Redistribution of Iron and Titanium in High-Pressure Ultramafic Rocks

NASA Astrophysics Data System (ADS)

Crossley, Rosalind J.; Evans, Katy A.; Reddy, Steven M.; Lester, Gregory W.

2017-11-01

The redox state of iron in high-pressure serpentinites, which host a significant proportion of Fe3+ in subduction zones, can be used to provide an insight into iron cycling and constrain the composition of subduction zone fluids. In this study, we use oxide and silicate mineral textures, interpretation of mineral parageneses, mineral composition data, and whole rock geochemistry of high-pressure retrogressed ultramafic rocks from the Zermatt-Saas Zone to constrain the distribution of iron and titanium, and iron oxidation state. These data provide an insight on the oxidation state and composition of fluids at depth in subduction zones. Oxide minerals host the bulk of iron, particularly Fe3+. The increase in mode of magnetite and observation of magnetite within antigorite veins in the investigated ultramafic samples during initial retrogression is most consistent with oxidation of existing iron within the samples during the infiltration of an oxidizing fluid since it is difficult to reconcile addition of Fe3+ with the known limited solubility of this species. However, high Ti contents are not typical of serpentinites and also cannot be accounted for by simple mixing of a depleted mantle protolith with the nearby Allalin gabbro. Titanium-rich phases coincide with prograde metamorphism and initial exhumation, implying the early seafloor and/or prograde addition and late mobilization of Ti. If Ti addition has occurred, then the introduction of Fe3+, also generally considered to be immobile, cannot be disregarded. We explore possible transport vectors for Ti and Fe through mineral texture analysis.

Evolution of strength and physical properties of carbonate and ultramafic rocks under hydrothermal conditions

NASA Astrophysics Data System (ADS)

Lisabeth, Harrison Paul

Interaction of rocks with fluids can significantly change mineral assemblage and structure. This so-called hydrothermal alteration is ubiquitous in the Earth's crust. Though the behavior of hydrothermally altered rocks can have planet-scale consequences, such as facilitating oceanic spreading along slow ridge segments and recycling volatiles into the mantle at subduction zones, the mechanisms involved in the hydrothermal alteration are often microscopic. Fluid-rock interactions take place where the fluid and rock meet. Fluid distribution, flux rate and reactive surface area control the efficiency and extent of hydrothermal alteration. Fluid-rock interactions, such as dissolution, precipitation and fluid mediated fracture and frictional sliding lead to changes in porosity and pore structure that feed back into the hydraulic and mechanical behavior of the bulk rock. Examining the nature of this highly coupled system involves coordinating observations of the mineralogy and structure of naturally altered rocks and laboratory investigation of the fine scale mechanisms of transformation under controlled conditions. In this study, I focus on fluid-rock interactions involving two common lithologies, carbonates and ultramafics, in order to elucidate the coupling between mechanical, hydraulic and chemical processes in these rocks. I perform constant strain-rate triaxial deformation and constant-stress creep tests on several suites of samples while monitoring the evolution of sample strain, permeability and physical properties. Subsequent microstructures are analyzed using optical and scanning electron microscopy. This work yields laboratory-based constraints on the extent and mechanisms of water weakening in carbonates and carbonation reactions in ultramafic rocks. I find that inundation with pore fluid thereby reducing permeability. This effect is sensitive to pore fluid saturation with respect to calcium carbonate. Fluid inundation weakens dunites as well. The addition of

Magnetic and gravity anomalies in the Sierra del Padre and Sierra del Tala, San Luis Province, Argentina: evidence of buried mafic ultramafic rocks

NASA Astrophysics Data System (ADS)

Kostadinoff, José; Alfredo Bjerg, Ernesto; Gregori, Daniel; Delpino, Sergio; Dimieri, Luis; Raniolo, Ariel; Mogessie, Aberra; Hoinkes, Georg; Hauzenberger, Christoph; Felfernig, Anja

2001-07-01

This paper presents the results of a geophysical study of the southern portion of the Sierra Grande de San Luis, San Luis Province, Argentina. A 26 mGal amplitude Bouguer anomaly (Charlone anomaly), measuring 40 km long by 7 km wide, between Sierra de los Padres and Zanjitas reflects the presence of high-density rocks located at approximately 2000 m depth. Geophysical models based on more than 300 gravimetric, magnetometric, and geological field measurements and observations suggest that the mafic-ultramafic belt of Sierra Grande de San Luis continues south of San Luis. The low magnitude of the terrestrial magnetic field anomalies indicates that these mafic-ultramafic rocks do not carry a base metal sulfides (BMS) mineralization. The Charlone gravimetric anomaly is generated by a belt of mafic- ultramafic rocks whose amplitude is comparable with that responsible for the Virorco-Las Aguilas gravimetric anomaly.

Field geology, geochronology and geochemistry of mafic-ultramafic rocks from Alxa, China: Implications for Late Permian accretionary tectonics in the southern Altaids

NASA Astrophysics Data System (ADS)

Jianyun, Feng; Wenjiao, Xiao

2013-04-01

The termination of orogenesis for the southern Altaids has been controversial. Systematical investigations of field geology, geochronology and geochemistry on mafic-ultramafic rocks from the northern Alxa of the southern Altaids were conducted to address the termination controversy. The newly discriminated mafic-ultramafic rocks belt is located at Bijiertai, Honggueryulin, and Qinggele areas, stretching from west to east for about 100 km in length. All of the three rock associations contact tectonically with the adjacent metamorphic and deformed Precambrian rocks as tectonic blocks or lenses, and are composed of peridotite, pyroxenite, gabbro, and serpentinite, most of which have subjected to pronounced alteration, i.e., serpentinization and chloritization. Geochemically, the rocks are characterized by a uniform trend of compositional distribution, e.g., with low SiO2-contents (42.51-52.21 wt.%) and alkalinity (Na2O+K2O) (0.01-5.45 wt.%, mostly less than 0.8 wt.%), and enriched in MgO (7.37-43.36 wt.%), with Mg# = 52.75-91.87. As the rocks have had strong alteration and have a wide range of loss-on-ignition (LOI: 0.44-14.07 wt.%), the rocks may be subjected to considerable alteration by either sea-water or metamorphic fluid. The REE and trace element patterns for the rocks show a relatively fractionated trend with LILE enrichment and HFSE depletion, similar to that of T-MORB between N-MORB and E-MORB, indicating that the parental melt resulted from the partial melting of oceanic lithospheric mantle overprinted by fluid alteration of island-arc subsequently. The ultramafic rocks are relics derived from the magma after large degree of partial melting of the oceanic lithospheric mantle with overprinted by island-arc processes under the influence of mid-ocean-ridge magmatism. LA - ICP MS U - Pb zircon ages of gabbros from the three spots are 274 ± 3 Ma (MSWD = 0.35), 306 ± 3 Ma (MSWD = 0.49), 262 ± 5 Ma (MSWD = 1.2), respectively, representing the formation ages of

Field geology, geochronology and geochemistry of mafic-ultramafic rocks from Alxa, China: Implications for Late Permian accretionary tectonics in the southern Altaids

NASA Astrophysics Data System (ADS)

Feng, Jianyun; Xiao, Wenjiao; Windley, Brian; Han, Chunming; Wan, Bo; Zhang, Ji'en; Ao, Songjian; Zhang, Zhiyong; Lin, Lina

2013-12-01

The time of termination of orogenesis for the southern Altaids has been controversial. Systematic investigations of field geology, geochronology and geochemistry on newly discriminated mafic-ultramafic rocks from northern Alxa in the southern Altaids were conducted to address the termination problem. The mafic-ultramafic rocks are located in the Bijiertai, Honggueryulin, and Qinggele areas, stretching from west to east for about 100 km. All rocks occur high-grade gneisses as tectonic lenses that are composed of peridotite, pyroxenite, gabbro, and serpentinite, most of which have undergone pronounced alteration, i.e., serpentinization and chloritization. Geochemically, the rocks are characterized by uniform compositional trends, i.e., with low SiO2-contents (42.51-52.21 wt.%) and alkalinity (Na2O + K2O) (0.01-5.45 wt.%, mostly less than 0.8 wt.%), and enrichments in MgO (7.37-43.36 wt.%), with Mg# = 52.75-91.87. As the rocks have been strongly altered and have a wide range of loss-on-ignition (LOI: 0.44-14.07 wt.%) values, they may have been subjected to considerable alteration by either seawater or metamorphic fluids. The REE and trace element patterns show a relatively fractionated trend with LILE enrichment and HFSE depletion, similar to that of T-MORB between N-MORB and E-MORB, indicating that the parental melt resulted from the partial melting of oceanic lithospheric mantle overprinted by fluid alteration of island-arc origin. The ultramafic rocks are relics derived from the magma after a large degree of partial melting of oceanic lithospheric mantle with superposed island arc processes under the influence of mid-ocean-ridge magmatism. LA-ICP MS U-Pb zircon ages of gabbros from three spots are 274 ± 3 Ma (MSWD = 0.35), 306 ± 3 Ma (MSWD = 0.49), 262 ± 5 Ma (MSWD = 1.2), respectively, representing the formation ages of the mafic-ultramafic rocks. Therefore, considering other previously published data, we suggest that the mafic-ultramafic rocks were products of

Thermodynamic constraints on hydrogen generation during serpentinization of ultramafic rocks

NASA Astrophysics Data System (ADS)

McCollom, Thomas M.; Bach, Wolfgang

2009-02-01

In recent years, serpentinized ultramafic rocks have received considerable attention as a source of H 2 for hydrogen-based microbial communities and as a potential environment for the abiotic synthesis of methane and other hydrocarbons within the Earth's crust. Both of these processes rely on the development of strongly reducing conditions and the generation of H 2 during serpentinization, which principally results from reaction of water with ferrous iron-rich minerals contained in ultramafic rocks. In this report, numerical models are used to investigate the potential influence of chemical thermodynamics on H 2 production during serpentinization. The results suggest that thermodynamic constraints on mineral stability and on the distribution of Fe among mineral alteration products as a function of temperature are likely to be major factors controlling the extent of H 2 production. At high temperatures (>˜315 °C), rates of serpentinization reactions are fast, but H 2 concentrations may be limited by the attainment of stable thermodynamic equilibrium between olivine and the aqueous fluid. Conversely, at temperatures below ˜150 °C, H 2 generation is severely limited both by slow reaction kinetics and partitioning of Fe(II) into brucite. At 35 MPa, peak temperatures for H 2 production occur at 200-315 °C, indicating that the most strongly reducing conditions will be attained during alteration within this temperature range. Fluids interacting with peridotite in this temperature range are likely to be the most productive sources of H 2 for biology, and should also produce the most favorable environments for abiotic organic synthesis. The results also suggest that thermodynamic constraints on Fe distribution among mineral alteration products have significant implications for the timing of magnetization of the ocean crust, and for the occurrence of native metal alloys and other trace minerals during serpentinization.

Microbial Fe biomineralization in mafic and ultramafic rocks

NASA Astrophysics Data System (ADS)

Templeton, A. S.; Mayhew, L.; McCollom, T.; Trainor, T.

2011-12-01

Fluid-filled microfractures within mafic and ultramafic rocks, such as basalt and peridotite, may be one of the most ubiquitous microbial habitats on the modern and ancient earth. In seafloor and subseafloor systems, one of the dominant energy sources is the oxidation of Fe by numerous potential oxidants under aerobic to anaerobic conditions. In particular, the oxidation of Fe may be directly catalyzed by microbial organisms, or result in the production of molecular hydrogen which can then fuel diverse lithotrophic metabolisms. However, it remains challenging to identify the dominant metabolic activities and unravel the microscale biogeochemical processes occuring within such rock-hosted systems. We are investigating the mechanisms of solid-state Fe-oxidation and biomineralization in basalt, olivine, pyroxenes and basalts, in the presence and absence of microbial organisms that can thrive across the full stability range of water. In this talk we will present synchrotron-based x-ray scattering and spectroscopic analyses of Fe speciation within secondary minerals formed during microbially-mediated vs. abiotic water-rock interactions. Determining the valence state and mineralogy of Fe-bearing phases is critical for determining the water-rock reaction pathways and identifying potential biominerals that may form; therefore, we will highlight new approaches for identifying key Fe transformations within complex geological media. In addition, many of our experimental studies involve the growth of lithotrophic biofilms on well-characterized mineral surfaces in order to determine the chemistry of the microbe-mineral interface during progressive electron-transfer reactions. By coupling x-ray spectroscopy, x-ray diffraction, and electron-microscopy measurements, we will also contrast the evolution of mineral surfaces that undergo microbially-mediated oxidative alteration against minerals surfaces that produce H2 to sustain anaerobic microbial communities.

Ultramafic rocks of the western Idaho suture zone: Asbestos Peak and Misery Ridge

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

Godchaux, M.M.; Bonnichsen, B.

1993-04-01

The Western Idaho Ultramafic Belt extends northward from the town of Weiser to the northern end of Dworshak Reservoir; in its northern portion most of the ultramafic bodies are localized along the suture zone where the Mesozoic oceanic accreted terranes meet the continental craton. Of the twenty bodies investigated, all are small, all are in fault contact with their metavolcanic and metasedimentary host rocks, all have been metamorphosed, and all display deformational fabrics in at least some portion of the outcrop area, suggesting that deformation continued after peak metamorphism. The degree of metamorphism ranges from incipient serpentinization to attainment ofmore » equilibrium in the upper amphibolite facies. Some bodies have been intruded by granitic dikes or pegmatite veins after emplacement, and have locally undergone contact metasomatism. Two particularly complex bodies, Asbestos Peak and Misery Ridge, were chosen for detailed petrographic and chemical study. Asbestos Peak is composed mostly of decussate anthophyllite-talc rock containing isolated patches of harzburgite protolith, and has blackwall border zones. Misery Ridge is composed mostly of coarse-grained sheared tremolite-talc schist without remnant protolith, and lacks true blackwall zones. Both bodies exhibit an unusual and enigmatic hornblende-poikiloblastic garnet-green spinel-skeletal ilmenite assemblage, present in some places as well-defined border zones and in other places as cross-cutting bodies.« less

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

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

-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.

Role of mafic and ultramafic rocks in drinking water quality and its potential health risk assessment, Northern Pakistan.

PubMed

Begum, Shaheen; Shah, Mohammad Tahir; Muhammad, Said; Khan, Sardar

2015-12-01

This study investigates the drinking water (groundwater and surface water) quality and potential risk assessment along mafic and ultramafic rocks in the Swat district of Khyber Pakhtunkhwa Provence, Pakistan. For this purpose, 82 groundwater and 33 surface water samples were collected and analyzed for physico-chemical parameters. Results showed that the majority of the physico-chemical parameters were found to be within the drinking water guidelines set by the World Health Organization. However, major cationic metals such as magnesium (Mg), and trace metals (TM) including iron (Fe), manganese (Mn), nickel (Ni), chromium (Cr) and cobalt (Co) showed exceeded concentrations in 13%, 4%, 2%, 20%, 20% and 55% of water samples, respectively. Health risk assessment revealed that the non-carcinogenic effects or hazard quotient values through the oral ingestion pathway of water consumption for the TM (viz., Fe, Cr and Mn) were found to be greater than 1, could result in chronic risk to the exposed population. Results of statistical analyses revealed that mafic and ultramafic rocks are the main sources of metal contamination in drinking water, especially Ni and Cr. Both Ni and Cr have toxic health effects and therefore this study suggests that contaminated sites should be avoided or treated for drinking and domestic purposes.

Bacterially Induced Weathering of Ultramafic Rock and Its Implications for Phytoextraction

PubMed Central

Kidd, Petra; Kuffner, Melanie; Prieto-Fernández, Ángeles; Hann, Stephan; Monterroso, Carmela; Sessitsch, Angela; Wenzel, Walter; Puschenreiter, Markus

2013-01-01

The bioavailability of metals in soil is often cited as a limiting factor of phytoextraction (or phytomining). Bacterial metabolites, such as organic acids, siderophores, or biosurfactants, have been shown to mobilize metals, and their use to improve metal extraction has been proposed. In this study, the weathering capacities of, and Ni mobilization by, bacterial strains were evaluated. Minimal medium containing ground ultramafic rock was inoculated with either of two Arthrobacter strains: LA44 (indole acetic acid [IAA] producer) or SBA82 (siderophore producer, PO4 solubilizer, and IAA producer). Trace elements and organic compounds were determined in aliquots taken at different time intervals after inoculation. Trace metal fractionation was carried out on the remaining rock at the end of the experiment. The results suggest that the strains act upon different mineral phases. LA44 is a more efficient Ni mobilizer, apparently solubilizing Ni associated with Mn oxides, and this appeared to be related to oxalate production. SBA82 also leads to release of Ni and Mn, albeit to a much lower extent. In this case, the concurrent mobilization of Fe and Si indicates preferential weathering of Fe oxides and serpentine minerals, possibly related to the siderophore production capacity of the strain. The same bacterial strains were tested in a soil-plant system: the Ni hyperaccumulator Alyssum serpyllifolium subsp. malacitanum was grown in ultramafic soil in a rhizobox system and inoculated with each bacterial strain. At harvest, biomass production and shoot Ni concentrations were higher in plants from inoculated pots than from noninoculated pots. Ni yield was significantly enhanced in plants inoculated with LA44. These results suggest that Ni-mobilizing inoculants could be useful for improving Ni uptake by hyperaccumulator plants. PMID:23793627

Geochemical behavior of ultramafic waste rocks with carbon sequestration potential: a case study of the Dumont Nickel Project, Amos, Québec.

PubMed

Kandji, El Hadji Babacar; Plante, Benoit; Bussière, Bruno; Beaudoin, Georges; Dupont, Pierre-Philippe

2017-04-01

The geochemical behavior of ultramafic waste rocks and the effect of carbon sequestration by these waste rocks on the water drainage quality were investigated using laboratory-scale kinetic column tests on samples from the Dumont Nickel Project (RNC Minerals, QC, Canada). The test results demonstrated that atmospheric CO 2 dissolution induced the weathering of serpentine and brucite within the ultramafic rocks, generating high concentrations of Mg and HCO 3 - with pH values ranging between 9 and 10 in the leachates that promote the precipitation of secondary Mg carbonates. These alkaline pH values appear to have prevented the mobilization of many metals; Fe, Ni, Cu, and Zn were found at negligible concentrations in the leachates. Posttesting characterization using chemical analyses, diffuse reflectance infrared Fourier transform (DRIFT), and scanning electron microscope (SEM) observations confirmed the precipitation of secondary hydrated Mg carbonates as predicted by thermodynamic calculations. The formation of secondary Mg carbonates induced cementation of the waste particles, resulting in the development of a hardpan.

Experimental evidence for chemo-mechanical coupling during carbon mineralization in ultramafic rocks

NASA Astrophysics Data System (ADS)

Lisabeth, H. P.; Zhu, W.; Kelemen, P. B.; Ilgen, A.

2017-09-01

Storing carbon dioxide in the subsurface as carbonate minerals has the benefit of long-term stability and immobility. Ultramafic rock formations have been suggested as a potential reservoir for this type of storage due to the availability of cations to react with dissolved carbon dioxide and the fast reaction rates associated with minerals common in ultramafic formations; however, the rapid reactions have the potential to couple with the mechanical and hydraulic behavior of the rocks and little is known about the extent and mechanisms of this coupling. In this study, we argue that the dissolution of primary minerals and the precipitation of secondary minerals along pre-existing fractures in samples lead to reductions in both the apparent Young's modulus and shear strength of aggregates, accompanied by reduction in permeability. Hydrostatic and triaxial deformation experiments were run on dunite samples saturated with de-ionized water and carbon dioxide-rich solutions while stress, strain, permeability and pore fluid chemistry were monitored. Sample microstructures were examined after reaction and deformation using scanning electron microscopy (SEM). The results show that channelized dissolution and carbonate mineral precipitation in the samples saturated with carbon dioxide-rich solutions modify the structure of grain boundaries, leading to the observed reductions in stiffness, strength and permeability. A geochemical model was run to help interpret fluid chemical data, and we find that the apparent reaction rates in our experiments are faster than rates calculated from powder reactors, suggesting mechanically enhanced reaction rates. In conclusion, we find that chemo-mechanical coupling during carbon mineralization in dunites leads to substantial modification of mechanical and hydraulic behavior that needs to be accounted for in future modeling efforts of in situ carbon mineralization projects.

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.

Mineral potential for nickel, copper, platinum group elements(PGE), and chromium deposits hosted in ultramafic rocks in the Islamic Republic of Mauritania (phase V, deliverable 67): Chapter G in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Taylor, Cliff D.; Marsh, Erin; Anderson, Eric D.

2015-01-01

PRISM-I summary documents mention the presence of mafic-ultramafic igneous intrusive rocks in several areas of Mauritania and a number of chromium (Cr) and copper-nickel (Cu-Ni (±Co, Au)) occurrences associated with them. Permissive geologic settings generally include greenstone belts of any age, layered mafic-ultramafic and unlayered gabbro-anorthosite intrusive complexes in cratonic settings, ophiolite complexes, flood basalt provinces, and fluid-rich shear zones cutting accumulations of mafic-ultramafic rocks. Regions of Mauritania having these characteristics that are discussed in PRISM-I texts include the Mesoarchean greenstone belts of the TasiastTijirit terrane in the southwestern Rgueïbat Shield, two separate layered ultramafic complexes in the Amsaga Complex west of Atar, serpentinized metadunites in Mesoarchean rocks of the Rgueïbat Shield in the Zednes map sheet, several lateritized annular mafic-ultramafic complexes in the Paleoproterozoic northwestern portion of the Rgueïbat Shield, and the serpentinized ophiolitic segments of the Gorgol Noir Complex in the axial portion of the southern Mauritanides. Bureau de Recherches Géologiques et Minières (BRGM) work in the “Extreme Sud” zone also suggests that small copper occurrences associated with the extensive Jurassic microgabbroic intrusive rocks in the Taoudeni Basin of southeastern Mauritania could have potential for magmatic Cu-Ni (PGE, Co, Au) sulfide mineralization. Similarly, Jurassic mafic intrusive rocks in the northeastern Taoudeni Basin may be permissive. Known magmatic Cu-Ni deposits of these types in Mauritania are few in number and some uncertainty exists as to the nature of several of the more important ones.

Petrology and geochemistry of meta-ultramafic rocks in the Paleozoic Granjeno Schist, northeastern Mexico: Remnants of Pangaea ocean floor

NASA Astrophysics Data System (ADS)

Torres-Sánchez, Sonia Alejandra; Augustsson, Carita; Jenchen, Uwe; Rafael Barboza-Gudiño, J.; Alemán Gallardo, Eduardo; Ramírez Fernández, Juan Alonso; Torres-Sánchez, Darío; Abratis, Michael

2017-08-01

The Granjeno Schist is a meta-volcanosedimentary upper Paleozoic complex in northeastern Mexico. We suggest different tectonic settings for metamorphism of its serpentinite and talc-bearing rocks based on petrographic and geochemical compositions. According to the REE ratios (LaN/YbN = 0.51 -20.0 and LaN/SmN = 0.72-9.1) and the enrichment in the highly incompatible elements Cs (0.1 ppm), U (2.8 ppm), and Zr (60 ppm) as well as depletion in Ba (1 - 15 ppm), Sr (1 -184 ppm), Pb (0.1 -14 ppm), and Ce (0.1 -1.9 ppm) the rocks have mid-ocean ridge and subduction zones characteristics. The serpentinite contains Al-chromite, ferrian chromite and magnetite. The Al-chromite is characterized by Cr# of 0.48 to 0.55 suggesting a MORB origin, and Cr# of 0.93 to 1.00 for the ferrian chromite indicates a prograde metamorphism. We propose at least two serpentinization stages of lithospheric mantle for the ultramafic rock of the Granjeno Schist, (1) a first in an ocean-floor environment at sub-greenschist to greenschist facies conditions and (2) later a serpentinization phase related to the progressive replacement of spinel by ferrian chromite and magnetite at greenschist to low amphibolite facies conditions during regional metamorphism. The second serpentinization phase took place in an active continental margin during the Pennsylvanian. We propose that the origin of the ultramafic rocks is related to an obduction and accretional event at the western margin of Pangea.

Serpentinization and fluid-rock interaction in Jurassic mafic and ultramafic sea-floor: constraints from Ligurian ophiolite sequences

NASA Astrophysics Data System (ADS)

Vogel, Monica; Früh-Green, Gretchen L.; Boschi, Chiara; Schwarzenbach, Esther M.

2014-05-01

The Bracco-Levanto ophiolitic complex (Eastern Liguria) represents one of the largest and better-exposed ophiolitic successions in the Northern Apennines. It is considered to be a fragment of heterogeneous Jurassic lithosphere that records tectono-magmatic and alteration histories similar to those documented along the Mid-Atlantic Ridge, such as at the 15°20'N area and the Atlantis Massif at 30°N. Structural and petrological studies on these rocks provide constraints on metamorphic/deformation processes during formation and hydrothermal alteration of the Jurassic oceanic lithosphere. We present a petrological and geochemical study of deformation processes and fluid-rock interaction in the Bracco-Levanto ophiolitic complex and compare these to modern oceanic hydrothermal systems, such as the Lost City Hydrothermal Field hosted in ultramafic rocks on the Atlantis Massif. A focus is on investigating mass transfer and fluid flow paths during high and low temperature hydrothermal activity, and on processes leading to hydrothermal carbonate precipitation and the formation of ophicalcites, which are characteristic of the Bracco-Levanto sequences. Major element and mineral compositional data allow us to distinguish a multiphase history of alteration characterized by: (1) widespread SiO2 metasomatism during progressive serpentinization, and (2) multiple phases of veining and carbonate precipitation associated with circulation of seawater and high fluid-rock ratios in the shallow ultramafic-dominated portions of the Jurassic seafloor. We observe regional variations in MgO, SiO2 and Al2O3, suggesting Si-flux towards stratigraphically higher units. In general, the ophicalcites have higher Si, Al and Fe concentrations and lower Mg than the serpentinite basement rocks or serpentinites with minimal carbonate veins. Bulk rock trace element data and Sr isotope ratios indicate seawater reacting with rocks of more mafic composition, then channeled towards stratigraphically higher

Sr and Nd isotope composition of the metamorphic, sedimentary and ultramafic xenoliths of Lanzarote (Canary Islands): Implications for magma sources

NASA Astrophysics Data System (ADS)

Aparicio, Alfredo; Tassinari, Colombo C. G.; García, Roberto; Araña, Vicente

2010-01-01

The lavas produced by the Timanfaya eruption of 1730-1736 (Lanzarote, Canary Islands) contain a great many sedimentary and metamorphic (metasedimentary), and mafic and ultramafic plutonic xenoliths. Among the metamorphosed carbonate rocks (calc-silicate rocks [CSRs]) are monomineral rocks with forsterite or wollastonite, as well as rocks containing olivine ± orthopyroxene ± clinopyroxene ± plagioclase; their mineralogical compositions are identical to those of the mafic (gabbros) and ultramafic (dunite, wherlite and lherzolite) xenoliths. The 87Sr/ 86Sr (around 0.703) and 143Nd/ 144Nd (around 0.512) isotope ratios of the ultramafic and metasedimentary xenoliths are similar, while the 147Sm/ 144Nd ratios show crustal values (0.13-0.16) in the ultramafic xenoliths and mantle values (0.18-0.25) in some CSRs. The apparent isotopic anomaly of the metamorphic xenoliths can be explained in terms of the heat source (basaltic intrusion) inducing strong isotopic exchange ( 87Sr/ 86Sr and 143Nd/ 144Nd) between metasedimentary and basaltic rocks. Petrofabric analysis also showed a possible relationship between the ultramafic and metamorphic xenoliths.

The Wenquan ultramafic rocks in the Central East Kunlun Fault zone, Qinghai-Tibet Plateau—crustal relics of the Paleo-Tethys ocean

NASA Astrophysics Data System (ADS)

Jia, Lihui; Meng, Fancong; Feng, Huibin

2018-06-01

The Wenquan ultramafic rocks, located in the East Kunlun Orogenic belt in the northeastern part of the Qinghai-Tibet Plateau, consist of dunite, wehrlite, olivine-clinopyroxenite and clinopyroxenite, and exhibit cumulate textures. Olivine from dunite has high Fo (forsterite, 90.0-91.8 wt%) and NiO content (0.15-0.42 wt%). Cr-spinels from all of the rocks in this suite are characterized by high Cr# (100×[Cr/(Cr + Al)], 67-91), low Mg# (100×[Mg/(Mg + Fe2+)], 17-35) and low TiO2 contents (mostly < 0.5 wt%). Clinopyroxene displays high Mg# (92-98) and low TiO2 content (0.002-0.099 wt%), similar to those in ophiolitic cumulates. Geochemically, the Wenquan ultramafic rocks show enrichment of LILE, Sr, and Ba, and depletion of Nb and Th. High-Mg# (mostly > 80) and low-CaO (< 0.08 wt%) olivine, high-Cr# (up to 91) spinel, and low Ti contents of clinopyroxene and Cr-spinel indicate that the Wenquan cumulates were generated by high-degree partial melting of a depleted oceanic lithosphere mantle. The ultramafic intrusion most likely evolved from high-Mg basaltic magmas (Mg# = 77.5) that underwent fractional crystallization and crustal contamination. Zircon grains from clinopyroxenites yield a U-Pb weighted mean age of 331 ± 2 Ma, which is nearly coeval with the formation age of the A'nyemaqen ophiolites. The Wenquan Carboniferous ophiolites are confirmed to exist in the Central East Kunlun Fault zone, whereas previous studies have considered them to be the Proterozoic ophiolites. The Wenquan ophiolite might be a relict of the Paleotethyan ocean, indicating that there were two cycles of oceanic-continental evolution along the Central East Kunlun Fault zone.

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

Abundance and distribution of ultramafic microbreccia in Moses Rock Dike: Quantitative application of AIS data

NASA Technical Reports Server (NTRS)

Mustard, John F.; Pieters, Carle M.

1987-01-01

Moses Rock dike is a Tertiary diatreme containing serpentinized ultramafic microbreccia (SUM). Field evidence indicates the SUM was emplaced first followed by breccias derived from the Permian strata exposed in the walls of the diatreme and finally by complex breccias containing basement and mantle derived rocks. SUM is found primarily dispersed throughout the matrix of the diatreme. Moses Rock dike was examined with Airborne Imaging Spectrometer (AIS) to map the distribution and excess of SUM in the matrix and to better understand the nature of the eruption which formed this explosive volcanic feature. AIS data was calibrated by dividing the suite of AIS data by data from an internal standard area and then multiplying this relative reflectance data by the absolute bidirectional reflectance of a selected sample from the standard area which was measured in the lab. From the calibrated AIS data the minerals serpentine, gypsum, and illite as well as desert varnish and the lithologies SUM and other sandstones were identified. SUM distribution and abundance in the matrix of the diatreme were examined in detail and two distinct styles of SUM dispersion were observed. The two styles are discussed in detail.

Petrology and metamorphic evolution of ultramafic rocks and dolerite dykes of the Betic Ophiolitic Association (Mulhacén Complex, SE Spain): evidence of eo-Alpine subduction following an ocean-floor metasomatic process

NASA Astrophysics Data System (ADS)

Puga, E.; Nieto, J. M.; Díaz de Federico, A.; Bodinier, J. L.; Morten, L.

1999-10-01

The Betic Ophiolitic Association, cropping out within the Mulhacén Complex (Betic Cordilleras), is made up of numerous metre- to kilometre-sized lenses of mafic and/or ultramafic and meta-sedimentary rocks. Pre-Alpine oceanic metasomatism and metamorphism caused the first stage of serpentinization in the ultramafic sequence of this association, which is characterized by local clinopyroxene (Cpx) breakdown and Ca-depletion, and complementary rodingitization of the basic dykes intruded in them. Subsequent eo-Alpine orogenic metamorphism developed eclogite facies assemblages in ultramafic and basic lithotypes, which were partly retrograded in Ab-Ep-amphibolite facies conditions during a meso-Alpine event. The heterogeneous development of the oceanic metasomatism in the ultramafic rock-types led to the patchy development of highly serpentinized Ca-depleted domains, without gradual transition to the host, and less serpentinized, Cpx-bearing ultramafites, mainly lherzolitic in composition. The high-pressure eo-Alpine recrystallization of these ultramafites in subduction conditions originated secondary harzburgites in the Ca-depleted domains, consisting of a spinifex-like textured olivine+orthopyroxene paragenesis, and a diopside+Ti-clinohumite paragenesis in the enclosing lherzolitic rocks. During the meso-Alpine event, secondary harzburgites were partly transformed into talc+antigorite serpentinites, whereas the diopside and clinohumite-bearing residual meta-lherzolites were mainly transformed into Cpx-bearing serpentinites. Relics of mantle-derived colourless olivine may be present in the more or less serpentinized secondary harzburgites. These relics are overgrown by the eo-Alpine brown pseudo-spinifex olivine, which contains submicroscopic inclusions of chromite, ilmenite and occasional halite and sylvite, inherited from its parental oceanic serpentine. The same type of mantle-derived olivine relics is also preserved within the Cpx-bearing serpentinites, although it

Microscale mapping of alteration conditions and potential biosignatures in basaltic-ultramafic rocks on early Earth and beyond.

PubMed

Grosch, Eugene G; McLoughlin, Nicola; Lanari, Pierre; Erambert, Muriel; Vidal, Olivier

2014-03-01

Subseafloor environments preserved in Archean greenstone belts provide an analogue for investigating potential subsurface habitats on Mars. The c. 3.5-3.4 Ga pillow lava metabasalts of the mid-Archean Barberton greenstone belt, South Africa, have been argued to contain the earliest evidence for microbial subseafloor life. This includes candidate trace fossils in the form of titanite microtextures, and sulfur isotopic signatures of pyrite preserved in metabasaltic glass of the c. 3.472 Ga Hooggenoeg Formation. It has been contended that similar microtextures in altered martian basalts may represent potential extraterrestrial biosignatures of microbe-fluid-rock interaction. But despite numerous studies describing these putative early traces of life, a detailed metamorphic characterization of the microtextures and their host alteration conditions in the ancient pillow lava metabasites is lacking. Here, we present a new nondestructive technique with which to study the in situ metamorphic alteration conditions associated with potential biosignatures in mafic-ultramafic rocks of the Hooggenoeg Formation. Our approach combines quantitative microscale compositional mapping by electron microprobe with inverse thermodynamic modeling to derive low-temperature chlorite crystallization conditions. We found that the titanite microtextures formed under subgreenschist to greenschist facies conditions. Two chlorite temperature groups were identified in the maps surrounding the titanite microtextures and record peak metamorphic conditions at 315 ± 40°C (XFe3+(chlorite) = 25-34%) and lower-temperature chlorite veins/microdomains at T = 210 ± 40°C (lower XFe3+(chlorite) = 40-45%). These results provide the first metamorphic constraints in textural context on the Barberton titanite microtextures and thereby improve our understanding of the local preservation conditions of these potential biosignatures. We suggest that this approach may prove to be an important tool in future

Carbonation of Subduction Interface Ultramafic Rocks and Implications for Deep Carbon Cycling: Evidence from Hybrid Serpentinite-Marble in the Voltri Massif, Italy

NASA Astrophysics Data System (ADS)

Scambelluri, M.; Bebout, G. E.; Gilio, M.; Belmonte, D.; Campomenosi, N.; Crispini, L.

2015-12-01

Release of COH fluids from hydrous minerals and carbonates influences element recycling and magmatism at subduction zones. Contradictory interpretations exist regarding the retention/storage of C in subducting plates and in the forearc to subarc mantle. Multiple lines of evidence indicate mobility of C in forearcs; however, the magnitude of this loss is highly uncertain[1-5]. A poorly constrained fraction of the 40-115 Mt/y of C initially subducted is released into fluids (e.g., by decarbonation, carbonate dissolution), and 18-43 Mt/y is returned at arc volcanoes[2-5, refs. therein]. The imbalance could reflect subduction into the deeper mantle or forearc/subarc storage[4-7]. We examine the fate of C in slab/interface ultramafic rocks, and by analogy serpentinized mantle wedge, via study of fluid-rock evolution of marble and variably carbonated serpentinite (Ligurian Alps). Based on petrography, and major/trace element and C and O isotope compositions, we demonstrate that serpentinite dehydration at 2-2.5 GPa, 550°C released aqueous fluids triggering breakdown of dolomite in nearby marbles, thus releasing C into fluids. Carbonate + olivine veins document flow of COH fluids; interaction of these COH fluids with serpentinite led to formation of high-pressure carbonated ultramafic-rock domains, thus resulting in retention of C in some rocks at an ancient subduction interface. We stress that lithologically complex interfaces could contain sites of both C release and C addition, further confounding estimates of net C loss at forearc and subarc depths [cf 4,5]. Sites of C retention, also including carbonate veins and graphite as reduced carbonate[7], could influence the transfer of slab C to at least the depths beneath volcanic fronts. 1. Poli S et al. 2009 EPSL; 2. Ague and Nicolescu 2014 Nat Geosci; 3. Cook-Collars et al. 2014 Chem Geol; 4. Collins et al. 2015 Chem Geol; 5. Kelemen and Manning 2015 PNAS; 6. Sapienza et al. 2009 CMP; 7 Galvez et al. 2013 Nat Geosci

Linking magnetic fabric and cumulate texture in layered mafic-ultramafic intrusions (Invited)

NASA Astrophysics Data System (ADS)

O Driscoll, B.; Stevenson, C.; Magee, C.

2013-12-01

Research on the magnetic fabrics of igneous rocks, pioneered by Balsley and Buddington[1] and Khan[2], has greatly contributed to our understanding of magma dynamics in lava flows, sheet intrusions and plutons over the past five decades. However, considerably few magnetic fabric studies have focused on layered mafic-ultramafic intrusions, particularly ';lopolithic' intrusions, despite the fact that such rocks may preserve a large range of small-scale kinematic structures potentially related to important magma chamber processes. This may be partly due to the fact that mafic-ultramafic cumulates commonly exhibit visible planar fabrics (mineral lamination), as well as compositional layering, in contrast to the frequent absence of such features in granite bodies or fine-grained mafic lava flows. Indeed, debates in the 1970s and 1980s on the development of layering and mineral fabrics in mafic-ultramafic intrusions, focused around the crystal settling versus in situ crystallisation paradigms, are classic in the subject of igneous petrology. Central to these debates is the notion that a wide range of magma chamber processes occur in layered mafic-ultramafic intrusions that are not frequently considered to occur in their relatively viscous granitic counterparts; in essence, the latter have historically been viewed as much more likely to ';freeze-in' a primary magma flow fabric whilst mafic-ultramafic intrusions are subjected to a more protracted solidification history. This wide array of potential initial sources for layering and mineral fabrics in layered mafic-ultramafic intrusions, together with the possible modification of textures at the postcumulus stage, demands a cautious application of any fabric analysis and presents a problem well-suited to interrogation by the AMS technique. The purpose of this contribution is to provide specific context on the application of AMS to elucidating the formation of cumulates in layered mafic-ultramafic intrusions. Examples of AMS

Geodiversity of hydrothermal processes along the Mid-Atlantic Ridge and ultramafic-hosted mineralization: A new type of oceanic Cu-Zn-Co-Au volcanogenic massive sulfide deposit

NASA Astrophysics Data System (ADS)

Fouquet, Yves; Cambon, Pierre; Etoubleau, Joël; Charlou, Jean Luc; Ondréas, Hélène; Barriga, Fernando J. A. S.; Cherkashov, Georgy; Semkova, Tatiana; Poroshina, Irina; Bohn, M.; Donval, Jean Pierre; Henry, Katell; Murphy, Pamela; Rouxel, Olivier

Several hydrothermal deposits associated with ultramafic rocks have recently been found along slow spreading ridges with a low magmatic budget. Three preferential settings are identified: (1) rift valley walls near the amagmatic ends of ridge segments; (2) nontransform offsets; and (3) ultramafic domes at inside corners of ridge transform-fault intersections. The exposed mantle at these sites is often interpreted to be a detachment fault. Hydrothermal cells in ultramafic rocks may be driven by regional heat flow, cooling gabbroic intrusions, and exothermic heat produced during serpentinization. Along the Mid-Atlantic Ridge (MAR), hydrothermal deposits in ultramafic rocks include the following: (1) sulfide mounds related to high-temperature low-pH fluids (Logatchev, Rainbow, and Ashadze); (2) carbonate chimneys related to low-temperature, high-pH fluids (Lost City); (3) low-temperature diffuse venting and high-methane discharge associated with silica, minor sulfides, manganese oxides, and pervasive alteration (Saldanha); and (4) stockwork quartz veins with sulfides at the base of detachment faults (15°05'N). These settings are closely linked to preferential circulation of fluid along permeable detachment faults. Compared to mineralization in basaltic environments, sulfide deposits associated with ultramafic rocks are enriched in Cu, Zn, Co, Au, and Ni. Gold has a bimodal distribution in low-temperature Zn-rich and in high-temperature Cu-rich mineral assemblages. The Cu-Zn-Co-Au deposits along the MAR seem to be more abundant than in ophiolites on land. This may be because ultramafic-hosted volcanogenic massive sulfide deposits on slow spreading ridges are usually not accreted to continental margins during obduction and may constitute a specific marine type of mineralization.

The Pioneer Ultramafic Complex of the Barberton Greenstone Belt, South Africa

NASA Astrophysics Data System (ADS)

Cooper, M. R.; Byerly, G. R.; Lowe, D. R.; Thompson, M. E.

2005-12-01

The 3.55-3.22 Ga Barberton Greenstone Belt is an approximately 100km x 30km northeast trending, isoclinally folded, volcanic and sedimentary succession surrounded by intrusive granitic rocks. It is perhaps Earth's best preserved mid-Archean supracrustal sequence and also among the most magnesian, making it an ideal location for studying compositionally distinct rocks of the Archean, such as komatiites. The Pioneer Ultramafic Complex has been interpreted as a komatiitic intrusion but we argue that it is a sequence of layered komatiitic flows and interbedded tuffs correlative with other komatiitic extrusive units of the 3.29 Ga Weltevreden Formation, the uppermost formation of the Onverwacht Group. The Pioneer Ultramafic Complex contains at least 900m of section in the study area, including at least 5 flow sets, with individual flows up to 100 m thick, sections of tuff up to 100m thick and additional thinner tuff units. The base of the sequence is in fault contact with the Sawmill Ultramafic Complex, which is similar to and perhaps correlative with the Pioneer. The top of the sequence is bounded by the Moodies Fault and slightly younger sedimentary rocks of the Fig Tree and Moodies Groups. Typical flows of the Pioneer have highly serpentinized olivine-rich cumulate bases, fresh olivine bearing peridotitic lithologies in central portions, and increasing pyroxene content, pyroxene size, and elongation of grains toward the flow tops. Three of the five flows are capped with random and/or oriented spinifex layers. The tuffs within this and other layered ultramafic complexes of the Barberton Greenstone Belt are mostly fine grained, slaty serpentinites that were previously interpreted as bedding horizontal zones of shearing. However, rare preservation of angular and vesicular lapilli, and more commonly cross-stratification in finer grained layers, provide strong evidence that these layers represent tuffs. High chromium and other trace element contents suggest they are

An Experimental Study on Characterization of Physical Properties of Ultramafic Rocks and Controls on Evolution of Fracture Permeability During Serpentinization at Hydrothermal Conditions

NASA Astrophysics Data System (ADS)

Farough, Aida

Serpentinization is a complex set of hydration reactions, where olivine and pyroxene are replaced by serpentine, magnetite, brucite, talc and carbonate minerals. Serpentinization reactions alter chemical, mechanical, magnetic, seismic, and hydraulic properties of the crust. To understand the complicated nature of serpentinization and the linkages between physical and chemical changes during the reactions, I performed flow-through laboratory experiments on cylindrically cored samples of ultramafic rocks. Each core had a well-mated through-going tensile fracture, to investigate evolution of fracture permeability during serpentinization. The samples were tested in a triaxial loading machine at an effective pressure of 30 MPa, and temperature of 260"aC, simulating a depth of 2 km under hydrostatic conditions. Fracture permeability decreased by one to two orders of magnitude during the 200 to 340 hour experiments. Electron microprobe and SEM data indicated the formation of needle-shaped crystals of serpentine composition along the walls of the fracture, and chemical analyses of sampled pore fluids were consistent with dissolution of ferromagnesian minerals. The rate of transformation of olivine to serpentine in a tensile fracture is calculated using the data on evolution of fracture permeability assuming the fracture permeability could be represented by parallel plates. Assuming the dissolution and precipitation reactions occur simultaneously; the rate of transformation at the beginning of the experiments was 10-8-10-9 (mol/m2s) and decreased monotonically by about an order of magnitude towards the end of the experiment. Results show that dissolution and precipitation is the main mechanism contributing to the reduction in fracture aperture. The experimental results suggest that the fracture network in long-lived hydrothermal circulation systems may be sealed rapidly as a result of mineral precipitation, and generation of new permeability resulting from a combination of

Earthquakes in the Mantle? Insights from Ultramafic Pseudotachylytes

NASA Astrophysics Data System (ADS)

Meado, A.; Ferre, E. C.; Ueda, T.; Ashwal, L. D.; Deseta, N.

2015-12-01

Deep earthquakes in subduction/collision zones may originate from mechanical failure of ultramafic rocks at mantle depths. Fault pseudotachylytes in peridotites have been attributed to seismic slip at depths >30 km. However, the possibility of frictional melting at shallower depths still exist. While pristine mantle rocks typically lack magnetite, postseismic serpentinization would likely involve formation of abundant multi-domain (MD) magnetite. Single-domain (SD) to pseudo-single domain (PSD) magnetite may also form in pseudotachylytes through breakdown of mafic silicates. Magnetite has a large magnetic susceptibility (Km). MD magnetite shows low magnetic remanence / magnetic saturation ratios (Mr/Ms) compared to SD-PSD magnetite. The formation of coseismic magnetite however would depend on fO2. Hence, in unserpentinized ultramafic pseudotachylytes, magnetite would form preferentially under shallow, high fO2 conditions. Coseismically deformed magnetite would result in a high anisotropy of magnetic susceptibility (AMS). Here, we present a predictive model of the magnetic properties and magnetic fabrics of ultramafic pseudotachylytes formed under four conditions: i) deep seismic slip and no syn- or postseismic serpentinization: low Km (<600 . 10^-6 [SI]), low Mr/Ms (<0.1), and low AMS (<1.1) ii) deep seismic slip followed by static serpentinization: high Km (>3,000 . 10^-6 [SI]), low Mr/Ms (<0.1), low AMS (<1.1) iii) deep or shallow seismic slip in previously serpentinized peridotites: high Km (>3,000 . 10^-6 [SI]), moderate Mr/Ms (0.1-0.5), high AMS (>1.5) iv) shallow seismic slip with no serpentinization: moderate Km (600-3,000 . 10^-6 [SI]), high Mr/Ms (>0.5), moderate AMS (1.1-1.5) We test these models using samples from the Balmuccia Massif (Italy) and the Schistes Lustrés (Corsica). These models may provide new constrains for ultramafic pseudotachylytes regarding their depth of formation and the timing of serpentinization.

Torngat ultramafic lamprophyres and their relation to the North Atlantic Alkaline Province

NASA Astrophysics Data System (ADS)

Tappe, Sebastian; Jenner, George A.; Foley, Stephen F.; Heaman, Larry; Besserer, Dean; Kjarsgaard, Bruce A.; Ryan, Bruce

2004-09-01

Geological mapping and diamond exploration in northern Quebec and Labrador has revealed an undeformed ultramafic dyke swarm in the northern Torngat Mountains. The dyke rocks are dominated by an olivine-phlogopite mineralogy and contain varying amounts of primary carbonate. Their mineralogy, mineral compositional trends and the presence of typomorphic minerals (e.g. kimzeyitic garnet), indicate that these dykes comprise an ultramafic lamprophyre suite grading into carbonatite. Recognized rock varieties are aillikite, mela-aillikite and subordinate carbonatite. Carbonatite and aillikite have in common high carbonate content and a lack of clinopyroxene. In contrast, mela-aillikites are richer in mafic silicate minerals, in particular clinopyroxene and amphibole, and contain only small amounts of primary carbonate. The modal mineralogy and textures of the dyke varieties are gradational, indicating that they represent end-members in a compositional continuum. The Torngat ultramafic lamprophyres are characterized by high but variable MgO (10-25 wt.%), CaO (5-20 wt.%), TiO2 (3-10 wt.%) and K2O (1-4 wt.%), but low SiO2 (22-37 wt.%) and Al2O3 (2-6 wt.%). Higher SiO2, Al2O3, Na2O and lower CO2 content distinguish the mela-aillikites from the aillikites. Whereas the bulk rock major and trace element concentrations of the aillikites and mela-aillikites overlap, there is no fractional crystallization relation between them. The major and trace element characteristics imply related parental magmas, with minor olivine and Cr-spinel fractionation accounting for intra-group variation. The Torngat ultramafic lamprophyres have a Neoproterozoic age and are spatially and compositionally closely related with the Neoproterozoic ultramafic lamprophyres from central West Greenland. Ultramafic potassic-to-carbonatitic magmatism occurred in both eastern Laurentia and western Baltica during the Late Neoproterozoic. It can be inferred from the emplacement ages of the alkaline complexes and

Rare Mineralogy in Alkaline Ultramafic Rocks, Western Kentucky Fluorspar District

NASA Astrophysics Data System (ADS)

Anderson, W.

2017-12-01

The alkaline ultramafic intrusive dike complex in the Western Kentucky Fluorspar District contains unusual mineralogy that was derived from mantle magma sources. Lamprophyre and peridotite petrologic types occur in the district where altered fractionated peridotites are enriched in Rare Earth Elements (REE) and some lamprophyre facies are depleted in incompatible elements. Unusual minerals in dikes, determined by petrography and X-ray diffraction, include schorlomite and andradite titanium garnets, astrophyllite, spodumene, niobium rutile, wüstite, fluoro-tetraferriphlogopite, villiaumite, molybdenite, and fluocerite, a REE-bearing fluoride fluorescent mineral. Mixing of MVT sphalerite ore fluids accompanies a mid-stage igneous alteration and intrusion event consistent with paragenetic studies. The presence of lithium in the spodumene and fluoro-tetraferriphlogopite suggests a lithium phase in the mineral fluids, and the presence of enriched REE in dikes and fluorite mineralization suggest a metasomatic event. Several of these rare minerals have never been described in the fluorspar district, and their occurrence suggests deep mantle metasomatism. Several REE-bearing fluoride minerals occur in the dikes and in other worldwide occurrences, they are usually associated with nepheline syenite and carbonatite differentiates. There is an early and late stage fluoride mineralization, which accompanied dike intrusion and was also analyzed for REE content. One fluorite group is enriched in LREE and another in MREE, which suggests a bimodal or periodic fluorite emplacement. Whole-rock elemental analysis was chondrite normalized and indicates that some of the dikes are slightly enriched in light REE and show a classic fractionation enrichment. Variations in major-element content; high titanium, niobium, and zirconium values; and high La/Yb, Zr/Y, Zr/Hf, and Nb/Ta ratios suggest metasomatized lithospheric-asthenospheric mantle-sourced intrusions. The high La/Yb ratios in some

Sub-micron Raman Mapping of Ultramafic Fault Rock Textures

NASA Astrophysics Data System (ADS)

Tarling, M. S.; Rooney, J. S.; Smith, S. A. F.; Gordon, K. C.

2016-12-01

Deciphering the often complex temporal and microstructural relationships between the serpentine group minerals - antigorite, chrysotile, lizardite and polygonal serpentine - is essential for a proper understanding of the serpentinization process in a range of geodynamic settings. Conventional techniques such as optical microscopy, quantitative XRD and SEM-EDS often fail to correctly identify the four varieties of serpentine. Transmission electron microscopy can be used to successfully identify these minerals, but complex sample preparation and very small sample sizes (1-10's microns) means that microstructural context is difficult to maintain. Building on previous work (Petriglieri et al. 2015, J. Raman Spectrosc.) that introduced a methodology for Raman mapping on thin sections, we present the initial results of large-area and high-resolution (at the optical limit) Raman mapping that allows us to unambiguously distinguish and contextualise the serpentine minerals within their microstructural context. Measurements were performed on flat, SYTON-polished petrographic thin sections using a Witec Raman microscope equipped with a piezoelectric nano-positioning x-y stage. With a laser wavelength of 532 nm and a 100x dry objective, spatial resolution approaching 360 nm, as predicted by the Abbe equation, can readily be achieved. Minerals are primarily discerned by examining the Raman peaks in the high wavenumber spectral range of 3600-3710 cm-1, corresponding to OH-stretching vibrations. To illustrate the technique, Raman maps were acquired on several samples from the Livingstone Fault, a major terrane boundary in New Zealand that is localized in a mélange of ultramafic rocks including harzburgite and serpentinite. The maps highlight fine-scale intergrowths of antigorite, lizardite, chrysotile and related minerals (e.g. brucite, magnetite) at a sub-micron level over large areas (10's of microns to mm scale), features that are inaccessible or not visible using other

Lithologic mapping of the Mordor, NT, Australia ultramafic complex by using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)

USGS Publications Warehouse

Rowan, L.C.; Mars, J.C.; Simpson, C.J.

2005-01-01

Spectral measurements made in the Mordor Pound, NT, Australia study area using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), in the laboratory and in situ show dominantly Al-OH and ferric-iron VNIR-SWIR absorption features in felsic rock spectra and ferrous-iron and Fe,Mg-OH features in the mafic-ultramafic rock spectra. ASTER ratio images, matched-filter, and spectral-angle mapper processing (SAM) were evaluated for mapping the lithologies. Matched-filter processing in which VNIR + SWIR image spectra were used for reference resulted in 4 felsic classes and 4 mafic-ultramafic classes based on Al-OH or Fe,Mg-OH absorption features and, in some, subtle reflectance differences related to differential weathering and vegetation. These results were similar to those obtained by match-filter analysis of HyMap data from a previous study, but the units were more clearly demarcated in the HyMap image. ASTER TIR spectral emittance data and laboratory emissivity measurements document a wide wavelength range of Si-O spectral features, which reflect the lithological diversity of the Mordor ultramafic complex and adjacent rocks. SAM processing of the spectral emittance data distinguished 2 classes representing the mafic-ultramafic rocks and 4 classes comprising the quartzose to intermediate composition rocks. Utilization of the complementary attributes of the spectral reflectance and spectral emittance data resulted in discrimination of 4 mafic-ultramafic categories; 3 categories of alluvial-colluvial deposits; and a significantly more completely mapped quartzite unit than could be accomplished by using either data set alone. ?? 2005 Elsevier Inc. All rights reserved.

Reassessment of the volume of the Las Aguilas mafic-ultramafic intrusives, San Luis, Argentina, based on an alternative geophysical model

NASA Astrophysics Data System (ADS)

Claudia, Zaffarana; Silvana, Geuna; Stella, Poma; Alberto, Patiño Douce

2011-10-01

In the Sierra de San Luis, Central Argentina, a belt of small and discontinuous lenses of mafic-ultramafic rocks intrude a polydeformed basement and are thought to be the cause of a local increase of the metamorphic grade from amphibolite to granulite facies conditions. This assumption was especially based on forward modelling of a huge gravity anomaly centered over the Sierra de San Luis, which lead some workers to think that a vast volume of mafic-ultramafic rocks lay in shallow levels. Here, we propose an alternative model to explain this anomaly, in which the mafic-ultramafic intrusion is not the ultimate source. Therefore, there is no need to propose a bigger size than that observed in outcrops for the mafic-ultramafic bodies. The thermal effect of the emplacement of mafic-ultramafic sills and dikes on the host rocks was estimated applying a simple analytical solution (error function) for heating of a semi-infinite half space (the country rocks) in contact with a hotter sheet of finite thickness (the mafic-ultramafic intrusion). Results indicate that the effect of the intrusion of these hot mafic magmas is local, because beyond a few hundred meters from the contact zone temperatures never exceed 600 °C, and a few km from the intrusion they barely increase 50 °C relative to the initial temperature. These results, together with the preservation of primary igneous characteristics (such as rhythmic layering) being overprinted by metamorphic textural changes, indicate that the intrusion occurred before regional deformation. It is suggested that the thermal anomaly in the Pringles Metamorphic Complex could have been mainly caused by factors inherent to their geodynamic setting.

Lower continental crust formation through focused flow in km-scale melt conduits: The zoned ultramafic bodies of the Chilas Complex in the Kohistan island arc (NW Pakistan)

NASA Astrophysics Data System (ADS)

Jagoutz, O.; Müntener, O.; Burg, J.-P.; Ulmer, P.; Jagoutz, E.

2006-02-01

Whole-rock and Sm-Nd isotopic data of the main units of the Chilas zoned ultramafic bodies (Kohistan paleo-island arc, NW Pakistan) indicate that ultramafic rocks and gabbronorite sequences stem from a common magma. However, field observations rule out formation of both ultramafic and mafic sequences in terms of gravitational crystal settling in a large magma chamber. Contacts between ultramafic and gabbronorite sequences show emplacement of the dunitic bodies into a semi-consolidated gabbronoritic crystal-mush, which in turn has intruded and reacted with the ultramafic rocks to produce concentric zoning. Field and petrological observations indicate a replacive origin of the dunite. Bulk Mg#'s of dunitic rocks range from 0.87-0.81 indicating that the dunite-forming melt underwent substantial fractionation-differentiation and that percolative fractional crystallization probably generated the dunitic core. The REE chemistry of clinopyroxene in primitive dunite samples and the Nd isotopic composition of ultramafic rocks are in equilibrium with the surrounding gabbronorite. Accordingly, liquids that formed the dunitic rocks and later the mafic sequence derived from a similar depleted source ( ɛNd˜4.8). We propose a mechanism for the comagmatic emplacement, where km-scale ultramafic bodies represent continuous channels reaching down into the upper mantle. The melt-filled porosity in these melt channels diminishes the mean-depth-integrated density difference to the surrounding rocks. Due to buoyancy forces, melt channels raise into the overlying crustal sequence. In the light of such processes, the ultramafic bodies are interpreted as melt channels through which the Chilas gabbronorite sequence was fed. The estimated basaltic-andesitic, low Mg# (˜0.53) bulk composition of the Chilas gabbronorite sequence closely matches estimates of lower crustal compositions. Since the mafic sequence originated from a primary, high Mg# (> 0.7) basaltic arc magma, differentiation of

Rhenium-osmium isotopes and highly siderophile elements in ultramafic rocks from the Eoarchean Saglek Block, northern Labrador, Canada: implications for Archean mantle evolution

NASA Astrophysics Data System (ADS)

Ishikawa, Akira; Suzuki, Katsuhiko; Collerson, Kenneth D.; Liu, Jingao; Pearson, D. Graham; Komiya, Tsuyoshi

2017-11-01

We determined highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) concentrations and 187Os/188Os ratios for ultramafic rocks distributed over the Eoarchean gneiss complex of the Saglek-Hebron area in northern Labrador, Canada in order to constrain to what extent variations in HSE abundances are recorded in Early Archean mantle that have well-resolved 182W isotope anomalies relative to the present-day mantle (∼+11 ppm: Liu et al., 2016). The samples analysed here have been previously classified into two suites: mantle-derived peridotites occurring as tectonically-emplaced slivers of lithospheric mantle, and metakomatiites comprising mostly pyroxenitic layers in supracrustal units dominated by amphibolites. Although previous Sm-Nd and Pb-Pb isotope studies provided whole-rock isochrons indicative of ∼3.8 Ga protolith formation for both suites, our whole-rock Re-Os isotope data on a similar set of samples yield considerably younger errorchrons with ages of 3612 ± 130 Ma (MSWD = 40) and 3096 ± 170 Ma (MSWD = 10.2) for the metakomatiite and lithospheric mantle suites, respectively. The respective initial 187Os/188Os = 0.10200 ± 18 for metakomatiites and 0.1041 ± 18 for lithospheric mantle rocks are within the range of chondrites. Re-depletion Os model ages for unradiogenic samples from the two suites are consistent with the respective Re-Os errorchrons (metakomatiite TRD = 3.4-3.6 Ga; lithospheric mantle TRD = 2.8-3.3 Ga). These observations suggest that the two ultramafic suites are not coeval. However, the estimated mantle sources for the two ultramafics suites are similar in terms of their broadly chondritic evolution of 187Os/188Os and their relative HSE patterns. In detail, both mantle sources show a small excess of Ru/Ir similar to that in modern primitive mantle, but a ∼20% deficit in absolute HSE abundances relative to that in modern primitive mantle (metakomatiite 74 ± 18% of PUM; lithospheric mantle 82 ± 10% of PUM), consistent with the �

The effect of carbon-rich fluid alteration on the mechanical and physical properties of ultramafic rocks from Linnejavrre, Norway

NASA Astrophysics Data System (ADS)

Lisabeth, H. P.; Zhu, W.

2016-12-01

Carbon dioxide interacts with mafic and ultramafic rocks on the ocean floor at fracture zones and detachment faults, and within ophiolite complexes. Steatized olivine-pyroxene or serpentinite rocks become talc-carbonate rocks, i.e., soapstones. If the fluids are extremely carbon-rich, the process can continue to completion, binding all the magnesium from olivine and pyroxene in magnesium carbonate, resulting in magnesite-quartz rocks known as listvenites. The structural, mechanical and mineralogical characteristics of these rocks can be long-lived and affect later tectonic deformation over the course of the supercontinent cycle, influencing the obduction of ophiolites and possibly the initiation of subduction. To ascertain the changes in physical and geomechanical characteristics of these rocks as they undergo carbonic alteration, we measure ultrasonic velocity, electrical resistivity and shear strength in a series of laboratory tests on samples collected from northern Norway, where the Linnajavrre Ophiolite contains representative samples of serpentinite, soapstone and listvenite. We discover that the rocks tend to become denser, more porous, weaker, and more electrically and acoustically impeditive as carbonation proceeds. Samples fail by highly localized brittle faulting with little dilatancy. Shear strength appears to correlate with talc abundance, with a steep drop-off from 5 to 20% talc. Deformed samples are examined under petrographic microscope to explore deformation micromechanisms. Our data suggest that the weakening observed in soapstones and listvenites compared to serpentinites is attributed to interconnected talc grains. Such carbonic alteration of oceanic serpentinites may help facilitate oceanic spreading, particularly along slow and ultraslow segments of mid-ocean ridges.

Serpentinization and carbonation of pristine continental ultramafic rocks and applications to the oceanic crust; H2O-CO2 alteration of dunites and re-distribution of Ni-Cu-PGE in sulphide deposits

NASA Astrophysics Data System (ADS)

Grant, Thomas; McEnroe, Suzanne; Eske Sørensen, Bjørn; Larsen, Rune; Pastore, Zeudia; Rune Grannes, Kim; Nikolaisen, Even

2017-04-01

Here, we document carbonation and serpentinization within a suite of ultramafic rocks from a continental setting. These ultramafic rocks vary from pristine dunites to varying degrees of serpentinization which locally penetrates the ultramafic complex. Hence, it allows us to observe a number of delicate serpentinization and carbonation reactions, otherwise lost during more extensive alteration or tectonic events. We use a multi-disciplinary approach using petrographic, EPMA, thermodynamic modelling and geophysical data to reveal how the initial stages of serpentization and carbonation in dunites affects the distribution of economic to sub-economic deposits of Ni-Cu and PGE. The data can then be applied to oceanic crust. The samples are dunites and poikilitic wehrlites from the Reinfjord Ultramafic complex, Seiland Igneous Province Northern Norway. The complex formed through crystallization of picritic melts in the lower continental crust. The dunites contain small amounts of interstitial clinopyroxene, sulphides and spinel, with local enrichments in Ni, Cu and PGE. Late magmatic CO2-H2O-S fluids reacted with the dunite forming clots of amphibole + dolomite + sulphides + enstatite, reaction rims of enstatite + dolomite, and inclusions trails of dolomite + enstatite + magnetite + CO2 fluid. Thermodynamic modelling reveals that these textures formed at pressures of >12 kbar and temperatures 850-950 °C, which would be consistent with the late magmatic history of the Reinfjord complex. The clots and reactions have local association with enrichments in gold-rich PGMs. A second stage of alteration involved H2O-dominated fluids. These formed predominantly lizardite serpentinization, as is often concentrated within highly localized fracture zones. Thermodynamic modelling shows that these formed <400°C, after the complex had been exhumed towards the surface of the crust. Local and more pervasive serpentinization interacted with the earlier formed carbonate bearing

A hydrological and geochemical analysis of chromium mobilization from serpentinized ultramafic rocks and serpentine soils at the McLaughlin Natural Reserve, Lake County, California

NASA Astrophysics Data System (ADS)

McClain, C.; Maher, K.; Fendorf, S.

2011-12-01

California recently adopted the nation's first Public Health Goal (PHG) for hexavalent chromium (Cr(VI)) in drinking water (0.02 μg/L) because recent studies show that Cr(VI) may be carcinogenic through ingestion. Approximately one third of drinking water sources in California tested for Cr(VI) have levels above 1 μg/L and thus may pose a risk to human health. Cr(VI) can enter drinking water directly from anthropogenic sources or from the release of Cr(III) in natural geogenic sources such as rocks, sediments and soils, and subsequent oxidation to Cr(VI) by manganese oxides. Ultramafic rocks and related soils and sediments have elevated Cr and Mn concentrations compared to other rock types. To study the release of Cr(VI) to water from geogenic sources we examined the local hydrology, groundwater, surface water, soils and sediment compositions within a serpentinized ultramafic terrain along Hunting Creek, a tributary to Putah Creek, at the McLaughlin Natural Reserve in the California Coast Ranges. The hydrology of the site is dominated by fracture flow: groundwater wells were screened in fractured serpentinite, and springs emanating from fractured serpentinite bedrock contribute to the baseflow of Hunting Creek. Soil profiles and bedrock were analyzed for major and trace elements by XRF to assess the fate of Cr during weathering and the distribution of manganese oxides. These factors, along with mineral surface areas, microbial activity, water content, and flow dynamics, collectively control the oxidation of Cr(III). The prevalence of Mg-HCO3 waters at this site indicates that waters are primarily interacting with serpentinites. Pyroxenes are slightly to highly undersaturated and amorphous silica is saturated. Smectite clays, chlorite, and hydromagnesite are supersaturated, indicating formation of secondary mineral phases is favorable and could lead to the inclusion of Cr(III). Total Cr concentrations in surface and groundwater vary from 0.1-26 μg/L and Cr

Catchment-wide weathering and erosion rates of mafic, ultramafic, and granitic rock from cosmogenic meteoric 10Be/9Be ratios

NASA Astrophysics Data System (ADS)

Dannhaus, N.; Wittmann, H.; Krám, P.; Christl, M.; von Blanckenburg, F.

2018-02-01

Quantifying rates of weathering and erosion of mafic rocks is essential for estimating changes to the oceans alkalinity budget that plays a significant role in regulating atmospheric CO2 levels. In this study, we present catchment-wide rates of weathering, erosion, and denudation measured with cosmogenic nuclides in mafic and ultramafic rock. We use the ratio of the meteoric cosmogenic nuclide 10Be, deposited from the atmosphere onto the weathering zone, to stable 9Be, a trace metal released by silicate weathering. We tested this approach in stream sediment and water from three upland forested catchments in the north-west Czech Republic. The catchments are underlain by felsic (granite), mafic (amphibolite) and ultramafic (serpentinite) lithologies. Due to acid rain deposition in the 20th century, the waters in the granite catchment exhibit acidic pH, whereas waters in the mafic catchments exhibit neutral to alkaline pH values due to their acid buffering capability. The atmospheric depositional 10Be flux is estimated to be balanced with the streams' dissolved and particulate meteoric 10Be export flux to within a factor of two. We suggest a correlation method to derive bedrock Be concentrations, required as an input parameter, which are highly heterogeneous in these small catchments. Derived Earth surface metrics comprise (1) Denudation rates calculated from the 10Be/9Be ratio of the "reactive" Be (meaning sorbed to mineral surfaces) range between 110 and 185 t km-2 y-1 (40 and 70 mm ky-1). These rates are similar to denudation rates we obtained from in situ-cosmogenic 10Be in quartz minerals present in the bedrock or in quartz veins in the felsic and the mafic catchment. (2) The degree of weathering, calculated from the fraction of 9Be released from primary minerals as a new proxy, is about 40-50% in the mafic catchments, and 10% in the granitic catchment. Lastly, (3) erosion rates were calculated from 10Be concentrations in river sediment and corrected for sorting

Evolution of fracture permeability of ultramafic rocks undergoing serpentinization at hydrothermal conditions: An experimental study

NASA Astrophysics Data System (ADS)

Farough, A.; Moore, D. E.; Lockner, D. A.; Lowell, R. P.

2016-01-01

We performed flow-through laboratory experiments on five cylindrically cored samples of ultramafic rocks, in which we generated a well-mated through-going tensile fracture, to investigate evolution of fracture permeability during serpentinization. The samples were tested in a triaxial loading machine at a confining pressure of 50 MPa, pore pressure of 20 MPa, and temperature of 260°C, simulating a depth of 2 km under hydrostatic conditions. A pore pressure difference of up to 2 MPa was imposed across the ends of the sample. Fracture permeability decreased by 1-2 orders of magnitude during the 200-330 h experiments. Electron microprobe and SEM data indicated the formation of needle-shaped crystals of serpentine composition along the walls of the fracture, and chemical analyses of sampled pore fluids were consistent with dissolution of ferro-magnesian minerals. By comparing the difference between fracture permeability and matrix permeability measured on intact samples of the same rock types, we concluded that the contribution of the low matrix permeability to flow is negligible and essentially all of the flow is focused in the tensile fracture. The experimental results suggest that the fracture network in long-lived hydrothermal circulation systems can be sealed rapidly as a result of mineral precipitation, and generation of new permeability resulting from a combination of tectonic and crystallization-induced stresses is required to maintain fluid circulation.

Evolution of fracture permeability of ultramafic rocks undergoing serpentinization at hydrothermal conditions: An experimental study

USGS Publications Warehouse

Farough, Aida; Moore, Diane E.; Lockner, David A.; Lowell, R.P.

2016-01-01

We performed flow-through laboratory experiments on five cylindrically cored samples of ultramafic rocks, in which we generated a well-mated through-going tensile fracture, to investigate evolution of fracture permeability during serpentinization. The samples were tested in a triaxial loading machine at a confining pressure of 50 MPa, pore pressure of 20 MPa, and temperature of 260°C, simulating a depth of 2 km under hydrostatic conditions. A pore pressure difference of up to 2 MPa was imposed across the ends of the sample. Fracture permeability decreased by 1–2 orders of magnitude during the 200–330 h experiments. Electron microprobe and SEM data indicated the formation of needle-shaped crystals of serpentine composition along the walls of the fracture, and chemical analyses of sampled pore fluids were consistent with dissolution of ferro-magnesian minerals. By comparing the difference between fracture permeability and matrix permeability measured on intact samples of the same rock types, we concluded that the contribution of the low matrix permeability to flow is negligible and essentially all of the flow is focused in the tensile fracture. The experimental results suggest that the fracture network in long-lived hydrothermal circulation systems can be sealed rapidly as a result of mineral precipitation, and generation of new permeability resulting from a combination of tectonic and crystallization-induced stresses is required to maintain fluid circulation.

Unraveling the Alteration History of Serpentinites and Associated Ultramafic Rocks from the Kampos HPLT Subduction Complex, Syros, Greece

NASA Astrophysics Data System (ADS)

Cooperdock, E. H. G.; Stockli, D. F.

2016-12-01

Serpentinization, hydration of peridotite, has a profound effect on fundamental tectonic and petrologic processes such as deformation of the lithosphere, bulk rheology, fluid-mobile element cycling and deep earth carbon cycling. Though numerous studies have investigated the petrology, structure and geochemistry of serpentinites, the absolute chronology of serpentinization remains elusive due to a lack of accessory minerals that can be dated using established geochronological techniques. Magnetite forms as a common secondary mineral in serpentinites from the fluid-induced breakdown reaction of primary peridotite minerals. Magnetite (U-Th)/He chronometry provides the potential to directly date the cooling of exhumed ultramafic bodies and the low-temperature fluid alteration of serpentinites. We present the first application of magnetite (U-Th)/He chronometry to date stages of alteration in ultramafic rocks from the Kampos mélange belt, a high-pressure low-temperature (HP-LT) subduction complex that experienced exhumation in the Miocene on the island of Syros, Greece. Two generations of magnetite are distinguishable by grain size, magnetite trace element geochemistry and (U-Th)/He age. Large magnetite grains (mm) from a chlorite schist and a serpentinite schist have distinct geochemical signatures indicative of formation during blackwall-related fluid alteration and record Mid-Miocene exhumation-related cooling ages, similar to zircon (U-Th)/He ages from northern Syros. Smaller grains (µm) from the serpentinite schist lack blackwall-related fluid signatures and record post-exhumation mineral formation associated with widespread high-angle Pliocene normal faulting. These results reveal evidence for multiple episodes of fluid-rock alteration, which has implications for the cooling history and local geochemical exchanges of this HP-LT terrane. Given the fundamental impact of serpentinizaton on a vast array of tectonic, petrological, and geochemical processes, the

Weathering and vegetation controls on nickel isotope fractionation in surface ultramafic environments (Albania)

NASA Astrophysics Data System (ADS)

Estrade, Nicolas; Cloquet, Christophe; Echevarria, Guillaume; Sterckeman, Thibault; Deng, Tenghaobo; Tang, YeTao; Morel, Jean-Louis

2015-08-01

The dissolved nickel (Ni) isotopic composition of rivers and oceans presents an apparent paradox. Even though rivers represent a major source of Ni in the oceans, seawater is more enriched in the heavier isotopes than river-water. Additional sources or processes must therefore be invoked to account for the isotopic budget of dissolved Ni in seawater. Weathering of continental rocks is thought to play a major role in determining the magnitude and sign of isotopic fractionation of metals between a rock and the dissolved product. We present a study of Ni isotopes in the rock-soil-plant systems of several ultramafic environments. The results reveal key insights into the magnitude and the control of isotopic fractionation during the weathering of continental ultramafic rocks. This study introduces new constraints on the influence of vegetation during the weathering process, which should be taken into account in interpretations of the variability of Ni isotopes in rivers. The study area is located in a temperate climate zone within the ophiolitic belt area of Albania. The serpentinized peridotites sampled present a narrow range of heavy Ni isotopic compositions (δ60Ni = 0.25 ± 0.16 ‰, 2SD n = 2). At two locations, horizons within two soil profiles affected by different degrees of weathering all presented light isotopic compositions compared to the parent rock (Δ60Nisoil-rock up to - 0.63 ‰). This suggests that the soil pool takes up the light isotopes, while the heavier isotopes remain in the dissolved phase. By combining elemental and mineralogical analyses with the isotope compositions determined for the soils, the extent of fractionation was found to be controlled by the secondary minerals formed in the soil. The types of vegetation growing on ultramafic-derived soils are highly adapted and include both Ni-hyperaccumulating species, which can accumulate several percent per weight of Ni, and non-accumulating species. Whole-plant isotopic compositions were found

Map showing the potential for mineral deposits associated with Precambrian mafic and ultramafic rocks in the Blacktail and Henrys Lake mountains and the Greenhorn and Ruby ranges of southwestern Montana

USGS Publications Warehouse

Hammarstrom, Jane M.; Van Gosen, Bradley S.; Carlson, Robert R.; Kulik, Dolores M.

1998-01-01

In response to requests from the Bureau of Land Management (BLM) and the U.S. Forest Service (USFS), the U.S. Geological Survey (USGS) conducted a mineral resource assessment in the Dillon BLM Resource Area in Beaverhead and Madison Counties, southwestern Montana. These agencies use mineral resource data in creating and updating land-use management plans for federal lands for the reasonably foreseeable future. Mineral resources that have not been developed in the past may be developed in the future, based on changing commodity demands and market conditions. Therefore, federal land managers need geologic information on known mineral occurrences as well as on areas that are permissive for the occurrence of undiscovered mineral resources. This map was prepared to provide this type of geologic information for mineral deposits that can be associated with ultramafic rocks. Areas of exposed Precambrian ultramafic rocks are labeled with uppercase letters (A-F). Sources of geologic maps used to compile this map are shown on the smaller index map ("Index to Geologic Mapping"); lowercase letters (a-m) on the index map are keyed to the reference list.

Geochemical constraints on sources of metabolic energy for chemolithoautotrophy in ultramafic-hosted deep-sea hydrothermal systems.

PubMed

McCollom, Thomas M

2007-12-01

Numerical models are employed to investigate sources of chemical energy for autotrophic microbial metabolism that develop during mixing of oxidized seawater with strongly reduced fluids discharged from ultramafic-hosted hydrothermal systems on the seafloor. Hydrothermal fluids in these systems are highly enriched in H(2) and CH(4) as a result of alteration of ultramafic rocks (serpentinization) in the subsurface. Based on the availability of chemical energy sources, inferences are made about the likely metabolic diversity, relative abundance, and spatial distribution of microorganisms within ultramafic-hosted systems. Metabolic reactions involving H(2) and CH(4), particularly hydrogen oxidation, methanotrophy, sulfate reduction, and methanogenesis, represent the predominant sources of chemical energy during fluid mixing. Owing to chemical gradients that develop from fluid mixing, aerobic metabolisms are likely to predominate in low-temperature environments (<20-30 degrees C), while anaerobes will dominate higher-temperature environments. Overall, aerobic metabolic reactions can supply up to approximately 7 kJ of energy per kilogram of hydrothermal fluid, while anaerobic metabolic reactions can supply about 1 kJ, which is sufficient to support a maximum of approximately 120 mg (dry weight) of primary biomass production by aerobic organisms and approximately 20-30 mg biomass by anaerobes. The results indicate that ultramafic-hosted systems are capable of supplying about twice as much chemical energy as analogous deep-sea hydrothermal systems hosted in basaltic rocks.

Oxygen regime of Siberian alkaline-ultramafic magmas

NASA Astrophysics Data System (ADS)

Ryabchikov, Igor; Kogarko, Liya

2017-04-01

Regimes of S2 and O2 are decisive factors controlling behavior of chalcophile and siderophile elements in magmatic processes. These parameters play important role during magmagenesis and in the course of crystallization and fluid mass transfer in magma chamber. Alkaline-ultramafic magmatism in Maymecha-Kotuy Province (Polar Siberia) is represented by giant intrusive complexes as well as by volcanics and dyke rocks, which include a well-known variety - meimechites. The latter are considered primary magmas of alkaline-ultramafic plutons in the region like for instance Guli intrusive complex. Sulfur content in primitive magmas estimated from the analyses of melt inclusions in olivine megacrysts from meimechites is close to 0.1 %. fO2 values calculated using olivine+clinopyroxene+spinel and spinel+melt oxygen barometers (1, 2) are 2-3 log units above QFM buffer. The relatively high oxygen potential at the early magmatic stage of alkaline-ultramafic Guli pluton provide predominance of sulfates among other forms of sulfur in the melt. This leads to the almost complete absence of sulfides in highly magnesian rocks. The oxidizing conditions exert important effect on behavior of many ore metals. At the stage of magma generation absence of sulfides in mantle materialresults in the presence of siderophile elements in metallic form and saturation of primary magmas in respect of metallic phases at an early stage of injection of the melt into the magma chamber. Later, under favorable circumstances during magma crystallization nuggets of precious metals may be formed. During further evolution of magmatic system fO2 and activity of oxidized sulfur decrease due to intensive crystallization of magnetite during the formation of koswites, then oxygen fugacity becomes even lower as a result serpentinization at a postmagmatic stage. These serpentization processes are caused by the displacement of reactions in the aqueous phase due to cooling towards the formation of methane and other

Origin of magnetic highs at ultramafic hosted hydrothermal systems: Insights from the Yokoniwa site of Central Indian Ridge

NASA Astrophysics Data System (ADS)

Fujii, Masakazu; Okino, Kyoko; Sato, Taichi; Sato, Hiroshi; Nakamura, Kentaro

2016-05-01

High-resolution vector magnetic measurements were performed on an inactive ultramafic-hosted hydrothermal vent field, called Yokoniwa Hydrothermal Field (YHF), using a deep-sea manned submersible Shinkai6500 and an autonomous underwater vehicle r2D4. The YHF has developed at a non-transform offset massif of the Central Indian Ridge. Dead chimneys were widely observed around the YHF along with a very weak venting of low-temperature fluids so that hydrothermal activity of the YHF was almost finished. The distribution of crustal magnetization from the magnetic anomaly revealed that the YHF is associated with enhanced magnetization, as seen at the ultramafic-hosted Rainbow and Ashadze-1 hydrothermal sites of the Mid-Atlantic Ridge. The results of rock magnetic analysis on seafloor rock samples (including basalt, dolerite, gabbro, serpentinized peridotite, and hydrothermal sulfide) showed that only highly serpentinized peridotite carries high magnetic susceptibility and that the natural remanent magnetization intensity can explain the high magnetization of Yokoniwa. These observations reflect abundant and strongly magnetized magnetite grains within the highly serpentinized peridotite. Comparisons with the Rainbow and Ashadze-1 suggest that in ultramafic-hosted hydrothermal systems, strongly magnetized magnetite and pyrrhotite form during the progression of hydrothermal alteration of peridotite. After the completion of serpentinization and production of hydrogen, pyrrhotites convert into pyrite or nonmagnetic iron sulfides, which considerably reduces their levels of magnetization. Our results revealed origins of the magnetic high and the development of subsurface chemical processes in ultramafic-hosted hydrothermal systems. Furthermore, the results highlight the use of near-seafloor magnetic field measurements as a powerful tool for detecting and characterizing seafloor hydrothermal systems.

Geothermobarometry for ultramafic assemblages from the Emeishan Large Igneous Province, Southwest China and the Nikos and Zulu Kimberlites, Nunavut, Canada

NASA Astrophysics Data System (ADS)

Zhao, D.

2009-05-01

To understand and contrast the origins of ultramafic assemblages from basaltic and kimberlitic rocks and their associated deposits, such as V-Ti magnetite and Ni-Cu-(PGE) sulfide deposits and diamond, applicable thermobarometers were evaluated and applied to the ultramafic assemblages from the Emeishan Large Igneous Province (ELIP), Southwest China and from the Nikos and Zulu Kimberlites of Nunavut, Canada. The ELIP is located in the Yangtze Block, Southwest China and composed of Permian Emeishan Flood basalt (EFB) and associated layered mafic-ultramafic intrusions. Some of these intrusions host V-Ti magnetite deposits; while others contain Ni-Cu-(PGE) sulfide deposits. It is not clear why some intrusions host magnetite deposits and others contain sulfide deposits. The P-T conditions for the ultramafic assemblages from the mafic-ultramafic intrusions in the ELIP were calculated in order to understand the origins and the associated mineral deposits. The ultramafic assemblages are peridotite, olivine pyroxenite, pyroxenite in the layered intrusions and the common minerals include spinel, olivine, clinopyroxene, orthopyroxene, and minor magnetite and ilmenite. Using a two pyroxene thermometer and a Ca-Mg exchange barometer between olivine and clinopyroxene, a spinel-olivine-clinopyroxene-orthopyroxene assemblage from the Xinjie intrusion yields a T-P of 905°C and 17 kbar; and a similar assemblage from the Jinbaoshan intrusion yields a T-P of 1124°C and 31 kbar. The Nikos kimberlite, near Elwin Bay on Somerset Island, is located at the northeast end of the northeast-southwest kimberlite zone; and the Zulu kimberlite is located on the neighboring Brodeur Peninsula of Baffin Island, Nunavut. The ultramafic assemblages from the Canadian Kimberlites include garnet lherzolite, garnet-spinel lherzolite, spinel lherzolite, dunite, garnet websterite, spinel websterite and garnet clinopyroxenite. The calculated P-T conditions are in the range of 760 to 1180°C and 25 to 60

Multistage crack seal vein and hydrothermal Ni enrichment in serpentinized ultramafic rocks (Koniambo massif, New Caledonia)

NASA Astrophysics Data System (ADS)

Cathelineau, Michel; Myagkiy, Andrey; Quesnel, Benoit; Boiron, Marie-Christine; Gautier, Pierre; Boulvais, Philippe; Ulrich, Marc; Truche, Laurent; Golfier, Fabrice; Drouillet, Maxime

2017-10-01

Sets of fractures and breccia sealed by Ni-rich silicates and quartz occur within saprock of the New Caledonian regolith developed over ultramafic rocks. The crystallization sequence in fractures is as follows: (1) serpentine stage: lizardite > polygonal serpentine > white lizardite; (2) Ni stage: Ni-Mg kerolite followed by red-brown microcrystalline quartz; and (3) supergene stages. The red-brown microcrystalline quartz corresponds to the very last stage of the Ni sequence and is inferred to have precipitated within the 50-95 °C temperature range. It constitutes also the main cement of breccia that has all the typical features of hydraulic fracturing. The whole sequence is therefore interpreted as the result of hydrothermal fluid circulation under medium to low temperature and fluctuating fluid pressure. Although frequently described as the result of a single downward redistribution of Ni and Mg leached in the upper part of the regolith under ambient temperature, the Ni silicate veins thus appear as the result of recurrent crack and seal process, corresponding to upward medium temperature fluid convection, hydraulic fracturing and subsequent fluid mixing, and mineral deposition.

An evaluation of thematic mapper simulator data for the geobotanical discrimination of rock types in Southwest Oregon

NASA Technical Reports Server (NTRS)

Weinstock, K. J.; Morrissey, L. A.

1984-01-01

Rock type identification may be assisted by the use of remote sensing of associated vegetation, particularly in areas of dense vegetative cover where surface materials are not imaged directly by the sensor. The geobotanical discrimination of ultramafic parent materials was investigated and analytical techniques for lithologic mapping and mineral exploration were developed. The utility of remotely sensed data to discriminate vegetation types associated with ultramafic parent materials in a study area in southwest Oregon were evaluated. A number of specific objectives were identified, which include: (1) establishment of the association between vegetation and rock types; (2) examination of the spectral separability of vegetation types associated with rock types; (3) determination of the contribution of each TMS band for discriminating vegetation associated with rock types and (4) comparison of analytical techniques for spectrally classifying vegetation.

Accessory and rock forming minerals monitoring the evolution of zoned mafic ultramafic complexes in the Central Ural Mountains

NASA Astrophysics Data System (ADS)

Krause, J.; Brügmann, G. E.; Pushkarev, E. V.

2007-04-01

This study describes major and trace element compositions of accessory and rock forming minerals from three Uralian-Alaskan-type complexes in the Ural Mountains (Kytlym, Svetley Bor, Nizhnii Tagil) for the purpose of constraining the origin, evolution and composition of their parental melts. The mafic-ultramafic complexes in the Urals are aligned along a narrow, 900 km long belt. They consist of a central dunite body grading outward into clinopyroxenite and gabbro lithologies. Several of these dunite bodies have chromitites with platinum group element mineralization. High Fo contents in olivine (Fo 92-93) and high Cr/(Cr + Al) in spinel (0.67-0.84) suggest a MgO-rich (> 15 wt.%) and Al 2O 3-poor ultramafic parental magma. During its early stages the magma crystallized dominantly olivine, spinel and clinopyroxene forming cumulates of dunite, wehrlite and clinopyroxenite. This stage is monitored by a common decrease in the MgO content in olivine (Fo 93-86) and the Cr/(Cr + Al) value of coexisting accessory chromite (0.81-0.70). Subsequently, at subsolidus conditions, the chromite equilibrated with the surrounding silicates producing Fe-rich spinel while Al-rich spinel exsolved chromian picotite and chromian titanomagnetite. This generated the wide compositional ranges typical for spinel from Uralian-Alaskan-type complexes world wide. Laser ablation analyses (LA-ICPMS) reveal that clinopyroxene from dunites and clinopyroxenite from all three complexes have similar REE patterns with an enrichment of LREE (0.5-5.2 prim. mantle) and other highly incompatible elements (U, Th, Ba, Rb) relative to the HREE (0.25-2.0 prim. mantle). This large concentration range implies the extensive crystallization of olivine and clinopyroxene together with spinel from a continuously replenished, tapped and crystallizing magma chamber. Final crystallization of the melt in the pore spaces of the cooling cumulate pile explains the large variation in REE concentrations on the scale of a thin

Chromian spinels in highly altered ultramafic rocks from the Sartohay ophiolitic mélange, Xinjiang, NW China

NASA Astrophysics Data System (ADS)

Qiu, Tian; Zhu, Yongfeng

2018-06-01

The Sartohay ophiolitic mélange is located in western Junggar (Xinjiang province, NW China), which is a major component of the core part of the Central Asian Orogenic Belt (CAOB). Chromian spinels in serpentinite, talc schist, carbonate-talc schist and listwaenite in Sartohay ophiolitic mélange retain primary compositions with Cr# of 0.39-0.65, Mg# = 0.48-0.67, and Fe3+# < 0.08. Chromian spinels in deformed listwaenite were initially transformed into Fe2+-rich chromite during shearing deformation followed by Fe3+-rich chromite at shallow levels. The Cr# and Fe3+# of Fe2+-rich chromite (Cr# = 0.59-0.86, Fe3+# = 0.01-0.12, Mg# = 0.35-0.61) and Fe3+-rich chromite (Cr# = 0.85-1.00, Fe3+# = 0.17-0.38, Mg# < 0.29) increase with decrease of Mg#. We propose a model to illustrate the evolution of chromian spinels in highly altered ultramafic rocks from the Sartohay ophiolitic mélange. Chromian spinels in serpentinite and talc schist were rimmed by Cr-magnetite, which was dissolved completely during transformation from serpentinite/talc schist to listwaenite. Chromian spinels were then transformed into Fe2+-rich chromite in shear zones, which characterized by high fluid/rock ratios. This Fe2+-rich chromite and/or chromian spinels could then be transformed into Fe3+-rich chromite in oxidizing conditions at shallow levels.

Rocks of the Columbia Hills

USGS Publications Warehouse

Squyres, S. W.; Arvidson, R. E.; Blaney, D.L.; Clark, B. C.; Crumpler, L.; Farrand, W. H.; Gorevan, S.; Herkenhoff, K. E.; Hurowitz, J.; Kusack, A.; McSween, H.Y.; Ming, D. W.; Morris, R.V.; Ruff, S.W.; Wang, A.; Yen, A.

2006-01-01

The Mars Exploration Rover Spirit has identified five distinct rock types in the Columbia Hills of Gusev crater. Clovis Class rock is a poorly sorted clastic rock that has undergone substantial aqueous alteration. We interpret it to be aqueously altered ejecta deposits formed by impacts into basaltic materials. Wishstone Class rock is also a poorly sorted clastic rock that has a distinctive chemical composition that is high in Ti and P and low in Cr. Wishstone Class rock may be pyroclastic or impact in origin. Peace Class rock is a sedimentary material composed of ultramafic sand grains cemented by significant quantities of Mg- and Ca-sulfates. Peace Class rock may have formed when water briefly saturated the ultramafic sands and evaporated to allow precipitation of the sulfates. Watchtower Class rocks are similar chemically to Wishstone Class rocks and have undergone widely varying degrees of near-isochemical aqueous alteration. They may also be ejecta deposits, formed by impacts into Wishstone-rich materials and altered by small amounts of water. Backstay Class rocks are basalt/trachybasalt lavas that were emplaced in the Columbia Hills after the other rock classes were, either as impact ejecta or by localized volcanic activity. The geologic record preserved in the rocks of the Columbia Hills reveals a period very early in Martian history in which volcanic materials were widespread, impact was a dominant process, and water was commonly present. Copyright 2006 by the American Geophysical Union.

The Rocks of the Columbia Hills

NASA Technical Reports Server (NTRS)

Squyres, Steven W.; Arvidson, Raymond E.; Blaney, Diana L.; Clark, Benton C.; Crumpler, Larry; Farrand, William H.; Gorevan, Stephen; Herkenhoff, Kenneth; Hurowitz, Joel; Kusack, Alastair;

Petrological significance of high-pressure ultramafic xenoliths from ultrapotassic rocks of Central Italy

NASA Astrophysics Data System (ADS)

Conticelli, Sandro; Peccerillo, Angelo

1989-08-01

cumulitic origin from previous potassic magmatic events cannot be excluded. The host lavas have compositions intermediate between high-silica lamproite and Roman-type ultrapotassic rock. They have high abundances of incompatible elements and radiogenic Sr, coupled with high Mg content, {MgO}/{CaO}, Ni and Cr. These features support a genesis in a residual upper mantle which has suffered partial melting with the extraction of basaltic liquids, followed by metasomatic events which caused an enrichment in incompatible elements and radiogenic Sr. The presence of mantle-derived ultramafic xenoliths in the torre Alfina lavas testifies for a rapid uprise of the magma which reached the surface without suffering fractional crystallization and significant interaction with the upper crust. Accordingly, the Torre Alfina lavas represent an unique example of primitive potassic liquid in Central Italy.

Petrological significance of high-pressure ultramafic xenoliths from ultrapotassic rocks of Central Italy

NASA Astrophysics Data System (ADS)

Conticelli, Sandro; Peccerillo, Angelo

1990-08-01

cumulitic origin from previous potassic magmatic events cannot be excluded. The host lavas have compositions intermediate between high-silica lamproite and Roman-type ultrapotassic rock. They have high abundances of incompatible elements and radiogenic Sr, coupled with high Mg content, {MgO}/{CaO}, Ni and Cr. These features support a genesis in a residual upper mantle which has suffered partial melting with the extraction of basaltic liquids, followed by metasomatic events which caused an enrichment in incompatible elements and radiogenic Sr. The presence of mantle-derived ultramafic xenoliths in the torre Alfina lavas testifies for a rapid uprise of the magma which reached the surface without suffering fractional crystallization and significant interaction with the upper crust. Accordingly, the Torre Alfina lavas represent an unique example of primitive potassic liquid in Central Italy.

Platinum-group element geochemistry of zoned ultramafic intrusive suites, Klamath Mountains, California and Oregon.

USGS Publications Warehouse

Gray, F.; Page, N.J.; Carlson, C.A.; Wilson, S.A.; Carlson, R.R.

1986-01-01

Analyses for platinum-group elements of the varied rock suites of three Alaskan-type ultramafic to mafic multi-intrusive bodies are reported. Ir and Ru are less than analytical sensitivities of 100 and 20 ppb; Rh is less than or near 1 ppb. Average Pd assays vary among the rocks within intrusive complexes and between the three complexes (6.3, 13.7, 36.4 ppb); average Pt assays vary little among the same samples (27.9, 60.9, 34.0 ppb). Statistically adjusted Pt/(Pt + Pd) ratios increase in each suite from gabbro through clinopyroxenite to olivine-rich rocks, possibly owing to Pd fractionation.-G.J.N.

Hyperspectral analysis of the ultramafic complex and adjacent lithologies at Mordor, NT, Australia

USGS Publications Warehouse

Rowan, L.C.; Simpson, C.J.; Mars, J.C.

2004-01-01

The Mordor Complex consists of a series of potassic ultramafic rocks which were intruded into Proterozoic felsic gneisses and amphibolite and are overlain by quartzite and unconsolidated deposits. In situ and laboratory 0.4 to 2.5 ??m reflectance spectra show Al-OH absorption features caused by absorption in muscovite, kaolinite, and illite/smectite in syenite, granitic gneiss, quartzite and unconsolidated sedimentary deposits, and Fe,Mg-OH features due to phlogopite, biotite, epidote, and hornblende in the mafic and ultramafic rocks. Ferrous-iron absorption positioned near 1.05 ??m is most intense in peridotite reflectance spectra. Ferric-iron absorption is intense in most of the felsic lithologies. HyMap data were recorded in 126 narrow bands from 0.43 to 2.5 ??m along a 7-km-wide swath with approximately 6-m spatial resolution. Correction of the data to spectral reflectance was accomplished by reference to in situ measurements of an extensive, alluvial plain. Spectral classes for matched filter processing were selected by using the pixel purity index procedure and analysis of in situ and laboratory spectra. Considering the spatial distribution of the resulting 14 classes, some classes were combined, which produced eight classes characterized by Al-OH absorption features, and three Fe,Mg-OH absorption-feature classes. Comparison of the distribution of these 11 spectral classes to a generalized lithologic map of the study area shows that the spectral distinction among the eight Al-OH classes is related to variations in primary lithology, weathering products, and vegetation density. Quartzite is represented in three classes, syenite corresponds to a single scattered class, quartz-muscovite-biotite schist defines a single very coherent class, and unconsolidated sediments are portrayed in four classes. The three mafic-ultramafic classes are distinguished on the basis of generally intense Fe,Mg-OH and ferrous-iron absorption features. A single class represents the

Formation of an ultramafic seafloor at the Southwest Indian Ridge 62°-65°E : internal structure of detachment faults and sparse volcanism documented by sidescan sonar and dredges

NASA Astrophysics Data System (ADS)

Cannat, M.; Sauter, D.; Rouméjon, S.

2012-12-01

In october 2010, the Smoothseafloor cruise (RV Marion Dufresne ) documented the continuous exposure, for the past 10 myrs, of mantle-derived ultramafic rocks in the seafloor of the ultra-slow Southwest Indian Ridge in two 50 to 100 km-wide magma-poor corridors centered respectively at 62°30'E and 64°35'E. The proposed interpretation (Sauter et al., AGU abstract 2011) involves successive large offset normal faults (or detachments) that expose ultramafic rocks alternatively in the southern (Antarctic), then in the northern (African) plates. In this presentation we focus on the most recent, near axis regions in these two ultramafic seafloor corridors. We show details of the sidescan sonar images with smooth, non-corrugated exposed detachment surfaces, and an intriguing pattern of pluridecameter-thick and locally anastomozing reflective and less reflective layers in the detachments footwall. Based on preliminary microstructural observations made on samples dredged in the same region, we tentatively interpret these layers as due to contrasted patterns of deformation in the ultramafics next to the fault. Testing this interpretation would be an attractive goal for future submersible and drilling cruises. Deformation types documented in the dredge samples range from heterogeneous plastic to semi-brittle deformation of the primary peridotite mineralogy, to brittle deformation of serpentinized ultramafic rocks. Magmatic rocks make less than 5% of the overal volume of our near axis dredges. These include variably sheared metagabbros, and unmetamorphosed balsalts. Sidescan sonar images show that these basalts form a thin (<200 m) highly discontinuous carapace over the exposed detachments. We show that these basalts are preferentially located along moderate offset normal faults that cut the detachments, or next to inferred breakaways. This observation leads us to propose a link between axial faulting and volcanism in these magma-poor sections of the ultra-slow spreading

Evaluation of ultramafic deposits in the Eastern United States and Puerto Rico as sources of magnesium for carbon dioxide sequestration

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

Fraser Goff; George Guthrie; Bruce Lipin

2000-04-01

In this report, the authors evaluate the resource potential of extractable magnesium from ultramafic bodies located in Vermont, the Pennsylvania-Maryland-District-of-Columbia (PA-MD-DC) region, western North Carolina, and southwestern Puerto Rico. The first three regions occur in the Appalachian Mountains and contain the most attractive deposits in the eastern United States. They were formed during prograde metamorphism of serpentinized peridotite fragments originating from an ophiolite protolith. The ultramafic rocks consist of variably serpentinized dunite, harzburgite, and minor iherzolite generally containing antigorite and/or lizardite as the major serpentine minor phases. Chrysotile contents vary from minor to major, depending on occurrence. Most bodies containmore » an outer sheath of chlorite-talc-tremolite rock. Larger deposits in Vermont and most deposits in North Carolina contain a core of dunite. Magnesite and other carbonates are common accessories. In these deposits, MgO ranges from 36 to 48 wt % with relatively pure dunite having the highest MgO and lowest H{sub 2}O contents. Ultramafic deposits in southwestern Puerto Rico consist of serpentinized dunite and harzburgite thought to be emplaced as large diapirs or as fragments in tectonic melanges. They consist of nearly pure, low-grade serpentinite in which lizardite and chrysotile are the primary serpentine minerals. Chlorite is ubiquitous in trace amounts. Magnesite is a common accessory. Contents of MgO and H{sub 2}O are rather uniform at roughly 36 and 13 wt %. Dissolution experiments show that all serpentinites and dunite-rich rocks are soluble in 1:1 mixtures of 35% HCl and water by volume. The experiments suggest that low-grade serpentinites from Puerto Rico are slightly more reactive than the higher grade, antigorite-bearing serpentinites of the Appalachian Mountains. The experiments also show that the low-grade serpentinites and relatively pure dunites contain the least amounts of

Dolines on ultramafic rocks : the case of the Southern Grande Terre of New Caledonia (SW Pacific)

NASA Astrophysics Data System (ADS)

Jeanpert, J.; Genthon, P.; Join, J. L.; Vendé-Leclerc, M.; Maurizot, P.; Sérino, J.

2014-12-01

New Caledonia (SW Pacific) presents an exceptional outcrop density of ultramafic rocks on nearly 1/3 of its territory. As result of tropical weathering and dissolution of the silicates that constitute the peridotites, extensive evidences of chemical weathering are observed (dolines, enlarged fractures, epikarst). In particular the South of the Grande Terre, called « Plaine des lacs » presents a landscape but also hydraulic behaviour similar to karstic aquifers, with numerous dolines generally observed as ponds. A morphometric study of these depressions is proposed based on field observations and on automatic mapping from the DEM obtained with LIDAR technology. From SIG calculations followed by manual cleaning, a 8601 dataset of dolines is defined on a 128 km2 area, whose area varies from 1 m2 to 2 km2 area. A statistical analysis is applied on the morphometric parameters of dolines and other factors as amount of precipitation or the distance to characteristic mophologic features (ridges, rivers). Fractal and alignment analysis are presented to detect the potential relationship between dolines, the phenomena involved in their formation and evolution. The role of chemical weathering, and of mechanical erosion are discussed as well as the condition required for doline formation. A comparison with limestone karsitification is drawn.

Organics in hydrothermal fluids from ultramafics on the Mid-Atlantic Ridge (MAR) - Abiogenic and/or biogenic origin?

NASA Astrophysics Data System (ADS)

Charlou, J.; Donval, J.; Fouquet, Y.; Jean-Baptiste, P.; Dehairs, F.; Holm, N.; Godfroy, A.

2005-12-01

Between 12°N and the Azores Triple Junction along the MAR, CH4 anomalies over axial ultramafic sites are common and point to the association of high or low temperature hydrothermal activity and mantle degassing indicative of ongoing serpentinization process. The general occurrence of isotopically-heavy methane shows the possible abiogenic synthesis of hydrocarbons in hydrothermal systems. The abiogenic formation of CH4 and more complex organic compounds is related to the process of serpentinization of mantellic rocks. Three sites (Logachev, 14°45'N; Rainbow, 36°14'N; Lost City Field, 30°N) are known on the MAR. New fresh fluids were recently sampled at Rainbow and Lost City by the French ROV-Victor during EXOMAR cruise (July 24 to August 28, 2005). The Rainbow and Lost City fluids issued from contrasted ultramafic environments are both enriched in H2, CH4 and hydrocarbons. Hydrogen gas represents more than 40 per cent total gas volume extracted from fluids. SPME (Solid Phase Micro-Extraction) and SBSE (Stir-Bar Sorptive Extraction) extraction techniques were used on board for organic recovery and the analysis was performed on shore by direct GC/MS or by Thermo-Desorption/GC/MS. The hydration of olivine and pyroxen minerals with conversion of Fe(II) to Fe(III) in magnetite during serpentinization leads to production of H2 and conversion of dissolved CO2 to reduced-C species including methane, ethane, propane. In addition heavier straight chain hydrocarbons as alcohols, aldehydes, ketones, aromatics, and cyclic compounds are identified at Rainbow. These compounds may be generated in ultramafic rocks through catalytic reactions (Fischer-Tropsch type reactions), but a biogenic contribution cannot be excluded. Abiogenic organic compounds may be produced from crystalline basement, from volcanic structures, from riftogenic zones and probably from sedimented margins.

Characterization of the Sukinda and Nausahi ultramafic complexes, Orissa, India by platinum-group element geochemistry

USGS Publications Warehouse

Page, N.J.; Banerji, P.K.; Haffty, J.

1985-01-01

Samples of 20 chromitite, 14 ultramafic and mafic rock, and 9 laterite and soil samples from the Precambrian Sukinda and Nausahi ultramafic complexes, Orissa, India were analyzed for platinum-group elements (PGE). The maximum concentrations are: palladium, 13 parts per billion (ppb); platinum, 120 ppb; rhodium, 21 ppb; iridium, 210 ppb; and ruthenium, 630 ppb. Comparison of chondrite-normalized ratios of PGE for the chromitite samples of lower Proterozoic to Archean age with similar data from Paleozoic and Mesozoic ophiolite complexes strongly implies that these complexes represent Precambrian analogs of ophiolite complexes. This finding is consistent with the geology and petrology of the Indian complexes and suggests that plate-tectonic and ocean basin developement models probably apply to some parts of Precambrian shield areas. ?? 1985.

Ultramafic Terranes and Associated Springs as Analogs for Mars and Early Earth

NASA Technical Reports Server (NTRS)

Blake, David; Schulte, Mitch; Cullings, Ken; DeVincezi, D. (Technical Monitor)

2002-01-01

Putative extinct or extant Martian organisms, like their terrestrial counterparts, must adopt metabolic strategies based on the environments in which they live. In order for organisms to derive metabolic energy from the natural environment (Martian or terrestrial), a state of thermodynamic disequilibrium must exist. The most widespread environment of chemical disequilibrium on present-day Earth results from the interaction of mafic rocks of the ocean crust with liquid water. Such environments were even more pervasive and important on the Archean Earth due to increased geothermal heat flow and the absence of widespread continental crust formation. The composition of the lower crust and upper mantle of the Earth is essentially the-same as that of Mars, and the early histories of these two planets are similar. It follows that a knowledge of the mineralogy, water-rock chemistry and microbial ecology of Earth's oceanic crust could be of great value in devising a search strategy for evidence of past or present life on Mars. In some tectonic regimes, cross-sections of lower oceanic crust and upper mantle are exposed on land as so-called "ophiolite suites." Such is the case in the state of California (USA) as a result of its location adjacent to active plate margins. These mafic and ultramafic rocks contain numerous springs that offer an easily accessible field laboratory for studying water/rock interactions and the microbial communities that are supported by the resulting geochemical energy. A preliminary screen of Archaean biodiversity was conducted in a cold spring located in a presently serpentinizing ultramafic terrane. PCR and phylogenetic analysis of partial 16s rRNA, sequences were performed on water and sediment samples. Archaea of recent phylogenetic origin were detected with sequences nearly identical to those of organisms living in ultra-high pH lakes of Africa.

Igneous and Ore-Forming Processes at the Roots of Giant - Ultra-Mafic Pluming System: the Seiland Igneous Comples, Norway

NASA Astrophysics Data System (ADS)

Larsen, R. B.; Iljina, M.; Schanke, M.

2012-12-01

SIP covers an area of 5500 km2 in N. Norway. 50 % of the volume comprises mafic layered or homogenous plg+px+Fe-Ti±ol gabbros. 25 % of the area comprises ultramafic intrusions, mostly peridotite and subsidiary pyroxenite and hornblendite. 25 % comprises calc-alkaline and alkaline plutons, respectively. Ultramafic plutons intersect gabbros and calc-alkaline plutons. Recent zircon U/Pb geochronology imply that SIP formed at 560-570 Ma, with mafic- and ultramafic rocks being emplaced in <4 Ma (Roberts et al., Geol. Mag, 2007). Geothermobarometry of contact metamorphic mineral assemblages, implies minimum depth of 20-30 kilometres. Accordingly, the Seiland province arguably provides a unique cross section through the deep-seated parts of a huge magmatic plumbing system. Sulphide Cu-Ni-(PGE) deposits are intimately associated with the ultramafic rock suite. One deposit from Stjernøy comprises sulphide dissiminations at the floor of a peridotitic pluton, another deposit occur at the floor of the Reinfjord ultramafic layered complex in the far West of SIP and the third deposit comprises vertical sulphide dykes in the interior of a hornblendite on the Øksfjord peninsula. Currently, only the Reinfjord deposit is studied in detail. The Reinfjord intrusions is layered and develops from olivine clinopyroxenites in the Lower Zone to wherlite in the Middle Zone to wehrlites and dunite in the Upper Zone. Earlier studies suggest parental melts with pyroxenitic compositions whereas the dunites and wherlites formed by fractional crystallization (Bennet et al., Bull. NGU, 405, 1-41). During our fieldwork we observed spectacular examples of cumulus structures, not previously reported, and including modally layered and modally graded dunite/wherlite, cross-bedding, slumping and mush-diapirs. Finally we saw an example of magma-replenishment where an olivine pyroxenitic magma was emplaced in to and mixed with the contemporary olivine/wherlite mushes!. The country rock gabbros were

Early onset of magma ocean crystallization revealed by coupled 146,147Sm-142,143Nd systematics of Nulliak ultramafics (3.78 Ga, Labrador)

NASA Astrophysics Data System (ADS)

Morino, P.; Caro, G.; Reisberg, L. C.

2015-12-01

Early onset of magma ocean crystallization revealed by coupled 146,147Sm-142,143Nd systematics of Nulliak ultramafics (3.78 Ga, Labrador) Precillia Morino1, Guillaume Caro1, Laurie Reisberg 1 1CRPG-CNRS, Université de Lorraine, Nancy, France Coupled 146,147Sm-142,143Nd systematics provides constraints on the timing of magma ocean crystallization on Mars, the Moon and Vesta. Estimates for the Earth's mantle, however, are less accurate owing to the sparsity of Eoarchean mantle-derived rocks with undisturbed 147Sm-143Nd systematics. This study attempts to establish a coherent 142,143Nd dataset for the Eoarchean mantle using well-preserved ultramafic rocks from the Nulliak assemblage (Labrador). Samples include meta-dunites, -pyroxenites and -peridotites exhibiting only minor serpentinization and limited element mobility. The presence of "Barberton type" komatiitic compositions (low Al/Ti, HREE depletion) is suggestive of a deep mantle source. 146,147Sm-142,143Nd and 187Re-187Os analyses yield a crystallization age of 3.78±0.09 Ga with ɛ143Ndi=1.5±0.2 and ɛ142Nd=8.6±2 ppm. This 142,143Nd signature yields a model age of mantle differentiation of 4.43±0.05 Ga (assuming a BSE with chondritic Sm/Nd and ɛ142Nd=0). Superchondritic Sm/Nd compositions for the BSE would translate into older model ages. Irrespective of the choice of primitive mantle composition, Nulliak ultramafics provide differentiation ages 100 Ma older than those estimated from Akilia tonalites but remarkably similar to that estimated from the 2.7 Ga Theo's flow (Abitibi). If Nulliak ultramafics originated from deep melting of a hot plume, their model age could reflect the early onset of magma ocean crystallization in the lowermost mantle.

Statistical analysis of the radon-222 potential of rocks in Virginia, U.S.A.

USGS Publications Warehouse

Brown, C. Erwin; Mose, D.G.; Mushrush, G.W.; Chrosniak, C.E.

1992-01-01

More than 3,200 indoor radon-222 (222Rn) measurements were made seasonally in an area of about 1,000 square kilometers of the Coastal Plain and Piedmont physiographic provinces in Virginia, U.S.A. Results of these measurements indicate that some geological units are associated, on the average, with twice as much indoor222Rn as other geological units, and that indoor222Rn varies seasonally. The Kruskal-Wallis test was used to test whether indoor222Rn concentrations for data gathered over the winter and summer seasons differ significantly by rock unit. The tests concluded that indoor222Rn concentrations for different rock units were not equal at the 5-percent significance level. The rocks associated with the highest median indoor222Rn concentration are specific rocks in the Mesozoic Culpeper basin, including shale and siltstone units with Jurassic diabase intrusives, and mica schists in the Piedmont physiographic province. The pre-Triassic Peters Creek Schist has the highest ranking in terms of indoor222Rn concentration. The rocks associated with the lowest indoor222Rn concentrations include coastal plain sediments, the Occoquan Granite, Falls Church Tonalite, Piney Branch Mafic and Ultramafic complex, and unnamed mafic and ultramafic inclusions, respectively. The rocks have been ranked according to observed222Rn concentration by transforming the average rank of indoor222Rn concentrations to z scores. ?? 1992 Springer-Verlag New York Inc.

Geochemical and tectonic implications on plate-interface evolution achieved from high-pressure ultramafic rocks in mélange settings

NASA Astrophysics Data System (ADS)

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

2014-12-01

Geochemical studies of fluid-mobile elements (FME) joined with B, Sr and Pb isotopic analyses of high-pressure mélanges terranes help constraining tectonic processes and mass transfer during accretion of slab and suprasubduction mantle in plate-interface domains. Here we focus on ultramafic rocks from two plate interface settings: (I) metasediment-dominated mélange (Cima di Gagnone, CdG, Adula Unit), where eclogite-facies de-serpentinized garnet peridotite and chlorite harzburgite lenses are embedded in paraschist; (II) dominated by high-pressure serpentinite (Erro-Tobbio, ET, and Voltri Units, VU, Ligurian Alps). CdG metaperidotite shows low [B], negative δ 11B and high Sr and Pb isotopic ratios. As, Sb loss from metasediment and gain by garnet and chlorite metaperidotite points to exchange between the two systems. Presence of As and Sb in eclogite-facies peridotite minerals and preferential low-T mobility of such elements suggest that exchange was during early subduction burial and prior to eclogitization. Based on high [B], positive δ11B, oxygen and hydrogen isotope, the ET serpentinties were recently interpreted as supra-subduction mantle flushed by slab fluids (Scambelluri & Tonarini, 2012, Geology, 40, 907-910). Their 206Pb/204Pb and 87Sr/86Sr isotope ratios range between 18.300-18.514 and 0.7048-0.7060, respectively. Compared with ET rocks, VU serpentinites have higher As, Sb (up to 1.3 and 0.39 ppm, respectively) and are enriched in radiogenic Sr (up to 0.7105 87Sr/86Sr). This signature reflects interaction with fluids that exchanged with sedimentary rocks, either in outer rise environments or during accretion atop the slab. In the above cases, the serpentinized mantle rocks fingerprint interaction with fluids from different sources, indicating a timing of accretion to plate interface domains. We provide evidence that serpentinized mantle slices of different size and provenance (slab or wedge) accreted to plate interface domains since early subduction

The mafic-ultramafic complex of Aniyapuram, Cauvery Suture Zone, southern India: Petrological and geochemical constraints for Neoarchean suprasubduction zone tectonics

NASA Astrophysics Data System (ADS)

Yellappa, T.; Venkatasivappa, V.; Koizumi, T.; Chetty, T. R. K.; Santosh, M.; Tsunogae, T.

2014-12-01

Several Precambrian mafic-ultramafic complexes occur along the Cauvery Suture Zone (CSZ) in Southern Granulite Terrain, India. Their origin, magmatic evolution and relationship with the associated high-grade rocks have not been resolved. The Aniyapuram Mafic-Ultramafic Complex (AMUC), the focus of the present study in southern part of the CSZ, is dominantly composed of peridotites, pyroxenites, gabbros, metagabbros/mafic granulites, hornblendites, amphibolites, plagiogranites, felsic granulites and ferruginous cherts. The rock types in the AMUC are structurally emplaced within hornblende gneiss (TTG) basement rocks and are highly deformed. The geochemical signature of the amphibolites indicates tholeiitic affinity for the protolith with magma generation in island arc-setting. N-MORB normalized pattern of the amphibolites show depletion in HFS-elements (P, Zr, Sm, Ti, and Y) and enrichment of LIL-elements (Rb, Ba, Th, Sr) with negative Nb anomalies suggesting involvement of subduction component in the depleted mantle source and formation in a supra-subduction zone tectonic setting. Our new results when correlated with the available age data suggest that the lithological association of AMUC represent the remnants of the Neoarchean oceanic lithosphere.

Non-zero Δ33S preserved in rocks from the Basal Ultramafic Sequence indicate crustal contamination in the most primitive magma of the Rustenburg Layered Suite (Bushveld Complex, South Africa)

NASA Astrophysics Data System (ADS)

Magalhaes, N.; Wilson, A.; Penniston-Dorland, S.; Farquhar, J.

2017-12-01

The sulfur isotope composition of the Rustenburg Layered Suite (RLS) of the Bushveld Complex is different than expected from a magma sourced from the mantle (Δ33S=0), as measurements indicate the presence of an Archean surface-derived sulfur component. The Basal Ultramafic Sequence (BUS) is thought to be the most primitive magma of the RLS, as it is the lowest in the stratigraphy, has the highest Mg# (>0.92) for primary phases (olivine and orthopyroxene), and is in direct contact with the Magaliesberg quartzite of the Pretoria Group.We have measured the composition of sulfides in rocks from the Lower Zone, Marginal Zone, and the BUS, which were sampled in a 2300m drill core from the Clapham area, in the eastern Bushveld Complex. While the rocks of the Lower Zone have a relatively homogeneous non-zero Δ33S of 0.065‰, comparable to previous findings, there is an abrupt increase in the value of Δ33S (up to +0.301‰) in the Marginal Zone, which may be consistent with the observation in hand sample of assimilation of country rocks. The BUS also shows a surface-derived signal (average of 0.040‰), which is the lowest measured for any zone of the RLS.The non-zero Δ33S found in the Basal Ultramafic Sequence is evidence of the contamination of the magma with surface-derived material. In the upper parts of the intrusion, the Δ33S signature relates to whole-rock Sr and Nd isotopes, and their relationship suggests multiple sources of contamination. However, the relationship between sulfur and in-situ strontium isotope compositions (plagioclase) in this section of the RLS is not as clear as it is further up in the stratigraphy. This might reflect small-scale processes during the magmatic chamber stage, different compositions of local wall rock compared to deeper contaminants, or the presence of decoupled behavior between the isotope systems.These differences in the sulfur isotope composition between the different stratigraphic layers have been preserved regardless of

Ultramafic-Hosted Talc-Magnesite Deposits

USGS Publications Warehouse

Robinson, Gilpin R.; Van Gosen, Bradley S.; Foley, Nora K.

2006-01-01

This presentation on the geology of ultramafic-hosted talc-magnesite deposits was given at the 42nd Forum on the Geology of Industrial Minerals, May 7-13, 2006, in Asheville, North Carolina (USA). Talc is a soft inert industrial mineral commodity commonly used as a component or filler in ceramic, paint, paper, plastic, roofing, and electrical applications. Ultramafic-hosted talc-magnesite deposits are important sources of talc.

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.

Magnetic exploration of a low-temperature ultramafic-hosted hydrothermal site (Lost City, 30°N, MAR)

NASA Astrophysics Data System (ADS)

Szitkar, Florent; Tivey, Maurice A.; Kelley, Deborah S.; Karson, Jeffrey A.; Früh-Green, Gretchen L.; Denny, Alden R.

2017-03-01

A 2003 high-resolution magnetic survey conducted by the Autonomous Underwater Vehicle ABE over the low-temperature, ultramafic-hosted hydrothermal field Lost City reveals a weak positive magnetic anomaly. This observation is in direct contrast to recent observations of strong positive magnetic anomalies documented over the high-temperature ultramafic-hosted hydrothermal vents fields Rainbow and Ashadze, which indicates that temperature may control the production of magnetization at these sites. The Lost City survey provides a unique opportunity to study a field that is, to date, one of a kind, and is an end member of ultramafic-hosted hydrothermal systems. Our results highlight the key contribution of temperature on magnetite production resulting from serpentinization reactions. Whereas high temperature promotes significant production and partitioning of iron into magnetite, low temperature favors iron partitioning into various alteration phases, resulting in a magnetite-poor rock. Moreover, the distribution of magnetic anomalies confirms results of a previous geological survey indicating the progressive migration of hydrothermal activity upslope. These discoveries contribute to the results of 25 yrs of magnetic exploration of a wide range of hydrothermal sites, from low- to high-temperature and from basalt- to ultramafic-hosted, and thereby validate using high-resolution magnetics as a crucial parameter for locating and characterizing hydrothermal sites hosting unique chemosynthetic-based ecosystems and potentially mineral-rich deposits.

Magmatic structure and geochemistry of the Luanga Mafic-Ultramafic Complex: Further constraints for the PGE-mineralized magmatism in Carajás, Brazil

NASA Astrophysics Data System (ADS)

Mansur, Eduardo Teixeira; Ferreira Filho, Cesar Fonseca

2016-12-01

The Luanga Complex is part of the Serra Leste Magmatic Suite, a cluster of PGE-mineralized mafic-ultramafic intrusions located in the northeastern portion of the Carajás Mineral Province. The Luanga Complex is a medium-sized layered intrusion consisting of three main zones: i. the lower Ultramafic Zone comprising ultramafic adcumulates (peridotite), ii. the Transition Zone comprising interlayered ultramafic and mafic cumulates (harzburgite, orthopyroxenite and norite) and iii. the upper Mafic Zone comprising a monotonous sequence of mafic cumulates (norite) with minor orthopyroxenite layers. Several PGE-mineralized zones occur in the Transition Zone but the bulk of the PGE resources are hosted within a 10-50 meter thick interval of disseminated sulfides at the contact of the Ultramafic and Transition Zones. The compositional range of cumulus olivine (Fo78.9-86.4) is comparable to those reported for layered intrusions originated from moderate primitive parental magmas. Mantle normalized alteration-resistant trace element patterns of noritic rocks are fractionated, as indicated by relative enrichment in LREE and Th, with negative Nb and Ta anomalies, suggesting assimilation of older continental crust. Ni contents in olivine in the Luanga Complex (up to 7500 ppm) stand among the highest values reported in layered intrusions globally. The highest Ni contents in olivine in the Luanga Complex occur in distinctively PGE enriched (Pt + Pd > 1 ppm) intervals of the Transition Zone, in both sulfide-poor and sulfide bearing (1-3 vol.%) rocks. The origin of the PGE- and Ni-rich parental magma of the Luanga Complex is discussed considering the upgrading of magmas through dissolution of previously formed Ni-rich sulfide melts. Our results suggest that high Ni contents in olivine and/or orthopyroxene provide an additional exploration tool for Ni-PGE deposits, particularly useful for target selection in large magmatic provinces.

Petrogenesis of metaultramafic rocks from the Quadrilátero Ferrífero and adjacent terrains, Minas Gerais, Brazil: Two events of ultramafic magmatism?

NASA Astrophysics Data System (ADS)

da Fonseca, Gabriela Magalhães; Jordt-Evangelista, Hanna; Queiroga, Gláucia Nascimento

2018-03-01

In the worldwide known Quadrilátero Ferrífero and the adjacent terrains, southeastern Brazil, many serpentinite and soapstone quarries, and some rare bodies of metaultramafic rocks that partially preserve minerals or textures from the original igneous protolith can be found. It is not known if the protoliths and the ages of the metaultramafic rocks found in the Quadrilátero Ferrífero (and its oriental basement) and Mineiro Belt regions are the same or if they represent distinct magmatic episodes. The petrogenetic investigation, specially concerning the REE contents, aimed to gather informations about the type of magmatism and the mantle source in order to compare the metaultramafic rocks of both regions. The interpretation of the data concerning petrography, mineral chemistry and geochemistry shows that the metaultramafic rocks are similar to komatiitic peridotites, with MgO contents > 22 wt % and TiO2 < 0.9 wt %. The plot of the REE for the lithotypes found in the Quadrilátero Ferrífero shows decrease in LREE possibly reflecting the depletion of the mantle source. On the other hand the samples from the Mineiro Belt are enriched in LREE suggesting a mantle source enriched in these elements. This enrichment may have been caused by mantle metassomatism that occurred during accretion of the Paleoproterozoic magmatic arc that generated the Mineiro belt. In this paper, we therefore suggest two periods of ultramafic magmatism. The first one found in the Archean basement of the Quadrilátero Ferrífero, with a depleted mantle source. The second occurred in the Paleoproterozoic basement of the Mineiro belt, having a metassomatized mantle as source.

A fossil venting system in the Feragen Ultramafic Body, Norway?

NASA Astrophysics Data System (ADS)

Dunkel, Kristina G.; Jamtveit, Bjørn; Austrheim, Håkon

2017-04-01

Carbonation of ultramafic rocks in ophiolites and on the seafloor has recently been the focus of extensive research, as this alteration reaction not only influences the carbon flux between hydro- and lithosphere, but also provides natural analogues for industrial CO2 sequestration. It is a significant part of the hydrothermal circulation in the oceanic crust, as demonstrated by carbonate precipitation at hydrothermal vents. We provide microstructural and geochemical data from a previously little known ophicarbonate occurrence in the Feragen Ultramafic Body, Sør-Trøndelag, Norway. Along the northern edge of the Feragen Ultramafic Body, strongly serpentinised peridotites are carbonated. In places, the carbonation took place pervasively, leading to the formation of soapstones consisting mainly of talc and magnesite. More common is the carbonation of serpentinite breccias. Within the clasts, some of the serpentine mesh centres are replaced by magnesite, and, subordinately, dolomite or calcium carbonate. Four types of matrix have been identified in different localities: fine-grained magnesite, coarse-grained calcium carbonate, brucite occurring in large fans (up to 1 mm in diameter), and dolomite. Inclusion trails in the coarse-grained calcium carbonates record botryoidal growth, indicating crystallisation from a fluid in open space, and a hexagonal precursor phase, suggesting that aragonite was replaced by calcite. Brucite-cemented serpentinite breccias occur very locally in two outcrops with a size less than 10 m2. Many of the brucite fans have a similar arrangement of inclusions, with an area rich in dolomite inclusions in the centre of the brucite crystals, and magnetite inclusions concentrated in the tips. Dolomite as a matrix phase often grows inwards from hexagonal, rectangular, rhomboidal, or irregular pores. Many dolomite grains are probably cast pseudomorphs after (calcitised) aragonite. Some carbonate crystals are crosscut or replaced by serpentine. The

Si-Metasomatism During Serpentinization of Jurassic Ultramafic Sea-floor: a Comparative Study

NASA Astrophysics Data System (ADS)

Vogel, M.; Frueh-Green, G. L.; Boschi, C.; Schwarzenbach, E. M.

2014-12-01

The Bracco-Levanto ophiolitic complex (northwestern Italy) represents one of the largest and better-exposed ophiolitic successions in the Northern Apennines. It is considered to be a fragment of heterogeneous Jurassic lithosphere that records tectono-magmatic and alteration histories similar to those documented along the Mid-Atlantic Ridge (MAR), such as at the 15°20'N area and the Atlantis Massif at 30°N. Structural and petrological studies on these rocks provide constraints on metamorphic/deformation processes during formation and hydrothermal alteration of the Jurassic oceanic lithosphere. We present a petrological and geochemical study of serpentinization processes and fluid-rock interaction in the Bracco-Levanto ophiolitic complex and compare these to published data from modern oceanic hydrothermal systems, such as the Lost City hydrothermal field hosted in serpentinites on the Atlantis Massif. Major element and mineral compositional data allow us to distinguish a multiphase history of alteration characterized by: (1) widespread Si-metasomatism during progressive serpentinization, and (2) multiple phases of veining and carbonate precipitation associated with circulation of seawater in the shallow ultramafic-dominated portions of the Jurassic seafloor, resulting in the formation of ophicalcites. In detail, regional variations in Si, Mg and Al content are observed in zones of ophicalcite formation, indicating metasomatic reactions and Si-Al transport during long-lived fluid-rock interaction and channelling of hydrothermal fluids. Rare earth element and isotopic analysis indicate that the Si-rich fluids are derived from alteration of pyroxenes to talc and tremolite in ultramafic rocks at depth. Comparison with serpentinites from the Atlantis Massif and 15°20'N indicates a similar degree of Si-enrichment in the modern seafloor and suggests that Si-metasomatism may be a fundamental process associated with serpentinization at slow-spreading ridge environments

A Hierarchical System for Evaluating the Biogenicity of Metavolcanic- and Ultramafic-Hosted Microalteration Textures in the Search for Extraterrestrial Life.

PubMed

McLoughlin, Nicola; Grosch, Eugene G

2015-10-01

The low-temperature alteration of submarine volcanic glasses has been argued to involve the activity of microorganisms, and analogous fluid-rock-microbial-mediated alteration has also been postulated on Mars. However, establishing the extent to which microbes are involved in volcanic glass alteration has proven to be difficult, and the reliability of resulting textural biosignatures is debated, particularly in the early rock record. We therefore propose a hierarchical scheme to evaluate the biogenicity of candidate textural biosignatures found in altered terrestrial and extraterrestrial basaltic glasses and serpentinized ultramafic rocks. The hierarchical scheme is formulated to give increasing confidence of a biogenic origin and involves (i) investigation of the textural context and syngenicity of the candidate biosignature; (ii) characterization of the morphology and size range of the microtextures; (iii) mapping of the geological and physicochemical variables controlling the occurrence and preservation of the microtextures; (iv) in situ investigation of chemical signatures that are syngenetic to the microtexture; and (v) identification of growth patterns suggestive of biological behavior and redox variations in the host minerals. The scheme results in five categories of candidate biosignature as follows: Category 1 indicates preservation of very weak evidence for biogenicity, Categories 2 through 4 indicate evidence for increasing confidence of a biogenic origin, and Category 5 indicates that biogenic origin is most likely. We apply this hierarchical approach to examine the evidence for a biogenic origin of several examples, including candidate bacterial encrustations in altered pillow lavas, granular and tubular microtextures in volcanic glass from the subseafloor and a Phanerozoic ophiolite, mineralized microtextures in Archean metavolcanic glass, and alteration textures in olivines of the martian meteorite Yamato 000593. The aim of this hierarchical approach

Al-augite and Cr-diopside ultramafic xenoliths in basaltic rocks from western United States

USGS Publications Warehouse

Wilshire, H.G.; Shervais, J.W.

1975-01-01

Ultramafic xenoliths in basalts from the western United States are divided into Al-augite and Cr-diopside groups. The Al-augite group is characterized by Al, Ti-rich augites, comparatively Fe-rich olivine and orthopyroxene, and Al-rich spinel, the Cr-diopside group by Cr-rich clinopyroxene and spinel and by Mg-rich olivine and pyroxenes. Both groups have a wide range of subtypes, but the Al-augite group is dominated by augite-rich varieties, and the Cr-diopside group by olivine-rich lherzolites. ?? 1975.

Multiple magmatism in an evolving suprasubduction zone mantle wedge: The case of the composite mafic-ultramafic complex of Gaositai, North China Craton

NASA Astrophysics Data System (ADS)

Yang, Fan; Santosh, M.; Tsunogae, T.; Tang, Li; Teng, Xueming

2017-07-01

The suprasubduction zone mantle wedge of active convergent margins is impregnated by melts and fluids leading to the formation of a variety of magmatic and metasomatic rock suites. Here we investigate a composite mafic-ultramafic intrusion at Gaositai, in the northern margin of the North China Craton (NCC). The hornblende gabbro-serpentinite-dunite-pyroxenite-gabbro-diorite suite surrounded by hornblendites of this complex has long been considered to represent an "Alaskan-type" zoned pluton. We present petrologic, mineral chemical, geochemical and zircon U-Pb and Lu-Hf data from the various rock types from Gaositai including hornblende gabbro, serpentinite, dunite, pyroxenite, diorite and the basement hornblendite which reveal the case of multiple melt generation and melt-peridotite interaction. Our new mineral chemical data from the mafic-ultramafic suite exclude an "Alaskan-type" affinity, and the bulk geochemical features are consistent with subduction-related magmatism with enrichment of LILE (K, Rb, and Ba) and LREE (La and Ce), and depletion of HFSE (Nb, Ta, Zr, and Hf) and HREE. Zircon U-Pb geochronology reveals that the hornblendites surrounding the Gaositai complex are nearly 2 billion years older than the intrusive complex and yield early Paleoproterozoic emplacement ages (2433-2460 Ma), followed by late Paleoproterozoic metamorphism (1897 Ma). The serpentinites trace the history of a long-lived and replenished ancient sub-continental lithospheric mantle with the oldest zircon population dated as 2479 Ma and 1896 Ma, closely corresponding with the ages obtained from the basement rock, followed by Neoproterozoic and Phanerozoic zircon growth. The oldest member in the Gaositai composite intrusion is the dunite that yields emplacement age of 755 Ma, followed by pyroxenite formed through the interaction of slab melt and wedge mantle peridotite at 401 Ma. All the rock suites also carry multiple population of younger zircons ranging in age from Paleozoic to

Petrogenesis of the Dalongkai ultramafic-mafic intrusion and its tectonic implication for the Paleotethyan evolution along the Ailaoshan tectonic zone (SW China)

NASA Astrophysics Data System (ADS)

Liu, Huichuan; Wang, Yuejun; Zi, Jian-Wei

2017-06-01

Layered ultramafic-mafic intrusions are usually formed in an arc/back-arc or intra-plate tectonic environment, or genetically related to a mantle plume. In this paper, we report on an ultramafic-mafic intrusion, the Dalongkai intrusion in the Ailaoshan tectonic zone (SW China), whose occurrence is closely associated with arc/back-arc magmatic rocks. The Dalongkai intrusion is composed of plagioclase-lherzolite, hornblende-peridotite, lherzolite and wehrlite at the bottom, cumulate plagioclase-pyroxenite at the middle part, changing to fine-grained gabbro towards the upper part of the intrusion, forming layering structure. Zircons from the plagioclase-pyroxenites and gabbros yielded U-Pb ages of 272.1 ± 1.7 Ma and 266.4 ± 5.8 Ma, respectively. The plagioclase-pyroxenites show cumulate textures, and are characterized by high MgO (25.0-28.0 wt.%; mg# = 80.6-82.3), Cr (1606-2089 ppm) and Ni (893-1203 ppm) contents, interpreted as early cumulate phases. By contrast, the gabbros have relatively lower mg# values (56.3-62.7), and Cr (157-218 ppm) and Ni (73-114 ppm) concentrations, and may represent frozen liquids. The plagioclase-pyroxenites and gabbros share similar chondrite-normalized REE patterns and primitive mantle-normalized trace element profiles which are analogous to those of typical back-arc basin basalts. The εNd(t) values for both rock types range from +2.20 to +4.22. These geochemical and isotopic signatures suggest that the Dalongkai ultramafic-mafic rocks originated from a MORB-like mantle source metasomatized by subduction-related, sediment-derived fluids. Our data, together with other geological evidence, indicate that the emplacement of the Dalongkai ultramafic-mafic intrusion most likely occurred in a back-arc extensional setting associated with subduction of the Ailaoshan Paleotethyan branch ocean during the Middle Permian, thus ruling out the previously speculated linkage to the Emeishan mantle plume, or to an intra-continental rift.

Geologic map of Harrat Hutaymah, with petrologic classification and distribution of ultramafic inclusions, Saudi Arabia

USGS Publications Warehouse

Thornber, Carl R.

1990-01-01

This map shows detailed geology of the Quaternary and Tertiary volcanic deposits that comprise Harrat Hutaymah and an updated and generalized compilation of the underlying Proterozoic and Paleozoic basement rocks. Quaternary alluvial cover and details of basement geology (that is, faults, dikes, and other features) are not shown. Volcanic unit descriptions and contact relations are based upon field investigation by the author and on compilation and revision of mapping Kellogg (1984; northern half of area) and Pallister (1984; southern half of area). A single K-Ar date of 1.80 ± 0.05 Ma for an alkali olivine basalt flow transected by the Al Hutaymah tuff ring (Pallister, 1984) provides the basis for an estimated late Tertiary to Quaternary age range for all harrat volcanic units other than unit Qtr (tuff reworked during Quaternary age time). Contact relations and unit descriptions for the basement rocks were compiled from Pallister (1984), Kellogg (1984 and 1985), DuBray (1984), Johnson and Williams (1984), Vaslet and others (1987), Cole and Hedge (1986), and Richter and others (1984). All rock unit names in this report are informal and capitalization follows Saudi Arabian stratigraphic nomenclature (Fitch, 1980). Geographic information was compiled from Pallister (1984), Kellogg (1984), and Fuller (in Johnson and Williams, 1984) and from field investigation by the author in 1986. The pie diagrams on the map show the distribution and petrology of ultramafic xenoliths of Harrat Hutaymah. The pie diagrams are explained by a detailed classification of ultramafic xenoliths that is introduced in this report.

Phenocrysts and megacrysts of olivines from ultramafic lamprophyres of the Chadobets and Il'bokich uplifts, Southwestern Siberia

NASA Astrophysics Data System (ADS)

Smirnova, Maria; Sazonova, Lyudmila; Nosova, Anna; Kargin, Alexey; Shcherbakov, Vasiliy

2017-04-01

in olivine (De Hooge et al., 2010). This geothermometer was calibrated for a wide compositional range, including kimberlites, and correspondingly, may be used for alkaline-ultrabasic lamprophyres. At pressures above 4 GPa, olivine phenocrysts fall in the field of olivine-kimberlite melt equilibrium (Girnis et al., 1995). The Il'bokich olivine phenocrysts were formed at higher temperature than the Chadobets phenocrysts: from 1240 to 1340oC for the Il'bokich rocks and from 1080 to 1225oC for the Chadobets rocks. In the P-T diagram showing the geotherm of 40 mV/m2, olivines from the Il'bokich and Chadobets lamprophyres lie to the right of the geotherm, which excludes the presence of xenogenic lithospheric mantle olivine in these rocks. De Hoog J.C.M., Gall L., Cornell D.H. 2010. Trace-element geochemistry of mantle olivine and application to mantle petrogenesis and geothermobarometry // Chem. Geol. 270.1: 196-21. Girnis A.V., Brey G.P., Ryabchikov I.D. 1995. Origin of group 1A kimberlites: fluid-saturated melting experiments at 45-55 kbar // EPSL. 134.3: 283-296. Tappe S., Foley S.F., Jenner G.A. et al. 2006. Genesis of Ultramafic Lamprophyres and Carbonatites at Aillik Bay, Labrador: a Consequence of Incipient Lithospheric Thinning beneath the North Atlantic Craton // J. Petrology. 47 (7). 1261-1315.

Airborne gamma-ray and magnetic anomaly signatures of serpentinite in relation to soil geochemistry, northern California

USGS Publications Warehouse

McCafferty, A.E.; Van Gosen, B. S.

2009-01-01

Serpentinized ultramafic rocks and associated soils in northern California are characterized by high concentrations of Cr and Ni, low levels of radioelements (K, Th, and U) and high amounts of ferrimagnetic minerals (primarily magnetite). Geophysical attributes over ultramafic rocks, which include airborne gamma-ray and magnetic anomaly data, are quantified and provide indirect measurements on the relative abundance of radioelements and magnetic minerals, respectively. Attributes are defined through a statistical modeling approach and the results are portrayed as probabilities in chart and map form. Two predictive models are presented, including one derived from the aeromagnetic anomaly data and one from a combination of the airborne K, Th and U gamma-ray data. Both models distinguish preferential values within the aerogeophysical data that coincide with mapped and potentially unmapped ultramafic rocks. The magnetic predictive model shows positive probabilities associated with magnetic anomaly highs and, to a lesser degree, anomaly lows, which accurately locate many known ultramafic outcrops, but more interestingly, locate potentially unmapped ultramafic rocks, possible extensions of ultramafic bodies that dip into the shallow subsurface, as well as prospective buried ultramafic rocks. The airborne radiometric model shows positive probabilities in association with anomalously low gamma radiation measurements over ultramafic rock, which is similar to that produced by gabbro, metavolcanic rock, and water bodies. All of these features share the characteristic of being depleted in K, Th and U. Gabbro is the only rock type in the study area that shares similar magnetic properties with the ultramafic rock. The aerogeophysical model results are compared to the distribution of ultramafic outcrops and to Cr, Ni, K, Th and U concentrations and magnetic susceptibility measurements from soil samples. Analysis of the soil data indicates high positive correlation between

Impact on the deep biosphere of CO2 geological sequestration in (ultra)mafic rocks and retroactive consequences on its fate

NASA Astrophysics Data System (ADS)

Ménez, Bénédicte; Gérard, Emmanuelle; Rommevaux-Jestin, Céline; Dupraz, Sébastien; Guyot, François; Arnar Alfreősson, Helgi; Reynir Gíslason, Sigurőur; Sigurőardóttir, Hólmfríiur

2010-05-01

Due to their reactivity and high potential of carbonation, mafic and ultramafic rocks constitute targets of great interest to safely and permanently sequestrate anthropogenic CO2 and thus, limit the potential major environmental consequences of its increasing atmospheric level. In addition, subsurface (ultra)mafic environments are recognized to harbor diverse and active microbial populations that may be stimulated or decimated following CO2 injection (± impurities) and subsequent acidification. However, the nature and amplitude of the involved biogeochemical pathways are still unknown. To avoid unforeseen consequences at all time scales (e.g. reservoir souring and clogging, bioproduction of H2S and CH4), the impact of CO2 injection on deep biota with unknown ecology, and their retroactive effects on the capacity and long-term stability of CO2 storage sites, have to be determined. We present here combined field and experimental investigations focused on the Icelandic pilot site, implemented in the Hengill area (SW Iceland) at the Hellisheidi geothermal power plant (thanks to the CarbFix program, a consortium between the University of Iceland, Reykjavik Energy, the French CNRS of Toulouse and Columbia University in N.Y., U.S.A. and to the companion French ANR-CO2FIX project). This field scale injection of CO2 charged water is here designed to study the feasibility of storing permanently CO2 in basaltic rocks and to optimize industrial methods. Prior to the injection, the microbiological initial state was characterized through regular sampling at various seasons (i.e., October '08, July '09, February '10). DNA was extracted and amplified from the deep and shallow observatory wells, after filtration of 20 to 30 liters of groundwater collected in the depth interval 400-980 m using a specifically developed sampling protocol aiming at reducing contamination risks. An inventory of living indigenous bacteria and archaea was then done using molecular methods based on the

Placer and lode platinum-group minerals in south Kalimantan, Indonesia: evidence for derivation from Alaskan-type ultramafic intrusions

USGS Publications Warehouse

Zientek, M.L.

1992-01-01

Platinum-group minerals occur in significant proportions in placer deposits in several localities in South Kalimantan. They consist of Pt-Fe alloy that may be intergrown with or contain inclusions of Ir-Os-Ru alloy, laurite and chromite. Alluvial PGM found along Sungai Tambanio are in part derived from chromatite schlieren in dunitic bodies intruded into clinopyroxene cumulates that may be part of an Alaskan-type ultramafic complex. A chromitite schlieren in serpentinite from one of these dunitic bodies is anomalous in PGE. The chondrite-normalized PGE pattern for this rock, pan concentrates from this area, and PGM concentrates from diamond-Au-PGM placer deposits have an "M'-shaped pattern enriched in Ir and Pt that is typical of PGE-mineralization associated with Alaskan-type ultramafic complexes. -Authors

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

Inherited Fe and Ti electron transition spectroscopic features in altered ultramafic-carbonatite intrusives

NASA Astrophysics Data System (ADS)

Shavers, E. J.; Ghulam, A.; Encarnacion, J. P.

2016-12-01

Spectroscopic reflectance in the visible to short-wave infrared region is an important tool for remote geologic mapping and is applied at scales from satellite to field measurements. Remote geologic mapping is challenging in regions subject to significant surficial weathering. Here we identify absorption features found in altered volcanic pipes and dikes in the Avon Volcanic District, Missouri, that are inherited from the original ultramafic and carbonatite lithology. Alteration ranges from small degree hydrothermal alteration to extensive laterization. The absorption features are three broad minima centered near 690, 890, and 1100 nm. Features in this region are recognized to be caused by ferric and ferrous Fe minerals including olivine, carbonates, chlorite, and goethite all of which are found among the Avon pipes and dikes that are in various stages of alteration. Iron-related intervalence charge transfer and crystal field perturbations of ions are the principal causes of the spectroscopic features in the visible to near-infrared region yet spectra are also distorted by factors like texture and the presence of opaque minerals known to reduce overall reflectance. In the Avon samples, Fe oxide content can reach >15 wt% leading to prominent absorption features even in the less altered ultramafics with reflectance curve maxima as low as 5%. The exaggerated minima allow the altered intrusive rocks to stand out among other weathered lithologies that will often have clay features in the region yet have lower iron concentration. The absorption feature centered near 690 nm is particularly noteworthy. Broad mineral-related absorption features centered at this wavelength are rare but have been linked to Ti3+ in octahedral coordination. The reduced form of Ti is not common in surface lithologies. Titanium-rich andradite has Ti3+ in the octahedral position, is resistant to weathering, is found among the Avon lithologies including ultramafic, carbonatite, and carbonated

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.

Unusual Rocks of the Yap Ridge - Metamorphosed Basal Cumulates of an Arc ?

NASA Astrophysics Data System (ADS)

Hawkins, J. W.; Castillo, P. R.; Batiza, R.

2002-12-01

The 8 to 9 km deep Yap trench, and adjacent Yap Ridge, extend from the southwest end of the Mariana Trench near 11o N, to near 7o 15' N where the trench swings west to intersect the Palau Trench. Unlike other western Pacific subduction systems, the Yap Ridge rises directly from the trench, it has no forearc, neither a remnant nor active volcanic arc, and no inclined seismic zone. The few seismic events recorded are mainly < 70 km depth. Yap Ridge crest depths range from 2.5 km to emergent; there are no emergent volcanoes. Rocks from the islands Yap and Map, are mainly strongly schistose, amphibole-rich, mafic and ultramafic rocks. Metamorphic lineations, and meter-sized mullions having lenticular cross-sections, define inclined (15o southerly dip) tectonic transport. Yap and Map schists are in greenschist facies (actinolite - chlorite - Na-plagioclase, rare titanite and epidote). Talc - tremolite schists, serpentinite, and chlorite-pyroxenite are less common. Small areas of altered andesite are present; quartz diorite and hornblende-rich gabbro occur as clasts in breccias, bomb craters yielded fragments of basalt and diabase. Scattered blankets of laterite several meters thick, and jungle, obscure many details. Deeper crustal rocks exposed on inner wall of Yap Trench, (5 - 2.5 km depths) include amphibolite (Al-hornblende-andesine-titanite) interlayered with calcite- diopside - grossularite marble, and calc-silicate gneisses. Rocks dredged from Yap Ridge include metabasite similar toYap schists, island arc tholeiite series basalt, basaltic andesite, and 2-PX gabbro. These have late Miocene ages (Beccaluva et al., AGU Mon. 23, 1980). Assuming isochemical behavior for immobile elements, protolith for mafic and ultramafic schists had high Mg# (52-83), CaO/Al2O3 0.7-6, Cr 288-1490, Ni 64-609, Zr 13-145, Y 3-28 (ppm).These data suggest picrite, high-Mg basalt, boninite, or OL-PX rich ultramafic cumulates as parents. REE data, e.g. negative slope and (La/Sm)N 0

Effects of interaction between ultramafic tectonite and mafic magma on Nd-Pb-Sr isotopic systems in the Neoproterozoic Chaya Massif, Baikal-Muya ophiolite belt

NASA Astrophysics Data System (ADS)

Amelin, Yuri V.; Ritsk, Eugeni Yu.; Neymark, Leonid A.

1997-04-01

Sm-Nd, Rb-Sr and U-Pb isotopic systems have been studied in minerals and whole rocks of harzburgites and mafic cumulates from the Chaya Massif, Baikal-Muya ophiolite belt, eastern Siberia, in order to determine the relationship between mantle ultramafic and crustal mafic sections. Geological relations in the Chaya Massif indicate that the mafic magmas were emplaced into, and interacted with older solid peridotite. Hand picked, acid-leached, primary rock-forming and accessory minerals (olivine, orthopyroxene, clinopyroxene and plagioclase) from the two harzburgite samples show coherent behavior and yield 147Sm/ 144Nd- 143Nd/ 144Nd and 238U/ 204Pb- 206Pb/ 204Pb mineral isochrons, corresponding to ages of 640 ± 58 Ma (95% confidence level) and 620 ± 71 Ma, respectively. These values are indistinguishable from the crystallization age of the Chaya mafic units of 627 ± 25 Ma (a weighted average of internal isochron Sm-Nd ages of four mafic cumulates). The Rb-Sr and Sm-Nd isotopic systems in the harzburgite whole-rock samples were disturbed by hydrothermal alteration. These alteration-related isotopic shifts mimic the trend of variations in primary isotopic compositions in the mafic sequence, thus emphasizing that isotopic data for ultramafic rocks should be interpreted with great caution. On the basis of initial Sr and Nd values, ultramafic and mafic rocks of the Chaya Massif can be divided into two groups: (1) harzburgites and the lower mafic unit gabbronorites withɛ Nd = +6.6 to +7.1 andɛ Sr = -11 to -16; and (2) websterite of the lower unit and gabbronorites of the upper mafic unit:ɛ Nd = +4.6 to +6.1 andɛ Sr = -8 to -9. Initial Pb isotopic ratios are identical in all rocks studied, with mean values of 206Pb/ 204Pb= 16.994 ± 0.023 and 207Pb/ 204Pb= 15.363 ± 0.015. The similarity of ages and initial isotopic ratios within the first group indicates that the isotopic systems in the pre-existing depleted peridotite were reset by extensive interaction with

Effects of interaction between ultramafic tectonite and mafic magma on Nd-Pb-Sr isotopic systems in the Neoproterozoic Chaya Massif, Baikal-Muya ophiolite belt

USGS Publications Warehouse

Amelin, Y.V.; Ritsk, E. Yu; Neymark, L.A.

1997-01-01

Sm-Nd, Rb-Sr and U-Pb isotopic systems have been studied in minerals and whole rocks of harzburgites and mafic cumulates from the Chaya Massif, Baikal-Muya ophiolite belt, eastern Siberia, in order to determine the relationship between mantle ultramafic and crustal mafic sections. Geological relations in the Chaya Massif indicate that the mafic magmas were emplaced into, and interacted with older solid peridotite. Hand picked, acid-leached, primary rock-forming and accessory minerals (olivine, orthopyroxene, clinopyroxene and plagioclase) from the two harzburgite samples show coherent behavior and yield 147Sm/144Nd- 143Nd/144Nd and 238U/204Pb-206Pb/204Pb mineral isochrons, corresponding to ages of 640 ?? 58 Ma (95% confidence level) and 620 ?? 71 Ma, respectively. These values are indistinguishable from the crystallization age of the Chaya mafic units of 627 ?? 25 Ma (a weighted average of internal isochron Sm-Nd ages of four mafic cumulates). The Rb-Sr and Sm-Nd isotopic systems in the harzburgite whole-rock samples were disturbed by hydrothermal alteration. These alteration-related isotopic shifts mimic the trend of variations in primary isotopic compositions in the mafic sequence, thus emphasizing that isotopic data for ultramafic rocks should be interpreted with great caution. On the basis of initial Sr and Nd values, ultramafic and mafic rocks of the Chaya Massif can be divided into two groups: (1) harzburgites and the lower mafic unit gabbronorites with ??Nd = +6.6 to +7.1 and ??Sr = -11 to -16; and (2) websterite of the lower unit and gabbronorites of the upper mafic unit: ??Nd = + 4.6 to + 6.1 and ??Sr = - 8 to -9. Initial Pb isotopic ratios are identical in all rocks studied, with mean values of 206Pb/204Pb = 16.994 ?? 0.023 and 207Pb/204Pb = 15.363 ?? 0.015. The similarity of ages and initial isotopic ratios within the first group indicates that the isotopic systems in the pre-existing depleted peridotite were reset by extensive interaction with basaltic

Integrated Experimental and Modeling Studies of Mineral Carbonation as a Mechanism for Permanent Carbon Sequestration in Mafic/Ultramafic Rocks

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

Wang, Zhengrong; Qiu, Lin; Zhang, Shuang

2014-09-30

A program of laboratory experiments, modeling and fieldwork was carried out at Yale University, University of Maryland, and University of Hawai‘i, under a DOE Award (DE-FE0004375) to study mineral carbonation as a practical method of geologic carbon sequestration. Mineral carbonation, also called carbon mineralization, is the conversion of (fluid) carbon dioxide into (solid) carbonate minerals in rocks, by way of naturally occurring chemical reactions. Mafic and ultramafic rocks, such as volcanic basalt, are natural candidates for carbonation, because the magnesium and iron silicate minerals in these rocks react with brines of dissolved carbon dioxide to form carbonate minerals. By trappingmore » carbon dioxide (CO 2) underground as a constituent of solid rock, carbonation of natural basalt formations would be a secure method of sequestering CO 2 captured at power plants in efforts to mitigate climate change. Geochemical laboratory experiments at Yale, carried out in a batch reactor at 200°C and 150 bar (15 MPa), studied carbonation of the olivine mineral forsterite (Mg 2SiO 4) reacting with CO 2 brines in the form of sodium bicarbonate (NaHCO 3) solutions. The main carbonation product in these reactions is the carbonate mineral magnesite (MgCO 3). A series of 32 runs varied the reaction time, the reactive surface area of olivine grains and powders, the concentration of the reacting fluid, and the starting ratio of fluid to olivine mass. These experiments were the first to study the rate of olivine carbonation under passive conditions approaching equilibrium. The results show that, in a simple batch reaction, olivine carbonation is fastest during the first 24 hours and then slows significantly and even reverses. A natural measure of the extent of carbonation is a quantity called the carbonation fraction, which compares the amount of carbon removed from solution, during a run, to the maximum amount that could have been removed if the olivine initially present

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

Descriptions of mineral occurrences and interpretation of mineralized rock geochemical data in the Stikine geophysical survey area, Southeastern Alaska

USGS Publications Warehouse

Taylor, Cliff D.

2003-01-01

tectonic activity to quiescence (such as conglomeratic and/or mafic volcaniclastics or flows overlain by platform carbonate or shale sequences), 2) presence and proximity to Late Triassic mafic-ultramafic intrusions, 3) presence of quartz-carbonate-fuchsite altered ultramafic bodies, 4) pyritic, graphitic shales, 5) presence of barite and/or iron-manganese-rich carbonates, 6) low-iron sphalerite and antimony-rich sulfosalt minerals, 7) a geochemical signature including Fe-Zn-Pb-Cu-Ag-Au-Sb-Hg-As-Cd-Ba-Mn-Mo-Tl and the ultramafic-related suite of elements Ni-Cr-Co, and 8) a geophysical signature characterized by the coincidence of a sharp resistivity contrast with evidence for buried intrusive rocks. Critical factors for the development of larger, economic orebodies are significant thickness of pyritic, graphitic shale indicating that a locally reducing sedimentary setting was established and that accumulation of an insulating shale blank occurred, and proximity to Late Triassic aged hypabyssal mafic-ultramafic intrusive rocks.

Deformation associated with the denudation of mantle-derived rocks at the Mid-Atlantic Ridge 13°-15°N: The role of magmatic injections and hydrothermal alteration

NASA Astrophysics Data System (ADS)

Picazo, Suzanne; Cannat, Mathilde; Delacour, AdéLie; EscartíN, Javier; RouméJon, StéPhane; Silantyev, Sergei

2012-09-01

Outcrops of deeply derived ultramafic rocks and gabbros are widespread along slow spreading ridges where they are exposed in the footwall of detachment faults. We report on the microstructural and petrological characteristics of a large number of samples from ultramafic exposures in the walls of the Mid-Atlantic Ridge (MAR) axial valley at three distinct locations at lat. 13°N and 14°45'N. One of these locations corresponds to the footwall beneath a corrugated paleo-fault surface. Bearing in mind that dredging and ROV sampling may not preserve the most fragile lithologies (fault gouges), this study allows us to document a sequence of deformation, and the magmatic and hydrothermal history recorded in the footwall within a few hundred meters of the axial detachment fault. At the three sampled locations, we find that tremolitic amphiboles have localized deformation in the ultramafic rocks prior to the onset of serpentinization. We interpret these tremolites as hydrothermal alteration products after evolved gabbroic rocks intruded into the peridotites. We also document two types of brittle deformation in the ultramafic rocks, which we infer could produce the sustained low magnitude seismicity recorded at ridge axis detachment faults. The first type of brittle deformation affects fresh peridotite and is associated with the injection of the evolved gabbroic melts, and the second type affects serpentinized peridotites and is associated with the injection of Si-rich hydrothermal fluids that promote talc crystallization, leading to strain localization in thin talc shear zones. We also observed chlorite + serpentine shear zones but did not identify samples with serpentine-only shear zones. Although the proportion of magmatic injections in the ultramafic rocks is variable, these characteristics are found at each investigated location and are therefore proposed as fundamental components of the deformation in the footwall of the detachment faults associated with denudation of

Source characteristics and tectonic setting of mafic-ultramafic intrusions in North Xinjiang, NW China: Insights from the petrology and geochemistry of the Lubei mafic-ultramafic intrusion

NASA Astrophysics Data System (ADS)

Chen, Bao-Yun; Yu, Jin-Jie; Liu, Shuai-Jie

2018-05-01

The newly discovered Lubei sulfide-bearing mafic-ultramafic intrusion forms the western extension of the Huangshan-Jin'erquan mafic-ultramafic intrusion belt in East Tianshan, NW China. The Lubei intrusion comprises hornblende peridotite, lherzolite, and harzburgite in its southern portion, gabbro in its middle portion, and hornblende gabbro in its northern portion. Intrusive relationships indicate that three magma pulses were involved in the formation of the intrusion, and that they were likely evolved from a common primitive magma. Estimated compositions of the Lubei primitive magma are similar to those of island arc calc-alkaline basalt except for the low Na2O and CaO contents of the Lubei primitive magma. This paper reports on the mineral compositions, whole-rock major and trace element contents, and Rb-Sr and Sm-Nd isotopic compositions of the Lubei intrusion, and a zircon LA-MC-ICP-MS U-Pb age for hornblende gabbro. The Lubei intrusion is characterized by enrichment in large-ion lithophile elements, depletion in high-field-strength elements, and marked negative Nb and Ta anomalies, with enrichment in chondrite-normalized light rare earth elements. It exhibits low (87Sr/86Sr)i ratios of 0.70333-0.70636 and low (143Nd/144Nd)i ratios of 0.51214-0.51260, with positive εNd values of +4.01 to +6.33. LA-ICP-MS U-Pb zircon ages yielded a weighted-mean age of 287.9 ± 1.6 Ma for the Lubei intrusion. Contemporaneous mafic-ultramafic intrusions in different tectonic domains in North Xinjiang show similar geological and geochemical signatures to the Lubei intrusion, suggesting a source region of metasomatized mantle previously modified by hydrous fluids from the slab subducted beneath the North Xinjiang region in the early Permian. Metasomatism of the mantle was dominated by hydrous fluids and was related to subduction of the Paleo-Asian oceanic lithosphere during the Paleozoic. Sr-Nd-Pb isotopic compositions suggest that the mantle source was a mixture of depleted mid

The Ultramafic Complex of Reinfjord: from the Magnetic Petrology to the Interpretation of the Magnetic Anomalies

NASA Astrophysics Data System (ADS)

Pastore, Zeudia; McEnroe, Suzanne; Church, Nathan; Fichler, Christine; ter Maat, Geertje W.; Fumagalli, Patrizia; Oda, Hirokuni; Larsen, Rune B.

2017-04-01

A 3D model of the geometry of the Reinfjord complex integrating geological and petrophysical data with high resolution aeromagnetic, ground magnetic and gravity data is developed. The Reinfjord ultramafic complex in northern Norway is one of the major ultramafic complexes of the Neoproterozoic Seiland Igneous Province (SIP). This province, now embedded in the Caledonian orogen, was emplaced deep in the crust (30 km of depth) and is believed to represent a section of the deep plumbing system of a large igneous province. The Reinfjord complex consists of three magmatic series formed during multiple recharging events resulting in the formation of a cylindrically zoned complex with a slightly younger dunite core surrounded by wehrlite and lherzolite units. Gabbros and gneiss form the host rock. The ultramafic complex has several distinct magnetic anomalies which do not match the mapped lithological boundaries, but are correlated with changes in magnetic susceptibilities. In particular, the deviating densities and magnetic susceptibilities at the northern side of the complex are interpreted to be due to serpentinization. Detailed studies of magnetic anomalies and magnetic properties of samples can provide a powerful tool for mapping petrological changes. Samples can have wide range of magnetic properties depending on composition, amount of ferromagnetic minerals, grain sizes and microstructures. Later geological processes such as serpentinization can alter this signal. Therefore a micro-scale study of magnetic anomalies at the thin section scale was carried out to understand better the link between the magnetic petrology and the magnetic anomalies. Serpentinization can significantly enhance the magnetic properties and therefore change the nature of the magnetic anomaly. The detailed gravity and magnetic model here presented shows the subsurface structure of the ultramafic complex refining the geological interpretation of the magnetic sources within it, and the local

Whole-rock and mineral compositional constraints on the magmatic evolution of the Ni-Cu-(PGE) sulfide ore-bearing Kevitsa intrusion, northern Finland

NASA Astrophysics Data System (ADS)

Luolavirta, Kirsi; Hanski, Eero; Maier, Wolfgang; Santaguida, Frank

2018-01-01

The 2.06 Ga mafic-ultramafic Kevitsa intrusion is located in the Central Lapland greenstone belt. The lower ultramafic part of the intrusion hosts a large disseminated Ni-Cu-(PGE) sulfide deposit with Ni tenors ranging widely from < 4 wt% (uneconomic false ore and contact mineralization) to 4-7 wt% (regular ore) and up to 40 wt% (Ni-PGE ore). The stratigraphy of the ultramafic cumulates is divided into the basal pyroxenite-gabbro (Basal series), olivine pyroxenite (OLPX), pyroxenite, and plagioclase-bearing (ol) websterite (pOLWB), of which the latter occurs together with minor microgabbros in the ore-bearing domain of the intrusion. Around the ore domain, the ultramafic cumulate succession records a simple lithological stratigraphy and modest and predictable variations in whole-rock and mineral compositions. The ore-bearing domain, in contrast, is characterized by a complex internal architecture, variations in whole-rock and mineral compositions, and the presence of numerous inclusions and xenoliths. The OLPXs are mainly composed of cumulus olivine (Fo77-89) and clinopyroxene (Mg#81-92) with variable amounts of oikocrystic orthopyroxene (Mg#79-84). They comprise the bulk of the ultramafic cumulates and are the dominant host rocks to the sulfide ore. The host rocks to the regular and false ore type are mineralogically and compositionally similar (Fo 80-83, mostly) and show mildly LREE-enriched REE patterns (CeN/YbN 2), characteristic for the bulk of the Kevitsa ultramafic cumulates. The abundance of orthopyroxene and magnetite is lowest in the host rocks to the Ni-PGE ore type, being in line with the mineral compositions of the silicates, which are the most primitive in the intrusion. However, it contrasts with the LREE-enriched nature of the ore type (CeN/YbN 7), indicating significant involvement of crustal material in the magma. The contrasting intrusive stratigraphy in the different parts of the intrusion likely reflects different emplacement histories. It is

Structural correction of paleomagnetic vectors dispersed about two fold axes and application to the Duke Island (Alaska) ultramafic complex

NASA Astrophysics Data System (ADS)

Bogue, Scott W.; Grommé, C. Sherman

2004-11-01

A new analysis of paleomagnetic data from the mid-Cretaceous (˜110 Ma) ultramafic complex at Duke Island (southeast Alaska) supports large poleward transport of the Insular superterrane relative to North America consistent with the Baja British Columbia hypothesis. Previous paleomagnetic work has shown that the characteristic remanence of the ultramafic complex predates kilometer-scale deformation of the very well developed cumulate layering but that the layering was not horizontal everywhere before the folding. It is possible, however, to estimate paleohorizontal for the Duke Island ultramafic complex because the postremanence deformation of the intrusion occurred about two well-defined and spatially separate fold axes. In such a case the tectonically rotated paleomagnetic directions should be distributed along small circles centered on each of the two fold axes. The ancient field direction will lie on both small circles and therefore will be identifiable as one of their two intersection points. Interpreted this way, the tectonically rotated remanence of the Duke Island ultramafic complex defines a mid-Cretaceous (i.e., ancient) field direction that is within 2° of the paleomagnetic direction found by assuming the cumulate layering was initially horizontal (despite the paleomagnetic evidence to the contrary) and performing the standard structure correction. The inferred mid-Cretaceous paleolatitude of Duke Island is 21.2° (2350 km) anomalous with respect to cratonic North America. This result is concordant with southerly paleolatitudes determined by many other workers from bedded rocks of terranes farther inboard in the Insular and Intermontane superterranes.

Genesis of the Permian Kemozibayi sulfide-bearing mafic-ultramafic intrusion in Altay, NW China: Evidence from zircon geochronology, Hf and O isotopes and mineral chemistry

NASA Astrophysics Data System (ADS)

Tang, Dongmei; Qin, Kezhang; Xue, Shengchao; Mao, Yajing; Evans, Noreen J.; Niu, Yanjie; Chen, Junlu

2017-11-01

The recently discovered Kemozibayi mafic-ultramafic intrusion and its associated magmatic Cu-Ni sulfide deposits are located at the southern margin of the Chinese Altai Mountain, Central Asian Orogenic Belt in north Xinjiang, NW China. The intrusion is composed of olivine websterite, norite, gabbro and diorite. Disseminated and net-textured Ni-Cu sulfide ores are hosted in the center of the gabbro. In this work, new zircon U-Pb ages, Hf-O isotopic and sulfide S isotopic data, and whole rock and mineral chemical analyses are combined in order to elucidate the characteristics of the mantle source, nature of subduction processes, degree of crustal contamination, geodynamic setting of bimodal magmatism in the region, and the metallogenic potential of economic Cu-Ni sulfide deposit at depth. SIMS zircon U-Pb dating of the gabbro yields Permian ages (278.3 ± 1.9 Ma), coeval with the Kalatongke Cu-Ni deposit and with Cu-Ni deposits in the Eastern Tianshan and Beishan areas. Several lines of evidence (positive εHf(t) from + 7.1 to + 13.3, Al2O3, TiO2 and SiO2 contents in clinopyroxene from olivine websterite, high whole rock TiO2 contents) suggest that the primary magma of the Kemozibayi intrusion was a calc-alkaline basaltic magma derived from depleted mantle, and that the degree of partial melting in the magma source was high. The evolution of the Kemozibayi mafic-ultramafic complex was strongly controlled by fractional crystallization and the crystallization sequence was olivine websterite, norite, and then gabbro. This is evidenced by whole rock Fe2O3 contents that are positively correlated with MgO and negatively correlated with Al2O3, CaO and Na2O, similar LREE enrichment and negative Nb, Ta, Hf anomalies in chondrite and primitive mantle-normalized patterns, and a decrease in total REE and trace elements contents and magnetite content from gabbro through to norite and olivine websterite. Varied and low εHf(t) (+ 7.1 to + 13.3) and high δ18O values (+ 6.4‰ to

Metasomatism-induced magnesium isotope fractionation in ultramafic rocks: Evidence from the Franciscan Complex, California

NASA Astrophysics Data System (ADS)

Li, W. Y.; Teng, F. Z.; Xiao, Y.

2016-12-01

To investigate the behaviour of Mg isotopes during metasomatic reactions between peridotites and infiltrating fluids along the slab-mantle interface, we analyzed Mg isotopic compositions of a set of well-characterized samples from the ultramafic blocks in the Franciscan Complex of California [1]. The Group 1 and Group 2 samples that were defined by the initial serpentinization and complete serpentinization of peridotites at temperatures of 450-500 ºC, respectively [1], have δ26Mg values (from -0.26 to -0.14‰) clustered around the mantle value. This suggests that Mg isotope fractionation during serpentinization by slab-derived fluids, if any, is small. By contrast, the Group 3 samples that were defined by the replacement of serpentine by talc [1], are enriched in heavy Mg isotopes (δ26Mg of -0.13 to -0.01‰). This may reflect the loss of light Mg isotopes into fluids during the dehydration reaction that produced talc from serpentine, which is consistent with previous observations that secondary clay minerals preferentially incorporate heavy Mg isotopes during water-rock interactions [2, 3]. The Group 4 samples that were defined by the further replacement of talc by tremolite [1], however, have light Mg isotopic compositions (δ26Mg of -0.50 to -0.41‰). Such a shift towards light Mg isotopic compositions likely results from metasomatism by fluids that derived from isotopically light carbonates, which is supported by the remarkably higher CaO content of Group 4 samples (from 6.9 to 9.2 wt%) than Group 3 ones (from 1.1 to 1.4 wt%). Collectively, significant Mg isotopic variations occur during metasomatism of peridotites in the mantle wedge, which would potentially lead to heterogeneous Mg isotopic compositions in arc lavas [4]. Therefore, Mg isotopes can be used as a powerful tracer of crust-mantle interaction at subduction zones. [1] King et al. (2003) Geol. Soc. Am. Bull. 115, 1097-1109. [2] Teng et al. (2010) Earth Planet. Sci. Lett. 300, 63-71. [3] Wimpenny

Platinum potential of mafic-ultramafic massifs in the western part of the Dambuka ore district (Upper Amur Region, Russia)

NASA Astrophysics Data System (ADS)

Melnikov, A. V.; Stepanov, V. A.; Moiseenko, V. G.

2016-02-01

New data on the Pt potential of mafic-ultramafic massifs of the Khani-Maya, Uldegit, and Dzhalta complexes in the western part of the Dambuka ore district are discussed. The Khani-Maya Complex is represented by metamorphosed gabbro, gabbronorites, gabbro anorthosites, subordinate pyroxenites, hornblendites, and peridotites. The Uldegit Complex is composed of pyroxenites, hornblendites, gabbro, gabbronorites, norites, troctolites, peridotites, dunites, actinolite-tremolites, serpentinites, anthophyllites, and tremolite-plagioclase rocks. The Dzhalta Complex is formed of peridotites, gabbro, eclogitized gabbro, hornblendites, cortlandites, and pyroxenites. All these complexes differ from each other by the concentrations of Ni, Cu, Co, Au, and platinoids depending on the composition of the constituting rocks and the presence of sulfide minerals.

Rocks of the early lunar crust

NASA Technical Reports Server (NTRS)

James, O. B.

1980-01-01

Data are summarized which suggest a model for the early evolution of the lunar crust. According to the model, during the final stages of accretion, the outer part of the moon melted to form a magma ocean approximately 300 km deep. This ocean fractionated to form mafic and ultramafic cumulates at depth and an overlying anorthositic crust made up of ferroan anorthosites. Subsequent partial melting in the primitive mantle underlying the crystallized magma ocean produced melts which segregated, moved upward, intruded the primordial crust, and crystallized to form layered plutons consisting of Mg-rich plutonic rocks. Intense impact bombardment at the lunar surface mixed and melted the rocks of the two suites to form a thick layer of granulated debris, granulitic breccias, and impact-melt rocks.

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

Geochemistry, Metamorphic Assemblages, and Microstructures in Small Ultramafic Bodies from the Northern Nason Terrane, Washington

NASA Astrophysics Data System (ADS)

Magloughlin, J. F.

2014-12-01

Ultramafic bodies ranging from <1 to 2500 m in length occur in multiple settings across the northern part of the Nason Terrane in the North Cascade Mountains of Washington State. Within the Wenatchee Ridge Orthogneiss (WRO) the bodies are approximately equidimensional, ranging from dm-scale metasomatized lenses up to an exposed diameter of (typically) approximately 40 m. Some bodies are completely serpentinized, but others include dunite, harzburgite, and rare seams of pyroxenite. Many are rimmed by blackwall (talc, phlogopite, tremolite, chlorite, serpentine) coinciding with the Late Cretaceous metamorphism. The Napeequa Ultramafic Body (NUB), cut through and well exposed by the Napeequa River west of Lake Wenatchee, is within the White River Shear Zone (WRSZ, Magloughlin & McEwan, 1988). Though highly variable, it consists of dunite and peridotite and is variably serpentinized with common Mg-amphibole. Assemblages include serp+carb+chl+talc+opq and suggest upper greenschist to low amphibolite facies overprinting. Rare high-strain zones resemble relict pseudotachylyte veins. More common are ultramylonitic zones with olivine grain sizes of <5 microns, suggesting terrane-boundary paleostresses of >250 MPa. The Nine Mile Creek Ultramafic Body (NMCUB) and Grave Ultramafic Body (GUB) are the largest bodies outside of the White River Shear Zone, and are approximately 300 m and 800 long, respectively. Both are characterized by ol+talc+amph along with chlorite pseudomorphs, commonly cut by <40 micron thick ribbons of calcite, and rarely containing Si defined by chromite. These tectonites contain fine-grained olivine, but post-deformational, metamorphic cummingtonite and tremolite. In both bodies, a moderate to strong foliation is developed. It is suggested both bodies are retrogressed garnet peridotites. An interesting problem is why the possible retrogressed garnet peridotite bodies are present south of the WRSZ and surrounded by the metatonalites of the WRO, but none

Deformation associated to exhumation of serpentinized mantle rocks in a fossil Ocean Continent Transition: The Totalp unit in SE Switzerland

NASA Astrophysics Data System (ADS)

Picazo, S.; Manatschal, G.; Cannat, M.; Andréani, M.

2013-08-01

Although the exhumation of ultramafic rocks in slow and ultraslow spreading Mid-Ocean Ridges and Ocean Continent Transitions (OCTs) has been extensively investigated, the deformation processes related to mantle exhumation are poorly constrained. In this paper we present a new geological map and a section across the exhumed serpentinized peridotites of the Totalp unit near Davos (SE Switzerland), and we propose that the Totalp unit is formed by two Alpine thrust sheets. Geological mapping indicates local exposure of a paleo-seafloor that is formed by an exhumed detachment surface and serpentinized peridotites. The top of the exhumed mantle rocks is made of ophicalcites that resulted from the carbonation of serpentine under static conditions at the seafloor. The ophicalcites preserve depositional contacts with Upper Jurassic to Lower Cretaceous pelagic sediments (Bernoulli and Weissert, 1985). These sequences did not exceed prehnite-pumpellyite metamorphic facies conditions, and locally escaped Alpine deformation. Thin mylonitic shear zones as well as foliated amphibole-bearing ultramafic rocks have been mapped. The age of these rocks and the link with the final exhumation history are yet unknown but since amphibole-bearing ultramafic rocks can be found as clasts in cataclasites related to the detachment fault, they pre-date detachment faulting. Our petrostructural study of the exhumed serpentinized rocks also reveals a deformation gradient from cataclasis to gouge formation within 150 m in the footwall of the proposed paleo-detachment fault. This deformation postdates serpentinization. It involves a component of plastic deformation of serpentine in the most highly strained intervals that has suffered pronounced grain-size reduction and a polyphase cataclastic overprint.

Slab break-off and the formation of Permian mafic-ultramafic intrusions in southern margin of Central Asian Orogenic Belt, Xinjiang, NW China

NASA Astrophysics Data System (ADS)

Song, Xie-Yan; Xie, Wei; Deng, Yu-Feng; Crawford, Anthony J.; Zheng, Wen-Qin; Zhou, Guo-Fu; Deng, Gang; Cheng, Song-Lin; Li, Jun

2011-11-01

The Baishiquan and Pobei Early Permian mafic-ultramafic intrusions were emplaced into Proterozoic metamorphic rocks in the Central Tianshan and the Beishan Fold Belt, northern Xinjiang, NW China. The Baishiquan intrusion comprises mainly gabbro, and mela-gabbro sills occurring within and along the margins of the gabbro body. In the Pobei intrusion, two distinct gabbroic packages, a lower gabbro and the main gabbro, are intruded and overlain by small cumulate wehrlite bodies. Both intrusions are characterized by enrichments of large ion lithophile elements and Th and U relative to the high field strength elements, and show strong negative Nb and Ta anomalies and positive K and Pb anomalies, leading to higher Th/Yb and Nb/Yb than in mid-ocean ridge basalt and ocean island basalt. These features are comparable with subduction-related mafic rocks and post-collisional magmas. Geological and geochemical considerations indicate that the parental magmas of the two intrusions were derived from decompression melting of ascending asthenosphere and reacted with overlying subduction-modified lithospheric mantle. We believe that these parental magmas were generated by post-collisional extension along the Chinese Tianshan, perhaps triggered by slab break-off or delamination of thickened lithosphere. Relatively lower (143Nd/144Nd)i and higher (87Sr/86Sr)i than other Permian mafic-ultramafic intrusions in the eastern Chinese Tianshan indicate that the parental magmas of these two intrusions experienced significant contamination by old crustal rocks.

Statistical analysis of Thematic Mapper Simulator data for the geobotanical discrimination of rock types in southwest Oregon

NASA Technical Reports Server (NTRS)

Morrissey, L. A.; Weinstock, K. J.; Mouat, D. A.; Card, D. H.

1984-01-01

An evaluation of Thematic Mapper Simulator (TMS) data for the geobotanical discrimination of rock types based on vegetative cover characteristics is addressed in this research. A methodology for accomplishing this evaluation utilizing univariate and multivariate techniques is presented. TMS data acquired with a Daedalus DEI-1260 multispectral scanner were integrated with vegetation and geologic information for subsequent statistical analyses, which included a chi-square test, an analysis of variance, stepwise discriminant analysis, and Duncan's multiple range test. Results indicate that ultramafic rock types are spectrally separable from nonultramafics based on vegetative cover through the use of statistical analyses.

Zircon and baddeleyite from the economic ultramafic-mafic Noril'sk-1 intrusion (Russia): Hf-isotope constraints on source composition

NASA Astrophysics Data System (ADS)

Malitch, K. N.; Belousova, E. A.; Badanina, I. Yu.; Griffin, W. L.

2012-04-01

The ultramafic-mafic Noril'sk-1 intrusion in the northwestern part of the Siberian Craton (Russia) represents one of three known Noril'sk-type, ore-bearing intrusions, which host one of the world's major economic sulphide platinum-group-element (PGE)-Cu-Ni deposits. Zircon and baddeleyite dated previously both by SHRIMP (i.e. 248.0 ± 3.7 Ma, Campbell et al. 1992) and ID-TIMS (251.1 ± 3.6 Ma, Kamo et al. 1996) have been restricted to one lithology (e.g. leucogabbro) of the Noril'sk-1 intrusion. To better constrain the age of igneous event and sources involved in its generation our multi-technique study utilized ten rock samples characteristic of unmineralized and mineralized lithologies. The rocks investigated comprise (from top to bottom) gabbro-diorite (sample N1-1), leucogabbro (N1-3), olivine-free gabbro (N1-2 and N1-4), olivine-bearing gabbro (N1-5), olivine gabbro (N1-6), plagiowehrlite and plagiodunite (N1-7), taxitic-textured rocks comprising melanotroctolite, olivine gabbro with relics of ultramafic rocks (N1-8, N1-9) and contact fine-grained gabbro (N1-10). Sulphide PGE-Cu-Ni ores occur in ultramafic (N1-7) and taxitic-textured rocks (N1-8 and N1-9), which have thickness of about 17 m, whereas the low-sulphide horizon of about 1 m thick occurs in the upper part of intrusion (N1-3). In situ U-Pb analyses of zircon from these rocks, combined with detailed study of crystal morphology and internal structure, identify four zircon populations (Malitch et al. 2012). The U-Pb ages of baddeleyite and the defined zircon populations cover a significant time span, from Late Paleozoic to Early Mesozoic (e.g., 290 ± 2.8; 261.3 ± 1.6; 245.7 ± 1.1; 236.5 ± 1.8 and 226.7 ± 0.9 Ma). The established distribution of U-Pb ages implies that crystallization of baddeleyite and zircon corresponds to several stages of protracted evolution of ultramafic-mafic magmas at deep-seated staging chambers and/or probably characterizes interaction of distinct magmas during formation

Ponderosa pine progenies: differential response to ultramafic and granitic soils

Treesearch

James L. Jenkinson

1974-01-01

Progenies of nine ponderosa pines native to one granitic and several ultramafic soils in the northern Sierra Nevada were grown on both soil types in a greenhouse. The progenies differed markedly in first-year growth on infertile ultramafic soils, but not on a fertile granitic soil. Growth differences between progenies were primarily related to differences in calcium...

Origin and evolution of the alkalic ultramafic rocks in the Coyote Peak diatreme, Humboldt County, California

USGS Publications Warehouse

Morgan, J.W.; Czamanske, G.K.; Gregory, Wandless A.

1985-01-01

Instrumental-neutron-activation analyses are reported for two uncontaminated rocks, a phlogopite-rich clot, and two contaminated rocks from the Coyote Peak diatreme, northwestern California. These data, combined with Nd, Sr, and Pb isotopic evidence, have been modeled to a multi-stage evolution for the uncontaminated rocks. Fertile mantle material (refractory elements 2.5?? chondritic abundances; Rb/Sr = 0.029 by weight) was depleted about 900 m.y. ago by congruent melting and removal of ~4% basaltic liquid; this depleted residue provided the source rock from which the Coyote Peak magma was ultimately derived. About 66 m.y. ago, the depleted mantle residue was incongruently melted in the presence of H2O and CO2 at a total pressure > 26 kb to yield ~0.5% of a Si-poor, Ca-rich melt. This melt then metasomatized depleted garnet-free harzburgite in the upper mantle at about 26 kb to produce a rock similar to phlogopite-bearing wehrlite. About 29 m.y. ago, this rock was subjected to an increase in pressure to >26 kb and incongruently melted to give ~0.5% of a second-stage melt resembling olivine melilitite in composition. Enroute to the surface, about 28% olivine and 2% titanomagnetite were lost from the highly fluid melt. Coarse-grained phlogopite-rich clots in the uncontaminated rocks apparently crystallized from a latestage liquid derived from the uncontaminated melt. Contaminated rocks appear to be the result of partial assimilation of, and dilution by, ~14% Franciscan graywacke country rock. The diatreme was emplaced near a converging plate margin where young hot oceanic mantle and crust of the Juan de Fuca plate was probably subducting obliquely beneath a thin lip of the North American plate. The unusual chemistry of the rocks may be the result of this complex tectonic setting which could also have included local strike-slip and extensional environments within the two plates pierced by the diatreme. ?? 1985.

Ectomycorrhizal fungal diversity associated with endemic Tristaniopsis spp. (Myrtaceae) in ultramafic and volcano-sedimentary soils in New Caledonia.

PubMed

Waseem, Muhammad; Ducousso, Marc; Prin, Yves; Domergue, Odile; Hannibal, Laure; Majorel, Clarisse; Jourand, Philippe; Galiana, Antoine

2017-05-01

New Caledonian serpentine (ultramafic) soils contain high levels of toxic heavy metals, in particular nickel, (up to 20 g kg -1 ) and are deficient in essential elements like carbon, nitrogen and phosphorus while having a high magnesium/calcium ratio. Although previous studies showed that ectomycorrhizal symbioses could play an important role in the adaptation of the endemic plants to ultramafic soils (FEMS Microbiol Ecol 72:238-49, 2010), none of them have compared the diversity of microbial communities from ultramafic vs non-ultramafic soils in New Caledonia. We explored the impact of edaphic characteristics on the diversity of ectomycorrhizal (ECM) fungi associated with different endemic species of Tristaniopsis (Myrtaceae) growing under contrasting soil conditions in the natural ecosystems of New Caledonia. ECM root tips were thus sampled from two different ultramafic sites (Koniambo massif and Desmazures forest) vs two volcano-sedimentary ones (Arama and Mont Ninndo). The molecular characterization of the ECM fungi through partial sequencing of the ITS rRNA gene revealed the presence of different dominant fungal genera including, both soil types combined, Cortinarius (36.1%), Pisolithus (18.5%), Russula (13.4%), Heliotales (8.2%) and Boletellus (7.2%). A high diversity of ECM taxa associated with Tristaniopsis species was found in both ultramafic and volcano-sedimentary soils but no significant differences in ECM genera distribution were observed between both soil types. No link could be established between the phylogenetic clustering of ECM taxa and their soil type origin, thus suggesting a possible functional-rather than taxonomical-adaptation of ECM fungal communities to ultramafic soils.

Experimental Constraints on the Origin of Lunar High-Ti Ultramafic Glasses

NASA Technical Reports Server (NTRS)

Wagner, T. P.; Grove, T. L.

1996-01-01

Phase equilibria and dissolution rate experiments are used to develop a petrogenetic model for the high-Ti lunar ultramafic glasses. Near-liquidus phase relations of the Apollo 14 black glass, the most Ti-rich lunar ultramafic glass, are determined to 2.2-GPa. The liquidus is saturated with Cr-spinel at 1-atm, olivine between approximately 0.5- and 1.5-GPa, and low-Ca pyroxene + Cr-spinel above 1.5-GPa. Ilmenite does not crystallize near the liquidus and implies that high-Ti ultramafic glasses are not produced by melting of an ilmenite-saturated source. We infer that high-Ti ultramafic magmas are derived from low-Ti ultramafic parent magmas by assimilation of ilmenite +/- clinopyroxene +/- urKREEP +/- pigeonite in the shallow lunar interior. Heat is provided by adiabatic ascent of the low-Ti ultramafic primary magmas from the deeper lunar interior and crystallization of olivine during assimilation. The assimilation reaction is modeled by mass balance and requires that ilmenite and high-Ca pyroxene are assimilated in a approximately 3:1 ratio, a much higher ratio than the proportion in which these minerals are thought to exist in the lunar interior. In an effort to understand the kinetic controls on this reaction, the dissolution of ilmenite is examined experimentally in both low- and high-Ti lunar magmas. We find that ilmenite dissolves incongruently to Cr-spinel and a high-Ti melt. The dissolution reaction proceeds by a diffusion-controlled mechanism. An assimilation model for the origin of high-Ti melts is developed that leaves the magma ocean cumulates in their initial stratigraphic positions and obviates source hybridization models that require lunar overturn.

Assessment of heavy metal contamination in sediment at Sukinda ultramafic complex using HAADF-STEM analysis.

PubMed

Equeenuddin, Sk Md; Pattnaik, Binaya Kumar

2017-10-01

The Sukinda ultramafic complex in Odisha has the largest chromite reserve in India. Sediment derived from ultramafic rocks has been enriched with various metals. Further, mining activities enhance the influx of metals into sediment by dumping mine overburden and tailings in the open area. Metal concentration in sediment is found in order of Cr Total (Cr) > Mn > Ni > Co > Zn > Cu with average concentration 26,778 mg/kg, 3098 mg/kg, 1813 mg/kg, 184 mg/kg, 116 mg/kg and 44 mg/kg respectively. Concentration of Cr(VI) varies from 5.25 to 26.47 mg/L with an average of 12.27 mg/L. Based on various pollution indices, it is confirmed that the area is severely contaminated. Nano-scale goethite, kaolinite, clinochlore and chromite have been identified and have high concentration of Cr, Co and Ni. Goethite has shown maximum metal retention potential as deciphered by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The HAADF-STEM mapping and principal component analysis indicate that Cr and Co mostly derived from chromite whereas Ni and Zn are derived from serpentine. Later, these metals co-precipitate and/or adsorbed onto the goethite and clay minerals. Fractionation study of metals confirms that Cu is the most mobile element followed by Zn. However, at low pH condition Ni is mobilized and likely to be bioavailable. Though Cr mostly occurs in residual fraction but as its concentration is very high, a small proportion of exchangeable fraction contributes significantly in terms of its bioavailability. Thus bioavailable Cr can pose severe threat to the environment in the Sukinda ultramafic complex. Copyright © 2017 Elsevier Ltd. All rights reserved.

Geochemical models of metasomatism in ultramafic systems: Serpentinization, rodingitization, and sea floor carbonate chimney precipitation

USGS Publications Warehouse

Palandri, J.L.; Reed, M.H.

2004-01-01

In a series of water-rock reaction simulations, we assess the processes of serpentinization of harzburgite and related calcium metasomatism resulting in rodingite-type alteration, and seafloor carbonate chimney precipitation. At temperatures from 25 to 300??C (P = 10 to 100 bar), using either fresh water or seawater, serpentinization simulations produce an assemblage commonly observed in natural systems, dominated by serpentine, magnetite, and brucite. The reacted waters in the simulations show similar trends in composition with decreasing water-rock ratios, becoming hyper-alkaline and strongly reducing, with increased dissolved calcium. At 25??C and w/r less than ???32, conditions are sufficiently reducing to yield H2 gas, nickel-iron alloy and native copper. Hyperalkalinity results from OH- production by olivine and pyroxene dissolution in the absence of counterbalancing OH- consumption by alteration mineral precipitation except at very high pH; at moderate pH there are no stable calcium minerals and only a small amount of chlorite forms, limited by aluminum, thus allowing Mg2+ and Ca2+ to accumulate in the aqueous phase in exchange for H+. The reducing conditions result from oxidation of ferrous iron in olivine and pyroxene to ferric iron in magnetite. Trace metals are computed to be nearly insoluble below 300??C, except for mercury, for which high pH stabilizes aqueous and gaseous Hg??. In serpentinization by seawater at 300??C, Ag, Au, Pd, and Pt may approach ore-forming concentrations in sulfide complexes. Simulated mixing of the fluid derived from serpentinization with cold seawater produces a mineral assemblage dominated by calcite, similar to recently discovered submarine, ultramafic rock-hosted, carbonate mineral deposits precipitating at hydrothermal vents. Simulated reaction of gabbroic or basaltic rocks with the hyperalkaline calcium- and aluminum-rich fluid produced during serpentinization at 300??C yields rodingite-type mineral assemblages, including

Fragmentation and growth processes in ultramafic pseudotachylites and associated wall rocks from Alpine Corsica

NASA Astrophysics Data System (ADS)

Dunkel, K.; Austrheim, H.; Plümper, O.; Ildefonse, B.; Ohl, M.; Jamtveit, B.

2017-12-01

Pseudotachylites, often taken as indicators of seismic slip, can form by comminution and/or melting. How the seismic energy released during a pseudotachylite-generating earthquake affects the wall rock surrounding the fault plane is not well known, although damage of the wall rock can have a substantial influence on the rheological properties of the rock and therefore on its further deformation and metamorphism. Micro- and nanostructures of pseudotachylites and their wall rocks in peridotites from Alpine Corsica have been characterized using optical, scanning and transmission electron microscopy, electron backscatter diffraction, and electron microprobe analysis. Pseudotachylites in dunites from the Cima di Gratera area in Cape Corse show a combination of comminution and melting. Olivine in the pseudotachylites is dislocation-rich whereas pyroxene is almost free of dislocations, indicating a fragmentation of the olivine during seismic slip and incomplete melting. The temperature pulse that induced melting was likely short-lived, since evidence for recovery in olivine is limited. Olivines in the wall rocks show a similarly high dislocation density and are strongly fragmented without being sheared. A fragmentation without shear strain, comparable to the "pulverization" described from shallower earthquakes, can probably only be explained by a high stress pulse released during a seismic event. Previous observations from the same area describe a transition from cataclastic wall rocks over mylonites and ultramylonites to pseudotachylite. This was taken as an indication that cataclasis weakened the rock and finally, in connection with thermal runaway, allowed for seismic slip. This difference between previous observations and those described here may be explained by a spatial heterogeneity in the deformation conditions. While earthquakes may have nucleated by self-localizing thermal runaway in cataclastic zones, they propagated also through previously undeformed rocks

Reproducing early Martian atmospheric carbon dioxide partial pressure by modeling the formation of Mg-Fe-Ca carbonate identified in the Comanche rock outcrops on Mars

NASA Astrophysics Data System (ADS)

Berk, Wolfgang; Fu, Yunjiao; Ilger, Jan-Michael

2012-10-01

The well defined composition of the Comanche rock's carbonate (Magnesite0.62Siderite0.25Calcite0.11Rhodochrosite0.02) and its host rock's composition, dominated by Mg-rich olivine, enable us to reproduce the atmospheric CO2partial pressure that may have triggered the formation of these carbonates. Hydrogeochemical one-dimensional transport modeling reveals that similar aqueous rock alteration conditions (including CO2partial pressure) may have led to the formation of Mg-Fe-Ca carbonate identified in the Comanche rock outcrops (Gusev Crater) and also in the ultramafic rocks exposed in the Nili Fossae region. Hydrogeochemical conditions enabling the formation of Mg-rich solid solution carbonate result from equilibrium species distributions involving (1) ultramafic rocks (ca. 32 wt% olivine; Fo0.72Fa0.28), (2) pure water, and (3) CO2partial pressures of ca. 0.5 to 2.0 bar at water-to-rock ratios of ca. 500 molH2O mol-1rock and ca. 5°C (278 K). Our modeled carbonate composition (Magnesite0.64Siderite0.28Calcite0.08) matches the measured composition of carbonates preserved in the Comanche rocks. Considerably different carbonate compositions are achieved at (1) higher temperature (85°C), (2) water-to-rock ratios considerably higher and lower than 500 mol mol-1 and (3) CO2partial pressures differing from 1.0 bar in the model set up. The Comanche rocks, hosting the carbonate, may have been subjected to long-lasting (>104 to 105 years) aqueous alteration processes triggered by atmospheric CO2partial pressures of ca. 1.0 bar at low temperature. Their outcrop may represent a fragment of the upper layers of an altered olivine-rich rock column, which is characterized by newly formed Mg-Fe-Ca solid solution carbonate, and phyllosilicate-rich alteration assemblages within deeper (unexposed) units.

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.

Structural development of the Red Hill portion of the Feather River ultramafic complex, Pulmas County, California

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

Weisenberg, C.W.

1979-01-01

The Feather River Ultramafic Complex is a partially serpentinized body of metamorphosed alpine peridotite and gabbro that lies along the northern part of the Melones fault zone, a NNW trending belt in the Northern Sierra Nevada. The complex was studied in the area of Red Hill, near the canyon of the North Fork, Feather River. The complex is separated from the Calaveras Terrain and Arlington Formation country rocks by steep faults; the Melones Fault on the east and the Rich Bar Fault on the west. Units recognized within the complex include Rich Bar metamorphic rocks, peridotite, metaperidotite, tremolite-olivine schist, hornblendemore » schist, and layered metagabbro. The Rich Bar metamorphic rocks are tectonic slices of amphibolite grade hornblende schist, mica schist, and quartzite found along the Rich Bar Fault. The complex shows evidence of 4 major events. E-1 (Pennsylvania-Permian) was formation of the peridotite-gabbro complex. E-2 (Permo-Triassic) consisted of pervasive shearing parallel to the Rich Bar Fault associated with initial emplacement within the Sierra Nevada. E-3 is believed to be compression and metamorphism (serpentinization) associated with the Nevadan orogeny. E-4 was associated with intrusion of nearby plutons. The regional association of the complex with late paleozoic arc volcanics of the Taylorsville area suggest formation near or under an island arc. Metamorphism during emplacement indicates association with the arc at that time. Left-lateral shear during emplacement along the Rich Bar Fault indicates NW directed thrusting when the layering in metagabbro is rotated to horizontal.« less

Early Precambrian mantle derived rocks in the southern Prince Charles Mountains, East Antarctica: age and isotopic constraints

USGS Publications Warehouse

Mikhalsky, E.V.; Henjes-Kunst, F.; Roland, N.W.

2007-01-01

Mafic and ultramafic rocks occurring as lenses, boudins, and tectonic slabs within metamorphic units in the southern Mawson Escarpment display mantle characteristics of either a highly enriched, or highly depleted nature. Fractionation of these mantle rocks from their sources may be as old as Eoarchaean (ca 3850 Ma) while their tectonic emplacement probably occurred prior to 2550 Ma (U-Pb SHRIMP data). These results provide for the first time evidence for Archaean suturing within East Antarctica. Similar upper mantle sources are likely present in the northern Mawson Escarpment. A younger age limit of these rocks is 2200 Ma, as indicated by presumably metamorphic zircon ages while their magmatic age may be constrained by single zircon dates at 2450-2250 Ma. The area of the northern Mawson Escarpment is most likely of ensimatic origin and includes mafic rocks which were derived from distinct mantle source(s) during Palaeoproterozoic time.

Chemical controls on fault behavior: weakening of serpentinite sheared against quartz-bearing rocks and its significance for fault creep in the San Andreas system

USGS Publications Warehouse

Moore, Diane E.; Lockner, David A.

2013-01-01

The serpentinized ultramafic rocks found in many plate-tectonic settings commonly are juxtaposed against crustal rocks along faults, and the chemical contrast between the rock types potentially could influence the mechanical behavior of such faults. To investigate this possibility, we conducted triaxial experiments under hydrothermal conditions (200-350°C), shearing serpentinite gouge between forcing blocks of granite or quartzite. In an ultramafic chemical environment, the coefficient of friction, µ, of lizardite and antigorite serpentinite is 0.5-0.6, and µ increases with increasing temperature over the tested range. However, when either lizardite or antigorite serpentinite is sheared against granite or quartzite, strength is reduced to µ ~ 0.3, with the greatest strength reductions at the highest temperatures (temperature weakening) and slowest shearing rates (velocity strengthening). The weakening is attributed to a solution-transfer process that is promoted by the enhanced solubility of serpentine in pore fluids whose chemistry has been modified by interaction with the quartzose wall rocks. The operation of this process will promote aseismic slip (creep) along serpentinite-bearing crustal faults at otherwise seismogenic depths. During short-term experiments serpentine minerals reprecipitate in low-stress areas, whereas in longer experiments new Mg-rich phyllosilicates crystallize in response to metasomatic exchanges across the serpentinite-crustal rock contact. Long-term shear of serpentinite against crustal rocks will cause the metasomatic mineral assemblages, which may include extremely weak minerals such as saponite or talc, to play an increasingly important role in the mechanical behavior of the fault. Our results may explain the distribution of creep on faults in the San Andreas system.

Mapping potentialy asbestos-bearing rocks using imaging spectroscopy

USGS Publications Warehouse

Swayze, G.A.; Kokaly, R.F.; Higgins, C.T.; Clinkenbeard, J.P.; Clark, R.N.; Lowers, H.A.; Sutley, S.J.

2009-01-01

Rock and soil that may contain naturally occurring asbestos (NOA), a known human carcinogen, were mapped in the Sierra Nevada, California, using the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) to determine if these materials could be uniquely identified with spectroscopy. Such information can be used to prepare or refine maps of areas that may contain minerals that can be asbestiform, such as serpentine and tremolite-actinolite, which were the focus of this study. Although thick vegetation can conceal underlying rock and soil, use of linear-mixture spectra calculated from spectra of dry grass and serpentine allowed detection of serpentine in some parts of the study area with up to ~80% dry-grass cover. Chaparral vegetation, which was dominantly, but not exclusively, found in areas underlain by serpentinized ultramafic rocks, was also mapped. Overall, field checking at 201 sites indicated highly accurate identification by AVIRIS of mineral (94%) and vegetation (89%) categories. Practical applications of AVIRIS to mapping areas that may contain NOA include locating roads that are surfaced with serpentine aggregate, identifying sites that may require enhanced dust control or other safety measures, and filling gaps in geologic mapping where field access is limited.

Deformation associated to exhumation by detachment faulting of upper mantle rocks in a fossil Ocean Continent Transition: The example of the Totalp unit in SE Switzerland

NASA Astrophysics Data System (ADS)

Picazo, S.; Manatschal, G.; Cannat, M.

2013-12-01

The exhumation of upper mantle rocks along detachment faults is widespread at Mid-Ocean Ridges and at the Ocean-Continent Transition (OCT) of rifted continental margins. Thermo-mechanical models indicate that significant strain softening of the fault rocks in the footwall is required in order to produce such large fault offsets. Our work focuses on deformation textures, and the associated mineralogy in ultramafic rocks sampled in the upper levels of the footwall next to the exhumation fault. We present two OCT examples, the Totalp relict of a paleo-Tethys OCT exposed in SE Switzerland, and the Iberian distal margin (ODP Leg 173 Site 1070). We built a new geological map and a section of the Totalp unit near Davos (SE Switzerland) and interpreted this area as a local exposure of a paleo-seafloor that is formed by an exhumed detachment surface and serpentinized peridotites. The top of the exhumed mantle rocks is made of ophicalcites that resulted from the carbonation of serpentine under static conditions at the seafloor. The ophicalcites preserve depositional contacts with Upper Jurassic to Lower Cretaceous pelagic sediments. These sequences did not exceed prehnite-pumpellyite metamorphic facies conditions, and locally escaped Alpine deformation. Thin mylonitic shear zones as well as foliated amphibole-bearing ultramafic rocks have been mapped. The age of these rocks and the link with the final exhumation history are yet unknown but since amphibole-bearing ultramafic rocks can be found as clasts in cataclasites related to the detachment fault, they pre-date detachment faulting. Our petrostructural study of the exhumed serpentinized rocks also reveals a deformation gradient from cataclasis to gouge formation within 150m in the footwall of the proposed paleo-detachment fault. This deformation postdates serpentinization. It involves a component of plastic deformation of serpentine in the most highly strained intervals that has suffered pronounced grain-size reduction and

Metamorphic style and development of the blueschist- to eclogite-facies rocks, Cyclades, Greece

NASA Astrophysics Data System (ADS)

Schumacher, J. C.; Brady, J. B.; Cheney, J. T.

2008-07-01

The island of Syros, Greece is part of the Attic-Cycladic blueschist belt, formed during Mesozoic Eurasia-Africa subduction. The rocks of Syros can be broadly divided into three tectono-stratigraphic units: (I) metamorphosed sedimentary and volcanic rocks (marble-schist sequence), (II) remnants of oceanic crust with fault-bounded packages of blueschist/eclogite-facies mafic rocks and serpentinite (mafic-ultramafic rocks) and (III) the Vari gneiss, which is a tectonic klippe. Low-temperature, high-pressure assemblages are found on several islands in the Cyclades. The best preserved of these rocks are on Syros and Sifnos islands. Mineral compositions and peak metamorphic assemblages are similar on both islands. Both islands are considered to share similar P-T histories with highest-pressure mineral assemblages reflecting conditions of at least 15 kbar and about 500°C.

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.

Mafic/Ultramafic xenoliths from Saurashtra peninsula of Gujarat; northwestern Deccan Trap, India

NASA Astrophysics Data System (ADS)

Naushad, M.; Behera, J. R.; Chakra, M.; Murthy, P. V.

2017-12-01

The crustal growth forming processes at the crust-mantle interface or within the crust due to magma underplating is important for the formation and emplacement of continental flood basalt and large igneous provinces. Mafic/ultramafic xenoliths from lower crust or upper mantle provide clue to characterize the underplated material and magmatic processes. Earlier study of ultramafic xenoliths suggested magma underplating and crustal growth in Kuchchh, Gujarat, northwestern Deccan Trap (NWDT). Absence of such xenoliths in Saurashtra peninsula (SP) of NWDT however could not supplement this. Here, we report the mafic/ultramafic xenoliths entrained in high MgO basaltic lava flows of NWDT of SP in Rajkot district of Gujarat, India. The xenoliths are medium to coarse grained, meso - to melanocratic, elongated to angular pyroxenite (Type-I), two pyroxenes gabbro (Type-II) and anorthosite (Type-III) showing sharp contact with host basalt flows. Type-I xenoliths dominated by clinopyroxene (cpx) (Wo49-45 En49-38) with olivine (ol) (Fo84-78), exhibit cumulate texture, Type-II composed of cpx (core-Wo49-48 En42-41), orthopyroxene (opx) (core- En77-76 Fs23-22) and plagioclase (plag) (Ab35-28 An71-64) and Type-III, composed dominantly of plag (Ab67-29 An68-28) with minor opx (En78-76 Fs20-18) and a grain of hercynite (Al2O3=59%) in close association with plag. The basaltic lavas are porphyritic containing ol (Fo88-75), cpx (Wo50-48 En39-37), plag (Ab43-26 An74-54) and opaques. Whole rock geochemical data of xenolith entrained lava flows indicates high MgO (10-11 wt%) with high Ni (421-430 ppm) and Cr (795-1076 ppm). The equilibration temperature calculated from cpx - opx (adjacent grain of cpx and opx, pair-A; inclusion of cpx within opx, pair-B) for Type-II xenolith indicates 778°C and 789°C (pair-A) and 821°C and 832°C (pair-B) at 5 kbar and 10 kbar pressure respectively. Present study suggests that the possibility of magma underplating at crust-mantle interface or presence

Geochemical, mineralogical and Re-Os isotopic constraints on the origin of Tethyan oceanic mantle and crustal rocks from the Central Pontides, northern Turkey

NASA Astrophysics Data System (ADS)

Çelik, Ömer Faruk; Marzoli, Andrea; Marschik, Robert; Chiaradia, Massimo; Mathur, Ryan

2018-02-01

Chromite, ultramafic and mafic rocks from Eldivan, Yapraklı, Ayli Dağ, Küre, Elekdağ and Kızılırmak in northern Turkey have been studied to determine their mineral and whole-rock geochemical, and Re-Os isotope geochemical characteristics. Most of the studied peridotites display depleted but commonly V-shaped chondrite-normalized rare-earth element (REE) patterns while some peridotites as well as pyroxenites from all areas exhibit light REE depleted patterns. Olivine (forsterite 82 to 92 mol%) and spinel (chromium number 13 to 63) in the studied peridotites exhibit a wide range of compositions. Compositions of spinels suggest that peridotites from Eldivan, Ayli Dağ and Küre experienced relatively large degrees of partial melting ( 15 and 19 wt%), whereas those of the Kızılırmak area most likely reflect lower melting degrees ( 4-6 wt%). Whole-rock and mineral chemical data indicate that the ultramafic rocks are similar to abyssal and supra-subduction zone peridotites. The ultramafic rocks of the investigated areas exhibit a wide range of 187Re/188Os (0.12 to 6.6) and measured 187Os/188Os (0.122-1.14), while the basaltic rocks from Küre, Eldivan and Kızılırmak areas have high 187Re/188Os (128-562) and measured 187Os/188Os (0.724-1.943). On the other hand, chromite from Eldivan, Elekdağ and Kızılırmak show high Os contents (21.81-44.04 ppb) and low 187Re/188Os (0.015-0.818) and 187Os/188Os (0.122-0.133). Re-Os model ages (TChur) for all analyzed samples yielded scattered ages ranging from Jurassic to Proterozoic. Overall, geochemical data are interpreted to reflect different degrees of partial melting, melt - rock interactions and metasomatic effects that produced a heterogeneous mantle in a supra-subduction setting.

Hydromechanical modeling of clay rock including fracture damage

NASA Astrophysics Data System (ADS)

Asahina, D.; Houseworth, J. E.; Birkholzer, J. T.

2012-12-01

Argillaceous rock typically acts as a flow barrier, but under certain conditions significant and potentially conductive fractures may be present. Fracture formation is well-known to occur in the vicinity of underground excavations in a region known as the excavation disturbed zone. Such problems are of particular importance for low-permeability, mechanically weak rock such as clays and shales because fractures can be relatively transient as a result of fracture self-sealing processes. Perhaps not as well appreciated is the fact that natural fractures can form in argillaceous rock as a result of hydraulic overpressure caused by phenomena such as disequlibrium compaction, changes in tectonic stress, and mineral dehydration. Overpressure conditions can cause hydraulic fracturing if the fluid pressure leads to tensile effective stresses that exceed the tensile strength of the material. Quantitative modeling of this type of process requires coupling between hydrogeologic processes and geomechanical processes including fracture initiation and propagation. Here we present a computational method for three-dimensional, hydromechanical coupled processes including fracture damage. Fractures are represented as discrete features in a fracture network that interact with a porous rock matrix. Fracture configurations are mapped onto an unstructured, three-dimensonal, Voronoi grid, which is based on a random set of spatial points. Discrete fracture networks (DFN) are represented by the connections of the edges of a Voronoi cells. This methodology has the advantage that fractures can be more easily introduced in response to coupled hydro-mechanical processes and generally eliminates several potential issues associated with the geometry of DFN and numerical gridding. A geomechanical and fracture-damage model is developed here using the Rigid-Body-Spring-Network (RBSN) numerical method. The hydrogelogic and geomechanical models share the same geometrical information from a 3D Voronoi

Three-dimensional model of an ultramafic feeder system to the Nikolai Greenstone mafic large igneous province, central Alaska Range

USGS Publications Warehouse

Glen, J.M.G.; Schmidt, J.M.; Connard, G.G.

2011-01-01

The Amphitheater Mountains and southern central Alaska Range expose a thick sequence of Triassic Nikolai basalts that is underlain by several mafic-ultramafic complexes, the largest and best exposed being the Fish Lake and Tangle (FL-T) mafic-ultramafic sills that flank the Amphitheater Mountains synform. Three-dimensional (3-D) modeling of gravity and magnetic data reveals details of the structure of the Amphitheater Mountains, such as the orientation and thickness of Nikolai basalts, and the geometry of the FL-T intrusions. The 3-D model (50 ?? 70 km) includes the full geographic extent of the FL-T complexes and consists of 11 layers. Layer surfaces and properties (density and magnetic susceptibility) were modified by forward and inverse methods to reduce differences between the observed and calculated gravity and magnetic grids. The model suggests that the outcropping FL-T sills are apparently connected and traceable at depth and reveals variations in thickness, shape, and orientation of the ultramafic bodies that may identify paths of magma flow. The model shows that a significant volume (2000 km3) of ultramafic material occurs in the subsurface, gradually thickening and plunging westward to depths exceeding 4 km. This deep ultramafic material is interpreted as the top of a keel or root system that supplied magma to the Nikolai lavas and controlled emplacement of related magmatic intrusions. The presence of this deep, keel-like structure, and asymmetry of the synform, supports a sag basin model for development of the Amphitheater Mountains structure and reveals that the feeders to the Nikolai are much more extensive than previously known. Copyright 2011 by the American Geophysical Union.

Deformation and Metasomatic Evolution at the Subduction Plate Interface As Viewed from Study of HP/UHP Metamorphic Rocks

NASA Astrophysics Data System (ADS)

Bebout, G. E.; Penniston-Dorland, S.

2014-12-01

We provide a view of lithologic makeup, deformation, and fluid-rock interaction along the deep forearc to subarc plate interface, based on insights gained from study of HP/UHP metamorphic rocks. Exposures of plate-boundary shear zones on which we base our perspective represent 30-80 km depths and are on Catalina Island and at Monviso, Syros, and New Caledonia. Each contains highly deformed zones with schistose matrix, commonly with a large ultramafic component, containing bodies of less deformed mafic, sedimentary, and ultramafic rocks. These "blocks" have varying geometries, are up to km-scale, and can preserve disparate P-T histories reflecting dynamics of incorporation and entrainment. Sheared matrices contain high-variance, hydrous mineral assemblages in some cases resembling metasomatic zones ("rinds") at block-matrix contacts, and rinds and matrices have homogenized isotopic compositions reflecting extensive fluid-rock interaction. Shearing and related physical juxtaposition of disparate metasomatic rocks can result in mixed or 'hybrid' chemical compositions. The chlorite-, talc-, and amphibole-rich schists developed by these processes can stabilize H2O to great depth and influence its cycling. Fluids (hydrous fluids, silicate melts) released within slabs necessarily interact with highly deformed, lithologically hybridized zones at the plate interface as they ascend to potentially enter mantle wedges. Fluids bearing chemical/isotopic signatures of hybrid rocks appear capable of producing arc magma compositions interpreted as reflecting multiple, chemically distinct fluids sources. Geophysical signatures of these rheologically weak zones are equivocal but many recognize the presence of zones of low seismic velocity at/near the top of slabs and attribute them to hydrated rocks. Whether rocks from this interface buoyantly ascend into mantle wedges, indicated in some theoretical models, remains largely untested by field and geophysical observations.

Spatial greenstone-gneiss relationships: Evidence from mafic-ultramafic xenolith distribution patterns

NASA Technical Reports Server (NTRS)

Glikson, A. Y.

1986-01-01

The distribution patterns of mafic-ultramafic xenoliths within Archaean orthogneiss terrain furnish an essential key for the elucidation of granite-greenstone relations. Most greenstone belts constitute mega-xenoliths rather than primary basin structures. Transition along strike and across strike between stratigraphically low greenstone sequences and xenolith chains demonstrate their contemporaneity. These terrains represent least deformed cratonic islands within an otherwise penetratively foliated deformed gneiss-greenstone crust. Whereas early greenstone sequences are invariably intruded by tonalitic/trondhjemitic/granodioritic gneisses, stratigraphically higher successions may locally overlap older gneiss terrains and their entrained xenoliths unconformably. The contiguity of xenolith patterns suggests their derivation as relics of regional mafic-ultramafic volcanic crustal units and places limits on horizontal movements between individual crustal blocks.

Mineral chemistry and petrology of highly magnesian ultramafic cumulates from the Sarve-Abad (Sawlava) ophiolites (Kurdistan, NW Iran): New evidence for boninitic magmatism in intra-oceanic fore-arc setting in the Neo-Tethys between Arabia and Iran

NASA Astrophysics Data System (ADS)

Allahyari, Khalil; Saccani, Emilio; Rahimzadeh, Bahman; Zeda, Ottavia

2014-01-01

The Sarve-Abad (Sawlava) ophiolitic complex consists of several tectonically dismembered ophiolitic sequences. They are located along the Main Zagros Thrust Zone, which marks the ophiolitic suture between the Arabian and Sanandaj-Sirjan continental blocks. They represent a portion of the southern Neo-Tethyan oceanic lithosphere, which originally existed between the Arabian (to the south) and Eurasian (to the north) continental margins. The Sarve-Abad ophiolites include cumulitic lherzolites bearing minor dunite and chromitite lenses in places. The main rock-forming minerals in ultramafic cumulates are cumulus olivine and inter-cumulus clinopyroxene and orthopyroxene. Minor (<5%) chromian spinel occurs as both cumulus and inter-cumulus phases.

P-T paths of ophiolite-related metamorphic rocks from the Dinaride ophiolite zone in Bosnia

NASA Astrophysics Data System (ADS)

Balen, Dražen; Massonne, Hans-Joachim; Koller, Friedrich; Theye, Thomas; Opitz, Joachim; Hrvatović, Hazim; Premužak, Lucija

2017-04-01

The Dinarides, an Alpine mountain chain in south-eastern Europe, is characterized by complex fold, thrust, and imbricate structures. Partially dismembered ophiolites, a regular part of the Inner Dinarides, are considered as separate ultramafic massifs. The large Krivaja-Konjuh ultramafic massif (KKUM) within the Dinaride Ophiolite Zone (DOZ), composed of tectonic spinel lherzolite, occurs as NE-dipping thrust sheet underlain by gradually decreasing, up to 1200 m thick, high- to medium-grade metamorphic rocks. The metamorphic rocks geochemically resemble MORB-like rocks with tholeiitic signature. Such metamorphic rocks, which originated from cumulate gabbro and/or troctolite, are mainly represented by granulite and amphibolite varieties (subordinate eclogite and epidote-amphibolite facies metamafic rocks are also present) with various proportions of amphibole, plagioclase, pyroxenes (diopside and hypersthene), garnet, corundum, sapphirine, spinel and quartz. These rocks vary in textures (granoblastic, porphyroblastic and nematoblastic) and grain size (coarse- to fine-grain varieties). Conventional thermobarometry of garnet- and clinopyroxene-bearing amphibolites directly beneath the contact to the overlying peridotite resulted in peak pressure (P) - temperature (T) conditions of 10-12 kbar (depth of ca. 35-40 km) and 745-830°C. Those amphibolites without clinopyroxene but with garnet experienced peak conditions of 7 kbar and 630°C. Amphibole + plagioclase amphibolite gave temperatures of 670-730 °C and lowermost-grade amphibolites yielded peak temperatures of 550°C. These estimates are thought to reflect the metamorphic conditions during the Late Jurassic obduction of the hot upper mantle part of the KKUM onto the ophiolite mélange. The hot obducted ultramafic fragments acted as a heat source for metamorphism that transformed cumulate gabbroic protolith into high- to medium-grade amphibolites and granulites. P-T pseudosections constructed for various

Metamorphic reactions in ruby corundum amphibolite from the Chunky Gal Mountain mafic-ultramafic complex, Clay County, North Carolina

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

Ranson, W.A.; Garihan, J.M.; Ulmer, K.E.

1992-01-01

Amphibolite outcrops of unusual mineralogy within the Chunky Gal Mountain mafic-ultramafic complex display cm-scale rhythmic layers with moderate-steep dips. Layers are troctolitic, gabbroic, and anorthositic in composition, locally in contact with dunite of the Buck Creek ultramafic body. Meta-gabbroic layers contain striking bladed, emerald green amphibole as the chief mafic phase and relict bronzite with reacted margins. An additional major phase is plagioclase, [approximately]An 95 based on microprobe analysis. Ruby corundum is a minor (> 5%) constituent, which in some of the gabbroic rocks is mantled by a reaction rim of fibrolite. The clinoamphibole has optical properties resembling magnesio-cummingtonite: colorlessmore » to pale green in plane light with (+) sign and 2V = 60--70[degree]. However, microprobe analysis of the clinoamphibole indicates alumino-magnesio-hornblende. Although the texture of the bronzite shows that it is breaking down, it is clear that the clinoamphibole and corundum could not be the reaction products without the addition of Al, Ca, and Si in an aqueous fluid. Associated meta-troctolitic layers contain plagioclase and coarse, anhedral olivines displaying an inner corona of bladed orthopyroxene, rimmed by symplectite. The granulite facies reactions is: plagioclase + olivine = clinopyroxene + garnet. The mesoscopic-scale proximity of troctolitic and gabbroic rhythmic layers indicates both underwent granulite facies metamorphism. Retrogression to amphibolite grade is apparent only in the gabbroic layers, resulting in assemblages distinguished locally by abundant emerald green clinoamphibole and corundum porphyroblasts rimmed by fibrolite.« less

Sr, Nd, and Pb isotopes of ultramafic xenoliths in volcanic rocks of Eastern China: enriched components EMI and EMII in subcontinental lithosphere

USGS Publications Warehouse

Tatsumoto, M.; Basu, A.R.; Wankang, H.; Junwen, W.; Guanghong, X.

1992-01-01

The UThPb, SmNd, and RbSr isotopic systematics of mafic and ultramafic xenolithic rocks and associated megacrystic inclusions of aluminous augite and garnet, that occur in three alkalic volcanic suites: Kuandian in eastern Liaoning Province, Hanluoba in Hebei Province, and Minxi in western Fujian Province, China are described. In various isotopic data plots, the inclusion data invariably fall outside the isotopic ranges displayed by the host volcanic rocks, testifying to the true xenolithic nature of the inclusions. The major element partitioning data on Ca, Mg, Fe, and Al among the coexisting silicate minerals of the xenoliths establish their growth at ambient mantle temperatures of 1000-1100??C and possible depths of 70-80 km in the subcontinental lithosphere. Although the partitioning of these elements reflects equilibrium between coexisting minerals, equilibria of the Pb, Nd, and Sr isotopic systems among the minerals were not preserved. The disequilibria are most notable with respect to the 206Pb 204Pb ratios of the minerals. On a NdSr isotopic diagram, the inclusion data plot in a wider area than that for oceanic basalts from a distinctly more depleted component than MORB with higher 143Nd 144Nd and a much broader range of 87Sr 86Sr values, paralleling the theoretical trajectory of a sea-water altered lithosphere in NdSr space. The garnets consistently show lower ?? and ?? values than the pyroxenes and pyroxenites, whereas a phlogopite shows the highest ?? and ?? values among all the minerals and rocks studied. In a plot of ??207 and ??208, the host basalts for all three areas show lower ??207 and higher ??208 values than do the xenoliths, indicating derivation of basalts from Th-rich (relative to U) sources and xenoliths from U-rich sources. The xenolith data trends toward the enriched mantle components, EMI and EMII-like, characterized by high 87Sr 86Sr and ??207 values but with slightly higher 143Nd 144Nd. The EMI trend is shown more distinctly by the host

Ultramafic lavas and high-Mg basaltic dykes from the Othris ophiolite complex, Greece

NASA Astrophysics Data System (ADS)

Baziotis, Ioannis; Economou-Eliopoulos, Maria; Asimow, Paul D.

2017-09-01

We evaluate the petrography and geochemistry of an unusual suite of subduction-related Phanerozoic high-MgO rocks from the Othris ophiolite complex in Greece, some of which have previously been described as komatiitic lavas. In particular, we study ultramafic, olivine-phyric lavas from the Agrilia area and high-Mg basaltic dykes from the Pournari area. We seek to define primary magmatic MgO contents and initial liquidus temperatures as well as the differentiation sequence and cooling rates experienced by the lavas and dykes. One of our goals is to relate the Othris case to known komatiite and boninite occurrences and to address whether Othris documents an important new constraint on the temporal evolution of ambient mantle temperature, plume-related magmatism, and subduction of oceanic lithosphere. We conclude that, despite whole-rock MgO contents of 31-33 wt%, the olivine-phyric lavas at Agrilia had an upper limit liquid MgO content of 17 wt% and are therefore picrites, not komatiites. The Agrilia lavas contain the unusual Ti-rich pyroxenoid rhönite; we discuss the significance of this occurrence. In the case of the Pournari high-Mg dykes, the distinctive dendritic or plumose clinopyroxene texture, though it resembles in some ways the classic spinifex texture of komatiites, is simply evidence of rapid cooling at the dyke margin and not evidence of extraordinarily high liquidus temperatures. We correlate the dendritic texture with disequilibrium mineral chemistry in clinopyroxene to constrain the cooling rate of the dyke margins.

Os and S isotope studies of ultramafic rocks in the Duke Island Complex, Alaska: variable degrees of crustal contamination of magmas in an arc setting and implications for Ni-Cu-PGE sulfide mineralization

NASA Astrophysics Data System (ADS)

Stifter, Eric C.; Ripley, Edward M.; Li, Chusi

2016-10-01

The Duke Island Complex is one of the several "Ural-Alaskan" intrusions of Cretaceous age that occur along the coast of SE Alaska. Significant quantities of magmatic Ni-Cu-PGE sulfide mineralization are locally found in the complex, primarily within olivine clinopyroxenites. Sulfide mineralization is Ni-poor, consistent with petrologic evidence which indicates that sulfide saturation was reached after extensive olivine crystallization. Olivine clinopyroxenites were intruded by magmas that produced sulfide-poor, adcumulate dunites. As part of a study to investigate the potential for Ni-rich sulfide mineralization in association with the dunites, a Re-Os and S isotope study of the dunites, as well as sulfide mineralization in the olivine clinopyroxenites, was initiated. Importantly, recent drilling in the complex identified the presence of sulfidic and carbonaceous country rocks that may have been involved in the contamination of magmas and generation of sulfide mineralization. γOs (110 Ma) values of two sulfidic country rocks are 1022 and 2011. δ34S values of the country rocks range from -2.6 to -16.1 ‰. 187Os/188Os ratios of sulfide minerals in the mineralization hosted by olivine clinopyroxenites are variable and high, with γOs (110 Ma) values between 151 and 2059. Extensive interaction with Re-rich sedimentary country rocks is indicated. In contrast, γOs (110 Ma) values of the dunites are significantly lower, ranging between 2 and 16. 187Os/188Os ratios increase with decreasing Os concentration. This inverse relation is similar to that shown by ultramafic rocks from several arc settings, as well as altered abyssal dunites and peridotites. The relation may be indicative of magma derivation from a sub-arc mantle that had experienced metasomatism via slab-derived fluids. Alternatively, the relation may be indicative of minor contamination of magma by crustal rocks with low Os concentrations but high 187Os/188Os ratios. A third alternative is that the low Os

Possible physicochemical facies of wehrlitization of ultramafic rocks in the mantle wedge under volcanoes of the Kuril-Kamchatka frontal zone

NASA Astrophysics Data System (ADS)

Sharapov, V. N.; Kuznetsov, G. V.; Chudnenko, K. V.

2016-04-01

A quantitative model describing the dynamics of the process of metasomatic wehrlitization of ultramafics is put forward. It is elaborated for the process taking place in permeable fault zones over a time span of 50 kyr with fluid source depths in the range of 150-50 km at initial temperatures of 1000-1200°C. The possibility of existence of two physical-chemical facies of this process has been demonstrated: one occurs at the level of garnet and the other is at the level of spinel depth facies. Their realization is related to the dependence of the activity of Mg-Ca-Si metasomatism against variation in the composition of low-molecular hydrocarbons in a fluid under conditions of changing T and P in a system.

Vesta Evolution from Surface Mineralogy: Mafic and Ultramafic Mineral Distribution

NASA Technical Reports Server (NTRS)

DeSanctis, M. C.; Ammannito, E.; Palomba, E.; Longobardo, A.; Mittlefehldt, D. W.; McSween, H. Y; Marchi, S.; Capria, M. T.; Capaccioni, F.; Frigeri, A.;

The Kimberlites and related rocks of the Kuruman Kimberlite Province, Kaapvaal Craton, South Africa

NASA Astrophysics Data System (ADS)

Donnelly, Cara L.; Griffin, William L.; O'Reilly, Suzanne Y.; Pearson, Norman J.; Shee, Simon R.

2011-03-01

The Kuruman Kimberlite Province is comprised of 16 small pipes and dikes and contains some of the oldest known kimberlites (>1.6 Ga). In this study, 12 intrusions are subdivided into three groups with distinct petrology, age, and geochemical and isotopic compositions: (1) kimberlites with groundmass perovskites defining a Pb-Pb isochron age of 1787 ± 69 Ma, (2) orangeite with a U-Pb perovskite age of 124 ± 16 Ma, and (3) ultramafic lamprophyres (aillikite and mela-aillikite) with a zircon U-Pb age of 1642 ± 46 Ma. The magma type varies across the Province, with kimberlites in the east, lamprophyres in the west and orangeite and ultramafic lamprophyres to the south. Differences in the age and petrogenesis of the X007 orangeite and Clarksdale and Aalwynkop aillikites suggest that these intrusions are probably unrelated to the Kuruman Province. Kimberlite and orangeite whole-rock major and trace element compositions are similar to other South African localities. Compositionally, the aillikites typically lie off kimberlite and orangeite trends. Groundmass mineral chemistry of the kimberlites has some features more typical of orangeites. Kimberlite whole-rock Sr and Nd isotopes show zoning across the Province. When the kimberlites erupted at ~1.8 Ga, they sampled a core volume (ca 50 km across) of relatively depleted SCLM that was partially surrounded by a rim of more metasomatized mantle. This zonation may have been related to the development of the adjacent Kheis Belt (oldest rocks ~2.0 Ga), as weaker zones surrounding the more resistant core section of SCLM were more extensively metasomatized.

Extensional tectonics during the igneous emplacement of the mafic-ultramafic rocks of the Barberton greenstone belt

NASA Technical Reports Server (NTRS)

Dewit, M. J.

1986-01-01

The simatic rocks (Onverwacht Group) of the Barberton greenstone belt are part of the Jamestown ophiolite complex. This ophiolite, together with its thick sedimentary cover occupies a complex thrust belt. Field studies have identified two types of early faults which are entirely confined to the simatic rocks and are deformed by the later thrusts and associated folds. The first type of fault (F1a) is regional and always occurs in the simatic rocks along and parallel to the lower contacts of the ophiolite-related cherts (Middle Marker and equivalent layers). These fault zones have previously been referred to both as flaser-banded gneisses and as weathering horizons. In general the zones range between 1-30m in thickness. Displacements along these zones are difficult to estimate, but may be in the order of 1-100 km. The structures indicate that the faults formed close to horizontal, during extensional shear and were therefore low angle normal faults. F1a zones overlap in age with the formation of the ophiolite complex. The second type of faults (F1b) are vertical brittle-ductile shear zones, which crosscut the complex at variable angles and cannot always be traced from plutonic to overlying extrusive (pillowed) simatic rocks. F1b zones are also apparently of penecontemporaneous origin with the intrusive-extrusive igneous processs. F1b zones may either represent transform fault-type activity or represent root zones (steepened extensions) of F1a zones. Both fault types indicate extensive deformation in the rocks of the greenstone belt prior to compressional overthrust tectonics.

The Cedars ultramafic mass, Sonoma County, California

USGS Publications Warehouse

Blake, M. Clark; Bailey, Edgar H.; Wentworth, Carl M.

2012-01-01

The Cedars ultramafic mass is a mantle fragment that consists of partially serpentinized spinel harzburgite and dunite. Compositional layering and a chromite lineation define a penetrative metamorphic foliation that almost certainly formed in the upper mantle. Although detailed petrofabric and mineral chemistry are presently lacking, it seems reasonable that the Cedars peridotite represents a slice of mantle tectonite that once formed the base of the Coast Range ophiolite, and not an abyssal peridotite tectonically emplaced within the Franciscan accretionary prism.

Geological constraints for muon tomography: The world beyond standard rock

NASA Astrophysics Data System (ADS)

Lechmann, Alessandro; Mair, David; Ariga, Akitaka; Ariga, Tomoko; Ereditato, Antonio; Käser, Samuel; Nishiyama, Ryuichi; Scampoli, Paola; Vladymyrov, Mykhailo; Schlunegger, Fritz

2017-04-01

In present day muon tomography practice, one often encounters an experimental setup in which muons propagate several tens to a few hundreds of meters through a material to the detector. The goal of such an undertaking is usually centred on an attempt to make inferences from the measured muon flux to an anticipated subsurface structure. This can either be an underground interface geometry or a spatial material distribution. Inferences in this direction have until now mostly been done, thereby using the so called "standard rock" approximation. This includes a set of empirically determined parameters from several rocks found in the vicinity of physicist's laboratories. While this approach is reasonable to account for the effects of the tens of meters of soil/rock around a particle accelerator, we show, that for material thicknesses beyond that dimension, the elementary composition of the material (average atomic weight and atomic number) has a noticeable effect on the measured muon flux. Accordingly, the consecutive use of this approximation could potentially lead into a serious model bias, which in turn, might invalidate any tomographic inference, that base on this standard rock approximation. The parameters for standard rock are naturally close to a granitic (SiO2-rich) composition and thus can be safely used in such environments. As geophysical surveys are not restricted to any particular lithology, we investigated the effect of alternative rock compositions (carbonatic, basaltic and even ultramafic) and consequentially prefer to replace the standard rock approach with a dedicated geological investigation. Structural field data and laboratory measurements of density (He-Pycnometer) and composition (XRD) can be merged into an integrative geological model that can be used as an a priori constraint for the rock parameters of interest (density & composition) in the geophysical inversion. Modelling results show that when facing a non-granitic lithology the measured muon

Subduction-related prograde metamorphism of the ultramafic members of the Central-Sudetic Ophiolite (SW Poland)

NASA Astrophysics Data System (ADS)

Wojtulek, Piotr; Puziewicz, Jacek; Ntaflos, Theodoros

2016-04-01

The Central-Sudetic Ophiolite (CSO) consists of Ślęża (SM), Braszowice-Brzeźnica (BBM), Szklary (SZM) and Nowa Ruda massifs. Ultramafic rocks occurring in ŚM, BBM and SM have MgO/SiO2 (0.82-1.20) and Al2O3/SiO2 (~0.01) ratios typical for serpentinized mantle peridotites. They are enriched in Cs, Pb and Sb and depleted in Rb, Ba, Nb, La, Ce, Sr, Zr, Er and Y relative to primitive mantle. The serpentinites are antigorite ones, pseudomorphic chrysotile varieties occur sparsely. Serpentinites from each massif contain specific non-serpentine phases. Ślęża serpentinites contain primary olivine-chromite aggregates, olivine and clinopyroxene aggregates interpreted as basaltic melt percolation phases, secondary olivine with magnetite inclusions (locally with cleavage) and secondary microcrystalline olivine-clinopyroxene-magnetite aggregates ("brownish aggregates") with bastite and mesh textures. The BBM serpentinites contain primary olivine-chromite aggregates, primary diopside grains, secondary magnetite-bearing olivine and tremolite. The SZM serpentinites contain olivine, tremolite and enstatite grains. Enstatite (Mg# = 92.8-93.0) contains >0.2 wt.% Cr2O3 and >0.7 Al2O3. All secondary non-serpentine phases are intergrown by antigorite. Very low overall trace element contents, Cs and high Pb-Sb anomalies of the CSO serpentinites are similar to subduction zone related serpentinites not affected by later fluid refertilization. Mineral assemblages shows prograde alteration of the rocks: (1) low-T serpentinization I forming pseudomorphic lizardite-chrysotile serpentinites; (2) antigorite recrystallization; (3) deserpentinization forming secondary olivine with magnetite inclusions, "brownish structures", tremolite and/or enstatite; (4) high-T serpentinization II forming antigorite intergrowths. Alteration degree is different in each massif: rocks from the SM are the most altered, they contain antigorite-olivine-enstatite-tremolite assemblage typical for temperatures

Origin of spinel lamella and/or inclusions in olivine of harzburgite form the Pauza ultramafic rocks from the Kurdistan region, northeastern Iraq

NASA Astrophysics Data System (ADS)

Mohammad, Y.; Maekawa, H.; Karim, K.

2009-04-01

Exsolution lamellae and octahedral inclusions of chromian spinel occur in olivine of harzburgite of the Pauza ultramafic rocks, Kurdistan region, northeastern Iraq. The lamella is up to 80μm long and up to 50 μm wide. The lamellae and octahedral inclusions of chromian spinel are distributed heterogeneously in the host olivine crystal. They are depleted in Al2O3 relative to the subhedral spinel grains in the matrix and spinel lamella in orthopyroxene. Olivine (Fo92 - 93) with spinel lamellae occurs as fine-grained crystals around orthopyroxene, whereas olivine (Fo90-91) free from spinel is found in matrix. Based on back-scattered images analyses, enrichments of both Cr # and Fe+3 in the chromian spinel lamella in olivine (replacive olivine) relative to that in adjacent orthopyroxene. As well as the compositions of chromian spinel lamellae host olivine are more Mg-rich than the matrix olivine. Furthermore the restriction of olivine with spinel lamellae and octahedral inclusions on around orthopyroxene, and the similarity of spinel lamella orientations in both olivine and adjacent orthopyroxene. This study concludes that the spinel inclusions in olivine are remnant (inherited from former orthopyroxene) spinel exsolution lamella in orthopyroxene, that has been formed in upper mantle conditions ( T = 1200 °C, P = 2.5 GPa ). Replacive olivine are formed by reaction of ascending silica poor melt and orthopyroxene in harzburgite as pressure decrease the solubility of silica-rich phase (orthopyroxene) in the system increase, therefore ascending melt dissolve pyroxene with spinel exsolution lamella and precipitate replacive olivine with spinel inclusions. We can conclude that the olivines with spinel lamella are not necessary to be original and presenting ultrahigh-pressure and/or ultra deep-mantle conditions as previously concluded. It has been formed by melting of orthopyroxene (orthopyroxene with spinel exsolution lamella = olivine with spinel lamellae and octahedral

Intrusive rocks northeast of Steamboat Springs, Park Range, Colorado, with a section on geochronology

USGS Publications Warehouse

Snyder, George L.; Hedge, Carl E.

1978-01-01

Major Precambrian and minor Tertiary intrusive rocks northeast of Steamboat Springs in the Park Range between 40?30' and 40?45' N. lat. are described and compared with related rocks elsewhere in Colorado and Wyoming. The Precambrian intrusives were emplaced in a sequence of high-grade interlayered felsic gneisses, amphibolites, and pelitic schists of sedimentary and volcanic origin. These rocks are cut by a major northeast-trending Precambrian shear zone where mainly left lateral movement of 1/ 2 to 1 mile is certain. Cumulative movement of many miles is possible. The Precambrian intrusives consist of a batholith, the Mount Ethel pluton, a smaller Buffalo Pass pluton, and small dikes or lenses of fine-grained porphyry, pegmatites, and ultramafics. The Mount Ethel pluton is an oval shaped body 7 miles wide by about 40 miles long (shown by geophysical data to extend beneath younger sediments in North Park). Outer batholithic contacts are sharp and dip steeply outward at about 85?. Five mappable internal variants consist, in order of decreasing age, of granodiorite, quartz monzonite porphyry of Rocky Peak, quartz monzonite of Roxy Ann Lake, granite and quartz monzonite, and. leucogranite. Internal contacts between these plutonic variants are sharp, and evidence of liquid-solid relationships abounds; despite this, all rocks except the granodiorite contribute to an Rb-Sr whole-rock isochron indicating emplacement about 1.4 b.y. (billion years) ago. The most important variants volumetrically are: the quartz monzonite porphyry of Rocky Peak, which forms an irregular 2-mile-thick carapace or mapped band around the west edge of the pluton and is lithologically similar to nearby Sherman Granite, and the quartz monzonite of Roxy Ann Lake, which forms most of the rest of the pluton and is lithologically similar to Silver Plume Granite. An apparent Sherman -Silver Plume dichotomy with similar rock types and similar relative ages is noted throughout Colorado plutons of that age

Electron-microprobe study of chromitites associated with alpine ultramafic complexes and some genetic implications

USGS Publications Warehouse

Bird, M.L.

1978-01-01

, suggest that the high-aluminum chromite was formed by metamorphic recrystallization of the ultramafic rocks and adjacent gabbro.

Alteration Mineralogy of Adirondack-class Rocks in Gusev Crater, Mars

NASA Astrophysics Data System (ADS)

Hamilton, V. E.; Ruff, S. W.

2009-12-01

amounts of oxides and basaltic glass (~15%). This ultramafic composition is similar to that derived from linear mixture modeling of the measured Mini-TES spectra, but differs in detail from the APXS-derived normative mineralogy and Mössbauer ol:px. These differences may be artifacts of the penetration depths and spot sizes of the measurements, or assumptions inherent in the conversions from chemistry and spectra to norms and abundances; work in progress is aimed at explaining these differences. The other shape is modeled with high-silica phases (29%), sulfates (~24%), olivine (~19%), pyroxene (~15%), and oxides (~12%), suggesting it represents a highly altered mineralogy. We linearly modeled the highest-quality measured spectra of Adirondack-class rocks using only the FATT-derived spectral shapes. Surface components are modeled by varying proportions of the two surface shapes, with all containing ≥40% of the ultramafic shape. These preliminary results suggest that Adirondack-class rocks are a single lithology exhibiting sulfate-bearing surface alteration that is variable from rock to rock. We are in the process of converting the mineralogies derived from measured and FATT-derived spectra into bulk oxides and will present quantitative comparisons with APXS data and qualitative comparisons with Mössbauer data.

Deportment of PGE and semimetals in the Volspruit deposit: the most ultramafic PGE horizon of the Bushveld Complex

NASA Astrophysics Data System (ADS)

Tanner, D.; McDonald, I.; Harmer, R. E. J.; Hughes, H. S. R.; Muir, D. D.

2017-12-01

The Volspruit deposit is a zone of disseminated magmatic sulphides carrying Ni-PGE (platinum-group element) mineralization in the Northern Limb of the Bushveld Complex, South Africa. It is one of the few known PGE prospects hosted by the lower ultramafic portion of a layered intrusion and the only known example in the Bushveld Complex. Volspruit therefore provides a unique insight into the processes governing mineralisation early in the Bushveld magmatic system. This study presents a detailed analysis from the northern portion of the Volspruit orebody combining mineralogical and textural observations with sulphide mineral trace element compositions. Electron microscopy reveals a diverse assemblage of Pt-, Pd- and Rh- dominant platinum-group minerals (PGM), electrum, Ag tellurides, Pb-chlorides, Pb-sulphides, U-oxide and monazite. Laser ablation ICP-MS has demonstrated that the Volspruit base metal sulphides have elevated PGE tenors but a range of S/Se values 1414-19319 - greater than other magmatic sulphide deposits in the northern Bushveld. The S/Se values are typical of crustal S and in agreement with previous S isotope data. These data imply a magma with initially high tenor sulphide liquid experienced local contamination from sedimentary S, leading to reduced tenors and elevated S/Se in sulphides coupled with a propensity of Pb- and Zn-bearing minerals (e.g., Pb-sulphide, Pb-chloride and sphalerite) in association with archetypal orthomagmatic sulphide assemblages. Our data demonstrate that assimilation of sedimentary rocks can modify sulphide melt evolution through the addition of metals such as Pb and Zn, not just contamination by sulphur. The Volspruit deposit illustrates the complexity of multi-stage processes governing mineralisation in the ultramafic portions of layered mafic intrusions.

Occurrence model for magmatic sulfide-rich nickel-copper-(platinum-group element) deposits related to mafic and ultramafic dike-sill complexes: Chapter I in Mineral deposit models for resource assessment

USGS Publications Warehouse

Schulz, Klaus J.; Woodruff, Laurel G.; Nicholson, Suzanne W.; Seal, Robert R.; Piatak, Nadine M.; Chandler, Val W.; Mars, John L.

2014-01-01

The sulfides in magmatic Ni-Cu deposits generally constitute a small volume of the host rock(s) and tend to be concentrated in the lower parts of the mafic and/or ultramafic bodies, often in physical depressions or areas marking changes in the geometry of the footwall topography. In most deposits, the sulfide mineralization can be divided into disseminated, matrix or net, and massive sulfide, depending on a combination of the sulfide content of the rock and the silicate texture. The major Ni-Cu sulfide mineralogy typically consists of an intergrowth of pyrrhotite (Fe7S8), pentlandite ([Fe, Ni]9S8), and chalcopyrite (FeCuS2). Cobalt, PGE, and gold (Au) are extracted from most magmatic Ni-Cu ores as byproducts, although such elements can have a significant impact on the economics in some deposits, such as the Noril’sk-Talnakh deposits, which produce much of the world’s palladium. In addition, deposits may contain between 1 and 15 percent magnetite associated with the sulfides.

Unraveling multiple phases of sulfur cycling during the alteration of ancient ultramafic oceanic lithosphere

NASA Astrophysics Data System (ADS)

Schwarzenbach, Esther M.; Gill, Benjamin C.; Johnston, David T.

2018-02-01

Ultramafic-hosted hydrothermal systems - characterized by ongoing serpentinization reactions - exert an important influence on the global sulfur cycle. Extensive water-rock interaction causes elemental exchange between seawater and the oceanic lithosphere, effectively removing sulfate from seawater through both abiogenic and biogenic processes. Here, we use bulk rock multiple sulfur isotope signatures (32S, 33S, 34S) and in situ sulfide analyses together with petrographic observations to track the sulfur cycling processes and the hydrothermal evolution of ancient peridotite-hosted hydrothermal systems. We investigate serpentinized peridotites from the Northern Apennine ophiolite in Italy and the Santa Elena ophiolite in Costa Rica and compare those with the Iberian Margin (Ocean Drilling Program (ODP) Leg 149 and 173) and the 15°20‧N Fracture Zone along the Mid-Atlantic Ridge (ODP Leg 209). In situ measurements of sulfides in the Northern Apennine serpentinites preserve a large range in δ34Ssulfide of -33.8 to +13.3‰ with significant heterogeneities within single sulfide grains and depending on mineralogy. Detailed mineralogical investigation and comparison with bulk rock Δ33Ssulfide and in situ δ34Ssulfide data implies a thermal evolution of the system from high temperatures (∼350 °C) that allowed thermochemical sulfate reduction and input of hydrothermal sulfide to lower temperatures (<120 °C) that permitted microbial activity. The change in temperature regime is locally preserved in individual samples and correlates with the progressive uplift and exposure of mantle rock associated with detachment faulting along a mid-ocean ridge spreading center. The Santa Elena peridotites preserve distinct signatures for fluid circulation at high temperatures with both closed system thermochemical sulfate reduction and input of mafic-derived sulfur. In addition, the peridotites provide strong evidence that low Ca2+ concentrations in peridotite-hosted systems can

Seismic Reflection Imaging of the Heat Source of an Ultramafic-Hosted Hydrothermal System (Rainbow, Mid-Atlantic Ridge 36° 10-17'N)

NASA Astrophysics Data System (ADS)

Canales, J. P.; Dunn, R. A.; Sohn, R. A.; Horning, G.; Arai, R.; Paulatto, M.

2015-12-01

Most of our understanding of hydrothermal systems and the nature of their heat sources comes from models and observations at fast and intermediate spreading ridges. In these settings, hydrothermal systems are mainly located within the axial zone of a spreading segment, hosted in basaltic rock, and primarily driven by heat extracted from crystallization of crustal melt sills. In contrast, hydrothermal systems at slow-spreading ridges like the Mid-Atlantic Ridge (MAR) show a great variety of venting styles and host-rock lithology, and are located in diverse tectonic settings like axial volcanic ridges, non-transform discontinuities (NTDs), the foot of ridge valley walls, and off-axis inside corner highs. Among MAR systems, the Rainbow hydrothermal field (RHF) stands out as an end-member of this diversity: an ultramafic-hosted system emitting H2 and CH4-rich fluids at high temperatures and high flow rates, which suggests a magmatic heat source despite the lack of evidence for recent volcanism and its location within an NTD with presumably low magma budget. We present 2D multichannel seismic reflection images across the Rainbow massif from the NSF-funded MARINER multidisciplinary geophysical study that reveal, for the first time, the magmatic system driving hydrothermal circulation in an ultramafic setting. Data were acquired in 2013 onboard the RV M. Langseth with an 8-km-long hydrophone streamer. The images have been obtained from pre-stack depth migrations using a regional 3D P-wave velocity model from a coincident controlled-source seismic tomography experiment using ocean bottom seismometers. Our images show a complex magmatic system centered beneath the RHF occupying an areal extent of ~3.7x6 km2, with partially molten sills ranging in depth between ~3.4 km and ~6.9 km below the seafloor. Our data also image high-amplitude dipping reflections within the massif coincident with strong lateral velocity gradients that may arise from detachment fault planes

Origin of ultramafic xenoliths containing exsolved pyroxenes from Hualalai Volcano, Hawaii

NASA Astrophysics Data System (ADS)

Bohrson, Wendy A.; Clague, David A.

1988-10-01

Hualalai Volcano, Hawaii, is best known for the abundant and varied xenoliths included in the historic 1800 Kaupulehu alkalic basalt flow. Xenoliths, which range in composition from dunite to anorthosite, are concentrated at 915-m elevation in the flow. Rare cumulate ultramafic xenoliths, which include websterite, olivine websterite, wehrlite, and clinopyroxenite, display complex pyroxene exsolution textures that indicate slow cooling. Websterite, olivine websterite, and one wehrlite are spinel-bearing orthopyroxene +olivine cumulates with intercumulus clinopyroxene +plagioclase. Two wehrlite samples and clinopyroxenite are spinel-bearing olivine cumulates with intercumulus clinopyroxene+orthopyroxene + plagioclase. Two-pyroxene geothermometry calculations, based on reconstructed pyroxene compositions, indicate that crystallization temperatures range from 1225° to 1350° C. Migration or unmixing of clinopyroxene and orthopyroxene stopped between 1045° and 1090° C. Comparisons of the abundance of K2O in plagioclase and the abundances of TiO2 and Fe2O3in spinel of xenoliths and mid-ocean ridge basalt, and a single 87Sr/ 86Sr determination, indicate that these Hualalai xenoliths are unrelated to mid-ocean ridge basalt. Similarity between the crystallization sequence of these xenoliths and the experimental crystallization sequence of a Hawaiian olivine tholeiite suggest that the parental magma of the xenoliths is Hualalai tholeiitic basalt. Xenoliths probably crystallized between about 4.5 and 9 kb. The 155° 230° C of cooling which took place over about 120 ka — the age of the youngest Hualalai tholeiitic basalt — yield maximum cooling rates of 1.3×10-3 1.91×10-3 °C/yr. Hualalai ultramafic xenoliths with exsolved pyroxenes crystallized from Hualalai tholeiitic basalt and accumulated in a magma reservoir located between 13 and 28 km below sealevel. We suspect that this reservoir occurs just below the base of the oceanic crust at about 19 km below sealevel.

Origin of ultramafic xenoliths containing exsolved pyroxenes from Hualalai Volcano, Hawaii

USGS Publications Warehouse

Bohrson, W.A.; Clague, D.A.

1988-01-01

Hualalai Volcano, Hawaii, is best known for the abundant and varied xenoliths included in the historic 1800 Kaupulehu alkalic basalt flow. Xenoliths, which range in composition from dunite to anorthosite, are concentrated at 915-m elevation in the flow. Rare cumulate ultramafic xenoliths, which include websterite, olivine websterite, wehrlite, and clinopyroxenite, display complex pyroxene exsolution textures that indicate slow cooling. Websterite, olivine websterite, and one wehrlite are spinel-bearing orthopyroxene +olivine cumulates with intercumulus clinopyroxene +plagioclase. Two wehrlite samples and clinopyroxenite are spinel-bearing olivine cumulates with intercumulus clinopyroxene+orthopyroxene + plagioclase. Two-pyroxene geothermometry calculations, based on reconstructed pyroxene compositions, indicate that crystallization temperatures range from 1225?? to 1350?? C. Migration or unmixing of clinopyroxene and orthopyroxene stopped between 1045?? and 1090?? C. Comparisons of the abundance of K2O in plagioclase and the abundances of TiO2 and Fe2O3in spinel of xenoliths and mid-ocean ridge basalt, and a single 87Sr/ 86Sr determination, indicate that these Hualalai xenoliths are unrelated to mid-ocean ridge basalt. Similarity between the crystallization sequence of these xenoliths and the experimental crystallization sequence of a Hawaiian olivine tholeiite suggest that the parental magma of the xenoliths is Hualalai tholeiitic basalt. Xenoliths probably crystallized between about 4.5 and 9 kb. The 155??-230?? C of cooling which took place over about 120 ka - the age of the youngest Hualalai tholeiitic basalt - yield maximum cooling rates of 1.3??10-3-1.91??10-3 ??C/yr. Hualalai ultramafic xenoliths with exsolved pyroxenes crystallized from Hualalai tholeiitic basalt and accumulated in a magma reservoir located between 13 and 28 km below sealevel. We suspect that this reservoir occurs just below the base of the oceanic crust at about 19 km below sealevel

Ultramafic lavas and pyroxene-spinifex high-Mg basaltic dykes from the Othris ophiolite complex, Greece

NASA Astrophysics Data System (ADS)

Baziotis, Ioannis; Economou-Eliopoulos, Maria; Asimow, Paul

2017-04-01

This study aims to constrain the physico-chemical conditions and processes associated with the origin of ultramafic lavas of the Agrilia formation and high-Mg basaltic dykes in the Pournari area within the Othris ophiolite complex, a supra-subduction zone ophiolite of Mesozoic age (Paraskevopoulos & Economou, 1986; Barth et al., 2008). Hand-sample-scale spinifex texture is lacking from the ultramafic lavas and, despite whole-rock MgO contents greater than 31 wt.%, we infer an upper bound of 17 wt.% MgO for the erupted liquid, and thus identify these lavas as picrites containing accumulated olivine. We use textural and compositional criteria to divide the crystals within the Agrilia lavas between pre-eruptive and post-eruptive growth phases. The high-Mg basaltic dyke margins display a distinctive thin-section-scale micro-spinifex texture of skeletal and plumose Al- and Fe-rich clinopyroxene surrounded by large crystals of orthopyroxene. Normally zoned clinopyroxene in the Agrilia lavas and clinopyroxene of various textures (skeletal, needle- and dendritic-like) and sizes in the Pournari dykes display anomalous enrichment in Al2O3 and FeO* with decreasing MgO that require rapid, disequilibrium growth. Quantitative characteristics of the micro-spinifex pyroxene textures (<10 μm in width and 50-100 μm in length) imply a cooling rate for the marginal parts of the Pournari dykes of at least 25 °K/hr and more likely 45-55 °K/hr (Faure et al., 2004) and rapid growth of clinopyroxene crystals at a linear rate of about 10-6 m/s (Welsch et al., 2016). MELTS models of the crystallization sequence of the Pournari dykes indicate that progressive low-pressure (500 bar) fractional crystallization of the ultramafic dyke liquid occurred under oxidized (QFM+2.0) and hydrous (at least 0.5 wt.% H2O) conditions. A hydrous magmatic parent for the Othris ophiolite as a whole is further supported by preliminary investigation of melt inclusions (5-20 μm in diameter) in fresh chromite

Petrology of metabasic and peridotitic rocks of the Songshugou ophiolite, Qinling orogen, China

NASA Astrophysics Data System (ADS)

Belic, Maximilian; Hauzenberger, Christoph; Dong, Yunpeng

2013-04-01

The Proterozoic Songshugou ophiolite outcrops as a rootless nappe which was emplaced into the southern margin of the Qinling Group. It consists mainly of amphibolite facies metamafic and -ultramafic rocks. Trace element geochemistry and isotope composition show that the mafic rocks are mainly E-MORB and T-MORB metabasalts (Dong et al., 2008b). Within the ophiolite sequence, ultramafic rocks consist mainly of peridotites and serpentinites. Particularly, extremely fresh dunites and harzburgites, are found which do not display a conspicuous metamorphic overprint. The low CaO (<0.39 wt.%) and Al2O3 (<0.51 wt.%) as well as high MgO (41-48 wt.%) contents classify them as depleted non-fertile mantle rocks. Chromite is found as disseminated phase but can sometimes form massive chromite bands. The platinumgroup mineral Laurite (RuS2) could be identified as inclusion in chromites. Usually part of Ru is substituted by Os and Ir. The metamafic rocks consist of garnet, amphibole, symplectitic pyroxenes, ilmenite, apatite, ±zoisite, ±sphene and show a strong metamorphic overprint. Garnet contains numerous inclusions in the core but are nearly inclusion free at the rim. The cores have sometimes snowball textures indicating initially syndeformative growth. Pure albite and prehnite were found in the central parts of the garnets. In the outer portions, pargasitic amphibole, rutile and rarely glaukophane were found. The symplectitic pyroxenes are of diopsidic composition which enclose prehnite and not albite, as common in retrograde eclogitic rocks. Different stages of garnet breakdown to plagioclase and amphibole, from thin plagioclase rims surrounding the garnets to plagioclase rich pseudomorphs, can be observed in different samples. Based on the glaukophane inclusions and symplectitic pyroxenes a high pressure metamorphic event can be concluded. The garnet breakdown to plagioclase and the symplectites clearly indicate a rapid exhumation phase. The age of the metamorphic event is

75 FR 37430 - Plymouth Rock Energy, LLC; Supplemental Notice That Initial Market-Based Rate Filing Includes...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-06-29

... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket No. ER10-1470-000] Plymouth Rock Energy, LLC; Supplemental Notice That Initial Market-Based Rate Filing Includes Request for Blanket... of Plymouth Rock Energy, LLC.'s application for market-based rate authority, with an accompanying...

A survey of lunar rock types and comparison of the crusts of earth and moon

NASA Technical Reports Server (NTRS)

Wood, J. A.

1977-01-01

The principal known types of lunar rocks are briefly reviewed, and their chemical relationships discussed. In the suite of low-KREEP highland rocks, Fe/(Fe + Mg) in the normative mafic minerals increases and the albite content of normative plagio-clase decreases as the total amount of normative plagioclase increases, the opposite of the trend predicted by the Bowen reaction principle. The distribution of compositions of rocks from terrestrial layered mafic intrusives is substantially different: here the analyses fall in several discrete clusters (anorthositic rocks, norites, granophyres and ferrogabbros, ultramafics), and the chemical trends noted above are not reproduced. It is suggested that the observed trends in lunar highland rocks could be produced by crystal fractionation in a deep global surface magma system if (1) plagiociase tended to float, upon crystallization, and (2) the magma was kept agitated and well mixed (probably by thermal convection) until crystallization was far advanced and relatively little residual liquid was left. After the crustal system solidified, but before extensive cooling had developed a thick, strong lithosphere, mantle convection was able to draw portions of the lunar anorthositic crust down into the mantle.

Ultramafic clasts from the South Chamorro serpentine mud volcano reveal a polyphase serpentinization history of the Mariana forearc mantle

NASA Astrophysics Data System (ADS)

Kahl, Wolf-Achim; Jöns, Niels; Bach, Wolfgang; Klein, Frieder; Alt, Jeffrey C.

2015-06-01

Serpentine seamounts located on the outer half of the pervasively fractured Mariana forearc provide an excellent window into the forearc devolatilization processes, which can strongly influence the cycling of volatiles and trace elements in subduction zones. Serpentinized ultramafic clasts recovered from an active mud volcano in the Mariana forearc reveal microstructures, mineral assemblages and compositions that are indicative of a complex polyphase alteration history. Petrologic phase relations and oxygen isotopes suggest that ultramafic clasts were serpentinized at temperatures below 200 °C. Several successive serpentinization events represented by different vein generations with distinct trace element contents can be recognized. Measured in situ Rb/Cs ratios are fairly uniform ranging between 1 and 10, which is consistent with Cs mobilization from sediments at lower temperatures and lends further credence to the low-temperature conditions proposed in models of the thermal structure in forearc settings. Late veins show lower fluid mobile element (FME) concentrations than early veins, suggesting a decreasing influence of fluid discharge from the subducting slab on the composition of the serpentinizing fluids. The continuous microfabric and mineral chemical evolution observed in the ultramafic clasts may have implications as to the origin and nature of the serpentinizing fluids. We hypothesize that opal and smectite dehydration produce quartz-saturated fluids with high FME contents and Rb/Cs between 1 and 4 that cause the early pervasive serpentinization. The partially serpentinized material may then be eroded from the basal plane of the suprasubduction mantle wedge. Serpentinization continued but the interacting fluids did not carry a pronounced sedimentary signature, either because FMEs were no longer released from the slab, or due to an en route loss of FMEs. Late chrysotile veins that document the increased access of fluids in a now fluid-dominated regime are

The influence of spreading rate, basement composition, fluid chemistry and chimney morphology on the formation of gold-rich SMS deposits at slow and ultraslow mid-ocean ridges

NASA Astrophysics Data System (ADS)

Knight, Robert D.; Roberts, Stephen; Webber, Alexander P.

2018-01-01

Seafloor massive sulphide (SMS) deposits are variably enriched in precious metals including gold. However, the processes invoked to explain the formation of auriferous deposits do not typically apply to mid-ocean ridge settings. Here, we show a statistically significant, negative correlation between the average gold concentration of SMS deposits with spreading rate, at non-sedimented mid-ocean ridges. Deposits located at slow spreading ridges (20-40 mm/a) have average gold concentrations of between 850 and 1600 ppb; however, with increasing spreading rate (up to 140 mm/a), gold concentrations gradually decrease to between 50 and 150 ppb. This correlation of gold content with spreading rate may be controlled by the degree and duration of fluid-rock interaction, which is a function of the heat flux, crustal structure (faulting) and the permeability of the source rocks. Deposits at ultraslow ridges, including ultramafic-hosted deposits, are particularly enriched in gold. This is attributed to the higher permeability of the ultramafic source rocks achieved by serpentinisation and the inherent porosity of serpentine minerals, combined with relatively high gold concentrations in peridotite compared with mid-ocean ridge basalt. Variations in fluid chemistry, such as reducing conditions and the potential for increased sulphur availability at ultramafic-hosted sites, may also contribute to the high concentrations observed. Beehive chimneys, which offer more favourable conditions for gold precipitation, may be more prevalent at ultramafic-hosted sites due to diffuse low-velocity venting compared with more focussed venting at basalt-hosted sites.

Conditional estimates of the number of podiform chromite deposits

USGS Publications Warehouse

Singer, D.A.

1994-01-01

A desirable guide for estimating the number of undiscovered mineral deposits is the number of known deposits per unit area from another well-explored permissive terrain. An analysis of the distribution of 805 podiform chromite deposits among ultramafic rocks in 12 subareas of Oregon and 27 counties of California is used to examine and extend this guide. The average number of deposits in this sample of 39 areas is 0.225 deposits per km2 of ultramafic rock; the frequency distribution is significantly skewed to the right. Probabilistic estimates can be made by using the observation that the lognormal distribution fits the distribution of deposits per unit area. A further improvement in the estimates is available by using the relationship between the area of ultramafic rock and the number of deposits. The number (N) of exposed podiform chromite deposits can be estimated by the following relationship: log10(N)=-0.194+0.577 log10(area of ultramafic rock). The slope is significantly different from both 0.0 and 1.0. Because the slope is less than 1.0, the ratio of deposits to area of permissive rock is a biased estimator when the area of ultramafic rock is different from the median 93 km2. Unbiased estimates of the number of podiform chromite deposits can be made with the regression equation and 80 percent confidence limits presented herein. ?? 1994 Oxford University Press.

Minerals and melt inclusions as keys to understanding magma reservoir processes during formation of volcanic and plutonic mafic-ultramafic complexes in the Maimecha Kotui Province (Polar Siberia)

NASA Astrophysics Data System (ADS)

Simonov, Vladimir; Vasiliev, Yurii; Kotlyarov, Alexey; Stupakov, Sergey

2016-04-01

Magmatic complexes in the Maimecha Kotui Province (Polar Siberia) attract attention of researchers because they contain ultramafic volcanic rocks - meimechites, being products of crystallization of the ultrabasic deep mantle melts (Sobolev et al., 1991, 2009, 2011; Ryabchikov et al., 2002; Vasiliev, Gora, 2014). Effusive meimechites together with intrusive dunites of the Guli massif form ancient (253-246 Ma) volcanic and plutonic association, in which also pyroxenites and alkaline rocks are situated. Conditions of formation of this association were established with the help of minerals and melt inclusions study. The cumulative structure of the Guli massif dunites consists of rather large (2-4 mm) olivine crystals and dividing them zones (0.5-0.7 mm), filled with fine grains of clinopyroxenes and ore minerals (magnetite, ilmenite and chromite). The extended forms of well faceted pyroxene crystals testify to their fast growth from melt between cumulative olivines. Thus, crystallization of clinopyroxenes and ore minerals leads to formation between olivines ore pyroxenites, which are presented in the Guli massif by independent bodies. Analysis of olivine, Cr-spinel and clinopyroxene compositions testify to similarity of conditions of the Guli massif dunites crystallization on the one hand with formation of platinum-bearing Uralian-Alaskan-type mafic-ultramafic complexes and with another - show participation of meimechite magma. Major element composition of melt inclusions in Cr-spinel has shown that dunites of the Guli massif were crystallized with participation of subalkaline picrite magmatic systems, that are relative to melts, responsible of formation of platinum-bearing mafic-ultramafic complexes and meimechites. Peculiarities of trace and rare-earth elements distribution in melt inclusions in Cr-spinel of dunites are actually similar to inclusions in olivine of meimechites. Overall, data on composition of inclusions directly testify to formation of considered

Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Ponte Nova alkaline mafic-ultramafic massif, SE Brazil

NASA Astrophysics Data System (ADS)

Azzone, Rogério Guitarrari; Montecinos Munoz, Patricio; Enrich, Gaston Eduardo Rojas; Alves, Adriana; Ruberti, Excelso; Gomes, Celsode Barros

2016-09-01

Crustal assimilation plus crystal fractionation processes of different basanite magma batches control the evolution of the Ponte Nova cretaceous alkaline mafic-ultramafic massif in SE Brazil. This massif is composed of several intrusions, the main ones with a cumulate character. Disequilibrium features in the early-crystallized phases (e.g., corrosion and sieve textures in cores of clinopyroxene crystals, spongy-cellular-textured plagioclase crystals, gulf corrosion texture in olivine crystals) and classical hybridization textures (e.g., blade biotite and acicular apatite crystals) provide strong evidence of open-system behavior. All samples are olivine- and nepheline-normative rocks with basic-ultrabasic and potassic characters and variable incompatible element enrichments. The wide ranges of whole-rock 87Sr/86Sri and 143Nd/144Ndi ratios (0.70432-0.70641 and 0.512216-0.512555, respectively) are indicative of crustal contribution from the Precambrian basement host rocks. Plagioclase and apatite 87Sr/86Sr ratios (0.70422-0.70927) obtained for the most primitive samples of each intrusion indicate disequilibrium conditions from early- to principal-crystallization stages. Isotope mixing-model curves between the least contaminated alkaline basic magma and heterogeneous local crustal components indicate that each intrusion of the massif is differentiated from the others by varied degrees of crustal contribution. The primary mechanisms of crustal contribution to the Ponte Nova massif involve the assimilation of host rock xenoliths during the development of the chamber environment and the assimilation of partial melts from the surrounding host rocks. Thermodynamic models using the melts algorithm indicate that parental alkaline basic magmas can be strongly affected by contamination processes subsequently to their initial stages of crystallization when there is sufficient energy to assimilate partial melts of crustal host rocks. The assimilation processes are considered to

Developing a thermal characteristic index for lithology identification using thermal infrared remote sensing data

NASA Astrophysics Data System (ADS)

Wei, Jiali; Liu, Xiangnan; Ding, Chao; Liu, Meiling; Jin, Ming; Li, Dongdong

2017-01-01

In remote sensing petrology fields, studies have mainly concentrated on spectroscopy remote sensing research, and methods to identify minerals and rocks are mainly based on the analysis and enhancement of spectral features. Few studies have reported the application of thermodynamics for lithology identification. This paper aims to establish a thermal characteristic index (TCI) to explore rock thermal behavior responding to defined environmental systems. The study area is located in the northern Qinghai Province, China, on the northern edge of the Qinghai-Tibet Plateau, where mafic-ultramafic rock, quartz-rich rock, alkali granite rock and carbonate rock are well exposed; the pixel samples of these rocks and vegetation were obtained based on relevant indices and geological maps. The scatter plots of TCI indicate that mafic-ultramafic rock and quartz-rich rock can be well extracted from other surface objects when interference from vegetation is lower. On account of the complexity of environmental systems, three periods of TCI were used to construct a three-dimensional scatter plot, named the multi-temporal thermal feature space (MTTFS) model. Then, the Bayes discriminant analysis algorithm was applied to the MTTFS model to extract rocks quantitatively. The classification accuracy of mafic-ultramafic rock is more than 75% in both training data and test data, which suggests TCI can act as a sensitive indicator to distinguish rocks and the MTTFS model can accurately extract mafic-ultramafic rock from other surface objects. We deduce that the use of thermodynamics is promising in lithology identification when an effective index is constructed and an appropriated model is selected.

Rhizosphere bacteria of Costularia spp. from ultramafic soils in New Caledonia: diversity, tolerance to extreme edaphic conditions, and role in plant growth and mineral nutrition.

PubMed

Gonin, Mathieu; Gensous, Simon; Lagrange, Alexandre; Ducousso, Marc; Amir, Hamid; Jourand, Philippe

2013-03-01

Rhizosphere bacteria were isolated from Costularia spp., pioneer sedges from ultramafic soils in New Caledonia, which is a hotspot of biodiversity in the South Pacific. Genus identification, ability to tolerate edaphic constraints, and plant-growth-promoting (PGP) properties were analysed. We found that 10(5) colony-forming units per gram of root were dominated by Proteobacteria (69%) and comprised 21 genera, including Burkholderia (28%), Curtobacterium (15%), Bradyrhizobium (9%), Sphingomonas (8%), Rhizobium (7%), and Bacillus (5%). High proportions of bacteria tolerated many elements of the extreme edaphic conditions: 82% tolerated 100 μmol·L(-1) chromium, 70% 1 mmol·L(-1) nickel, 63% 10 mmol·L(-1) manganese, 24% 1 mmol·L(-1) cobalt, and 42% an unbalanced calcium/magnesium ratio (1/16). These strains also exhibited multiple PGP properties, including the ability to produce ammonia (65%), indole-3-acetic acid (60%), siderophores (52%), and 1-aminocyclopropane-1-carboxylate (ACC) deaminase (39%); as well as the capacity to solubilize phosphates (19%). The best-performing strains were inoculated with Sorghum sp. grown on ultramafic substrate. Three strains significantly enhanced the shoot biomass by up to 33%. The most successful strains influenced plant nutrition through the mobilization of metals in roots and a reduction of metal transfer to shoots. These results suggest a key role of these bacteria in plant growth, nutrition, and adaptation to the ultramafic constraints.

77 FR 45599 - CED Rock Springs, Inc.; Supplemental Notice That Revised Market-Based Rate Tariff Filing Includes...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-08-01

... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket Nos. ER02-2546-000; ER02-2546-001] CED Rock Springs, Inc.; Supplemental Notice That Revised Market- Based Rate Tariff Filing...-referenced proceeding of CED Rock Springs, Inc.'s tariff revision filing, noting that such filing includes a...

Komatiites and nickel sulphide orebodies of the Black Swan area, Yilgarn Craton, Western Australia. 1. Petrology and volcanology of host rocks

NASA Astrophysics Data System (ADS)

Hill, R. E. T.; Barnes, S. J.; Dowling, S. E.; Thordarson, T.

2004-11-01

The Black Swan Succession is a bimodal association of dacitic and komatiitic volcanic rocks located about 50 km NNE of Kalgoorlie, within the 2.7-Ga Eastern Goldfields greenstone province of the Yilgarn Craton. The komatiite stratigraphy comprises a steep dipping, east facing package about 700 m in maximum thickness and about 2.5 km in strike length (Fig. 1), which hosts a number of economically exploitable Ni sulphide orebodies including the Silver Swan massive ore shoot (approximately half a million tonnes at about 10.5% Ni). The sequence can be subdivided into a Lower Felsic Unit, comprising coherent and autobrecciated facies of multiple dacite lava flows; an upper Eastern and lower Western Ultramafic Unit, each showing marked lateral facies variation, and an Upper Felsic Unit coeval with the Eastern Ultramafic Unit. The komatiite sequence has been metamorphosed at sub-greenschist facies in the presence of high proportions of CO2-rich fluid, giving rise to pervasive talc carbonate and talc carbonate quartz assemblages, with extensive preservation of pseudomorphed igneous textures. Cores of lizardite serpentinite are present in the thickest parts of the ultramafic succession. The degree of penetrative deformation is generally very low, and original stratigraphic relationships are largely intact in much of the sequence. The Eastern Ultramafic Unit and Western Ultramafic Unit are interpreted as components of a single large komatiite flow field, representing overlapping stages in the emplacement of a series of distributory lava pathways and flanking sheet flows. The Western Ultramafic Unit which hosts the bulk of the high-grade massive and disseminated ores is a sequence dominated by coarse-grained olivine cumulates, 2 km wide and up to 500 m thick, with major magma pathways represented by thick, homogenous olivine mesocumulate piles at its northern and southern ends: respectively 400 and 200 m thick. The sequence between the two major pathways consists of olivine

Ar-Ar ages, Sr-Nd isotope geochemistry, and implications for the origin of the silicate rocks of the Jacupiranga ultramafic-alkaline complex (Brazil)

NASA Astrophysics Data System (ADS)

Chmyz, Luanna; Arnaud, Nicolas; Biondi, João Carlos; Azzone, Rogério Guitarrari; Bosch, Delphine; Ruberti, Excelso

2017-08-01

The Jacupiranga Complex is one of several Meso-Cenozoic alkaline intrusive complexes along the margins of the intracratonic Paraná Basin in southern Brazil. The complex encompasses a wide range of rock-types, including dunites, wehrlites, clinopyroxenites, melteigites-ijolites, feldspar-bearing rocks (diorites, syenites, and monzonites), lamprophyres and apatite-rich carbonatites. While carbonatites have been extensively investigated over the last decades, little attention has been paid to the silicate rocks. This study presents new geochonological and geochemical data on the Jacupiranga Complex, with particular emphasis on the silicate lithotypes. 40Ar/39Ar ages for different lithotypes range from 133.7 ± 0.5 Ma to 131.4 ± 0.5 Ma, while monzonite zircon analyzed by SHRIMP yields a U-Pb concordia age of 134.9 ± 1.3 Ma. These ages indicate a narrow time frame for the Jacupiranga Complex emplacement, contemporaneous with the Paraná Magmatic Province. Most of the Jacupiranga rocks are SiO2-undersaturated, except for a quartz-normative monzonite. Based on geochemical compositions, the Jacupiranga silicate lithotypes may be separated into two magma-evolution trends: (1) a strongly silica-undersaturated series, comprising part of the clinopyroxenites and the ijolitic rocks, probably related to nephelinite melts and (2) a mildly silica-undersaturated series, related to basanite parental magmas and comprising the feldspar-bearing rocks, phonolites, lamprophyres, and part of the clinopyroxenites. Dunites and wehrlites are characterized by olivine compositionally restricted to the Fo83-84 interval and concentrations of CaO (0.13-0.54 wt%) and NiO (0.19-0.33 wt%) consistent with derivation by fractional crystallization, although it is not clear whether these rocks belong to the nephelinite or basanite series. Lamprophyre dikes within the complex are considered as good representatives of the basanite parental magma. Compositions of calculated melts in equilibrium with

Alteration minerals in impact-generated hydrothermal systems - Exploring host rock variability

NASA Astrophysics Data System (ADS)

Schwenzer, Susanne P.; Kring, David A.

2013-09-01

Impact-generated hydrothermal systems have been previously linked to the alteration of Mars’ crust and the production of secondary mineral assemblages seen from orbit. The sensitivity of the resultant assemblages has not yet been evaluated as a function of precursor primary rock compositions. In this work, we use thermochemical modeling to explore the variety of minerals that could be produced by altering several known lithologies based on martian meteorite compositions. For a basaltic host rock lithology (Dhofar 378, Humphrey) the main alteration phases are feldspar, zeolite, pyroxene, chlorite, clay (nontronite, kaolinite), and hematite; for a lherzolithic host rock lithology (LEW 88516) the main alteration phases are amphibole, serpentine, chlorite, clay (nontronite, kaolinite), and hematite; and for an ultramafic host rock lithology (Chassigny) the main minerals are secondary olivine, serpentine, magnetite, quartz, and hematite. These assemblages and proportions of phases in each of those cases depend on W/R and temperature. Integrating geologic, hydrologic and alteration mineral evidence, we have developed a model to illustrate the distribution of alteration assemblages that occur in different levels of an impact structure. At the surface, hot, hydrous alteration affects the ejecta and melt sheet producing clay and chlorite. Deeper in the subsurface and depending on the permeability of the rock, a variety of minerals - smectite, chlorite, serpentine, amphiboles and hematite - are produced in a circulating hydrothermal system. These modeled mineral distributions should assist with interpretation of orbital observations and help guide surface exploration by rovers and sample return assets.

Does a Heavy Fe-Isotope Composition of Akilia Quartz-Amphibole-Pyroxene Rocks Necessitate a BIF Origin?

PubMed

Whitehouse, M J; Schoenberg, R; Fedo, C M; Kamber, B S

2015-10-01

The age and origin of the quartz-amphibole-pyroxene (qap) gneiss from the island of Akilia, southern West Greenland, have been the subject of intense debate since the light C-isotope composition of graphite inclusions in apatite was interpreted to indicate the presence of Earth's earliest biological activity. Although this claim for biogenic relicts has been vigorously challenged, the possibility that the rocks might represent some of Earth's earliest water-lain sediments and, hence, a suitable repository for life remains an open question. While some workers have suggested that the entire sequence represents an originally mafic-ultramafic igneous precursor subsequently modified by metasomatism, quartz injection, high-grade metamorphism, and extreme ductile deformation, others maintain that at least a small part of the sequence retains geochemical characteristics indicative of a chemical sedimentary origin. Fractionated Fe isotopes with δ(56)Fe values similar to those observed in Isua BIF have been reported from high-SiO2 units of qap and used to support a chemical sedimentary protolith for the qap unit. Here, we present new Fe isotope data from all lithologic variants in the qap gneiss on Akilia, including layers of undisputed ultramafic igneous origin. Since the latter require introduction of fractionated Fe into at least part of the qap unit, we argue that Fe isotopes must therefore be treated with considerable caution when used to infer BIF for part or all of the qap protolith.

Metamorphic assemblages and the direction of flow of metamorphic fluids in four instances of serpentinization

USGS Publications Warehouse

Barnes, I.; Rapp, J.B.; O'Neil, J.R.; Sheppard, R.A.; Gude, A.J.

1972-01-01

Fluids related to Serpentinization are of at least three types. The first reported (Barnes and O'Neil, 1969) is a fluid of local meteoric origin, the chemical and thermodynamic properties of which are entirely controlled by olivine, orthopyroxene, brucite, and serpentine reactions. It is a Ca+2-OH-1 type and is shown experimentally to be capable of reacting with albite to yield calcium hydroxy silicates. Rodingites may form where the Ca+2-OH-1 type waters flow across the ultramafic contact and react with siliceous country rock. The second type of fluid has its chemical composition largely controlled before it enters the ultramafic rocks, but reactions within the ultramafic rocks fix the thermodynamic properties by reactions of orthopyroxene, olivine, calcite, brucite, and serpentine. The precipitation of brucite from this fluid clearly shows that fluid flow allows reaction products to be deposited at a distance from the point of solution. Thus, textural evidence for volume relations during Serpentinization may not be valid. The third type of fluid has its chemical properties fixed in part before the reactions with ultramafic rocks, in part by the reactions of orthopyroxene, olivine, and serpentine and in part by reactions with siliceous country rock at the contact. The reactions of the ultramafic rock and country rock with the fluid must be contemporaneous and require flow to be along the contact. This third type of fluid is grossly supersaturated with talc and tremolite, both found along the contact. The occurrence of magadiite, kenyaite, mountainite, and rhodesite along the contact is probably due to a late stage low-temperature reaction of fluids of the same thermodynamic properties as those that formed the talc and tremolite at higher temperatures. Oxygen isotope analyses of some of these minerals supports this conclusion. Rodingites form from Ca+2-rich fluids flowing across the contact; talc and tremolite form from silica-rich fluids flowing along the contact

Impacts of ultramafic outcrops in Peninsular Malaysia and Sabah on soil and water quality.

PubMed

Tashakor, Mahsa; Modabberi, Soroush; van der Ent, Antony; Echevarria, Guillaume

2018-05-08

This study focused on the influence of ultramafic terrains on soil and surface water environmental chemistry in Peninsular Malaysia and in the State of Sabah also in Malaysia. The sampling included 27 soils from four isolated outcrops at Cheroh, Bentong, Bukit Rokan, and Petasih from Peninsular Malaysia and sites near Ranau in Sabah. Water samples were also collected from rivers and subsurface waters interacting with the ultramafic bodies in these study sites. Physico-chemical parameters (including pH, EC, CEC) as well as the concentration of major and trace elements were measured in these soils and waters. Geochemical indices (geoaccumulation index, enrichment factor, and concentration factor) were calculated. Al 2 O 3 and Fe 2 O 3 had relatively high concentrations in the samples. A depletion in MgO, CaO, and Na 2 O was observed as a result of leaching in tropical climate, and in relation to weathering and pedogenesis processes. Chromium, Ni, and Co were enriched and confirmed by the significant values obtained for Igeo, EF, and CF, which correspond to the extreme levels of contamination for Cr and high to moderate levels of contamination for Ni and Co. The concentrations of Cr, Ni, and Co in surface waters did not reflect the local geochemistry and were within the permissible ranges according to WHO and INWQS standards. Subsurface waters were strongly enriched by these elements and exceeded these standards. The association between Cr and Ni was confirmed by factor analysis. The unexpected enrichment of Cu in an isolated component can be explained by localized mineralization in Sabah.

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.

Cobalt—Styles of deposits and the search for primary deposits

USGS Publications Warehouse

Hitzman, Murray W.; Bookstrom, Arthur A.; Slack, John F.; Zientek, Michael L.

2017-11-30

Cobalt (Co) is a potentially critical mineral. The vast majority of cobalt is a byproduct of copper and (or) nickel production. Cobalt is increasingly used in magnets and rechargeable batteries. More than 50 percent of primary cobalt production is from the Central African Copperbelt. The Central African Copperbelt is the only sedimentary rock-hosted stratiform copper district that contains significant cobalt. Its presence may indicate significant mafic-ultramafic rocks in the local basement. The balance of primary cobalt production is from magmatic nickel-copper and nickel laterite deposits. Cobalt is present in several carbonate-hosted lead-zinc and copper districts. It is also variably present in Besshi-type volcanogenic massive sulfide and siliciclastic sedimentary rock-hosted deposits in back arc and rift environments associated with mafic-ultramafic rocks. Metasedimentary cobalt-copper-gold deposits (such as Blackbird, Idaho), iron oxide-copper-gold deposits, and the five-element vein deposits (such as Cobalt, Ontario) contain different amounts of cobalt. None of these deposit types show direct links to mafic-ultramafic rocks; the deposits may result from crustal-scale hydrothermal systems capable of leaching and transporting cobalt from great depths. Hydrothermal deposits associated with ultramafic rocks, typified by the Bou Azzer district of Morocco, represent another type of primary cobalt deposit.In the United States, exploration for cobalt deposits may focus on magmatic nickel-copper deposits in the Archean and Proterozoic rocks of the Midwest and the east coast (Pennsylvania) and younger mafic rocks in southeastern and southern Alaska; also, possibly basement rocks in southeastern Missouri. Other potential exploration targets include—The Belt-Purcell basin of British Columbia (Canada), Idaho, Montana, and Washington for different styles of sedimentary rock-hosted cobalt deposits;Besshi-type VMS deposits, such as the Greens Creek (Alaska) deposit and

Tungsten residence in silicate rocks: implications for interpreting W isotopic compositions

NASA Astrophysics Data System (ADS)

Liu, J.; Pearson, G. D.; Chacko, T.; Luo, Y.

2015-12-01

High-precision measurements of W isotopic ratios have boosted recent exploration of early Earth processes from the small W isotope anomalies observable in some Hadean-Archean rocks. However, before applying W isotopic data to understand the geological processes responsible for the formation of these rocks, it is critical to evaluate whether the rocks' present W contents and isotopic compositions reflect that of the protolith or the effects of secondary W addition/mobilization. To investigate this issue, we have carried out in situ concentration measurements of W and other HFSEs in mineral phases and alteration assemblages within a broad spectrum of rocks using LA-ICP-MS. Isotope dilution whole-rock W concentration measurements are used along with modes calculated from mineral and bulk rock major element data to examine the mass balance for W and other elements. In general, W is positively correlated with Nb, Ta, Ti, Sn, Mo and U, indicating similar geochemical behavior. Within granitic gneisses and amphibolites, biotite, hornblende, titanite and ilmenite control the W budget, while plagioclase and k-feldspar have little effect. For granulites, pyroxenites and eclogites, titanite, rutile, ilmenite, magnetite and sulfide, as well as grain boundary alteration assemblages dominate the W budget, while garnet, clinopyroxene, orthopyroxene and plagioclase have little or no W. Within mantle harzburgites and dunites, major phases such as olivine, clinopyroxene, orthopyroxene and spinel/chromite have very low concentrations of W, Nb, Ta, Sn and Mo. Instead, these elements are concentrated along grain boundaries and within sulfide/mss. Mass balance shows that for granitic gneisses and amphibolites, the rock-forming minerals can adequately account for the whole-rock W budget, whereas for ultramafic rocks such as pyroxenites, eclogites and harzburgites and dunites, significant W is hosted along grain boundaries, indicating that metamorphism and melt/fluid metasomatism can

Archaean tectonic systems: A view from igneous rocks

NASA Astrophysics Data System (ADS)

Moyen, Jean-François; Laurent, Oscar

2018-03-01

This work examines the global distribution of Archaean and modern igneous rock's compositions, without relying on preconceptions about the link between rock compositions and tectonic sites (in contrast with "geotectonic" diagrams). Rather, Archaean and modern geochemical patterns are interpreted and compared in terms of source and melting conditions. Mafic rocks on the modern Earth show a clear chemical separation between arc and non-arc rocks. This points to the first order difference between wet (arc) and dry (mid-ocean ridges and hotspots) mantle melting. Dry melts are further separated in depleted (MORB) and enriched (OIB) sources. This three-fold pattern is a clear image of the ridge/subduction/plume system that dominates modern tectonics. In contrast, Archaean mafic and ultramafic rocks are clustered in an intermediate position, between the three main modern types. This suggests that the Archaean mantle had lesser amounts of clearly depleted or enriched portions; that true subductions were rare; and that the distinction between oceanic plateaus and ridges may have been less significant. Modern granitic rocks dominantly belong to two groups: arc-related granitoids, petrologically connected to arc basalts; and collision granitoids, related to felsic sources. In contrast, the Archaean record is dominated by the TTG suite that derives from an alkali-rich mafic source (i.e. altered basalt). The geochemical diversity of the TTG suite points to a great range of melting depths, from ca. 5 to > 20 kbar. This reveals the absence of large sedimentary accumulations, again the paucity of modern-like arc situations, and the importance played by reworking of an earlier basaltic shell, in a range of settings (including some proto-subduction mechanisms). Nonetheless, granitoids in each individual region show a progressive transition towards more modern-looking associations of arc-like and peraluminous granites. Collectively, the geochemical evidence suggests an Archaean Earth

Platinum, palladium, and rhodium analyses of ultramafic and mafic rocks from the Stillwater Complex, Montana

USGS Publications Warehouse

Page, Norman J; Riley, Leonard Benjamin; Haffty, Joseph

1969-01-01

Analyses by a combination fire- assay-solution-optical-emission spectrographic method of 137 rocks from the Stillwater Complex, Mont., indicate that platinum, palladium, and rhodium are preferentially concentrated in chromitite zones. The A chromitite zone (21 samples) has an average of 988.9 ppb (pans per billion, 10-9) Pt, 2290.2 ppb Pd, and 245.9 ppb Rh and reaches a maximum (to date) of 8,000 ppb Pt, 11,000 ppb Pd, and 1,700 ppb Rh.

Disequilibrium growth of olivine in mafic magmas revealed by phosphorus zoning patterns of olivine from mafic-ultramafic intrusions

NASA Astrophysics Data System (ADS)

Xing, Chang-Ming; Wang, Christina Yan; Tan, Wei

2017-12-01

Olivine from mafic-ultramafic intrusions rarely displays growth zoning in major and some minor elements, such as Fe, Mg and Ni, due to fast diffusion of these elements at high temperatures. These elements in olivine are thus not useful in deciphering magma chamber processes, such as magma convection, multiple injection and mixing. High-resolution X-ray elemental intensity mapping reveals distinct P zoning patterns of olivine from two mafic-ultramafic intrusions in SW China. Polyhedral olivine grains from lherzolite and dunite of the Abulangdang intrusion show P-rich dendrites similar to those observed in volcanic rocks. Rounded olivine grains from net-textured Fe-Ti oxide ores of the Baima layered intrusion have irregular P-rich patches/bands crosscut and interlocked by P-poor olivine domains. P-rich patches/bands contain 250 to 612 ppm P, much higher than P-poor olivine domains with 123 to 230 ppm P. In electron backscattered diffraction (EBSD) maps, P-rich patches/bands within a single olivine grain have the same crystallographic orientation, indicating that they were remnants of the same crystal. Thus, both P-rich patches/bands and P-poor olivine domains in the same grain show a disequilibrium texture and clearly record two-stage growth. The P-rich patches/bands are likely the remnants of a polyhedral olivine crystal that formed in the first stage, whereas the P-poor olivine domains containing rounded Ti-rich magnetite and Fe-rich melt inclusions may have formed from an Fe-rich ambient melt in the second stage. The complex P zoning of olivine can be attributed to the dissolution of early polyhedral olivine and re-precipitation from the Fe-rich ambient melt. The early polyhedral olivine was in chemical disequilibrium with the ambient melt that may have been developed by silicate liquid immiscibility in a crystal mush. Our study implies that olivine crystals in igneous cumulates with an equilibrium appearance may have experienced disequilibrium growth processes

Geochemistry of reduced gas related to serpentinization of the Zambales ophiolite, Philippines

USGS Publications Warehouse

Abrajano, T.A.; Sturchio, N.C.; Kennedy, B.M.; Lyon, G.L.; Muehlenbachs, K.; Böhlke, J.K.

1990-01-01

Methane-hydrogen gas seeps with mantle-like C and noble gas isotopic characteristics issue from partially serpentinized ultramafic rocks in the Zambales ophiolite, Philippines. New measurements of noble gas and 14C isotope abundances, rock/mixed-volatile equilibrium calculations, and previous chemical and isotopic data suggest that these reduced gases are products of periodotite hydration. The gas seeps are produced in rock-dominated zones of serpentinization, and similar gases may be ubiquitous in ultramafic terranes undergoing serpentinization.

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

Shock metamorphism of planetary silicate rocks and sediments: Proposal for an updated classification system

NASA Astrophysics Data System (ADS)

Stöffler, Dieter; Hamann, Christopher; Metzler, Knut

2018-01-01

We reevaluate the systematics and geologic setting of terrestrial, lunar, Martian, and asteroidal "impactites" resulting from single or multiple impacts. For impactites derived from silicate rocks and sediments, we propose a unified and updated system of progressive shock metamorphism. "Shock-metamorphosed rocks" occur as lithic clasts or melt particles in proximal impactites at impact craters, and rarely in distal impactites. They represent a wide range of metamorphism, typically ranging from unshocked to shock melted. As the degree of shock metamorphism, at a given shock pressure, depends primarily on the mineralogical composition and the porosity of a rock or sediment sample, different shock classification systems are required for different types of planetary rocks and sediments. We define shock classification systems for eight rock and sediment classes which are assigned to three major groups of rocks and sediments (1) crystalline rocks with classes F, M, A, and U; (2) chondritic rocks (class C); and (3) sedimentary rocks and sediments with classes SR, SE, and RE. The abbreviations stand for felsic (F), mafic (M), anorthositic (A), ultramafic (U), sedimentary rocks (SR), unconsolidated sediments (SE), and regoliths (RE). In each class, the progressive stages of shock metamorphism are denominated S1 to Sx. These progressive shock stages are introduced as: S1-S7 for F, S1-S7 for M, S1-S6 for A, S1-S7 for U, S1-S7 for C, S1-S7 for SR, S1-S5 for SE, and S1-S6 for RE. S1 stands for "unshocked" and Sx (variable between S5 and S7) stands for "whole rock melting." We propose a sequence of symbols characterizing the degree of shock metamorphism of a sample, i.e., F-S1 to F-S7 with the option to add the tabulated pressure ranges (in GPa) in parentheses.

Mineralogical, chemical, and physical properties of the regolith overlying crystalline rocks, Fairfax County, Virginia: a preliminary report

USGS Publications Warehouse

Leo, Gerhard W.; Pavich, M.J.; Obermeier, Stephen F.

1977-01-01

Undisturbed cores of saprolite developed on crystalline rocks of the Piedmont Province in Fairfax County, Virginia have been obtained using a combination of Shelby tubes, Denison sampler, and modified diamond core-drilling. The principal purpose of the core study is to correlate variations in chemistry, mineralogy and texture with engineering properties throughout the weathering profile. Coring sites were chosen to obtain a maximum depth of weathering on diverse lithologies. The rocks investigated include pelitic schist, metagraywacke, granite, diabase and serpentinite. Four to twelve samples per core were selected, depending on thickness of 1) the weathering profile (from about 1 m in serpentinite to more than 30 m in pelitic schist) and on 2) megascopic changes in saprolite character for analysis of petrography, texture, clay mineralogy andd major element chemistry. Shear strength and compressibility were determined on corresponding segments of core. Standard penetration tests were performed adjacent to coring sites to evaluate engineering properties in situ. Geochemical changes of saprolite developed from each rock type follow predictable trends from fresh rock to soil profile, with relative Increases in Si, Ti, Al, Fe3+ and H20; variable K; and relative loss of Fe 2+, Mg, Ca, and Na. These variations are more pronounced in the weathering profiles over mafic and ultramafic rocks than metagraywacke. Clay minerals in granite, schist and metagraywacke saprolite are kaolinite, dioctahedral vermiculite, interlayered micavermiculite, and minor illite. Gibbsite is locally developed in near-surface samples of schist. Standard penetration test data for the upper 7 m of saprolite over schist and metagraywacke suggest alternations between stronger and weaker horizons than probably reflect variations in lithology including the presence of quartz lenses. Results for granite saprolite are most consistent but indicate lower strength. Shear strength increases fairly regularly

Geological setting, emplacement mechanism and igneous evolution of the Atchiza mafic-ultramafic layered suite in north-west Mozambique

NASA Astrophysics Data System (ADS)

Ibraimo, Daniel Luis; Larsen, Rune B.

2015-11-01

The Atchiza mafic and ultramafic-layered suite (hereafter, "Atchiza Suite) crops out in an area 330 km2 west of the Mozambican Tete province. In an early account of the geology of this intrusion, it was considered the continuation of the Great Dyke of Zimbabwe, an idea that was aborted after detailed studies. Nevertheless, the Ni concentrations in the Atchiza outcrop rocks are considerable. Our investigation used field evidence, hand specimens and petrography descriptions, mineral chemistry studies using electron microprobe analysis and tectonic analysis to arrive at a plausible mineralogical composition and understanding of the tectonic setting for the igneous evolution. The mineral composition from the Atchiza Suite indicates that these are cumulates. The magmatic segregation from the petrographic and mineral composition reasoning indicates that dunite-lherzolitic peridotite-olivine gabbro-gabbronorite-gabbro-pegmatitic gabbro is the rock formation sequence. Olivine and chromite were the first phases formed, followed by pyroxene and plagioclase. In addition, it is shown that these minerals are near-liquidus crystallization products of basaltic magma with olivine Fo: 87.06 in dunite, mean values of clinopyroxene are (Wo: 36.4, En: 48.0, Fs: 15.2), orthopyroxene (Wo: 2.95, En: 73.0, Fs: 24.2) and plagioclase An: 71.3, respectively. Opaque minerals comprise Fe-Ti oxides and (Fe, Cr) spinel up to 4.8 vol.%, but chromitite layers are not present. Most of the opaque minerals are interstitial to pyroxene. Sulphides are common in gabbros, with pyrrhotite, pentlandite, chalcopyrite, pyrite and covellite together comprising 0.4-2.0 vol.%. The whole rock Rare Earth Element (REE) concentrations are mainly a result of differentiation, but slight crustal contamination/assimilation contributed to the REE contents. In addition, they also show Eu enrichment, suggesting that plagioclase fractionation was important in the rock. The Atchiza Suite preserves a deep-seated plumbing

The Ni-Cu-PGE mineralized Brejo Seco mafic-ultramafic layered intrusion, Riacho do Pontal Orogen: Onset of Tonian (ca. 900 Ma) continental rifting in Northeast Brazil

NASA Astrophysics Data System (ADS)

Salgado, Silas Santos; Ferreira Filho, Cesar Fonseca; Caxito, Fabrício de Andrade; Uhlein, Alexandre; Dantas, Elton Luiz; Stevenson, Ross

2016-10-01

The Brejo Seco mafic-ultramafic Complex (BSC) occurs at the extreme northwest of the Riacho do Pontal Orogen Internal Zone, in the northern margin of the São Francisco Craton in Northeast Brazil. The stratigraphy of this medium size (3.5 km wide and 9 km long) layered intrusion consists of four main zones, from bottom to top: Lower Mafic Zone (LMZ; mainly troctolite), Ultramafic Zone (UZ; mainly dunite and minor troctolite); Transitional Mafic Zone (TMZ; mainly troctolite) and an Upper Mafic Zone (UMZ; gabbro and minor anorthosite, troctolite, and ilmenite magnetitite). Ni-Cu-PGE mineralization occurs at the contact of the UZ with the TMZ, consisting of an up to 50 m thick stratabound zone of disseminated magmatic sulfides. An Mg-tholeiitic affinity to the parental magma is indicated by the geochemical fractionation pattern, by the magmatic crystallization sequence and by the elevated Fo content in olivine. A Smsbnd Nd isochron yielded an age of 903 ± 20 Ma, interpreted as the age of crystallization, with initial εNd = 0.8. Evidence of interaction of the BSC parental magma with sialic crust is given by the Rare Earth and trace element patterns, and by slightly negative and overall low values of εNd(900 Ma) in between -0.2 and +3.3. Contrary to early interpretations that it might constitute an ophiolite complex, based mainly on the geochemistry of the host rocks (Morro Branco metavolcanosedimentary complex), here we interpret the BSC as a typical layered mafic-ultramafic intrusion in continental crust, related to an extensional regime. The BSC is chrono-correlated to mafic dyke swarms, anorogenic granites and thick bimodal volcanics of similar age and tectonic setting in the São Francisco Craton and surrounding areas. Intrusion of the BSC was followed by continued lithospheric thinning, which led to the development of the Paulistana Complex continental rift volcanics around 888 Ma and ultimately to plate separation and the generation of new oceanic crust (Monte

Polyphase serpentinization history of Mariana forearc mantle: observations on the microfabric of ultramafic clasts from ODP Leg 195, Site 1200

NASA Astrophysics Data System (ADS)

Kahl, Wolf-Achim; Jöns, Niels; Bach, Wolfgang; Klein, Frieder

2013-04-01

In the forearc of the Mariana subduction zone system, a number of seamounts form from extrusion of blueschist and serpentine mud. Ocean Drilling Program Leg 195 drilled the South Chamorro seamount, where ultramafic clasts occur within the mud matrix. These clasts show a complex serpentinization history, which bears the potential for tracking the alteration history during uplift and cooling of mantle wedge rocks to the seafloor. Moreover, the microfabrics of the highly serpentinized harzburgite and dunite clasts exhibit evidence for multiple fracturing events in the forearc mantle. These, in turn, lead to fluid influx and varied styles of serpentinization of harzburgite and dunite. The serpentinized ultramafic clasts exhibit a variety of microfabrics that range from virtually undeformed to strongly deformed samples. Pervasively serpentinized harzburgites feature either an equigranular fabric of serpentinized olivine and orthopyroxene crystals, or different vein generations related to multiple stages of serpentinization. Several types of fluid pathways in harzburgites are present: (i) veins containing brucite and iron oxides, developed linearly without marked conformance with the rock fabric. In places, these veins developed mm-cm wide halos with finger-shaped serpentinization fronts. Veins of type (i) are either developed as syntaxial veins from a single crack-seal event with large magnetite crystals growing from one wall to the other (as confirmed with high-resolution X-ray microtomography), or formed by multiple fluid events. (ii) serpentine veins that encompass regions of marginally serpentinized, microgranular olivine and large orthopyroxene crystals. (iii) extensional serpentine veins (known as "Frankenstein" type). In the clasts studied, their occurrence is restricted to the halo region of type (i) veins. (iv) as a late-stage feature, extensional veins documenting multiple crack-seal events can be present in the serpentinites (either in undeformed regions with

Prospecting for Diverse Igneous Rock Types on Mars: Pixl on "black Beauty" Nwa 7533

NASA Astrophysics Data System (ADS)

Liu, Y.; Flannery, D.; Allwood, A.; Thompson, D. R.; Hodyss, R. P.; Clark, B. C.; Elam, W. T.; Hurowitz, J.

2015-12-01

In order to understand the evolution of the Martian crust and mantle, we need to acquire and analyze samples of igneous rocks other than the basaltic and ultramafic lithologies represented by the majority of Martian meteorites. Recent results from the Curiosity Rover demonstrate that diverse rock types exist in some Martian sedimentary environments in the form of conglomerate components or float, some of which shed light on the nature of early Martian crust (e.g., Sautter et al., 2015). We are developing investigation strategies for the in-situ instruments that will be flown on the Mars 2020 rover. These instruments will be used to inform the sampling campaigns required for future sample return missions. To achieve this, we applied PIXL (Planetary Instrument for X-ray Lithochemistry), an instrument for the Mars 2020 rover mission, to the meteorite NWA 7533. This meteorite is a pairing of NWA 7034, known informally as "Black Beauty", a new type of Martian meteorite that is broadly similar to the average composition of the Martian crust. This type of meteorite is essentially a 'conglomerate', with many diverse rock types, including mafic, feldspathic, and exotic rock fragments such as feldspar-ilmenite-phosphate clasts, as observed using higher-spatial resolution and higher sensitivity laboratory instruments (e.g., Agee et al., 2013; Humayun et al., 2014; Santos et al., 2015). Using PIXL, we analyzed a mm-scale cut and polished surface and applied algorithms developed by the PIXL team to semi-autonomously define and group regions containing similar lithological components (Thompson et al., 2015). PIXL data rapidly reveal distinctive zircon-bearing lithologies and feldspar-ilmenite-phosphate clasts similar to the detailed petrographic and mineralogical observations. Results suggest that PIXL readily identifies lithologies with minerals and elements (e.g., Rb and Sr) that are important for geochronology studies.

Origin of Magnetic High at Basalt-Ultramafic Hosted Hydrothermal Vent Field in the Central Indian Ridge

NASA Astrophysics Data System (ADS)

Fujii, M.; Okino, K.; Sato, T.; Sato, H.; Nakamura, K.

2014-12-01

Hydrothermal alteration processes can change crustal magnetization by destruction and creation of magnetic minerals. In the Yokoniwa hydrothermal vent field (YHVF), located at the NTO-massif in the Central Indian Ridge, a high magnetization zone (with ~12 A/m in ~200 m-scale) was discovered by previous deepsea AUV survey. Basalts and ultramafic rocks were found around the YHVF, however the origin of magnetic high and its relationship with hydrothermal activity are remains to be investigated. Therefore, we conducted additional magnetic field measurement, rock sampling, and geological observation using submersible Shinkai 6500 during the YK09-13 and YK13-03 cruises. Vector geomagnetic field were obtained along the dive tracks at an altitude of ~ 10 m. The crustal absolute magnetization is estimated using the 2D and 3D forward modeling technique. The values of magnetization show ~10 A/m just around the YHVF. This value is consistent with that of equivalent magnetization deduced from AUV data. Rock magnetic characters were measured for 8 basalts, 4 dolerites, 5 sulfides, and 30 serpentinized peridotites (SPs). The measurements of NRM, magnetic susceptibility, magnetic hysteresis, low (6-300K) and high (50-700°C) temperature magnetization curves were performed. The estimated magnetization values are 0.1-6 A/m in basalts, 0.2-0.6 A/m in dolerites, and <0.1 A/m in sulfides. The SPs show strong magnetization of 0.4-11 A/m. The magnetic grain sizes ranges over single domain to pseudo-single domain. The temperature-magnetization curves clearly show the Verway transition and Currie temperature of 580 °C, therefore magnetic carrier of SPs is supposed as pure magnetite, which is created during serpentinization process. Serpentinization degree (Sd) was also estimated by grain density measurement based on empirical formula from Oufi et al., 2002. Amount of magnetite was also estimated from saturation magnetization. The results show that the values of Sd vary in a range from 17

Cobalt and scandium partitioning versus iron content for crystalline phases in ultramafic nodules

USGS Publications Warehouse

Glassley, W.E.; Piper, D.Z.

1978-01-01

Fractionation of Co and Sc between garnets, olivines, and clino- and orthopyroxenes, separated from a suite of Salt Lake Crater ultramafic nodules that equilibrated at the same T and P, is strongly dependent on Fe contents. This observation suggests that petrogenetic equilibrium models of partial melting and crystal fractionation must take into account effects of magma composition, if they are to describe quantitatively geochemical evolutionary trends. ?? 1978.

Mid Ocean Ridge Processes at Very Low Melt Supply : Submersible Exploration of Smooth Ultramafic Seafloor at the Southwest Indian Ridge, 64 degree E

NASA Astrophysics Data System (ADS)

Cannat, M.; Agrinier, P.; Bickert, M.; Brunelli, D.; Hamelin, C.; Lecoeuvre, A.; Lie Onstad, S.; Maia, M.; Prampolini, M.; Rouméjon, S.; Vitale Brovarone, A.; Besançon, S.; Assaoui, E. M.

2017-12-01

Mid-ocean ridges are the Earth's most extensive and active volcanic chains. They are also, particularly at slow spreading rates, rift zones, where plate divergence is in part accommodated by faults. Large offset normal faults, also called detachments, are characteristic of slow-spreading ridges, where they account for the widespread emplacement of mantle-derived rocks at the seafloor. In most cases, these detachments occur together with ridge magmatism, with melt injection and faulting interacting to shape the newly formed oceanic lithosphere. Here, we seek to better understand these interactions and their effects on oceanic accretion by studying the end-member case of a ridge where magmatism is locally almost absent. The portion of the Southwest Indian ridge we are studying has an overal low melt supply, focused to discrete axial volcanoes, leaving almost zero melt to intervening sections of the axial valley. One of these nearly amagmatic section of the ridge, located at 64°E, has been the focus of several past cruises (sampling, mapping and seismic experiments). Here we report on the most recent cruise to the area (RV Pourquoi Pas? with ROV Victor; dec-jan 2017), during which we performed high resolution mapping, submersible exploration and sampling of the ultramafic seafloor and of sparse volcanic formations. Our findings are consistent with the flip-flop detachment hypothesis proposed for this area by Sauter et al. (Nature Geosciences, 2013; ultramafic seafloor forming in the footwall of successive detachment faults, each cutting into the footwall of the previous fault, with an opposite polarity). Our observations also document the extent and geometry of deformation in the footwall of a young axial detachment, the role of mass-wasting for the evolution of this detachment, and provide spectacular evidence for serpentinization-related hydrothermal circulation and for spatial links between faults and volcanic eruptions.

Using MicroFTIR to Map Mineral Distributions in Serpentinizing Systems

NASA Astrophysics Data System (ADS)

Johnson, A.; Kubo, M. D.; Cardace, D.

2016-12-01

Serpentinization, the water-rock reaction forming serpentine mineral assemblages from ultramafic precursors, can co-occur with the production of hydrogen, methane, and diverse organic compounds (McCollom and Seewald, 2013), evolving water appropriate for carbonate precipitation, including in ophiolite groundwater flow systems and travertine-producing seeps/springs. Serpentinization is regarded as a geologic process important to the sustainability of the deep biosphere (Schrenk et al., 2013) and the origin of life (Schulte et al., 2006). In this study, we manually polished wafers of ultramafic rocks/associated minerals (serpentinite, peridotite, pyroxenite, dunite; olivine, diopside, serpentine, magnetite), and travertine/constituent minerals (carbonate crusts; calcite, dolomite), and observed mineral boundaries and interfaces using µFTIR analysis in reflection mode. We used a Thermo Nicolet iS50 FTIR spectrometer coupled with a Continuum IR microscope to map minerals/boundaries. We identify, confirm, and document FTIR wavenumber regions linked to serpentinite- and travertine-associated minerals by referencing IR spectra (RRUFF) and aligning with x-ray diffraction. The ultramafic and carbonate samples are from the following field localities: McLaughlin Natural Reserve - a UC research reserve, Lower Lake, CA; Zambales, PH; Ontario, CA; Yellow Dog, MI; Taskesti, TK; Twin Sisters Range, WA; Sharon, MA; Klamath Mountains, CA; Dun Mountain, NZ; and Sussex County, NJ. Our goals are to provide comprehensive µFTIR characterization of mineral profiles important in serpentinites and related rocks, and evaluate the resolving power of µFTIR for the detection of mineral-encapsulated, residual organic compounds from biological activity. We report on µFTIR data for naturally occurring ultramafics and travertines and also estimate the limit of detection for cell membrane components in mineral matrices, impregnating increasing mass proportions of xanthan gum in a peridotite sand

Ages, geochemistry and tectonic implications of the Cambrian igneous rocks in the northern Great Xing'an Range, NE China

NASA Astrophysics Data System (ADS)

Feng, Zhiqiang; Liu, Yongjiang; Li, Yanrong; Li, Weimin; Wen, Quanbo; Liu, Binqiang; Zhou, Jianping; Zhao, Yingli

2017-08-01

The Xinlin-Xiguitu suture zone, located in the Great Xing'an Range, NE China, in the eastern segment of the Central Asian Orogenic Belt (CAOB), represents the boundary between the Erguna and Xing'an micro-continental blocks. The exact location of the Xinlin-Xiguitu suture zone has been debated, especially, the location of the northern extension of the suture zone. In this study, based on a detailed field, geochemical, geochronological and Sr-Nd-Hf isotope study, we focus our work on the Cambrian igneous rocks in the Erguna-Xing'an block. The Xinglong granitoids, mainly include ∼520 Ma diorite, ∼470 Ma monzogranite and ∼480 Ma pyroxene diorite. The granitoids show medium to high-K calc-alkaline series characteristics with post-collision granite affinity. The circa 500 Ma granitoids have low εHf (t) values (-16.6 to +2.2) and ancient two-stage model (TDM2) ages between 1317 Ma and 2528 Ma. These results indicate the primary magmas of the Xinglong granitoids were probably derived from the partial melting of a dominantly Paleo-Mesoproterozoic ;old; crustal source with possible different degrees of addition of juvenile materials, and formed in a post-collision tectonic setting after the amalgamation of the Erguna and Xing'an blocks. Compared with the Xinglong granitoids, the Duobaoshan igneous rocks are consisted of the approximately coeval rhyolitic tuffs (491 ± 5 Ma) and ultramafic intrusions (497 ± 5 Ma) within the Duobaoshan Formation. They are generally enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti), consistent with the geochemistry of igneous rocks from island arcs or active continental margins. The ultramafic rocks have high positive εHf (t) values (+1.3 to +15) and εNd (t) (+1.86 to +2.28), and relatively young two-stage model (TDM2) ages and low initial 87Sr/86Sr ratios (0.70628-0.70853), indicating the partial melting of a depleted mantle source from a subducted slab in

Palladium, platinum, rhodium, iridium and ruthenium in chromite- rich rocks from the Samail ophiolite, Oman.

USGS Publications Warehouse

Page, N.J.; Pallister, J.S.; Brown, M.A.; Smewing, J.D.; Haffty, J.

1982-01-01

30 samples of chromitite and chromite-rich rocks from two stratigraphic sections, 250 km apart, through the basal ultramafic member of the Samail ophiolite were spectrographically analysed for platinum-group elements (PGE) and for Co, Cu, Ni and V. These data are reported as are Cr/(Cr + Al), Mg/(Mg + Fe) and wt.% TiO2 for most samples. The chromitite occurs as pods or lenses in rocks of mantle origin or as discontinuous layers at the base of the overlying cumulus sequence. PGE abundances in both sections are similar, with average contents in chromite-rich rocks: Pd 8 ppb, Pt 14 ppb, Rh 6 ppb, Ir 48 ppb and Ru 135 ppb. The PGE data, combined with major-element and petrographic data on the chromitite, suggest: 1) relatively larger Ir and Ru contents and highest total PGE in the middle part of each section; 2) PGE concentrations and ratios do not correlate with coexisting silicate and chromite abundances or chromite compositions; 3) Pd/PGE, on average, increases upward in each section; 4) Samail PGE concentrations, particularly Rh, Pt and Pd, are lower than the average values for chromite-rich rocks in stratiform intrusions. 2) suggests that PGEs occur in discrete alloy or sulphide phases rather than in the major oxides or silicates, and 4) suggests that chromite-rich rocks from the oceanic upper mantle are depleted in PGE with respect to chondrites. L.C.C.

Geologic Map of the Upper Wolf Island Creek Watershed, Reidsville Area, Rockingham County, North Carolina

USGS Publications Warehouse

Horton, J. Wright; Geddes, Donald J.

2006-01-01

This geologic map provides a foundation for hydrogeologic investigations in the Reidsville area of Rockingham County, north-central North Carolina. The 16-mi2 area within the Southeast Eden and Reidsville 7.5-min quadrangles includes the watershed of Wolf Island Creek and its tributary, Carroll Creek, upstream of their confluence. Layered metamorphic rocks in this area of the Milton terrane, here informally named the Chinqua-Penn metamorphic suite, include a heterogeneous mica gneiss and schist unit that contains interlayers and lenses of white-mica schist, felsic gneiss, amphibolite, and ultramafic rock; a felsic gneiss that contains interlayers of amphibolite, white-mica schist, and minor ultramafic lenses; and a migmatitic biotite gneiss. Crushed stone is produced from an active quarry in the felsic gneiss. Igneous intrusive rocks include a mafic-ultramafic assemblage that may have originated as mafic intrusive bodies containing ultramafic cumulates, a foliated two-mica granite informally named the granite of Reidsville, and unmetamorphosed Jurassic diabase dikes. The newly recognized Carroll Creek shear zone strikes roughly east-west and separates heterogeneous mica gneiss and schist to the north from structurally overlying felsic gneiss to the south. Regional amphibolite-facies metamorphism accompanied polyphase ductile deformation in the metamorphic rocks. Two phases of isoclinal to tight folding and related penetrative deformation, described as D1 and D2, were followed by phases of high-strain mylonitic deformation in shear zones and late gentle to open folding. Later brittle deformation produced minor faults, steep joints, foliation-parallel parting, and sheeting joints. The metamorphic and igneous rocks are mantled by saprolite and residual soil derived from weathering of the underlying bedrock, and unconsolidated Quaternary alluvium occupies the flood plains of Wolf Island Creek and its tributaries. The geologic map delineates lithologic and structural

Cortlandtitic enclaves associated with calc-alkaline granites from Tapia-Asturias (Hercynian Belt, northwestern Spain)

NASA Astrophysics Data System (ADS)

Galán, G.; Suárez, O.

1989-10-01

Petrographic and mineralogical characteristics of amphibole-olivine- and pyroxene-bearing ultramafic rocks from Asturias (NW Spain) are dealt with in this paper. These rocks are of cortlandtitic type and occur as small rare enclaves in basic rocks related to Hercynian calc-alkaline, post-tectonic epizonal granites, in the northwest of the Iberian Peninsula. These particular ultramafic enclaves are characterized by poikilitic cumulate microtexture. Olivine (Fo 77-81), spinel, from chromite to pleonaste composition, enstatite, subordinated diopside and sulphides are included in large brown calcic amphibole crystals displaying an irregular zonation. Phlogopite and plagioclase are also found, in a much lower proportion, between the large amphibole crystals. Mineral assemblage and chemical composition of minerals indicate formation conditions of 1150°C, 7-8 kbar of Ptotal and PH 2O < Ptotal. These rocks could represent the earlier products of fractional crystallization from a hydrated high-alumina basalt involved in the genesis of the calc-alkaline granites. This basic magma would start crystallizing at a relatively deep level, carrying up the first products of its crystallization during its ascent.

Iron transformations during low temperature alteration of variably serpentinized rocks from the Samail ophiolite, Oman

NASA Astrophysics Data System (ADS)

Mayhew, Lisa E.; Ellison, Eric T.; Miller, Hannah M.; Kelemen, Peter B.; Templeton, Alexis S.

2018-02-01

Partially serpentinized peridotites in the Samail ophiolite in the Sultanate of Oman currently undergo low temperature alteration and hydration both at shallow levels, with water recently in contact with the atmosphere, and at depth, with anoxic, reducing fluids. However, it is unclear how changes in the distribution and oxidation state of Fe are driving the production of energy-rich gases such as hydrogen and methane detected in peridotite catchments. We track the Fe transformations in a suite of outcrop samples representing a subset of the spectrum of least to most altered end-members of the Oman peridotites. We use microscale mineralogical and geochemical analyses including QEMSCAN, Raman spectroscopy, synchrotron radiation X-ray fluorescence (XRF) mapping, and electron microprobe wavelength dispersive spectroscopy. The less-altered peridotites possess a diversity of Fe-bearing phases including relict primary minerals (e.g. olivine, pyroxene, chromite) and secondary phases (e.g. serpentine and brucite). Raman spectroscopy and electron microprobe data (Si/(Mg + Fe)) indicate that much of the serpentine is significantly intergrown with brucite on the sub-micron scale. These data also indicate that the Fe content of the brucite ranges from 10 to 20 wt% FeO. The mineral assemblage of the highly reacted rocks is less diverse, dominated by serpentine and carbonate while olivine and brucite are absent. Magnetite is relatively rare and mainly associated with chromite. Goethite and hematite, both Fe(III)-hydroxides, were also identified in the highly altered rocks. Whole rock chemical analyses reflect these mineralogical differences and show that Fe in the partially serpentinized samples is on average more reduced (∼0.40-0.55 Fe3+/FeTotal) than Fe in the highly reacted rocks (∼0.85-0.90 Fe3+/FeTotal). We propose that olivine, brucite, chromite and, perhaps, serpentine in the less-altered peridotites act as reactive phases during low temperature alteration of the Oman

Mineralogy of Surface Serpentinite Outcrops in the Coast Range Ophiolite: Implications for the Deep Biosphere and Astrobiology

NASA Astrophysics Data System (ADS)

Mccann, A. R.; Cardace, D.; Carnevale, D.; Ehlmann, B. L.

2011-12-01

California contains a number of ultramafic (Fe- and Mg rich) rock bodies, including the Coast Range Ophiolite, a block of oceanic crust and upper mantle tectonically emplaced onto land. These ultramafic rocks are primarily composed of olivine and pyroxene, both of which are stable at the high temperatures and pressures in the deep subsurface where they crystallize but become unstable at low temperature and low pressure conditions near the surface. They are highly reduced rocks, creating chemical disequilibria, which can theoretically provide energy to chemoautotrophic organisms. Serpentinization (serpentine-forming) reactions between the rocks and water produce hydrogen molecules, which can be metabolized by diverse organisms. Earth and Mars have shown evidence of similar early geologic histories, possibly with widespread reducing habitable environments (Schulte et al., 2006). Recent data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) have shown serpentine-bearing outcrops near Nili Fossae (21 N, 282 W) and elsewhere in Mars' cratered highlands. Serpentine-bearing outcrops are rare, but their presence confirms that such systems involving the aqueous alteration of ultramafic rocks were active in the past (specifically during the Noachian epoch (older than ~3.7 billion years), possibly producing aqueous habitats suitable for chemoautotrophic life (Ehlmann et al., 2010). Remotely sensed data cannot confirm whether there is active serpentinization on Mars, however exposed, presently serpentinizing ultramafics in terrestrial ophiolites such as those of the California Coast Range provide points of comparison for similar Martian rocks. Volume expansion during serpentinization fractures the host rock, exposing new reaction surfaces, allowing further serpentinization. If subsurface liquid water is present on Mars, serpentinization may still be occurring. We will provide x-ray diffraction and petrographic data for surface serpentinites from the Coast

Some Speculations Concerning The Abitibi Greenstone Belt As A Possible Analog To The Early Martian Crust

NASA Astrophysics Data System (ADS)

Russell, M.; Allwood, A.; Anderson, R. B.; Atkinson, B.; Beaty, D.; Bristow, T. F.; Ehlmann, B. L.; Grotzinger, J. P.; Hand, K. P.; Halevy, I.; Hurowitz, J. A.; Knoll, A.; McCleese, D. J.; Milliken, R.; Stolper, D. A.; Stolper, E. M.; Tosca, N. J.; Agouron Mars Simulation Field Team

2011-12-01

The Noachian crust of Mars comprises basaltic and, potentially, komatiitic lavas derived from a hot mantle slightly more reducing and sulfur-rich than that of the Earth. Ultramafic volcanic sequences of the ~2.7Ga Tisdale Group of the Abitibi Greenstone Belt, Ontario, provide a potential analog to these early martian lavas. The Abitibi rocks are a possible source of quartz veins carrying, in places, pyrite, carbonate and gold. These were hydrothermally introduced into volcanic and sedimentary rocks during greenschist metamorphism. Kilometer-scale talc-magnesite zones, resulting from the carbonation of serpentinized ultramafics, may have been the source and seawater, with some magmatic addition, was probably responsible for the pervasive alteration, although the chemical nature of hydrothermal fluids circulating in such piles depends upon the temperature of wall-rock interactions and is largely independent of fluid origin. Any sulfides and gold in unaltered ultramafic putative source rocks may have been lost to the invasive convective fluids. Given high heat flow and the presence of a hydrosphere, hydrothermal convection cells were probably the main mechanism of heat transfer through the crust on both planets. Exploration of the Abitibi belt provides a template for possible martian exploration strategies. Orbital remote sensing indicates that some ultramafic rocks on Mars have also been serpentinized and isolated areas of magnesite have been recently discovered, overlying altered mafic crust, with characteristic ridges at scales of a few hundred meters. While cogent arguments have been made favoring sedimentary exhalative accumulations of hydrothermal silica of the kind that are known to harbor bacteria on our own planet, no in situ siliceous sinters or even quartz veins have been identified with certainty on Mars. Here, we report on the mineralogic and visible to infrared spectral characteristics of mafic and ultramafic lithologies at Abitibi for comparison to

Integration of 3 Consecutive Years of Aqueous Geochemistry Monitoring Serpentinization at the Coast Range Ophiolite Microbial Observatory (CROMO), Northern California, USA

NASA Astrophysics Data System (ADS)

Cardace, D.; Hoehler, T. M.; McCollom, T. M.; Schrenk, M. O.; Kubo, M. D.

2014-12-01

In August 2011, a set of 8 groundwater monitoring wells were established in actively serpentinizing ultramafic rocks of the Coast Range Ophiolite near Lower Lake, CA, as a NASA Astrobiology Institute project (Cardace et al., 2013). These wells have enabled repeated sampling and analysis of aqueous geochemistry, which we now present in an integrated model of the progress of serpentinization at this locality. The Coast Range Ophiolite Microbial Observatory (CROMO) plumbs groundwaters percolating through a tectonic mélange of Jurassic-aged oceanic crust, with blocks of metabasalt and metagabbro, variably serpentinized ultramafics, Great Valley Sequence sedimentary rocks including the Jurassic Knoxville formation and the Cretaceous Crack Canyon formation, as well as rocks resulting from silica-carbonate alteration of serpentinites (marginal listvenites). All of these rock units are accessible in the McLaughlin Natural Reserve (administered by the University of California-Davis). In this work, we report on persistent geochemical trends in CROMO waters, which are gas-rich, high pH (11+), Ca2+-OH- type waters, contrast their characteristics with other continental sites of serpentinization and deep sea serpentinizing vent systems, and place the evolution of these waters in a water-rock reaction context based on geochemical modeling.

Sulfur and carbon geochemistry of the Santa Elena peridotites: Comparing oceanic and continental processes during peridotite alteration

NASA Astrophysics Data System (ADS)

Schwarzenbach, Esther M.; Gill, Benjamin C.; Gazel, Esteban; Madrigal, Pilar

2016-05-01

Ultramafic rocks exposed on the continent serve as a window into oceanic and continental processes of water-peridotite interaction, so called serpentinization. In both environments there are active carbon and sulfur cycles that contain abiogenic and biogenic processes, which are eventually imprinted in the geochemical signatures of the basement rocks and the calcite and magnesite deposits associated with fluids that issue from these systems. Here, we present the carbon and sulfur geochemistry of ultramafic rocks and carbonate deposits from the Santa Elena ophiolite in Costa Rica. The aim of this study is to leverage the geochemistry of the ultramafic sequence and associated deposits to distinguish between processes that were dominant during ocean floor alteration and those dominant during low-temperature, continental water-peridotite interaction. The peridotites are variably serpentinized with total sulfur concentrations up to 877 ppm that is typically dominated by sulfide over sulfate. With the exception of one sample the ultramafic rocks are characterized by positive δ34Ssulfide (up to + 23.1‰) and δ34Ssulfate values (up to + 35.0‰). Carbon contents in the peridotites are low and are isotopically distinct from typical oceanic serpentinites. In particular, δ13C of the inorganic carbon suggests that the carbon is not derived from seawater, but rather the product of the interaction of meteoric water with the ultramafic rocks. In contrast, the sulfur isotope data from sulfide minerals in the peridotites preserve evidence for interaction with a hydrothermal fluid. Specifically, they indicate closed system abiogenic sulfate reduction suggesting that oceanic serpentinization occurred with limited input of seawater. Overall, the geochemical signatures preserve evidence for both oceanic and continental water-rock interaction with the majority of carbon (and possibly sulfate) being incorporated during continental water-rock interaction. Furthermore, there is

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

Talking Rocks.

ERIC Educational Resources Information Center

Rice, Dale; Corley, Brenda

1987-01-01

Discusses some of the ways that rocks can be used to enhance children's creativity and their interest in science. Suggests the creation of a dramatic production involving rocks. Includes basic information on sedimentary, igneous, and metamorphic rocks. (TW)

Mapping the Mineral Resource Base for Mineral Carbon-Dioxide Sequestration in the Conterminous United States

USGS Publications Warehouse

Krevor, S.C.; Graves, C.R.; Van Gosen, B. S.; McCafferty, A.E.

2009-01-01

This database provides information on the occurrence of ultramafic rocks in the conterminous United States that are suitable for sequestering captured carbon dioxide in mineral form, also known as mineral carbon-dioxide sequestration. Mineral carbon-dioxide sequestration is a proposed greenhouse gas mitigation technology whereby carbon dioxide (CO2) is disposed of by reacting it with calcium or magnesium silicate minerals to form a solid magnesium or calcium carbonate product. The technology offers a large capacity to permanently store CO2 in an environmentally benign form via a process that takes little effort to verify or monitor after disposal. These characteristics are unique among its peers in greenhouse gas disposal technologies. The 2005 Intergovernmental Panel on Climate Change report on Carbon Dioxide Capture and Storage suggested that a major gap in mineral CO2 sequestration is locating the magnesium-silicate bedrock available to sequester the carbon dioxide. It is generally known that silicate minerals with high concentrations of magnesium are suitable for mineral carbonation. However, no assessment has been made in the United States that details their geographical distribution and extent, nor has anyone evaluated their potential for use in mineral carbonation. Researchers at Columbia University and the U.S. Geological Survey have developed a digital geologic database of ultramafic rocks in the conterminous United States. Data were compiled from varied-scale geologic maps of magnesium-silicate ultramafic rocks. The focus of our national-scale map is entirely on ultramafic rock types, which typically consist primarily of olivine- and serpentine-rich rocks. These rock types are potentially suitable as source material for mineral CO2 sequestration.

New data on carbonatites of the Il'mensky-Vishnevogorsky alkaline complex, the southern Urals, Russia

NASA Astrophysics Data System (ADS)

Nedosekova, I. L.

2007-04-01

Carbonatites that are hosted in metamorphosed ultramafic massifs in the roof of miaskite intrusions of the Il’mensky-Vishnevogorsky alkaline complex are considered. Carbonatites have been revealed in the Buldym, Khaldikha, Spirikha, and Kagan massifs. The geological setting, structure of carbonatite bodies, distribution of accessory rare-metal mineralization, typomorphism of rock-forming minerals, geochemistry, and Sr and Nd isotopic compositions are discussed. Dolomite-calcite carbonatites hosted in ultramafic rocks contain tetraferriphlogopite, richterite, accessory zircon, apatite, magnetite, ilmenite, pyrrhotite, pyrite, and pyrochlore. According to geothermometric data and the composition of rock-forming minerals, the dolomite-calcite carbonatites were formed under K-feldspar-calcite, albite-calcite, and amphibole-dolomite-calcite facies conditions at 575-300°C. The Buldym pyrochlore deposit is related to carbonatites of these facies. In addition, dolomite carbonatites with accessory Nb and REE mineralization (monazite, aeschynite, allanite, REE-pyrochlore, and columbite) are hosted in ultramafic massifs. The dolomite carbonatites were formed under chlorite-sericite-ankerite facies conditions at 300-200°C. The Spirikha REE deposit is related to dolomite carbonatite and alkaline metasomatic rocks. It has been established that carbonatites hosted in ultramafic rocks are characterized by high Sr, Ba, and LREE contents and variable Nb, Zr, Ti, V, and Th contents similar to the geochemical attributes of calcio-and magnesiocarbonatites. The low initial 87Sr/86Sr = 0.7044-0.7045 and ɛNd ranging from 0.65 to -3.3 testify to their derivation from a deep mantle source of EM1 type.

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 ur

Litho- and chemostratigraphy of the Flatreef PGE deposit, northern Bushveld Complex

NASA Astrophysics Data System (ADS)

Grobler, D. F.; Brits, J. A. N.; Maier, W. D.; Crossingham, A.

2018-05-01

The Flatreef is a world-class platinum-group element (PGE) deposit recently discovered down-dip from existing mining and exploration operations on the northern limb of the Bushveld Complex. Current indicated resources stand at 42 Moz PGE (346 Mt with 3.8 g/t Pt+Pd+Rh+Au, 0.32% Ni and 0.16% Cu) which, in the case of Pt, is equivalent to 10 years global annual production, making it one of the largest PGE deposits on earth. The grade and thickness of the Flatreef mineralised interval is highly unusual, with some drill core intersections containing up to 4.5 g/t Pt+Pd+Rh+Au over 90 m in drill core. Here, we document the down-dip and along-strike litho- and chemostratigraphy of the Flatreef and its footwall and hanging wall rocks, based on a diamond drill core database totalling > 720 km. At the base of the sequence intersected in the drill cores are up to 700-m-thick sills of ultramafic rocks (dunite, harzburgite, pyroxenite) emplaced into pelitic, dolomitic, and locally quartzitic and evaporitic rocks belonging to the Duitschland Formation of the Transvaal Supergroup. Next is an approximately 100-200-m sequence of low-grade-sulphide-mineralised, layered mafic-ultramafic rocks containing abundant sedimentary xenoliths and, in places, several chromite seams or stringers. This is overlain by a 100-m-thick sequence of well-mineralised mafic-ultramafic rocks (the Flatreef sensu strictu), overlain by a laterally persistent mottled compositional analogies at the base of > 1 km of homogenous Main Zone gabbronorite. Based on stratigraphic, lithological and compositional alanalogies to the layered rocks in the eastern and western Bushveld Complex, we correlate the Flatreef and its chromite bearing footwall rocks with the Upper Critical Zone, notably the interval between the UG2 chromitite and the Bastard Reef as found elsewhere in the Bushveld Complex. This includes recognition of a Merensky Reef correlative. The ultramafic rocks below the main chromitite seam (UG2 correlative

Oceanic mantle rocks reveal evidence for an ancient, 1.2-1.3 Ga global melting event

NASA Astrophysics Data System (ADS)

Dijkstra, A. H.; Sergeev, D.; McTaminey, L.; Dale, C. W.; Meisel, T. C.

2011-12-01

It is now increasingly being recognized that many oceanic peridotites are refertilized harzburgites, and that the refertilization often masks an extremely refractory character of the original mantle rock 'protolith'. Oceanic peridotites are, when the effects of melt refertilization are undone, often too refractory to be simple mantle melting residues after the extraction of mid-ocean ridge basalts at a spreading center. Rhenium-osmium isotope analysis is a powerful method to look through the effects of refertilization and to obtain constraints on the age of the melting that produced the refractory mantle protolith. Rhenium-depletion model ages of such anomalously refractory oceanic mantle rocks - found as abyssal peridotites or as mantle xenoliths on ocean islands - are typically >1 Ga, i.e., much older than the ridge system at which they were emplaced. In my contribution I will show results from two case studies of refertilized anciently depleted mantle rocks (Macquarie Island 'abyssal' peridotites and Lanzarote mantle xenoliths). Interestingly, very refractory oceanic mantle rocks from sites all around the world show recurring evidence for a Mesoproterozoic (~1.2-1.3 Ga) melting event [1]. Therefore, oceanic mantle rocks seem to preserve evidence for ancient melting events of global significance. Alternatively, such mantle rocks may be samples of rafts of ancient continental lithospheric mantle. Laser-ablation osmium isotope 'dating' of large populations of individual osmium-bearing alloys from mantle rocks is the key to better constrain the nature and significance of these ancient depletion events. Osmium-bearing alloys form when mantle rocks are melted to high-degrees. We have now extracted over >250 detrital osmium alloys from placer gold occurrences in the river Rhine. These alloys are derived from outcrops of ophiolitic mantle rocks in the Alps, which include blocks of mantle rocks emplaced within the Tethys Ocean, and ultramafic lenses of unknown

Lower crustal xenoliths, Chinese Peak lava flow, central Sierra Nevada.

USGS Publications Warehouse

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

1986-01-01

This assemblage of pyroxenite, peridotite and mafic granulite xenoliths in the toe of a 10 m.y. trachybasalt flow remnant overlying late Cretaceous granitic rocks, indicates the presence of a mafic-ultramafic complex beneath this part of central California; orthopyroxenites, websterites and clinopyroxenites are dominant. A few of the xenoliths contain ovoid opaque patches that are apparently pseudomorphs after garnet and have pyralspite garnet compositions; using a garnet-orthopyroxene geobarometer, they indicate a lower crustal depth of approx 40 km. Abundant mafic granulites can be subdivided into those with Al2O3 = or 15% and showing considerable scatter on oxide variation diagrams. The high-alumina granulite xenoliths have relatively low 87Rb/86Sr but high 87Sr/86Sr, whereas the low-alumina and ultramafic xenoliths have a wide range of 87Rb/86Sr, but lower 87Sr/86Sr; the isotopic data indicate roughly the same age as that of overlying granitic plutons (approx 100 m.y.). However, the granitic rocks have initial 87Sr/86Sr ratios intermediate between those of the high-alumina and ultramafic xenoliths, suggesting that they result from the mixing of basaltic magma (represented by the ultramafic rocks) and crustal materials, with subsequent crystal fractionation.-R.A.H.

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.

Effects of geodynamic setting on the redox state of fluids released by subducted mantle lithosphere

NASA Astrophysics Data System (ADS)

Evans, K. A.; Reddy, S. M.; Tomkins, A. G.; Crossley, R. J.; Frost, B. R.

2017-05-01

high hydrogen activity (aH2). Ultramafic rocks are associated with two distinctly different fluid compositions during pre-subduction and subduction serpentinisation. Initially, while olivine is in equilibrium with infiltrating fluid, mineral assemblages that include awaruite in the rocks buffer fluids to H2-bearing, low aO2 compositions. Deserpentinisation of incompletely serpentinised rocks in which awaruite is present also produces H2-bearing fluids. Once awaruite is exhausted, H2-poor, high aO2 fluids co-exist with awaruite-absent assemblages, and deserpentinisation of such rocks would produce H2O-rich fluids. Thus, deserpentinisation of ultramafic rocks could produce either hydrogen-bearing fluids that could infiltrate and reduce the sub-arc mantle, or more oxidised fluids, which could transfer redox budget to other geochemical reservoirs such as the sub-arc mantle. Therefore, the redox contribution of subducted ultramafic rocks to the deep Earth and sub-arc mantle depends on the extent of protolith serpentinisation. Pre-subduction settings that promote extensive serpentinisation by oxidised fluids at high fluid:rock ratios in open systems, such as slow and ultraslow spreading ridges, transform faults, oceanic core complexes, and exhumed mantle at rifted continental margins, may produce more oxidised fluids than those associated with less pervasive serpentinisation and fluids that may be rock-buffered to a reduced state.

Multi-isotope tracing of CO2 leakage and water-rock interaction in a natural CCS analogue.

NASA Astrophysics Data System (ADS)

Kloppmann, Wolfram; Gemeni, Vasiliki; Lions, Julie; Koukouzas, Nikolaos; Humez, Pauline; Vasilatos, Charalampos; Millot, Romain; Pauwels, Hélène

2015-04-01

Natural analogues of CO2 accumulation and, potentially, leakage, provide a highly valuable opportunity to study (1) geochemical processes within a CO2-reservoir and the overlying aquifers or aquicludes, i.e. gas-water-rock interactions, (2) geology and tightness of reservoirs over geological timescales, (3) potential or real leakage pathways, (3) impact of leakage on shallow groundwater resources quality, and (4) direct and indirect geochemical indicators of gas leakage (Lions et al., 2014, Humez et al., 2014). The Florina Basin in NW Macedonia, Greece, contains a deep CO2-rich aquifer within a graben structure. The graben filling consists of highly heterogeneous Neogene clastic sediments constituted by components from the adjacent massifs including carbonates, schists, gneiss as well as some ultramafic volcanic rocks. Clay layers are observed that isolate hydraulically the deep, partly artesian aquifer. Organic matter, in form of lignite accumulations, is abundant in the Neogene series. The underlying bedrocks are metamorphic carbonates and silicate rocks. The origin of the CO2 accumulation is controversial (deep, partially mantle-derived D'Allessandro et al., 2008 or resulting from thermal decomposition of carbonates, Hatziyannis and Arvanitis, 2011). Groundwaters have been sampled from springs and borewells over 3 years at different depths. First results on major, minor and trace elements give evidence of water-rock interaction, mainly with carbonates but also with ultramafic components but do not indicate that CO2-seepage is the principal driver of those processes (Gemeni et al., submitted). Here we present isotope data on a selection of groundwaters (δ2H , δ18O, δ13CTDIC, 87Sr/86Sr, δ11B, δ7Li). Stable isotopes of water indicate paleo-recharge for some of the groundwaters, limited exchange with gaseous CO2 and, in one case, possibly thermal exchange processes with silicates. Sr isotope ratios vary between marine ratios and radiogenic values indicating

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

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.

The magnetic signature of ultramafic-hosted hydrothermal systems (Invited)

NASA Astrophysics Data System (ADS)

Szitkar, F.; Dyment, J.; Honsho, C.; Horen, H.; Fouquet, Y.

2013-12-01

While the magnetic response of basalt-hosted hydrothermal sites is well known, that of ultramafic-hosted hydrothermal sites (UMHS) remains poorly documented. Here we present the magnetic signature of three of the six UMHS investigated to date on the Mid-Atlantic Ridge, i.e. sites Rainbow, Ashadze (1 and 2), and Logachev. Two magnetic signatures are observed. Sites Rainbow and Ashadze 1 are both characterized by a positive reduced-to-the-pole magnetic anomaly, i.e. a positive magnetization contrast. Conversely, sites Ashadze 2 and Logachev do not exhibit any clear magnetic signature. Rock-magnetic measurements on samples from site Rainbow reveal a strong magnetization (~30 A/m adding induced and remanent contributions) borne by sulfide-impregnated serpentinites; the magnetic carrier being magnetite. This observation can be explained by three (non exclusive) processes: (1) higher temperature serpentinization at the site resulting in the formation of more abundant / more strongly magnetized magnetite; (2) the reducing hydrothermal fluid protecting magnetite at the site from the oxidation which otherwise affects magnetite in contact with seawater; and (3) the formation of primary (hydrothermal) magnetite. We apply a new inversion method developed by Honsho et al. (2012) to the high-resolution magnetic anomalies acquired 10 m above seafloor at sites Rainbow and Ashadze 1. This method uses the Akaike Bayesian Information Criterion (ABIC) and takes full advantage of the near-seafloor measurements, avoiding the upward-continuation (i.e. loss of resolution) of other inversion schemes. This inversion reveals a difference in the intensity of equivalent magnetization obtained assuming a 100 m thick magnetic layer, ~30 A/m at site Rainbow and only 8A/m at site Ashadze, suggesting a thinner or less magnetized source for the latter. Hydrothermal sites at Ashadze 2 and Logachev are much smaller (of the order of 10 m) than the previous ones (several 100 m). These sites, known as

Accreted seamounts in North Tianshan, NW China: Implications for the evolution of the Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Yang, Gaoxue; Li, Yongjun; Kerr, Andrew C.; Tong, Lili

2018-03-01

The Carboniferous Bayingou ophiolitic mélange is exposed in the North Tianshan accretionary complex in the southwestern part of the Central Asian Orogenic Belt (CAOB). The mélange is mainly composed of serpentinised ultramafic rocks (including harzburgite, lherzolite, pyroxenite, dunite and peridotite), pillowed and massive basalts, layered gabbros, radiolarian cherts, pelagic limestones, breccias and tuffs, and displays block-in-matrix structures. The blocks of ultramafic rocks, gabbros, basalts, cherts, and limestones are set in a matrix of serpentinised ultramafic rocks, massive basalts and tuffs. The basaltic rocks in the mélange show significant geochemical heterogeneity, and two compositional groups, one ocean island basalt-like, and the other mid-ocean ridge-like, can be distinguished on the basis of their isotopic compositions and immobile trace element contents (such as light rare earth element enrichment in the former, but depletion in the latter). The more-enriched basaltic rocks are interpreted as remnants/fragments of seamounts, derived from a deep mantle reservoir with low degrees (2-3%) of garnet lherzolite mantle melting. The depleted basalts most likely formed by melting of a shallower spinel lherzolite mantle source with ∼15% partial melting. It is probable that both groups owe their origin to melting of a mixture between plume and depleted MORB mantle. The results from this study, when integrated with previous work, indicate that the Junggar Ocean crust (comprising a significant number of seamounts) was likely to have been subducted southward beneath the Yili-Central Tianshan block in the Late Devonian-Early Carboniferous. The seamounts were scraped-off and accreted along with the oceanic crust in an accretionary wedge to form the Bayingou ophiolitic mélange. We present a model for the tectonomagmatic evolution of this portion of the CAOB involving prolonged intra-oceanic subduction with seamount accretion.

Subducted slab-plume interaction traced by magnesium isotopes in the northern margin of the Tarim Large Igneous Province

NASA Astrophysics Data System (ADS)

Cheng, Zhiguo; Zhang, Zhaochong; Xie, Qiuhong; Hou, Tong; Ke, Shan

2018-05-01

Incorporation of subducted slabs may account for the geochemical and isotopic variations of large igneous provinces (LIPs). However, the mechanism and process by which subducted slabs are involved into magmas is still highly debated. Here, we report a set of high resolution Mg isotopes for a suite of alkaline and Fe-rich rocks (including basalts, mafic-ultramafic layered intrusions, diabase dykes and mantle xenoliths in the kimberlitic rocks) from Tarim Large Igneous Province (TLIP). We observed that δ26 Mg values of basalts range from -0.29 to - 0.45 ‰, -0.31 to - 0.42 ‰ for mafic-ultramafic layered intrusions, -0.28 to - 0.31 ‰ for diabase dykes and -0.29 to - 0.44 ‰ for pyroxenite xenoliths from the kimberlitic rocks, typically lighter than the normal mantle source (- 0.25 ‰ ± 0.04, 2 SD). After carefully precluding other possibilities, we propose that the light Mg isotopic compositions and high FeO contents should be ascribed to the involvement of recycled sedimentary carbonate rocks and pyroxenite/eclogite. Moreover, from basalts, through layered intrusions to diabase dykes, (87Sr/86Sr)i values and δ18OV-SMOW declined, whereas ε (Nd) t and δ26 Mg values increased with progressive partial melting of mantle, indicating that components of carbonate rock and pyroxenite/eclogite in the mantle sources were waning over time. In combination with the previous reported Mg isotopes for carbonatite, nephelinite and kimberlitic rocks in TLIP, two distinct mantle domains are recognized for this province: 1) a lithospheric mantle source for basalts and mafic-ultramafic layered intrusions which were modified by calcite/dolomite and eclogite-derived high-Si melts, as evidenced by enriched Sr-Nd-O and light Mg isotopic compositions; 2) a plume source for carbonatite, nephelinite and kimberlitic rocks which were related to magnesite or periclase/perovskite involvement as reflected by depleted Sr-Nd-O and extremely light Mg isotopes. Ultimately, our study suggests

New U Pb SHRIMP zircon age for the Schurwedraai alkali granite: Implications for pre-impact development of the Vredefort Dome and extent of Bushveld magmatism, South Africa

NASA Astrophysics Data System (ADS)

Graham, I. T.; De Waal, S. A.; Armstrong, R. A.

2005-12-01

The Schurwedraai alkali granite is one of a number of prominent ultramafic-mafic and felsic intrusions in the Neoarchaean to Palaeoproterozoic sub-vertical supracrustal collar rocks of the Vredefort Dome, South Africa. The alkali granite intruded the Neoarchaean Witwatersrand Supergroup and has a peralkaline to peraluminous composition. A new zircon SHRIMP crystallization age of 2052 ± 14 Ma for the Schurwedraai alkali granite places it statistically before the Vredefort impact event at 2023 ± 4 Ma and within the accepted emplacement interval of 2050-2060 Ma of the Bushveld magmatic event. The presence of the alkali granite and associated small ultramafic-mafic intrusions in the Vredefort collar rocks extends the southern extremity of Bushveld-related intrusions to some 120 km south of Johannesburg and about 150 km south of the current outcrop area of the Bushveld Complex. The combined effect of these ultramafic-mafic and felsic bodies may have contributed to a pronouncedly steep pre-impact geothermal gradient in the Vredefort area, and to the amphibolite-grade metamorphism observed in the supracrustal collar rocks of the Vredefort Dome.

Massive production of abiotic methane during subduction evidenced in metamorphosed ophicarbonates from the Italian Alps

PubMed Central

Vitale Brovarone, Alberto; Martinez, Isabelle; Elmaleh, Agnès; Compagnoni, Roberto; Chaduteau, Carine; Ferraris, Cristiano; Esteve, Imène

2017-01-01

Alteration of ultramafic rocks plays a major role in the production of hydrocarbons and organic compounds via abiotic processes on Earth and beyond and contributes to the redistribution of C between solid and fluid reservoirs over geological cycles. Abiotic methanogenesis in ultramafic rocks is well documented at shallow conditions, whereas natural evidence at greater depths is scarce. Here we provide evidence for intense high-pressure abiotic methanogenesis by reduction of subducted ophicarbonates. Protracted (≥0.5–1 Ma), probably episodic infiltration of reduced fluids in the ophicarbonates and methanogenesis occurred from at least ∼40 km depth to ∼15–20 km depth. Textural, petrological and isotopic data indicate that methane reached saturation triggering the precipitation of graphitic C accompanied by dissolution of the precursor antigorite. Continuous infiltration of external reducing fluids caused additional methane production by interaction with the newly formed graphite. Alteration of high-pressure carbonate-bearing ultramafic rocks may represent an important source of abiotic methane, with strong implications for the mobility of deep C reservoirs. PMID:28223715

Pre-Cenozoic basement rocks of the Proto-Philippine Sea Plate: Constraints for the birthplace of the Izu-Bonin-Mariana Arc

NASA Astrophysics Data System (ADS)

Tani, K.; Ishizuka, O.; Horie, K.; Barth, A. P.; Harigane, Y.; Ueda, H.

2016-12-01

The Izu-Bonin-Mariana Arc is widely regarded to be a typical intra-oceanic arc, with the oceanic Pacific Plate subducting beneath the Philippine Sea Plate, an evolving complex of active and inactive arcs and back-arc basins. However, little is known about the origin of the proto-Philippine Sea Plate, which existed along with the Pacific Plate at the time of subduction initiation in the Eocene. To investigate the crustal structures of the proto-Philippine Sea Plate, we conducted manned-submersible and dredge surveys in the Daito Ridges and the Kyushu-Palau Ridge. The Daito Ridges comprise the northwestern Philippine Sea Plate along with what are regarded as remnants of the proto-Philippine Sea Plate. Submersible observations and rock sampling revealed that the Daito Ridges expose deep crustal sections of gabbroic, granitic, metamorphic, and ultra-mafic rocks, along with volcanic rocks ranging from basalt to andesite. Mesozoic magmatic zircon U-Pb ages have been obtained from the plutonic rocks, and whole-rock geochemistry of the igneous rocks indicates arc origins. Furthermore, mafic schist collected from the Daito Ridge has experienced amphibolite facies metamorphism, with phase assemblages suggesting that the crust was thicker than 20 km at the time. Similar amphibolite-facies metamorphic rocks with Proterozoic zircons have been recovered in the southern Kyushu-Palau Ridge, indicating that such distinctively older basement rocks exist as isolated tectonic blocks within the present Philippine Sea Plate. These finds show that the parts of the Daito Ridges and Kyushu-Palau Ridge represent developed crustal sections of the Pre-Cenozoic arc that comprises part of the proto-Philippine Sea Plate, and, together with the tectonic reconstruction of the proto-Philippine Sea Plate (Deschamps and Lallemand 2002, JGR), they suggest that subduction of the Izu-Bonin-Mariana Arc initiated at the continental margin of the Southeast Asia.

Rocks and Minerals.

ERIC Educational Resources Information Center

Naturescope, 1987

1987-01-01

Provides background information on rocks and minerals, including the unique characteristics of each. Teaching activities on rock-hunting and identification, mineral configurations, mystery minerals, and growing crystals are provided. Reproducible worksheets are included for two of the activities. (TW)

TEM Study of Intergranular Fluid Distributions in Rocks at a Nanometer Scale

NASA Astrophysics Data System (ADS)

Hiraga, T.; Anderson, I. M.; Kohlstedt, D. L.

2002-12-01

The distribution of intergranular fluids in rocks plays an essential role in fluid migration and rock rheology. Structural and chemical analyses with sub-nanometer resolution is possible with transmission and scanning-transmission electron microscopy; therefore, it is possible to perform the fine-scale structural analyses required to determine the presence or absence of very thin fluid films along grain boundaries. For aqueous fluids in crustal rocks, Hiraga et al. (2001) observed a fluid morphology controlled by the relative values of the solid-solid and solid-fluid interfacial energies, which resulted in well-defined dihedral angles. Their high-resolution transmission electron microscopy (TEM) observations demonstrate that grain boundaries are tight even at a nanometer scale, consistent with the absence of aqueous fluid films. For partially molten ultra-mafic rocks, two conflicting conclusions have been reached: nanometer-thick melt films wet grain boundaries (Drury and Fitz Gerald 1996; De Kloe et al. 2000) versus essentially all grain boundaries are melt-free (Vaughan et al. 1982; Kohlstedt 1990). To resolve this conflict, Hiraga et al. (2002) examined grain boundaries in quenched partially molten peridotites. Their observations demonstrate the following: (i) Although a small fraction of the grains are separated by relatively thick (~1 μm) layers of melt, lattice fringe images obtained with a high-resolution TEM reveal that most of the remaining boundaries do not contain a thin amorphous phase. (ii) In addition, the composition of olivine-olivine grain boundaries was analyzed with a nano-beam analytical scanning TEM with a probe size of <2 nm. Although the grain boundaries contained no melt film, the concentration of Ca, Al and Ti were enhanced near the boundaries. The segregation of these elements to the grain boundaries formed enriched regions <7 nm wide. A similar pattern of chemical segregation was detected in subsolidus systems. Creep experiments on the

Rock ramp design guidelines

USGS Publications Warehouse

Mooney, David M.; Holmquist-Johnson, Christopher L.; Broderick, Susan

2007-01-01

Rock ramps or roughened channels consist of steep reaches stabilized by large immobile material (riprap). Primary objectives for rock ramps include: Create adequate head for diversionMaintain fish passage during low-flow conditionsMaintain hydraulic conveyance during high-flow conditionsSecondary objectives for rock ramp design include:Emulate natural systemsMinimize costsThe rock ramp consists of a low-flow channel designed to maintain biologically adequate depth and velocity conditions during periods of small discharges. The remainder of the ramp is designed to withstand and pass large flows with minimal structural damage. The following chapters outline a process for designing rock ramps.

Trace element partitioning in rock forming minerals of co-genetic, subduction-related alkaline and tholeiitic mafic rocks in the Ural Mountains, Russia

NASA Astrophysics Data System (ADS)

Krause, J.; Brügmann, G. E.; Pushkarev, E. V.

2009-04-01

The partitioning of trace elements between rock forming minerals in igneous rocks is largely controlled by physical and chemical parameters e.g. temperature, pressure and chemical composition of the minerals and the coexisting melt. In the present study partition coefficients for REE between hornblende, orthopyroxene, feldspars, apatite and clinopyroxene in a suite of co-genetic alkaline and tholeiitic mafic rocks from the Ural Mountains (Russia) were calculated. The results give insights to the influence of the chemical composition of the parental melt on the partitioning behaviour of the REE. Nepheline-bearing, alkaline melanogabbros (tilaites) are assumed to represent the most fractionated products of the melt that formed the ultramafic cumulates in zoned mafic-ultramafic complexes in the Ural Mountains. Co-genetic with the latter is a suite of olivine gabbros, gabbronorites and hornblende gabbros formed from a tholeiitic parental melt. Negative anomalies for the HFSE along with low Nb and Ta contents and a positive Sr anomaly indicate a subduction related origin of all parental melts. The nepheline gabbros consist predominantly of coarse-grained clinopyroxene phenocrysts in a matrix of fine grained clinopyroxene, olivine, plagioclase, K-feldspar and nepheline with accessory apatite. The tholeiitic gabbros have equigranular to porphyric textures with phenocrysts of olivine, pyroxene and hornblende in a plagioclase rich matrix with olivine hornblende, pyroxene and accessory apatite. Element concentrations of adjacent matrix grains and rims of phenochrysts were measured with LA-ICPMS. The distribution of REE between hornblende and clinopyroxene in the tholeiitic rocks is similar for most of the elements (DHbl•Cpx(La-Tm) = 2.7-2.8, decreasing to 2.6 and 2.4 for Yb and Lu, respectively). These values are about two times higher than published data (e.g. Ionov et al. 1997). Partition coefficients for orthopyroxene/clinopyroxene systematically decrease from the HREE

Reconnaissance geology of the Precambrian rocks in the Bi'r Ghamrah quadrangle, Kingdom of Saudi Arabia

USGS Publications Warehouse

Overstreet, William C.; Whitlow, Jesse William

1972-01-01

Three sequences of volcanic and sedimentary rocks are identified in the Precambrian rocks of the Bi'r Ghamrah quadrangle at the eastern edge of the Precambrian Shield in central Saudi Arabia. The oldest sequence is called the Bi'r Khountina Group. It consists of conglomerate marble, andesite, and graywacke. Unconformably overlying this group is a sequence of graywacke with minor lava called the Murdama Group. In a small area in the southern part of the quadrangle, these rocks are unconformably overlain by rhyolitic tuff and rhyolite tentatively correlated with the Shammar Rhyolite. The older of these sedimentary and volcanic rocks were intruded by diorite and gabbro and by a large pluton of alkalic granite. A contact metamorphic aureole was formed in the Bi'r Khountina and Murdama Groups adjacent to the granite, and feeder dikes of the Sbmmmar Rhyolite(?) intrude the granite. The Bi'r Khountina Group is folded into a south-plunging asymmetrical anticlinorium, the west limb of which is repeated across northwest-trending faults. The Murdama Group appears to have been folded along the same axes, but the contact aureole against the alkalic granite and the imprint of the west-northwest striking Najd fault zone cause the rocks of the Murdama Group to appear to trend westward. Results of spectrographic and chemical analyses of wadi sand, heavy-mineral concentrates, and detrital magnetite show small anomalies. The ultramafic rocks intruded prior to the deposition of the Murdama Group are the source of anomalous chromium and lanthanum and of threshold nickel, scandium, and vanadium. The intrusive rocks younger than the Murdama Group are sources for anomalous lead and threshold silver, boron, barium, beryllium, zirconium, lanthanum, and tin. One small ancient working, probably opened for gold, is present, and at least four places in the Precambrian part of the quadrangle ere potentially favorable for gold, silver, and lead. Chromite is a potential resource in the

Woodcock Bog Research Natural Area: guidebook supplement 40

Treesearch

Reid Schuller; Susan J. Fritts; Mark Mousseaux

2010-01-01

This guidebook describes Woodcock Bog Research Natural Area (RNA), a 114-ha (281-ac) area located within the Klamath-Siskiyou ecoregion in southwestern Oregon. The RNA includes a hanging fen and stream segment on ultramafic rock and derived soils. Numerous plant species occur within the fens that are endemic to the Klamath-Siskiyou Mountains of southwestern Oregon and...

Hydrogeologic controls on episodic H2 release from precambrian fractured rocks--energy for deep subsurface life on earth and mars.

PubMed

Sherwood Lollar, B; Voglesonger, K; Lin, L-H; Lacrampe-Couloume, G; Telling, J; Abrajano, T A; Onstott, T C; Pratt, L M

2007-12-01

Dissolved H(2) concentrations up to the mM range and H(2) levels up to 9-58% by volume in the free gas phase are reported for groundwaters at sites in the Precambrian shields of Canada and Finland. Along with previously reported dissolved H(2) concentrations up to 7.4 mM for groundwaters from the Witwatersrand Basin, South Africa, these findings indicate that deep Precambrian Shield fracture waters contain some of the highest levels of dissolved H(2) ever reported and represent a potentially important energy-rich environment for subsurface microbial life. The delta (2)H isotope signatures of H(2) gas from Canada, Finland, and South Africa are consistent with a range of H(2)-producing water-rock reactions, depending on the geologic setting, which include both serpentinization and radiolysis. In Canada and Finland, several of the sites are in Archean greenstone belts characterized by ultramafic rocks that have under-gone serpentinization and may be ancient analogues for serpentinite-hosted gases recently reported at the Lost City Hydrothermal Field and other hydrothermal seafloor deposits. The hydrogeologically isolated nature of these fracture-controlled groundwater systems provides a mechanism whereby the products of water-rock interaction accumulate over geologic timescales, which produces correlations between high H(2) levels, abiogenic hydrocarbon signatures, and the high salinities and highly altered delta (18)O and delta (2)H values of these groundwaters. A conceptual model is presented that demonstrates how periodic opening of fractures and resultant mixing control the distribution and supply of H(2) and support a microbial community of H(2)-utilizing sulfate reducers and methanogens.

Widespread abiotic methane in chromitites.

PubMed

Etiope, G; Ifandi, E; Nazzari, M; Procesi, M; Tsikouras, B; Ventura, G; Steele, A; Tardini, R; Szatmari, P

2018-06-07

Recurring discoveries of abiotic methane in gas seeps and springs in ophiolites and peridotite massifs worldwide raised the question of where, in which rocks, methane was generated. Answers will impact the theories on life origin related to serpentinization of ultramafic rocks, and the origin of methane on rocky planets. Here we document, through molecular and isotopic analyses of gas liberated by rock crushing, that among the several mafic and ultramafic rocks composing classic ophiolites in Greece, i.e., serpentinite, peridotite, chromitite, gabbro, rodingite and basalt, only chromitites, characterized by high concentrations of chromium and ruthenium, host considerable amounts of 13 C-enriched methane, hydrogen and heavier hydrocarbons with inverse isotopic trend, which is typical of abiotic gas origin. Raman analyses are consistent with methane being occluded in widespread microfractures and porous serpentine- or chlorite-filled veins. Chromium and ruthenium may be key metal catalysts for methane production via Sabatier reaction. Chromitites may represent source rocks of abiotic methane on Earth and, potentially, on Mars.

Rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones

USGS Publications Warehouse

Kirby, S.H.

1985-01-01

Emphasized in this paper are the deformation processes and rheologies of rocks at high temperatures and high effective pressures, conditions that are presumably appropriate to the lower crust and upper mantle in continental collision zones. Much recent progress has been made in understanding the flexure of the oceanic lithosphere using rock-mechanics-based yield criteria for the inelastic deformations at the top and base. At mid-plate depths, stresses are likely to be supported elastically because bending strains and elastic stresses are low. The collisional tectonic regime, however, is far more complex because very large permanent strains are sustained at mid-plate depths and this requires us to include the broad transition between brittle and ductile flow. Moreover, important changes in the ductile flow mechanisms occur at the intermediate temperatures found at mid-plate depths. Two specific contributions of laboratory rock rheology research are considered in this paper. First, the high-temperature steady-state flow mechanisms and rheology of mafic and ultramafic rocks are reviewed with special emphasis on olivine and crystalline rocks. Rock strength decreases very markedly with increases in temperature and it is the onset of flow by high temperature ductile mechanisms that defines the base of the lithosphere. The thickness of the continental lithosphere can therefore be defined by the depth to a particular isotherm Tc above which (at geologic strain rates) the high-temperature ductile strength falls below some arbitrary strength isobar (e.g., 100 MPa). For olivine Tc is about 700??-800??C but for other crustal silicates, Tc may be as low as 400??-600??C, suggesting that substantial decoupling may take place within thick continental crust and that strength may increase with depth at the Moho, as suggested by a number of workers on independent grounds. Put another way, the Moho is a rheological discontinuity. A second class of laboratory observations pertains to

A reconnaissance view of tungsten reservoirs in some crustal and mantle rocks: Implications for interpreting W isotopic compositions and crust-mantle W cycling

NASA Astrophysics Data System (ADS)

Liu, Jingao; Pearson, D. Graham; Chacko, Thomas; Luo, Yan

2018-02-01

High-precision measurements of W isotopic ratios have enabled increased exploration of early Earth processes. However, when applying W isotopic data to understand the geological processes, it is critical to recognize the potential mobility of W and hence evaluate whether measured W contents and isotopic compositions reflect the primary petrogenetic processes or instead are influenced by the effects of secondary inputs/mobility. Furthermore, if we are to better understand how W is partitioned between different minerals during melting and metasomatic processes it is important to document the likely sinks for W during these processes. In addition, an understanding of the main hosts for W in the crust and mantle is critically important to constrain how W is cycled and stored in the crust-mantle geochemical cycle. As a first step to investigate these issues, we have carried out in situ concentration measurements of W and other HFSEs in mineral phases within a broad spectrum of crustal and mantle rocks, along with whole-rock concentration measurements. Mass balance shows that for tonalitic gneiss and amphibolite, the major rock-forming minerals can adequately account for the bulk W budget, and for the pristine ultramafic rocks, olivine and orthopyroxene are the major controlling phases for W whereas for metasomatized ultramafic rocks, significant W is hosted in Ti-bearing trace phases (e.g., rutile, lindsleyite) along grain boundaries or is inferred to reside in cryptic W-bearing trace phases. Formation or decomposition of these phases during secondary processes could cause fractionation of W from other HFSEs, and also dramatically modify bulk W concentrations in rocks. For rocks that experienced subsequent W enrichment/alteration, their W isotopic compositions may not necessarily represent their mantle sources, but could reflect later inputs. The relatively small suite of rocks analyzed here serves as a reconnaissance study but allows some preliminary speculations on

Petrology of ultramafic xenoliths from Loihi Seamount, Hawaii

USGS Publications Warehouse

Clague, D.A.

1988-01-01

Ultramafic xenoliths were recovered in four alkalic lava flows from Loihi Seamount at depths between 2200 and 1400 m. No xenolith bearing flows were sampled near the summit despite a concentrated dredge program. The flows, three of alkalic basalt and one of basanite, contain common olivine megacrysts and small xenoliths of dunite, rarer harzburgite, and a single wehrlite. Olivine megacrysts as large as 8 mm are Fo84-88.6 and contain magnesiochromite inclusions with 1.1-3.5 wt.% TiO2. Dunite contains Fo83.5-88.5 olivine, meganesiochromite with 1.5-6.9 wt.% TiO2 (avg. 3.2 wt.), and extremely rare chrome-rich diopside. The wehrlite contains euhedral Fo85.9 olivine and magnesiochromite with 1.9-4.7 wt.% TiO2, poikilitically enclosed in chrome-rich diposide (Wo45.4En48.0s6.6). Most of the olivine megacrysts, dunite, and the wehrlite are cumulates of Loihi alkalic lavas that accumulated in a magma storage zone located at least 16 km below sea level. The rarity of dunite related to tholeiitic magmas supports the interpretation that the alkalic lavas at Loihi generally predate the tholeiitic lavas. -from Author

ASTER spectral sensitivity of carbonate rocks - Study in Sultanate of Oman

NASA Astrophysics Data System (ADS)

Rajendran, Sankaran; Nasir, Sobhi

2014-02-01

Remote sensing satellite data plays a vital role and capable in detecting minerals and discriminating rock types for explorations of mineral resources and geological studies. Study of spectral absorption characters of remotely sensed data are under consideration by the exploration and mining companies, and demonstrating the spectral absorption characters of carbonates on the cost-effective multispectral image (rather than the hyperspectral, Lidar image) for easy understanding of all geologists and exploration communities of carbonates is very much important. The present work is an integrated study and an outcome of recently published works on the economic important carbonate rocks, includes limestone, marl, listwaenites and carbonatites occurred in parts of the Sultanate of Oman. It demonstrates the spectral sensitivity of such rocks for simple interpretation over satellite data and describes and distinguishes them based on the absorptions of carbonate minerals in the spectral bands of advanced spaceborne thermal emission and reflection radiometer (ASTER) for mapping and exploration studies. The study results that the ASTER spectral band 8 discriminates the carbonate rocks due to the presence of predominantly occurred carbonate minerals; the ASTER band 5 distinguishes the limestones and marls (more hydroxyl clay minerals) from listwaenite (hydrothermally altered rock) due to the presence of altered minerals and the ASTER band 4 detects carbonatites (ultramafic intrusive alkaline rocks) which contain relatively more silicates. The study on the intensity of the total absorptions against the reflections of these rocks shows that the limestones and marls have low intensity in absorptions (and high reflection values) due to the presence of carbonate minerals (calcite and dolomite) occurred in different proportions. The listwaenites and carbonatites have high intensity of absorptions (low reflection values) due to the occurrence of Mn-oxide in listwaenites and carbonates

My Pet Rock

ERIC Educational Resources Information Center

Lark, Adam; Kramp, Robyne; Nurnberger-Haag, Julie

2008-01-01

Many teachers and students have experienced the classic pet rock experiment in conjunction with a geology unit. A teacher has students bring in a "pet" rock found outside of school, and the students run geologic tests on the rock. The tests include determining relative hardness using Mohs scale, checking for magnetization, and assessing luster.…

Oxygen and hydrogen isotopic composition of the fluid during formation of anthophyllite metaultramafic rocks in the Sysert metamorphic complex, central Urals

NASA Astrophysics Data System (ADS)

Murzin, V. V.

2014-12-01

The oxygen (δ18O) and hydrogen (δD) isotopic composition of H2O-bearing minerals was studied for the ore-bearing amphibole metaultramafic rocks, which are the products of the early regional (435 ± 44 Ma) and late local (260 ± 6 Ma) silicic metasomatose in the Sysert metamorphic complex. The gold-sulfide mineralization of the Karas'evogorskoe deposit and anthophyllite-asbestos bodies of the Tersut deposit are related to the regional and local metasomatose combined with plagiogranitization and potassium granitization, respectively. The H2O-bearing minerals of metasomatites (anthophyllite, tremolite, talc) of the Karas'evogorskoe and Tersut deposits are characterized by heavier δ18O (9.8 to 12.2 and 7.6 to 9.4‰, respectively) and lighter ·D (87 to -91 and -56 to -67‰, respectively) values. The calculated isotopic composition of the fluid in equilibrium with these minerals indicates a heterogeneous source of water for the fluids related to the formation of metasomatites and the metamorphic origin of fluids. During the regional metasomatose, this fluid was a result of equilibrium of the deep fluid with volcanosedimentary rocks enriched in the heavy oxygen isotope. At the local metasomatose, the metamorphic fluid was formed by interaction of magmatic water produced by potassium granitization with ultramafic rocks.

Mesoproterozoic juvenile mafic-ultramafic magmatism in the SW Amazonian Craton (Rio Negro-Juruena province): SHRIMP U-Pb geochronology and Nd-Sr constraints of the Figueira Branca Suite

NASA Astrophysics Data System (ADS)

Teixeira, Wilson; Geraldes, Mauro C.; D'Agrella-Filho, Manoel S.; Santos, João O. S.; Sant'Ana Barros, Márcia A.; Ruiz, Amarildo S.; Corrêa da Costa, Paulo C.

2011-12-01

The Figueira Branca Suite (FBS) comprises a layered mafic-ultramafic complex which together with mafic-felsic plugs makes up a string of NW-trending intrusive bodies that are emplaced into the Jauru domain (Rio Negro-Juruena province; 1.80-1.60 Ga). This domain comprises Orosirian calc-alkaline rocks and coeval metamorphic volcanic-sedimentary associations, intruded by voluminous granitoid plutons resulted from outboard Cachoeirinha (1587-1522 Ma) and Santa Helena (1485-1420 Ma) accretionary orogens that eventually created the Rondonian-San Ignacio province along the SW margin of the proto-Amazonian Craton. SHRIMP U-Pb age in zircon for one cumulatic gabbro from the FBS yielded a concordia intercept age of 1425.5 ± 8.0 Ma (MSWD = 1.11). Another gabbroic plug which crops out to the East gives a similar within error concordia intercept zircon age of 1415.9 ± 6.9 Ma (MSWD = 0.25), whereas a nearby monzogranite yields a concordia intercept zircon age of 1428.9 ± 2.8 Ma (MSWD = 1.30). All these results are crystallization ages and constrain an important intraplate magmatic event within the Orosirian continental crust at the time of outboard Santa Helena orogen. On the other hand, igneous titanite from another gabbro located to the West of the FBS yielded a weighted mean 207Pb/ 206Pb crystallization age of 1541 ± 23 Ma (MSWD = 0.74). Therefore this rock is not genetically associated with the FBS, as previously suggested by the field information. Additional Nd-Sr isotopic analyses of the FBS mafic-ultramafic rocks and coeval gabbro showed comparable ɛNd(1.42Ga) values (+3.0 to +4.7) and variable ɛSr(1.42Ga) ones (-39.1 to -8.1). These data plot in the depleted field quadrant of the Nd-Sr diagram, indicating a significant influence of the MORB end-member reservoir in the magma genesis. This interpretation is similarly supported by comparison of the Nd evolutionary path of the FBS with those that characterize the isotopic evolution of the Jauru crust and the

The thermal maturation degree of organic matter from source rocks revealed by wells logs including examples from Murzuk Basin, Libya

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

Negoita, V.; Gheorghe, A.

1995-08-01

The customary technique used to know the organic matter quantity per rock volume it as well as the organic matter maturation stage is based on geochemical analyses accomplished on a preselected number of samples and cuttings drawn from boreholes during the drilling period. But the same objectives can be approached without any extra cost using the continuous measurements of well logs recorded in each well from the ground surface to the total depth. During the diagenetic stage, the identification of potential source rocks out of which no hydrocarbon have been generated may be carried out using a well logging suitemore » including Gamma Ray Spectrometry, the Compensated Neutron/Litho Density combination and a Dual Induction/Sonic Log. During the catagenetic stage the onset of oil generation brings some important changes in the organic matter structure as well as in the fluid distribution throughout the pore space of source rocks. The replacement of electric conductive water by electric non-conductive hydrocarbons, together with water and oil being expelled from source rocks represent a process of different intensities dependent of time/temperature geohistory and kerogen type. The different generation and expulsion scenarios of hydrocarbons taking place during the catagenetic and metagenetic stages of source rocks are very well revealed by Induction and Laterolog investigations. Several crossplots relating vitrinite reflectance, total organic carbon and log-derived physical parameters are illustrated and discussed. The field applications are coming from Murzuk Basin, where Rompetrol of Libya is operating.« less

Geochemistry of ultramafic xenoliths from Kapfenstein, Austria: evidence for a variety of upper mantle processes

NASA Astrophysics Data System (ADS)

Kurat, G.; Palme, H.; Spettel, B.; Baddenhausen, Hildegard; Hofmeister, H.; Palme, Christl; Wänke, H.

1980-01-01

Major, minor, and trace element contents have been determined in seven ultramafic xenoliths, the host basanite, and some mineral separates from xenoliths from Kapfenstein, Austria. Most of the xenoliths represent residues after extraction of different amounts of basaltic liquid. Within the sequence Iherzolite to harzburgite contents of Al, Ca, Ti, Na, Sc, V, Cr and the HREE decrease systematically with increasing Mg/Fe and decreasing Yb/Sc. Although all samples are depleted in highly incompatible elements, the less depleted end of our suite very closely approaches the chondritic Yb/Sc ratio and consequently the primitive upper mantle composition. Chromium behaved as a non-refractory element. Consequently it should have higher abundances in basalts than observed, suggesting that most basalts experienced Cr fractionation by chromite separation during ascent. Several processes have been active in addition to partial melting within the upper mantle beneath Kapfenstein: (1) a hornblendite has been identified as wet alkali-basaltic mobilisate; (2) an amphibole Iherzolite is the product of alkali-basalt metasomatism of a common depleted Iherzolite; (3) two amphibole Iherzolites contain evidence for rather pure water metasomatism of normal depleted Iherzolites; (4) a garnet-spinel websterite was a tholeiitic liquid trapped within the upper mantle and which suffered a subsequent partial melting event (partial remobilization of a mobilisate). (5) Abundances of highly incompatible elements are generally very irregular, indicating contamination of upper mantle rocks by percolating liquids (in the mantle). Weathering is an important source of contamination: e.g. U mobilization by percolating groundwater. Contamination of the xenoliths by the host basanite liquid can only amount to approximately 5.5 × 10 -4 parts. Distributions of minor and trace elements between different minerals apparently reflect equilibrium and vary with equilibration temperature.

An alkaline spring system within the Del Puerto ophiolite (California USA): A Mars analog site

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

Blank, J.G.; Green, S.; Blake, D.

2008-10-01

Mars appears to have experienced little compositional differentiation of primitive lithosphere, and thus much of the surface of Mars is covered by mafic lavas. On Earth, mafic and ultramafic rocks present in ophiolites, oceanic crust and upper mantle that have been obducted onto land, are therefore good analogs for Mars. The characteristic mineralogy, aqueous geochemistry, and microbial communities of cold-water alkaline springs associated with these mafic and ultramafic rocks represent a particularly compelling analog for potential life-bearing systems. Serpentinization, the reaction of water with mafic minerals such as olivine and pyroxene, yields fluids with unusual chemistry (Mg-OH and Ca-OH watersmore » with pH values up to {approx}12), as well as heat and hydrogen gas that can sustain subsurface, chemosynthetic ecosystems. The recent observation of seeps from pole-facing crater and canyon walls in the higher Martian latitudes supports the hypothesis that even present conditions might allow for a rockhosted chemosynthetic biosphere in near-surface regions of the Martian crust. The generation of methane within a zone of active serpentinization, through either abiogenic or biogenic processes, could account for the presence of methane detected in the Martian atmosphere. For all of these reasons, studies of terrestrial alkaline springs associated with mafic and ultramafic rocks are particularly timely. This study focuses on the alkaline Adobe Springs, emanating from mafic and ultramafic rocks of the California Coast Range, where a community of novel bacteria is associated with the precipitation of Mg-Ca carbonate cements. The carbonates may serve as a biosignature that could be used in the search for evidence of life on Mars.« less

Aqueous Geochemical Dynamics at the Coast Range Ophiolite Microbial Observatory and The Case for Subsurface Mixing of Regional Groundwaters

NASA Astrophysics Data System (ADS)

Cardace, D.; Schrenk, M. O.; McCollom, T. M.; Hoehler, T. M.

2017-12-01

Serpentinization is the aqueous alteration (or hydration) of olivine and pyroxene minerals in ultramafic rocks, occurring in the seabed and ultramafic units on continents, such as at the Coast Range Ophiolite (CRO) in northern California, USA. Mineral products of serpentinization include serpentine, magnetite, brucite, talc, oxyhydroxides, carbonates, and diverse clay minerals. Such mineral transformations generate extremely high pH solutions with characteristic cation and dissolved metal loads, transmitting CH4, H2, and CO gas mixtures from depth; deep life in ultramafic terrains is thought to be fueled by chemical energy derived from these geochemical reactions. The installation of 8 groundwater monitoring wells in the CRO has allowed frequent monitoring since 2011. Influx of deeply sourced, serpentinization-influenced waters is evidenced by related geochemical shifts (e.g., pH, oxidation-reduction potential), but is apparently mixing with other, regionally important groundwater types. Evaluation salinity loads in concert with other parameters, we model the mixing scenario of this site of ongoing scientific study and experimentation.

Formation of pyroxenite layers in the Totalp ultramafic massif (Swiss Alps) - Insights from highly siderophile elements and Os isotopes

NASA Astrophysics Data System (ADS)

van Acken, David; Becker, Harry; Walker, Richard J.; McDonough, William F.; Wombacher, Frank; Ash, Richard D.; Piccoli, Phil M.

2010-01-01

Pyroxenitic layers are a minor constituent of ultramafic mantle massifs, but are considered important for basalt generation and mantle refertilization. Mafic spinel websterite and garnet-spinel clinopyroxenite layers within Jurassic ocean floor peridotites from the Totalp ultramafic massif (eastern Swiss Alps) were analyzed for their highly siderophile element (HSE) and Os isotope composition. Aluminum-poor pyroxenites (websterites) display chondritic to suprachondritic initial γOs (160 Ma) of -2 to +27. Osmium, Ir and Ru abundances are depleted in websterites relative to the associated peridotites and to mantle lherzolites worldwide, but relative abundances (Os/Ir, Ru/Ir) are similar. Conversely, Pt/Ir, Pd/Ir and Re/Ir are elevated. Aluminum-rich pyroxenites (clinopyroxenites) are characterized by highly radiogenic 187Os/ 188Os with initial γOs (160 Ma) between +20 and +1700. Their HSE composition is similar to that of basalts, as they are more depleted in Os, Ir and Ru compared to Totalp websterites, along with even higher Pt/Ir, Pd/Ir and Re/Ir. The data are most consistent with multiple episodes of reaction of mafic pyroxenite precursor melts with surrounding peridotites, with the highest degree of interaction recorded in the websterites, which typically occur in direct contact to peridotites. Clinopyroxenites, in contrast, represent melt-dominated systems, which retained the precursor melt characteristics to a large extent. The melts may have been derived from a sublithospheric mantle source with high Pd/Ir, Pt/Ir and Re/Os, coupled with highly radiogenic 187Os/ 188Os compositions. Modeling indicates that partial melting of subducted, old oceanic crust in the asthenosphere could be a possible source for such melts. Pentlandite and godlevskite are identified in both types of pyroxenites as the predominant sulfide minerals and HSE carriers. Heterogeneous HSE abundances within these sulfide grains likely reflect subsolidus processes. In contrast, large grain

Modelling of Surface Fault Structures Based on Ground Magnetic Survey

NASA Astrophysics Data System (ADS)

Michels, A.; McEnroe, S. A.

2017-12-01

The island of Leka confines the exposure of the Leka Ophiolite Complex (LOC) which contains mantle and crustal rocks and provides a rare opportunity to study the magnetic properties and response of these formations. The LOC is comprised of five rock units: (1) harzburgite that is strongly deformed, shifting into an increasingly olivine-rich dunite (2) ultramafic cumulates with layers of olivine, chromite, clinopyroxene and orthopyroxene. These cumulates are overlain by (3) metagabbros, which are cut by (4) metabasaltic dykes and (5) pillow lavas (Furnes et al. 1988). Over the course of three field seasons a detailed ground-magnetic survey was made over the island covering all units of the LOC and collecting samples from 109 sites for magnetic measurements. NRM, susceptibility, density and hysteresis properties were measured. In total 66% of samples with a Q value > 1, suggests that the magnetic anomalies should include both induced and remanent components in the model.This Ophiolite originated from a suprasubduction zone near the coast of Laurentia (497±2 Ma), was obducted onto Laurentia (≈460 Ma) and then transferred to Baltica during the Caledonide Orogeny (≈430 Ma). The LOC was faulted, deformed and serpentinized during these events. The gabbro and ultramafic rocks are separated by a normal fault. The dominant magnetic anomaly that crosses the island correlates with this normal fault. There are a series of smaller scale faults that are parallel to this and some correspond to local highs that can be highlighted by a tilt derivative of the magnetic data. These fault boundaries which are well delineated by the distinct magnetic anomalies in both ground and aeromagnetic survey data are likely caused by increased amount of serpentinization of the ultramafic rocks in the fault areas.

The Rock Cycle

ERIC Educational Resources Information Center

Singh, Raman J.; Bushee, Jonathan

1977-01-01

Presents a rock cycle diagram suitable for use at the secondary or introductory college levels which separates rocks formed on and below the surface, includes organic materials, and separates products from processes. (SL)

Carbonation of mantle peridotites: implications for permanent geological CO2 capture and storage

NASA Astrophysics Data System (ADS)

Paukert, A. N.; Matter, J. M.; Kelemen, P. B.; Marsala, P.; Shock, E.

2012-12-01

In situ carbonation of mantle peridotites serves as a natural analog to engineered mineral carbonation for geological CO2 capture and storage. For example, mantle peridotite in the Samail Ophiolite, Oman naturally captures and stores about 5x104 tons of atmospheric CO2 per year as carbonate minerals, and has been doing so for the past 50,000 years [Kelemen et al., 2011]. Our reaction path modeling of this system shows that the natural process is limited by subsurface availability of dissolved inorganic carbon, and that the rate of CO2 mineralization could be enhanced by a factor of 16,000 by injecting CO2 into the peridotite aquifer at 2 km depth and a fugacity of 100 bars. Injecting CO2 into mafic or ultramafic rock formations has been presumed difficult, as fractured crystalline rocks typically have low porosity and permeability; however these factors have yet to be comprehensively studied. To determine the actual value of these hydrogeological factors, this winter we carried out a multifaceted study of deep boreholes (up to 350m) in the mantle peridotite and the Moho transition zone of the Samail Ophiolite. A suite of physical and chemical parameters were collected, including slug tests for hydraulic conductivity, geophysical well logs for porosity and hydraulic conductivity, drill chips for extent and composition of secondary mineralization, and water and dissolved gas samples for chemical composition. All of these factors combine to provide a comprehensive look at the chemical and physical processes underlying natural mineral carbonation in mantle peridotites. Understanding the natural process is critical, as mineral carbonation in ultramafic rocks is being explored as a permanent and relatively safe option for geologic carbon sequestration. While injectivity in these ultramafic formations was believed to be low, our slug test and geophysical well log data suggest that the hydraulic conductivity of fractured peridotites can actually be fairly high - up to

Regional metamorphism in the Condrey Mountain Quadrangle, north-central Klamath Mountains, California

USGS Publications Warehouse

Hotz, Preston Enslow

1979-01-01

Fork in this region is composed of siliceous phyllite and phyllitic quartzite and is believed to be the metamorphosed equivalent of rocks over which it is thrust. In the Yreka-Fort Jones area, potassium-argon determinations on mica from the blueschist facies in the Stuart Fork gave ages of approximately 220 m.y. (Late Triassic) for the age of metamorphism. Rocks of the amphibolite facies structurally overlie the Condrey Mountain Schist along a moderate to steeply dipping thrust fault. The amphibolite terrane is composed of amphibolite and metasedimentary rocks in approximately equal amounts accompanied by many bodies of serpentinite and a number of gabbro and dioritic plutons. Most of the amphibolite is foliated, but some is nonfoliated; the nonfoliated amphibolite has an amphibolite mineralogy and commonly a relict volcanic rock texture. The nonfoliated amphibolite occurs on the southern and eastern borders of the amphibolite terrane between the areas offoliated amphibolite and the overly ing metavolcanic and metasedimentary rocks. Hornblende and plagioclase (An30-35) are the characteristic minerals, indicating that the rocks are of the almandine-amphibolite metamorphic facies. The metasedimentary rocks interbedded with the amphibolites include siliceous schist and phyllite, minor quartzite, and subordinate amounts of marble. Potassium-argon age dates obtained on hornblende from foliated amphibolite yield ages of 146?4 and 148? 4 m.y., suggesting a Late Jurassic metamorphic episode. Mafic and ultramafic rocks are widespread in the amphibolite terrane but are almost entirely absent from the area of greenschist facies metavolcanic and metasedimentary rocks. The ultramafic rocks, predominantly serpentinite, occur as a few large bodies and many small tabular concordant bodies interleaved with the foliated rocks. The ultramafic rocks include harzburgite and d1lIlite and their serpentinized equivalents. In the Condrey Mountain quadrangle, probably more t

Rock pushing and sampling under rocks on Mars

USGS Publications Warehouse

Moore, H.J.; Liebes, S.; Crouch, D.S.; Clark, L.V.

1978-01-01

Viking Lander 2 acquired samples on Mars from beneath two rocks, where living organisms and organic molecules would be protected from ultraviolet radiation. Selection of rocks to be moved was based on scientific and engineering considerations, including rock size, rock shape, burial depth, and location in a sample field. Rock locations and topography were established using the computerized interactive video-stereophotogrammetric system and plotted on vertical profiles and in plan view. Sampler commands were developed and tested on Earth using a full-size lander and surface mock-up. The use of power by the sampler motor correlates with rock movements, which were by plowing, skidding, and rolling. Provenance of the samples was determined by measurements and interpretation of pictures and positions of the sampler arm. Analytical results demonstrate that the samples were, in fact, from beneath the rocks. Results from the Gas Chromatograph-Mass Spectrometer of the Molecular Analysis experiment and the Gas Exchange instrument of the Biology experiment indicate that more adsorbed(?) water occurs in samples under rocks than in samples exposed to the sun. This is consistent with terrestrial arid environments, where more moisture occurs in near-surface soil un- der rocks than in surrounding soil because the net heat flow is toward the soil beneath the rock and the rock cap inhibits evaporation. Inorganic analyses show that samples of soil from under the rocks have significantly less iron than soil exposed to the sun. The scientific significance of analyses of samples under the rocks is only partly evaluated, but some facts are clear. Detectable quantities of martian organic molecules were not found in the sample from under a rock by the Molecular Analysis experiment. The Biology experiments did not find definitive evidence for Earth-like living organisms in their sample. Significant amounts of adsorbed water may be present in the martian regolith. The response of the soil

New Ages for Gorgona Island, Colombia: Implications for Previous Petrogenetic and Tectonic Models

NASA Astrophysics Data System (ADS)

Serrano Duran, L.; Lopez Martinez, M.; Ferrari, L.

2007-05-01

The Gorgona Island, located 50 km to the west of the Colombian Pacific coast, is the only known site with Phanerozoic komatiites in the world besides a key element in several reconstruction of the interaction between the Caribbean and the South America Plate. The Gorgona komatiites are part of an igneous complex that also includes picritic basalts and breccias, gabbros and peridotites (dunites and wherlites), and is covered by deformed mid-Eocene and younger underformed marine sediments. Datings of the igneous rocks were only performed on basalts and include an 86 Ma K-Ar age, an 88.9 ± 1.2 Ma weighted mean of four Ar-Ar ages and an 89.2 ± 5.2 Ma Re-Os isochron age from basalts. Gorgona rocks are affected by reverse faulting with a general eastward vergence. The island is the only subaerially exposed part of a NE elongated sliver accreted in a dextral transpressional regime to the South America continental margin between the Late Eocene and the Early Miocene. Petrologic studies found large spread in radiogenic isotopes and incompatible trace element ratios in Gorgona ultramafic rocks, which have been interpreted as requiring at least two different sources of: 1) a depleted mantle responsible for the generation of the komatiites and most basalts, and 2) an enriched mantle responsible for some rarer enriched basalts and picrites. Despite the large compositional and isotopic heterogeneity the most common interpretation is that the Gorgona ultramafic rocks are the product of a single mantle plume, although it has recently proposed that this would be a separate plume from that generating the bulk of the Caribbean plateau at ~90 Ma. Our new study focused on the geochronology of the Gorgona igneous suite as we consider that this tectonically and petrologically complex island is unlike to have such a narrow age range. We attempted to date eight samples of komatiites, basalts and gabbros by Ar-Ar laser step heating. For four of these samples we successfully obtain

Petrogenesis of siliceous high-Mg series rocks as exemplified by the Early Paleoproterozoic mafic volcanic rocks of the Eastern Baltic Shield: enriched mantle versus crustal contamination

NASA Astrophysics Data System (ADS)

Bogina, Maria; Zlobin, Valeriy; Sharkov, Evgenii; Chistyakov, Alexeii

2015-04-01

The Early Paleoproterozoic stage in the Earth's evolution was marked by the initiation of global rift systems, the tectonic nature of which was determined by plume geodynamics. These processes caused the voluminous emplacement of mantle melts with the formation of dike swarms, mafic-ultramafic layered intrusions, and volcanic rocks. All these rocks are usually considered as derivatives of SHMS (siliceous high-magnesian series). Within the Eastern Baltic Shield, the SHMS volcanic rocks are localized in the domains with different crustal history: in the Vodlozero block of the Karelian craton with the oldest (Middle Archean) crust, in the Central Block of the same craton with the Neoarchean crust, and in the Kola Craton with a heterogeneous crust. At the same time, these rocks are characterized by sufficiently close geochemical characteristics: high REE fractionation ((La/Yb)N = 4.9-11.7, (La/Sm)N=2.3-3.6, (Gd/Yb)N =1.66-2.74)), LILE enrichment, negative Nb anomaly, low to moderate Ti content, and sufficiently narrow variations in Nd isotope composition from -2.0 to -0.4 epsilon units. The tectonomagmatic interpretation of these rocks was ambiguous, because such characteristics may be produced by both crustal contamination of depleted mantle melts, and by generation from a mantle source metasomatized during previous subduction event. Similar REE patterns and overlapping Nd isotope compositions indicate that the studied basaltic rocks were formed from similar sources. If crustal contamination en route to the surface would play a significant role in the formation of the studied basalts, then almost equal amounts of contaminant of similar composition are required to produce the mafic rocks with similar geochemical signatures and close Nd isotopic compositions, which is hardly possible for the rocks spaced far apart in a heterogeneous crust. This conclusion is consistent with analysis of some relations between incompatible elements and their ratios. In particular, the

Behaviour of Ni-PGE-Au-Cu in mafic-ultramafic volcanic suites of the 2.7 Ga Kambalda Sequence, Kalgoorlie Terrane, Yilgarn Craton

NASA Astrophysics Data System (ADS)

Said, Nuru; Kerrich, Robert; Maier, W. D.; McCuaig, Campbell

2011-05-01

The 2.7 Ga Kambalda Sequence comprises a mafic to ultramafic dominated volcanic rock sequence of the Kalgoorlie Terrane, Yilgarn Craton, Western Australia. The Sequence is divided into Lower and Upper Units separated by the Kambalda Komatiite Formation. Five basalt suites of the Lower Unit are tholeiitic where MgO spans 5-10 wt.% MgO, with minor assimilation-fractional crystallization (AFC), whereas six volcanic suites identified in the Upper Unit are tholeiitic to komatiitic-basalts with MgO 24-5 wt.% having generally greater degrees of AFC. Upper suites plot at Al 2O 3/TiO 2 (17-26) close to the primitive mantle ratio of 21, and Pt + Pd (19-31 ppb), whereas the PGE-depleted Lower basalts plot at generally lower Al 2O 3/TiO 2 (<16) and Pt + Pd (<10 ppb). Most suites have an average Pt/Pd ratio of 1.11, despite large variations in MgO contents, broadly consistent with the Pt/Pd ratio in the primitive mantle. On primitive mantle-normalised PGE plots, Upper suites generally display less fractionated patterns of the IPGE (Os, Ir, Ru and Rh) from the PPGE (Pt and Pd) relative to the Lower basalts. Most suites exhibit patterns with positive slopes reflecting relative enrichment of Pd, Pt, Au and Cu relative to Ni and IPGE. In suites of both Units, the concentrations of Ir and Ru fall with decreasing MgO contents, indicating their broadly compatible behaviour during magmatic evolution that involved AFC. Platinum and Pd behave as incompatible elements in the high-MgO suites, whereas Pt and Pd behave compatibly during crystallisation of the Lower basalt magmas, an interpretation consistent with progressively higher Cu/Pt and Cu/Pd ratios at decreasing MgO contents, and with falling Pt/Ti, collectively due to sulphur saturation induced by AFC as recorded in an antivariance of Pd/Ir with Nb/Th, a monitor of AFC. Collectively, the data suggest that several of the Lower Basalt suites crystallised under sulphide-saturated conditions, whereas most of the Upper Basalt Sequences

Characterizing the nature of melt-rock reaction in peridotites from the Santa Elena Ophiolite, NW Costa Rica

NASA Astrophysics Data System (ADS)

Carr, D.; Loocke, M. P.; Snow, J. E.; Gazel, E.

2017-12-01

The Santa Elena Ophiolite (SEO), located on the northwestern coast of Costa Rica, consists primarily of preserved oceanic mantle and crustal rocks thrust above an accretionary complex. The SEO is predominantly characterized by mantle peridotites (i.e., primarily spinel lherzolite with minor amounts of harzburgite and dunite) cut and intruded by minor pegmatitic gabbros, layered gabbros, plagiogranites, and doleritic and basaltic dykes. Previous studies have concluded that the complex formed in a suprasubduction zone (SSZ) setting based on the geochemical nature of the layered gabbros and plagiogranites (i.e., depleted LREE and HFSE and enriched LILE and Pb), as well, as the peridotites (i.e., low-TiO2, Zr, and V, and high MgO, Cr, and Ni)(Denyer and Gazel, 2009). Eighteen ultramafic samples collected during the winter 2010/2011 field season (SECR11) exhibit abundant evidence for melt-rock reaction (e.g., disseminated plagioclase and plagioclase-spinel, clinopyroxene-spinel, and plagioclase-clinopyroxene symplectites) and provide a unique opportunity to characterize the textural and chemical nature of melt-rock reaction in the SEO. We present the results of a petrologic investigation (i.e., petrography and electron probe microanalysis) of 28 thin sections (19 spinel lherzolites, of which 14 are plagioclase-bearing, 4 pyroxenite veins, and 5 harzburgites) derived from the SECR11 sample set. The results of this investigation have the potential to better our understanding of the nature of melt generation and migration and melt-rock interaction in the SEO mantle section and shed further light on the complex petrogenetic history of the SEO. Denyer, P., Gazel, E., 2009, Journal of South American Earth Sciences, 28:429-442.

Diamond and moissanite in ophiolitic mantle rocks and podiform chromitites: A deep carbon source?

NASA Astrophysics Data System (ADS)

Yang, J.; Xu, X.; Wiedenbeck, M.; Trumbull, R. B.; Robinson, P. T.

2010-12-01

Diamonds are known from a variety of occurreces, mainly from mantle-derived kimberlites, meteorite impact craters, and continental deep subduction and collision zones. Recently, an unusual mineral group was discovered in the Luobusa ophiolitic chromitites from the Yarlung Zangbu suture, Tibet, which probably originated from a depth of over 300 km in the mantle. Minerals of deep origin include coesite apparently pseudomorphing stishovite, and diamond as individual grains or inclusions in OsIr alloy. To determine if such UHP and unusual minerals occur elsewhere, we collected about 1.5 t of chromitite from two orebodies in an ultramafic body in the Polar Urals. Thus far, more than 60 different mineral species have been separated from these ores. The most exciting discovery is the common occurrence of diamond, a typical UHP mineral in the Luobusa chromitites. These minerals are very similar in composition and structure to those reported from the Luobusa chromitites. So far diamond and/or moissanite have been discovered from many different ophiolitic ultramafic rocks, including in-situ grains in polished chromitite fragments. These discoveries demonstrate that the Luobusa ophiolite is not a unique diamond-bearing massif. Secondary ion mass spectrometric (SIMS) analysis shows that the ophiolite-hosted diamond has a distinctive 13C-depleted isotopic composition (δ13C from -18 to -28‰, n=70), compatible to the ophiolite-hosted moissanite (δ13C from -18 to -35‰, n=36), both are much lighter than the main carbon reservoir in the upper mantle (δ13C near -5‰). The compiled data from moissanite from kimberlites and other mantle settings share the characteristic of strongly 13C-depleted isotopic composition. This suggests that diamond and moissanite originates from a separate carbon reservoir in the mantle or that its formation involved strong isotopic fractionation. Subduction of biogenic carbonaceous material could potentially satisfy both the unusual isotopic and

Types and Mechanisms of Alterations on the Mesozoic Ophiolites (Lake Van Region-Turkey): Petrographical and Geochemical Approach

NASA Astrophysics Data System (ADS)

Yazıcı, Ömer; Üner, Tijen; Mutlu, Sacit; Depçi, Tolga

2017-04-01

Mesozoic ophiolites are widely located in the eastern part of Lake Van Basin. The ophiolitic rocks deformed during the rifting and/or closure period of the Neo-Tethyan Ocean are observed as tectonic slices in the region. These ophiolites are represented by volcano-sedimentary units, isolated dikes, and mafic-ultramafic rocks. The formation, emplacement and post-emplacement processes of these ophiolitic rocks can be understood owing to alterations as rodingitization, serpentinization, and listwaenitization. Three stages of sequent mineralization are detected in the ophiolitic rocks. First stage is pyrometasomatization, represented by metamorphic minerals (garnet, chlorite etc.), observed in intruded dikes. Second stage is hydrothermal alteration of mafic-ultramafic rocks namely serpentinization. Listwaenite alteration is the last stage of mineralization. According to petrographical investigations, garnet+chlorite+diopsite minerals are detected in rodengites. The conversion of the plagioclase minerals to the calcsilicatic minerals in rodengites suggests that these rocks are metasomatic rocks produced by Ca-rich fluids derived from serpentinization of the ultramafic rocks. The serpentine minerals (chrysotile-lizardite) can be distinguished from each other by their morphology as being platy or fibrous. Listwaenite alteration is followed by the formation of carbonate, silica, oxides and hydroxides. Chemical analysis of these rocks show that the listwaenites have an enrichment in Ni and Co contents while the rodingites have low SiO2 and high CaO and MgO values (SiO2 28,50 - 36,67%, CaO 11,99 - 20,88%, and MgO 7,99 - 17,73%). Alteration types observed on the ophiolitic rocks demonstrate that these rocks are metamorphised by low pressure and low to middle temperature conditions (greenshist facies). Serpentinization is pointing out an alteration which occurred during the emplacement of the ophiolites or the latter period. This study has been supported by Project number 2013

Devonian alkaline magmatic belt along the northern margin of the North China Block: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Zhang, Qi-Qi; Zhang, Shuan-Hong; Zhao, Yue; Liu, Jian-Min

2018-03-01

Some Devonian magmatic rocks have been identified from the northern margin of the North China Block (NCB) in recent years. However, their petrogenesis and tectonic setting are still highly controversial. Here we present new geochronological, Sr-Nd-Hf isotopic and whole-rock chemical data on several newly identified and previously reported Devonian alkaline complexes, including mafic-ultramafic rocks (pyroxenites and gabbros), alkaline rocks (syenites, monzonites) and alkaline granites in the northern NCB. We firstly identified some mafic-ultramafic rocks coeval with monzonite and quartz monzonite in the Sandaogou and Wulanhada alkaline intrusions. New zircon U-Pb dating of 16 samples from the Baicaigou, Gaojiacun, Sandaogou, Wulanhada and Chifeng alkaline intrusions combined with previous geochronological results indicate that the Devonian alkaline rocks emplaced during the early-middle Devonian at around 400-380 Ma and constitute an E-W-trending alkaline magmatic belt that extend ca. 900 km long along the northern margin of the NCB. Whole-rock geochemical and Sr-Nd-Hf isotopic data reveal that the Devonian alkaline rocks were mainly originated from partial melting of a variably enriched lithospheric mantle with different involvement of ancient lower crustal component and fractional crystallization. The Devonian alkaline magmatic belt rocks in the northern NCB are characterized by very weak or no deformations and were most likely related to post-collision extension after arc-continent collision between the Bainaimiao island arc and the northern margin of North China Craton during the latest Silurian. Partial melting of subcontinental lithospheric mantle to produce the Devonian alkaline magmatic rocks suggests that the northern North China Craton has an inhomogeneous, variably enriched subcontinental lithospheric mantle and was characterized by significant vertical crustal growth during the Devonian period.

Life detection at a Mars analogue site of present-day serpentinization in the Tablelands Ophiolite of Newfoundland (Invited)

NASA Astrophysics Data System (ADS)

Morrill, P. L.; Szponar, N.; Brazelton, W. J.; Woodruff, Q.; Schrenk, M. O.; Bower, D. M.; Steele, A.

2010-12-01

The Tableland Ophiolite was created during the collision of Laurentia and Gondwana continents ca. 470 million years ago. Ultramafic mantle rocks, from the ancient sea bed that once separated these continents, were thrusted westward onto the old continental margin, which is now Western Newfoundland. Weathering due to recent glaciations has left large areas of ultramafic rock at the surface and created fissures for fluid flow. As a result serpentinization is occurring as fresh water penetrates the unaltered ultramafic rock. Serpentinization is of particular interest because, through hydration of ultramafic rock, this reaction produces H2 and the reducing conditions necessary for abiogenic hydrocarbon synthesis, while also producing conditions amenable for chemolithotrophic life. Therefore sites of active serpentinization can be the source of either abiogenic or biogenic organics, or both. Serpentinization is a suspected (past or present) source of (detected or putative) hydrocarbons on Mars, Titan and Europa, hence these astrobodies may be potentially habitable or once habitable environments. The Tablelands Ophiolite is an analogue site that is ideal for testing methods of life detection in an extreme environment of high pH and low microbial biomass characteristic of sites of serpentinization. Multiple ultrabasic reducing springs characteristic of present-day serpentinization have been identified and characterized based on their geochemistry and microbiology. Field-based instruments were deployed for the detection of microbial activity (ATP), microbial cell wall material, and mineralogy, in yet untested high pH and low biomass environment. In this talk I will give an overview of the in situ measurements of life detection and put these measurements in context of geochemistry, microbiology, carbon source and reaction pathways, and I will discuss what we have learned that will help us plan for future mission measurements.

Arrested diatreme development: Standing Rocks East, Hopi Buttes, Navajo Nation, USA

NASA Astrophysics Data System (ADS)

Lefebvre, Nathalie S.; White, James D. L.; Kjarsgaard, Bruce A.

2016-01-01

Maar-diatreme volcanoes, defined by their relatively large pyroclastic debris-filled subsurface structures and craters that cut into the pre-eruptive land surface, are typically found in small-volume mafic to ultramafic monogenetic volcanic fields. Diatremes are associated with strong explosions throughout most of their development, focused along feeder dikes and generally attributed to magma-water interaction, or high magmatic volatiles. Detailed mapping of the magnificently exposed Standing Rocks East (SRE) diatreme shows evidence of additional eruptive complexity, and offers new insights into how the plumbing and vent structures of small-volume volcanoes evolve during an eruption. SRE is part of a larger, basanitic volcanic complex that includes several diatremes formed along a series of irregular, offset NW-SE trending dikes exposed 300 m below the pre-eruptive land surface. Its similarly oriented elliptical-shaped diatreme structure comprises predominantly country rock lithic-rich breccia of coarse inhomogeneously mixed wall-rock blocks sourced from above and below the current surface, plus sparse juvenile material. Domains of pyroclastic deposits crosscut the country rock breccia deposits, and the best exposed is the NW massif rising 35 m above the current erosional surface. It represents a cross-section of an evolving crater floor, and comprises matrix-rich lapilli tuff and spatter deposits cut by irregularly distributed dikes, some with very complex textures. The most significant deposit, in terms of volume, is an unbedded lapilli tuff that is poorly sorted and has a well-mixed population of wall-rock and juvenile clast varieties, thus resembling deposits typical of diatremes. It is overlain by and locally intercalated with spatter deposits, and this irregular contact demarcates the base of what was during eruption an uneven, evolving crater floor. The generally massive, variably welded spatter deposits constitute mostly lapilli-sized juvenile clasts with

Water-Rock Interactions in the Peridotite Aquifer of the Oman-UAE Ophiolite: Strontium Isotopic Ratio and Geochemical Evolution of Groundwater

NASA Astrophysics Data System (ADS)

Bompard, Nicolas; Matter, Juerg; Teagle, Damon

2016-04-01

The peridotite aquifer in Wadi Tayin, Sultanate of Oman, is a perfect example of natural carbonation of ultramafic rocks. In situ mineral carbonation is considered the most safest and permanent option of CO2 Capture and Sequestration (CCS). However, the process itself is yet to be characterised and a better understanding of the mechanisms involved in natural mineral carbonation is needed before geo-engineering it. We used the 87Sr/86Sr system to follow the water-rock interactions along the groundwater flowpath in the peridotite aquifer and to determine the sources of divalent cations (Mg2+, Ca2+) required for mineral carbonation. The Sr-isotope data of groundwater show that the aquifer rocks are the main source for divalent cations (Mg2+, Ca2+ and Sr2+) and secondary carbonates are their main sink. The groundwater 87Sr/86Sr ratio evolves with its pH: from 87Sr/86Sr = 0.7087 (n=3) to 0.7082 (n=8) between pH 7 and 8, and from 0.7086 (n=6) at pH 9 to 0.07075 (n=9) at pH 11. This evolution seems to support a two-step model for the water-rock interactions in the peridotite aquifer. From pH 7 to 8, secondary Ca-carbonate precipitation buffers the pH rise resulting from peridotite serpentinisation. From pH 9 to 11, peridotite serpentinisation drives the pH to alkaline condition. The change from a Mg-rich to a Ca-rich groundwater at pH 9 seems to confirm the two-step model.

Origin of ultramafic-hosted magnesite on Margarita Island, Venezuela

NASA Astrophysics Data System (ADS)

Abu-Jaber, N. S.; Kimberley, M. M.

1992-06-01

Ultramafic-hosted deposits of magnesite (MgCO3) have been studied on Margarita Island, Venezuela, to elucidate the source of carbon and conditions of formation for this type of ore. Petrographic, mineralogic, and δ18O data indicate that magnesite precipitated on Margarita in near-surface environments at low P and T. δ13C ranges from -9 to -16‰ PDB within the magnesite and -8 to -10‰ PDB within some calcite and dolomite elsewhere on the island. The isotopically light dolomite fills karst and the calcite occurs as stock-work veins which resemble the magnesite deposits. These carbon isotopic ratios are consistent with a deep-seated source rather than an overlying source from a zone of surficial weathering. However, there is not much enrichment of precious metals and no enrichment of heavy rare-earth elements, as would be expected if the carbon had migrated upward as aqueous carbonate ions. The carbon probably has risen as a gaseous mixture of CO2 and CH4 which partially dissolved in near-surface water before leaching cations and precipitating as magnesite and other carbonates. The process probably is ongoing, given regional exhalation of carbonaceous gases.

Asteroidal Differentiation Processes Deduced from Ultramafic Achondrite Ureilite Meteorites

NASA Technical Reports Server (NTRS)

Downes, Hilary; Mittlefehldt, David W.; Hudson, Pierre; Romanek, Christopher S.; Franchi, Ian

2006-01-01

Ureilites are the second largest achondrite group. They are ultramafic achondrites that have experienced igneous processing whilst retaining some degree of nebula-derived chemical heterogeneity. They differ from other achondrites in that they contain abundant carbon and their oxygen isotope compositions are very heterogeneous and similar to those of the carbonaceous chondrite anhydrous mineral line. Their carbonaceous nature and some compositional characteristics indicative of nebular origin suggest that they are primitive materials that form a link between nebular processes and early periods of planetesimal accretion. However, despite numerous studies, the exact origin of ureilites remains unclear. Current opinion is that they represent the residual mantle of an asteroid that underwent silicate and Fe-Ni-S partial melting and melt removal. Recent studies of short-lived chronometers indicate that the parent asteroid of the ureilites differentiated very early in the history of the Solar System. Therefore, they contain important information about processes that formed small rocky planetesimals in the early Solar System. In effect, they form a bridge between nebula processes and differentiation in small planetesimals prior to accretion into larger planets and so a correct interpretation of ureilite petrogenesis is essential for understanding this critical step.

Rock Music's Place in the Library.

ERIC Educational Resources Information Center

Politis, John

1983-01-01

Discussion of the importance of rock music as an expression of aural culture includes its history, rock music today, and the development of a rock music collection in the library (placement of collection and books which aid in developing a collection of permanent value). Three references are included. (EJS)

Very early Archean crustal-accretion complexes preserved in the North Atlantic craton

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

Nutman, A.P.; Collerson, K.D.

1991-08-01

The North Atlantic craton contains very early Archean supracrustal rocks, orthogneisses, and massive ultramafic rocks. Most units of supracrustal rocks are dominated by mafic volcanic rocks, layered gabbros, and banded iron formations, bust some also contain abundant felsic volcanic-sedimentary rocks, quartzites, and marbles. Some quartzites contain detrital zircons derived from rocks identical in age to felsic volcanic-sedimentary rocks in these sequences (ca. 3800 Ma) and also from older (ca. 3850 Ma) sources. The presence of the ca. 3850 Ma detrital zircons suggests that the supracrustal units containing them were deposited on, or close to, ca. 3850 Ma sialic crust. Themore » massive ultramafic rocks have chemical affinities to upper mantle rocks. The voluminous suites of tonalitic gneisses are dominated by 3700-3730 Ma bodies that intrude the supracrustal sequences, but they also locally contain components with ages between 3820 and 3920 Ma. The diverse supracrustal units, upper mantle rocks, and {ge} 3820 Ma components in the gneisses were tectonically interleaved in very early Archean convergent plate boundaries, giving rise to accretion complexes. In the period 3700-3730 Ma, voluminous tonalitic magmas produced by partial melting of predominantly mafic rocks in the base of the accretion complexes were emplaced at higher levels, forming juvenile continental crust and leaving behind a refractory lower crustal to upper mantle substrate.« less

Effects of mother lode-type gold mineralization on 187Os/188Os and platinum group element concentrations in peridotite: Alleghany District, California

USGS Publications Warehouse

Walker, R.J.; Böhlke, J.K.; McDonough, W.F.; Li, Ji

2007-01-01

Osmium isotope compositions and concentrations of Re, platinum group elements (PGE), and Au were determined for host peridotites (serpentinites and barzburgites) and hydrothermally altered ultramafic wall rocks associated with Mother Lode-type hydrothermal gold-quartz vein mineralization in the Alleghany district, California. The host peridotites have Os isotope compositions and Re, PGE, and Au abundances typical of the upper mantle at their presumed formation age during the late Proterozoic or early Paleozoic. The hydrothermally altered rocks have highly variable initial Os isotope compositions with ??os, values (% deviation of 187OS/188OS from the chondritic average calculated for the approx. 120 Ma time of mineralization) ranging from -1.4 to -8.3. The lowest Os isotope compositions are consistent with Re depletion of a chondritic source (e.g., the upper mantle) at ca. 1.6 Ga. Most of the altered samples are enriched in Au and have depleted and fractionated abundances of Re and PGE relative to their precursor peridotites. Geoehemical characteristics of the altered samples suggest that Re and some PGE were variably removed from the ultramafic rocks during the mineralization event. In addition to Re, the Pt and Pd abundances of the most intensely altered rocks appear to have been most affected by mineralization. The 187Os-depleted isotopic compositions of some altered rocks are interpreted to be a result of preferential 187Os loss via destruction of Re-rich phases during the event. For these rocks, Os evidently is not a useful tracer of the mineralizing fluids. The results do, however, provide evidence for differential mobility of these elements, and mobility of 187Os relative to the initial bulk Os isotope composition during hydrothermal metasomatic alteration of ultramafic rocks. ?? 2007 Society of Economic Geologists, Inc.

Characterization of Possible Carbonatites in Southeast Missouri

NASA Astrophysics Data System (ADS)

Shavers, E. J.; Wulamu, A.; Encarnacion, J. P.; Luetkemeyer, P. B.

2014-12-01

Carbonatite is an igneous rock containing greater than 50% carbonate minerals. These rocks are the most common host of REE mineralization and may contain other economic deposits such as uranium, fluorine and niobium. Several researchers have mentioned the presence of a carbonatite phase interspersed among the olivine melilitite-alnöite dikes and diatremes of southeast Missouri, yet a comprehensive validation of this occurrence has, so far, remained elusive. Here we present petrographic, cathodoluminescence, stable isotope and Vis-NIR analysis which support the presence of a carbonatite magma. We identify apparently single generation calcite groundmass surrounding country rock xenoliths and olivine-cored mafic spheroids altered to carbonate and opaque minerals. We present stable isotope data for twenty samples of intrusive and country rock from across the study area. δ18O values for all rock types exhibit little variation with values between 21.9 ‰ and 28.1 ‰ (VSMOW), possibly the result of outgassing during emplacement. Measured δ13C values of (1) carbonate country rocks are between -0.1 ‰ and -2.9 ‰ (VPDB), (2) ultramafic and carbonate-rich mafic rocks range from -3.0 ‰ to -4.6 ‰ (VPDB) and (3) carbonate-rich rocks with volcanic textures, as well as carbonate veins within mafic rocks, fall between -5.4 ‰ to -8.2 ‰ (VPDB). We suggest that this data and initial petrographic observations indicate (1) limited fluid-rock interaction as the host rock clasts have retained their original isotopic signature, (2) an initial ultramafic phase enriched in 13C by a small amount of sedimentary rock due to low initial C content, (3) mantle sourced carbonate fluids entraining fragments of the ultramafic phase and xenoliths. However, future electron microprobe studies may allow us to further constrain the causes for the observed isotopic shifts. We compare laboratory reflectance measurements of a dolomitic intrusive and adjacent dolomite country rock. Absorption

Transformation of Serpentinite to Listvenite as Recorded in the Vein History of Rocks From Oman Drilling Project Hole BT1B

NASA Astrophysics Data System (ADS)

Manning, C. E.; Kelemen, P. B.; Michibayashi, K.; Harris, M.; Urai, J. L.; de Obeso, J. C.; Jesus, A. P. M.; Zeko, D.

2017-12-01

Oman Drilling Project Hole BT1B intersected 191 m of listvenite (magnesite + quartz rock) and serpentinite in the hanging wall of the basal thrust of the Oman ophiolite. Recovery was 100%. Listvenite is the dominant lithology in the upper plate rocks (166 m). Its shows wide color and textural variation, including pseudomorphic replacement of serpentinized peridotite. Serpentinite was encountered in two main contiguous intervals totaling 25 m. In light of the strongly metasomatic nature for the origin of listvenite, a substantial portion of the core description effort was dedicated to characterization of the complex veining history recorded in the hole. Dense veining is recorded in both lithologies. The density of <1 mm veins is >200/m. The density of veins >1 mm was 50-100/m, with somewhat higher densities recorded in serpentinite than in listvenite. In order of oldest to youngest, the main vein types in serpentinite are microscopic mesh-textured serpentine veins, macroscopic serpentine veins, carbonate-oxide veins, and carbonate veins. The vein paragenesis in listvenite is: early carbonate-oxide veins, followed by carbonate and carbonate-quartz veins, then late carbonate veins. The carbonate-oxide and carbonate veins are shared by the lithologies and hold clues to the transformation of ultramafic rocks to listvenite. Carbonate-oxide veins form a distinctive set that is interpreted to be the earliest record of carbonate formation in serpentinite. They contain Fe-oxide, usually hematite, on a medial line, with antitaxial magnesite crystals growing outward and showing terminations against wall rock minerals. Antitaxial textures may be evidence of positive reaction volumes. In serpentinite, secondary serpentine after earlier serpentine is common at vein margins. Carbonate-oxide veins are the earliest observed in listvenite, where they may form isolated veins to dense, aligned networks that impart a foliated texture. In some cases, they appear to predate replacement of

Scattering from Rock and Rock Outcrops

DTIC Science & Technology

2015-09-30

Scattering from Rock and Rock Outcrops Derek R. Olson The Pennsylvania State University Applied Research Laboratory, P.O. Box 30 State...In terms of target detection and classification, scattering from exposed rock on the seafloor, (i.e., individual rocks and rock outcrops) presents...levels, and other statistical measures of acoustic scattering from rocks and rock outcrops is therefore critical. Unfortunately (and curiously

On the original igneous source of Martian fines

NASA Technical Reports Server (NTRS)

Baird, A. K.; Clark, B. C.

1981-01-01

The composition of the silicate portion of Martian regolith fines indicates derivation of the fines from mafic to ultramafic rocks, probably rich in pyroxene. Rock types similar in chemical and mineralogical composition include terrestrial Archean basalts and certain achondrite meteorites. If these igneous rocks weathered nearly isochemically, the nontronitic clays proposed earlier as an analog to Martian fines could be formed. Flood basalts of pyroxenitic lavas may be widespread and characteristic of early volcanism on Mars, analogous to maria flood basalts on the moon and early Precambrian basaltic komatiites on earth. Compositional differences between lunar, terrestrial, and Martian flood basalts may be related to differences in planetary sizes and mantle compositions of the respective planetary objects.

Estimation of continental Os/Os values by using Os/Os and Nd/Nd ratios in marine manganese nodules.

PubMed

Turekian, K K; Luck, J M

1984-12-01

The relationship between (187)Os/(186)Os and (143)Nd/(144)Nd in different manganese nodule fields is used to determine the (187)Os/(186)Os ratio of the continental terrains bounding the major ocean basins. The Atlantic Ocean drainages yield (187)Os/(186)Os of about 11; the Pacific Ocean, between 25 and 36; and the western Indian Ocean, 20. By assuming a two-component continental crust composed of "ultramafic rocks" (high Os concentration, low (187)Os/(186)Os) and "granite" with only radiogenic (187)Os produced in accessory Re-bearing molybdenite, the ultramafic contribution to weathering is about 0.2%. Some or most of this may come from the alteration of oceanic ultramafics.

Petrology and geochemistry of lithic fragments separated from the Apollo 15 deep-drill core

NASA Technical Reports Server (NTRS)

Lindstrom, M. M.; Nielsen, R. L.; Drake, M. J.

1977-01-01

Petrological and geochemical analysis of lithic fragments separated from the Apollo 15 deep-drill core showed these fragments to fall into the essentially the same range of rock types as observed in surface soil samples and large rock samples. Three particles are singled out as being of special interest. One sample is a mare basalt containing extremely evolved phases. The particle may represent small-scale imperfect crystal/liquid separation in a lava flow. A green glass particle is not the ultramafic emerald green glass described from the Apollo 15 site, but rather an ANT-like light green color, and has a quite different chemical composition from the ultramafic variety. One mare basalt displays a positive Eu anomaly and is enriched in plagioclase relative to olivine plus pyroxene.

Laboratory investigations of the effects of nitrification-induced acidification on Cr cycling in vadose zone material partially derived from ultramafic rocks

USGS Publications Warehouse

Mills, Christopher T.; Goldhaber, Martin B.

2012-01-01

Sacramento Valley (California, USA) soils and sediments have high concentrations of Cr(III) because they are partially derived from ultramafic material. Some Cr(III) is oxidized to more toxic and mobile Cr(VI) by soil Mn oxides. Valley soils typically have neutral to alkaline pH at which Cr(III) is highly immobile. Much of the valley is under cultivation and is both fertilized and irrigated. A series of laboratory incubation experiments were conducted to assess how cultivation might impact Cr cycling in shallow vadose zone material from the valley. The first experiments employed low (7.1 mmol N per kg soil) and high (35 mmol N kg− 1) concentrations of applied (NH4)2SO4. Initially, Cr(VI) concentrations were up to 45 and 60% greater than controls in low and high incubations, respectively. After microbially-mediated oxidation of all NH4+, Cr(VI) concentrations dropped below control values. Increased nitrifying bacterial populations (estimated by measurement of phospholipid fatty acids) may have increased the Cr(VI) reduction capacity of the vadose zone material resulting in the observed decreases in Cr(VI). Another series of incubations employed vadose zone material from a different location to which low (45 meq kg− 1) and high (128 meq kg− 1) amounts of NH4Cl, KCl, and CaCl2 were applied. All treatments, except high concentration KCl, resulted in mean soil Cr(VI) concentrations that were greater than the control. High concentrations of water-leachable Ba2 + (mean 38 μmol kg− 1) in this treatment may have limited Cr(VI) solubility. A final set of incubations were amended with low (7.1 mmol N kg− 1) and high (35 mmol N kg− 1) concentrations of commercial liquid ammonium polyphosphate (APP) fertilizer which contained high concentrations of Cr(III). Soil Cr(VI) in the low APP incubations increased to a concentration of 1.8 μmol kg− 1 (5 × control) over 109 days suggesting that Cr(III) added with the APP fertilizer was more

Petrology and Rock Magnetism of the peridotites of Pindos Ophiolite (Greece), insights into the serpentinization process

NASA Astrophysics Data System (ADS)

Bonnemains, D.; Carlut, J. H.; Mevel, C.; Andreani, M.; Escartin, J.; Debret, B.

2015-12-01

We present a petrological and magnetic study of a suite of serpentinized peridotites from the Pindos ophiolite spanning a wide range in the degree of serpentinization (from ~10 to 100%). The Pindos ophiolite, in Northern Greece, is a portion of Late Triassic oceanic lithosphere obducted during the convergence of the Apulian and Pelagonian micro-continents. This ophiolite is interpreted mainly as the result of a supra-subduction zone spreading process but its complete history remains largely unknown. Therefore, it is not clear when the ultramafic section was exposed to fluid circulation that resulted in its serpentinization. Element partitioning during serpentinization reactions is dependent on parameters such as temperature and water-rock ratio. In particular, they affect the behavior of the iron released by olivine, which can be taken up either by magnetite, serpentine and/or brucite. Analyses of the reaction products are therefore a key to constrain the conditions during the main stage of the alteration. Our study was designed to gain insight on the conditions prevailing during hydration. Our results indicate that even fully serpentinized samples have a very low magnetization and magnetite content. Moreover, microprobe and μXanes results show that serpentine is the main host of iron in the divalent but also trivalent form. These results are compared with a set of data from serpentinized ultramafics sampled from the ocean floors, as well as from various other ophiolites. We suggest that serpentinization at Pindos occurred at relatively low-temperature (less than 200 °C), therefore not at a ridge environment. In addition, we stress that the presence of trivalent iron in serpentine indicates that serpentinization may remain a producer of hydrogen even when very little magnetite is formed.

Anomalously low strength of serpentinite sheared against granite and implications for creep on the Hayward and Calaveras Faults

USGS Publications Warehouse

Moore, Diane E.; Lockner, David A.; Ponce, David A.

2010-01-01

Serpentinized ophiolitic rocks are juxtaposed against quartzofeldspathic rocks at depth across considerable portions of the Hayward and Calaveras Faults. The marked compositional contrast between these rock types may contribute to fault creep that has been observed along these faults. To investigate this possibility, we are conducting hydrothermal shearing experiments to look for changes in frictional properties resulting from the shear of ultramafic rock juxtaposed against quartzose rock units. In this paper we report the first results in this effort: shear of bare-rock surfaces of serpentinite and granite, and shear of antigorite-serpentinite gouge between forcing blocks of granitic rock. All experiments were conducted at 250°C. Serpentinite sheared against granite at 50 MPa pore-fluid pressure is weaker than either rock type separately, and the weakening is significantly more pronounced at lower shearing rates. In contrast, serpentinite gouge sheared dry between granite blocks is as strong as the bare granite surface. We propose that the weakening is the result of a solution-transfer process involving the dissolution of serpentine minerals at grain-to-grain contacts. Dissolution of serpentine is enhanced by modifications to pore-fluid chemistry caused by interaction of the fluid with the quartz-bearing rocks. The compositional differences between serpentinized ultramafic rocks of the Coast Range Ophiolite and quartzofeldspathic rock units such as those of the Franciscan Complex may provide the mechanism for aseismic slip (creep) in the shallow crust along the Hayward, Calaveras, and other creeping faults in central and northern California.

The Resurrection Peninsula ophiolite

USGS Publications Warehouse

Nelson, Steven W.; Miller, M.L.; Dumoulin, Julie A.; Nelson, Steven W.; Hamilton, Thomas D.

1989-01-01

The Resurrection Peninsula forms the east side of Resurrection Bay (fig. 3). Relief ranges from 437 m (1,434 ft) at the southern end of the peninsula to more than 1,463 m (4,800 ft) opposite the head of the bay. All rock units composing the informally named Resurrection Peninsula ophiolite of Nelson and others (1987) are visible or accessible by boat."Ophiolite" has been a geologic term since 1827 (Coleman, 1977). The term "ophiolite" initially referred to the rock serpentinite; the Greek root "ophi" (meaning snake or serpent) alluded to the greenish, mottled, and shiny appearance of serpentinites. In 1927, Steinmann described a rock association in the Alps, sometimes known as the "Steinmann Trinity', consisting of serpentine, diabase and spilitic lavas, and chert. Recognition of this suite led to the idea that ophiolites represent submarine magmatism that took place early in the development of a eugeosyncline. In the early 1970s the Steinmann Trinity was reconsidered in light of the plate tectonic theory, new petrologic studies, and the recognition of abducted oceanic lithosphere in orogenic belts of the world. In 1972 at a Geological Society of America Penrose Conference (Anonymous, 1972) the term "ophiolite" was defined as a distinctive assemblage of mafic to ultramafic rocks, with no emphasis on their origin. A complete ophiolite should contain, from bottom to top:1) Tectonized ultramafic rocks (more or less serpentinized)2) Gabbro complex containing cumulus textures and commonly cumulus peridotites3) Mafic sheeted-dike complex, grading upward into;4) Submarine pillow lavas of basaltic composition. Common associated rock types include plagiogranite (Na-rich) and an overlying sedimentary section typically dominated by chert.

Provenance and composition of unusually chrome and nickel-rich bucket-shaped pottery from Rogaland (southwestern Norway)

NASA Astrophysics Data System (ADS)

Zimmermann, Udo; Kristoffersen, Elna Siv; Fredriksen, Per Ditlef; Bertolino, Silvana A. R.; Andò, Sergio; Bersani, Danilo

2016-05-01

We report results from FE-SEM-EDS, geochemical, mineralogical analyses and Raman spectroscopy of pottery of bucket-shaped ceramic from Rogaland (southwestern Norway) dated between the 5th and 6th Century. The study reveals a very rare pottery composition including asbestos-group minerals and an unusual enrichment in compatible elements like Cr (8-27 × Post Archean average shale (PAS), McLennan et al., 2006), Ni (2-8 × normal shale) and Co (2-3 × PAS). X-Rray diffraction and Raman spectroscopy could pinpoint that Ni is introduced by specific Ni-rich talc mineral and chlorite minerals and Cr occurs in a rare Cr-rich talc, and possibly in a Cr-chlorite, these minerals are the most abundant in the pottery, which is supported by strong enrichment in Mg (10-20 × PAS). The addition of Mg, Cr, Ni and Co and other compatible trace elements is to our current knowledge not caused by anthropogenic activity but related to the used materials, which are alteration products of mafic and ultramafic rocks or genetically related to mafic and ultramafic rocks. Rocks of this type are exposed in vicinity of the sampling areas in a region called Karmøy, hosting a world famous ophiolite complex, which is identified as the major source for the mafic and ultramafic component, as the next succession of a similar composition is far further north located in Norway and a number of rock types on Karmøy matches the chemical composition of the pottery. The here reported composition is spectacular and extremely rare - if ever found - in pottery. Our study shows that unusual material sources have been used in pottery production, and this opens for discussion whether the materials were deliberately selected by the manufacturers, thereby expressing a specific social function, in a time period where more functional clay types and additives, and certainly functional and sufficient for use in pottery, where abundant in areas of Rogaland closer to where the pots were found.

Genetic relationship between deformation and low-Ca content in olivine from magmatic systems: evidence from the Poyi ultramafic intrusion, NW China

NASA Astrophysics Data System (ADS)

Yao, Zhuo-sen; Qin, Ke-zhang; Xue, Sheng-chao

2017-12-01

The deformation features (e.g., undulose extinction and subgrain boundaries) and low Ca content (<1000 ppm) of high-Fo olivine have been widely used as indictors for the mantle origin of olivine in the past. However, grains with these characteristics are also found in some crustal intrusions, e.g., Duke Island and Bushveld complexes. Here, we study this type of olivine in the Poyi ultramafic intrusion, NW China, to trace the formation of these unusual features in magmatic systems. As a result of the possible Ca-depleted parental melt and low Ca olivine/melt partition coefficient, olivine from the Poyi intrusion is extremely depleted in Ca. On the other hand, it has been confirmed that trace elements with large ionic radii (e.g., Ca2+ and Al3+) are chemically segregated at the grain boundary of olivine, exerting a dragging influence on grain boundary processes (named as solute drag effect). In this regard, the low Ca content in olivine weakens the solute drag effect, and in doing so it enhances the rate and strength of grain deformation, which occurs to accommodate the stress derived by fast compaction of the crystal mush in Poyi intrusion. Therefore, there is a genetic relationship between the plastic deformation and low Ca content in olivines from magmatic cumulates, and this link is one of the reasons causing the widespread deformation observed in Ca-depleted olivine from Poyi and other intrusions. What is more important, this work fills the gaps in the interpretation of this type of olivine in volcanic rocks.

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.

Geology and mineral deposits of the Hekimhan-Hasancelebi iron district, Turkey

USGS Publications Warehouse

Jacobson, Herbert S.; Kendiro'glu, Zeki; ,; Celil, Bogaz; ,; Onder, Osman; Gurel, Nafis

1972-01-01

An area of 210 sq km was investigated in the Hekimhan-Hasancelebi district. of central Turkey as part of the Maden Tetkik ve Arama Institusu(MTA)-U. S. Geological Survey(USGS) mineral exploration and training project to explore for iron deposits and to provide on-.the-job training for MTA geologists. The rocks of the area are Cretaceous and Tertiary sedimentary and volcanic rocks intruded by syenite and a serpentinized mafic and ultramafic complex and overlain unconformably by late .Tertiary basalt. The base of the section is a thick mafic volcanic-sedimentary sequence with diverse rocks that include conglomerate, sandstone, shale, tuff, limestone, and basalt. The upper part of the sequence is metasomatized near syenite contacts. The sequence is conformably overlain by trachyte and unconformably overlain by massive limestone. Overlying the limestone is a Tertiary sedimentary sequence which is dominantly conglomerate and sandstone with local limestone and volcanic rocks. This series is in turn overlain by olivine basalt. Mineral deposits are associated with the two types of intrusive rocks. Hematite-magnetite in the Karakuz mine area and in the Bahcedami-Hasancelebi area is related to the syenite, and siderite in the Deveci mine area is possibly related to the mafic-ultramafic rocks. Significant iron resources are found, only in the Karakuz and Deveci areas. In the Karakuz area disseminations, veins, and replacements consisting of hematite and magnetite are present. Most of the material is low grade. In the Deveci mine area a large deposit of siderite apparently is a replacement of carbonate beds adjacent to serpentinized igneous rock. The upper part of the siderite deposit is weathered and enriched to a mixture of iron and manganese oxides of direct shipping ore grade. Additional investigation of both the Karakuz and .Deveci mine areas is recommended including: 1. A detailed gravity and magnetic survey of part of the Karakuz area. 2. Diamond drilling at both the

Metallogeny of the nikolai large igneous province (LIP) in southern alaska and its influence on the mineral potential of the talkeetna mountains

USGS Publications Warehouse

Schmidt, J.M.; Rogers, R.K.

2007-01-01

Recent geologic mapping has identified areas of extrusive basalts of the Middle to Late Triassic Nikolai Greenstone within the Wrangellia terrane that extend at least 80 km southwest of their previously known extent. Abundant dolerite sills of similar composition intrude Paleozoic and Mesozoic stratigraphy below the Nikolai throughout the central Talkeetna Mountains. The Talkeetna Mountains, therefore, have newly identified potential for copper, nickel, and platinum-group elements (PGEs) as disseminated, net-textured, or massive magmatic sulfide deposits hosted in mafic and ultramafic sill-form complexes related to emplacement of the Nikolai. Because of their potential high grades, similar magmatic sulfide targets have been the focus of increasing mineral exploration activity over the last decade in the Amphitheater Mountains and central Alaska Range, 100-200 km to the northeast. The Nikolai Greenstone, associated intrusions, and their metamorphosed equivalents also have potential to host stratabound disseminated "basaltic copper" deposits. Sedimentary and metasedimentary rocks overlying the Nikolai have the potential to host stratabound, disseminated, or massive "reduced-facies" type Cu-Ag deposits. Ultramafic rocks have been identified only in the extreme northeastern Talkeetna Mountains to date. However, coincident gravity and magnetic highs along the leading (northwestern) edge of and within Wrangellia in the Talkeetna and Clearwater Mountains suggest several areas that are highly prospective for ultramafic rocks related to extrusion of Nikolai lavas. In particular, the distribution, geometry, and composition of sills within the pre-Nikolai stratigraphy and the structural and tectonic controls on intrusive versus extrusive rock distribution deserve serious examination. Copyright ?? 2007 The Geological Society of America.

Silica-undersaturated reaction zones at a crust-mantle interface in the Highland Complex, Sri Lanka: Mass transfer and melt infiltration during high-temperature metasomatism

NASA Astrophysics Data System (ADS)

Fernando, G. W. A. R.; Dharmapriya, P. L.; Baumgartner, Lukas P.

2017-07-01

Sri Lanka is a crucial Gondwana fragment mostly composed of granulitic rocks in the Highland Complex surrounded by rocks with granulite to amphibolite grade in the Vijayan and Wanni Complex that were structurally juxtaposed during Pan-African orogeny. Fluids associated with granulite-facies metamorphism are thought to have controlled various lower crustal processes such as dehydration/hydration reactions, partial melting, and high-temperature metasomatism. Chemical disequilibrium in the hybrid contact zone between a near peak post-tectonic ultramafic enclave and siliceous granulitic gneiss at Rupaha within the Highland Complex produced metasomatic reaction zones under the presence of melt. Different reaction zones observed in the contact zone show the mineral assemblages phlogopite + spinel + sapphirine (zone A), spinel + sapphirine + corundum (zone B), corundum ( 30%) + biotite + plagioclase zone (zone C) and plagioclase + biotite + corundum ( 5%) zone (zone D). Chemical potential diagrams and mass balance reveal that the addition of Mg from ultramafic rocks and removal of Si from siliceous granulitic gneiss gave rise to residual enrichment of Al in the metasomatized mineral assemblages. We propose that contact metasomatism between the two units, promoted by melt influx, caused steady state diffusional transport across the profile. Corundum growth was promoted by the strong residual Al enrichment and Si depletion in reaction zone whereas sapphirine may have been formed under high Mg activity near the ultramafic rocks. Modelling also indicated that metasomatic alteration occurred at ca. 850 °C at 9 kbar, which is consistent with post-peak metamorphic conditions reached during the initial stage of exhumation in the lower crust and with temperature calculations based on conventional geothermometry.

Field and petrological study of metasomatism and high-pressure carbonation from lawsonite eclogite-facies terrains, Alpine Corsica

NASA Astrophysics Data System (ADS)

Piccoli, Francesca; Vitale Brovarone, Alberto; Ague, Jay J.

2018-04-01

This study presents new field and petrological data on carbonated metasomatic rocks from the lawsonite-eclogite units of Alpine Corsica. These rocks form along major, slab-scale lithological boundaries of the subducted Alpine Tethys plate. Our results indicate that a large variety of rocks ranging from metamafic/ultramafic to metafelsic can react with carbon-bearing fluids, leading to carbon sequestration at high-pressure conditions. The process of carbonation includes both replacement of silicates by high-pressure carbonate, and carbonate veining. The field, microstructural and mineralogical data strongly suggest that the metasomatism was mediated by the infiltration of external fluids of mixed origin, including both mafic/ultramafic and metasedimentary sources. Our results support the following three-step evolution: (i) Release of aqueous fluids by lawsonite and/or antigorite breakdown at depth; (ii) Fluid channelization along the base of the metasedimentary pile of the subducted lithospheric plate and related reactive fluid flow leading to carbonate mineral dissolution; (iii) Further interactions of the resulting carbon-bearing fluids with slab-forming rocks at depths of ca. 70 km and carbonation of pre-existing silicate-rich lithologies. This study highlights the importance of carbonate-bearing fluids evolving along down-T, down-P paths, such as along slab-parallel lithological boundaries, for the sequestration of carbon in subduction zones, and suggests that similar processes may also operate in collisional settings. Fig. S2: Petrogenetic grid in the CaFMASH+CO2 system for the antigorite and clinopyroxene carbonation reactions, together with grossular forming reaction during decarbonation. Reactions are written with the high T assemblage to the right of the = sign.

Nickel-tolerant ectomycorrhizal Pisolithus albus ultramafic ecotype isolated from nickel mines in New Caledonia strongly enhance growth of the host plant Eucalyptus globulus at toxic nickel concentrations.

PubMed

Jourand, Philippe; Ducousso, Marc; Reid, Robert; Majorel, Clarisse; Richert, Clément; Riss, Jennifer; Lebrun, Michel

2010-10-01

Ectomycorrhizal (ECM) Pisolithus albus (Cooke & Massee), belonging to the ultramafic ecotype isolated in nickel-rich serpentine soils from New Caledonia (a tropical hotspot of biodiversity) and showing in vitro adaptive nickel tolerance, were inoculated to Eucalyptus globulus Labill used as a Myrtaceae plant-host model to study ectomycorrhizal symbiosis. Plants were then exposed to a nickel (Ni) dose-response experiment with increased Ni treatments up to 60 mg kg( - )(1) soil as extractable Ni content in serpentine soils. Results showed that plants inoculated with ultramafic ECM P. albus were able to tolerate high and toxic concentrations of Ni (up to 60 μg g( - )(1)) while uninoculated controls were not. At the highest Ni concentration tested, root growth was more than 20-fold higher and shoot growth more than 30-fold higher in ECM plants compared with control plants. The improved growth in ECM plants was associated with a 2.4-fold reduction in root Ni concentration but a massive 60-fold reduction in transfer of Ni from root to shoots. In vitro, P. albus strains could withstand high Ni concentrations but accumulated very little Ni in its tissue. The lower Ni uptake by mycorrhizal plants could not be explained by increased release of metal-complexing chelates since these were 5- to 12-fold lower in mycorrhizal plants at high Ni concentrations. It is proposed that the fungal sheath covering the plant roots acts as an effective barrier to limit transfer of Ni from soil into the root tissue. The degree of tolerance conferred by the ultramafic P. albus isolates to growth of the host tree species is considerably greater than previously reported for other ECM. The primary mechanisms underlying this improved growth were identified as reduced Ni uptake into the roots and markedly reduced transfer from root to shoot in mycorrhizal plants. The fact that these positive responses were observed at Ni concentrations commonly observed in serpentinic soils suggests that

Intrusive rocks and plutonic belts of southeastern Alaska, U.S.A.

USGS Publications Warehouse

Brew, David A.; Morrell, Robert P.; Roddick, J.A.

1983-01-01

About 30 percent of the 175,000-km2 area of southeastern Alaska is underlain by intrusive igneous rocks. Compilation of available information on the distribution, composition, and ages of these rocks indicates the presence of six major and six minor plutonic belts. From west to east, the major belts are: the Fairweather-Baranof belt of early to mid-Tertiary granodiorite; the Muir-Chichagof belt of mid-Cretaceous tonalite and granodiorite; the Admiralty-Revillagigedo belt of porphyritic granodiorite, quartz diorite, and diorite of probable Cretaceous age; the Klukwan-Duke belt of concentrically zoned or Alaskan-type ultramafic-mafic plutons of mid-Cretaceous age within the Admiralty-Revillagigedo belt; the Coast Plutonic Complex sill belt of tonalite of unknown, but perhaps mid-Cretaceous, age; and the Coast Plutonic Complex belt I of early to mid-Tertiary granodiorite and quartz monzonite. The minor belts are distributed as follows: the Glacier Bay belt of Cretaceous and(or) Tertiary granodiorite, tonalite, and quartz diorite lies within the Fair-weather-Baranof belt; layered gabbro complexes of inferred mid-Tertiary age lie within and are probably related to the Fairweather-Baranof belt; the Chilkat-Chichagof belt of Jurassic granodiorite and tonalite lies within the Muir-Chichagof belt; the Sitkoh Bay alkaline, the Kendrick Bay pyroxenite to quartz monzonite, and the Annette and Cape Fox trondhjemite plutons, all interpreted to be of Ordovician(?) age, together form the crude southern southeastern Alaska belt within the Muir-Chichagof belt; the Kuiu-Etolin mid-Tertiary belt of volcanic and plutonic rocks extends from the Muir-Chichagof belt eastward into the Admiralty-Revillagigedo belt; and the Behm Canal belt of mid- to late Tertiary granite lies within and next to Coast Plutonic Complex belt II. In addition, scattered mafic-ultramafic bodies occur within the Fairweather-Baranof, Muir-Chichagof, and Coast Plutonic Complex belts I and II. Palinspastic

Juxtaposition of Neoproterozoic units along the Baruda - Tulu Dimtu shear-belt in the East African Orogen of western Ethiopia

USGS Publications Warehouse

Braathen, A.; Grenne, Tor; Selassie, M.G.; Worku, T.

2001-01-01

Amalgamation of East and West Gondwanaland during the Neoproterozoic East African Orogen is recorded by several shear-belts or 'suture zones', some of which are associated with ultramafic and mafic complexes that have been interpreted as ophiolite fragments. The Baruda shear-belt is a major structure of this type that belongs to the N-S trending Barka - Tulu Dimtu zone. The significance of this zone has been studied within a transect in western Ethiopia which covers a variety of metasedimentary and metavolcanic sequences, ultramafic rocks and synkinematic intrusive complexes. All rocks participated in the regional D1 event as reflected in a penetrative steep foliation in supracrustal rocks and marginal parts of the intrusions. Highly strained rocks contain a stretching lineation that plunge to the east. The several-km thick Baruda shear-belt, comprising mylonitic supracrustal and plutonic rocks including mafic-ultramafic mega-lenses, is the most prominent expression of this event. Shear-sense indicators demonstrate top-to-the-west shear. Subsequent D2 deformation is recorded in 2-300 m wide, N-S striking, subvertical shear-zones with subhorizontal stretching lineation relatable to sinistral transcurrent movements. Our data indicate that rock units on either side of the Baruda shear-belt are related, rather than being exotic to each other as implied in suture zone models, since there is no major lithologic or metamorphic difference, geochemical data on metavolcanic rocks and pre-tectonic intrusions suggest a paleotectonic link, and style and extent of deformation is similar across the shear-belt. A tentative model for the transect suggests an arc and back-arc setting which experienced later continental collision and tectonic shortening. The initial setting was that of a shallow marine platform characterised by carbonates and sandstones, which covered extensive areas prior to break-up of a pre-existing supercontinent. Continental convergence is first recorded in high

Magmatic ore deposits in layered intrusions - Descriptive model for reef-type PGE and contact-type Cu-Ni-PGE deposits

USGS Publications Warehouse

Zientek, Michael L.

2012-01-01

Layered, ultramafic to mafic intrusions are uncommon in the geologic record, but host magmatic ore deposits containing most of the world's economic concentrations of platinum-group elements (PGE) (figs. 1 and 2). These deposits are mined primarily for their platinum, palladium, and rhodium contents (table 1). Magmatic ore deposits are derived from accumulations of crystals of metallic oxides, or immiscible sulfide, or oxide liquids that formed during the cooling and crystallization of magma, typically with mafic to ultramafic compositions. "PGE reefs" are stratabound PGE-enriched lode mineralization in mafic to ultramafic layered intrusions. The term "reef" is derived from Australian and South African literature for this style of mineralization and used to refer to (1) the rock layer that is mineralized and has distinctive texture or mineralogy (Naldrett, 2004), or (2) the PGE-enriched sulfide mineralization that occurs within the rock layer. For example, Viljoen (1999) broadly defined the Merensky Reef as "a mineralized zone within or closely associated with an unconformity surface in the ultramafic cumulate at the base of the Merensky Cyclic Unit." In this report, we will use the term PGE reef to refer to the PGE-enriched mineralization, not the host rock layer. Within a layered igneous intrusion, reef-type mineralization is laterally persistent along strike, extending for the length of the intrusion, typically tens to hundreds of kilometers. However, the mineralized interval is thin, generally centimeters to meters thick, relative to the stratigraphic thickness of layers in an intrusion that vary from hundreds to thousands of meters. PGE-enriched sulfide mineralization is also found near the contacts or margins of layered mafic to ultramafic intrusions (Iljina and Lee, 2005). This contact-type mineralization consists of disseminated to massive concentrations of iron-copper-nickel-PGE-enriched sulfide mineral concentrations in zones that can be tens to hundreds

Archaean ultra-depleted komatiites formed by hydrous melting of cratonic mantle.

PubMed

Wilson, A H; Shirey, S B; Carlson, R W

2003-06-19

Komatiites are ultramafic volcanic rocks containing more than 18 per cent MgO (ref. 1) that erupted mainly in the Archaean era (more than 2.5 gigayears ago). Although such compositions occur in later periods of Earth history (for example, the Cretaceous komatiites of Gorgona Island), the more recent examples tend to have lower MgO content than their Archaean equivalents. Komatiites are also characterized by their low incompatible-element content, which is most consistent with their generation by high degrees of partial melting (30-50 per cent). Current models for komatiite genesis include the melting of rock at great depth in plumes of hot, diapirically rising mantle or the melting of relatively shallow mantle rocks at less extreme, but still high, temperatures caused by fluxing with water. Here we report a suite of ultramafic lava flows from the Commondale greenstone belt, in the southern part of the Kaapvaal Craton, which represents a previously unrecognized type of komatiite with exceptionally high forsterite content of its igneous olivines, low TiO(2)/Al(2)O(3) ratio, high silica content, extreme depletion in rare-earth elements and low Re/Os ratio. We suggest a model for their formation in which a garnet-enriched residue left by earlier cratonic volcanism was melted by hydration from a subducting slab.

U-Pb dating of large zircons in low-temperature jadeitite from the Osayama serpentinite melange, southwest Japan: insights into the timing of serpentinization

USGS Publications Warehouse

Tsujimori, T.; Liou, J.G.; Wooden, J.; Miyamoto, T.

2005-01-01

Crystals of zircon up to 3 mm in length occur in jadeitite veins in the Osayama serpentinite mélange, Southwest Japan. The zircon porphyroblasts show pronounced zoning, and are characterized by both low Th/U ratios (0.2-0.8) and low Th and U abundances (Th = 1-81 ppm; U = 6-149 ppm). They contain inclusions of high-pressure minerals, including jadeite and rutile; such an occurrence indicates that the zircon crystallized during subduction-zone metamorphism. Phase equilibria and the existing fluid-inclusion data constrain P-T conditions to P > 1.2 GPa at T > 350°C for formation of the jadeitite. Most U/Pb ages obtained by SHRIMP-RG are concordant, with a weighted mean 206Pb/238U age of 472 ± 8.5 Ma (MSWD = 2.7, n = 25). Because zircon porphyroblasts contain inclusions of high-pressure minerals, the SHRIMP U-Pb age represents the timing of jadeitite formation, i.e., the timing of interaction between alkaline fluid and ultramafic rocks in a subduction zone. Although this dating does not provide a direct time constraint for serpentinization, U-Pb ages of zircon in jadeitite associated with serpentinite result in new insights into the timing of fluid-rock interaction of ultramafic rocks at a subduction zone and the minimum age for serpentinization.

Can ectomycorrhizal symbiosis and belowground plant traits be used as ecological tools to mitigate erosion on degraded slopes in the ultramafic soils of New Caledonia?

NASA Astrophysics Data System (ADS)

Demenois, Julien; Carriconde, Fabian; Rey, Freddy; Stokes, Alexia

2015-04-01

New Caledonia is an archipelago in the South West Pacific located just above the Tropic of Capricorn. The main island is bisected by a continuous mountain chain whose highest peaks reach more than 1 600 m. With mean annual rainfall above 2 000 mm in the South of the main island, frequent downpours and steep slopes, its soils are prone to water erosion. Deforestation, fires and mining activity are the main drivers of water erosion. Stakes are high to mitigate the phenomenon: extraction of nickel from ultramafic substrates (one third of the whole territory) is the main economic activity; New Caledonia is considered as a biodiversity hotspot. Restoration ecology is seen as a key approach for tackling such environmental challenges. Soil microorganisms could play significant roles in biological processes such as plant nutrition and plant resistance to abiotic and biotic stresses. Microorganisms could increase soil aggregate stability and thus mitigate soil erodibility. Plant roots increase soil cohesion through exudation and decomposition processes. To date, few studies have collected data on the soil aggregate stability of steep slopes affected by erosion and, to our knowledge, interactions between ectomycorrhizas (ECM), roots and erodibility of ultramafic soils have never been considered. The objective of our study is to assess the influence of ECM symbiosis and plant root traits on the erodibility of ultramafic soils of New Caledonia and answer the following questions: 1/ What is the influence of plant root traits of vegetal communities and ECM fungal diversity on soil erodibility? 2/ What are the belowground plant traits of some mycorrhized endemic species used in ecological restoration? 3/ What is the influence of plant root traits and ECM fungal inoculation on soil erodibility? At the scale of plant communities, five types of vegetation have been chosen in the South of the main island: degraded ligno-herbaceous shrubland, ligno-herbaceous shrubland, degraded humid

Ultramafic xenoliths from the Bearpaw Mountains, Montana, USA: Evidence for multiple metasomatic events in the lithospheric mantle beneath the Wyoming craton

USGS Publications Warehouse

Downes, H.; Macdonald, R.; Upton, B.G.J.; Cox, K.G.; Bodinier, J.-L.; Mason, P.R.D.; James, D.; Hill, P.G.; Hearn, B.C.

2004-01-01

Ultramafic xenoliths in Eocene minettes of the Bearpaw Mountains volcanic field (Montana, USA), derived from the lower lithosphere of the Wyoming craton, can be divided based on textural criteria into tectonite and cumulate groups. The tectonites consist of strongly depleted spinel lherzolites, harzbugites and dunites. Although their mineralogical compositions are generally similar to those of spinel peridotites in off-craton settings, some contain pyroxenes and spinels that have unusually low Al2O3 contents more akin to those found in cratonic spinel peridotites. Furthermore, the tectonite peridotites have whole-rock major element compositions that tend to be significantly more depleted than non-cratonic mantle spinel peridotites (high MgO, low CaO, Al2O3 and TiO2) and resemble those of cratonic mantle. These compositions could have been generated by up to 30% partial melting of an undepleted mantle source. Petrographic evidence suggests that the mantle beneath the Wyoming craton was re-enriched in three ways: (1) by silicate melts that formed mica websterite and clinopyroxenite veins; (2) by growth of phlogopite from K-rich hydrous fluids; (3) by interaction with aqueous fluids to form orthopyroxene porphyroblasts and orthopyroxenite veins. In contrast to their depleted major element compositions, the tectonite peridotites are mostly light rare earth element (LREE)-enriched and show enrichment in fluid-mobile elements such as Cs, Rb, U and Pb on mantle-normalized diagrams. Lack of enrichment in high field strength elements (HFSE; e.g. Nb, Ta, Zr and Hf) suggests that the tectonite peridotites have been metasomatized by a subduction-related fluid. Clinopyroxenes from the tectonite peridotites have distinct U-shaped REE patterns with strong LREE enrichment. They have 143Nd/144Nd values that range from 0??5121 (close to the host minette values) to 0??5107, similar to those of xenoliths from the nearby Highwood Mountains. Foliated mica websterites also have low 143Nd

Rho-associated coiled-coil containing kinases (ROCK)

PubMed Central

Julian, Linda; Olson, Michael F

2014-01-01

Rho-associated coiled-coil containing kinases (ROCK) were originally identified as effectors of the RhoA small GTPase.1–5 They belong to the AGC family of serine/threonine kinases6 and play vital roles in facilitating actomyosin cytoskeleton contractility downstream of RhoA and RhoC activation. Since their discovery, ROCK kinases have been extensively studied, unveiling their manifold functions in processes including cell contraction, migration, apoptosis, survival, and proliferation. Two mammalian ROCK homologs have been identified, ROCK1 (also called ROCK I, ROKβ, Rho-kinase β, or p160ROCK) and ROCK2 (also known as ROCK II, ROKα, or Rho kinase), hereafter collectively referred to as ROCK. In this review, we will focus on the structure, regulation, and functions of ROCK. PMID:25010901

Chemistry and mineralogy of garnet pyroxenites from Sabah, Malaysia

USGS Publications Warehouse

Morgan, B.A.

1974-01-01

Garnet pyroxenites and corundum-garnet amphibolites from the Dent peninsula of eastern Sabah (North Borneo) occur as blocks in a slump breccia deposit of late Miocene age. The earliest formed minerals include pyrope-almandine garnet, tschermakitic augite, pargasite, and rutile. Cumulate textures are present in two of the six specimens studied. The earlier fabric has been extensively brecciated and partly replaced by plagioclase, ilmenite, and a fibrous amphibole. The bulk composition and mineralogy of these rocks are similar to those of garnet pyroxenite lenses within ultramafic rocks. Estimated temperature and pressure for the origin of the Sabah garnet pyroxenites is 850??150?? C and 19??4 kbar. ?? 1974 Springer-Verlag.

Automatic Rock Detection and Mapping from HiRISE Imagery

NASA Technical Reports Server (NTRS)

Huertas, Andres; Adams, Douglas S.; Cheng, Yang

2008-01-01

This system includes a C-code software program and a set of MATLAB software tools for statistical analysis and rock distribution mapping. The major functions include rock detection and rock detection validation. The rock detection code has been evolved into a production tool that can be used by engineers and geologists with minor training.

Recording of Supernovae in Rock Art, A Case Study at the Paint Rock Pictograph Site

NASA Astrophysics Data System (ADS)

Houston, Gordon L.; Simonia, Irakli; NA

2017-01-01

The Paint Rock pictographs in central Texas and their use as solar markers were formally reported for the first time by Dr. R. Robert Robbins at the 1999 AAS meeting #193 in Austin, Texas. He reported the operations of the winter solstice marker and suggested the possibility of more, including a summer solstice solar marker. Since this first report, there have been many informal studies of the Paint Rock site. In 1955, William C. Miller made the first interpretation of rock art as depicting images of the Crab supernova of AD 1054, which has produced many reports at other rock art sites in the American Southwest, including one at Paint Rock. All of these claims have a star and crescent configuration. Recently, these claims have been dismissed. We propose that the second panel at Paint Rock is representative of Tycho Brahe's supernovae SN1572. Miller set up a set of restrictions and criteria to evaluate these potential claims. We discuss Miller's criteria and two additional sets of criteria to evaluate representations of historical records of supernovae sightings. Two sets of characteristics of supernovae are provided, the first being galactic location and the second observational characteristics of naked eye supernovae. Employing astronomical software, we show that the panel at Paint Rock meets the restrictions and criteria discussed, that leads to high confidence in stating it records Tycho Brahe's supernova SN1572.

Zapping Rocks on Mars

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

Wiens, Roger

Better understanding Mars means better understanding its geology. That’s why, sitting atop NASA’s Curiosity rover, is ChemCam, an instrument built by Los Alamos National Laboratory that shoots lasers at Martian rocks and analyzes the data. After nearly 1,500 rock zaps, ChemCam has uncovered some surprising facts about the Red Planet, including the discovery of igneous rocks. Soon, a new Los Alamos-built instrument—the SuperCam—will ride aboard the Mars 2020 rover and bring with it enhanced capabilities to unlock new secrets about the planet.

The Production of Methane, Hydrogen, and Organic Compounds in Ultramafic-Hosted Hydrothermal Vents of the Mid-Atlantic Ridge

PubMed Central

Charlou, J.L.; Holm, N.G.; Mousis, O.

2015-01-01

Abstract Both hydrogen and methane are consistently discharged in large quantities in hydrothermal fluids issued from ultramafic-hosted hydrothermal fields discovered along the Mid-Atlantic Ridge. Considering the vast number of these fields discovered or inferred, hydrothermal fluxes represent a significant input of H2 and CH4 to the ocean. Although there are lines of evidence of their abiogenic formation from stable C and H isotope results, laboratory experiments, and thermodynamic data, neither their origin nor the reaction pathways generating these gases have been fully constrained yet. Organic compounds detected in the fluids may also be derived from abiotic reactions. Although thermodynamics are favorable and extensive experimental work has been done on Fischer-Tropsch-type reactions, for instance, nothing is clear yet about their origin and formation mechanism from actual data. Since chemolithotrophic microbial communities commonly colonize hydrothermal vents, biogenic and thermogenic processes are likely to contribute to the production of H2, CH4, and other organic compounds. There seems to be a consensus toward a mixed origin (both sources and processes) that is consistent with the ambiguous nature of the isotopic data. But the question that remains is, to what proportions? More systematic experiments as well as integrated geochemical approaches are needed to disentangle hydrothermal geochemistry. This understanding is of prime importance considering the implications of hydrothermal H2, CH4, and organic compounds for the ocean global budget, global cycles, and the origin of life. Key Words: Hydrogen—Methane—Organics—MAR—Abiotic synthesis—Serpentinization—Ultramafic-hosted hydrothermal vents. Astrobiology 15, 381–399. PMID:25984920

Rock Drilling Performance Evaluation by an Energy Dissipation Based Rock Brittleness Index

NASA Astrophysics Data System (ADS)

Munoz, H.; Taheri, A.; Chanda, E. K.

2016-08-01

To reliably estimate drilling performance both tool-rock interaction laws along with a proper rock brittleness index are required to be implemented. In this study, the performance of a single polycrystalline diamond compact (PDC) cutter cutting and different drilling methods including PDC rotary drilling, roller-cone rotary drilling and percussive drilling were investigated. To investigate drilling performance by rock strength properties, laboratory PDC cutting tests were performed on different rocks to obtain cutting parameters. In addition, results of laboratory and field drilling on different rocks found elsewhere in literature were used. Laboratory and field cutting and drilling test results were coupled with values of a new rock brittleness index proposed herein and developed based on energy dissipation withdrawn from the complete stress-strain curve in uniaxial compression. To quantify cutting and drilling performance, the intrinsic specific energy in rotary-cutting action, i.e. the energy consumed in pure cutting action, and drilling penetration rate values in percussive action were used. The results show that the new energy-based brittleness index successfully describes the performance of different cutting and drilling methods and therefore is relevant to assess drilling performance for engineering applications.

Petrology of the igneous rocks

NASA Technical Reports Server (NTRS)

Mccallum, I. S.

1987-01-01

Papers published during the 1983-1986 period on the petrology and geochemistry of igneous rocks are discussed, with emphasis on tectonic environment. Consideration is given to oceanic rocks, subdivided into divergent margin suites (mid-ocean ridge basalts, ridge-related seamounts, and back-arc basin basalts) and intraplate suites (oceanic island basalts and nonridge seamounts), and to igneous rocks formed at convergent margins (island arc and continental arc suites), subdivided into volcanic associations and plutonic associations. Other rock groups discussed include continental flood basalts, layered mafic intrusions, continental alkalic associations, komatiites, ophiolites, ash-flow tuffs, anorthosites, and mantle xenoliths.

A regional soil and sediment geochemical study in northern California

USGS Publications Warehouse

Goldhaber, M.B.; Morrison, J.M.; Holloway, J.M.; Wanty, R.B.; Helsel, D.R.; Smith, D.B.

2009-01-01

Regional-scale variations in soil geochemistry were investigated in a 20,000-km2 study area in northern California that includes the western slope of the Sierra Nevada, the southern Sacramento Valley and the northern Coast Ranges. Over 1300 archival soil samples collected from the late 1970s to 1980 in El Dorado, Placer, Sutter, Sacramento, Yolo and Solano counties were analyzed for 42 elements by inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry following a near-total dissolution. These data were supplemented by analysis of more than 500 stream-sediment samples from higher elevations in the Sierra Nevada from the same study site. The relatively high-density data (1 sample per 15 km2 for much of the study area) allows the delineation of regional geochemical patterns and the identification of processes that produced these patterns. The geochemical results segregate broadly into distinct element groupings whose distribution reflects the interplay of geologic, hydrologic, geomorphic and anthropogenic factors. One such group includes elements associated with mafic and ultramafic rocks including Cr, Ni, V, Co, Cu and Mg. Using Cr as an example, elevated concentrations occur in soils overlying ultramafic rocks in the foothills of the Sierra Nevada (median Cr = 160 mg/kg) as well as in the northern Coast Ranges. Low concentrations of these elements occur in soils located further upslope in the Sierra Nevada overlying Tertiary volcanic, metasedimentary and plutonic rocks (granodiorite and diorite). Eastern Sacramento Valley soil samples, defined as those located east of the Sacramento River, are lower in Cr (median Cr = 84 mg/kg), and are systematically lower in this suite compared to soils from the west side of the Sacramento Valley (median Cr = 130 mg/kg). A second group of elements showing a coherent pattern, including Ca, K, Sr and REE, is derived from relatively silicic rocks types. This group occurs at elevated

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

Possible polyphase metamorphic evolution of high grade metabasic rocks from the Songshugou ophiolite, Qinling orogen, China

NASA Astrophysics Data System (ADS)

Belic, Maximilian; Hauzenberger, Christoph; Dong, Yunpeng; Chen, Danling

2014-05-01

cycle or developed during a separate event. The financial support by Eurasia-Pacific Uninet is gratefully acknowledged. Dong, Y.P., Zhou, M.F., Zhang, G.W., Zhou, D.W., Liu, L., Zhang, Q., 2008. The Grenvillian Songshugou ophiolite in the Qinling Mountains, Central China: implications for the tectonic evolution of the Qinling orogenic belt. Journal of Asian Earth Science 32 (5-6), 325-335. Zhang, Z.J., 1999. Metamorphic evolution of garnet-clinopyroxene-amphibole rocks from the Proterozoic Songshugou mafic-ultramafic complex, Qinling Mountains, central China. The Island Arc, 8, 259-280.

An integrated study of geochemistry and mineralogy of the Upper Tukau Formation, Borneo Island (East Malaysia): Sediment provenance, depositional setting and tectonic implications

NASA Astrophysics Data System (ADS)

Nagarajan, Ramasamy; Roy, Priyadarsi D.; Kessler, Franz L.; Jong, John; Dayong, Vivian; Jonathan, M. P.

2017-08-01

An integrated study using bulk chemical composition, mineralogy and mineral chemistry of sedimentary rocks from the Tukau Formation of Borneo Island (Sarawak, Malaysia) is presented in order to understand the depositional and tectonic settings during the Neogene. Sedimentary rocks are chemically classified as shale, wacke, arkose, litharenite and quartz arenite and consist of quartz, illite, feldspar, rutile and anatase, zircon, tourmaline, chromite and monazite. All of them are highly matured and were derived from a moderate to intensively weathered source. Bulk and mineral chemistries suggest that these rocks were recycled from sedimentary to metasedimentary source regions with some input from granitoids and mafic-ultramafic rocks. The chondrite normalized REE signature indicates the presence of felsic rocks in the source region. Zircon geochronology shows that the samples were of Cretaceous and Triassic age. Comparable ages of zircon from the Tukau Formation sedimentary rocks, granitoids of the Schwaner Mountains (southern Borneo) and Tin Belt of the Malaysia Peninsular suggest that the principal provenance for the Rajang Group were further uplifted and eroded during the Neogene. Additionally, presence of chromian spinels and their chemistry indicate a minor influence of mafic and ultramafic rocks present in the Rajang Group. From a tectonic standpoint, the Tukau Formation sedimentary rocks were deposited in a passive margin with passive collisional and rift settings. Our key geochemical observation on tectonic setting is comparable to the regional geological setting of northwestern Borneo as described in the literature.

Zapping Rocks on Mars

ScienceCinema

Wiens, Roger

2018-01-16

Better understanding Mars means better understanding its geology. That’s why, sitting atop NASA’s Curiosity rover, is ChemCam, an instrument built by Los Alamos National Laboratory that shoots lasers at Martian rocks and analyzes the data. After nearly 1,500 rock zaps, ChemCam has uncovered some surprising facts about the Red Planet, including the discovery of igneous rocks. Soon, a new Los Alamos-built instrument—the SuperCam—will ride aboard the Mars 2020 rover and bring with it enhanced capabilities to unlock new secrets about the planet.

Thermal Inertia of Rocks and Rock Populations

NASA Technical Reports Server (NTRS)

Golombek, M. P.; Jakosky, B. M.; Mellon, M. T.

2001-01-01

The effective thermal inertia of rock populations on Mars and Earth is derived from a model of effective inertia versus rock diameter. Results allow a parameterization of the effective rock inertia versus rock abundance and bulk and fine component inertia. Additional information is contained in the original extended abstract.

Rock-Fluid Interactions Under Stress: How Rock Microstructure Controls The Evolution of Porosity and Permeability

NASA Astrophysics Data System (ADS)

Vanorio, T.

2016-12-01

Monitoring chemo-mechanical processes geophysically — e.g., fluid disposal or storage, thermal and chemical stimulation of reservoirs, or natural fluids simply entering a new system in the subsurface— raises numerous concerns because of the likelihood of fluid-rock chemical interactions and our limited ability to decipher the geophysical signature of coupled processes. One of the missing links is coupling the evolution of porosity, permeability, and velocity of rocks together with reactive transport, since rocks deform and their microstructure evolves, as a result of chemical reactions under stress. This study describes recent advances in rock-physics experiments to understand the effects of dissolution-induced compaction on acoustic velocity, porosity, and permeability. Data observation includes time-lapse experiments and imaging tracking transport and elastic properties, the rock microstructure, and the pH and chemical composition of the fluid permeating the rock. Results show that the removal of high surface area, mineral phases such as microcrystalline calcite and clay appears to be mostly responsible for dissolution-induced compaction. Nevertheless, it is the original rock microstructure and its response to stress that ultimately defines how solution-transfer and rock compaction feed back upon each other. This work has a dual aim: understanding the mechanisms underlying permanent modifications to the rock microstructure and providing a richer set of experimental information to inform the formulation of new simulations and rock modeling.

Semi-Automated Identification of Rocks in Images

NASA Technical Reports Server (NTRS)

Bornstein, Benjamin; Castano, Andres; Anderson, Robert

2006-01-01

Rock Identification Toolkit Suite is a computer program that assists users in identifying and characterizing rocks shown in images returned by the Mars Explorer Rover mission. Included in the program are components for automated finding of rocks, interactive adjustments of outlines of rocks, active contouring of rocks, and automated analysis of shapes in two dimensions. The program assists users in evaluating the surface properties of rocks and soil and reports basic properties of rocks. The program requires either the Mac OS X operating system running on a G4 (or more capable) processor or a Linux operating system running on a Pentium (or more capable) processor, plus at least 128MB of random-access memory.

The Widespread Distribution of Komatiitic Tuffs in the 3.3 Ga Weltevreden Formation, Barberton Greenstone Belt, South Africa

NASA Astrophysics Data System (ADS)

Thompson, M. E.; Lowe, D. R.; Byerly, G. R.

2007-12-01

The 3.5-3.2 Ga Barberton greenstone belt is a heavily deformed, 10-15 km thick succession of volcanic and sedimentary rocks representing one of the best preserved Paleoarchean supracrustal sequences known. It consists of the basal volcanic-dominated Onverwacht Group and the overlying sedimentary-dominated Fig Tree and Moodies Groups. Major volcanic rocks in the BGB include komatiites, tholeiitic basalts, and dacites. Although flow rocks and fragmental deposits have been identified representing all extrusive magma types, the abundance of komatiitic volcaniclastic units is remarkable considering the mechanical difficulties in explosively erupting low viscosity ultramafic lava. In the Onverwacht Group, most komatiitic tuffs contain 85-95 wt% SiO2, due to early silicification, and very low concentrations of most other elements, making original compositions somewhat uncertain. However, in the northernmost part of the BGB, north of the Inyoka Fault, the ~ 3.3 Ga Weltevreden Formation is composed largely of komatiitic flow rocks, tuffs, layered ultramafic complexes, and subordinate black and banded cherts. Previous studies have established the extrusive nature of the komatiites, but there are also many thick interlayered slaty units, previously interpreted as sheared flow rocks, which show cross-bedding, soft-sediment deformation, and other features indicating an alternate derivation. These units range from 2 to 80 m thick and may represent 10% or more of the overall stratigraphy of the Weltevreden Formation. They are characterized by low-temperature serpentinization that has commonly preserved original elemental abundances, enabling a more precise determination of primary komatiitic liquid composition. These rocks are magnesium rich, with MgO ranging from 23 to 36 wt%, and high Ni (~1500 ppm) and Cr (~2600 ppm) contents typical of komatiites. Several possible mechanisms could have produced these rocks, including (1) erosion and transport of pre-existing komatiitic flow

Tektites in cretaceous-tertiary boundary rocks on Haiti and their bearing on the Alvarez impact extinction hypothesis

NASA Astrophysics Data System (ADS)

Izett, G. A.

1991-11-01

Observational and geochemical data for glass objects recently discovered, by Izett et al. (1990), in K-T boundary rocks on the island of Haiti are presented. The presence of tektites, which are of terrestrial impact origin, in the same bed with a Pt-metal abundance anomaly and shocked mineral grains enormously strengthens the impact component of the Alvarez K-T impact extinction hypothesis. Shocked quartz grains in samples of the Haitian K-T boundary marker bed are about the same size as those at the K-T boundary sites in western North America. Petrographic observations indicate that the K-T marker bed on Haiti is not a primary air fall unit composed entirely of impact ejecta. It contains a small volcanogenic component of locally derived material admixed with the impact ejecta during deposition on the seafloor. The major and trace element composition of the Haitian tektites, in particular, the high Rb and REE content, suggests that the target material melted during the K-T impact was sedimentary with an average composition of andesite, not mafic or ultramafic oceanic crust.

Rock sampling. [apparatus for controlling particle size

NASA Technical Reports Server (NTRS)

Blum, P. (Inventor)

1971-01-01

An apparatus for sampling rock and other brittle materials and for controlling resultant particle sizes is described. The device includes grinding means for cutting grooves in the rock surface and to provide a grouping of thin, shallow, parallel ridges and cutter means to reduce these ridges to a powder specimen. Collection means is provided for the powder. The invention relates to rock grinding and particularly to the sampling of rock specimens with good size control.

Recent advances in analysis and prediction of Rock Falls, Rock Slides, and Rock Avalanches using 3D point clouds

NASA Astrophysics Data System (ADS)

Abellan, A.; Carrea, D.; Jaboyedoff, M.; Riquelme, A.; Tomas, R.; Royan, M. J.; Vilaplana, J. M.; Gauvin, N.

2014-12-01

The acquisition of dense terrain information using well-established 3D techniques (e.g. LiDAR, photogrammetry) and the use of new mobile platforms (e.g. Unmanned Aerial Vehicles) together with the increasingly efficient post-processing workflows for image treatment (e.g. Structure From Motion) are opening up new possibilities for analysing, modeling and predicting rock slope failures. Examples of applications at different scales ranging from the monitoring of small changes at unprecedented level of detail (e.g. sub millimeter-scale deformation under lab-scale conditions) to the detection of slope deformation at regional scale. In this communication we will show the main accomplishments of the Swiss National Foundation project "Characterizing and analysing 3D temporal slope evolution" carried out at Risk Analysis group (Univ. of Lausanne) in close collaboration with the RISKNAT and INTERES groups (Univ. of Barcelona and Univ. of Alicante, respectively). We have recently developed a series of innovative approaches for rock slope analysis using 3D point clouds, some examples include: the development of semi-automatic methodologies for the identification and extraction of rock-slope features such as discontinuities, type of material, rockfalls occurrence and deformation. Moreover, we have been improving our knowledge in progressive rupture characterization thanks to several algorithms, some examples include the computing of 3D deformation, the use of filtering techniques on permanently based TLS, the use of rock slope failure analogies at different scales (laboratory simulations, monitoring at glacier's front, etc.), the modelling of the influence of external forces such as precipitation on the acceleration of the deformation rate, etc. We have also been interested on the analysis of rock slope deformation prior to the occurrence of fragmental rockfalls and the interaction of this deformation with the spatial location of future events. In spite of these recent advances

Fragment Size Distribution of Blasted Rock Mass

NASA Astrophysics Data System (ADS)

Jug, Jasmin; Strelec, Stjepan; Gazdek, Mario; Kavur, Boris

2017-12-01

Rock mass is a heterogeneous material, and the heterogeneity of rock causes sizes distribution of fragmented rocks in blasting. Prediction of blasted rock mass fragmentation has a significant role in the overall economics of opencast mines. Blasting as primary fragmentation can significantly decrease the cost of loading, transport, crushing and milling operations. Blast fragmentation chiefly depends on the specific blast design (geometry of blast holes drilling, the quantity and class of explosive, the blasting form, the timing and partition, etc.) and on the properties of the rock mass (including the uniaxial compressive strength, the rock mass elastic Young modulus, the rock discontinuity characteristics and the rock density). Prediction and processing of blasting results researchers can accomplish by a variety of existing software’s and models, one of them is the Kuz-Ram model, which is possibly the most widely used approach to estimating fragmentation from blasting. This paper shows the estimation of fragmentation using the "SB" program, which was created by the authors. Mentioned program includes the Kuz-Ram model. Models of fragmentation are confirmed and calibrated by comparing the estimated fragmentation with actual post-blast fragmentation from image processing techniques. In this study, the Kuz-Ram fragmentation model has been used for an open-pit limestone quarry in Dalmatia, southern Croatia. The resulting calibrated value of the rock factor enables the quality prognosis of fragmentation in further blasting works, with changed drilling geometry and blast design parameters. It also facilitates simulation in the program to optimize blasting works and get the desired fragmentations of the blasted rock mass.

Extension Within The Australia-Eurasia Collision: The Metamorphic Rocks Of Central Sulawesi, Indonesia

NASA Astrophysics Data System (ADS)

Watkinson, I. M.; Hall, R.; Hennig, J.; Forster, M.

2012-12-01

Low-angle mylonitic fabrics from the metamorphic basement of central Sulawesi reveal a complex history of extension from the late Miocene to the present-day. Sulawesi is situated in the convergent triple junction between the Australian, Eurasian and Philippine Sea plates. The island is cut by the Palu-Koro and Matano faults, major active strike-slip zones that were initiated no earlier than about 5 Ma and have previously been attributed to collision-related processes. Within, and to the north and east of the strike-slip faults, are a suite of metamorphic complexes that include mica schists, schistose amphibolites, gneisses, migmatites, granulites, eclogites, marbles and ultramafic rocks including garnet peridotites. Mylonitic fabrics are widespread throughout the metamorphic rocks. The orientation of the mylonitic foliation is highly variable but typically dips less than 30°. Kinematic indicators record transport directions dominantly between top-to-the-NW and top-to-the-NE. Medium to high-grade mylonites, particularly in the south and west, are associated with ductile boudinage of eclogite and kyanite-bearing layers, 'snowball' garnet porphyroclasts, dynamic recrystallisation of feldspar and amphibole, and mylonitic deformation was locally synchronous with partial melting. Medium to high-grade mylonites are commonly overprinted by isoclinal asymmetric similar folds. Low grade mylonites are characterised by quartz recrystallisation only. Mica growth during mylonitic deformation is recorded by young 40Ar-39Ar plateaux between 5.05 ± 0.01 Ma and 2.07 ± 0.03 Ma in the west and 11.33 ± 0.02 Ma in the east. Undeformed aplitic dykes of similar composition to the migmatite leucosomes locally cross-cut the migmatitic mylonites and have yielded a biotite 40Ar-39Ar plateau of 3.62 ± 0.02 Ma. In the east the mylonitic fabric is cut by a low-angle detachment surface expressed as anomalously corrugated topography. On the basis of lithologic variation, shear

Grinding into Soft, Powdery Rock

NASA Technical Reports Server (NTRS)

2004-01-01

This hole in a rock dubbed 'Clovis' is the deepest hole drilled so far in any rock on Mars. NASA's Mars Exploration Rover Spirit captured this view with its microscopic imager on martian sol 217 (Aug. 12, 2004) after drilling 8.9 millimeters (0.35 inch) into the rock with its rock abrasion tool. The view is a mosaic of four frames taken by the microscopic imager. The hole is 4.5 centimeters (1.8 inches) in diameter. Clovis is key to a developing story about environmental change on Mars, not only because it is among the softest rocks encountered so far in Gusev Crater, but also because it contains mineral alterations that extend relatively deep beneath its surface. In fact, as evidenced by its fairly crumbly texture, it is possibly the most highly altered volcanic rock ever studied on Mars.

Scientific analysis shows that the rock contains higher levels of the elements sulfur, chlorine, and bromine than are normally encountered in basaltic rocks, such as a rock dubbed 'Humphrey' that Spirit encountered two months after arriving on Mars. Humphrey showed elevated levels of sulfur, chlorine, and bromine only in the outermost 2 millimeters (less than 0.1 inch) of its surface. Clovis shows elevated levels of the same elements along with the associated softness of the rock within a borehole that is 4 times as deep. Scientists hope to compare Clovis to other, less-altered rocks in the vicinity to assess what sort of water-based processes altered the rock. Hypotheses include transport of sulfur, chlorine, and bromine in water vapor in volcanic gases; hydrothermal circulation (flow of volcanically heated water through rock); or saturation in a briny soup containing the same elements.

In this image, very fine-grained material from the rock has clumped together by electrostatic attraction and fallen into the borehole. NASA/JPL/Cornell/USGS

Lithogeochemical character of the near-surface bedrock in the Connecticut, Housatonic, and Thames River Basins

USGS Publications Warehouse

Robinson, Gilpin R.; Peper, John D.; Steeves, Peter A.; Desimone, Leslie A.

1999-01-01

This data layer shows the generalized lithologic and geochemical (lithogeochemical) character of near-surface bedrock in the Connecticut, Housatonic, and Thames River Basins and several other small basins that drain into Long Island Sound from Connecticut. The area includes most of Connecticut, western Massachusetts, eastern Vermont, western New Hampshire, and small parts of Rhode Island, New York, and Quebec, Canada.Bedrock geologic rock units are classified into 29 lithogeochemical rock units, on the basis of the relative reactivity of their constituent minerals to dissolution and other weathering reactions and the presence of carbonate or sulfide minerals. The 29 lithogeochemical units (28 of which can be found in the study area) can be grouped into 6 major categories: (1) carbonate-rich rocks, (2) carbonate-poor, clastic sedimentary rocks restricted to distinct depositional basins, (3) metamorphosed, clastic sedimentary rocks (primarily noncalcareous), (4) mafic igneous rocks and their metamorphic equivalents, (5) ultramafic rocks, and (6) felsic igneous and plutonic rocks and their metamorphic equivalents. The lithogeochemical rock units also are grouped into nine lithologic and physiographic provinces (lithophysiographic domains), which can be further grouped into three major regions: (1) western highlands and lowlands, (2) central lowlands, and (3) eastern highlands.

Rock Content Influence on Soil Hydraulic Properties

NASA Astrophysics Data System (ADS)

Parajuli, K.; Sadeghi, M.; Jones, S. B.

2015-12-01

Soil hydraulic properties including the soil water retention curve (SWRC) and hydraulic conductivity function are important characteristics of soil affecting a variety of soil properties and processes. The hydraulic properties are commonly measured for seived soils (i.e. particles < 2 mm), but many natural soils include rock fragments of varying size that alter bulk hydraulic properties. Relatively few studies have addressed this important problem using physically-based concepts. Motivated by this knowledge gap, we set out to describe soil hydraulic properties using binary mixtures (i.e. rock fragment inclusions in a soil matrix) based on individual properties of the rock and soil. As a first step of this study, special attention was devoted to the SWRC, where the impact of rock content on the SWRC was quantified using laboratory experiments for six different mixing ratios of soil matrix and rock. The SWRC for each mixture was obtained from water mass and water potential measurements. The resulting data for the studied mixtures yielded a family of SWRC indicating how the SWRC of the mixture is related to that of the individual media, i.e., soil and rock. A consistent model was also developed to describe the hydraulic properties of the mixture as a function of the individual properties of the rock and soil matrix. Key words: Soil hydraulic properties, rock content, binary mixture, experimental data.

Nature and geodynamic setting of the protoliths of the UHP metamorphic Complex and migmatites in Bixiling area, the Dabie Orogen, China

NASA Astrophysics Data System (ADS)

Li, H.; Jahn, B.; Wang, D.; Yu, H.; Liu, Z.; Hou, G.

2013-12-01

As the largest coesite-bearing mafic-ultramafic body in the Dabie-Sulu orogen, the Bixiling Complex is composed of meta-ultramafic rocks, MgAl-rich eclogites and FeTi-rich eclogites. The FeTi-rich eclogites are further divided into low-Si-high-Fe type (Type I) and high-Si-low-Fe type (Type II) according to their mineral assemblages and bulk chemical composition. Field, petrographic, petrological and geochemical characteristics of these rocks, although suffered an ultra-high pressure metamorphism, still show a magmatic differentiation process among the protoliths of the meta-ultramafic rocks, MgAl-rich eclogites and Type I FeTi-rich eclogites. A small degree of lower crustal contamination occurred during their magma chamber process. Amphibolite is widespread in the periphery of the complex. Non-foliation and fine-grained texture are their obvious characteristics. Geochemical and isotopic affinities suggest that the amphibolites represent a product of complete retrogression from type II FeTi-rich eclogites. The UHP complex is enclosed in granitic gneisses, which variably include two-mica plagioclase gneiss, epidote two-mica plagioclase gneiss, or white-mica plagioclase gneiss. They all show TTG, especially trondjhemitic composition. A migmatite outcrop was found near the northeastern end of the complex. The migmatites consist of dark colored, non-foliated amphibolites and light-colored, fine-grained trondhjemitic gneisses. Field occurrences, microstructures observed under optical microscope and SEM, Sr-Nd isotopic data suggest an origin of partial melting. Chemical composition of two stages of amphiboles occurred in both the amphibolites and the trondhjemitic gneisses also imply a partial melting process occurred. Trace element, Sr-Nd isotope and SHRIMP zircon U-Pb dating of MgAl-rich eclogite, amphibolites and trondhjemite suggest that the migmatites represent a partial melting of crustal materials at about 780Ma, possibly accompanied by the coeval emplacement of a

Floods in the Rock River basin, Iowa

USGS Publications Warehouse

Heinitz, Albert J.

1973-01-01

Flood profiles for the Rock River include those for the 1962, 1964, 1965, 1969, and the computed 25- and 50-year floods. On the Little Rock River and Otter Creek, profiles include those for the 1969 flood and the computed 25- and 50-year floods. Low-water profiles are shown for all reaches.

Intrusive rocks of the Holden and Lucerne quadrangles, Washington; the relation of depth zones, composition, textures, and emplacement of plutons

USGS Publications Warehouse

Cater, Fred W.

1982-01-01

The core of the northern Cascade Range in Washington consists of Precambrian and upper Paleozoic metamorphic rocks cut by numerous plutons, ranging in age from early Triassic to Miocene. The older plutons have been eroded to catazonal depths, whereas subvolcanic rocks are exposed in the youngest plutons. The Holden and Lucerne quadrangles span a -sizeable and representative part of this core. The oldest of the formations mapped in these quadrangles is the Swakane Biotite Gneiss, which was shown on the quadrangle maps as Cretaceous and older in age. The Swakane has yielded a middle Paleozoic metamorphic age, and also contains evidence of zircon inherited from some parent material more than 1,650 m.y. old. In this report, the Swakane is assigned an early Paleozoic or older age. It consists mostly of biotite gneiss, but interlayered with it are scattered layers and lenses of hornblende schist and gneiss, clinozoisite-epidote gneiss, and quartzite. Thickness of the Swakane is many thousands of meters, and the base is not exposed. The biotite gneiss is probably derived from a pile of siliceous volcanic rocks containing scattered sedimentary beds and basalt flows. Overlying the Swakane is a thick sequence of eugeosynclinal upper Paleozoic rocks metamorphosed to amphibolite grade. The sequence includes quartzite and thin layers of marble, hornblende schist and gneiss, graphitic schist, and smaller amounts of schist and gneiss of widely varying compositions. The layers have been tightly and complexly folded, and, in places, probably had been thrust over the overlying Swakane prior to metamorphism. Youngest of the supracrustal rocks in the area are shale, arkosic sandstone, and conglomerate of the Paleocene Swauk Formation. These rocks are preserved in the Chiwaukum graben, a major structural element of the region. Of uncertain age, but possibly as old as any of the intrusive rocks in the area, are small masses of ultramafic rocks, now almost completely altered to

Rock shape, restitution coefficients and rockfall trajectory modelling

NASA Astrophysics Data System (ADS)

Glover, James; Christen, Marc; Bühler, Yves; Bartelt, Perry

2014-05-01

Restitution coefficients are used in rockfall trajectory modelling to describe the ratio between incident and rebound velocities during ground impact. They are central to the problem of rockfall hazard analysis as they link rock mass characteristics to terrain properties. Using laboratory experiments as a guide, we first show that restitution coefficients exhibit a wide range of scatter, although the material properties of the rock and ground are constant. This leads us to the conclusion that restitution coefficients are poor descriptors of rock-ground interaction. The primary problem is that "apparent" restitution coefficients are applied at the rock's centre-of-mass and do not account for rock shape. An accurate description of the rock-ground interaction requires the contact forces to be applied at the rock surface with consideration of the momentary rock position and spin. This leads to a variety of rock motions including bouncing, sliding, skipping and rolling. Depending on the impact configuration a wide range of motions is possible. This explains the large scatter of apparent restitution coefficients. We present a rockfall model based on newly developed hard-contact algorithms which includes the effects of rock shape and therefore is able to reproduce the results of different impact configurations. We simulate the laboratory experiments to show that it is possible to reproduce run-out and dispersion of different rock shapes using parameters obtained from independent tests. Although this is a step forward in rockfall trajectory modelling, the problem of parametersing real terrain remains.

Igneous Rocks

NASA Astrophysics Data System (ADS)

Doe, Bruce R.

“Igneous Rocks was written for undergraduate geology majors who have had a year of college-level chemistry and a course in mineralogy … and for beginning graduate students. Geologists working in industry, government, or academia should find this text useful as a guide to the technical literature up to 1981 and as an overview of topics with which they have not worked but which may have unanticipated pertinence to their own projects.” So starts the preface to this textbook.As one who works part time in research on igneous rocks, especially as they relate to mineral deposits, I have been looking for such a book with this avowed purpose in a field that has a choking richness of evolving terminology and a bewildering volume of interdisciplinary literature. In addition to the standard topics of igneous petrology, the book contains a chapter on the role of igneous activity in the genesis of mineral deposits, its value to geothermal energy, and the potential of igneous rocks as an environment for nuclear waste disposal. These topics are presented rather apologetically in the preface, but the author is to be applauded for including this chapter. The apology shows just how new these interests are to petrology. Recognition is finally coming that, for example, mineral deposits are not “sports of nature,” a view held even by many economic geologists as recently as the early 1960's; instead they are perfectly ordinary geochemical features formed by perfectly ordinary geologic processes. In fact, the mineral deposits and their attendant alteration zones probably have as much to tell us about igneous rocks as the igneous rocks have to tell us about mineral deposits.

The surface orientation of some Apollo 14 rocks.

NASA Technical Reports Server (NTRS)

Hoerz, F.; Morrison, D. A.; Hartung, J. B.

1972-01-01

Detailed stereomicroscopic studies of the distribution of microcraters, soil covers, and glass coatings were performed to reconstruct the most recent surface orientations of selected Apollo 14 rocks. Surface orientations could be established for rocks 14053, 14073, 14301, 14303, 14307, 14310, and 14311 (which includes rock 14308). A tentative orientation of rock 14055 is suggested, and comments concerning the surface history of rocks 14302, 14305, and 14318 are presented. The examination of rocks 14066, 14306, and 14321 indicates that these specimens have complicated surface histories that prevent reconstruction of their orientation by the criteria that were established in these stereomicroscopic studies.

Experimental and Thermodynamic Constraints on Serpentinization: Implications for Fluid Chemistry, Abiotic Synthesis of Hydrocarbons, and Subsurface Microbial Processes

NASA Astrophysics Data System (ADS)

McCollom, T. M.

2005-12-01

Serpentinized rocks have received a great deal of attention in recent years, primarily because they are believed to play significant roles in supporting autotrophic, hydrogen-based microbial communities and in the abiotic synthesis of methane and other organic compounds. Both of these processes are a consequence of the high H2 concentrations generated by reaction of water with ultramafic rocks during serpentinization. The amount of H2 produced during serpentinization is dependent on both thermodynamic and kinetic constraints, which can be evaluated through numerical thermodynamic models and laboratory experiments. Because olivine is thermodynamically stable at temperatures above ~375°C, alteration of ultramafic rocks at higher temperatures generates only minor amounts of H2. Even at lower temperatures olivine may equilibrate with the fluid after only partial reaction, so that olivine may persist stably in partially serpentinized rocks. Olivine only becomes completely unstable at ~315°C, so that the maximum potential for H2 production only occurs at or below this temperature. At high temperatures, serpentinization proceeds rapidly, so that thermodynamic constraints provide the primary control on H2 production. However, the rate of serpentinization becomes sufficiently slow below ~150°C that the residence of time of fluids may prevent high concentrations of H2 from accumulating. Since H2 generation during serpentinization is primarily attributable to conversion of ferrous Fe in olivine to ferric Fe in magnetite, another factor that may limit H2 production is the sequestration of ferrous Fe in brucite or serpentine. Some serpentines and brucites are reported to contain significant amounts of Fe, but these data are somewhat uncertain because the analyses may include microcrystalline magnetite. Although the thermodynamic properties of solid solutions of these minerals are highly uncertain, the available data suggest that the Fe content of serpentines and brucite may

Were the world's youngest eclogites (NW D'Entrecasteaux Islands, Papua New Guinea) exhumed in rising gneiss domes or by shear on a deep-seated fault?

NASA Astrophysics Data System (ADS)

Little, T. A.; Hacker, B.; Seward, G.

2008-12-01

nearly plate-motion parallel. Shear indicators diverge across the dome crests, suggesting of an inward flow of deeper rocks into the dome; or are locally variable, consistent with bulk irrotational deformation. In the gneisses (both core and carapace), conjugate shear-band microstructures and near-orthorhombic quartz LPOs, and back-rotation of mantled porphyroclasts indicate that ductile strain in domes was near plane, but that it was not simple shear (and included significant vertical shortening). The LPO's of the deepest rocks record activity of the high-T prism-[c] and prism- slip systems, whereas the outermost carapace rocks record basal- and rhomb- slip. The data reveal that deformational temperatures increased toward the dome centers, rather than outwardly into the carapace. Quartz LPO's in both dome and carapace are of uniformly modest intensity (~2-3 times random). Feldspar LPO's suggest slip on the (010)[001] or (010)[100] systems, and in some cases a shear sense opposite to quartz. While we cannot resolve how the eclogitic rocks ascended isothermally from the mantle into the lower crust, the simplest model invokes diapiric ascent (with decompression melting), ponding and lateral spreading along the Moho during early Woodlark Basin rifting. Subsequent exhumation of these rocks from the lower crust involved continued upward movement and vertical shortening of the gneisses combined with subhorizontal rift-parallel flow. Finally, normal faulting and minor erosion exhumed these rocks through the ultramafic cover to their present levels.

Estimating the Wet-Rock P-Wave Velocity from the Dry-Rock P-Wave Velocity for Pyroclastic Rocks

NASA Astrophysics Data System (ADS)

Kahraman, Sair; Fener, Mustafa; Kilic, Cumhur Ozcan

2017-07-01

Seismic methods are widely used for the geotechnical investigations in volcanic areas or for the determination of the engineering properties of pyroclastic rocks in laboratory. Therefore, developing a relation between the wet- and dry-rock P-wave velocities will be helpful for engineers when evaluating the formation characteristics of pyroclastic rocks. To investigate the predictability of the wet-rock P-wave velocity from the dry-rock P-wave velocity for pyroclastic rocks P-wave velocity measurements were conducted on 27 different pyroclastic rocks. In addition, dry-rock S-wave velocity measurements were conducted. The test results were modeled using Gassmann's and Wood's theories and it was seen that estimates for saturated P-wave velocity from the theories fit well measured data. For samples having values of less and greater than 20%, practical equations were derived for reliably estimating wet-rock P-wave velocity as function of dry-rock P-wave velocity.

Geodynamic evolution of the Sabzevar zone, northern central Iranian micro-continent

NASA Astrophysics Data System (ADS)

Omrani, Hadi; Moazzen, Mohssen; Oberhänsli, Roland

2018-02-01

The Northern Central Iranian Micro-continent (CIM) represents Neotethys-related oceanic crust remnants, emplaced due to convergence between CIM and Eurasia plates during Eocene. Mafic and ultramafic units are exposed along the northern part of the CIM in the Sabzevar area. The geology and field relation of Sabzevar ophiolite indicate northward subduction of the Sabzevar basin. The average whole rock chemistry of mafic (gabbros) and ultramafic samples (lherzolite, harzburgite and dunite) is characterized by a range of MgO of 11.16-31.88, CaO 5.22-11.53 and Al2O3 2.77-14.57, respectively. Low LREE/HREE ratio of ultramafic samples is accompanied by enrichment of large ion lithophile elements (LILE) such as Sr, Pb and K. Mafic samples show two distinct groups with low and high LREE/HREE ratios. The spider diagram of mafic samples indicates enrichment in Sr, Pb and K and depletion in REE. Petrological and geochemical evidence and field relations show that the mafic rocks formed in a supra-subduction zone setting. Petrological studies reveal the role of fractional crystallization and assimilation effect by released fluids during subduction related generation of the Sabzevar mafic rocks. We suggest that the studied mafic rocks likely represent the basement of an initial island arc, which was generated in a supra-subduction zone setting within the Neotethys branch of the Sabzevar Ocean at the north of CIM. Copper, gold and chromite mineralizations are studied in relation to island arc setting and supra-subduction environment. Similarities in lithology, ophiolite age and mineralization between Sabzevar ophiolite and Bardaskan-Torbat Heydariyeh ophiolites testify for their separation due to rotation (or faulting) of the Central Iranian Micro-continent.

Isotopic ages for alkaline igneous rocks, including a 26 Ma ignimbrite, from the Peshawar plain of northern Pakistan and their tectonic implications

NASA Astrophysics Data System (ADS)

Ahmad, Irshad; Khan, Shuhab; Lapen, Thomas; Burke, Kevin; Jehan, Noor

2013-01-01

New isotopic ages on zircons from rocks of the Peshawar Plain Alkaline Igneous Province (PPAIP) reveal for the first time the occurrence of ignimbritic Cenozoic (Oligocene) volcanism in the Himalaya at 26.7 ± 0.8 Ma. Other new ages confirm that PPAIP rift-related igneous activity was Permian and lasted from ˜290 Ma to ˜250 Ma. Although PPAIP rocks are petrologically and geochemically typical of rifts and have been suggested to be linked to rifting on the Pangea continental margin at the initiation of the Neotethys Ocean, there are no documented rift-related structures mapped in Permian rocks of the Peshawar Plain. We suggest that Permian rift-related structures have been dismembered and/or reactivated during shortening associated with India-Asia collision. Shortening in the area between the Main Mantle Thrust (MMT) and the Main Boundary Thrust (MBT) may be indicative of the subsurface northern extension of the Salt Range evaporites. Late Cenozoic sedimentary rocks of the Peshawar Plain deposited during and after Himalayan thrusting occupy a piggy-back basin on top of the thrust belt. Those sedimentary rocks have buried surviving evidence of Permian rift-related structures. Igneous rocks of the PPAIP have been both metamorphosed and deformed during the Himalayan collision and Cenozoic igneous activity, apart from the newly recognized Gohati volcanism, has involved only the intrusion of small cross-cutting granitic bodies concentrated in areas such as Malakand that are close to the MMT. Measurements on Chingalai Gneiss zircons have confirmed the occurrence of 816 ± 70 Ma aged rocks in the Precambrian basement of the Peshawar Plain that are comparable in age to rocks in the Malani igneous province of the Rajasthan platform ˜1000 km to the south.

The potassic sedimentary rocks in Gale Crater, Mars, as seen by ChemCam on board Curiosity: Potassic Sedimentary Rocks, Gale Crater

DOE PAGES

Le Deit, L.; Mangold, N.; Forni, O.; ...

2016-05-13

The Mars Science Laboratory rover Curiosity encountered potassium-rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio-deltaic depositional system. Furthermore, from ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K 2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations then reveals that the mean K 2Omore » abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K-bearing minerals, mafic silicates, Fe-oxides, and Fe-hydroxide/oxyhydroxides. Possible K-bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K-bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium-rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater.« less

The potassic sedimentary rocks in Gale Crater, Mars, as seen by ChemCam on board Curiosity: Potassic Sedimentary Rocks, Gale Crater

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

Le Deit, L.; Mangold, N.; Forni, O.

The Mars Science Laboratory rover Curiosity encountered potassium-rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio-deltaic depositional system. Furthermore, from ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K 2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations then reveals that the mean K 2Omore » abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K-bearing minerals, mafic silicates, Fe-oxides, and Fe-hydroxide/oxyhydroxides. Possible K-bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K-bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium-rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater.« less

What lies beneath: geophysical mapping of a concealed Precambrian intrusive complex along the Iowa–Minnesota border

USGS Publications Warehouse

Drenth, Benjamin J.; Anderson, Raymond R.; Schulz, Klaus J.; Feinberg, Joshua M.; Chandler, Val W.; Cannon, William F.

2015-01-01

Large-amplitude gravity and magnetic highs over northeast Iowa are interpreted to reflect a buried intrusive complex composed of mafic–ultramafic rocks, the northeast Iowa intrusive complex (NEIIC), intruding Yavapai province (1.8–1.72 Ga) rocks. The age of the complex is unproven, although it has been considered to be Keweenawan (∼1.1 Ga). Because only four boreholes reach the complex, which is covered by 200–700 m of Paleozoic sedimentary rocks, geophysical methods are critical to developing a better understanding of the nature and mineral resource potential of the NEIIC. Lithologic and cross-cutting relations interpreted from high-resolution aeromagnetic and airborne gravity gradient data are presented in the form of a preliminary geologic map of the basement Precambrian rocks. Numerous magnetic anomalies are coincident with airborne gravity gradient (AGG) highs, indicating widespread strongly magnetized and dense rocks of likely mafic–ultramafic composition. A Yavapai-age metagabbro unit is interpreted to be part of a layered intrusion with subvertical dip. Another presumed Yavapai unit has low density and weak magnetization, observations consistent with felsic plutons. Northeast-trending, linear magnetic lows are interpreted to reflect reversely magnetized diabase dikes and have properties consistent with Keweenawan rocks. The interpreted dikes are cut in places by normally magnetized mafic–ultramafic rocks, suggesting that the latter represent younger Keweenawan rocks. Distinctive horseshoe-shaped magnetic and AGG highs correspond with a known gabbro, and surround rocks with weaker magnetization and lower density. Here, informally called the Decorah complex, the source body has notable geophysical similarities to Keweenawan alkaline ring complexes, such as the Coldwell and Killala Lake complexes, and Mesoproterozoic anorogenic complexes, such as the Kiglapait, Hettasch, and Voisey’s Bay intrusions in Labrador. Results presented here suggest that

Nickel speciation in several serpentine (ultramafic) topsoils via bulk synchrotron-based techniques

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

Siebecker, Matthew G.; Chaney, Rufus L.; Sparks, Donald L.

2017-07-01

Serpentine soils have elevated concentrations of trace metals including nickel, cobalt, and chromium compared to non-serpentine soils. Identifying the nickel bearing minerals allows for prediction of potential mobility of nickel. Synchrotron-based techniques can identify the solid-phase chemical forms of nickel with minimal sample treatment. Element concentrations are known to vary among soil particle sizes in serpentine soils. Sonication is a useful method to physically disperse sand, silt and clay particles in soils. Synchrotron-based techniques and sonication were employed to identify nickel species in discrete particle size fractions in several serpentine (ultramafic) topsoils to better understand solid-phase nickel geochemistry. Nickel commonlymore » resided in primary serpentine parent material such as layered-phyllosilicate and chain-inosilicate minerals and was associated with iron oxides. In the clay fractions, nickel was associated with iron oxides and primary serpentine minerals, such as lizardite. Linear combination fitting (LCF) was used to characterize nickel species. Total metal concentration did not correlate with nickel speciation and is not an indicator of the major nickel species in the soil. Differences in soil texture were related to different nickel speciation for several particle size fractionated samples. A discussion on LCF illustrates the importance of choosing standards based not only on statistical methods such as Target Transformation but also on sample mineralogy and particle size. Results from the F-test (Hamilton test), which is an underutilized tool in the literature for LCF in soils, highlight its usefulness to determine the appropriate number of standards to for LCF. EXAFS shell fitting illustrates that destructive interference commonly found for light and heavy elements in layered double hydroxides and in phyllosilicates also can occur in inosilicate minerals, causing similar structural features and leading to false positive

Rocks.

ERIC Educational Resources Information Center

Lee, Alice

This science unit is designed for limited- and non-English speaking students in a Chinese bilingual education program. The unit covers rock material, classification, characteristics of types of rocks, and rock cycles. It is written in Chinese and simple English. At the end of the unit there is a list of main terms in both English and Chinese, and…

Origin of narrow terranes and adjacent major terranes occurring along the denali fault in the eastern and central alaska range, alaska

USGS Publications Warehouse

Nokleberg, W.J.; Richter, D.H.

2007-01-01

Several narrow terranes occur along the Denali fault in the Eastern and Central Alaska Range in Southern Alaska. These terranes are the Aurora Peak, Cottonwood Creek, Maclaren, Pingston, and Windy terranes, and a terrane of ultramafic and associated rocks. Exterior to the narrow terranes to the south is the majorWrangellia island arc composite terrane, and to the north is the major Yukon Tanana metamorphosed continental margin terrane. Overlying mainly the northern margin of the Wrangellia composite terrane are the Kahiltna overlap assemblage to the west, and the Gravina- Nutzotin-Gambier volcanic-plutonic- sedimentary belt to the east and southeast. The various narrow terranes are interpreted as the result of translation of fragments of larger terranes during two major tectonic events: (1) Late Jurassic to mid-Cretaceous accretion of the Wrangellia island arc composite terrane (or superterrane composed of the Wrangellia, Peninsular, and Alexander terranes) and associated subduction zone complexes; and (2) starting in about the Late Cretaceous, dextral transport of the Wrangellia composite terrane along the Denali fault. These two major tectonic events caused: (1) entrapment of a lens of oceanic lithosphere along the suture belt between the Wrangellia composite terrane and the North American Craton Margin and outboard accreted terranes to form the ultramafic and mafic part of the terrane of ultramafic and associated rocks, (2) subsequent dextral translation along the Denali fault of the terrane of ultramafic and associated rocks, (3) dextral translation along the Denali fault of the Aurora Peak, Cottonwood Creek, and Maclaren and continental margin arc terranes from part of the Coast plutonic-metamorphic complex (Coast-North Cascade plutonic belt) in the southwest Yukon Territory or Southeastern Alaska, (4) dextral translation along the Denali fault of the Pingston passive continental margin from a locus along the North American Continental Margin, and (5

Mineralogy and geochemistry of the Neo-Tethyan Orhaneli ultramafic suite, NW Turkey: Evidence for the initiation and evolution of magmatic processes in a developing crust-mantle boundary

NASA Astrophysics Data System (ADS)

Uysal, Ibrahim; Dokuz, Abdurrahman; Kapsiotis, Argyris; Kaliwoda, Melanie; Karsli, Orhan; Müller, Dirk; Aydin, Faruk

2017-04-01

The eastern Orhaneli ophiolitic massif, located in NW Anatolia, Turkey, forms part of the northwestern branch of the so-called Neotethys Ocean across the Izmir-Ankara-Erzincan Suture Zone. It is comprised mainly of a well preserved ultramafic suite, dominated by voluminous dunite exposures, accompanied by subsidiary harzburgite occurrences. The entire suite is commonly cross cut by a complex network of relatively undeformed clinopyroxenite veins. Clinopyroxene and spinel compositions in harzburgites are moderately depleted, whereas their whole-rock heavy rare earth element (HREE) abundances are consistent with harzburgite formation after approximately 19% dry melting of a spinel-bearing fertile mantle protolith at an extentional geotectonic regime. Nevertheless, textural data indicate that protracted dissolution of pyroxene coupled with precipitation of olivine happened during the transformation of harzburgites to replacive dunites, containing olivine with high Fo [Fo = 100×Mg/(Mg + Fe2+)] content (91.3-94.2) and spinel with elevated Cr# [100×Cr/(Cr + Al)] values (78-82). Such highly depleted mineralogical signatures imply that dunite for harzburgite substitution occurred under hydrous melting conditions in the mantle region above a subducted oceanic slab. Enrichments in incompatible elements (e.g., Cs, Rb and Sr) and the characteristic U-shaped chondrite-normalized rare earth elements (REE) profiles exhibited by replacive dunites along with the elevated TiO2 (0.20-0.36 wt.%) contents in their accessory spinels indicate that the reactive melt had an intermediate affinity between boninite and island arc tholeiite (IAT) regimes. The metasomatic reaction triggered an additional 8% melting of the harzburgite residue. The resultant melt fractionated (,almost in situ,) to crystallize cumulate dunites composed of olivine with relatively high Fo content (88.8-92.3), spinel with moderate Cr# values (62-74), as well as clinopyroxene with a depleted composition (low TiO2

A High-Resolution Multitechniques Approach to Characterize Bio-Organo-Mineral Associations Within Rock Samples: Tracking Biological vs Abiotic Processes? Towards a Better Understanding of the Deep Carbon Cycle.

NASA Astrophysics Data System (ADS)

Pisapia, C.

2015-12-01

Among all elements, carbon plays one of the major roles for the sustainability of life on Earth. Past considerations of the carbon cycle have mainly focused on surface processes occurring at the atmosphere, oceans and shallow crustal environments. By contrast, little is known about the Deep Carbon cycle whereas both geochemical and biological processes may induce organic carbon production and/or consumption at depth. Indeed, the nowadays-recognized capability of geochemical processes such as serpentinization to generate abiotic organic compounds as well as the existence of a potentially important intraterrestrial life raises questions about the limit of biotic/abiotic carbon on Earth's deep interior and how it impacts global biogeochemical cycles. It is then mandatory to increase our knowledge on the nature and extent of carbon reservoirs along with their sources, sinks and fluxes in the subsurface. This implies to be able to finely characterize organomineral associations within crustal rocks although it might be hampered by the scarceness and heterogeneous micrometric spatial distribution of organic molecules in natural rocks. We then developed an in situ analytical strategy based on the combination of high-resolution techniques to track organic molecules at the pore level in natural rocks and to determine their biological or abiotic origin. We associated classical high-resolution techniques and synchrotron-based imaging techniques in order to characterize their nature and localization (SEM/TEM, coupled CLSM/Raman spectroscopy, Tof-SIMS) along with their 3D-distribution relatively to mineral phases (S-FTIR, S-DeepUV, XANES, Biphoton microscopy). The effectiveness of this approach to shed light on the speciation and nature of carbon in subsurface environments will be illustrated through the study of (i) subsurface ecosystems and abiotic organic carbon within ultramafic rocks of the oceanic lithosphere as putative analogs for the nature and functioning of primitive

The role of tectonic damage and brittle rock fracture in the development of large rock slope failures

NASA Astrophysics Data System (ADS)

Brideau, Marc-André; Yan, Ming; Stead, Doug

2009-01-01

Rock slope failures are frequently controlled by a complex combination of discontinuities that facilitate kinematic release. These discontinuities are often associated with discrete folds, faults, and shear zones, and/or related tectonic damage. The authors, through detailed case studies, illustrate the importance of considering the influence of tectonic structures not only on three-dimensional kinematic release but also in the reduction of rock mass properties due to induced damage. The case studies selected reflect a wide range of rock mass conditions. In addition to active rock slope failures they include two major historic failures, the Hope Slide, which occurred in British Columbia in 1965 and the Randa rockslides which occurred in Switzerland in 1991. Detailed engineering geological mapping combined with rock testing, GIS data analysis and for selected case numerical modelling, have shown that specific rock slope failure mechanisms may be conveniently related to rock mass classifications such as the Geological Strength Index (GSI). The importance of brittle intact rock fracture in association with pre-existing rock mass damage is emphasized though a consideration of the processes involved in the progressive-time dependent development not only of though-going failure surfaces but also lateral and rear-release mechanisms. Preliminary modelling data are presented to illustrate the importance of intact rock fracture and step-path failure mechanisms; and the results are discussed with reference to selected field observations. The authors emphasize the importance of considering all forms of pre-existing rock mass damage when assessing potential or operative failure mechanisms. It is suggested that a rock slope rock mass damage assessment can provide an improved understanding of the potential failure mode, the likely hazard presented, and appropriate methods of both analysis and remedial treatment.

Typology of mafic-ultramafic complexes in Hoggar, Algeria: Implications for PGE, chromite and base-metal sulphide mineralisation

NASA Astrophysics Data System (ADS)

Augé, Thierry; Joubert, Marc; Bailly, Laurent

2012-02-01

With the aims to bring new information about the typology and mineral potential of mafic-ultramafic complexes of the Hoggar, detailed petrological and chemical characterisation were performed on serpentinite bands and layered intrusions. The serpentinite bands locally contain pods, layers and disseminations of chromite showing all the characteristics (mode of occurrence, composition, nature and composition of silicate inclusions, etc.) of an "ophiolite" chromite. Some chromite concentrations in the serpentinite bands also contain inclusions of platinum-group minerals (described for the first time in the Hoggar) such as ruarsite (RuAsS), an Os, Ru, Ir alloy, and complex Os, Ir, Ru sulfarsenides and arsenides. The serpentinite probably corresponds to remnants of oceanic lithosphere—more specifically from the upper part of the mantle sequence, generally where chromitite pods are most abundant, and the basal part of the cumulate series with stratiform chromite concentrations—and marks suture zones; the rest of the oceanic crust has not been preserved. Considering the typology of the serpentinites bands, their potential for precious- and base-metals is suspected to be low. Of the two layered mafic-ultramafic intrusions that were studied, the In Tedeini intrusion has a wehrlite core intruded by olivine gabbronorite and surrounded by an olivine gabbro aureole; three orthocumulate units, containing disseminated magmatic base-metal sulphides and with a plagioclase composition varying around An 58.1 and An 63.3, that could have been derived from a single magma. The East Laouni intrusion has a basal unit of olivine gabbronorite with specific silicate oxide intergrowths, and an upper unit of more differentiated gabbro, both units containing disseminated magmatic Ni-Cu sulphides indicative of early sulphide immiscibility; the mineral composition of these two cumulate units indicates that they also could have been derived from a single magmatic episode. The characteristic of

68. LITTLE ROCK AND PALMDALE IRRIGATION DISTRICT, LITTLE ROCK DAM: ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

68. LITTLE ROCK AND PALMDALE IRRIGATION DISTRICT, LITTLE ROCK DAM: STRESS SHEET, SHEET 4; MAY, 1918. Littlerock Water District files. - Little Rock Creek Dam, Little Rock Creek, Littlerock, Los Angeles County, CA

Elastic Rock Heterogeneity Controls Brittle Rock Failure during Hydraulic Fracturing

NASA Astrophysics Data System (ADS)

Langenbruch, C.; Shapiro, S. A.

2014-12-01

For interpretation and inversion of microseismic data it is important to understand, which properties of the reservoir rock control the occurrence probability of brittle rock failure and associated seismicity during hydraulic stimulation. This is especially important, when inverting for key properties like permeability and fracture conductivity. Although it became accepted that seismic events are triggered by fluid flow and the resulting perturbation of the stress field in the reservoir rock, the magnitude of stress perturbations, capable of triggering failure in rocks, can be highly variable. The controlling physical mechanism of this variability is still under discussion. We compare the occurrence of microseismic events at the Cotton Valley gas field to elastic rock heterogeneity, obtained from measurements along the treatment wells. The heterogeneity is characterized by scale invariant fluctuations of elastic properties. We observe that the elastic heterogeneity of the rock formation controls the occurrence of brittle failure. In particular, we find that the density of events is increasing with the Brittleness Index (BI) of the rock, which is defined as a combination of Young's modulus and Poisson's ratio. We evaluate the physical meaning of the BI. By applying geomechanical investigations we characterize the influence of fluctuating elastic properties in rocks on the probability of brittle rock failure. Our analysis is based on the computation of stress fluctuations caused by elastic heterogeneity of rocks. We find that elastic rock heterogeneity causes stress fluctuations of significant magnitude. Moreover, the stress changes necessary to open and reactivate fractures in rocks are strongly related to fluctuations of elastic moduli. Our analysis gives a physical explanation to the observed relation between elastic heterogeneity of the rock formation and the occurrence of brittle failure during hydraulic reservoir stimulations. A crucial factor for understanding

Rock.XML - Towards a library of rock physics models

NASA Astrophysics Data System (ADS)

Jensen, Erling Hugo; Hauge, Ragnar; Ulvmoen, Marit; Johansen, Tor Arne; Drottning, Åsmund

2016-08-01

Rock physics modelling provides tools for correlating physical properties of rocks and their constituents to the geophysical observations we measure on a larger scale. Many different theoretical and empirical models exist, to cover the range of different types of rocks. However, upon reviewing these, we see that they are all built around a few main concepts. Based on this observation, we propose a format for digitally storing the specifications for rock physics models which we have named Rock.XML. It does not only contain data about the various constituents, but also the theories and how they are used to combine these building blocks to make a representative model for a particular rock. The format is based on the Extensible Markup Language XML, making it flexible enough to handle complex models as well as scalable towards extending it with new theories and models. This technology has great advantages as far as documenting and exchanging models in an unambiguous way between people and between software. Rock.XML can become a platform for creating a library of rock physics models; making them more accessible to everyone.

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.

Cuttability Assessment of Selected Rocks Through Different Brittleness Values

NASA Astrophysics Data System (ADS)

Dursun, Arif Emre; Gokay, M. Kemal

2016-04-01

Prediction of cuttability is a critical issue for successful execution of tunnel or mining excavation projects. Rock cuttability is also used to determine specific energy, which is defined as the work done by the cutting force to excavate a unit volume of yield. Specific energy is a meaningful inverse measure of cutting efficiency, since it simply states how much energy must be expended to excavate a unit volume of rock. Brittleness is a fundamental rock property and applied in drilling and rock excavation. Brittleness is one of the most crucial rock features for rock excavation. For this reason, determination of relations between cuttability and brittleness will help rock engineers. This study aims to estimate the specific energy from different brittleness values of rocks by means of simple and multiple regression analyses. In this study, rock cutting, rock property, and brittleness index tests were carried out on 24 different rock samples with different strength values, including marble, travertine, and tuff, collected from sites around Konya Province, Turkey. Four previously used brittleness concepts were evaluated in this study, denoted as B 1 (ratio of compressive to tensile strength), B 2 (ratio of the difference between compressive and tensile strength to the sum of compressive and tensile strength), B 3 (area under the stress-strain line in relation to compressive and tensile strength), and B 9 = S 20, the percentage of fines (<11.2 mm) formed in an impact test for the Norwegian University of Science and Technology (NTNU) model as well as B 9p (B 9 as predicted from uniaxial compressive, Brazilian tensile, and point load strengths of rocks using multiple regression analysis). The results suggest that the proposed simple regression-based prediction models including B 3, B 9, and B 9p outperform the other models including B 1 and B 2 and can be used for more accurate and reliable estimation of specific energy.

Contrasted hydrothermal activity along the South-East Indian Ridge (130°E-140°E): From crustal to ultramafic circulation

NASA Astrophysics Data System (ADS)

Boulart, Cédric; Briais, Anne; Chavagnac, Valérie; Révillon, Sidonie; Ceuleneer, Georges; Donval, Jean-Pierre; Guyader, Vivien; Barrere, Fabienne; Ferreira, Nicolas; Hanan, Barry; Hémond, Christophe; Macleod, Sarah; Maia, Marcia; Maillard, Agnès.; Merkuryev, Sergey; Park, Sung-Hyun; Ruellan, Etienne; Schohn, Alexandre; Watson, Sally; Yang, Yun-Seok

2017-07-01

Using a combined approach of seafloor mapping, MAPR and CTD survey, we report evidence for active hydrothermal venting along the 130°-140°E section of the poorly-known South-East Indian Ridge (SEIR) from the Australia-Antarctic Discordance (AAD) to the George V Fracture Zone (FZ). Along the latter, we report Eh and CH4 anomalies in the water column above a serpentinite massif, which unambiguously testify for ultramafic-related fluid flow. This is the first time that such circulation is observed on an intermediate-spreading ridge. The ridge axis itself is characterized by numerous off-axis volcanoes, suggesting a high magma supply. The water column survey indicates the presence of at least ten distinct hydrothermal plumes along the axis. The CH4:Mn ratios of the plumes vary from 0.37 to 0.65 denoting different underlying processes, from typical basalt-hosted to ultramafic-hosted high-temperature hydrothermal circulation. Our data suggest that the change of mantle temperature along the SEIR not only regulates the magma supply, but also the hydrothermal activity. The distribution of hydrothermal plumes from a ridge segment to another implies secondary controls such as the presence of fractures and faults along the axis or in the axial discontinuities. We conclude from these results that hydrothermal activity along the SEIR is controlled by magmatic processes at the regional scale and by the tectonics at the segment scale, which influences the type of hydrothermal circulation and leads to various chemical compositions. Such variety may impact global biogeochemical cycles, especially in the Southern Ocean where hydrothermal venting might be the only source of nutrients.

Quantitative bedrock geology of east and Southeast Asia (Brunei, Cambodia, eastern and southeastern China, East Timor, Indonesia, Japan, Laos, Malaysia, Myanmar, North Korea, Papua New Guinea, Philippines, far-eastern Russia, Singapore, South Korea, Taiwan, Thailand, Vietnam)

NASA Astrophysics Data System (ADS)

Peucker-Ehrenbrink, Bernhard; Miller, Mark W.

2004-01-01

We quantitatively analyze the area-age distribution of sedimentary, igneous and metamorphic bedrock based on data from the most recent digital geologic maps of East and Southeast Asia (Coordinating Committee for Coastal and Offshore Geosciences Programmes in East and Southeast Asia (CCOP) and the Geologic Survey of Japan, 1997; 1:2,000,000), published as Digital Geoscience Map G-2 by the Geological Survey of Japan. Sedimentary rocks, volcanic rocks, plutonic rocks, ultramafic rocks and metamorphic rocks cover 73.3%, 8.5%, 8.8%, 0.9%, and 8.6% of the surface area, respectively. The average ages of major lithologic units, weighted according to bedrock area, are as follows: sedimentary rocks (average stratigraphic age of 123 Myr/median age of 26 Myr), volcanic rocks (84 Myr/20 Myr), intrusive rocks (278 Myr/195 Myr), ultramafic rocks (unknown) and metamorphic rocks (1465 Myr/1118 Myr). The variability in lithologic composition and age structure of individual countries reflects the complex tectonic makeup of this region that ranges from Precambrian cratons (e.g., northeast China and North Korea) to Mesozoic-Cenozoic active margins (e.g., Japan, the Philippines, Indonesia and New Guinea). The spatial resolution of the data varies from 44 km2 per polygon (Japan) to 1659 km2 per polygon (Taiwan) and is, on average (490 km2/polygon), similar to our previous analyses of the United States of America and Canada. The temporal and spatial resolution is sufficiently high to perform age-area analyses of individual river basins larger than ˜10,000 km2 and to quantitatively evaluate the relationship between bedrock geology and river chemistry. As many rivers draining tropical, mountainous islands of East and Southeast Asia have a disproportionate effect on the dissolved and particulate load delivered to the world oceans, bedrock geology in such river drainage basins disproportionately affect ocean chemistry.

"Rock Garden"

NASA Image and Video Library

1997-10-14

This false color composite image of the Rock Garden shows the rocks "Shark" and "Half Dome" at upper left and middle, respectively. Between these two large rocks is a smaller rock (about 0.20 m wide, 0.10 m high, and 6.33 m from the Lander) that was observed close-up with the Sojourner rover (see PIA00989). http://photojournal.jpl.nasa.gov/catalog/PIA00987

Identification of Cr-magnetite in Neoproterozoic serpentinites resulting of Cr-Spinel alteration in a past hydrothermal system: Aït Ahmane ultramafic unit (Bou Azzer ophiolite, Anti Atlas, Morocco)

NASA Astrophysics Data System (ADS)

Hodel, Florent; Macouin, Mélina; Carlut, Julie; Triantafyllou, Antoine; Berger, Julien; Trindade, Ricardo; Ennih, Nasser; Rousse, Sonia

2017-04-01

If magnetite is a common serpentinization product, centimetric, massive and almost pure magnetite veins are rarely observed in serpentinites. Unique examples of these, in the Aït Ahmane ultramafic unit (Bou Azzer Neoproterozoic ophiolite, Anti-Atlas, Morocco), offer the opportunity to assess the hydrothermal processes that prevailed at the end of the Precambrian. Pseudomorphic lizardite/chrysotile texture of unaltered serpentinites suggests an oceanic-like first serpentinization stage, under static and low temperature conditions (T <350 °C). Nevertheless, abundance of magnetite (up to 7.86 wt. %) and absence of brucite, attest that serpentinization probably took place over 200 °C. Magnetic measurements reveal a lower magnetite content in hydrothermalized serpentinites hosting the magnetite veins, with lowest values (down to 0.58 wt. %) for bleached serpentinites constituting the wall rock of veins. Fresh serpentinites are characterized by relatively small sized magnetite grains, mainly pseudo-single domain magnetites. Hysteresis parameters and first order reversal curves (FORC) diagram denote a magnetic grains size that increases with the alteration. This well-marked tendency is also reveals by a shift of the isothermal remanent magnetization (IRM) components toward lower coercivities for altered serpentinites. This grain size increase is associated with the emergence of a new magnetic phase with the hydrothermal alteration, the Cr-magnetite, evidenced by thermomagnetic measurements with Tc around 540 °C. This ultimate Cr-spinel alteration product is associated with another Cr-spinel alteration mineral, the ferritchromite, also identifiable on thermomagnetic curves by a rapid increase of the magnetite susceptibility at 130 °C due to its transformation during heating. Thermomagnetic curves allow us to propose a proxy, the CrM/M ratio providing a quantification of the Cr-magnetite contribution to the magnetic susceptibility, relatively to the pure magnetite one

Rock burst governance of working face under igneous rock

NASA Astrophysics Data System (ADS)

Chang, Zhenxing; Yu, Yue

2017-01-01

As a typical failure phenomenon, rock burst occurs in many mines. It can not only cause the working face to cease production, but also cause serious damage to production equipment, and even result in casualties. To explore how to govern rock burst of working face under igneous rock, the 10416 working face in some mine is taken as engineering background. The supports damaged extensively and rock burst took place when the working face advanced. This paper establishes the mechanical model and conducts theoretical analysis and calculation to predict the fracture and migration mechanism and energy release of the thick hard igneous rock above the working face, and to obtain the advancing distance of the working face when the igneous rock fractures and critical value of the energy when rock burst occurs. Based on the specific conditions of the mine, this paper put forward three kinds of governance measures, which are borehole pressure relief, coal seam water injection and blasting pressure relief.

Geotechnical Descriptions of Rock and Rock Masses.

DTIC Science & Technology

1985-04-01

determined in the field on core speci ns by the standard Rock Testing Handbook Methods . afls GA DTIC TAB thannounod 13 Justifiatlo By Distributin...to provide rock strength descriptions from the field. The point-load test has proven to be a reliable method of determining rock strength properties...report should qualify the reported spacing values by stating the methods used to determine spacing. Preferably the report should make the determination

Leaching of S, Cu, and Fe from disseminated Ni-(Fe)-(Cu) sulphide ore during serpentinization of dunite host rocks at Mount Keith, Agnew-Wiluna belt, Western Australia

NASA Astrophysics Data System (ADS)

Gole, Martin J.

2014-10-01

Komatiite-hosted disseminated Ni sulphide deposits in the Agnew-Wiluna greenstone belt occur both above and below the olivine isograd that was imposed on the greenstone sequence during the M2 metamorphic/deformation event. Deposits in the northern and central part of the belt and that are located below the isograd (Mount Keith, Honeymoon Well and West Jordan) have complex sulphide mineralogy and strongly zoned sulphide assemblages. These range from least-altered assemblages of pentlandite-pyrrhotite-chalcopyrite±pyrite to altered assemblages of pentlandite±chalcopyrite, pentlandite-heazlewoodite (or millerite), heazlewoodite (or millerite), and rarely to heazlewoodite-native Ni. Deposits to the south and that are above of the olivine isograd (Six Mile, Goliath North) are dominated by less complex magmatic assemblages with a lower proportion of weakly altered pentlandite±chalcopyrite assemblages. More altered assemblages are uncommon in these deposits and occur as isolated patches around the periphery of the deposits. The sulphide zonation is reflected by whole-rock reductions in S, Cu, Fe and Zn, whereas Ni, Pt and Pd and, with some exceptions, Co are conservative. The leaching of S, Cu, Fe and Zn from sulphide assemblages and the whole rock was initiated by highly reduced conditions that were produced during low fluid/rock ratio serpentinization. Consumption of H2O resulted in Cl, a component of the fluid, being concentrated sufficiently to stabilise iowaite as part of lizardite-rich assemblages. Once the rate of olivine hydration reactions declined and during and after expansion and associated fracturing of the ultramafic sequence allowed higher fluid access, a more fluid-dominated environment formed and new carbonate-bearing fluid gained access to varying extents to the ultramafic rock sequence. This drove Cl from iowaite (to form pyroaurite) and caused the sulphide assemblages to be altered from the original magmatic assemblages and compositions to those

Database on unstable rock slopes in Norway

NASA Astrophysics Data System (ADS)

Oppikofer, Thierry; Nordahl, Bo; Bunkholt, Halvor; Nicolaisen, Magnus; Hermanns, Reginald L.; Böhme, Martina; Yugsi Molina, Freddy X.

2014-05-01

Several large rockslides have occurred in historic times in Norway causing many casualties. Most of these casualties are due to displacement waves triggered by a rock avalanche and affecting coast lines of entire lakes and fjords. The Geological Survey of Norway performs systematic mapping of unstable rock slopes in Norway and has detected up to now more than 230 unstable slopes with significant postglacial deformation. This systematic mapping aims to detect future rock avalanches before they occur. The registered unstable rock slopes are stored in a database on unstable rock slopes developed and maintained by the Geological Survey of Norway. The main aims of this database are (1) to serve as a national archive for unstable rock slopes in Norway; (2) to serve for data collection and storage during field mapping; (3) to provide decision-makers with hazard zones and other necessary information on unstable rock slopes for land-use planning and mitigation; and (4) to inform the public through an online map service. The database is organized hierarchically with a main point for each unstable rock slope to which several feature classes and tables are linked. This main point feature class includes several general attributes of the unstable rock slopes, such as site name, general and geological descriptions, executed works, recommendations, technical parameters (volume, lithology, mechanism and others), displacement rates, possible consequences, hazard and risk classification and so on. Feature classes and tables linked to the main feature class include the run-out area, the area effected by secondary effects, the hazard and risk classification, subareas and scenarios of an unstable rock slope, field observation points, displacement measurement stations, URL links for further documentation and references. The database on unstable rock slopes in Norway will be publicly consultable through the online map service on www.skrednett.no in 2014. Only publicly relevant parts of

Art Rocks with Rock Art!

ERIC Educational Resources Information Center

Bickett, Marianne

2011-01-01

This article discusses rock art which was the very first "art." Rock art, such as the images created on the stone surfaces of the caves of Lascaux and Altimira, is the true origin of the canvas, paintbrush, and painting media. For there, within caverns deep in the earth, the first artists mixed animal fat, urine, and saliva with powdered minerals…

Numerical modelling of fluid-rock interactions: Lessons learnt from carbonate rocks diagenesis studies

NASA Astrophysics Data System (ADS)

Nader, Fadi; Bachaud, Pierre; Michel, Anthony

2015-04-01

Quantitative assessment of fluid-rock interactions and their impact on carbonate host-rocks has recently become a very attractive research topic within academic and industrial realms. Today, a common operational workflow that aims at predicting the relevant diagenetic processes on the host rocks (i.e. fluid-rock interactions) consists of three main stages: i) constructing a conceptual diagenesis model including inferred preferential fluids pathways; ii) quantifying the resulted diagenetic phases (e.g. depositing cements, dissolved and recrystallized minerals); and iii) numerical modelling of diagenetic processes. Most of the concepts of diagenetic processes operate at the larger, basin-scale, however, the description of the diagenetic phases (products of such processes) and their association with the overall petrophysical evolution of sedimentary rocks remain at reservoir (and even outcrop/ well core) scale. Conceptual models of diagenetic processes are thereafter constructed based on studying surface-exposed rocks and well cores (e.g. petrography, geochemistry, fluid inclusions). We are able to quantify the diagenetic products with various evolving techniques and on varying scales (e.g. point-counting, 2D and 3D image analysis, XRD, micro-CT and pore network models). Geochemical modelling makes use of thermodynamic and kinetic rules as well as data-bases to simulate chemical reactions and fluid-rock interactions. This can be through a 0D model, whereby a certain process is tested (e.g. the likelihood of a certain chemical reaction to operate under specific conditions). Results relate to the fluids and mineral phases involved in the chemical reactions. They could be used as arguments to support or refute proposed outcomes of fluid-rock interactions. Coupling geochemical modelling with transport (reactive transport model; 1D, 2D and 3D) is another possibility, attractive as it provides forward simulations of diagenetic processes and resulting phases. This

Lithological architecture and petrography of the Mako Birimian greenstone belt, Kédougou-Kéniéba Inlier, eastern Senegal

NASA Astrophysics Data System (ADS)

Dabo, Moussa; Aïfa, Tahar; Gning, Ibrahima; Faye, Malick; Ba, Mamadou Fallou; Ngom, Papa Malick

2017-07-01

The new lithological and petrographic data obtained in the Mako sector are analyzed in the light of the geochemical data available in the literature. It consists of ultramaic, mafic rocks of tholeiitic affinities associated with intermediate and felsic rocks of calc-alkaline affinities and with intercalations of sedimentary rocks. The whole unit is intruded by Eburnean granitoids and affected by a greenschist to amphibolite facies metamorphism related to a high grade hydrothermalism. It consists of: (i) ultramafic rocks composed of a fractional crystallization succession of lherzolites, wehrlites and pyroxenites with mafic rock inclusions; (ii) layered, isotropic and pegmatitic metagabbros which gradually pass to metabasalts occur at the top; (iii) massive and in pillow metabasalts with locally tapered vesicles, completely or partially filled with quartzo-feldspathic minerals; (iv) quarzites locally overlying the mafic rocks and thus forming the top of the lower unit. This ultramafic-mafic lower unit presents a tholeiitic affinity near to the OIB or N-MORB. It represents the Mako Ophiolitic Complex (MOC), a lithospheric fragment of Birimian lithospheric crust. The upper unit is a mixed volcanic complex arranged in the tectonic corridors. From bottom to top it comprises the following: (i) andesitic, and (ii) rhyodacitic and rhyolitic lava flows and tuffs, respectively. They present a calc-alkaline affinity of the active margins. Three generations of Eburnean granitoids are recognized: (i) early (2215-2160 Ma); (ii) syn-tectonics (2150-2100 Ma) and post-tectonics (2090-2040 Ma). The lithological succession, geochemical and metamorphic characteristics of these units point to an ophiolitic supra-subduction zone.

Portrait of a giant deep-seated magmatic conduit system: The Seiland Igneous Province

NASA Astrophysics Data System (ADS)

Larsen, Rune B.; Grant, Thomas; Sørensen, Bjørn E.; Tegner, Christian; McEnroe, Suzanne; Pastore, Zeudia; Fichler, Christine; Nikolaisen, Even; Grannes, Kim R.; Church, Nathan; ter Maat, Geertje W.; Michels, Alexander

2018-01-01

The Seiland Igneous Province (SIP), Northern Norway, contains > 5000 km2 of mafic and ultramafic intrusions with minor alkaline, carbonatite and felsic rocks that were intruded into the lower continental crust at a depth of 25 to as much as 35 km. The SIP can be geochemically and temporally correlated to numerous dyke swarms throughout Scandinavia at 560-610 Ma, and is linked to magmatic provinces in W-Greenland and NE-America that are collectively known as the Central Iapetus Magmatic Province (CIMP). Revised mapping show that the SIP exposes 85-90% layered tholeiitic- alkaline- and syeno-gabbros, 8-10% peridotitic complexes, 2-5% carbonatite, syenite and diorite that formed within a narrow (< 10 Ma) time frame in the Ediacaran (560-570 Ma). Large peridotite complexes were emplaced into the still hot and unconsolidated gabbro (no dating available) and are regarded as the main-conduit systems. Gravimetric data implies an average thickness of igneous rocks of 4-5 km and also features six deep lithospheric roots of ultramafic rocks extending min 9 km into the crust. Together, the root structures represent the main volcanic conduits conveying thousands of km3 of mafic-ultramafic melts from the asthenosphere to the lithosphere. The ultramafic complexes were predominantly emplaced into the layered gabbros at four major igneous centres, respectively, Nordre Brumandsfjord, Melkvann, Kvalfjord and Reinfjord. All complexes are situated in a right-way-up position and are steep sided forming large plugs. A marginal hybrid zone forms at the contact with country-rock and transitions gradually from olivine-mela-gabbro over pyroxenites that grades in to an olivine-clinopyroxenite zone, which is followed by a wehrlite zone and, finally, the centre of the complexes comprises pure dunite. From pyroxenite to dunite, olivine changes from Fo72 to Fo85 and clinopyroxene from Di80 to Di92 i.e. the complexes observe a reverse fractional crystallisation sequence with time. Parental melt

Overexpression of ROCK1 and ROCK2 inhibits human laryngeal squamous cell carcinoma

PubMed Central

Zhang, Junbo; He, Xue; Ma, Yueying; Liu, Yanli; Shi, Huaiyin; Guo, Weiwei; Liu, Liangfa

2015-01-01

Rho-associated coiled-coil containing protein kinase (ROCK) over-expression has been implicated in the progression of many tumor types. The aim of this study was to explore the roles of ROCK1 and ROCK2 in human laryngeal squamous cell carcinoma (LSCC). ROCK1 and ROCK2 expression levels were examined in 50 cases of human LSCC samples by immunohistochemistry. Effects of ROCK1 and ROCK2 on LSCC cell proliferation and motility were investigated in the presence of the ROCK inhibitor Y-27632. The results showed that ROCK1 expression was positively correlated with tumor size and lymph node metastasis (P < 0.05); ROCK2 positively correlated with tumor size (P < 0.05). Inhibition of ROCK1 and ROCK2 by Y-27632 significantly inhibits proliferation, migration, and invasion of LSCC cells. Our data indicate that expression of ROCK1 and ROCK2 are closely associated with tumor growth and lymph node metastasis of LSCC. Thus, these two ROCK isoforms may be useful as molecular makers for LSCC diagnosis and may be useful therapeutic targets as well. PMID:25755711

Lithogeochemical character of near-surface bedrock in the New England coastal basins

USGS Publications Warehouse

Robinson, Gilpin R.; Ayotte, Joseph D.; Montgomery, Denise L.; DeSimone, Leslie A.

2002-01-01

This geographic information system (GIS) data layer shows the generalized lithologic and geochemical, termed lithogeochemical, character of near-surface bedrock in the New England Coastal Basin (NECB) study area of the U.S. Geological Survey's National Water Quality Assessment (NAWQA) Program. The area encompasses 23,000 square miles in western and central Maine, eastern Massachusetts, most of Rhode Island, eastern New Hampshire and a small part of eastern Connecticut. The NECB study area includes the Kennebec, Androscoggin, Saco, Merrimack, Charles, and Blackstone River Basins, as well as all of Cape Cod. Bedrock units in the NECB study area are classified into lithogeochemical units based on the relative reactivity of their constituent minerals to dissolution and the presence of carbonate or sulfide minerals. The 38 lithogeochemical units are generalized into 7 major groups: (1) carbonate-bearing metasedimentary rocks; (2) primarily noncalcareous, clastic sedimentary rocks with restricted deposition in discrete fault-bounded sedimentary basins of Mississipian or younger age; (3) primarily noncalcareous, clastic sedimentary rocks at or above biotite-grade of regional metamorphism; (4) mafic igneous rocks and their metamorphic equivalents; (5) ultramafic rocks; (6) felsic igneous rocks and their metamorphic equivalents; and (7) unconsolidated and poorly consolidated sediments.

The Usability of Rock-Like Materials for Numerical Studies on Rocks

NASA Astrophysics Data System (ADS)

Zengin, Enes; Abiddin Erguler, Zeynal

2017-04-01

The approaches of synthetic rock material and mass are widely used by many researchers for understanding the failure behavior of different rocks. In order to model the failure behavior of rock material, researchers take advantageous of different techniques and software. But, the majority of all these instruments are based on distinct element method (DEM). For modeling the failure behavior of rocks, and so to create a fundamental synthetic rock material model, it is required to perform related laboratory experiments for providing strength parameters. In modelling studies, model calibration processes are performed by using parameters of intact rocks such as porosity, grain size, modulus of elasticity and Poisson ratio. In some cases, it can be difficult or even impossible to acquire representative rock samples for laboratory experiments from heavily jointed rock masses and vuggy rocks. Considering this limitation, in this study, it was aimed to investigate the applicability of rock-like material (e.g. concrete) to understand and model the failure behavior of rock materials having complex inherent structures. For this purpose, concrete samples having a mixture of %65 cement dust and %35 water were utilized. Accordingly, intact concrete samples representing rocks were prepared in laboratory conditions and their physical properties such as porosity, pore size and density etc. were determined. In addition, to acquire the mechanical parameters of concrete samples, uniaxial compressive strength (UCS) tests were also performed by simultaneously measuring strain during testing. The measured physical and mechanical properties of these extracted concrete samples were used to create synthetic material and then uniaxial compressive tests were modeled and performed by using two dimensional discontinuum program known as Particle Flow Code (PFC2D). After modeling studies in PFC2D, approximately similar failure mechanism and testing results were achieved from both experimental and

Occurrence and mineral chemistry of chromite and related silicates from the Hongshishan mafic-ultramafic complex, NW China with petrogenetic implications

NASA Astrophysics Data System (ADS)

Ruan, Banxiao; Yu, Yingmin; Lv, Xinbiao; Feng, Jing; Wei, Wei; Wu, Chunming; Wang, Heng

2017-10-01

The Hongshishan mafic-ultramafic complex is located in the western Beishan Terrane, NW China, and hosts an economic Ni-Cu deposit. Chromite as accessory mineral from the complex is divided into three types based on its occurrence and morphology. Quantitative electron probe microanalysis (EPMA) have been conducted on the different types of chromites. Type 1 chromite occurs as inclusions within silicate minerals and has relatively homogeneous composition. Type 2 chromite occurs among serpentine, as interstitial phase. Type 3 chromite is zoned and exhibits a sudden change in compositions from core to rim. Type 1 chromite occurs in olivine gabbro and troctolite showing homogeneous composition. This chromite is more likely primary. Interstitial type 2 and zoned type 3 chromite has compositional variation from core to rim and is more likely modified. Abundant inclusions of orthopyroxene, phlogopite and hornblende occur within type 2 and type 3 chromites. The parental melt of type 1 chromite has an estimated composition of 14.5 wt% MgO, 12.3 wt% Al2O3 and 1.9 wt% TiO2 and is characterized by high temperature, picritic affinity, hydrous nature and high Mg and Ti contents. Compositions of chromite and clinopyroxene are distinct from those of Alaskan-type complexes and imply that the subduction-related environment is not reasonable. Post orogenic extension and the early Permian mantle plume are responsible for the emplacement of mafic-ultramafic complexes in the Beishan Terrane. The cores of zoned chromites are classified as ferrous chromite and the rims as ferrian chromite. The formation of ferrian rim involves reaction of ferrous chromite, forsterite and magnetite to produce ferrian chromite and chlorite, or alternaively, the rim can be simply envisioned as the result of external addition of magnetite in solution to the already formed ferrous chromite.

Documenting the light sensitivity of Spanish Levantine rock art paintings

NASA Astrophysics Data System (ADS)

del Hoyo-Meléndez, J. M.; Lerma, J. L.; López-Montalvo, E.; Villaverde, V.

2015-08-01

A case study to evaluate the use of microfading spectrometry (MFS) for the study of colored systems found in prehistoric rock art paintings was conducted in the Cova Remígia rock-shelter, Castellón (Spain). This rock shelter is part of the rock art sites of the Mediterranean basin on the Iberian Peninsula included in UNESCO's World Heritage List. Some of the paintings belonging to this group are exposed to environmental factors including natural daylight, wind and rain, depending on the time of the day and the season of the year. Therefore, their preservation is a major concern to stakeholders and researchers responsible for protecting and studying these prehistoric paintings. The experimental work in Cova Remigia focused on measuring the reflectance curves (400-700 nm) and determining the photostability of various areas containing red and black pigments on the rock art paintings. The preliminary results indicate that MFS is a suitable technique for studying the response to light of rock/pigment systems found in rock art sites. The advantages and limitations of the technique are discussed.

Rock Games.

ERIC Educational Resources Information Center

Topal, Cathy Weisman

1985-01-01

Elementary school children are given cards containing specific criteria for doing one or two tasks: sorting or arranging rocks. Sorting tasks involve children in picking out rocks with particular characteristics, such as color or shape. In the arranging tasks children are asked to arrange rocks according to size or value. (RM)

Collecting Rocks.

ERIC Educational Resources Information Center

Barker, Rachel M.

One of a series of general interest publications on science topics, the booklet provides those interested in rock collecting with a nontechnical introduction to the subject. Following a section examining the nature and formation of igneous, sedimentary, and metamorphic rocks, the booklet gives suggestions for starting a rock collection and using…

Rock flows

NASA Technical Reports Server (NTRS)

Matveyev, S. N.

1986-01-01

Rock flows are defined as forms of spontaneous mass movements, commonly found in mountainous countries, which have been studied very little. The article considers formations known as rock rivers, rock flows, boulder flows, boulder stria, gravel flows, rock seas, and rubble seas. It describes their genesis as seen from their morphological characteristics and presents a classification of these forms. This classification is based on the difference in the genesis of the rubbly matter and characterizes these forms of mass movement according to their source, drainage, and deposit areas.

Redistribution of iron and titanium in subduction zones: insights from high-pressure serpentinites

NASA Astrophysics Data System (ADS)

Crossley, Rosalind; Evans, Katy; Reddy, Steven; Lester, Gregory

2017-04-01

The redox state, quantity and composition of subduction zone fluids influence the transport and precipitation of elements including those which are redox-sensitive, of economic importance such as Cu, Au and Ag, and those considered to be immobile, which include Fe3+. However, subduction zone fluids remain poorly understood. The redox state of Fe in high-pressure ultramafic rocks, which host a significant proportion of Fe3+, can be used to provide an insight into Fe cycling and constrain the composition of subduction zone fluids. In this work, a combination of the study of oxide and silicate mineral textures, interpretation of mineral parageneses, mineral composition data, and the whole rock geochemistry of high-pressure retrogressed ultramafic rocks from the Zermatt-Saas Zone constrains the distribution of iron and titanium, and oxidation state of iron, to provide constraints on fluids at depth in subduction zones. Oxide minerals host the bulk of the iron, particularly Fe3+. The increase in mode of magnetite during initial retrogression is most consistent with oxidation of existing iron within the samples during the infiltration of an oxidising fluid since it is difficult to reconcile addition of Fe3+ with the known limited solubility of this species. These fluids may be sourced from hybrid samples and/or serpentinites at greater depths. However, high Ti contents are not typical of serpentinites and additionally cannot be accounted for by simple mixing of a depleted mantle protolith with the nearby Allalin gabbro. Titanium-rich samples are suggested to result from fluid-facilitated hybridisation of gabbro and serpentinite protoliths prior to peak metamorphism, and provides the tantalising possibility that Ti, an element generally perceived as immobile, has been added to the rock during this process. If Ti addition has occurred, then the introduction of Fe3+, also generally considered to be immobile, cannot be disregarded. Aluminosilicate complexing could provide a

A textural and compositional investigation on the source and timing of iron oxidation and titanium enrichment in high-pressure serpentinites

NASA Astrophysics Data System (ADS)

Crossley, R.; Evans, K. A.; Reddy, S.; Lester, G. W.

2016-12-01

The redox state, quantity and composition of subduction zone fluids influence the transport and precipitation of elements including those which are redox-sensitive, of economic importance such as Cu, Au and Ag, and those considered to be immobile, which include Fe3+. However, subduction zone fluids remain poorly understood. The redox state of Fe in high-pressure ultramafic rocks, which host a significant proportion of Fe3+, can be used to provide an insight into Fe cycling and constrain the composition and possible source of subduction zone fluids. In this work, we use a combination of oxide mineral textures, mineral parageneses, mineral composition data, and whole rock geochemistry of high-pressure retrogressed ultramafic rocks from the Zermatt-Saas Zone to constrain the distribution and oxidation state of iron, and to provide insights on the nature of fluids at depth within subduction zones. Oxide minerals host the bulk of the iron, particularly Fe3+. The increase in mode of magnetite during initial retrogression is most consistent with oxidation of existing iron via the infiltration of an oxidising fluids since it is difficult to reconcile addition of Fe3+ with the known limited solubility of this species. In addition, fluid-mediated or mechanical mixing with other lithologies in the slab could introduce elements and alter the bulk composition of serpentinites. However, the high Ti content of one sample cannot be explained by simple mixing of a depleted mantle protolith with the nearby Allalin gabbros, and provides the tantalising possibility that Ti, an element generally perceived as immobile, has been added to the rock. While we cannot completely exclude the possibility of pre-subduction Ti addition, textural analysis of Ti-rich minerals suggest mobilisation of Ti during subduction on at least a centimetre scale. If Ti addition has occurred, then the introduction of Fe3+, also generally considered to be immobile, cannot be disregarded. The Al-rich nature of

Replacement processes in crystalline rocks

NASA Astrophysics Data System (ADS)

John, Timm; Putnis, Andrew

2010-05-01

A substantial question in metamorphism is what is the mechanism that dominates the conversion of one mineral assemblage to another in response to a change in the ambient physical and/or chemical conditions. Petrological, microstructural, and isotopic data indicate that aqueous fluids must be involved even in the reequilibration of large-scale systems. Fluid-mineral reactions take place by dissolution - precipitation processes, but converting one solid rock to another requires pervasive, either dominantly advective or diffusive fluid-mediated transport through the entire rock. The generation of reaction-induced porosity and the spatial and temporal coupling of dissolution and precipitation can account for fluid and element transport through rocks and the replacement of one mineral assemblage by another. To determine the mechanism of metamorphic reactions we refer to examples of interfaces and reaction textures which contain both the "before" (precursor) and "after" mineral assemblages - case studies where the process of conversion is frozen in. We will illustrate some aspects of the role of fluids in metamorphic reactions and discuss how reactive fluids can pervasively infiltrate a rock. The examples we will use are focussed on crystalline rocks and include reactions from the lower continental crust, the subducting oceanic crust, and the continental upper crust to show that except at very high-temperature conditions, essentially the same mechanisms are responsible for converting rocks to thermodynamically more stable mineral assemblages for given Pressure-Temperature-fluid composition (P-T-X) conditions.

Rock Magnetic Properties of Remagnetised Devonian and Carboniferous Carbonate and Clastic Rocks From The NE Rhenish Massif, Germany

NASA Astrophysics Data System (ADS)

Zwing, A.; Matzka, J.; Bachtadse, V.; Soffel, H. C.

Previous studies on remagnetised carbonate rocks from the North American and Eu- ropean Variscides reported characteristic rock magnetic properties which are thought to be diagnostic for a chemical remagnetisation event. Their hysteresis properties with high ratios of Mrs/Ms and Hcr/Hc indicate the presence of a mixture of single-domain and superparamagnetic magnetite (Jackson, et al. 1990). In order to test if this fin- gerprint can be identified in remagnetised carbonate and clastic rocks from the NE Rhenish Massif, Germany, a series of rock magnetic experiments has been carried out. The hysteresis properties of the remagnetised clastic rocks indicate the domi- nance of large MD particles, as can be expected for detrital sediments. The carbon- ates yield significantly higher ratios of Mrs/Ms and Hcr/Hc than the clastic rocks, but only partly correspond to the characteristic properties of remagnetised carbon- ates described above. The latter might be attributed to detrital input into the carbonate platforms. Additional low-temperature remanence measurements show a wide vari- ety of phenomena, including Verwey transitions and indications for the presence of superparamagnetic grains. However, the low-temperature experiments do not allow a straightforward discrimination between the clastic and carbonate rocks and suggest more complex magnetomineralogies than expected from the hysteresis measurements alone.

Rock Finding

ERIC Educational Resources Information Center

Rommel-Esham, Katie; Constable, Susan D.

2006-01-01

In this article, the authors discuss a literature-based activity that helps students discover the importance of making detailed observations. In an inspiring children's classic book, "Everybody Needs a Rock" by Byrd Baylor (1974), the author invites readers to go "rock finding," laying out 10 rules for finding a "perfect" rock. In this way, the…

Rock Art

ERIC Educational Resources Information Center

Henn, Cynthia A.

2004-01-01

There are many interpretations for the symbols that are seen in rock art, but no decoding key has ever been discovered. This article describes one classroom's experiences with a lesson on rock art--making their rock art and developing their own personal symbols. This lesson allowed for creativity, while giving an opportunity for integration…

Trace element mobility at the slab-mantle interface: constraints from "hybrid

NASA Astrophysics Data System (ADS)

Marocchi, M.; Tropper, P.; Mair, V.; Bargossi, G. M.; Hermann, J.

2009-04-01

Subduction mélanges and hybrid rocks are considered, together with mafic rocks, metasediments and serpentinite as an important volatile-bearing portion of subducting slabs (cf. Spandler et al., 2008 and references therein; Miller et al., 2009). In particular, metasomatic rocks occurring in exhumed HP mélanges have recently attracted growing interest for two main reasons: i) metasomatic rocks forming at the interface between ultramafic and crustal rocks of subducting slabs constitute new bulk compositions which can affect the redistribution of major and trace elements and modify the composition of slab fluids moving to the mantle wedge and ii) these mineral assemblages, consisting mainly of hydrous phases can potentially store and transport water at great depth in subduction zones. Ultramafic rocks belonging to the Hochwart peridotite (Ulten Zone, central-eastern Italian Alps) preserve a series of metasomatic mineral zones generated by infiltration of hydrous fluids/melts, which occurred at the gneiss-peridotite interface (Tumiati et al., 2007; Marocchi et al., 2009). The peridotite body of Mt. Hochwart represents an almost unique occurrence where subduction-related mantle metasomatism can be studied on an outcrop scale. The ultramafic body consists of metaperidotites 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-bearing gneiss country rocks. The formation of the metasomatic zones composed exclusively of hydrous phases involved extensive H2O-metasomatism as already documented for the Ulten peridotites (Scambelluri et al., 2006; Marocchi et al., 2007). Whole-rock geochemistry and trace element 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

Permanganate diffusion and reaction in sedimentary rocks.

PubMed

Huang, Qiuyuan; Dong, Hailiang; Towne, Rachael M; Fischer, Timothy B; Schaefer, Charles E

2014-04-01

In situ chemical oxidation using permanganate has frequently been used to treat chlorinated solvents in fractured bedrock aquifers. However, in systems where matrix back-diffusion is an important process, the ability of the oxidant to migrate and treat target contaminants within the rock matrix will likely determine the overall effectiveness of this remedial approach. In this study, a series of diffusion experiments were performed to measure the permanganate diffusion and reaction in four different types of sedimentary rocks (dark gray mudstone, light gray mudstone, red sandstone, and tan sandstone). Results showed that, within the experimental time frame (~2 months), oxidant migration into the rock was limited to distances less than 500 μm. The observed diffusivities for permanganate into the rock matrices ranged from 5.3 × 10(-13) to 1.3 × 10(-11) cm(2)/s. These values were reasonably predicted by accounting for both the rock oxidant demand and the effective diffusivity of the rock. Various Mn minerals formed as surface coatings from reduction of permanganate coupled with oxidation of total organic carbon (TOC), and the nature of the formed Mn minerals was dependent upon the rock type. Post-treatment tracer testing showed that these Mn mineral coatings had a negligible impact on diffusion through the rock. Overall, our results showed that the extent of permanganate diffusion and reaction depended on rock properties, including porosity, mineralogy, and organic carbon. These results have important implications for our understanding of long-term organic contaminant remediation in sedimentary rocks using permanganate. Copyright © 2014 Elsevier B.V. All rights reserved.

Qualitative evaluation of rock weir field performance and failure mechanisms

USGS Publications Warehouse

Mooney, David M.; Holmquist-Johnson, Christopher L.; Holburn, Elaina

2007-01-01

River spanning loose-rock structures provide sufficient head for irrigation diversion, permit fish passage over barriers, protect banks, stabilize degrading channels, activate side channels, reconnect floodplains, and create in-channel habitat. These structures are called by a variety of names including rock weirs, alphabet (U-, A-, V-, W-) weirs, Jhooks, and rock ramps. These structures share the common characteristics of:Loose rock construction materials (individually placed or dumped rocks with little or no concrete);Extents spanning the width of the river channel; andAn abrupt change in the water surface elevation at low flows.

Bedrock Geology and Asbestos Deposits of the Upper Missisquoi Valley and Vicinity, Vermont

USGS Publications Warehouse

Cady, Wallace Martin; Albee, Arden Leroy; Chidester, A.H.

1963-01-01

conglomerate in which the mineral chloritoid is common. The overlying Moretown formation, also of Middle Ordovician age, contains granulite and slate, also greenstone and amphibolite of the Coburn Hill volcanic member. The Shaw Mountain formation, made up of conglomerate, phyllite, and limestone, is the oldest Silurian unit. The Shaw Mountain formation is succeeded by the Northfield slate of Middle Silurian age. The igneous rocks of the region include various ultramafic plutonic rocks, such as dunite, peridotite, and serpentinite, probably of Late Ordovician age; sills and nearly concordant dikes of metagabbro of Late Ordovician age; biotite granite plutons or Middle or Late Devonian age, most notably on Eltey Mountain; and hypabyssallamprophyre, probably of late Permian age. Metamorphic zoning is shown by the distribution of rocks of the epidote-amphibolite facies and the greenschist facies in and near the Green Mountains, and near Coburn Hill and Eltey Mountain. Metasomatism related to regional metamorphism has produced porphyroblasts and quartz segregations in the sedimentary and volcanic rocks, and steatitization and carbonatization of serpentinite. Contact metamorphism has formed rocks of the epidote-amphibolite facies near granite plutons, and probably calc-silicate rock at the contacts of ultramafic plutons. The axial anticline of the Green Mountain anticlinorium and other anticlines and synclines to the east are the major longitudinal structural features of the area. These structures are complicated by transverse folds, particularly a syncline in the vicinity of Tillotson Peak. Early minor cross folds that are best developed in the Hazens Notch formation are believed to be genetically related to the transverse folds. The axial planes of the cross folds are folded about the axes of the later longitudinal folds of the Green Mountain anticlinorium. The longitudinal and transverse fold systems probably formed in the same episode of defor

Mg isotope systematics during magmatic processes: Inter-mineral fractionation in mafic to ultramafic Hawaiian xenoliths

NASA Astrophysics Data System (ADS)

Stracke, A.; Tipper, E. T.; Klemme, S.; Bizimis, M.

2018-04-01

Observed differences in Mg isotope ratios between bulk magmatic rocks are small, often on a sub per mill level. Inter-mineral differences in the 26Mg/24Mg ratio (expressed as δ26Mg) in plutonic rocks are on a similar scale, and have mostly been attributed to equilibrium isotope fractionation at magmatic temperatures. Here we report Mg isotope data on minerals in spinel peridotite and garnet pyroxenite xenoliths from the rejuvenated stage of volcanism on Oahu and Kauai, Hawaii. The new data are compared to literature data and to theoretical predictions to investigate the processes responsible for inter-mineral Mg isotope fractionation at magmatic temperatures. Theory predicts up to per mill level differences in δ26Mg between olivine and spinel at magmatic temperatures and a general decrease in Δ26Mgolivine-spinel (=δ26Mgolivine - δ26Mgspinel) with increasing temperature, but also with increasing Cr# in spinel. For peridotites with a simple petrogenetic history by melt depletion, where increasing depletion relates to increasing melting temperatures, Δ26Mgolivine-spinel should thus systematically decrease with increasing Cr# in spinel. However, most natural peridotites, including the Hawaiian spinel peridotites investigated in this study, are overprinted by variable extents of melt-rock reaction, which disturb the systematic primary temperature and compositionally related olivine-spinel Mg isotope systematics. Diffusion, subsolidus re-equilibration, or surface alteration may further affect the observed olivine-spinel Mg isotope fractionation in peridotites, making Δ26Mgolivine-spinel in peridotites a difficult-to-apply geothermometer. The available Mg isotope data on clinopyroxene and garnet suggest that this mineral pair is a more promising geothermometer, but its application is restricted to garnet-bearing igneous (garnet pyroxenites) and metamorphic rocks (eclogites). Although the observed δ26Mg variation is on a sub per mill range in bulk magmatic rocks

Drilling the Oceanic Lower Crust and Mantle

DTIC Science & Technology

1989-11-01

East Pacific Rise near 21 ...A. Bideau, R.D. and Hekinian, R. 1983, Ultramafics and mafic rocks from the Garret transform fault near 13󈧢’S on the East Pacific Rise : igneous...Science Foundation. older crust formed at the East Pacific Rise . The JOIDES Planning Committee should immediately constitute a Deep Crustal

Geochemical evidence of present-day serpentinization

USGS Publications Warehouse

Barnes, I.; LaMarche, Valmore C.; Himmelberg, G.

1967-01-01

Ultrabasic (pH > 11) water issues from some fresh ultramafic bodies. The properties of the ultrabasic solutions are believed to be due to current reactions yielding serpentine from primary olivines and pyroxenes. The low concentrations of divalent iron, divalent magnesium, and dissolved silica from the serpentinization require an increase in rock volume.

Geochemical evidence of present-day serpentinization.

PubMed

Barnes, I; Lamarche, V C; Himmelberg, G

1967-05-12

Ultrabasic (pH > 11) water issues from some fresh ultramafic bodies. The properties of the ultrabasic solutions are believed to be due to current reactions yielding serpentine from primary olivines and pyroxenes. The low concentrations of divalent airon. divalent magnesium, and dissolved silica from the serpentinization require an increase in rock volume.

Science Rocks!

ERIC Educational Resources Information Center

Prestwich, Dorothy; Sumrall, Joseph; Chessin, Debby A.

2010-01-01

It all began one Monday morning. Raymond could not wait to come to large group. In his hand, he held a chunk of white granite he had found. "Look at my beautiful rock!" he cried. The rock was passed around and examined by each student. "I wonder how rocks are made?" wondered one student. "Where do they come from?"…

Theory of wing rock

NASA Technical Reports Server (NTRS)

Hsu, C. H.; Lan, C. E.

1984-01-01

A theory is developed for predicting wing rock characteristics. From available data, it can be concluded that wing rock is triggered by flow asymmetries, developed by negative or weakly positive roll damping, and sustained by nonlinear aerodynamic roll damping. A new nonlinear aerodynamic model that includes all essential aerodynamic nonlinearities is developed. The Beecham-Titchener method is applied to obtain approximate analytic solutions for the amplitude and frequency of the limit cycle based on the three degree-of-freedom equations of motion. An iterative scheme is developed to calculate the average aerodynamic derivatives and dynamic characteristics at limit cycle conditions. Good agreement between theoretical and experimental results is obtained.

Analysis of metal tolerance in Rhizobium leguminosarum strains isolated from an ultramafic soil.

PubMed

Rubio-Sanz, Laura; Brito, Belén; Palacios, Jose

2018-02-01

Natural habitats containing high amounts of heavy metals provide a valuable source of bacteria adapted to deal with metal toxicity. A functional analysis of the population of legume endosymbiotic bacteria in an ultramafic soil was undertaken by studying a collection of Rhizobium leguminosarum bv viciae (Rlv) isolates obtained using pea as trap plant. One of the isolates, Rlv UPM1137, was selected on the basis of its higher tolerance to nickel and cobalt and presence of inducible mechanisms for such tolerance. A random transposon mutagenesis of Rlv UPM1137 allowed the generation of 14 transposant derivatives with increased nickel sensitivity; five of these transposants were also more sensitive to cobalt. Sequencing of the insertion sites revealed that one of the transposants (D2250) was affected in a gene homologous to the cation diffusion facilitator gene dmeF first identified in the metal-resistant bacterium Cupriavidus metallidurans CH34. The symbiotic performance of D2250 and two other transposants bearing single transposon insertions was unaffected under high-metal conditions, suggesting that, in contrast to previous observations in other Rlv strain, metal tolerance in UPM1137 under symbiotic conditions might be supported by functional redundancy between several mechanisms. © FEMS 2018. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Mechanism of Rock Burst Occurrence in Specially Thick Coal Seam with Rock Parting

NASA Astrophysics Data System (ADS)

Wang, Jian-chao; Jiang, Fu-xing; Meng, Xiang-jun; Wang, Xu-you; Zhu, Si-tao; Feng, Yu

2016-05-01

Specially thick coal seam with complex construction, such as rock parting and alternative soft and hard coal, is called specially thick coal seam with rock parting (STCSRP), which easily leads to rock burst during mining. Based on the stress distribution of rock parting zone, this study investigated the mechanism, engineering discriminant conditions, prevention methods, and risk evaluation method of rock burst occurrence in STCSRP through setting up a mechanical model. The main conclusions of this study are as follows. (1) When the mining face moves closer to the rock parting zone, the original non-uniform stress of the rock parting zone and the advancing stress of the mining face are combined to intensify gradually the shearing action of coal near the mining face. When the shearing action reaches a certain degree, rock burst easily occurs near the mining face. (2) Rock burst occurrence in STCSRP is positively associated with mining depth, advancing stress concentration factor of the mining face, thickness of rock parting, bursting liability of coal, thickness ratio of rock parting to coal seam, and difference of elastic modulus between rock parting and coal, whereas negatively associated with shear strength. (3) Technologies of large-diameter drilling, coal seam water injection, and deep hole blasting can reduce advancing stress concentration factor, thickness of rock parting, and difference of elastic modulus between rock parting and coal to lower the risk of rock burst in STCSRP. (4) The research result was applied to evaluate and control the risk of rock burst occurrence in STCSRP.

Biomarker insights into microbial activity in the serpentinite-hosted ecosystem of the Semail Ophiolite, Oman

NASA Astrophysics Data System (ADS)

Newman, S. A.; Lincoln, S. A.; Shock, E.; Kelemen, P. B.; Summons, R. E.

2012-12-01

Serpentinization is a process in which ultramafic and mafic rocks undergo exothermic reactions when exposed to water. The products of these reactions, including methane, hydrogen, and hydrogen sulfide, can sustain microbially dominated ecosystems [1,2,3]. Here, we report the lipid biomarker record of microbial activity in carbonate veins of the Semail Ophiolite, a site currently undergoing serpentinization [4]. The ophiolite, located in the Oman Mountains in the Sultanate of Oman, was obducted onto the Arabian continental margin during the closure of the southern Tethys Ocean (~70 Ma) [5]. We detected bacterial and archaeal glycerol dialkyl glycerol tetraether (GDGT) lipids in Semail carbonates. In addition to archaeal isoprenoidal GDGTs with 0-3 cyclopentane moieties, we detected crenarchaeol, an iGDGT containing 4 cyclopentane and 1 cyclohexane moiety. Crenarchaeol biosynthesis is currently understood to be limited to thaumarchaea, representatives of which have been found to fix inorganic carbon in culture. We also analyzed isoprenoidal diether lipids, potentially derived from methanogenic euryarchaea, as well as non-isoprenoidal diether and monoether lipids that may be indicative of methane cycling bacteria. The stable carbon isotopic composition of these compounds is potentially useful in determining both their origin and the origin of methane detected in ophiolite fluids. We compare our results to those found at the Lost City Hydrothermal Field, a similar microbially-dominated ecosystem fueled by serpentinization processes [3]. Modern serpentinite-hosted ecosystems such as this can serve as analogs for environments in which ultramafic and mafic rocks were prevalent (e.g. early Earth and other early terrestrial planets). Additionally, an analysis of modern serpentinite systems can help assess conditions promoting active carbon sequestration in ultramafic rocks [6]. References [1] Russell et al. (2010). Geobiology 8: 355-371. [2] Kelley et al. (2005). Science

Rollerjaw Rock Crusher

NASA Technical Reports Server (NTRS)

Peters, Gregory; Brown, Kyle; Fuerstenau, Stephen

2009-01-01

The rollerjaw rock crusher melds the concepts of jaw crushing and roll crushing long employed in the mining and rock-crushing industries. Rollerjaw rock crushers have been proposed for inclusion in geological exploration missions on Mars, where they would be used to pulverize rock samples into powders in the tens of micrometer particle size range required for analysis by scientific instruments.

Geologic Map of the Eastern Three-Quarters of the Cuyama 30' x 60' Quadrangle, California

USGS Publications Warehouse

Kellogg, Karl S.; Minor, Scott A.; Cossette, Pamela M.

2008-01-01

intrusive and metamorphic rocks. The Jurassic to late Paleozoic intrusive rocks include diorite, gabbro, and ultramafic rocks, and the metasedimentary rocks include marble, quartzite, schist, and gneiss.

Implications of 187Os isotopic heterogeneities in a mantle plume: evidence from Gorgona Island and Curaçao

NASA Astrophysics Data System (ADS)

Walker, Richard J.; Storey, Michael; Kerr, Andrew C.; Tarney, John; Arndt, Nicholas T.

1999-03-01

Recent work has suggested that the mafic-ultramafic volcanism in evidence throughout portions of the Caribbean, Central America, and northern South America, including the islands of Gorgona and Curaçao, was generated as part of a middle-Cretaceous, large igneous province. New Re-Os isochron results for tholeiitic basalts from Gorgona and Curaçao indicate crystallization ages of 89.2 ± 5.2 and 85.6 ± 8.1 Ma, respectively, consistent with reported Ar ages. The Gorgona ultramafic suite shows a large range in initial Os isotopic composition, with γ Os values ranging from -0.5 to +12.4. This large range reflects isotopic heterogeneities in the mantle source similar to those observed for modern ocean island basalts. In contrast to ocean island basalts, however, Os isotopic compositions do not correlate with variations in Nd, Sr, or Pb isotopic compositions, which are within the range of depleted mid-ocean ridge basalts. The processes that produced these rocks evidently resulted in the decoupling of Os isotopes from the Nd, Sr, and Pb isotopic systems. Picrites from Curaçao have very uniform, chondritic initial Os isotopic compositions, with initial γ Os values ranging only from -0.4 to ±1.4. Basalts from Curaçao, however, define an isochron with a 187Os-enriched initial isotopic composition (γ Os = +9.5). In contrast to the 187Os-enriched ultramafic rocks from Gorgona, the enrichment in these basalts could have resulted from lithospheric contamination. If the Gorgona and Curaçao rocks were derived from the same plume, Os results, combined with Sr, Nd, and Pb data indicate a heterogeneous plume, with multiple compositionally and isotopically distinct domains. The Os isotopic results require derivation of Os from a minimum of two distinct reservoirs, one with a composition very similar to the chondritic average and one with long-term enriched Re/Os. Oceanic crustal recycling has been invoked to explain most of the 187Os enrichments that have been observed in

Evaluation of ASR potential of quartz-rich rocks by alkaline etching of polished rock sections

NASA Astrophysics Data System (ADS)

Šachlová, Šárka; Kuchařová, Aneta; Pertold, Zdeněk; Přikryl, Richard

2015-04-01

standard AMBT (folowing ASTM C1260). The etching experiment is regarded to be feasible method to quantify ASR potential of quartz- (resp. SiO2-) rich rocks. Employement of the method: (1) decreases potential error from less experienced operator; (2) minimizes the volume of the rock need to be analyzed; (3) enables to visualize microscopic features where ASR originates; and (4) enables to identify alkali-reactive components in the rocks. The main disadvatage of the method is regarded in the restriction to quartz- (resp. SiO2-) rich rocks. If other minerals are included in the rocks their role in ASR should be considered. These minerals can be excluded from the analysis in case they are not reactive and if their content is very low (e.g. accesory minerals). If the minerals contribute to ASR (e.g. albite, micas), these mineral phases should be included in the analysis. Then the application of PIA needs to be modified in respect to different grey shades of individual minerals.

Carbon-dioxide storage in the subsurface: towards an understanding of crack development in the cap-rock including phase transition processes

NASA Astrophysics Data System (ADS)

Häberle, K.; Ehlers, W.

2012-04-01

Supercritical CO2 can be injected into deep saline aquifers to reduce the amount of CO2 in the atmosphere and thus, lessen the impact on the global warming. Qualified reservoirs should be in a sufficient depth to guarantee the thermodynamical environment for the supercritical state of CO2. Furthermore, an impermeable cap-rock layer must confine the reservoir layer, in order to collect the CO2 in the desired region. In CO2 storage it is crucial to guarantee the safety of the storage site and to eliminate possibilities of leakage. Therefore, deformation processes of the rock matrix and the cap-rock layer, which might be induced by the high pressure injection of CO2, must be investigated. The increase in stress may also cause crack development in the cap-rock layer. These could either be new developing fractures or the break-up of already existing but cemented cracks or faults. If such cracks occur, CO2 could migrate to shallower regions where the temperature and pressure cannot support the supercritical condition of the CO2 anymore. Thus, it is important to describe the phase transition process between supercritical, liquid and gaseous CO2. This requires a proper understanding of the thermodynamical behaviour of CO2 within the reservoir. The Theory of Porous Media (TPM) provides a useful continuum-mechanical basis to describe real natural systems in a thermodynamically consistent way. Hence, the TPM is applied to model multiphasic flow of CO2 and water and include elasto-plastic solid deformations of the porous matrix. The Peng-Robinson equation is implemented as a cubic equation of state to describe the phase behaviour of CO2 in the liquid, gaseous and supercritical region. However, in the two-phase region the isotherms show a horizontal section and kinks at the boiling and vapour curve. This cannot be represented by a continuously differentiable function such as the Peng-Robinson equation. To circumvent this problem, the Antoine equation provides additional

A mid-Archaean ophiolite complex, Barberton Mountain land

NASA Technical Reports Server (NTRS)

Dewit, M. J.; Hart, R.; Hart, R.

1986-01-01

New field observations and structurally restored geologic sections through the southern part of 3.5-3.6 Ga Barberton greenstone belt show that its mafic to ultramafic rocks form a pseudostratigraphy comparable to that of Phanerozoic ophiolites; this ancient ophiolite is referred to as the Jamestown ophiolite complex. It consists of an intrusive-extrusive mafic-ultramafic section, underlain by a high-temperature tectono-metamorphic residual peridotitic base, and is capped by a chert-shale sequence which it locally intrudes. Geochemical data support an ophiolitic comparison. Fraction of high temperature melting PGE's 2500 C in the residual rocks suggest a lower mantle origin for the precursors of this crust. An oceanic rather than arc-related crustal section can be inferred from the absence of contemporaneous andesites. The entire simatic section has also been chemically altered during its formation by hyrothermal interaction with the Archean hydrosphere. The most primitive parent liquids, from which the extrusive sequence evolved, may have been picritic in character. Rocks with a komatiitic chemistry may have been derived during crystal accumulation from picrite-crystal mushes (predominantly olivine-clinopyroxene) and/or by metasomatism during one or more subsequent episodes of hydration-dehydration. The Jamestown ophiolite complex provides the oldest record with evidence for the formation of oceanic lithosphere at constructive tectonic boundaries.

Multiple melting stages and refertilization as indicators for ridge to subduction formation: The New Caledonia ophiolite

NASA Astrophysics Data System (ADS)

Ulrich, Marc; Picard, Christian; Guillot, Stéphane; Chauvel, Catherine; Cluzel, Dominique; Meffre, Sébastien

2010-03-01

The origin of the New Caledonia ophiolite (South West Pacific), one of the largest in the world, is controversial. This nappe of ultramafic rocks (300 km long, 50 km wide and 2 km thick) is thrust upon a smaller nappe (Poya terrane) composed of basalts from mid-ocean ridges (MORB), back arc basins (BABB) and ocean islands (OIB). This nappe was tectonically accreted from the subducting plate prior and during the obduction of the ultramafic nappe. The bulk of the ophiolite is composed of highly depleted harzburgites (± dunites) with characteristic U-shaped bulk-rock rare-earth element (REE) patterns that are attributed to their formation in a forearc environment. In contrast, the origin of spoon-shaped REE patterns of lherzolites in the northernmost klippes was unclear. Our new major element and REE data on whole rocks, spinel and clinopyroxene establish the abyssal affinity of these lherzolites. Significant LREE enrichment in the lherzolites is best explained by partial melting in a spreading ridge, followed by near in-situ refertilization from deeper mantle melts. Using equilibrium melting equations, we show that melts extracted from these lherzolites are compositionally similar to the MORB of the Poya terrane. This is used to infer that the ultramafic nappe and the mafic Poya terrane represent oceanic lithosphere of a single marginal basin that formed during the late Cretaceous. In contrast, our spinel data highlights the strong forearc affinities of the most depleted harzburgites whose compositions are best modeled by hydrous melting of a source that had previously experienced depletion in a spreading ridge. The New Caledonian boninites probably formed during this second stage of partial melting. The two melting events in the New Caledonia ophiolite record the rapid transition from oceanic accretion to convergence in the South Loyalty Basin during the Late Paleocene, with initiation of a new subduction zone at or near the ridge axis.

Introduction to the Apollo collections. Part 1: Lunar igneous rocks

NASA Technical Reports Server (NTRS)

Mcgee, P. E.; Warner, J. L.; Simonds, C. H.

1977-01-01

The basic petrographic, chemical, and age data is presented for a representative suite of igneous rocks gathered during the six Apollo missions. Tables are given for 69 samples: 32 igneous rocks and 37 impactites (breccias). A description is given of 26 basalts, four plutonic rocks, and two pyroclastic samples. The textural-mineralogic name assigned each sample is included.

Theory of wing rock

NASA Technical Reports Server (NTRS)

Hsu, C.-H.; Lan, C. E.

1985-01-01

Wing rock is one type of lateral-directional instabilities at high angles of attack. To predict wing rock characteristics and to design airplanes to avoid wing rock, parameters affecting wing rock characteristics must be known. A new nonlinear aerodynamic model is developed to investigate the main aerodynamic nonlinearities causing wing rock. In the present theory, the Beecham-Titchener asymptotic method is used to derive expressions for the limit-cycle amplitude and frequency of wing rock from nonlinear flight dynamics equations. The resulting expressions are capable of explaining the existence of wing rock for all types of aircraft. Wing rock is developed by negative or weakly positive roll damping, and sustained by nonlinear aerodynamic roll damping. Good agreement between theoretical and experimental results is obtained.

Tectonics of some Amazonian greenstone belts

NASA Technical Reports Server (NTRS)

Gibbs, A. K.

1986-01-01

Greenstone belts exposed amid gneisses, granitoid rocks, and less abundant granulites along the northern and eastern margins of the Amazonian Craton yield Trans-Amazonican metamorphic ages of 2.0-2.1 Ga. Early proterozoic belts in the northern region probably originated as ensimatic island arc complexes. The Archean Carajas belt in the southeastern craton probably formed in an extensional basin on older continental basement. That basement contains older Archean belts with pillow basalts and komatiites. Belts of ultramafic rocks warrant investigatijon as possible ophiolites. A discussion follows.

Rb-Sr, K-Ar, and stable isotope evidence for the ages and sources of fluid components of gold-bearing quartz veins in the northern Sierra Nevada foothills metamorphic belt, California

USGS Publications Warehouse

Böhlke, John Karl; Kistler, R. W.

1986-01-01

Gold-bearing quartz veins occur in and near major fault zones in deformed oceanic and island-arc rocks west of the main outcrop of the Sierra Nevada composite batholith. Veins typically occupy minor reverse faults that crosscut blueschist to amphibolite-grade metamorphic rocks whose metamorphic ages range from early Paleozoic to Jurassic. Vein micas and carbonate-quartz-mica assemblages that formed by hydrothermal metasomatism of ultramafic wall rocks in the Alleghany, Grass Valley, Washington, and Mother Lode districts yield concordant K-Ar and Rb-Sr ages. The dated veins are significantly younger than prograde metamorphism, penetrative deformation, and accretion of their host rocks to the continental margin. New and previously published mineralization ages from 13 localities in the Sierra foothills range from about 140 to 110 m.y. ago, with mean and median between 120 and 115 m.y. The age relations suggest that mineralizing fluids were set in motion by deep magmatic activity related to the resumption of east-dipping subduction along the western margin of North America following the Late Jurassic Nevadan collision event.CO 2 -bearing fluids responsible for metasomatism and much of the vein mica, carbonate, albite, and quartz deposition in several northern mines were isotopically heavy (delta 18 O [asymp] 8-14ppm; delta D between about -10 and -50ppm) and do not resemble seawater, magmatic, or meteoric waters. Metasomatic and vein-filling mica, dolomite, magnesite, and quartz in altered ultramafic rocks generally formed from fluids with similar Sr and O isotope ratios at a given locality. Consistent quartz-mica delta 18 O fractionations (delta 18 O (sub Q-M) = 4.5-4.9ppm) from various localities imply uniform equilibration temperatures, probably between 300 degrees and 350 degrees C. On a local (mine) scale, fluids responsible for both carbonate alteration of mafic and ultramafic wall rocks and albitic alteration of felsic and pelitic rocks had similar Sr isotope

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.

Tectonic constraints on a deep-seated rock slide in weathered crystalline rocks

NASA Astrophysics Data System (ADS)

Borrelli, Luigi; Gullà, Giovanni

2017-08-01

Deep-seated rock slides (DSRSs), recognised as one of the most important mass wasting processes worldwide, involve large areas and cause several consequences in terms of environmental and economic damage; they result from a complex of controlling features and processes. DSRSs are common in Calabria (southern Italy) where the complex geo-structural setting plays a key role in controlling the geometry of the failure surface and its development. This paper describes an integrated multi-disciplinary approach to investigate a DSRS in Palaeozoic high-grade metamorphic rocks of the Sila Massif; it focuses on the definition of the internal structure and the predisposing factors of the Serra di Buda landslide near the town of Acri, which is a paradigm for numerous landslides in this area. An integrated interdisciplinary study based on geological, structural, and geomorphological investigations-including field observations of weathering grade of rocks, minero-petrographic characterisations, geotechnical investigations and, in particular, fifteen years of displacement monitoring-is presented. Stereoscopic analysis of aerial photographs and field observations indicate that the Serra di Buda landslide consists of two distinct compounded bodies: (i) an older and dormant body ( 7 ha) and (ii) a more recent and active body ( 13 ha) that overlies the previous one. The active landslide shows movement linked to a deep-seated translational rock slide (block slide); the velocity scale ranges from slow (1.6 m/year during paroxysmal stages) to extremely slow (< 16 mm/year during stable creep stages). The geological structures and rock weathering have played a key role in the landslide's initiation and further development. Steep slope angles, rugged topography, river deepening and erosion at the toe of the slope are also responsible for the formation of this landslide. In particular, the landslide shows a strongly tectonic constraint: the flanks are bounded by high-angle faults, and the

Processes and controls in swelling anhydritic clay rocks

NASA Astrophysics Data System (ADS)

Mutschler, Thomas; Blum, Philipp; Butscher, Christoph

2015-04-01

Referring to the swelling of anhydritic clay rocks in tunneling, Leopold Müller-Salzburg noted in the third volume on tunneling of his fundamental text book on rock engineering that "a truly coherent explanation of these phenomena is still owing" (Müller-Salzburg 1978, p. 306). This valuation is still true after more than three decades of research in the field of swelling anhydritic clay rocks. One of the reasons is our limited knowledge of the processes involved in the swelling of such rocks, and of the geological, mineralogical, hydraulic, chemical and mechanical controls of the swelling. In this contribution, a review of processes in swelling anhydritic clay rocks and of associated controls is presented. Also numerical models that aim at simulating the swelling processes and controls are included in this review, and some of the remaining open questions are pointed out. By focusing on process-oriented work in this review, the presentation intends to stimulate further research across disciplines in the field of swelling anhydritic clay rocks to finally get a step further in managing the swelling problem in geotechnical engineering projects. Keywords: swelling; anhydritic clay rocks; review

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.

Sojourner near the Rock Garden

NASA Technical Reports Server (NTRS)

1997-01-01

This image of the Sojourner rover was taken near the end of daytime operations on Sol 42. The rover is between the rocks 'Wedge' (left) and 'Flute Top' (right). Other rocks visible include 'Flat Top' (behind Flute Top) and those in the Rock Garden, at the top of the frame. The cylindrical object extending from the back end of Sojourner is the Alpha Proton X-Ray Spectrometer.

Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology (Caltech). The Imager for Mars Pathfinder (IMP) was developed by the University of Arizona Lunar and Planetary Laboratory under contract to JPL. Peter Smith is the Principal Investigator.

Earth Science: Rocks. Grade 4. Anchorage School District Elementary Science Program.

ERIC Educational Resources Information Center

Anchorage School District, AK.

This unit contains six lessons on rocks for fourth graders. It describes materials, supplementary materials (including films, units, and books) schedule, unit introduction, and background information for teachers. Lessons include: (1) "Rocks Are Everywhere"; (2) "Chart Making"; (3) "Things Are Breaking Up"; (4)…

Characterization and sources of colored dissolved organic matter in a coral reef ecosystem subject to ultramafic erosion pressure (New Caledonia, Southwest Pacific).

PubMed

Martias, Chloé; Tedetti, Marc; Lantoine, François; Jamet, Léocadie; Dupouy, Cécile

2018-03-01

The eastern lagoon of New Caledonia (NC, Southwest Pacific), listed as a UNESCO World Heritage site, hosts the world's second longest double-barrier coral reef. This lagoon receives river inputs, oceanic water arrivals, and erosion pressure from ultramafic rocks, enriched in nickel (Ni) and cobalt (Co). The aim of this study was to characterize colored dissolved organic matter (CDOM), as well as to determine its main sources and its possible relationships (through the use of Pearson correlation coefficients, r) with biogeochemical parameters, plankton communities and trace metals in the NC eastern lagoon. Water samples were collected in March 2016 along a series of river/lagoon/open-ocean transects. The absorption coefficient at 350nm (a 350 ) revealed the influence of river inputs on the CDOM distribution. The high values of spectral slope (S 275-295 , >0.03m -1 ) and the low values of specific ultraviolet absorbance (SUVA 254 , <4Lmg-C -1 m -1 ) highlighted the photodegradation of CDOM in surface waters. The application of parallel factor analysis (PARAFAC) on excitation-emission matrices (EEMs) allowed the identification of four CDOM components: (1) one humic- and one tyrosine-like fluorophores. They had terrestrial origin, exported through rivers and undergoing photo- and bio-degradation in the lagoon. These two fluorophores were linked to manganese (Mn) in southern rivers (r=0.46-0.50, n=21, p<0.05). (2) A tryptophan-like fluorophore, which exhibited higher levels offshore. It would be potentially released from the coral reef. (3) A second tyrosine-like ("tyrosine 2-like") fluorophore. Linked to Prochlorococcus cyanobacteria (r=0.39, n=47, p<0.05), this fluorophore would have an oceanic origin and enter in the lagoon through its southern and northern extremities. It also displayed relationships with Ni and Co content (r=0.53-0.54, n=21, p<0.05). This work underlines the diversity of CDOM sources in the NC eastern lagoon. Copyright © 2017 Elsevier B.V. All

Experimentally determined rock-fluid interactions applicable to a natural hot dry rock geothermal system

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

Charles, R.W.; Holley, C.E. Jr.; Tester, J.W.

1980-02-01

The Los Alamos Scientific Laboratory is pursuing laboratory and field experiments in the development of the Hot Dry Rock concept of geothermal energy. The field program consists of experiments in a hydraulically fractured region of low permeability in which hot rock is intercepted by two wellbores. These experiments are designed to test reservoir engineering parameters such as: heat extraction rates, water loss rates, flow characteristics including impedance and buoyancy, seismic activity and fluid chemistry. Laboratory experiments have been designed to provide information on the mineral reactivity which may be encountered in the field program. Two experimental circulation systems have beenmore » built to study the rates of dissolution and alteration in dynamic flow. Solubility studies have been done in agitated systems. To date, pure minerals, samples of the granodiorite from the actual reservoir and Tijeras Canyon granite have been reacted with distilled water and various solutions of NaCl, NaOH, and Na/sub 2/CO/sub 3/. The results of these experimental systems are compared to observations made in field experiments done in a hot dry rock reservoir at a depth of approximately 3 km with initial rock temperatures of 150 to 200/sup 0/C.« less

Hydrated Spinel Websterite Xenoliths From Moses Rock Diatreme, Navajo Volcanic Field: Metasomatism in the Mantle Wedge of the Colorado Plateau Above the De-watering Farallon Plate

NASA Astrophysics Data System (ADS)

Schulze, D. J.; Chow, R.; Helmstaedt, H. H.

2016-12-01

Expansion and density decrease in ultramafic rocks in the mantle wedge above the subducted and dewatering Farallon Plate in the Cenozoic may have been the driving force behind uplift of the Colorado Plateau. Here we document the effects of such hydration on spinel websterites that resulted in rocks dominated by pargasitic amphibole, Mg-chlorite and Cr-magnetite/chromite. Xenoliths of spinel websterite from the Moses Rock diatreme in the Navajo Volcanic Field on the Colorado Plateau have granoblastic to mosaic porphyroclastic texture. Porphyroclasts (up to 2 cm across) of lamellar intergrowths of clinopyroxene and orthopyroxene are set in a granular matrix of sub-equal amounts of the two pyroxenes. Both pyroxenes are magnesian and aluminous, with Mg/(Mg+Fe) in the range 0.89 to 0.93 and Al2O3 contents of approximately 4.0 to 9.5 wt%. Many samples contain aluminous spinel with Al/(Al+Cr) = 0.82 to 0.94. The effects of hydration on these samples exist as partial to complete replacement of the pyroxenes by amphibole (tremolite/edenite/pargasite/magnesio-hornblende), pseudomorphing original pyroxene textures, and replacement of primary spinel by Cr-rich magnetite or chromite with Al/(Al+Cr) = 0.07 to 0.35 intergrown with, and surrounded by, clinochlore. Unusual minerals associated with replacement of primary spinel include one example with corundum + zoisite, one with secondary garnet (molar Ca:Mg:Fe = 20:40:40) and two samples with aluminous talc (5 to 7 wt% Al2O3). By analogy with Alpine peridotites and mantle xenolith suites from basalt occurrences, the spinel websterites probably existed as veins and lenses in spinel peridotite of the shallow upper mantle beneath the Colorado Plateau prior to hydration. De-watering of the subducted Farallon Plate in Cenozoic time was likely the source of water-rich fluids that caused the hydration at fairly shallow depths (within amphibole stability), as suggested for hydration of spinel peridotite xenoliths from the Buell Park and

The fracture criticality of crustal rocks

NASA Astrophysics Data System (ADS)

Crampin, Stuart

1994-08-01

The shear-wave splitting observed along almost all shear-wave ray paths in the Earth's crust is interpreted as the effects of stress-aligned fluid-filled cracks, microcracks, and preferentially oriented pore space. Once away from the free surface, where open joints and fractures may lead to strong anisotropy of 10 per cent or greater, intact ostensibly unfractured crustal rock exhibits a limited range of shear-wave splitting from about 1.5 to 4.5 per cent differential shear-wave velocity anisotropy. Interpreting this velocity anisotropy as normalized crack densities, a factor of less than two in crack radius covers the range from the minimum 1.5 per cent anisotropy observed in intact rock to the 10 per cent observed in heavily cracked almost disaggregated near-surface rocks. This narrow range of crack dimensions and the pronounced effect on rock cohesion suggests that there is a state of fracture criticality at some level of anisotropy between 4.5 and 10 per cent marking the boundary between essentially intact, and heavily fractured rock. When the level of fracture criticality is exceeded, cracking is so severe that there is a breakdown in shear strength, the likelihood of progressive fracturing and the dispersal of pore fluids through enhanced permeability. The range of normalized crack dimensions below fracture criticality is so small in intact rock, that any modification to the crack geometry by even minor changes of conditions or minor deformation (particularly in the presence of high pore-fluid pressures) may change rock from being essentially intact (below fracture criticality) to heavily fractured (above fracture criticality). This recognition of the essential compliance of most crustal rocks, and its effect on shear-wave splitting, has implications for monitoring changes in any conditions affecting the rock mass. These include monitoring changes in reservoir evolution during hydrocarbon production and enhanced oil recovery, and in monitoring changes before

Rocks Can Wow? Yes, Rocks Can Wow!

ERIC Educational Resources Information Center

Hardman, Sally; Luke, Sue

2016-01-01

Rocks and fossils appear in the National Curriculum of England science programmes of study for children in year 3 (ages 7-8). A frequently asked question is "How do you make the classification of rocks engaging?" In response to this request from a school, a set of interactive activities was designed and organised by tutors and students…

Nd-isotopes in selected mantle-derived rocks and minerals and their implications for mantle evolution

USGS Publications Warehouse

Basu, A.R.; Tatsumoto, M.

1980-01-01

The Sm-Nd systematics in a variety of mantle-derived samples including kimberlites, alnoite, carbonatite, pyroxene and amphibole inclusions in alkali basalts and xenolithic eclogites, granulites and a pyroxene megacryst in kimberlites are reported. The additional data on kimberlites strengthen our earlier conclusion that kimberlites are derived from a relatively undifferentiated chondritic mantle source. This conclusion is based on the observation that the e{open}Nd values of most of the kimberlites are near zero. In contrast with the kimberlites, their garnet lherzolite inclusions show both time-averaged Nd enrichment and depletion with respect to Sm. Separated clinopyroxenes in eclogite xenoliths from the Roberts Victor kimberlite pipe show both positive and negative e{open}Nd values suggesting different genetic history. A whole rock lower crustal scapolite granulite xenolith from the Matsoku kimberlite pipe shows a negative e{open}Nd value of -4.2, possibly representative of the base of the crust in Lesotho. It appears that all inclusions, mafic and ultramafic, in kimberlites are unrelated to their kimberlite host. The above data and additional Sm-Nd data on xenoliths in alkali basalts, alpine peridotite and alnoite-carbonatites are used to construct a model for the upper 200 km of the earth's mantle - both oceanic and continental. The essential feature of this model is the increasing degree of fertility of the mantle with depth. The kimberlite's source at depths below 200 km in the subcontinental mantle is the most primitive in this model, and this primitive layer is also extended to the suboceanic mantle. However, it is clear from the Nd-isotopic data in the xenoliths of the continental kimberlites that above 200 km the continental mantle is distinctly different from their suboceanic counterpart. ?? 1980 Springer-Verlag.

Bounce Rock Dimple

NASA Technical Reports Server (NTRS)

2004-01-01

This panoramic camera image shows the hole drilled by the Mars Exploration Rover Opportunity's rock abrasion tool into the rock dubbed 'Bounce' on Sol 65 of the rover's journey. The tool drilled about 7 millimeters (0.3 inches) into the rock and generated small piles of 'tailings' or rock dust around the central hole, which is about 4.5 centimeters (1.7 inches) across. The image from sol 66 of the mission was acquired using the panoramic camera's 430 nanometer filter.

The abundances of components of the lunar soils by a least-squares mixing model and the formation age of KREEP.

NASA Technical Reports Server (NTRS)

Schonfeld, E.; Meyer, C., Jr.

1972-01-01

A least-square mixing model incorporating mare basalts, KREEP basalts, anorthosites, anorthositic gabbros, ultramafics, granites, and meteorites was used to estimate the abundances of rock components in lunar soil from the Apollo 11, 12, 15, Luna 16, and Surveyor 5 and 6 landing sites. The predominance of iron-rich mare basalt at the sites is indicated.

Quantifying rock mass strength degradation in coastal rock cliffs

NASA Astrophysics Data System (ADS)

Brain, Matthew; Lim, Michael; Rosser, Nick; Petley, David; Norman, Emma; Barlow, John

2010-05-01

Although rock cliffs are generally perceived to evolve through undercutting and cantilever collapse of material, the recent application of high-resolution three-dimensional monitoring techniques has suggested that the volumetric losses recorded from layers above the intertidal zone produce an equally significant contribution to cliff behaviour. It is therefore important to understand the controls on rockfalls in such layers. Here we investigate the progressive influence of subaerial exposure and weathering on the geotechnical properties of the rocks encountered within the geologically complex coastal cliffs of the northeast coast of England, UK. Through a program of continuous in situ monitoring of local environmental and tidal conditions and laboratory rock strength testing, we aim to better quantify the relationships between environmental processes and the geotechnical response of the cliff materials. We have cut fresh (not previously exposed) samples from the three main rock types (sandstone, mudstone and shale) found within the cliff to uniform size, shape and volume, thus minimizing variability and removing previous surface weathering effects. In order to characterise the intact strength of the rocks, we have undertaken unconfined compressive strength and triaxial strength tests using high pressure (400 kN maximum axial load; 64 MPa maximum cell pressure) triaxial testing apparatus. The results outline the peak strength characteristics of the unweathered materials. We then divided the samples of each lithology into different experimental groups. The first set of samples remained in the laboratory at constant temperature and humidity; this group provides our control. Samples from each of the three rock types were located at heights on the cliff face corresponding with the different lithologies: at the base (mudstone), in the mid cliff (shale) and at the top of the cliff (sandstone). This subjected them to the same conditions experienced by the in situ cliff

Microbial communities in carbonate rocks-from soil via groundwater to rocks.

PubMed

Meier, Aileen; Singh, Manu K; Kastner, Anne; Merten, Dirk; Büchel, Georg; Kothe, Erika

2017-09-01

Microbial communities in soil, groundwater, and rock of two sites in limestone were investigated to determine community parameters differentiating habitats in two lithostratigraphic untis. Lower Muschelkalk and Middle Muschelkalk associated soils, groundwater, and rock samples showed different, but overlapping microbial communities linked to carbon fluxes. The microbial diversities in soil were highest, groundwater revealed overlapping taxa but lower diversity, and rock samples were predominantly characterized by endospore forming bacteria and few archaea. Physiological profiles could establish a differentiation between habitats (soil, groundwater, rock). From community analyses and physiological profiles, different element cycles in limestone could be identified for the three habitats. While in soil, nitrogen cycling was identified as specific determinant, in rock methanogenesis linked carbonate rock to atmospheric methane cycles. These patterns specifically allowed for delineation of lithostratigraphic connections to physiological parameters. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Impact of fluid-rock chemical interactions on tracer transport in fractured rocks.

PubMed

Mukhopadhyay, Sumit; Liu, H-H; Spycher, N; Kennedy, B M

2013-11-01

In this paper, we investigate the impact of chemical interactions, in the form of mineral precipitation and dissolution reactions, on tracer transport in fractured rocks. When a tracer is introduced in fractured rocks, it moves through the fracture primarily by advection and it also enters the stagnant water of the surrounding rock matrix through diffusion. Inside the porous rock matrix, the tracer chemically interacts with the solid materials of the rock, where it can precipitate depending on the local equilibrium conditions. Alternatively, it can be dissolved from the solid phase of the rock matrix into the matrix pore water, diffuse into the flowing fluids of the fracture and is advected out of it. We show that such chemical interactions between the fluid and solid phases have significant impact on tracer transport in fractured rocks. We invoke the dual-porosity conceptualization to represent the fractured rocks and develop a semi-analytical solution to describe the transient transport of tracers in interacting fluid-rock systems. To test the accuracy and stability of the semi-analytical solution, we compare it with simulation results obtained with the TOUGHREACT simulator. We observe that, in a chemically interacting system, the tracer breakthrough curve exhibits a pseudo-steady state, where the tracer concentration remains more or less constant over a finite period of time. Such a pseudo-steady condition is not observed in a non-reactive fluid-rock system. We show that the duration of the pseudo-state depends on the physical and chemical parameters of the system, and can be exploited to extract information about the fractured rock system, such as the fracture spacing and fracture-matrix interface area. © 2013.

Opportunity Rocks!

NASA Technical Reports Server (NTRS)

2004-01-01

This high-resolution image captured by the Mars Exploration Rover Opportunity's panoramic camera shows in superb detail a portion of the puzzling rock outcropping that scientists are eagerly planning to investigate. Presently, Opportunity is on its lander facing northeast; the outcropping lies to the northwest. These layered rocks measure only 10 centimeters (4 inches) tall and are thought to be either volcanic ash deposits or sediments carried by water or wind. The small rock in the center is about the size of a golf ball.

Orogenic potassic mafic magmatism, a product of alkaline-peraluminous mixing ? Variscan 'calc-alkaline' rocks from the Central Iberian and Ossa Morena Zones, Central Spain.