical procedures. Concentrations of most elements in C-horizon soils showed a positive correlation with silt and (or) clay content and were higher in surficial materials mapped as till, thick till, and (or) fines. Element concentrations in C-horizon soils showed significant differences among the underlying geologic provinces and were highest overlying the Grenville Belt and (or) the Grenville Shelf Sequence Provinces in western CT. These rocks consist mainly of carbonates and the relatively high element concentrations in overlying soils likely result from less influence of dilution by quartz compared to other provinces. Element concentrations in C-horizon soils in CT were compared with those in samples from other New England states overlying similar lithologic bedrock types. The upper range of As concentrations in C-horizon soils overlying the New Hampshire-Maine (NH-ME) Sequence in CT was 15 mg/kg, lower than the upper range of 24 mg/kg in C-horizon soils overlying the same sequence in ME. In CT, U concentration means were significantly higher in C-horizon soils overlying Avalonian granites, and U concentrations ranged as high as 14 mg/kg, compared to those in C-horizon soil samples collected from other New England states, which ranged as high as 6.1 mg/kg in a sample in NH overlying the NH-ME Sequence. Element concentrations in C-horizon soils in CT were compared with those in samples collected from shallower depths. Concentrations of most major elements were highest in C-horizon soil samples, including Al, Ca, Fe, K, Na, and Ti, but element concentrations showed a relatively similar pattern in A-horizon and surficial soil samples among the underlying geologic provinces. Trace element concentrations, including Ba, W, Ga, Ni, Cs, Rb, Sr, Th, Sc, and U, also were higher in C-horizon soil samples than in overlying soil samples. Concentrations of Mg, and several trace elements, including Mn, P, As, Nb, Sn, Be, Bi, Hg, Se, Sb, La, Co, Cr, Pb, V, Y, Cu, Pb, and Zn were highest in some A-horizon or surficial soils, and indicate possible contributions from anthropogenic sources. Because element concentrations in soils above the C horizon are more likely to be affected by anthropogenic factors, concentration ranges in C-horizon soils and their spatially varying geologic associations should be considered when estimating background concentrations of elements in CT soils.

Simultaneous leaching of arsenite, arsenate, selenite and selenate, and their migration in tunnel-excavated sedimentary rocks: I. Column experiments under intermittent and unsaturated flow.

PubMed

Tabelin, Carlito Baltazar; Sasaki, Ryosuke; Igarashi, Toshifumi; Park, Ilhwan; Tamoto, Shuichi; Arima, Takahiko; Ito, Mayumi; Hiroyoshi, Naoki

2017-11-01

Rocks excavated in tunnel construction projects for roads and railways throughout Japan often leached out hazardous trace elements like arsenic (As) and selenium (Se) upon their exposure to the environment. In nature, the various oxyanionic species of As and Se not only coexist but also exhibit contrasting adsorption-desorption behaviors, so speciation is a crucial factor in their migration through natural geologic media. In this study, the leaching and transport of arsenite (As III ), arsenate (As V ), selenite (Se IV ) and selenate (Se VI ) in four tunnel-excavated rocks from the Cretaceous-Paleocene Yezo forearc basin were investigated using laboratory column experiments supplemented by batch leaching experiments. The single- and consecutive-batch leaching results revealed that As III , As V , Se IV and Se VI were released simultaneously, which could be attributed to the rapid dissolution of trace evaporite salts found in the rocks. Arsenic in the leachates was also predominated by As V while Se IV and Se VI concentrations were nearly equal, which are both consistent with predictions of equilibrium Eh-pH diagrams. Under intermittent and unsaturated flow, however, periods when As III and Se VI predominated in the effluents were observed. Spatial distributions of As and Se species with depth at the end of the column experiments suggest that migrations of As III , As V and Se IV were delayed, the extent of which depended on the rock. These results indicate that migration and speciation of As and Se in the rocks are controlled by preferential adsorption-desorption reactions, the effects of which were most probably magnified by changes in the pH and concentrations of coexisting ions due to intermittent and unsaturated flow. Copyright © 2017 Elsevier Ltd. All rights reserved.

Selective uptake of uranium and thorium by some vegetables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yusof, A.M.; Ghazali, Z.; Rahman, S.A.

1996-12-31

Uranium and thorium are trace elements in the actinide series found naturally in the atmosphere and can enter the human body through ingestion of food or by drinking. To establish baseline information for current and future environmental assessment due to pollution, especially in foodstuff, by heavy and trace metals, biological samples such as locally grown vegetables were analyzed for uranium and thorium contents. The terrain in most parts of the Malaysian peninsula consists of monazite-bearing rocks or soil that can be found extensively in areas related to tin-mining operations. Abandoned mining areas provide suitable sites for vegetable cultivation where mostmore » vegetables in the lowlands are grown.« less

Geochemical constraints on the petrogenesis of the pyroclastic rocks in Abakaliki basin (Lower Benue Rift), Southeastern Nigeria

NASA Astrophysics Data System (ADS)

Chukwu, Anthony; Obiora, Smart C.

2018-05-01

The pyroclastic rocks in the Cretaceous Abakaliki basin occur mostly as oval-shaped bodies, consisting of lithic/lava and vitric fragments. They are commonly characterized by parallel and cross laminations, as well contain xenoliths of shale, mudstone and siltstones from the older Asu River Group of Albian age. The rocks are basic to ultrabasic in composition, comprising altered alkali basalts, altered tuffs, minor lapillistones and agglomerates. The mineral compositions are characterized mainly by laths of calcic plagioclase, pyroxene (altered), altered olivines and opaques. Calcite, zeolite and quartz represent the secondary mineral constituents. Geochemically, two groups of volcaniclastic rocks, are distinguished: alkaline and tholeiitic rocks, both represented by fresh and altered rock samples. The older alkali basalts occur within the core of the Abakaliki anticlinorium while the younger tholeiites occur towards the periphery. Though most of the rocks are moderate to highly altered [Loss on ignition (LOI, 3.43-22.07 wt. %)], the use of immobile trace element such as Nb, Zr, Y, Hf, Ti, Ta and REEs reflect asthenospheric mantle source compositions. The rocks are enriched in incompatible elements and REEs (∑REE = 87.98-281.0 ppm for alkaline and 69.45-287.99 ppm for tholeiites). The ratios of La/Ybn are higher in the alkaline rocks ranging from 7.69 to 31.55 compared to the tholeiitic rocks which range from 4.4 to 16.89 and indicating the presence of garnet-bearing lherzolite in the source mantle. The spidergrams and REEs patterns along with Zr/Nb, Ba/Nb, Rb/Nb ratios suggest that the rocks were generated by a mantle plume from partial melting of mixed enriched mantle sources (HIMU, EMI and EMII) similar to the rocks of the south Atlantic Ocean such as St. Helena (alkaline rocks) and Ascension rocks (tholeiitic rocks). The rocks were formed in a within-plate setting of the intra-continental rift type similar to other igneous rocks in the Benue Rift and are not related to any subduction event as previously suggested.

Crustal forensics in arc magmas

NASA Astrophysics Data System (ADS)

Davidson, Jon P.; Hora, John M.; Garrison, Jennifer M.; Dungan, Michael A.

2005-01-01

The geochemical characteristics of continental crust are present in nearly all arc magmas. These characteristics may reflect a specific source process, such as fluid fluxing, common to both arc magmas and the continental crust, and/or may reflect the incorporation of continental crust into arc magmas either at source via subducted sediment, or via contamination during differentiation. Resolving the relative mass contributions of juvenile, mantle-derived material, versus that derived from pre-existing crust of the upper plate, and providing these estimates on an element-by-element basis, is important because: (1) we want to constrain crustal growth rates; (2) we want to quantitatively track element cycling at convergent margins; and (3) we want to determine the origin of economically important elements and compounds. Traditional geochemical approaches for determining the contributions of various components to arc magmas are particularly successful when applied on a comparative basis. Studies of suites from multiple magmatic systems along arcs, for which differentiation effects can be individually constrained, can be used to extrapolate to potential source compositions. In the Lesser Antilles Arc, for example, differentiation trends from individual volcanoes are consistent with open-system evolution. However, such trends do not project back to a common primitive magma composition, suggesting that differentiation modifies magmas that were derived from distinct mantle sources. We propose that such approaches should now be complemented by petrographically constrained mineral-scale isotope and trace element analysis to unravel the contributing components to arc magmas. This innovative approach can: (1) better constrain true end-member compositions by returning wider ranges in geochemical compositions among constituent minerals than is found in whole rocks; (2) better determine magmatic evolution processes from core-rim isotopic or trace element profiles from the phases contained in magmas; and (3) constrain rates of differentiation by applying diffusion-controlled timescales to element profiles. An example from Nguaruhoe Volcano, New Zealand, underscores the importance of such a microsampling approach, showing that mineral isotopic compositions encompass wide ranges, that whole-rock isotopic compositions are consequently simply element-weighted averages of the heterogeneous crystal cargo, and that open-system evolution is proved by core-rim variations in Sr isotope ratios. Nguaruhoe is just one of many systems examined through microanalytical approaches. The overwhelming conclusion of these studies is that crystal cargoes are not truly phenocrystic, but are inherited from various sources. The implication of this realization is that the interpretation of whole-rock isotopic data, including the currently popular U-series, needs careful evaluation in the context of petrographic observations.

Decoupling of the Assimilation and Fractionation Signatures in a MASH Zone: Evidence from the Sierra Valle Fértil Mafic Zone, Argentina

NASA Astrophysics Data System (ADS)

Walker, B. A., Jr.; Bergantz, G. W.; Otamendi, J.; Ducea, M. N.; Cristofolini, E.

2015-12-01

The Sierra Valle Fértil (SVF) in northern Argentina is a tilted Ordovician fossil arc complex with continuous exposure from paleodepths of ~10 km to ~30 km. The system is layered when viewed at a large scale: shallow, granodiorite plutons give way to a heterogeneous granodiorite-tonalite zone, which in turn grades into a gabbro-tonalite zone at the base of the section. A metapelitic country rock package is interlayered throughout the magmatic complex, allowing for determination of emplacement depths within the section. Our work focuses on the lowermost domain of the SVF, as it preserves what we consider to be a frozen example of a MASH zone. Here, dominant rock types are hornblende gabbronorite and tonalitie variants, which appear to be interfingered as dm- to 10s of m-scale sheets. Mappable ultramafic pods containing dunites, websterites, troctolites, and minor anorthosites are also present. Field relations are consistent with a complex series of intrusive events. Much of the SVF mafic zone compositional array can be modeled by fractional crystallization where the mafic rocks are cumulate assemblages and the intermediate rocks are the daughter magmas. Amphibole and, perhaps more importantly, Fe-Ti oxide crystallization are likely the principal agents of silica enrichment. Metapelitic rocks exposed throughout the SVF are likely the vestiges of a country rock package that was melted (or reacted) and incorporated into SVF magmas, but field and compositional evidence for assimilation is cryptic in the mafic zone. While isotopic data (Sr, Nd, O) seem to implicate crustal contributions to the SVF mafic zone, incompatible major and trace elements typically associated with an "assimilation signature" (e.g., K, Rb, Ba) are sparse. Such elements are abundant in the metapelites and in igneous rocks farther up section. We interpret this isotopic and elemental decoupling as a byproduct of prolonged MASH processes in the lower crust. A high temperature and an increasingly mafic environment likely resulted in the development of a crystal mush inhospitable to crustally contributed incompatible elements. Over time, these elements were thoroughly flushed out of the MASH zone via melt extraction. Isotopes, then, may be the only residual evidence of assimilation within the SVF mafic zone.

High-silica Rocks from Oceans, Arcs and Ophiolites: What Can They Tell Us About Ophiolite Origins?

NASA Astrophysics Data System (ADS)

Perfit, M. R.; Lundstrom, C.; Wanless, V. D.

2015-12-01

Although the volumes of high-silica rocks in submarine oceanic and supra-subduction zone environments are not well constrained, their common occurrence, field relations and compositions have led to various hypotheses suggesting that silicic intrusions (plagiogranites) in ophiolites formed by similar processes to high-silica volcanic rocks at mid-ocean ridge (MOR) or island arc environments. Geochemical attributes of andesite-rhyolite suites from MOR (East Pacific Rise, Juan de Fuca Ridge, Galapagos Spreading Center, Pacific-Antarctic Rise) and back-arc basins (Manus Basin, Lau Basin, East Scotia Ridge) show both similarities and differences to plagiogranitic suites (qtz. diorite-tonalite-trondhjemite) from ophiolites (Troodos and Semail). Both suites are commonly attributed to: extreme (>90%) fractional crystallization of basaltic melts; fractional crystallization coupled with assimilation of hydrated oceanic crust (AFC); or partial melting of preexisting crust. Normalized incompatible trace element patterns show either highly elevated, relatively flat patterns with negative Eu and Sr anomalies similar to high silica volcanics or have complimentary patterns with low abundance, more depleted patterns with positive Eu and Sr anomalies. None of the mechanisms, however, provide a consistent explanation for the compositional and isotopic variations that are observed among plagiogranites. In fact, ophiolitic plagiogranites can have at least two petrogenetic signatures - one indicative of a MORB parent and another that has been related to later, off-axis formation associated with supra-subduction zone magmatism. Based on thermal gradient experiments, the systematic changes in Fe and Si stable isotope ratios with differentiation observed in ophiolite and MOR high-silica suites may result from melt-mineral reactions within a temperature gradient near the boundaries of MOR magma lenses. Comparative major element, trace element and isotopic data will be presented from MOR, BAB and ophiolites to address questions of their origins. Although the mechanism(s) by which plagiogranite bodies form and their relationship to andesitic to rhyolitic lavas still remains enigmatic geochemical comparisons between them provide important clues toward understanding their petrotectonic origins.

Mechanical Mixing and Metamorphism of Mafic and Ultramafic Lithologies during Mylonisis at the ST. Paul Transform System, Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Adrião, Á.; Maia, M.; Hemond, C.; Kaczmarek, M. A.; Briais, A.; Vincent, C.; Brunelli, D.

2017-12-01

The St. Paul Transform System offsets by 630 km the Equatorial Mid Atlantic Ridge at 1° N. It consists of four major faults separating three intra transform ridge axes. This region shows a transition from a transpressive, hot spot affected, regional-scale shear zone to the North to a region dominated by a particular oceanic core complex spreading to the South (Vincent et al., this congress). Samples collected in the region during the COLMEIA cruise (Maia et al., 2016) were studied for textures and whole-rock major and trace element contents. All samples experienced pervasive deformation at ductile to brittle conditions overprinted by late low-T alteration. Mylonitic and ultramylonitic rocks can be grouped in three main types: peridotitic, gabbroic and talc-chlorite schist. Peridotitic ultramylonites preserve few opx, cpx and sp porphyroclasts; they have homogeneous nano-micro grain size groundmass, banded foliation and late amphibole and sulfide crystallization. Locally S-C fabric overprints the mylonitic texture. Micro cracks, filled with serpentine, chlorite and oxides are common, as well fluid inclusions trails in olivine and plagioclase crystals of peridotite and gabbros respectively. Major and trace element content of the peridotitic mylonites plot in the depleted field of the abyssal peridotites; however, they present marked LREE enrichment and Eu positive anomaly. Gabbroic and talc-chlorite mylonites display REE-enriched patterns (up to 100x CI) and variable Eu anomalies. Major elements show a remarkable linear trend in the talc-chlorite group suggesting mixing of pure talc and chlorite end-members. These compositional characteristics suggest variable assimilation of MORB and E-MORB during mylonisis or early melt-rock interaction and hydrothermal evolution at variable metamorphic conditions. Vincent et al., 2017. Particular Oceanic Core Complex evolution …; this congress Maia et al., 2016. Extreme mantle uplift and exhumation ... Nat. Geo. doi:10.1038/ngeo2759

Zircon/fluid trace element partition coefficients measured by recrystallization of Mud Tank zircon at 1.5 GPa and 800-1000 °C

NASA Astrophysics Data System (ADS)

Ayers, John C.; Peters, Timothy J.

2018-02-01

Hydrothermal zircon grains have trace element characteristics such as low Th/U, high U, and high rare earth element (REE) concentrations that distinguish them from magmatic, metamorphic, and altered zircon grains, but it is unclear whether these characteristics result from distinctive fluid compositions or zircon/fluid fractionation effects. New experiments aimed at measuring zircon/fluid trace element partition coefficients Dz/f involved recrystallizing natural Mud Tank zircon with low trace element concentrations in the presence of H2O, 1 m NaOH, or 1 m HCl doped with ∼1000 ppm of rare earth elements (REE), Y, U and Th and ∼500 ppm of Li, B, P, Nb, Ba, Hf, and Ta. Experiments were run for 168 h at 1.5 GPa, 800-1000 °C, and fO2 = NNO in a piston cylinder apparatus using the double capsule method. LA-ICP-MS analysis shows that run product zircon crystals have much higher trace element concentrations than in Mud Tank zircon starting material. Dz/f values were estimated from run product zircon analyses and bulk composition using mass balance. Most elements behave incompatibly, with median Dz/f being highest for Hf = 8 and lowest for B = 0.02. Addition of NaOH or HCl had little influence on Dz/f values. Dz/f for LREE are anomalously high, likely due to contamination of run product zircon with quenched solutes enriched in incompatible elements, so DLREE were estimated using lattice strain theory. Brice curves for +3 ions yield zircon/fluid DLu/DLa of ∼800-5000. A Brice curve fit to +4 ions yielded DCe4+ values. Estimated concentrations of Ce3+ and Ce4+ show that the average Ce4+/Ce3+ in zircon of 27 is much higher than in fluid of 0.02. Th and U show little fractionation, with median DTh/DU = 0.7, indicating that the low Th/U in natural hydrothermal zircon is inherited from the fluid. Natural fluid compositions estimated from measured Dz/f and published compositions of hydrothermal zircon grains from aplite and eclogite reflect the mineralogy of the host rock, e.g., fluid in equilibrium with eclogite garnet is depleted in heavy REE relative to middle REE, and has low Th/U.

Laser ablation ICP-MS analysis on nano-powder pellets and applications to granite bulk rock analysis

NASA Astrophysics Data System (ADS)

Wu, Shitou; Karius, Volker; Wörner, Gerhard

2017-04-01

Granites are a ubiquitous component of the continental crust and knowing their precise trace element signatures is essential in understanding the origins and evolution of the continental crust. ICP-MS bulk analysis of granite is generally conducted on solution after acid-digestion. However this technique has several deficiencies related to the difficulty of completely dissolving accessary minerals such as zircon and the instability/adsorption of high valence trace elements (Nb, Ta et al.) in acid solutions. The development of a nano-powder pellet technique by using wet milling procedure, and its combination with laser ablation ICP-MS has been proposed to overcome these problems. In this study, we produced nano-powders from a series of granite rock standards by wet milling in agate using a high power planetary ball mill instrument. The procedure was tested and optimized by modifying parameters (ball to powder ratio, water to powder ratio, milling power etc.). Characterization of nano-powders was conducted by various techniques including electron microprobe (EMP), secondary electron imaging, polarizing microscope, and laser particle size analyzer (LPSA) and laser scanning confocal microscope (LSCM). Particle sizes range from a few nm to 5 μm with a small secondary mode at around 10 to 20 μm that probably represent particle aggregates rather than remaining crystal grains after milling. Pellets of 5 mm in diameter were pressed into molds of cellulose at 1.75 *103 N/cm2. Surface roughness of the pellets was measured by LSCM and gave a Ra of 0.494 μm, which is an order higher than the surface of polished ATGH-G reference glass surface (Ra: 0.048 μm), but sufficient for laser ablation. Sources of contamination either from abrading agate balls or from ultrapure water were evaluated and quantified. The homogeneity of powder pellets down to less than 5 μm size was documented based on EMPA element mapping and statistical analyses of LA-ICP-MS in discrete spot and line scanning analytical mode. We report data from major to trace element (to < 0.1 ppm) of currently available international granite reference materials (JG-2, JG-3, GWB07103, GEB07111, GSP-2 and G-3) to evaluate analytical precision and accuracy of LA-ICP-MS measurements. Our results illustrate the potential of this method for high precision analysis of trace elements and e.g. Zr/Hf and Nb/Ta ratios in granites.

Trace elements in Gem-Quality Diamonds - Origin and evolution of diamond-forming fluid inclusions

NASA Astrophysics Data System (ADS)

Pearson, Graham; Krebs, Mandy; Stachel, Thomas; Woodland, Sarah; Chinn, Ingrid; Kong, Julie

2017-04-01

In the same way that melt inclusions in phenocrysts have expanded our idea of melt formation and evolution in basalts, studying fluids trapped in diamonds is providing important new constraints on the nature of diamond-forming fluids. Fibrous and cloudy diamonds trap a high but variable density of fluid inclusions and so have been extensively studied using major and trace element compositions. In contrast, constraining the nature of the diamond-forming fluid for high purity gem-quality diamonds has been restricted by the rarity of available high quality trace element data. This is due to the extremely low concentrations of impurities that gem diamonds contain - often in the ppt range. The recent discovery of fluids in gem diamonds showing similar major element chemistry to fluid-rich diamonds suggest that many diamonds may share a common spectrum of parental fluids. Here we test this idea further. Recent advances in analytical techniques, in particular the development of the "off-line" laser ablation pre-concentration approach, have allowed fully quantitative trace element data to be recovered from "fluid-poor", high quality gem diamonds. We present trace element data for gem diamonds from a variety of locations from Canada, S. Africa and Russia, containing either silicate or sulphide inclusions to examine possible paragenetic or genetic differences between fluids. REE abundance in the "gem" diamonds vary from 0.1 to 0.0001 x chondrite. To a first order, we observe the same spectrum of trace element compositions in the gem diamonds as that seen in fluid-rich "fibrous" diamonds, supporting a common origin for the fluids. REE patterns range from extremely flat (Ce/Yb)n 2.5 to 5 (commonly in sulphide-bearing diamonds) to >70, the latter having significantly greater inter-element HFSE/LILE fractionation. In general, the fluids from the sulphide-bearing diamonds are less REE-enriched than the silicate-bearing diamonds, but the ranges overlap significantly. The very large range in REE fractionation mimics very closely that produced in high pressure (5-6 GPa) experimental melts of CO2-H2O fluxed peridotite. Hence, the elemental characteristics of the fluids could be reconciled by the diamonds growing from such melts over a range of T and hence F, with the sulphide-bearing diamonds generally being produced by larger fraction (higher T) melts that have reacted less with their wall rocks. It is also possible that the less REE enriched fluids are consistent with derivation from more reduced CH4-bearing fluids that have lower solute capacity than oxidised fluids. This option is being evaluated.

Crystallization conditions and controls on trace element residence in the main minerals from the Pedra Branca Syenite, Brazil: An electron microprobe and LA-ICPMS study

NASA Astrophysics Data System (ADS)

Carvalho, Bruna Borges; Janasi, Valdecir de Assis

2012-11-01

Major and trace-element microanalyses of the main minerals from the 610 Ma Pedra Branca Syenite, southeast Brazil, allow inferences on intensive parameters of magmatic crystallization and on the partition of trace-elements among these minerals, with important implications for the petrogenetic evolution of the pluton. Two main syenite types make up the pluton, a quartz-free syenite with tabular alkali feldspar (laminated silica-saturated syenite, LSS, with Na-rich augite + phlogopite + hematite + magnetite + titanite + apatite) and a quartz-bearing syenite (laminated silica-oversaturated syenite, LSO, with scarce corroded plagioclase plus diopside + biotite ± hornblende + ilmenite ± magnetite + titanite + apatite). Both types share a remarkable enrichment in incompatible elements as K, Ba, Sr, P and LREE. Apatite saturation temperatures of ~ 1060-1090 °C are the best estimates of liquidus, whereas the pressure of emplacement, based on Al-in-hornblende barometry, is estimated as 3.3 to 4.8 kbar. Although both units crystallized under oxidizing conditions, oxygen fugacity was probably higher in LSS, as shown by higher mg# of the mafic minerals and higher hematite contents in Hem-Ilmss. In contrast with the Ca-bearing alkali-feldspar from LSO, which hosts most of the whole-rock Sr and Pb, virtually Ca-free alkali-feldspar from LSS hosts ~ 50% of whole-rock Sr and ~ 80% of Pb, the remainder of these elements being shared by apatite, pyroxene and titanite. This contrast reflects a strong crystal-chemical control, whereby a higher proportion of an element with similar ratio and charge (Ca2 +) enhances the residence of Sr and Pb in the M-site of alkali feldspar. The more alkaline character of the LSS magma is inferred to have inhibited zircon saturation; Zr + Hf remained in solution until late in the crystallization, and were mostly accommodated in the structure of Ca-Na pyroxene and titanite, which are one order of magnitude richer in these elements compared to the same minerals in LSO, where most of Zr and Hf are inferred to reside in zircon. The REE, Th and U reside mostly in titanite and apatite; D(REE)Tit/Ap raises steadily from 1 to 6 from La to Tb then remains constant up to Lu in the LSO sample; these values are about half as much in the LSS sample, where lower contents of incompatible elements in titanite are attributed to its greater modal abundance and earlier crystallization.

Geochemistry and tectonic implications of the Early Carboniferous Keketuobie intrusion in the West Junggar foldbelt, NW China

NASA Astrophysics Data System (ADS)

Deng, Yu-Feng; Yuan, Feng; Zhou, Taofa; Hollings, Pete; Zhang, Dayu

2018-06-01

The Keketuobie intrusion is situated in the northern part of the West Junggar foldbelt at the southern margin of the Central Asian Orogeic Belt. The intrusion consists of medium- to coarse-grained gabbro, fine-grained gabbro and diorite. Igneous zircons from the medium- to coarse-grained gabbro yielded a LA-ICP-MS U-Pb age of 320.8 ± 5.7 Ma, indicating that the intrusion was emplaced in the Early Carboniferous. The intrusive contact between the medium- to coarse-grained gabbro and the fine-grained gabbro indicates they formed from distinct magma pulses. Magnetite crystals from the fine-grained gabbro have lower V2O3 but higher TiO2 and Al2O3 contents than those of the medium- to coarse-grained gabbro, suggesting that the fine-grained gabbro crystallized in a relatively higher fO2 and temperature magma than the medium- to coarse-grained gabbro. The Keketuobie intrusive rocks are characterized by enriched large ion lithophile elements and depleted high field strength elements relative to N-MORB with restricted (87Sr/86Sr)t ratios (0.70370-0.70400) and εNd(t) values (+5.85 to +6.97). The petrography and geochemistry are comparable to those of subduction-related volcanic rocks. The trace elements and isotopic compositions of the mafic intrusive rocks suggest that the primary magmas were derived from mixing of metasomatized lithospheric mantle and depleted asthenospheric melts, perhaps triggered by slab break-off. The Keketuobie intrusion is younger than adjacent ophiolite sequences, island arc volcanic rocks and porphyry deposits, but predates the post-collisional A-type granites and bimodal volcanic rocks in the district, suggesting that the Keketuobie intrusion likely formed in a syn-collisional setting.

Trace element composition of rutile and Zr-in-rutile thermometry in meta-ophiolitic rocks from the Kazdağ Massif, NW Turkey

NASA Astrophysics Data System (ADS)

Şengün, Fırat; Zack, Thomas

2016-08-01

In northwest Turkey, ophiolitic meta-gabbros are exposed on the Kazdağ Massif located in the southern part of the Biga Peninsula. Trace element composition of rutile and Zr-in-rutile temperatures were determined for meta-gabbros from the Kazdağ Massif. The Zr content of all rutiles range from 176 to 428 ppm and rutile grains usually have a homogeneous Zr distribution. The rutile grains from studied samples in the Kazdağ Massif are dominated by subchondritic Nb/Ta (11-19) and Zr/Hf ratios (20-33). Nb/Ta and Zr/Hf show positive correlation, which is probably produced by silicate fractionation. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents. The core of rutile grains are generally characterized by low Nb/Ta ratios of 17-18 whereas the rims exhibit relatively high Nb/Ta ratios of 19-23. Trace element analyses in rutile suggest that these rutile grains were grown from metamorphic fluids. The P-T conditions of meta-gabbros were estimated by both Fe-Mg exchange and Zr-in-rutile thermometers, as well as by the Grt-Hb-Plg-Q geothermobarometer. The temperature range of 639 to 662 °C calculated at 9 kbar using the Zr-in-rutile thermometer is comparable with temperature estimates of the Fe-Mg exchange thermometer, which records amphibolite-facies metamorphism of intermediate P-T conditions. The P-T conditions of meta-ophiolitic rocks suggest that they occur as a different separate higher-pressure tectonic slice in the Kazdağ metamorphic sequence. Amphibolite-facies metamorphism resulted from northward subduction of the İzmir-Ankara branch of the Neo-Tethyan Ocean under the Sakarya Zone. Metamorphism was followed by internal imbrication of the Kazdağ metamorphic sequence resulting from southerly directed compression during the collision.

Polybaric evolution of phonolite, trachyte, and rhyolite volcanoes in Eastern Marie Byrd Land, Antarctica: Controls on peralkalinity and silica saturation

USGS Publications Warehouse

LeMasurier, W.E.; Futa, K.; Hole, M.; Kawachi, Y.

2003-01-01

In the Marie Byrd Land volcanic province, peralkaline and metaluminous trachytes, phonolites, and rhyolites occur in 18 large shield volcanoes that are closely associated in time and space. They are arrayed radially across an 800 km wide structural dome, with the oldest at the crest and the youngest around the flanks. Several lines of evidence suggest that these rocks evolved via open-system, polybaric fractionation. We have used mass balance modeling of major elements together with trace-element data and mineral chemistry to help explain the evolution of this diverse suite of felsic rocks, which appear to have been generated coevally in isolated magma chambers, and erupted close to each other in patterns related to tectonic uplift and extension within the West Antarctic rift system. Isotopic and trace-element data indicate that this occurred with only minimal crustal contamination. We focus on volcanoes of the Executive Committee Range and Mount Murphy, where we find good representation of basalts and felsic rocks within a small area. Our results suggest that the felsic rocks were derived from basaltic magmas that differentiated at multiple levels during their passage to the surface: first to ferrogabbroic compositions near the base of the lithosphere, then to intermediate compositions near the base of the crust, and finally to felsic compositions in mid- to upper crustal reservoirs. The high-pressure history has been largely masked by low-pressure processes. The best indications of a high-pressure history are the mineral phases in cumulate nodules and their correlation with modeling results, with REE anomalies, and with the composition of an unusual gabbroic intrusion. Silica saturation characteristics are believed to have originated in magma chambers near the base of the crust, via fractionation of variable proportions of kaersutite and plagioclase. Development of peralkalinity in felsic rocks took place in upper crustal reservoirs by fractionating a high ratio of plagioclase to clinopyroxene under conditions of low pH2O. With increasing pH2O, the ratio plagioclase/clinopyroxene in the fractionated assemblage decreases and metaluminous liquids resulted. Crustal contamination seems to have had a role in suppressing peralkalinity, and was probably a factor in the origin of high-silica metaluminous rhyolite, but metaluminous rocks are uncommon. The volume and diversity of felsic rocks were probably enhanced by the structure of the lithosphere, the persistence of plume activity, and the immobility of the Antarctic plate. Mechanical boundaries at the base of the lithosphere and crust, and within the crust, appear to have acted as filters, trapping magmas at multiple levels, and prolonging the fractionation process. Final volumes would have been further enhanced by repeated refluxing of the same magma chambers, controlled by plume activity and plate immobility.

Stratigraphy, geochemistry and tectonic significance of the Oligocene magmatic rocks of western Oaxaca, southern Mexico

USGS Publications Warehouse

Martiny, B.; Martinez-Serrano, R. G.; Moran-Zenteno, D. J.; MacIas-Romo, C.; Ayuso, R.A.

2000-01-01

In Western Oaxaca, Tertiary magmatic activity is represented by extensive plutons along the continental margin and volcanic sequences in the inland region. K-Ar age determinations reported previously and in the present work indicate that these rocks correspond to a relatively broad arc in this region that was active mainly during the Oligocene (~ 35 to ~ 25 Ma). In the northern sector of western Oaxaca (Huajuapan-Monte Verde-Yanhuitlan), the volcanic suite comprises principally basaltic andesite to andesitic lavas, overlying minor silicic to intermediate volcaniclastic rocks (epiclastic deposits, ash fall tuffs, ignimbrites) that were deposited in the lacustrine-fluvial environment. The southern sector of the volcanic zone includes the Tlaxiaco-Laguna de Guadalupe region and consists of intermediate to silicic pyroclastic and epiclastic deposits, with silicic ash fall tuffs and ignimbrites. In both sectors, numerous andesitic to dacitic hypabyssal intrusions (stocks and dikes) were emplaced at different levels of the sequence. The granitoids of the coastal plutonic belt are generally more differentiated than the volcanic rocks that predominate in the northern sector and vary in composition from granite to granodiorite. The studied rocks show large-ion lithophile element (LILE) enrichment (K, Rb, Ba, Th) relative to high-field-strength (HFS) elements (Nb, Ti, Zr) that is characteristic of subduction-related magmatic rocks. On chondrite-normalized rare earth element diagrams, these samples display light rare earth element enrichment (LREE) and a flat pattern for the heavy rare earth elements (HREE). In spite of the contrasting degree of differentiation between the coastal plutons and inland volcanic rocks, there is a relatively small variation in the isotopic composition of these two suites. Initial 87Sr/86Sr ratios obtained and reported previously for Tertiary plutonic rocks of western Oaxaca range from 0.7042 to 0.7054 and ??Nd values, from -3.0 to +2.4, and for the volcanic rocks, from 0.7042 to 0.7046 and 0 +2.6. The range of these isotope ratios and those reported for the basement rocks in this region suggest a relatively low degree of old crustal involvement for most of the studied rocks. The Pb isotopic compositions of the Tertiary magmatic rocks also show a narrow range [(206Pb/204Pb) = 18.67-18.75; (207Pb/204Pb) = 15.59-15.62; (208Pb/204Pb) = 38.44-38.59], suggesting a similar source region for the volcanic and plutonic rocks. Trace elements and isotopic compositions suggest a mantle source in the subcontinental lithosphere that has been enriched by a subduction component. General tectonic features in this region indicate a more active rate of transtensional deformation for the inland volcanic region than along the coastal margin during the main events of Oligocene magmatism. The lower degree of differentiation of the inland volcanic sequences, particularly the upper unit of the northern sector, compared to the plutons of the coastal margin, suggests that the differentiation of the Tertiary magmas in southern Mexico was controlled to a great extent by the characteristics of the different strain domains. (C) 2000 Elsevier Science B.V. All rights reserved.

Status of and changes in water quality monitored for the Idaho statewide surface-water-quality network, 1989—2002

USGS Publications Warehouse

Hardy, Mark A.; Parliman, Deborah J.; O'Dell, Ivalou

2005-01-01

Idaho has. Although erodable soils are likely a cause of elevated turbidities, suspended-sediment concentrations were not strongly correlated with turbidities. Dissolved-solids and hardness concentrations were strongly correlated. This is probably because the limestones present in some basins are more soluble than the igneous rocks that predominate in others. Low hardness in streams of northern Idaho, where watersheds are underlain by resistant igneous rocks, enhances the toxicity of some trace elements to aquatic life in these streams. Only a few measurements of dissolved-oxygen concentrations at six sites were less than 6.0 milligrams per liter, the Idaho minimum criterion for protection of aquatic organisms. High supersaturations of dissolved oxygen at four sites suggest excessive photosynthetic activity by algal communities. Nighttime monitoring would help determine whether dissolved-oxygen concentrations at these sites might fall below the Idaho criterion. Data from four sites suggest that dissolved-oxygen concentrations may have decreased over time. The pH at 15 sites sometimes fell outside the range specified (6.5-9.0) for the protection of aquatic organisms in Idaho streams. Values exceeded 9.0 at 10 sites, probably because of excessive algal photosynthetic activity in waters where carbonate rocks are present. Values were sometimes less than 6.5 at five sites in areas of mountain bedrock geology where pH is likely to be naturally low. Mining activities also may contribute to low pH at some of these sites. Inorganic nitrogen and total phosphorus concentrations commonly exceeded those considered sufficient for supporting excess algal production (0.3 and 0.1 milligrams per liter, respectively). Data from a few sites suggest that nitrogen and(or) phosphorus concentrations might be changing over time. Low concentrations of nitrogen and phosphorus at six sites, most representing forested basins, might make them good candidates as reference sites that represent naturally occurring nutrient concentrations. Trace elements examined for this report were cadmium, copper, lead, mercury, selenium, and zinc. In water, many trace-element concentrations were below the minimum analytical reporting levels. Concentrations of cadmium, copper, lead, and zinc generally were highest in mined and other mineral-rich basins in northern Idaho. Concentrations of mercury were

Miocene calc-alkaline heritage in the pliocene postcollisional volcanism of monte arci (Sardinia, Italy)

NASA Astrophysics Data System (ADS)

Cioni, Roberto; Clocchiatti, Robert; Di Paola, Giovanni M.; Santacroce, Roberto; Tonarini, Sonia

1982-10-01

At Monte Arci alkaline (hawaiites to trachytes), subalkaline with a marked calc-alkaline character (basalts to dacites) and rhyolitic lavas were erupted almost simultaneously in Late Pliocene time. Major- and trace-element chemistry, microprobe mineralogy and isotopic data suggest a partial melting origin for both rhyolites and subalkaline rocks. Different sources are however inferred for two rock series: homogeneous, calc-alkaline in nature for subalkaline rocks; unhomogeneous, richer in 87Sr, for rhyolitic ones. Crystal fractionation differentiation from subcrustal alkali-basalts should have been the main process in the genesis of alkaline rocks. Large-scale contaminations with rhyolitic and/or alkaline rocks are evident in many of these lavas. Such a complicated magmatic association characterizes an area where volcanism related to post-collisional tensional movements in Pliocene time superimposes to Middle Miocene calc-alkaline basic volcanism related to previous subduction processes. The Pliocene volcanic history of Monte Arci emphasizes the influence of the paleogeodynamic environment on the nature of magmas erupted in post-continental collision areas, that are frequently difficult to arrange in the usual schemas connecting magma composition with tectonic setting.

Petrogenesis and origin of the Upper Jurassic-Lower Cretaceous magmatism in Central High Atlas (Morocco): Major, trace element and isotopic (Sr-Nd) constraints

NASA Astrophysics Data System (ADS)

Essaifi, Abderrahim; Zayane, Rachid

2018-01-01

During an uplift phase, which lasted ca. 40 Ma, from the Late Jurassic (165 Ma) to the Early Cretaceous (125 Ma), transitional to moderately alkaline magmatic series were emplaced in the Central High Atlas. The corresponding magmatic products include basaltic lava flows erupted within wide synclines and intrusive complexes composed of layered mafic intrusions and monzonitic to syenitic dykes emplaced along narrow anticlinal ridges. The igneous rock sequence within the intrusive complexes is composed of troctolites, olivine-gabbros, oxide-gabbros, monzonites and syenites. The chemical compositions of the various intrusive rocks can be accounted for by crystal accumulation, fractional crystallization and post-magmatic remobilization. The evolution from the troctolites to the syenites was mainly controlled by a fractional crystallization process marked by early fractionation of olivine, plagioclase and clinopyroxene, followed by separation of biotite, amphibole, apatite, and Ti-magnetite. Hydrothermal activity associated with emplacement of the intrusions within the Jurassic limestones modified the elemental and the Sr isotopic composition of the hydrothermally altered rocks In particular the monzonitic to syenitic dykes underwent an alkali metasomatism marked by depletion in K and Rb and enrichment in Na and Sr. As a result, their Sr isotopic composition was shifted towards higher initial Sr isotopic ratios (0.7067-0.7075) with respect to the associated gabbros (0.7036-0.7046). On the contrary, the Nd isotopic compositions were preserved from isotope exchange with the limestones and vary in a similar range to those of the gabbros (+1.6 < εNdi < +4.1). The isotopic and the trace element ratios of the uncontaminated samples were used to constrain the source characteristics of this magmatism. The Sr-Nd isotopic data and the incompatible element ratios (e.g. La/Nb, Zr/Nb, Th/U, Ce/Pb) are consistent with generation from an enriched upper mantle similar to an ocean island basalt source. Melting of the subcontinental metasomatized lithosphere is tentatively related to small-scale shallow mantle upwelling and asthenospheric uprise at the triple junction between the western High Atlas, the Middle Atlas and the eastern High Atlas domains during a period of relative tectonic quiescence.

Purdue Rare Isotope Measurement Laboratory

NASA Astrophysics Data System (ADS)

Caffee, M.; Elmore, D.; Granger, D.; Muzikar, P.

2002-12-01

The Purdue Rare Isotope Measurement Laboratory (PRIME Lab) is a dedicated research and service facility for accelerator mass spectrometry. AMS is an ultra-sensitive analytical technique used to measure low levels of long-lived cosmic-ray-produced and anthropogenic radionuclides, and rare trace elements. We measure 10Be (T1/2 = 1.5 My), 26Al (.702 My), 36Cl (.301 My), and 129I (16 My), in geologic samples. Applications include dating the cosmic-ray-exposure time of rocks on Earth's surface, determining rock and sediment burial ages, measuring the erosion rates of rocks and soils, and tracing and dating ground water. We perform sample preparation and separation chemistries for these radio-nuclides for our internal research activities and for those external researchers not possessing this capability. Our chemical preparation laboratories also serve as training sites for members of the geoscience community developing these techniques at their institutions. Research at Purdue involves collaborators among members of the Purdue Departments of Physics, Earth and Atmospheric Sciences, Chemistry, Agronomy, and Anthropology. We also collaborate and serve numerous scientists from other institutions. We are currently in the process of modernizing the facility with the goals of higher precision for routinely measured radio-nuclides, increased sample throughput, and the development of new measurement capabilities for the geoscience community.

Melting depths associated with Jack Hills zircons crystallization as revealed by in situ trace element measurements

NASA Astrophysics Data System (ADS)

Profeta, L.; Ducea, M. N.; Gehrels, G. E.

2016-12-01

The Jack Hills zircons hosted within the Narryer Gneiss Complex, Yilgarn craton have ages from 4.4 Ga up to Mesoarchean. These zircons crystallized from low temperature granitoid magmas (Harrison, 2009). Here, we use trace element measurements obtained simultaneously with U-Pb ages using LA-ICP-MS on 276 Jack Hills zircons in order to estimate the depth of melting. La/Yb are converted to whole rock equivalent values using newly determined REE -whole rock partition coefficients (Chapman et al., 2016). La/Yb are subsequently transformed into depth estimates using the correlation between whole rock La/Yb and crustal thickness put forward in Profeta et al. (2015) for modern arcs. Our data pertains to 4.2 to 3.2 Ga zircons, which are supplemented with previously published data on 4.4.-4.3 Ga zircons (Peck et al. 2001). Depth estimates are averaged over 100 Ma bins, revealing a remarkably constant trend throughout the investigated period with values around 50 ± 10 km. We interpret that these depths may not be the result of a thick continental crust, as is the case for modern arcs, but rather the existence of different melting conditions during the Hadean and Paleoarchean due to elevated thermal regimes within the mantle. The high La/Yb whole rock ratios (with computed values greater than 10) coupled with elevated mantle temperatures point towards granitoid generation from partial melting of hydrated basalts (e.g. Martin et al., 2014). [1] Harrison, T.M., Annu. Rev. Earth Planet. Sci. 37, 479-505 (2009). [2] Chapman, J. B. et al., Chem. Geol. 439, 59-70 (2016). doi: 10.1016/j.chemgeo.2016.06.014. [3] Profeta, L. et al., Sci. Rep. 5, 17786 (2015). doi: 10.1038/srep17786 [4] Peck, W. et al., Cosmochim. Acta 65, 4215-4229 (2001). doi: 10.1016/S0016-7037(01)00711-6 [5] Martin, H. et al. Lithos 198, 1-13 (2014). doi: 10.1016/j.lithos.2014.02.017

a Baseline Study of Physico-Chemical Parameters and Trace Metals in Waters of Manakudy, South-West Coast of India

NASA Astrophysics Data System (ADS)

Subramanian, M.; Muthumanikkam, J.

2013-05-01

The transport of trace metals from the land to ocean has a number of different routes and efficiencies. The sources of toxic elements into the rivers to be debouched into the sea through estuaries are either weathered naturally from the soils and rocks or introduced anthropogenically from point or non-point sources, in labile form or in particulate form. However, recent studies indicate that the transport of trace elements to the aquatic environment is much more complex than what has been thought. The chemistry and ecology of an estuarine system are entirely different from the fluvial as well as the marine system. Estuarine environment is characterized by a constantly changing mixture of salt and freshwater. In the present study area Manakudy estuary is situated about 8 kilometres north west of Kanyakumari (Latitude N 08 05 21.8 and Longitude E 077 29 03.7). To gain a better understanding of the geochemical behavior of physico-chemical parameters and trace elements in the estuary and to examine variations in associated chemical changes, 20 water samples were collected throughout the Manakudy estuary, a minor river in south-western India. These samples, collected in typical dry season during 2012, were analyzed for physico-chemical parameters, dissolved major and trace elements. Our results show that dissolved Na, Mg, Ca and Cl behave conservatively along the salinity gradient. The concentration of nutrients is normal and they are due to the higher organic activity in soils as well as faster rates of chemical weathering reaction in the source region. The concentration of major ions is due to tidal influence and it increases with salinity and the nutrients do behave non-conservatively due to biogenic removal. The conservative behaviour of the trace metals with salinity has been strongly affected by the introduction of these metals by external sources. Even though the trace metals in the contaminated water have been removed and incorporated in sediments due to flocculation, the concentration of these metals did not decrease. S.MUTHUSAMY M.sc.,M.phil., RESEARCH SCHOLAR UNIVERSITY OF MADRAS CHENNAI,TAMILNADU INDIA

Direct evidence of the feedback between climate and nutrient, major, and trace element transport to the oceans

NASA Astrophysics Data System (ADS)

Eiriksdottir, Eydis Salome; Gislason, Sigurður Reynir; Oelkers, Eric H.

2015-10-01

Climate changes affect weathering, denudation and riverine runoff, and therefore elemental fluxes to the ocean. This study presents the climate effect on annual fluxes of 28 dissolved elements, and organic and inorganic particulate fluxes, determined over 26-42 year period in three glacial and three non-glacial river catchments located in Eastern Iceland. Annual riverine fluxes were determined by generating robust correlations between dissolved element concentrations measured from 1998 to 2003 and suspended inorganic matter concentrations measured from 1962 to 2002 with instantaneous discharge measured at the time of sampling in each of these rivers. These correlations were used together with measured average daily discharge to compute daily elemental fluxes. Integration of these daily fluxes yielded the corresponding annual fluxes. As the topography and lithology of the studied glacial and non-glacial river catchments are similar, we used the records of average annual temperature and annual runoff to examine how these parameters and glacier melting influenced individual element fluxes to the oceans. Significant variations were found between the individual elements. The dissolved fluxes of the more soluble elements, such as Mo, Sr, and Na are less affected by increasing temperature and runoff than the insoluble nutrients and trace elements including Fe, P, and Al. This variation between the elements tends to be more pronounced for the glacial compared to the non-glacial rivers. These observations are interpreted to stem from the stronger solubility control on the concentrations of the insoluble elements such that they are less affected by dilution. The dilution of the soluble elements by increasing discharge in the glacial rivers is enhanced by a relatively low amount of water-rock interaction; increased runoff due to glacial melting tend to be collected rapidly into river channels limiting water-rock interaction. It was found that the climate effect on particle transport from the glacial rivers is far higher than all other measured fluxes. This observation, together with the finding that the flux to the oceans of biolimiting elements such as P and Fe is dominated by particulates, suggests that particulate transport by melting glaciers have a relatively strong effect on the feedback between continental weathering, atmospheric chemistry, and climate regulation over geologic time.

Tracing subduction zone fluid-rock interactions using trace element and Mg-Sr-Nd isotopes

NASA Astrophysics Data System (ADS)

Wang, Shui-Jiong; Teng, Fang-Zhen; Li, Shu-Guang; Zhang, Li-Fei; Du, Jin-Xue; He, Yong-Sheng; Niu, Yaoling

2017-10-01

Slab-derived fluids play a key role in mass transfer and elemental/isotopic exchanges in subduction zones. The exhumation of deeply subducted crust is achieved via a subduction channel where fluids from various sources are abundant, and thus the chemical/isotopic compositions of these rocks could have been modified by subduction-zone fluid-rock interactions. Here, we investigate the Mg isotopic systematics of eclogites from southwestern Tianshan, in conjunction with major/trace element and Sr-Nd isotopes, to characterize the source and nature of fluids and to decipher how fluid-rock interactions in subduction channel might influence the Mg isotopic systematics of exhumed eclogites. The eclogites have high LILEs (especially Ba) and Pb, high initial 87Sr/86Sr (up to 0.7117; higher than that of coeval seawater), and varying Ni and Co (mostly lower than those of oceanic basalts), suggesting that these eclogites have interacted with metamorphic fluids mainly released from subducted sediments, with minor contributions from altered oceanic crust or altered abyssal peridotites. The positive correlation between 87Sr/86Sr and Pb* (an index of Pb enrichment; Pb* = 2*PbN/[CeN + PrN]), and the decoupling relationships and bidirectional patterns in 87Sr/86Sr-Rb/Sr, Pb*-Rb/Sr and Pb*-Ba/Pb spaces imply the presence of two compositionally different components for the fluids: one enriched in LILEs, and the other enriched in Pb and 87Sr/86Sr. The systematically heavier Mg isotopic compositions (δ26Mg = - 0.37 to + 0.26) relative to oceanic basalts (- 0.25 ± 0.07) and the roughly negative correlation of δ26Mg with MgO for the southwestern Tianshan eclogites, cannot be explained by inheritance of Mg isotopic signatures from ancient seafloor alteration or prograde metamorphism. Instead, the signatures are most likely produced by fluid-rock interactions during the exhumation of eclogites. The high Rb/Sr and Ba/Pb but low Pb* eclogites generally have high bulk-rock δ26Mg values, whereas high Pb* and 87Sr/86Sr eclogites have mantle-like δ26Mg values, suggesting that the two fluid components have diverse influences on the Mg isotopic systematics of these eclogites. The LILE-rich fluid component, possibly derived from mica-group minerals, contains a considerable amount of isotopically heavy Mg that has shifted the δ26Mg of the eclogites towards higher values. By contrast, the 87Sr/86Sr- and Pb-rich fluid component, most likely released from epidote-group minerals in metasediments, has little Mg so as not to modify the Mg isotopic composition of the eclogites. In addition, the influence of talc-derived fluid might be evident in a very few eclogites that have low Rb/Sr and Ba/Pb but slightly heavier Mg isotopic compositions. These findings represent an important step toward a broad understanding of the Mg isotope geochemistry in subduction zones, and contributing to understanding why island arc basalts have averagely heavier Mg isotopic compositions than the normal mantle.

Trace element behavior and P-T-t evolution during partial melting of exhumed eclogite in the North Qaidam UHPM belt (NW China): Implications for adakite genesis

NASA Astrophysics Data System (ADS)

Zhang, Guibin; Niu, Yaoling; Song, Shuguang; Zhang, Lifei; Tian, Zuolin; Christy, Andrew G.; Han, Lei

2015-06-01

We have studied trace element behavior and timing of decompression melting of UHP rocks during exhumation recorded in the magmatic products, i.e., the melt phase (leucosomes), cumulate (garnetite) and residue (amphibolitized eclogite) from a single outcrop in the south Dulan area, North Qaidam UHPM belt, NW China. Two distinct episodes of partial melting are recognized. First, Grt-free tonalitic-trondhjemitic leucosome melts with higher silica crystallized at 424.0 ± 2.7 Ma. Garnets grew in the leucosome melt but fractionated out to form garnetite cumulates along with Ti-rich phases (rutile and titanite), strengthening the adakitic signature of the leucosome. Later Grt-bearing leucosome melts with an age of 412.4 ± 2.9 Ma cross-cut boudins and layers of amphibolitized eclogite. Geochemical investigation of bulk-rocks and in situ minerals verifies the genetic relationship between the amphibolitized eclogite and the tonalitic-trondhjemitic melts. Zircons from the amphibolitized eclogite have older (> 700 Ma) protolith ages, with subsequent eclogite-facies metamorphism, retrograde granulite-facies overprinting and partial melting. Phase modeling and Zr-in-rutile thermometry calculations in combination with zircon geochronology reveal the evolution P-T-t path for the exhumation and the partial melting of the deeply subducted continental crust at the North Qaidam subduction zone in the Early Paleozoic.

Zircon Zoning, Trace Elements and U-Pb Dates Reveal Crustal Foundering Beneath the Pamir

NASA Astrophysics Data System (ADS)

Hacker, B. R.; Shaffer, M. E. F.; Ratschbacher, L.; Kylander-Clark, A. R.

2017-12-01

Xenoliths that erupted in the SE Pamir of Tajikistan at 11.2 Ma from 1000-1050°C and 90 km depth illuminate what happens when crust founders into the mantle. The xenoliths are a broad range of crustal rock types and contain abundant xenoliths whose U-Pb isotopic ratios and trace-element contents were examined by laser-ablation split stream inductively coupled plasma mass spectrometry. Cathodoluminescence imaging of the grains shows igneous cores with oscillatory zoning overprinted by substantial recrystallization. The bulk of the U-Pb dates are concordant and range from 160 Ma to 11 Ma. The range of dates suggest that the xenoliths were likely derived from the Jurassic-Cretaceous Andean-style magmatic arc and its Proterozoic-Mesozoic host rocks along the southern margin of Asia. The zircons show distinct changes in Eu anomaly, Lu/Gd ratio, and Ti concentrations that are interpreted to indicate garnet growth and minimal heating at 22-20 Ma, and then 200-300°C of heating, 25 km of burial, and alkali-carbonate melt injection at 14-11 Ma. These changes are interpreted to coincide with: i) heat input due to Indian slab breakoff at 22‒20 Ma; ii) rapid thickening and foundering of the Pamir lithosphere at 14‒11 Ma, prior to and synchronous with collision between deep Indian and Asian lithospheres beneath the Pamir.

Geochemistry and origin of regional dolomites

NASA Astrophysics Data System (ADS)

Hanson, G. N.; Meyers, W. J.

1989-12-01

The major goal of the carbonate research program at Stony Brook is to better understand the conditions and processes leading to regional diagenesis of carbonate rocks. Our research focuses on studies of ancient, massive dolostones, but we are also studying limestone diagenesis for its own importance, and as it relates to dolomitization. Our approach has been to carry out a very detailed petrographic and geochemical case study to the Mississippian Burlington-Keokuk Fms. of Iowa, Illinois and Missouri, and to develop this as a testing ground for new geochemical and modelling techniques, and for testing various models for regional dolomitization in epicontinental carbonates. The ideas and techniques developed in our Burlington-Keokuk studies are being expanded and applied to carbonate sequences of other ages (Devonian to Neogene), and other tectono-sedimentary settings. The emphasis of this report will be on new developments and results on the Burlington-Keokuk studies and on our diagenetic studies of other strata. Recent research on Burlington-Keokuk rocks include development and application of boron isotopes and the U--Th--Pb system to dolomite studies, investigations of porosity and permeability in the dolostones. Projects on other strata include dolomitization and limestones diagenesis of Devonian carbonates of Alberta and Western Australia, Miocene reefal carbonates of Spain, Neogene carbonates of Curacao and Bonaire, Waulsortian limestones of Ireland, modelling of trace elements and stable isotopes, and experimental growth of calcites to investigate crystallographic controls of trace element incorporation.

Lunar and Planetary Science XXXV: Lunar Rocks from Outer Space

NASA Technical Reports Server (NTRS)

2004-01-01

The following topics were discussed: Mineralogy and Petrology of Unbrecciated Lunar Basaltic Meteorite LAP 02205; LAP02205 Lunar Meteorite: Lunar Mare Basalt with Similarities to the Apollo 12 Ilmenite Basalt; Mineral Chemistry of LaPaz Ice Field 02205 - A New Lunar Basalt; Petrography of Lunar Meteorite LAP 02205, a New Low-Ti Basalt Possibly Launch Paired with NWA 032; KREEP-rich Basaltic Magmatism: Diversity of Composition and Consistency of Age; Mineralogy of Yamato 983885 Lunar Polymict Breccia with Alkali-rich and Mg-rich Rocks; Ar-Ar Studies of Dhofar Clast-rich Feldspathic Highland Meteorites: 025, 026, 280, 303; Can Granulite Metamorphic Conditions Reset 40Ar-39Ar Ages in Lunar Rocks? [#1009] A Ferroan Gabbronorite Clast in Lunar Meteorite ALHA81005: Major and Trace Element Composition, and Origin; Petrography of Lunar Meteorite PCA02007, a New Feldspathic Regolith Breccia; and Troilite Formed by Sulfurization: A Crystal Structure of Synthetic Analogue

Geochemistry and petrogenesis of the Laramie anorthosite complex, Wyoming

USGS Publications Warehouse

Fountain, J.C.; Hodge, D.S.; Allan, Hills F.

1981-01-01

A geochemical investigation of the Laramie anorthosite complex determined that monsonite associated with the complex are characterized by positive Eu anomalies and display a regular variation in composition with distance from the monzonite/county rock contact. Anorthositic rocks have major and trace element abundance typical of similar complexes. The internal variations in the monzonite were produced by in situ fractionation and contamination. The data indicate that anorthosite and monzonite cannot be comagmatic. It is proposed that the anorthosite and monzonite of the complex evolved from two distinct magmas, and that two stages of anatectic melting contributed to the evolution of the monzonite. An initial stage of partial melting was induced by intrusion of a gabbroic anorthosite magma into the lower crust; a second partial melting event occurred after emplacement where heat from the intrusions melted country rocks resulting in extensive contamination ofthe monzonite. ?? 1981.

New observations on the quartz monzodiorite-granite suite. [in lunar soil

NASA Technical Reports Server (NTRS)

Marvin, U. B.; Holmberg, B. B.; Lindstrom, M. M.; Martinez, R. R.

1991-01-01

Five new fragments of quartz monzodiorite (QMD) were identified in particles from soil 15403, which was collected from the boulder sampled as rock 15405, an impact-melt breccia containing clasts of KREEP basalt, QMD, granite, and a more primitive alkali norite. Petrographic and geochemical studies of the fragments show considerable variation in modal proportions and bulk composition. This heterogeneity is due to unrepresentative sampling in small fragments of coarse-grained rocks. Variations in the proportions of accessory minerals have marked effects on incompatible-trace-element concentrations and ratios. Semiquantitative calculations support the derivation of QMD from 60-percent fractional crystallization of a KREEP basalt magma as suggested by Hess (1989). Apollo 15 KREEP basalt cannot be the actual parent magma because the evolved rocks predate volcanic KREEP basalts. It is suggested that ancient KREEP basalt magmas have crystallized as plutons, with alkali norite clasts offering the only direct evidence of this precursor.

Geochemistry and petrogenesis of serpentinite from the Ingalls ophiolite complex, central Cascades, Washington

NASA Astrophysics Data System (ADS)

MacDonald, J. H., Jr.; Milliken, S. H.; Zalud, K. M.

2017-12-01

The Jurassic Ingalls ophiolite complex is located in the central Cascades, Washington State. This ophiolite predominantly consists of three variably serpentinized mantle units. Serpentinite occurs as massive replacing peridotite, or as highly sheared fault zones cutting other rocks. Mylonitic serpentinite forms a large-scale mélange in the middle of the ophiolite, and is interpreted as a fracture zone. Whole-rock and mineral geochemistry of the massive serpentinite was done to understand the metasomatic process and identify the possible protoliths of these rocks. Whole-rock major and trace elements of the massive serpentinite are similar to modern peridotites. The majority of samples analyzed are strongly serpentinized, while a few were moderately to weakly altered. Ca, Mg, and Al suggest these rocks formed from serpentinized harzburgite and dunite with minor lherzolite. All samples have positive Eu/Eu*. Serpentinites plot in fields defined by modern abyssal and forearc peridotites. Trace elements suggests the protoliths underwent variable amounts of mantel depletion (5-20%). Serpentine and relic igneous minerals were analyzed by EPMA at the Florida Center for Analytical Electron Microscopy. The serpentine dose not chemically display brucite mixing, has minor substitution of Fe, Ni, and Cr for Mg, and minor Al substitution for Si. Bastites have higher Ni than replaced olivine. Mineral chemistry, high LOI, and X-ray diffraction suggest lizardite is the primary serpentine polymorph, with minor chrysotile also occurring. Relic Al-chromite and Cr-spinel commonly have Cr-magnetite rims. These relic cores have little SiO2 and Fe3+, suggesting the spinels are well preserved. Most spinels plot in overlap fields defined by abyssal and arc peridotite, while two samples plot entirely in arc fields. Relic olivine have Fo90 to Fo92 and plot along the mantle array. Relic pyroxene are primarily enstatite, with lesser high-Ca varieties. Relic minerals plot near fields defined by harzburgite, dunite, and lherzolite from unaltered Ingalls peridotite. The massive serpentinite likely formed by low T (< 300°C), and possibly low pressure, hydrothermal alteration of harzburgite, dunite and lherzolite. The protoliths were variably depleted mantle residues from a possible supra-subduction zone setting.

Transfer of volatiles and metals from mafic to felsic magmas in composite magma chambers: An experimental study

NASA Astrophysics Data System (ADS)

Guo, Haihao; Audétat, Andreas

2017-02-01

In order to determine the behavior of metals and volatiles during intrusion of mafic magma into the base of silicic, upper crustal magma chambers, fluid-rock partition coefficients (Dfluid/rock) of Li, B, Na, S, Cl, K, Mn, Fe, Rb, Sr, Ba, Ce, Cu, Zn, Ag, Cd, Mo, As, Se, Sb, Te, W, Tl, Pb and Bi were determined experimentally at 2 kbar and 850 °C close to the solidus of mafic magma. In a first step, volatile-bearing mafic glasses were prepared by melting a natural basaltic trachyandesite in the presence of volatile-bearing fluids at 1200 °C/10 kbar in piston cylinder presses. The hydrous glasses were then equilibrated in subsequent experiments at 850 °C/2 kbar in cold-seal pressure vessels, which caused 80-90% of the melt to crystallize. After 0.5-2.0 days of equilibration, the exsolved fluid was trapped by means of in-situ fracturing in the form of synthetic fluid inclusions in quartz. Both the mafic rock residue and the fluid inclusions were subsequently analyzed by laser-ablation ICP-MS for major and trace elements. Reverse experiments were conducted by equilibrating metal-bearing aqueous solutions with rock powder and then trapping the fluid. In two additional experiments, information on relative element mobilities were obtained by reacting fluids that exsolved from crystallizing mafic magma with overlying silicic melts. The combined results suggest that under the studied conditions S, Cl, Cu, Se, Br, Cd and Te are most volatile (Dfluid/rock >10), followed by Li, B, Zn, As, Ag, Sb, Cs, W, Tl, Pb and Bi (Dfluid/rock = 1-10). Less volatile are Na, Mg, K, Ca, Mn, Fe, Rb, Sr, Mo and Rb (Dfluid/rock 0.1-1), and the least fluid-mobile elements are Al, Si, Ti, Zr, Ba and Ce (Dfluid/rock <0.1). This trend is broadly consistent with relative element volatilities determined on natural high-temperature fumarole gases, although some differences exist. Based on the volatility data and measured mineral-melt and sulfide-melt partition coefficients, volatile fluxing in felsic natural samples may be identified by Cu, Se, Te and Cd-enrichment in magmatic sulfides, and by As, Se, Cd and Bi-enrichment in magmatic apatite.

Trace-metal sources and their release from mine wastes: examples from humidity cell tests of hardrock mine waste and from Warrior Basin coal

USGS Publications Warehouse

Diehl, S.F.; Smith, Kathleen S.; Desborough, G.A.; White, W.W.; Lapakko, K.A.; Goldhaber, Martin B.; Fey, David L.

2003-01-01

To assess the potential impact of metal and acid contamination from mine-waste piles, it is important to identify the mineralogic source of trace metals and their mode of occurrence. Microscopic analysis of mine-waste samples from both hard-rock and coalmine waste samples demonstrate a microstructural control, as well as mineralogic control, on the source and release of trace metals into local water systems. The samples discussed herein show multiple periods of sulfide mineralization with varying concentrations of trace metals. In the first case study, two proprietary hard-rock mine-waste samples exposed to a series of humidity cell tests (which simulate intense chemical weathering conditions) generated acid and released trace metals. Some trace elements of interest were: arsenic (45-120 ppm), copper (60-320 ppm), and zinc (30-2,500 ppm). Untested and humidity cell-exposed samples were studied by X-ray diffraction, scanning electron microscope with energy dispersive X-ray (SEM/EDX), and electron microprobe analysis. Studies of one sample set revealed arsenic-bearing pyrite in early iron- and magnesium-rich carbonate-filled microveins, and iron-, copper-, arsenic-, antimony-bearing sulfides in later crosscutting silica-filled microveins. Post humidity cell tests indicated that the carbonate minerals were removed by leaching in the humidity cells, exposing pyrite to oxidative conditions. However, sulfides in the silica-filled veins were more protected. Therefore, the trace metals contained in the sulfides within the silica-filled microveins may be released to the surface and (or) ground water system more slowly over a greater time period. In the second case study, trace metal-rich pyrite-bearing coals from the Warrior Basin, Alabama were analyzed. Arsenic-bearing pyrite was observed in a late-stage pyrite phase in microfaults and microveins that crosscut earlier arsenic.

Evidence from Ocean Drilling Program Leg 149 mafic igneous rocks for oceanic crust in the Iberia Abyssal Plain ocean-continent transition zone

NASA Astrophysics Data System (ADS)

Seifert, Karl E.; Chang, Cheng-Wen; Brunotte, Dale A.

1997-04-01

Leg 149 of the Ocean Drilling Program explored the ocean-continent transition (OCT) on the Iberia Abyssal Plain and its role in the opening of the Atlantic Ocean approximately 130 Ma. Mafic igneous rocks recovered from Holes 899B and 900A have Mid-Ocean Ridge Basalt (MORB) trace element and isotopic characteristics indicating that a spreading center was active during the opening of the Iberia Abyssal Plain OCT. The Hole 899B weathered basalt and diabase clasts have transitional to enriched MORB rare earth element characteristics, and the Hole 900A metamorphosed gabbros have MORB initial epsilon Nd values between +6 and +11. During the opening event the Iberia Abyssal Plain OCT is envisioned to have resembled the central and northern parts of the present Red Sea with localized spreading centers and magma chambers producing localized patches of MORB mafic rocks. The lack of a normal ocean floor magnetic anomaly pattern in the Iberia Abyssal Plain means that a continuous spreading center similar to that observed in the present southern Red Sea was not formed before spreading ceased in the Iberia Abyssal Plain OCT and jumped to the present Mid-Atlantic Ridge.

Petrography and trace element signatures in silicates and Fe-Ti-oxides from the Lanjiahuoshan deposit, Panzhihua layered intrusion, Southwest China

NASA Astrophysics Data System (ADS)

Gao, Wenyuan; Ciobanu, Cristiana L.; Cook, Nigel J.; Huang, Fei; Meng, Lin; Gao, Shang

2017-12-01

Permian mafic-ultramafic layered intrusions in the central part of the Emeishan Large Igneous Province (ELIP), Southwestern China, host Fe-Ti-V-oxide ores that have features which distinguish them from other large layered intrusion-hosted deposits. The origin of these ores is highly debated. Careful petrographic examination, whole rock analysis, electron probe microanalysis, and measurement and mapping of trace element concentrations by laser ablation inductively coupled plasma mass spectrometry in all major and minor minerals (clinopyroxene, plagioclase, olivine, amphibole, titanomagnetite, ilmenite, pleonaste and pyrrhotite) has been undertaken on samples from the Lanjiahuoshan deposit, representing the Middle, Lower and Marginal Zone of the Panzhihua intrusion. Features are documented that impact on interpretation of intrusion petrology and with implications for genesis of the Fe-Ti-V-oxide ores. Firstly, there is evidence, as symplectites between clinopyroxene and plagioclase, for introduction of complex secondary melts. Secondly, reaction between a late hydrothermal fluid and clinopyroxene is recognized, which has led to formation of hydrated minerals (pargasite, phlogopite), as well as a potassium metasomatic event, postdating intrusion solidification, which led to formation of K-feldspar. Lastly, partitioning of trace elements between titanomagnetite and silicates needs to consider scavenging of metals by ilmenite (Mn, Sc, Zr, Nb, Sn, Hf and Ta) and sulfides, as well as the marked partitioning of Co, Ni, Zn, Ga, As and Sb into spinels exsolved from titanomagnetite. The role of these less abundant phases may have been understated in previous studies, highlighting the importance of petrographic examination of complex silicate-oxide-sulfide assemblages, as well as the need for a holistic approach to trace element analysis, acknowledging all minerals within the assemblage.

Geochemistry of sandstones from the Pliocene Gabir Formation, north Marsa Alam, Red Sea, Egypt: Implication for provenance, weathering and tectonic setting

NASA Astrophysics Data System (ADS)

Zaid, Samir M.

2015-02-01

Petrographic, major and trace element compositions of sandstones from the Pliocene Gabir Formation, Central Eastern Desert, Egypt have been investigated to determine their provenance, intensity of paleo-weathering of the source rocks and their depositional tectonic setting. Gabir Formation is composed mainly of sandstones alternating with limestone and shale beds. The Gabir sandstone is yellowish gray to yellowish brown color, calcareous and fossiliferous. The composition of this formation refers to shallow warm agitated marine conditions. Texturally, Gabir sandstones are immature, poorly sorted and grain supported. Abundance of feldspars indicates rapid deposition of sediments from a nearby source rocks. Their average modal composition (Q71.35F16.6L12.05), classifies them as sublitharenite and arkose with subordinate litharenite and subarkose, which is also supported by geochemical study. Chemical analyses revealed that sandstones have high SiO2, K2O > Na2O, and low Fe2O3 values, which are consistent with the modal data. Also, sandstone samples are enriched in most trace elements such as Ba, Sr, Ni, Cr and Zr and depleted in U and Th. The petrography and geochemistry suggest that Gabir sandstones were deposited in an active continental margin basin. They were mainly derived from granitic and low grade metamorphic sources. The CIA values (41.69-74.84) of the Gabir sandstones indicate low to moderate degree of chemical weathering, which may reflect cold and/or arid climate conditions in the source area. The source rocks are probably identified to be Proterozoic granites, metagabbros and metavolcanics, which must have been exposed during rifting, initiated during Oligocene and continued till post Miocene.

Insights into the emplacement of upper-crustal plutons and their relationship to large silicic calderas, from field relationships, geochronology, and zircon trace element geochemistry in the Stillwater - Clan Alpine caldera complex, western Nevada, USA

NASA Astrophysics Data System (ADS)

Colgan, Joseph P.; John, David A.; Henry, Christopher D.; Watts, Kathryn E.

2018-01-01

Geologic mapping, new U-Pb zircon ages, and new and published 40Ar/39Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed at least six nested silicic calderas and underlying granitic plutons to crustal depths locally ≥ 9 km. Both caldera-forming rhyolitic tuffs and underlying plutons were emplaced in two episodes, one from about 30.4-28.2 Ma that included the Deep Canyon, Job Canyon, and Campbell Creek calderas and underlying plutons, and one from about 25.3-24.8 Ma that included the Louderback Mountains, Poco Canyon, and Elevenmile Canyon calderas and underlying plutons. In these two 1-2 m.y. periods, almost the entire Mesozoic upper crust was replaced by Oligocene intrusive and extrusive rocks to depths ≥ 9 km over an estimated total area of 1500 km2 (pre-extension). Zircon trace element geochemistry indicates that some plutonic rock can be solidified residual magma from the tuff eruptions. Most plutons are not solidified residual magma, although they directly underlie calderas and were emplaced along the same structures shortly after to as much as one million years after caldera formation. Magma chambers and plutons grew by floor subsidence accommodated by downward transfer of country rocks. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada is underlain by a complexly zoned mid-Cenozoic batholith assembled in discrete pulses that coincided with formation of large silicic calderas up to 2500-5000 km3.

Field occurrence and geochemical characteristics of the baryte mineralization in Lessel and Ihugh areas, Lower Benue Trough, Nigeria

NASA Astrophysics Data System (ADS)

Labe, Ngukposu A.; Ogunleye, Paul O.; Ibrahim, Aliyu A.

2018-06-01

The Lessel and Ihugh areas are underlain by Precambrian rocks comprising of banded gneiss, medium-grained muscovite granite, coarse-grained biotite muscovite granite, and Turonian arenaceous Lessel Sandstone in the Lower Benue Trough, southeastern Nigeria. Baryte mineralization occurs at Lessel-Mbagwa, Ihugh and Bunde commonly as vein and cavity type deposits within NE-SW and NW-SE trending fracture zones. Major oxides and trace element analysis of baryte and the host rocks was undertaken using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), in order to establish the geochemical characteristics and to constrain the origin of the baryte mineralization. The data revealed enrichment in Ba and Sr and depletion in SiO2, TiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, LILEs, HFSEs relative to background values obtained from sandstones and granitic rocks in the area. Baryte mineralization from Lessel-Mbagwa, Bunde and Ihugh is marked by positive Gd (17.1-21.4) and negative Eu (0.02-0.05) anomalies. Negative Ce anomaly (0.06) is evident in barytes from Lessel-Mbagwa and Bunde whereas baryte from Ihugh is characterized by positive Ce anomaly (1.3). The structurally controlled nature of the mineralization, depleted major and trace elements concentration in the barytes in addition to REE anomalies indicate that mixing of a strongly differentiated residual Ba-bearing fluid and sulphur-rich seawater occurred under low temperature and oxidizing-reducing conditions. The tectonic event which occurred during the Santonian to Early Campanian reactivated the NE-SW, NW-SE structural pathways in the basement gneiss and also created similar structures in the Turonian Lessel Sandstone.

Origin and significance of the 2011 El Hierro xeno-pumice

NASA Astrophysics Data System (ADS)

Zaczek-Pedroza, Kirsten; Troll, Valentin R.; Deegan, Frances M.; Meade, Fiona C.; Burchardt, Steffi; Carracedo, Juan C.; Klügel, Andreas; Harris, Chris; Wiesmaier, Sebastian; Berg, Sylvia E.; Barker, Abigail K.

2014-05-01

During the first week of the 2011/2012 submarine eruption off El Hierro (Canary Islands), peculiar light-coloured pumiceous rocks (xeno-pumice) were found floating on the sea. The appearance of these rocks led to a potentially inappropriate response from the authorities, because the rocks were viewed as likely indicators of high-silica magma and possible explosive eruptive behaviour. However, the eruption remained a relatively minor and dominantly effusive event and the origin and significance of these peculiar xeno-pumice rocks for volcanic monitoring remains unresolved. Three contrasting models have been put forward, describing them as: a) recycled hydrothermally altered felsic magmatic rocks (Meletlidis et al., 2012, Geophys. Res. Lett., 39:L17302), b) sediment-contaminated high-silica magma (Sigmarsson et al., 2013, Contrib. Mineral. Petrol., 165:601-622) or c) frothy xenoliths from pre-island sedimentary strata that were melted while immersed in magma (Troll et al., 2012, Solid Earth, 3:97-110). Here, we combine the three available datasets to assess the origin of El Hierro xeno-pumice in the light of texture, mineralogy, major and trace element composition, and oxygen isotope characteristics in order to discuss their significance. We note that: 1) Sedimentary relicts occur frequently in xeno-pumice samples with occasionally observed relict bedding. 2) Vesicle sizes are extremely variable, which documents multiple degassing events. The vesicles are biggest especially close to sedimentary relicts, likely the result of a complex mix of minerals and porewaters originally present. 3) The mineral assemblage of xeno-pumice includes quartz, smectite, illite, wollastonite, jasper and mica (XRD) and is akin to marine sedimentary rocks in the region (Hoernle, 1998, J. Petrol.,39:859-880; Robertson & Stillman, 1979, J. Geol. Soc., 136:47 -60; Aparicio et al., 2006, Geol. Mag. 143:181 -193). 4) CIPW norms calculated from xeno-pumice major element compositions show the samples to be Si-oversaturated, partly corundum-normative, but with not magmatic mineral components in the norm. 5) Trace element concentrations of xeno-pumice are unlike any magmatic rocks from El Hierro and La Palma, but similar to known sedimentary rocks from the region. 6) A distinct Eu anomaly, typical for continentally derived sediment, is present in xeno-pumice but absent in El Hierro and La Palma magmatic rocks. Lastly, 7) Oxygen isotope values range from 9.1 to 11.6 o (n=6), which are elevated with respect to magmatic rocks from the Canaries (5.2 to ~ 7 o), but are characteristic for sediment derived from a mixture of continental (S- and I-type) granite sources. The combined datasets allow for a more thorough discussion on the origin of El Hierro xeno-pumice and we conclude that xeno-pumice is compositionally akin to sedimentary rocks from the region, but strikingly dissimilar to magmatic rocks from El Hierro and La Palma. We suggest a dominantly sedimentary origin for xeno-pumice. Xeno-pumice is therefore not an indicator for explosive felsic magma within volcanic plumbing systems, but a reflection of magma-crust interaction during ascent and emplacement. The occurrence of similar frothy sedimentary xenoliths in recent and historical eruptions on Lanzarote, Gran Canaria, Tenerife and La Palma make a case for xeno-pumice being a common phenomenon in the region.

Generation of Silicic Melts in the Early Izu-Bonin Arc Recorded by Detrital Zircons in Proximal Arc Volcaniclastic Rocks From the Philippine Sea

NASA Astrophysics Data System (ADS)

Barth, A. P.; Tani, K.; Meffre, S.; Wooden, J. L.; Coble, M. A.; Arculus, R. J.; Ishizuka, O.; Shukle, J. T.

2017-10-01

A 1.2 km thick Paleogene volcaniclastic section at International Ocean Discovery Program Site 351-U1438 preserves the deep-marine, proximal record of Izu-Bonin oceanic arc initiation, and volcano evolution along the Kyushu-Palau Ridge (KPR). Pb/U ages and trace element compositions of zircons recovered from volcaniclastic sandstones preserve a remarkable temporal record of juvenile island arc evolution. Pb/U ages ranging from 43 to 27 Ma are compatible with provenance in one or more active arc edifices of the northern KPR. The abundances of selected trace elements with high concentrations provide insight into the genesis of U1438 detrital zircon host melts, and represent useful indicators of both short and long-term variations in melt compositions in arc settings. The Site U1438 zircons span the compositional range between zircons from mid-ocean ridge gabbros and zircons from relatively enriched continental arcs, as predicted for melts in a primitive oceanic arc setting derived from a highly depleted mantle source. Melt zircon saturation temperatures and Ti-in-zircon thermometry suggest a provenance in relatively cool and silicic melts that evolved toward more Th and U-rich compositions with time. Th, U, and light rare earth element enrichments beginning about 35 Ma are consistent with detrital zircons recording development of regional arc asymmetry and selective trace element-enriched rear arc silicic melts as the juvenile Izu-Bonin arc evolved.

Geochemistry of Woranso-Mille Pliocene basalts from west-central Afar, Ethiopia: Implications for mantle source characteristics and rift evolution

NASA Astrophysics Data System (ADS)

Alene, Mulugeta; Hart, William K.; Saylor, Beverly Z.; Deino, Alan; Mertzman, Stanley; Haile-Selassie, Yohannes; Gibert, Luis B.

2017-06-01

The Woranso-Mille (WORMIL) area in the west-central Afar, Ethiopia, contains several Pliocene basalt flows, tuffs, and fossiliferous volcaniclastic beds. We present whole-rock major- and trace-element data including REE, and Sr-Nd-Pb isotope ratios from these basalts to characterize the geochemistry, constrain petrogenetic processes, and infer mantle sources. Six basalt groups are distinguished stratigraphically and geochemically within the interval from 3.8 to 3 Ma. The elemental and isotopic data show intra- and inter-group variations derived primarily from source heterogeneity and polybaric crystallization ± crustal inputs. The combined Sr-Nd-Pb isotope data indicate the involvement of three main reservoirs: the Afar plume, depleted mantle, and enriched continental lithosphere (mantle ± crust). Trace element patterns and ratios further indicate the basalts were generated from spinel-dominated shallow melting, consistent with significantly thinned Pliocene lithosphere in western Afar. The on-land continuation of the Aden rift into western Afar during the Pliocene is reexamined in the context of the new geochemistry and age constraints of the WORMIL basalts. The new data reinforce previous interpretations that progressive rifting and transformation of the continental lithosphere to oceanic lithosphere allows for increasing asthenospheric inputs through time as the continental lithosphere is thinned. Accepted trace element values for BHVO-2 are those recently recommended by Jochum et al. (2016) rounded to provide the same significant figures as the data. Ternary model after Schilling et al. (1992); Endmembers from Rooney et al. (2012).

Production of hybrid granitic magma at the advancing front of basaltic underplating: Inferences from the Sesia Magmatic System (south-western Alps, Italy)

NASA Astrophysics Data System (ADS)

Sinigoi, Silvano; Quick, James E.; Demarchi, Gabriella; Klötzli, Urs S.

2016-05-01

The Permian Sesia Magmatic System of the southwestern Alps displays the plumbing system beneath a Permian caldera, including a deep crustal gabbroic complex, upper crustal granite plutons and a bimodal volcanic field dominated by rhyolitic tuff filling the caldera. Isotopic compositions of the deep crustal gabbro overlap those of coeval andesitic basalts, whereas granites define a distinct, more radiogenic cluster (Sri ≈ 0.708 and 0.710, respectively). AFC computations starting from the best mafic candidate for a starting melt show that Nd and Sr isotopic compositions and trace elements of andesitic basalts may be modeled by reactive bulk assimilation of ≈ 30% of partially depleted crust and ≈ 15%-30% gabbro fractionation. Trace elements of the deep crustal gabbro cumulates require a further ≈ 60% fractionation of the andesitic basalt and loss of ≈ 40% of silica-rich residual melt. The composition of the granite plutons is consistent with a mixture of relatively constant proportions of residual melt delivered from the gabbro and anatectic melt. Chemical and field evidence leads to a conceptual model which links the production of the two granitic components to the evolution of the Mafic Complex. During the growth of the Mafic Complex, progressive incorporation of packages of crustal rocks resulted in a roughly steady state rate of assimilation. Anatectic granite originates in the hot zone of melting crust located above the advancing mafic intrusion. Upward segregation of anatectic melts facilitates the assimilation of the partially depleted restite by stoping. At each cycle of mafic intrusion and incorporation, residual and anatectic melts are produced in roughly constant proportions, because the amount of anatectic melt produced at the roof is a function of volume and latent heat of crystallization of the underplated mafic melt which in turn produces proportional amounts of hybrid gabbro cumulates and residual melt. Such a process can explain the restricted range in isotopic compositions of most rhyolitic and granitic rocks of the Permo-Carboniferous province of Europe and elsewhere. Sheet labelled "XRF standard analyses" reports replicate analyses normalized to 100 obtained by XRF on international standards analyzed along with our samples. Sheet labelled "XRF replicate sample analyses" reports replicate XRF analyses on two samples of our data set. ICP-MS analyses from Acme Analytical Laboratories Ltd. are shown for comparison. Sheet labelled "ICP-MS analyses" reports replicate analyses of trace elements on standard SO18, its official value and replicate analyses of two our samples provided by Acme Analytical Laboratories Ltd. Sheet labelled "kinzigite". Major and trace elements of amphibolite-facies paragneiss samples of the Kinzigite Formation from the roof of the Mafic Complex. In bold data by ICP-MS, other data by XRF. For Ba, Rb and Sr XRF data were included in the average estimate to increase the statistics. The last column reports the average data of amphibolite-facies rocks from the Kinzigite Formation from Schnetger (1994). Sheet labelled "PBB paragneiss". Data for granulite-facies paragneiss samples in the septa of the paragneiss bearing belt (PBB). XRF data for Ba and Sr were included in the average estimate to increase the statistics (Rb excluded because close to detection limit for XRF in many samples). The last column reports the average data of granulite-facies rocks from Val Strona (stronalite) from Schnetger (1994). Sheet labelled "PBB charnockite". Data for charnockitic rocks included in paragneiss septa. XRF data for Ba and Sr were included in the average estimate to increase the statistics (Rb excluded because close to detection limit for XRF in many samples). Sheet labelled "computed crustal assimilant". Reports the average compositions of paragneiss in amphibolite and granulite facies from this work and from Schnetger (1994). The bulk composition of the septa is computed as 70% paragneiss and 30% charnockite, as roughly estimated in the field. The partially depleted assimilant is computed as a 50/50 mixture of amphibolite- and granulite facies rocks. Sheet labelled "anatectic products" includes leucosomes at the roof of the Mafic Complex, anatectic granites from this work and from the Atesina Volcanic district (Rottura et al., 1998). In bold data by ICP-MS, other data by XRF. Sheet labelled "Valle Mosso granite" reports the whole rock compositions of granitic rocks of the pluton, distinguishing samples from upper and lower granite. XRF data for Ba, Rb and Sr were included in the average estimate to increase the statistics. The last column reports the bulk composition of the pluton, estimated as 70% lower and 30% upper granite. Sheet labelled "Rhyolite" reports whole rock and average compositions of rhyolite. Sheet labelled "UMC gabbro" reports whole rock compositions of gabbros from the upper Mafic Complex. Samples are grouped as pertaining to the "Upper Zone" and "Main Gabbro" according the subdivision of Rivalenti et al. (1975). Gt gabbro = garnet-bearing gabbro. In bold data by ICP-MS, other data by XRF. For Ba and Sr XRF data were included in the average estimate to increase the statistics. Sheet labelled "computed average UMC" reports the whole composition of upper Mafic complex, estimated as 30% Upper Zone and 70% Main Gabbro. Sheet labelled "mafic rocks in middle crust" reports the whole rock compositions from the mafic pod PST262, intruded at the boundary between Ivrea Zone and Serie dei Laghi at 287 ± 5 Ma (Klötzli et al., 2014) and mafic dikes and an enclave intruded in the lower Valle Mosso granite. Sheet labelled "mafic volcanic rocks" reports the whole rock compositions of basaltic andesite and andesite from the Sesia Magmatic System. The average composition is computed excluding altered samples and XRF data for trace elements. Sr and Nd isotope data from this work and previous publications. Sheet labelled "compositions for modelling" reports a summary of the average compositions of the components used for the computations. Sheet labelled "Kd used for AFC and FC modelling" reports the Kd values and percent of mineral phases used in the AFC and FC computations (from Claeson and Meurer, 2004; Rollinson, 1993; Green et al., 2000; Namur et al., 2011). Sheet labelled "trace elements modelling" reports the results of AFC, bulk mixing and FC computations on trace elements. The enclosed figure illustrates the bulk mixing lines between Campore and average crust or anatectic granite respectively. Mixing required getting the composition of andesitic basalt with average crust and anatectic granite varies from 33 to 63% respectively (see text for consequences). The AFC path from Campore to andesitic basalts overlaps the bulk mixing lines. The shape of the mixing line between residual and anatectic melt results in the poor sensibility of Nd to the addition of anatectic melt to the residual one (εNd remains within the field of mafic rocks up to 80% addition of anatectic melt). Sheet labelled "major elements modelling" reports the results of mass balance computations on major-elements based on bulk mixing and XL-FRAC (Stormer and Nicholls, 1978). Sheet labelled "EC-RAXFC modelling" reports input data and results obtained by EC-RAXFC code (Bohrson and Spera, 2007) to simulate the energy constrained AFC from Campore to andesitic basalt. Liquidus temperature and specific heat of magma and assimilant (tlm, tla, cpm, cpa) as well as heat of crystallization and fusion (hm, ha) were obtained by Rhyolite-Melts code (Gualda et al., 2012) at P = 6 kbar (intermediate pressure between the roof and the deepest rocks of the Mafic Complex; Demarchi et al., 1998), assuming QFM + 2, and H2O content = 0.5 for Campore and = 1.0 for assimilant (intermediate between kinzigite and stronalite from Schnetger, 1994). Initial temperature of assimilant (tlo) was assumed equal to the solidus temperature (ts), which results around 850° from the experimental melting of natural metapelite (Vielzeuf and Holloway, 1988). Non-linear melting functions were chosen within the range of values suggested by Bohrson and Spera (2007). Recharge magma (R) was set = 0 because the homogeneity of the Upper Mafic Complex is best explained if each new mafic pulse is injected at the new neutral buoyancy level, above a dense and partially depleted restite, and may be treated as a single pulse. X was set = 1 assuming that all anatectic melt enters the mafic magma. Different simulations were run using alternatively bulk partition coefficients of Sr and Nd for the assimilant (Da) reported for "standard" upper crust by Bohrson and Spera (2001; 1.5 and 0.25, respectively), Da estimated from our data set (2.15 and 2.6, respectively) and intermediate values. For the mafic magma, the bulk D values (Dm) of 0.77 for Sr and 0.34 for Nd result from the Kd and percent of mineral phases used in the AFC computation. Lat-long grid for samples reported in OS tables.

Chemical and oxygen isotope zonings in garnet from subducted continental crust record mineral replacement and metasomatism

NASA Astrophysics Data System (ADS)

Vho, Alice; Rubatto, Daniela; Regis, Daniele; Baumgartner, Lukas; Bouvier, Anne-Sophie

2017-04-01

Garnet is a key mineral in metamorphic petrology for constraining pressure, temperature and time paths. Garnet can preserve multiple growth stages due to its wide P-T stability field and the relatively slow diffusivity for major and trace elements at sub-solidus temperatures. Pressure-temperature-time-fluid paths of the host rock may be reconstructed by combining metamorphic petrology with microscale trace element and oxygen isotope measurements in garnet. Subduction zones represent relevant geological settings for geochemical investigation of element exchanges during aqueous fluid-rock interactions. The Sesia Zone consists of a complex continental sequence containing a variety of mono-metamorphic and poly-metamorphic lithologies such as metagranitoids, sediments and mafic boudins. The precursor Varisican-Permian amphibolite-facies basement (6-9 kbar 650-850°C; Lardeaux and Spalla, 1991; Robyr et al., 2013) experienced high pressure metamorphism (15-22 kbar 500-550°C; Regis, et al. 2014; Robyr et al., 2013) during Alpine subduction. In different lithologies of the Internal Complex (Eclogitic Micaschist Complex), including metabasites from the Ivozio Complex, Ti-rich metasediments from Val Malone and pre-Alpine Mn-quartzites associated to metagabbros from Cima Bonze, garnet is abundant and shows a variety of complex textures that cannot be reconciled with typical growth zoning, but indicate resorption and replacement processes and possible metasomatism. In-situ, microscale oxygen isotopes analysis of garnet zones was performed by ion microprobe with the SwissSIMS Cameca IMS 1280-HR at University of Lausanne and SHRIMP-SI at the Australian National University. Each sample has a distinct δ18O composition, and the δ18O values show different degrees of variation between domains. Homogeneously low values of < 5‰ are measured in the garnets from the Ivozio Complex metagabbro. Intragrain variations of up to 3.5‰ in the porphyroblasts from Val Malone metasediments, and variations up to 6.5‰ in Cima Bonze garnets suggest significant metasomatic replacement from external fluids. The combination of oxygen isotopes, trace element geochemistry and P-T modelling allows reconstructing the major stages of metasomatism, as well as identifying the nature of the fluid interacting with the rock at each metamorphic stage. REFERENCES Lardeaux, J. M., & Spalla, M. I. (1991). From granulites to eclogites in the Sesia zone (Italian Western Alps): A record of the opening and closure of the Piedmont ocean. Journal of Metamorphic Geology, 9, 35-59. Regis, D., Rubatto, D., Darling, J., Cenki-Tok, B., Zucali, M., & Engi, M. (2014). Multiple metamorphic stages within an eclogite-facies terrane (Sesia Zone, Western Alps) revealed by Th-U-Pb petrochronology. Journal of Petrology, 55(7), 1429-1456. Robyr, M., Darbellay, B., & Baumgartner, L. P. (2014). Matrix-dependent garnet growth in polymetamorphic rocks of the Sesia zone, Italian Alps. Journal of Metamorphic Geology, 32(1), 3-24.

Adakite petrogenesis

NASA Astrophysics Data System (ADS)

Castillo, Paterno R.

2012-03-01

Adakite was originally proposed as a genetic term to define intermediate to high-silica, high Sr/Y and La/Yb volcanic and plutonic rocks derived from melting of the basaltic portion of oceanic crust subducted beneath volcanic arcs. It was also initially believed that adakite only occurs in convergent margins where young and, thus, still hot oceanic slabs are being subducted. Currently, adakite covers a range of arc rocks ranging from primary slab melt, to slab melt hybridized by peridotite, to melt derived from peridotite metasomatized by slab melt. Adakites can occur in arc settings where unusual tectonic conditions can lower the solidi of even older slabs and their source also includes subducted sediments. Results of adakite studies have generated controversies due to (1) the specific genetic definition of adakite but its reliance on trace element chemistry for its distinguishing characteristics, (2) curious association of adakite with alkalic rocks enriched in high field-strength elements and Cu-Au mineral deposits and (3) existence of adakitic rocks produced through other petrogenetic processes. Other studies have shown that adakitic rocks and a number of the previously reported adakites are produced through melting of the lower crust or ponded basaltic magma, high pressure crystal fractionation of basaltic magma and low pressure crystal fractionation of water-rich basaltic magma plus magma mixing processes in both arc or non-arc tectonic environments. Thus, although adakite investigations enrich our understanding of material recycling and magmatic processes along convergent margins, economic deposits and crustal evolutionary processes, the term adakite should be used with extreme caution.

Geological structure and ore mineralization of the South Sopchinsky and Gabbro-10 massifs and the Moroshkovoe Lake target, Monchegorsk area, Kola Peninsula, Russia

NASA Astrophysics Data System (ADS)

Pripachkin, Pavel V.; Rundkvist, Tatyana V.; Miroshnikova, Yana A.; Chernyavsky, Alexey V.; Borisenko, Elena S.

2016-12-01

The South Sopchinsky massif (SSM), Gabbro-10 (G-10) massif, and Moroshkovoe Lake (ML) target Monchegorsk area, Kola Peninsula, are located at the junction of the Monchepluton and Monchetundra layered intrusions. The intrusions were studied in detail as they are targets for platinum-group element (PGE) mineralization. The rocks in these targets comprise medium- to coarse-grained mesocratic to leucocratic gabbronorites, medium-grained mesocratic to melanocratic norites and pyroxenites, and various veins mainly comprising norite, plagioclase-amphibole-magnetite rocks, and quartz-magnetite rocks. The veins contain Ni-Cu-PGE mineralization associated with magnetite and chromite. In all targets, the contacts between gabbronorite and norite-pyroxenite are undulating, and the presence of magmatic (intrusive) breccias suggests that these rocks formed through mingling of two distinct magmatic pulses. In places, the gabbronorites clearly crosscut the modal layering of the norites and pyroxenites. Trace element data indicate that the gabbronorites have similar compositions to rocks of the upper part of the Monchetundra intrusion, whereas the norites and pyroxenites resemble rocks from the lower to intermediate stratigraphic levels of the Monchepluton, such as in the Nude-Poaz and Sopcha massifs. Sulfide mineralization in the studied targets principally consists of secondary bornite, millerite, and chalcopyrite. In contrast, the primary sulfide assemblage within the layered sequence of the adjacent Monchepluton is characterized by pentlandite, chalcopyrite, and pyrrhotite. Therefore, the mineralization in the studied targets is interpreted to be of a contact style. We argue that the studied area represents the contact zone between gabbronorites of the Monchetundra intrusion and norites and pyroxenites of the Monchepluton. In addition, the rocks were overprinted by postmagmatic veining and remobilization of contact style sulfide and PGE mineralization.

Aluminum Solubility Mechanisms in Quartz: Implications for Al-in-Quartz Thermobarometry

NASA Astrophysics Data System (ADS)

Was, E.; Thomas, J. B.; Nachlas, W. O.

2016-12-01

Trace element thermobarometers in minerals are becoming increasingly important tools for studying geologic processes in many different geologic environments. The solubility of some trace-level (i.e. <1000 ppmw) components in minerals can be measured and used to estimate the pressure (P) and/or temperature (T) of mineral crystallization. To date, quartz has been useful for trace element thermobarometry (based on its Ti content) due to its common occurrence in many rock types and therefore can provide information on a wide range of petrologic processes. However, this technique relies on an independent constraint on T (or P) to calculate P (or T), which can be difficult to obtain in some rocks. To add to the utility of quartz as a thermobarometer, we have experimentally co-crystallized quartz and aluminosilicates at elevated P-T conditions to determine Al solubilities in quartz, which will allow use of the crossing isopleths method to determine a unique P and T solution from two independent techniques (using Ti and Al) in the same mineral. Preliminary experiments demonstrate that Al concentrations in quartz vary systematically with P and T, and also show that Al is soluble at greater levels than Ti. The success of an Al-in-quartz thermobarometer relies on determining both the variations in Al solubility across P-T space as well as the solubility mechanism for Al substitution into the quartz structure. To determine these parameters, we use Fourier transform infrared spectroscopy (FTIR) to quantify H+ contents as a charge-balancing ion for Al3+ to replace Si4+, electron microprobe (EPMA) to measure Al concentrations, and nuclear magnetic resonance spectroscopy (NMR) to determine the coordination environment of Al in quartz.

Plate tectonics and continental basaltic geochemistry throughout Earth history

NASA Astrophysics Data System (ADS)

Keller, Brenhin; Schoene, Blair

2018-01-01

Basaltic magmas constitute the primary mass flux from Earth's mantle to its crust, carrying information about the conditions of mantle melting through which they were generated. As such, changes in the average basaltic geochemistry through time reflect changes in underlying parameters such as mantle potential temperature and the geodynamic setting of mantle melting. However, sampling bias, preservation bias, and geological heterogeneity complicate the calculation of representative average compositions. Here we use weighted bootstrap resampling to minimize sampling bias over the heterogeneous rock record and obtain maximally representative average basaltic compositions through time. Over the approximately 4 Ga of the continental rock record, the average composition of preserved continental basalts has evolved along a generally continuous trajectory, with decreasing compatible element concentrations and increasing incompatible element concentrations, punctuated by a comparatively rapid transition in some variables such as La/Yb ratios and Zr, Nb, and Ti abundances approximately 2.5 Ga ago. Geochemical modeling of mantle melting systematics and trace element partitioning suggests that these observations can be explained by discontinuous changes in the mineralogy of mantle partial melting driven by a gradual decrease in mantle potential temperature, without appealing to any change in tectonic process. This interpretation is supported by the geochemical record of slab fluid input to continental basalts, which indicates no long-term change in the global proportion of arc versus non-arc basaltic magmatism at any time in the preserved rock record.

High-resolution K-Ar dating of a complex magmatic system: The example of Basse-Terre Island (French West Indies)

NASA Astrophysics Data System (ADS)

Ricci, J.; Quidelleur, X.; Pallares, C.; Lahitte, P.

2017-10-01

For the first time in the Lesser Antilles volcanic arc, we combine for one island, 123 K-Ar ages, with 133 major and trace elements geochemical analyses, in order to better constrain the volcanic history of Basse-Terre Island. In this study, nine new ages have been obtained from the southern part of the island, and complemented with eighty-three new major and trace element analyses of samples collected across the island. The southern part of Basse-Terre Island has been the loci of volcanic activity since the last 200 kyr. It is characterized by the construction of the Grande-Découverte Volcanic Complex (GDVC) composed by the Grande-Découverte - Soufrière (GDS) and the Trois-Rivières Madeleine Field (TRMF). After the onset of construction at least at 205 ± 28 ka, the GDVC displays strikingly continuous activity between 140 ± 13 and 56 ± 3 ka, followed by a 30 kyr volcanic hiatus, which is coeval with the hiatus also observed for the TRMF activity. Two new ages of 125 ± 14 and 140 ± 13 ka obtained on a lava flow from the Grande-Découverte caldera wall suggest the presence of a depression, resulting of a major flank collapse and/or explosive event, before 140 ka. Finally, a new age of 9 ± 6 ka, obtained from outcrops exposed on the edge of the Class River, in the north of the GDVC, allows us to calculate channel incision rates between 11 and 56 mm/yr. These values are consistent with incision rates determined on other volcanic islands with similar climates. In a broad sense, the petrology and geochemistry of Basse-Terre Island rocks appear fairly homogeneous, with mainly andesite and basaltic-andesite rocks and typical features of volcanic-arc lavas. Nevertheless, in detail, various magmatic processes can be discerned. Most variations are principally controlled by crystal-melt fractionation-accumulation, but major and trace elements also highlight episodic magmatic recharge, involving magma mixing. There are also indications for assimilation of crustal rocks with continental affinity, as well as mantle input of slab-derived fluids. Trace element ratios suggest the presence of at least two different magmatic sources characterized by different partial melting rates and different continental contributions for Basse-Terre Island. Different massifs show a bimodal behavior, with the Basal Complex, the Axial Chain (Piton de Bouillante and Southern Axial Chain), the Monts-Caraïbes volcanoes and the Sans-Toucher volcano in the first group, and the Septentrional Chain, and the Grande-Découverte Volcanic Complex (GDS and TRMF) in the second. Given the unique amount of time-constrained geochemical data, this study provides a complete and detailed investigation of volcanic evolution in the central part of the Lesser Antilles active arc.

Trace elements transport in western Siberia rivers across a permafrost gradient

NASA Astrophysics Data System (ADS)

Pokrovsky, O. S.; Manasypov, R. M.; Loiko, S.; Krickov, I. A.; Kopysov, S. G.; Kolesnichenko, L. G.; Vorobyev, S. N.; Kirpotin, S. N.

2015-11-01

Towards a better understanding of trace element transport in permafrost-affected Earth surface environments, we sampled ∼ 60 large and small rivers (< 100 to ≤ 150 000 km2 watershed area) of Western Siberia Lowland (WSL) during spring flood and summer and winter base-flow across a 1500 km latitudinal gradient covering continuous, discontinuous, sporadic and permafrost-free zones. Analysis of ∼ 40 major and trace elements in dissolved (< 0.45 μm) fraction allowed establishing main environmental factors controlling the transport of metals and trace elements in rivers of this environmentally important region. No statistically significant effect of the basin size on most TE concentration was evidenced. Three category of trace elements were distinguished according to their concentration - latitude pattern: (i) increasing northward in spring and winter (Fe, Al, Ga (only winter), Ti (only winter), REEs, Pb, Zr, Hf, Th (only winter)), linked to leaching from peat and/or redox processes and transport in the form of Fe-rich colloids, (ii) decreasing northward during all seasons (Sr, Mo, U, As, Sb) marking the underground water influence of river feeding and (iii) elements without distinct trend from S to N whose variations within each latitude range were higher than the difference between latitudinal ranges (B, Li, Ti (except summer), Cr, V, Mn, Zn, Cd, Cs, Hf, Th). In addition to these general features, specific, northward increase during spring period was mostly pronounced for Fe, Mn, Co, Zn and Ba and may stem from a combination of enhanced leaching from the topsoil and vegetation and bottom waters of the lakes (spring overturn). A spring time northward decrease was observed for Ni, Cu, Zr, Rb. The southward increase in summer was strongly visible for Fe, Ni, Ba, Rb and V, probably due to peat/moss release (Ni, Ba, Rb) or groundwater feeding (Fe, V). The Principal Component Analysis demonstrated two main factors potentially controlling the ensemble of TE concentration variation. The first factor, responsible for 16-20 % of overall variation, included trivalent and tetravalent hydrolysates, Cr, V, and DOC and presumably reflected the presence of organo-mineral colloids, as also confirmed by previous studies in Siberian rivers. The 2nd factor (8-14 % variation) was linked to the latitude of the watershed and acted on elements affected by the groundwater feeding (DIC, Sr, Mo, As, Sb, U), whose concentration decreased significantly northward during all seasons. Overall, the rank of environmental factors on TE concentration in western Siberian rivers was latitude (3 permafrost zones) > season > watershed size. The effect of the latitude was minimal in spring for most TE but highly visible for Sr, Mo, Sb and U. The main factors controlling the shift of river feeding from surface and subsurface flow to deep underground flow in the permafrost-bearing zone were the depth of the active (unfrozen) seasonal layer and its position in organic or mineral horizons of the soil profile. In the permafrost-free zone, the relative role of carbonate mineral-bearing base rock feeding vs. bog water feeding determined the pattern of trace element concentration and fluxes in rivers of various size as a function of season. Comparison of obtained TE fluxes in WSL rivers with those of other subarctic rivers demonstrated reasonable agreement for most trace elements; the lithology of base rocks was the major factor controlling the magnitude of TE fluxes. The climate change in western Siberia and permafrost boundary migration will affect essentially the elements controlled by underground water feeding (DIC, alkaline-earth elements (Ca, Sr), oxyanions (Mo, Sb, As) and U). The thickening of the active layer may increase the export of trivalent and tetravalent hydrolysates in the form of organo-ferric colloids. Plant litter-originated divalent metals present as organic complexes may be retained via adsorption on mineral horizon. However, due to various counterbalanced processes controlling element source and sinks in plants - peat - mineral soil - river systems, the overall impact of the permafrost thaw on TE export from the land to the ocean may be smaller than that foreseen by merely active layer thickening and permafrost boundary shift.

Mobilization of Trace Metals in an Experimental Carbon Sequestration Scenario

NASA Astrophysics Data System (ADS)

Marcon, V.; Kaszuba, J. P.

2012-12-01

Mobilizing trace metals with injection of supercritical CO2 into deep saline aquifers is a concern for geologic carbon sequestration. The potential for leakage from these systems requires an understanding of how injection reservoirs interact with the overlying potable aquifers. Hydrothermal experiments were performed to evaluate metal mobilization and mechanisms of release in a carbonate storage reservoir and at the caprock-reservoir boundary. Experiments react synthetic Desert Creek limestone and/or Gothic Shale, formations in the Paradox Basin, Utah, with brine that is close to equilibrium with these rocks. A reaction temperature of 1600C accelerates the reaction kinetics without changing in-situ water-rock reactions. The experiments were allowed to reach steady state before injecting CO2. Changes in major and trace element water chemistry, dissolved carbon and sulfide, and pH were tracked throughout the experiments. CO2 injection decreases the pH by 1 to 2 units; concomitant mineral dissolution produces elevated Ba, Cu, Fe, Pb, and Zn concentrations in the brine. Concentrations subsequently decrease to approximately steady state values after 120-330 hours, likely due to mineral precipitation as seen in SEM images and predicted by geochemical modeling. In experiments that emulate the caprock-reservoir boundary, final Fe (0.7ppb), an element of secondary concern for the EPA, and Pb (0.05ppb) concentrations exceed EPA limits, whereas Ba (0.140ppb), Cu (48ppb), and Zn (433ppb) values remain below EPA limits. In experiments that simulate deeper reservoir conditions, away from the caprock boundary, final Fe (3.5ppb) and Pb (0.017ppb) values indicate less mobilization than seen at the caprock-reservoir boundary, but values still exceed EPA limits. Barium concentrations always remain below the EPA limit of 2ppb, but are more readily mobilized in experiments replicating deeper reservoir conditions. In both systems, transition elements Cd, Cr, Cu, Pb and Zn behave in a similar manner, increasing in concentration with injection but continually decreasing after about 830 hours until termination of the experiment. SEM images and geochemical models indicate initial dissolution of all rocks and minerals, re-precipitation of Ca-Mg-Fe carbonates and Fe-sulfides, and precipitation of anhydrite in both systems. Calcite dissolves more readily than dolomite in these experiments, but re-precipitates in veins on dolomite. If brines leak from a storage reservoir and mix with a potable aquifer, the experimental results suggest that Ba, Cu, and Zn will not be contaminants of concern. Pb, Fe and As (still under consideration) initially exceed the EPA threshold and may require careful attention in a sequestration scenario. However, experimentally observed trends of decreasing trace metal concentration suggest that these metals could become less of a concern during the life of a carbon repository. Finally, the caprock plays an active role in trace metal mobilization in the system. The caprock provides a source of metals, although subsequent precipitation may remove metals from solution.

Determination of lithium in rocks by distillation

USGS Publications Warehouse

Fletcher, M.H.

1949-01-01

A method for the quantitative extraction and recovery of lithium from rocks is based on a high temperature volatilization procedure. The sample is sintered with a calcium carbonate-calcium chloride mixture at 1200?? C. for 30 minutes in a platinum ignition tube, and the volatilization product is collected in a plug of Pyrex glass wool in a connecting Pyrex tube. The distillate, which consists of the alkali chlorides with a maximum of 5 to 20 mg. of calcium oxide and traces of a few other elements, is removed from the apparatus by dissolving in dilute hydrochloric acid and subjected to standard analytiaal procedures. The sinter residues contained less than 0.0005% lithium oxide. Lithium oxide was recovered from synthetic samples with an average error of 1.1%.

Sodium metasomatism along the Melones fault zone, Sierra Nevada foothills, California, USA

USGS Publications Warehouse

Albino, G.V.

1995-01-01

Albitite, locally aegirine- and riebeckite-bearing, formed as a result of sodium metasomatism of felsic dykes and argillites along the Melones Fault Zone near Jamestown, California. Pyrite, magnetite, hematite and titanite are common in small amounts in altered dykes. The dykes were originally plagioclase-hornblende porphyritic, and had major and trace element abundances typical of calc-alkaline rocks, whereas they now have Na2O contents as high as 11.40%. Mass balance calculations indicate that alteration involved addition of large amounts of sodium, and the removal of SiO2 and K2O. Textural preservation, combined with volume factors calculated from specific gravity and whole rock analytical data, indicate that Na-metasomatism was essentially isovolumetric. -from Author

The Origin of Fibrous Calcite Veins: Aragonite?

NASA Astrophysics Data System (ADS)

Elburg, M. A.; Bons, P. D.

2005-12-01

Truly fibrous calcite veins occur mainly in carbonaceous shales and are characterised by high length:width ratios of their fibres (>10). Previous studies on their Sr isotopic geochemistry (Elburg et al., 2002: Geol. Soc. London Spec. Publ. 200, 103-118; Hilgers and Sindern, 2005: Geofluids, in press) have shown that some of the material could be derived from the local wall rock. These studies also showed that the veins were always enriched in Sr compared to the calcite in the host rocks. Aragonite can contain significantly more Sr than calcite, while it also tends to have a fibrous crystal habit. It is therefore possible that the fibrous habit of these veins, which now consist of calcite, are a reflection of their initial aragonitic mineralogy, rather than of any special tectonic regime during their formation. This idea was investigated by analysing the major and trace element geochemistry of selected fibrous and non-fibrous calcite veins from Arkaroola (northern Flinders Ranges, Australia). The fibrous vein analysed for major elements contains less than 1% MgCO3, whereas calcite in the host rock, with which it is in Sr isotopic equilibrium, contains 18% MgCO3. Calcite can contain significant Mg, whereas the aragonitic structure cannot accomodate this ion, so this result is consistent with the idea of an original aragonitic mineralogy of the veins. The fibrous veins show an enrichment in the middle rare earth elements (REE) compared to the calcite in the host rock and blocky veins. In a Post-Archean Average Shale normalised diagram, Eu is more strongly enriched compared to its neighbouring elements in the fibrous veins, but not in the host calcite, blocky veins, or in the silicate fraction of the host rock, suggesting more reducing conditions during fibrous vein formation. This data cannot be used as direct evidence for the fibrous veins' aragonitic mineralogy. It does, however, show that significant differences exist between calcite in host rocks, blocky and fibrous calcite veins, and this data should be incorporated in any model explaining the origin of fibrous veins.

Processes involved in the formation of magnesian-suite plutonic rocks from the highlands of the Earth's Moon

NASA Technical Reports Server (NTRS)

Snyder, Gregory A.; Neal, Clive R.; Taylor, Lawrence A.; Halliday, Alex N.

1995-01-01

The earliest evolution of the Moon likely included the formation of a magma ocean and the subsequent development of anorthositic flotation cumulates. This primary anorthositic crust was then intruded by mafic magmas which crystallized to form the lunar highlands magnesian suite. The present study is a compilation of petrologic, mineral-chemical, and geochemical information on all pristine magnesian-suite plutonic rocks and the interpretation of this data in light of 18 'new' samples. Of these 18 clasts taken from Apollo 14 breccias, 12 are probably pristine and include four dunites, two norites, four troctolites, and two anorthosites. Radiogenic isotopic whole rock data also are reported for one of the 'probably pristine' anorthositic troctolites, sample 14303,347. The relatively low Rb content and high Sm and Nd abundances of 14303,347 suggest that this cumulate rock was derived from a parental magma which had these chemical characteristics. Trace element, isotopic, and mineral-chemical data are used to interpret the total highlands magnesian suite as crustal precipitates of a primitive KREEP (possessing a K-, rare earth element (REE)-, and P-enriched chemical signature) basalt magma. This KREEP basalt was created by the mixing of ascending ultramafic melts from the lunar interior with urKREEP (the late, K-, REE-, and P-enriched residuum of the lunar magma ocean). A few samples of the magnesian suite with extremely elevated large-ion lithophile elements (5-10x other magnesian-suite rocks) cannot be explained by this model or any other model of autometasomatism, equilibrium crystallization, or 'local melt-pocket equilibrium' without recourse to an extremely large-ion lithophile element-enriched parent liquid. It is difficult to generate parental liquids which are 2-4 x higher in the REE than average lunar KREEP, unless the liquids are the basic complement of a liquid-liquid pair, i.e., the so-called 'REEP-fraction,' from the silicate liquid immiscibility of urKREEP. Scarce age information on lunar rocks suggests that magnesian-suite magmatism was initiated at progressively more recent time from the northeast to the southwest on the lunar nearside from 4.45 to 4.25 Ga.

Magmatic evolution of Panama Canal volcanic rocks: A record of arc processes and tectonic change.

PubMed

Farris, David W; Cardona, Agustin; Montes, Camilo; Foster, David; Jaramillo, Carlos

2017-01-01

Volcanic rocks along the Panama Canal present a world-class opportunity to examine the relationship between arc magmatism, tectonic forcing, wet and dry magmas, and volcanic structures. Major and trace element geochemistry of Canal volcanic rocks indicate a significant petrologic transition at 21-25 Ma. Oligocene Bas Obispo Fm. rocks have large negative Nb-Ta anomalies, low HREE, fluid mobile element enrichments, a THI of 0.88, and a H2Ocalc of >3 wt. %. In contrast, the Miocene Pedro Miguel and Late Basalt Fm. exhibit reduced Nb-Ta anomalies, flattened REE curves, depleted fluid mobile elements, a THI of 1.45, a H2Ocalc of <1 wt. %, and plot in mid-ocean ridge/back-arc basin fields. Geochemical modeling of Miocene rocks indicates 0.5-0.1 kbar crystallization depths of hot (1100-1190°C) magmas in which most compositional diversity can be explained by fractional crystallization (F = 0.5). However, the most silicic lavas (Las Cascadas Fm.) require an additional mechanism, and assimilation-fractional-crystallization can reproduce observed compositions at reasonable melt fractions. The Canal volcanic rocks, therefore, change from hydrous basaltic pyroclastic deposits typical of mantle-wedge-derived magmas, to hot, dry bi-modal magmatism at the Oligocene-Miocene boundary. We suggest the primary reason for the change is onset of arc perpendicular extension localized to central Panama. High-resolution mapping along the Panama Canal has revealed a sequence of inward dipping maar-diatreme pyroclastic pipes, large basaltic sills, and bedded silicic ignimbrites and tuff deposits. These volcanic bodies intrude into the sedimentary Canal Basin and are cut by normal and subsequently strike-slip faults. Such pyroclastic pipes and basaltic sills are most common in extensional arc and large igneous province environments. Overall, the change in volcanic edifice form and geochemistry are related to onset of arc perpendicular extension, and are consistent with the idea that Panama arc crust fractured during collision with South America forming the observed Canal extensional zone.

Uranium, yttrium, and rare earth elements accumulation during the Cretaceous anoxic events in carbonaceous rocks in the Pacific Ocean

NASA Astrophysics Data System (ADS)

Savelyeva, Olga; Philosofova, Tatyana; Bergal-Kuvikas, Olga; Savelyeva, Svetlana

2017-04-01

We have studied the carbonate-siliceous section of paleooceanic Albian-Cenomanian deposits on the Kamchatsky Mys peninsula (Eastern Kamchatka, Russia) [1].The section is represented by a rhythmic alternation of planktonic limestones and jaspers, accumulated in the open ocean environment. The rhythmicity can be attributed to climate variations that reflect a fluctuation of astronomical parameters (Milankovitch cycles) [2, 3].The section contains two beds enriched in organic carbon, corresponding to the two oceanic anoxic events - MCE and OAE2 [3]. The maximum content of organic matter in those beds reaches 68%. Our geochemical studies revealed an enrichment of the carbonaceous rocks in some major and trace elements including PGE, in comparison with the surrounding limestone and jasper [4].The accumulation of the ore elements in carbonaceous beds is caused by euxinic conditions during sedimentation.The content of uranium, yttrium, and rare earth elements in carbonaceous rocks is up to 60, 142 and 312 ppm respectively. Phosphate grains (bone detritus) with microinclusions of yttrium and uranium minerals were revealed in the carbonaceous rocks using the scanning electron microscope. These data prove the hypothesis of the sorbtion of U and Y by phosphate detritus from seawater. Microprobe analysis also showed an increased content of Cu, Zn, V in some pyrite framboids, which indicates that these elements are fixed in rocks by Fe-sulphide phase or organic matter under euxinic conditions. Our research may bring us closer to understanding the mechanism of syngenetic accumulation of metals in the black shales. This work was supported by the RFBR (No. 16-05-00546). [1] Palechek, T.N., Savelyev, D.P., Savelyeva, O.L. (2010) Stratigraphy and Geological Correlation 18, (1) 63-82. [2] Savelyeva, O.L. (2010). Vestnik Kraunts. Nauki o zemle 1 (15), 45-55 (in Russian). [3] Savelyev, D.P., Savelyeva, O.L., Palechek, T.N., Pokrovsky, B.G. (2012) Geophysical Research Abstracts, 14, EGU2012-1940. [4] Savelyeva, O., Palesskiy, S., Savelyev, D. (2015) Goldschmidt Abstracts, 2015. 2779.

Zircon Lu-Hf isotope systematics and U-Pb geochronology, whole-rock Sr-Nd isotopes and geochemistry of the early Jurassic Gokcedere pluton, Sakarya Zone-NE Turkey: a magmatic response to roll-back of the Paleo-Tethyan oceanic lithosphere

NASA Astrophysics Data System (ADS)

Karsli, Orhan; Dokuz, Abdurrahman; Kandemir, Raif

2017-05-01

The early Mesozoic was a critical era for the geodynamic evolution of the Sakarya Zone as transition from accretion to collision events in the region. However, its complex evolutionary history is still debated. To address this issue, we present new in situ zircon U-Pb ages and Lu-Hf isotope data, whole-rock Sr-Nd isotopes, and mineral chemistry and geochemistry data of plutonic rocks to better understand the magmatic processes. The Gokcedere pluton is mainly composed of gabbro and gabbroic diorite. LA-ICP-MS zircon U-Pb dating reveals that the pluton was emplaced in the early Jurassic (177 Ma). These gabbros and gabbroic diorites are characterized by relatively low SiO2 content of 47.09 to 57.15 wt% and high Mg# values varying from 46 to 75. The samples belong to the calc-alkaline series and exhibit a metaluminous I-type character. Moreover, they are slightly enriched in large ion lithophile elements (Rb, Ba, Th and K) and light rare earth elements and depleted in high field strength elements (Nb and Ti). Gabbroic rocks of the pluton have a depleted Sr-Nd isotopic composition, including low initial 87Sr/86Sr ranging from 0.705124 to 0.705599, relatively high ɛ Nd ( t) values varying from 0.1 to 3.5 and single-stage Nd model ages ( T DM1 = 0.65-0.95 Ga). In situ zircon analyses show that the rocks have variable and positive ɛ Hf ( t) values (4.6 to 13.5) and single-stage Hf model ages ( T DM1 = 0.30 to 0.65 Ga). Both the geochemical signature and Sr-Nd-Hf isotopic composition of the gabbroic rocks reveal that the magma of the studied rocks was formed by the partial melting of a depleted mantle wedge metasomatized by slab-derived fluids. The influence of slab fluids is mirrored by their trace-element characteristics. Trace-element modeling suggests that the primary magma was generated by a low and variable degree of partial melting ( 5-15%) of a depleted and young lithospheric mantle wedge consisting of phlogopite- and spinel-bearing lherzolite. Heat to melt the mantle material was supplied by the ascendance of a hot asthenosphere triggered by the roll-back of the Paleo-Tethyan oceanic lithosphere. The rising melts were accompanied by fractional crystallization and encountered no or minor crustal contamination en route to the surface. Taking into account these geochemical data and integrating them with regional geological evidence, we propose a slab roll-back model; this model suggests that the Gokcedere gabbroic pluton originated in a back-arc extensional environment associated with the southward subduction of the Paleo-Tethyan oceanic lithosphere during the early Jurassic period. Such an extensional event led to the opening of the northern branch of the Neotethys as a back-arc basin. Consequently, we conclude that the gabbroic pluton was related to intensive extensional tectonic events, which peaked during the early Jurassic in response to the roll-back of Paleo-Tethyan oceanic slab in the final stage of oceanic closure.

Magma feeding system of Kutcharo and Mashu calderas, Hokkaido, Japan: Evidence of a common basaltic magma evolving into two distinct rock series

NASA Astrophysics Data System (ADS)

Miyagi, I.; Itoh, J.; Nguyen, H.

2009-12-01

Kutcharo and its adjacent Mashu volcanoes are located in NE Hokkaido, about 150 km west of the Kurile trench. The latest major activity of Kutcharo was 35 thousand years ago (termed KP I) produced about 50 km3 D.R.E, Mashu meanwhile became active after KP I. To understand the magma feeding system of adjoining but distinct Kutcharo (medium-K) and Mashu (low-K) volcanoes, we examined major and trace element, and Sr, Nd, and Pb isotopic compositions of whole rocks. We also studied phenocryst chemical zoning and chemical compositions of melt inclusions in phenocryst. The chemical results of melt inclusions show no distinction between medium- and low-K as being recognized in bulk rock chemistry of the volcanoes. Instead, the results form a smooth trend between low-K rock series and high-K rhyolitic melt end-member (as high as 5 wt. % K2O). There is no significant difference Sr, Nd and Pb isotopes between basalt and rhyolite suggesting genetic relationship. Moreover, the trace element distribution patterns show enrichment increasing gradually from the basalt to rhyolite via andesite indicating fractional crystallization evolution. Chemical zoning in plagioclase phenocryst in KP I (An 80-40) suggest that basaltic magma injected repeatedly into a voluminous felsic magma chamber of Kutcharo volcano. Chemical compositions of olivine phenocryst show that Kutcharo (Fo 86) was hotter as compared to Mashu (Fo 75). Application of MELTS program (Ghiorso and Sack, 1995) on composition of the basaltic melt end-member suggests that crystallization or subsequent re-melting of the basalt may produce medium- to high-K rhyolite melt, and mixing of the rhyolite with basalt may form the observed medium-K Kutcharo and low-K Mashu rock series. It is estimated that total volume of the basaltic magma supplied intermittently beneath the volcanoes was several folds to 10 times larger than the erupted rhyolite magma. And that the basalt injection may be more intensive beneath Kutcharo, leading to the formation of a thermal structure that has a peak at Kutcharo and lowers gradually toward Mashu. The thermal structure may explain the observed difference in erupted volumes and rock series between two volcanoes. This research project has been conducted under the research contract with Nuclear and Industrial Safety Agency (NISA).

Geochemistry, Nd-Pb Isotopes, and Pb-Pb Ages of the Mesoproterozoic Pea Ridge Iron Oxide-Apatite–Rare Earth Element Deposit, Southeast Missouri

USGS Publications Warehouse

Ayuso, Robert A.; Slack, John F.; Day, Warren C.; McCafferty, Anne E.

2016-01-01

Iron oxide-apatite and iron oxide-copper-gold deposits occur within ~1.48 to 1.47 Ga volcanic rocks of the St. Francois Mountains terrane near a regional boundary separating crustal blocks having contrasting depleted-mantle Sm-Nd model ages (TDM). Major and trace element analyses and Nd and Pb isotope data were obtained to characterize the Pea Ridge deposit, improve identification of exploration targets, and better understand the regional distribution of mineralization with respect to crustal blocks. The Pea Ridge deposit is spatially associated with felsic volcanic rocks and plutons. Mafic to intermediate-composition rocks are volumetrically minor. Data for major element variations are commonly scattered and strongly suggest element mobility. Ratios of relatively immobile elements indicate that the felsic rocks are evolved subalkaline dacite and rhyolite; the mafic rocks are basalt to basaltic andesite. Granites and rhyolites display geochemical features typical of rocks produced by subduction. Rare earth element (REE) variations for the rhyolites are diagnostic of rocks affected by hydrothermal alteration and associated REE mineralization. The magnetite-rich rocks and REE-rich breccias show similar REE and mantle-normalized trace element patterns.Nd isotope compositions (age corrected) show that: (1) host rhyolites have ɛNd from 3.44 to 4.25 and TDM from 1.51 to 1.59 Ga; (2) magnetite ore and specular hematite rocks display ɛNd from 3.04 to 4.21 and TDM from 1.6 to 1.51 Ga, and ɛNd from 2.23 to 2.81, respectively; (3) REE-rich breccias have ɛNd from 3.04 to 4.11 and TDM from 1.6 to 1.51 Ga; and (4) mafic to intermediate-composition rocks range in ɛNd from 2.35 to 3.66 and in TDM from 1.66 to 1.56. The ɛNd values of the magnetite and specular hematite samples show that the REE mineralization is magmatic; no evidence exists for major overprinting by younger, crustal meteoric fluids, or by externally derived Nd. Host rocks, breccias, and magnetite ore shared a common origin from a similar source.Lead isotope ratios are diverse: (1) host rhyolite has 206Pb/204Pb from 24.261 to 50.091; (2) Pea Ridge and regional galenas have 206Pb/204Pb from 16.030 to 33.548; (3) REE-rich breccia, magnetite ore, and specular hematite rock are more radiogenic than galena; (4) REE-rich breccias have high 206Pb/204Pb (38.122–1277.61) compared to host rhyolites; and (5) REE-rich breccias are more radiogenic than magnetite ore and specular-hematite rock, having 206Pb/204Pb up to 230.65. Radiogenic 207Pb/206Pb age estimates suggest the following: (1) rhyolitic host rocks have ages of ~1.50 Ga, (2) magnetite ore is ~1.44 Ga, and (3) REE-rich breccias are ~1.48 Ga. These estimates are broadly consistent and genetically link the host rhyolite, REE-rich breccia, and magnetite ore as being contemporaneous.Alteration style and mineralogical or textural distinctions among the magnetite-rich rocks and REE-rich breccias do not correlate with different isotopic sources. In our model, magmatic fluids leached metals from the coeval felsic rocks (rhyolites), which provided the metal source reflected in the compositions of the REE-rich breccias and mineralized rocks. This model allows for the likelihood of contributions from other genetically related felsic and intermediate to more mafic rocks stored deeper in the crust. The deposit thus records an origin as a magmatic-hydrothermal system that was not affected by Nd and Pb remobilization processes, particularly if these processes also triggered mixing with externally sourced metal-bearing fluids. The Pea Ridge deposit was part of a single, widespread, homogeneous mixing system that produced a uniform isotopic composition, thus representing an excellent example of an igneous-dominated system that generated coeval magmatism and REE mineralization. Geochemical features suggest that components in the Pea Ridge deposit originated from sources in an orogenic margin. Basaltic magmatism produced by mantle decompression melting provided heat for extracting melts from the middle or lower crust. Continual addition of mafic magmas to the base of the subcontinental lithosphere, in a back-arc setting, remelted calc-alkaline rocks enriched in metals that were stored in the crust.The St. Francois Mountains terrane is adjacent to the regional TDM line (defined at a value of 1.55 Ga) that separates ~1600 Ma basement to the west, from younger basements to the east. Data for Pea Ridge straddle the TDM values proposed for the line. The Sm-Nd isotope system has been closed since formation of the deposit and the original igneous signatures have not been affected by cycles of alteration or superimposed mineralizing events. No evidence exists for externally derived Nd or Sm. The source region for metals within the Pea Ridge deposit had a moderate compositional variation and the REE-rich breccias and mineralized rocks are generally isotopically homogeneous. The Pea Ridge deposit thus constitutes a distinctive isotopic target for use as a model in identifying other mineralized systems that may share the same metal source in the St. Francois Mountains terrane and elsewhere in the eastern Granite-Rhyolite province.

Critical elements in Carlin, epithermal, and orogenic gold deposits

USGS Publications Warehouse

Goldfarb, Richard J.; Hofstra, Albert H.; Simmons, Stuart F.

2016-01-01

Carlin, epithermal, and orogenic gold deposits, today mined almost exclusively for their gold content, have similar suites of anomalous trace elements that reflect similar low-salinity ore fluids and thermal conditions of metal transport and deposition. Many of these trace elements are commonly referred to as critical or near-critical elements or metals and have been locally recovered, although typically in small amounts, by historic mining activities. These elements include As, Bi, Hg, In, Sb, Se, Te, Tl, and W. Most of these elements are now solely recovered as by-products from the milling of large-tonnage, base metal-rich ore deposits, such as porphyry and volcanogenic massive sulfide deposits.A combination of dominance of the world market by a single country for a single commodity and a growing demand for many of the critical to near-critical elements could lead to future recovery of such elements from select epithermal, orogenic, or Carlin-type gold deposits. Antimony continues to be recovered from some orogenic gold deposits and tellurium could potentially be a primary commodity from some such deposits. Tellurium and indium in sphalerite-rich ores have been recovered in the past and could be future commodities recovered from epithermal ores. Carlin-type gold deposits in Nevada are enriched in and may be a future source for As, Hg, Sb, and/or Tl. Some of the Devonian carbonaceous host rocks in the Carlin districts are sufficiently enriched in many trace elements, including Hg, Se, and V, such that they also could become resources. Thallium may be locally enriched to economic levels in Carlin-type deposits and it has been produced from Carlin-like deposits elsewhere in the world (e.g., Alsar, southern Macedonia; Lanmuchang, Guizhou province, China). Mercury continues to be recovered from shallow-level epithermal deposits, as well as a by-product of many Carlin-type deposits where refractory ore is roasted to oxidize carbon and pyrite, and mercury is then captured in air pollution control devices.

Fate and transport of heavy metals and radioelements in groundwater aquifers of Al-Qunfudhah and Wadi Haliy quadrangles, southwest of Saudi Arabia

NASA Astrophysics Data System (ADS)

Bajabaa, S. A.; Abd El-Naby, H.; Dawood, Y.

2009-12-01

The fate and transport of heavy metals and radioelements in groundwater aquifers in five wadis located in the Al Qunfudhah and Wadi Haliy quadrangles were investigated. These wadis are an important source of water to the Red Sea coastal plain. Copper, zinc and other base-metals mineralization occur at eastern parts of these quadrangles that dominates the water catchments area of these wadis. Water, rock and soil samples were collected from all wadis and they were analyzed for major, trace elements, heavy metals and stable isotopes. The chemical and isotopic results showed active water/rock interaction. The preliminary investigation of the data analyses showed some samples with high heavy metals and uranium contents. Generally, the uranium and heavy metal contents are higher in samples collected from the upstream area of each wadi where the crystalline rocks are exposed and direct contact with the runoff. The uranium contents were as high as 120 ppb in some water samples. These elevated values are mainly due to two factors water rock interaction and concentration through evaporation. It was also observed to have elevated heavy metal contents near mining activates, which suggests that these mining activates are playing an important role in mobilizing the heavy elements and in turn affecting the water quality in these wadis.

Composition of the earth's upper mantle-I. Siderophile trace elements in ultramafic nodules

USGS Publications Warehouse

Morgan, J.W.; Wandless, G.A.; Petrie, R.K.; Irving, A.J.

1981-01-01

Seven siderophile elements (Au, Ge, Ir, Ni, Pd, Os, Re) were determined by radiochemical neutron activation analysis in 19 ultramafic rocks, which are spinel lherzollites-xenoliths from North and Central America, Hawaii and Australia, and garnet Iherzolitexenoliths from Lesotho. Abundances of the platinum metals are very uniform in spinel lherzolites averaging 3.4 ?? 1.2 ppb Os, 3.7 ?? 1.1 ppb Ir, and 4.6 ?? 2.0 ppb Pd. Sheared garnet lherzolite PHN 1611 has similar abundances of these elements, but in 4 granulated garnet lherzolites, abundances are more variable. In all samples, the Pt metals retain cosmic ( Cl-chondrite) ratios. Abundances of Au and Re vary more than those of Pt metals, but the Au/Re ratio remains close to the cosmic value. The fact that higher values of Au and Re approach cosmic proportions with respect to the Pt metals, suggests that Au and Re have been depleted in some ultramafic rocks from an initially chondrite-like pattern equivalent to about 0.01 of Cl chondrite abundances. The relative enrichment of Au and Re in crustal rocks is apparently the result of crust-mantle fractionation and does not require a special circumstance of core-mantle partitioning. Abundances of moderately volatile elements Ni, Co and Ge are very uniform in all rocks, and are much higher than those of the highly siderophile elements Au, Ir, Pd, Os and Re. When normalized to Cl chondrites, abundances of Ni and Co are nearly identical, averaging 0.20 ?? 0.02 and 0.22 ?? 0.02, respectively; but Ge is only 0.027 ?? 0.004. The low abundance of Ge relative to Ni and Co is apparently a reflection of the general depletion of volatile elements in the Earth. The moderately siderophile elements cannot be derived from the same source as the highly siderophile elements because of the marked difference in Cl chondrite-normalized abundances and patterns. We suggest that most of the Ni, Co and Ge were enriched in the silicate by the partial oxidation of pre-existing volatile-poor Fe-Ni, whereas the corresponding highly siderophile elements remained sequestered by the surviving metal. The highly siderophile elements may have been introduced by a population of ~103 large (~1022 g) planetisimals, similar to those forming the lunar mare basins. ?? 1981.

The emerging Medical and Geological Association.

USGS Publications Warehouse

Finkelman, R.B.; Centeno, J.A.; Selinus, O.

2005-01-01

The impact on human health by natural materials such as water, rocks, and minerals has been known for thousands of years but there have been few systematic, multidisciplinary studies on the relationship between geologic materials and processes and human health (the field of study commonly referred to as medical geology). In the past few years, however, there has been a resurgence of interest in medical geology. Geoscientists working with medical researchers and public health scientists have made important contributions to understanding novel exposure pathways and causes of a wide range of environmental health problems such as: exposure to toxic levels of trace essential and non-essential elements such as arsenic and mercury; trace element deficiencies; exposure to natural dusts and to radioactivity; naturally occurring organic compounds in drinking water; volcanic emissions, etc. By linking with biomedical/public health researchers geoscientists are finally taking advantage of this age-old opportunity to help mitigate environmental health problems. The International Medical Geology Association has recently been formed to support this effort.

Tektites, Apollo, the Crust, and Planets: A Life with Trace Elements

NASA Astrophysics Data System (ADS)

Taylor, Stuart Ross

2016-06-01

Stuart Ross Taylor, MSc (University of New Zealand), PhD (Indiana University), ScD (University of Oxford), FAA, AC, always called Ross, grew up on a farm near Ashburton, New Zealand. Ross has worked on a wide variety of topics in trace element geochemistry, including the composition and evolution of the Moon, the continental crust, tektites, impact glasses, and island arc rocks. In 1969 he carried out the first chemical analysis of the first returned lunar sample at NASA in Houston. He has published 10 books and 240 papers in scientific journals. He was awarded the V.M. Goldschmidt Award of the Geochemical Society in 1993. In 1994 he was elected a Foreign Associate of the National Academy of Sciences. In 1998, he was awarded the Leonard Medal of the Meteoritical Society, in 2002 the Bucher Medal of the American Geophysical Union, and in 2012 the Shoemaker Distinguished Lunar Scientist Medal of the NASA Lunar Science Institute. Asteroid 5670 is named Rosstaylor.

The Emerging Medical and Geological Association

PubMed Central

Finkelman, Robert B; Centeno, Jose A; Selinus, Olle

2005-01-01

The impact on human health by natural materials such as water, rocks, and minerals has been known for thousands of years but there have been few systematic, multidisciplinary studies on the relationship between geologic materials and processes and human health (the field of study commonly referred to as medical geology). In the past few years, however, there has been a resurgence of interest in medical geology. Geoscientists working with medical researchers and public health scientists have made important contributions to understanding novel exposure pathways and causes of a wide range of environmental health problems such as: exposure to toxic levels of trace essential and non-essential elements such as arsenic and mercury; trace element deficiencies; exposure to natural dusts and to radioactivity; naturally occurring organic compounds in drinking water; volcanic emissions, etc. By linking with biomedical/public health researchers geoscientists are finally taking advantage of this age-old opportunity to help mitigate environmental health problems. The International Medical Geology Association has recently been formed to support this effort. PMID:16555612

The geochemistry of carbonatites revisited: Two major types of continental carbonatites and their trace-element signatures

NASA Astrophysics Data System (ADS)

Chakhmouradian, A.

2009-04-01

There have been several attempts to systematize the geochemistry of carbonatites, most recently by Samoilov (1984), Nelson et al. (1988), Woolley and Kempe (1989), and Rass (1998). These studies revealed a number of important geochemical characteristics that can be used to track the evolutionary history of these rocks, distinguish them from modally similar metamorphic parageneses, and aid in mineral exploration for rare earths, niobium and other resources commonly associated with carbonatites. Important breakthroughs in the understanding of carbonatite petrogenesis and numerous reports of new carbonatite localities made in the past two decades lay the ground for a critical re-assessment of the geochemistry of these rocks. A new representative database of whole-rock carbonatite analyses was compiled from the post-1988 literature and various unpublished sources. The database contains 820 analyses encompassing calcio-, magnesio- and ferrocarbonatites from 174 localities (ca. one-third of the total number of carbonatites known worldwide) reduced to ca. 350 analyses following the approach of Woolley and Kempe (1989). Carbonatites emplaced in oceanic settings (e.g., Cape Verde), ophiolite belts (e.g., Oman), or those of uncertain tectonic affinity (e.g., El Picacho in Mexico) were not included. Two major types of continental carbonatites can be distinguished on the basis of their geological setting and trace-element geochemistry: (1) carbonatites emplaced in rifts and smaller-scale extensional structures developed in stable Archean cratons or paleo-orogenic belts, and (2) carbonatites emplaced in collisional settings following the orogenesis. In both settings, the most common and best-studied type of carbonatite is calcite carbonatite (predominantly intrusive with a small percentage of extrusive occurrences), which accounts for 62% of the analyses included in the database. Both types of carbonatite are typically associated with alkaline silicate lithologies (meleigites, nepheline syenites, etc.), but those associated with type-1 rocks are typically Na-rich and silica-undersaturated, whereas type-2 carbonatites are associated with K-rich silica-saturated to undersaturated syenites. Type-1 carbonatites are notably different from their type-2 counterparts in showing higher abundances of high-field-strength elements (HFSE = Ti, Zr, Hf, Nb, Ta), Rb, U and V, but lower levels of Sr, Ba, Pb, rare-earth elements, F and S. Key element ratios are also different in the two carbonatite types; in particular, Rb/K, Nb/Ta, Zr/Hf and Ga/Al values are consistently higher in type-1 samples. Notably, some element ratios (e.g., Co/Ni and Y/Ho) are very similar in both groups. Type-2 carbonatites commonly show a 13C-depleted signature relative to the "primary carbonatite" range (Deines, 1989). The observed differences in geological setting and geochemistry indicate the existence of two distinct carbonatite sources in the subcontinental lithosphere: amphibole-bearing lherzolite producing type-1 rocks (cf. Chakhmouradian, 2006), and subducted oceanic crust (rutile-bearing eclogite?) yielding type-2 melts depleted in HFSE, but enriched in light carbon, large-ion-incompatible elements, F and S. References: Chakhmouradian, A.R. (2006) High-field-strength elements in carbonatitic rocks: Geochemistry, crystal chemistry and significance for constraining the sources of carbonatites. Chem. Geol., 235, 138-160. Deines, P. (1989) Stable isotope variations in carbonatites. In: Carbonatites: Genesis and Evolution (K. Bell, Ed.). Unwin Hyman, London, 301-359. Nelson, D.R., Chivas, A.R., Chappell, B.V. and McCulloch, M.T. (1988) Geochemical and isotopic systematic in carbonatites and implications for the evolution of ocean-island sources. Geochim. Cosmochim. Acta, 52, 1-17. Rass, I.T. (1998) Geochemical features of carbonatite indicative of the composition, evolution, and differentiation of their mantle magmas. Geochem. Int., 36, 107-116. Samoilov, V.S. (1984) Geochemistry of Carbonatites. Nauka, Moscow (in Russ.). Woolley, A.R. and Kempe, D.R.C. (1989) Carbonatites: nomenclature, average chemical compositions, and element distribution. In: Carbonatites: Genesis and Evolution (K. Bell, Ed.). Unwin Hyman, London, 1-14.

Remarkable isotopic and trace element trends in potassic through sodic Cretaceous plutons of the Yukon-Koyukuk Basin, Alaska, and the nature of the lithosphere beneath the Koyukuk terrane

USGS Publications Warehouse

Arth, Joseph G.; Criss, Robert E.; Zmuda, Clara C.; Foley, Nora K.; Patton, W.W.; Miller, T.P.

1989-01-01

During the period from 110 to 80 m.y. ago, a 450-km-long magmatic belt was active along the northern margin of Yukon-Koyukuk basin and on eastern Seward Peninsula. The plutons intruded Upper Jurassic(?) and Lower Cretaceous volcanic arc rocks and Cretaceous sedimentary rocks in Yukon-Koyukuk basin and Proterozoic and lower Paleozoic continental rocks in Seward Peninsula. Within Yukon-Koyukuk basin, the plutons vary in composition from calc-alkalic plutons on the east to potassic and ultrapotassic alkalic plutons on the west. Plutons within Yukon-Koyukuk basin were analyzed for trace element and isotopic compositions in order to discern their origin and the nature of the underling lithosphere. Farthest to the east, the calc-alkalic rocks of Indian Mountain pluton are largely tonalite and sodic granodiorite, and have low Rb (average 82 ppm), high Sr (>600 ppm), high chondrite-normalized (cn) Ce/Yb (16–37), low δ18O (+6.5 to +7.1), low initial 87Sr/86Sr (SIR) (0.704), and high initial 143Nd/144Nd (NIR) (0.5126). These rocks resemble those modelled elsewhere as partial melts and subsequent fractionates of basaltic or gabbroic metaigneous rocks, and may be products of melting in the deeper parts of the Late Jurassic(?) and Early Cretaceous volcanic arc. Farthest to the west, the two ultrapotassic bodies of Selawik and Inland Lake are high in Cs (up to 93 ppm), Rb (up to 997 ppm), Sr, Ba, Th, and light rare earth elements, have high (Ce/Yb)cn (30, 27), moderate to low δ18O (+8.4, +6.9), high SIR (0.712, 0.710), and moderate NIR (0.5121–0.5122). These rocks resemble rocks of Australia and elsewhere that were modelled as melts of continental mantle that had been previously enriched in large cations. This mantle may be Paleozoic or older. The farthest west alkalic pluton of Selawik Hills is largely monzonite, quartz monzonite, and granite; has moderate Rb (average 284 ppm), high Sr (>600 ppm), high (Ce/Yb)cn (15–25), moderate δ18O (+8.3 to +8.6), high SIR (0.708–0.712), and moderate NIR (0.5121–0.5122). These rocks may be the product of interaction of magma derived from old continental mantle and magma derived from old continental crust. Plutons between eastern and western extremes show completely gradational variations in the concentration of K and Rb and in the isotopic compositions of Sr, Nd, and O. These plutons probably originated either by melting in a mixed source composed of a Paleozoic or older continental section (mantle + crust) overlain by Mesozoic mafic arc rocks, or by mixing of ultrapotassic to potassic magmas from continental sources (mantle + crust), and tonalitic magmas from arc sources. We infer from these results that the northwest portion of Yukon-Koyukuk basin is underlain by a substantial continental basement of Paleozoic or greater age. This basement probably thins out to the east. There is no geochemical evidence for continental basement east of about longitude 157°, or along a belt of at least 50 km width flanking Ruby Geanticline as far to the southwest as about longitude 161°. These areas are probably underlain by oceanic and Mesozoic arc rocks.

U-Pb ages and geochemistry of zircon from Proterozoic plutons of the Sawatch and Mosquito ranges, Colorado, U.S.A.: Implications for crustal growth of the central Colorado province

USGS Publications Warehouse

Moscati, Richard J.; Premo, Wayne R.; Dewitt, Ed; Wooden, Joseph L.

2017-01-01

A broad study of zircons from plutonic rocks of the Sawatch and Mosquito ranges of west-central Colorado (U.S.A.) was undertaken to significantly refine the magmatic chronology and chemistry of this under-studied region of the Colorado province. This region was chosen because it lies just to the north of the suspected arc-related Gunnison-Salida volcano-plutonic terrane, which has been the subject of many recent investigations—and whose origin is still debated. Our new results provide important insights into the processes active during Proterozoic crustal evolution in this region, and they have important ramifications for broader-scope crustal evolution models for southwestern North America.Twenty-four new U-Pb ages and sequentially acquired rare-earth element (REE), U, Th, and Hf contents of zircon have been determined using the sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG). These zircon geochemistry data, in conjunction with whole-rock major- and trace-element data, provide important insights into zircon crystallization and melt fractionation, and they help to further constrain the tectonic environment of magma generation.Our detailed zircon and whole-rock data support the following three interpretations:(1) The Roosevelt Granite in the southern Sawatch Range was the oldest rock dated at 1,766 ± 7 Ma, and it intruded various metavolcanic and metasedimentary rocks. Geochemistry of both whole-rock and zircon supports the contention that this granite was produced in a magmatic arc environment and, therefore, is likely an extension of the older Dubois Greenstone Belt of the Gunnison Igneous Complex (GIC) and the Needle Mountains (1,770–1,755 Ma). Rocks of the younger Cochetopa succession of the GIC, the Salida Greenstone Belt, and the Sangre de Cristo Mountains (1,740–1,725 Ma) were not found in the Sawatch and Mosquito ranges. This observation strongly suggests that the northern edge of the Gunnison-Salida arc terrane underlies the southern portion of the Sawatch and Mosquito ranges.(2) Calc-alkalic to alkali-calcic magmas intruded this region approximately 55 m.y. after the Roosevelt Granite with emplacement of pre-deformational plutons at ca. 1,710 Ma (e.g., Henry Mountain Granite and diorite of Denny Creek), and this continued for at least 30 m.y., ending with emplacement of post-deformational plutons at ca. 1,680 Ma (e.g., Kroenke Granodiorite, granite of Fairview Peak, and syenite of Mount Yale). The timing of deformation can be constrained to sometime after intrusion of the diorite of Denny Creek and likely before the emplacement of the undeformed granite of Fairview Peak. Geochemistry of both whole-rock and zircon indicates that the older group of ca. 1,710-Ma plutons formed at shallower depths, and then they intruded the younger group of more deeply generated, commonly peraluminous and sodic plutons. Although absent in the Sawatch and Mosquito ranges, Mazatzal-age (ca. 1,680–1,620 Ma) plutonic rocks are present regionally. Inherited zircon components of Mazatzal-age were found as cores in some 1.4-Ga Sawatch and Mosquito Range zircons, indicating the likelihood of a relatively local source. These combined data suggest the possibility that all were produced within a continental-margin magmatic arc created as a result of southward-migrating (slab rollback?), north-dipping subduction to the south of the region.(3) Widespread Mesoproterozoic plutonism—with emplacement at various depths and exhibiting bimodal geochemistry—is recognized in 16 different samples. An older group of predominantly peraluminous, yet magnesian granitoids (e.g., granodiorite of Sayers, granite of Taylor River, and the St. Kevin Granite) were emplaced between ca. 1,450 and 1,425 Ma. These geochemical parameters suggest moderate degrees of partial melting in a low-pressure environment. Three younger metaluminous, but ferroan plutons (diorite of Grottos, diorite of Mount Elbert, and granodiorite of Mount Harvard), probably represent a final magmatic pulse at ca. 1,416 Ma.A comprehensive treatment of zircon REE and whole-rock trace-element behavior from Proterozoic rocks is scarce. Discriminant U/Yb versus Y diagrams using zircon data show that the Sawatch and Mosquito plutons are of continental origin, not oceanic. Additional bivariate diagrams incorporating cation ratio combinations of Gd, Ce, Yb, U, Th, Hf, and Eu offer refined insight into differences in fractionation trends and depth of magma generation for the various plutons. These interpretations, on the basis of zircon trace-element data, are mirrored in the whole-rock geochemistry data.

Fluid-rock Interactions recorded in Serpentinites subducted to 60-80 km Depth

NASA Astrophysics Data System (ADS)

Peters, D.; John, T.; Scambelluri, M.; Pettke, D. T.

2016-12-01

The HP metamorphic serpentinised peridotites of Erro-Tobbio (ET, Italy) offer a unique possibility to study fluid-rock interactions in subducted ultrabasic rocks that reached 550-650°C at 2-2.5 GPa. They contain metamorphic olivine + Ti-clinohumite in both the serpentinite matrix and veins cutting the rock foliation, interpreted to represent partial serpentinite dehydration fluid pathways [1,2] being variably retrogressed as e.g., indicated by chrysotile/lizardite mesh textures in vein olivine in strongly altered samples. This study aims to constraining the origin of fluid(s) and the scale(s) of fluid-rock interaction based on major to trace element systematics employing detailed bulk rock (nanoparticulate pressed powder pellet LA-ICP-MS [3] and ion chromatography / liquid ICP-MS analysis), and in situ mineral analysis (work in progress). Bulk data show moderate fluid-mobile element (FME) enrichment for Cs, Rb, Ba, Pb, As, and Sb (up to 100 times primitive mantle (PM)), W (1000 PM), and B (10000 PM). Alkali over U ratios of compiled serpentinite data (n ˜ 620) reveal distinctive global FME enrichment trends for MOR vs. forearc (FA) serpentinisation. ET serpentinites fall into the latter, indicating both sediment-equilibrated fluids and the preservation of characteristic FME enrichment patterns in HP serpentinites. Petrography reveals a multiphase evolution of the HP veins including retrograde serpentinisation, whereas serpentinite hosts have remained largely unaffected by retrogression. Comparison of vein vs. wall rock bulk data indicate vein-forming fluids in equilibrium with wall rocks, however, without evidence for external fluid ingress. The preservation of multiple fluid-rock interaction episodes and the lack of external fluid ingress in the ET HP serpentinites indicate near-closed system behaviour throughout subduction and imprint of characteristic fluid signatures onto the mantle. [1] Scambelluri et al. (1995) Geology, 23, 459-462. [2] John et al. (2011) Earth Planet Sci Lett 308, 65-76. [3] Peters and Pettke (2016) GGR, DOI: 10.1111/ggr.12125.

Phosphates at the Surface of Mars: Primary Deposits and Alteration Products

NASA Technical Reports Server (NTRS)

Yen, Albert S.; Gellert, Ralf; Clark, Benton C.; Ming, Douglas W.; Mittlefehldt, David W.; Arvidson, Raymond E.; McSween, Harry Y., Jr.; Schroder, Christian

2014-01-01

Phosphorus is an essential element in terrestrial organisms and thus characterizing the occurrences of phosphate phases at the martian surface is crucial in the assessment of habitability. The Alpha Particle X-Ray Spectrometers onboard Spirit, Opportunity and Curiosity discovered a variety of primary and secondary phosphate phases allowing direct comparisons across the three landing sites. The Spirit rover at Gusev Crater encountered the "Wishstone/Watchtower" class of P-rich (up to 5.2 wt% P2O5) rocks interpreted to be alkaline volcanic rocks with a physical admixture of approximately 10 to 20% merrillite [Usui et al 2008]. These rocks are characterized by elevated Ti and Y and anomalously low Cr and Ni, which could largely reflect the nature of the protoliths: Evolved magmatic rocks. Many of these chemical signatures are also found in pyroclastic deposits at nearby "Home Plate" and in phosphate precipitates derived from fluid interactions with these rocks ("Paso Robles" soils). The Opportunity rover at Meridiani Planum recently analyzed approximately 4 cm clast in a fine-grained matrix, one of numerous rocks of similar appearance at the rim of Endeavour Crater. This clast, "Sarcobatus," has minor enrichments in Ca and P relative to the matrix, and like the P-rich rocks at Gusev, Sarcobatus also shows elevated Al and Ti. On the same segment of the Endeavour rim, subsurface samples were found with exceptional levels of Mn (approximately 3.5 wt% MnO). These secondary and likely aqueous deposits contain strong evidence for associated Mg-sulfate and Ca-phosphate phases. Finally, the Curiosity traverse at Gale crater encountered P-rich rocks compositionally comparable to Wishstone at Gusev, including elevated Y. Phosphorous-rich rocks with similar chemical characteristics are prevalent on Mars, and the trace and minor element signatures provide constraints on whether these are primary deposits, secondary products of physical weathering or secondary products of chemical weathering.

Geochemistry of approximately 1.9 Ga sedimentary rocks from northeastern Labrador, Canada

NASA Technical Reports Server (NTRS)

Hayashi, K. I.; Fujisawa, H.; Holland, H. D.; Ohmoto, H.

1997-01-01

Fifty-eight rock chips from fifteen samples of sedimentary rocks from the Ramah Group (approximately 1.9 Ga) in northeastern Labrador, Canada, were analyzed for major and minor elements, including C and S, to elucidate weathering processes on the Earth's surface about 1.9 Ga ago. The samples come from the Rowsell Harbour, Reddick Bight, and Nullataktok Formations. Two rock series, graywackes-gray shales of the Rowsell Harbour, Reddick Bight and Nullataktok Formations, and black shales of the Nullataktok Formation, are distinguishable on the basis of lithology, mineralogy, and major and trace element chemistry. The black shales show lower concentrations than the graywackes-gray shales in TiO2 (0.3-0.7 wt% vs. 0.7-1.8 wt%), Al2O3 (9.5-20.1 wt% vs. 13.0-25.0 wt%), and sigma Fe (<1 wt% vs. 3.8-13.9 wt% as FeO). Contents of Zr, Th, U, Nb, Ce, Y, Rb, Y, Co, and Ni are also lower in the black shales. The source rocks for the Ramah Group sediments were probably Archean gneisses with compositions similar to those in Labrador and western Greenland. The major element chemistry of source rocks for the Ramah Group sedimentary rocks was estimated from the Al2O3/TiO2 ratios of the sedimentary rocks and the relationship between the major element contents (e.g., SiO2 wt%) and Al2O3/TiO2 ratios of the Archean gneisses. This approach is justified, because the Al/Ti ratios of shales generally retain their source rock values; however, the Zr/Al, Zr/Ti, and Cr/Ni ratios fractionate during the transport of sediments. The measured SiO2 contents of shales in the Ramah Group are generally higher than the estimated SiO2 contents of source rocks by approximately 5 wt%. This correction may also have to be applied when estimating average crustal compositions from shales. Two provenances were recognized for the Ramah Group sediments. Provenance I was comprised mostly of rocks of bimodal compositions, one with SiO2 contents approximately 45 wt% and the other approximately 65 wt%, and was the source for most sedimentary rocks of the Ramah Group, except for black shales of the Nullataktok Formation. The black shales were apparently derived from Provenance II that was comprised mostly of felsic rocks with SiO2 contents approximately 65 wt%. Comparing the compositions of the Ramah Group sedimentary rocks and their source rocks, we have recognized that several major elements, especially Ca and Mg, were lost almost entirely from the source rocks during weathering and sedimentation. Sodium and potassium were also leached almost entirely during the weathering of the source rocks. However, significant amounts of Na were added to the black shales and K to all the rock types during diagenesis and/or regional metamorphism. The intensity of weathering of source rocks for the Ramah Group sediments was much higher than that of typical Phanerozoic sediments, possibly because of a higher PCO2 in the Proterozoic atmosphere. Compared to the source rock values, the Fe3+/Ti ratios of many of the graywackes and gray shales of the Ramah Group are higher, the Fe2+/Ti ratios are lower, and the sigma Fe/Ti ratios are the same. Such characteristics of the Fe geochemistry indicate that these sedimentary rocks are comprised of soils formed by weathering of source rocks under an oxygen-rich atmosphere. The atmosphere about 1.9 Ga was, therefore, oxygen rich. Typical black shales of Phanerozoic age exhibit positive correlations between the organic C contents and the concentrations of S, U, and Mo, because these elements are enriched in oxygenated seawater and are removed from seawater by organic matter in sediments. However, such correlations are not found in the Ramah Group sediments. Black shales of the Ramah Group contain 1.7-2.8 wt% organic C, but are extremely depleted in sigma Fe (<1 wt% as FeO), S (<0.3 wt%), U (approximately l ppm), Mo (<5 ppm), Ni (<2 ppm), and Co (approximately 0 ppm). This lack of correlation, however, does not imply that the approximately 1.9 Ga atmosphere-ocean system was anoxic. Depletion of these elements from the Ramah Group sediments may have occurred during diagenesis.

Major and Trace Element Geochemistry and Os Isotopic Compositions of Komatiites From Dundonald Beach, Abitibi Greenstone Belt, Canada

NASA Astrophysics Data System (ADS)

Gangopadhyay, A.; Walker, R. J.; Sproule, R. A.; Lesher, C.

2003-12-01

We have examined the major and trace elements, and Os isotopic compositions of a suite of cumulate and spinifex textured komatiitic rocks from the Dundonald Beach area, part of the ˜2.7 Ga Abitibi greenstone Belt, Ontario, Canada. This suite of rocks forms a series from peridotitic komatiites (MgO ˜ 42 wt.% on a volatile-free basis) to komatiitic basalts (MgO ˜8 wt.%). Based on major element oxide ratios (e.g. Al2O3/TiO2 ˜21-26 and CaO/Al2O3 typically <= 1) and unfractionated HREE characteristics (e.g. (Gd/Yb)N ˜0.9-1.1), these rocks are similar to the spatially associated Al-undepleted komatiites from Alexo and Munro Townships. Also, these rocks are strongly LREE-depleted ((La/Sm)N = 0.41-0.67; (Ce/Yb)N = 0.41-0.70)) and have variable total REE (4-22 ppm). A strong negative correlation between Mg# and total REEs suggests that the REE patterns of these rocks are primary features of their mantle source. The Re-Os isotope results for whole-rock komatiites and chromite separates from a single flow yield a model 3 isochron age of 2606 +/- 55 Ma. This age is slightly younger ( ˜50 Ma) compared to the U-Pb zircon ages of the associated volcanics reported from the presumed extension of the same Kidd-Munro assemblage in Alexo and Munro Townships. The initial 187Os/188Os ratio (0.1090 +/- 0.0019) obtained from the regression is essentially chondritic (γ Os(T) = -0.2 +/- 1.7). The peridotitic komatiites have the highest Os concentrations and low 187Re/188Os ratios (up to ˜4.2 ppb and < 0.5, respectively) among the whole rocks, whereas the komatiitic basalts have relatively low Os concentrations ( ˜0.3 ppb) and high 187Re/188Os ratios ( ˜3.1-11.9). For these komatiites, Os was compatible with the mantle residue (DOsmantle-melt ˜7.6), whereas Re was moderately incompatible (DRe ˜0.6), typical of most komatiitic magmas. The absence of a strong correlation between Os and Ni concentrations in the whole-rocks suggests that the distribution of Os in these rocks is not primarily controlled by fractionation of olivine. The apparent DReol+chmt/liq. ( ˜0.7), on the other hand, suggests that Re was moderately incompatible in olivine and/or chromite during the differentiation of komatiitic magmas. A chondritic initial Os isotopic composition for the mantle source for these komatiites is consistent with that previously reported for the komatiites from Alexo and Munro Townships. Our Os isotopic results for Dundonald komatiites, combined with those reported for Alexo and Pyke Hill komatiites, therefore, suggest that a major portion of the ˜2.7 Ga mantle source for the komatiites in the Abitibi greenstone belt was dominated by Os with chondritic isotopic compositions. Also, the LREE-depleted, yet chondritic Os isotopic composition for the mantle source of these komatiites is indistinguishable from the projected chondritic composition of the contemporaneous depleted convective upper mantle.

Watson: A new link in the IIE iron chain

NASA Technical Reports Server (NTRS)

Olsen, Edward; Davis, Andrew; Clarke, Roy S., Jr.; Schultz, Ludolf; Weber, Hartwig W.; Clayton, Robert; Mayeda, Toshiko; Jarosewich, Eugene; Sylvester, Paul; Grossman, Lawrence

1994-01-01

Watson, which was found in 1972 in South Australia, contains the largest single silicate rock mass seen in any known iron meteorite. A comprehensive study has been completed on this unusual meteorite: petrography, metallography, analyses of the silicate inclusion (whole rock chemical analysis, INAA, RNAA, noble gases, and oxygen isotope analysis) and mineral compositions (by electron microprobe and ion microprobe). The whole rock has a composition of an H-chondrite minus the normal H-group metal and troilite content. The oxygen isotope composition is that of the silicates in the IIE iron meteorites and lies along an oxygen isotope fractionation line with the H-group chondrites. Trace elements in the metal confirm Watson is a new IIE iron. Whole rock Watson silicate shows an enrichment in K and P (each approximately 2X H-chondrites). The silicate inclusion has a highly equilibrated igneous (peridotite-like) texture with olivine largely poikilitic within low-Ca pyroxene: olivine (Fa20), opx (Fs17Wo3), capx (Fs9Wo14)(with very fine exsolution lamellae), antiperthite feldspar (An1-3Or5) with less than 1 micron exsolution lamellae (An1-3Or greater than 40), shocked feldspar with altered stoichiometry, minor whitlockite (also a poorly characterized interstitial phosphate-rich phase) and chromite, and only traces of metal and troilite. The individual silicate minerals have normal chondritic REE patterns, but whitlockite has a remarkable REE pattern. It is very enriched in light REE (La is 720X C1, and Lu is 90X C1, as opposed to usual chonditic values of approximately 300X and 100-150X, respectively) with a negative Eu anomaly. The enrichment of whole rock K is expressed both in an unusually high mean modal Or content of the feldspar, Or13, and in the presence of antiperthite.

Determining the physical and chemical processes behind four caldera-forming eruptions in rapid succession in the San Juan caldera cluster, Colorado, USA

NASA Astrophysics Data System (ADS)

Curry, A. C.; Caricchi, L.; Lipman, P. W.

2017-12-01

A primary goal of volcanology is to understand the frequency and magnitude of large, explosive volcanic eruptions to mitigate their impact on society. Recent studies show that the average magma flux and the time between magma injections into a given magmatic-volcanic system fundamentally control the frequency and magnitude of volcanic eruptions, yet these parameters are unknown for many volcanic regions on Earth. We focus on major and trace element chemistry of individual phases and whole-rock samples, initial zircon ID-TIMS analyses, and zircon SIMS oxygen isotope analyses of four caldera-forming ignimbrites from the San Juan caldera cluster in the Southern Rocky Mountain volcanic field, Colorado, to determine the physical and chemical processes leading to large eruptions. We collected outflow samples along stratigraphy of the three caldera-forming ignimbrites of the San Luis caldera complex: the Rat Creek Tuff ( 150 km3), Cebolla Creek Tuff ( 250 km3), and Nelson Mountain Tuff (>500 km3); and we collected samples of both outflow and intracaldera facies of the Snowshoe Mountain Tuff (>500 km3), which formed the Creede caldera. Single-crystal sanidine 40Ar/39Ar ages show that these large eruptions occurred in rapid succession between 26.91 ± 0.02 Ma (Rat Creek Tuff) and 26.87 ± 0.02 Ma (Snowshoe Mountain Tuff), providing an opportunity to investigate the temporal evolution of magmatic systems feeding large, explosive volcanic eruptions. Major and trace element analyses show that the first and last eruption of the San Luis caldera complex (Rat Creek Tuff and Nelson Mountain Tuff) are rhyolitic to dacitic ignimbrites, whereas the Cebolla Creek Tuff and Snowshoe Mountain Tuff are crystal-rich, dacitic ignimbrites. Trace elements show enrichment in light rare-earth elements (LREEs) over heavy rare-earth elements (HREEs), and whereas the trace element patterns are similar for each caldera cycle, trace element values for each ignimbrite show variability in HREE concentrations. This variability indicates that these large eruptions sampled a magmatic system with some degree of internal heterogeneity. These results have implications for the chemical and physical processes, such as magmatic flux and injection periodicity, leading to the formation of large magmatic systems prior to large, explosive eruptions.

Development of continental lithospheric mantle as reflected in the chemistry of the Mesozoic Appalachian Tholeiites, U.S.A.

NASA Astrophysics Data System (ADS)

Pegram, William J.

1990-03-01

Geochemical analyses of dikes, sills, and volcanic rocks of the Mesozoic Appalachian Tholeiite (MAT) Province of the easternmost United States provide evidence that continental tholeiites are derived from continental lithospheric mantle sources that are genetically and geochronologically related to the overlying continental crust. Nineteen olivine tholeiites and sixteen quartz tholeiites from the length of this province, associated in space and time with the last opening of the Atlantic, display significant isotopic heterogeneity: initial ɛ Nd = +3.8 to -5.7; initial 87Sr/ 86Sr= 0.7044-0.7072; 206Pb/ 204Pb= 17.49-19.14; 207Pb/ 204Pb= 15.55-15.65; 208Pb/ 204Pb= 37.24-39.11. In Pb sbnd Pb space, the MAT define a linear array displaced above the field for MORB and thus resemble oceanic basalts with DUPAL Pb isotopic traits. A regression of this array yields a secondary Pb sbnd Pb isochron age of ≈ 1000 Ma (μ 1 = 8.26), similar to Sm/Nd isochrons from the southern half of the province and to the radiometric age of the Grenville crust underlying easternmost North America. The MAT exhibit significant trace element ratio heterogeneity (e.g., Sm/Nd= 0.226-0.327) and have trace element traits similar to convergent margin magmas [e.g., depletions of Nb and Ti relative to the rare earth elements on normalized trace element incompatibility diagrams, Ba/Nb ratios (19-75) that are significantly greater than those of MORB, and low TiO 2 (0.39-0.69%)]. Geochemical and geological considerations very strongly suggest that the MAT were not significantly contaminated during ascent through the continental crust. Further, isotope and trace element variations are not consistent with the involvement of contemporaneous MORB or OIB components. Rather, the materials that control the MAT incompatible element chemistry were derived from subcontinental lithospheric mantle. Thus: (1) the MAT/arc magma trace element similarities; (2) the Pb sbnd Pb and Sm/Nd isochron ages; and (3) the need for a method of introducing an ancient (> 2-3 Ga) Pb component into subcontinental mantle that cannot be much older than 1 Ga leads to a model whereby the MAT were generated by the melting of sediment-contaminated arc mantle that was incorporated into the continental lithosphere during arc activity preceding the Grenville Orogeny (≈ 1000 Ma).

Water quality, sediment quality, and stream-channel classification of Rock Creek, Washington, D.C., 1999-2000

USGS Publications Warehouse

Anderson, Anita L.; Miller, Cherie V.; Olsen, Lisa D.; Doheny, Edward J.; Phelan, Daniel J.

2002-01-01

Rock Creek Park is within the National Capital Region in Washington, D.C., and is maintained by the National Park Service. Part of Montgomery County, Maryland, and part of the District of Columbia drain into Rock Creek, which is a tributary of the Potomac River. Water quality in Rock Creek is important to biotic life in and near the creek, and in the Potomac River Basin and the Chesapeake Bay. The water quality of the Rock Creek Basin has been affected by continued urban and agricultural growth and development. The U.S. Geological Survey, in cooperation with the National Park Service, investigated water quality and sediment quality in Rock Creek over a 2-year period (1998?2000), and performed a stream-channel classification to determine the distribution of bottom sediment in Rock Creek. This report presents and evaluates water quality and bottom sediment in Rock Creek for water years 1999 (October 1, 1998 to September 30, 1999) and 2000 (October 1, 1999 to September 30, 2000). A synoptic surface-water assessment was conducted at five stations from June 23 to June 25, 1999, a temporal surface-water assessment was conducted at one station from February 18, 1999 to September 26, 2000, and bed-sediment samples were collected and assessed from three stations from August 17 to August 19, 1999. The synoptic surface-water assessment included pesticides (parent compounds and selected transformation products), field parameters, nutrients, and major ions. The temporal surface-water assessment included pesticides (parent compounds and selected transformation products) and field parameters. The bed-sediment assessment included trace elements and organic compounds (including low- and high-molecular weight polycyclic aromatic hydrocarbons, poly-chlorinated biphenyls, pesticides, and phthalates). Some, but not all, of the pesticides known to be used in the area were included in the synoptic water-quality assessment, the temporal water-quality assessment, and the bed-sediment assessment. In addition to the water-quality and sediment-quality assessments, a Rosgen stream-channel classification was performed on a 900-foot-long segment of Rock Creek. In the synoptic water-quality assessment, two pesticides were found to be above published criteria for the protection of aquatic life. In the temporal water-quality assessment, four pesticides were found to be above published criteria for the protection of aquatic life. In the bed-sediment assessment, 8 trace elements, 14 polycyclic aromatic hydrocarbons, 6 pesticides, and 1 phthalate compound were found to be above published criteria for the protection of aquatic life. In the Rosgen classification, a comparison to a previous classification for this segment showed an increase in sands and other fine-grained sediments in the creek bed.

Element Mass Balance in Soils : the Mount Cameroon Case

NASA Astrophysics Data System (ADS)

Dia, A.; Chauvel, C.; Bulourde, M.

2002-12-01

Mount Cameroon is an active volcano located in Central Africa. Its location in a tropical climate area leads to abundant vegetation and intense weathering conditions that favor rapid alteration. Soils develop rapidly on the flanks of the volcano. We measured major and trace element contents as well as Pb, Nd and Sr isotopic compositions in three soil sections developed on basaltic tuffaceous units. Each section comprises 2-3 units, the upper portions of which are altered to soil (Andepts). The starting material is pyroclastic alkali basalt characterized by marked enrichment in trace elements. To determine the element flux during soil formation, two corrections have to be performed: (1) the parental rock composition has to be determined and (2) addition of Saharan dust as evidenced by [1] has to be corrected for. The starting rock composition is constrained using the Al/Fe vs C.I.A. relationship and the uppermost part of each soil is corrected for its eolian dust contribution (*10%). The budget for each element can then be estimated in the soils. Calculations are performed relative to an `immobile' element whose concentration is assumed to be unchanged during soil formation. We chose Th as a reference because its behavior during magmatic processes is similar to those of U, Rb, Ba, Cs and K which are known to be mobile during weathering processes. Results of the element budget calculations show that: alkali and alkaline earth elements are leached out of the soils (~ 50%). Silica losses (~ 30%) are also clear in all samples. For the other elements, systematic differences exist between bottom and top parts of each soil. The uppermost levels display significant changes Ni, U, Pb, P, Ni and Co contents. These mobilities are most probably related to hydrolysis of primary magmatic minerals triggered by the biological activity. Since the three studied sections correspond to the superposition of several soils where new tephra cover an older soil to be the basis of the formation of a new and younger soil, the element mass balance depends both on the paleoclimate conditions that prevailed during exposure to surface conditions, and on the duration of the exposure to air before the soil was covered by a new eruption. [1] Chauvel C., Dia A and Bulourde M., GCA, Vol 66, 14A, p A132, 2002.

Trace elements in tourmalines from massive sulfide deposits and tourmalinites: Geochemical controls and exploration applications

USGS Publications Warehouse

Griffin, W.L.; Slack, J.F.; Ramsden, A.R.; Win, T.T.; Ryan, C.G.

1996-01-01

Trace element contents of tourmalines from massive sulfide deposits and tourmalinites have been determined in situ by proton microprobe; >390 analyses were acquired from 32 polished thin sections. Concentrations of trace elements in the tourmalines vary widely, from <40 to 3,770 ppm Mn, <4 to 1,800 ppm Ni, <2 to 1,430 ppm Cu, <9 to 4,160 ppm Zn, 3 to 305 ppm Ga, <6 to 1,345 ppm Sr, <10 to 745 ppm Sn, <49 to 510 ppm Ba, and <3 to 4,115 ppm Pb. Individual grains and growth zones are relatively homogeneous, suggesting that these trace elements are contained within the crystal structure of the tourmaline, and are not present in inclusions. The highest base metal contents are in ore-related tourmaline samples from Kidd Creek (Ontario), Broken Hill (Australia), and Sazare (Japan). Tourmaline data from these and many other massive sulfide deposits cluster by sample and display broadly linear trends on Zn vs. Fe plots, suggesting chemical control by temperature and hydrothermal and/or metamorphic fluid-mineral equilibria. Significant Ni occurs only in samples from the Kidd Creek Cu-Zn-Pb-Ag deposit, which is associated with a large footwall ultramafic body. An overall antithetic relationship between Zn and Ni probably reflects fluid source controls. Mn is correlated with Fe in tourmalines from barren associations, and possibly in some tourmalines associated with sulfide vein deposits. Sn increases systematically with Fe content irrespective of association; the highest values are found in schorls from granites. Other trace elements are generally uncorrelated with major element concentrations (e.g., Sr-Ca). Base metal proportions in the tourmalines show systematic patterns on ternary Cu-Pb-Zn diagrams that correlate well with the major commodity metals in the associated massive sulfide deposits. For example, data for tourmalines from Cu-Zn deposits (e.g., Ming mine, Newfoundland) fall mainly on the Cu-Zn join, whereas those from Pb-Zn deposits (e.g., Broken Hill, Australia) plot on the Pb-Zn join; no data fall on the Cu-Pb join, consistent with the lack of this metal association in massive sulfide deposits. The systematic relationship between base metal proportions in the tourmalines and the metallogeny of the host massive sulfide deposits indicates that the analyzed tourmalines retain a strong chemical signature of their original hydrothermal formation, in spite of variable metamorphic recrystallization. Such trace element patterns in massive sulfide tourmalines may be useful in mineral exploration, specifically for the evaluation of tourmaline concentrations in rocks, soils, and stream sediments.

Petrogenesis of the Alaskan-type mafic-ultramafic complex in the Makkah quadrangle, western Arabian Shield, Saudi Arabia

NASA Astrophysics Data System (ADS)

Habtoor, Abdelmonem; Ahmed, Ahmed Hassan; Harbi, Hesham

2016-10-01

The Makkah quadrangle is a part of the Jeddah terrane in the Precambrian basement, Western Arabian Shield of Saudi Arabia. Gabal Taftafan mafic-ultramafic complex lies within the central part of the Makkah quadrangle. The Taftafan mafic-ultramafic complex is a well-differentiated rock association which comprises of dunite core, hornblende- and plagioclase-bearing peridotites, troctolite, clinopyroxenite and marginal gabbro, in a distinctive zonal structure. The bulk-rock geochemistry of the Taftafan mafic-ultramafic rocks is characterized by a tholeiitic/sub-alkaline affinity with high Mg in the ultramafic core (0.84) and is systematically decreased towards the marginal gabbro (0.60). The patterns of trace elements show enrichment in the fluid-mobile elements (Sr, Ba) and a pronounced negative Nb anomaly which reflect a hydrous parental magma generated in a subduction tectonic setting. The mafic-ultramafic rocks of the Taftafan complex have low total rare earth elements (REE) displaying sub-parallel patterns leading to the assumption that these rocks are comagmatic and are formed by fractional crystallization from a common magma type. The platinum-group elements (PGE) content of all rock types in the Taftafan complex is very low, with ∑ PPGE > ∑ IPGE; displaying slightly positive slopes of the PGE distribution patterns. The chemistry of ferromagnesian minerals is characterized by a high forsterite (Fo) olivine with wide range (Fo91-67), from ultramafic core to the marginal gabbro, Ca-rich diopsidic clinopyroxene, and calcic hornblende. Orthopyroxene is almost absent from all rock types, or very rare when present. Hornblende and Ca-plagioclase possess the longest crystallization history since they are present in almost all rock types of the complex. Spinels in the dunite and hornblende-bearing peridotite core show homogeneous composition with intermediate Cr# (0.53-0.67). Plagioclase-bearing peridotite and troctolite have two exsolved types of spinel; Al-rich and Fe-rich varieties. All spinel varieties in the mafic-ultramafic rocks have high Fe3 + and TiO2 contents. The estimated melt composition in equilibrium with Gabal Taftafan complex is mostly similar to that of the SSZ boninitic magmas. The Taftafan mafic-ultramafic rocks show many similarities with the Alaskan-type mafic-ultramafic complexes, including the internal zonal lithology, bulk rock geochemistry, and mineral chemistry. Thus, it is neither related to a fragment of ophiolite sequence nor to the stratiform mafic-ultramafic intrusion. The location of the Taftafan complex along a major fracture zone parallel to the suture between Jeddah and Asir terranes in addition to the aforementioned striking similarities to the Alaskan-type complexes, suggests a formation in subduction-related setting from a common hydrous mafic magma.

Characterisation of bed sediments and suspension of the river Po (Italy) during normal and high flow conditions.

PubMed

Davide, Vignati; Pardos, Michel; Diserens, Jérôme; Ugazio, Giancarlo; Thomas, Richard; Dominik, Janusz

2003-07-01

Grain-size distribution, major elements, nutrients and trace metals were determined in bed sediments and suspension collected at 10 representative sites along the river Po under normal and high flow conditions. Grain-size distribution and major element composition of suspension highlighted the presence of two distinct particle populations in the upper-middle Po (coarser particles, lower carbonate content) and in the lower Po (finer particles, higher carbonate content). This change partly reflects the geological differences between the two parts of the basin, and also the presence of a hydroelectric power plant at Isola Serafini (Piacenza). With respect to environmental quality issues, bed sediments and suspension provide similar results. A moderate nutrient pollution is found in all but the uppermost parts of the river basin, while the most significant inputs of trace metals appear to originate from the urban areas of Turin and Milan. Calculation of sediment enrichment factors identifies Cd, Cu, Hg and Zn as the most impacted elements by human activities. On the other hand, the high levels of Ni and Cr throughout the river seem to derive mainly from the presence of basic rocks in the upper and middle parts of the basin. Both nutrient and trace metal particulate concentrations substantially decrease under high flow conditions possibly due to "flushing" of contaminated bed sediments and resuspension of coarser material. Under normal flow conditions, water hydrochemistry and concentrations of some elements (As, Ca, Cr, Cu, K, Mg, Mn, Na, Ni, and Pb) in the dissolved phase (<0.45 microm) were also determined. Calculation of trace metals partition coefficients shows that the relative importance of the particulate and water phases varies in response to water hydrochemistry and suspended solid content, but that most elements achieve a conditional equilibrium in the lower stretches of the river Po. These results are the first of this kind reported for the whole river course and highlight the factors and mechanisms controlling the origin, mobility and fate of nutrients and trace metals in the river Po.

Pollution evaluation of total and acid-leachable trace elements in surface sediments of Hooghly River Estuary and Sundarban Mangrove Wetland (India).

PubMed

Mondal, Priyanka; Reichelt-Brushett, Amanda J; Jonathan, M P; Sujitha, S B; Sarkar, Santosh Kumar

2018-02-01

The present work investigated the spatial distribution and ecological risk assessment of total and mild acid-leachable trace elements in surface sediments (top 0-10 cm; grain size ≤ 63 μm) along the Hooghly (Ganges) River Estuary and Sundarban Mangrove Wetland, India. The trace elements, analyzed by ICPMS, showed wide range of variations with the following descending order (mean values expressed in milligrams per kilogram): Fe (25,050 ± 4918) > Al (16,992 ± 4172) > Mn (517 ± 102) > Zn (53 ± 18) > Cu (33 ± 11) > Cr (29 ± 7) > Ni (27 ± 6) > Pb (14 ± 3) > As (5 ± 1) > Se (0.37 ± 0.10) > Cd (0.17 ± 0.13) > Ag (0.16 ± 0.19) > Hg (0.05 ± 0.10). In the acid-leachable fraction, Cd (92%) is dominated followed by Pb (81%), Mn (77%), Cu (70%), and Se (58%) indicating their high mobility, imposing negative impact on the adjacent benthos. The sediment pollution indices (both enrichment factor and contamination factor) suggested severe pollution by Ag at the sampling site Sajnekhali, a wildlife sanctuary in Sundarban. The mean probable effect level quotient indicated that surface sediments in the vicinity of the studied region have 21% probability of toxicity to biota. The result of multivariate analyses affirms lithogenic sources (e.g., weathering parent rocks, dry deposition) for As, Pb, Cr, Cu, and Ni, whereas Cd and Hg originated from anthropogenic activities (such as urban and industrial activities). Both human-induced stresses and natural processes controlled trace element accumulation and distribution in the estuarine system, and remedial measures are required to mitigate the potential impacts of these hazardous trace elements.

Late Permian to Early Oligocene granitic magmatism of the Phan Si Pan uplift area, NW Vietnam: their relationship to Phanerozoic crustal evolution of Southwest China

NASA Astrophysics Data System (ADS)

Pham, T. T.; Shellnutt, G.

2015-12-01

The Phan Si Pan uplift area of NW Vietnam is a part of the Archean to Paleoproterozoic Yangtze Block, Southwest China. This area is of particular interest because it experienced a number of Phanerozoic crustal building events including the Emeishan Large Igneous Province, the India-Eurasia collision and Ailaoshan - Red River Fault displacement. In the Phan Si Pan uplift area, there are at least three different geochronological complexes, including: (1) Late Permian, (2) Eocene and (3) Early Oligocene. (1) The Late Permian silicic rocks are alkali ferroan A1-type granitic rocks with U/Pb ages of 251 ± 3 to 254 ± 3 Ma. The Late Permian silicic rocks of Phan Si Pan uplift area intrude the upper to middle crust and are considered to be part of the ELIP that was displaced during the India-Eurasian collision along the Ailaoshan-Red River Fault shear zone and adjacent structures (i.e. Song Da zone). Previous studies suggest the Late Permian granitic rocks were derived by fractional crystallization of high - Ti basaltic magma. (2) The Eocene rocks are alkali ferroan A1-type granites (U/Pb ages 49 ± 0.9 Ma) and are spatially associated with the Late Permian granitic rocks. The trace element ratios of this granite are similar to the Late Permian rocks (Th/Nb=0.2, Th/Ta = 2.5, Nb/U = 24, Nb/La =1.2, Sr/Y=1). The origin of the Eocene granite is uncertain but it is possible that it formed by fractional crystallization of a mafic magma during a period of extension within the Yangtze Block around the time of the India-Eurasia collision. (3) The Early Oligocene granite is characterized as a peraluminous within-plate granite with U/Pb ages of 31.3 ± 0.4 to 34 ± 1 Ma. The Early Oligocene granite has trace element ratios (Th/Nb = 2.1, Th/Ta = 22.6, Nb/U = 4.4, Nb/La = 0.4, Sr/Y = 60.4) similar to crust melts. The high Sr/Y ratio (Sr/Y = 20 - 205) indicates a lower crust source that was garnet-bearing. The Phan Si Pan uplift was neither a subduction zone nor an arc environment, during the Early Oligocene thus the granite may have formed as the result of partial melting lower crust by heat from an unknown within plate hot zone (mantle plume?).

The volcanic acidification of glacial Lake Caviahue, Province of Neuquen, Argentina

NASA Astrophysics Data System (ADS)

Varekamp, Johan C.

2008-12-01

Lake Caviahue (northern Patagonia, Argentina) is a large glacial lake acidified by volcanic fluids from Copahue volcano. The lake and the feeding rivers were sampled annually from 1997 till early 2006, including the eruptive period of 2000. Lake Caviahue waters evolved over time, with the most concentrated waters in 2000 during the eruptive period, followed by gradual dilution that was interrupted by renewed acidification in 2003-2004. Inversion of the lake water data and application of a dynamic non-steady state model for the lake provides our best quantitative estimates for the variation in element fluxes over the 9-year period. The model flux results agree well with most of the measured fluxes. The Copahue hydrothermal system had gently declining element fluxes between 1997 and mid-1999, although the lake was still becoming more concentrated. About 2-3 months before the 2000 eruption, element fluxes increased strongly, but the hydrothermal fluxes almost shutoff directly after the main eruptive events. The fluxes of several elements recovered post-2001, with an increase in element fluxes in 2003-2004; the lake became more dilute between 2004 and 2006. The intrusion of new magma into the hydrothermal system just prior to the 2000 eruption led to enhanced water rock interaction, with higher concentrations of the rock forming elements in the fluids, and the hot spring flow rate increased as a result of the higher pressure in the reservoir. The fluids became saturated in alunite and jarosite, and they were already saturated with anhydrite. Precipitation of these minerals possibly led to a decreased permeability of the hydrothermal reservoir, leading to the strongly reduced element fluxes just after the eruption. In addition, K, Al and S were retained in the newly precipitated minerals as well, further diminishing their export. The acidification in 2003-2004 may have resulted from a new small intrusion of magma or resulted from seismic activity that created new permeability and fresh rock surfaces for water rock interaction. The volcano is a significant source of toxic trace elements such as F, As, B and Li as well as a nutrient (P) for the local watershed. Monitoring of the hydrothermal fluids in the river that drains Copahue, especially the S/Cl, Mg/Cl and Mg/K values as well as the magnitude of the element fluxes would provide the best information for eruption forecasting for this volcano.

Trace Element Characteristics of the New Shergottite LEW88516

NASA Astrophysics Data System (ADS)

Wadhwa, M.; Crozaz, G.

1992-07-01

LEW88516, a meteorite collected in Antarctica, has recently been identified as a shergottite (Mason and Satterwhite, 1991). The shergottites belong to a group of unique achondritic meteorites, the SNCs, for which Mars has been suggested as the parent body. From preliminary petrologic and geochemical studies, it appears that LEW88516 is closely related to the shergottite ALHA77005. Like ALHA77005, LEW88516 is composed of two distinct lithologies; one consists of large (mm-sized) pyroxenes poikilitically enclosing olivine crystals, and the other is represented by interstitial areas that contain small pyroxenes, olivine, maskelynite, whitlockite, and opaques (Lindstrom et al., 1992). Besides mineralogy and texture, whole rock chemical characteristics of these two shergottites also appear to be strikingly similar (Lindstrom et al., 1992; Boynton et al., 1992). We measured REE and other selected trace elements in individual mineral phases present in LEW88516, and compared the results with similar data obtained for ALHA77005 by Lundberg et al. (1990). Analyses were made on a thin section of LEW88516 with an ion microprobe; trace elements concentrations were measured in poikilitic and interstitial pyroxenes (augites and pigeonites), maskelynite, whitlockite, and glass. The total REE inventory of LEW88516 is dominated by whitlockite, although this mineral, as in ALHA77005, is present in only small modal abundance. Maskelynite in LEW88516 is characterized by a positive Eu anomaly that is approximately twice as large as that present in the maskelynite in ALHA77005, although the rest of the REE are present in lower abundances. The homogeneous, crystallite-free glass in LEW88516 is slightly enriched relative to LEW88516 bulk rock REE abundances, and has a REE pattern that is parallel to the ALHA77005 whole rock REE pattern. Pyroxenes in LEW88516 are zoned in their trace element concentrations, as are the pyroxenes in ALHA77005. Elemental abundances (e.g., REE, Y, Ti, Zr, Cr, V) for the two meteorites follow the same trends. The compositional range of the pyroxenes in LEW88516, however, appears to be smaller than that for pyroxenes in ALHA77005. The data confirm that indeed LEW88516 and ALHA77005 are petrogenetically related. As discussed in Lundberg et al. (1990) for ALHA77005, the intercumulus melt in LEW88516, once trapped in the cumulus pile, crystallized as a closed system. The question as to whether the two meteorites are paired or not cannot be resolved until the terrestrial and cosmic ray exposure ages of LEW88516 are determined. The differences in the trace element compositional ranges of the pyroxenes, as well as in the REE abundances in the other minerals (particularly maskelynite) in LEW88516 and ALHA77005 could simply be an artifact of sampling during analysis (particularly in the case of the pyroxenes) and/or heterogeneity within a sample, and therefore do not preclude that the two meteorites are paired. On the other hand, it is possible that the two meteorites represent distinct falls. In either case, it is evident that they were generated by the same/similar igneous processes on their parent body. References: Boynton W.V., Hill D.H., and Kring D.A. (1992) Lunar Planet. Sci. (abstract) 23, 147-148. Lindstrom M.M., Mittlefehldt D.W., Treiman A.H., Wentworth S.J., Gooding J.L., Monis R.V., Keller L.P., and McKay G. (1992) Lunar Planet. Sci. (abstract) 23, 783-784. Lundberg L.L., Crozaz G., and McSween H.Y., Jr. (1990) Geochim. Cosmochim. Acta. 54, 2535-2547. Mason B. and Satterwhite C. (1991) Antarctic Meteorite Newsletter 14:2, 19.

Origin of enormous trace metal enrichments in weathering mantles of Jurassic carbonates: evidence from Sr, Nd and Pb isotopes

NASA Astrophysics Data System (ADS)

Hissler, C.; Stille, P.; Juilleret, J.; Iffly, J.; Perrone, T.; Morvan, G.

2013-12-01

Weathering mantels are widespread worldwide and include lateritic, sandy and kaolinite-rich saprolites and residuals of partially dissolved carbonate rocks. These old regolith systems have a complex history of formation and may present a polycyclic evolution due to successive geological and pedogenetic processes that affected the profile. Until now, only few studies highlighted the unusual content of associated trace elements in this type of weathering mantle. For instance, these enrichments can represent about five times the content of the underlying Bajocian to Oxfordian limestone/marl complexes, which have been relatively poorly studied compared to weathering mantle developed on magmatic bedrocks. Up to now, neither soil, nor saprolite formation has to our knowledge been geochemically elucidated. Therefore, the aim of this study was to examine more closely the soil forming dynamics and the relationship of the chemical soil composition to potential sources (saprolite, Bajocian silty marls and limestones, atmospheric particles deposition...). Of special interest has also been the origin of trace metals and the processes causing their enrichments. Especially Rare Earth Element (REE) distribution patterns and Sr, Nd and Pb isotope ratios are particularly well suited to identify trace element migration, to recognize origin and mixing processes and, in addition, to decipher possible anthropogenic and/or "natural" atmosphere-derived contributions to the soil. Moreover, leaching experiments shall help to identify mobile phases in the soil system. This may inform on the stability of trace elements and especially on their behaviour in these Fe-enriched carbonate systems. Trace metal migration and enrichments were studied on a cambisol developing on an underlying Jurassic limestone. The base is strongly enriched among others in rare earth elements (ΣREE: 2640ppm) or redox-sensitive elements such as Fe (44 wt.%), V (920ppm), Cr (700ppm), Zn (550ppm), As (260ppm), Co (45ppm) and Cd (2.4ppm). The underlying limestone and marl show, compared to average world carbonates, enrichments in the same elements and trace element distribution patterns similar to the soil suggesting their close genetic relationship. Pb, Sr and Nd isotope data allow to identify three principal components in the soil: a silicate-rich phase at close to the surface, a strongly trace metal enriched component at the bottom of the soil profile and an anthropogenic, atmosphere- derived component detected in the soil leachates. The isotopic mixing curves defined by the soil samples point to the close genetic connection between upper and lowermost soil horizons. The Nd isotopic composition of the leachates of all soil horizons are in contrast to the untreated soil and residual soil samples very homogeneous suggesting that the leachable phases of the upper and lower soil horizons are genetically connected. The downward migration of the trace metals is stopped at this soil level due to the presence of important secondary calcite precipitations, smectite and Fe-oxide accumulations. Mass balance calculations indicate that the enrichment process goes along with a volume increase relative to the bottom soil horizons.

Geochemistry of serpentinites in subduction zones: A review

NASA Astrophysics Data System (ADS)

Deschamps, Fabien; Godard, Marguerite; Guillot, Stéphane; Hattori, Kéiko

2013-04-01

Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zones geodynamics. Their presence and effective role in this environment is acknowledged notably by geophysical, geochemical and field observations of (paleo-) subduction zones. In this context, with the increasing amount of studies concerning serpentinites in subduction environments, a huge geochemical database was created. Here, we present a review of the geochemistry of serpentinites, based on the compilation of ~ 900 geochemical analyses of abyssal, mantle wedge and subducted serpentinites. The aim was to better understand the geochemical evolution of these rocks during their subduction history as well as their impact in the global geochemical cycle. When studying serpentinites, it is often a challenge to determine the nature of the protolith and their geological history before serpentinisation. The present-day (increasing) geochemical database for serpentinites indicates little to no mobility of incompatible elements at the scale of the hand-sample in most serpentinized peridotites. Thus, Rare Earth Elements (REE) distribution can be used to identify the initial protolith for abyssal and mantle wedge serpentinites, as well as magmatic processes such as melt/rock interactions taking place before serpentinisation. In the case of subducted serpentinites, the interpretation of trace element data is more difficult due to secondary enrichments independent of the nature of the protolith, notably in (L)REE. We propose that these enrichments reflect complex interactions probably not related to serpentinisation itself, but mostly to fluid/rock or sediment/rock interactions within the subduction channel, as well as intrinsic feature of the mantle protolith which could derive from the continental lithosphere exhumed at the ocean-continent transition. Additionally, during the last ten years, numerous studies have been carried out, notably using in situ approaches, to better constrain the geochemical budget of fluid-mobile elements (FME; e.g. B, Li, Cl, As, Sb, U, Th, Sr) stored in serpentinites and serpentine phases. These elements are good markers of the fluid/rock interactions taking place during serpentinisation. Today, the control of serpentinites on the behaviour of these elements, from their incorporation to their gradually release during subduction, is better understood. Serpentinites must be considered as a component of the FME budget in subduction zones and their role, notably on arc magmas composition, is undoubtedly underestimated presently in the global geochemical cycle.

The parent magma of xenoliths in shergottite EETA79001: Bulk and trace element composition inferred from magmatic inclusions

NASA Technical Reports Server (NTRS)

Treiman, Allan H.; Lindstrom, David J.; Martinez, Rene R.

1994-01-01

The SNC meteorites are samples of the Martian crust, so inferences about their origins and parent magmas are of wide planetologic significance. The EETA79001 shergottite, a basalt, contains xenoliths of pyroxene-olivine cumulate rocks which are possibly related to the ALHA77005 and LEW88516 SNC lherzolites. Olivines in the xenoliths contain magmatic inclusions, relics of magma trapped within the growing crystals. The magmatic inclusions allow a parent magma composition to be retrieved; it is similar to the composition reconstructed from xenolith pyroxenes by element distribution coefficients. The xenolith parent magma is similar but not identical to parent magmas for the shergottite lherzolites.

Surface chemistry and mineralogy. [of planet Mars

NASA Technical Reports Server (NTRS)

Banin, A.; Clark, B. C.; Waenke, H.

1992-01-01

The accumulated knowledge on the chemistry and mineralogy of Martian surface materials is reviewed. Pertinent information obtained by direct analyses of the soil on Mars by the Viking Landers, by remote sensing of Mars from flyby and orbiting spacecraft, by telescopic observations from earth, and through detailed analyses of the SNC meteorites presumed to be Martian rocks are summarized and analyzed. A compositional model for Mars soil, giving selected average elemental concentrations of major and trace elements, is suggested. It is proposed that the fine surface materials on Mars are a multicomponent mixture of weathered and nonweathered minerals. Smectite clays, silicate mineraloids similar to palagonite, and scapolite are suggested as possible major candidate components among the weathered minerals.

Partitioning of radionuclides and trace elements in phosphogypsum and its source materials based on sequential extraction methods.

PubMed

Santos, A J G; Mazzilli, B P; Fávaro, D I T; Silva, P S C

2006-01-01

Phosphogypsum is a waste produced by the phosphate fertilizer industry. Although phosphogypsum is mainly calcium sulphate dihydrate, it contains elevated levels of impurities, which originate from the source phosphate rock used in the phosphoric acid production. Among these impurities, radionuclides from 238U and 232Th decay series are of most concern due to their radiotoxicity. Other elements, such as rare earth elements (REE) and Ba are also enriched in the phosphogypsum. The bioavailability of radionuclides (226Ra, 210Pb and 232Th), rare earth elements and Ba to the surrounding aquatic system was evaluated by the application of sequential leaching of the phosphogypsum samples from the Brazilian phosphoric acid producers. The sequential extraction results show that most of the radium and lead are located in the "iron oxide" (non-CaSO4) fraction, and that only 13-18% of these radionuclides are distributed in the most labile fraction. Th, REE and Ba were found predominantly in the residual phase, which corresponds to a small fraction of the phosphate rock or monazite that did not react and to insoluble compounds such as sulphates, phosphates and silicates. It can be concluded that although all these elements are enriched in the phosphogypsum samples they are not associated with CaSO4 itself and therefore do not represent a threat to the surrounding aquatic environment.

Trace elements in native and transplanted Fontinalis antipyretica and Platyhypnidium riparioides from rivers polluted by uranium mining.

PubMed

Kosior, Grzegorz; Steinnes, Eiliv; Samecka-Cymerman, Aleksandra; Lierhagen, Syverin; Kolon, Krzysztof; Dołhańczuk-Śródka, Agnieszka; Ziembik, Zbigniew

2017-03-01

The past uranium/polymetallic mining activities in the Sudety (SW Poland) left abandoned mines, pits, and dumps of waste rocks with trace elements and radionuclides which may erode or leach out and create a potential risk for the aquatic ecosystem, among others. In the present work four rivers affected by effluents from such mines were selected to evaluate the application of aquatic mosses for the bioindication of 56 elements. Naturally growing F. antipyretica and P. riparioides were compared with transplanted samples of the same species. The results demonstrate serious pollution of the examined rivers, especially with As, Ba, Fe, Mn, Pb, Ti, U and Zn, reaching extremely high concentrations in native moss samples. In the most polluted rivers native F. antipyretica and P. riparioides samples showed significantly higher concentrations of As, Ba, Cu, Fe, La, Nd, Ni, Pb, U and Zn than corresponding transplanted samples, whereas at less polluted sites a reverse situation was sometimes observed. Transplanted moss moved from clean to extremely polluted rivers probably protects itself against the accumulation of toxic elements by reducing their uptake. Selection of native or transplanted F. antipyretica and P. riparioides depended on the pollution load. Copyright © 2016. Published by Elsevier Ltd.

Crustal Anatexis by Upwelling Mantle Melts in the N.Atlantic Igneous Province: the Isle of Rum, NW Scotland.

NASA Astrophysics Data System (ADS)

Hertogen, J.; Meyer, R.; Nicoll, G.; Troll, V. R.; Ellam, R. M.; Emeleus, C. H.

2008-12-01

Crustal anatexis is a common process in the rift-to-drift evolution during continental breakup and the formation of Volcanic Rifted Margins (VRM) systems. 'Early felsic-later mafic' volcanic rock associations on the Continent Ocean Boundary (COB) of the N.Atlantic Ocean have been sampled by ODP drilling on the SE Greenland margin and the the Vøring Plateau (Norwegian Sea). Such associations also occur further inland in the British Paleocene Igneous Province, such as on the Isle of Rum (e.g., Troll et al., Contrib. Min. Petrol., 2004, 147, p.722). Sr and Nd isotope and trace element geochemistry show that the Rum rhyodacites are the products of melting of Lewisian amphibolite gneiss. There are no indications of a melt contribution from Lewisian granulite gneiss. The amphibolite gneiss parent rock had experienced an ancient Cs and Rb loss, possibly during a Caledonian event, which caused 87Sr/86Sr heterogeneity in the crustal source of silicic melts. The dacites and early gabbros of Rum are mixtures of crustal melts and primary mantle melts. Rare Earth Element modelling shows that late stage picritic melts on Rum are close analogues for the parent melts of the Rum Layered Suite, and for the mantle melts that caused crustal anatexis of the Lewisian gneiss. These primary mantle melts have close affinities to MORB whose trace element content varies from slightly depleted to slightly enriched. The 'early felsic-later mafic' volcanic associations from Rum, and from the now drowned seaward dipping wedges on the shelf of SE Greenland and on the Vøring Plateau show geochemical differences that result from variations in the regional crustal composition and the depth at which crustal anatexis took place.

Eocene to Oligocene volcanism in the Mariana fore-arc and crustal melting

NASA Astrophysics Data System (ADS)

Hartman, B.; Reagan, M.; Hickey-Vargas, R.; Hanan, B.; Blichert-Toft, J.

2003-04-01

Recently collected volcanic rocks from the Mariana fore-arc islands of Saipan and Rota provide evidence that the genesis of silicic magmas in the IBM system involves extensive crustal melting. Rhyolites from the island of Saipan are unusually high in silica for an oceanic island arc setting. They also are unique in the Izu-Bonin-Mariana (IBM) system in that they erupted during the earliest stages of subduction (45--46 Ma), but have "mature arc" major element, trace element, and isotopic compositions. For example, the rhyolites have flat REE patterns and pronounced negative Nb anomalies. These trace element patterns are nearly identical to those Oligocene (36--32 Ma) "early arc" andesites and dacites on Saipan, Guam, and Rota. All of the aforementioned lavas also have similar 207Pb/204Pb and 208Pb/204Pb values that plot along a trend that stretches from West Philippine basin basalt compositions toward those Pacific siliceous sediments. In contrast, Eocene volcanic rocks from other locations in the IBM arc are basaltic to boninitic and have U-shaped REE patterns and small to nonexistent Nb anomalies. The Pb isotopic compositions of these samples are similar to Pacific basin volcanics and volcanogenic sediments. Mathematical modeling suggests that the Saipan rhyolites were most likely derived by partial melting of an arc-like amphibolite crust and not through crystal fractionation of a "protoarc" boninite series magma. The data and these modelings suggest that a piece of preexisting arc-like amphibolite crust was trapped in the Mariana fore-arc early in its evolution. The Saipan rhyolites were produced by melting this crust at relatively shallow depths.

Three types of element fluxes from metabasite into peridotite in analogue experiments: Insights into subduction-zone processes

NASA Astrophysics Data System (ADS)

Perchuk, A. L.; Yapaskurt, V. O.; Griffin, W. L.; Shur, M. Yu.; Gain, S. E. M.

2018-03-01

Piston-cylinder experiments with natural rocks and mineral separates were carried out at 750-900 °C and 2.9 GPa, conditions relevant to hot subduction zones, to study the mechanisms of metasomatic alteration of mantle-wedge rocks such as dunite and lherzolite, and the transfer of trace elements released from a carbonate-bearing amphibolite during its eclogitization. Element transfer from the slab to the mantle lithologies occurred in porous-, focused- and diffusive-flow regimes that remove melt and carbon, and partially water, from the metabasite layer. Porous flow is recorded by dissolution of clinopyroxene and growth of orthopyroxene ± garnet ± magnesite ± chlorite along grain boundaries in the peridotite layers, but is invisible in the metabasite layers. Porous flow of the same fluids/melts produces harzburgite mineralogy in both dunite and lherzolite. The transformation of lherzolite to harzburgite reflects breakdown of clinopyroxene in the lherzolite and diffusion of the liberated calcium into the metabasite layer, i.e. against the direction of major fluid/melt flow. Focused flow develops along the side walls of the capsules, producing a melt-free omphacite ± phengite ± quartz paragenesis in the metabasite, and melt segregations, separated from the host peridotite layers by newly-formed omphacite ± garnet ± phlogopite + orthopyroxene + magnesite. Diffusive flow leads to the formation of orthopyroxene ± magnesite ± garnet reaction zones at the metabasite-peridotite interface and some melt-peridotite interfaces. Melt segregations in the peridotite layers at 850-900 °C are rich in LREE and LILE, strongly depleted in Y and HREE, and have higher Sr/Y and La/Yb ratios than island arc andesites, dacites and rhyolites. These features, and negative anomalies in Nb-Ta and low Nb/Ta, resemble those of high-silica adakites and TTGs, but K2O is high compared to TTGs. Metasomatism in the dunite layer changes the REE patterns of dunite, recording chromatographic fractionation during porous melt flow. During metabasite-lherzolite interaction, the metabasite layer becomes mildly enriched in LREE; the lherzolite layer, in contrast, is generally depleted in LREE relative to the initial composition. This also indicates element transfer against the direction of fluid flow. Trace-element profiling reveals the development of Eu anomalies in the peridotite layers and the diffusion of many trace elements out of both layers toward the contact zone. The documented processes may be applicable to both Phanerozoic and Precambrian subduction zones.

Volume gain during shearing of the Whatley Mill Gneiss, Pine Mountain Basement massif, eastern Alabama--A trace element approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salpas, P.A.; Daniell, N.

1993-03-01

The Whatley Mill Gneiss is the most voluminous exposure of the Pine Mountain Basement massif in eastern Alabama. Its type lithology is a proto-mylonitic gneiss composed of K-spar augen, up to 5 cm in diameter, in a finer matrix of biotite, microcline, and quartz. Granulite-facies mineral assemblages in the Whatley Mill Gneiss have been completely retrograded to amphibolite- and greenschist-facies assemblages in response to deformation that produced shear zones paralleling the foliation of the gneiss. The augen gneiss and its associated mylonites are well-exposed in a creek bed in Chewacla State Park. At this location the mineralogy of the mylonitesmore » is dominated by quartz indicating that shearing was associated with influx of a silica-rich fluid. A detailed geochemical study of these rocks shows that the augen gneiss displays relatively little variation in its major and trace element compositions while the quartz-rich mylonites display wider ranges, are enriched in SiO[sub 2] and depleted in the REE and other incompatible trace elements relative to the augen gneiss. When standard composition/volume calculations are applied to the mylonites the results show (1) the bulk of all of the elements, including the REE, were immobile during shearing with the exceptions of Si and Al which were added; and, (2) volume changes calculated using the REE as immobile elements range from +70% to +350%. Though these volume changes seem excessive, they apply to meter-thick shear zones which may actually represent only a small fraction of the total volume of the augen gneiss. Consistent with previous interpretations of these shear zones, the calculated volume gains imply shearing during extension.« less

Geochemistry and origin of regional dolomites. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanson, G.N.; Meyers, W.J.

1995-05-01

The main goal of our research on dolomites has been to better understand the composition of the fluids and processes of the fluid-rock interaction responsible for the formation of massive dolostones occurring over regional scales within sedimentary sequences. Understanding the timing of dolomitization, the fluids responsible for the dolomitization and the timing of the development of porosity has major economic ramifications in that dolomites are major oil reservoirs often having better reservoir properties than associated limestones. Our approach has been to apply trace element, major element, petrographic, crystallographic, stable isotope and radiogenic isotope systems to test models for the originsmore » of dolomites and to give information that may allow us to develop new models. Fluid compositions and processes are evaluated through the use of numerical models which we have developed showing the simultaneous evolution of the trace element and isotope systems during dolomitization. Our research has included the application of B, O, C, Sr, Nd and Pb isotope systematics and the trace elements Mn, Fe St, rare earth elements, Rb, Ba, U, Th, Pb, Zn, Na, Cl, F and SO{sub 4}{sup 2-}. Analyses are possible on individual cements or dolomite types using micro-sampling or microprobe techniques. The microprobe techniques used include synchrotron X-ray microprobe analysis at Brookhaven National Laboratory or electron microprobe at Stony Brook. Lack of a modern analogue for ancient massive dolostones has limited the application of the uniformitarian concept to developing models for the ancient regional dolostones. In addition it has not been possible to synthesize dolomite in the laboratory under conditions similar to the sedimentary or diagenetic possible environments in which the dolomites must have formed.« less

Lu-Hf total-rock age for the Amîtsoq gneisses, West Greenland

USGS Publications Warehouse

Pettingill, H.S.; Patchett, P.J.

1981-01-01

Lu-Hf total-rock data for the Amîtsoq gneisses of West Greenland yield an age of 3.55±0.22Gy(2σ), based on the decay constant λ176Lu=1.96×10−11y−1, and an initial176Hf/177Hf ratio of 0.280482±33. The result is in good agreement with Rb-Sr total-rock and U-Pb zircon ages. In spite of severe metamorphism of the area at 2.9 Gy, zircons from two of the samples have remained on the total-rock line, and define points close to the initial Hf ratio. The initial176Hf/177Hf lies close to a chondritic Hf isotopic evolution curve from 4.55 Gy to present. This is consistent with the igneous precursors to the Amîtsoq gneisses having been derived from the mantle at or shortly before 3.6 Gy. Anomalous relationships between Hf concentration and the176Lu/177Hf ratio may suggest that trace element abundances in the Amîtsoq gneisses are partly controlled by processes related to metamorphism.

Provenance of the Walash-Naopurdan back-arc-arc clastic sequences in the Iraqi Zagros Suture Zone

NASA Astrophysics Data System (ADS)

Ali, Sarmad A.; Sleabi, Rajaa S.; Talabani, Mohammad J. A.; Jones, Brian G.

2017-01-01

Marine clastic rocks occurring in the Walash and Naopurdan Groups in the Hasanbag and Qalander areas, Kurdistan region, Iraqi Zagros Suture Zone, are lithic arenites with high proportions of volcanic rock fragments. Geochemical classification of the Eocene Walash and Oligocene Naopurdan clastic rocks indicates that they were mainly derived from associated sub-alkaline basalt and andesitic basalt in back-arc and island arc tectonic settings. Major and trace element geochemical data reveal that the Naopurdan samples are chemically less mature than the Walash samples and both were subjected to moderate weathering. The seaway in the southern Neotethys Ocean was shallow during both Eocene and Oligocene permitting mixing of sediment from the volcanic arcs with sediment derived from the Arabian continental margin. The Walash and Naopurdan clastic rocks enhance an earlier tectonic model of the Zagros Suture Zone with their deposition occurring during the Eocene Walash calc-alkaline back-arc magmatism and Early Oligocene Naopurdan island arc magmatism in the final stages of intra-oceanic subduction before the Miocene closure and obduction of the Neotethys basin.