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Sample records for monazite geochronology geochemistry

  1. Provisional zircon and monazite uranium-lead geochronology for selected rocks from Vermont

    USGS Publications Warehouse

    Aleinikoff, John N.; Ratcliffe, Nicholas M.; Walsh, Gregory J.

    2011-01-01

    This report presents the results of zircon and monazite uranium-lead (U-Pb) geochronologic analyses of 24 rock samples. The samples in this study were collected from mapped exposures identified while conducting either new, detailed (1:24,000-scale) geologic quadrangle mapping or reconnaissance mapping, both of which were used for compilation of the bedrock geologic map of Vermont. All of the collected samples were judged to be igneous rocks (either intrusive or extrusive) on the basis of field relations and geochemistry. The one exception is the Okemo Quartzite on Ludlow Mountain. These geochronologic data were used to supplement regional correlations between igneous suites on the basis of similar geochemistry and geologic mapping.

  2. Origin of an unusual monazite-xenotime gneiss, Hudson Highlands, New York: SHRIMP U-Pb geochronology and trace element geochemistry

    USGS Publications Warehouse

    Aleinikoff, John N.; Grauch, Richard I.; Mazdab, Frank K.; Kwak, Loretta; Fanning, C. Mark; Kamo, Sandra L.

    2012-01-01

    A pod of monazite-xenotime gneiss (MXG) occurs within Mesoproterozoic paragneiss, Hudson Highlands, New York. This outcrop also contains granite of the Crystal Lake pluton, which migmatized the paragneiss. Previously, monazite, xenotime, and zircon from MXG, plus detrital zircon from the paragneiss, and igneous zircon from the granite, were dated using multi-grain thermal ionization mass spectrometry (TIMS). New SEM imagery of dated samples reveals that all minerals contain cores and rims. Thus TIMS analyses comprise mixtures of age components and are geologically meaningless. New spot analyses by sensitive high resolution ion microprobe (SHRIMP) of small homogeneous areas on individual grains allows deconvolution of ages within complexly zoned grains. Xenotime cores from MXG formed during two episodes (1034 ± 10 and 1014 ± 3 Ma), whereas three episodes of rim formation are recorded (999 ± 7, 961 ± 11, and 874 ± 11 Ma). Monazite cores from MXG mostly formed at 1004 ± 4 Ma; rims formed at 994 ± 4, 913 ± 7, and 890 ± 7 Ma. Zircon from MXG is composed of oscillatory-zoned detrital cores (2000-1170 Ma), plus metamorphic rims (1008 ± 7, 985 ± 5, and ∼950 Ma). In addition, MXG contains an unusual zircon population composed of irregularly-zoned elongate cores dated at 1036 ± 5 Ma, considered to be the time of formation of MXG. The time of granite emplacement is dated by oscillatory-zoned igneous cores at 1058 ± 4 Ma, which provides a minimum age constraint for the time of deposition of the paragneiss. Selected trace elements, including all REE plus U and Th, provide geochemical evidence for the origin of MXG. MREE-enriched xenotime from MXG are dissimilar from typical HREE-enriched patterns of igneous xenotime. The presence of large negative Eu anomalies and high U and Th in monazite and xenotime are uncharacteristic of typical ore-forming hydrothermal processes. We conclude that MXG is the result of unusual metasomatic processes during high grade

  3. Lower Carboniferous post-orogenic granites in central-eastern Sierra de Velasco, Sierras Pampeanas, Argentina: U-Pb monazite geochronology, geochemistry and Sr-Nd isotopes

    NASA Astrophysics Data System (ADS)

    Grosse, Pablo; Söllner, Frank; Báez, Miguel A.; Toselli, Alejandro J.; Rossi, Juana N.; de La Rosa, Jesus D.

    2009-07-01

    The central-eastern part of the Sierra de Velasco (Sierras Pampeanas, NW Argentina) is formed by the large Huaco (40 × 30 km) and Sanagasta (25 × 15 km) granite massifs and the small La Chinchilla stock (2 × 2 km). The larger granites intrude into Ordovician metagranitoids and crosscut Devonian (?) mylonitic shear zones, whereas the small stock sharply intrudes into the Huaco granite. The two voluminous granites are biotitic-muscovitic and biotitic porphyritic syeno- to monzogranites. They contain small and rounded tonalitic and quartz-dioritic mafic microgranular enclaves. The small stock is an equigranular, zinnwaldite- and fluorite-bearing monzogranite. The studied granites are silica-rich (SiO2 >70%), potassium-rich (K2O >4%), ferroan, alkali-calcic to slightly calk-alkalic, and moderately to weakly peraluminous (A/CNK: 1.06-1.18 Huaco granite, 1.01-1.09 Sanagasta granite, 1.05-1.06 La Chinchilla stock). They have moderate to strong enrichments in several LIL (Li, Rb, Cs) and HFS (Nb, Ta, Y, Th, U) elements, and low Sr, Ba and Eu contents. U-Pb monazite age determinations indicate Lower Carboniferous crystallization ages: 350-358 Ma for the Huaco granite, 352.7 ± 1.4 Ma for the Sanagasta granite and 344.5 ± 1.4 Ma for the La Chinchilla stock. The larger granites have similar ɛNd values between -2.1 and -4.3, whereas the younger stock has higher ɛNd of -0.6 to -1.4, roughly comparable to the values obtained for the Carboniferous San Blas granite (-1.4 to -1.7), located in the north of the sierra. The Huaco and Sanagasta granites have a mainly crustal source, but with some participation of a more primitive, possibly mantle-derived, component. The main crustal component can be attributed to Ordovician peraluminous metagranitoids. The La Chinchilla stock derives from a more primitive source, suggesting an increase with time in the participation of the primitive component during magma genesis. The studied granites were generated during a post-orogenic period

  4. The Triassic reworking of the Yunkai massif (South China): EMP monazite and U-Pb zircon geochronologic evidence

    NASA Astrophysics Data System (ADS)

    Chen, Cheng-Hong; Liu, Yung-Hsin; Lee, Chi-Yu; Sano, Yuji; Zhou, Han-Wen; Xiang, Hua; Takahata, Naoto

    2017-01-01

    Geohistory of the Yunkai massif in South China Block is important in understanding the geodynamics for the build-up of this block during the Phanerozoic orogenies. To investigate this massif, we conduct EMP monazite and U-Pb zircon geochronological determinations on mineral inclusions and separate for seventeen samples in four groups, representing metamorphic rocks from core domain, the Gaozhou Complex (amphibolite facies, NE-striking) and the Yunkai Group (greenschist facies, NW-striking) of this massif and adjacent undeformed granites. Some EMP monazite ages are consistent with the NanoSIMS results. Monazite inclusions, mostly with long axis parallel to the cleavage of platy and elongated hosts, give distinguishable age results for NW- and NE-trending deformations at 244-236 Ma and 236-233 Ma, respectively. They also yield ages of 233-230 Ma for core domain gneissic granites and 232-229 Ma for undefomed granites. Combining U-Pb zircon ages of the same group, 245 Ma and 230 Ma are suggested to constrain the time of two phases of deformation. Aside from ubiquity of Triassic ages in studied rocks, ages of detrital monazite in the meta-sandstone match the major U-Pb zircon age clusters of the metamorphic rock that are largely concentrated at Neoproterozoic (1.0-0.9 Ga) and Early Paleozoic (444-431 Ma). Based on these geochronological data, Triassic is interpreted as representing the time for recrystallization of these host minerals on the Early Paleozoic protolith, and the also popular Neoproterozoic age is probably inherited. With this context, Yunkai massif is regarded as a strongly reactivated Triassic metamorphic terrain on an Early Paleozoic basement which had incorporated sediments with Neoproterozoic provenances. Triassic tectonic evolution of the Yunkai massif is suggested to have been controlled by converging geodynamics of the South China and Indochina Blocks as well as mafic magma emplacement related to the Emeishan large igneous province (E-LIP).

  5. Linking monazite geochronology with fluid infiltration and metamorphic histories: Nature and experiment

    NASA Astrophysics Data System (ADS)

    Shazia, J. R.; Harlov, D. E.; Suzuki, K.; Kim, S. W.; Girish-Kumar, M.; Hayasaka, Y.; Ishwar-Kumar, C.; Windley, B. F.; Sajeev, K.

    2015-11-01

    Migmatised metapelites from the Kodaikanal region, central Madurai Block, southern India have undergone ultrahigh-temperature metamorphism (950-1000 °C; 7-8 kbar). In-situ electron microprobe Th-U-Pb isochron (CHIME) dating of monazites in a leucosome and surrounding silica-saturated and silica-poor restites from the same outcrop indicates three principal ages that can be linked to the evolutionary history of these rocks. Monazite grains from the silica-saturated restite have well-defined, inherited cores with thick rims that yield an age of ca. 1684 Ma. This either dates the metamorphism of the original metapelite or is a detrital age of inherited monazite. Monazite grains from the silica-poor restite, thick rims from the silica-saturated restite, and monazite cores from the leucosome have ages ranging from 520 to 540 Ma suggesting a mean age of 530 Ma within the error bars. In the leucosome the altered rim of the monazite gives an age of ca. 502 Ma. Alteration takes the form of Th-depleted lobes of monazite with sharp curvilinear boundaries extending from the monazite grain rim into the core. We have replicated experimentally these altered rims in a monazite-leucosome experiment at 800 °C and 2 kbar. This experiment, coupled with earlier published monazite-fluid experiments involving high pH alkali-bearing fluids at high P-T, helps to confirm the idea that alkali-bearing fluids, in the melt and along grain boundaries during crystallization, were responsible for the formation of the altered monazite grain rims via the process of coupled dissolution-reprecipitation.

  6. Tectonic evolution of high-grade metamorphic terranes in central Vietnam: Constraints from large-scale monazite geochronology

    NASA Astrophysics Data System (ADS)

    Nakano, Nobuhiko; Osanai, Yasuhito; Owada, Masaaki; Nam, Tran Ngoc; Charusiri, Punya; Khamphavong, Keo

    2013-09-01

    Several metamorphic complexes in Southeast Asia have been interpreted as Precambrian basement, characterized by amphibolite to granulite facies metamorphism. In this paper, we re-evaluate the timing of this thermal event based on the large-scale geochronology and compositional variation of monazites from amphibolite to granulite facies metamorphic terranes in central Vietnam. Most of the samples in this study are from metamorphic rocks (n = 38) and granitoids (n = 11) in the Kontum Massif. Gneisses (n = 6) and granitoids (n = 5) from the Hai Van Migmatite Complex and the Truong Son Belt, located to the north of the massif, were also studied. Two distinct thermal episodes (245-230 Ma and 460-430 Ma) affected Kontum Massif gneisses, while a single dominant event at 240-220 Ma is recorded in the gneisses from the Hai Van Complex and the Truong Son Belt. Monazites from granitoids commonly yield an age of 240-220 Ma. Mesoproterozoic ages (1530-1340 Ma) were obtained only from monazite cores that are surrounded by c. 440 Ma overgrowths. Thermobarometric results, combined with concentrations of Y2O3, Ce2O3, and heavy rare earth elements in monazite, and recently reported pressure-temperature paths suggest that Triassic ages correspond to retrograde metamorphism following decompression from high- to medium-pressure/temperature conditions. Ordovician-Silurian ages reflect low-pressure/temperature metamorphism accompanied by isobaric heating during prograde metamorphism. Some samples were affected by both metamorphic events. We conclude that high-grade metamorphism observed in so-called Precambrian basement terranes in central Vietnam occurred during both the Permian-Triassic and the Ordovician-Silurian, while peraluminous granitoid magmatism is Triassic. Additionally, our preliminary analyses for U-Pb zircon age and whole-rock chemistry of granitic gneisses from the Truong Song Belt suggests the presence of the Ordovician-Silurian volcanic arc magmatism in the region. Based

  7. LASS U-Th-Pb monazite and rutile geochronology of felsic high-pressure granulites (Rhodope, N Greece): Effects of fluid, deformation and metamorphic reactions in local subsystems

    NASA Astrophysics Data System (ADS)

    Wawrzenitz, Nicole; Krohe, Alexander; Baziotis, Ioannis; Mposkos, Evripidis; Kylander-Clark, Andrew R. C.; Romer, Rolf L.

    2015-09-01

    The specific chemical composition of monazite in shear zones is controlled by the syndeformation dissolution-precipitation reactions of the rock-forming minerals. This relation can be used for dating deformation, even when microfabric characteristics like shape preferred orientation or intracrystalline deformation of monazite itself are missing. Monazite contemporaneously formed in and around the shear zones may have different compositions. These depend on the local chemical context rather than reflecting successive crystallization episodes of monazite. This is demonstrated in polymetamorphic, mylonitic high-pressure (HP) garnet-kyanite granulites of the Alpine Sidironero Complex (Rhodope UHP terrain, Northern Greece). The studied mylonitic rocks escaped from regional migmatization at 40-36 Ma and from subsequent shearing through cooling until 36 Ma. In-situ laser-ablation split-stream inductively-coupled plasma mass spectrometry (LASS) analyses have been carried out on monazite from micro-scale shear zones, from pre-mylonitic microlithons as well as of monazite inclusions in relictic minerals complimented by U-Pb data on rutile and Rb-Sr data of biotite. Two major metamorphic episodes, Mesozoic and Cenozoic, are constrained. Chemical compositions, isotopic characteristics and apparent ages systematically vary among monazite of four different microfabric domains (I-IV). Within three pre-mylonitic domains (inclusions in (I) pre-mylonitic kyanite and (II) garnet porphyroclasts, and (III) in pre-mylonitic microlithons) monazite yields ages of ca. 130-150 Ma for HP-granulite metamorphism, in line with previous geochronological results in the area. Patchy alteration of the pre-mylonitic monazite by intra-grain dissolution-precipitation processes variably increased negative Eu anomaly and reduced the HREE contents. The apparent age of this altered monazite is reduced. Monazite in the syn-mylonitic shear bands (IV) differs in chemical composition from unaltered and

  8. High-spatial-resolution isotope geochemistry of monazite (U-Pb & Sm-Nd) and zircon (U-Pb & Lu-Hf) in the Old Woman and North Piute Mountains, Mojave Desert, California

    NASA Astrophysics Data System (ADS)

    Phillips, Stacy E.; Hanchar, John M.; Miller, Calvin F.; Fisher, Christopher M.; Lancaster, Penny J.; Darling, James R.

    2014-05-01

    Recent improvements in analytical capabilities allow us to reveal details of magmatic processes at an increasingly finer spatial and temporal scale. In situ analyses of the isotopic and trace element composition of accessory minerals at the sub-grain scale have proven to be effective tools for solving a wide range of geological problems. This study presents new data on accessory minerals including monazite & zircon, examined by in situ LA-ICP-MS and Laser Ablation Split Stream (LASS) techniques, analyzing multiple isotopic systems (U-Pb + Sm-Nd, and U-Pb + Lu-Hf in monazite and zircon, respectively) in order to track geochemical changes over time through a magmatic system. The late Cretaceous granitoids of the Old Woman Mountains in the Mojave Desert, California, provide an excellent opportunity to apply these analytical techniques. The peraluminous granites of the Sweetwater Wash, Painted Rock, and North Piute plutons represent different depths of the magmatic system, and are well understood in terms of field relations and whole-rock geochemistry. A preliminary study on the Sweetwater Wash monazites (Fisher et al., in preparation) has revealed significant inter-grain isotopic heterogeneity in the ɛNd composition of the source region (~1700 Ma); however, the U-Pb ages show an isotopic resetting during emplacement at ~75 Ma. This decoupling of U-Pb and Sm-Nd isotopic systems is suggested by Fisher et al. to be due to recrystallisation and/or dissolution-reprecipitation of monazite. If grain boundary diffusion of Pb overrides the more kinetically limited volume diffusion, then the U-Pb systematics will be reset while Sm and Nd remain immobile in the monazite structure as essential structural components of the lattice. This new data will allow the further investigation of these preliminary results, providing new insights into the observed isotopic disequilibrium, with the LASS technique accurately linking the multiple isotopic systems. This will provide important

  9. Petrology, phase equilibria and monazite geochronology of granulite-facies metapelites from deep drill cores in the Ordos Block of the North China Craton

    NASA Astrophysics Data System (ADS)

    He, Xiao-Fang; Santosh, M.; Bockmann, Kiara; Kelsey, David E.; Hand, Martin; Hu, Jianmin; Wan, Yusheng

    2016-10-01

    Among the various Precambrian crustal blocks in the North China Craton (NCC), the geology and evolution of the Ordos Block remain largely enigmatic due to paucity of outcrop. Here we investigate granulite-facies metapelites obtained from deep-penetrating drill holes in the Ordos Block and report petrology, calculated phase equilibria and in-situ monazite LA-ICP-MS geochronology. The rocks we studied are two samples of cordierite-bearing garnet-sillimanite-biotite metapelitic gneisses and one graphite-bearing, two-mica granitic gneiss. The peak metamorphic age from LA-ICP-MS dating of monazite in all three samples is in the range of 1930-1940 Ma. The (U + Pb)-Th chemical ages through EPMA dating reveals that monazite occurring as inclusions in garnet are older than those in the matrix. Calculated metamorphic phase diagrams for the cordierite-bearing metapelite suggest peak P-T conditions ca. 7-9 kbar and 775-825 °C, followed by decompression and evolution along a clockwise P-T path. Our petrologic and age data are consistent with those reported from the Khondalite Belt in the Inner Mongolia Suture Zone in the northern part of the Ordos Block, suggesting that these granulite-facies metasediments represent the largest Paleoproterozoic accretionary belt in the NCC.

  10. Application of Geochronology and Geochemistry of Speleothems to Hydrologic Change

    NASA Astrophysics Data System (ADS)

    Banner, J. L.; Musgrove, M.; Mickler, P. J.; Mack, L. E.; James, E. W.

    2001-12-01

    in spite of the many complexities of regional and local variability both within and between aquifer systems, climate signals are discernable. Coupled studies of speleothems and the modern groundwater system help constrain mechanisms that link hydrologic and climatic processes over multiple timescales. The calibration of modern speleothem geochemistry and growth rates with aquifer and climatic measurements is a new research avenue toward this end.

  11. U-Pb geochronology of zircon and monazite from Mesoproterozoic granitic gneisses of the northern Blue Ridge, Virginia and Maryland, USA

    USGS Publications Warehouse

    Aleinikoff, J.N.; Burton, W.C.; Lyttle, P.T.; Nelson, A.E.; Southworth, C.S.

    2000-01-01

    Mesoproterozoic granitic gneisses comprise most of the basement of the northern Blue Ridge geologic province in Virginia and Maryland. Lithology, structure, and U-Pb geochronology have been used to subdivide the gneisses into three groups. The oldest rocks, Group 1, are layered granitic gneiss (1153 ?? 6 Ma), hornblende monzonite gneiss (1149 ?? 19 Ma), porphyroblastic granite gneiss (1144 ?? 2 Ma), coarse-grained metagranite (about 1140 Ma), and charnockite (>1145 Ma?). These gneisses contain three Proterozoic deformational fabrics. Because of complex U-Pb systematics due to extensive overgrowths on magmatic cores, zircons from hornblende monzonite gneiss were dated using the sensitive high-resolution ion microprobe (SHRIMP), whereas all other ages are based on conventional U-Pb geochronology. Group 2 rocks are leucocratic and biotic varieties of Marshall Metagranite, dated at 1112??3 Ma and 1111 ?? 2 Ma respectively. Group 3 rocks are subdivided into two age groups: (1) garnetiferous metagranite (1077 ?? 4 Ma) and quartz-plagioclase gneiss (1077 ?? 4 Ma); (2) white leucocratic metagranite (1060 ?? 2 Ma), pink leucocratic metagranite (1059 ?? 2), biotite granite gneiss (1055 ?? 4 Ma), and megacrystic metagranite (1055 ?? 2 Ma). Groups 2 and 3 gneisses contain only the two younger Proterozoic deformational fabrics. Ages of monazite, seprated from seven samples, indicate growth during both igneous and metamorphic (thermal) events. However, ages obtained from individual grains may be mixtures of different age components, as suggested by backscatter electron (BSE) imaging of complexly zoned grains. Analyses of unzoned monazite (imaged by BSE and thought to contain only one age component) from porphyroblastic granite gneiss yield ages of 1070, 1060, and 1050 Ma. The range of ages of monazite (not reset to a uniform date) indicates that the Grenville granulite event at about 1035 Ma did not exceed about 750??C. Lack of evidence for 1110 Ma growth of monazite in

  12. Coupling thermodynamic modeling and high-resolution in situ LA-ICP-MS monazite geochronology: evidence for Barrovian metamorphism late in the Grenvillian history of southeastern Ontario

    NASA Astrophysics Data System (ADS)

    McCarron, Travis; Gaidies, Fred; McFarlane, Christopher R. M.; Easton, R. Michael; Jones, Peter

    2014-12-01

    The Flinton Group is a greenschist to upper amphibolite facies package of metasediments in southeastern Ontario that was metamorphosed during the Ottawan Orogeny. Thermodynamic modeling of metapelitic mineral assemblages suggests an increase in peak conditions of metamorphism across the 40 km wide study area from 3.5 to 7.9 kbar and 540 to 715 °C. Garnet isopleth thermobarometry applied to the cores of compositionally zoned porphyroblasts reveals remarkably similar P-T conditions of initial crystallization at approximately 3.7-4.0 kbar and 512-520 °C, corresponding to a relatively high geothermal gradient of ca. 34-45 °C km-1. It is inferred from modeling and reaction textures that metamorphism was along Barrovian P-T paths. Major and trace element zoning in garnet from one sample records a complex growth history as evidenced by major and trace element zoning and the distribution of xenotime, allanite and monazite inclusions. High-resolution (6 μm) LA-ICP-MS U-Pb geochronology performed on monazite in the rock matrix and included in the outer 150 μm of garnet rim-ward of a Y annulus revealed an age of 976 ± 4 Ma. The age is interpreted to reflect monazite growth at the expense of allanite and apatite late in garnet's growth history over the P-T interval 4.5-6.8 kbar and 540-640 °C. This new age estimate for near peak metamorphism fits well into the regional framework but is significantly younger than previously reported ages for Ottawan metamorphism. Based on microstructures this new age suggests that compressional tectonics were operating much later in the history of the Grenville of southeastern Ontario than previously thought.

  13. U-Pb geochronology and geochemistry of the Morro-Islay volcanic complex, southern California

    NASA Astrophysics Data System (ADS)

    Beck, M. D.; Johnston, S. M.

    2011-12-01

    The Morro-Islay volcanic complex is an important reference point in southern California used to reconstruct the tectonic setting of the North American continental margin during the early evolution of the San Andreas Fault. The age and petrologic formation of the Morro-Islay volcanic complex directly affects the accuracy of these reconstructions, and therefore its geologic properties should be reexamined as new techniques become available. Here, we present new U-Pb geochronology and geochemistry results to place constraints on the timing of the Morro-Islay volcanic complex and add to the existing geochemical database. Samples for U-Pb analysis were collected from felsic units exposed at Cerro Cabrillo to the west and Islay Hill to the east, and processed in the mineral separation laboratory at Cal Poly San Luis Obispo to extract zircons. U-Pb isotopic ratios for individual zircon grains were then determined using laser ablation ICP mass spectrometry in the dual-ICP laboratory at the University of California, Santa Barbara. The age of Cerro Cabrillo was determined to be 26.7 +0.2/-0.1 Ma and the age of Islay Hill was determined to be 26.7 +0.1/-0.1 Ma. Geochemical samples, preferentially selected for the most mafic compositions identified in thin section, were collected from Morro Rock and Cerro Cabrillo, both near the western end of the complex. Despite point counts that suggested relatively high mafic content in the two samples, whole rock geochemistry from these samples yielded high silica concentrations with Morro Rock classified as a dacite and Cerro Cabrillo Classified as a rhyolite. Both samples contain significant trace element depletions in Nb, Ta, Sr, and Ti, with subtle negative Eu anomalies and flat HREE signatures. This new data significantly tightens the age range for the formation of the Morro-Islay volcanic complex and supports previous tectonic reconstructions of Southern California in the Oligocene. In addition, the new geochemical and

  14. Geochemistry and 40Ar/39Ar geochronology of the ophiolite in Northern Xinjiang

    NASA Astrophysics Data System (ADS)

    Qinqin, Xu; Jianqing, Ji

    2010-05-01

    As the remnant of ancient oceanic crust, ophiolite is extremely important to reconstruct the framework of ancient ocean and continent. There are several ophiolite belts in Northern Xinjiang, assuming planar distribution, and they are generally related to different faults since Paleozoic in the outcrops. This paper presents a systematic study of geochemistry and geochronology of the gabbro, diabase and basalt of ophiolite collected from different regions in Northern Xinjiang. The intermediate and basic rocks in ophiolite show similar patterns in primitive mantle-normalized REE and trace elements diagrams with MORB and different from IAT, indicating that the ophiolite may be formed in mid-ocean ridge. Their Sr, Nd and Pb isotopic compositions also show that they have mid-ocean ridge environment affinity. Additionally, their Sr, Nd and Pb isotopic ratios are similar respectively, suggesting the same source area, and they also have positive epsilon Nd values(4.40 ~ 8.04), which indicates they likely originate from the depleted mantle. The previous and the author's researches show that the forming time of ophiolite in Northern Xinjiang is early Paleozoic, but 40Ar/39Ar ages of gabbro, diabase and basalt are in the range of 396 ~ 226Ma (mainly from 350 to 250Ma), and no ages of early Paleozoic are gained. Moreover, this time coincides with the timing of late Paleozoic post-collisional plutonism, indicating the ophiolite in Northern Xinjiang was reworked by the late thermal events. The ophiolite widely exposed in Northern Xinjiang have similar characteristics of occurrence, lithologic association and isotopes in spite of diverse special features, which indicates that a relatively uniform and integrated source region has existed in Northern Xinjiang since Paleozoic. It is likely to infer that this source region is related with the long lasting remnant oceanic basin and the related lithosphere since Paleozoic in North Xinjiang. Key Words: Ophiolite, 40Ar/39Ar age

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

    USGS Publications Warehouse

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

    2009-01-01

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

  16. Geochronology and geochemistry of volcanic glasses associated with early Homo sapiens in Ethiopia.

    NASA Astrophysics Data System (ADS)

    Morgan, L. E.; Renne, P. R.; Woldegabriel, G.; White, T. D.

    2005-12-01

    In past work at hominid sites in Ethiopia, 40Ar/39Ar dating was used to constrain obsidian from the base of the Upper Herto Member of the Bouri Formation to 160 ± 2 ka. An overlying vitric tuff was then geochemically correlated to one from the Konso region of Ethiopia, which is constrained to be older than 154 ± 7 ka, thus leaving only 6 ± 7 ky between eruption and deposition of the fossils and artifacts at Herto. To continue these studies, we have collected and are currently analyzing obsidian and associated volcanic ashes from Middle Stone Age (MSA) archaeological and paleontological sites in the Middle Awash, Ethiopia. Distinctive geochemical signatures among most obsidian fragments collected (n=20 per site) suggest that obsidian was being derived from a variety of sources. By comparing our geochemical data with that from known obsidian deposits in Ethiopia and elsewhere in East Africa, we hope to determine the source localities for the obsidian and thus gauge the extent of trade networks during the MSA. Thus, by characterizing obsidian using both 40Ar/39Ar geochronology and trace element geochemistry, will make it possible to temporally refine the stratigraphy and prehistory at hominid sites, which in turn improves understanding of hominid behavior and evolution.

  17. Early Acadian exhumation history of garnet-kyanite schists from western Massachusetts determined by LASS analysis of metamorphic monazite (Invited)

    NASA Astrophysics Data System (ADS)

    Peterman, E. M.; Snoeyenbos, D. R.; Kylander-Clark, A. R.

    2013-12-01

    Assessing the mechanics of exhumation (e.g. steady vs. episodic processes) requires constraints on the timing and rates of metamorphism and deformation, which can be accomplished by directly dating minerals that formed along the exhumation path. This research focuses on metamorphic monazites contained in restitic high-pressure garnet-kyanite schists from the Goshen Dome in western Massachusetts that record exhumation during the early Acadian. We employ the laser ablation split stream (LASS) technique to simultaneously collect geochronological and geochemical information from the same volume of material. By measuring in situ, LASS analysis allows coordination of petrology, geochemistry and geochronology to reconstruct the timing of metamorphic mineral growth concomitant with exhumation. The gar + ky × crd schists analyzed in this study contain monazite in a variety of petrographic contexts, some of which are interpreted to represent prograde metamorphism. Because we are concerned with exhumation, this contribution focuses on matrix monazite. Matrix monazites are generally aligned with their long axes parallel to foliation. All grains have at least one metamorphic overgrowth, and many grains have multiple generations of overgrowths, thus presenting a detailed record of events. The majority of the matrix monazite cores are 378 to 374 Ma with variable Y concentrations and REE trends. From 375 to 371 Ma, monazite depleted in Y with steep HREE profiles and higher LREE concentrations overgrew pre-existing cores or formed as neoblasts. Dates from most of these monazite domains cluster around 374 to 373 Ma. Neoblasts are typically elongated parallel to the foliation. From 370 to 369 Ma, overgrowths have intermediate Y concentrations with shallower HREE trends and intermediate LREE concentrations, indicating growth during garnet breakdown; these domains are commonly overgrowths with a consistent thickness (ca. 10-15 um), but some domains are more rounded. A pulse of

  18. Cold seep carbonates along the Norwegian margin, insights into U-Th geochronology and S geochemistry

    NASA Astrophysics Data System (ADS)

    Cremiere, A.; Lepland, A.; Wing, B. A.; Sahy, D.; Condon, D. J.; Chand, S.; Noble, S. R.; Bui, T. H.; Thorsnes, T.; Brunstad, H.

    2015-12-01

    Cold seep carbonates along the Norwegian margin, insights into U-Th geochronology and S geochemistryAuthigenic carbonate crusts form in shallow subsurface of marine sediments due to the microbial anaerobic oxidation of methane (AOM). As a result they are unique archives of the locus and intensity of past methane seepage that can be dated by using U-daughter decay affording the unique opportunity to constrain the absolute timing of methane release events. Because AOM is mainly driven by the microbial reduction of seawater sulfate, multiple sulfur isotope compositions of paired carbonate-associated sulfate (CAS) and pyrite in seep carbonates taken as proxies for porewater sulfate and sulfide, respectively, have the potential to reconstruct the biogeochemical conditions under which seep carbonates precipitate. Methane-derived carbonate crusts were collected from several seepage sites on the Norwegian continental shelf, including sites in the North Sea, the Norwegian Sea and the Barents Sea. The U-Th dating results constrain the main episode of carbonate crust formation in the Barents and Norwegian seas during the time interval between 14 and 7 ka. Such ages suggest that the methane seepage along the northern Norwegian margin was most active after the collapse of the Scandinavian ice sheet and deglaciation of the area that took place at about 15 ka. The methane flux for the carbonate crust formation was likely provided by the dissociation of methane hydrates that extensively formed in underlying sediments during the last glacial period, but became unstable due to depressuring effects of retreating ice sheet. The precipitation of studied North Sea carbonate crusts occurred more recently, from 6 to 1 ka, suggesting that their formation is unrelated to the glacial history of the area. The paired sulfur stable isotope compositions of pyrite-CAS record a large range of fractionation factors (from 30 to 70 ‰) reflecting change of sulfate-reduction rates possibly controlled

  19. U Pb zircon and monazite geochronology of Variscan magmatism related to syn-convergence extension in Central Northern Portugal

    NASA Astrophysics Data System (ADS)

    Valle Aguado, B.; Azevedo, M. R.; Schaltegger, U.; Martínez Catalán, J. R.; Nolan, J.

    2005-05-01

    The Viseu area is located in the Central Iberian Zone of the Iberian Variscan Belt and hosts numerous post-thickening, collision-related granitoids intruded into upper and middle crustal levels. The present paper reports high precision U-Pb zircon and monazite ages for four plutons of the Viseu area: the syn-kinematic granitoids of Maceira (314±5 Ma), Casal Vasco (311±1 Ma) and Junqueira (307.8±0.7 Ma) and the late-kinematic biotite monzogranites of Cota (306±9 Ma). This points to a synchronous emplacement of the different syn-kinematic plutons shortly followed by the intrusion of the late-kinematic granites and shows that the Upper Carboniferous plutonism occurred within a short time span of ca. 10 million years. The ascent of granite magmas took place after an extensional tectonic event (D 2) and is coeval with dextral and sinistral crustal-scale transcurrent shearing (D 3). Field and petrographical evidence suggest a narrow time-span between peak T metamorphic conditions and the intrusion of granitic melts which implies very fast uplift rates accommodated through active tectonic exhumation. Magma compositions evolve through time, reflecting an increasing involvement of mid-crustal sources and the underplating effect of an upwelling asthenospheric mantle at the base of a thinning and stretching continental crust.

  20. Stratigraphy, geochronology, geochemistry and tectonic setting of the Mesozoic Nazas Formation, north-central Mexico

    NASA Astrophysics Data System (ADS)

    Bartolini, Claudio

    Late Triassic to Middle Jurassic volcanic-sedimentary sequences that were part of the Mesozoic continental-margin of western North America are exposed in northern and central Mexico. These sequences have been grouped into the Nazas Formation and crop out in the states of Durango, Coahuila, Zacatecas, and San Luis Potosi. The Nazas Formation consists of 2,500 m or more of volcanic and pyroclastic rocks and interbedded clastic sedimentary rocks that were deposited in alluvial fan and fluvial depositional systems that developed in intra-arc basins, mainly fault-bound grabens and topographic depressions within an extending Mesozoic volcanic arc. Major and trace element geochemistry of volcanic rocks suggests that the volcanic suite is calc-alkaline and includes rhyolite, dacite, rhyodacite, andesite, trachyandesite and rare basalt. Pyroclastic rocks are basically air-fall tuffs and volcanic breccias. The sedimentary strata include conglomerate, sandstone, shale, and siltstone, locally red in color. Geochronology (Ar-Ar, K-Ar and Rb-Sr) and field evidence indicate that the age of the Nazas Formation ranges from Late Triassic to Middle Jurassic, but the peak of arc volcanism appears to be Early and Middle Jurassic. The Mesozoic magmatic arc in Mexico has a northwest trend and extends from Sonora to Chiapas. The arc structure is more than 2,000 km long, and possibly up to 150 km wide. The width of the arc is uncertain due to the limited number of surface outcrops, however, it did not extend east into the Gulf of Mexico. Arc-related magmatism began in latest Triassic time, but the peak of arc evolution occurred during the Early and Middle Jurassic. By Oxfordian time, the arc was deeply dissected and eroded, and magmatic activity had ceased. A marine transgression from the Gulf of Mexico covered most of the Nazas arc, depositing the initial sediments of the Oxfordian Zuloaga Limestone in the Mexican Geosyncline. Jurassic crustal extension in the Gulf of Mexico was

  1. Deciphering igneous and metamorphic events in high-grade rocks of the Wilmington complex, Delaware: Morphology, cathodoluminescence and backscattered electron zoning, and SHRIMP U-Pb geochronology of zircon and monazite

    USGS Publications Warehouse

    Aleinikoff, J.N.; Schenck, W.S.; Plank, M.O.; Srogi, L.A.; Fanning, C.M.; Kamo, S.L.; Bosbyshell, H.

    2006-01-01

    High-grade rocks of the Wilmington Complex, northern Delaware and adjacent Maryland and Pennsylvania, contain morphologically complex zircons that formed through both igneous and metamorphic processes during the development of an island-arc complex and suturing of the arc to Laurentia. The arc complex has been divided into several members, the protoliths of which include both intrusive and extrusive rocks. Metasedimentary rocks are interlayered with the complex and are believed to be the infrastructure upon which the arc was built. In the Wilmingto n Complex rocks, both igneous and metamorphic zircons occur as elongate and equant forms. Chemical zoning, shown by cathodoluminescence (CL), includes both concentric, oscillatory patterns, indicative of igneous origin, and patchwork and sector patterns, suggestive of metamorphic growth. Metamorphic monazites are chemically homogeneous, or show oscillatory or spotted chemical zoning in backscattered electron images. U-Pb geochronology by sensitive high resolution ion microprobe (SHRIMP) was used to date complexly zoned zircon and monazite. All but one member of the Wilmington Complex crystallized in the Ordovician between ca. 475 and 485 Ma; these rocks were intruded by a suite of gabbro-to-granite plutonic rocks at 434 ?? Ma. Detrital zircons in metavolcanic and metasedimentary units were derived predominantly from 0.9 to 1.4 Ga (Grenvillian) basement, presumably of Laurentian origin. Amphibolite to granulite facies metamorphism of the Wilmington Complex, recorded by ages of metamorphic zircon (428 ?? 4 and 432 ?? 6 Ma) and monazite (429 ?? 2 and 426 ?? 3 Ma), occurred contemporaneously with emplacement of the younger plutonic rocks. On the basis of varying CL zoning patterns and external morphologies, metamorphic zircons formed by different processes (presumably controlled by rock chemistry) at slightly different times and temperatures during prograde metamorphism. In addition, at least three other thermal episodes are

  2. Geochronology of granulite, charnockite and gneiss in the poly-metamorphosed Gaozhou Complex (Yunkai massif), South China: Emphasis on the in-situ EMP monazite dating

    NASA Astrophysics Data System (ADS)

    Chen, Cheng-Hong; Liu, Yung-Hsin; Lee, Chi-Yu; Xiang, Hua; Zhou, Han-Wen

    2012-07-01

    The in-situ EMP (electron microprobe) monazite age dating performed directly in the polished sections, in addition to the conventional U-Pb zircon and EMP monazite age dating on grains from heavy mineral concentrates, has been applied to the granulite, charnockite and gneiss in the Gaozhou Complex of the Yunkai massif in South China. While the conventional dating systems all give Caledonian ages, the in-situ EMP monazite ages provide more information to reveal not only detailed age groups pertaining to the Caledonian orogeny but also traces of later thermal events overprinting these rocks. For granulites, although some monazites present zoning (concentric, patchy and complex) in the BSE images, no discernable age differences are observed. Resetting of the Th-U-Pb monazite dating system under the high temperature condition could be the reason. Ages of homogeneous monazite in garnet porphyroblast (ca. 440 Ma) of the garnet-cordierite granulite that match nicely with the U-Pb zircon ages are systematically older than those in the matrix (ca. 430 Ma). The same case of two age groups is also present in the orthopyroxene-biotite granulite as revealed by monazite inclusions in plagioclase and orthopyroxene and those in quartz, respectively. For charnockites, despite similar ages of ca. 430 Ma are given by monazite in biotite and zircon in the rock, significant younger ages are obtained from monazites with particular features. Relict monazites with a breakdown texture to form successive layers of apatite and allanite in the rim as well as those which are close to the biotite-chlorite microvein always show a similar age of ca. 230 Ma. Moreover, tiny monazites in close association with the garnetiferous corona mainly surrounding orthopyroxene give rise to another age group around 370 Ma. For gneissic rocks, monazites enclosed by quartz give 434 Ma and those setting in the chlorite-epidote microvein of a paragneiss yield 237 Ma, consistent with the U-Pb zircon core-rim age

  3. Monazite stability, composition and geochronology as tracers of Paleoproterozoic events at the eastern margin of the East European Craton (Taratash complex, Middle Urals)

    NASA Astrophysics Data System (ADS)

    Sindern, Sven; Gerdes, Axel; Ronkin, Yuri L.; Dziggel, Annika; Hetzel, Ralf; Schulte, Bernd Aloys

    2012-02-01

    The Precambrian Taratash complex (Middle Urals) is one of the rare windows into the Palaeoproterozoic and earlier history of the eastern margin of the East European Craton. Monazite from intensively deformed rocks within a major amphibolite-facies shear zone in the Taratash complex has been investigated by means of electron-probe microanalysis and laser-ablation SF-ICP-MS. Metamorphic and magmatic cores of monazite from metasedimentary and metagranitoid rocks yield U-Pb ages of 2244 ± 19 and 2230 ± 22 Ma (± 2 σ) and record a previously unknown pre-deformational HT-metamorphic event in the Taratash complex. Subsequent dissolution-reprecipitation of monazite, during shear zone formation under amphibolite-facies conditions, caused patchy zonation and chemical alteration of the recrystallised monazite domains, leading to higher cheralite and huttonite components. This process, which was mediated by a probable (alkali + OH)-bearing metamorphic fluid also caused a total resetting of the U-Pb-system. The patchy domains yield concordant U-Pb-ages between 2052 ± 16 and 2066 ± 22 Ma, interpreted as the age of the shear zone. In line with previously published ages of high grade metamorphism and migmatisation, the data may point to a Palaeoproterozoic orogenic event at the eastern margin of the East European Craton. Post-deformational fluid-induced greenschist-facies retrogression caused partial to complete breakdown of monazite to fluorapatite, REE + Y-rich epidote, allanite and Th-orthosilicate.The retrograde assemblages either form coronas around monazite, or occur as dispersed reaction zones, indicating that the REE, Y, and Th were mobile at least on the thin section scale. The greenschist-facies metamorphic fluid was aqueous and rich in Ca. Monazite affected by advanced breakdown responded to the retrogression by incorporating the cheralite or huttonite components during a fluid-induced dissolution-reprecipitation process. This event did not reset the U

  4. The Anari and Tapirapua Jurassic formations, western Brazil: Paleomagnetism, geochemistry and geochronology

    NASA Astrophysics Data System (ADS)

    Montes-Lauar, C. R.; Pacca, I. G.; Melfi, A. J.; Piccirillo, E. M.; Bellieni, G.; Petrini, R.; Rizzieri, R.

    1994-12-01

    The Anari and Tapirapua formations are very similar from the point of view of paleomagnetic, geochronological and geochemical results. They date from around 197 Ma and the flows are mainly tholeiitic basalts with a low TiO2 and incompatible element content. The magnetic carriers in rocks from these two formations were highly oxidized titanomagnetites, maghemites and, probably, titanomaghemites. Paleomagnetic analysis has shown that the magnetizations are all normal in polarity and virtual geomagnetic poles obtained for both formations are indistinguishable at the 95% confidence level. The calculated mean for these poles is 250.3 deg E, 65.5 deg S (N = 15; A95 = 3.6 deg; KSC = 1578). This pole is compatible with Jurassic poles which have been determined for South America or transposed from Africa.

  5. Geochemistry and Geochronology of Middle Tertiary Volcanic Rocks of the Central Chiricahua Mountains, Southeast Arizona

    USGS Publications Warehouse

    du Bray, Edward A.; Pallister, John S.; Snee, Lawrence W.

    2004-01-01

    Middle Tertiary volcanic rocks of the central Chiricahua Mountains in southeast Arizona are the westernmost constituents of the Eocene-Oligocene Boot Heel volcanic field of southwestern New Mexico and southeastern Arizona. About two dozen volumetric ally and stratigraphically significant volcanic units are present in this area. These include large-volume, regionally distributed ash-flow tuffs and smaller volume, locally distributed lava flows. The most voluminous of these units is the Rhyolite Canyon Tuff, which erupted 26.9 million years ago from the Turkey Creek caldera in the central Chiricahua Mountains. The Rhyolite Canyon Tuff consists of 500-1,000 cubic kilometers of rhyolite that was erupted from a normally zoned reservoir. The tuff represents sequential eruptions, which became systematically less geochemically evolved with time, from progressively deeper levels of the source reservoir. Like the Rhyolite Canyon Tuff, other ashflow tuffs preserved in the central Chiricahua Mountains have equivalents in nearby, though isolated mountain ranges. However, correlation of these other tuffs, from range to range, has been hindered by stratigraphic discontinuity, structural complexity, and various lithologic similarities and ambiguities. New geochemical and geochronologic data presented here enable correlation of these units between their occurrences in the central Chiricahua Mountains and the remainder of the Boot Heel volcanic field. Volcanic rocks in the central Chiricahua Mountains are composed dominantly of weakly peraluminous, high-silica rhyolite welded tuff and rhyolite lavas of the high-potassium and shoshonitic series. Trace-element, and to a lesser extent, major-oxide abundances are distinct for most of the units studied. Geochemical and geochronologic data depict a time and spatial transgression from subduction to within-plate and extensional tectonic settings. Compositions of the lavas tend to be relatively homogeneous within particular units. In

  6. Along-Strike Variations in the Timing of Melt Crystallization and Metamorphism Across Central and Eastern Bhutan: New Insights from LASS Monazite Geochronology and Trace-Element Abundances

    NASA Astrophysics Data System (ADS)

    Gordon, S. M.; Kauffman, R.; Gonzales-Clayton, B.; Kylander-Clark, A. R.; Agustsson, K. S.; Long, S. P.

    2014-12-01

    Continent-continent collisional systems represent the largest orogens on Earth and provide locations to study processes that drive the transition from contraction and crustal thickening to extension and collapse. The Greater Himalayan Zone (GHZ) exposed along strike of the Himalayan orogen contains exhumed mid-crustal metasedimentary rocks. To better understand the history of burial, crustal flow, and partial melting during the early stages of Himalayan tectonics in the Eocene to ~40 Myr into its orogenic evolution, monazite was analyzed from five migmatitic gneisses and five host gneisses exposed across two transects within central and eastern Bhutan. Monazite was analyzed in situ by the split-stream laser-ablation (LASS) ICPMS technique, which allows simultaneous collection of U-Th-Pb isotopes and trace-element abundances. The migmatites from the eastern Bhutan transect yield monazite dates that record melt crystallization as young as ca. 15-13 Ma. The host gneisses yield similar to younger (down to ca. 11 Ma) dates, documenting coeval to continued metamorphism of the GHZ. In comparison, melt crystallization in the central Bhutan rocks ended by ca. 18 Ma, and metamorphic monazite from a metapelite record metamorphism until ca. 14 Ma. In the migmatite and host-rock samples from both transects, the trace-element data show an inverse correlation between date and the HREE concentration. This trend likely documents the breakdown of garnet, which probably coincides with the first stages of GHZ exhumation. Thus, the LASS data showed that garnet breakdown and GHZ exhumation occurred from ca. 18 to 14 Ma in eastern Bhutan and ca. 20 to 17 Ma in central Bhutan. The new monazite data suggest different histories for the melt crystallization, metamorphism, and exhumation of the GHZ rocks between central and eastern Bhutan, even though the present day rocks from the two transects are only exposed ~60 km apart. Moreover, in comparison to other parts of the eastern Himalaya, the

  7. Petrography, geochemistry and geochronology of granite hosted rhyodacites associated with a disseminated pyrite mineralization (Arnolz, Southern Bohemian Massif, Austria)

    NASA Astrophysics Data System (ADS)

    Göd, Richard; Kurzweil, Johannes; Klötzli, Urs

    2016-09-01

    The study focuses on a subvolcanic rhyodacite dyke intruding a fine grained biotite granite and paragneisses of the South Bohemian Massif, part of the Variscan Orogenic Belt in Central Europe. The subvertical dyke strikes NNE, displays a thickness of about 30 m and has been traced by boulder mapping for approximately 7 km. The rhyodacites have been affected by two hydrothermal fluids. An older one of oxidizing condition giving rise to a reddish to brownish type of rock (Type I) and a younger fluid of reducing condition causing a greenish variety (Type II). The hydrothermal alteration is associated with the formation of the clay minerals chlorite, sericite, kaolinite and smectite and a disseminated pyrite mineralization. Bulk chemistries of the rhyodacites emphasize the hydrothermal alterations to be isochemical with the exception of sulphur enriched up to a maximum of 0.6 wt%. Trace element composition of the rhyodacites points to a barren geochemical environment in terms of base and precious elements. Sulphur isotope investigations of pyrites from the rhyodacites and the hosting granites respectively yield d34S data ranging from +0.07 to -2.22 ‰, emphasizing a magmatic origin of the sulphur. Geochronological investigations yield in situ U/Pb zircon ages of 312 ± 4 Ma for the biotite granite and of 292 ± 4 Ma for the rhyodacitic dykes indicating a time gap of ≈ 20 Ma between these two intrusive events. A contemporaneous but geochemically specialized granitic intrusion associated with NW striking "felsitic" dykes occurs about 10 to 20 km to the NW of Arnolz. However, the rhyodacites around Arnolz differ significantly from these felsitic dykes in their geochemistry and alteration phenomena which points to a different magmatic source. This coincides with a change in the orientation of the dykes from a NW direction controlling the geochemically specialized intrusions in the NW to a dominating NNE direction mirrored by the studied rhyodacites at Arnolz.

  8. Igneous rocks of Arctic Ocean deep sea ridges: new data on petrology, geochemistry and geochronology

    NASA Astrophysics Data System (ADS)

    Petrov, Oleg; Morozov, Andrey; Shokalsky, Sergey; Sobolev, Nikolay; Kashubin, Sergey; Shevchenko, Sergey; Sergeev, Sergey; Belyatsky, Boris; Shatov, Vitaly; Petrov, Eugeny

    2015-04-01

    The aggregate results of studies of igneous rocks, collected from the central part of the Arctic Ocean during scientific marine expeditions «Arctic-2000, 2005, 2007 and 2012» are presented and discussed in the frame of modern understanding of High Polar Arctic tectonic constraint. Petrological, geochemical and isotope-geochronological studies of more than 500 samples have shown that the sedimentary rocks are of dominated population among the rock fragments dredged from deep-sea bottom, and represented by metamorphosed dolomite and quartz sandstone, limestone, sometimes with the Devonian - Permian fauna. Igneous rocks are 10-15% only (Archean and Paleoproterozoic gneissouse granites and gabbro, Neoproterozoic dolerite) and metamorphic rocks (green shales, metabasites, gneisses). Apparently, these rocks are part of the acoustic basement underlying the Late Mesozoic - Cenozoic layered loose sediments. In addition to the dredged fragments of the ancient mafic rocks, some samples were taken as a core during deep-water drilling in the northern and southern slopes of the Mendeleev Ridge and represented by trachybasalts, marking the border of Late-Cenozoic deposit cover and acoustic basement and quite similar in composition to those of Early-Late Cretaceous basalts form northward of the Chukchi Plateau seamounts, Alpha Ridge, Franz Josef Land, De Long islands and other parts of the large igneous province of the High Arctic (HALIP). Video-filming of Mendeleev Ridge escarps proofs the existing of rock outcrops and supports local origin of most of the rock fragments found in the sampling areas. Thus the continental type of the earth's crust of the Central Arctic Ridges basement is based on all obtained results of our study of sea-bottom excavated rock material.

  9. Geochronology and geochemistry of pre-Jurassic superterranes in Marie Byrd Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Pankhurst, R. J.; Weaver, S. D.; Bradshaw, J. D.; Storey, B. C.; Ireland, T. R.

    1998-02-01

    Marie Byrd Land, Antarctica, is a major part of the proto-Pacific supercontinental margin. On the basis of new geochronological and geochemical data relating to its pre-Jurassic evolution, Marie Byrd Land is subdivided into western or interior ("Ross") and eastern or exterior ("Amundsen") provinces, equivalent to two superterranes in New Zealand. The Ross province is characterized by Cambrian? metagraywackes and I-type orthogneiss dated at 505±5 Ma by U-Pb SHRIMP (Sensitive High Resolution Ion Microprobe). Its magmatic record consists of Devonian-Carboniferous (375±5 Ma and circa 339±6 Ma), predominantly I-type granitoids, and further minor granitic magmatism in Permo-Triassic times. This Paleozoic history is comparable to that of the Gondwana margin in northern Victoria Land, western New Zealand, and SE Australia. The Amundsen province has no observed Paleozoic graywacke succession; evidence from Rb-Sr and U-Pb SHRIMP dating supports calc-alkaline granitoid events in Ordovician/Silurian (450-420 Ma) and Permian (276±2 Ma) times. The latter may be the previously unknown source of Permian volcanic detritus in the Ellsworth and Transantarctic mountains. The Amundsen province is considered to be the equivalent of the Median Tectonic Zone of New Zealand, and arc magmatism of comparable ages is found in the Antarctic Peninsula and Thurston Island. The underlying lithosphere of the two provinces may be distinguished by Nd isotope data; granitoids and metasedimentary rocks of the Ross province have Meso-Proterozoic Nd model ages, generally 1300-1500 Ma, compared to 1000-1300 Ma for the Amundsen province. On the basis of published palaeomagnetic data, the two provinces amalgamated to form Marie Byrd Land in mid-Cretaceous times, only shortly before rifting of the New Zealand continental block away from Antarctica.

  10. Miocene silicic volcanism in southwestern Idaho: Geochronology, geochemistry, and evolution of the central Snake River Plain

    USGS Publications Warehouse

    Bonnichsen, B.; Leeman, W.P.; Honjo, N.; McIntosh, W.C.; Godchaux, M.M.

    2008-01-01

    New 40Ar-39Ar geochronology, bulk rock geochemical data, and physical characteristics for representative stratigraphic sections of rhyolite ignimbrites and lavas from the west-central Snake River Plain (SRP) are combined to develop a coherent stratigraphic framework for Miocene silicic magmatism in this part of the Yellowstone 'hotspot track'. The magmatic record differs from that in areas to the west and east with regard to its unusually large extrusive volume, broad lateral scale, and extended duration. We infer that the magmatic systems developed in response to large-scale and repeated injections of basaltic magma into the crust, resulting in significant reconstitution of large volumes of the crust, wide distribution of crustal melt zones, and complex feeder systems for individual eruptive events. Some eruptive episodes or 'events' appear to be contemporaneous with major normal faulting, and perhaps catastrophic crustal foundering, that may have triggered concurrent evacuations of separate silicic magma reservoirs. This behavior and cumulative time-composition relations are difficult to relate to simple caldera-style single-source feeder systems and imply complex temporal-spatial development of the silicic magma systems. Inferred volumes and timing of mafic magma inputs, as the driving energy source, require a significant component of lithospheric extension on NNW-trending Basin and Range style faults (i.e., roughly parallel to the SW-NE orientation of the eastern SRP). This is needed to accommodate basaltic inputs at crustal levels, and is likely to play a role in generation of those magmas. Anomalously high magma production in the SRP compared to that in adjacent areas (e.g., northern Basin and Range Province) may require additional sub-lithospheric processes. ?? Springer-Verlag 2007.

  11. Resolving arc processes through detrital zircon U-Pb geochronology and geochemistry: a case study from the southern California Mesozoic convergent margin

    NASA Astrophysics Data System (ADS)

    Johnston, S. M.; Kylander-Clark, A. R.

    2015-12-01

    Detrital zircon geochronology has been widely exploited to establish temporal characteristics in sedimentary source terranes. Detrital zircon geochemistry, however, has been largely overlooked given results from continentally derived igneous zircon that show subtle intersample variation in trace-element concentrations, and which make correlation between detrital zircon and their host terrane difficult. Nevertheless, recent studies suggest systematically variable geochemistry in McCoy Mountain detrital zircons derived from the southern California Mesozoic arc, and our preliminary data from the Peninsular Ranges batholith indicates strong correlations between whole-rock and zircon geochemistry. Here, we present coupled U-Pb geochronology and geochemistry measured by laser ablation split stream ICPMS on detrital zircons from Nacimiento block forearc sediments in Central California to characterize temporal and geochemical trends in the adjacent Mesozoic arc terrane. 1098 grains of Mesozoic age analyzed from 22 samples in the Nacimiento block define three periods of high magmatic flux in the Permian (270-250 Ma), Jurassic (170-140 Ma), and late Cretaceous (115-90 Ma). Zircon from the Permian arc is the least abundant of the three magmatic pulses, although they consistently display elevated Yb/Gd and U/Yb. Jurassic zircons display consistently low U/Yb, variably elevated Yb/Gd, abruptly higher Th/U and LREE from 155-145, and abruptly lower REE concentrations from 145-140 Ma. Zircon from the Cretaceous arc displays gradually increasing U/Yb, Th/U and LREE, with abruptly decreasing Yb/Gd at 95 Ma. The geochemical trends observed in the Nacimiento block detrital zircons of Cretaceous age are strikingly similar to temporal changes in geochemistry known from Cretaceous arc rocks of the Mojave and Peninsular Ranges, and strongly suggest a southern California provenance for Nacimiento block sediments. Furthermore, the similarity of geochemical trends between Cretaceous detrital

  12. Geochronology, geochemistry and tectonic evolution of the Western and Central cordilleras of Colombia

    NASA Astrophysics Data System (ADS)

    Villagómez, Diego; Spikings, Richard; Magna, Tomas; Kammer, Andreas; Winkler, Wilfried; Beltrán, Alejandro

    2011-08-01

    Autochthonous rocks of the pre-Cretaceous continental margin of NW South America (the Tahami Terrane) are juxtaposed against a series of para-autochthonous rock units that assembled during the Early Cretaceous. Allochthonous, oceanic crust of the Caribbean Large Igneous Province collided with and accreted onto the margin during the Late Cretaceous. We present the first regional-scale dataset of zircon U-Pb LA-ICP-MS ages for intrusive and metamorphic rocks of the autochthonous Tahami Terrane, Early Cretaceous igneous para-autochthonous rocks and accreted oceanic crust. The U-Pb zircon data are complemented by multiphase 40Ar/ 39Ar crystallization and cooling ages. The geochronological data are combined with whole rock major oxide, trace element and REE data acquired from the same units to constrain the tectonic origin of the rock units and terranes exposed in the Western Cordillera, Cauca-Patía Valley and the Central Cordillera of Colombia. The Tahami Terrane includes lower Paleozoic orthogneisses (~ 440 Ma) that may have erupted during the active margin stage of the Rheic Ocean. Basement gneisses were intruded by Permian, continental arc granites during the final assembly of Pangea. Triassic sedimentary rocks were subsequently deposited in rift basins and partially melted during high-T metamorphism associated with rifting of western Pangea during 240-220 Ma. Continental arc magmatism during 180-145 Ma is preserved along the whole length of the Central Cordillera and was followed by an Early Cretaceous out-board step of the arc axis and the inception of the Quebradagrande Arc that fringed the continental margin. Back-stepping of the arc axis may have been caused by the collision of buoyant seamounts, which were coeval with plateau rocks exposed in the Nicoya Peninsular of Costa Rica. Rapid westward drift of South America closed the Quebradagrande basin in the late Aptian and caused medium-high P-T metamorphic rocks of the Arquía Complex to exhume and obduct onto

  13. Geochemistry and zircon geochronology of Late Proterozoic leucogranites north of Boston, eastern Massachusetts

    SciTech Connect

    Markus, R.; Hon, R. . Geology and Geophysics); Dunning, G. . Dept. of Earth Sciences)

    1993-03-01

    An igneous sequence that includes Late Precambrian volcanics (Lynn Volcanics) and granites, granodiorites, tonalites, plus diorites of the Dedham North suite, is located in a tectonic block bounded by the Walden Pond and Northern Boundary Faults north of the Boston Basin. Within the block between the rhyolites and granodiorites is a several hundred foot wide zone of leucogranites that contains frequent roof pendants in various stages of partial melting. The migmatitic nature of the pendants suggests that the leucogranites were locally derived by melt extraction from the partially melted pendant xenoliths. U-Pb zircon ages were obtained from samples of the leucogranite, granodiorite and diorite. Their crystallization ages are: leucogranite 609 [+-] 4 Ma, granodiorite 607 [+-] 4 Ma, and diorite 606 [+-] 3 Ma. All three samples yield ages that are identical within their statistical error limits and all three samples contain inherited component with average mid-Proterozoic ages. Major and trace element geochemistry of 43 samples of all representative types show that the predominantly pelitic'' layers underwent extensive partial melting and that the leucogranites represent a minimum granite melt at 0.5 to 2.0 kb of P(H2O). Geochemical modeling also supports the origin by partial melting of the pendant inclusions. Once formed, the leucogranite melts were then mixed with mafic magmas which must have also been the provider of the necessary heat to sustain the partial melting process. The data indicate that the Dedham North plutonic suite was formed at shallow crustal levels and that its compositional range is a result of magma mixing of varying proportions between the leucogranite and mafic melts.

  14. Geology, geochronology and geochemistry of a basanitic volcano, White Island, Ross Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Cooper, Alan F.; Adam, Lotte J.; Coulter, Roseanne F.; Eby, G. Nelson; McIntosh, William C.

    2007-09-01

    White Island, Ross Sea, Antarctica is a Plio-Pleistocene basanite to tephriphonolite shield volcano, forming part of the Erebus Province, McMurdo Volcanic Group. Four new 40Ar/ 39Ar dates extend the age of surface volcanism from a previously determined 0.17 Ma to 5.05 ± 0.31 Ma. A U/Pb age on zircon in an anorthoclasite nodule extends White Island magmatism back to 7.65 ± 0.69 Ma. Volcanism was predominantly subaerial with eruption of agglutinated spatter-clast breccias and lava flows from vents with a NNE structural alignment. An early phase of inferred subaqueous/subglacial activity formed pillow breccias. Two nunataks in the southern part of the island comprise basanitic tuff cones, composed of poorly bedded pyroclastic deposits dominated by sideromelane lapilli, and containing horizons rich in accretionary and armoured lapilli. Many of the basanites have compositions of near-primary magmas and contain an assortment of Cr-diopside and Al-augite suite mantle nodules, lower crustal gabbros, mafic granulites, and assorted megacrysts. Peridotites are dominated by spinel facies inclusions, but include plagioclase-spinel lherzolites derived from shallow mantle beneath the tectonically thinned and attenuated Ross Sea lithosphere. Mantle nodules contain accessory amounts of pale brown, metasomatic amphibole. Volcanic geochemistry is compatible with fractionation of olivine, pyroxene, titano-magnetite and minor apatite from a basanite parent yielding tephriphonolite residual liquids. Magmatism is focused along, or at the termination of, Cenozoic rift basins in the Ross Sea. The regional McMurdo Volcanic Group distribution and tectonic setting, and the history of Erebus Province volcanic centres are difficult to reconcile in terms of active mantle plumes. Instead, more randomly distributed magmatism is inferred to result from rift-related decompression melting of previously enriched mantle that may have been fertilized by plume interaction prior to Gondwana

  15. Geochronology, geochemistry, and petrology of the Precambrian Sandia granite, Albuquerque, New Mexico

    SciTech Connect

    Majumdar, A.

    1985-01-01

    The Precambrian Sandia granite of north-central New Mexico belongs to the 1.2-1.6 Ga crustal province of the western USA. The granite shows an intrusive contact with the metamorphic country rocks. The Rb-Sr whole rock isochron age of the country rocks is 1.61 +/- 0.06 Ga, (/sup 87/Sr//sup 86/Sr)/sub 0/ = 0.705 +/- 0.001. The culmination of the intrusion of the Sandia granite took place at 1.44 +/- 0.04 GA. (/sup 87/Sr//sup 86/)/sub 0/ = 0.7054 +/- 0.0005. Rb-Sr ages on biotite-whole rock pairs and an /sup 40/Ar//sup 39/Ar dating of a biotite from the granite indicate final cooling to 300-350/sup 0/C at 1.33 Ga. This suggests slow cooling of the granite at rates which averaged 4/sup 0/C/Ma for about 100 Ma after its emplacement; during this period the Rb-Sr isotope system perhaps remained partially open. The Sandia granite shows compositional variation from granodiorite to quartz monzonite in both the northern and southern blocks. The field geology, petrology, and geochemistry of the two blocks suggest that they form a single pluton. Both the Sandia granite and mesocratic, two pyroxene granulite xenoliths therein give an ..delta../sup 18/O value of +8.0 +/- 0.5% indicating (meta)igneous source ricks for each of them. These values tend to rule out Condie's (1978) favored hypothesis for magma generation of 30-50% partial melting of siliceous gradulites. Rather, they favor an alternative hypothesis, equally satisfactory from the geochemical viewpoint, involving 5-10% melt of a gabbroic or two-pyroxene granulite parent rock in the lower crust. The Sandia granite, and by implication, the other high-Ca granitic rocks of the western USA thus do not seem to represent addition of new mantle-derived materials to the middle-late Proterozoic crust of this section of the continent.

  16. El Ventorrillo, a paleostructure of Popocatépetl volcano: insights from geochronology and geochemistry

    NASA Astrophysics Data System (ADS)

    Sosa-Ceballos, G.; Macías, J. L.; García-Tenorio, F.; Layer, P.; Schaaf, P.; Solís-Pichardo, G.; Arce, J. L.

    2015-10-01

    Volcán Popocatépetl (México) was constructed over the remains of a volcanic paleostructure. Based on fieldwork, 40Ar/39Ar dating, U-Pb dating, and geochemistry, we have determined the age, chemistry, and location of this paleostructure and named it El Ventorrillo. Most remnants of El Ventorrillo are covered by deposits from subsequent activity of Popocatépetl, except for the El Abanico scarp and the Barranca de Nexpayantla, where the stratigraphy of El Ventorrillo eruptive products can be investigated. Inception of volcanism at El Ventorrillo occurred at 331 ± 10 ka with emission of the Nexpayantla andesitic lavas, and continued with extrusion of the Yoloxochitl (267 ± 31 ka) and microwave (227 ± 6 ka) domes. Intrusion of dikes occurred at 298 ± 94 and 230 ± 3 ka. Activity at El Ventorrillo continued with the emission of lavas that built the El Abanico scarp (193 ± 29 to 96 ± 8 ka) and continued until the Tutti Frutti eruption destroyed the cone 14.1 kyr ago. El Ventorrillo magmas produced rocks divided into two mineralogical groups. The first group contains biotite-amphibole-rich rocks and the second group consists of biotite-amphibole-free lavas. The rocks that contain biotite and amphibole are older than 198 ± 13 ka, whereas the rocks with no hydrous phases are younger than 227 ± 6 ka and contain skarn and granodiorite xenoliths. We interpret the change to an anhydrous mineral assemblage and the occurrence of skarn and granodiorite xenoliths as evidence for the formation of a new, shallower reservoir. A granodiorite xenolith was chosen for 40Ar/39Ar dating and U-Pb zircon analyses. The U-Pb method yielded an age of 540 ± 110 ka and the 40Ar/39Ar an age of 109 ± 24 ka. These ages are interpreted to indicate granodiorite crystallization (540 ± 110 ka), which metamorphosed the calcareous basement beneath Popocatépetl into skarn and an influx of magma (109 ± 24 ka) that reheated the granodiorite. Major and trace elements, Sr, Nd, and Pb isotopic

  17. Elucidating the magmatic history of the Austurhorn silicic intrusive complex (southeast Iceland) using zircon elemental and isotopic geochemistry and geochronology

    NASA Astrophysics Data System (ADS)

    Padilla, A. J.; Miller, C. F.; Carley, T. L.; Economos, R. C.; Schmitt, A. K.; Coble, M. A.; Wooden, J. L.; Fisher, C. M.; Vervoort, J. D.; Hanchar, J. M.

    2016-09-01

    The Austurhorn intrusive complex (AIC) in southeast Iceland comprises large bodies of granophyre and gabbro, and a mafic-silicic composite zone (MSCZ) that exemplifies magmatic interactions common in Icelandic silicic systems. Despite being one of Iceland's best-studied intrusions, few studies have included detailed analyses of zircon, a mineral widely recognized as a valuable tracer of the history and evolution of its parental magma(s). In this study, we employ high spatial resolution zircon elemental and isotopic geochemistry and U-Pb geochronology as tools for elucidating the complex construction and magmatic evolution of Austurhorn's MSCZ. The trace element compositions of AIC zircon crystals form a broad but coherent array that partly overlaps with the geochemical signature for zircons from Icelandic silicic volcanic rocks. Typical of Icelandic zircons, Hf concentrations are relatively low (<10,000 ppm) and Ti concentrations range from 5 to 40 ppm (Ti-in-zircon model temperatures = 761-981 °C). Zircon δ18O values vary from +2.2 to +4.8 ‰, consistent with magmatic zircons from other Icelandic silicic rocks, and preserve evidence for recycling of hydrothermally altered crust as a significant contribution to the generation of silicic magmas within the AIC. Zircon ɛ Hf values generally range from +11 to +15. This range overlaps with that of Icelandic basalts from off-rift settings as well as the least depleted rift basalts, suggesting that the AIC developed within a transitional rift environment. In situ zircon U-Pb ages yield a weighted mean of 6.52 ± 0.03 Ma for the entire complex, but span a range of ~320 kyr, from 6.35 ± 0.08 to 6.67 ± 0.06 Ma (2 σ SE). Gabbros and the most silicic units make up the older part of this range, while granophyres and intermediate units make up the younger part of the complex, consistent with field relationships. We interpret the ~320 kyr range in zircon ages to represent the approximate timescale of magmatic construction

  18. The Ellsworth terrane, coastal Maine: Geochronology, geochemistry, and Nd-Pb isotopic composition - Implications for the rifting of Ganderia

    USGS Publications Warehouse

    Schulz, K.J.; Stewart, D.B.; Tucker, R.D.; Pollock, J.C.; Ayuso, R.A.

    2008-01-01

    The Ellsworth terrane is one of a number of fault-bounded blocks that occur along the eastern margin of Ganderia, the western-most of the peri-Gondwanan domains in the northern Appalachians that were accreted to Laurentia in the Paleozoic. Geologic relations, detrital zircon ages, and basalt geochemistry suggest that the Ellsworth terrane is part of Ganderia and not an exotic terrane. In the Penobscot Bay area of coastal Maine, the Ellsworth terrane is dominantly composed of bimodal basalt-rhyolite volcanic sequences of the Ellsworth Schist and unconformably overlying Castine Volcanics. We use new U-Pb zircon geochronology, geochemistry, and Nd and Pb isotopes for these volcanic sequences to constrain the petrogenetic history and paleotectonic setting of the Ellsworth terrane and its relationship with Ganderia. U-Pb zircon geochronology for rhyolites indicates that both the Ellsworth Schist (508.6 ?? 0.8 Ma) and overlying Castine Volcanics (503.5 ?? 2.5 Ma) are Middle Cambrian in age. Two tholefitic basalt types are recognized. Type Tb-1 basalt, present as pillowed and massive lava flows and as sills in both units, has depleted La and Ce ([La/Nd]N = 0.53-0.87) values, flat heavy rare earth element (REE) values, and no positive Th or negative Ta anomalies on primitive mantle-normalized diagrams. In contrast, type Th-2 basalt, present only in the Castine Volcanics, has stightly enriched LREE ([La/Yb]N = 1.42-2.92) values and no Th or Th anomalies. Both basalt types have strongly positive ??Nd (500) values (Th-1 = +7.9-+8.6; Th-2 = +5.6-+7.0) and relatively enriched Pb isotopic compositions (206Ph/204Pb = 18.037-19.784; 207/204Pb = 15.531-15.660; 2088Pb/204Pb = 37.810-38.817). The basalts have compositions transitional between recent normal and enriched mid-ocean-ridge basalt, and they were probably derived by partial melting of compositionatly heterogeneous asthenosphenc mantle. Two types of rhyolite also are present. Type R-1 rhyolite, which mostly occurs as tuffs

  19. Geochemistry

    ERIC Educational Resources Information Center

    Ailin-Pyzik, Iris B.; Sommer, Sheldon E.

    1977-01-01

    Enumerates some of the research findings in geochemistry during the last year, including X-ray analysis of the Mars surface, trace analysis of fresh and esterarine waters, and analysis of marine sedements. (MLH)

  20. Rhyolite volcanism at Öræfajökull Volcano, Iceland - geochemistry, field relations & 40Ar/39Ar geochronology

    NASA Astrophysics Data System (ADS)

    Walker, Angela; Burgess, Ray; McGarvie, David; Smellie, John

    2010-05-01

    Öræfajökull is Iceland's largest stratovolcano, situated at the southern tip of Vatnajökull Glacier in the south east of the island. Its position away from the extensional tectonic forces of the rift zone has enabled the build-up of a substantial edifice 2110m in height. The majority of the volcanic edifice, including its 5km wide caldera is covered by glacial ice, leaving only the southern flanks of the volcano exposed. This area of South East Iceland has been completely glaciated at least 16 times in the last 5 million years (Helgason and Duncan, 2001) and evidence from previous field studies suggests that throughout periods in the geological past, Öræfajökull and the surrounding area were covered by ice to a much greater extent than we see today (Stevenson et al., 2006). The volcano has erupted twice since historical records began, in 1727 and 1362, the latter being one of Iceland's most explosive historical eruptive events producing over 6x109m3 of rhyolitic tephra (Selbekk and Trønnes, 2007). However, the abundance of hyaloclastite present across much of the exposed southern flank of the edifice suggests that Öræfajökull has been at its most active during glacial periods (Prestvik, 1979). The post-eruptive geomorphic evolution of volcanic deposits at Öræfajökull has been dominated by volcano-ice interaction and characteristic glaciovolcanic landforms are evident at many exposures. A multidisciplinary approach combining field observation, geochemistry and isotope geochronology is being utilised in order to establish the geological evolution of the Goðafjall area on the southern flanks of Öraefajökull and a record of regional minimum ice thicknesses during the development of the volcanic edifice throughout the varying climatic conditions of the mid to late Quaternary. Individual eruptive events have been identified in the field using a combination of traditional field mapping techniques and geochemistry, and the units are being dated using 40Ar

  1. Petrology, major and trace element geochemistry, geochronology, and isotopic composition of granitic intrusions from the vicinity of the Bosumtwi impact crater, Ghana

    NASA Astrophysics Data System (ADS)

    Losiak, Anna; Schulz, Toni; Buchwaldt, Robert; Koeberl, Christian

    2013-09-01

    The Bosumtwi crater is 10.5 km in diameter, 1.07 Ma old, well preserved impact structure located in Ghana (centered at 06°30‧N, 01°25‧W). It was excavated in rocks of the Early Proterozoic Birimian Supergroup, part of the West African craton. Here, we present a full and detailed characterization of the three granitoid complexes and one mafic dike in the vicinity of the Bosumtwi crater in terms of petrology, major and trace element geochemistry, geochronology, and isotopic composition. This allows us to characterize magmatic evolution of the West African Craton in this area and better understand the geological framework and target rocks of the impact. This study shows that the similar composition (strongly peraluminous muscovite granites and granodiorites) and age (between 2092 ± 6 Ma and 2098 ± 6 Ma) of all granitic intrusions in the proximity of the Bosumtwi crater suggest that they are co-genetic. Granitoids were probably formed as a result of anatexis of TTGs (or rocks derived from them) at relatively low pressure and temperature. We propose that the intrusions from the Bosumtwi area are genetically related to the Banso granite occurring to the east of the crater and can be classified as basin-type, late-stage granitoids. Also a mafic dike located to the NE of the Bosumtwi crater seems to be genetically related to those felsic intrusions. Based on those findings a revised version of the geological map of the Bosumtwi crater area is proposed.

  2. Constraints on the collision and the pre-collision tectonic configuration between India and Asia from detrital geochronology, thermochronology, and geochemistry studies in the lower Indus basin, Pakistan

    NASA Astrophysics Data System (ADS)

    Zhuang, Guangsheng; Najman, Yani; Guillot, Stephane; Roddaz, Martin; Antoine, Pierre-Olivier; Metais, Gregoire; Carter, Andrew; Marivaux, Laurent; Solangi, Sarfraz

    2016-04-01

    The timing of India-Asia suturing in the Western Himalaya is complex, with the relative timings of collision between the Indian plate and Asian plate with the Kohistan Island arc and a proposed Tethyan Himalayan microcontinent, debated. Here we present an integrated provenance study of geochronology, thermochronology, and geochemistry on the late Cretaceous-Pleistocene sediments from the lower Indus basin on the Indian plate. The detrital zircon U-Pb and fission track data show a reversal in sediment source from a pure Indian signature to increasing inputs from the suture zone and the Asian plate between the middle Paleocene and early Oligocene. The Nd and Sr isotopes narrow down this change to 50 Ma by revealing input of Asian detritus and the establishment of a Nd & Sr isotopic pattern similar to that of the present-day Indus Fan by 50 Ma, with no significant variations up section, contrary to what might be expected if later major collisions had occurred. Our isotopic data indicate that since 50 Ma, Greater India was occupied by a fluvial-deltaic system, analogous to the present-day Indus and named as the Paleo-Indus, which has been transporting Asian detritus southward across the suture zone and Kohistan-Ladakh arc. This suggests that no other ocean basins were located between India and Asia after this time in this region. Our data require that in the west, the India-Asia collision was accomplished by ˜50 Ma.

  3. Paleomagnetism, Geochronology, and Geochemistry of the Type Section of the Stanislaus Group: Reference Parameters from the Stable Sierra Nevada Microplate, CA

    NASA Astrophysics Data System (ADS)

    Farner, M. J.; Pluhar, C. J.; Asami, R.; Putirka, K. D.; Busby, C.; Renne, P. R.

    2012-12-01

    The Late Miocene Stanislaus Group, of California and Nevada is composed of Table Mountain Formation, Eureka Valley Tuff, and Dardanelles Formation. This ~9.0-~10.2 million year old unit interrupted Miocene andesitic arc volcanism in the Sierra Nevada, providing a regional lithostratigraphic marker that has been used extensively to reconstruct tilt and uplift of the range, Neogene tectonics of the Walker Lane Belt, magmagenetic processes beneath the Sierra Nevada, and lithospheric evolution of the Sierra Nevada and Eastern California. A recent study (Koerner et al, 2009) produced a measured section and geologic map of the Stanislaus Group type section, but until now this locality has never seen comprehensive multidisciplinary study of the geochronology, geochemistry, and magnetostratigraphy of the site and to integrate this into the overall understanding of the Stanislaus Group. Stratigraphy, geochemistry, and paleomagnetism from the type section suggest addition of a basal trachyte lava flow member to the Eureka Valley tuff and adds an additional intermediate-polarity lava flow to Table Mountain Formation magnetostratigraphy. This study dates the youngest member of the Stanislaus Group, the Dardanelles Formation, by 40Ar/39Ar radioisotopic dating for the first time, yielding an age of 9.048 ± 0.017 Ma. Paleomagnetic results verify the previous paleomagnetic reference direction from the Sierra Nevada microplate for the Tollhouse Flat Member of the Eureka Valley Tuff (King et al., 2007). However, our work revises the By-Day Member reference direction to D = 349.6°, I = 51.9° n = 8, α95 = 3.0°, k = 346. This difference is because the prior work analyzed By-Day localities within the tectonically-active Walker Lane Belt. The revised reference direction is critical for measurements of relative vertical-axis rotation studies in the Walker Lane. Our study also demonstrates that little to no vertical-axis rotation of the Sierra Nevada microplate has occurred since

  4. CO2 outburst events in relation to seismicity: Constraints from microscale geochronology, geochemistry of late Quaternary vein carbonates, SW Turkey

    NASA Astrophysics Data System (ADS)

    Ünal-İmer, Ezgi; Uysal, I. Tonguç; Zhao, Jian-Xin; Işık, Veysel; Shulmeister, James; İmer, Ali; Feng, Yue-Xing

    2016-08-01

    Vein and breccia carbonates precipitated in a highly fractured/faulted carbonate bedrock in SW Turkey were investigated through high-resolution U-series geochronology, microstructural and geochemical studies including C-O-Sr isotope and rare-earth element and yttrium (REY) analyses. Petrographical observations and geochronological data are interpreted as evidence that the calcite veins formed through a crack-seal mechanism, mostly accompanied/initiated by intensive hydraulic fracturing of the host limestone in response to high-pressure fluids, which is manifested by multi-stage breccia deposits. Microscale U-series dates (272.6-20.5 kyr) and geochemical compositions of the vein/breccia samples provide information on the timing and mechanism of the vein formation and identify the source of CO2-bearing fluids responsible for the carbonate precipitation. δ18OVPDB and δ13CVPDB values of the calcite veins range between -5.9 and -1.7‰, and -10.6 and -4.6‰, respectively. The isotopic compositions of the veins show highly fluctuating values as calcite grew successively perpendicular to vein walls, which, in combination with microstructural and geochronological constraints, are interpreted to reflect episodic CO2 degassing events associated with seismic and aseismic deformation. Oxygen and Sr isotope compositions (δ18OVPDB: -5.9 to -1.7‰; 87Sr/86Sr: 0.7082 to 0.7085) together with REY concentrations indicate deep infiltration of meteoric waters with various degrees of interactions mostly with the host limestone and siliciclastic parts of the basement rocks. Oxygen and carbon isotope compositions suggest CO2 degassing through intensive limestone dissolution. While majority of the veins display similar Post-Archaean Australian Shale (PAAS)-normalised REY variations, some of the veins show positive EuPAAS anomalies, which could be indicative of contributions from a deeply derived, heated, and reduced fluid component, giving rise to multiple fluid sources for the

  5. Geochemistry and geochronology of granitoids in the Kibi-Asamankese area of the Kibi-Winneba volcanic belt, southern Ghana

    NASA Astrophysics Data System (ADS)

    Anum, Solomon; Sakyi, Patrick Asamoah; Su, Ben-Xun; Nude, Prosper M.; Nyame, Frank; Asiedu, Daniel; Kwayisi, Daniel

    2015-02-01

    In Ghana the West African Craton is represented by Birimian and Tarkwaian rocks with extensive granitoid bodies. Granitoids from Asamankese area of the Kibi-Winneba volcanic belt, southern Ghana were analysed for major and trace element contents and found to be characterised by highly-fractionated REE, enrichments, in LILE, and depletion in Nb, Ta and Sr. The LILE enrichment relative to strong Nb-Ta depression, indicates that these granitoids were emplaced in an active margin. Based on field relations, geochemical composition and geochronological data, the granitoids from the Kibi-Asamankese area can be divided into three types, namely; the Eburnean biotite granodiorite (2133-2127 Ma) and hornblende granodiorite (2147 Ma), and the Pre-Eburnean gneissic biotite granite (2193 Ma). The geochemical data of the studied rocks plot in the tholeiitic field, whereas on the A/CNK-A/NK diagram, they generally fall within the metaluminous field, with A/CNK values between 0.69 and 0.88. U-Pb dating of zircons in the granitoids yielded ages ranging from 2193 to 2127 Ma, which are among the oldest ages obtained from the granitoid plutons in Ghana. Such high-precision geochronological data indicate that magmatism occurred over a time-span of about 70 Ma. This provides further evidence that the period 2.1-2.2 Ga was one of the important stages of Birimian magmatism that led to the generation of the granitoids. From the above-mentioned ages, it is possible to link the geological activities to crustal processes and establish the cyclic geotectonic evolution in the West African Craton over time as part of an arc-back-arc basin system.

  6. Rapid forearc spreading between 130 and 120 Ma: Evidence from geochronology and geochemistry of the Xigaze ophiolite, southern Tibet

    NASA Astrophysics Data System (ADS)

    Dai, Jingen; Wang, Chengshan; Polat, Ali; Santosh, M.; Li, Yalin; Ge, Yukui

    2013-07-01

    The Cretaceous Xigaze ophiolite is best exposed at the central Yarlung Zangbo Suture Zone (YZSZ, Tibet) which also includes the Gangdese arc and the Xigaze forearc basin. This study reports new geochronological and geochemical data for this ophiolite to revisit its geodynamic and petrogenetic evolution. The Xigaze peridotites have low CaO and Al2O3 contents and U-shaped Rare Earth Element (REE) patterns, suggesting that they are residues after moderate to high degrees of partial melting and were modified by infiltration of Light Rare Earth Element (LREE)-enriched boninitic melts. The Xigaze crustal rocks belong to two groups: Mid-Ocean Ridge Basalt (MORB)-like rocks and boninitic rocks showing a uniform LREE depletion and flat to LREE enrichment on chondrite-normalized patterns, respectively. Geochemically, both groups show the influence of subducting oceanic slab-derived fluids. LA-ICPMS zircon U-Pb and Lu-Hf analyses from dolerite and quartz diorite dikes, which intruded into the mantle peridotite, and dolerite sheeted sills show that they were generated between 127 and 124 Ma. The zircons possess positive εHf(t) values ranging from + 7.5 to + 17.3. Taking into account the geological and geochronological characteristics of the central-western YZSZ, we propose that ophiolites in this region formed in a forearc spreading setting through rapid slab rollback during subduction initiation between 130 and 120 Ma. Following this stage of spreading, the forearc was stabilized and the zone of melting migrated beneath the Gangdese arc producing the voluminous Late Cretaceous granitoids displaying depleted mantle-type Hf isotopic compositions. Our model provides a new explanation for the generation and evolution of forearc-type ophiolites.

  7. Geochronology and geochemistry of zircon from the northern Western Gneiss Region: Insights into the Caledonian tectonic history of western Norway

    NASA Astrophysics Data System (ADS)

    Gordon, Stacia M.; Whitney, Donna L.; Teyssier, Christian; Fossen, Haakon; Kylander-Clark, Andrew

    2016-03-01

    The Western Gneiss Region (WGR) of Norway is divided by the Møre-Trøndelag shear zone (MTSZ) into a southern region that contains domains of Caledonian ultrahigh-pressure (UHP) metamorphic rocks (> 2.5 GPa) and a northern area of similar Caledonian-aged rocks that record a maximum pressure reported thus far of 1.5 GPa. Although both regions contain similar lithologies (primarily migmatitic quartzofeldspathic gneiss containing mafic lenses) and structural relationship of basement rocks to infolded nappes, this difference in maximum pressure implies a difference in tectonic history (continental subduction south of the shear zone, none to the north) and raises questions about the role of the MTSZ in the metamorphic history (including exhumation) of the WGR. Previous geochronology results indicated a difference in timing of peak metamorphism (older in north, younger in south). In order to better understand the tectonic history of the northern WGR and the MTSZ, and in particular the late- to post-Caledonian tectonic history, U-Pb zircon geochronology and trace-element abundances were obtained using the split-stream, laser-ablation ICPMS technique from metabasaltic lenses and migmatitic quartzofeldspathic host rocks from the structurally lowest exposed region of the northern WGR (Roan Peninsula basement), as well as leucosomes from an intercalated portion of the Seve Nappe Complex and a pegmatite in the MTSZ. Zircon from Roan gneiss and metabasite yield metamorphic ages of ca. 410-406 Ma, and zircon from a variety of migmatite samples (foliation-parallel leucosome to dikes) indicate melt crystallization at ca. 410 to 405 Ma. The Seve Nappe leucosomes yield only early Caledonian dates that cluster at ca. 437 Ma and ca. 465 Ma, suggesting that the allochthons in this region did not experience (or record) the same Scandian tectonic history as the basement rocks. Zircon from a weakly deformed pegmatite dike within the MTSZ crystallized at ca. 404 Ma, indicating that this

  8. Geochemistry and Re-Os geochronology of the organic-rich sedimentary rocks in the Jingtieshan Fe-Cu deposit, North Qilian Mountains, NW China

    NASA Astrophysics Data System (ADS)

    Yang, Xiuqing; Zhang, Zuoheng; Li, Chao; Duan, Shigang; Jiang, Zongsheng

    2016-04-01

    The Jingtieshan Group in the North Qilian Mountains, NW China, is dominantly composed of banded iron formations (BIFs), copper deposits and organic-rich sedimentary rocks (ORS, carbonaceous phyllite). X-ray diffraction analysis of the ORS shows the mineral assemblage to be quartz + clay minerals. The total organic carbon contents show a range of 0.44-1.72%. Here we present the results of the geochemistry and Re-Os geochronology of the ORS from the Jingtieshan Group. The high values of Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Plagioclase Index of Alteration (PIA), and Th/U ratio, indicate intense weathering. The Al2O3/TiO2, Zr/Sc, Th/Sc, La/Th ratios, high rare earth elements abundances, light rare earth elements enrichment (normalized to chondrite), and distinctly negative Eu anomalies, suggest that the Jingtieshan Group ORS were derived mainly from felsic volcanic units. The new Re-Os isochron age of 1308 ± 100 Ma (2σ, n = 6, MSWD = 23) broadly overlap with the previous published ages determined using Sm-Nd and U-Pb isotope systems. The new age represents the depositional age of the Jingtieshan Group, as well that of BIF in the Jingtieshan area. Furthermore, the initial 187Os/188Os ratios (0.44 ± 0.07) indicate that the Os in the seawater was dominantly derived from hydrothermal fluids (∼75%). The Ce anomaly (Ce/Ce∗ = 0.95-1.00) and V/(V + Ni) ratios (0.71-0.86), as well as the lack of enrichment in redox-sensitive trace elements such as U, V, Zn, Pb, Cu, Ni, Cr, Co and Mn, together with the presence of overlying BIF, suggest that the Jingtieshan area represents a ferruginous deep-water succession. This, and intense submarine hydrothermal activities contributed to the deposition of the Jingtieshan BIF.

  9. Geology, geochronology, and geochemistry of basaltic flows of the Cat Hills, Cat Mesa, Wind Mesa, Cerro Verde, and Mesita Negra, central New Mexico

    USGS Publications Warehouse

    Maldonado, F.; Budahn, J.R.; Peters, L.; Unruh, D.M.

    2006-01-01

    The geochronology, geochemistry, and isotopic compositions of basaltic flows erupted from the Cat Hills, Cat Mesa, Wind Mesa, Cerro Verde, and Mesita Negra volcanic centres in central New Mexico indicate that each of these lavas had unique origins and that the predominant mantle involved in their production was an ocean-island basalt type. The basalts from Cat Hills (0.11 Ma) and Cat Mesa (3.0 Ma) are similar in major and trace element composition, but differences in MgO contents and Pb isotopic values are attributed to a small involvement of a lower crustal component in the genesis of the Cat Mesa rocks. The Cerro Verde rock is comparable in age (0.32 Ma) to the Cat Hills lavas, but it is more radiogenic in Sr and Nd, has higher MgO contents, and has a lower La/Yb ratio. This composition is explained by the melting of an enriched mantle source, but the involvement of another crustal component cannot be disregarded. The Wind Mesa rock is characterized by similar age (4.01 Ma) and MgO contents, but it has enriched rare-earth element contents compared with the Cat Mesa samples. These are attributed to a difference in the degree of partial melting of the Cat Mesa source. The Mesita Negra rock (8.11 Ma) has distinctive geochemical and isotopic compositions that suggest a different enriched mantle and that large amounts of a crustal component were involved in generating this magma. These data imply a temporal shift in magma source regions and crustal involvement, and have been previously proposed for Rio Grande rift lavas. ?? 2006 NRC Canada.

  10. U-Pb geochronology and geochemistry of the McCoy Mountains Formation, southeastern California: A Cretaceous retroarc foreland basin

    USGS Publications Warehouse

    Barth, A.P.; Wooden, J.L.; Jacobson, C.E.; Probst, K.

    2004-01-01

    The timing of deposition of fluvial sediments now forming the >7-km-thick McCoy Mountains Formation is one of the key uncertainties in reconstructing the Mesozoic poleogeography of southern California and western Arizona. Ion-microprobe U-Pb geochronologic data for individual zircons from nine sandstones from the McCoy Mountains type section and six associated igneous rocks provide significant new constraints on the tectonic setting and the timing of deposition within the northwest-trending McCoy basin. U-Pb zircon data from a metavolcanic rock of the underlying Dome Rock sequence in the Palen Mountains confirm that the McCoy Mountains Formation was deposited after regional Middle to Late Jurassic arc magmatism. U-Ph zircon data from a Late Cretaceous granodiorite intruding the formation in the Coxcomb Mountains confirm that the formation was deformed and metamorphosed prior to 73.5 ?? 1.3 Ma. Populations of detrital zircons vary systematically with both rock type and stratigraphic height; lithic arkoses predominantly derived from the west have consistently more abundant younger zircons than do litharenite sandstones predominantly derived from the north, and the youngest zircons yield maximum depositional ages that decrease from 116 Ma near the base to 84 Ma near the top of the section. The detrital-zircon data permit a Late Jurassic age for the basal, comparatively quartz-rich sandstone. However, the data further suggest that >90% of the formation was deposited between middle Early and middle Late Cretaceous time. These results are consistent with the hypothesis that most of the McCoy Mountains Formation represents a retroarc foreland basin, deposited behind the active, evolving Cretaceous Cordilleran continental-margin magmatic arc that lay to the west and in the foreland of the actively deforming Cretaceous Maria fold-and-thrust belt.

  11. Black monazite from Taiwan

    USGS Publications Warehouse

    Matzko, J.J.; Overstreet, W.C.

    1977-01-01

    Two forms of detrital monazite are known in offshore bars in southwestern Taiwan: a yellow-green to colorless form and an unusual but abundant pelletlike form, generally black but also colored gray or brown. These black pellets, which are about 160 by 200 microns in size, are composed of fine-grained monazite crystals from 2 to 20 microns in size. The pellets are associated with highly variable amounts of discrete grains of detrital quartz, rutile, amphibole, tourmaline, and other minerals. Intergrown with the monazite are quartz, a cerium oxide mineral, chlorite, sulfides, and other minerals. Opaqueness of the pelletlike monazite is due principally to the cryptocrystalline nature of part of the monazite; only a small part of the opaqueness can be attributed to opaque inclusions. The black pelletlike monazite lacks thorium and has a high content of europium. In this respect, as in color, shape, size, and inclusions, the pelletlike monazite differs from the yellow-green detrital monazite. Despite the fact that they occur together in the littoral placers, they appear to have had different origins. The yellow-green monazite originated as an accessory mineral in plutonic rocks and has accumulated at the coast through erosion and transport. The origin of the pelletlike monazite is as yet unknown, but it is here inferred that it originated in unconsolidated coastal plain sediments through migration of cerium from the detrital monazite during weathering, and of the intermediate weight mobile rare earths from clay minerals during diagenesis. Possibly these pelletlike grains are detrital particles formed through erosion and transport from originally larger aggregates cemented by diagenetic monazite.

  12. Decoding polyphase migmatites using monazite petrochronology

    NASA Astrophysics Data System (ADS)

    Yakymchuk, C.; Brown, M.; Korhonen, F. J.; Piccoli, P. M.; Siddoway, C. S.

    2014-12-01

    Unraveling the P-T-t evolution of deep crustal rocks requires the use of multiple high-temperature geochronometers integrated with careful petrography and quantitative phase equilibria modeling. As an example, in situ U-Pb monazite ages and Lu-Hf garnet geochronology are used to distinguish mineral parageneses associated with overprinting suprasolidus metamorphic events in migmatitic paragneisses and orthogneisses from the Fosdick migmatite-granite complex in West Antarctica. Then phase equilibria modeling is used to quantify the P-T conditions for each event. In the Fosdick complex, U-Pb monazite ages define two populations at 365-300 Ma (minor population; cores of polychronic grains) and 120-96 Ma (dominant population; monochronic grains and rims of polychronic grains). For seven samples, Lu-Hf ages of garnet range from 116 to 111 Ma, which are interpreted to record the approximate timing of peak metamorphism during the overprinting Cretaceous metamorphic event. Phase equilibria modeling constrains peak P-T conditions to 720-800°C at 0.45-1.0 GPa for the older (Devonian-Carboniferous) metamorphic event and 850-880°C at 0.65-0.80 GPa for the overprinting Cretaceous event. This younger metamorphic event is dominant throughout the Fosdick complex; it has extensively reworked evidence of the older metamorphic event as indicated by resorbed Devonian-Carboniferous cores of polychronic monazite grains that are always surrounded by Cretaceous overgrowths. Within the Cretaceous monazite population, the paucity of ages predating peak metamorphism suggests that prograde monazite growth was limited or prograde monazite was obliterated. Y-enriched overgrowths on monazite spatially associated with cordierite and biotite yield ages of 106-97 Ma, which are interpreted to record growth during breakdown of garnet in the presence of melt in the course of exhumation and cooling of the complex. Most monazite in the Cretaceous population yields ages that range from 106 to 96 Ma with

  13. Geochronology, geochemistry and origins of the Paleozoic-Triassic plutons in the Langshan area, western Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

    Wang, Zeng-Zhen; Han, Bao-Fu; Feng, Li-Xia; Liu, Bo

    2015-01-01

    The Langshan area is the northeastern part of the Alxa block and adjacent to the Inner Mongolia-Da Hinggan Orogenic Belt (IMDOB) to the north, and geochronological and geochemical studies of the Langshan plutons would be helpful for unraveling the relationship of the magmatism in the Langshan area with that in the IMDOB. Based on zircon U-Pb ages presented in this study and in published papers, five magmatic stages are recognized in Langshan area: Late Silurian (∼418 Ma), Carboniferous (328-304 Ma), Early Permian (294-272 Ma), Late Permian (260-254 Ma) and Middle-Late Triassic (245-227 Ma). The Late Silurian two-mica granite is peraluminous and has a source from ancient continental crust, indicating a collision event. The late Early Carboniferous mafic plutons are subalkaline, show appinitic affinities, and may originate from the subduction-modified continental lithospheric mantle. The late Early Permian granodiorite is weakly peraluminous and high-K calc-alkaline and may be derived from ancient continental crust, while the late Early Permian alkaline gabbro-diorite displays EM I-like Sr-Nd isotopic signatures, indicating an enriched subcontinental lithospheric mantle source. The Late Permian granodiorite is calc-alkaline and peraluminous and may result from the partial melting of ancient lower continental crust, whereas the Late Permian leuconorite belongs to low-K tholeiitic series and has a cumulate origin from an enriched mantle source with the input of juvenile mantle materials. The Paleozoic-Triassic magmatic stages in the Langshan area are consistent with the main magmatic periods in the northern NCC, which are the Late Silurian to Middle Devonian (∼418-386 Ma) and Early Carboniferous to Late Triassic (∼342-211 Ma, with three magmatic stages of Carboniferous, Permian and Triassic). Especially, the Carboniferous to Late Triassic magmatic period in the northern NCC are closely comparable with that in the IMDOB, indicating the two domains might be

  14. Evolution of Pleistocene to Holocene eruptions in the Lesser Caucasus Mts:Insights from geology, petrology, geochemistry and geochronology

    NASA Astrophysics Data System (ADS)

    Savov, Ivan; Meliksetian, Khachatur; Connor, Charles; Karakhanian, Arkadi; Sugden, Patrick; Navasardyan, Gevorg; Halama, Ralf; Ishizuka, Osamu; Connor, Laura; Karapetian, Sergei

    2016-04-01

    Both effusive and highly explosive (VEI>5) and often voluminous caldera volcanism has developed atop the collision zone between the Arabian and the Eurasian plates. Currently what is exposed on the Anatolian-Armenian-Iranian active orogenic plateau is post-Mesozoic felsic to intermediate collision-related plutons, and mostly collision or post-collision related Quaternary volcanic structures. We have studied in detail the volcanism, tectonics and geophysics on the territory of E.Turkey and Armenia, where several large stratovolcanoes (Ararat, Lesser Ararat, Aragats, Tsghuk, Ishkhanasar) are surrounded by distinct monogenetic volcanic fields (distributed volcanism). These large in volume stratovolcanoes and the associated low volume monogenetic cones range from normal calk-alkaline to high-K shoshonitic in affinity, with their products ranging from basanites to high K trachytes and rhyolites. Several volcanic provinces, namely Kechut/Javakheti, Aragats, Gegham, Vardenis and Syunik are recognized in Armenia and each of them has > 100 mapped volcanoes. These have distinct geochemical (mineral chemistry, trace element and Sr-Nd-B isotope systematics) and petrological (melt eruption temperatures and volatile contents) fingerprints that may or may not vary over time. Age determinations and volcano-stratigraphy sections for each of the case studies we aim to present shows that the volcanism includes a continuous record from Pleistocene to Holocene, or even historical eruptions. The excellent volcano exposures and the now complete high resolution database (GIS), geological mapping, and new and improved K-Ar and Ar-Ar geochronology, uniquely allows us to evaluate the driving forces behind the volcanism in this continent-continent collision setting that is uniquely associated with long lasting eruption episodes. We shall compare the now well studied historical/Holocene eruptions with those pre-dating them, with the aim to identify possible geochemical or petrological

  15. Resetting Monazite Dates by Fluid Moderated Coupled Dissolution-Reprecipitation

    NASA Astrophysics Data System (ADS)

    Williams, M. L.; Jercinovic, M. J.; Harlov, D. E.; Budzyn, B.

    2009-12-01

    Monazite has increasingly been used as a geochronometer, especially in deformed and metamorphosed rocks. Monazite is appropriate for this application because it has a very broad compositional range, and can be produced in a number of chemical reactions. Because diffusion is slow, monazite compositions tend to be preserved as core and rim domains. Ideally, the compositional and textural domains can be linked with structural fabrics and/or metamorphic reactions and thus, provide a means of directly dating the deformation events or metamorphic reactions. The use of multidomain monazite to constrain stages in a P-T history depends on the assumption that compositions and ages are essentially unmodified during subsequent events. Although closure temperatures are certainly high, recent studies suggest that under some circumstances, monazite compositions (and possibly dates) can be modified by fluid-moderated coupled dissolution-reprecipitation processes. This is particularly important for geochronologic studies because the replacement process may not involve the complete removal of some components, such as Pb, and thus spurious dates, either older or younger than the true age, could possibly result. We show results of one experimental investigation in which the starting monazite was strikingly altered to a new monazite composition by solid state dissolution-reprecipitation processes. In some grains, the new monazite occurs in regular domains near the grain boundaries, and might be misinterpreted as overgrowths. In other grains, new monazite occurs internally, near inclusions or microfractures or as irregular patchy domains. Altered domains are generally distinctive and distinguishable from growth domains. The new compositions are extremely uniform from grain to grain (Th: initial= 7.0 wt. %; altered = 2.0 wt%). The altered monazite domains are free of Pb. Thus, at least in this example, the monazite date was essentially reset to zero. The results suggest that it is

  16. Geochronology and geochemistry of the high Mg dioritic dikes in Eastern Tianshan, NW China: Geochemical features, petrogenesis and tectonic implications

    NASA Astrophysics Data System (ADS)

    Li, Deng-Feng; Zhang, Li; Chen, Hua-Yong; Hollings, Pete; Cao, Ming-Jian; Fang, Jing; Wang, Cheng-Ming; Lu, Wan-Jian

    2016-01-01

    Zircon U-Pb ages of high Mg dioritic dikes in the Mesoproterozoic Kawabulake Group in the Eastern Tianshan area, NW China indicate that they were emplaced in the Early Carboniferous at 353-348 Ma. The dikes consist of medium-grained plagioclase and hornblende with minor clinopyroxene and trace quartz. They are characterized by intermediate SiO2 (60-62 wt.%), low TiO2 (0.63-0.71 wt.%), relatively high Al2O3 (15.1-15.8 wt.%) and MgO contents (3.45-4.15 wt.%) with Mg# generally higher than 56 (56-59). The geochemistry of the high Mg diorites suggest they were formed by similar magmatic processes to sanukitoid high Mg Andesites such as those of the Setouchi volcanic belt, Japan. Zircons from the high Mg dioritic dikes have εHf(t) values of -6.8 to +14.5. The dominantly positive values suggest a juvenile source, whereas the small number of negative values suggests mature components were also incorporated into the source. Similarly, the positive εNd(t) values (0 to +2.2) are interpreted to reflect a juvenile source whereas the negative values of (-5.2 to 0) suggest participation of old crustal rocks in the petrogenesis of the diorites. The variable εHf(t) and εNd(t) values suggest that the mature material was assimilated during magma ascent rather than in the mantle wedge which would result in more uniform values. Mass balance calculations suggest that the dioritic dikes were derived from sources composed of approximately 97% juvenile mantle-derived material and 3% sediment. Petrographic, elemental, and isotopic evidence suggest that the dioritic dikes were generated by partial melting of depleted mantle that migrated into the shallow crust where it assimilated older sedimentary rocks of the Mesoproterozoic Kawabulake Group.

  17. Petrology, geochemistry and geochronology of the magmatic suite from the Jianzha Complex, central China: Petrogenesis and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Li, Xiaowei; Mo, Xuanxue; Bader, Thomas; Scheltens, Mark; Yu, Xuehui; Dong, Guochen; Huang, Xiongfei

    2014-12-01

    The intermediate-mafic-ultramafic rocks in the Jianzha Complex (JZC) at the northern margin of the West Qinling Orogenic Belt have been interpreted to be a part of an ophiolite suite. In this study, we present new geochronological, petrological, geochemical and Sr-Nd-Hf isotopic data and provide a different interpretation. The JZC is composed of dunite, wehrlite, olivine clinopyroxenite, olivine gabbro, gabbro, and pyroxene diorite. The suite shows characteristics of Alaskan-type complexes, including (1) the low CaO concentrations in olivine; (2) evidence of crystal accumulation; (3) high calcic composition of clinopyroxene; and (4) negative correlation between FeOtot and Cr2O3 of spinels. Hornblende and phlogopite are ubiquitous in the wehrlites, but minor orthopyroxene is also present. Hornblende and biotite are abundant late crystallized phases in the gabbros and diorites. The two pyroxene-bearing diorite samples from JZC yield zircon U-Pb ages of 245.7 ± 1.3 Ma and 241.8 ± 1.3 Ma. The mafic and ultramafic rocks display slightly enriched LREE patterns. The wehrlites display moderate to weak negative Eu anomalies (0.74-0.94), whereas the olivine gabbros and gabbros have pronounced positive Eu anomalies. Diorites show slight LREE enrichment, with (La/Yb)N ratios ranging from 4.42 to 7.79, and moderate to weak negative Eu anomalies (Eu/Eu∗ = 0.64-0.86). The mafic and ultramafic rocks from this suite are characterized by negative Nb-Ta-Zr anomalies as well as positive Pb anomalies. Diorites show pronounced negative Ba, Nb-Ta and Ti spikes, and typical Th-U, K and Pb peaks. Combined with petrographic observations and chemical variations, we suggest that the magmatism was dominantly controlled by fractional crystallization and crystal accumulation, with limited crustal contamination. The arc-affinity signature and weekly negative to moderately positive εNd(t) values (-2.3 to 1.2) suggest that these rocks may have been generated by partial melting of the juvenile

  18. U-Pb-Th geochronology of monazite and zircon in albitite metasomatites of the Rožňava-Nadabula ore field (Western Carpathians, Slovakia): implications for the origin of hydrothermal polymetallic siderite veins

    NASA Astrophysics Data System (ADS)

    Hurai, V.; Paquette, J.-L.; Lexa, O.; Konečný, P.; Dianiška, I.

    2015-10-01

    Sodic metasomatites (albitites) occur around and within siderite veins in the southern part of the Gemeric tectonic unit of the Western Carpathians. Accessory minerals of the metasomatites represented by monazite, zircon, apatite, rutile, tourmaline and siderite are basically identical with the quartz-tourmaline stage of other siderite and stibnite veins of the tectonic unit. Statistical analysis of chemical Th-U(total)-Pb isochron method (CHIME) of monazite dating yielded Jurassic-Cretaceous ages subdivided into 3-4 modes, spreading over time interval between 78 and 185 Ma. In contrast, LA-ICPMS 206Pb/238U dating carried out on the same monazite grains revealed a narrow crystallization interval, showing ages of Th-poor cores with phengite inclusions identical within the error limit with Th-rich rims with cauliflower-like structure. The determined lower intercept at 139 ± 1 Ma overlapped the Vallanginian-Berriasian boundary, thus corroborating the model of formation of hydrothermal vein structures within an arcuate deformation front built up in the Variscan basement as a response to Early Cretaceous compression, folding and thrusting. In contrast, associated zircons are considerably older than the surrounding Early-Palaeozoic volcano-sedimentary rocks, showing Neoproterozoic ages. The zircon grains in albitite metasomatites are thus interpreted as fragments of Pan-African magmatic detritus incorporated in the vein structures by buoyant hydrothermal fluids.

  19. Constraints on the collision and the pre-collision tectonic configuration between India and Asia from detrital geochronology, thermochronology, and geochemistry studies in the lower Indus basin, Pakistan

    NASA Astrophysics Data System (ADS)

    Zhuang, Guangsheng; Najman, Yani; Guillot, Stéphane; Roddaz, Martin; Antoine, Pierre-Olivier; Métais, Grégoire; Carter, Andrew; Marivaux, Laurent; Solangi, Sarfraz H.

    2015-12-01

    Knowledge of the timing of India-Asia collision is a fundamental prerequisite for understanding the evolution of the Himalayan-Tibetan orogen and its role in global climate, oceanic chemistry, and ecological evolution. Despite much active research, the basic pre-collision tectonic configuration and the timing of terminal India-Asia suturing remain debated. For example, debates regarding when and how the intervening Kohistan-Ladakh arc was sutured with India and Asia still remain elusive; some models propose the arc collided with Asia at about 100 Ma, with India-Asia collision at ca. 55 Ma, whilst a newer model proposed the arc's collision with India at 50 Ma and subsequently with Asia at 40 Ma. Another example is the recent proposition that an oceanic Greater India Basin separated the Tethyan Himalaya microcontinent from the remaining Indian plate until 20- 25 Ma with the consumption of this oceanic basin marking the final collision at this time. These controversies relate to whether the commonly documented 50 Ma contact represents the terminal India-Asia suturing or the amalgamation between various arcs or microcontinents with India or Asia. Here we present an integrated provenance study of geochronology, thermochronology, and geochemistry on the late Cretaceous-Pleistocene sediments from the lower Indus basin on the Indian plate. The detrital zircon U-Pb and fission track data show a reversal in sediment source from a pure Indian signature to increasing inputs from the suture zone and the Asian plate between the middle Paleocene and early Oligocene. The Nd and Sr isotopes narrow down this change to 50 Ma by revealing input of Asian detritus and the establishment of a Nd & Sr isotopic pattern similar to the present-day Indus Fan by 50 Ma, with no significant variations up section, contrary to what might be expected if later major collisions had occurred. Our isotopic data indicate that Greater India was occupied by a fluvial-deltaic system, analogous to the

  20. The syncollisional granitoid magmatism and continental crust growth in the West Kunlun Orogen, China - Evidence from geochronology and geochemistry of the Arkarz pluton

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Niu, Yaoling; Hu, Yan; Liu, Jinju; Ye, Lei; Kong, Juanjuan; Duan, Meng

    2016-02-01

    The West Kunlun orogenic belt (WKOB) at the northwest margin of the Greater Tibetan Plateau records seafloor subduction, ocean basin closing and continental collision with abundant syncollisional granitoids in response to the evolution of the Proto- and Paleo-Tethys Oceans from the early-Paleozoic to the Triassic. Here we present a combined study of detailed zircon U-Pb geochronology, whole-rock major and trace elements and Sr-Nd-Hf isotopic geochemistry on the syncollisional Arkarz (AKAZ) pluton with mafic magmatic enclaves (MMEs) exposed north of the Mazha-Kangxiwa suture (MKS) zone. The granitoid host rocks and MMEs of the AKAZ pluton give the same late Triassic age of ~ 225 Ma. The granitoid host rocks are metaluminous granodiorite and monzogranite. They have initial 87Sr/86Sr of 0.70818 to 0.70930, εNd(225 Ma) = - 4.61 to - 3.91 and εHf(225 Ma) = - 3.01 to 0.74. The MMEs are more mafic than the host with varying SiO2 (51.00-63.24 wt.%) and relatively low K2O (1.24-3.02 wt.%), but have similar Sr-Nd-Hf isotope compositions to the host ((87Sr/86Sr)i = 0.70830-0.70955, εNd(225 Ma) = - 4.88 to - 4.29, εHf(225 Ma) = - 2.57 to 0.25). Both the host and MMEs have rare earth element (REE) and trace element patterns resembling those of bulk continental crust (BCC). The MMEs most likely represent cumulate formed from common magmas parental to the granitoid host. The granitoid magmatism is best explained as resulting from melting of amphibolite of MORB protolith during continental collision, which produces andesitic melts with a remarkable compositional similarity to the BCC and the inherited mantle-like isotopic compositions. Simple isotopic mixing calculations suggest that ~ 80% ocean crust and ~ 20% continental materials contribute to the source of the AKAZ pluton. Thus, the hypothesis "continental collision zones as primary sites for net continental crust growth" is applicable in the WKOB as shown by studies in southern Tibet, East Kunlun and Qilian orogens. In

  1. Geochemistry, geochronology, and origin of the Neoarchean Planalto Granite suite, Carajás, Amazonian craton: A-type or hydrated charnockitic granites?

    NASA Astrophysics Data System (ADS)

    Feio, G. R. L.; Dall'Agnol, R.; Dantas, E. L.; Macambira, M. J. B.; Gomes, A. C. B.; Sardinha, A. S.; Oliveira, D. C.; Santos, R. D.; Santos, P. A.

    2012-10-01

    New whole-rock geochemistry and LA-MC-ICPMS and Pb-evaporation geochronological data were obtained on zircon from the Neoarchean Planalto suite granites and associated charnockitic rocks of the Canaã area of the Carajás province, eastern Amazonian craton, Brazil. The Pb-evaporation ages of three samples from the Planalto suite are around 2730 Ma (2733 ± 2 Ma, 2731 ± 1 Ma and 2736 ± 4 Ma), whereas U-Pb LA-MC-ICPMS concordia ages obtained for these samples are 2729 ± 17 Ma, 2710 ± 10 Ma, and 2706 ± 5 Ma, respectively. An orthopyroxene quartz gabbro associated with the Pium complex and Planalto suite yielded a U-Pb concordia age of 2735 ± 5 Ma, interpreted as its crystallization age. The Planalto suite granites and the charnockitic rocks associated with the Mesoarchean Pium complex were probably crystallized at 2730 ± 10 Ma. The Planalto granites have ferroan character and are similar geochemically to reduced A-type granites. In previous studies, they have been classified as such, despite the fact that they are syntectonic. The tectonic setting and the association between the Planalto suite and charnockitic series led us to classify these biotite-hornblende granites as hydrated granites of the charnockitic series. The Planalto suite and the Neoarchean charnockitic magmas were more probably derived by partial melting of mafic to intermediate tholeiitic orthopyroxene-bearing rocks similar to those of the Pium complex. At 2.76 Ga, upwelling of asthenospheric mantle in an extensional setting propitiated the formation of the Carajás basin. Later on, at ca. 2.73 Ga, heat input associated with underplate of mafic magma induced partial melting of mafic to intermediate lower crustal rocks, originating the Planalto and charnockitic magmas. The emplacement of these magmas occurred under active regional stress and resultant major shear zones found in the Canaã dos Carajás area. The close association between the Planalto suite and charnockitic rocks suggests that they

  2. Thorium Diffusion in Monazite

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.

    2006-05-01

    Diffusion of thorium has been characterized in synthetic monazite under dry conditions. The synthetic monazites (either pure CePO4, NdPO4, or a mixed LREE phosphate containing Ce, Nd, and Sm) were grown via a Na2CO3-MoO3 flux method. The source of diffusant for the experiments were either synthesized ThSiO4 or CaTh(PO4)2 powders. Experiments were performed by placing source and monazite in Pt capsules and annealing capsules in 1 atm furnaces for times ranging from 10 days to a few hours, at temperatures from 1400 to 1550C. The Th distributions in the monazite were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation was obtained for diffusion in monazite: DSm = 7.2x103 exp(-814 kJ mol-1/RT) m2sec-1 The diffusivity of Th was similar for monazites containing a single REE and the mixed LREE phosphates. Th diffusion was also similar for experiments run using the Th silicate and Ca-Th phosphate sources, suggesting that the substitutional mechanism for Th in monazite, i.e, Th+4 + Si+4 for REE+3 + P+5 with the ThSiO4 source, and Th+4 + Ca+2 for 2REE+3 with the CaTh(PO4)2 source, does not significantly affect Th diffusivities, and that Th is likely the rate-limiting species. Th diffusion in monazite is about 4 orders of magnitude slower than Pb diffusion (Cherniak et al., 2004). This contrasts with findings of Gardes et al. (2005) who determined that Pb, Th and REE diffusivities in monazite are similar. Th diffusion in zircon (Cherniak et al., 1997) is about an order of magnitude slower than in monazite, but with similar activation energy for diffusion. The smaller diffusivities in zircon may be a consequence of the larger disparity in size between Th and the Zr site in zircon as compared with Th and the REE site in monazite. Nonetheless, Th is essentially immobile in monazite with respect to exchange by volume diffusion under most geologic conditions; these findings may have implications for containment of high- level actinide

  3. The Siderian-Orosirian magmatism in the Gavião Paleoplate, Brazil: U-Pb geochronology, geochemistry and tectonic implications

    NASA Astrophysics Data System (ADS)

    Pereira Cruz, Simone Cerqueira; Figueiredo Barbosa, Johildo Salomão; Pinto, Marilda Santos; Peucat, Jean-Jacques; Paquette, Jean Louis; Santos de Souza, Jailma; de Souza Martins, Violeta; Júnior, Farid Chemale; Carneiro, Mauricio Antonio

    2016-08-01

    The southern portion of the Gavião Paleoplate is composed by Archean orthogneisses, Archean-Paleoproterozoic metavolcano-sedimentary rocks and Siderian-Rhyacian-Orosirian granitoids. Petrographic, geochemical, U-Pb (Laser Ablation, ICPMS) and Sm-Nd data are presented for five Paleoproterozoic granitoids that were recently mapped: Jussiape II, Lagoa das Almas, Humaitá, Belo Campo and Broco granitoids. These granitoids present U-Pb zircon (LA-ICPMS) ages of 2052 ± 43, 2114 ± 24, 2140 ± 9, 2049 ± 23 and 2038 ± 8 Ma, respectively. In addition to these granitoids, another twenty-five ones were identified and studied by several authors, resulting in a total of twenty-nine plutons. Despite the previous petrography, geochemistry and geochronology studies that have been performed, no model had been proposed to explain the tectonic setting of this extensive granitogenesis. Integration of the new data and the literature has been done and corresponds to the second part of the article. Based on U-Pb dating and geochemical data, Siderian-Rhyacian-Orosirian granitoids of the southern Gavião Paleoplate were classified into five groups, or five suites: 1 (2324 ± 6 to 2091 ± 6.6 Ma), 2a (2054 -6/+8 to 2041 ± 23 Ma), 2b (2066 ± 37 to 2019 ± 32 Ma), 2c (2058 ± 8 to 1852 ± 50 Ma) and 2d (2049 ± 12 to 1929 ± 16 Ma). The granitoids of Group 1 present heterogeneous deformation, while the granitoids of groups 2a to 2d are generally not deformed. Usually the rocks are potassic, but sodic granitic rocks can be found in samples of groups 1, 2c and 2d. Several chemical classification parameters are presented and discussed herein, but it is noteworthy that the granitoids of Group 1 are mainly classified as calcic to calc-alkalic, while the rocks of the second group are mostly classified as alkalic ones. In the remaining groups, the samples vary between calc-alkalic and alkali-calcic. The ɛNd values range between 4.0 and -15.4 and suggest an important and varied share of the

  4. A review of the geochronology and geochemistry of Late Yanshanian (Cretaceous) plutons along the Fujian coastal area of southeastern China: Implications for magma evolution related to slab break-off and rollback in the Cretaceous

    NASA Astrophysics Data System (ADS)

    Li, Zhen; Qiu, Jian-Sheng; Yang, Xue-Mei

    2014-01-01

    The Cretaceous plutonic suites in the Fujian coastal area include abundant I-type and A-type granitoids and lesser gabbroids. They are important components of the Late Yanshanian magmatic belt along the southeastern coast of China, and define a linear NNE-SSW-trending belt of magmatism. Geochronological, geochemical and geological data from thirty intrusions are summarised in this paper, and the data provide distinct magmatic, geochemical and tectonic patterns in the area. A compilation of geochronological data for these intrusive rocks indicates emplacement mainly from around 125 to 90 Ma, with a major peak from 115 to 90 Ma, and a subordinate peak from 125 to 115 Ma. Besides their temporal and spatial coexistence, all these intrusive rocks have similar geochemical patterns which point to involvement of components from a depleted asthenospheric mantle source for the parental magmas, most probably by magma mixing. The first appearance of sparse I-type granitoids with post-collisional extensional granite affinities, and the emplacement of the Baijuhuajian and Suzhou A-type granites, mark the beginning of extension during the Early Cretaceous at ca. 125 to 119 Ma. The subsequent development of bimodal magmatism at 115 to 90 Ma, with numerous arc-related mafic gabbros and I-type granites, together with some A-type granites, suggests that this major igneous event took place as a response to back-arc extension. On the basis of petrology, geochronology, tectonics, and elemental and isotopic geochemistry, we speculate that break-off and rollback of the subducting Palaeo-Pacific Plate during the Cretaceous were responsible for the Late Yanshanian regional tectono-magmatic evolution in the area. We suggest that this process facilitated a strong and rapid linear upwelling of the asthenospheric mantle beneath the coastal area of southeastern China, with consequential extension of the overlying continental lithosphere, and ultimately the large-scale Late Yanshanian magmatism

  5. The behaviour of monazite from greenschist facies phyllites to anatectic gneisses: An example from the Chugach Metamorphic Complex, southern Alaska.

    PubMed

    Gasser, Deta; Bruand, Emilie; Rubatto, Daniela; Stüwe, Kurt

    2012-03-01

    Monazite is a common accessory mineral in various metamorphic and magmatic rocks, and is widely used for U-Pb geochronology. However, linking monazite U-Pb ages with the PT evolution of the rock is not always straightforward. We investigated the behaviour of monazite in a metasedimentary sequence ranging from greenschist facies phyllites into upper amphibolites facies anatectic gneisses, which is exposed in the Eocene Chugach Metamorphic Complex of southern Alaska. We investigated textures, chemical compositions and U-Pb dates of monazite grains in samples of differing bulk rock composition and metamorphic grade, with particular focus on the relationship between monazite and other REE-bearing minerals such as allanite and xenotime. In the greenschist facies phyllites, detrital and metamorphic allanite is present, whereas monazite is absent. In lower amphibolites facies schists (~ 550-650 °C and ≥ 3.4 kbar), small, medium-Y monazite is wide-spread (Mnz1), indicating monazite growth prior and/or simultaneous with growth of garnet and andalusite. In anatectic gneisses, new low-Y, high-Th monazite (Mnz2) crystallised from partial melts, and a third, high-Y, low-Th monazite generation (Mnz3) formed during initial cooling and garnet resorption. U-Pb SHRIMP analysis of the second and third monazite generations yields ages of ~ 55-50 Ma. Monazite became unstable and was overgrown by allanite and/or allanite/epidote/apatite coronas within retrograde muscovite- and/or chlorite-bearing shear zones. This study documents polyphase, complex monazite growth and dissolution during a single, relatively short-lived metamorphic cycle.

  6. Geology, geochemistry, geochronology, and economic potential of Neogene volcanic rocks in the Laguna Pedernal and Salar de Aguas Calientes segments of the Archibarca lineament, northwest Argentina

    NASA Astrophysics Data System (ADS)

    Richards, J. P.; Jourdan, F.; Creaser, R. A.; Maldonado, G.; DuFrane, S. A.

    2013-05-01

    This study presents new geochemical, geochronological, isotopic, and mineralogical data, combined with new geological mapping for a 2400 km2 area of Neogene volcanic rocks in northwestern Argentina near the border with Chile, between 25°10‧S and 25°45‧S. The area covers the zone of intersection between the main axis of the Cordillera Occidental and a set of NW-SE-trending structures that form part of the transverse Archibarca lineament. This lineament has localized major ore deposits in Chile (e.g., the late Eocene La Escondida porphyry Cu deposit) and large volcanic centers such as the active Llullaillaco and Lastarría volcanoes on the border between Chile and Argentina, and the Neogene Archibarca, Antofalla, and Cerro Galán volcanoes in Argentina. Neogene volcanic rocks in the Laguna Pedernal and Salar de Aguas Calientes areas are mostly high-K calc-alkaline in composition, and range from basaltic andesites, through andesites and dacites, to rhyolites. Magmatic temperatures and oxidation states, estimated from mineral compositions, range from ~ 1000 °C and ∆FMQ ≈ 1.0-1.5 in andesites, to ~ 850 °C and ∆FMQ ≈ 1.5-2.0 in dacites and rhyolites. The oldest rocks consist of early-middle Miocene andesite-dacite plagioclase-pyroxene-phyric lava flows and ignimbrites, with 40Ar/39Ar ages ranging from 17.14 ± 0.10 Ma to 11.76 ± 0.27 Ma. Their major and trace element compositions are typical of the Andean Central Volcanic Zone, and show strong crustal contamination trends for highly incompatible elements such as Cs, Rb, Th, and U. These rocks are geochemically grouped as sub-suite 1. This widespread intermediate composition volcanism was followed in the middle-late Miocene by a period of more focused rhyodacitic flow-dome complex formation. These felsic rocks are characterized by less extreme enrichments in highly incompatible elements, and increasing depletion of heavy rare earth elements. These rocks are geochemically grouped as sub-suite 2. The

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

    USGS Publications Warehouse

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

    2013-01-01

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

  8. Geochronology, geochemistry, and tectonic characterization of Quaternary large-volume travertine deposits in the southwestern United States and their implications for CO2 sequestration

    NASA Astrophysics Data System (ADS)

    Priewisch, Alexandra

    Travertines are freshwater carbonates that precipitate from carbonic groundwater due to the degassing of CO2. Travertine deposits are often situated along faults that serve as conduits for CO2-charged groundwater and their geochemistry often records mixing of deeply-derived fluids and volatiles with shallow meteoric water. Travertines are surface expressions of dynamic mantle processes related to the tectonic setting. This dissertation includes four chapters that focus on different aspects of travertine formation and their scientific value. They are excellent, although underestimated, diagnostic tools for climatology, hydrology, tectonics, geochemistry, geomicrobiology, and they can inform carbon sequestration models. Quaternary large-volume travertine deposits in New Mexico and Arizona occur in an extensional tectonic stress regime on the southeastern Colorado Plateau and along the Rio Grande rift. They accumulated above fault systems during episodes of high hydraulic head in confined aquifers, increased regional volcanic activity, and high input of mantle-derived volatiles such as CO 2 and He. Stable isotope and trace element geochemistry of travertines is controlled by groundwater geochemistry as well as the degassing of CO 2. The geochemical composition allows for distinguishing different travertine facies and evaluating past groundwater flow. The travertine deposits in New Mexico are interpreted to be extinct CO2 fields due to the large volumes that accumulated and in analogy to the travertine deposits in Arizona that are associated with an active CO2-gas field. Travertines are natural analogues for CO2 leakage along fault systems that bypassed regional cap rocks and they provide important insight into the migration of CO2 from a reservoir to the surface. The volume of travertine can be used to infer the integrated CO2 leakage along a fault system over geologic time. This leakage is estimated as: (1) CO2 that becomes fixed in CaCO3/travertine (tons of carbon

  9. U-Pb Geochronology, Geochemistry and Kinematic Analyses of Subduction-Related Late Triassic Basins in Northern Chile (24.5º-26ºS).

    NASA Astrophysics Data System (ADS)

    Espinoza, M. E.

    2015-12-01

    In northern Chile (24.5°-26°S) two Pre-Andean depocenters crop out: the Cifuncho basin in the Coastal Cordillera and the Profeta basin in the Precordillera. These basins have been classically interpreted as a continental rifting unrelated to subduction during the period prior to the Andean orogenic cycle. However, recent petrographic and geochemical data suggest the development of these basins in an active subduction system. In order to test this hypothesis and to establish the geologic evolution of the basins and the strain field during the rifting process, we present preliminary U-Pb geochronological and geochemical data together with structural analyses of synrift structures. The geochronological data along the Cifuncho and Profeta basins, show a main continental sedimentary deposition during the Norian to Raethian. Volcanosedimentary rocks show a main detrital supply of Early Permian age (~297-283 Ma). This input can be associated with the volcanic La Tabla Formation and/or the exhumation of Permian granitoids. A minor supply close to ~478 Ma is related to a source from the Lower Ordovician arc (~480 Ma), suggesting the tectonic exhumation of this source to the east of the Profeta basin during the Late Triassic. On the other hand, structural analysis was carried in third and four order extensional faults (<10 m of slip) along the Profeta basin. Most of the faults show a clear synrift character with the development of fault controlled growing strata. The kinematic analyses evidence a variability in the orientation of the maximum strain axes from a main northwest to a subordinate northeast direction of extension. Thus, the intimate relation between the continental sedimentary deposition and a proximal volcanism of intermediate composition and calk-alkaline affinity, suggests the development of these basins in a supra-subduction setting during the Late Triassic. Structural data probably reflect local variation in the strain field across the basins.

  10. Monazite petrochronology from the UHP Western Gneiss Region, Norway

    NASA Astrophysics Data System (ADS)

    Holder, R. M.; Hacker, B. R.; Kylander-Clark, A. R.

    2013-12-01

    To understand the significance of U/Th-Pb chronology, dates from accessory minerals need to be tied to petrological conditions such as pressure, temperature, and mineral assemblage. This work examines monazite composition, petrologic texture, and U/Th-Pb dates acquired via LASS (laser ablation split stream) geochronology from pelites across the ultrahigh-pressure (UHP) Western Gneiss Region, Norway (WGR), to evaluate the range in monazite compositions preserved in UHP terranes and determine the petrologic reasons for the observed compositions. Proterozoic monazites (1600 & 1100-900 Ma) occur in amphibolite- to granulite-facies rocks across the WGR and as garnet inclusions in eclogite- and amphibolite-facies rocks. The oldest Paleozoic monazites have dates of 460 Ma (1 sample), sector zoning, and show typical HREE profiles (Gd/Yb <1000). Four samples have dates of 430-420 Ma, and a decrease in HREE with time (up to Gd/Yb >10000), but no trend in Eu/Eu*, compatible with garnet + plagioclase stable conditions during prograde metamorphism. Three samples from the Sørøyane UHP domain have dates of 410-405 Ma, depleted HREE (Gd/Yb >1000), weaker Eu anomalies, 2-3% common Pb, and, in one sample, high Sr contents relative to younger monazites in the same rock (0.6 vs <0.1 wt%). High Gd/Yb ratios, weak Eu/Eu*, and relatively high Sr concentrations are compatible with garnet-stable, plagioclase-absent conditions during (U)HP metamorphism. Except for the samples listed above, most monazites measured from the WGR have concordant dates from 400-390 Ma with increasing HREE concentrations over time, compatible with garnet resorbtion during the decompression that followed the (U)HP metamorphism. Two of the 430-420 Ma and most of the 400-390 Ma monazites have rims that vary laterally in width and composition, in the form of finger- to scallop-shaped embayments. These rims have large variation in U/Th, U/Pb and Th/Pb ratios, suggesting that alteration, by a fluid or other mechanism

  11. Paleoproterozoic crustal evolution in the East Sarmatian Orogen: Petrology, geochemistry, Sr-Nd isotopes and zircon U-Pb geochronology of andesites from the Voronezh massif, Western Russia

    NASA Astrophysics Data System (ADS)

    Terentiev, R. A.; Savko, K. A.; Santosh, M.

    2016-03-01

    Andesites and related plutonic rocks are major contributors to continental growth and provide insights into the interaction between the mantle and crust. Paleoproterozoic volcanic rocks are important components of the East Sarmatian Orogen (ESO) belonging to the East European Craton, although their petrogenesis and tectonic setting remain controversial. Here we present petrology, mineral chemistry, bulk chemistry, Sr-Nd isotopes, and zircon U-Pb geochronological data from andesites and related rocks in the Losevo and Vorontsovka blocks of the ESO. Clinopyroxene phenocrysts in the andesites are depleted in LREE, and enriched in HFSE (Th, Nb, Zr, Hf, Ti) and LILE (Ba, Sr). Based on the chemistry of pyroxenes and whole rocks, as well as Fe-Ti oxides, we estimate a temperature range of 1179 to 1262 °С, pressures of 11.3 to 13.0 kbar, H2O content of 1-5 wt.%, and oxygen fu gacity close to the MH buffer for the melts of the Kalach graben (KG) and the Baygora area (BA) andesites. Our zircon U-Pb geochronological data indicate new zircon growth during the middle Paleoproterozoic as displayed by weighted mean 207Pb/206Pb ages of 2047 ± 17 Ma and 2040 ± 16 Ma for andesite and dacite-porphyry of the BA, and 2050 ± 16 Ma from high-Mg basaltic andesite of the KG. The andesites and related rocks of the KG and BA are characterized by high magnesium contents (Mg # up to 0.68). All these volcanic rocks are depleted in LREE and HFSE, and display negative Nb and Ti anomalies relative to primitive mantle. The high-Mg bulk composition, and the presence of clinopyroxene phenocrysts suggests that the parent melts of the KG and BA suite were in equilibrium with the mantle rocks. The rocks show positive εNd(T) values and low initial 87Sr/86Sr, suggesting that the magmas were mostly derived from metasomatized mantle source. The geochemical differences between the two andesite types are attributed to: the predominance of fractional crystallization, and minor role of contamination in

  12. Detrital zircon U-Pb geochronology, Lu-Hf isotopes and REE geochemistry constrains on the provenance and tectonic setting of Indochina Block in the Paleozoic

    NASA Astrophysics Data System (ADS)

    Wang, Ce; Liang, Xinquan; Foster, David A.; Fu, Jiangang; Jiang, Ying; Dong, Chaoge; Zhou, Yun; Wen, Shunv; Van Quynh, Phan

    2016-05-01

    In situ U-Pb geochronology, Lu-Hf isotopes and REE geochemical analyses of detrital zircons from Cambrian-Devonian sandstones in the Truong Son Belt, central Vietnam, are used to provide the information of provenance and tectonic evolution of the Indochina Block. The combined detrital zircon age spectra of all of the samples ranges from 3699 Ma to 443 Ma and shows with dominant age peaks at ca. 445 Ma and 964 Ma, along with a number of age populations at 618-532 Ma, 1160-1076 Ma, 1454 Ma, 1728 Ma and 2516 Ma. The zircon age populations are similar to those from time equivalent sedimentary sequences in continental blocks disintegrated from the East Gondwana during the Phanerozoic. The younger zircon grains with age peaks at ca. 445 Ma were apparently derived from middle Ordovician-Silurian igneous and metamorphic rocks in Indochina. Zircons with ages older than about 600 Ma were derived from other Gondwana terrains or recycled from the Precambrian basement of the Indochina Block. Similarities in the detrital zircon U-Pb ages suggest that Paleozoic strata in the Indochina, Yangtze, Cathaysia and Tethyan Himalayas has similar provenance. This is consistent with other geological constrains indicating that the Indochina Block was located close to Tethyan Himalaya, northern margin of the India, and northwestern Australia in Gondwana.

  13. Geochemistry and Sr-Nd isotopes of the subvolcanic sill complex and sandstone geochronology from María Magdalena island, Nayarit, Mexico

    NASA Astrophysics Data System (ADS)

    Villanueva, D.; Schaaf, P. E.; Hernandez, T.; Solis, G.; Weber, B.; Pompa, V.

    2013-12-01

    María Magdalena island is part of the Islas Marías archipielago, located at the mouth of the Gulf of California. Understanding the nature and origin of the archipelago is very important for reconstructing the paleoposition of Baja California Peninsula prior to the opening of the Gulf of California. We present the first geochemical, isotopic and geochronologic data from María Magdalena, a lithologically different island compared to the rest of the archipelago. María Magdalena island is located southeast of María Madre and northeast of María Cleofas islands and is composed by a sedimentary sequence of sandstones and minor shale, which is intruded by gabbroic sills. The sedimentary sequence dips approximately 20 degrees to the NW. The thickness of sills range from 1 to 3 meters with mineralogical variations of plagioclase +/- orthopyroxene +/- clinopyroxene +/- hornblende and some altered olivine crystals. Textures are mostly porphyritic with plagioclase crystals sizes up to 5 cm and olivines up to 5 mm. The gabbroic sills show SiO2 contents from 42.7 to 47.5 wt. %; TiO2 from 0.8 to 2 wt. %; Fe2O3t from 7.7 to 11.9 wt. %; MgO from 6.2 to 19.8 wt. % and of CaO from 6 to 11.6 wt. %, indicating mafic to ultramafic compositions. A multielement spider diagram as well as REE patterns show compositions very similar to N-MORB or even peridotites, which is confirmed by 87Sr/86Sr values from 0.70273 to 0.70497, and 143Nd/144Nd values from 0.513003 to 0.513100. U-Pb single zircon geochronology of the intruded sandstones display the following age distribution: eight crystals show ages from 80 to 86 Ma, three crystals have ages from 61 to 72 Ma, and three are around 21 Ma which constrains a maximum sandstone deposition age. Consequently, the sills must be younger than 21 Ma. There is not much lithological similarity with neighboring María Madre island to the NW (containing a metamorphic complex, granitoids and acid volcanic roks) and with María Cleofas island to the SE

  14. Geochronology and Geochemistry of a Late Cretaceous Granitoid Suite, Santa Rosa Range, Nevada: Linking Arc Magmatism in Northwestern Nevada to the Sierra Nevada Batholith

    NASA Astrophysics Data System (ADS)

    Brown, K.; Stuck, R.; Hart, W. K.

    2010-12-01

    Throughout the Mesozoic, an arc-trench system dominated the western margin of North America. One of the principal records of this system’s evolution is a discontinuous alignment of deeply eroded batholiths, which represent the once-active roots of ancient volcanic systems. Although these batholiths extend from Alaska to Mexico, there is a prominent (~500 km) gap located in present-day Nevada that contains scattered plutons that are hypothesized to be similar in age and origin to the larger batholiths. The current understanding of these isolated plutons, however, remains limited to regional isotopic studies aimed at identifying major crustal boundaries and structural studies focused on emplacement mechanisms. Therefore, detailed petrogenetic studies of the plutons exposed within the Santa Rosa Range (SRR) of NW Nevada will better characterize magmatism in this region, placing them within a regional context that explores the hypothesized links between the intrusions of NW Nevada to the Sierra Nevada batholith (SNB). A compilation of published geochronology from this region shows that plutons in the SRR are broadly coeval with the Cathedral Range Intrusive Epoch (~95-83 Ma) and the Shaver Sequence (~118-105 Ma) of the SNB. Preliminary Rb-Sr geochronology from the Granite Peak stock reveals a previously unrecognized period of magmatism (ca. 85.0 Ma) in this region. Therefore, ongoing work will more completely characterize the timing of magmatic pulses in this region and their relationships to the SNB. Preliminary petrographic, geochemical, and isotopic observations suggest that two distinct compositional/textural groups exist: the Santa Rosa/ Andorno group (SRA) and Granite Peak/ Sawtooth group (GPS). The chemical and isotopic variations between the two groups suggest that they were not consanguineous. Whereas the SRA group is generally more mafic (64-72 wt% SiO2) and metaluminous, the GPS group is more felsic (72- 76 wt% SiO2) and peraluminous. This observation is

  15. Geochronology and geochemistry of the Parashi granitoid, NE Colombia: Tectonic implication of short-lived Early Eocene plutonism along the SE Caribbean margin

    NASA Astrophysics Data System (ADS)

    Cardona, A.; Weber, M.; Valencia, V.; Bustamante, C.; Montes, C.; Cordani, U.; Muñoz, C. M.

    2014-03-01

    The Parashi granitoid of northeasternmost Colombia intrudes the Upper Cretaceous to Lower Paleocene accretionary complex formed by the collision of the Caribbean arc and the continental margin of South America. This granitoid presently separated of the continental margin includes a major quartzdiorite body with andesite to dacite dikes and mafic enclaves. Zircon U-Pb LA-MC-ICP-MS and K-Ar geochronology on the quartzdiorite and the dikes suggest that crystallization extended from ca. 47 to 51 Ma. Major and trace elements are characterized by a medium-K, immature continental arc signature and high Al2O3, Na2O and Ba-Sr contents. Initial 87Sr/86Sr isotopic values range between 0.7050 and 0.7054, with 143Nd/144Nd = 0.51235-0.51253, ɛNd and ɛHf values from -0.81 to -4.40 and -4.4 and -5.2. Major and trace element ratios and isotopic modeling suggest that sedimentary and/or quartzofeldspathic crustal sources were mixed with a mafic melt input. The petrotectonic and geological constraints derived from this granitoid suggest that Parashi plutonism records an immature, oblique subduction-zone setting in which the presence of a high-temperature mantle realm and strong plate coupling associated to upper crust subduction caused the partial fusion of a previously tectonically underplated mafic crust and associated metasediments exposed in the continental margin. The limited temporal expression of this magmatism and the transition to a regional magmatic hiatus are related to a subsequent change to strongly and slow oblique tectonics in the Caribbean-South America plate interactions and the underflow of a relatively thick slab of Caribbean oceanic crust.

  16. Geochemistry and geochronology of the blueschist in the Heilongjiang Complex and its implications in the late Paleozoic tectonics of eastern NE China

    NASA Astrophysics Data System (ADS)

    Ge, Mao-hui; Zhang, Jin-jiang; Liu, Kai; Ling, Yi-yun; Wang, Meng; Wang, Jia-min

    2016-09-01

    The Paleozoic to early Mesozoic tectonic framework and evolution of Northeast China, especially the Jiamusi block and its related structural belts, are highly debated. In this paper, geochemical, geochronological and isotopic analyses were carried out on the blueschist in the Heilongjiang Complex to address these issues. The Heilongjiang Complex defines the suture belt between the Jiamusi block and the Songliao block in NE China, and the blueschist is a major composition for this complex, coexisting with mafic-ultramafic rocks, greenschist, quartzite and mica schist. The blueschist has a mineral association of sodic amphibole, epidote, chlorite, phengite, albite and quartz with accessory phases of apatite, titanite, zircon and ilmenite. Together with the lithological association, the major and trace element compositions present that the protoliths of the blueschist can be divided into the alkaline and tholeiitic basalts and have OIB affinities, formed in an ocean island setting, indicated by the (La/Yb) N values of 3.57 - 11.54, and the (La/Sm) N values of 0.69 - 3.64. The high and positive εNd (t) values of + 3.7 to + 9.0, and relative enrichment in Nb (vs. Th) and Ta (vs. U) show that both the alkaline and tholeiitic basalts may be derived from the asthenospheric mantle with insignificant crustal contamination. Magmatic zircons from the blueschist in Yilan area yield a 206Pb/238U age of 281 ± 3 Ma, interpreted as its protolithic age. The youngest ages of 200 Ma of the detrital zircons in the associated mica schist from Mudanjiang area place constraints on the timing of metamorphism for the blueschist. These indicate that a big ocean existed between the Jiamusi and Songliao blocks at least since the early Permian, and the blueschist formed since the late Triassic to late Jurassic by the subduction of this ocean. Such an ocean during the Permian - Jurassic is difficult to be interpreted by the tectonic evolution of the Paleo-Asian Ocean.

  17. Evolution of the Cretaceous magmatism in the Apuseni-Timok-Srednogorie metallogenic belt and implications for the geodynamic reconstructions: new insight from geochronology, geochemistry and isotope studies

    NASA Astrophysics Data System (ADS)

    von Quadt, A.; Peytcheva, I.; Heinrich, C. A.; Frank, M.; Cvetkovic, V.

    2003-04-01

    Most major Cu-Au (-PGE) deposits in the Carpathian Balkan orogen are related to a 1500 km long belt of Upper Cretaceous magmatism extending from southern Romania through Yugoslavia to Bulgaria, with a likely continuation southeast of the Black Sea into Turkey, known as the Apuseni Banat Timok Srednogorie (ABTS) belt (Popov et al., 2000). In the frame of ABTS belt a new investigation was started to reveal the relation between Cretaceous magmatism and the Cu-Au-PGE deposits across the belt in East Serbia (Yugoslavia) and the Panagyurishte district (Bulgaria). The Late Cretaceous (Palaeogene?) magmatism of East Serbia developed along the Timok Magmatic Complex (TMC) in the east and the Ridanj Krepoljin Zone (RKZ) in the west. High precision U-Pb single zircon dating and a combination of isotope tracing, geochronological data as well as petrological data were used to provide additional data for the geodynamic evolution. A maximum life span of 2.5 Ma could be calculated for the first phase of volcanic activity in TMC, starting with the Amf-andesites of Veliki Kravelj (86.29 ± 0.32 Ma) and finishing with the Timozites (84.66 ± 0.5 Ma). Ore bearing magmatism in a single deposit (Veliki Kravelj) extended a maximum of 0.6 Ma ("pre-ore": 86.29 ± 0.32 Ma, "post-ore": 86.17 ± 0.15 Ma). Preliminary data for the dacites (70.3 ± 3.5 Ma) outcropping near Krepoljin give evidence for a shifting of the volcanic activity from TMC to RKZ together with changing the ore-deposit type from Cu-Au-PGE (TMC) to Pb-Zn-Cu (RKZ). Isotope tracing give evidence for mantle dominated source with increasing of crustal contamination in the same direction: (87Sr/86Sr ratios: 0.70388 to 0.706050, e-Hf-zircon data: +12 in TMC to +4.5 in RKZ). The Panagyurishte district (Bulgaria) show a duration time of the magmatic activity of 14 Ma, starting in the north at 92 Ma and finishing in the south at 78 Ma. Ore-related magmatism becomes younger in the same direction but finishes with 86 Ma. Multiple short

  18. Geochronology and geochemistry of eclogites from the Mariánské Lázně Complex, Czech Republic: Implications for Variscan orogenesis

    NASA Astrophysics Data System (ADS)

    Beard, Brian L.; Medaris-Jr, L. Gordon; Johnson, Clark M.; Jelínek, Emil; Tonika, J.; Riciputi, Lee R.

    The Mariánské Lázně complex (MLC) is located in the Bohemian Massif along the north-western margin of the Teplá-Barrandian microplate and consists of metagabbro, amphibolite and eclogite, with subordinate amounts of serpentinite, felsic gneiss and calc-silicate rocks. The MLC is interpreted as a metaophiolite complex that marks the suture zone between the Saxothuringian rocks to the north-west and the Teplá-Barrandian microplate to the south-east. Sm-Nd geochronology of garnet-omphacite pairs from two eclogite samples yields ages of 377+/-7, and 367+/-4Ma. Samples of eclogite and amphibolite do not define a whole rock Sm-Nd isochron, even though there is a large range in Sm/Nd ratio, implying that the suite of samples may not be cogenetic. Eclogites do not have correlated ɛNd values and initial 87Sr/86Sr ratios. Five of the eight eclogite samples have high ɛNd values (+10.2 to +7.1) consistent with derivation from a MORB-like source, but variable 87Sr/86Sr ratios (0.7033 to 0.7059) which probably reflect hydrothermal seawater alteration. Three other eclogite samples have lower ɛNd values (+5.4 to -0.8) and widely variable 87Sr/86Sr ratios (0.7033 to 0.7096). Such low ɛNd values are inconsistent with derivation from a MORB source and may reflect a subduction or oceanic island basalt component in their source. The MLC is an important petrotectonic element in the Bohemian Massif, providing evidence for Cambro-Ordovician formation of oceanic crust and interaction with seawater, Late Devonian (Frasnian-Famennian) high- and medium-pressure metamorphism related to closure of a Saxothuringian ocean basin, Early Carboniferous (Viséan) thrusting of the Teplá terrane over Saxothuringian rocks and Late Viséan extension.

  19. Geochronology, geochemistry and Sr-Nd-Hf isotopes of mafic dikes in the Huicheng Basin: Constraints on intracontinental extension of the Qinling orogen

    NASA Astrophysics Data System (ADS)

    Li, Wei; Dong, Yunpeng; Guo, Anlin; Liu, Xiaoming; Wang, Yuejun; Liu, Wenhang; Yang, Yuanzhen

    2015-05-01

    The diabase dikes intruded the Lower Cretaceous sandstone in the Huicheng Basin are key to understanding the Mesozoic tectonic evolution of the Qinling orogen. LA-ICP-MS zircon U-Pb dating yields a crystallization age of 107 ± 1 Ma for them. The dikes have low contents of SiO2 (42.46-50.16 wt.%), MgO (3.47-5.59 wt.%) with low Mg# of 49-59, and TiO2 (1.35-1.63 wt.%), high TFe2O3 (8.15-9.36 wt.%), Al2O3 (14.75-17.23 wt.%) and K2O (0.87-3.61 wt.%). Their Ni and Cr contents are in range of 16.8-111 and 45.7-315 ppm, respectively. They are significantly enriched in light rare earth elements and large ion lithophile elements (e.g., Cs, Pb and Ba), and depleted in Rb, K, P, and Ti. The dikes show relatively high whole-rock initial 87Sr/86Sr ratios (0.7071-0.7079) and negative εNd (t) values (-1.5 to -4.8) with single-stage Nd model ages of 941-1186 Ma. In addition, they have low zircon εHf (t) values (-8.6 to +3.5) with single-stage Hf model ages of 674-1117 Ma. Both elemental and isotopic geochemistry suggests that the magma of these dikes has undergone significant crystallization fractionation of olivine and pyroxene but weak crustal contamination during magma evolution. They were derived from partial melting of an enriched lithospheric mantle source. Together with regional geological data, these results suggest that the Qinling orogen experienced an intracontinental extension during the late Early Cretaceous.

  20. Geochronology and geochemistry of the Badaguan porphyry Cu-Mo deposit in Derbugan metallogenic belt of the NE China, and their geological significances

    NASA Astrophysics Data System (ADS)

    Gao, Bingyu; Zhang, Lianchang; Jin, Xindi; Li, Wenjun; Chen, Zhiguang; Zhu, Mingtian

    2016-03-01

    The Badaguan porphyry Cu-Mo deposit belongs to the Derbugan metallogenic belt, which is located in the Ergun block, NE China. In the mining area, the Cu-Mo mineralization mainly occurs in quartz diorite porphyry and is hosted within silicified-sericitized and sericite alteration zone. Geochemical results of the host porphyry is characterized by high SiO2, high Al2O3, low MgO, weak positive Eu anomalies and clearly HREE depletion, high Sr, low Y and low Yb, similar to those of adakite. The Sr-Nd isotopic composition of the host porphyry displays an initial (87Sr/86Sr)i ratio of 0.7036-0.7055 and positive Nd( t) values of +0.1 to +0.6, which are similar to the OIB, reflecting the source of the host porphyry may derive from subducted ocean slab, and the new lower crust also had some contribution to the magma sources. The SIMS zircon U-Pb age from the host porphyry is 229 ± 2 Ma. The Re-Os isochron age for the molybdenite in the deposit is 225 ± 2 Ma closed to zircon U-Pb age of the host porphyry, indicating that Cu-Mo mineralization event occurred in Triassic. Combining the geology-geochemistry of the host porphyry and the regional tectonic evolution, we infer that the subduction processes of Mongol-Okhotsk oceanic slab under the Ergun block led to the formation of the Badaguan porphyry Cu-Mo deposit during the Triassic.

  1. PROCESSING OF MONAZITE SAND

    DOEpatents

    Calkins, G.D.; Bohlmann, E.G.

    1957-12-01

    A process for the recovery of thorium, uranium, and rare earths from monazite sands is presented. The sands are first digested and dissolved in concentrated NaOH, and the solution is then diluted causing precipitation of uranium, thorium and rare earth hydroxides. The precipitate is collected and dissolved in HCl, and the pH of this solution is adjusted to about 6, precipitating the hydroxides of thorium and uranium but leaving the rare earths in solution. The rare earths are then separated from the solution by precipitation at a still higher pH. The thorium and uranium containing precipitate is redissolved in HNO/sub 3/ and the two elements are separated by extraction into tributyl phosphate and back extraction with a weakly acidic solution to remove the thorium.

  2. Petrography, geochemistry, and geochronology of granitoid rocks in the Neoproterozoic-Paleozoic Lufilian?Zambezi belt, Zambia: Implications for tectonic setting and regional correlation

    NASA Astrophysics Data System (ADS)

    Katongo, Crispin; Koller, Friedrich; Kloetzli, Urs; Koeberl, Christian; Tembo, Francis; Waele, Bert De

    2004-12-01

    There are several pre-orogenic Neoproterozoic granitoid and metavolcanic rocks in the Lufilian-Zambezi belt in Zambia and Zimbabwe that are interpreted to have been emplaced in a continental-rift setting that is linked to the break-up of the Rodinia supercontinent. However, no geochemical data were previously available for these rocks in the Zambian part of the belt to support this model. We conducted petrographic and whole-rock chemical analyses of the Neoproterozoic Nchanga Granite, Lusaka Granite, Ngoma Gneiss and felsic metavolcanic rocks from the Lufilian-Zambezi belt in Zambian, in order to evaluate their chemical characteristics and tectonic settings. Other magmatic rocks of importance for understanding the evolution of the belt in Zambia, included in this study, are the Mesoproterozoic Munali Hills Granite and associated amphibolites and the Mpande Gneiss. The Neoproterozoic rocks have monzogranitic compositions, aluminum-saturation indices (ASI) < 1.1, and high contents of high field strength elements (HFSE) and rare earth elements (REE). The chondrite-normalised spider diagrams are similar to those of A-type granites from the Lachlan fold belt and show negative Sr, P, and Ti anomalies. On various tectonic discrimination diagrams the Neoproterozoic rocks plot mainly in A-type granite fields. These petrographic and trace element compositions indicate that these rocks are A-type felsic rocks, but they do not have features of granites and rhyolites emplaced in true continental-rift settings, as previously suggested. On the basis of the A-type features and independent regional geological and geochronological data, we suggest that the Neoproterozoic granitoid and felsic metavolcanic rocks were emplaced during the earliest extensional stages of continental rifting in the Lufilian-Zambezi belt. The apparent continental-arc like chemistry of the granitoid and felsic metavolcanic rocks is thus inferred to be inherited from calcalkaline sources. The Mesoproterozoic

  3. Petrology, geochemistry and U-Pb geochronology of magmatic rocks from the high-sulfidation epithermal Au-Cu Chelopech deposit, Srednogorie zone, Bulgaria

    NASA Astrophysics Data System (ADS)

    Chambefort, Isabelle; Moritz, Robert; von Quadt, Albrecht

    2007-10-01

    The Chelopech deposit is one of the largest European gold deposits and is located 60 km east of Sofia, within the northern part of the Panagyurishte mineral district. It lies within the Banat-Srednegorie metallogenic belt, which extends from Romania through Serbia to Bulgaria. The magmatic rocks define a typical calc-alkaline suite. The magmatic rocks surrounding the Chelopech deposit have been affected by propylitic, quartz-sericite, and advanced argillic alteration, but the igneous textures have been preserved. Alteration processes have resulted in leaching of Na2O, CaO, P2O5, and Sr and enrichment in K2O and Rb. Trace element variation diagrams are typical of subduction-related volcanism, with negative anomalies in high field strength elements (HFSE) and light element, lithophile elements. HFSE and rare earth elements were relatively immobile during the hydrothermal alteration related to ore formation. Based on immobile element classification diagrams, the magmatic rocks are andesitic to dacitic in compositions. Single zircon grains, from three different magmatic rocks spanning the time of the Chelopech magmatism, were dated by high-precision U-Pb geochronology. Zircons of an altered andesitic body, which has been thrust over the deposit, yield a concordant 206Pb/238U age of 92.21 ± 0.21 Ma. This age is interpreted as the crystallization age and the maximum age for magmatism at Chelopech. Zircon analyses of a dacitic dome-like body, which crops out to the north of the Chelopech deposit, give a mean 206Pb/238U age of 91.95 ± 0.28 Ma. Zircons of the andesitic hypabyssal body hosting the high-sulfidation mineralization and overprinted by hydrothermal alteration give a concordant 206Pb/238U age of 91.45 ± 0.15 Ma. This age is interpreted as the intrusion age of the andesite and as the maximum age of the Chelopech epithermal high-sulfidation deposit. 176Hf/177Hf isotope ratios of zircons from the Chelopech magmatic rocks, together with published data on the

  4. Geochemistry and U-Pb zircon geochronology of the pegmatites in Ede area, southwestern Nigeria: A newly discovered oldest Pan African rock in southwestern Nigeria

    NASA Astrophysics Data System (ADS)

    Adetunji, A.; Olarewaju, V. O.; Ocan, O. O.; Ganev, V. Y.; Macheva, L.

    2016-03-01

    Field and petrographic studies, whole rock geochemistry and in-situ LA-ICP-MS geochemical and isotopic U-Pb measurements on zircons have been performed on granitic pegmatites of Ede area, southwestern Nigeria with a view to characterize them, determining their mineralization potentials, petrogenetic attributes and emplacement age. The pegmatites are hosted by migmatite gneiss complex, biotite-muscovite schist and associated quartzite. The textural and mineralogical characteristics of these pegmatites indicate the occurrence of two main varieties, namely, muscovite pegmatite and garnet pegmatite. Of less importance are inclusions and pods of graphic granite, quartz-microcline aplitic and pegmatitic bodies. At the present level of erosion, the parent igneous rocks of the pegmatites are not exposed. The two dominant pegmatite varieties show slightly different chemical peculiarities but similar peraluminous character. The average K/Rb ratios of 165 and 163, respectively, for muscovite and garnet pegmatites combined with other trace element compositions are indicative of affinity to muscovite class of pegmatite which are generally not promising for rare elements mineralization. However, the unusually high concentration of bismuth in the zircons indicates Bi mineralization in the area which can either be in the pegmatites or host rocks. The Nb/Ta ratios for both muscovite and garnet pegmatites range from 0.7 to 15.2 and 1.0 to 14.8, respectively. These Nb/Ta ratios and Eu anomalies are statistically similar for both pegmatites. These probably indicate the pegmatites crystallized from a common source but separated into crystallization paths that produced different pegmatite varieties through liquid-liquid immiscibity mechanism. In-situ measurements of REE, P, Y, Nb, Hf, Ta, Bi, Th and U of individual zircon grains show the existence of two chemically and texturally different domains which are indicative of alteration that may be due to interface-coupled dissolution

  5. Mid-Neoproterozoic intraplate magmatism in the northern margin of the Southern Granulite Terrane, India: Constraints from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Deeju, T. R.; Santosh, M.; Yang, Qiong-Yan; Pradeepkumar, A. P.; Shaji, E.

    2016-11-01

    The northern margin of the Southern Granulite Terrane in India hosts a number of mafic, felsic and alkaline magmatic suites proximal to major shear/paleo-suture zones and mostly represents magmatism in rift-settings. Here we investigate a suite of gabbros and granite together with intermediate (dioritic) units generated through mixing and mingling of a bimodal magmatic suite. The massive gabbro exposures represent the cumulate fraction of a basic magma whereas the granitoids represent the product of crystallization in felsic magma chambers generated through crustal melting. Diorites and dioritic gabbros mostly occur as enclaves and lenses within host granitoids resembling mafic magmatic enclaves. Geochemistry of the felsic units shows volcanic arc granite and syn-collisional granite affinity. The gabbro samples show mixed E-MORB signature and the magma might have been generated in a rift setting. The trace and REE features of the rocks show variable features of subduction zone enrichment, crustal contamination and within plate enrichment, typical of intraplate magmatism involving the melting of source components derived from both depleted mantle sources and crustal components derived from older subduction events. The zircons in all the rock types show magmatic crystallization features and high Th/U values. Their U-Pb data are concordant with no major Pb loss. The gabbroic suite yields 206Pb/238U weighted mean ages in the range of 715 ± 4-832.5 ± 5 Ma marking a major phase of mid Neoproterozoic magmatism. The diorites crystallized during 206Pb/238U weighted mean age of 724 ± 6-830 ± 2 Ma. Zircons in the granite yield 206Pb/238U weighted mean age of 823 ± 4 Ma. The age data show broadly similar age ranges for the mafic, intermediate and felsic rocks and indicate a major phase of bi-modal magmatism during mid Neoproterozoic. The zircons studied show both positive and negative εHf(t) values for the gabbros (-6.4 to 12.4), and negative values for the diorites (-7

  6. Palaeoproterozoic continental arc magmatism, and Neoproterozoic metamorphism in the Aravalli-Delhi orogenic belt, NW India: New constraints from in situ zircon U-Pb-Hf isotope systematics, monazite dating and whole-rock geochemistry

    NASA Astrophysics Data System (ADS)

    Kaur, Parampreet; Zeh, Armin; Chaudhri, Naveen

    2017-04-01

    Presently, the extent, origin and petrogenesis of late Palaeoproterozoic (ca. 1.85 Ga) magmatism in the north-central Aravalli-Delhi orogenic belt, NW India and subsequent metamorphic overprints are poorly constrained. Results of new in situ zircon U-Pb-Hf isotope analyses in combination with whole-rock elemental and isotopic data provide the first hard evidence that granitoid magmatism occurred in a continental magmatic arc setting between 1.86 and 1.81 Ga. The Hf-Nd model ages of 3.0-2.6 Ga and inherited zircon grains of 3.3-2.5 Ga indicate abundant reworking of Archaean crust. Flat HREE patterns with negative Eu anomalies furthermore reveal that the granitoids were generated from garnet-free and plagioclase-rich sources at shallow depths. Significant isotope variation among granitoid samples (εHft = -3.7 to -9.0; εNdt = -4.8 to -7.9) indicate that the reworked Archaean crust was not completely homogenised during the Palaeoproterozoic. This is best reflected by zircon Hf-isotope variation of ca. 9.5 epsilon units within the oldest granitoid sample. Zircon grains from this sample define three discrete Hf-isotope groups at εHf1.86Ga = -8.9, -4.8 and -1.6. These are interpreted to result from mixing of zircon-saturated magmas derived from three distinct sources within the crust prior to solidification. A monazite U-Pb isochron age of 868 ± 4 Ma from one of the granitoid samples furthermore indicates that the Aravalli fold belt was affected by an important post-magmatic overprint, perhaps related to the widespread metasomatic, granulite metamorphic and/or magmatic events during the same time span.

  7. Differentiating Detrital and Metamorphic Monazite in Greenschist-Facies Sandstones From the Witwatersrand Supergroup

    NASA Astrophysics Data System (ADS)

    Muhling, J. R.; Rasmussen, B.

    2009-05-01

    , calcite and titanate, and monazite has been partially replaced by fine intergrowths of allanite, apatite and Th-silicate. Careful characterisation of monazite in low-grade metasedimentary rocks can distinguish detrital grains from metamorphic, and open the way for precise geochronology of low-temperature events.

  8. Paleoproterozoic magmatism across the Archean-Proterozoic boundary in central Fennoscandia: Geochronology, geochemistry and isotopic data (Sm-Nd, Lu-Hf, O)

    NASA Astrophysics Data System (ADS)

    Lahtinen, Raimo; Huhma, Hannu; Lahaye, Yann; Lode, Stefanie; Heinonen, Suvi; Sayab, Mohammad; Whitehouse, Martin J.

    2016-10-01

    characterized by both I-type and A-type (CFGC/A) intermediate and felsic granitoids. The I-type granitoids are divided into two groups at ≥ 1885 Ma and ≤ 1882 Ma, where the latter overlap in age with the CFGC/A granitoids. Both I-type CFGC and CFGC/A granitoids are interpreted to have formed from mixing of Paleoproterozoic SCLM-derived melts with crustal melts from hydrous and dry intermediate-felsic igneous sources, respectively. The geochemistry, dominantly δ18O values below 6.5‰ in zircons and TDM (2.11-2.42 Ga) of the CFGC granitoids favor the occurrence of older crust (ca. 2.1-2.0 Ga) in their genesis. The BZ granitoids are similar in age but more juvenile with TDM ages between 1.94 Ga and 2.16 Ga. The 1.92 Ga granodiorite in the BB is correlated with juvenile gneissic tonalites and granodiorites found from the AP boundary. We suggest that the present high-velocity lower crust under the CFGC is composed of melt-extracted granulites (crustal source age ≥ 2.0 Ga) and mafic cumulates which both formed during 1.90-1.88 Ga arc magmatism. The ≤ 1.88 Ga stage represents the end of compression/transpression and is followed by 1.87-1.86 Ga buckling, forming the Bothnian Oroclines.

  9. METHOD OF PROCESSING MONAZITE SAND

    DOEpatents

    Welt, M.A.; Smutz, M.

    1958-08-26

    A process is described for recovering thorium, uranium, and rare earth values from monazite sand. The monazite sand is first digested with sulfuric acid and the resulting "monazite sulfate" solution is adjusted to a pH of between 0.4 and 3.0, and oxalate anions are added causing precipitation of the thorium and the rare earths as the oxalates. The oxalate precipitate is separated from the uranium containing supernatant solution, and is dried and calcined to the oxides. The thorium and rare earth oxides are then dissolved in nitric acid and the solution is contacted with tribntyl phosphate whereby an organic extract phase containing the cerium and thorium values is obtained, together with an aqueous raffinate containing the other rare earth values. The organic phase is then separated from the aqueous raffinate and the cerium and thorium are back extracted with an aqueous medium.

  10. Dating Shearing and Exhumation in the Eastern Adriondack Mountains: Integrating Monazite into Microstructural and Petrologic Studies

    NASA Astrophysics Data System (ADS)

    Williams, M. L.; Jercinovic, M. J.; McLelland, J. M.; Wong, M.

    2010-12-01

    Absolute age constraints on deformation events are critical for interpreting the tectonic history of orogenic belts. Constraints are commonly indirect, for example, interpreting relationships with dated igneous rocks. In-situ mapping and dating of monazite is a promising alternative for directly dating tectonic processes. Monazite is a fabric-forming mineral that is typically aligned with foliations and lineations. It can contain aligned inclusions or occur as aligned inclusions in other phases. Compositional domains in polygenetic monazite can define sigma and delta tails, strain shadows, or fracture- fillings that can be kinematically linked to deformation. Significantly, the growth or breakdown of monazite (and other accessory phases) can be understood in terms of silicate reactions that are linked to deformation (i.e. low-Y monazite domains associated with garnet growth during crustal thickening). Typically, a small number of monazite grains have unambiguous microstructural relationships. Thus, a “Rosetta Stone” approach can be successful. Full-section compositional maps are used to locate all accessory minerals in structural context. A subset of grains are mapped and analyzed to define the general sequence of monazite growth events in the rock or region. Finally, high-resolution compositional single-grain images are used to identify the rare “Rosetta” grains that can place specific timing constraints. An example involves unraveling the timing of shear-related structures in the eastern Adirondack Mountains, NY. Pervasive east-dipping fabrics with east-plunging lineations indicate a major, relatively late-stage event of east-directed (normal) shearing. Polygenetic monazite within the garnet-rich gneisses of this region can be used to directly constrain this event. Relatively rare monazite (inner) cores are ca. 1170 Ma, probably reflecting Shawinigan orogenesis. Dominant interior domains “outer cores” are ca 1050 Ma, reflecting high-P-T Ottawan

  11. Geochronology and Nd isotope geochemistry of the Gameleira Cu-Au deposit, Serra dos Carajás, Brazil: 1.8-1.7 Ga hydrothermal alteration and mineralization

    NASA Astrophysics Data System (ADS)

    Pimentel, Márcio M.; Lindenmayer, Zara G.; Laux, Jorge H.; Armstrong, Richard; de Araújo, Janice Caldas

    2003-01-01

    . The geochronological data suggest that the Gameleira Cu-Au mineralization is related to a Paleoproterozoic (ca. 1.83 Ga) episode of hydrothermal activity and is not Archaean. The younger ages of ca. 1.70-1.73 might be interpreted as products of the lower blocking temperatures of biotite in relation to the Ar-Ar and Sm-Nd isotopic systems. Combined with previous geochemistry and stable isotope data, the Nd isotopic data suggest that the mineralizing fluids were derived from, or strongly interacted with, a Paleoproterozoic crustal granite, possibly similar in age and composition to the Pojuca granite.

  12. Interpretation of U-Th-Pb in-situ ages of hydrothermal monazite-(Ce) and xenotime-(Y): evidence from a large-scale regional study in clefts from the western alps

    NASA Astrophysics Data System (ADS)

    Grand'Homme, A.; Janots, E.; Bosse, V.; Seydoux-Guillaume, A. M.; De Ascenção Guedes, R.

    2016-12-01

    In eleven Alpine clefts of the western Alps, in-situ dating of monazite-(Ce) and xenotime-(Y) has been attempted to gain insights on possible disturbances of the geochronological U-Th-Pb systems and age interpretations in hydrothermal conditions. In most clefts, monazite-(Ce) in-situ 208Pb/232Th dating using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) yields well-resolved ages (with errors typically <0.3 Ma, quoted at the 2σ level), indicative of a short duration monazite-(Ce) growth. However, monazite-(Ce) dating demonstrates two successive episodes of growth separated by several million years within two single clefts. Only in one cleft, complex age mixture in a porous and complex zoned monazite-(Ce) suggests disturbance of the 208Pb/232Th ages due to replacement by dissolution-precipitation processes. While some U-Pb ages are coherent with the 208Pb/232Th ages, U-Pb ages are generally disturbed by significant 206Pb excess in monazite-(Ce) with high Th/U ratio (>100). Xenotime-(Y) has remarkably high Th/U ratios and U-Pb dating is also disturbed by 206Pb excess, whereas 208Pb/232Th dating gave well-resolved ages (34.9 ± 0.5 Ma), close to but higher than the monazite-(Ce) age obtained in the same cleft (32.3 ± 0.3 Ma). Correlation of the monazite-(Ce) U-Th-Pb age dataset with other geochronological data suggests for monazite-(Ce) precipitation at periods of high tectonic activity. In the external massifs, monazite-(Ce) dating confirms a polyphased transpressive regime with activity periods around 13-11 Ma and 8-6 Ma. Older monazite-(Ce) ages in the Argentera massif (20.6 ± 0.3 Ma) are consistent with the regional diachronism in the western external Alps. In the 2 clefts of the internal massifs, monazite-(Ce) dating provides first ages of hydrothermal activity: the monazite-(Ce) age at 32.3 ± 0.3 Ma coincides with the exhumation along the Penninic front, but the monazite-(Ce) age at 23.3 ± 0.2 Ma is complex to attribute to a

  13. Monazite deposits of the southeastern Atlantic States

    USGS Publications Warehouse

    Mertie, John Beaver

    1953-01-01

    Monazite, a phosphate of the rare earths, is the principal mineral from which the cerium earths and thorium are obtained. Fluviatile monazite placers were mined in the Piedmont province of North and South Carolina from 1887 to 1911, and again intermittently from 1915 to 1917; but the principal sources In recent years have been the beach placers of India and Brazil. In 1946, an embargo was placed on the exportation of Indian monazite, and the Brazilian production has not increased materially to replace this loss. Accordingly monazite in recent years has become a scarce commodity. The principal domestic sources from which monazite may be recovered commercially are in Idaho and in the Piedmont province of the southeastern States. Some monazite is now being produced in Idaho, and a small output is being recovered as a byproduct of heavy mineral mining in Florida. The southeastern placers were not exhausted by the earlier mining and new deposits have been discovered; but production from this region awaits adequate exploration. The country rock of the southeastern Piedmont province is a complex assemblage of metamorphic and igneous rocks. The monazite occurs in two belts. A western belt has been traced from east-central Virginia for 600 miles southwestward into Alabama; and an eastern belt has been traced from the vicinity of Fredericksburg, Va., south-southwestward for 200 miles into North Carolina. Monazite-bearing rocks near. Rion, S. C., appear to indicate a southwestward continuation of the eastern belt. The western, or principal belt, includes the placers that were formerly mined in North and South Carolina. These placers were sampled, and the monazite was separated from the best of the samples, for mineralogical and chemical analysis. The tabulated results show a mean tenor, in the headwater placers of highest grade, of 8.4 pounds of monazite to the cubic yard. Farther downstream where mining must be done to obtain larger yardages, the tenor will be much lower

  14. METHOD OF PROCESSING MONAZITE SAND

    DOEpatents

    Calkins, G.D.

    1957-10-29

    A method is given for the pretreatment of monazite sand with sodium hydroxide. When momazite sand is reacted with sodium hydroxide, the thorium, uranium, and rare earths are converted to water-insoluble hydrous oxides; but in the case of uranium, the precipitate compound may at least partly consist of a slightly soluble uranate. According to the patent, monazite sand is treated with an excess of aqueous sodium hydroxide solution, and the insoluble compounds of thorium, uranium, and the rare earths are separated from the aqueous solution. This solution is then concentrated causing sodium phosphate to crystallize out. The crystals are removed from the remaining solution, and the solution is recycled for reaction with a mew supply of momazite sand.

  15. Constraints on Alpine hydrothermal activity and deformation from U-Th-Pb dating of cleft monazite and xenotime (Western Alps)

    NASA Astrophysics Data System (ADS)

    Grand'Homme, Alexis; Janots, Emilie; Bosse, Valerie; Seydoux-Guillaume, Anne-Magali; De Ascencao, Roger

    2016-04-01

    In this large-scale regional study, age of hydrothermal monazite (and xenotime) precipitation has been investigated through in-situ U-Th-Pb dating of crystals collected in 11 clefts (veins) taken in the internal and external massifs (Western Alps). The investigated clefts are composed of quartz, chlorite (± epidote), albite and millimetric accessory minerals (monazite, apatite, xenotime, anatase, rutile). Prior to dating, cleft monazite composition was thoroughly studied to reveal potential zoning. In-situ dating through different compositional domains of single monazite crystal yields well-resolved Th-Pb ages (typically with 0.1-0.3 Ma resolution) indicating for growth episodes with short duration. Comparison of U-Pb and Th-Pb dating indicates that the U-Pb systematics appears successful to date cleft monazite with low Th/U ratio (typically <30). In one cleft, in which monazite and xenotime coexist, xenotime was dated using the monazite analytical protocol. Hydrothermal xenotime has remarkably high Th/U ratio and U-Pb dating shows evidence of 206Pb excess. In comparison, Th-Pb dating gives robust ages (35.2 ± 0.8 Ma) that are close but higher than the monazite date obtained in the same cleft (32.3 ± 0.3 Ma). Brief episodic monazite crystallization is likely attributed to enhanced hydrothermal activity during periods of higher tectonic activity. Correlation with other geochronological data suggests that it occurs in a host-rock that already cooled down at temperature close or below to the zircon fission track. In the Belledonne massif, the new monazite ages confirm for two periods of hydrothermal activity at around 11-13 Ma and 8-6 Ma, respectively. Only one vertical cleft monazite was investigated in the Mont-Blanc massif but it gives an age that is similar to the early population of the Belledonne massif (11.1 ± 0.2 Ma). Monazite dating therefore suggests for similar late-stage tectonic activity from Belledonne up to the Aar massifs, likely due to dextral

  16. Geochemistry, geochronology, mineralogy, and geology suggest sources of and controls on mineral systems in the southern Toquima Range, Nye County, Nevada; with geochemistry maps of gold, silver, mercury, arsenic, antimony, zinc, copper, lead, molybdenum, bismuth, iron, titanium, vanadium, cobalt, beryllium, boron, fluorine, and sulfur; and with a section on lead associations, mineralogy and paragenesis, and isotopes

    USGS Publications Warehouse

    Shawe, Daniel R.; Hoffman, James D.; Doe, Bruce R.; Foord, Eugene E.; Stein, Holly J.; Ayuso, Robert A.

    2003-01-01

    Geochemistry maps showing the distribution and abundance of 18 elements in about 1,400 rock samples, both mineralized and unmineralized, from the southern Toquima Range, Nev., indicate major structural and lithologic controls on mineralization, and suggest sources of the elements. Radiometric age data, lead mineralogy and paragenesis data, and lead-isotope data supplement the geochemical and geologic data, providing further insight into timing, sources, and controls on mineralization. Major zones of mineralization are centered on structural margins of calderas and principal northwest-striking fault zones, as at Round Mountain, Manhattan, and Jefferson mining districts, and on intersections of low-angle and steep structures, as at Belmont mining district. Paleozoic sedimentary rocks, mostly limestones (at Manhattan, Jefferson, and Belmont districts), and porous Oligocene ash-flow tuffs (at Round Mountain district) host the major deposits, although all rock types have been mineralized as evidenced by numerous prospects throughout the area. Principal mineral systems are gold-silver at Round Mountain where about 7 million ounces of gold and more than 4 million ounces of silver has been produced; gold at Gold Hill in the west part of the Manhattan district where about a half million ounces of gold has been produced; gold-mercury-arsenic-antimony in the east (White Caps) part of the Manhattan district where a few hundred thousand ounces of gold has been produced; and silver-lead-antimony at Belmont where more than 150,000 ounces of silver has been produced. Lesser amounts of gold and silver have been produced from the Jefferson district and from scattered mines elsewhere in the southern Toquima Range. A small amount of tungsten was produced from mines in the granite of the Round Mountain pluton exposed east of Round Mountain, and small amounts of arsenic, antimony, and mercury have been produced elsewhere in the southern Toquima Range. All elements show unique

  17. Progress report of southeastern monazite exploration, 1952

    USGS Publications Warehouse

    Overstreet, W.C.; Theobald, P.K.; White, A.M.; Cuppels, N.P.; Caldwell, D.W.; Whitlow, J.W.

    1953-01-01

    Reconnaissance of placer monazite during the field season of 1952 covered 6,600 square miles drained by streams in the western Piedmont of Virginia 5 North Carolina, South Carolina,, and Georgia. Emphasis during this investigation was placed on the area between the Savannah River at the border of South Carolina and Georgia and the Catawba River in North Carolina because it contains most of the placers formerly mined for monaziteo Four other areas along the strike of the monazite-bearing crystalline rocks were also studied, They center around Mt. Airy, N.C., Athens, Ga. Griffin, Ga. and LaGrange, Ga. In the Savannah River Catawba River district, studies indicate that even the highest grade stream deposits of more than 10 million cubic yards of alluvium contain less than 1 pound of monazite per cubic yard. The average grade of the better deposits is about 0 0 5 pound of monazite per cubic yard. Only trace amounts of niobium, tantalum, and tin have been detected in the placers. Tungsten is absent. Locally gold adds a few cents per cubic yard to the value of placer ground. The best deposits range in size from 1 to 5 million cubic yards and contain 1 to 2 pounds of monazite to the cubic yard. Hundreds of placers smaller than 1 million cubic yards exceed 2 pounds of monazite to the cubic yard and locally attain an average of 10 pounds Monazite deposits around Athens, Ga., are similar to the smaller deposits in the central part of the Savannah River - Catawba River district. A few small very low-grade monazite placers were found near Mt. Airy, N.C., Griffin, Ga., and LaGrange Ga., but they are of no economic value. The larger the flood plain and the farther it lies from the source of the stream, the lower is the monazite content of the sediment. Monazite cannot be profitably mined .from the crystalline rocks in the five areas. The alluvial placers are in stream sediments of post-Wisconsin age. Some pre-Wisconsin terrace gravel of small areal extent is exposed but it

  18. Structural interpretation of the Steenkampskraal monazite deposit, Western Cape, South Africa

    NASA Astrophysics Data System (ADS)

    Basson, I. J.; Muntingh, J. A.; Jellicoe, B. C.; Anthonissen, C. J.

    2016-09-01

    The Steenkampskraal Monazite Mine was first established in 1952, to extract monazite ore for the production of thorium and rare earth element (REE) concentrate. Refurbishment of the mine in recent years has required the re-inspection and re-evaluation of the mineralized monazite zone (MMZ). This contribution presents a structural review of the MMZ and its emplacement, based on recent data and its setting at the southern extent of the Bushmanland Sub-province of the Namaqua-Natal Metamorphic Belt. New surface and underground mapping confirm that the MMZ is a moderately-dipping body within gneissic host rocks on the southern limb of a broad F3 antiform. Thickness variations, both down-dip and along-strike, are the result of D2 and D3 deformation. The MMZ has been locally transected and steepened by subsequent late-D3, "steep-structures", which are typical of the Okiep copper district, ∼150 km north of Steenkampskraal. Geochronological data suggest that the MMZ was intruded, emplaced or formed at 1046 ± 7.5 Ma, at the start of the D3 Klondikean Episode (1040-1020 Ma). Unlike the analogous copper-bearing Koperberg Suite in the Okiep Copper district, the MMZ was not intruded into Klondikean-aged steep structures, but was rather transected and steepened by these. Local steepening of the otherwise moderately-dipping to flat-lying MMZ makes it locally amenable to detection by soil sampling and radiometric surveys.

  19. U-Pb monazite ages in amphibolite- to granulite-facies orthogneiss reflect hydrous mineral breakdown reactions: Sveconorwegian Province of SW Norway

    NASA Astrophysics Data System (ADS)

    Bingen, Bernard; van Breemen, Otto

    In the Rogaland-Vest Agder terrain of the Sveconorwegian Province of SW Norway, two main Sveconorwegian metamorphic phases are reported: a phase of regional metamorphism linked to orogenic thickening (M1) and a phase of low-pressure thermal metamorphism associated with the intrusion of the 931 +/- 2 Ma anorthosite-charnockite Rogaland igneous complex (M2). Phase M1 reached granulite facies to the west of the terrane and M2 culminated locally at 800-850 °C with the formation of dry osumilite-bearing mineral associations. Monazite and titanite U-Pb geochronology was conducted on 17 amphibolite- to granulite-facies orthogneiss samples, mainly from a suite of 1050 +2/-8 Ma calc-alkaline augen gneisses, the Feda suite. In these rocks, prograde negatively discordant monazite crystallized during breakdown of allanite and titanite in upper amphibolite facies at 1012-1006 Ma. In the Feda suite and other charnockitic gneisses, concordant to slightly discordant monazite at 1024-997 Ma probably reflects breakdown of biotite during granulite-facies M1 metamorphism. A spread of monazite ages down to 970 Ma in biotite +/- hornblende samples possibly corresponds to the waning stage of this first event. In the Feda suite, a well defined monazite growth episode at 930-925 Ma in the amphibolite-facies domain corresponds to major clinopyroxene formation at the expense of hornblende during M2. Growth or resetting of monazite was extremely limited during this phase in the granulite-facies domain, up to the direct vicinity of the anorthosite complex. The M2 event was shortly followed by cooling through ca. 610 °C as indicated by tightly grouped U-Pb ages of accessory titanite and titanite relict inclusions at 918 +/- 2 Ma over the entire region. A last generation of U-poor monazite formed during regional cooling below 610 °C, in hornblende-rich samples at 912-904 Ma. This study suggests: (1) that monazite formed during the prograde path of high-grade metamorphism may be preserved; (2

  20. The pace of continental deformation and geochronology

    NASA Astrophysics Data System (ADS)

    Parrish, R. R.

    2007-12-01

    Continental tectonics and geochronology have had a symbiotic relationship for many decades. A diverse range of chronometers has been applied to tectonic problems and to quantify rates of geological processes. These chronometers include U-Th-Pb, Ar-Ar, ZFTA, U-Th-He, and other systems and fall into geo-chronomters that date geological events (i.e. mineral crystallisation concurre3nt with igneous or metamorphic mineral growth) and thermo-chronometers (dating the time of cooling during exhumation, for example). With advances in linking mineral chemistry of accessory minerals to metamorphic reactions, it goes without saying that careful petrology, petrography, mineral chemistry and imaging are essential to arriving at an appropriate interpretation of U-Th-Pb dates of accessory minerals in metamorphic rocks (e.g. monazite, zircon, titanite). Examples from the Himalaya will be used to illustrate how ID-TIMS and intra-crystal SIMS and LA-ICP-MS U-Th-Pb dating can be used to elucidate P-T-t paths of metamorphic rocks during metamorphism and exhumation. By contrast, an emerging area of study involves using single detrital minerals to reconstruct provenance and patterns of erosion in mountain systems. Because these detrital minerals (mica, monazite, zircon, rutile, allanite, titanite, etc.) have been separated from their petrographic context, interpretations based upon ages of these minerals will be much less constrained and it is all the more important to ask 'what do the dates mean?'. Further examples will be presented that attempt to explore whether a comprehensive approach to mineral provenance analysis in sedimentary materials (chronology, mineral chemistry, isotopes) can provide an accurate and useful snapshot of the geological characteristics of a portion of a mountain system undergoing erosion and exhumation. What can be reconstructed by this approach and what are its limitations? Of particular interest are monazite, rutile, garnet, and zircon which may provide

  1. Analyses and economic potential of monazite in Liberia

    USGS Publications Warehouse

    Rosenblum, Sam

    1974-01-01

    Eleven monazite samples from Liberia, including seven from beach sands, were analyzed by the X-ray fluorescence method. The monazite samples, containing only one-half percent impurities, were obtained by use of a hot Clerici-solution procedure for purification which was devised by the author. The percentage of the rare-earth elements in Liberian monazite concentrates does not differ greatly from that of monazite sands elsewhere in the world. The average of the 11 samples shows less praseodymium and neodymium than Russian and American monazites, but more cerium. Liberian coastal sands apparently contain sufficient reserves of monazite (and other heavy minerals of commerce) to encourage mining. A feasibility study of production and marketing of monazite from Liberian beach sands is recommended.

  2. Geochemistry and zircon U-Pb geochronology of the ultramafic and mafic rocks emplaced within the anatectic series of the Variscan Pyrenees: The example of the Gavarnie-Heas dome (France)

    NASA Astrophysics Data System (ADS)

    Kilzi, Mohammad A.; Grégoire, Michel; Bosse, Valérie; Benoît, Mathieu; Driouch, Youssef; de Saint Blanquat, Michel; Debat, Pierre

    2016-02-01

    The origin and evolution of ultramafic (UM), mafic (M) and intermediate rocks emplaced within the metamorphic and anatectic series of the middle crust of the Variscan segment of the Pyrenees are defined in the light of new isotopic data U-Pb zircon ages, and Sr, Nd isotopic ratios. In the Gavarnie-Heas dome (central Pyrenees), ultramafic, mafic and intermediate rocks form three massifs several kilometers in size emplaced within the anatectic series: (i) the Gloriettes massif, which mostly consists of norites with enclaves of ultramafic rocks; (ii) the Troumouse massif, which comprises intermediate rocks (gabbro-diorite and diorite) with norite enclaves, and (iii) the Aguila massif, which consists of intermediate rocks with hornblendite enclaves. U-Pb zircon geochronology (first data for these rock types in the Axial Zone of the Pyrenees) revealed an age of 294 Ma for the diorite crystallization and correlatively for the crystallization of the anatectic granite. This new radiometric age allows us to suggest that the Variscan orogeny continued at least until the Early Permian and spread over around 30 Ma. The Nd and Sr isotopic compositions of all UM and M samples plot within the field of the continental crust. Two scenarios can explain the genesis and the emplacement of the components of the magmatic suite: i) evolution of mantle melts and contamination (AFC); ii) evolution of melts originating from a heterogeneous source (mantle + crust) at the local or regional scale. The strong crustal affinity of all UM and M rock types from Gavarnie-Heas leads us to favor the second scenario.

  3. Geochronology, Nd isotopes and reconnaissance geochemistry of volcanic and metavolcanic rocks of the São Luís Craton, northern Brazil: Implications for tectonic setting and crustal evolution

    NASA Astrophysics Data System (ADS)

    Klein, Evandro L.; Luzardo, Renê; Moura, Candido A. V.; Lobato, Denise C.; Brito, Reinaldo S. C.; Armstrong, Richard

    2009-02-01

    New field work, in addition to zircon geochronology, Nd isotopes and reconnaissance geochemical data allow the recognition of Paleoproterozoic volcanic and metavolcanic sequences in the São Luís Craton of northern Brazil. These sequences record at least five volcanic pulses occurring probably in three distinct epochs and in different tectonic settings. (1) The Pirocaua Formation of the Aurizona Group comprises early arc-related calc-alkaline metapyroclastic rocks of 2240 ± 5 Ma formed from juvenile protoliths in addition to minor older crustal components. (2) The Matará Formation of the Aurizona Group holds mafic tholeiitic and ultramafic metavolcanic rocks of back arc and/or island arc setting, which are likely coeval to the Pirocaua Formation. (3) The Serra do Jacaré volcanic unit is composed of tholeiitic basalts and predominantly metaluminous, normal- to high- K calc-alkaline andesites of 2164 ± 3 Ma formed in mature arc or active continental margin from juvenile protoliths along with subordinate older (Paleoproterozoic) materials and associated to the main calc-alkaline orogenic stage. (4) The Rio Diamante Formation consists of late-orogenic metaluminous, medium- K, calc-alkaline rhyolite to dacite and tuffs of 2160 ± 8 Ma formed in continental margin setting from reworked Paleoproterozoic crust (island arc) with incipient Archean contribution. (5) The Rosilha volcanic unit is composed of weakly peraluminous, medium- K, calc-alkaline dacite and tuff formed probably at about 2068 Ma from reworked crustal protoliths. As a whole the volcanic and metavolcanic rocks record and characterized better the previously proposed orogenic evolution of the São Luís Craton.

  4. U-Th-Total Pb ages in monazites of the Los Pedroches batholith (Spain): evidence of postcrsytallization events

    NASA Astrophysics Data System (ADS)

    García de Madinabeitia, S.; Santos Zalduegui, J. F.; Carracedo, M.; Gil Ibarguchi, J. I.

    2003-04-01

    The U-Th-total Pb composition of monazite determined by electron microprobe methods has been successfully applied in geochronology using different age calculation procedures (1). One of the main problems in the use of this geochronological tool is the impossibility to asses the degree of discordance of the minerals analyzed. The Los Pedroches batholith of the Central-Iberian Zone (S Spain) is a late-Hercynian magmatic alignment essentially formed by a granodiorite unit and several granite intrusions. The batholith was emplaced subsequently to the main Hercynian deformation phase during upper Westphalian to lower Stephanian times (ca. 300 Ma). The emplacement was controlled by a crustal-scale shear zone trending N120--130E developed in a transtensional regime (2). There is no evidence of major deformational events after the emplacement. Thirty representative monazites from four granitic plutons (Santa Eufemia, El Guijo, Cerro Mogábar, Cardeña-Virgen de La Cabeza) of the Los Pedroches batholith have been analyzed by electron microprobe using standard procedures described in (3). Data obtained from 166 analyses were processed and plotted on different diagrams proposed for U-Th-total Pb dating assessment (1, 3, 4). In U/Pb vs. Th/Pb diagrams, analyzed monazites exhibit gradual variations in U, Th and Pb contents, but deviate from the reference isochron lines. Data sets for each pluton show considerable scatter on age histograms which also prevent obtaining ages with reasonable errors. Yet, individual monazite grains show variable patterns and generally present the higher frequency of data at ca. 300 Ma with tails down to ca. 250 Ma. On the other hand, data plotted on the ThO_2* (%) vs. PbO (%) diagrams generally crosscut in PbO negative values, indicating some Pb loss after mineral crystallization. It appears, therefore, that despite the absence of field, structural and geophysical evidence of post-emplacement deformation and recrystallization in granites, the

  5. Radiation damage in zircon and monazite

    SciTech Connect

    Meldrum, A.; Boatner, L.A.; Weber, W.J.; Ewing, R.C.

    1998-07-01

    Monazite and zircon respond differently to ion irradiation and to thermal and irradiation-enhanced annealing. The damage process (i.e., elastic interactions leading to amorphization) in radioactive minerals (metamictization) is basically the same as for the ion-beam-irradiated samples with the exception of the dose rate which is much lower in the case of natural samples. The crystalline-to-metamict transition in natural samples with different degrees of damage, from almost fully crystalline to completely metamict, is compared to the sequence of microstructures observed for ion-beam-irradiated monazite and zircon. The damage accumulation process, representing the competing effects of radiation-induced structural disorder and subsequent annealing mechanisms (irradiation-enhanced and thermal) occurs at much higher temperatures for zircon than for monazite. The amorphization dose, expressed as displacements per atom, is considerably higher in the natural samples, and the atomic-scale process leading to metamictization appears to develop differently. Ion-beam-induced amorphization data were used to calculate the {alpha}-decay-event dose required for amorphization in terms of a critical radionuclide concentration, i.e., the concentration above which a sample of a given age will become metamict at a specific temperature. This equation was applied to estimate the reliability of U-Pb ages, to provide a qualitative estimate of the thermal history of high-U natural zircons, and to predict whether actinide-bearing zircon or monazite nuclear waste forms will become amorphous (metamict) over long timescales.

  6. Petrogenesis of late Paleozoic volcanic rocks from the Daheshen Formation in central Jilin Province, NE China, and its tectonic implications: Constraints from geochronology, geochemistry and Sr-Nd-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Yu, Qian; Ge, Wen-Chun; Yang, Hao; Zhao, Guo-Chun; Zhang, Yan-Long; Su, Li

    2014-04-01

    We present geochronological, geochemical, whole-rock Sr-Nd and zircon Hf-isotopic data for late Paleozoic volcanic rocks from the Daheshen Formation in central Jilin Province, northeastern China, and constrain the petrogenesis of the volcanic rocks and late Paleozoic tectonic evolution of the northern margin of the Northern China Craton, which is regarded as the eastern segment of the Central Asian Orogenic Belt (CAOB). Lithologically, the Daheshen Formation is composed mainly of rhyolite, rhyolitic tuff, dacite and andesite, with minor basalt. The zircons from three rhyolites, two dacites, one rhyolitic tuff and one basalt are euhedral-subhedral, display oscillatory zoning and have high Th/U ratios (0.50-2.28), implying a magmatic origin. LA-ICP-MS zircon U-Pb age data indicate that the volcanic rocks from the Daheshen Formation formed during Late Carboniferous-Early Permian time (302-299 Ma). Geochemically, late Paleozoic volcanic rocks have SiO2 = 52.13-81.77 wt.% and K2O = 0.86-6.88 wt.%, belonging to mid-K to high-K calc-alkaline series. These rocks are characterized by enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs, such as Nb, Ta, and Ti) and heavy rare earth elements (HREEs), with affinities to igneous rocks forming in an active continental margin setting. All volcanic rocks have depleted Nd isotopic compositions (ɛNd(t) = + 2.4 to + 2.5 for the basalts and + 5.8 to + 7.1 for the andesites and dacites, respectively). In situ Hf isotopic results of zircon from the rhyolites show that they have ɛHf(t) = - 1.1 to + 10.6. All these geochemical features indicate that the andesites, dacites, and rhyolites likely originated from the partial melting of Meso-Neoproterozoic accreted lower crust (Hf and Nd model ages (TDM2) of 1384-662 Ma and 1061-800 Ma, respectively). In contrast, the basalts were derived from the partial fusion of a depleted lithospheric mantle that

  7. Geochemistry and Sm-Nd geochronology of the metasomatised mafic rocks in the Khetri complex, Rajasthan, NW India: Evidence of an Early Cryogenian metasomatic event in the northern Aravalli orogen

    NASA Astrophysics Data System (ADS)

    Kaur, Parampreet; Chaudhri, Naveen; Hofmann, Albrecht W.; Raczek, Ingrid; Okrusch, Martin

    2013-01-01

    processes varied on a local scale depending on the fluid composition. A whole-rock-mineral (clinopyroxene and scapolite) Sm-Nd isochron of the scapolitised clinopyroxenite at Dosi yields an age of 831 ± 15 Ma. Synthesis of this age data along with previously published geochronological data indicate an important Early Cryogenian (850-830 Ma) metasomatic event in the northern Aravalli orogen, which is also synchronous with the Erinpura granite event in the southern Aravalli orogen.

  8. Geochemistry, U-Pb geochronology, Sm-Nd and O isotopes of ca. 50 Ma long Ediacaran High-K Syn-Collisional Magmatism in the Pernambuco Alagoas Domain, Borborema Province, NE Brazil

    NASA Astrophysics Data System (ADS)

    Francisco da Silva Filho, Adejardo; de Pinho Guimarães, Ignez; Santos, Lucilene; Armstrong, Richard; Van Schmus, William Randall

    2016-07-01

    The Pernambuco Alagoas (PEAL) domain shows the major occurrence of granitic batholiths of the Borborema Province, NE Brazil, with Archean to Neoproterozoic range of Nd TDM model ages, giving clues on the role of granites during the Brasiliano orogeny. SHRIMP U/Pb zircon geochronological data for seven granitic intrusions of the PEAL domain divide the studied granitoids into three groups: 1) early-to syn-collision granitoids with crystallization ages ca. 635 Ma (Serra do Catú pluton), 2) syn-collision granitoids with crystallization ages 610-618 Ma (Santana do Ipanema, Água Branca, Mata Grande and Correntes plutons) and 3) late-to post-collision granitoids with ages of ca. 590 Ma (Águas Belas, and Cachoeirinha plutons). The intrusions of group 1 and 2, except the Mata Grande and Correntes plutons, show Nd TDM model ages ranging from 1.2 to 1.5 Ga, while the granitoids from group 3, and Mata Grande Pluton and Correntes plutons have Nd TDM model ages ranging from 1.7 to 2.2 Ga. The studied granitoids with ages <600 Ma are high-K, calc-alkaline, shoshonitic and those with ages <600 Ma are transitional high-K calc-alkaline to alkaline. The volcanic arc signatures associated with the Paleoproterozoic Nd TDM model ages are interpreted as inherited from the source rocks. The oldest ages and lower Nd TDM model ages are recorded from granitoids intruded in the southwest part of the PEAL domain, suggesting that these intrusions are associated with slab-tearing during convergence between the PEAL and the Sergipano domains. Zircon oxygen isotopic data in some of the studied plutons, together with the available Nd isotopic data suggest that the Brasiliano orogeny strongly reworked older crust, of either Paleoproterozoic or Tonian ages. The studied granitoids are coeval with calc-alkaline granitoids of the Transversal Zone and Sergipano domains and rare high-K calc-alkaline granitoids from the Transversal Zone domain. Such large volumes of high-K granitoids with

  9. 40Ar/39Ar Geochronology, Isotope Geochemistry (Sr, Nd, Pb), and petrology of alkaline lavas near Yampa, Colorado: migration of alkaline volcanism and evolution of the northern Rio Grande rift

    USGS Publications Warehouse

    Cosca, Michael A.; Thompson, Ren A.; Lee, John P.; Turner, Kenzie J.; Neymark, Leonid A.; Premo, Wayne R.

    2014-01-01

    Volcanic rocks near Yampa, Colorado (USA), represent one of several small late Miocene to Quaternary alkaline volcanic fields along the northeast margin of the Colorado Plateau. Basanite, trachybasalt, and basalt collected from six sites within the Yampa volcanic field were investigated to assess correlations with late Cenozoic extension and Rio Grande rifting. In this paper we report major and trace element rock and mineral compositions and Ar, Sr, Nd, and Pb isotope data for these volcanic rocks. High-precision 40Ar/39Ar geochronology indicates westward migration of volcanism within the Yampa volcanic field between 6 and 4.5 Ma, and the Sr, Nd, and Pb isotope values are consistent with a primary source in the Proterozoic subcontinental lithospheric mantle. Relict olivine phenocrysts have Mg- and Ni-rich cores, whereas unmelted clinopyroxene cores are Na and Si enriched with finely banded Ca-, Mg-, Al-, and Ti-enriched rims, thus tracing their crystallization history from a lithospheric mantle source region to one in contact with melt prior to eruption. A regional synthesis of Neogene and younger volcanism within the Rio Grande rift corridor, from northern New Mexico to southern Wyoming, supports a systematic overall southwest migration of alkaline volcanism. We interpret this Neogene to Quaternary migration of volcanism toward the northeast margin of the Colorado Plateau to record passage of melt through subvertical zones within the lithosphere weakened by late Cenozoic extension. If the locus of Quaternary alkaline magmatism defines the current location of the Rio Grande rift, it includes the Leucite Hills, Wyoming. We suggest that alkaline volcanism in the incipient northern Rio Grande rift, north of Leadville, Colorado, represents melting of the subcontinental lithospheric mantle in response to transient infiltration of asthenospheric mantle into deep, subvertical zones of dilational crustal weakness developed during late Cenozoic extension that have been

  10. Early Cretaceous arc volcanic suite in Cebu Island, Central Philippines and its implications on paleo-Pacific plate subduction: Constraints from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Deng, Jianghong; Yang, Xiaoyong; Zhang, Zhao-Feng; Santosh, M.

    2015-08-01

    The Philippine island arc system is a collage of amalgamated terranes of oceanic, continental and island arc affinities. Here we investigate a volcanic suite in Cebu Island of central Philippines, including basalt, diabase dike, basaltic pyroclastic rock and porphyritic andesite. LA-ICP-MS U-Pb geochronology of zircon grains from the porphyritic andesite and pyroclastic rock yielded ages of 126 ± 3 Ma and 119 ± 2 Ma, respectively, indicating an Early Cretaceous age. The age distribution of the detrital zircons from river sand in the area displays a peak at ca. 118 Ma, close to the age of the pyroclastic rock. The early Cretaceous volcanic rocks in the central Philippines were previously regarded as parts of ophiolite complexes by most investigators, whereas the Cebu volcanics are distinct from these, and display calc-alkaline affinity and island arc setting, characterized by high LREE/HREE ratios and low HFSE contents. These features are similar to the Early Cretaceous arc basalts in the Amami Plateau and east Halmahera in the northernmost and southernmost West Philippine Basin respectively. Zircon Hf isotopes of the pyroclastic rocks show depleted nature similar to those of the Amami Plateau basalts, implying the subducted Pacific-type MORB as probable source. Zircon Hf isotopes of the porphyritic andesite show slight enrichment relative to that of the pyroclastic rocks and MORB, indicating subducted sediments as a minor end-member in the source. The Hf isotopic compositions of the volcanic rocks are also reflected in the detrital zircons from the river sands. We propose that the volcanic rocks of Cebu Island were derived from partial melting of sub-arc mantle wedge which was metasomatized by dehydration of subducted oceanic crust together with minor pelagic sediments. Within the tectonic environment of Southeast Asia during Early Cretaceous, the volcanic rocks in Cebu Island can be correlated to the subduction of paleo-Pacific plate. The Early Cretaceous

  11. Evolution of the Mazatzal province and the timing of the Mazatzal orogeny: Insights from U-Pb geochronology and geochemistry of igneous and metasedimentary rocks in southern New Mexico

    USGS Publications Warehouse

    Amato, J.M.; Boullion, A.O.; Serna, A.M.; Sanders, A.E.; Farmer, G.L.; Gehrels, G.E.; Wooden, J.L.

    2008-01-01

    New U-Pb zircon ages, geochemistry, and Nd isotopic data are presented from three localities in the Paleoproterozoic Mazatzal province of southern New Mexico, United States. These data help in understanding the source regions and tectonic setting of magmatism from 1680 to 1620 Ma, the timing of the Mazatzal orogeny, the nature of postorogenic maginatism, Proterozoic plate tectonics, and provide a link between Mazatzal subblocks in Arizona and northern New Mexico. The data indicate a period from 1680 to 1650 Ma in which juvenile felsic granitoids were formed, and a later event between 1646 and 1633 Ma, when these rocks were deformed together with sedimentary rocks. No evidence of pre-1680 Ma rocks or inherited zircons was observed. The igneous rocks have ENd(t) from -1.2 to +4.3 with most between +2 and +4, suggesting a mantle source or derivation from similar-aged crust. Nd isotope and trace element concentrations are consistent with models for typical are magmatism. Detrital zircon ages from metasedimentary rocks indicate that sedimentation occurred until at least 1646 Ma. Both local and Yavapai province sources contributed to the detritus. All of the samples older than ca. 1650 Ma are deformed, whereas undeformed porphyroblasts were found in the contact aureole of a previously dated 1633 Ma gabbro. Regionally, the Mlazatzal orogeny occurred mainly between 1654 and 1643 Ma, during final accretion of a series of island arcs and intervening basins that may have amalgamated offshore. Rhyolite magmatism in the southern Mazatzal province was coeval with gabbro intrusions at 1633 Ma and this bimodal magmatism may have been related to extensional processes following arc accretion. ?? 2007 Geological Society of America.

  12. Constraining metamorphic rates through allanite and monazite petrochronology: a case study from the Miyar Valley (High Himalayan Crystalline of Zanskar, NW India)

    NASA Astrophysics Data System (ADS)

    Robyr, Martin; Goswami-Banerjee, Sriparna

    2014-05-01

    porphyroblasts yield respective ages of 33.6 ± 0.9 Ma and 29.5 ± 0.2 Ma, constraining the time elapsed between allanite crystallization (~ 420 °C) and monazite crystallization (~ 600°C). These data indicate that the rock needed ~ 4 Myr to be subducted from the 420 °C isotherm down to the 600°C isotherm, implying a heating rate of ca. 45°C/m.y. References Robyr, M., Epard, J.-L. & El Korh, A., 2014. Structural, metamorphic and geochronological relations between the Zanskar Shear Zone and the Miyar Shear Zone (NW Indian Himalaya): Evidence for two distinct tectonic structures and implications for the evolution of the High Himalayan Crystalline of Zanskar. Journal of Asian Earth Sciences, 79, 1-15. Robyr, M., Hacker, B. R. & Mattinson, J. M., 2006. Doming in compressional orogenic settings: New geochronological constraints from the NW Himalaya. Tectonics, 25. Robyr, M., Vannay, J. C., Epard, J. L. & Steck, A., 2002. Thrusting, extension, and doming during the polyphase tectonometamorphic evolution of the High Himalayan Crystalline Zone in NW India. Journal of Asian Earth Sciences, 21, 221-239.

  13. Petrology, geochemistry and zircon U-Pb geochronology of a layered igneous complex from Akarui Point in the Lützow-Holm Complex, East Antarctica: Implications for Antarctica-Sri Lanka correlation

    NASA Astrophysics Data System (ADS)

    Kazami, Sou; Tsunogae, Toshiaki; Santosh, M.; Tsutsumi, Yukiyasu; Takamura, Yusuke

    2016-11-01

    The Lützow-Holm Complex (LHC) of East Antarctica forms part of a complex subduction-collision orogen related to the amalgamation of the Neoproterozoic supercontinent Gondwana. Here we report new petrological, geochemical, and geochronological data from a metamorphosed and disrupted layered igneous complex from Akarui Point in the LHC which provide new insights into the evolution of the complex. The complex is composed of mafic orthogneiss (edenite/pargasite + plagioclase ± clinopyroxene ± orthopyroxene ± spinel ± sapphirine ± K-feldspar), meta-ultramafic rock (pargasite + olivine + spinel + orthopyroxene), and felsic orthogneiss (plagioclase + quartz + pargasite + biotite ± garnet). The rocks show obvious compositional layering reflecting the chemical variation possibly through magmatic differentiation. The metamorphic conditions of the rocks were estimated using hornblende-plagioclase geothermometry which yielded temperatures of 720-840 °C. The geochemical data of the orthogneisses indicate fractional crystallization possibly related to differentiation within a magma chamber. Most of the mafic-ultramafic samples show enrichment of LILE, negative Nb, Ta, P and Ti anomalies, and constant HFSE contents in primitive-mantle normalized trace element plots suggesting volcanic arc affinity probably related to subduction. The enrichment of LREE and flat HREE patterns in chondrite-normalized REE plot, with the Nb-Zr-Y, Y-La-Nb, and Th/Yb-Nb/Yb plots also suggest volcanic arc affinity. The felsic orthogneiss plotted on Nb/Zr-Zr diagram (low Nb/Zr ratio) and spider diagrams (enrichment of LILE, negative Nb, Ta, P and Ti anomalies) also show magmatic arc origin. The morphology, internal structure, and high Th/U ratio of zircon grains in felsic orthogneiss are consistent with magmatic origin for most of these grains. Zircon U-Pb analyses suggest Early Neoproterozoic (847.4 ± 8.0 Ma) magmatism and protolith formation. Some older grains (1026-882 Ma) are regarded as

  14. Subduction-related Late Carboniferous to Early Permian Magmatism in the Eastern Pontides, the Camlik and Casurluk plutons: Insights from geochemistry, whole-rock Sr-Nd and in situ zircon Lu-Hf isotopes, and U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Karsli, Orhan; Dokuz, Abdurrahman; Kandemir, Raif

    2016-12-01

    Late Carboniferous to early Permian granitoid rocks represent a volumetrically minor component of the Eastern Pontide lithosphere, but they preserve useful information about the region's tectonomagmatic history. The Casurluk and Camlik plutons primarily consist of gabbro, gabbroic diorite, diorite, monzogabbro, monzodiorite and monzonite, which intrude early to middle Carboniferous granitic basement rocks in the region. In this study, we use in situ zircon U-Pb ages and Lu-Hf isotopic values, whole-rock Sr-Nd isotopic values, and mineral chemistry and geochemistry of these plutons to determine petrogenesis and crustal evolution; we also discuss geodynamic implications. LA-ICP-MS zircon U-Pb dating of magmatic zircons from the rocks suggests that the plutons were emplaced during the late Carboniferous to early Permian (302 Ma). The metaluminous and I-type intrusive rocks belong to the high-K calc-alkaline series. In addition, they are relatively enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs); they are depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs), such as Nb and Ti. All of the samples have homogeneous initial ISr values (0.70675 to 0.70792) and low εNd (t) values (- 5.1 to - 3.3). Zircons from the rocks of both plutons have uniform negative to slightly positive εHf (t) values (- 3.5 to 1.4) and old Hf two-stage model ages (1323 to 1548 Ma), implying that they have the same source, as well as suggesting the involvement of old enriched lithospheric mantle materials during their magma genesis. These results, combined with the εHf (t) values and two-stage model ages, demonstrate that the primary magmas were derived from partial melting of old lithospheric mantle material metasomatized by subduction-related fluids. Considering other regional geological data from the Sakarya Zone where these plutons formed, we conclude that late Carboniferous to early Permian magmatism in the area

  15. Geochemistry, Sr-Nd-Pb isotopes and geochronology of amphibole- and mica-bearing lamprophyres in northwestern Iran: Implications for mantle wedge heterogeneity in a palaeo-subduction zone

    NASA Astrophysics Data System (ADS)

    Aghazadeh, Mehraj; Prelević, Dejan; Badrzadeh, Zahra; Braschi, Eleonora; van den Bogaard, Paul; Conticelli, Sandro

    2015-02-01

    Lamprophyres of different age showing distinctive mineralogy, geochemistry and isotopic ratios are exposed in northwestern Iran. They can be divided into Late Cretaceous sannaite, Late Oligocene-Early Miocene camptonite (amphibole-bearing) and Late Miocene minette (mica-bearing) and spessartite (amphibole-bearing) lamprophyres. Sannaites have high-Ti amphibole along with high-Ti and Al clinopyroxene, and they are characterised by homogeneous enrichment in incompatible trace elements with troughs at Pb. Spessartites have hornblende and low-Al and Ti clinopyroxene, and they are characterised by enriched incompatible trace element pattern with depletions of Nb, Ta, Pb, and Ti with respect to large ion lithophile elements. Minettes have high-Ti and Al brown mica and low-Al and Ti clinopyroxene, and similar to spessartite, are characterised by fractionation of high field strength elements with respect to large ion lithophile elements, with troughs at Nb, Ta, and Ti and a peak at Pb. Minettes show high initial 87Sr/86Sr values up to 0.70760 and low initial 143Nd/144Nd down to 0.512463 with a negative correlation, consistent with the trace element distribution related with an enriched mantle source modified after sediment recycling during subduction and continental collision. Cretaceous sannaites and Early Miocene spessartites show low initial 87Sr/86Sr approaching 0.70447 and high 143Nd/144Nd values up to 0.512667, which are consistent with a depleted within-plate mantle source. Minette and spessartite lamprophyres show high initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values, whereas sannaites have lower, but variable, initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values with respect to those of calc-alkaline lamprophyres. Minettes originated by partial melting of a metasomatised lithospheric mantle following siliciclastic sediment recycling by subduction. In contrast, sannaites were generated from the partial melting of a similar lithospheric mantle that was

  16. The Oldest Known Caldera Associated with the Yellowstone Hotspot: New Geologic Mapping, Geochemistry, and 40Ar/39Ar Geochronology for the Northern McDermitt Volcanic Field, Northern Nevada and Southeastern Oregon

    NASA Astrophysics Data System (ADS)

    Benson, T. R.; Mahood, G. A.

    2015-12-01

    McDermitt Volcanic Field (MVF) of Nevada and Oregon is one of three major caldera centers associated with Mid-Miocene Steens/Columbia River flood basalts. Pioneering geologic mapping of MVF by Rytuba and McKee (1984) and subsequent work established four main ignimbrites within the field. Our new 40Ar/39Ar ages (FCT=28.02 Ma) are 16.41±0.02 (±2σ) Ma for Tuff of Oregon Canyon, 16.35±0.04 Ma for Tuff of Trout Creek Mountains, 16.30±0.04 Ma for Tuff of Long Ridge, and 15.56±0.08 Ma for Tuff of Whitehorse Creek. We have mapped two previously unrecognized overlapping calderas that we interpret as sources for Tuff of Oregon Canyon and Tuff of Trout Creek. These ~20-km diameter calderas lie north of the well-known McDermitt Caldera; a smaller 7-km caldera that formed on eruption of the Tuff of Whitehorse Creek is nested within them. Argon ages and geochemistry of alkali rhyolite lava domes in the northern MVF define two populations: ~16.6-16.3 Ma associated with the newly recognized calderas, and ~15.5-15.3 Ma outlining the margins of the younger Whitehorse Caldera. Consistent with both ignimbrites erupting from the same evolving magma system, the high-silica alkali rhyolite Tuff of Oregon Canyon lies on compositional trends defined by the Tuff of Trout Creek, which is zoned from a moderately crystal-rich high-silica alkali rhyolite to a strongly porphyritic low-silica alkali rhyolite. They both are distinguished from the Tuff of Long Ridge from McDermitt Caldera by their higher Zr/Rb, and relatively high FeO* concentrations distinguish all MVF ignimbrites from ignimbrites from the nearby High Rock Caldera Complex, where the oldest caldera formed on eruption of the Idaho Canyon Tuff at 16.38±0.02 Ma (Coble and Mahood, in review). The Tuff of Trout Creek rests conformably on the Tuff of Oregon Canyon west and southwest of the calderas, where they overlie a thick stack of Steens Basalt lavas. To the east and southeast the two ignimbrites are separated by as much as

  17. Dithizone method for determination of lead in monazite

    USGS Publications Warehouse

    Powell, R.A.; Kinser, C.A.

    1958-01-01

    In the determination of lead in monazite-to be used as the basis for geologic age measurements-it was necessary to eliminate interferences due to the presence of phosphates of thorium and the rare earth metals. The method involves attacking the monazite samples with hot, concentrated sulfuric acid, then taking them up with dilute nitric acid. Lead is extracted as the dithizonate and determined spectrophotometrically at 520 m??. Rapid determinations were made with good reproducibility on a series of monazite samples.

  18. Tectono-magmatic evolution of the Chihuahua-Sinaloa border region in northern Mexico: Insights from zircon-apatite U-Pb geochronology, zircon Hf isotope composition and geochemistry of granodiorite intrusions

    NASA Astrophysics Data System (ADS)

    Mahar, Munazzam Ali; Goodell, Philip C.; Feinstein, Michael Nicholas

    2016-11-01

    We present the whole-rock geochemistry, LA-ICP-MS zircon-apatite U-Pb ages and zircon Hf isotope composition of the granodioritic plutons at the southwestern boundary of Chihuahua with the states of Sinaloa and Sonora. These granodiorites are exposed in the north and south of the Rio El Fuerte in southwest Chihuahua and northern Sinaloa. The magmatism spans over a time period of 37 Ma from 90 to 53 Ma. Zircons are exclusively magmatic with strong oscillatory zoning. No inheritance of any age has been observed. Our new U-Pb dating ( 250 analyses) does not support the involvement of older basement lithologies in the generation of the granitic magmas. The U-Pb apatite ages from granodiorites in southwest Chihuahua vary from 52 to 70 Ma. These apatite ages are 1 to 20 Ma younger than the corresponding zircon U-Pb crystallization ages, suggesting variable cooling rates from very fast to 15 °C/Ma ( 800 °C to 500 °C) and shallow to moderate emplacement depths. In contrast, U-Pb apatite ages from the Sinaloa batholith are restricted from 64 to 61 Ma and are indistinguishable from the zircon U-Pb ages range from 67 to 60 Ma within the error, indicating rapid cooling and very shallow emplacement. However, one sample from El Realito showed a larger difference of 20 Ma in zircon-apatite age pair: zircon 80 ± 0.8 Ma and apatite 60.6 ± 4 Ma, suggesting a slower cooling rate of 15 °C/Ma. The weighted mean initial εHf (t) isotope composition (2σ) of granodiorites varies from + 1.8 to + 5.2. The radiogenic Hf isotope composition coupled with previous Sr-Nd isotope data demonstrates a significant shift from multiple crustal sources in the Sonoran batholithic belt to the predominant contribution of the mantle-derived magmas in the southwest Chihuahua and northern Sinaloa. Based on U-Pb ages, the absence of inheritance, typical high Th/U ratio and radiogenic Hf isotope composition, we suggest that the Late Cretaceous-Paleogene magmatic rocks in this region are not derived from

  19. The legacy of monazite processing in Brazil.

    PubMed

    da Costa Lauria, Dejanira; Rochedo, Elaine R R

    2005-01-01

    The exploitation of natural resources containing naturally occurring radionuclides may lead to enhanced levels of radioactive isotope and enhanced potential for exposure to naturally occurring radionuclides in products, by-products, residues or wastes. Such resources include, for instance, monazite, the processing of which, in Brazil, generated a great amount of radioactive residues, being stored in buried concrete tanks, in temporary storage buildings and in sealed trenches. In addition, during the 1980s there were no radiological protection rules concerning the storage and transportation of these kinds of residues. Mineral radioactive residues were used as landfills and the residues of chemical processes contaminated floors and buildings. The decommissioning process and cleaning of old plants have generated tons of wastes that has been added to previously produced wastes. This paper reports and discusses the cycle of monazite in Brazil and its consequences in terms of site remediation and amount of wastes and residues generated and stored.

  20. Monazite in Atlantic shore-line features

    USGS Publications Warehouse

    Dryden, Lincoln; Miller, Glen A.

    1954-01-01

    This report is a survey of present and potential production of monazite from part of the Maryland-Florida section of the Atlantic Coastal Plain. The part of the Coastal Plain covered here is the outer (shore-ward) half. In this area, all the large heavy-mineral placers so far discovered occur in sand bodies that, by their shape, size, orientation, and lithology, appear to be ancient beaches, spits, bars, or dunes. Smaller placers have produced from recent shore-line features. The inner part of the Coastal Plain, to be treated in another report, is underlain generally by older rocks, ranging in age from Cretaceous to older Pleistocene. Only two large heavy-mineral placers are now in production at Trail Ridge, and near Jacksonville, both in Florida. Production is planned for the near future near Yulee, Fla.: in Folkston, Ga.: and at one or two localities in eastern North Carolina. Each of these three will produce monazite as a byproduct; the total new reserve for the three placers is about 33,000 tons of monazite. In large heavy-mineral placers of this type, monazite has not been found to run more than about 1 percent of total heavy minerals. In some large placers, notably Trail Ridge, it is almost or completely lacking. No reason for its sporadic occurrence has been found in this investigation. Two placers of potential economic value have been found by this project in Virginia, one west and one east of Chesapeake Bay. Neither is of promise for monazite production, but if they serve to open up exploration or production in the area, there is a chance for monazite as a byproduct from other placers. A discovery of considerable scientific interest has to do with the occurrence of two different suites of heavy minerals in the Coastal Plain, at least south of Virginia. One, an “older” suite, lacks epidote, hornblende, and garnet; this suite occurs in all older formations and in Pleistocene deposits lying above about 50 or 60 feet above sea level. The other,

  1. Monazite Th-Pb age depth profiling

    SciTech Connect

    Grove, M.; Harrison, T.M.

    1999-06-01

    The significant capabilities of the ion microprobe for thermochronometric investigations of geologic materials remain largely unexploited. Whereas {sup 208}Pb/{sup 232}Th spot analysis allows {approximately} 10-mm-scale imaging of Pb loss profiles or overgrowths in sectioned monazite grains, the spatial resolution offered by depth profiling into the surface region of natural crystals is more than two orders of magnitude higher. The authors document here the ability of the high-resolution ion microprobe to detect {sup 208}Pb/{sup 232}Th age differences of < 1 m.y. with better than 0.05 {micro}m depth resolution in the outer micron of Tertiary monazites from the hanging wall of the Himalayan Main Central thrust. Age gradients on this scale are inaccessible to ion microprobe spot analysis or conventional thermal ionization mass spectrometry. Interpretation of the near-surface {sup 208}Pb distributions with available monazite Pb diffusion data illustrates the potential of the approach for recovering continuous, high-temperature thermal history information not previously available.

  2. Systematic variation of rare earths in monazite

    USGS Publications Warehouse

    Murata, K.J.; Rose, H.J.; Carron, M.K.

    1953-01-01

    Ten monazites from widely scattered localities have been analyzed for La, Ce, Pr, Nd, Sm, Gd, Y and Th by means of a combined chemical and emission spectrographic method. The analytical results, calculated to atomic percent of total rare earths (thorium excluded), show a considerable variation in the proportions of every element except praseodymium, which is relatively constant. The general variation trends of the elements may be calculated by assuming that the monazites represent different stages in a fractional precipitation process, and by assuming that there is a gradational increase in the precipitability of rare earth elements with decreasing ionic radius. Fractional precipitation brings about an increase in lanthanum and cerium, little change in praseodymium, and a decrease in neodymium, samarium, gadolinium, and yttrium. Deviations from the calculated lines of variation consist of a simultaneous, abnormal increase or decrease in the proportions of cerium, praseodymium, and neodymium with antipathetic decrease or increase in the proportions of the other elements. These deviations are ascribed to abnormally high or low temperatures that affect the precipitability of the central trio of elements (Ce, Pr, Nd) relatively more than that of the other elements. The following semiquantitative rules have been found useful in describing the composition of rare earths from monazite: 1. 1. The sum of lanthanum and neodymium is very nearly a constant at 42 ?? 2 atomic percent. 2. 2. Praseodymium is very nearly constant at 5 ?? 1 atomic percent. 3. 3. The sum of Ce, Sm, Gd, and Y is very nearly a constant at 53 ?? 3 atomic percent. No correlation could be established between the content of Th and that of any of the rare earth elements. ?? 1953.

  3. A Critical Look at NORM In The Monazite Cycle

    NASA Astrophysics Data System (ADS)

    Paschoa, Anselmo S.; da Cunha, Kenya Dias

    2008-08-01

    Thorium, cerium, lanthanum and other rare earths have been extracted from monazite sands for a long time due to several reasons. At the end of the XIX century monazite sands from Brazilian beaches were concentrated gravimetrically to be clandestinely transported to Europe to be used in the manufacture of fabric bags to be burned. Those bags when burning had their brightness enhanced by a mixture of thorium, lanthanum and cerium. The thorium oxide (ThO2) percentages found in monazite concentrates from several parts of the world range from 1 to 11%. While not burned or processed chemically monazite concentrate can be considered hazardous only due to gamma radiation and 220Rn (thoron) inhalation by those who stay very close to storage piles. In old monazite plants the thoron concentration in air reached levels higher than 20 kBqṡm-3. Fortunately, the industrial hygiene improved with time and today's monazite separation plants do not present such high thoron concentrations. Old and recent data from rare earth processing plants suggest that occupational annual doses indoors may be up to two orders of magnitude higher than the worldwide average effective dose reported by the United Nations Scientific Committee on the Effects of the Atomic Radiation (UNSCEAR) due to the inhalation of thoron. Consumer products, like fabric bags used in gas or kerosene lamps have 232Th concentrations of the order of 150 Bqṡg-1. Remnants of the monazite industrial cycle can present 228Ra activity concentrations as high as 5.0 kBqṡg-1. Piles of monazite concentrates were kept for strategic reasons during cold war times in several places of the territories of the United States and the former Soviet Union. Cleanup at those sites may be hazardous mostly due to high concentrations of thoron daughters that may be inhaled by workers. The paper will take a critical look at the naturally occurring radioactive materials (NORM) extant in the monazite cycle and its remnants.

  4. A Monazite-bearing clast in Apollo 17 melt breccia

    NASA Technical Reports Server (NTRS)

    Jolliff, Bradley L.

    1993-01-01

    A phosphate-rich clast in a pigeonite-plagioclase mineral assemblage occurs in Apollo 17 impact-melt breccia 76503,7025. The clast, measuring 0.9 x 0.4 mm in thin section, contains 3.3 percent (volume) apatite (Ca5P3O12(F,Cl)), 0.8 percent whitlockite (Ca16(Mg,Fe)2REE2P14O56), and trace monazite ((LREE)PO4). Major minerals include 26 percent pigeonite, En53-57FS34-35W08-13, and 69 percent plagioclase, An84-92Ab7-15Oro.6-1.1. Troilite, ilmenite, and other accessory minerals constitute less than 1 percent of the assemblage and Fe-metal occurs along fractures. Also present in the melt breccia as a separate clast is a fragment of felsite. Based on the association of these clasts and their assemblages, a parent lithology of alkali-anorthositic monzogabbro is postulated. Monazite occurs in the phosphate-bearing clast as two less than 10 micron grains intergrown with whitlockite. The concentration of combined REE oxides in monazite is 63.5 percent and the chondrite-normalized REE pattern is strongly enriched in LREE, similar to lunar monazite in 10047,68 and terrestrial monazite. Thorium concentration was not measured in monazite, but based on oxide analyses of approximately 100 percent (including interpolated values for REE not measured), substantial Th concentration is not indicated, similar to monazite in 10047,68. Measured monazite/whitlockite REE ratios are La: 11, Ce: 8, Sm: 3.6, Y: 0.9, and Yb: 0.5. Compositions of monazite and coexisting whitlockite and apatite are given.

  5. A dithizone method for the determination of lead in monazite

    USGS Publications Warehouse

    Powell, R.A.; Kinser, C.A.

    1956-01-01

    In determining lead in monazite [(Ce,La,Th)PO4]--to be used as the basis for geologic age measurements--it was necessary to eliminate interferences due to the presences of phosphates of thorium and the rare-earth metals. The method, in which monazite samples are attacked with hot concentrated sulfuric acid, taken up with dilute nitric acid, lead extracted as the dithizonate and then determined spectrophotometrically at 520 mμ, was successfully applied to a series of monazite samples. Rapid determinations were made with good reproducibility.

  6. Complexities of Lu-Hf geochronology in convergent orogens

    NASA Astrophysics Data System (ADS)

    Mulcahy, S. R.; Vervoort, J. D.

    2015-12-01

    Subduction, terrane accretion, and arc magmatism leave a complex and sometimes incomplete record of metamorphism and deformation. The range of metamorphic temperatures and assemblages produced throughout the tectonic evolution of a single orogen often requires multiple isotopic systems to date distinct events. Lu-Hf geochronology, notably, has proven successful for dating metamorphism from a variety of bulk compositions spanning temperatures <350-850 C. We review the success of applying Lu-Hf geochronology in combination with other isotopic systems to date metamorphism from range of metamorphic conditions within convergent margins. We then discuss some complexities of Lu-Hf geochronology when dating samples with complicated metamorphic histories. Garnet and lawsonite isochrons often exhibit excess scatter (high MSWD's) that can be attributed to a number of factors: secondary mineral inclusions, prolonged garnet growth durations, disequilibrium at low temperatures, and polyphase metamorphic histories. Samples with high-Hf inclusions in isotopic equilibrium host phases can lead to decreased precision, but still produce meaningful ages. At high temperatures Lu-Hf ages may date peak metamorphism, cooling from peak temperatures, or result in spurious ages because of preferential retention of 176Hf over 176Lu in garnet. Despite these complexities, and perhaps because of them, new aspects of the metamorphic history may be revealed that are not readily recorded by other isotopic systems. Minerals other than garnet and lawsonite, particularly apatite, and perhaps epidote, offer exciting new possibilities for Lu-Hf geochronology. Careful fieldwork, detailed petrology and geochemistry, and collaborative efforts using multiple isotopic systems offer the best approach to solving tectonic problems in convergent orogens.

  7. The Argon Geochronology Experiment (AGE)

    NASA Technical Reports Server (NTRS)

    Swindle, T. D.; Bode, R.; Fennema, A.; Chutjian, A.; MacAskill, J. A.; Darrach, M. R.; Clegg, S. M.; Wiens, R. C.; Cremers, D.

    2006-01-01

    This viewgraph presentation reviews the Argon Geochronology Experiment (AGE). Potassium-Argon dating is shown along with cosmic ray dating exposure. The contents include a flow diagram of the Argon Geochronology Experiment, and schematic diagrams of the mass spectrometer vacuum system, sample manipulation mechanism, mineral heater oven, and the quadrupole ion trap mass spectrometer. The Laser-Induced Breakdown Spectroscopy (LIBS) Operation with elemental abundances is also described.

  8. Composition of monazites from pegmatites in eastern Minas Gerais, Brazil

    USGS Publications Warehouse

    Murata, K.J.; Dutra, C.V.; da Costa, M.T.; Branco, J.J.R.

    1959-01-01

    Two zoned pegmatites in south-eastern Minas Gerais were sampled in detail for their content of monazite and xenotime and the monazite was analysed for certain of the rare-earth elements and thorium. The ratio of xenotime to monazite increases in both pegmatites from the wall toward the quartz core. The content of the less basic rare-earth elements and of thorium in monazite rises in the same direction. These variation trends suggest that during the crystallization of these pegmatites there was a fractionation of the elements leading to a more or less steady enrichment of the less basic rare-earth elements and of thorium in the residual fluids. One mode of explaining these observed effects postulates that the rare-earth elements and thorium were present in pegmatitic fluids as co-ordination complexes rather than as simple cations. ?? 1959.

  9. Plasticity In High Temperature Materials: Tantalum and Monazite

    DTIC Science & Technology

    2014-03-12

    AFRL-OSR-VA-TR-2014-0065 PLASTICITY IN HIGH TEMPERATURE MATERIALS: TANTALUM AND MONAZITE Jeffrey Kysar THE TRUSTEES OF COLUMBIA UNIVERSITY IN THE...Agency Air Force Office of Scientific Research Title of Project Plasticity in High Temperature Materials: Tantalum and Monazite February 28, 2014...centered cu- bic tantalum , the methodology also demonstrated a relationship between dislocation mean free path length and GND density. A framework to

  10. Characterization of Minerals of Geochronological Interest by EPMA and Atom Probe Tomography

    NASA Astrophysics Data System (ADS)

    Snoeyenbos, D.; Jercinovic, M. J.; Reinhard, D. A.; Hombourger, C.

    2012-12-01

    Isotopic and chemical dating techniques for zircon and monazite rely on several assumptions: that initial common Pb is low to nonexistent, that the analyzed domain is chronologically homogeneous, and that any relative migration of radiogenic Pb and its parent isotopes has not exceeded the analyzed domain. Yet, both zircon and monazite commonly contain significant submicron heterogeneities that may challenge these assumptions and can complicate the interpretation of chemical and isotopic data. Compositional mapping and submicron quantitative analysis by EPMA and FE-EPMA have been found to be useful techniques both for the characterization of these heterogeneities, and for quantitative geochronological determinations within the analytical limits of these techniques and the statistics of submicron sampling. Complementary to high-resolution EPMA techniques is Atom Probe Tomography (APT), wherein a specimen with dimensions of a few hundreds of nanometers is field evaporated atom by atom. The original position of each atom is identified, along with its atomic species and isotope. The result is a reconstruction allowing quantitative three-dimensional study of the specimen at the atomic scale, with low detection limits and high mass resolution. With the introduction of laser-induced thermal pulsing to achieve field evaporation, the technique is no longer limited to conductive specimens. There exists the capability to explore the compositional and isotopic structure of insulating materials at sub-nanometer resolution. Minerals of geochronological interest have been studied by an analytical method involving first compositional mapping and submicron quantitative analysis by EPMA and FE-EPMA, and subsequent use of these data to select specific sites for APT specimen extraction by FIB. Examples presented include 1) zircon from the Taconian of New England, USA, containing a fossil resorption front included between an unmodified igneous core, and a subsequent metamorphic

  11. Detrital geochronology of unroofing magmatic complexes

    NASA Astrophysics Data System (ADS)

    Malusà, Marco Giovanni; Villa, Igor Maria; Vezzoli, Giovanni; Garzanti, Eduardo

    2010-05-01

    . 110, 985-1009 (1998). DeCelles, P. G., Gehrels, G. E., Najman, Y., Martin, A. J., Carter, A., Garzanti, E. Detrital geochronology and geochemistry of Cretaceous-Early Miocene strata of Nepal: implications for timing and diachroneity of initial Himalayan orogenesis. Earth Planet. Sci. Lett. 227, 313-330 (2004). Jäger, E. in Rb-Sr Altersbestimmungen an Glimmern der Zentralalpen, Beitr. Geol. Karte Schweiz NF 134 (eds. Jäger, E., Niggli, E. & Wenk, E.) 28-31 (Bern, Kümmerly & Frey, 1967). Dodson, M. H. Closure temperature in cooling geochronological and petrological systems. Contr. Miner. Petrol. 40, 259-274 (1973). Giger, M. & Hurford, A. J. Tertiary intrusives of the Central Alps: their Tertiary uplift, erosion, redeposition and burial in the south-alpine foreland. Eclogae geol. Helv. 82, 857-866 (1989). Garzanti, E. & Malusà, M. G. The Oligocene Alps: Domal unroofing and drainage development during early orogenic growth. Earth Planet. Sci. Lett. 268, 487-500 (2008). Villa, I. M. From nanometer to megameter: Isotopes, atomic-scale processes, and continent-scale tectonic models. Lithos 87, 155-173 (2006).

  12. Late Devonian - Early Carboniferous polyphase metamorphic evolution of the Orlica-Śnieżnik Dome (NE Bohemian Massif, Poland): evidence from Th-U-total Pb monazite dating

    NASA Astrophysics Data System (ADS)

    Budzyń, Bartosz; Jastrzębski, Mirosław; Stawikowski, Wojciech

    2014-05-01

    younger age domains of 371-356 Ma and 336-331 Ma are defined by monazite from four K-feldspar free light quartzites (SF), and two K-feldspar bearing light quartzite (SF). Similar two age domains of 372-363 Ma and 342-332 Ma yields monazite from six mica schists (SF), with a faint record of ca. 406 Ma in one of these samples. The geochronological results suggest polyphase Devono-Carboniferous metamorphic evolution that embraced at least two tectonometamorphic episodes. Microstructures indicate that the record of 370-360 Ma ages presumably defines a progressive metamorphism, whereas pervasive record of 340-330 Ma ages presumably reflects the superimposed penetrative shearing connected with exhumation. There is no evidence of pre-Variscan regional or contact metamorphism of the Młynowiec-Stronie Group. Cambrian to Ordovician monazites developed only in K-feldspar bearing rocks, i.e. orthogneisses and light quartzites (SF), which suggests growth of the Early Palaeozoic monazites during formation of their, respectively, magmatic and partially volcanic protoliths. Acknowledgements. The project was funded by the National Science Center of Poland, grant number DEC 2011/03/B/ST10/05638.

  13. Electron microprobe observations of PB diffusion in metamorphosed detrital monazites

    NASA Astrophysics Data System (ADS)

    Suzuki, K.; Adachi, M.; Kajizuka, I.

    1994-12-01

    Electron microprobe analyses have been made on monazite grains from paragneiss samples in the andalusite-sillimanite transition (620 +/- 15 C) and sillimanite-orthoclase (680 +/- 15 C) zones of the Cretaceous Ryoke metamorphic belt, southwest Japan. Monazites from pelitic gneisses are of metamorphic origin, euhedral to subhedral and chronologically homogeneous, giving chemical Th-U-total Pb isochron (CHIME) ages of 98.8 +/- 3.3 - 98.0 +/- 3.2 Ma. Two psammitic gneisses of individual metamorphic grade contain both metamorphic monazite grains and detrital ones as old as ca. 1700 Ma. Most detrital monazite grains are heterogeneous in the ThO2 and UO2 concentrations and have multiple or single rims as young as ca. 100 Ma. Several detrital monazite grains are well rounded in form, exhibit homogeneous Th and U distributions and show a Pb diffusion profile in the margin. The width of the diffusion zones is approximately constant throughout grains from each psammitic gneiss: 18-22 micrometers for 620 C and 48-58 micrometers for 680 C. Assuming the isothermal diffusion of Pb from homogeneous monazite spheres during a 5 Ma duration of peak metamorphism, we obtain diffusion coefficients of 1.9 (+/- 0.3) x 10-21 and 1.5 (+/- 0.3) x 10-20 sq cm/s at 620 C and 680 C, respectively. These data derive an activation energy of 2.44 (+2.85/-1.26) x 105 J/mol and a frequency factor of 3.4 x 10-7 (8.5 x 10-12 - 2.2 x 107 sq cm/s, taking account of uncertainties of +/- 15 C in the temperatures and of +/- 20% in the diffusion coefficients. The diffusion parameters obtained from natural samples in this study provide a reliable insight into the closure temperature for Pb in monazite that has been poorly understood so far.

  14. Heat capacities of lanthanide and actinide monazite-type ceramics

    NASA Astrophysics Data System (ADS)

    Kowalski, Piotr M.; Beridze, George; Vinograd, Victor L.; Bosbach, Dirk

    2015-09-01

    (Ln, An)xPO4 monazite-type ceramics are considered as potential matrices for the disposal of nuclear waste. In this study we computed the heat capacities and the standard entropies of these compounds using density functional perturbation theory. The calculations of lanthanide monazites agree well with the existing experimental data and provide information on the variation of the standard heat capacities and entropies along the lanthanide series. The results for AnPO4 monazites are similar to those obtained for the isoelectronic lanthanide compounds. This suggests that the missing thermodynamic data on actinide monazites could be similarly computed or assessed based on the properties of their lanthanide analogs. However, the computed heat capacity of PuPO4 appear to be significantly lower than the measured data. We argue that this discrepancy might indicate potential problems with the existing experimental data or with their interpretation. This shows a need for further experimental studies of the heat capacities of actinide-bearing, monazite-type ceramics.

  15. Bioleaching of rare earth elements from monazite sand.

    PubMed

    Brisson, Vanessa L; Zhuang, Wei-Qin; Alvarez-Cohen, Lisa

    2016-02-01

    Three fungal strains were found to be capable of bioleaching rare earth elements from monazite, a rare earth phosphate mineral, utilizing the monazite as a phosphate source and releasing rare earth cations into solution. These organisms include one known phosphate solubilizing fungus, Aspergillus niger ATCC 1015, as well as two newly isolated fungi: an Aspergillus terreus strain ML3-1 and a Paecilomyces spp. strain WE3-F. Although monazite also contains the radioactive element Thorium, bioleaching by these fungi preferentially solubilized rare earth elements over Thorium, leaving the Thorium in the solid residual. Adjustments in growth media composition improved bioleaching performance measured as rare earth release. Cell-free spent medium generated during growth of A. terreus strain ML3-1 and Paecilomyces spp. strain WE3-F in the presence of monazite leached rare earths to concentrations 1.7-3.8 times those of HCl solutions of comparable pH, indicating that compounds exogenously released by these organisms contribute substantially to leaching. Organic acids released by the organisms included acetic, citric, gluconic, itaconic, oxalic, and succinic acids. Abiotic leaching with laboratory prepared solutions of these acids was not as effective as bioleaching or leaching with cell-free spent medium at releasing rare earths from monazite, indicating that compounds other than the identified organic acids contribute to leaching performance.

  16. Microstructural observation and chemical dating on monazite from the Shilu Group, Hainan Province of South China: Implications for origin and evolution of the Shilu Fe-Co-Cu ore district

    NASA Astrophysics Data System (ADS)

    Xu, Deru; Kusiak, Monika A.; Wang, Zhilin; Chen, Huayong; Bakun-Czubarow, Nonna; Wu, Chuanjun; Konečný, Patrik; Hollings, Peter

    2015-02-01

    New monazite chemical U-Th-total-Pb (CHIME) ages, combined with microstructural observations, mineral compositions, and whole-rock geochemistry, indicate that the large-scale, banded iron formation (BIF)-type Shilu Fe-Co-Cu ore district in Hainan Province, South China is a multistage product of sedimentation, metamorphism, and hydrothermal-metasomatic alteration associated with multiple orogenies. Two types of monazite, i.e. "polygenetic" and "metamorphic", were identified. The "polygenetic monazite" comprises a magmatic and/or metamorphic core surrounded by a metamorphic rim, and shows complex zoning. Breakdown corona structure, with a core of monazite surrounded by a mantle of fluorapatite, allanite, and/or epidote as concentric growth rings, is commonly observed. This type of monazite yielded three main CHIME-age peaks at ca. 980 Ma, ca. 880 Ma and ca. 450 Ma. The ages which range up to ca. 880 Ma for detrital cores, record a pre-deformational magmatic and/or metamorphic event(s), and is considered to be the depositional time-interval of the Shilu Group and interbedded BIFs in a marine, back-arc foreland basin likely due to the Grenvillian or South China Sibao orogeny. After deposition, the Shilu district was subjected to an orogenic event, which is recorded by the syndeformational metamorphic monazite with ca. 560-450 Ma population. Probably this event not only caused amphibolite facies metamorphism and associated regional foliation S1 but also enriched the original BIFs, and most likely corresponds to the "Pan-African" and/or the South China Caledonian orogeny. The post-deformational "metamorphic" monazite occurs mostly as inclusions in garnet and shows ca. 260 Ma age. It likely represents the Late Permian post-magmatic hydrothermal and related retrograde event(s) initiated by the Indosinian orogeny due to the closure of the Paleo-Tethys. The breakdown of monazite to secondary coronal mineral phases as well as the Fe-remobilization and associated skarnization

  17. National Geochronological Database

    USGS Publications Warehouse

    Revised by Sloan, Jan; Henry, Christopher D.; Hopkins, Melanie; Ludington, Steve; Original database by Zartman, Robert E.; Bush, Charles A.; Abston, Carl

    2003-01-01

    The National Geochronological Data Base (NGDB) was established by the United States Geological Survey (USGS) to collect and organize published isotopic (also known as radiometric) ages of rocks in the United States. The NGDB (originally known as the Radioactive Age Data Base, RADB) was started in 1974. A committee appointed by the Director of the USGS was given the mission to investigate the feasibility of compiling the published radiometric ages for the United States into a computerized data bank for ready access by the user community. A successful pilot program, which was conducted in 1975 and 1976 for the State of Wyoming, led to a decision to proceed with the compilation of the entire United States. For each dated rock sample reported in published literature, a record containing information on sample location, rock description, analytical data, age, interpretation, and literature citation was constructed and included in the NGDB. The NGDB was originally constructed and maintained on a mainframe computer, and later converted to a Helix Express relational database maintained on an Apple Macintosh desktop computer. The NGDB and a program to search the data files were published and distributed on Compact Disc-Read Only Memory (CD-ROM) in standard ISO 9660 format as USGS Digital Data Series DDS-14 (Zartman and others, 1995). As of May 1994, the NGDB consisted of more than 18,000 records containing over 30,000 individual ages, which is believed to represent approximately one-half the number of ages published for the United States through 1991. Because the organizational unit responsible for maintaining the database was abolished in 1996, and because we wanted to provide the data in more usable formats, we have reformatted the data, checked and edited the information in some records, and provided this online version of the NGDB. This report describes the changes made to the data and formats, and provides instructions for the use of the database in geographic

  18. A 30 Myr record of retrograde metamorphism and multiple generations of monazite and garnet in western MA revealed by coordinated LASS and EPMA

    NASA Astrophysics Data System (ADS)

    Peterman, E. M.; Burton, Z. F. M.; Rubel, J. N.; Snoeyenbos, D. R.; Kylander-Clark, A. R.

    2014-12-01

    Garnet-kyanite-cordierite pelitic schists with relict phosphatic garnets thought to record ultrahigh-pressure metamorphism (e.g., Snoeyenbos and Koziol, 2008) crop out along the western margin of the Goshen Dome in western Massachusetts. These schists contain monazite inclusions within Grt, Ky, Crd, Bt, Pl, Qz, and Chl. Compositional maps via EPMA-WDS show overgrowths on each monazite grain, indicating that each grain records multiple metamorphic events. We analyzed monazite in situ using laser-ablation split-stream (LASS) ICPMS to correlate the geochemical and age domains and to reconstruct the polyphase metamorphic history. We used WDS compositional maps of Y and Th, and ICPMS Gd/Yb ratios and U/Pb ages to define the timing of major garnet growth and breakdown processes, and melting and/or fluid-rich metamorphism. For example, decreasing Gd/Yb and high Y concentrations are consistent with garnet breakdown; highly variable Gd/Yb indicate melting and/or fluid-rich metamorphism (e.g., Stearns et al., 2013). The following cumulative histories are interpreted from two samples (B and G). In both samples, decreasing Gd/Yb in monazite suggest garnet breakdown from c. 398 to 387 Ma. Data from sample B (n = 644 analyses) indicate two additional phases of garnet growth: 382 to 377 Ma and 375 to 369 Ma (see figure). Data from sample G (n = 231 analyses) also indicate two additional phases of garnet growth: 387 to 381 Ma and 379 to 369 Ma. The final garnet growth event affecting both samples is marked by the most variable Gd/Yb ratios in monazite from all petrographic contexts and is consistent with melting or a fluid-rich metamorphic event. These data are most consistent with metamorphism during emplacement to crustal levels in the early Acadian, and a substantial overprint during the regional thermal maximum. This complex record can only be unraveled by collecting geochronologic and geochemical data in situ to preserve the petrographic context of each grain, thus

  19. Monazite U-Th-Pb EPMA and zircon U-Pb SIMS chronological constraints on the tectonic, metamorphic, and thermal events in the inner part of the Variscan orogen, example from the Sioule series, French Massif Central

    NASA Astrophysics Data System (ADS)

    Do Couto, Damien; Faure, Michel; Augier, Romain; Cocherie, Alain; Rossi, Philippe; Li, Xian-Hua; Lin, Wei

    2016-03-01

    In the northern Variscan French Massif Central, the Sioule metamorphic series exposes from top to bottom the tectonic superposition of the Upper Gneiss Unit (UGU), Lower Gneiss Unit (LGU), and Para-autochthonous Unit (PAU). The nappe stacking developed throughout two prograde syn-metamorphic events: D1 is a top-to-the-SW shearing coeval with a probable Devonian migmatization and D2 is a top-to-the-NW shearing event. Both events were completed before the unconformable deposition of the undeformed and unmetamorphosed "Tufs anthracifères" formation, dated at ca 330 Ma (Late Visean). Furthermore, the UGU experienced a high-pressure metamorphism ascribed to a D0 event during which eclogite or granulite crystallized in several parts of the UGU. Monazite U-Th-Pb and zircon U-Pb SIMS datings were carried out in order to constrain the ages of these D0, D1, and D2 tectono-metamorphic events. These new geochronological results are placed in a P-T-t diagram constructed for the UGU, LGU, and PAU. Monazite sampled in UGU, LGU, and PAU rocks yields similar 365-350 Ma ages consistent with the D2 event dated in other places of the French Massif Central. A zoned monazite grain from a granulitic paragneiss yields 416 ± 15 and 362 ± 14 Ma ages interpreted as those of the D0 and D2 events, respectively. Zircon from the same granulitic paragneiss yields SIMS ages at 343 ± 2 and 328 ± 2 Ma that are interpreted as recrystallization processes associated with post-thickening thermal events, possibly recording the onset of orogenic collapse of the Northern Massif Central. It is worth to note that neither monazite nor zircon recorded the D1 event.

  20. Behaviour of apatite during partial melting of metapelites and consequences for prograde suprasolidus monazite growth

    NASA Astrophysics Data System (ADS)

    Yakymchuk, Chris

    2017-03-01

    The suprasolidus behaviour of apatite and monazite is examined for an average metapelite composition using phase equilibria modelling coupled with solubility equations of these minerals. Both closed- and open-system scenarios are considered. Partial melting above the solidus requires apatite and monazite breakdown in order to saturate the anatectic melt in phosphorus and the light rare earth elements. In general, melt loss is predicted to increase the stability of apatite and monazite at high temperature. Most apatite is predicted to survive up to ultrahigh temperature conditions except for rocks with low bulk phosphorus concentrations. By contrast, most monazite is expected to be consumed by UHT conditions. Thorium substitution in monazite is expected to increase the stability of monazite to higher temperatures. The presence of LREE-rich apatite decreases the stability of monazite above the solidus, but the breakdown of this apatite during anatexis may generate prograde monazite at the apatite-melt interface in local pockets of melt oversaturation. However, prograde suprasolidus monazite along grain boundaries is expected to be consumed during further partial melting or during melt homogenization when an interconnected melt network develops. Anatectic melts are predicted to be saturated with respect to apatite except at UHT conditions and for rocks with low initial P2O5 bulk concentrations.

  1. Origins of organic geochemistry

    USGS Publications Warehouse

    Kvenvolden, K.A.

    2008-01-01

    When organic geochemistry actually began as a recognized geoscience is a matter of definition and perspective. Constraints on its beginning are placed by the historical development of its parent disciplines, geology and organic chemistry. These disciplines originated independently and developed in parallel, starting in the latter half of the 18th century and flourishing thereafter into the 21st century. Organic geochemistry began sometime between 1860 and 1983; I argue that 1930 is the best year to mark its origin.

  2. Thermodynamic studies on charge-coupled substituted synthetic monazite

    NASA Astrophysics Data System (ADS)

    Rawat, D.; Phapale, S.; Mishra, R.; Dash, S.

    2017-04-01

    Phosphate-based monazite ceramic is considered worldwide as a potential crystalline host matrix for immobilization of long-lived tri- and tetra-valent actinides present in high-level nuclear waste. Monazite is chemically stable with respect to the leaching processes and has high radiation stability. The present paper describes the influence of charged coupled (Ca2+, Th4+) substitution in place of La3+ on thermodynamic stability of synthetic monazite ceramics. XRD-analysis of Ca, Th substituted LaPO4 viz., La1-xCax/2Thx/2PO4 (0 ≤ x ≤ 1) points to the formation of ideal solid-solution in the entire range of composition. However, thermodynamic analysis indicates deviation from ideal solid-solution with a minima at x = 0.25. The substituted La1-xCax/2Thx/2PO4 system is found to be iso-entropic and stabilized mainly by enthalpy. Enthalpies of formation as a function of Ca2+, Th4+ substitution were analysed to provide insights into the development of thermodynamically stable nuclear waste matrix.

  3. U-Th-PbT Monazite Gechronology in the South Carpathian Basement: Variscan Syn-Metamorphic Tectonic Stacking and Long-Lasting Post-Peak Decompressional Overprints

    NASA Astrophysics Data System (ADS)

    Săbău, G.; Negulescu, E.

    2012-12-01

    Dating metamorphic events appears to be unsatisfactorily addressed by most of the widely-employed and otherwise accurate and productive isotopic techniques, because the phases and systems investigated do not directly relate to the metamorphic events themselves. An adequate answer to this challenge is instead provided by microprobe-assisted chemical U-Th-PbT monazite geochronology, by its spatial resolution, truly in situ character and the possibility to reference analyses against well-defined textural environments and features, as well as a qualitative timeframe derived therefrom. Though chemical U-Th-PbT monazite geochronology is increasingly applied to seek answers ranging form a general characterization to fine details of the thermotectonic evolution of magmatic and metamorphic rocks, there are so far, unlike in the case of isotopic geochronological methods, no clearly defined standard analytical and data processing protocols. Two main reasons for this have to be mentioned, namely that chemical U-Th-PbT chronology is actually a proxy for isotopic geochronology, and the quantification of the errors and their propagation cannot be directly assessed because apparent ages are related to the measured element concentrations by an implicit function, the law of radioactive decay. Current approaches rely on treating calculated individual age values as primary data, a priori grouping of analyses supposed (and subsequently tested) to be coeval, and their statistical processing in order to obtain age values. An alternative approach we applied in basement units of the South Carpathians consists in an explicit approximation of the age formula and associated errors propagated from element concentrations to age values, and individual treatment of each age datum. The separation of the age clusters from the overall age spectrum of each sample was operated by tracing the variations of the normalized age gradient on the age spectrum sorted by increasing age values, and fine

  4. "SHRIMP geochronology for the 1450 Ma Lakhna dyke swarm: Its implication for the presence of Eoarchaean crust in the Bastar Craton and 1450-517 Ma depositional age for Purana basin (Khariar), Eastern Indian Peninsula": Comment

    NASA Astrophysics Data System (ADS)

    Basu, Abhijit; Bickford, M. E.

    2011-11-01

    As critical comments to the recent paper by Ratre et al. (2010, Journal of Asian Earth Sciences 39, 565-577) we cite U-Pb SHRIMP and CHIME ages of magmatic and detrital zircon and monazite from the Chhattisgarh and the Khariar basins in the Bastar craton to argue that these basins closed ca. 1000 Ma. We further argue that geochronologic data, geological evidence, and geological logic strongly indicate that sedimentation in the Khariar basin did not continue up to or beyond 517 Ma, as stated by Ratre et al. (op. cit).

  5. Monazite chemical age and composition correlations, an insight in the Palaeozoic evolution of the Leaota Massif, South Carpathians

    NASA Astrophysics Data System (ADS)

    Săbău, Gavril; Negulescu, Elena

    2015-04-01

    Notwithstanding remarkable advantages of monazite microprobe U-Th-PbT geochronology of metamorphic formations, such as the direct investigation of a metamorphic mineral in a truly in situ setting, unequalled spatial resolution, and cost-effective analyses, it essentially remains affected by indeterminations as regards the accuracy and the representativity of the results. Besides the experimental hurdles related to trace element analyses with the microprobe (sensitivity, background and overlap effects) the method faces two main biases, firstly its inherently blind status emerging from the aprioric assumption of isotopic equilibrium, and secondly the marked susceptibility of monazite to fluid-stimulated chemical recrystallization and compositional resetting (e. g. Kelly et al. 2012). Age spectra obtained from individual sampled habitually display a significant scatter of calculated age data, in such a way that the separation of coherent and geologically relevant populations may often represent a substantial challenge. The interpretation of the results greatly benefits from the qualitative analysis of the textural and paragenetic setting or a trial-and error quantitative statistical assessment of distinct age clusters (Montel et al., 1996), though still maintaining a variable degree of subjectivity, as in any interpretative process not fully sustained by quantitative analysis. Additional dependable support can be gained from further qualitative parameters characterizing, besides the distribution of individual age data, also the global chemical composition of the analysed monazite grains, as well as the relationship to the corresponding metamorphic assemblages (Săbău & Negulescu, 2013). The quantitative assessment of the age patterns of individual samples can be achieved by plotting the normalized age gradient from the sorted age pattern, allowing distinction of quasi-gaussian distribution domains likely to correspond to coherent age clusters of geologic significance

  6. Radioactive Dating: A Method for Geochronology.

    ERIC Educational Resources Information Center

    Rowe, M. W.

    1985-01-01

    Gives historical background on the discovery of natural radiation and discusses various techniques for using knowledge of radiochemistry in geochronological studies. Indicates that of these radioactive techniques, Potassium-40/Argon-40 dating is used most often. (JN)

  7. Formation of monazite via prograde metamorphic reactions among common silicates: implications for age determinations

    NASA Astrophysics Data System (ADS)

    Kohn, Matthew J.; Malloy, Margaret A.

    2004-01-01

    Three lines of evidence from schists of the Great Smoky Mountains, NC, indicate that isogradic monazite growth occurred at the staurolite-in isograd at ˜600°C: (1) Monazite is virtually absent below the staurolite-in isograd, but is ubiquitous (several hundred grains per thin section) in staurolite- and kyanite-grade rocks. (2) Many monazite grains are spatially associated with biotite coronas around garnets, formed via the reaction Garnet + Chlorite + Muscovite = Biotite + Plagioclase + Staurolite + H 2O. (3) Garnets contain high-Y annuli that result from prograde dissolution of garnet via the staurolite-in reaction, followed by regrowth, and rare monazite inclusions occur immediately outside the annulus and in the matrix, but not in the garnet core. Larger monazite grains also exhibit quasi-continuous Th zoning with high Th cores and low Th rims, consistent with monazite growth via a single reaction and fractional crystallization during prograde growth. Common silicates may host sufficient P and LREEs that reactions among them can produce observable LREE phosphate. Specifically phosphorus contents of garnet and plagioclase are hundreds of parts per million, and dissolution of garnet and recrystallization of plagioclase could form thousands of phosphate grains several micrometers in diameter per thin section. LREEs may be more limiting, but sheet silicates and plagioclase can contain tens to ˜100 (?) ppm LREE, so recrystallization of these silicates to lower LREE contents could produce hundreds of grains of monazite per thin section. Monazite ages, determined via electron and ion microprobes, are ˜400 Ma, directly linking prograde Barrovian metamorphism of the Western Blue Ridge with the "Acadian" orogeny, in contrast to previous interpretations that metamorphism was "Taconian" (˜450 Ma). Interpretation of ages from metamorphic monazite grains will require prior chemical characterization and identification of relevant monazite-forming reactions, including

  8. Constraints on the timing of Co-Cu ± Au mineralization in the Blackbird district, Idaho, using SHRIMP U-Pb ages of monazite and xenotime plus zircon ages of related Mesoproterozoic orthogneisses and metasedimentary rocks

    USGS Publications Warehouse

    Aleinikoff, John N.; Slack, John F.; Lund, Karen; Evans, Karl V.; Fanning, C. Mark; Mazdab, Frank K.; Wooden, Joseph L.; Pillers, Renee M.

    2012-01-01

    The Blackbird district, east-central Idaho, contains the largest known Co reserves in the United States. The origin of strata-hosted Co-Cu ± Au mineralization at Blackbird has been a matter of controversy for decades. In order to differentiate among possible genetic models for the deposits, including various combinations of volcanic, sedimentary, magmatic, and metamorphic processes, we used U-Pb geochronology of xenotime, monazite, and zircon to establish time constraints for ore formation. New age data reported here were obtained using sensitive high resolution ion microprobe (SHRIMP) microanalysis of (1) detrital zircons from a sample of Mesoproterozoic siliciclastic metasedimentary country rock in the Blackbird district, (2) igneous zircons from Mesoproterozoic intrusions, and (3) xenotime and monazite from the Merle and Sunshine prospects at Blackbird. Detrital zircon from metasandstone of the biotite phyllite-schist unit has ages mostly in the range of 1900 to 1600 Ma, plus a few Neoarchean and Paleoproterozoic grains. Age data for the six youngest grains form a coherent group at 1409 ± 10 Ma, regarded as the maximum age of deposition of metasedimentary country rocks of the central structural domain. Igneous zircons from nine samples of megacrystic granite, granite augen gneiss, and granodiorite augen gneiss that crop out north and east of the Blackbird district yield ages between 1383 ± 4 and 1359 ± 7 Ma. Emplacement of the Big Deer Creek megacrystic granite (1377 ± 4 Ma), structurally juxtaposed with host rocks in the Late Cretaceous ca. 5 km north of Blackbird, may have been involved in initial deposition of rare earth elements (REE) minerals and, possibly, sulfides. In situ SHRIMP ages of xenotime and monazite in Co-rich samples from the Merle and Sunshine prospects, plus backscattered electron imagery and SHRIMP analyses of trace elements, indicate a complex sequence of Mesoproterozoic and Cretaceous events. On the basis of textural relationships

  9. Monazite-type SrCr O4 under compression

    NASA Astrophysics Data System (ADS)

    Gleissner, J.; Errandonea, D.; Segura, A.; Pellicer-Porres, J.; Hakeem, M. A.; Proctor, J. E.; Raju, S. V.; Kumar, R. S.; Rodríguez-Hernández, P.; Muñoz, A.; Lopez-Moreno, S.; Bettinelli, M.

    2016-10-01

    We report a high-pressure study of monoclinic monazite-type SrCr O4 up to 26 GPa. Therein we combined x-ray diffraction, Raman, and optical-absorption measurements with ab initio calculations, to find a pressure-induced structural phase transition of SrCr O4 near 8-9 GPa. Evidence of a second phase transition was observed at 10-13 GPa. The crystal structures of the high-pressure phases were assigned to the tetragonal scheelite-type and monoclinic AgMn O4 -type structures. Both transitions produce drastic changes in the electronic band gap and phonon spectrum of SrCr O4 . We determined the pressure evolution of the band gap for the low- and high-pressure phases as well as the frequencies and pressure dependencies of the Raman-active modes. In all three phases most Raman modes harden under compression, however the presence of low-frequency modes which gradually soften is also detected. In monazite-type SrCr O4 , the band gap blueshifts under compression, but the transition to the scheelite phase causes an abrupt decrease of the band gap in SrCr O4 . Calculations showed good agreement with experiments and were used to better understand the experimental results. From x-ray-diffraction studies and calculations we determined the pressure dependence of the unit-cell parameters of the different phases and their ambient-temperature equations of state. The results are compared with the high-pressure behavior of other monazites, in particular PbCr O4 . A comparison of the high-pressure behavior of the electronic properties of SrCr O4 (SrW O4 ) and PbCr O4 (PbWO4) will also be made. Finally, the possible occurrence of a third structural phase transition is discussed.

  10. Monazite-type SrCrO4 under compression

    DOE PAGES

    Gleissner, J.; Errandonea, Daniel; Segura, A.; ...

    2016-10-20

    We report a high-pressure study of monoclinic monazite-type SrCrO4 up to 26 GPa. Therein we combined x-ray diffraction, Raman, and optical-absorption measurements with ab initio calculations, to find a pressure-induced structural phase transition of SrCrO4 near 8-9 GPa. Evidence of a second phase transition was observed at 10-13 GPa. The crystal structures of the high-pressure phases were assigned to the tetragonal scheelite-type and monoclinic AgMnO4-type structures. Both transitions produce drastic changes in the electronic band gap and phonon spectrum of SrCrO4. We determined the pressure evolution of the band gap for the low- and high-pressure phases as well as themore » frequencies and pressure dependencies of the Raman-active modes. In all three phases most Raman modes harden under compression, however the presence of low-frequency modes which gradually soften is also detected. In monazite-type SrCrO4, the band gap blueshifts under compression, but the transition to the scheelite phase causes an abrupt decrease of the band gap in SrCrO4. Calculations showed good agreement with experiments and were used to better understand the experimental results. From x-ray-diffraction studies and calculations we determined the pressure dependence of the unit-cell parameters of the different phases and their ambient-temperature equations of state. The results are compared with the high-pressure behavior of other monazites, in particular PbCrO4. A comparison of the high-pressure behavior of the electronic properties of SrCrO4 (SrWO4) and PbCrO4 (PbWO4) will also be made. Lastly, the possible occurrence of a third structural phase transition is discussed.« less

  11. Assembling and disassembling california: A zircon and monazite geochronologic framework for proterozoic crustal evolution in southern California

    USGS Publications Warehouse

    Barth, A.P.; Wooden, J.L.; Coleman, D.S.; Vogel, M.B.

    2009-01-01

    The Mojave province in southern California preserves a comparatively complete record of assembly, postorogenic sedimentation, and rifting along the southwestern North American continental margin. The oldest exposed rocks are metasedimentary gneisses and amphibolite, enclosing intrusive suites that range from tonalite and quartz mon-zodiorite to granite with minor trondhjemite. Discrete magmatic episodes occurred at approximately 1790-1730 and 1690-1640 Ma. Evidence from detrital and premagmatic zircons indicates that recycling of 1900-1790 Ma Paleopro-terozoic crust formed the unique isotopic character of the Mojave province. Peak metamorphic conditions in the Mojave province reached middle amphibolite to granulite facies; metamorphism occurred locally from 1795 to 1640 Ma, with widespread evidence for metamorphism at 1711-1689 and 1670-1650 Ma. Structures record early, tight to isoclinal folding and penetrative west-vergent shear during the final metamorphic event in the west Mojave province. Proterozoic basement rocks are overlain by siliciclastic-carbonate sequences of Mesoproterozoic, Neoproterozoic, and Cambrian age, recording environmental change over the course of the transition from stable Mojave crust to the rifted Cordilleran margin. Neoproterozoic quartzites have diverse zircon populations inconsistent with a southwest North American source, which we infer were derived from the western conjugate rift pair within Rodinia, before establishment of the miogeocline. Neoproterozoic-Cambrian miogeoclinal clastic rocks record an end to rifting and establishment of the Cordilleran miogeocline in southern California by latest Neoproterozoic to Early Cambrian time. ?? 2009 by The University of Chicago.

  12. Chemical distribution of hazardous natural radionuclides during monazite mineral processing.

    PubMed

    Hamed, Mostafa M; Hilal, M A; Borai, E H

    2016-10-01

    It is very important to calculate the radioactivity concentration for low-grade monazite ore (50%) and different other materials produced as results of chemical processing stages to avoid the risk to workers. Chemical processing of low-grade monazite pass through different stages, washing by hydrochloric acid and digested with sulfuric acid and influence of pH on the precipitation of rare earth elements has been studied. The radioactivity concentrations of (238)U((226)Ra) and (232)Th as well as (40)K were calculated in crude low-grade ore and found to be 54,435 ± 3138, 442,105 ± 29,200 and 5841 ± 345 Bq/kg, respectively. These values are greatly higher than the exempt levels 25 Bq/kg. After chemical digestion of the ore, the results demonstrated that un-reacted material contains significant radioactivity reached to approximately 8, 13 and 23% for (238)U, (232)Th and (40)K, respectively. The results show that 60% of (232)Th are located in the digested white slurry with small portions of (238)U and (40)K. Most of (238)U radioactivity is extracted in the green phosphoric acid which produced from conversion of P2O5 by H2SO4 into phosphoric acid. The average values of the Raeq for monazite ore, un-reacted black precipitate, white precipitate, brown precipitate and crystalline material samples were calculated and found to be 687,095 ± 44,921, 85,068 ± 5339, 388,381 ± 22,088, 313,046 ± 17,923 and 4531 ± 338 Bq/kg, respectively. The calculated values of Raeq are higher than the average world value (it must be less than 370 Bq/kg). Finally the external hazardous, internal hazardous and Iγr must be less than unity. This means that specific radiation protection program must be applied and implemented during monazite processing.

  13. New geochronological history of the Mbuji-Mayi Supergroup (Proterozoic, DRC) through U-Pb and Sm-Nd dating

    NASA Astrophysics Data System (ADS)

    François, Camille; Baludikay, Blaise K.; Storme, Jean-Yves; Baudet, Daniel; Paquette, Jean-Louis; Fialin, Michel; Debaille, Vinciane; Javaux, Emmanuelle J.

    2016-04-01

    The Mbuji-Mayi Supergroup, DRC is located between the Archean-Paleoproterozoic Kasai Craton and the Mesoproterozoic Kibaran Belt. This sedimentary sequence, unaffected by regional metamorphism, preserves a large diversity of well-preserved acritarchs (organic-walled microfossils), evidencing the diversification of complex life (early eukaryotes) for the first time in mid-Proterozoic redox stratified oceans of Central Africa (Baludikay et al., in review). This Supergroup is composed of two distinct lithostratigraphic successions (i) BI Group: a lower siliciclastic sequence (ca. 1175 Myr to ca. 882 Myr or ca. 1050 Myr (Cahen, 1954; Holmes & Cahen, 1955; Delpomdor et al., 2013) unconformably overlying the ca. 2.82-2.56 Gyr granitoid Dibaya Complex to the North (Cahen & Snelling; recent notice on DRC geological map); and (ii) BII Group: a poorly age-constrained upper carbonate sequence with sparse shales . Basaltic lavas (including pillow lavas) overlying the Mbuji-Mayi Supergroup were dated around 950 Myr (Cahen et al., 1974; Cahen et al., 1984). To better constraint the age of this Supergroup in the Meso-Neoproterozoic limit, we combine different geochronological methods, in particular on diagenetic minerals such as monazite (Montel et al., 1996; Rasmussen & Muhling, 2007) and xenotime (McNaughton et al., 1999) but also on detrital zircons. For the BI Group, results of in situ U-Pb dating with LA-ICP-MS on monazite, xenotime and zircon (Laboratoire Magmas et Volcans, Clermont-Ferrand) provide ages between 2.9 and 1.2 Gyr for zircons and between 1.4 and 1.03 Gyr for monazites and xenotimes. New results of in situ U-Th-Pb dating of well-crystallized monazites and xenotimes with Electron MicroProbe (Camparis, UPMC, Paris), highlight that some crystals display zonations with an inherited core older than 1125 Myr and diagenetic rims around 1050-1075 Myr. This suggests that the diagenesis of BI Group is younger than 1175 Myr (Delpomdor et al., 2013) and probably around

  14. Polymetamorphic evolution of the upper part of the Iezer Complex (Leaota Massif, South Carpathians) constrained by petrological data and monazite ages

    NASA Astrophysics Data System (ADS)

    Negulescu, Elena; Săbău, Gavril; Massonne, Hans-Joachim

    2015-04-01

    The Leaota Massif in Romania consists of a flat-lying sequence of five structurally concordant units displaying mutual and partly internal lithologic and metamorphic contrasts. The lower part of the lithologic sequence is the Iezer Complex, a medium-grade psammopelitic unit with a structurally concordant thin granite sill located at its upper part. The lower limit of the granite is marked discontinuously by hornfels, also present as enclaves, which experienced intense strain and a subsequent low-pressure thermal overprint. Both granite and hornfels were affected by a medium-temperature, medium- to high-pressure event (Săbău, 2000). This event was also identified in gneisses below the hornfels. These rocks contain the assemblage garnet-phengite-chloritoid-kyanite which had overprinted an older garnet-kyanite-staurolite-biotite-muscovite assemblage. Available U-Th zircon ages indicate 472.7 ± 7.3 Ma (Balintoni et al. 2009) for the granite. Monazite geochronology (Săbău & Negulescu, 2013) reveals for the associated hornfels (1) inherited ages of 528 ± 17.86 Ma overprinted by pervasive Ordovician contact metamorphism (462 ± 4.54 Ma), slightly postdating the age of magmatic zircon in the granite, (2) Silurian to Early Devonian recrystallization episodes, and (3) a Variscan medium- to high-pressure metamorphic overprint responsible for the garnet-phengite-kyanite assemblage. New petrological and geochronological data constraining the polymetamorphic evolution of the upper part of the Iezer Complex were acquired from kyanite-garnet mylonitic gneisses made up of large garnet porphyroclasts embedded in a strongly deformed matrix. Large garnets are rich in quartz, phengite, epidote, kyanite, rutile, and ilmenite inclusions. Biotite, chlorite, apatite, monazite, and Al-cerite inclusions are also present. Garnet porphyroclasts are wrapped by laminae of small garnet - white mica - biotite - quartz or zoisite - kyanite - plagioclase alternating with bands made up of fine

  15. Timing of Deformation in the Central Metasedimentary Belt Boundary Thrust Zone (CMBbtz), southern Ontario, Canada, from Electron Microprobe Dating of Monazite

    NASA Astrophysics Data System (ADS)

    Markley, M. J.; Dunn, S. R.; Peck, W. H.; Jercinovic, M. J.; Williams, M. L.

    2015-12-01

    In the Grenville Province of Southern Ontario, the Central Metasedimentary Belt boundary thrust zone (CMBbtz) is a crustal-scale tectonic boundary between the older, granulite-facies Central Gneiss Belt to the NW and the younger, amphibolite-facies Central Metasedimentary Belt to the SE. Although there are a range of tectonic models for the CMBbtz, most workers agree it is a major tectonic boundary that accommodated ductile thrusting and crustal shortening during the Ottawan phase of the Grenville Orogeny (~1080-1020 Ma). Some studies suggest that ductile thrusting in the CMBbtz was roughly synchronous with synorogenic extensional collapse below an orogenic lid. Previous geochronological studies also provide evidence of earlier deformation and/or metamorphic events in the CMBbtz, although the relation between deformation in the CMBbtz to the Elzeviran (~1230 Ma) and Shawinigan (~1180 Ma) orogenies is unclear. Our study is the first to report in situ electron microprobe monazite (mnz) dates from amphibolite-grade ortho- and para-gneisses of the CMBbtz. Our results are broadly consistent with other chronometers. We present dates from 132 age-domains within 83 mnz grains in 14 samples. Although our data provide strong evidence for deformation and metamorphism along the length of the CMBbtz during the Ottawan (1080-1020 Ma), we also report two other clusters of ages: 1140-1110 Ma and 1230-1170 Ma. The latter cluster falls between the widely accepted ranges for the Elzeviran and Shawinigan orogenies. In addition, some individual outcrops, particularly those in Killaloe and Minden, show mnz ages spanning over 200 m.y., and the setting and compositions of individual monazite domains allow us to link mnz growth to episodes of garnet growth during multiple events. Together these data indicate an unexpectedly continuous and long-lived period of deformation and metamorphism in the CMBbtz.

  16. Sulfate incorporation in monazite lattice: potential for dating the cycle of sulfur in metamorphic belts

    NASA Astrophysics Data System (ADS)

    Laurent, Antonin; Seydoux-Guillaume, Anne-Magali; Duchene, Stéphanie; Bingen, Bernard; Bosse, Valérie

    2016-04-01

    Monazite is a common accessory mineral in magmatic and metamorphic rocks that often shows complex chemical zoning at the μm- to nm-scale. The large number of cations that may be accommodated in its lattice, makes monazite particularly responsive to changes in the rock-forming minerals and fluid composition. Chemical zoning resulting from replacement or overgrowth may coincide, or not, with age zoning derived from U-Th-Pb isotopes. In this study, we focus on the potential for monazite to record both the redox condition of its crystalizing medium and an absolute U-Th-Pb isotopic age, during polyphase metamorphism in the Proterozoic province of Rogaland, S. Norway. The metamorphic evolution of several samples is derived from phase diagrams and the oxygen fugacity estimated from the FeO/Fe2O3 ratio measured by titration. Monazite grains were mapped at high spatial resolution for minor elements with electron microprobe, revealing convolute chemical zoning. Some of these zones yield appreciable content of S (up to 7000 ppm), accommodated following the Ca2+ + S6+ = REE3+ + P5+ substitution vector. The incorporation of sulfate in monazite has been subsequently investigated by TEM thanks to site specific FIB preparations. Besides, LA-ICP-MS U-Pb isotopic ages of monazite grains show a remarkable correlation with the sulfate content. It is therefore possible to distinguish different generations of monazite based on their S-content. From our petrological study we conclude that sulfate-bearing monazite reflects incongruent melting of Fe-Cu-As sulfides under oxidizing conditions, coeval with biotite dehydration melting. Monazite may therefore be used to probe the presence of sulfur in anatectic melts from high-grade terrains at a specific point in time. This property can be used to investigate the mineralization potential of a given geological event within a larger orogenic framework.

  17. Dating rock deformation with monazite: The impact of dissolution precipitation creep

    NASA Astrophysics Data System (ADS)

    Wawrzenitz, Nicole; Krohe, Alexander; Rhede, Dieter; Romer, Rolf L.

    2012-03-01

    The U-Th-Pb system of monazite behaves differently dependent on the deformation mechanism - dissolution precipitation creep (DPC) or dislocation creep - activated in the hosting metamorphic rocks. This can be exploited to use monazite for dating deformation, as is shown in rocks subsequently deformed by dislocation creep and DPC. In rock layers intensely deformed by DPC, mineral reactions, particularly the dissolution of feldspar and apatite increased the alkali-content and reactivity of the fluid. This in turn led to dissolution of old predeformative monazite grains. New synmetamorphic monazite grains formed as the result of inter-grain transport of material over distances within the grain-scale. This process efficiently led to complete resetting of the monazite U-Th-Pb system, even at temperatures prevailing during greenschist facies conditions. The chemical composition of the new monazite records the dissolution of the old feldspar by a less pronounced negative Eu anomaly compared to old monazite. The shape of the monazite grains that precipitated during creep indicates the sense of shear in the shear zone, thus linking the obtained ages directly to the map-scale tectonic transport. In rock layers predominantly deformed by dislocation creep, old monazite grains survived intense mylonitization and high strain, and show a core-rim structure. The cores are patchy, reflecting intra-grain, coupled dissolution-reprecipitation replacement processes. A wide range in apparent, geologically inaccurate Th/Pb and U/Pb ages among the patchy zones is the result of incomplete removal of in-situ grown radiogenic Pb from the patchy domains, depletion of Th and U and the redistribution of Th and U among the domains. Exclusively in the rims of the old monazite, the chemical composition correlates to that of the syndeformative monazites, and the U-Th-Pb system reflects the subsequent DPC. Accordingly, rocks pervasively deformed by DPC should be preferably used to obtain monazite

  18. Zircon and monazite response to prograde metamorphism in the Reynolds Range, central Australia

    NASA Astrophysics Data System (ADS)

    Rubatto, Daniela; Williams, Ian S.; Buick, Ian S.

    2001-01-01

    We report an extensive field-based study of zircon and monazite in the metamorphic sequence of the Reynolds Range (central Australia), where greenschist- to granulite-facies metamorphism is recorded over a continuous crustal section. Detailed cathodoluminescence and back-scattered electron imaging, supported by SHRIMP U-Pb dating, has revealed the different behaviours of zircon and monazite during metamorphism. Monazite first recorded regional metamorphic ages (1576 ± 5 Ma), at amphibolite-facies grade, at ˜600 °C. Abundant monazite yielding similar ages (1557 ± 2 to 1585 ± 3 Ma) is found at granulite-facies conditions in both partial melt segregations and restites. New zircon growth occurred between 1562 ± 4 and 1587 ± 4 Ma, but, in contrast to monazite, is only recorded in granulite-facies rocks where melt was present (≥700 °C). New zircon appears to form at the expense of pre-existing detrital and inherited cores, which are partly resorbed. The amount of metamorphic growth in both accessory minerals increases with temperature and metamorphic grade. However, new zircon growth is influenced by rock composition and driven by partial melting, factors that appear to have little effect on the formation of metamorphic monazite. The growth of these accessory phases in response to metamorphism extends over the 30 Ma period of melt crystallisation (1557-1587 Ma) in a stable high geothermal regime. Rare earth element patterns of zircon overgrowths in leucosome and restite indicate that, during the protracted metamorphism, melt-restite equilibrium was reached. Even in the extreme conditions of long-lasting high temperature (750-800 °C) metamorphism, Pb inheritance is widely preserved in the detrital zircon cores. A trace of inheritance is found in monazite, indicating that the closure temperature of the U-Pb system in relatively large monazite crystals can exceed 750-800 °C.

  19. Shocked monazite chronometry: integrating microstructural and in situ isotopic age data for determining precise impact ages

    NASA Astrophysics Data System (ADS)

    Erickson, Timmons M.; Timms, Nicholas E.; Kirkland, Christopher L.; Tohver, Eric; Cavosie, Aaron J.; Pearce, Mark A.; Reddy, Steven M.

    2017-03-01

    Monazite is a robust geochronometer and occurs in a wide range of rock types. Monazite also records shock deformation from meteorite impact but the effects of impact-related microstructures on the U-Th-Pb systematics remain poorly constrained. We have, therefore, analyzed shock-deformed monazite grains from the central uplift of the Vredefort impact structure, South Africa, and impact melt from the Araguainha impact structure, Brazil, using electron backscatter diffraction, electron microprobe elemental mapping, and secondary ion mass spectrometry (SIMS). Crystallographic orientation mapping of monazite grains from both impact structures reveals a similar combination of crystal-plastic deformation features, including shock twins, planar deformation bands and neoblasts. Shock twins were documented in up to four different orientations within individual monazite grains, occurring as compound and/or type one twins in (001), (100), ( 10bar{1} ), {110}, { 212 }, and type two (irrational) twin planes with rational shear directions in [0bar{1}bar{1}] and [bar{1}bar{1}0]. SIMS U-Th-Pb analyses of the plastically deformed parent domains reveal discordant age arrays, where discordance scales with increasing plastic strain. The correlation between discordance and strain is likely a result of the formation of fast diffusion pathways during the shock event. Neoblasts in granular monazite domains are strain-free, having grown during the impact events via consumption of strained parent grains. Neoblastic monazite from the Inlandsee leucogranofels at Vredefort records a 207Pb/206Pb age of 2010 ± 15 Ma (2 σ, n = 9), consistent with previous impact age estimates of 2020 Ma. Neoblastic monazite from Araguainha impact melt yield a Concordia age of 259 ± 5 Ma (2 σ, n = 7), which is consistent with previous impact age estimates of 255 ± 3 Ma. Our results demonstrate that targeting discrete microstructural domains in shocked monazite, as identified through orientation mapping, for in

  20. Variscan Collisional Magmatism and Deformation In The Viseu Area (northern Central Portugal) - Constraints From U-pb Geochronology of Granitoids

    NASA Astrophysics Data System (ADS)

    Azevedo, M. R.; Aguado, B. V.; Scaltegger, U.; Nolan, J.; Martins, M. R.; Medina, J.

    The Viseu area is located in the innermost zone of the Iberian Variscan Fold Belt (the Central Iberian Zone). It consists of abundant post-thickening, collision related grani- toids intruded into upper and middle crustal levels. The ascent of granite magmas took place after an extensional tectonic event (D2) and is coeval with D3 dextral and sinis- tral crustal-scale transcurrent shear zones. In the northern part of the area, the presence of a well preserved Upper Carboniferous tectonic basin filled with deformed conti- nental clastic sediments, bounded by contemporaneously exhumed deep crustal rocks and intruded by late-tectonic granites documents an episode of extension involving basin subsidence, uplift and erosion of the basement and granite magmatism in a post- thickening, but syn-convergent scenario. Convergence is manifested by strike-slip tec- tonics and basin inversion. According to structural criteria, the Variscan granitoids can be subdivided into two major groups: (1) syn-D3 granitoids including two dif- ferent petrological associations, highly peraluminous leucogranite and granodiorite- monzogranite intrusions and (2) late-D3 granitoids comprising slightly metaluminous to peraluminous granodiorites and monzogranites. Four plutons representing the syn- D3 leucogranites (Junqueira) and monzogranites (Maceira and Casal Vasco) and the late-D3 biotite granites (Cota) yielded U-Pb zircon + monazite or monazite ages of 310 Ma, 311 Ma, 311 Ma and 306 Ma, respectively. This points to a synchronous emplacement of the different syn-D3 plutons shortly followed by the intrusion of the late-D3 granites and suggests that the Upper Carboniferous plutonism occurred within a short time span of ca. 5 myr. Stratigraphic markers show that the oldest continental sediments in the Carboniferous basin are Westphalian whilst field relationships in- dicate that the deformation occurred prior to the intrusion of the late-D3 granitoids. Precise U-Pb geochronology proves that basin

  1. Monazite and allanite U-Th-Pb vs mica 39Ar-40Ar ages in equilibrated metasediments: closure behavior and closure temperatures

    NASA Astrophysics Data System (ADS)

    Allaz, J.; Engi, M.; Berger, A.; Janots, E.; Villa, I. M.

    2009-12-01

    The art of geochronology implies identification of processes, so as to correctly interpret an isotopic age as (1) crystallization, (2) cooling, or (3) meaningless owing to inheritance and/or late mineral recrystallization. We address here a field calibration of 39Ar-40Ar ages against U-Th-Pb ages. We demonstrate that detailed petrological, micro-textural and micro-chemical investigations are a necessary prerequisite for meaningful geochronology. The Barrovian metamorphism in the Alps results from the collision of Europe and Apulia and reaches its thermal maximum (upper amphibolite facies) in the Central Alps. Age estimates for the Alpine orogeny have long been controversial, despite a multitude of studies. Based on the resetting of Rb-Sr and K-Ar ages in muscovite from polymetamorphic gneisses, Jäger [1] had proposed an age of 38±2 Ma for the Barrovian metamorphism, corresponding to a “closure temperature TC” (following [2]) of 350 °C for K-Ar in muscovite. However, a uniform Eocene age for the metamorphism in the Central Alps was in conflict already with early monazite and xenotime U-Pb ages from the same area, namely 30 Ma in the southern, and ~20 Ma in the northern part (e.g. [3]). A recent study [4] both confirmed the young monazite ages in the north (SHRIMP U-Pb of 18-19 Ma near Tmax = 570 °C), and demonstrated that ca. 30 Ma ago this part of the belt was still heating up, as allanite grew prograde near 440 °C. These results once more prove isotopic inheritance, and therefore underestimation of mica K-Ar TC, in Jäger’s [1] samples. To avoid isotopic inheritance problems we selected only Mesozoic metasediments from the northern Central Alps. We screened all samples by PTAX: many had undergone a variety of retrogression reactions and calculations show petrological disequilibrium; we favored those in near-ideal petrological equilibrium. 39Ar-40Ar ages for mica separates from equilibrium samples yield ages between 18.93±0.83 and 15.79±0.11 Ma for

  2. The data of geochemistry

    USGS Publications Warehouse

    Clarke, Frank Wigglesworth

    1924-01-01

    Upon the subject of geochemistry a vast literature exists, but it is widely scattered and portions of it are difficult of access. The general treatises, like the classical works of Bischof and of Koth, are not recent, and great masses of modern data are as yet uncorrelated. The American material alone is singularly rich, but most of it has been accumulated since Roth's treatise was published. The science of chemistry, moreover, has undergone great changes during the last 25 years, and many subjects now appear under new and generally unfamiliar aspects. The methods and principles of physical chemistry are being more and more applied to the solution of geochemical problems,1 as is shown by the well-known researches of Van't Hoff upon the Stassfurt salts and the magmatic studies of Vogt, Doelter, and others. The great work in progress at the geophysical laboratory of the Carnegie Institution is another illustration of the change now taking place in geochemical investigation. To bring some of the data together, to formulate a few of the problems and to present certain general conclusions in their modern form are the purposes of this memoir. It is not an exhaustive monograph upon geochemistry, but rather a critical summary of what is now known, and a guide to the more important literature of the subject. If it does no more than to make existing data available to the reader, its preparation will be justified.

  3. Linking microstructures, petrology and in situ U-(Th)-Pb geochronology to constrain P-T-t-D evolution of the Greather Himalyan Sequences in Western Nepal (Central Himalaya)

    NASA Astrophysics Data System (ADS)

    Iaccarino, Salvatore; Montomoli, Chiara; Carosi, Rodolfo; Langone, Antonio

    2013-04-01

    Last advances in forward modelling of metamorphic rocks and into the understanding of accessories minerals behaviour, suitable for geochronology (e.g. zircon and monazite), during metamorphism, bring new insights for understanding the evolution of metamorphic tectonites during orogenic cycles (Williams and Jercinovic, 2012 and reference therein). One of the best exposure of high- to medium grade- metamorphic rocks, is represented by the Greater Himalayan Sequence (GHS) in the Himalayan Belt, one of the most classic example of collisional orogen. Recent field work in Mugu Karnali valley, Western Nepal (Central Himalaya), identified a compressional top to the South ductile shear zone within the core of the GHS, named Magri Shear Zone (MSZ), developed in a high temperature regime as testified by quartz microstructures and syn-kinematic growth of sillimanite. In order to infer the tectono-metamorphic meaning of MSZ, a microstructural study coupled with pseudosection modelling and in situ U-(Th)-Pb monazite geochronology was performed on selected samples from different structural positions. Footwall sample constituted by (Grt + St ± Ky) micaschist shows a prograde garnet growth (cores to inner rims zoning), from ~500°C, ~0.60GPa (close to garnet-in curve) to ~580°C, ~1.2 GPa temporal constrained between 21-18 Ma, by medium Y cores to very low Y mantles monazite micro-chemical/ages domain . In this sample garnet was still growing during decompression and heating at ~640°C, ~0.75 GPa (rims), and later starts to be consumed, in conjunction with staurolite growth at 15-13 Ma, as revealed by high Y rims monazite micro-chemical/ages domain. Hanging-wall mylonitic samples have a porphyroclastic texture, with garnet preserve little memory of prograde path. Garnet near rim isoplets and matrix minerals intersect at ~700°C and ~0.70 GPa. A previous higher P stage, at ~1.10 GPa ~600°C, is testified by cores of larger white mica porhyroclasts. Prograde zoned allanite (Janots

  4. Spectrochemical determination of thorium in monazite by the powder-d.c. arc technique

    USGS Publications Warehouse

    Dutra, C.V.; Murata, K.J.

    1954-01-01

    Thorium in monazite is determined by a d.c. carbon-arc technique using zirconium as the internal standard. The analytical curve for Th II 2870.413 A??/Zr II 2844-579 A?? is established by means of synthetic standards containing graduated amounts of thoria and 0.500 per cent zirconia in pegmatite base (60 parts quartz, 40 parts microchne, and 1 part ferric oxide). Monazite samples are diluted 14-fold with pegmatite base that contains 0.538 per cent ZrO2, so that the zirconia content of the resulting mixture is also 0.500 per cent. In addition, both the standards and the diluted monazites are mixed with one-half their weight of powdered graphite. Approximately 25 mg of the prepared samples are arced to completion at 15.5 to 17.5 amperes. With the 14-fold dilution employed, the accurate range of the method is 3 to 20 per cent thoria in the original monazite. The coefficient of variation for a single determination is 4 per cent at the 7 per cent thoria level. Tests with synthetic unknowns and chemically analyzed monazites show a maximum error of ??10 per cent of the thoria content. If niobium is substituted for zirconium as the internal standard, there is a loss of precision. Platinum as the internal standard gives results of good precision but introduces a marked sensitivity to matrix effects. ?? 1954.

  5. Age trends in garnet-hosted monazite inclusions from upper amphibolite facies schist in the northern Grouse Creek Mountains, Utah

    NASA Astrophysics Data System (ADS)

    Hoisch, Thomas D.; Wells, Michael L.; Grove, Marty

    2008-11-01

    We performed in situ Th-Pb dating of monazite in upper amphibolite facies pelitic schist from the Grouse Creek Mountains in northwest Utah. Sixty-six ages from inclusions in four garnet grains range from 37 to 72 Ma and decrease with radial distance from garnet cores. The age range of 30 matrix monazite grains overlaps and extends to younger ages than inclusions (25-58 Ma). The monazite grains are not intersected by cracks in the garnets, through which dissolution, reprecipitation or Pb loss might occur, and are generally too small (<20 μm) to allow for more than one age determination on any one grain. Processes that might explain inclusion ages that decrease with radial distance from garnet cores include: (1) Pb diffusion in monazite, (2) dissolution and reprecipitation of monazite, and (3) co-crystallization of monazite and garnet. After consideration of these possibilities, it is concluded that the co-crystallization of monazite and garnet is the most plausible, with monazite neoblasts deriving REE s from the breakdown of muscovite. Garnet ages derived by regression of the inclusion ages and assuming a constant rate of volume increase during garnet growth yield model ages with a maximum difference between core and rim of 22 m.y.

  6. In-situ Rb-Sr geochronology

    NASA Astrophysics Data System (ADS)

    Anderson, F. S.; Nowicki, K.; Whitaker, T.

    This paper reports on the first rubidium-strontium (Rb-Sr) radiometric dates using a Laser Desorption Resonance Ionization Mass Spectrometry (LDRIMS) instrument capable of being miniaturized for flight to another planet. The LDRIMS instrument produces dates in under 24 hours, requires minimal sample preparation, and avoids the interference and mass resolution issues associated with other geochronology measurements. We have begun testing the bench-top prototype on the Boulder Creek Granite (BCG), from Colorado, comprised primarily of a gneissic quartz monzonite and granodiorite; whole rock Rb-Sr TIMS measurements result in dates of 1700± 40 Ma [1]. Data reduction of the LDRIMS Rb-Sr measurements on calibrated repeat runs result in a date for the BCG of 1.727± 0.087 Ga (n=288, MSWD=1). Most geochronology applications are willing to accept an MSWD up to ~2.7; at MSWD=2, the precision improves to ± 0.062 Ga. This technology is moving from lab prototype to field deployable instrument, and provides an opportunity to directly address the science goals of Mars Sample Return (MSR) within the bounds posed by current scientific, fiscal, and political pressures on the Mars program. Additionally, LDRIMS could potentially be flown to the Moon under the Discovery or New Frontiers program. We posit that in-situ geochronology missions to Mars to triage and validate samples for Mars Sample Return (MSR) are technically feasible in the 2018-2022 time frame.

  7. Sulfide Mineralogy and Geochemistry

    NASA Astrophysics Data System (ADS)

    Dilles, John

    2007-02-01

    Reviews in Mineralogy and Geochemistry Series, Volume 61 David J. Vaughan, Editor Geochemical Society and Mineralogical Society of America; ISBN 0-939950-73-1 xiii + 714 pp.; 2006; $40. Sulfide minerals as a class represent important minor rock-forming minerals, but they are generally known as the chief sources of many economic metallic ores. In the past two decades, sulfide research has been extended to include important roles in environmental geology of sulfide weathering and resultant acid mine drainage, as well as in geomicrobiology in which bacteria make use of sulfides for metabolic energy sources. In the latter respect, sulfides played an important role in early evolution of life on Earth and in geochemical cycling of elements in the Earth's crust and hydrosphere.

  8. Disequilibrium Textures vs Equilibrium Modelling: Geochronology at the Crossroads

    NASA Astrophysics Data System (ADS)

    Villa, I. M.

    2007-12-01

    Observations made by electron microscopy show the processes affecting minerals at the atomic scale. The majority of reported analyses demonstrate chemical disequilibrium. A classic example are overgrowths of one mineral generation by a secondary one, which may be recognized on textural grounds. Disequilibrium recrystallization is promoted by water, which is everywhere on this planet (granites, contact aureoles, regional metamorphism, faults). It is mostly easier and energetically less costly to recrystallize a mineral at any temperature than to induce genuine volume diffusion in it. However, these observations are only relevant to geochronologists if chemical disequilibria are also accompanied by isotopic disequilibria. If a mineral mixture gives a mixed isotope record, then the interpretation of ages does not come cheap. If, on the contrary, diffusive reequilibration of the isotopic record is faster than that of chemical heterogeneities, then the petrology and microchemistry of a mineral could be ignored and its apparent age termed a "cooling age". First principle arguments and experimental data of the last decade concordantly show that the diffusivity of radiogenic isotopes is never higher than that of major elements forming the mineral structure. And indeed, end- member ages of mineral mixtures can be unravelled if the petrogenesis is understood. This was first shown by CL images of zircon grains (Gebauer et al, Schweiz Min Pet Mitt 68 (1988) 485-490). Similar progress was reported on monazite (Williams et al, Ann Rev Earth Planet Sci 35 (2007) 137-175), amphibole (Belluso et al, Eur J Mineral 12 (2000) 45-62), K-feldspar (Nyfeler et al, Schweiz Min Pet Mitt 78 (1998) 11-21), biotite (Villa et al, Water Rock Interaction 10 (2001) 1589-92). The mechanism for resetting the isotope record in nature thus seems more dependent on the availability of water to enhance disequilibrium recrystallization than on reaching a preset temperature. Intercomparison of laboratory

  9. Sulphate incorporation in monazite lattice and dating the cycle of sulphur in metamorphic belts

    NASA Astrophysics Data System (ADS)

    Laurent, Antonin T.; Seydoux-Guillaume, Anne-Magali; Duchene, Stéphanie; Bingen, Bernard; Bosse, Valérie; Datas, Lucien

    2016-11-01

    Microgeochemical data and transmission electron microscope (TEM) imaging of S-rich monazite crystals demonstrate that S has been incorporated in the lattice of monazite as a clino-anhydrite component via the following exchange Ca2+ + S6+ = REE3+ + P5+, and that it is now partly exsolved in nanoclusters (5-10 nm) of CaSO4. The sample, an osumilite-bearing ultra-high-temperature granulite from Rogaland, Norway, is characterized by complexly patchy zoned monazite crystals. Three chemical domains are distinguished as (1) a sulphate-rich core (0.45-0.72 wt% SO2, Th incorporated as cheralite component), (2) secondary sulphate-bearing domains (SO2 >0.05 wt%, partly clouded with solid inclusions), and (3) late S-free, Y-rich domains (0.8-2.5 wt% Y2O3, Th accommodated as the huttonite component). These three domains yield distinct isotopic U-Pb ages of 1034 ± 6, 1005 ± 7, and 935 ± 7 Ma, respectively. Uranium-Th-Pb EPMA dating independently confirms these ages. This study illustrates that it is possible to discriminate different generations of monazite based on their S contents. From the petrological context, we propose that sulphate-rich monazite reflects high-temperature Fe-sulphide breakdown under oxidizing conditions, coeval with biotite dehydration melting. Monazite may therefore reveal the presence of S in anatectic melts from high-grade terrains at a specific point in time and date S mobilization from a reduced to an oxidized state. This property can be used to investigate the mineralization potential of a given geological event within a larger orogenic framework.

  10. Geochronologic, Thermochronologic, and Thermobarometric Constraints on the Tectonic Evolution of the Northeastern Pamir

    NASA Astrophysics Data System (ADS)

    Robinson, A. C.; Yin, A.; Manning, C. E.; Harrison, T. M.; Hei, W.; Xiong, M. Y.; Feng, W. X.

    2001-12-01

    exhumation of the Kongur Shan (and Muztaghata) massifs along the Kongur normal fault. High grade metamorphism in the Kongur Shan massif due to tectonic burial is constrained to be ~ 9 Ma from in-situ SIMS monazite geochronology. A 10 Ma biotite 40Ar/39Ar age from two km west of the ductile shear zone is interpreted to roughly indicate the timing of initiation of normal faulting.

  11. Doming in compressional orogenic settings: New geochronological constraints from the NW Himalaya

    NASA Astrophysics Data System (ADS)

    Robyr, Martin; Hacker, Bradley R.; Mattinson, James M.

    2006-04-01

    In the central and southeastern parts of the Himalayas, the High Himalayan Crystalline (HHC) high-grade rocks are mainly exhumed in the frontal part of the range, as a consequence of a tectonic exhumation controlled by combined thrusting along the Main Central Thrust (MCT) and extension along the South Tibetan Detachment System (STDS). In the NW Himalaya, however, the hanging wall of the MCT in the frontal part of the range consists mainly of low- to medium-grade metasediments (Chamba zone), whereas most of the amphibolite facies to migmatitic gneisses of the HHC of Zanskar are exposed in a more internal part of the orogen as a large-scale dome structure referred to as the Gianbul dome. This Gianbul dome is cored by migmatitic paragneisses formed at peak conditions of 800°C and 8 kbar. This migmatitic core is symmetrically surrounded by rocks of the sillimanite, kyanite ± staurolite, garnet, biotite, and chlorite mineral zones. The structural data from the Miyar-Gianbul Valley section reveal that the Gianbul dome is bounded by two major converging thrust zones, the Miyar Thrust Zone and the Zanskar Thrust Zone, which were reactivated as ductile zones of extension referred to as the Khanjar Shear Zone (KSZ) and the Zanskar Shear Zone (ZSZ), respectively. Geochronological dating of monazites from various migmatites and leucogranite in the core of the Gianbul dome indicates ages between 26.6 and 19.8 Ma. These results likely reflect a high-temperature stage of the exhumation history of the HHC of Zanskar and consequently constrain the onset of extension along both the ZSZ and the KSZ to start shortly before 26.6 Ma. Several recent models interpret that ductile extrusion of the high-grade, low-viscosity migmatites of HHC reflects combined extension along the ZSZ and thrusting along the MCT. Hence our new data constrain the onset of the thrusting along the MCT to start shortly before 26.6 Ma.

  12. Geochronology, geochemistry, and tectonic environment of porphyry mineralization in the central Alaska Peninsula

    USGS Publications Warehouse

    Wilson, Frederic H.; Cox, Dennis P.

    1983-01-01

    Porphyry type sulfide systems on the central Alaska Peninsula occupy a transition zone between the Aleutian island magmatic arc and the continental magmatic arc of southern Alaska. Mineralization occurs associated with early and late Tertiary magmatic centers emplaced through a thick section of Mesozoic continental margin clastic sedimentary rocks. The systems are of the molybdenum-rich as opposed to gold-rich type and have anomalous tungsten, bismuth, and tin, attributes of continental-margin deposits, yet gravity data suggest that at least part of the study area is underlain by oceanic or transitional crust. Potassium-argon age determinations indicate a variable time span of up to 2 million years between emplacement and mineralization in a sulfide system with mineralization usually followed by postmineral intrusive events. Finally, mineralization in the study area occurred at many times during the time span of igneous activity and should be an expected stage in the history of a subduction related magmatic center.

  13. Geology, geochemistry, and geochronology of volcanic rocks between Cuauhtemoc and La Junta, central Chihahua, Mexico

    NASA Astrophysics Data System (ADS)

    Duex, T. W.

    The 1200 sq Km area straddles the boundary between the Sierra Madre Occidental and Basin and Range physiographic provinces and contains three north-northwest trending, block-faulted mountain ranges. The stratigraphy includes a 200 m thick sequence of ash-flow tuffs with subordinate mafic flows that either overlie or are interlayered with the ash-flow tuffs. This sequence overlies an approximately equal thickness of rhyolitic to dacitic flows and tuffs. At the base of the section occurs a distinctly different and thinner (about 50 m thick) sequence of flows, tuffs, and volcaniclastic sediments that is more nearly intermediate in average composition. In the northwest part of the area a Pb-Zn mine is found within a ridge of Lower Cretaceous limestone and shale that was intruded by a granitic stock. With the exception of thick ash-flow sheets, most units are localized and lenticular, precluding correlation of volcanic units between ranges. No large calderas were found although volcanic vents are suspected in several areas.

  14. The Jurassic-early Cretaceous Ilo batholith of southern coastal Peru: geology, geochronology and geochemistry

    NASA Astrophysics Data System (ADS)

    Boekhout, Flora; Sempere, Thierry; Spikings, Richard; Schaltegger, Urs

    2010-05-01

    The Ilo batholith (17°00 - 18°30 S) crops out in an area of about 20 by 100 km, along the coast of southern Peru. This batholith is emplaced into the ‘Chocolate‘ Formation of late Permian to middle Jurassic age, which consists of more than 1000 m of basaltic and andesitic lavas, with interbedded volcanic agglomerates and breccias. The Ilo Batholith is considered to be a rarely exposed fragment of the Jurassic arc in Peru. Our aim is to reconstruct the magmatic evolution of this batholith, and place it within the context of long-lasting magma genesis along the active Andean margin since the Paleozoic. Sampling for dating and geochemical analyses was carried out along several cross sections through the batholith that were exposed by post-intrusion eastward tilting of 20-30°. Sparse previous work postulates early to middle Jurassic and partially early Cretaceous emplacement, on the basis of conventional K/Ar and 40Ar/39Ar dating methods in the Ilo area. Twenty new U-Pb zircon ages (LA-ICP-MS and CA-ID-TIMS) accompanied by geochemical data suggests the Ilo batholith formed via the amalgamation of middle Jurassic and early Cretaceous, subduction-related plutons. Preliminary Hf isotope studies reveal a primitive mantle source for middle Jurassic intrusions. Additional Sr, Nd and Hf isotope analyses are planned to further resolve the source regions of different pulses of plutonic activity. We strongly suggest that batholith emplacement was at least partly coeval with the emplacement of the late Permian to middle Jurassic Chocolate Formation, which was deposited in an extensional tectonic regime. Our age results and geochemical signature fit into the scheme of episodic emplacement of huge amounts of subduction related magmatism that is observed throughout the whole Andean event, particularly during the middle Jurassic onset of the first Andean cycle (southern Peru, northern Chile and southern Argentina). Although the exact geodynamic setting remains to be precisely defined, these events can be linked to extensional episodes during the breakup of Pangea, which commenced at 230-220 Ma along the western South American margin, with a period of rifting, and culminated in the Jurassic with arc and back-arc extension.

  15. A Tale of Two Magma Series: Geochronology and Geochemistry of Volcanism on Grenada, Lesser Antilles

    NASA Astrophysics Data System (ADS)

    White, W. M.; Devine *Deceased, J. D.; Copeland, P.

    2015-12-01

    Volcanic rocks from Grenada have long been recognized to belong to two distinct magma series: the olivine microphyric M-series and the ankaramitic, calcium-rich C-series. Mafic members of both series are readily distinguished on the basis of both major and trace element compositions and radiogenic isotope ratios, with the M-series having more radiogenic Sr and Pb and less radiogenic Nd than the C-series. The two series evolve along distinct paths to compositionally and isotopically similar silica-rich hornblende andesites and dacites. We report 29 new 40Ar/39Ar dates ranging from 0.06 to 6.06 Ma, which are notably younger than previous K-Ar ages ranging up to 21 Ma, perhaps reflecting non-atmospheric inherited Ar. The two series have erupted contemporaneously and ages of both series tend to cluster in two periods: 0 to 1.7 Ma and 4.8 to 6 Ma. The oldest lavas are located in the northeastern and southwestern ends of the island. There is little or no systematic variation in chemistry with age. A dike intruding Tufton Hall Formation (THF) sediments in the south of the island is much older at 37.8 Ma; C-series isotope ratios correlate with MgO, which has previously been interpreted as a consequence of fractional crystallization and assimilation (AFC) of marine sediments. Isotope ratios of M-series lavas, in contrast, show no systematic variation with MgO. We agree that the C-series magmas have experienced AFC, but argue that the assimilant is simply the M-series products that makes up two-thirds of the mass of the island. A variety of evidence supports this interpretation. First, K2O/Na2O ratios decrease with decreasing MgO in the C-series. Second, the THF is volcanogenic likely derived from ancestral volcanoes and also are not a suitable isotopic end-member. Third, O isotope ratios in clinopyroxenes correlate with radiogenic isotope ratios, but not with MgO. Finally, the most differentiated C-series lavas are indistinguishable, isotopically and otherwise, from M-series compositions. Such auto-assimilation may be common in volcanic systems, and may affect the M-series as well, but only becomes apparent in cases such as this where magmas are compositionally distinct from the volcanic edifice they rise through.

  16. Geochronology, Geochemistry and Petrogenesis of the Intermediate and Acid Dykes in Linzhou Basin, Southern Tibet

    NASA Astrophysics Data System (ADS)

    Dong, M.; Zhao, Z.; Zhu, D. C.; Dong, G.; Mo, X.

    2015-12-01

    The Linzizong volcanic succession (also called Linzizong Group, ~65-45 Ma), which occurred in southern Gangdese magmatic belt in response to the collision processes between India and Eurasia continents, have been well studied in the Linzhou Basin, to the northeast of Lhasa. Our research obtains some new results of zircon U-Pb, Hf isotopic data, and whole rock major and trace elements geochemical data of the intermediate (diorite porphyry) to acid (granite porphyry) dykes intruded into the Linzizong volcanics in Linzhou Basin. These dykes intruded into Dianzhong and Nianbo formations of Linzizong Group. All the samples are sub-alkaline, varying from calc-alkaline to high-K calc-alkaline series. They are peraluminous (A/CNK>1.1). The diorite porphyry, intruded in 62.4Ma with positive zircon Hf isotopes (ɛHf(t)=+5.1~+7.6), have similar composition to the andesitic rocks from Dianzhong Formation. The granite porphyries, intruded between 55.1Ma and 61.1Ma, with ɛHf(t) ranging from -1.1 to +10.4, have comparable composition with the rhyolitic Nianbo Formation. A series of evidences, including: (1) the samples have positive, mantle-like Hf feature (average ɛHf(t)=+5.9 of 86 samples); (2) wide-range variation of ɛHf(t) in samples (3.5~8.8 ɛ units in the four granite porphyries), which implying an inhomogeneous source regions; (3) magma-mixing trend in the plots of FeOT against MgO, suggesting that the magma-mixing processes that have taken place in the southern Gangdese belt, can also be applied to explain the origin of these dykes in Linzhou Basin. The dykes intruded coeval or shortly later than their equivalent volcanic rocks (Dianzhong and Nianbo formations), are in the transitional settings from subduction of Tethyan oceanic crust to the collisional between India and Eurasia continents.

  17. Petrology, geochemistry, and geochronology of trondhjemites from the Qori Complex, Neyriz, Iran

    NASA Astrophysics Data System (ADS)

    Fazlnia, Abdolnaser; Schenk, Volker; van der Straaten, François; Mirmohammadi, Mirsaleh

    2009-10-01

    Metamorphism, magmatism, and thrusting were the result of subduction of Neotethys beneath the continental-margin arc of the Sanandaj-Sirjan shear zone (SSSZ) during the Mesozoic. The Qori metamorphic complex is a part of the southern SSSZ. Leuco-granitic (trondhjemitic) rocks crop out in the Qori metamorphic complex and are rare rock types in the SSSZ. These rocks have intruded into the marbles and garnet amphibolites, the highest grade metamorphic rocks of the Qori metamorphic complex, and in some outcrops, a transitional boundary between the amphibolites and the granitoids can be distinguished. The granitoids are granular in texture and consist of plagioclase (albite-oligoclase), quartz ± K-feldspar ±muscovite and subordinate garnet, spinel, rutile, and apatite which primarily occur as inclusions in the main phases. The peraluminous trondhjemitic rocks are enriched in Na 2O and SiO 2 and depleted in FeO, MgO, and CaO. Similarities with some trondhjemitic liquids produced through partial melting of amphibolites or hydrous basalts (i.e., low-Al 2O 3 content, less than 15 wt.%; low Ba, Sr, TiO 2, and Eu content, all with negative anomalies; moderately enriched LREEs and Y, and flat HREE patterns) suggest that the evolution of the parental magma was controlled by residual plagioclases during partial melting of a garnet amphibolite source. Concentrations of ferromagnesian elements, Mg, Fe, and Mn, are low, suggesting that the granitic rocks were not produced by high degrees of partial melting. Furthermore, they display low amounts of ferromagnesian components from the protolith (garnet amphibolite). This is supported by consideration of compatible elements, especially Cr, Ni and Ti (and the less robust HREE), which respectively show very high and high bulk partition coefficients for relatively small degrees (< 20%) of partial melting of the source. The partial melting of the garnet amphibolites occurred at pressures and temperatures between 7.5 and 9.5 kbar (at a depth of 25 to 32 km) and 680 and 720 °C, respectively, based on the Grt-Hbl and Hbl-Pl thermometers and a Grt-Hbl-Pl-Qtz barometer. Precise U-Th zircon SHRIMP ages of the trondhjemite show magmatic ages of 147.4 ± 0.76 Ma, Volgian, Late Jurassic, and suggest that Neotethys began to subduct beneath the continental-margin arc of the SSSZ. As a result of this process, an arc-related metamorphism occurred, leading to the development of the garnet amphibolites in the Qori metamorphic complex.

  18. Application of geochronology/geochemistry of zircon in understanding the construction of the Peninsular Range Batholith

    NASA Astrophysics Data System (ADS)

    Kylander-Clark, A. R.; Johnston, S. M.

    2015-12-01

    Trace-element signatures of zircon are becoming increasingly used as a tool to infer the petrologic history of the rock from which that zircon crystallized. In this study, we sampled 11 igneous rocks from west to east across the northern Peninsular Ranges Batholith (PRB) to test how well REE patterns in zircon reflect those of the whole rock in arc magmas (granodiorite-tonalite). Previous studies of the PRB show two transitions from west to east, with respect to their REE patterns; transition 1) a decrease in HREE, from the west to the central PRB, and 2) an increase in LREE from the central to the eastern PRB. Whole rock samples in this study, analyzed by XRF and ICPMS, reproduce this pattern and thus provide a variety of REE signatures with which to test whether zircon can be used as a proxy for whole-rock data. Zircon from the 11 samples was analyzed by LASS (Laser Ablation Split Stream) ICP-MS, to measure both the age of the zircons and their trace-element compositions. In general, as expected, ages young from west (ca. 104 Ma) to east (ca. 90 Ma). Patterns of HREE in zircon correlate well with those of the whole rock, whereas the LREE correlation is weak. The distribution coefficient for HREE between zircon and whole rock, however, decreases with increasing HREE. Possibilities for this negative relation include: 1) minor changes in whole-rock chemistry, as samples become slightly more felsic from west to east, 2) changes in crystallization temperature from west to east, and 3) sampling bias of HREE-poor zircon rims with HREE fractionated in zircon cores. Other trace element data measured in zircon and whole rock include P, Ti, Y, Nb, Hf, Ta, Th, and U and provide interesting results. Nb and Ta show a moderate correlation between zircon and whole rock, but the Nb/Ta ratio does not. Also, though U correlates well between whole rock and zircon and Th/U correlates well between zircon and age, the Th/U ratio of the zircon is negatively correlated with the whole rock; thus, in this case, Th/U changes in zircon are not a good indication of Th/U trends overall. Finally, Ti in zircon correlates strongly with location and whole-rock HREE concentration, indicating that either temperatures and/or Ti activity were higher in the west, early in the construction of the batholith.

  19. Geochronology, geochemistry and tectonic implications of Late Triassic granites in the Mongolian Altai Mountains

    NASA Astrophysics Data System (ADS)

    Dash, Batulzii; Boldbaatar, Enkhjargal; Zorigtkhuu, Oyun-Erdene; Yin, An

    2016-03-01

    Although the closure of the Paleo-Asian Ocean in western China and western Mongolia occurred in the Late Carboniferous and Early Permian, widespread intra-continental magmatism continued to occur across this region from the Late Permian to the end of the Triassic. In this study we document field relationships and geochemical characterization of a Late Triassic felsic intrusive complex in the western Mongolian Altai. The plutonic complex occurs as sills, dikes, and small stocks and its composition varies from biotite granite, two-mica granite, to leucogranite. Structurally, the plutonic complex occurs in the hanging wall of a segment of the regionally extensively (>1500 km long) Irtysh-Ertix-Bulgan thrust zone. As the plutonic bodies both cut and are deformed by the shear fabrics in this regional thrust shear zone, the duration of felsic magmatism and regional thrusting was temporally overlapping. This suggests that magmatism was coeval with crustal thickening. Major- and trace-element data and isotopic analysis of granitoid samples from our study area indicate that the felsic intrusions were derived from partial melting of meta-sediments, with the biotite and two-mica granite generated through vapor-absent melting and the leucogranite from flux melting. Although the Mongolian Altai intrusions were clearly originated from anatexis, coeval granite in the Chinese Altai directly west of our study area in the hanging wall of the Irtysh-Ertix-Bulgan thrust was derived in part from mantle melting. To reconcile these observations, we propose a Himalayan-style intracontinental-subduction model that predicts two geologic settings for the occurrence of felsic magmatism: (1) along the intracontinental thrust zone where granite was entirely generated by anatexis and (2) in the hanging wall of the intracontinental thrust where convective removal and/or continental subduction induced mantle melting.

  20. Monazite trace-element and isotopic signatures of high-pressure metamorphism: examples from the Western Gneiss region, Norway

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Monazite U-Pb and trace-element data were gathered using LASS (laser-ablation split-stream ICP-MS) from the Western Gneiss region, Norway, to investigate how trace-element composition can be used to differentiate (ultra)high-pressure monazite from low-pressure monazite. Monazite from six samples contains up to 3 % common Pb, despite high U and Th concentrations. These high common-Pb monazites are characterized by high Sr, weak Eu anomalies, and low Y+HREE. The high common-Pb and Sr abundances and the weak Eu/Eu* are interpreted to reflect the absence of feldspar at (U)HP, and the low Y+HREE content is attributed to fractionation of those elements into garnet. Sr and common Pb in monazite provide a tool for constraining the timing and duration of (U)HP metamorphism. More generally, Sr in monazite is a potential indicator of feldspar instability and may be applicable in other geologic settings, such as igneous systems in which the abundance of feldspar changes due to melting and crystallization. Sr is expected to be more reliable than Eu and Eu/Eu* as a tracer of feldspar stability, because Sr partitioning is less strongly influenced by oxidation state.

  1. Establishing Denudation Chronology through Weathering Geochronology

    NASA Astrophysics Data System (ADS)

    Riffel, S. B.; Vasconcelos, P. M.; Farley, K. A.; Carmo, I. O.

    2011-12-01

    Planar landforms - erosion surfaces - are used as temporal markers in denudation chronology. These surfaces are interpreted as the result of long-term weathering and denudation controlled by a specific base level within a given time-interval characterized by long-term tectonic stability. The presence of several planar landforms at distinct elevations is interpreted as evidence for distinct denudation events, separated by periods of tectonic reactivation and crustal uplift. We selected an area in the Paraná-La Plata basin, southern Brazil (25°S lat.) to investigate if the application of weathering geochronology by the 40Ar/39Ar and (U-Th)/He methods could permit differentiating different elevation landsurfaces. We dated supergene Mn oxyhydroxides by 40Ar/39Ar geochronology and coexisting supergene Fe oxyhydroxides by the (U-Th)/He method from one of the three regional landsurfaces - The First, Second, and Third Paraná plateaus - previously identified in this area. Two sites were sampled from the Second Paraná Plateau: a ferricrust at Serra das Almas (7 hand specimens of goethite at 1080 m of altitude) and deeply weathered ferricretes and saprolites at Vila Velha (11 hand specimens of cryptomelane and 14 of goethite at 910 m of altitude). The Serra das Almas sites hosts a stratified weathering profile with ferricrust, and mottle zone. The Vila Velha site results from intense weathering that led to the precipitation of well-crystallized supergene minerals precipitated within fractures in the saprolites. The geochronological results are correlatable between the two sites and the two distinct methods (40Ar/39Ar and (U-Th)/He), and they reveal three generations of weathering and mineral precipitation: Late Eocene-Oligocene, Early Miocene, and Pleistocene. The geochronological results suggested that the Second Paraná Plateau formed by regional erosion during the Oligocene, and that this landsurface has been continuously exposed to weathering and erosion since then

  2. Two Phase Monazite/Xenotime 30LaPO4-70YPO4 Coating of Ceramic Fiber Tows (Postprint)

    DTIC Science & Technology

    2008-04-01

    micrograph of as-deposited (Y,La)PO4 fiber coatings on Nextel 720, showing a thin film of AlPO4 in the coating fiber interphase. January 2008 Two Phase...monazite solid-solution. Both monazite and xenotime are present in the (Y,La) monazite/xenotime coating in roughly equal amounts. A thin film of...wt% alumina doped sols , AlPO4 films were not observed at the fiber-coating interface (Fig. 8). SEM observations show significant variations in coating

  3. Characterization of Compressive Creep Behavior of Oxide/Oxide Composite with Monazite Coating at Elevated Temperature

    DTIC Science & Technology

    2006-03-01

    Materials, and Structures: A. Ed. Mrityunjay Singh and Todd Jensen. Westerville, OH: The American Ceramic Society, 2001. 5. Antti, M-L, E. Lara-Curzio... Emmanuel E. Boakye, Pavel Mogilevsky, and Michael K. Cinibulk. “Effectiveness of Monazite Coatings in Oxide/Oxide Composites after Long-Term Exposure

  4. Metamorphic and structural evolution of the Straits Schist, W. Connecticut: U-PB monazite constraints

    SciTech Connect

    Lanzirotti, A.; Hanson, G.N. . Dept. of Earth and Space Sciences)

    1993-03-01

    U-Pb dating of monazites from two outcrops of The Straits Schist south of Waterbury Dome precisely constrains the timing of Acadian metamorphism and deformation. Synkinematic pegmatites which parallel schistosity are common in The Straits Schist south of Waterbury. A pegmatite at the type-section of The Straits Schist east of Straitsville yields U-Pb monazite ages of 385 [+-] 2.5 Ma. At both outcrops the axial planar schistosity is defined by muscovites and biotites which wrap around axes of folds but are not themselves deformed, suggesting they represent a recrystallized fabric. Monazites in the schists at both outcrops display petrographic evidence of grain boundary pinning against mica surfaces and growth across muscovite-biotite grain boundaries, consistent with growth during or after biotite and muscovite crystallization. Monazites from the schist at Straitsville and Naugatuck yield U-Pb ages of 383 [+-] 3 Ma. The U-Pb data, coupled with field and petrographic observations, suggest that pegmatite intrusion, deformation, and metamorphic recrystallization occurred within 3 Ma of about 383 Ma.

  5. The Influence of Interfacial Roughness on Fiber Sliding in Oxide Composites with La-Monazite Interphases

    NASA Technical Reports Server (NTRS)

    Davis, J. B.; Hay, R. S.; Marshall, D. B.; Morgan, P. E. D.; Sayir, A.; Gray, Hugh R. (Technical Monitor); Farmer, Serene C. (Technical Monitor)

    2002-01-01

    Room temperature debonding and sliding of La-Monazite coated fibers is assessed using a composite with a polycrystalline alumina matrix and fibers of several different single crystal (mullite, sapphire) and directionally solidified eutectic (Al2O3/Y3Al5O12 and Al2O3/Y-ZrO2) compositions. These fibers provide a range of residual stresses and interfacial roughnesses. Sliding occurred over a debond crack at the fiber-coating interface when the sliding displacement and surface roughness were relatively small. At large sliding displacements with relatively rough interfaces, the monazite coatings were deformed extensively by fracture, dislocations and occasional twinning, whereas the fibers were undamaged. Dense, fine-grained (10 nm) microstructures suggestive of dynamic recrystallization were also observed in the coatings. Frictional heating during sliding is assessed. The possibility of low temperature recrystallization is discussed in the light of the known resistance of monazite to radiation damage. The ability of La-Monazite to undergo plastic deformation relatively easily at low temperatures may be enabling for its use as a composite interface.

  6. CHIME monazite dating using FE-EPMA equipped with R=100 mm spectrometers

    NASA Astrophysics Data System (ADS)

    Shibata, K.; Shimizu, M.; Suzuki, K.; Sueoka, S.; Niwa, M.

    2015-12-01

    The age spectrum of detrital monazite grains is used to unravel the tectono-thermal history of the pre-Neogene terranes, which is required for geological disposal of high-level radioactive waste on tectonically active Japanese Islands. The CHIME (Chemical Th-U-total Pb isochron method, Suzuki and Adachi, 1991) is best suited for dating of detrital monazite whose grains are not chronologically uniform. In the previous studies (eg, Suzuki, 2011), EPMA equipped with conventional R=140 mm spectrometers was used for measurement of U, Th and Pb. However the spectrometers have low count rate of measurement of Pb. The JEOL JXA-8530F FE-EPMA equipped with R=100 mm spectrometers has been applied for the CHIME monazite dating. The intrinsic responses of each of the R=100 mm spectrometers for PbMβ are around ten times higher than that of the R=140 mm spectrometer. The R=100 mm spectrometers permits obtaining high count rate, which enables us to shorten measurement time than before. As these spectrometers have peculiar spectral interference, the method reported by Amli and Griffin (1978) is applied for correction of the interference. In order to verify the dating using the FE-EPMA and the interference correction method, two distinct age groups of monazite were measured. The ages were 425±25 Ma for monazite from Cooma granite in southeastern Australia, which had dated by SHRIMP as 432.8 ± 3.5 Ma (Williams, 2001) and 67 ± 7 Ma for monazite of the Kojaku granite in southwestern Japan, which is corresponding to the LA-ICP-MS U-Pb zircon ages of 68.5 ± 0.7 Ma. These results indicate that the FE-EPMA and the interference correction method are useful for the CHIME monazite dating and for revealing the tectono-thermal history of the terranes. This study was carried out under a contract with Agency of Natural Resources and Energy(ANRE), part of Ministry of Economy, Trade and Industry (METI) of Japan as part of its R&D supporting program for developing geological disposal technology.

  7. Kyanite-garnet gneisses of the Kåfjord Nappe - North Norwegian Caledonides: P-T conditions and monazite Th-U-Pb dating

    NASA Astrophysics Data System (ADS)

    Ziemniak, Grzegorz; Kośmińska, Karolina; Majka, Jarosław; Janák, Marian; Manecki, Maciej

    2016-04-01

    The Kåfjord Nappe is the part of the Skibotn Nappe Complex traditionally ascribed to the Upper Allochthon of the North Norwegian Caledonides. Pressure-temperature (P-T) conditions and metamorphic age of the Kåfjord Nappe are not well constrained, geochronological data are limited to a single Rb-Sr age of c. 440 Ma (Dangla et al. 1978). Metamorphic evolution of kyanite-garnet gneisses of the Kåfjord Nappe is presented here. The kyanite-garnet gneisses are associated with a few meters thick amphibolite lenses. The gneisses mainly consist of quartz, plagioclase, biotite, muscovite, garnet, kyanite, and rutile. Retrograde minerals are represented by sillimanite and chlorite. Garnet occurs as two textural types. Garnet-I forms euhedral porphyroblasts with multiple small inclusions. Profiles through garnet-I show chemical zonation in all components. The composition varies from Alm64-68Prp11-16Grs13-18Sps2-8 in the core to Alm68-70Prp17-18Grs10-13Sps1-3 in the rim. Garnet-II is subhedral to anhedral, its core is inclusion-rich, whereas rim contains only single inclusions. Chemical composition of garnet-II is similar to that of the garnet-I rim. P-T conditions have been estimated using the garnet-biotite-muscovite-plagioclase (GBPM) geothermobarometer (Holdaway, 2001; Wu, 2014). Calculated peak P-T metamorphic conditions are 610-625 °C and 7.6-8.2 kbar corresponding to the amphibolite facies conditions. Phase equilibrium modelling in the NCKFMMnASH system yields peak metamorphic conditions of c. 620 °C at 8 kbar. Growth conditions of garnet-I core modelled in the NCKFMMnASH system are c. 570 °C at 9.7 kbar. Chemical Th-U-total Pb monazite dating has been performed. Preliminary dating results from the kyanite-garnet gneiss of the Kåfjord Nappe yield an array of dates from 468 Ma to 404 Ma. There is a correlation between an increase of yttrium content and decrease of monazite single dates. Compositional maps confirm an increase of yttrium towards the rim of the

  8. Provenance implications of Th U Pb electron microprobe ages from detrital monazite in the Carboniferous Upper Silesia Coal Basin, Poland

    NASA Astrophysics Data System (ADS)

    Kusiak, Monika Agnieszka; Kędzior, Artur; Paszkowski, Mariusz; Suzuki, Kazuhiro; González-Álvarez, Ignacio; Wajsprych, Bolesław; Doktor, Marek

    2006-05-01

    This paper reports the results of CHIME (chemical Th-U-Pb isochron method) dating of detrital monazites from Carboniferous sandstones in the Upper Silesia Coal Basin (USCB). A total of 4739 spots on 863 monazite grains were analyzed from samples of sandstone derived from six stratigraphic units in the sedimentary sequence. Age distributions were identified in detrital monazites from the USCB sequence and correlated with specific dated domains in potential source areas. Most monazites in all samples yielded ca. 300-320 Ma (Variscan) ages; however, eo-Variscan, Caledonian and Cadomian ages were also obtained. The predominant ages are comparable to reported ages of certain tectonostratigraphic domains in the polyorogenic Bohemian Massif (BM), which suggests that various crystalline lithologies in the BM were the dominant sources of USCB sediments.

  9. Geochemistry of sedimentary ore deposits

    SciTech Connect

    Maynard, J. B.

    1983-01-01

    A text providing a sedimentological treatment of a study on ore deposits, and especially as related to geochemistry. Excellently documented (about 5000 citations). Well indexed with the index of deposits and localities separated. Contents, Iron. Copper and silver. Aluminum and nickel. Manganese. Uranium. Lead and zinc. Volcanic-sedimentary ores. Appendix. Indexes.

  10. Medical geochemistry of tropical environments

    NASA Astrophysics Data System (ADS)

    Dissanayake, C. B.; Chandrajith, Rohana

    1999-10-01

    Geochemically, tropical environments are unique. This uniqueness stems from the fact that these terrains are continuously subjected to extreme rainfall and drought with resulting strong geochemical fractionation of elements. This characteristic geochemical partitioning results in either severe depletion of elements or accumulation to toxic levels. In both these situations, the effect on plant, animal and human health is marked. Medical geochemistry involves the study of the relationships between the geochemistry of the environment in which we live and the health of the population living in this particular domain. Interestingly, the relationships between geochemistry and health are most marked in the tropical countries, which coincidentally are among the poorest in the world. The very heavy dependence on the immediate environment for sustainable living in these lands enables the medical geochemist to observe correlations between particular geochemical provinces and the incidence of certain diseases unique to these terrains. The aetiology of diseases such as dental and skeletal fluorosis, iodine deficiency disorders, diseases of humans and animals caused by mineral imbalances among others, lie clearly in the geochemical environment. The study of the chemistry of the soils, water and stream sediments in relation to the incidence of geographically distributed diseases in the tropics has not only opened up new frontiers in multidisciplinary research, but has offered new challenges to the medical profession to seriously focus attention on the emerging field of medical geochemistry with the collaboration of geochemists and epidemiologists.

  11. Experimental and geologic evaluation of monazite (U-Th)/He thermochronometry: Catnip Sill, Catalina Core Complex, Tucson, AZ

    NASA Astrophysics Data System (ADS)

    Peterman, E. M.; Hourigan, J. K.; Grove, M.

    2014-10-01

    Monazite is a petrologically important and analytically promising target for (U-Th)/He thermochronology. Previous studies have reported highly variable He diffusion results from monazite from a single sample and demonstrated that composition can significantly affect He diffusion parameters. In this study, we performed incremental heating of single monazite grains to experimentally determine the 4He diffusion properties of reference monazite ‘554’ that occurs within a peraluminous two-mica granite from the Catnip Sill within the Catalina Core complex, Arizona. Assuming that the grain size defines the diffusion geometry, the six experiments yielded Ea values of 212 to 238±5 kJ mol (1σ) and Do values of 15.7 to 103 cm s with one value of 784 cm s. Monazite (U-Th)/He data from five grains yielded closure temperatures of 291 to 262 °C (± c. 15 °C) and ages of 23.8-20.3 (±∼1.2;2σ) Ma; the weighted mean age is 21.8±0.73 (MSWD=1.83, n=5) and the weighted mean closure temperature is 282±6 °C (MSWD=0.96, n=5;1σ). We tested the accuracy of these results by comparing our monazite thermochronology data with monazite Th/Pb depth profiling results, the 40Ar/39Ar thermal history for the Catnip Sill constrained using coexisting muscovite, biotite, and K-feldspar, and published regional zircon and apatite fission track results. The monazite Th/Pb data indicate emplacement of the Catnip Sill at ∼45 Ma. The 40Ar/39Ar muscovite and biotite data indicate cooling from 460 to 350 °C from 27 to 26 Ma. K-feldspar MDD modeling suggests cooling from 360 to 240 °C from 26 to 24 Ma. Zircon fission track data indicate cooling through 250 °C between 29 and 20 Ma. Additional cooling through 110 °C is recorded by apatite fission track ages of 19-16 Ma. Because the monazite thermochronology results are reproducible and consistent with the thermal history constrained by the other chronometers, our results 1) confirm the accuracy of the 4He diffusion kinetics from monazite

  12. Magmatism as a response to exhumation of the Priest River complex, northern Idaho: Constraints from zircon U-Pb geochronology and Hf isotopes

    NASA Astrophysics Data System (ADS)

    Stevens, L. M.; Baldwin, J. A.; Crowley, J. L.; Fisher, C. M.; Vervoort, J. D.

    2016-10-01

    Zircon and monazite U-Pb geochronology and zircon Hf isotopes place constraints on the temporal and source relationships between crustal anatexis, magmatism, and exhumation of the Priest River metamorphic core complex, northern Idaho. Granitoids that intruded the migmatitic, pelitic Hauser Lake gneiss include the < 76.5 ± 0.1 Ma Spokane granite, 50.13 ± 0.02 Ma Silver Point quartz monzonite, c. 47.9 Ma Wrencoe granodiorite, < 46.4 ± 1.8 Ma Rathdrum granite, and a < 49.8 ± 0.4 Ma leucocratic dike. Cretaceous magmatism preceded the c. 64 Ma peak metamorphism (recorded by monazite) of the Hauser Lake gneiss, whereas discrete pulses of Eocene magmatic activity post-date the onset of exhumation by 10 Ma. The relative timing of pluton emplacement in the Priest River complex indicates that it was primarily a response to decompression rather than a cause. The mylonitized Silver Point and undeformed Wrencoe plutons bracket the end of a rapid phase of exhumation to c. 50-48 Ma. Zircon εHf(i) values and Lu-Hf isotope evolution indicate that the Silver Point and Wrencoe plutons crystallized from homogeneous magmas sourced from Archean-Proterozoic basement orthogneisses, whereas the Spokane granite and two leucocratic units appear to have been produced by partial melting of the Hauser Lake gneiss. Comparison of the Priest River complex with other deeply exhumed northern Cordilleran complexes indicates variability in the timing and, therefore, relative influences of partial melting and magmatism on the initiation of exhumation, which must be accounted for in numerical models of metamorphic core complex formation and evolution.

  13. Molecular environmental geochemistry

    NASA Astrophysics Data System (ADS)

    O'Day, Peggy A.

    1999-05-01

    The chemistry, mobility, and bioavailability of contaminant species in the natural environment are controlled by reactions that occur in and among solid, aqueous, and gas phases. These reactions are varied and complex, involving changes in chemical form and mass transfer among inorganic, organic, and biochemical species. The field of molecular environmental geochemistry seeks to apply spectroscopic and microscopic probes to the mechanistic understanding of environmentally relevant chemical processes, particularly those involving contaminants and Earth materials. In general, empirical geochemical models have been shown to lack uniqueness and adequate predictive capability, even in relatively simple systems. Molecular geochemical tools, when coupled with macroscopic measurements, can provide the level of chemical detail required for the credible extrapolation of contaminant reactivity and bioavailability over ranges of temperature, pressure, and composition. This review focuses on recent advances in the understanding of molecular chemistry and reaction mechanisms at mineral surfaces and mineral-fluid interfaces spurred by the application of new spectroscopies and microscopies. These methods, such as synchrotron X-ray absorption and scattering techniques, vibrational and resonance spectroscopies, and scanning probe microscopies, provide direct chemical information that can elucidate molecular mechanisms, including element speciation, ligand coordination and oxidation state, structural arrangement and crystallinity on different scales, and physical morphology and topography of surfaces. Nonvacuum techniques that allow examination of reactions in situ (i.e., with water or fluids present) and in real time provide direct links between molecular structure and reactivity and measurements of kinetic rates or thermodynamic properties. Applications of these diverse probes to laboratory model systems have provided fundamental insight into inorganic and organic reactions at

  14. Autonomous anorthosites of the Anabar Shield: Age, geochemistry, and formation mechanism

    NASA Astrophysics Data System (ADS)

    Glukhovskii, M. Z.; Kuz'min, M. I.; Bayanova, T. B.; Bazhenova, G. N.; Lyalina, L. M.; Serov, P. A.

    2015-10-01

    The new high-accuracy data on U-Pb zircon geochronology, Sm-Nd systematics, and geochemistry of anorthosites of the Anabar Shield are discussed. It is established that anorthosite massifs are composed of gabbro-anorthosites (1.96 Ga old) and oligoclasites (1.93 Ga old) in association with monzodiorites (1.84-1.90 Ga old) and porphyroblastic granites. These rocks were generated in the Archean (3.2-2.7 Ga ago) in the lower crust from quartz-diorite melts under the plume tectonics regime in line with the filterpressing mechanism. The rocks were successively exhumed to upper levels of the crust owing to the Paleoproterozoic impact-triggered process to form a tectonically juxtaposed complementary magmatic complex.

  15. Invited review article: Recent developments in isotope-ratio mass spectrometry for geochemistry and cosmochemistry.

    PubMed

    Ireland, Trevor R

    2013-01-01

    Mass spectrometry is fundamental to measurements of isotope ratios for applications in isotope geochemistry, geochronology, and cosmochemistry. Magnetic-sector mass spectrometers are most common because these provide the best precision in isotope ratio measurements. Where the highest precision is desired, chemical separation followed by mass spectrometric analysis is carried out with gas (noble gas and stable isotope mass spectrometry), liquid (inductively coupled plasma mass spectrometry), or solid (thermal ionization mass spectrometry) samples. Developments in in situ analysis, including ion microprobes and laser ablation inductively coupled plasma mass spectrometry, have opened up issues concerning homogeneity according to domain size, and allow ever smaller amounts of material to be analyzed. While mass spectrometry is built solidly on developments in the 20th century, there are new technologies that will push the limits in terms of precision, accuracy, and sample efficiency. Developments of new instruments based on time-of-flight mass spectrometers could open up the ultimate levels of sensitivity per sample atom.

  16. Alteration and breakdown of xenotime-(Y) and monazite-(Ce) in granitic rocks of the Western Carpathians, Slovakia

    NASA Astrophysics Data System (ADS)

    Broska, Igor; Williams, C. Terry; Janák, Marian; Nagy, Géza

    2005-05-01

    In the granitic rocks of the Western Carpathians, xenotime-(Y) occurs both as a late-stage magmatic mineral, and as a secondary post-magmatic phase. Magmatic xenotime occurs with monazite and displays minor compositional zonation involving Si, Th and U. The source of elements for the formation of secondary xenotime-(Y) in the granitic rocks results from leaching of P and (Y+REE), mainly from zircon and apatite. Both xenotime-(Y) and monazite-(Ce) are unstable during fluid-activated overprinting. Low temperature alteration of monazite in S-type granites leads to the formation of apatite enriched in the britholite component, but low to medium grades of metamorphism result in the formation of apatite and LREE enriched epidote (partly allanite) as a corona enclosing the monazite-(Ce) core. Xenotime-(Y) shows a similar alteration pattern, but with different REE distributions within the products. At greenschist/amphibolite facies, rims of secondary Y-rich apatite and Y-rich epidote form around xenotime-(Y). In low-Ca granites however, apatite is missing from this alteration assemblage as xenotime-(Y) breaks down directly to Y-enriched epidote. The relative mobilities of the heavy and light REE are different during breakdown of monazite and xenotime. The fluid responsible for the breakdown of monazite and xenotime contains elements released from alteration of anorthite (Ca) and biotite (Si, Al and F).

  17. History of the recognition of organic geochemistry in geoscience

    USGS Publications Warehouse

    Kvenvolden, K.A.

    2002-01-01

    The discipline of organic geochemistry is an outgrowth of the application of the principles and methods of organic chemistry to sedimentary geology. Its origin goes back to the last part of the nineteenth century and the first part of the twentieth century concurrent with the evolution of the applied discipline of petroleum geochemistry. In fact, organic geochemistry was strongly influenced by developments in petroleum geochemistry. Now, however, organic geochemistry is considered an umbrella geoscience discipline of which petroleum geochemistry is an important component.

  18. The growth of the continental crust: Constraints from radiogenic isotope geochemistry

    NASA Technical Reports Server (NTRS)

    Taylor, Paul N.

    1988-01-01

    Most models for evolution of continental crust are expressed in the form of a diagram illustrating the cumulative crustal mass (normalized relative to the present crustal mass) as a function of time. Thus, geochronological data inevitably play a major role in either constructing or testing crustal growth models. For all models, determining the start-time for effective crustal accretion is of vital importance. To this end, the continuing search for, and reliable characterization of, the most ancient crustal rock-units remains a worthy enterprise. Another important role for geochronology and radiogenic isotope geochemistry is to assess the status of major geological events as period either of new crust generation or of reworking of earlier formed continental crust. For age characterization of major geological provinces, using the critieria outined, the mass (or volume) of crust surviving to the present day should be determinable as a function of crust formation age. More recent developments, however, appear to set severe limitations on recycling of crust, at least by the process of sediment subduction. In modeling crustal growth without recycling, valuable constaints on growth rate variations through time can be provided if variations in the average age of the continental crust can be monitored through geological history. The question of the average age of the exposed continental crust was addressed by determining Sm-Nd crustal residence model ages (T-CR) for fine-grained sediment loads of many of the world's major rivers.

  19. Chemical and ceramic methods toward safe storage of actinides using monazite. 1998 annual progress report

    SciTech Connect

    Morgan, P.E.D.; Boatner, L.A.

    1998-06-01

    'The use of ceramic monazite, (La,Ce)PO{sub 4}, for sequestering actinides, especially plutonium, and some other radioactive waste elements (rare earths e.g.) and thus isolating them from the environment has been championed by Lynn Boatner of ORNL. It may be used alone or, as it is compatible with many other minerals in nature, can be used in composite combinations. Natural monazite, which almost invariably contains Th and U, is often formed in hydrothermal pegmatites and is extremely water resistant--examples are known where the mineral has been washed out of rocks (becoming a placer mineral as on the beach sands of India, Australia, Brazil etc.) then reincorporated into new rocks with new crystal overgrowths and then washed out again--being 2.5--3 billion years old. During this demanding water treatment it has retained Th and U. Where very low levels of water attack have been seen (in more siliceous waters), the Th is tied up as new ThSiO{sub 4} and remains immobile. Lest it be thought that rare-earths are rare or expensive, this is not so. In fact, the less common lanthanides such as gadolinium, samarium, europium, and terbium, are necessarily extracted and much used by, e.g., the electronics industry, leaving La and Ce as not-sufficiently-used by-products. The recent development of large scale use of Nd in Nd-B-Fe magnets has further exaggerated this. Large deposits of the parent mineral bastnaesite are present in the USA and in China. (Mineral monazite itself is not preferred due to its thorium content.) In the last 5 years it has become apparent show that monazite (more specifically La-monazite) is an unrecognized/becoming-interesting ceramic material. PuPO4 itself has the monazite structure; the PO{sub 4} 3-unit strongly stabilizes actinides and rare earths in their trivalent state. Monazite melts without decomposition (in a closed system) at 2,074 C and, being compatible with common ceramic oxides such as alumina, mullite, zirconia and YAG, is useful in

  20. Analysis of monazite, zircon, and apatite from the southeastern Piedmont. National uranium resource evaluation program

    SciTech Connect

    Karfunkel, B S; Fay, W M; Price, V Jr

    1981-12-01

    Two hundred sixty-three monazite, 191 zircon, and 16 apatite grains from 52 stream-sediment locations in the Southeastern Piedmont were analyzed by electron microprobe for one of the following suites of elements: Ca, La, Ce, Pr, Nd, Sm, Eu, Gd, Er, Dy, Y, Th, U, P, and F, or Ca, La, Ce, Fe, Er, Hf, Y, Th, U, P, Zr, Mg, Al, and Si. Monazite samples that had high uranium or thorium content and zircon samples that had high hafnium or iron content from a total of six locations were reanalyzed to confirm the initial results. This report contains a description of sample collection and preparation procedures, analytical methods, tables of analyses, and a statistical summary of analyses.

  1. Quaternary evolution of the rivers of northeast Hainan Island, China: Tracking the history of avulsion from mineralogy and geochemistry of river and delta sands

    NASA Astrophysics Data System (ADS)

    Pe-Piper, Georgia; Piper, David J. W.; Wang, Ying; Zhang, Yongzhan; Trottier, Corwin; Ge, Chendong; Yin, Yong

    2016-03-01

    The mineralogy and geochemistry of sands were investigated in the Nandu and Wanquan rivers, Hainan Island, China, to determine the history of avulsion in the lower reaches of the Nandu River. The study also provided the opportunity to assess the utility of geochemical analysis of sands as a provenance tool. Much of the heavy mineral fraction in the rivers consists of subangular Fe-Ti oxide and Fe-(hydr)oxide minerals, and less stable minerals such as amphibole, epidote, and andalusite, whereas rounded resistant ilmenite, rutile, tourmaline and zircon predominate on the deltaic coast. Mineral assemblage and chemical composition of individual samples are related to specific source areas and river tributaries. The results demonstrate northwestwards flow of the Nandu River during the mid-Holocene and earlier avulsion of the river to the northeast coast, probably during a Late Pleistocene marine highstand. Minor basement tilting, producing little relief, was sufficient to divert the lower reaches of rivers, and this effect was enhanced where basalt flows dammed former river courses. Bulk sample REE geochemistry is largely controlled by the relative abundance of monazite, allanite, titanite, zircon and epidote, derived principally from granites. Detrital geochemistry alone shows too much variability to interpret provenance. However, a smaller number of heavy mineral analyses provide an understanding of the mineralogical origins of geochemical variation, thus enabling interpretations of provenance.

  2. Rethinking early Earth phosphorus geochemistry

    PubMed Central

    Pasek, Matthew A.

    2008-01-01

    Phosphorus is a key biologic element, and a prebiotic pathway leading to its incorporation into biomolecules has been difficult to ascertain. Most potentially prebiotic phosphorylation reactions have relied on orthophosphate as the source of phosphorus. It is suggested here that the geochemistry of phosphorus on the early Earth was instead controlled by reduced oxidation state phosphorus compounds such as phosphite (HPO32−), which are more soluble and reactive than orthophosphates. This reduced oxidation state phosphorus originated from extraterrestrial material that fell during the heavy bombardment period or was produced during impacts, and persisted in the mildly reducing atmosphere. This alternate view of early Earth phosphorus geochemistry provides an unexplored route to the formation of pertinent prebiotic phosphorus compounds, suggests a facile reaction pathway to condensed phosphates, and is consistent with the biochemical usage of reduced oxidation state phosphorus compounds in life today. Possible studies are suggested that may detect reduced oxidation state phosphorus compounds in ancient Archean rocks. PMID:18195373

  3. Monazite RW-1: a homogenous natural reference material for SIMS U-Pb and Th-Pb isotopic analysis

    NASA Astrophysics Data System (ADS)

    Ling, Xiao-Xiao; Huyskens, Magdalena H.; Li, Qiu-Li; Yin, Qin-Zhu; Werner, Ronald; Liu, Yu; Tang, Guo-Qiang; Yang, Ya-Nan; Li, Xian-Hua

    2016-10-01

    Well-characterized matrix-matched natural mineral references of known age are an important prerequisite for SIMS (secondary ion mass spectrometry) U-Th-Pb dating. We have characterized RW-1, a 44 g yellowish-brown single monazite specimen from a Norwegian pegmatite as an excellent hi-Th reference material for secondary ion mass spectrometric U-Th-Pb dating. A total of 206 secondary ion mass spectrometric analyses over six analytical sessions were performed on different monazite fragments of RW-1. The analyses resulted in 207Pb-based common lead corrected 206Pb/238U ages and Th-Pb ages with overall 2 % (2 SD = standard deviation) variations, indicating the good U-Th-Pb system homogeneity. The homogeneity of Th content of 11.8 ± 1.0 wt% (2 SD) and Th/U of 42 ± 3 (2 SD) make this crystal also a good compositional reference material. We used the combined ID-TIMS(Pb)/ID-MC-ICP-MS(U) technique (i.e. isotope dilution thermal ionization mass spectrometry for Pb, and isotope dilution multi-collector inductively-coupled plasma mass spectrometry for U) to determine U-Pb ages of the monazite samples studied. The mean 207Pb/235U age of 904.15 ± 0.26 Ma (95 % confidence level) is recommended as the best estimate crystallization age for RW-1 monazite. Considering that the most commonly distributed U-Pb monazite reference materials have rather low ThO2, we suggest that this RW-1 monazite with its ThO2 of 13.5 wt% is a suitable reference material providing investigators more confidence when dating high-Th monazite unknowns.

  4. EARTHTIME: Teaching geochronology to high school students

    NASA Astrophysics Data System (ADS)

    Bookhagen, Britta; Buchwaldt, Robert; McLean, Noah; Rioux, Matthew; Bowring, Samuel

    2010-05-01

    The authors taught an educational module developed as part of the EARTHTIME (www.earth-time.org) outreach initiative to 215 high school students from a Massachusetts (USA) High School as part of an "out-of-school" field trip. The workshop focuses on uranium-lead (U-Pb) dating of zircons and its application to solving a geological problem. The theme of our 2.5-hour module is the timing of the K-T boundary and a discussion of how geochronology can be used to evaluate the two main hypotheses for the cause of the concurrent extinction—the Chicxlub impact and the massive eruption of the Deccan Traps. Activities are divided into three parts: In the first part, the instructors lead hands-on activities demonstrating how rock samples are processed to isolate minerals by their physical properties. Students use different techniques, such as magnetic separation, density separation using non-toxic heavy liquids, and mineral identification with a microscope. We cover all the steps from sampling an outcrop to determining a final age. Students also discuss geologic features relevant to the K-T boundary problem and get the chance to examine basalts, impact melts and meteorites. In the second part, we use a curriculum developed for and available on the EARTHTIME website (http://www.earth-time.org/Lesson_Plan.pdf). The curriculum teaches the science behind uranium-lead dating using tables, graphs, and a geochronology kit. In this module, the students start by exploring the concepts of half-life and exponential decay and graphically solving the isotopic decay equation. Manipulating groups of double-sided chips labeled with U and Pb isotopes reinforces the concept that an age determination depends on the Pb/U ratio, not the absolute number of atoms present. Next, the technique's accuracy despite loss of parent and daughter atoms during analysis, as well as the use of isotopic ratios rather than absolute abundances, is explained with an activity on isotope dilution. Here the students

  5. Rejuvenation effects during plastic deformation of Zircon: geochronological implications

    NASA Astrophysics Data System (ADS)

    Kovaleva, Elizaveta; Klötzli, Urs

    2013-04-01

    -deformation events and hosted by the shear zones? How to evaluate the significance of isotopic-system resetting in deformed domains? How to estimate the possibility of dating the deformation events and what is the reliability of such dating? A complex of methods is used for this research: transmitted and reflected light microscopy, CL (cathode luminescence) imaging for growth history, BSE (backscattered electrons) imaging for orientation and chemical contrast, SE (secondary elements) pictures for surface relief, SHRIMP (Sensitive High Resolution Ion Microprobe) for age dating, EBSD for crystallographic orientations. We suppose that careful combination of all these methods will lead to better understanding of some internal processes which happen with mineral during its evolution in host rocks. References: Moser D.E., Davis W.J., Reddy S.M., Flemming R.L., Hart R.J., 2009. Zircon U-Pb strain chronometry reveals deep impact-triggered flow. Earth and Planetary Science Letters 277, 73-79. Reddy, S.M., Timms, N.E., Pantleon, W., Trimby, T., 2007. Quantitative characterization of plastic deformation of zircon and geological implications. Contributions to Mineralogy and Petrology 153, 625-645. Reddy, S.M., Timms, N.E., 2010. Deformation of zircon and implications for geochemistry and geochronology. Source Abstracts with Programs - Geological Society of America 42 (5), 634.

  6. Statistics of large detrital geochronology datasets

    NASA Astrophysics Data System (ADS)

    Saylor, J. E.; Sundell, K. E., II

    2014-12-01

    Implementation of quantitative metrics for inter-sample comparison of detrital geochronological data sets has lagged the increase in data set size, and ability to identify sub-populations and quantify their relative proportions. Visual comparison or application of some statistical approaches, particularly the Kolmogorov-Smirnov (KS) test, that initially appeared to provide a simple way of comparing detrital data sets, may be inadequate to quantify their similarity. We evaluate several proposed metrics by applying them to four large synthetic datasets drawn randomly from a parent dataset, as well as a recently published large empirical dataset consisting of four separate (n = ~1000 each) analyses of the same rock sample. Visual inspection of the cumulative probability density functions (CDF) and relative probability density functions (PDF) confirms an increasingly close correlation between data sets as the number of analyses increases. However, as data set size increases the KS test yields lower mean p-values implying greater confidence that the samples were not drawn from the same parent population and high standard deviations despite minor decreases in the mean difference between sample CDFs. We attribute this to the increasing sensitivity of the KS test when applied to larger data sets, which in turn limits its use for quantitative inter-sample comparison in detrital geochronology. Proposed alternative metrics, including Similarity, Likeness (complement to Mismatch), and the coefficient of determination (R2) of a cross-plot of PDF quantiles, point to an increasingly close correlation between data sets with increasing size, although they are the most sensitive at different ranges of data set sizes. The Similarity test is most sensitive to variation in data sets with n < 100 and is relatively insensitive to further convergence between larger data sets. The Likeness test reaches 90% of its asymptotic maximum at data set sizes of n = 200. The PDF cross-plot R2 value

  7. Building Interactive Visualizations for Geochronological Data

    NASA Astrophysics Data System (ADS)

    Zeringue, J.; Bowring, J. F.; McLean, N. M.; Pastor, F.

    2014-12-01

    Since the early 1990s, Ken Ludwig's Isoplot software has been the tool of choice for visualization and analysis of isotopic data used for geochronology. The software is an add-in to Microsoft Excel that allows users to generate visual representations of data. However, recent changes to Excel have made Isoplot more difficult to use and maintain, and the software is no longer supported. In the last several years, the Cyber Infrastructure Research and Development Lab for the Earth Sciences (CIRDLES), at the College of Charleston, has worked collaboratively with geochronologists to develop U-Pb_Redux, a software product that provides some of Isoplot's functionality for U-Pb geochronology. However, the community needs a full and complete Isoplot replacement that is open source, platform independent, and not dependent on proprietary software. This temporary lapse in tooling also presents a tremendous opportunity for scientific computing in the earth sciences. When Isoplot was written for Excel, it gained much of the platform's flexibility and power but also was burdened with its limitations. For example, Isoplot could not be used outside of Excel, could not be cross-platform (so long as Excel wasn't), could not be embedded in other applications, and only static images could be produced. Nonetheless this software was and still is a powerful tool that has served the community for more than two decades and the trade-offs were more than acceptable. In 2014, we seek to gain flexibility not available with Excel. We propose that the next generation of charting software be reusable, platform-agnostic, and interactive. This new software should allow scientists to easily explore—not just passively view—their data. Beginning in the fall of 2013, researchers at CIRDLES began planning for and prototyping a 21st-century replacement for Isoplot, which we call Topsoil, an anagram of Isoplot. This work is being conducted in the public domain at https://github.com/CIRDLES/topsoil. We

  8. National geochronological and natural radioelement data bases

    USGS Publications Warehouse

    Zartman, Robert E.; Bush, Charles A.; Abston, C.C.

    1995-01-01

    This CD-ROM contains both the National Geochronological Data Base [NGDB] and the Natural Radioelement Data Base [NRDB]. Supporting location, geologic, and reference information is provided for both data bases. The NGDB is a compilation of more than 30,000 individual published Pb-alpha, fission-track, K-Ar, Rb-Sr, U-Th-Pb, and Sm-Nd rock and mineral ages reported on approximately 18,000 dated samples from the United States. A program is provided to search the data files by latitude and longitude, state, analytical method, and age range. The NGDB is provided as quote-comma delimited files that can be entered into most commercial spreadsheet programs. The NRDB gives gamma-ray spectrometric analyses of the natural radioelements (U, Th, and K) for more than 8500 whole-rock samples obtained under the USGS Natural Radioelement Distribution Project. A program is provided to search the data files by state, keyword, U content, Th content, and K content.

  9. Growth, preservation of Paleoproterozoic-shear-zone-hosted monazite, north of the Western Dharwar Craton (India), and implications for Gondwanaland assembly

    NASA Astrophysics Data System (ADS)

    Rekha, S.; Bhattacharya, A.

    2013-10-01

    We examine the conditions and processes of growth and preservation of multiaged monazite in micaceous matrix and in garnet porphyroblasts in staurolite-kyanite mica schists hosted in a hitherto-undiscovered shear zone that limits the northern extent of the Western Dharwar Craton (WDC), India. Garnet in the footwall schists grew during mid-crustal (600 ± 40 °C, 7.3 ± 1.2 kbar) loading and cooling as a consequence of the northward transport of the WDC lithologies. U-Th-Pb (total) ages in monazites in the matrix and in post-tectonic garnets yield well-defined peaks at 2.5, 2.2 and 1.9 Ga. In garnet, 2.5 and 2.2 Ga monazite grains, and 2.2 Ga monazites with 2.5 Ga cores are commonly occluded, but monazites with 1.9 Ga mantles around older cores are rare. By contrast, in the matrix, 1.9 Ga monazite grains and monazite with 1.9 Ga mantles around older cores are prominent, but the peak age frequencies of the two older populations are significantly lower than for monazites hosted as inclusions in garnet. Both in the matrix and garnet, the low-Th, high-Y domains in monazites yield the two older peak ages, while the 1.9 Ga ages correspond to the high-Th, low-Y domains. The preponderance of older ages in monazite hosted as inclusions in garnet relative to matrix monazites is because garnets formed between 2.2 and 1.9 Ga shielded the older monazites from dissolution-precipitation at 1.9 Ga. A few 1.9 Ga monazites hosted as inclusions in the garnet rims suggest renewed garnet growth at post-1.9 Ga. Multiple Pb-Pb age populations (2.5, 2.25, 2.1 and 1.8 Ga) in detrital zircon in the Sahanataha Group north of the Paleoarchean Antongil-Masora block (NE Madagascar) are identical to the multiple monazites ages north of the WDC, inferred to share a similar history and to be contiguous with the Antongil-Masora block in pre-Jurassic reconstructions of the Gondwanaland. We suggest the newly discovered Paleoproterozoic tectonic zone continued westward into Madagascar north of the

  10. [Book review] The geochronology and evolution of Africa

    USGS Publications Warehouse

    Wilson, Frederic H.

    1987-01-01

    This book was written 'to provide an up-to-date data bank from which those wishing to construct models concerned with the evolution of Africa .... can draw.' As such, it attempts a survey of 'integrated geology and geochronology' of the African continent throughout the Precambrian and into the Phanerozoic. Political and language divisions often hinder the synthesis of continent-wide data, therefore, this well-indexed inventory of selected data and synthesis of present geochronological knowledge for Africa as a whole provides an important reference for researchers and explorationists, many of whom have limited access to complete collections of the geological literature of Africa.

  11. Detrital Zircon Geochronology Applied to Basin Analysis

    NASA Astrophysics Data System (ADS)

    Gehrels, G. E.

    2014-12-01

    During the past ~15 years, detrital zircon geochronology has developed into a powerful tool for analyzing sedimentary features and processes. One of the most common applications is to use the ages of the youngest detrital zircons in a sample to constrain the maximum age of deposition. In an ideal case, for example in a region with active volcanism, the youngest zircon grains would have crystallized immediately prior to deposition and the lag time between crystallization and deposition is negligible. Such ages provide opportunities for reconstructing the chrono-stratigraphy of a sedimentary sequence, and establishing the chrono-correlation of sedimentary units and surfaces across broad regions. Most sedimentary units also yield detrital zircon grains that significantly predate deposition (because of the extreme durability of zircon). The ages of these grains provide a fingerprint (or chrono-facies) that can be used for comparison of sedimentary units. Such comparisons have traditionally been based on the presence/absence of age populations, but with larger data sets it is becoming possible to determine proportions of ages in a robust fashion, and thereby compare strata much more quantitatively. Common methodology for conducting these types of analyses is to determine ages for several hundred detrital zircon grains from each sample, with random selection of grains to generate a robust age distribution. If necessary, additional analyses are conducted on "young-looking" grains to improve precision on the max depo age. Such analyses commonly yield max depo ages that are reliable to 1-2%. Determining whether a max depo age approximates true depo age commonly requires geologic arguments (e.g., presence of volcanic lithic fragments, size/shape of the youngest zircon crystals, order of youngest ages in a sedimentary sequence). In addition to these chronologic applications, detrital zircon ages provide powerful tools for determining provenance, reconstructing dispersal

  12. Mechanical, Chemical and Microstructural Characterization of Monazite-Coated Silicon Carbide Fibers

    NASA Technical Reports Server (NTRS)

    Bansal, N. P.; Wheeler, D. R.; Chen, Y. L.

    2000-01-01

    Tensile strengths of as-received Hi-Nicalon and Sylramic fibers and those having monazite surface coatings, deposited by atmospheric pressure chemical vapor deposition, were measured at room temperature and the Weibull statistical parameters determined. The average tensile strengths of uncoated Hi-Nicalon and Sylramic fibers were 3.19 +/- 0.73 and 2.78 +/- 0.53 GPa with a Weibull modulus of 5.41 and 5.52, respectively. The monazite-coated Hi-Nicalon and Sylramic fibers showed strength loss of approx. 10 and 15 percent, respectively, compared with the as-received fibers. The elemental compositions of the fibers and the coatings were analyzed using scanning Auger microprobe and energy dispersive X-ray spectroscopy. The LaPO4 coating on Hi-Nicalon fibers was approximately stoichiometric and about 50 nm thick. The coating on the Sylramic fibers extended to a depth of about 100 to 150 nm. The coating may have been stoichiometric LaPO4 in the first 30 to 40 nm of the layer. However, the surface roughness of Sylramic fiber made this profile somewhat difficult to interpret. Microstructural analyses of the fibers and the coatings were done by scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction. Hi-Nicalon fiber consists of fine beta-SiC nanocrystals ranging in size from 1 to 30 mn embedded in an amorphous matrix. Sylramic is a polycrystalline stoichiometric silicon carbide fiber consisting of submicron beta-SiC crystallites ranging from 100 to 300 nm. Small amount of TiB2 nanocrystallites (approx. 50 nm) are also present. The LaPO4 coating on Hi-Nicalon fibers consisted of a chain of peanut shape particles having monazite-(La) structure. The coating on Sylramic fibers consisted of two layers. The inner layer was a chain of peanut shape particles having monazite-(La) structure. The outer layer was comprised of much smaller particles with a microcrystalline structure.

  13. Tracing irradiation-induced defect state of monazite by photoluminescence of rare Earth elements

    NASA Astrophysics Data System (ADS)

    Panczer, G.; Seydoux-Guillaume, A. M.; Montel, J. M.; Champagnon, B.

    2003-04-01

    Natural monazite is known in contrast to zircon, to almost never be found in the metamict state (Ewing, 1975) despite the fact that it received intensive radiation doses during geologic history by U and Th incorporation. Radiation damages in natural monazite seems to be limited to isolated domains within the crystal (Meldrum et al., 1998). Such property controlled the fact that the monazite lattice is easily healed even at low temperature as it was shown by TEM, XRD and Raman spectrometry (Seydoux-Guillaume et al., 2002). In order to estimate the degree of disorder and the healing of defects we used trivalent neodymium as an internal luminescent probe (Gaft et al., 2001). As a matter of fact the radiative electronic transitions of rare earth elements are very sensible to the short-range crystallographic order around them. Three natural monazites thermally untreated and quenched at 450, 500, 700, 800 and 1000^oC were analyzed under 514 nm Argon laser excitation with a Renishaw microspectrometer. Nd3+ emission was recorded in the range of 750 nm to 1 μm. The ^4F3/2 rightarrow ^4I9/2 transition parameters (position and width) show that 1) the position of the Stark levels do not change during thermal treatment, and 2) that the emission line widths decrease continuously (from 25 to 37%) from room temperature to 1000^oC. These results indicates that before annealing, sub sites of Nd were present with slight different environments induced by internal irradiation induced displacement of ions around them (short range disorder). After thermal treatment a continuous reorganization of the lattice occurs up to 1000^oC with quite strong rearrangement of the environment around the rare-earth leading to a decrease of the Nd sub site number. Thus, the luminescent probe reveals that defect healing continue at much higher temperatures than what was previously reported indicating that luminescence is a very sensible tool to appreciate the degree of disorder in mineral phases. Gaft M

  14. Inter-atomic potentials for radiation damage studies in CePO4 monazite

    NASA Astrophysics Data System (ADS)

    Jolley, Kenny; Asuvathraman, Rajaram; Smith, Roger

    2017-02-01

    An original empirical potential used for modelling phosphate glasses is adapted to be suitable for use with monazite (CePO4) so as to have a consistent formulation for radiation damage studies of phosphates. This is done by adding a parameterisation for the Ce-O interaction to the existing potential set. The thermal and structural properties of the resulting computer model are compared to experimental results. The parameter set gives a stable monazite structure where the volume of the unit cell is almost identical to that measured experimentally, but with some shrinkage in the a and b lengths and a small expansion in the c direction compared to experiment. The thermal expansion, specific heat capacity and estimates of the melting point are also determined. The estimate of the melting temperature of 2500 K is comparable to the experimental value of 2318 ± 20 K, but the simulated thermal expansion of 49 ×10-6 K-1 is larger than the usually reported value. The simulated specific heat capacity at constant pressure was found to be approximately constant at 657 J kg-1 K-1 in the range 300-1000 K, however, this is not observed experimentally or in more detailed ab initio calculations.

  15. Multiple generations of monazite growth in metapelites of the Wepawaug Schist, southern Connecticut

    SciTech Connect

    Lanzirotti, A.; Hanson, G.N. . Dept. of Earth and Space Sciences)

    1992-01-01

    The Wepawaug Schist, part of the Orange Milford Belt of southern Connecticut, consists dominantly of micaceous phyllites and schists. A progression in metamorphic zonation from chlorite through kyanite grade occurs within 3 km. There were previously no constraints on either the depositional age of the Wepawaug Schist or the time of metamorphism. Concordant U-Pb sphene ages of 457 [+-] 3 Ma for the Woodbridge granite, which cuts the Wepawaug Schist, mean that the metapelites are older than late Ordovician. Kyanite grade rocks contain two distinct monazite populations within a single outcrop: (1) Crystals from a graphitic schist are clear, round, and xenoblastic. They have [approximately]0.9 wt.% Th, Sm/Nd = 0.12--0.14, and display pronounced chemical zonation. These give normality discordant U-Pb ages that define an upper intercept age of 420 [+-] 12 Ma. (2) In a less graphitic schist they are light yellow, idioblastic, tabular crystals that cut muscovites. They have Sm/Nd = 0.16 and [approximately] 2.6 wt.% Th and give concordant U-Pb ages of 377 [+-] 3 Ma. The authors suggest that the Wepawaug Schist is older than 457 Ma and was affected by two events which resulted in monazite growth, one during the Middle Devonian (377 Ma) and one in the Late Silurian (420 Ma).

  16. Concomitant Leaching and Electrochemical Extraction of Rare Earth Elements from Monazite.

    PubMed

    Maes, Synthia; Zhuang, Wei-Qin; Rabaey, Korneel; Alvarez-Cohen, Lisa; Hennebel, Tom

    2017-02-07

    Rare earth elements (REEs) have become increasingly important in modern day technologies. Unfortunately, their recycling is currently limited, and the conventional technologies for their extraction and purification are exceedingly energy and chemical intensive. New sustainable technologies for REE extraction from both primary and secondary resources would be extremely beneficial. This research investigated a two-stage recovery strategy focused on the recovery of neodymium (Nd) and lanthanum (La) from monazite ore that combines microbially based leaching (using citric acid and spent fungal supernatant) with electrochemical extraction. Pretreating the phosphate-based monazite rock (via roasting) dramatically increased the microbial REE leaching efficiency. Batch experiments demonstrated the effective and continued leaching of REEs by recycled citric acid, with up to 392 mg of Nd L(-1) and 281 mg of La L(-1) leached during seven consecutive 24 h cycles. Neodymium was further extracted in the catholyte of a three-compartment electrochemical system, with up to 880 mg of Nd L(-1) achieved within 4 days (at 40 A m(-2)). Meanwhile, the radioactive element thorium and counterions phosphate and citrate were separated effectively from the REEs in the anolyte, favoring REE extraction and allowing sustainable reuse of the leaching agent. This study shows a promising technology that is suitable for primary ores and can further be optimized for secondary resources.

  17. Petrogenesis, Geochemistry and REE Mineralization of the Ilmenite-series Granitoids in Northern Palawan, Philippines

    NASA Astrophysics Data System (ADS)

    Padrones, J. T.; Imai, A.; Takahashi, R.; Gabo, J. A. S.; Tani, K.

    2015-12-01

    A sliver of the Palawan Continental Block associated with the Late Yanshanian magmatism was recently recognized in northern Palawan, Philippines. This intrusive unit is the Late Cretaceous Daroctan granites. This granitic intrusive body, as well as the Middle Miocene Kapoas granitoids, were studied for their petrogenesis. The REE mineralization was also examined because of the I-type and ilmenite-series character of the granitoids and the close spatial and temporal relationship with the granitic units in southern and eastern China, which are viable sources for ion-adsorption type REE mineralization. The granitic intrusive rocks being investigated in this study are composed of biotite granodiorite and biotite granites. Both intrusive units are characterized by high-K calc-alkaline, intermediate I and S-types, and peraluminous. Despite the difference in ages, the geochemistry of both intrusive units shows distinct similarities which suggest same source materials, the partial melting of middle to lower continental crust. The granitoids in the Kapoas show higher light rare earth element (LREE) enrichment than that in the Daroctan but the weathered granitic crusts show higher enrichment in the Daroctan granites compared to the parent granitic rocks. Sequential leaching extraction for REE, Y, and Nb using 8 reagents which selectively dissolved REEs with different mode of occurence (i.e. water soluble, ion-exchangeable salts, Pb- displaceable, acid soluble, Mn-oxide occluded, organically-bound, amorphous Fe-oxide occluded, and crystalline Fe-oxide occluded) show that the Daroctan granites has a potential of ion-adsorption type REE resource with 60 - 73% adsorbed ΣREE. On the other hand, about 18 - 28% adsorbed ΣREE was extracted in the Kapoas granitoid samples. Only monazite occurs as the residual REE-bearing mineral in the Kapoas granitoids, while monazite and xenotime occur in the Daroctan granite. In both samples, mica minerals were altered to vermiculite, which

  18. Geochemistry

    ERIC Educational Resources Information Center

    Brett, Robin; Hanshaw, Bruce B.

    1978-01-01

    The past year has seen the development of certain fields of geochemical research including Nd-Sm isotope studies of meteorites and ancient terrestrial rocks; the use of the consortium approach of assembling a multidisciplined team to tackle a problem; and the handling and analysis of small quantities of materials. (Author/MA)

  19. U-Th-Pb ion microprobe analysis of monazite from the Paleoproterozoic Karrat rare earth element (REE) deposit, western Greenland

    NASA Astrophysics Data System (ADS)

    Mott, A.; Grove, M.; Bird, D. K.

    2012-12-01

    The Karrat rare earth element (REE) deposit is located at 72°N on the Niaqornakavsak peninsula of Qeqertarssuq Island on the western coast of Greenland. Metasomatic alteration of an amphibolite host rock by carbonatite derived fluids resulted in REE mineralization in the Karrat Isfjord area. REE in the mineralization are primarily found in bastnasite, allanite, and monazite. In-situ analysis of monazite was conducted on samples obtained from three sites of mineralization: (1) the primary deposit at Niaqornakavsak consisting of a single distinct ~30m thick unit; (2) at Umiamako Nuna 7 km to the east of Niaqornakavsak where the majority of REE mineralization occurs within the first 20m of the surface; and (3) a 6m thick REE-rich vein 100m below the surface at Umiamako Nuna. Formation ages for monazite at Niaqornakavsak, Umiamako Nuna (surface), and Umiamako Nuna (vein) have been calculated using 207Pb/206Pb, 206Pb/238U, and 208Pb/232Th isotope ratios. Multiple isotope ratios were examined to determine the ideal method of monazite analysis based on the inherent issues of low U content of monazite, difficulties measuring 204Pb, common Pb corrections, and peak interferences resulting from high concentrations of REE. 208Pb/232Th analysis resulted in the best precision and smallest spread of values. Energy filtering was applied to 208Pb/232Th analyses in an effort to reduce interferences at several peaks. Although all three isotope ratio analyses result in a Paleoproterozoic age similar to the timing of convergence of the North Atlantic craton, Rae craton, and Aasiat domain as well as the emplacement of the Prøven Igneous Complex in Greenland (1.95-1.80Ga), the values range between 1.7-1.9Ga depending on the isotope ratio.

  20. Monazite and zircon as major carriers of Th, U, and Y in peraluminous granites: examples from the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Breiter, Karel

    2016-12-01

    The chemical compositions of zircon and monazite and the relationships between the contents of Th, U, Y, and REE in both minerals and in the bulk samples of their parental rocks were studied in three Variscan composite peraluminous granite plutons in the Bohemian Massif. It was established that granites of similar bulk composition contain zircon and monazite of significantly different chemistry. Monazite typically contains 5-13 wt% (rarely up to 28 wt%) ThO2, 0.4-2 wt% (up to 8.2 wt%) UO2, and 0.5-2 wt% (up to 5 wt%) Y2O3, whereas zircon typically contains less than 0.1 wt% (rarely up to 1.7 wt%) ThO2, less than 1 wt% UO2 (in the Plechý/Plockenstein granite, commonly, 1-2 wt% and scarcely up to 4.8 wt% UO2), and less than 1 wt% Y2O3 (in the Nejdek pluton often 2-5, maximally 7 wt% Y2O3). Monazite is an essential carrier of thorium, hosting more than 80 % of Th in all studied granites. Monazite also appears to be an important carrier of Y (typically 14-16 %, and in the Melechov pluton, up to 81 % of the total rock content) and U (typically 18-35 % and occasionally 6-60 % of the total rock budget). The importance of zircon for the rock budget of all the investigated elements in granites is lower: 4-26 % U, 5-17 % Y, and less than 5 % Th.

  1. Ordovician appinites in the Wugongshan Domain of the Cathaysia Block, South China: Geochronological and geochemical evidence for intrusion into a local extensional zone within an intracontinental regime

    NASA Astrophysics Data System (ADS)

    Zhong, Yufang; Ma, Changqian; Liu, Lei; Zhao, Junhong; Zheng, Jianping; Nong, Junnian; Zhang, Zejun

    2014-06-01

    Palaeozoic mafic igneous rocks are potentially significant in constraining the tectonic nature and evolution of the Kwangsian Orogeny in the eastern South China Block, yet they have received little attention because of their limited outcrop. Geochemistry and geochronology was carried out on newly identified Ordovician ultramafic-mafic appinites in the Wugongshan Domain of the Cathaysia Block. Seven appinite samples yielded 206Pb/238U crystallisation ages ranging from 452 ± 4 Ma to 473 ± 3 Ma. Abundant 480-500 Ma zircon xenocrysts and/or inherited zircons were found in the appinites, possibly indicating an earlier magmatism episode in the early Palaeozoic period. The Wugongshan appinites are ultramafic to mafic in composition, and the ultramafic rocks display features of cumulates (high concentrations of MgO, Fe2O3t, Cr, Ni, and low concentrations of total alkali and total rare earth elements [REE]). The appinite geochemistry displays: relatively flat chondrite normalised REE patterns with slight enrichment in light REE and weak negative Eu anomalies; enrichment in large-ion lithophile elements (such as Rb, K), and weak depletion in Nb-Ta in primitive mantle normalised trace element patterns. We suggest that the Wugongshan appinites likely originated from an ancient metasomatised mantle, and that crustal assimilation, fractional crystallisation (AFC), magma mingling and hydration were involved in the petrogenetic process, based on the combination of geochemistry, crust-like bulk Sr, Nd and zircon Hf isotopic compositions (εNd (t) = - 8.2 to - 3.2, initial 87Sr/86Sr ratios of 0.7067-0.7144, zircon εHf (t) values peaking at - 9 to - 3) and regional geological data. Further considering the alignment and chronology of the appinites, we suggest that the appinitic magmas probably were emplaced along the Jiangshan-Shaoxing Fault in a local extensional zone in an intracontinental regime in the early Palaeozoic.

  2. Revised Geochronology and Magnetostratigraphy of Northwest Iceland

    NASA Astrophysics Data System (ADS)

    Riishuus, M. S.; Duncan, R. A.; Kristjansson, L.

    2013-12-01

    .5-15.0 Ma - and at a significantly higher growth rate. This suggests that the period of volcanic quiescence, during which the lignite-bearing laterites were deposited, was long-lived (1-1.5 Myr). Our results also reveal significant variations in growth rates SW-NE along strike of the lava pile, presumably reflecting differences in the volcanic productivity along the rift zone, as well as higher resolution of temporal growth rate variations from 17 to 8 Ma (~350 m/Myr @ 17-15 Ma, ~2200m/Myr @ 14.5-13.8 Ma, ~700m/Myr @ 13.8-11.6 Ma, ~1500m/Myr @ 11.6-10.6 Ma, ~800m/Myr @ 10.5-8 Ma) than hitherto thought. At several stratigraphic levels the new absolute ages are significantly older than the recalculated age data from earlier studies. This requires reassessment of the correlation of the observed polarity patterns with the Geomagnetic Polarity Time Scale. McDougall, I., Kristjansson, L. and Saemundsson, K., 1984. Magnetostratigraphy and geochronology of Northwest Iceland. Journal of Geophysical Research 89, 7029-7060.

  3. Prolonged history of episodic fluid flow in giant hematite ore bodies: Evidence from in situ U Pb geochronology of hydrothermal xenotime

    NASA Astrophysics Data System (ADS)

    Rasmussen, Birger; Fletcher, Ian R.; Muhling, Janet R.; Thorne, Warren S.; Broadbent, Graeme C.

    2007-06-01

    Absolute ages for hydrothermal mineralization and fluid flow are critical for understanding the geological processes that concentrate metals in the Earth's crust, yet many ore deposits remain undated because suitable mineral chronometers have not been found. The origin of giant hematite ore deposits, which are hosted in Precambrian banded-iron formations (BIFs), remains contentious. Several models have been formulated based on different sources and timing for the mineralizing fluids; supergene-metamorphic, syn-orogenic, late-orogenic extensional collapse and syn-extensional. Precise geochronology of the ore offers a means of discriminating between these models. In this study, two U-Pb chronometers, xenotime and monazite, have been identified in high-grade hematite ore bodies from the Mount Tom Price mine in the Hamersley Province, northwestern Australia. Both phosphate minerals occur as inclusions within the hematite ore and as coarser crystals intergrown with martite (hematite pseudomorph after magnetite) and microplaty hematite, indicating that the xenotime and monazite precipitated during mineralization. In situ U-Pb dating by ion microprobe indicates that both phosphate minerals grew during multiple discrete events. Our results suggest that ore genesis may have commenced as early as ˜ 2.15 Ga, with subsequent hydrothermal remobilization and/or mineralization at ˜ 2.05 Ga, ˜ 1.84 Ga, ˜ 1.67 Ga, ˜ 1.59 Ga, ˜ 1.54 Ga, ˜ 1.48 Ga and ˜ 0.85 Ga. The location of the ore bodies along ancient fault systems, and the coincidence of at least some of the U-Pb phosphate dates with episodes of tectonothermal activity in the adjacent Proterozoic Capricorn Orogen, implies that fluids were channelled through major structures in the southern Pilbara Craton during discrete phases of tectonic compression and extension. Our results show that the hematite ore bodies formed at sites of repeated focussed hydrothermal fluid flow. In contrast to the aforementioned models, our

  4. Microstructural, geothermobarometric and geochronological constraints on the complex Alpine collisional history recorded on the low-grade "Psunj Complex" metamorphic rocks of the Slavonian Mts. (Croatia)

    NASA Astrophysics Data System (ADS)

    Balen, Dražen

    2014-05-01

    Metamorphic rocks of the Slavonian Mts. (NE Croatia) cropping out on the SW edge of the Pannonian Basin belong to the Bihor nappe system of Tisia Mega-Unit i.e. of the lithospheric fragment broken off from the southern margin of the European plate. The present-day position of this Unit resulted from complex regional-scale Mesozoic and Cenozoic movements during the Alpine-Carpathian-Dinaridic orogenic system geodynamic evolution. Usually, the metamorphic rocks of the Slavonian Mts. are interpreted as a part of igneous-metamorphic complex belonging to metamorphic belt formed during or even prior to the Variscan orogeny. Until recently, the Alpine metamorphic evolution was considered insignificant and often neglected or described just in general terms due to considerable lack of geothermobarometric, phase equilibrium, fossil and/or geochronological age constraints. The chlorite schists are widely distributed lithology in the area, comprising simple peak metamorphic mineral assemblage chlorite + plagioclase (albite) + muscovite + quartz ± garnet and are associated to the local complex called Psunj complex (PsC). Metamorphic conditions for non-garnetiferous chlorite schists are obtained with chlorite (Al(IV)) thermometry and white mica barometry are 300 °C and 2.4±0.6 kbar. The chlorite schists are thrusted over (~ to the NE) microtectonically similar chloritoid-bearing schists that reached peak P-T values of 3.5-4 kbar and 340-380 °C. At least two distinct penetrative low-grade metamorphic foliations recorded in the chlorite schists are accompanied by existence of different populations of small (~3.5 µm) low-Th monazites, giving an average age 99±15 Ma. Histogram of obtained ages shows two peaks at 120 and 80 Ma while age modelling recognized two peaks at 113±20 and 82±23 Ma. First Alpine (113±20 Ma) event represents a rare record of late Early Cretaceous thermal event that affected Bihor nappe system. The age contradicts common opinion that Bihor nappe

  5. Divisions of geologic time-major chronostratigraphic and geochronologic units

    USGS Publications Warehouse

    ,

    2010-01-01

    Effective communication in the geosciences requires consistent uses of stratigraphic nomenclature, especially divisions of geologic time. A geologic time scale is composed of standard stratigraphic divisions based on rock sequences and is calibrated in years. Over the years, the development of new dating methods and the refinement of previous methods have stimulated revisions to geologic time scales. Advances in stratigraphy and geochronology require that any time scale be periodically updated. Therefore, Divisions of Geologic Time, which shows the major chronostratigraphic (position) and geochronologic (time) units, is intended to be a dynamic resource that will be modified to include accepted changes of unit names and boundary age estimates. This fact sheet is a modification of USGS Fact Sheet 2007-3015 by the U.S. Geological Survey Geologic Names Committee.

  6. Th-Pb Monazite-in-Garnet Ages From the Greater Himalayan Sequence of Central Nepal

    NASA Astrophysics Data System (ADS)

    Gehrels, G.; Decelles, P.; Martin, A.

    2007-12-01

    431 new Th-Pb ages have been determined from rocks of the Greater Himalayan Sequence (GHS) of central Nepal. Some of these ages are reported by Martin et al. (2007, Chem. Geol.), most have not been reported previously. 42 samples were collected from transects along Kali Gandaki, Modi Khola, Seti Nadi, Madi Nadi, Nayu Ridge, and Marsyangdi Nadi in the Annapurna region, with three transects extending across the GHS and three transects concentrated near the base of the sequence. Garnet crystals were extracted from the samples, and monazite inclusions were identified by BSE imaging and then analyzed by LA-MC-ICPMS with a 10 micron laser beam. Where possible, inclusions were sampled from both cores and rims of the garnet crystals. The resulting ages belong to four groups: (1) 3 ages (all cores) between 801 Ma and 1407 Ma that are inherited from GHS protoliths, (2) 42 ages (all cores) from 550 Ma to 400 Ma (peak age of 487 Ma) that record early Paleozoic prograde metamorphism, (3) 102 ages (nearly all cores) scattered between 400 Ma and ~50 Ma that are interpreted as early Paleozoic grains which have experienced either Pb loss or overgrowth of Tertiary monazite, and (4) 284 ages (2/3 cores, 1/3 rims) between ca. 50 Ma and ca. 10 Ma, with cores only slightly (avg of 1.5 m.y.) older than rims. The Tertiary ages consistently young northward/upsection from ca. 35 to ca. 18 Ma, and in Marsyangdi Nadi define two separate panels that are interpreted to be imbricated along a north-dipping thrust fault. This fault is near the base of sillimanite-bearing rocks, similar to the Langtang thrust (Kohn et al. 2005, JMG), and may be partly responsible for the inverted metamorphic gradient discussed by many previous workers. Our preferred structural scenario is that the Tertiary monazite ages record progressive burial of the GHS by shortening in the Tethyan thrust belt between ca. 35 and ca. 18 Ma, termination of this metamorphism due to onset of motion along the MCT, and ca. 10 Ma

  7. Disturbance versus preservation of U-Th-Pb ages in monazite during fluid-rock interaction: textural, chemical and isotopic in situ study in microgranites (Velay Dome, France)

    NASA Astrophysics Data System (ADS)

    Didier, A.; Bosse, V.; Boulvais, P.; Bouloton, J.; Paquette, J.-L.; Montel, J.-M.; Devidal, J.-L.

    2013-06-01

    Monazite is extensively used to date crustal processes and is usually considered to be resistant to diffusive Pb loss. Nevertheless, fluid-assisted recrystallisation is known to be capable of resetting the monazite chronometer. This study focuses on chemical and isotopic disturbances in monazite grains from two microgranite intrusions in the French Central Massif (Charron and Montasset). Petrologic data and oxygen isotopes suggest that both intrusions have interacted with alkali-bearing hydrothermal-magmatic fluids. In the Charron intrusion, regardless of their textural location, monazite grains are sub-euhedral and cover a large domain of compositions. U-Pb chronometers yield a lower intercept age of 297 ± 4 Ma. An inherited component at 320 Ma is responsible for the scattering of the U-Th-Pb ages. The Montasset intrusion was later affected by an additional F-rich crustal fluid with crystallisation of Ca-REE-fluorocarbonates, fluorite, calcite and chloritisation. Pristine monazite is chemically homogeneous and displays 208Pb/232Th and 206Pb/238U concordant ages at 307 ± 2 Ma. By contrast, groundmass monazite shows dissolution-recrystallisation features associated with apatite and thorite precipitation (Th-silicate) and strong chemical reequilibration. 208Pb/232Th ages are disturbed and range between 270 and 690 Ma showing that the Th/Pb ratio is highly fractionated during the interaction with fluids. Apparent U-Pb ages are older due to common Pb incorporation yielding a lower intercept age at 312 ± 10 Ma, the age of the pristine monazite. These results show that F-rich fluids are responsible for Th mobility and incorporation of excess Pb, which thus strongly disturbed the U-Th-Pb chronometers in the monazite.

  8. Geochronological constraints on the evolution of El Hierro (Canary Islands)

    NASA Astrophysics Data System (ADS)

    Becerril, Laura; Ubide, Teresa; Sudo, Masafumi; Martí, Joan; Galindo, Inés; Galé, Carlos; Morales, Jose María; Yepes, Jorge; Lago, Marceliano

    2016-01-01

    New age data have been obtained to time constrain the recent Quaternary volcanism of El Hierro (Canary Islands) and to estimate its recurrence rate. We have carried out 40Ar/39Ar geochronology on samples spanning the entire volcanostratigraphic sequence of the island and 14C geochronology on the most recent eruption on the northeast rift of the island: 2280 ± 30 yr BP. We combine the new absolute data with a revision of published ages onshore, some of which were identified through geomorphological criteria (relative data). We present a revised and updated chronology of volcanism for the last 33 ka that we use to estimate the maximum eruptive recurrence of the island. The number of events per year determined is 9.7 × 10-4 for the emerged part of the island, which means that, as a minimum, one eruption has occurred approximately every 1000 years. This highlights the need of more geochronological data to better constrain the eruptive recurrence of El Hierro.

  9. Detrital Zircon U-Pb Geochronology Applied to Tectonics

    NASA Astrophysics Data System (ADS)

    Gehrels, George

    2014-05-01

    Detrital zircon geochronology is rapidly developing into an essential tool in Earth science research because of the widespread occurrence of zircon in sedimentary systems; the wide range of information that can be extracted from zircon crystals; the ability to determine ages with reasonable precision, accuracy, and efficiency; and the wide range of new ideas about how to use detrital zircon geochronologic information. The U-Pb system is particularly powerful because three chronometers are available (238U+206Pb, 235U+207Pb, and 232Th+208Pb), but challenges arise because of complexities from inheritance and Pb loss. Ages can be used to constrain the age of deposition of the host sediment, reconstruct provenance, characterize a sedimentary unit, and characterize many different aspects of source regions. Detrital zircon geochronology has an exciting future given the growth history recorded in individual crystals; the variety of detrital minerals that can provide complementary information; and the large number of geochemical, isotopic, and chronologic systems that can be applied to these minerals.

  10. A direct comparison of the ages of detrital monazite versus detrital zircon in Appalachian foreland basin sandstones: Searching for the record of Phanerozoic orogenic events

    NASA Astrophysics Data System (ADS)

    Hietpas, Jack; Samson, Scott; Moecher, David

    2011-10-01

    The provenance potential of detrital monazite was investigated by in situ measurement of 232Th- 208Pb dates of grains isolated from six Middle Carboniferous-Permian sandstones from the Appalachian foreland basin. Provenance assessment of these units was previously investigated by measuring U-Pb crystallization ages of detrital zircon (Thomas et al., 2004; Becker et al., 2005, 2006). Approximately 90% of the detrital zircon ages record Mesoproterozoic or older ages, with only 10% recording the three major pulses of tectonism (Taconian, Acadian and Alleghanian) that are the hallmark of the Appalachian Orogen. 232Th- 208Pb ages of detrital monazite, however, strongly record the complex phases of Paleozoic orogenesis. Nearly 65% of the ages record Paleozoic events, while 35% record Neoproterozoic or older ages. In several of the analyzed sandstones, detrital monazite ages record Paleozoic orogenic events that are completely missed by detrital zircon ages, demonstrating that monazite ages more accurately reflect the character of the sediment source rocks. The inferred maximum age of sediment deposition, as determined by the youngest monazite grains, is ~ 550 Ma younger for two of the analyzed sandstones compared to depositional constraints based on the youngest detrital zircon. The different physical properties and petrogenesis of zircon and monazite are interpreted to be factors for the dramatic differences in sediment provenance information provided by each mineral. The results from this study have important implications for determining sediment provenance, constraining maximum age of sediment deposition, and developing robust regional tectonic models.

  11. Characterization of PAH matrix with monazite stream containing uranium, gadolinium and iron

    NASA Astrophysics Data System (ADS)

    Pal, Sangita; Meena, Sher Singh; Goswami, D.

    2016-05-01

    Uranium (U) gadolinium(Gd) and iron (Fe) containing alkaline waste simulated effluent (relevant to alkaline effluent of monazite ore) has been treated with a novel amphoteric resin viz, Polyamidehydroxamate (PAH) containing amide and hydroxamic acid groups. The resin has been synthesized in an eco-friendly manner by polymerization nad conversion to functional groups characterized by FT-IR spectra and architectural overview by SEM. Coloration of the loaded matrix and de-coloration after extraction of uranium is the special characteristic of the matrix. Effluent streams have been analyzed by ICP-AES, U loaded PAH has been characterized by FT-IR, EXAFS, Gd and Fe by X-ray energy values of EDXRF at 6.053 Kev and 6.405 Kev respectively. The remarkable change has been observed in Mössbauer spectrum of Fe-loaded PAH samples.

  12. It's About Time: How Accurate Can Geochronology Become?

    NASA Astrophysics Data System (ADS)

    Harrison, M.; Baldwin, S.; Caffee, M. W.; Gehrels, G. E.; Schoene, B.; Shuster, D. L.; Singer, B. S.

    2015-12-01

    As isotope ratio precisions have improved to as low as ±1 ppm, geochronologic precision has remained essentially unchanged. This largely reflects the nature of radioactivity whereby the parent decays into a different chemical species thus putting as much emphasis on the determining inter-element ratios as isotopic. Even the best current accuracy grows into errors of >0.6 m.y. during the Paleozoic - a span of time equal to ¼ of the Pleistocene. If we are to understand the nature of Paleozoic species variation and climate change at anything like the Cenozoic, we need a 10x improvement in accuracy. The good news is that there is no physical impediment to realizing this. There are enough Pb* atoms in the outer few μm's of a Paleozoic zircon grown moments before eruption to permit ±0.01% accuracy in the U-Pb system. What we need are the resources to synthesize the spikes, enhance ionization yields, exploit microscale sampling, and improve knowledge of λ correspondingly. Despite advances in geochronology over the past 40 years (multicollection, multi-isotope spikes, in situ dating), our ability to translate a daughter atom into a detected ion has remained at the level of 1% or so. This means that a ~102 increase in signal can be achieved before we approach a physical limit. Perhaps the most promising approach is use of broad spectrum lasers that can ionize all neutrals. Radical new approaches to providing mass separation of such signals are emerging, including trapped ion cyclotron resonance and multi-turn, sputtered neutral TOF spectrometers capable of mass resolutions in excess of 105. These innovations hold great promise in geochronology but are largely being developed for cosmochemistry. This may make sense at first glance as cosmochemists are classically atom-limited (IDPs, stardust) but can be a misperception as the outer few μm's of a zircon may represent no more mass than a stardust mote. To reach the fundamental limits of geochronologic signals we need to

  13. AGE (Argon Geochronology Experiment): An Instrument for Geochronology on the Surface of Mars

    NASA Technical Reports Server (NTRS)

    Swindle, T. D.; Bode, R.; Boynton, W. V.; Kring, D. A.; Williams, M.; Chutjian, A.; Darrach, M. R.; Cremers, D. A.; Wiens, R. C.; Baldwin, S. L.

    2003-01-01

    As our knowledge of the planet Mars continues to grow, one parameter that remains elusive is the absolute chronology of the planet s geological history. Although crater counts have provided a robust relative chronology, impactor fluxes are poorly enough known that there are places on Mars where the absolute age is uncertain by a factor of two or more. To resolve these uncertainties, it will be necessary to either analyze well-documented samples returned to the Earth from the Martian surface or to perform in situ measurements with sufficient precision. Sample return is still at least a decade away, and even then it might be from a biologically interesting area that might be geologically complex. Hence an in situ measurement, within an uncertainty of 20% or better, could greatly improve our knowledge of the history of Mars. With funding from the Planetary Instrument Definition and Development Program (PIDDP), we have been working on an instrument to perform potassium-argon (K-Ar) and cosmic-ray exposure (CRE) dating in situ on the surface of Mars. For either of these techniques, it is necessary to measure the abundance of one or more major or minor elements (K in the case of KAr; all majors and minors in the case of CRE) and the abundance and isotopes composition of a noble gas (Ar in the case of K-Ar; He, Ne and Ar for CRE dating). The technology for either of these types of measurements exists, but has never before been integrated for a spacecraft. We refer to the instrument as AGE, the Argon Geochronology Experiment (although we will measure the noble gases He and Ne as well for CRE ages). We report here on the basic components that go into such an instrument, both those that use existing technology and those that had to be developed to create the integrated package.

  14. Late Paleozoic to Early Mesozoic arc-related magmatism in southeastern Korea: SHRIMP zircon geochronology and geochemistry

    NASA Astrophysics Data System (ADS)

    Yi, Keewook; Cheong, Chang-sik; Kim, Jeongmin; Kim, Namhoon; Jeong, Youn-Joong; Cho, Moonsup

    2012-11-01

    Phanerozoic granitoids are widespread in the Korean Peninsula and form a part of the East Asian Cordilleran-type granitoid belt extending from southeastern China to Far East Russia. Here we present SHRIMP zircon U-Pb ages and geochemical and Nd isotopic compositions of Late Paleozoic to Early Jurassic granitoid plutons in the northern Gyeongsang basin, southeastern Korea; namely the Jangsari, Yeongdeok, Yeonghae, and Satkatbong plutons. The granite and associated gabbroic rocks from the Jangsari pluton were coeval and respectively dated at 257.3 ± 2.0 Ma and 255.7 ± 1.4 Ma. This result represents the first finding of a Late Paleozoic pluton in South Korea. Three granite samples from the Yeongdeok pluton yielded a slightly younger age span ranging from 252.9 ± 2.5 Ma to 246.7 ± 2.1 Ma. Two diorite samples from the Yeonghae pluton gave much younger ages of 195.1 ± 1.9 Ma and 196.3 ± 1.6 Ma. An Early Jurassic age of 192.4 ± 1.6 Ma was also obtained from a diorite sample from the Satkatbong pluton. The mineral assemblage and Al2O3/(Na2O + K2O) versus Al2O3/(CaO + Na2O + K2O) relationship indicate that all the analyzed plutons are subduction zone granitoids. Enrichments in large-ion-lithophile-elements and depletions in high-field-strength-elements of these plutons are also concordant with geochemical characteristics typical for the subduction zone magma. The presence of Late Permian to Early Triassic arc system is in contrast with the conventional idea that the arc magmatism along the continental margin of the Korean Peninsula has commenced from Early Jurassic after the termination of Triassic collisional orogenesis. The ɛNd(t) values of the granitoid plutons are consistently positive (2.4-4.6), suggesting that crustal residence time of the basement beneath the Gyeongsang basin is relatively short. Moreover, the reevaluation of previously-published data reveals that geochemical compositions of the Yeongdeok pluton are compatible with those of high-silica adakites; La/Yb = 37.5-114.6, Sr/Y = 138.2-214.0, SiO2 = 62.9-72.0 wt.%, Al2O3 = 15.5-17.0 wt.%, Sr = 562-1173 ppm, MgO = 0.4-1.6 wt.%, Y = 3-6 ppm, Yb = 0.18-0.45 ppm, and Eu/Eu* = 0.92-1.31. The occurrence of adakites in southeastern Korea, and presumably in the Hida belt of central-western Japan, is indicative of a hot subduction regime developing at least partly along the East Asian continental margin during the Permian-Triassic transition period.

  15. Geochemistry, geochronology and isotope geology of Nakfa intrusive rocks, northern Eritrea: products of a tectonically thickened Neoproterozoic arc crust

    NASA Astrophysics Data System (ADS)

    Teklay, M.; Kröner, A.; Mezger, K.

    2001-08-01

    The north-south-trending Neoproterozoic volcano-sedimentary plutonic associations in northern Eritrea are part of the Nubian Shield. The Nakfa intrusive rocks range in composition from gabbro to syeno-diorite to granite and alkaline syenite and intrude supracrustal rocks of volcanic and sedimentary origin. All granitoid rocks are metaluminous or slightly peraluminous and have typical I-type chemical signatures. The calc-alkaline intrusive rocks and the alkaline syenites have geochemical characteristics (e.g. low Nb values) typical of arc intrusives and plot as volcanic arc granites on various discriminant diagrams. Single zircon evaporation Pb-Pb ages and conventional multigrain U-Pb ages on zircons and titanites yielded emplacement ages of ˜620-640 Ma. These are comparable to those of adjacent juvenile terranes in the Nubian Shield. No pre-Pan-African rocks have so far been found in northern Eritrea. Isotopic data show a limited range, with initial ɛ Nd values ranging from 3.5 to 5.6 and initial Sr ratios from 0.7018 to 0.7037. The high positive initial ɛ Nd values and low initial Sr ratios indicate that the granitoid rocks were derived from a mantle and/or juvenile crustal source with no, or only insignificant, contribution from an older continental component. This is further supported by the absence of inherited zircons and the lack of rocks of continental affinity. Leached K-feldspars from Nakfa intrusive rocks have Pb isotope ratios ( 206Pb/ 204Pb = 17.60-17.88, 207Pb/ 204Pb = 15.49-15.53 and 208Pb/ 204Pb = 37.12-37.37) similar to those for 'oceanic leads' from Saudi Arabia, which are interpreted as manifesting a mantle source. Hence, the Pb isotope ratios, in agreement with the Sr and Nd isotopic data, indicate an insignificant involvement of older crustal components in the generation of Pan-African crust in northern Eritrea. The ages and isotopic characteristics of the Nakfa intrusive rocks are comparable to those of adjacent juvenile terranes in the Arabian-Nubian Shield and strengthen models for the generation of large volumes of juvenile continental crust during Neoproterozoic times. A substantial number of Nakfa granitoid rocks show geochemical characteristics (low Y, high Sr/Y and steeper REE pattern), indicating that crust formation involved the fractional crystallisation of mafic magma and the melting of lower crust.

  16. Geochronology and geochemistry of the rocks associated with a late proterozoic ophiolite in West Pokot, NW Kenya

    NASA Astrophysics Data System (ADS)

    Ries, A. C.; Vearncombe, J. R.; Price, R. C.; Shackleton, R. M.

    1992-01-01

    Mafic and ultramafic rocks in the W Pokot area, NW Kenya are identified as parts of a dismembered ophiolite. They lie within the late Proterozoic Mozambique Belt and are associated with metasediments and calc-alkaline volcanics and intruded by granitic rocks. All these rocks are allochthonous, thrust westwards towards the Archaean Tanzanian Craton. The calc-alkaline volcanics, which are chemically similar to present-day island-arc volcanic rocks, give a Rb/Sr whole-rock isochron age of 663 ± 49 Ma, and the associated metasediments give an age of 584 ± 25 Ma, both ages interpreted as dating a regional amphibolitefacies metamorphism. These rocks are intruded by the Marich Granite from which a Rb/Sr whole-rock isochron age of 593 ± 50 Ma was obtained with an 87Sr/ 86Sr initial ratio of 0/7072 ± 5 implying some crustal contamination either from the magmatite complex, which structurally underlies the ophiolitic rocks, or from deeper crustal rocks. The age spectrum is broadly similar to that established for similar sequences of rocks northwards along strike in Sudan, Egypt and Saudi Arabia. There is no support for the view that these high-grade metamorphic rocks of this part of the Mozambique Belt are an older series underlying the lower grade Late Prpterozoic rocks of NE Africa and Saudi Arabia.

  17. U-Pb SHRIMP geochronology and trace-element geochemistry of coesite-bearing zircons, North-East Greenland Caledonides

    USGS Publications Warehouse

    McClelland, W.C.; Power, S.E.; Gilotti, J.A.; Mazdab, F.K.; Wopenka, B.

    2006-01-01

    Obtaining reliable estimates for the timing of eclogite-facies metamorphism is critical to establishing models for the formation and exhumation of high-pressure and ultrahigh-pressure (UHP) metamorphic terranes in collisional orogens. The presence of pressure-dependent phases, such as coesite, included in metamorphic zircon is generally regarded as evidence that zircon growth occurred at UHP conditions and, ifdated, should provide the necessary timing information. We report U-Pb sensitive high-resolution ion microprobe (SHRIMP) ages and trace-element SHRIMP data from coesite-bearing zircon suites formed during UHP metamorphism in the North- East Greenland Caledonides. Kyanite eclogite and quartzofeldspathic host gneiss samples from an island in J??kelbugt (78??00'N, 18??04'W) contained subspherical zircons with well-defined domains in cathodoluminescence (CL) images. The presence of coesite is confirmed by Raman spectroscopy in six zircons from four samples. Additional components of the eclogite-facies inclusion suite include kyanite, omphacite, garnet, and rutile. The trace-element signatures in core domains reflect modification of igneous protolith zircon. Rim signatures show flat heavy rare earth element (HREE) patterns that are characteristic of eclogite-facies zircon. The kyanite eclogites generally lack a Eu anomaly, whereas a negative Eu anomaly persists in all domains of the host gneiss. The 207Pb- corrected 206Pb/238U ages range from 330 to 390 Ma for the host gneiss and 330-370 Ma for the kyanite eclogite. Weighted mean 206Pb/238U ages for coesite-bearing domains vary from 364 ?? 8 Ma for the host gneiss to 350 ?? 4 Ma for kyanite eclogite. The combined U-Pb and REE data interpreted in conjunction with observed CL domains and inclusion suites suggest that (1) Caledonian metamorphic zircon formed by both new zircon growth and recrystallization, (2) UHP metamorphism occurred near the end of the Caledonian collision, and (3) the 30-50m.y. span of ages records long residence times at eclogite-facies conditions for the UHProcks of North-East Greenland. This spread in observed ages is interpreted to be characteristic of metamorphic rocks that have experienced relatively long (longer than 10 m.y.) residence times at UHP conditions. ?? 2006 Geological Society of America.

  18. Geochronology and geochemistry of Eocene potassic felsic intrusions in the Nangqian basin, eastern Tibet: Tectonic and metallogenic implications

    NASA Astrophysics Data System (ADS)

    Xu, Yue; Bi, Xian-Wu; Hu, Rui-Zhong; Chen, You-wei; Liu, He-qing; Xu, Lei-luo

    2016-03-01

    The Jinshajiang-Ailaoshan copper belt is the most significant porphyry copper belt in eastern Tibet. In the northern segment of this belt within the Nangqian basin, which occurs 100 km east of the Yulong porphyry copper deposit, several felsic intrusions have been recently discovered. The Yulong porphyry copper deposit is one of the largest porphyry copper deposits in China, and it is associated with peraluminous adakitic rocks formed in a post-collisional setting. The Nangqian felsic intrusions vary from syenite porphyry to monzonite porphyry in rock types. No significant Cu-Au mineralization has been found in the Nangqian felsic intrusions despite extensive exploration in recent years. LA-ICP-MS zircon U-Pb dating reveals that the Nangqian syenite porphyry and monzonite porphyry were emplaced at 35.6±0.3 Ma and from 39.5±0.3 to 37.4±0.3 Ma, respectively, similar to the age of the Yulong porphyry copper deposit. The Nangqian felsic intrusions are characterized by metaluminous compositions (A/CNK = 0.82-1.01), and they share some common features with shoshonites such as high K2O contents (4.58-5.58 wt.%), high K2O/Na2O ratios (0.92-1.28), LREE-LILE enrichments and negative Nb-Ta-Ti-P anomalies, as well as with adakites derived from an eclogite-facies source with high Al2O3 (14.98-15.74 wt.%), Sr (954-2190 ppm), Sr/Y (68-132) and La/Yb (53-85), and low Y and Yb contents. The Nangqian felsic intrusions have high initial 87Sr/86Sr (0.7050-0.7055), variable εNd(t) (- 0.31-1.43) and small variations in (206Pb/204Pb)i (18.68-18.74), (207Pb/204Pb)i (15.53-15.62) and (208Pb/204Pb)i (38.51-38.80). Zircon crystals from both syenite and monzonite porphyries are characterized by positive εHf(t) from 5.2 to 8.5. The results suggest that the syenite and monzonite magmas were differentiated from parental shoshonitic melts by fractional crystallization of olivine, clinopyroxene and minor feldspar. The parent magmas originated from a lithospheric mantle metasomatized by slab-derived fluids or melts during continental subduction. The differences in both sources and depths of partial melting may explain the difference in the extent of Cu-Au mineralization between the Yulong and Nangqian porphyries.

  19. Mechanisms and timescales of generating eruptible rhyolitic magmas at Yellowstone caldera from zircon and sanidine geochronology and geochemistry

    USGS Publications Warehouse

    Stelten, Mark; Cooper, Kari M.; Vazquez, Jorge A.; Calvert, Andrew T.; Glessner, Justin G

    2015-01-01

    We constrain the physical nature of the magma reservoir and the mechanisms of rhyolite generation at Yellowstone caldera via detailed characterization of zircon and sanidine crystals hosted in three rhyolites erupted during the (ca. 170 – 70 ka) Central Plateau Member eruptive episode – the most recent post-caldera magmatism at Yellowstone. We present 238U-230Th crystallization ages and trace-element compositions of the interiors and surfaces (i.e., unpolished rims) of individual zircon crystals from each rhyolite. We compare these zircon data to 238U- 230Th crystallization ages of bulk sanidine separates coupled with chemical and isotopic data from single sanidine crystals. Zircon age and trace-element data demonstrate that the magma reservoir that sourced the Central Plateau Member rhyolites was long-lived (150 – 250 kyr) and genetically related to the preceding episode of magmatism, which occurred ca. 256 ka. The interiors of most zircons in each rhyolite were inherited from unerupted material related to older stages of Central Plateau Member magmatism or the preceding late Upper Basin Member magmatism (i.e., are antecrysts). Conversely, most zircon surfaces crystallized near the time of eruption from their host liquids (i.e., are autocrystic). The repeated recycling of zircon interiors from older stages of magmatism demonstrates that sequentially erupted Central Plateau Member rhyolites are genetically related. Sanidine separates from each rhyolite yield 238U-230Th crystallization ages at or near the eruption age of their host magmas, coeval with the coexisting zircon surfaces, but are younger than the coexisting zircon interiors. Chemical and isotopic data from single sanidine crystals demonstrate that the sanidines in each rhyolite are in equilibrium with their host melts, which considered along with their near-eruption crystallization ages suggests that nearly all CPM sanidines are autocrystic. The paucity of antecrystic sanidine crystals relative to antecrystic zircons require a model where eruptible rhyolites are generated by extracting melt and zircons from a long-lived mush of immobile crystal-rich magma. In this process the larger sanidine crystals remain trapped in the locked crystal network. The extracted melts (plus antecrystic zircon) amalgamate into a liquid dominated (i.e., eruptible) magma body that is maintained as a physically distinct entity relative to the bulk of the long-lived crystal mush. Zircon surfaces and sanidines in each rhyolite crystallize after melt extraction/amalgamation and their ages constrain the residence time of eruptible magmas at Yellowstone. Residence times of the large volume rhyolites (~40 – 70 km3) are ≤ 1 kyr (conservatively < 6 kyr), which suggests that large volumes of rhyolite can be generated rapidly by extracting melt from a crystal mush. Because the lifespan of the crystal mush that sourced the Central Plateau Member rhyolites is two orders of magnitude longer than the residence time of eruptible magma bodies within the reservoir, it is apparent that the Yellowstone magma reservoir spends most of its time in a largely-crystalline (i.e., uneruptible) state, similar to the present-day magma reservoir, and that eruptible magma bodies are ephemeral features.

  20. Geochronology and geochemistry of lithologies of the Tabuaço W-prospect area (Northern Portugal)

    NASA Astrophysics Data System (ADS)

    Cerejo, Tiago; Francisco Santos, Jose; Sousa, Joao Carlos; Castanho, Nuno; Sergio, Gabriel; Ribeiro, Sara

    2016-04-01

    This work is focussed on lithologies occurring at Quinta de São Pedro das Águias, which is located in the Tabuaço prospect (an area of 45 km2 where exploration for W-skarn deposits is taking place, in northern Portugal, close to the Douro valley). At Quinta de São Pedro das Águias several lithologies are recognized: "normal" phyllites, black phyllites (graphite-bearing), marbles, calcsilicate (s.s.) rocks and skarns (sometimes, scheelite-bearing), belonging to the Bateiras Formation, of the Douro Group (one of the two major subdivisions of the Neoproterozoic-Cambrian Dúrico-Beirão Supergroup); Paredes da Beira-Tabuaço granite; several aplitic and pegmatitic bodies. The studied area belongs to the Central Iberian Zone, a geotectonic unit of the Iberian Variscan Chain. Rb-Sr isotope analyses done in the scope of this work, provided a 316 ± 7 Ma whole-rock isochron (MSWD = 1.7; initial 87Sr/86Sr = 0.7146) for the granitoids, using the 87Rb decay constant recently recommended by IUPAC-IUGS (Villa et al., 2015). This date is interpreted here as the emplacement age of those rocks, during a late stage of the Variscan D3. The granite revealed a S-type nature, namely because it is a muscovite granite, it shows a peraluminous composition (average A/CNK = 1.28), and the Sr and Nd isotope fingerprints (-8.9 ≤ ɛNd(316Ma) ≤ -7.8; +0.7105 ≤ 87Sr/86Sr(316Ma) ≤ 0.7182) fit into the composition of metasedimentary crust. The analysed phyllites show the following isotopic compositions: -9.7 ≤ ɛNd(316Ma) ≤ -8.2; +0.7148 ≤ 87Sr/86Sr(316Ma) ≤ 0.7188. Therefore, the isotope signatures, at 316 Ma, of the granite and of the studied metapelites overlap, suggesting that the parental magma was generated by anatexis of Grupo do Douro metasediments. According to their petrographic, geochemical and isotopic features, aplites and pegmatites are viewed as extreme differentiates from the granite. São Pedro das Águias metapelites show biotite zone parageneses. Geochemically, their REE normalized patterns are very similar to those displayed by NIBAS and by other upper crustal reference compositions. Isotopically, especially due to their lower ɛNd316, the studied metapelites are clearly distinct from the Grupo das Beiras metasediments (the other major division of the Dúrico-Beirão Supergroup), and, instead, they resemble other metasedimentary units of the Iberian Massif. Several lines of evidence, namely the isotope data (-8.1 ≤ ɛNd(316Ma) ≤ -6.4; +0.7090 ≤ 87Sr/86Sr(316Ma) ≤ 0.7102) and the occurrence of fine intercalations of sub-mm layers enriched in phyllosilicates, suggest that calcsilicate (s.l.) rocks owe their composition not only to metasomatism that accompanied the granite intrusion, but also to an inheritance from their protoliths, which should have resulted from mixed sedimentation, both chemical and terrigenous. This work was financially supported by: - FEDER funds trough Operational Programme Competitiveness Factors - COMPETE and by national funds through FCT - Fundação para a Ciência e a Tecnologia in the scope of projects Petrochron (PTDC/CTE-GIX/112561/2009) and Geobiotec (UID/GEO/04035/2013); - Colt Resources. Reference: Villa, I.M., De Bièvre, P., Holden, N.E., Renne, P.R., 2015. IUPAC-IUGS recommendation on the half life of 87Rb. Geochim. Cosmochim. Acta 164, 382-385.

  1. Prolonged Eclogite-Facies Metamorphism: Evidence From Geochronology and Trace Element Geochemistry, North Qaidam UHP Terrane, NW China

    NASA Astrophysics Data System (ADS)

    Mattinson, C. G.; Wooden, J. L.; Mazdab, F. K.; Liou, J. G.; Bird, D. K.; Wu, C.

    2006-12-01

    Amphibolite-facies felsic gneisses near Dulan, at the southeast end of the North Qaidam terrane, enclose minor (<10 vol%) eclogite and peridotite which record ultra-high pressure (UHP) metamorphism. Field relations, and coesite inclusions in zircons from paragneiss suggest that felsic, mafic, and ultramafic rocks all experienced UHP metamorphism and a common amphibolite-facies retrogression. SHRIMP-RG U-Pb and REE analyses of zircons from four eclogites yield weighted mean ages of 449--422 Ma; REE patterns (flat HREE, no Eu anomaly) and inclusions of garnet, omphacite, and rutile indicate that these ages record eclogite-facies metamorphism. Trace element variations in zircon are similar to core-to-rim trace element zoning of coexisting garnet revealed by LA-ICP-MS analysis. The coherent field relations, and the similar range of individual ages in each sample suggests that the ~25 m.y. age range reflects the duration of eclogite-facies conditions. Ti-in-zircon thermometry results show considerable spread, but may suggest cooling from 650-700°C (442--449 Ma) to 600-650°C (433--422 Ma). One group of zircons yields 770--810°C temperatures, possibly related to granulite-facies overprinting during exhumation. In contrast to Ti-in-zircon, Zr- in-rutile thermometry yields tightly clustered results of 590°C for all four eclogites and one 426 ± 4 Ma paragneiss. The ~25 m.y. duration as well as possible cooling during eclogite-facies metamorphism suggests the UHP rocks decoupled from the downgoing plate, and were refrigerated by continued, structurally deeper subduction. In the Lüliang Shan (350 km NW) in the North Qaidam terrane, eclogite and garnet peridotite ages of 414-- 495 Ma suggest that this locality also records a protracted eclogite-facies history. Evidence of prolonged eclogite-facies metamorphism in other HP/UHP localities (Greenland, Norway, Alps, Dabie-Sulu) suggests that eclogite-facies residence times of >15--25 m.y. may be globally significant in continental subduction/collision zones.

  2. Geology, isotope geochemistry and geochronology of the Jinshachang carbonate-hosted Pb-Zn deposit, southwest China

    NASA Astrophysics Data System (ADS)

    Zhou, Jia-Xi; Bai, Jun-Hao; Huang, Zhi-Long; Zhu, Dan; Yan, Zai-Fei; Lv, Zhi-Cheng

    2015-02-01

    The Jinshachang Pb-Zn deposit, an exceptionally radiogenic Pb-enriched sulfide deposit, hosted by dolostone of the Upper Sinian (Neoproterozoic) Dengying Formation and the Lower Cambrian Meishucun Formation, is located in the western Yangtze Block, about 300 km northeast of Kunming city in southwest China. Ore bodies in this deposit are dominated by strata-bound type and steeply dipping vein type. Primary ores in these two types are composed of sphalerite, galena, fluorite, barite and quartz with massive, banded, veined and disseminated structures. Twenty-seven ore bodies in the Jinshachang deposit host 4.6 million tons of sulfide ores at average grades of 4.07 wt.% Pb and 5.03 wt.% Zn. Quartz separates from the sulfide ores have δDH2O values ranging from -137‰ to -86.2‰ with an average of -114‰ (n = 7), lower than those of magmatic, metamorphic and meteoric water, suggesting a contribution of organic water. δ34SCDT values of ninety-one sulfide separates range from +1.1‰ to +13.4‰ with an average of +5.7‰, lower than those of evaporites (δ34SCDT = +15‰ to +35‰) in the Cambrian to Triassic sedimentary strata in NE Yunnan province. δ34SCDT values of eight barite separates range from +32‰ to +35‰ (average +34‰), within the range of evaporites. These data suggest that S2- in the hydrothermal fluids derived from evaporites by thermo-chemical sulfate reduction (TSR), whereas SO42- directly originated from the evaporites. Six sulfide separates have highly radiogenic 206Pb/204Pb ratios ranging from 20.74 to 21.18 (average 20.92), 207Pb/204Pb ratios ranging from 15.85 to 15.89 (average 15.87), and 208Pb/204Pb ratios ranging from 40.89 to 41.42 (average 41.16). The Pb isotopes of the sulfides plot above the upper crust Pb average evolution curve and overlap the Cambrian sedimentary rocks, but are different from the Sinian dolostone. This indicates a crustal source of Pb most likely derived from the Cambrian sedimentary rocks. The initial 87Sr/86Sr ratio of seven main stage sphalerite separates from the Jinshachang deposit is 0.713, which is higher than those of the Upper Sinian Dengying Formation dolostone (0.708-0.710), Lower Cambrian carbonates (0.708-0.710), Devonian to Lower Permian sedimentary rocks (0.707-0.711) and Middle Permian Emeishan flood basalts (0.704-0.708), and lower than those of the Proterozoic folded basement rocks (0.724-0.729), but similar to those of Lower Cambrian black shale (0.712-0.714). Therefore, the Sr isotope data of the sphalerite support the view that the Lower Cambrian sedimentary rocks, in particular the black shale, were important source of metals. The main stage sphalerite separates have an Rb-Sr isotopic age of 206.8 ± 3.7 Ma, reflecting the timing of Pb-Zn mineralization. This study suggests that the Jinshachang Pb-Zn deposit is an epigenetic, thrust fold-controlled and strata-bound deposit with fluids and metals derived from the Cambrian sedimentary strata.

  3. Organic geochemistry - A retrospective of its first 70 years

    USGS Publications Warehouse

    Kvenvolden, K.A.

    2006-01-01

    Organic geochemistry had its origin in the early part of the 20th century when organic chemists and geologists realized that detailed information on the organic materials in sediments and rocks was scientifically interesting and of practical importance. The generally acknowledged "father" of organic geochemistry is Alfred E. Treibs (1899-1983), who discovered and described, in 1936, porphyrin pigments in shale, coal, and crude oil, and traced the source of these molecules to their biological precursors. Thus, the year 1936 marks the beginning of organic geochemistry. However, formal organization of organic geochemistry dates from 1959 when the Organic Geochemistry Division (OGD) of The Geochemical Society was founded in the United States, followed 22 years later (1981) by the establishment of the European Association of Organic Geochemists (EAOG). Organic geochemistry (1) has its own journal, Organic Geochemistry (beginning in 1979) which, since 1988, is the official journal of the EAOG, (2) convenes two major conferences [International Meeting on Organic Geochemistry (IMOG), since 1962, and Gordon Research Conferences on Organic Geochemistry (GRC), since 1968] in alternate years, and (3) is the subject matter of several textbooks. Organic geochemistry is now a widely recognized geoscience in which organic chemistry has contributed significantly not only to geology (i.e., petroleum geochemistry, molecular stratigraphy) and biology (i.e., biogeochemistry), but also to other disciplines, such as chemical oceanography, environmental science, hydrology, biochemical ecology, archaeology, and cosmochemistry.

  4. Evidence for Late Cretaceous-early Tertiary lower plate mylonitization and extension in the Harcuvar metamorphic core complex, Arizona: Evidence from U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Wrobel, A.; Wong, M.; Singleton, J. S.

    2014-12-01

    results raise questions about the time scales of core complex development and the role of tectonic inheritance in Miocene extension. U-Pb zircon and monazite geochronology currently in progress will further refine the timing of plutonic and metamorphic events and their role in the development of this core complex.

  5. Geochronology of the Xihuashan composite granitic body and tungsten mineralization, Jiangxi province, south China.

    USGS Publications Warehouse

    McKee, E.H.; Rytuba, J.J.; Xu, Keqin

    1987-01-01

    One of the goals of this visit was to collect samples of different granitic rocks in the pluton for radiometric dating to establish the geochronology of intrusion, alteration, and mineralization. This report summarises geochronologic studies during a visit by Chinese and US scientists to the Xihuashan mine.-after Authors

  6. Proterozoic polymetamorphism in the Quanji Block, northwestern China: Evidence from microtextures, garnet compositions and monazite CHIME ages

    NASA Astrophysics Data System (ADS)

    Wang, Qinyan; Pan, Yuanming; Chen, Nengsong; Li, Xiaoyan; Chen, Haihong

    2009-05-01

    The Quanji Block, situated close to the triple junction of three major Precambrian terranes in China (i.e., the North China Craton, the Yangtze Block and the Tarim Block), is composed of Precambrian metamorphic crystalline basement and an unmetamorphosed Mesozoic-Paleozoic sedimentary cover; it has been interpreted as a remnant continental fragment. Microtextural relationships, garnet trace element compositions, and monazite CHIME ages in paragneisses, schists and granitic leucosomes show two episodes of regional metamorphism in the Quanji Block basement. The first regional metamorphism and accompaning anatexis took place at ˜1.93 Ga; the second regional metamorphism occurred between ˜1.75 and ˜1.71 Ga. Mineral compositions of the first metamorphism, including those of monazite, were significantly disturbed by the second event. These two regional metamorphic episodes were most likely linked to assembly and breakup of the supercontinent Columbia, respectively.

  7. Post-peak, fluid-mediated modification of granulite facies zircon and monazite in the Trivandrum Block, southern India

    NASA Astrophysics Data System (ADS)

    Taylor, Richard J. M.; Clark, Chris; Fitzsimons, Ian C. W.; Santosh, M.; Hand, M.; Evans, Noreen; McDonald, Brad

    2014-08-01

    The quarry at Kottavattom in the Trivandrum Block of southern India contains spectacular examples of fluid-assisted alteration of high-grade metamorphic rocks. Garnet-biotite gneiss has undergone a change in mineral assemblage to form submetre scale orthopyroxene-bearing patches, later retrogressed to form an amphibole-bearing lithology. These patches, often referred to as arrested or incipient charnockite, crosscut the original metamorphic foliation and are typically attributed to passage of a low aH2O fluid through the rock. Whilst this conversion is recognised as a late stage process, little detailed chronological work exists to link it temporally to metamorphism in the region. Zircon and monazite analysed from Kottavattom not only record metamorphism in the Trivandrum Block but also show internal, lobate textures crosscutting the original zoning, consistent with fluid-aided coupled dissolution-reprecipitation during formation of the orthopyroxene-bearing patches. High-grade metamorphism at the quarry occurred between the formation of metamorphic monazite at ~585 Ma and the growth of metamorphic zircon at ~523 Ma. The fluid-assisted alteration of the garnet-biotite gneiss is poorly recorded by altered zircon with only minimal resetting of the U-Pb system, whereas monazite has in some cases undergone complete U-Pb resetting and records an age for fluid infiltration at ~495 Ma. The fluid event therefore places the formation of the altered patches at least 25 Myr after the zircon crystallisation in the garnet-biotite gneiss. The most likely fluid composition causing the modification and U-Pb resetting of zircon and monazite is locally derived hypersaline brine.

  8. The Role of the Ion Microprobe in Solid-Earth Geochemistry

    NASA Astrophysics Data System (ADS)

    Hauri, E. H.

    2002-12-01

    Despite the early success of the electron microprobe in taking petrology to the micron scale, and the widespread use of mass spectrometers in geochemistry and geochronology, it was not until the mid-1970s that the ion microprobe came into its own as an in situ analytical tool in the Earth sciences. Despite this inauspicious beginning, secondary ion mass spectrometry (SIMS) was widely advertised as a technology that would eventually eclipse thermal ion mass spectrometry (TIMS) in isotope geology. However this was not to happen. While various technical issues in SIMS such as interferences and matrix effects became increasingly clear, an appreciation grew for the complimentary abilities of SIMS and TIMS that, even with the advent of ICP-MS, continues to this day. Today the ion microprobe is capable of abundance measurements in the parts-per-billion range across nearly the entire periodic table, and SIMS stable isotope data quality is now routinely crossing the 1 per mil threshold, all at the micron scale. Much of this success is due to the existence of multi-user community facilities for SIMS research, and the substantial efforts of interested scientists to understand the fundamentals of sputtered ion formation and their application to geochemistry. Recent discoveries of evidence for the existence of ancient crust and oceans, the emergence of life on Earth, the large-scale cycling of surficial materials into the deep Earth, and illumination of fundamental high-pressure phenomena have all been made possible by SIMS, and these (and many more) discoveries owe a debt to the vision of creating and supporting multi-user community facilities for SIMS. The ion microprobe remains an expensive instrument to purchase and maintain, yet it is also exceedingly diverse in application. Major improvements in SIMS, indeed in all mass spectrometry, are visible on the near horizon. Yet the geochemical community cannot depend on commercial manufacturers alone to design and build the next

  9. Bonding characteristics, thermal expansibility, and compressibility of RXO(4) (R = rare earths, X = P, As) within monazite and zircon structures.

    PubMed

    Li, Huaiyong; Zhang, Siyuan; Zhou, Shihong; Cao, Xueqiang

    2009-05-18

    Systematically theoretical research was performed on the monazite- and zircon-structure RXO(4) (R = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; X = P, As) series by using the chemical bond theory of dielectric description. The chemical bond properties of R-O and X-O bonds were presented. In the zircon phase, the covalency fractions of X-O bonds increased in the order of V-O < As-O < P-O, which was in accordance with the ionic radii and electronegative trends, and the covalency fractions of R-O bonds varied slightly due to the lanthanide contraction. While in the monazite phase, both R-O and X-O bonds were divided into two groups by their covalency fractions. The contributions from the bond to the lattice energy, linear thermal expansion coefficient (LTEC), and bulk modulus were explored. The X-O bonds with short bond lengths and high chemical valence made greater contributions to the lattice energy and performed nearly rigidly during the deformation. A regular variation of lattice energy, LTEC, and bulk modulus with the ionic radii of the lanthanides was observed in both monazite and zircon phases.

  10. U-Th-Pb geochronology of the Massabesic Gneiss and the granite near Milford, South-Central New Hampshire: New evidence for avalonian basement and taconic and alleghenian disturbances in Eastern New England

    USGS Publications Warehouse

    Aleinikoff, J.N.; Zartman, R.E.; Lyons, J.B.

    1979-01-01

    U-Th-Pb systematics for zircon and monazite from Massabesic Gneiss (paragneiss and orthogneiss) and the granite near Milford, New Hampshire, were determined. Zircon morphology suggests that the paragneiss may be volcaniclastic (igneous) in origin, and thus the age data probably record the date (minimum of 646 m.y.) at which the rock was extruded. A two-stage lead-loss model is proposed to explain the present array of data points on a concordia diagram. Orthogneiss ages range only narrowly and are clustered around 475 m.y. Data for the granite of Milford, New Hampshire, are scattered, but may be interpreted in terms of inheritance and modern lead loss, yielding a crystallization age of 275 m.y. This is the only known occurrence of Avalonian-type basement in New Hampshire and as such provides evidence for the location of the paleo-Africa-paleo- North America suture. The geochronology also further documents the occurrence of disturbances during the Ordovician and Permian. ?? 1979 Springer-Verlag.

  11. Geochemistry of coalbed gas - a review

    USGS Publications Warehouse

    Clayton, J.L.

    1998-01-01

    Coals are both sources and reservoirs of large amounts of gas that has received increasing attention in recent years as a largely untapped potential energy resource. Coal mining operations, such as ventilation of coalbed gas from underground mines, release coalbed CH4 into the atmosphere, an important greehouse gas whose concentration in the atmosphere is increasing. Because of these energy and environmental issues, increased research attention has been focused on the geochemistry of coalbed gas in recent years. This paper presents a summary review of the main aspects of coalbed gas geochemistry and current research advances.Coals are both sources and reservoirs of large amounts of gas that has received increasing attention in recent years as a largely untapped potential energy resource. Coal mining operations, such as ventilation of coalbed gas from underground mines, release coalbed CH4 into the atmosphere, an important greenhouse gas whose concentration in the atmosphere is increasing. Because of these energy and environmental issues, increased research attention has been focused on the geochemistry of coalbed gas in recent years. This paper presents a summary review of the main aspects of coalbed gas geochemistry and current research advances.

  12. U.S. National Committee for Geochemistry

    ERIC Educational Resources Information Center

    Geotimes, 1974

    1974-01-01

    Reports highlights of the April, 1973 meeting of the U.S. National Committee for Geochemistry. Some of the topics reported on were: The Geophysics Research Board, deep drilling, exchange of geochemists with China and the activities of the Subcommittee on Geochemical Environment in Relation to Health and Disease. (BR)

  13. Geochemical, geochronological characterization and tectonic setting of the metamorphic rocks from the Biga Peninsula, NW Turkey

    NASA Astrophysics Data System (ADS)

    Şengün, F.; Tunç, Ä.°. O.; Yiǧitbaş, E.

    2012-04-01

    The Biga Peninsula in the northwest Turkey is one of the world's important natural laboratories to study geochronology due to having complex geology. The Biga Peninsula has different metamorphic basements including Kazdağ Massif, Çamlıca metamorphics, Kemer metamorphics and Karadağ Massif under cover of the Cenozoic volcano-sedimentary association. The Çamlıca metamorphic assemblage are one of the most critical regions for understanding of the geology of northwestern Turkey. The Çamlıca metamorphic association located on the westernmost part of Turkey is mainly composed of the Andıktası formation, the Dedetepe formation and the Salihler formation, from bottom to top. Metasedimentary rocks of the Çamlıca metamorphics have high SiO2 and medium Al2O3 and TiO2 values. The protolith of these metasediments is arkose-subarkose and greywacke. However, whole-rock geochemistry for the HP eclogite/blueschist within the Çamlıca metamorphics suggests that their protolith was basalt with high TiO2 and K2O-Na2O content and Nb/Y ratios. REE pattern and trace element contents of the HP eclogite/blueschist similar to typical MORB based on tectonic discrimination diagrams. The metavolcanic rocks occurring on the lowest part of the Çamlıca metamorphicassociation has andesitic composition with calc-alkaline character. All metavolcanic rocks in this unit cluster within the volcanic arc field. Zircon grains from metavolcanic rocks and HP eclogite/blueschists were dated by LA-ICPMS. Zircon ages of two metavolcanic samples yielded 328.6 ± 3.5 Ma and 343.2 ± 2.6 Ma, respectively. These ages are interpreted as the time of protolith crystallization of metavolcanic rocks. Moreover, zircon ages from HP eclogite/blueschist yielded 338 ± 1.8 Ma (Early Carboniferous) which is interpreted as the age of protolith crystallization of HP eclogite/blueschist. Geochemical and isotopic data indicate that Early Carboniferous Variscan ages within the Sakarya Zone may form the eastern

  14. Electron-microprobe Th-U-Pb monazite dating in Early-Palaeozoic high-grade gneisses as a completion of U-Pb isotopic ages (Wilson Terrane, Antarctica)

    NASA Astrophysics Data System (ADS)

    Schulz, B.; Schüssler, U.

    2013-08-01

    The electron microprobe (EMP) Th-U-Pb monazite bulk chemical dating method was applied to granulite-facies rocks of the Wilson Terrane in Antarctica. A combination of this method to isotopic U-Pb-SHRIMP ages for the evaluation of metamorphic processes required the analysis of reference monazites. These can be subdivided into three groups: a) Monazite with variable total Pb at constant Th (e.g. VK-1) is unsuitable for EMP data evaluation; b) Monazite with highly variable total Pb and Th, but with at least some Th/Pb approximating an apparent isochrone (e.g. MPN) is partly useful; and c) Monazite with constant Th/Pb at high Th (e.g. Madmon monazite) is best suitable for the combined approach and can be additionally used to improve the Th calibration for EMP. Study of monazite in grain mounts and in thin sections led to partly different but complementary results: Older monazites with EMP ages up to 680 Ma occur mainly in a grain mount from diatexite and metatexite and are interpreted as detrital relics. Some of these monazites show structures and mineral-chemical zonation trends resembling metasomatism by alkali-bearing fluids. A marked mobility of Th, P, Ce, Si and U is observed. The age of the metasomatic event can be bracketed between 510 and 450 Ma. Furthermore, in the grain mount and in numerous petrographic thin sections of migmatites and gneisses, the EMP Th-U-Pb and SHRIMP U-Pb monazite data uniformly signal a major metamorphic event with a medium-pressure granulite facies peak between 512 and 496 Ma. Subsequent isothermal uplift and then amphibolite-facies conditions between 488 and 466 Ma led to crystallisation of pristine monazite. The high-grade metamorphic event, related to the Ross Orogeny, can be uniformly traced more than 600 km along strike in the Wilson Terrane.

  15. Altered volcanic ash layers of the Late Cretaceous San Felipe Formation, Sierra Madre Oriental (Northeastern Mexico): Usbnd Pb geochronology, provenance and tectonic setting

    NASA Astrophysics Data System (ADS)

    Velasco-Tapia, Fernando; Martínez-Paco, Margarita; Iriondo, Alexander; Ocampo-Díaz, Yam Zul Ernesto; Cruz-Gámez, Esther María; Ramos-Ledezma, Andrés; Andaverde, Jorge Alberto; Ostrooumov, Mikhail; Masuch, Dirk

    2016-10-01

    A detailed petrographic, geochemical, and Usbnd Pb geochronological study of altered volcanic ash layers, collected in eight outcrops of the Late Cretaceous San Felipe Formation (Sierra Madre Oriental, Northeastern Mexico), has been carried out. The main objectives have been: (1) to establish a deposit period, and (2) to propose a reliable provenance-transport-deposit-diagenetic model. These volcano-sedimentary strata represent the altered remains of vitreous-crystalline ash (main grains: quartz + K-feldspar (sanidine) + Na-plagioclase + zircon + biotite; groundmass: glass + calcite + clinochlore + illite) deposited and preserved in a shallow, relatively large in area, open platform environment. Major and trace element geochemistry indicate that parent volcanism was mainly rhyodacitic to rhyolitic in composition. Discrimination diagrams suggest a link to continental arc transitional to extension tectonic setting. Usbnd Pb geochronology in zircon has revealed that the volcanic ash was released from their sources approximately during the range 84.6 ± 0.8 to 73.7 ± 0.3 Ma, being transported to the depocenters. Burial diagenesis process was marked by: (a) a limited recycling, (b) the partial loss of original components (mainly K-feldspar, plagioclase, biotite and glass), and (c) the addition of quartz, calcite, illite and clinochlore. The location of the source area remains uncertain, although the lack of enrichment in Zr/Sc ratio suggests that ashes were subjected to relatively fast and short-distance transport process. El Peñuelo intrusive complex, at 130-170 km west of the depocenters, is the nearest known zone of active magmatism during the Upper Cretaceous. This intermediate to felsic pluton, characterized by a geochemical affinity to post-orogenic tectonic setting, could be linked to the volcanic sources.

  16. Combined Raman and photoluminescence spectroscopic investigation of He-irradiation effects in monazite

    NASA Astrophysics Data System (ADS)

    Lenz, C.; Petautschnig, C.; Akhmadaliev, S.; Hanf, D.; Talla, D.; Nasdala, L.

    2012-04-01

    We present first results of a study addressing effects of the corpuscular self-irradiation on stress/strain and optical properties (in particular the photoluminescence behaviour) in monazite-(Ce). For this, natural samples, and synthetic CePO4 crystals mildly doped with Nd3+, were irradiated with 7.7 MeV He ions, which are analogues of alpha particles generated in the 214Po → 210Pb decay event (238U decay series). Light-ion irradiation was preferred over heavy-ion irradiation (i.e., ~100 keV heavy ions as analogues of alpha recoils) for two reasons. First, MeV He ions penetrate much deeper into mineral targets (tens of micrometres vs. a few hundred angstroms), resulting in irradiated volumes that are "measurable" using micro-spectroscopy techniques. Second, the depth distribution profiles of nuclear and electronic energy losses vary appreciably in the case of MeV He ions. The latter is most helpful in assigning observed effects to either point defects created or target ionisation. The irradiations were done at the 3 MV Tandem accelerator of the Helmholtz-Zentrum Dresden-Rossendorf (Germany). The fluences applied varied in the range 1013-1017 He/cm2. The degree of disturbance of the short-range order in the samples irradiated was evaluated from the broadening of the ν1(PO4) Raman band (symmetric PO4 stretching; A1g mode) near 970 cm-1 [1,2]. The majority of the damage created was observed near 28 μm into the monazite-(Ce) targets, i.e., near the ends of the helium trajectories. Here, the ν1(PO4) Raman band may broaden appreciably, from 2.2 cm-1 (in the case of synthetic CePO4) to well above 20 cm-1. The generation of additional damage was also observed upon He irradiation of naturally radiation-damaged monazite-(Ce). By contrast, there was no indication of any annealing effect of the MeV He ions irradiated in these samples (compare [3]; a similar effect of alpha-assisted annealing was suspected by [4] in the discussion of fission tracks). Sharp luminescence

  17. Monazite and titanite U-Pb dating of Caledonian high-grade metamorphism in the Mid-Scandinavian Caledonides, Norway: a combined SHRIMP and ID-TIMS approach

    NASA Astrophysics Data System (ADS)

    Bingen, B.; Davis, W. J.; Hamilton, M. A.; Osmundsen, P. T.; Nordgulen, Ø.

    2003-04-01

    Crystals of metamorphic monazite commonly display age domains related to distinct episodes of growth or secondary crystallization. SHRIMP analyses of monazite in metapelite samples from north-central Norway, demonstrate homogeneous monazite populations, with unimodal age distribution. ID-TIMS analyses of single-grain or small fractions give reliable and precise estimates for the timing of monazite growth. Monazite, titanite and zircon U-Pb data constrain the duration of high-grade Scandian metamorphism to be 25 m.y. in this part of the orogen (426-401 Ma) and underscore the importance of late-Scandian extensional detachments as tectonometamorphic breaks between the Central Norway Basement Window (CNBW) and overlying nappes of the Upper (Köli nappes) and Uppermost Allochthons (Helgeland nappes). The CNBW is a core complex-like culmination trending ENE-WSW, made of high-pressure amphibolite-facies (locally granulite-facies) Proterozoic gneisses and in-folded supracrustal rocks. Monazite from a garnet-kyanite gneiss yields an age of 426 +/- 1 Ma reflecting conspicuous migmatization in the rock. Monazite in two garnet +/- kyanite gneisses with minor staurolite yields ages of 420 +/-2 and 403 +/-5 Ma. A deformed garnet-bearing granitic dyke yields a zircon intrusion age of 417 +/- 5 Ma. Titanite in four samples of calc-silicate gneiss and marble define a tight cluster between 403 and 401 +/-2 Ma. Titanite pre-dates top-WSW ductile extensional shearing along the Høybakken detachment in the SW of the CNBW and consequently constrains final exhumation of the window to be younger than 401 Ma. The Upper and Uppermost allochthons overlying the CNBW are made of greenshist to amphibolite-facies supracrustal rocks and plutonic complexes intruded at ca. 495, 480, 460, 445 and 428 Ma. Scandian translation of these outboard nappes onto Baltica occurred after 428 Ma. In the eastern Helgeland nappes, monazite in mica gneiss and titanite in amphibole gneiss and marble range from 431

  18. Multiple Basinal Fluid Events in the Lower Belt Supergroup, Montana: Constraints From CHIME Ages and REE Patterns of Monazites

    NASA Astrophysics Data System (ADS)

    Gonzalez-Alvarez, I.; Kusiak, M. A.

    2004-05-01

    Chemical dates (CHIME) on 105 spots and REE patterns of monazites were obtained from coarse sandstones and siltstones in the Mesoproterozoic siliciclastic Appekunny and Grinnell formations, lower Belt Supergroup, Montana, by EMPA. At least three post-depositional events induced by basinal fluids can be recognized: (a) red coloration accompanied by a major K-addition; (b) a green overprint of red siltstones; and (c) dolomitization. Fluid advection in the unmineralized lower Belt is pervasive and may have been alkaline and oxidizing. These three events progressively modified the primary geochemical characteristics of the siliciclastic rocks. Calculated ages show similar ranges in the fine and coarse-grained facies. For siltstones there are two age clusters: (1) at 1,801 ± 21 to 1,968 ± 26 Ma, as well as (2) at 854 ± 7 to 962 ± 13 Ma. Coarse sandstones show similar age clusters (3) at 1,831 ± 14 to 1,982 ± 12 Ma, and (4) at 803 ± 6 to 944 ± 9 Ma. A wide range of dates plots between the clusters for both facies. Clusters (1) and (3) are interpreted as the result of detrital monazites from a source area ~1.8 to 1.9 Ga old. Mineralogical variations and trace element systematic reveal basinal brines, which mobilized MREE and HREE, locally generating secondary monazites, influencing large domains of the lower Belt. The lower Belt Supergroup is estimated to have been deposited between 1.47 Ga and 1.45 Ga; consequently, the second age cluster for sandstones and siltstones is viewed as constraining the timeframe of a major basinal fluid event at ~0.80 to 0.96 Ga. That event is clearly distinct from the hydrothermal system associated with the Sullivan sedex base metal deposit at the base of the Belt. Ages between the clusters are interpreted either as secondary, formed during additional basinal fluid events or as reset of detrital monazites. Accordingly, the Belt basin was intermittently an open system to fluids from ~1.47 to ~0.80 Ga. Chondrite-normalized REE patterns

  19. Whole-Rock Geochemistry and Zircon U-Pb Isotopes of the Late Cretaceous Granitoids of the Eastern Taurus (turkey): Implications for Petrogenesis and Geodynamic Setting

    NASA Astrophysics Data System (ADS)

    Beyarslan, Melahat; Lin, Yu-Chin; Chung, Sun-Lin; Feyzi Bingol, Ahmet; Yildirim, Esra

    2015-04-01

    The granitoid plutons out crop largely in the Eastern Taurus, in Turkey. New data, including a combination of field relation, U-Pb zircon geochronology and rock geochemistry on the granitoids in the Eastern Taurus of the Tethyan orogen in Turkey, come from four plutons ( Pertek, Baskil, Göksun and Şifrin). Pertek, Baskil and Göksun plutons consist mainly of diorite, quartz-diorites, tonalite, granodiorites and granites of I-type, with minor monzonite, the Şifrin pluton consists of syenogranite, syenite, monzogranite, monzonite. U-Pb zircon geochronology of four samples of diorite and granite from Pertek and Baskil plutons indicate ages of 86±2 - 79 ± 1Ma. U-Pb zircon geochronology of four samples from the Şifrin granitoid yield ages 77±1-72±1 Ma. Considering these ages, emplacement of the plutons took place during Late Cretaceous (Santonian-Campanian), from 86 to 72 Ma. Although the SiO2 of rocks forming granitoids varies in wide range ( 46.792- 74.092 wt%), they show arc and syn-collision geochemical affinity, with enrichment of LILE (K, Rb, Sr and Ba) and depletion of HFSE (Nb, Ta and Ti) and P. Geochemical data indice that the diorite, tonalite and granodiorite are low-K tholeiite, monzodiorite, monzogranite, granite and K-granite are calc-alkaline and high-K calc-alkaline and monzonite, syenomonzonite and syenite of Şifrin pluton and some samples of the Pertek pluton are shoshonitic. The Eastern Taurus granitoids would be formed by partial melting of possible juvenile arc-derived rocks during subduction of the South Branch of the Neo-Tethyan oceanic crust and subsequent arc-continent collision.

  20. Traditional applications and novel approaches in Lu-Hf geochronology

    NASA Astrophysics Data System (ADS)

    Herwartz, D.; Nagel, T. J.; Sandmann, S.; Vitale Brovarone, A.; Rexroth, S.; Rojas-Agramonte, Y.; Froitzheim, N.; Kröner, A.; Skublov, S. G.; Münker, C.

    2012-04-01

    Lutetium-Hf geochronology is currently becoming a routine method for dating metamorphism of garnet bearing rocks, such as eclogites. Prograde garnet growth ages are mostly preserved because blocking temperatures exceed 630 °C [1] and prograde Lu zoning patterns have even been observed in samples that were exposed to temperatures above 800 °C [2]. Here we discuss Lu-Hf ages from various eclogite localities, such as the Northern Tianshan, Kyrgyzstan (~ 470 Ma), the Kola Peninsula, Russia (~ 1900 Ma) [3], Cuba (~70 Ma and ~124 Ma), Alpine Corsica (~ 34 Ma) and the Tauern Window (~32.7 Ma). Age precisions are in the order of 0.1 to 1 % and all ages can be safely attributed to the timing of garnet growth. Some samples, however, contain two garnet populations which complicates Lu-Hf geochronology. In the Adula Nappe (Central Alps) relict garnet has survived a second orogenic cycle, including subduction to mantle depth. By carefully separating the two garnet populations present within the same eclogite sample we obtained a minimum Variscan age of 333 Ma and a maximum Alpine age of 38 Ma [4]. A similar relationship is now evident in samples from the Tauern Window (Eastern Alps), where only one population of garnet generation is visible macroscopically. However, few relics of Variscan garnet inside Alpine garnet are observed in electron microprobe element maps and are also evident from isotopic heterogeneity in 176Lu/177Hf vs. 176Hf/177Hf space. Garnet relics stemming from previous metamorphic events are frequently observed in HP units around the world and the Lu-Hf system is a promising tool to resolve the respective growth ages. Apart from garnet, lawsonite Lu-Hf geochronology was recently identified as a new tool to investigate subduction processes [5]. Here we present a lawsonite Lu-Hf isochron 37,6 ± 1.4 Ma (MSWD = 0.30; n =5) from a lawsonite blueschist from Alpine Corsica. The lawsonite slightly predates the timing of garnet growth (~34 Ma) in three eclogite

  1. Geology and geochronology of the Spirit Mountain batholith, southern Nevada: Implications for timescales and physical processes of batholith construction

    USGS Publications Warehouse

    Walker, B.A.; Miller, C.F.; Lowery, Claiborne L.; Wooden, J.L.; Miller, J.S.

    2007-01-01

    The Spirit Mountain batholith (SMB) is a ??? 250??km2 composite silicic intrusion located within the Colorado River Extensional Corridor in southernmost Nevada. Westward tilting of 40-50?? has exposed a cross-section from the roof through deep levels of the batholith. Piecemeal construction is indicated by zircon geochronology, field relations, and elemental geochemistry. Zircon U/Pb data (SHRIMP) demonstrates a ??? 2??million year (17.4-15.3??Ma) history for the SMB. Individual samples contain zircons with ages that span the lifetime of the batholith, suggesting recycling of extant zircon into new magma pulses. Field relations reveal several distinct intrusive episodes and suggest a common injection geometry of stacked horizontal sheets. The largest unit of the SMB is a gradational section (from roof downward) of high-silica leucogranite through coarse granite into foliated quartz monzonite. Solidification of this unit spans most of the history of the batholith. The 25??km ?? 2??km leucogranite was emplaced incrementally as subhorizontal sheets over most or all of the history of this section, suggesting repeated fractional crystallization and melt segregation events. The quartz monzonite and coarse granite are interpreted to be cumulate residuum of this fractionation. Age data from throughout this gradational unit show multiple zircon populations within individual samples. Subsequent distinct intrusions that cut this large unit, which include minor populations of zircons that record the ages of earlier events in construction of the batholith, preserve a sheeted, sill-on-sill geometry. We envision the SMB to have been a patchwork of melt-rich, melt-poor, and entirely solid zones throughout its active life. Preservation of intrusion geometries and contacts depended on the consistency of the host rock. Zircons recycled into new pulses of magma document remobilization of previously emplaced crystal mush, suggesting the mechanisms by which evidence for initial

  2. Magnetic measurements of the transuranium elements and charge state characterization of actinides in monazite. Progress report

    SciTech Connect

    Huray, P. G.

    1980-01-01

    A micromagnetic susceptometer for the purpose of measuring extremely small sample quantities (on the microgram level) was designed, constructed, and calibrated in previous years. (The 1979 progress report gives details of its operation.) This device has operated without significant downtime in this funding period, and much progress has been made in the magnetic characterization of elements beyond Am in the periodic table. This program has roughly doubled man's knowledge of magnetism in Cm, Bk, and Cf, and includes the only Es magnetic measurements to date. The incorporation of an automatic data collection system in this period has made analysis much more accurate, and has allowed quicker turnaround of compounds and metals for study. Results obtained for the compounds and metals studied this year are summarized. The lanthanide orthophosphates are being investigated as an alternate means of primary containment for high-level actinide wastes. Researchers at the Oak Ridge National Laboratory are involved in preparation of actinide-doped compounds for all of the lanthanide transition series (La through Lu) for a study of leaching characteristics and E.S.R. classification. To aid this study the charge state of /sup 237/Np or /sup 57/Fe has been identified, either in the as-prepared compounds or following radioactive decay of /sup 241/Am via the Moessbauer Effect. The final charge state will be an influential variable in the immobilization characteristics of the waste products stored in this synthetic monazite form. 10 figures, 1 table. (RWR)

  3. First-principles study of point defects in CePO4 monazite

    NASA Astrophysics Data System (ADS)

    Yi, Yong; Zhao, Xiaofeng; Teng, Yuancheng; Bi, Beng; Wang, Lili; Wu, Lang; Zhang, Kuibao

    2016-12-01

    CePO4 monazite is an important radiation-resistant material that may act as a potential minor actinides waste form. Here, we present the results of the calculations for the basic radiation defect modellings in CePO4 crystals, along with the examination of their defect formation energies and effect of the defect concentrations. This study focused on building a fully-relaxed CePO4 model with the step iterative optimization from the DFT-GGA calculations using the VASP and CASTEP databases. The results show that the Frenkel defect configuration resulting from the center interstitials has a lower energy when compared to two adjacent orthophosphate centers (the saddle point position). High formation energies were found for all the types of intrinsic Frenkel and vacancy defects. The formation energies conform to the following trend (given in the decreasing order of energy): Ce Frenkel (12.41 eV) > O Frenkel (11.02 eV) > Ce vacancy (9.09 eV) > O vacancy (6.69 eV). We observed almost no effect from the defect concentrations on the defect formation energies.

  4. Precambrian organic geochemistry - Preservation of the record

    NASA Technical Reports Server (NTRS)

    Hayes, J. M.; Wedeking, K. W.; Kaplan, I. R.

    1983-01-01

    A review of earlier studies is presented, and new results in Precambrian organic geochemistry are discussed. It is pointed out that two lines of evidence can be developed. One is based on structural organic chemistry, while the other is based on isotopic analyses. In the present investigation, the results of both structural and isotopic investigations of Precambrian organic matter are discussed. Processes and products related to organic geochemistry are examined, taking into account the carbon cycle, an approximate view of the principal pathways of carbon cycling associated with organic matter in the present global ecosystem, processes affecting sedimentary organic matter, and distribution and types of organic matter. Attention is given to chemical fossils in Precambrian sediments, kerogen analyses, the determination of the structural characteristics of kerogen, and data concerning the preservation of the Precambrian organic geochemical record.

  5. Microcrystals of Th-rich monazite (La) with a negative Ce anomaly in metadiorite and their role for documenting Cretaceous metamorphism in the Slavonian Mountains (Croatia)

    NASA Astrophysics Data System (ADS)

    Starijaš Mayer, Biljana; Krenn, Erwin; Finger, Fritz

    2014-04-01

    Microcrystals (1-15 μm) of unusual monazite (La) with 41-47 mol% cheralite [ThCa(PO4)2] component and a strong negative Ce anomaly are described from a metadiorite from the SW Slavonian Mountains, Psunj, Croatia. The dioritic host rock still shows a relictic igneous fabric on macroscopic scale. However, metamorphic reaction textures can be recognized in thin section. These include partial recrystallization of igneous plagioclase to albite coupled with the formation of epidote. Furthermore, partial replacement of igneous hornblende by a fine-grained orthoamphibole-chamosite-epidote paragenesis can be observed and replacement of ilmenite by titanite. The compositions of the metamorphic minerals indicate upper greenschist facies conditions (460-500 °C according to two-feldspar geothermometry) under a high oxygen fugacity. Microstructures show that the monazite crystals belong to the metamorphic paragenesis and formed at the expense of magmatic allanite. Their negative Ce anomalies reflect the oxidizing conditions of metamorphism. Application of the xenotime in monazite solvus geothermometer provides unrealistically high temperatures of ~500-660 °C which disagree with the greenschist facies metamorphic paragenesis. We interpret that the presence of cheralite has a profound effect on the nature of the monazite-xenotime solvus curve and hence the existing calibrations of this geothermometer may be generally unsuitable for cheralite-rich monazite. An important geological result is that the Th-U-total Pb ages of the monazite grains are uniformingly Upper Cretaceous. Our data thus suggest that the imprint of the Alpine orogeny on the Slavonian Mountains was stronger than presumed until now.

  6. Apparent partial resetting of U-Th-Pb systems in experimentally altered monazite resulting from nano-mixtures due to incomplete replacement.

    NASA Astrophysics Data System (ADS)

    Grand'homme, Alexis; Janots, Emilie; Seydoux-Guillaume, Anne-Magali; Guillaume, Damien; Bosse, Valérie; Magnin, Valérie

    2016-04-01

    Hydrothermal alteration experiments of natural monazite crystals (Manangotry, Madagascar; 555 Ma) under alkali conditions (NaOH 1M in 18O doped solution) at low temperature conditions (300, 400, 500 and 600°C), 200 MPa, were conducted to clarify the origin of unsupported Pb (radiogenic or not) in altered monazite (Seydoux-Guillaume et al., 2012). At 300°C, no evidence of monazite replacement was observed. From 400 to 600°C, experimental products show a replacement texture with pristine monazite (Mnz1) surrounded by an alteration rim with a different composition (SEM and EPMA). In the altered domains, in-situ isotopic and chemical U-Th-Pb dating yields intermediate ages between original monazite (555 Ma) and complete experimental resetting (0 Ma). Incomplete resetting is due to the systematic presence of Pb in altered domains, whose concentration decreases with increasing temperature. Transmission Electron Microscope (TEM) observations reveal an incomplete replacement of Mnz1 by a secondary monazite (Mnz2), free of Pb, within the altered domain. The latter domain, apparently homogeneous in BSE images, is in fact constituted by closely associated nano-mixtures of Mnz1 and Mnz2. Furthermore, the volume of Mnz2 within the altered domain, i.e. the efficiency of replacement, increases with increasing temperature. Apparent partial resetting of U-Th-Pb systems results from the unavoidable nano-mixture of different proportion of Mnz1 and Mnz2 within the analytical microvolume (EPMA, LA-ICP-MS). This study therefore indicates that the micrometric resolution (even the 5 μm3 for EPMA) of in-situ dating techniques may be not sufficient to solve such nano-replacement domains, especially when alteration occurs at low-temperature. Ref: Seydoux-Guillaume, A.-M., Montel, J.-M., Bingen, B., Bosse, V., de Parseval, P., Paquette, J.-L., Janots, E., and Wirth, R., (2012). Chemical Geology, v. 330-331, p. 140-158.

  7. A precise 232Th-208Pb chronology of fine-grained monazite: Age of the Bayan Obo REE-Fe-Nb ore deposit, China

    USGS Publications Warehouse

    Wang, Jingyuan; Tatsumoto, M.; Li, X.; Premo, W.R.; Chao, E.C.T.

    1994-01-01

    We have obtained precise Th-Pb internal isochron ages on monazite and bastnaesite for the world's largest known rare earth elements (REE)-Fe-Nb ore deposit, the Bayan Obo of Inner Mongolia, China. The monazite samples, collected from the carbonate-hosted ore zone, contain extremely small amounts of uranium (less than 10 ppm) but up to 0.7% ThO2. Previous estimates of the age of mineralization ranged from 1.8 to 0.255 Ga. Magnetic fractions of monazite and bastnaesite samples (<60-??m size) showed large ranges in 232Th 204Pb values (900-400,000) and provided precise Th-Pb internal isochron ages for paragenetic monazite mineralization ranging from 555 to 398 Ma within a few percent error (0.8% for two samples). These results are the first indication that REE mineralization within the giant Bayan Obo ore deposit occurred over a long period of time. The initial lead isotopic compositions (low 206Pb 204Pb and high 208Pb 204Pb) and large negative ??{lunate}Nd values for Bayan Obo ore minerals indicate that the main source(s) for the ores was the lower crust which was depleted in uranium, but enriched in thorium and light rare earth elements for a long period of time. Zircon from a quartz monzonite, located 50 km south of the ore complex and thought to be related to Caledonian subduction, gave an age of 451 Ma, within the range of monazite ages. Textural relations together with the mineral ages favor an epigenetic rather than a syngenetic origin for the orebodies. REE mineralization started around 555 Ma (disseminated monazite in the West, the Main, and south of the East Orebody), but the main mineralization (banded ores) was related to the Caledonian subduction event ca. 474-400 Ma. ?? 1994.

  8. The Potassium-Argon Laser Experiment (KArLE): In Situ Geochronology for Planetary Missions

    NASA Astrophysics Data System (ADS)

    Cohen, B. A.

    2016-10-01

    KArLE is intended to yield in situ geochronology data and enhance functionality of existing flight instruments using flight hardware that would be reliable, reconfigurable and adaptable to multiple partner instruments and mission architectures.

  9. Fluid-induced dissolution breakdown of monazite from Tso Morari complex, NW Himalayas: evidence for immobility of trace elements

    NASA Astrophysics Data System (ADS)

    Upadhyay, Dewashish; Pruseth, Kamal Lochan

    2012-08-01

    Primary igneous monazite from the Polokongka La granite of the Tso Morari complex in the western Himalayas has been partially replaced by a three-layered corona of metamorphic fluor-apatite, allanite + U- and Th-bearing phases (huttonite + brabantite), and epidote. The alteration is related to high-pressure amphibolite-facies (10-11 kbar and 587-695 °C) fluid-induced retrogression of the ultra-high-pressure granite during exhumation after India-Asia collision. The corona textures can be explained by pseudomorphic partial replacement of the original monazite to apatite and allanite via a fluid-mediated coupled dissolution-reprecipitation process. Mass balance calculations using the volume proportions and compositions of coronal minerals show that the REE, U, Th, Pb, Ba and P were conserved and not transported outside the alteration corona. The formation of fluor-apatite, allanite, huttonite and coffinite from monazite and the immobility of REE, U and Th require an influx of alkali- and F-bearing, Ca-rich fluid having high Ca/Na into the corona. We are aware of only two other occurrences of such alteration textures, and these have several similarities in terms of geodynamic setting and P-T histories of the host rocks. We suggest that there may be a common mechanism of exhumation style, and source and composition of fluids during retrogression of granitoid rocks in collisional orogens and that such breakdown textures can be used to identify metagranites that have experienced high-P metamorphism in continental collision zones, which is otherwise difficult to constrain due to the high variance of the mineral assemblages in these rocks.

  10. Nd Isotope and U-Th-Pb Age Mapping of Single Monazite Grains by Laser Ablation Split Stream Analysis

    NASA Astrophysics Data System (ADS)

    Fisher, C. M.; Hanchar, J. M.; Miller, C. F.; Phillips, S.; Vervoort, J. D.; Martin, W.

    2015-12-01

    Monazite is a common accessory mineral that occurs in medium to high grade metamorphic and Ca-poor felsic igneous rocks, and often controls the LREE budget (including Sm and Nd) of the host rock in which it crystallizes. Moreover, it contains appreciable U and Th, making it an ideal mineral for determining U-Th-Pb ages and Sm-Nd isotopic compositions, both of which are readily determined using in situ techniques with very high spatial resolution like LA-MC-ICPMS. Here, we present the results of laser ablation split stream analyses (LASS), which allows for simultaneous determination of the age and initial Nd isotopic composition in a single analysis. Analyses were done using a 20mm laser spot that allowed for detailed Nd isotope mapping of monazite grains (~30 analyses per ~250mm sized grain). Combined with LREE ratios (e.g., Sm/Nd, Ce/Gd, and Eu anomalies) these results yield important petrogenetic constraints on the evolution of peraluminous granites from the Old Woman-Piute batholith in southeastern California. Our findings also allow an improved understanding of the causes of isotope heterogeneity in granitic rocks. U-Th-Pb age mapping across the crystals reveals a single Cretaceous age for all grains with precision and accuracy typical of laser ablation analyses (~2%). In contrast, the concurrent Nd isotope mapping yields homogeneous initial Nd isotope compositions for some grains and large initial intra-grain variations of up to 8 epsilon units in others. The grains that yield homogeneous Nd isotope compositions have REE ratios suggesting that they crystallized in a fractionally crystallizing magma. Conversely, other grains, which also record fractional crystallization of both feldspar and LREE rich minerals, demonstrate a change in the Nd isotope composition of the magma during crystallization of monazite. Comparison of inter- and intra-grain Nd isotope compositions reveals further details on the potential mechanisms responsible for isotope heterogeneity

  11. Three decades of geochronologic studies in the New England Appalachians

    USGS Publications Warehouse

    Zartman, R.E.

    1988-01-01

    Over the past 30 years, both isotope geochronology and plate tectonics grew from infancy into authoritative disciplines in the geological sciences. The existing geochronlogy is summarized into a map and table emphasizing the temporal construction of the New England Appalachians. By using lithotectonic zones as the building blocks of the orogen, seven such zones are defined in terms of pre-, syn-, and post-assembly geologic history. The boundaries between these zones are faults in most cases, some of which may have had recurring movement to further complicate any plate-tectonic scenario. A delineation of underlying Grenvillian, Chain Lakes, and Avalonian basement is also attempted, which now can make use of isotopes in igneous rocks as petrogenic indicators to supplement the rare occurrences of basement outcrop within mobile zones of the orogen. -from Author

  12. Laser-Ablation (U-Th)/He Geochronology

    NASA Astrophysics Data System (ADS)

    Hodges, K.; Boyce, J.

    2003-12-01

    Over the past decade, ultraviolet laser microprobes have revolutionized the field of 40Ar/39Ar geochronology. They provide unprecedented information about Ar isotopic zoning in natural crystals, permit high-resolution characterization of Ar diffusion profiles produced during laboratory experiments, and enable targeted dating of multiple generations of minerals in thin section. We have modified the analytical protocols used for 40Ar/39Ar laser microanalysis for use in (U-Th)/He geochronologic studies. Part of the success of the 40Ar/39Ar laser microprobe stems from fact that measurements of Ar isotopic ratios alone are sufficient for the calculation of a date. In contrast, the (U-Th)/He method requires separate analysis of U+Th and 4He. Our method employs two separate laser microprobes for this process. A target mineral grain is placed in an ultrahigh vacuum chamber fitted with a window of appropriate composition to transmit ultraviolet radiation. A focused ArF (193 nm) excimer laser is used to ablate tapered cylindrical pits on the surface of the target. The liberated material is scrubbed with a series of getters in a fashion similar to that used for 40Ar/39Ar geochronology, and the 4He abundance is determined using a quadrupole mass spectrometer with well-calibrated sensitivity. A key requirement for calculation of the 4He abundance in the target is a precise knowledge of the volume of the ablation pit. This is the principal reason why we employ the ArF excimer for 4He analysis rather than a less-expensive frequency-multiplied Nd-YAG laser; the excimer creates tapered cylindrical pits with extremely reproducible and easily characterized geometry. After 4He analysis, U and Th are measured on the same sample surface using the more familiar technique of laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Our early experiments have been done using a frequency-quintupled Nd-YAG microprobe (213nm), While the need to analyze U+Th and He in separate

  13. Component geochronology in the polyphase ca. 3920 Ma Acasta Gneiss

    USGS Publications Warehouse

    Mojzsis, Stephen J.; Cates, Nicole L.; Caro, Guillaume; Trail, Dustin; Abramov, Oleg; Guitreau, Martin; Blichert-Toft, Janne; Hopkins, Michelle D.; Bleeker, Wouter

    2014-01-01

    The oldest compiled U–Pb zircon ages for the Acasta Gneiss Complex in the Northwest Territories of Canada span about 4050–3850 Ma; yet older ca. 4200 Ma xenocrystic U–Pb zircon ages have also been reported for this terrane. The AGC expresses at least 25 km2 of outcrop exposure, but only a small subset of this has been documented in the detail required to investigate a complex history and resolve disputes over emplacement ages. To better understand this history, we combined new ion microprobe235,238U–207,206Pb zircon geochronology with whole-rock and zircon rare earth element compositions ([REE]zirc), Ti-in-zircon thermometry (Tixln) and 147Sm–143Nd geochronology for an individual subdivided ∼60 cm2 slab of Acasta banded gneiss comprising five separate lithologic components. Results were compared to other variably deformed granitoid-gneisses and plagioclase-hornblende rocks from elsewhere in the AGC. We show that different gneissic components carry distinct [Th/U]zirc vs. Tixln and [REE]zirc signatures correlative with different zircon U–Pb age populations and WR compositions, but not with 147Sm–143Nd isotope systematics. Modeled  [REE] from lattice-strain theory reconciles only the ca. 3920 Ma zircons with the oldest component that also preserves strong positive Eu∗ anomalies. Magmas which gave rise to the somewhat older (inherited) ca. 4020 Ma AGC zircon age population formed at ∼IW (iron–wüstite) to

  14. Component geochronology in the polyphase ca. 3920 Ma Acasta Gneiss

    NASA Astrophysics Data System (ADS)

    Mojzsis, Stephen J.; Cates, Nicole L.; Caro, Guillaume; Trail, Dustin; Abramov, Oleg; Guitreau, Martin; Blichert-Toft, Janne; Hopkins, Michelle D.; Bleeker, Wouter

    2014-05-01

    The oldest compiled U-Pb zircon ages for the Acasta Gneiss Complex in the Northwest Territories of Canada span about 4050-3850 Ma; yet older ca. 4200 Ma xenocrystic U-Pb zircon ages have also been reported for this terrane. The AGC expresses at least 25 km2 of outcrop exposure, but only a small subset of this has been documented in the detail required to investigate a complex history and resolve disputes over emplacement ages. To better understand this history, we combined new ion microprobe 235,238U-207,206Pb zircon geochronology with whole-rock and zircon rare earth element compositions ([REE]zirc), Ti-in-zircon thermometry (Tixln) and 147Sm-143Nd geochronology for an individual subdivided ˜60 cm2 slab of Acasta banded gneiss comprising five separate lithologic components. Results were compared to other variably deformed granitoid-gneisses and plagioclase-hornblende rocks from elsewhere in the AGC. We show that different gneissic components carry distinct [Th/U]zirc vs. Tixln and [REE]zirc signatures correlative with different zircon U-Pb age populations and WR compositions, but not with 147Sm-143Nd isotope systematics. Modeled DWRzircon [REE] from lattice-strain theory reconciles only the ca. 3920 Ma zircons with the oldest component that also preserves strong positive Eu∗ anomalies. Magmas which gave rise to the somewhat older (inherited) ca. 4020 Ma AGC zircon age population formed at ˜IW (iron-wüstite) to

  15. Mineralogy and geochemistry of claystones from the Guadalupian-Lopingian boundary at Penglaitan, South China: Insights into the pre-Lopingian geological events

    NASA Astrophysics Data System (ADS)

    Zhong, Yu-Ting; He, Bin; Xu, Yi-Gang

    2013-01-01

    The Guadalupian-Lopingian (G/L) boundary, at a stratigraphically well-documented outcrop in Penglaitan, Guangxi Autonomous Region, South China, has been approved as the Global Stratotype Section and Point (GSSP). Several volcanic ashes or tuffs occur at this boundary, but their mineralogy and geochemistry are not available yet and no reliable age for this boundary has been obtained. A combined study of mineralogy, geochemistry and geochronology has been carried out in this study on six layers of claystones collected below (Group 1) and above (Group 2) the G/L boundary at the Penglaitan section. Both Group 1 and Group 2 claystones are likely clastic in origin, rather than volcanic ashes as previously thought. Thus the Penglaitan claystones are not suitable for age determination of the G/L boundary. They are significantly different in terms of mineralogy and geochemistry. Specifically, Group 1 claystones are likely derived from a mafic source which is genetically related to the Emeishan large igneous province, therefore providing additional evidence for the synchroneity between the G/L boundary mass extinction and the Emeishan volcanism. Group 2 samples were derived from a felsic source, of which zircons yield an age spectrum peaked at 262 ± 3 Ma, undistinguishable within the uncertainty from the currently accepted G/L boundary age (260.4 ± 0.4 Ma). Nevertheless, Group 2 samples are not related to Emeishan volcanism, because their negative zircon ɛHf(t) values differ significantly from those of Emeishan magmas and trace element compositions of zircons are indicative of an arc source, rather than a within-plate source. In consideration of paleogeographic reconstruction, we propose that the Group 2 claystones may have been derived from continental arcs during the palaeo-Tethys evolution. This is the first sedimentary evidence for Permian continental arc in the northern margin of palaeo-Tethys.

  16. Building the EarthChem System for Advanced Data Management in Igneous Geochemistry

    NASA Astrophysics Data System (ADS)

    Lehnert, K.; Walker, J. D.; Carlson, R. W.; Hofmann, A. W.; Sarbas, B.

    2004-12-01

    Several mature databases of geochemical analyses for igneous rocks are now available over the Internet. The existence of these databases has revolutionized access to data for researchers and students allowing them to extract data sets customized to their specific problem from global data compilations with their desktop computer within a few minutes. Three of the database efforts - PetDB, GEOROC, and NAVDAT - have initiated a collaborative effort called EarthChem to create better and more advanced and integrated data management for igneous geochemistry. The EarthChem web site (http://www.earthchem.org/) serves as a portal to the three databases and information related to EarthChem activities. EarthChem participants agreed to establish a dialog to minimize duplication of effort and share useful tools and approaches. To initiate this dialog, a workshop was run by EarthChem in October, 2003 to discuss cyberinfrastructure needs in igneous geochemistry (workshop report available at the EarthChem site). EarthChem ran an information booth with database and visualization demonstrations at the Fall 2003 AGU meeting (and will have one in 2004) and participated in the May 2003 GERM meeting in Lyon, France where we provided the newly established Publishers' Round Table a list of minimum standards of data reporting to ease the assimilation of data into the databases. Aspects of these suggestions already have been incorporated into new data policies at Geochimica et Cosmochimica Acta and Chemical Geology (Goldstein et al. 2004), and are under study by the Geological Society of America. EarthChem presented its objectives and activities to the Solid Earth Sciences community at the Annual GSA Meeting 2003 (Lehnert et al, 2003). Future plans for EarthChem include expanding the types and amounts of data available from a single portal, giving researchers, faculty, students, and the general public the ability to search, visualize, and download geochemical and geochronological data for a

  17. Performance of DFT+U method for prediction of structural and thermodynamic parameters of monazite-type ceramics.

    PubMed

    Blanca Romero, Ariadna; Kowalski, Piotr M; Beridze, George; Schlenz, Hartmut; Bosbach, Dirk

    2014-07-05

    We performed a density functional theory (DFT) study of the monazite-type ceramics using DFT+U method, where the Hubbard U parameters are derived ab initio, with the main goal in testing the predictive power of this computational method for modeling of f-electron materials that are of interest in nuclear waste management. We show that DFT+U approach with PBEsol as the exchange-correlation functional significantly improves description of structures and thermodynamic parameters of lanthanide-bearing oxides and monazites over commonly used standard DFT (PBE) approach. We found that it is essential to use the Hubbard U parameter derived for a given element and a given structure to reproduce the structural parameters of the measured materials. We obtained exceptionally good description of the structural parameters with U parameter derived using the linear response approach of Cococcioni and de Gironcoli (Phys. Rev. B 2005, 71, 035105). This shows that affordable methods, such as DFT+U with a clever choice of exchange-correlation functional and the Hubbard U parameter can lead to a good description of f-electron materials.

  18. Using Eu(3+) as an atomic probe to investigate the local environment in LaPO4-GdPO4 monazite end-members.

    PubMed

    Huittinen, Nina; Arinicheva, Yulia; Schmidt, Moritz; Neumeier, Stefan; Stumpf, Thorsten

    2016-12-01

    In the present study, we have investigated the luminescent properties of Eu(3+) as a dopant in a series of synthetic lanthanide phosphates from the monazite group. Systematic trends in the spectroscopic properties of Eu(3+) depending on the size of the host cation and the dopant to ligand distance have been observed. Our results show that the increasing match between host and dopant radii when going from Eu(3+)-doped LaPO4 toward the smaller GdPO4 monazite decreases both the full width at half maximum of the Eu(3+) excitation peak, as well as the (7)F2/(7)F1 emission band intensity ratio. The decreasing Ln⋯O bond distance within the LnPO4 series causes a systematic bathochromic shift of the Eu(3+) excitation peak, showing a linear dependence of both the host cation size and the Ln⋯O distance. The linear relationship can be used to predict the energy band gap for Eu(3+)-doped monazites for which no Eu(3+) luminescent data is available. Finally, mechanisms for metal-metal energy transfer between host and dopant lanthanides have been explored based on recorded luminescence lifetime data. Luminescence lifetime data for Eu(3+) incorporated in the various monazite hosts clearly indicated that the energy band gap between the guest ion emission transition and the host ion absorption transition can be correlated to the degree of quenching observed in these materials with otherwise identical geometries and chemistries.

  19. Thermal history of low metamorphic grade Paleoproterozoic sedimentary rocks of the Penokean orogen, Lake Superior region: Evidence for a widespread 1786 Ma overprint based on xenotime geochronology

    USGS Publications Warehouse

    Vallini, D.A.; Cannon, W.F.; Schulz, K.J.; McNaughton, N.J.

    2007-01-01

    Paleoproterozoic strata in northern Michigan, Wisconsin, and Minnesota were deposited between 2.3 and 1.75 Ga within the rifted margin and subsequent foreland basin of the Penokean orogen. These strata show evidence for multiple regional metamorphic events previously attributed entirely to the Penokean orogeny (1875-1835 Ma). Metasandstones from the Marquette Range Supergroup and the Animikie, Mille Lacs, and North Range Groups were sampled at multiple localities across Minnesota, Wisconsin and Michigan for metamorphic xenotime suitable for in situ SHRIMP U-Pb geochronology. All samples are from the northern Penokean foreland basin where the metamorphic grade is greenschist to sub-greenschist and the strata are virtually undeformed. Xenotime U-Pb ages in these samples have a bimodal population with means of 1786 ?? 4 Ma (n = 32) and 1861 ?? 10 Ma (n = 9). Xenotime of both ages are contained in metasandstones from the basal Chocolay Group in Michigan and Wisconsin and the Mille Lacs Group and North Range Groups in Minnesota. The older age records a regional low-temperature thermal event that is slightly older than the overlying Menominee Group in Michigan and the Animikie Group in Minnesota and Ontario. This 1861 Ma event coincides with regional uplift that led to the formation of the unconformity between the Menominee Group and the overlying Baraga Group in Michigan; hence xenotime growth must have occurred at shallow burial depths. Younger units from the Menominee and Baraga Groups in Michigan and the Animikie Group in Minnesota, record only the 1786 Ma event. A dominant 1800-1790 Ma metamorphic monazite population that overprints Penokean-interval monazite has been documented within amphibolite- to granulite-facies rocks immediately north of the Niagara Fault Zone within the vicinity of gneiss domes and granitic plutons. In contrast, the 1786 Ma xenotime ages are from low-grade, virtually undeformed rocks 50-150 km from the high-grade zones and thus do not appear

  20. Simultaneous in situ determination of U-Pb and Sm-Nd isotopes in monazite by laser ablation ICP-MS

    NASA Astrophysics Data System (ADS)

    Goudie, Dylan J.; Fisher, Christopher M.; Hanchar, John M.; Crowley, James L.; Ayers, John C.

    2014-06-01

    are presented for in situ simultaneous determination of U-Pb and Sm-Nd isotopes in monazite using the Laser Ablation Split-Stream (LASS) method. This method uses a laser ablation system coupled to a magnetic-sector inductively coupled plasma mass spectrometer (HR) (ICP-MS) for measuring U-Pb isotopes and a multicollector (MC) ICP-MS for measuring Sm-Nd isotopes. Ablated material is split using a Y-connector and transported simultaneously to both mass spectrometers. In addition to Sm and Nd isotopes, the MC-ICP-MS is configured to also acquire Ce, Nd, Sm, Eu, and Gd elemental abundances. This approach provides age, tracer isotope, and trace element data in the same ablation volume, reducing sampling problems associated with fine-scale zoning in accessory minerals and minimizing the material needed for ablation. Precision and accuracy of the U-Pb method (and the precision of the Sm-Nd method) is demonstrated with results from well-characterized monazite reference materials. The LASS results agree within uncertainty with the isotope dilution thermal ionization mass spectrometry (ID-TIMS) U-Pb dates. The accuracy of the Sm-Nd method is assessed by comparing the LA-MC-ICP-MS results with ID-TIMS determinations on a well-characterized, in-house monazite reference material. The LASS method is then applied to monazite from the Birch Creek Pluton in the White Mountains of California as a case study to illustrate the utility of this method for solving geologic problems. The U-Pb ages and Sm-Nd isotopic data from the LASS method support the conclusions drawn from previous results that monazite can record timing and information about the source region(s) of hydrothermal fluids.

  1. U-Pb Geochronology of Hydrous Silica (Siebengebirge, Germany)

    NASA Astrophysics Data System (ADS)

    Tomaschek, Frank; Nemchin, Alexander; Geisler, Thorsten; Heuser, Alexander; Merle, Renaud

    2015-04-01

    Low-temperature, hydrous weathering eventually leads to characteristic products such as silica indurations. Elevated U concentrations and the ability of silica to maintain a closed system permits silica to be dated by the U-Pb method, which, in turn, will potentially allow constraining the timing of near-surface processes. To test the feasibility of silica U-Pb geochronology, we sampled opal and chalcedony from the Siebengebirge, Germany. This study area is situated at the terminus of the Cenozoic Lower Rhine Basin on the Rhenish Massif. The investigated samples include silicified gravels from the Mittelbachtal locality, renowned for the embedded wood opal. Structural characterization of the silica phases (Raman spectroscopy) was combined with in situ isotopic analyses, using ion microprobe and LA-ICPMS techniques. In the Siebengebirge area fluviatile sediments of Upper Oligocene age were covered by an extended trachyte tuff at around 25 Ma. Silica is known to indurate some domains within the tuff and, in particular, certain horizons within the subjacent fluviatile sediments ('Tertiärquarzite'). Cementation of the gravels occurred during at least three successive growth stages: early paracrystalline silica (opal-CT), fibrous chalcedony, and late microcrystalline quartz. It has traditionally been assumed that this silica induration reflects intense weathering, more or less synchronous with the deposition of the volcanic ashes. Results from U-Pb geochronology returned a range of discrete 206Pb-238U ages, recording a protracted silicification history. For instance, we obtained 22 ± 1 Ma for opal-CT cement from a silicified tuff, 16.6 ± 0.5 Ma for silicified wood and opal-CT cement in the fluviatile gravels, as well as 11 ± 1 Ma for texturally late chalcedony. While silicification of the sampled tuff might be contemporaneous with late-stage basalts, opaline silicification of the subjacent sediments and their wood in the Mittelbachtal clearly postdates active

  2. Solid-state synthesis of monazite-type compounds containing tetravalent elements.

    PubMed

    Bregiroux, Damien; Terra, Olivier; Audubert, Fabienne; Dacheux, Nicolas; Serin, Virgine; Podor, Renaud; Bernache-Assollant, Didier

    2007-11-26

    On the basis of optimized grinding/heating cycles developed for several phosphate-based ceramics, the preparation of brabantite and then monazite/brabantite solid solutions loaded with tetravalent thorium, uranium, and cerium (as a plutonium surrogate) was examined versus the heating temperature. The chemical reactions and transformations occurring when heating the initial mixtures of AnO2/CeO2, CaHPO(4).2H2O (or CaO), and NH4H2PO4 were identified through X-ray diffraction (XRD) and thermogravimetric/differential thermal analysis experiments. The incorporation of thorium, which presents only one stabilized oxidation state, occurs at 1100 degrees C. At this temperature, all the thorium-brabantite samples appear to be pure and single phase as suggested by XRD, electron probe microanalyses, and micro-Raman spectroscopy. By the same method, tetravalent uranium can be also stabilized in uranium-brabantite, i.e., Ca0.5U0.5PO4, after heating at 1200 degrees C. Both brabantites, Ca0.5Th0.5PO4 and Ca0.5U0.5PO4, begin to decompose when increasing the temperature to 1400 and 1300 degrees C, respectively, leading to a mixture of CaO and AnO2 by the volatilization of P4O10. In contrast to the cases of thorium and uranium, cerium(IV) is not stabilized during the heating treatment at high temperature. Indeed, the formation of Ca0.5Ce0.5PO4 appears impossible, due to the partial reduction of cerium(IV) into cerium(III) above 840 degrees C. Consequently, the systems always appear polyphase, with compositions of CeIII1-2xCeIVxCaxPO4 and Ca2P2O7. The same conclusion can be also given when discussing the incorporation of cerium(IV) into La1-2xCeIIIx-yCeIVyCay(PO4)1-x+y. This incomplete incorporation of cerium(IV) confirms the results obtained when trying to stabilize tetravalent plutonium in Ca0.5PuIV0.5PO4 samples.

  3. The Isotope Geochemistry of Abyssal Peridotites and Related Rocks

    DTIC Science & Technology

    1993-06-01

    Oceanography/ Applied Ocean Science San d E n g in e e r in g ftoo I • •OFTI DOCTORAL DISSERTATION I The Isotope Geochemistry of Abyssal Peridotites and...Related Rocks "- . .. .. .. 1 , ".:i• . Jonathan E. Snow , ’ I .June 1993 I .o. I I I WHOI-93-36 I The Isotope Geochemistry of Abyssal Peridotites and...States Government. This thesis should be cited as: Jonathan E. Snow, 1993. The Isotope Geochemistry of Abyssal Peridotites and Related Rocks. Ph.D

  4. Uplifting of the Jiamusi Block in the eastern Central Asian Orogenic Belt, NE China: evidence from basin provenance and geochronology

    NASA Astrophysics Data System (ADS)

    Liu, Yongjiang; Wen, Quanbo; Han, Guoqing; Li, Wei

    2010-05-01

    The main part of Jiamusi Block, named as Huanan-Uplift, is located in the northeastern Heilongjiang, China. The Huanan-Uplift is surrounded by many relatively small Mesozoic-Cenozoic basins, e.g. Sanjiang Basin, Hulin Basin, Boli Basin, Jixi Basin, Shuangyashan Basin and Shuanghua Basin. However previous research works were mainly focused on stratigraphy and palaeontology of the basins, therefore, the coupling relation between the uplift and the surrounding basins have not been clear. Based on the field investigations, conglomerate provenance studies of the Houshigou Formation in Boli Basin, geochronology of the Huanan-Uplift basement, we have been studied the relationships between Huanan-Uplift and the surrounding basins. The regional stratigraphic correlations indicates that the isolated basins in the area experienced the same evolution during the period of the Chengzihe and the Muling Formations (the Early Cretaceous). The paleogeography reconstructions suggest that the area had been a large-scale basin as a whole during the Early Cretaceous. The Huanan-Uplift did not exist. The paleocurrent directions, sandstone and conglomerate provenance analyses show that the Huanan-Uplift started to be the source area of the surrounding basins during the period of Houshigou Formation (early Late Cretaceous), therefore, it suggests that the Jiamusi Block commenced uplift in the early Late Cretaceous. The granitic gneisses in Huanan-Uplift give 494-415 Ma monazite U-Th-total Pb ages, 262-259 Ma biotite and 246-241 Ma K-feldspar 40Ar/39Ar ages. The cooling rates of 1-2 ℃/Ma from 500-260 Ma and 10-11 ℃/Ma from 260-240 Ma have been calculated based on the ages. This suggests that the Jiamusi Block had a rapid exhumation during late Permian, which should be related to the closure of the Paleo-Asian Ocean between the Siberian and North China continents. It is concluded that during the late Paleozoic the Jiamusi Block was stable with a very slow uplifting. With the closure of

  5. Complete zircon and chromite digestion by sintering of granite, rhyolite, andesite and harzburgite rock reference materials for geochronological purposes

    NASA Astrophysics Data System (ADS)

    Bokhari, Syed Nadeem H.; Meisel, Thomas

    2014-05-01

    Zircon (ZrSiO4) is a common accessory mineral in nature that occurs in a wide variety of sedimentary, igneous, and metamorphic rocks. Zircon has the ability to retain substantial chemical and isotopic information that are used in range of geochemical and geo- chronological investigations. Sample digestion of such rock types is a limiting factor due to the chemical inertness of zircon (ZrSiO4) tourmaline, chromite, barite, monazite, sphene, xenotime etc. as the accuracy of results relies mainly on recovery of analytes from these minerals. Dissolution by wet acid digestions are often incomplete and high blank and total dissolved solids (TDS) contents with alkali fusions lead to an underestimation of analyte concentrations. Hence an effective analytical procedure, that successfully dissolves refractory minerals such as zircon is needed to be employed for reliable analytical results. Na2O2 digestion [1] was applied in characterisation of granite (G-3), rhyolite (MRH), andesite (MGL-AND) and harzburgite (MUH-1) powdered reference material with solution based ICP-MS analysis. In this study we undertake a systematic evaluation of decomposition time and sample:Na2O2 ratio and test portion size after minimising effect of all other constraints that makes homogeneity ambiguous. In recovering zircon and chromite 100 mg test portion was mixed with different amounts of Na2O2 i.e. 100-600 mg. Impact of decomposition time was observed by systematically increasing heating time from 30-45 minutes to 90-120 minutes at 480°C. Different test portion sizes 100-500 mg of samples were digested to control variance of inhomogeneity. An improved recovery of zirconium in zircon in granite (G-3), rhyolite MRH), andesite (MGL-AND) and chromite in harzburgite (MUH-1) was obtained by increasing heating time (2h) at 480°C and by keeping (1:6) ratio of sample:Na2O2. Through this work it has been established that due to presence of zircon and chromite, decomposition time and sample:Na2O2 ratio has

  6. Radiogenic heating to ultrahigh temperature: Geochronology and 4+ thermometry across southern Madagascar

    NASA Astrophysics Data System (ADS)

    Horton, F.; Hacker, B. R.; Kylander-Clark, A. R.

    2014-12-01

    As zones of focused metamorphism, melting, and ductile deformation, hot crustal sections are especially important for understanding the evolution of the lower crust in convergent orogens, such as Tibet. One of the best exposed crustal sections that reached ultrahigh-temperature (UHT: >900° C) is in southern Madagascar. There, the association of UHT mineral assemblages with exceptionally high concentrations of radioactive heat-producing elements begs the question of whether radiogenic heating caused UHT. Partial melting, retrogression and rapid elemental diffusion at high temperature, however, have left a complex record of radiometric dates that span 150 Myr (~650-500 Ma), making it difficult to address this question. We apply laser-ablation split-stream ICPMS (LASS) petrochronology and 4+ cation thermometry to better constrain the lengthscales and timescales over which high temperatures were sustained in southern Madagascar. By deciphering complex intragrain (re)crystallization textures of zircon and monazite from a broad geographical area, we deduce that orogenesis lasted >60 Myr. Specifically, 600-540 Ma zircon and monazite with HREE depletion suggest (re)crystallization in the presence of garnet. All monazite show negative Eu anomalies (compatible with the presence of plagioclase), but ~570 to ~530 Ma monazite has more-pronounced anomalies. Ti-in-zircon and Zr-in-rutile thermometry confirm ultrahigh temperatures within a restricted area of ~100 x 200 km. These thermal and chronologic constraints allow us to evaluate the potential causes of heating. Measured K, Th, and U contents of rocks within the UHT domain indicate an average heat-production rate of >4 μW/m3, sufficient to produce UHT metamorphism in 60-km thick crust within 60 Myr. We conclude that high concentrations of heat-producing elements caused focused heat production in young metasedimentary rocks that were sandwiched between older crustal domains. We speculate that ultrahigh temperatures caused by

  7. Amino acid geochronology of raised beaches in south west Britain

    NASA Astrophysics Data System (ADS)

    Bowen, D. Q.; Sykes, G. A.; Reeves (nee Henry), Alayne; Miller, G. H.; Andrews, J. T.; Brew, J. S.; Hare, P. E.

    Based on (1) the epimerization of L:isoleucine to D:alloisoleucine ( {D}/{L} ratios) in Patella vulgata, Littorina littorea, L. littoralis, L. saxatilis, Littorina species and Nucella lapillus from raised beaches in south west Britain, (2) statistical analysis of the {D}/{L} ratios, and (3) lithostratigraphic and geomorphic evaluation, three ( {D}/{L}) Stages are proposed. The {D}/{L} ratios for all the species measured are converted to a Patella vulgata standard. The three ( {D}/{L}) Stages are: (1) The Minchin Hole ( {D}/{L}) Stage, {D}/{L} ratios 0.175 ± 0.014, defined at a stratotype in Minchin Hole Cave, Gower, Wales. (2) A provisionally defined, but as yet, unamed ( {D}/{L}) Stage, because of the current unavailability of a suitable stratotype, with {D}/{L} ratios of 0.135 ± 0.014 (3) The Pennard ( {D}/{L}) Stage, {D}/{L} ratios 0.105 ± 0.016, defined at a stratotype in Minchin Hole Cave, Gower, Wales. Two geochronological models of the three high sea-level events representing the {D}/{L} Stages are constrained by uranium-series age determinations on stalagmite interbedded with marine beds in Minchin Hole and Bacon Hole Caves, Gower, Wales. A potential 'fixed point' in model evaluation is an age determination which is equivalent to Oxygen Isotope Sub-stage 5e (122 ka). The two models are:

  8. In-Situ Geochronology as a Mission-Enabling Technology

    NASA Technical Reports Server (NTRS)

    Coleman, Max; Hecht, Michael; Hurowitz, Joel; Neidholdt, Evan; Polk, James; Sinha, Mahadeva P.; Sturhahn, Wolfgang; Zimmerman, Wayne

    2012-01-01

    Although there are excellent estimates of ages of terrains on Mars from crater counting, even a few absolute ages would serve to validate the calibration. Results with uncertainties, although much larger than those that could be achieved in labs on Earth, would be extremely valuable. While there are other possibilities for in-situ geochronology instruments, we describe here to alternative technologies, being developed in JPL. There are two common features of both. The first is analysis by means of miniature mass spectrometer. The second is use of laser sampling to reduce or avoid sample handling, preparation and pre-treatment and equally importantly, to allow analysis of individual, textually resolved minerals in coarse-grained rocks. This textural resolved minerals in coarse-grained rocks. This textural resolution will aid in selection of grains more or less enriched in the relevant elements and allow construction of isochrons for more precise dating. Either of these instruments could enable missions to Mars and other planetary bodies.

  9. Geochronology of wadi tushka: lost tributary of the nile.

    PubMed

    Haynes, C V

    1980-10-03

    The Sadat Canal, now under construction, is designed to drain excess water from Lake Nasser to the Western Desert by way of Wadi Tushka, a sand-filled, dry-wash tributary of the Nile 34 kilometers north of Abu Simbel. Core-drilling logs made by the Aswan High Dam Authority prior to excavation of the Sadat Canal and along 48 kilometers of its axis reveal as much as 33 meters of unconsolidated sand and gravel over Mesozoic bedrock and under surficial dune sand and playa muds of Holocene age. Excavation of the canal revealed Acheulean artifacts 6.7 meters below the surface in fluvial sediments capped by a buried, red calcic paleosol. These data are interpreted as evidence for the existence of a major tributary of the Nile during the late middle Pleistocene. The tributary drained the Kiseiba-Dungul Depression and possibly the Kharga Depression as well. Chalcedony-armored mudstones in the depressions are believed to be saline lake deposits possibly related to a lake that drained to the Nile by way of Wadi Tushka, thus entrenching the divide between the depression and the valley. Gross correlations with Pleistocene deposits of the Nile Valley and the Kharga Depression are based upon archeological evidence only until more precise geochronology can be applied to the problem.

  10. Geochronology of Playas Lake, NM and Willcox Playa, Arizona

    NASA Astrophysics Data System (ADS)

    Kowler, A.

    2008-12-01

    Playa lake basins contain valuable archives of late Quaternary paleoclimatic conditions in the southwestern United States. Previous research on lake basins in the region has revealed several pluvial intervals post- dating the last full glacial period; however, the timing of these intervals can only be assessed through the collective analysis of individual lake-level histories. While previous studies of lake core sediments have provided baseline data for climate modelers, the accuracy of most lake chronologies has been limited by uncertainties associated with 14C reservoir corrections. Further, most studies have used the sedimentological, chemical, and biological characteristics of lake sediments to infer relative lake-level. In contrast, radiocarbon-dated shoreline deposits-although unfortunately rare-can provide accurate information about the timing and duration of high stands, as well as a record of absolute lake-level during these events. Recent investigations of shoreline and spring sediments from playa lake basins provide preliminary geochronological and paleoenvironmental information about effective precipitation in the Southwest during the late Pleistocene and early Holocene. The results of ongoing investigations at Willcox Playa, Arizona, and Playas lake, New Mexico, are presented here.

  11. U-Pb zircon and monazite dating of a mafic-ultramafic complex and its country rocks

    NASA Astrophysics Data System (ADS)

    Gebauer, D.; Bernard-Griffiths, J.; Grünenfelder, M.

    1981-05-01

    U-Pb data on zircons from the largest mafic-ultramafic body (6×2 km) of the French Central Massif (Sauviat-sur-Vige) yield the following age results: Primary magmatic crystallization of the gabbroic and peridotitic protoliths took place in the Cambro-Ordovician (496±25/17 m.y.). Variable transformation under eclogite facies conditions was Hercynian (320±29/36 m.y.). The same age pattern, derived by U-Pb monazite analyses, was found also for the immediate country rocks, i.e. kyanite bearing, coarse-grained metagranites occurring to the W and N of the Sauviat massif. Due to the fact that there is no regional Hercynian high-grade metamorphism in this part of the French Central Massif (e.g. Duthou 1977; Bernard-Griffiths 1975), both mafic-ultramafic complex as well as immediate felsic country rocks must have been emplaced tectonically into pre-Hercynian (Acadian±Caledonian) crustal rocks. The cause for such a Hercynian tectonism is thought to be due to continent-continent collision of the Spanish with the Armorican plate. Preliminary U-Pb zircon results on one eclogite sample taken about 50 km S of the Sauviat complex indicate also an Early Palaeozoic age for the magmatic protolith and a Hercynian transformation into eclogite, combined with and/or followed by tectonic emplacement. However, opposite to the continental Sauviat massif, we are probably dealing here with oceanic material, possibly deposited in an Early Palaeozoic marginal sea basin. Thus, subduction and tectonic emplacement of oceanic crust into continental crust terminated in this area also in the Hercynian. Concerning U-Pb systematics of zircon and monazite the following conclusions can be drawn: 1) U-Pb systems of primary magmatic zircons of mafic and ultramafic rocks are only weakly disturbed during static eclogite facies metamorphism ( T>820° C; P> 15 kbar); 2) New- and overgrowth of zircon during eclogite facies metamorphism seems to be the major cause for the degree of discordance; 3

  12. Monazite, iron oxide and barite exsolutions in apatite aggregates from CCSD drillhole eclogites and their geological implications

    NASA Astrophysics Data System (ADS)

    Sun, Xiaoming; Tang, Qian; Sun, Weidong; Xu, Li; Zhai, Wei; Liang, Jinlong; Liang, Yeheng; Shen, Kun; Zhang, Zeming; Zhou, Bing; Wang, Fangyue

    2007-06-01

    We have identified abundant exsolutions in apatite aggregates from eclogitic drillhole samples of the Chinese Continental Scientific Drilling (CCSD) project. Electron microscope and laser Raman spectroscopy analyses show that the apatite is fluorapatite, whereas exsolutions that can be classified into four types: (A) platy to rhombic monazite exsolutions; (B) needle-like hematite exsolutions; (C) irregular magnetite and hematite intergrowths; and (D) needle-like strontian barite exsolutions. The widths and lengths of type A monazite exsolutions range from about 6-10 μm (mostly 6 μm) and about 50-75 μm, respectively. Type B exsolutions are parallel with the C axis of apatite, with widths ranging from 0.5 to 2 μm, with most around 1.5 μm, and lengths that vary dramatically from 6 to 50 μm. Type C exsolutions are also parallel with the C axis of apatite, with lengths of ˜30-150 μm and widths of ˜10 to 50 μm. Type D strontian barite exsolutions coexist mostly with type B hematite exsolutions, with widths of about 9 μm and lengths of about 60-70 μm. Exsolutions of types B, C and D have never been reported in apatites before. Most of the exsolutions are parallel with the C axis of apatite, implying that they were probably exsolved at roughly the same time. Dating by the chemical Th-U-total Pb isochron method (CHIME) yields an U-Pb isochron age of 202 ± 28 Ma for monazite exsolutions, suggesting that these exsolutions were formed during recrystallization and retrograde metamorphism of the exhumed ultrahigh pressure (UHP) rocks. Quartz veins hosting apatite aggregates were probably formed slightly earlier than 202 Ma. Abundant hematite exsolutions, as well as coexistence of magnetite/hematite and barite/hematite in the apatite, suggest that the oxygen fugacity of apatite aggregates is well above the sulfide-sulfur oxide buffer (SSO). Given that quartz veins host these apatite aggregates, they were probably deposited from SiO 2-rich hydrous fluids formed during

  13. Insights into Igneous Geochemistry from Trace Element Partitioning

    NASA Technical Reports Server (NTRS)

    Jones, J. H.; Hanson, B. Z.

    2001-01-01

    Partitioning of trivalent elements into olivine are used to explore basic issues relevant to igneous geochemistry, such as Henry's law. Additional information is contained in the original extended abstract.

  14. POLLUTION PREVENTION OPPORTUNITY ASSESSMENT - GEOCHEMISTRY LABORATORY AT SANDIA NATIONAL LABORATORIES

    EPA Science Inventory

    These reports summarize pollution prevention opportunity assessments conducted jointly by EPA and DOE at the Geochemistry Laboratory and the Manufacturing and Fabrication Repair Laboratory at the Department of Energy's Sandia National Laboratories facility in Albuquerque, New Mex...

  15. Computational Studies in Molecular Geochemistry and Biogeochemistry

    SciTech Connect

    Felmy, Andrew R.; Bylaska, Eric J.; Dixon, David A.; Dupuis, Michel; Halley, James W.; Kawai, R.; Rosso, Kevin M.; Rustad, James R.; Smith, Paul E.; Straatsma, TP; Voth, Gregory A.; Weare, John H.; Yuen, David A.

    2006-04-18

    The ability to predict the transport and transformations of contaminants within the subsurface is critical for decisions on virtually every waste disposal option facing the Department of Energy (DOE), from remediation technologies such as in situ bioremediation to evaluations of the safety of nuclear waste repositories. With this fact in mind, the DOE has recently sponsored a series of workshops on the development of a Strategic Simulation Plan on applications of high perform-ance computing to national problems of significance to the DOE. One of the areas selected for application was in the area of subsurface transport and environmental chemistry. Within the SSP on subsurface transport and environmental chemistry several areas were identified where applications of high performance computing could potentially significantly advance our knowledge of contaminant fate and transport. Within each of these areas molecular level simulations were specifically identified as a key capability necessary for the development of a fundamental mechanistic understanding of complex biogeochemical processes. This effort consists of a series of specific molecular level simulations and program development in four key areas of geochemistry/biogeochemistry (i.e., aqueous hydrolysis, redox chemistry, mineral surface interactions, and microbial surface properties). By addressing these four differ-ent, but computationally related, areas it becomes possible to assemble a team of investigators with the necessary expertise in high performance computing, molecular simulation, and geochemistry/biogeochemistry to make significant progress in each area. The specific targeted geochemical/biogeochemical issues include: Microbial surface mediated processes: the effects of lipopolysacchardies present on gram-negative bacteria. Environmental redox chemistry: Dechlorination pathways of carbon tetrachloride and other polychlorinated compounds in the subsurface. Mineral surface interactions: Describing

  16. Composition and chemical microprobe dating of U-Th-bearing minerals. Part I. Monazites from the Urals and Siberia

    NASA Astrophysics Data System (ADS)

    Votyakov, S. L.; Khiller, V. V.; Shchapova, Yu. V.

    2012-12-01

    To develop chemical microprobe timing of U-Th-bearing minerals, monazite grains from several localities in the Ural and Siberia have been dated using upgraded measurement techniques and age calculation based on original software. The samples were taken from pegmatites of the Ilmeny Mountains and the Ilmeny-Vishnevy Mountains Complex in the South Urals; pegmatites from the Adui granitic pluton and its framework in the Central Urals; gneisses and granulites of the Taratash Complex in the South Urals; and felsic gneisses from the Transangara region of the Yenisei Ridge. Scrutiny of the composition, heterogeneity, and chemical substitution of U and Th ions is a necessary stage of chemical dating aimed at estimating the degree of closeness of the U-Th-Pb system and unbiased screening of analytical data. The results obtained have been compared with the known isotopic ages of the studied minerals; the compared data are satisfactorily consistent.

  17. Comparison of ultraviolet femtosecond and nanosecond laser ablation inductively coupled plasma mass spectrometry analysis in glass, monazite, and zircon.

    PubMed

    Poitrasson, Franck; Mao, Xianglei; Mao, Samuel S; Freydier, Rémi; Russo, Richard E

    2003-11-15

    We compared the analytical performance of ultraviolet femtosecond and nanosecond laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). The benefit of ultrafast lasers was evaluated regarding thermal-induced chemical fractionation, that is otherwise well known to limit LA-ICPMS. Both lasers had a Gaussian beam energy profile and were tested using the same ablation system and ICPMS analyzer. Resulting crater morphologies and analytical signals showed more straightforward femtosecond laser ablation processes, with minimal thermal effects. Despite a less stable energy output, the ultrafast laser yielded elemental (Pb/U, Pb/Th) and Pb isotopic ratios that were more precise, repeatable, and accurate, even when compared to the best analytical conditions for the nanosecond laser. Measurements on NIST glasses, monazites, and zircon also showed that femtosecond LA-ICPMS calibration was less matrix-matched dependent and therefore more versatile.

  18. Structural, vibrational, and thermochemical properties of the monazite-type solid solution La1-xPrxPO4

    NASA Astrophysics Data System (ADS)

    Hirsch, A.; Kegler, P.; Alencar, I.; Ruiz-Fuertes, J.; Shelyug, A.; Peters, L.; Schreinemachers, C.; Neumann, A.; Neumeier, S.; Liermann, H.-P.; Navrotsky, A.; Roth, G.

    2017-01-01

    The monazite-type solid solution La1-xPrxPO4 was synthesized by solid-state reaction and extensively investigated using electron microprobe and thermogravimetric analyses, differential scanning and high-temperature oxide melt solution calorimetry, powder X-ray diffraction, infrared and Raman spectroscopy. Lattice parameters and Ln-O bond lengths show a decrease with increasing Pr content. A small excess volume is observed for the solid solution. IR spectra of the solid solution members present no detectable differences, while a blue shift of the PO4-related modes is seen in the Raman data. This shift can be attributed to the lanthanide contraction. Within errors, calorimetry data show no systematic deviation from an ideal behavior, though one might interpret the data as an indication of a slightly asymmetric mixture. All data indicate that deviations from ideality of the solid solution - if present - are very small.

  19. Atomistic modeling and experimental studies of radiation damage in monazite-type LaPO4 ceramics

    NASA Astrophysics Data System (ADS)

    Ji, Yaqi; Kowalski, Piotr M.; Neumeier, Stefan; Deissmann, Guido; Kulriya, Pawan K.; Gale, Julian D.

    2017-02-01

    We simulated the threshold displacement energies (Ed), the related displacement and defect formation probabilities, and the energy barriers in LaPO4 monazite-type ceramics. The obtained Ed values for La, P, O primary knock-on atoms (PKA) are 56 eV, 75 eV and 8 eV, respectively. We found that these energies can be correlated with the energy barriers that separate the defect from the initial states. The Ed values are about twice the values of energy barriers, which is explained through an efficient dissipation of the PKA kinetic energy in the considered system. The computed Ed were used in simulations of the extent of radiation damage in La0.2Gd0.8PO4 solid solution, investigated experimentally. We found that this lanthanide phosphate fully amorphises in the ion beam experiments for fluences higher than ∼1013 ions/cm2.

  20. Environmental geochemistry at the global scale

    USGS Publications Warehouse

    Plant, J.; Smith, D.; Smith, B.; Williams, L.

    2001-01-01

    Land degradation and pollution caused by population pressure and economic development pose a threat to the sustainability of the earth's surface, especially in tropical regions where a long history of chemical weathering has made the surface environment particularly fragile. Systematic baseline geochemical data provide a means of monitoring the state of the environment and identifying problem areas. Regional surveys have already been carried out in some countries, and with increased national and international funding they can be extended to cover the rest of the land surface of the globe. Preparations have been made, under the auspices of the International Union of Geological Surveys (IUGS) and the International Association of Geochemistry and Cosmochemistry (IAGC) for the establishment of just such an integrated global database. ?? 2001 NERC. Published by Elsevier Science Ltd.

  1. Aspects of the magmatic geochemistry of bismuth

    USGS Publications Warehouse

    Greenland, L.P.; Gottfried, D.; Campbell, E.Y.

    1973-01-01

    Bismuth has been determined in 74 rocks from a differentiated tholeiitic dolerite, two calc-alkaline batholith suites and in 66 mineral separates from one of the batholiths. Average bismuth contents, weighted for rock type, of the Great Lake (Tasmania) dolerite, the Southern California batholith and the Idaho batholith are, 32, 50 and 70 ppb respectively. All three bodies demonstrate an enrichment of bismuth in residual magmas with magmatic differentiation. Bismuth is greatly enriched (relative to the host rock) in the calcium-rich accessory minerals, apatite and sphene, but other mineral analyses show that a Bi-Ca association is of little significance to the magmatic geochemistry of bismuth. Most of the bismuth, in the Southern California batholith at least, occurs in a trace mineral phase (possibly sulfides) present as inclusions in the rock-forming minerals. ?? 1973.

  2. Microbial Sulfur Geochemistry in Mine Systems (Invited)

    NASA Astrophysics Data System (ADS)

    Warren, L. A.; Norlund, K. L.; Hitchcock, A.

    2010-12-01

    Acid mine drainage (AMD), metal laden, acidic water, is the most pressing mining environmental issue on a global scale. While it is well recognized that the activity of autotrophic Fe and S bacteria amplify the oxidation of the sulfidic wastes, thereby generating acidity and leaching metals; the underlying microbial geochemistry is not well described. This talk will highlight results revealing the importance of microbial cooperation associated with a novel sulfur-metabolizing consortium enriched from mine waters. Results generated by an integrated approach, combining field characterization, geochemical experimentation, scanning transmission X-ray microscopy (STXM), and fluorescence in situ hybridization (FISH) [1]describing the underlying ecological drivers, the functionally relevant biogeochemical architecture of the consortial macrostructure as well as the identities of this environmental sulphur redox cycling consortium will be presented. The two common mine bacterial strains involved in this consortium, Acidithiobacillus ferroxidans and Acidiphilium sp., are specifically spatially segregated within a macrostructure (pod) of extracellular polymeric substance (EPS) that enables coupled sulphur oxidation and reduction reactions despite bulk, oxygenated conditions. Identical pod formation by type culture strains was induced and linked to ecological conditions. The proposed sulphur geochemistry associated with this bacterial consortium produces 40-90% less acid than expected based on abiotic AMD models, with implications for both AMD mitigation and AMD carbon flux modeling. We are currently investigating the implications of these sulphur-processing pods for metal dynamics in mine systems. These results demonstrate how microbes can orchestrate their geochemical environment to facilitate metabolism, and underscore the need to consider microbial interactions and ecology in constraining their geochemical impacts. [1] Norlund, Southam, Tyliszcczak, Hu, Karunakaran, Obst

  3. Present status of the geochronology of the early Precambrian of South India

    NASA Technical Reports Server (NTRS)

    Gopalan, K.; Srinivasan, R.

    1988-01-01

    The present status of Precambrian geochronology of South India was summarized. Support was offered for Raith's conclusion of an extensive 3.3 to 3.4-Ga tonalite-forming event. Evidence that the Sargur supracrustal sequence predates this event, however, remains equivocal. The only reliably dated supracrustal rocks are the similar to 3.0-Ga Chitradurga acid volcanics, and these are separated from the older Bababudan supracrustals by a major gneiss-forming event. A major unsolved problem relates to the timing of the Sargur supracrustals in relation to the basal units of the Dharwar succession. An appeal was made for more geochronological work on South Indian samples.

  4. Duration of Louisville hotspot volcanism at IODP 330 sites Canopus, Burton, and Rigil via 40Ar/39Ar geochronology

    NASA Astrophysics Data System (ADS)

    Cohen, B. E.; Vasconcelos, P. M.; Koppers, A. A.; Thiede, D. S.

    2013-12-01

    The Louisville seamount trail is a chain of intraplate volcanoes constructed over the past ~80 million years, as the Pacific plate moved 4300 km over a long-lived mantle melting anomaly. During IODP Expedition 330, over 800 m of alkaline mafic volcanic lavas, as well as interbedded and overlying sediments, were recovered from five of these seamounts in the older (~80-50 Ma) part of the chain. In this study we have undertaken geochronology of the volcanic units to provide time constraints for the magmatic evolution of the volcanoes. Sixteen of these drilled lava flows have been successfully dated using MAP-215-50 spectrometers, with six samples analyzed at Oregon State University (Koppers et al. 2012) and 12 flows analyzed at The University of Queensland. To check for consistency, two lava flows were dated at both laboratories; both samples yielded results within 2σ error. To minimize the effects of seawater alteration, only samples with well-crystallized groundmass were picked, and material cleaned via HNO3 and HCl acid pretreatment. Plateaus comprise 61 to 87% of the 39Ar released, and 40Ar/36Ar vs. 39Ar/36Ar correlation diagrams reveal all samples contained trapped argon within error of modern-day atmosphere. All ages determined are consistent with stratigraphic constraints, and we interpret the results to be reliable estimates of eruption ages. Units from Burton Guyot (site U1376A) yield ages from 70.8 × 0.5 to 64.1 × 0.5 Ma (2σ, using the atmospheric argon ratio and decay constants from Steiger & Jäger (1978) and a Fish Canyon sanidine age of 28.02 (Renne et al. 1998)). This long (~7 Ma) duration is consistent with petrologic evidence for substantial post-shield volcanic activity at this site. Meanwhile, at Canopus (site U1372A) and Rigil (sites U1373A and U1374A), lavas from the base, middle, and top of the respective volcanic piles yielded ages within analytical error. At the two deepest sites (U1372A and 1374A) 187 and 505 m of volcanic rocks were

  5. Geology, zircon geochronology, and petrogenesis of Sabalan volcano (northwestern Iran)

    NASA Astrophysics Data System (ADS)

    Ghalamghash, J.; Mousavi, S. Z.; Hassanzadeh, J.; Schmitt, A. K.

    2016-11-01

    Sabalan Volcano (NW Iran) is an isolated voluminous (4821 m elevation; > 800 km2) composite volcano that is located within the Arabia-Eurasia collision zone. Its edifice was assembled by recurrent eruptions of trachyandesite and dacite magma falling into a relatively restricted compositional range (56-67% SiO2) with high-K calc-alkaline and adakitic trace element (Sr/Y) signatures. Previous K-Ar dating suggested protracted eruptive activity between 5.6 and 1.4 Ma, and a two stage evolution which resulted in the construction of the Paleo- and Neo-Sabalan edifices, respectively. The presence of a topographic moat surrounding Neo-Sabalan and volcanic breccias with locally intense hydrothermal alteration are indicative of intermittent caldera collapse of the central part of Paleo-Sabalan. Volcanic debris-flow and debris-avalanche deposits indicate earlier episodes of volcanic edifice collapse during the Paleo-Sabalan stage. In the Neo-Sabalan stage, three dacitic domes extruded to form the summits of Sabalan (Soltan, Heram, and Kasra). Ignimbrites and minor pumice fall-out deposits are exposed in strongly dissected drainages that in part have breached the caldera depression. Lavas and pyroclastic rocks are varyingly porphyritic with Paleo-Sabalan rocks being trachyandesites carrying abundant phenocrysts (plagioclase + amphibole + pyroxene + biotite). The Neo-Sabalan rocks are slightly more evolved and include dacitic compositions with phenocrysts of plagioclase + amphibole ± alkali-feldspar ± quartz. All Sabalan rock types share a common accessory assemblage (oxides + apatite + zircon). High spatial resolution and sensitivity U-Pb geochronology using Secondary Ionization Mass Spectrometry yielded two clusters of zircon ages which range from 4.5 to 1.3 Ma and 545 to 149 ka, respectively (all ages are averages of multiple determinations per sample). U-Th zircon geochronology for selected Neo-Sabalan rocks agrees with the U-Pb ages, with the youngest zircon rims dating

  6. Episodic growth of Mt. Shasta, CA, documented by argon geochronology

    NASA Astrophysics Data System (ADS)

    Calvert, A. T.; Christiansen, R. L.

    2011-12-01

    eruptive focus shifted 1.5 km north (Misery Hill) between 50-35 ka, erupting silicic andesite and mafic dacite onto all sectors of the volcano. Flank vents directly south and north erupted domes and lavas 20-15 ka. At ~11 ka a voluminous episode began with the subplinian Red Banks pumice followed shortly by Shastina andesite/dacite lavas, domes, and pyroclastic flows, and soon after by Black Butte flank dacites. Existing 14C geochronology, and stratigraphic studies of the deposits show no eruptive breaks and constrain the episode to have lasted less than a few hundred years. Subsequent Holocene eruptions all issued from the modern summit (Hotlum cone), producing at least 10 large lava flows directed toward the NE sector, along with pyroclastic and debris flows, and a summit dome. Preliminary argon geochronology in progress dates summit lavas at 8.8, 5.8 and 4.7 ka.

  7. An Astronomically Dated Standard in 40Ar/39Ar Geochronology?

    NASA Astrophysics Data System (ADS)

    Kuiper, K.; Hilgen, F.; Krijgsman, W.; Wijbrans, J.

    2003-12-01

    The standard geological time scale of Berggren et al. (1995) and Cande and Kent (1995) is calibrated with different absolute dating techniques, i.e. the Plio - Pleistocene relies on astronomical tuning, and older parts of the time scale are based on radio-isotopic (40Ar/39Ar and U/Pb) calibration methods. In the new edition of the standard geological timescale (Lourens et al., to be published in 2004) the entire Neogene will rely on astronomical dating. Therefore, it is of crucial importance that all dating methods produce equivalent absolute ages when the same geological event is dated. The Mediterranean Neogene provides an excellent opportunity to compare different dating methods by isotopic dating (40Ar/39Ar, U/Pb) of volcanic ash layers intercalated in astronomically dated sediments. Here we will show that in spite of potential errors in all methods, we succeeded to intercalibrate the 40Ar/39Ar and astronomical methods, arriving at astronomically calibrated age of 28.24 +/- 0.01 Ma for the in 40Ar/39Ar geochronology commonly used standard FCT sanidine. The advantage of an astronomically calibrated FCT above a K/Ar calibrated standard is a smaller error in the absolute age due to the lack of uncertainties related to 40K and radiogenic 40Ar contents in the primary standard and a decreasing influence of errors in the decay constant (branching ratio is not required). In addition to an astronomically calibrated FCT age we propose to introduce an astronomically dated standard. A direct astronomically dated standard can be regarded as a "primary" standard and does not require intercalibration with other standards, thus reducing analytical (and geological) uncertainties. Ash layers intercalated in sedimentary sequences in the Melilla Basin, Morocco appear to be the most suitable for this purpose. A reliable astronomical time control is available and intercalated ash layers contain sanidine phenocrysts up to 2 mm. Four ash layers are not or barely affected by

  8. The Violent Early Solar System, as Told by Sample Geochronology

    NASA Technical Reports Server (NTRS)

    Cohen, Barbara

    2013-01-01

    One of the legacies of the samples collected by the Apollo and Luna missions is the link forged between radiometric ages of rocks and relative ages according to stratigraphic relationships and impact crater size-frequency distributions. Our current understanding of the history of the inner solar system is based on the relative chronology of individual planets, tied to the absolute geochronology of the Moon via these important samples. Sample ages have enabled us to infer that impact-melt breccias from Apollo 14 and 15 record the formation of the Imbrium Basin, those from the highland massifs at Apollo 17 record the age of Serenitatis, those from the KREEP-poor Apollo 16 site record the age of Nectaris, and materials from Luna 24 record the age of Crisium. Ejecta from smaller and younger craters Copernicus and Tycho were sampled at Apollo 12 and 17, respectively, and local craters such as Cone at Apollo 14, and North Ray and South Ray at Apollo 16 were also sampled and ages determined for those events. Much of what we understand about the lunar impact flux is based on these ages. Samples from these nearside locations reveal a preponderance of impact-disturbed or recrystallized ages between 3.75 and 3.95 billion years. Argon and lead loss (and correlated disturbances in the Rb-Sr system) have been attributed to metamorphism of the lunar crust by an enormous number of impacts in a brief pulse of time, called the Lunar Cataclysm or Late Heavy Bombardment. Subsequent high-precision geochronometric analyses of Apollo samples and lunar highlands meteorites show a wider range of ages, but very few older than 4 Ga. The paucity of ancient impact melt rocks has been interpreted to mean that either that most impact basins formed at this time, or that ejecta from the large, near-side, young basins dominates the Apollo samples.

  9. Geochronology and petrogenesis of Middle Permian S-type granitoid in southeastern Guangxi Province, South China: Implications for closure of the eastern Paleo-Tethys

    NASA Astrophysics Data System (ADS)

    Li, Yan-Jun; Wei, Jun-Hao; Santosh, M.; Tan, Jun; Fu, Le-Bing; Zhao, Shao-Qing

    2016-07-01

    The Bangxi-Chenxing suture zone is an important region to address the history of closure of the eastern Paleo-Tethys ocean. Among the widespread S-type granite batholiths in the SE Guangxi Province adjacent to this suture is the Nali granodiorite. Here we report zircon U-Pb ages, major and trace element geochemistry, and Sr-Nd-Hf isotope geochemistry of a newly found Middle Permian S-type granite in this region. LA-ICP-MS zircon U-Pb geochronology yields emplacement ages of 265 ± 2 to 262 ± 2 Ma for the Nali granodiorite. Both the inner and outer phases are characterized by variable SiO2 (66.91-71.39 wt.%), high Al2O3 (12.99-14.04 wt.%), K2O + Na2O (4.78-5.98 wt.%), and A/CNK values (1.11-1.50), resembling those of typical S-type granites. The rocks are enriched in Rb, Th, U and light rare earth elements with weak negative Eu anomalies, and show depletion in Nb, Ta, Ti, with typical arc-like affinity. They have relatively high (87Sr/86Sr)i ratios of 0.7228 to 0.7331, low εNd(t) values of - 13.6 to - 11.9, and low zircon εHf(t) values (- 21.9 to - 8.8). High whole-rock Nd isotopic model ages (2.00-2.02 Ga) and zircon Hf isotopic model ages (1.59-2.20 Ga), indicate that they might have been generated by partial melting of ancient lower crust with minor contribution from mantle sources. The granodiorite shows continental arc affinity and likely formed within a subduction setting. By combining previously extant data for Permo-Triassic arc-/collision-related magmatism in the Jinshajiang-Ailaoshan-Song Ma and Bangxi-Chenxing suture zones, we propose that the subduction of the eastern Paleo-Tethys might have started during Middle Permian triggered by the northward subduction of the Indochina Block (ICB) beneath the South China Block (SCB) and closure during Middle Triassic.

  10. Geochronology, petrogenesis and tectonic settings of pre- and syn-ore granites from the W-Mo deposits (East Kounrad, Zhanet and Akshatau), Central Kazakhstan

    NASA Astrophysics Data System (ADS)

    Li, GuangMing; Cao, MingJian; Qin, KeZhang; Evans, Noreen J.; Hollings, Pete; Seitmuratova, Eleonora Yusupovha

    2016-05-01

    There is significant debate regarding the mineralization ages of the East Kounrad, Zhanet and Akshatau W-Mo deposits of Central Kazakhstan, and the petrogenesis and tectono-magmatic evolution of the granites associated with these deposits. To address these issues, we present molybdenite Re-Os dating, zircon U-Pb dating, whole rock geochemistry as well as Sr-Nd-Pb and zircon O-Hf isotopic analyses on the pre-mineralization and ore-forming granites. U-Pb dating of zircons from pre-mineralization granitic rocks yield Late Carboniferous ages of 320-309 Ma, whereas ore-forming granites have Early Permian ages of 298-285 Ma. Molybdenite Re-Os isotopic data indicate a mineralization age of ~ 296 Ma at East Kounrad, ~ 294 Ma at Akshatau and ~ 285 Ma at Zhanet. The pre-ore and ore-forming granites are high-K calc-alkaline, metaluminous to slightly peraluminous I-type granites. The pre-mineralization granites are relatively unfractionated, whereas the ore-forming granites are highly fractionated. The fractionating mineral phases are probably K-feldspar, apatite, Ti-bearing phases and minor plagioclase. The pre-mineralization and ore-forming rocks are characterized by similar Sr-Nd-Pb-Hf-O isotopic compositions ((87Sr/86Sr)i = 0.70308-0.70501, εNd (t) = - 0.5 to + 2.8, 207Pb/204Pb = 15.60-15.82, zircon εHf (t) = + 1.2 to + 15.6 and δ18O = + 4.6 to + 10.3‰), whole rock TDMC (Nd) (840-1120 Ma) and zircon TDMC (Hf) (320-1240 Ma). The isotopic characteristics are consistent with a hybrid magma source caused by 10-30% assimilation of ancient crust by juvenile lower crust. The geochronology and geochemistry of these granites show that the Late Carboniferous pre-mineralization granitic rocks formed during subduction, whereas the Early Permian ore-forming, highly fractionated granite probably underwent significant fractionation with a restite assemblage of K-feldspar, apatite, Ti-bearing phases and minor plagioclase and developed during collision between the Yili and Kazakhstan

  11. Geochronology, structural evolution of the Tierra Colorada area, and tectonic implications for southern Mexico and Chortís block connections

    NASA Astrophysics Data System (ADS)

    Solari, L. A.; Torres de Leon, R.; Hernandez Pineda, G.; Sole', J.; Solis Pichardo, G.; Hernandez Treviño, T.

    2006-05-01

    The Tierra Colorada area is considered the best exposure of the northern limit between the Xolapa Complex and the Paleozoic-Precambrian Mixteca and Zapotecan terranes of southern Mexico. Geochemistry (major, trace, and REE) and geochronology on deformed granitoids in Tierra Colorada area show evidence of subduction-related magmatism during Mesozoic and Cenozoic. El Pozuelo granite, dated at 129 Ma (concordant U-Pb single-zircon age) is a foliated body, with local porphyric facies. Foliation is penetrative and characterized by oriented micas and stretched quartz. Geochemically it shows a metaluminous character, with arc-related trace and REE patterns. Because it cuts across high-grade gneisses of the Xolapa Complex, its intrusion postdates the second phase of metamorphism in the Xolapa Complex (> 130 Ma), which generated the orthogneisses-migmatites sequence. El Salitre granite (55 Ma, Rb-Sr 4 point isochron) is a foliated peraluminous body with a pronounced negative Zr anomaly. The protomylonitic Las PiÑas granite (54 +/- 6 Ma, U-Pb lower intercept) is characterized by ductile fabric, recognized by cinematic indicators such as mica fish, and indicates a top-to-the NNW sense of shear, dated at 50 +/- 1 Ma and 45.3 +/- 2 Ma (K-Ar on Bt, and Rb-Sr Bt-WR isochron, respectively), ages that indicate the time of ductile deformation along La Venta shear zone, as N-dipping detachment under low greenschist facies conditions. El Salitre and Las PiÑas granites are linked because of their similar HREE patterns. The Tierra Colorada, Xaltianguis and San Juan del Reparo granites, with calcalkaline subduction-related geochemistry, lack of penetrative deformation, and their ages of 30-34 Ma (U-Pb on zircons) constitute the last recognized granitic pulse in this area, post-dating the S-verging thrust of the Morelos limestones on top of sheared granites and volcanics. Together with previously published ages of magmatism in the studied area, we demonstrate here that calcalkaline

  12. A combined study of the equation of state of monazite-type lanthanum orthovanadate using in situ high-pressure diffraction and ab initio calculations.

    PubMed

    Ermakova, Olga; López-Solano, Javier; Minikayev, Roman; Carlson, Stefan; Kamińska, Agata; Głowacki, Michał; Berkowski, Marek; Mujica, Andrés; Muñoz, Alfonso; Paszkowicz, Wojciech

    2014-06-01

    Lanthanum orthovanadate (LaVO4) is the only stable monazite-type rare-earth orthovanadate. In the present paper the equation of state of LaVO4 is studied using in situ high-pressure powder diffraction at room temperature, and ab initio calculations within the framework of the density functional theory. The parameters of a second-order Birch-Murnaghan equation of state, i.e. those fitted to the experimental and theoretical data, are found to be in perfect agreement - in particular, the bulk moduli are almost identical, with values of 106 (1) and 105.8 (5) GPa, respectively. In agreement with recent reported experimental data, the compression is shown to be anisotropic. Its nature is comparable to that of some other monazite-type compounds. The softest compression direction is determined.

  13. The Timing of Early Magmatism and Extension in the Southern East African Rift: Tracking Geochemical Source Variability with 40Ar/39Ar Geochronology at the Rungwe Volcanic Province, SW Tanzania

    NASA Astrophysics Data System (ADS)

    Mesko, G. T.; Class, C.; Maqway, M. D.; Boniface, N.; Manya, S.; Hemming, S. R.

    2014-12-01

    The Rungwe Volcanic Province is the southernmost expression of volcanism in the East African Rift System. Rungwe magmatism is focused in a transfer zone between two weakly extended rift segments, unlike more developed rifts where magmatism occurs along segment axes (e.g. mid-ocean ridges). Rungwe was selected as the site of the multinational SEGMeNT project, an integrated geophysical, geochronological and geochemical study to determine the role of magmatism during early stage continental rifting. Argon geochronology is underway for an extensive collection of Rungwe volcanic rocks to date the eruptive sequence with emphasis on the oldest events. The age and location of the earliest events remains contested, but is critical to evaluating the relationship between magmatism and extension. Dated samples are further analyzed to model the geochemistry and isotopic signature of each melt's source and define it as lithospheric, asthenospheric, or plume. Given the goals, the geochronology focuses on mafic lavas most likely to preserve the geochemical signature of the mantle source. Groundmass was prepared and analyzed at the LDEO AGES lab. Twelve preliminary dates yield ages from 8.5 to 5.7Ma, consistent with prior results, supporting an eruptive episode concurrent with tectonic activity on the Malawi and Rukwa border faults (Ebinger et al., JGR 1989; 1993). Three additional samples yield ages from 18.51 to 17.6 Ma, consistent with the 18.6 ±1.0 Ma age obtained by Rasskazov et al. (Russ. Geology & Geophys. 2003). This eruptive episode is spatially limited to phonolite domes in the Usangu Basin and a mafic lava flow on the uplifted Mbeya Block. These eruptions predate the current tectonic extensional structure, suggesting magmatism predates extension, or that the two are not highly interdependent. No Rungwe samples dated yet can be the source of the of 26Ma carbonatitic tuffs in the nearby Songwe River Basin sequence (Roberts et al., Nature Geoscience 2012). Isochron ages

  14. U-Pb garnet, sphene, monazite, and rutile ages: Implications for the duration of high-grade metamorphism and cooling histories, Adirondack Mts. , New York

    SciTech Connect

    Mezger, K.; Rawnsley, C.M.; Hanson, G.N. ); Bohlen, S.R. )

    1991-05-01

    Garnet ages for the Lowlands range from 1,168-1,127 Ma, those from the central and southern Highlands from 1,154-1,013 Ma. Metamorphism in the Highlands may not have occurred as a single event but rather in several discrete thermal pulses. An age of 1,153 {plus minus} 3 Ma was determined for garnets in the syn-regional metamorphic contact aureole of the Diana syenite, consistent with that of the syenite intrusion, 1 155 {plus minus} 4 Ma. Garnets just outside the contact aureole give an age of 1,168 {plus minus} 6 Ma. In the Lowlands, monazite yielded an age of 1,161 {plus minus} 1 Ma, rutiles yielded ages of 1,005 {plus minus} 2 Ma and 953 {plus minus} 4 Ma, and sphene ages range from 1,156 to 1,103 Ma. In the Highlands, monazite yielded an age of 1,033 {plus minus} 1 Ma, rutiles yielded ages of 911 {plus minus} 2 Ma and 885 {plus minus} 2 and sphenes from 1,033 Ma to 991 Ma. The rutile and monazite ages indicate that both terranes cooled at time-integrated rates of ca. 1.5C/Ma for at least 150 Ma following the last phase of high-grade metamorphism. The Lowlands cooled to ca. 400C by ca. 1,000 Ma and the Highlands by ca. 900 Ma. The mineral ages indicate that metamorphic pressures and temperatures recorded by thermobarometry correspond to conditions attained polychronically over 150 Ma or more. Mineral ages combined with temperature estimates for peak metamorphism indicate that the closure temperature for the U-Pb system is >800C in garnet, 640-730C in monazite, and 500-670C in sphene.

  15. The Potassium-Argon Laser Experiment (KARLE): In Situ Geochronology for Planetary Robotic Missions

    NASA Technical Reports Server (NTRS)

    Cohen, B. A.; Devismes, D.; Miller, J. S.; Swindle, T. D.

    2014-01-01

    Isotopic dating is an essential tool to establish an absolute chronology for geological events, including crystallization history, magmatic evolution, and alteration events. The capability for in situ geochronology will open up the ability for geochronology to be accomplished as part of lander or rover complement, on multiple samples rather than just those returned. An in situ geochronology package can also complement sample return missions by identifying the most interesting rocks to cache or return to Earth. The K-Ar Laser Experiment (KArLE) brings together a novel combination of several flight-proven components to provide precise measurements of potassium (K) and argon (Ar) that will enable accurate isochron dating of planetary rocks. KArLE will ablate a rock sample, measure the K in the plasma state using laser-induced breakdown spectroscopy (LIBS), measure the liberated Ar using mass spectrometry (MS), and relate the two by measuring the volume of the ablated pit by optical imaging. Our work indicates that the KArLE instrument is capable of determining the age of planetary samples with sufficient accuracy to address a wide range of geochronology problems in planetary science. Additional benefits derive from the fact that each KArLE component achieves analyses useful for most planetary surface missions.

  16. RADIOIODINE GEOCHEMISTRY IN THE SRS SUBSURFACE ENVIRONMENT

    SciTech Connect

    Kaplan, D.; Emerson, H.; Powell, B.; Roberts, K.; Zhang, S.; Xu, C.; Schwer, K.; Li, H.; Ho, Y.; Denham, M.; Yeager, C.; Santschi, P.

    2013-05-16

    Iodine-129 is one of the key risk drivers for several Savannah River Site (SRS) performance assessments (PA), including that for the Low-Level Waste Disposal Facility in E-Area. In an effort to reduce the uncertainty associated with the conceptual model and the input values used in PA, several studies have recently been conducted dealing with radioiodine geochemistry at the SRS. The objective of this report was to review these recent studies and evaluate their implications on SRS PA calculations. For the first time, these studies measured iodine speciation in SRS groundwater and provided technical justification for assuming the presence of more strongly sorbing species (iodate and organo-iodine), and measured greater iodine sediment sorption when experiments included these newly identified species; specifically they measured greater sorption coefficients (K{sub d} values: the concentration ratio of iodine on the solid phase divided by the concentration in the aqueous phase). Based on these recent studies, new best estimates were proposed for future PA calculations. The new K{sub d} values are greater than previous recommended values. These proposed K{sub d} values reflect a better understanding of iodine geochemistry in the SRS subsurface environment, which permits reducing the associated conservatism included in the original estimates to account for uncertainty. Among the key contributing discoveries supporting the contention that the K{sub d} values should be increased are that: 1) not only iodide (I{sup -}), but also the more strongly sorbing iodate (IO{sub 3}{sup -}) species exists in SRS groundwater (average total iodine = 15% iodide, 42% iodate, and 43% organoiodine), 2) when iodine was added as iodate, the measured K{sub d} values were 2 to 6 times greater than when the iodine was added as iodide, and perhaps most importantly, 3) higher desorption (10 to 20 mL/g) than (ad)sorption (all previous studies) K{sub d} values were measured. The implications of this

  17. Metamorphic conditions and CHIME monazite ages of Late Eocene to Late Oligocene high-temperature Mogok metamorphic rocks in central Myanmar

    NASA Astrophysics Data System (ADS)

    Maw Maw Win; Enami, Masaki; Kato, Takenori

    2016-03-01

    The high temperature (T)/pressure (P) regional Mogok metamorphic belt is situated in central Myanmar, and is mainly composed of pelitic gneisses, amphibolites, marbles, and calc-silicate rocks. The garnet-biotite-plagioclase-sillimanite-quartz assemblage and its partial system suggest equilibrium P/T conditions of 0.6-1.0 GPa/780-850 °C for the peak metamorphic stage, and 0.3-0.5 GPa/600-680 °C for the exhumation and hydration stage. Monazite grains show complex compositional zoning consisting of three segments-I, II, and III. Taking into consideration the monazite zoning and relative misfit curves, the calculated chemical Th-U-total Pb isochron method (CHIME) monazite age data (284 spot analyses) indicated four age components: 49.3 ± 2.6-49.9 ± 7.9, 37.8 ± 1.0-38.1 ± 1.7, 28.0 ± 0.8-28.8 ± 1.6, and 23.7 ± 1.3 Ma (2σ level). The ages of the Late Eocene and Late Oligocene epochs were interpreted as the peak metamorphic stage of upper-amphibolite and/or granulite facies and the postdated hydration stage, respectively.

  18. Radiation resistance of LaPO4 (monazite structure) and YbPO4 (zircon structure) from data of computer simulation

    NASA Astrophysics Data System (ADS)

    Grechanovsky, A. E.; Eremin, N. N.; Urusov, V. S.

    2013-09-01

    The radiation resistance of the monazite LaPO4 and the compound YbPO4 (zircon structure type) has been investigated using the computer simulation. The number of Frenkel pairs, which are formed in the structure of these minerals after the passage of a primary knock-on thorium atom with an energy of 30 keV, has been calculated by the molecular dynamics method. The formation of Frenkel pairs and their recombination in the motion of recoil nuclei in the structure of the studied minerals have been discussed. It has been shown that the probability of the "survival" of Frenkel pairs in the LaPO4 monazite is significantly lower than in the YbPO4 compound. The tendency of these minerals toward amorphization under radiation damage has been described numerically. The obtained results have demonstrated that one of the main factors determining the radiation resistance of orthophosphates LnPO4 is the type of crystal structure, and the compounds with the monazite structure are more radiation resistant than the compounds with the zircon structure.

  19. Probing structural homogeneity of La1-xGdxPO4 monazite-type solid solutions by combined spectroscopic and computational studies

    NASA Astrophysics Data System (ADS)

    Huittinen, N.; Arinicheva, Y.; Kowalski, P. M.; Vinograd, V. L.; Neumeier, S.; Bosbach, D.

    2017-04-01

    Here we study the homogeneity of Eu3+-doped La1-xGdxPO4 (x = 0, 0.11, 0.33, 0.55, 0.75, 0.92, 1) monazite-type solid solutions by a combination of Raman and time-resolved laser fluorescence spectroscopies (TRLFS) with complementary quasi-random structure-based atomistic modeling studies. For the intermediate La0.45Gd0.55PO4 composition we detected a significant broadening of the Raman bands corresponding to the lattice vibrations of the LnO9 polyhedron, indicating much stronger distortion of the lanthanide cation site than the PO4 tetrahedron. A distortion of the crystal lattice around the dopant site was also confirmed in our TRLFS measurements of Eu3+ doped samples, where both the half width (FWHM) of the excitation peaks and the 7F2/7F1 ratio derived from the emission spectra increase for intermediate solid-solution compositions. The observed variation in FWHM correlates well with the simulated distribution of Eu···O bond distances within the investigated monazites. The combined results imply that homogenous Eu3+-doped La1-xGdxPO4 monazite-type solid solutions are formed over the entire composition range, which is of importance in the context of using these ceramics for immobilization of radionuclides.

  20. In-Situ Geochronology: Extending Larims to Pb-Pb Isocrhons

    NASA Astrophysics Data System (ADS)

    Whitaker, Tom; Anderson, Scott; Levine, Jonathan

    2016-04-01

    Introduction: We have previously described development of Laser Ablation Resonance Ionization Mass Spectrometry (LARIMS) for in-situ determination of the radiometric age of rocks using isotope ratios of Rb and Sr [1,2]. LARIMS uses laser resonance excitation of the target elements, which provides elemental selectivity, thus eliminating isobaric interferences with little or no sample preparation and allowing thousands of samples to be measured in significantly shorter periods of time than traditional methods. We have recently begun research that aims to extend the Rb-Sr capability to include Pb-Pb measurements. Preliminary measurements of Standard Reference Material 612 (SRM-612) from the National Institute of Standards and Technology (NIST) demonstrate that resonance ionization of Pb can measure samples with as little as 0.12 ppm total Pb. Background: In-situ LARIMS will enable measurements of 1) isotope geochemistry relevant for chronology and igneous evolution, 2) light isotopes relevant for habitability, life, and climate history, as well as 3) elemental abundances relevant to understanding local and regional geology. In particular, the elemental selectivity of LARIMS makes isotopic geochronology measurements possible that heretofore required extensive sample preparation and were thought to be practically impossible for in-situ measurements. For example, we have used Rb-Sr LARIMS to analyze a piece of the Martian meteorite Zagami and the Duluth Gabbro, a lunar analogue. In these measurements, we obtained isochron ages consistent with the published ages within 200 Ma. Pb-Pb geochronology is well-suited for LARIMS analysis. The use of a single element simplifies the laser system and eliminates inter-element fractionation that can be problematic in Rb-Sr analysis or other multi-element LARIMS measurements. In general, there is less interference at masses corresponding to Pb isotopes than at lighter masses. However, there are potential interferences such as Hg and

  1. DOE workshop: Sedimentary systems, aqueous and organic geochemistry

    SciTech Connect

    Not Available

    1993-07-01

    A DOE workshop on sedimentary systems, aqueous and organic geochemistry was held July 15-16, 1993 at Lawrence Berkeley Laboratory. Papers were organized into several sections: Fundamental Properties, containing papers on the thermodynamics of brines, minerals and aqueous electrolyte solutions; Geochemical Transport, covering 3-D imaging of drill core samples, hydrothermal geochemistry, chemical interactions in hydrocarbon reservoirs, fluid flow model application, among others; Rock-Water Interactions, with presentations on stable isotope systematics of fluid/rock interaction, fluid flow and petotectonic evolution, grain boundary transport, sulfur incorporation, tracers in geologic reservoirs, geothermal controls on oil-reservoir evolution, and mineral hydrolysis kinetics; Organic Geochemistry covered new methods for constraining time of hydrocarbon migration, kinetic models of petroleum formation, mudstones in burial diagenesis, compound-specific carbon isotope analysis of petroleums, stability of natural gas, sulfur in sedimentary organic matter, organic geochemistry of deep ocean sediments, direct speciation of metal by optical spectroscopies; and lastly, Sedimentary Systems, covering sequence stratigraphy, seismic reflectors and diagenetic changes in carbonates, geochemistry and origin of regional dolomites, and evidence of large comet or asteroid impacts at extinction boundaries.

  2. Proterozoic geochronologic and isotopic boundary in NW Arizona

    SciTech Connect

    Chamberlain, K.R.; Bowring, S.A. )

    1990-05-01

    U-Pb ages determined from zircon, sphene, and apatite in conjunction with Pb isotopic analyses of alkali feldspar establish a regional geochronological framework and constrain the location of a major north-trending Proterozoic crustal boundary in northwestern Arizona. Two regions west of the boundary (Hualapai Mountains and Lost Basin Range-Garnet Mountain) are characterized by complex U-Pb zircon systematics, evidence for inheritance of an older zircon component (1.8-2.3 Ga), and elevated {sup 207}Pb/{sup 204}Pb from feldspars compared to the east. Although the discordia patterns are complex, supracrustal rocks are interpreted to be ca. 1.73 Ga and are intruded by plutonic rocks ca. 1.70 Ga. Deformation is younger than ca. 1.70 Ga foliated granites and older than the 1,682 {plus minus} 4 Ma Garnet Mt. monzogranite. The rocks in one area east of the boundary (Cottonwood Cliffs) are characterized by relatively simple U-Pb zircon systematics, no evidence for inheritance of any older component, and feldspar {sup 207}/{sup 204}Pb near model mantle values. Supracrustal rocks are older than 1.73 Ga, as they are intruded by a 1,730 {plus minus} 9 Ma foliated granodiorite. Timing of deformation is constrained by the late syn-kinematic Valentine granite dated at 1,713 {plus minus} 12 Ma. Mineral ages indicate that the rocks on either side of the boundary had different cooling histories and inferentially, different uplift histories. West of the boundary, the cooling history is inferred from minerals separated from an amphibolite: metamorphic zircon is 1,687 +13/{minus}8 Ma, sphene is 1,660 {plus minus} 5 Ma, hornblende has a {sup 40}Ar/{sup 39}Ar age of 1,552 {plus minus} 5 Ma, and apatite has a U-Pb age of 1,520 {plus minus} 45 Ma. East of the boundary an amphibolite has sphene with an age of 1,670 {plus minus} 11 Ma and apatite with an age of 1,630 {plus minus} 8 Ma.

  3. Geochronology of Quaternary glaciations from the tropical Cordillera Huayhuash, Peru

    NASA Astrophysics Data System (ADS)

    Hall, Sarah R.; Farber, Daniel L.; Ramage, Joan M.; Rodbell, Donald T.; Finkel, Robert C.; Smith, Jacqueline A.; Mark, Bryan G.; Kassel, Christopher

    2009-12-01

    The Cordillera Huayhuash in the central Peruvian Andes (10.3°S, 76.9°W) is an ideal mountain range in which to study regional climate through variations in paleoglacier extents. The range trends nearly north-south with modern glaciers confined to peaks >4800 m a.s.l. Geomorphology and geochronology in the nearby Cordillera Blanca and Junin Plain reveal that the Peruvian Andes preserve a detailed record of tropical glaciation. Here, we use ASTER imagery, aerial photographs, and GPS to map and date glacial features in both the western and eastern drainages of the Cordillera Huayhuash. We have used in situ produced cosmogenic 10Be concentrations in quartz bearing erratics on moraine crests and ice-polished bedrock surfaces to develop an exposure age chronology for Pleistocene glaciation within the range. We have also collected sediment cores from moraine-dammed lakes and bogs to provide limiting 14C ages for glacial deposits. In contrast to the ranges to the north and south, most glacial features within the Cordillera Huayhuash are Lateglacial in age, however we have identified features with ages that span ˜0.2 to ˜38 ka with moraine sets marking the onset of glacier retreat at ˜0.3 ka, ˜9-10 ka, ˜13-14 ka, ˜20-22 ka, and >26 ka. The range displays a pronounced east-west variation in maximum down-valley distance from the headwall of moraine crests with considerably longer paleoglaciers in the eastern drainages. Importantly, Lateglacial paleoglaciers reached a terminal elevation of ˜4000 m a.s.l. on both sides of the Cordillera Huayhuash; suggesting that temperature may have been a dominant factor in controlling the maximum glacier extent. We suggest that valley morphology, specifically valley slope, strongly influences down-valley distance to the maximum glacier extent and potential for moraine preservation. While regionally there is an extensive record of older (>50 ka) advances to the north (Cordillera Blanca) and to the south (Junin region), the apparent

  4. Surface geochemistry of the clay minerals

    PubMed Central

    Sposito, Garrison; Skipper, Neal T.; Sutton, Rebecca; Park, Sung-ho; Soper, Alan K.; Greathouse, Jeffery A.

    1999-01-01

    Clay minerals are layer type aluminosilicates that figure in terrestrial biogeochemical cycles, in the buffering capacity of the oceans, and in the containment of toxic waste materials. They are also used as lubricants in petroleum extraction and as industrial catalysts for the synthesis of many organic compounds. These applications derive fundamentally from the colloidal size and permanent structural charge of clay mineral particles, which endow them with significant surface reactivity. Unraveling the surface geochemistry of hydrated clay minerals is an abiding, if difficult, topic in earth sciences research. Recent experimental and computational studies that take advantage of new methodologies and basic insights derived from the study of concentrated ionic solutions have begun to clarify the structure of electrical double layers formed on hydrated clay mineral surfaces, particularly those in the interlayer region of swelling 2:1 layer type clay minerals. One emerging trend is that the coordination of interlayer cations with water molecules and clay mineral surface oxygens is governed largely by cation size and charge, similarly to a concentrated ionic solution, but the location of structural charge within a clay layer and the existence of hydrophobic patches on its surface provide important modulations. The larger the interlayer cation, the greater the influence of clay mineral structure and hydrophobicity on the configurations of adsorbed water molecules. This picture extends readily to hydrophobic molecules adsorbed within an interlayer region, with important implications for clay–hydrocarbon interactions and the design of catalysts for organic synthesis. PMID:10097044

  5. Geochemistry of vanadium (V) in Chinese coals.

    PubMed

    Liu, Yuan; Liu, Guijian; Qu, Qinyuan; Qi, Cuicui; Sun, Ruoyu; Liu, Houqi

    2016-10-11

    Vanadium in coals may have potential environmental and economic impacts. However, comprehensive knowledge of the geochemistry of V in coals is lacking. In this study, abundances, distribution and modes of occurrence of V are reviewed by compiling >2900 reported Chinese coal samples. With coal reserves in individual provinces as the weighting factors, V in Chinese coals is estimated to have an average abundance of 35.81 μg/g. Large variation of V concentration is observed in Chinese coals of different regions, coal-forming periods, and maturation ranks. According to the concentration coefficient of V in coals from individual provinces, three regions are divided across Chinese coal deposits. Vanadium in Chinese coals is probably influenced by sediment source and sedimentary environment, supplemented by late-stage hydrothermal fluids. Specifically, hydrothermal fluids have relatively more significant effect on the enrichment of V in local coal seams. Vanadium in coals is commonly associated with aluminosilicate minerals and organic matter, and the modes of V occurrence in coal depend on coal-forming environment and coal rank. The Chinese V emission inventory during coal combustion is estimated to be 4906 mt in 2014, accounting for 50.55 % of global emission. Vanadium emissions by electric power plants are the largest contributor.

  6. Monazite Growth from the Eocene to the Miocene: New Interpretations of the Metamorphic History of Greater Himalayan Rocks in the Eastern Himalaya

    NASA Astrophysics Data System (ADS)

    Gordon, S. M.; Kauffman, R.; Gonzales-Clayton, B.; Long, S. P.; Kylander-Clark, A. R.

    2015-12-01

    Across the Himalaya, mid- to lower-crustal Greater-Himalayan (GH) rocks have been exhumed during active continent-continent collision. In the eastern Himalaya within Bhutan, GH rocks are divided into an upper and lower level by an intra-GH shear zone, the Kakthang thrust (KT). To decipher the metamorphic, melt-crystallization and exhumation history of the GH rocks exposed above and below the KT, monazite from metapelites and migmatites was dated and trace elements were analyzed by laser-ablation, split-stream ICPMS. The trace elements from the monazite were used to track when the rocks were at near-peak conditions (based on the depletion of HREE and the likely presence of garnet during monazite growth) versus likely undergoing initial exhumation and garnet breakdown (based on an increase in HREE). Samples were collected from two N-S transects that cross the KT in central and eastern Bhutan. The eastern transect reveals a progressive younging of near-peak metamorphism within the GH, with dates of ca. 23-20 Ma for the structurally-highest sample versus ca. 18-16 Ma in the structurally-lowest sample. The youngest dates from all structural levels of the eastern Bhutan metapelites are 13-15 Ma; the same analyses yield higher HREE abundances, suggesting garnet breakdown during their (re)crystallization. The migmatites yield ca. 14-16 Ma melt-crystallization ages, consistent with the GH having undergone cooling and initial exhumation to cause garnet breakdown by ca. 15 Ma. In comparison, the central Bhutan transect reveals older near-peak metamorphic ages, with garnet-stable monazite populations at ca. 48­-46 Ma within the KT zone, ca. 38-30 Ma for rocks in the middle of the upper-GH, and ca. 25-22 Ma for the structurally-highest sample. Youngest monazites from the central Bhutan transect that yield growth or recrystallization at garnet-unstable conditions range from ca. 17-26 Ma. These results suggest earlier metamorphism and exhumation of GH rocks in central Bhutan

  7. The origin of the 1.73-1.70 Ga anorogenic Ulkan volcano-plutonic complex, Siberian platform, Russia: inferences from geochronological, geochemical and Nd-Sr-Pb isotopic data

    USGS Publications Warehouse

    Larin, A.M.; Amelin, Yu. V.; Neymark, L.A.; Krymsky, R. Sh

    1997-01-01

    The Ulkan volcano-plutonic complex, a part of a 750 km Bilyakchian-Ulkan anorogenic belt, is located in the eastern part of the Archean-Paleoproterozoic Aldan shield. The tectonic position and geochemistry indicate that the Ulkan Complex is a typical A-type or intraplate magmatic association. The felsic volcanics of the Uian Group and granitoids of the North Uchur Massif, the major igneous components of the Ulkan Complex, have U-Pb zircon and monazite ages between 1721±1 Ma and 1703±18 Ma. Together with the spatially associated 1736±6 Ma Dzhugdzhur anorthosite massif, the Ulkan Complex forms a typical Proterozoic anorthosite-granite-volcanic association with the minimum duration of formation of 12 m.y. Initial εNd values between 0 and 1.1, similar for the Uian felsic volcanics, early granitoid phases of the North Uchur Massif and high-grade metamorphic basement rocks, indicate, along with geochemical data, that the crustal source of the Ulkan parental magmas may be similar to the basement rocks. The higher εNd(T) values of -0.3 to +1.9 in the later North Uchur granitoids and associated ore-bearing metasomatites, and relatively low time-integrated Rb/Sr, U/Pb, and Th/U estimated for their sources, may demonstrate involvement of variable amounts of a depleted mantle-derived component in the generation of later phases of the North Uchur Massif. The preferred model of formation of magmas parental to the Ulkan Complex involves thermal interaction of an uprising mantle diapir with Paleoproterozoic lower crust, which was accompanied by chemical interaction between a fluid derived from the diapir, with the lower crustal rocks.

  8. EarthChem: International Collaboration for Solid Earth Geochemistry in Geoinformatics

    NASA Astrophysics Data System (ADS)

    Walker, J. D.; Lehnert, K. A.; Hofmann, A. W.; Sarbas, B.; Carlson, R. W.

    2005-12-01

    The current on-line information systems for igneous rock geochemistry - PetDB, GEOROC, and NAVDAT - convincingly demonstrate the value of rigorous scientific data management of geochemical data for research and education. The next generation of hypothesis formulation and testing can be vastly facilitated by enhancing these electronic resources through integration of available datasets, expansion of data coverage in location, time, and tectonic setting, timely updates with new data, and through intuitive and efficient access and data analysis tools for the broader geosciences community. PetDB, GEOROC, and NAVDAT have therefore formed the EarthChem consortium (www.earthchem.org) as a international collaborative effort to address these needs and serve the larger earth science community by facilitating the compilation, communication, serving, and visualization of geochemical data, and their integration with other geological, geochronological, geophysical, and geodetic information to maximize their scientific application. We report on the status of and future plans for EarthChem activities. EarthChem's development plan includes: (1) expanding the functionality of the web portal to become a `one-stop shop for geochemical data' with search capability across databases, standardized and integrated data output, generally applicable tools for data quality assessment, and data analysis/visualization including plotting methods and an information-rich map interface; and (2) expanding data holdings by generating new datasets as identified and prioritized through community outreach, and facilitating data contributions from the community by offering web-based data submission capability and technical assistance for design, implementation, and population of new databases and their integration with all EarthChem data holdings. Such federated databases and datasets will retain their identity within the EarthChem system. We also plan on working with publishers to ease the assimilation

  9. Applications of New Synthetic Uranium Reference Materials for Geochemistry Research (Invited)

    NASA Astrophysics Data System (ADS)

    Richter, S.; Weyer, S.; Alonso, A.; Aregbe, Y.; Kuehn, H.; Eykens, R.; Verbruggen, A.; Wellum, R.

    2009-12-01

    For many applications in geochemistry research isotope ratio measurements play a significant role. In geochronology isotope abundances of uranium and its daughter products thorium and lead are being used to determine the age and history of various samples of geological interest. For measuring the isotopic compositions of these elements by mass spectrometry, suitable isotope reference materials are needed to validate measurement procedures and to calibrate multi-collector and ion counting detector systems. IRMM is a recognized provider for nuclear isotope reference materials to the nuclear industry and nuclear safeguards authorities, which are also being applied widely for geochemical applications. The preparation of several new synthetic uranium reference materials at IRMM during the recent five years has provided significant impacts on geochemical research. As an example, the IRMM-074 series of gravimetrically prepared uranium mixtures for linearity testing of secondary electron multipliers (SEMs) has been applied for the redetermination of the secular equilibrium 234U/238U value and the 234U half-life by Cheng et al (2009). Due to the use of IRMM-074, results with smaller uncertainties were obtained, which are shifted by about 0.04% compared to the commonly used values published earlier by Cheng et al. in 2000. This has a significant impact for U isotope measurements in geochemistry.. As a further example, the new double spike IRMM-3636 with a 233U/236U ratio of 1:1 and an expanded uncertainty as low as 0.016% (coverage factor k=2, 95% confidence level) was prepared gravimetrically. This double spike allows internal mass fractionation correction for high precision 235U/238U ratio measurements of close to natural samples. Using the new double spike IRMM-3636, the 235U/238U ratios for several commonly used natural U standard materials from NIST/NBL and IRMM, such as e.g. NBS960 (=NBL CRM-112a), NBS950a,b and IRMM-184, have been re-measured with improved precision

  10. Tracing recent environmental changes and pedogenesis using geochemistry and micromorphology of alluvial soils, Sabie-Sand River Basin, South Africa

    NASA Astrophysics Data System (ADS)

    Eze, Peter N.; Knight, Jasper; Evans, Mary

    2016-09-01

    Three pedons on the alluvial terraces of the Sabie-Sand River Basin within Kruger National Park, South Africa, were studied to improve our understanding of recent environmental changes, and assess degree of chemical weathering and pedogenesis in the area using geochemical and micromorphology proxies. Particle-size distributions were obtained using Malvern Mastersizer; soil geochemistry was determined by XRF and thin sections by routine laboratory procedures. The soils are predominantly sandy (> 94% sand in all samples). The mean phi-values of the soils had little variation suggesting that reworking of sediments upwards in individual profiles produced a more uniform pedogenesis rather than coming from different physical sources. Calcification is the dominant pedogenic process in these alluvial soils. The Chemical Index of Alteration (CIA) proved a more suitable index than Chemical Index of Weathering (CIW) for evaluating weathering in the terraces. The micromass and b-fabrics are mostly granostriated and partly brown mosaic speckled. MISECA values for the degree of soil development range from 4 to 9, which mean weakly to moderately-developed soils. Coarse secondary calcite nodules and coatings are responsible for cementation as observed in pedon 2, which suggests calcium carbonate precipitation from periodical flooding and evaporating groundwater events. The features and diagnostic properties of the soils on the alluvial terraces along the Sabie-Sand River provide evidence for land surface impacts of recent environmental changes in this internationally important conservation area. Precise dating of calcium carbonate precipitates is, however, needed to put the observed evidence into a wider geochronological perspective.

  11. Microbiology and Geochemistry of Antarctic Paleosols

    NASA Astrophysics Data System (ADS)

    Mahaney, W. C.; Malloch, D.; Hancock, R. G. V.; Campbell, I. B.; Sheppard, D.

    2000-08-01

    Samples of ancient soils from horizons in paleosols from the Quartermain Mountains (Aztec and New Mountain areas of the Antarctic Dry Valleys) were analyzed for their chemical composition and microbiology to determine the accumulation and movement of salts and other soluble constituents. The salt concentrations are of special interest because they are considered to be a function of age, derived in part from nearby oceanic and high altitude atmospheric sources. The geochemistry of ancient Miocene-age paleosols in these areas is the direct result of the deposition and weathering of till, derived principally from dolerite and sandstone source rock, in association with airborne-influxed salts. Paleosols nearer the coast have greater contents of chlorine, and farther inland near the Inland Ice Sheet, nitrogen tends to increase on a relative basis. The accumulation and vertical distribution of salts and other soluble chemical elements indicate relative amounts of movement in the profile over long periods of time, to the order of several million years. Iron, both in total concentration and in the form of various extracts, indicates it can be used as a geochronometer to assess the buildup of goethite plus hematite over time in the paleosols. Trends for ferrihydrite, a partially soluble Fe-hydroxide, shows limited profile translocation that might be related to the movement of salt. Six of the eight selected subsamples from paleosol horizons in three soil profiles contained nil concentrations of bacteria and fungi. However, two horizons at depths of between three to eight centimeters yielded several colonies of the fungi Beauveria bassiana and Penicillium spp., indicating some input of organic carbon. Beauveria bassiana is often reported in association with insects and is used commercially for the biological control of some insect pests. Penicillium species are commonly isolated from Arctic, temperate and tropical soils and are known to utilize a wide variety of organic

  12. Pacific ferromanganese crust geology and geochemistry

    SciTech Connect

    Andreev, S.I.; Vanstein, B.G.; Anikeeva, L.I. )

    1990-06-01

    Cobaltiferous ferromanganese crusts form part of a large series of oceanic ferromanganese oxide deposits. The crusts show high cobalt (commonly over 0.4%), low nickel and copper sum (0.4-0.8%), considerably high manganese (18-20%), and iron (14-18%). Less abundant elements in crusts are represented by molybdenum and vanadium; the rare-earth elements cerium, lanthenum, and yttrium; and the noble metals platinum and rhodium. Co-rich crusts form at water depths of 600 to 2,500 m. Crust thicknesses range from millimeters to 15-17 cm, averaging 2-6 cm. The most favorable conditions for 4-10 cm thick crusts to occur is at water depths of 1,200-2,200 m. The crusts formed on basaltic, calcareous, siliceous, and breccia bedrock surfaces provided there were conditions preventing bottom sedimentation at them. If the sedimentation takes place, it may be accompanied by nodules similar in composition to the crusts. The most favorable topography for extensive crust formation is considered to be subdued (up to 20{degree}) slopes and summit platforms of conical seamounts, frequently near faults and their intersection zones. Subhorizontal guyot summits do not usually favor crust growth. Crust geochemistry is primarily defined by mineralogy and manganese hydroxides (vernadite)/iron ratio. The first associated group of compounds includes cobalt, nickel, molybdenum, vanadium, cerium, and titanium; the other is strontium, yttrium, cerium, and cadmium. The aluminosilicate phase is associated with titanium, iron, chromium, and vanadium; phosphate biogenic phase includes copper, nickel, zinc, lead, and barium. The crucial point in cobaltiferous crust formation is their growth rate on which is dependent the degree of ferromanganese matrix sorption saturation with cobalt. The optimum for cobalt-rich ferromanganese ores is the conditions facilitating long-term and continuous hydrogenic processes.

  13. Geochemistry of tin (Sn) in Chinese coals.

    PubMed

    Qu, Qinyuan; Liu, Guijian; Sun, Ruoyu; Kang, Yu

    2016-02-01

    Based on 1625 data collected from the published literature, the geochemistry of tin (Sn) in Chinese coals, including the abundance, distribution, modes of occurrence, genetic types and combustion behavior, was discussed to make a better understanding. Our statistic showed the average Sn of Chinese coal was 3.38 mg/kg, almost two times higher than the world. Among all the samples collected, Guangxi coals occupied an extremely high Sn enrichment (10.46 mg/kg), making sharp contrast to Xinjiang coals (0.49 mg/kg). Two modes of occurrence of Sn in Chinese coals were found, including sulfide-bounded Sn and clay-bounded Sn. In some coalfields, such as Liupanshui, Huayingshan and Haerwusu, a response between REEs distribution and Sn content was found which may caused by the transportation of Sn including clay minerals between coal seams. According to the responses reflecting on REEs patterns of each coalfield, several genetic types of Sn in coalfields were discussed. The enrichment of Sn in Guangxi coals probably caused by Sn-rich source rocks and multiple-stage hydrothermal fluids. The enriched Sn in western Guizhou coals was probably caused by volcanic ashes and sulfide-fixing mechanism. The depletion of Sn in Shengli coalfield, Inner Mongolia, may attribute to hardly terrigenous input and fluids erosion. As a relative easily volatilized element, the Sn-containing combustion by-products tended to be absorbed on the fine particles of fly ash. In 2012, the emission flux of Sn by Chinese coal combustion was estimated to be 0.90 × 10(9) g.

  14. Petrogenesis and geochemistry of the Late Carboniferous rear-arc (or back-arc) pillow basaltic lava in the Bogda Mountains, Chinese North Tianshan

    NASA Astrophysics Data System (ADS)

    Xie, Wei; Luo, Zhen-Yu; Xu, Yi-Gang; Chen, Yi-Bing; Hong, Lu-Bing; Ma, Liang; Ma, Qiang

    2016-02-01

    The tectonic nature of the Chinese Tianshan Orogen during the Late Paleozoic has been long disputed. With aims of providing constraints on this issue, an integrated study of geochronology and geochemistry has been carried out on the Late Carboniferous pillow basaltic lava of the Qijiagou Group from the Bogda Mountains, Chinese North Tianshan. Zircon SHRIMP U-Pb dating of a dacite ignimbrite, which is in conformable contact with the pillow lava, suggests that they were erupted at ~ 311 Ma. The pillow cores and rims show different petrological and geochemical characteristics, suggesting post-magmatic seafloor hydrothermal alteration. Nevertheless, both pillow cores and rims have the MORB-like Sr-Nd-Hf isotopes and arc-like trace element compositions. Clinopyroxene and plagioclase from the pillow lavas are compositionally different from those of the mafic rocks related to the Tarim mantle plume. These observations, together with the tholeiitic index (THI > 1) and the Fe/Mn ratios (53-57) of them, indicate that the Bogda pillow lavas may have been generated from a dry and depleted mantle source metasomatized by sediment-derived melts. Compared with basalts of the Izu-Bonin arc-back-arc system, the Bogda Late Carboniferous basaltic lavas show great resemblance to the Izu-Bonin rear-arc basalt (including the arc-like back-arc basalt) in terms of major and trace element and mineral compositions. It suggests that these basalts were likely formed in a rear-arc or back-arc environment.

  15. Cosmogenic Nuclides, River Geochemistry, and Lanforms Reconstruction Methods Comparison to Study the Coopling Between Chemical Weahering and Mechanical Erosion in a Steep Reunion Island Basin.

    NASA Astrophysics Data System (ADS)

    Gayer, E.; Louvat, P.; Michon, L.

    2014-12-01

    Understanding mechanisms that modify landscapes is essential for risk assessment in tropical islands. Because measurements of erosion rates are critical for understanding landform evolution, the use of cosmogenic isotopes in river sediments and the use of river load geochemistry have grown rapidly in recent years.In this study we aim to estimate erosion rate of an highly eroded drainage area of the Réunion Island and we compare 3 methods of measurment : i) from cosmogenic 3He concentrations [3Hec], ii) from river geochemistry and iii) from landforms reconstruction in order to estimate chemical weathering, mechanical erosion, and to understand the message provided by each method.The basin under invistagation is the Rivière Langevin Canyon, located on the south flank of the Piton de la Fournaise Volcano (PdF). Helium concentrations and isotopic ratios have been measured in olivine rich sands from the Langevin river. [3Hec] have been calculated using: (i) the 3He/4He ratio measured by crushing and (ii) the 3He and 4He concentrations measured by melting the resulting powder. Digital elevation model derivatives and K-Ar geochronological data have been used to reconstruct the PdF morphology and calculate the volume of material eroded over the past 65Ka. Finally, dissolved and suspended loads in Langevin river will be analysed for their major and trace elements contents in order to characterise both chemical and mechanical erosion products. A soil will also be analysed in order to estimate the chemical weathering of the bedrock and to understand soil formation in the studied basin. Initial results indicate 3Hec average erosion rates of 4.9±11.6 mm/yr and 4.7±0.1 mm/yr from PdF morphology reconstruction. Cosmogenic and landform reconstruction results show a reasonable agreement. However, the lack of olivine in the sampled soil rises the question of river sediment olivine sources. Such olivine need to be delivered either by deep-seated catastrophic events either from no

  16. New Mexico Geochronology Research Laboratory: Zuni-Bandera volcanic field road log

    SciTech Connect

    Laughlin, A.W.; Charles, R.; Reid, K.; White, C.

    1993-04-01

    This field conference was designed to assemble a group of Quaternary researchers to examine the possibility of using the Zuni-Bandera volcanic field in western New Mexico as a test area for evaluating and calibrating various Quaternary dating techniques. The Zuni-Bandera volcanic-field is comprised of a large number of basaltic lava flows ranging in age from about 700 to 3 ka. Older basalts are present in the Mount Taylor volcanic field to the north. Geologic mapping has been completed for a large portion of the Zuni-Bandera volcanic field and a number of geochronological investigations have been initiated in the area. While amending this conference, please consider how you might bring your expertise and capabilities to bear on solving the many problem in Quaternary geochronology.

  17. New Mexico Geochronology Research Laboratory: Zuni-Bandera volcanic field road log

    SciTech Connect

    Laughlin, A.W.; Charles, R.; Reid, K.; White, C.

    1993-01-01

    This field conference was designed to assemble a group of Quaternary researchers to examine the possibility of using the Zuni-Bandera volcanic field in western New Mexico as a test area for evaluating and calibrating various Quaternary dating techniques. The Zuni-Bandera volcanic-field is comprised of a large number of basaltic lava flows ranging in age from about 700 to 3 ka. Older basalts are present in the Mount Taylor volcanic field to the north. Geologic mapping has been completed for a large portion of the Zuni-Bandera volcanic field and a number of geochronological investigations have been initiated in the area. While amending this conference, please consider how you might bring your expertise and capabilities to bear on solving the many problem in Quaternary geochronology.

  18. The Potassium-Argon Laser Experiment (KArLE): In Situ Geochronology for Planetary Robotic Missions

    NASA Technical Reports Server (NTRS)

    Cohen, Barbara

    2016-01-01

    The Potassium (K) - Argon (Ar) Laser Experiment (KArLE) will make in situ noble-gas geochronology measurements aboard planetary robotic landers and roverss. Laser-Induced Breakdown Spectroscopy (LIBS) is used to measure the K abun-dance in a sample and to release its noble gases; the evolved Ar is measured by mass spectrometry (MS); and rela-tive K content is related to absolute Ar abundance by sample mass, determined by optical measurement of the ablated volume. KArLE measures a whole-rock K-Ar age to 10% or better for rocks 2 Ga or older, sufficient to resolve the absolute age of many planetary samples. The LIBS-MS approach is attractive because the analytical components have been flight proven, do not require further technical development, and provide complementary measurements as well as in situ geochronology.

  19. Zircon U-Pb geochronology and geochemistry of two episodes of granitoids from the northwestern Zhejiang Province, SE China: Implication for magmatic evolution and tectonic transition

    NASA Astrophysics Data System (ADS)

    Li, Zilong; Zhou, Jing; Mao, Jianren; Santosh, M.; Yu, Minggang; Li, Yinqi; Hu, Yizhou; Langmuir, Charles H.; Chen, Zhongxing; Cai, Xiongxiang; Hu, Yanhua

    2013-10-01

    Granitoids (175-80 Ma) representing a prominent Yanshanian (Jurassic to Cretaceous) magmatic event in South China widely intrude the Precambrian crystalline basement and Paleozoic strata. Here we report zircon U-Pb age data, geochemical characteristics and Sr-Nd isotopes of the Late Jurassic and Early Cretaceous granitoids from the northwestern Zhejiang Province (ZXB) of southeastern China. Our results reveal two distinct episodes for the Yanshanian magmatism. The Jiemeng and Datongkeng granodiorites formed at 148.6 ± 1.1 Ma, whereas the Huangshitan, Jiuligang and Ruhong aluminous A-type granites were generated between 129.0 ± 0.6 Ma and 126.1 ± 1.1 Ma. The two magmatic phases represent a tectonic transition from an active continental margin to post-orogenic setting during the Late Jurassic (ca. 150 Ma) to Early Cretaceous (ca. 128 Ma). Geochemically, these intrusions are granodioritic to granitic in composition and show an affinity of S-type and A-type granitoids, respectively. The S-type granodiorites of Jiemeng and Datongkeng are characterized by moderate SiO2 (65.0-69.6 wt.%), high K2O + Na2O (5.0-7.6 wt.%), K2O/Na2O (1.2-1.5), Zr (31-109 ppm), Sr (71-190 ppm) and high field strength elements, low to intermediate Mg#, and moderate Nb depletion. The A-type granites of Huangshitan, Jiuligang and Ruhong are characterized by high SiO2 (72.7-77.2 wt.%), K2O + Na2O (6.9-8.8 wt.%), K2O/Na2O (1.3-2.1), FeT/(FeT + Mg), Ga (17-29 ppm, > 20 ppm commonly), Zr (96-197 ppm) and Sr (8-45 ppm) with slight Nb depletion. The S-type granodiorites have higher Mg#, A/NK, Sr, Sr/Ba, Sr/Y, (La/Yb)N, and LREE/HREE, and lower SiO2, K2O + Na2O, Ga and Zr with weak negative Eu anomalies compared to those of the A-type granites with negative Eu anomalies. All these rocks show Y/Nb ratios > 1.2, high initial 87Sr/86Sr (ISr) ratios and low ɛNd(t), and are depleted in Nb, Ti and Sr, indicating crustal origin with subduction zone signatures. We suggested that the ZXB S-type granitic bodies might have been derived from the Mesoproterozoic metamorphic basement rocks through partial melting induced by mantle-derived magma, followed by limited fractional crystallization. The ZXB aluminous A-type granites were also derived from a similar magma source but underwent fractional crystallization at higher crustal levels. The A-type granites in the ZXB correlate with a post-orogenic tectonic setting. A geological comparison between ZXB and adjacent areas indicates that the geochemical features of the ZXB A-type granites are comparable with the Baijuhuajian A-type granites and also the adjacent areas A-type granites, but are distinct from the Late Cretaceous A-type granites (105-90 Ma) distributed along the southeastern coastal area of South China. We correlate the formation of the ZXB S-type granodiorites to inland compression associated with the subduction and collision of the paleo-Pacific plate in the Late Jurassic (170-145 Ma). In contrast, the A-type granites formed under a post-orogenic setting during the Early Cretaceous period (145-120 Ma) resulting from lithospheric thinning and continent extension accompanied by slab roll-back of the paleo-Pacific plate following the subduction-collision event.

  20. Mineral paragenesis, geochemistry and geochronology investigations of the Carlin-type gold deposits at the Goldstrike property, northern Nevada: Implications for ore genesis, igneous petrogenesis and mineral exploration

    NASA Astrophysics Data System (ADS)

    Almeida, Carolina Michelin De

    The Goldstrike property is located in northern Nevada and contains one of the largest and highest-grade Carlin-type gold deposits. The majority of the Eocene Au mineralization (e.g., Ore I) is hosted in intensely altered Paleozoic lower plate impure carbonate rocks, and is characterized by strong to moderate silicification, higher calculated pyrite and ore-related element concentrations (e.g., As, Cu, Hg, Ni, Tl, Sb, W, and Zn) than Ore II, which is weakly altered. However, both ore types contain similar Au concentration in whole rock and pyrite chemistry analyses. Lithogeochemical and microprobe data suggest that the Paleozoic sedimentary rocks may have been a major source of Cd, Mo, Ni, U, V, and Zn and minor As, Cu, Hg, and Se. The Jurassic lamprophyre dikes might have been a significant source of Ba, Co, and Se, and minor Au, and some of the Jurassic and Eocene intrusive rocks may have provided some Fe. Moreover, the Eocene magmas are interpreted to be the main source of auriferous mineralizing fluids. Trace element abundances and ratios of the Jurassic intrusive rocks suggest that they are shoshonitic and formed from a metasomatized mantle-derived magma, crystal fractionation, and crustal contamination. The Eocene dikes, also shoshonitic, are considerably more evolved and contaminated than the studied Jurassic rocks. Furthermore, Ar-Ar results show that the Jurassic rocks were negligibly affected by the Eocene thermal event, and that temperature of mineralizing fluids were below the closure temperature of biotite (< 350°C). A magmatic-related model is proposed to explain the formation of the Carlin-type gold deposits at the studied area. In this model, Au and the ore-related elements were exsolved along with volatiles by degassing of a deep and large plutonic complex during its early stage of crystallization. As these magmatic-hydrothermal fluids moved upward along major conduits (e.g., NNW-striking faults), they may have interacted with a Fe-rich fluid, pervasively altering the Paleozoic impure carbonate rocks (e.g., carbonate dissolution, silicification, pyritization) and forming Ore I. Subsequently, these fluids moved laterally further away from the major conduits, became cooler, less acidic, and depleted in ore-related elements and interacted with the Fe-bearing host rocks (e.g., sulfidation), favoring the precipitation of Ore II.

  1. Petrogenesis of granitoids in the eastern section of the Central Qilian Block: Evidence from geochemistry and zircon U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Li, Jiyong; Niu, Yaoling; Chen, Shuo; Sun, Wenli; Zhang, Yu; Liu, Yi; Ma, Yuxin; Hu, Zhenxing; Zhang, Guorui

    2016-08-01

    The Caledonian-age Qilian Orogenic Belt at the northern margin of the Greater Tibetan Plateau comprises abundant granitoids that record the histories of the orogenesis. We report here our study of these granitoids from two localities. The Qingchengshan (QCS) pluton, which is situated in the eastern section of the Central Qilian Block, is dated at ~430-420 Ma. It has high-K calc-alkaline composition with high SiO2 (> 70 wt%), enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSEs), and varying degrees of negative Sr and Eu anomalies. The granitoids in the Tongwei (TW) area, 150 km east of the QCS, are complex, the majority of which are dated at ~440 Ma, but there also exist younger, ~230 Ma intrusions genetically associated with the Qinling Orogeny. The Paleozoic TW intrusions also have high SiO2, fractionated REE (rare earth element) patterns, but a negligible Eu anomaly. The whole rock Sr-Nd-Hf isotopic compositions suggest that all these Paleozoic granitoids are consistent with melting-induced mixing of a two-component source, which is best interpreted as the combination of last fragments of subducted/subducting ocean crust with terrigenous sediments. The mantle isotopic signature of these granitoids (87Sr/86Sri: 0.7038 to 0.7100, ɛNd(t): -4.8 to -1.3, ɛHf(t): -0.7 to +4.0) reflects significant (~70 %) contribution of the ocean crust derived in no distant past from the mantle at ocean ridges with an inherited mantle isotopic signature. Partial melting of such ocean crust plus terrigenous sediments in response to the ocean closing and continental collision (between the Qilian and Alashan Blocks) under amphibolite facies conditions is responsible for the magmatism. Varying extents of fractional crystallization (±plagioclase, ±amphibole, ±garnet, ±zircon) of the parental magmas produced the observed QCS and TW granitoids. We note that sample HTC12-01 in the TW area shows an A-type or highly fractionated granite signature characterized by elevated abundances and a flat pattern of REEs, weak Nb-Ta anomaly, conspicuous negative Sr and Eu anomalies (Sr/Sr* = 0.09, Eu/Eu* = 0.22), and thus the high 87Sr/86Sr ratio (0.7851), and moderate ɛNd(t) (-4.9) and ɛHf(t) (-2.0), pointing to the significant mantle contribution. Compared with the Paleozoic granitoids, the ~230 Ma granitoids in the TW area represented by sample JPC12-02 have higher initial 87Sr/86Sr (0.7073) and lower ɛNd(t) (-6.2) and ɛHf(t) (-4.5) values, offering an ideal opportunity for future studies on tectonic effects of juxtaposition of younger orogenesis on an older orogen.

  2. The distribution, geochronology and geochemistry of early Paleozoic granitoid plutons in the North Altun orogenic belt, NW China: Implications for the petrogenesis and tectonic evolution

    NASA Astrophysics Data System (ADS)

    Meng, Ling-Tong; Chen, Bai-Lin; Zhao, Ni-Na; Wu, Yu; Zhang, Wen-Gao; He, Jiang-Tao; Wang, Bin; Han, Mei-Mei

    2017-01-01

    Abundant early Paleozoic granitoid plutons are widely distributed in the North Altun orogenic belt. These rocks provide clues to the tectonic evolution of the North Altun orogenic belt and adjacent areas. In this paper, we report an integrated study of petrological features, U-Pb zircon dating, in situ zircon Hf isotope and whole-rock geochemical compositions for the Abei, 4337 Highland and Kaladawan Plutons from north to south in the North Altun orogenic belt. The dating yielded magma crystallization ages of 514 Ma for the Abei Pluton, 494 Ma for the 4337 Highland Pluton and 480-460 Ma for the Kaladawan Pluton, suggesting that they are all products of oceanic slab subduction because of the age constraint. The Abei monzogranites derived from the recycle of Paleoproterozoic continental crust under low-pressure and high-temperature conditions are products of subduction initiation. The 4337 Highland granodiorites have some adakitic geochemical signatures and are sourced from partial melting of thickened mafic lower continental crust. The Kaladawan quartz diorites are produced by partial melting of mantle wedge according to the positive εHf(t) values, and the Kaladawan monzogranite-syenogranite are derived from partial melting of Neoproterozoic continental crust mixing the juvenile underplated mafic material from the depleted mantle. These results, together with existing data, provide significant information about the evolution history of oceanic crust subduction during the 520-460 Ma. The initiation of subduction occurred during 520-500 Ma with formation of Abei Pluton; subsequent transition from steep-angle to flat-slab subduction at ca.500 Ma due to the arrival of buoyant oceanic plateaus, which induces the formation of 4337 Highland Pluton. With ongoing subduction, the steep-angle subduction system is reestablished to cause the formation of 480-460 Ma Kaladawan Pluton. Meanwhile, it is this model that account for the temporal-spatial distribution of these early Paleozoic magmatic rocks in the North Altun orogenic belt.

  3. Early Paleozoic subduction processes of the Paleo-Asian Ocean: Insights from geochronology and geochemistry of Paleozoic plutons in the Alxa Terrane

    NASA Astrophysics Data System (ADS)

    Liu, Qian; Zhao, Guochun; Sun, Min; Han, Yigui; Eizenhöfer, Paul R.; Hou, Wenzhu; Zhang, Xiaoran; Zhu, Yanlin; Wang, Bo; Liu, Dongxing; Xu, Bing

    2016-10-01

    The Alxa Terrane is situated in a key area between the North China and Tarim cratons. Paleozoic magmatic records in this terrane place important constraints on the subduction processes of the southern Paleo-Asian Ocean. New data of zircon U-Pb ages and whole-rock elemental and isotopic data reveal two groups of intermediate to felsic plutons in the Alxa Terrane. One group consists of diorites and granitoids that were emplaced at ca. 460-440 Ma and characterized by lower Al2O3/TiO2 ratios and higher TiO2 contents, implying high temperature-low pressure crystallization conditions and a shallow source region. The second group is dominated by granitoids aged at ca. 420-407 Ma and displays high Sr and Ba, low Y and high rare earth elements, with very high Sr/Y ratios and mostly positive Eu anomalies. These characteristics imply low temperature-high pressure crystallization conditions and source regions at deep crustal levels where garnet is stable in the residual phase. Both of the two groups are mostly calc-alkaline to high-K calc-alkaline, depleted in Nb, Ta and Ti and enriched in Ba, K and Sr, indicative of an arc affinity most likely related to the southward subduction of the Paleo-Asian Ocean. Zircon εHf(t) and whole-rock εNd(t) values of these magmatic rocks decrease from 458 Ma to 440 Ma and increase from 417 Ma to 407 Ma, whereas whole-rock initial 87Sr/86Sr ratios display an opposite trend. Such an isotopic change suggests a tectonic switch from an advancing to a retreating subduction regime at 407 Ma. Synthesized data from this and previous studies suggest that the 460-400 Ma magmatic arc in the Alxa Terrane represented the western extension of the Paleozoic arc belt on the northern margin of the North China Craton.

  4. Geochemistry and zircon U-Pb geochronology of granitoids in the East Kunlun Orogenic Belt, northern Tibetan Plateau: origin and tectonic implications

    NASA Astrophysics Data System (ADS)

    Zhou, Bo; Dong, Yunpeng; Zhang, Feifei; Yang, Zhao; Sun, Shengsi; He, Dengfeng

    2016-11-01

    The East Kunlun Orogenic Belt (EKOB) in the northern margin of the Tibet Plateau is characterized by widespread granitic plutons, which are keys to understanding the tectonic evolution of the EKOB. The Zhiyu pluton, newly recognized in the central part of the EKOB, mainly consists of monzogranites, biotite granites and quartz diorites. Their LA-ICPMS zircon U-Pb results show formation ages of 447 ± 1.6 Ma, 448 ± 2.5 Ma and 408 ± 1.8 Ma. The monzogranites and biotite granites are characterized by relatively high Sr (208-631 ppm), low Y (4.28-15.82 ppm) and Yb (0.44-1.59 ppm) contents, thus resulting in elevated Sr/Y (30-105) and (La/Yb)N (4-79) ratios, indicating geochemical features of adakitic rocks. These adakitic granites are medium- to high-K, calcic or calc-alkaline in composition, and display a weak peraluminous character. They have low MgO (0.57-1.84 wt.%, average 1.01 wt.%), Mg# (40-53, average 45), as well as low Cr (3.67-17.98 ppm, average 7.19 ppm) and Ni (2.59-9.30 ppm, average 4.71 ppm) contents. These rocks are enriched in LREE, and show negligible or variable positive Eu anomalies (Eu/Eu∗ = 0.61-3.80, average 1.45) and significant negative Nb and Ta anomalies. Majority of the zircon grains from these adakitic granitic rocks have positive εHf(t) values of 0.09-5.21 with two-stage model ages ranging from 1.1 Ga to 1.6 Ga. These features are compatible with those of adakitic rocks derived from a thickened lower crust in the garnet stability field. Their formation is mainly controlled by the process of crust thickening following the closure of the Qimantag Ocean. The younger quartz diorites belong to medium- to high-K, calc-alkalic or alkali-calcic and metaluminous series, and exhibit a relatively high MgO (2.23-5.18 wt.%) and Mg# (40-56, average 50.11), with significant LREE enrichment and negative Eu anomalies, as well as depletion of Nb, Ta. In addition, the quartz diorites have an enriched εHf(t) values ranging from -5.25 to -3.19. Combining the regional tectonic data, we infer that the younger quartz diorites were derived from enriched lithospheric mantle sources and contaminated by the crustal materials in a post-collision extensional setting.

  5. U-Pb geochronology, geochemistry, and H-O-S-Pb isotopic compositions of the Leqingla and Xin'gaguo skarn Pb-Zn polymetallic deposits, Tibet, China

    NASA Astrophysics Data System (ADS)

    Wang, Liqiang; Cheng, Wenbin; Tang, Juxing; Kang, Haoran; Zhang, Yan; Li, Zhuang

    2016-01-01

    The Leqingla and Xin'gaguo deposits are two representative skarn Pb-Zn polymetallic deposits of the Gangdese Pb-Zn polymetallic belt, Tibet, China. LA-ICP-MS zircon U-Pb dating of the mineralization-related biotite granites from both the Leqingla and Xin'gaguo deposits yielded weighted mean ages of 60.8 Ma and 56.5 Ma, respectively, which can be inferred as their mineralization ages. The Leqingla biotite granite is characterized by high Al2O3, total Fe, Na2O, and low K2O. In comparison, the Xin'gaguo biotite granite is characterized by relative higher K2O but lower Al2O3, total Fe, and Na2O. Geochemical and mineralogical characteristics indicate that the Leqingla and Xin'gaguo biotite granites are calc-alkaline I-type granite and High K calc-alkaline I-type granite, respectively. Both the Leqingla and Xin'gaguo biotite granites are enrichment in LREE and LILEs and depletion in HFSEs, and they were formed at the India-Asia collision stage. δ18O and δD values for the Leqingla and Xin'gaguo deposits are -8.8‰ to 5.3‰ and -140.4‰ to -90.1‰, -4.5‰ to 7.0‰ and -117.3‰ to -81.0‰, respectively, indicating magma fluids mixed with meteoric water in ore-forming fluids. δ34S values (-11.6‰ to -0.3‰) of ore sulfides from the Leqingla deposit show characteristics of biogenetic sulfur isotope compositions, suggesting sulfur for the Leqingla deposit were sourced from wall rocks of the Mengla and Luobadui Formation, which are rich in organic materials. δ34S values of ore sulfides from the Xin'gaguo deposits show bimodal distribution (-5.0‰ to -1.6‰ and 1.6-2.1‰), indicating sulfur in the Xin'gaguo deposit were derived from both wall rocks and magma. In the Leqingla deposit, most ore sulfides have the similar Pb isotopic compositions with that of the mineralization-related biotite granite, suggesting the biotite granite supplied most of the ore-forming metals. Pb isotopic compositions of ore sulfides and Hf isotopic compositions of biotite granite show that the majority of ore-forming metals are derived from mantle components of partial melting of the Neo-Tethys Ocean slab, with some upper crust materials of the Lhasa terrane. Pb isotopic compositions of ore sulfides from the Xin'gaguo deposit are similar to that of the Leqingla deposit, indicating they have the similar sources of ore-forming metals.

  6. Geochronology and Geochemistry of Igneous Rocks from the Laoshankou District, North Xinjiang: Implications for the Late Paleozoic Tectonic Evolution and Metallogenesis of East Junggar

    NASA Astrophysics Data System (ADS)

    Liang, Pei; Chen, Huayong; Hollings, Pete; Wu, Chao; Xiao, Bing; Bao, Zhiwei; Xu, Deru

    2016-12-01

    The Fe-Cu mineralization of the Laoshankou district is located in the Dulate Late Paleozoic island arc at the northern margin of East Junggar terrane, Northwest China and is hosted by volcanic rocks of the Middle Devonian Beitashan Formation. LA-ICP-MS U-Pb dating of zircon constrains the timing of crystallization of biotite diorites and quartz syenites in the Laoshankou district to 379 ± 2 Ma and 376 ± 2 Ma, respectively. The volcanic rocks are calc-alkaline in composition and are characterised by LILE and LREE enrichments and HFSE depletions, consistent with a subduction-related affinity. The relatively depleted Nb, Ta, Zr, Hf and Th, enriched Sr and Ba, elevated Mg#, positive εNd(t) values (5.5 and 5.6), low (87Sr/86Sr)i ratios (0.7042 and 0.7044) and MORB-like Pb-isotope characters all suggest that they were derived from a depleted mantle wedge metasomatized by slab-derived fluids, without crustal contamination. The biotite diorite shows slightly metaluminous compositions and is geochemically similar to the volcanic rocks, suggesting that they were derived from the same depleted mantle source. The lack of correlation between SiO2 and initial Sr, Nd ratios suggests that fractional crystallization dominated the petrogenesis of the biotite diorite with only weak crustal contamination. The geochemical characteristics of the quartz syenite are distinct from the volcanic rocks and the biotite diorite. The positive εHf(t), εNd(t), high Th/La (0.17-0.53), Th/Yb (1.62-4.39), low Ce/Th (2.87-10.13) ratios and positive trends of SiO2 versus (87Sr/86Sr)i and (143Nd/144Nd)i indicate the quartz syenite is likely the product of a depleted mantle wedge metasomatized by slab-derived fluids and subducted sediment-derived melts that underwent crustal contamination during passage through the crust. The low abundance of Th, Yb, Ta and La, indicate that all the intrusive rocks from 379 to 376 Ma in the Laoshankou district formed in an island arc rather than a continental margin arc. The northern margin of East Junggar was related to the southward subduction of the Kuerti-Erqis Ocean (a branch of the Paleo-Asian Ocean) between the Altay and the Dulate arcs in this period, consistent with the presence of Nb-enriched basalts and boninites in the north of the Dulate arc and the island arc rather than back arc setting of the igneous rocks in the Laoshankou district. For metallogenesis in the northern margin of East Junggar, arc-related Fe-Cu-Au and porphyry Cu mineralization was dominated. There is large potential to find several Late Paleozoic arc-related Fe-Cu-Au mineralizations in North Xinjiang.

  7. Geochronology, geochemistry and Sr-Nd-Pb isotopic constraints on the origin of the Qian’echong porphyry Mo deposit, Dabie orogen, east China

    NASA Astrophysics Data System (ADS)

    Gao, Yang; Mao, Jingwen; Ye, Huishou; Li, Faling; Li, Yongfeng; Luo, Zhengzhuan; Xiong, Bikang; Meng, Fang

    2014-05-01

    The giant Qian’echong porphyry molybdenum deposit is located in the Dabie orogen, east China. The molybdenum mineralization mainly occurs as molybdenite-bearing quartz veins hosted by the Devonian Nanwan Formation in the external contact zone of the Qian’echong stock. The Qian’echong stock comprises an earlier formed monzogranite and a later formed granite porphyry. Sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb dating constrains the timing of crystallization of the monzogranite and granite porphyry to 130 ± 2 and 129 ± 2 Ma, respectively. The Re-Os model ages of six molybdenite samples range from 127.9 ± 1.9 to 129.7 ± 1.9 Ma with an isochron age of 129.4 ± 1.5 Ma, which are all consistent within errors with the zircon U-Pb ages, indicating an Early Cretaceous magmatic and mineralization event. The Qian’echong granites have moderate negative Eu anomalies and are relatively enriched in light rare earth elements (REE), but depleted in heavy REE, Y, and high field strength elements (HFSE; e.g., Nb, Ta, and Ti). The Qian’echong granites are I-type rather than A- or S-type, and they have high (87Sr/86Sr)i (0.706771-0.710326) and low ɛNd(t) (-25.5 to -16.8). Two-stage Nd model ages (T2DM) vary between 2.29 and 2.99 Ga. Sr-Nd-Pb isotopic data suggest that the Qian’echong granites were not derived from the North China Craton (NCC), but rather were generated from the Yangtze Craton (YC) lower crust. Paleoproterozoic inherited zircon age and whole-rock chemical and Sr-Nd-Pb isotopic data suggest that the Qian’echong granites were derived mainly from partial melting of ultrahigh pressure eclogites, with incorporation of some Paleoproterozoic to Archean YC crustal materials at lower crustal levels. Delamination or foundering of eclogitic lower crust, which extensively occurred in the Dabie orogen during the Early Cretaceous, had not taken place beneath the Qian’echong deposit when it formed. The Qian’echong molybdenum deposit formed in an extensional setting in the Dabie orogen, and may have been associated with a change in the subduction direction of the Izanagi (or Paleo-Pacific) Plate after 135 Ma.

  8. Geochemistry and geochronology of carbonate-hosted base metal deposits in the southern Brooks Range, Alaska: temporal association with VMS deposits and metallogenic implications

    USGS Publications Warehouse

    Kelly, Karen; Slack, John; Selby, David

    2009-01-01

    The Brooks Range contains enormous accumulations of zinc and copper, either as VMS or sediment-hosted deposits. The Ruby Creek and Omar deposits are Cu-Co stratabound deposits associated with dolomitic breccias. Numerous volcanogenic Cu-Zn (+/-Ag, Au) deposits are situated ~20 km north of the Ruby Creek deposit. The carbonate-hosted deposits consist of chalcopyrite and bornite that fill open spaces, replace the matrix of the breccias, and occur in later cross-cutting veins. Cobaltiferous pyrite, chalcocite, minor tennantite-tetrahedrite, galena, and sphalerite are also present. At Ruby Creek, phases such as carrollite, renierite, and germanite occur rarely. The deposits have undergone post-depositional metamorphism (Ruby Creek, low greenschist facies; Omar, blueschist facies). The unusual geochemical signature includes Cu-Co +/- Ag, As, Au, Bi, Ge, Hg, Sb, and U with sporadic high Re concentrations (up to 2.7 ppm). New Re-Os data were obtained for chalcopyrite, bornite, and pyrite from the Ruby Creek deposit (analyses of sulfides from Omar are in progress). The data show extremely high Re abundances (hundreds of ppb, low ppm) and contain essentially no common Os. The Re-Os data provide the first absolute ages of ore formation for the Ruby Creek deposit and demonstrate that the Re-Os systematics of pyrite, chalcopyrite, and bornite are unaffected by greenschist metamorphism. The Re-Os data show that the main phase of Cu mineralization occurred at 384 +/-4.2 Ma, which coincides with zircon U-Pb ages from igneous rocks that are spatially and genetically associated with VMS deposits. This suggests a temporal link between regional magmatism and hydrothermal mineralization.

  9. Zircon U-Pb geochronology and geochemistry of low-grade metamorphosed volcanic rocks from the Dantazi Complex: Implications for the evolution of the North China Craton

    NASA Astrophysics Data System (ADS)

    Ge, Songsheng; Zhai, Mingguo; Li, Tiesheng; Peng, Peng; Santosh, M.; Shan, Houxiang; Zuo, Pengfei

    2015-11-01

    The late Neoarchean witnessed the cratonization of the North China Craton (NCC) through amalgamation of several micro-blocks to form a coherent basement. The Archean orthogneisses and supracrustal rocks in this craton have experienced various grades of metamorphism ranging up to upper amphibolite and granulite facies at ∼2500 Ma. Recently, a suite of low-grade metamorphosed (greenschist to lower amphibolite facies) volcanic rocks was discovered in the late Neoarchean Dantazi Complex in northern Hebei province. These meta-volcanic rocks consist of bimodal basalt-andesite and trachyte-dacite with a SiO2 gap between 54.4 wt.% and 60.7 wt.%. Here we report SHRIMP zircon U-Pb ages of 2490 ± 19 Ma (MSWD = 2.0) and 2502 ± 8 Ma (MSWD = 0.83) from the meta-mafic and meta-felsic volcanics, respectively, representing the timing of igneous activity. All the meta-mafic volcanic rocks display coherent trace element and REE patterns which are characterized by enriched LILE and LREE but depleted HFSE and HREE ((La/Yb)N = 6.29-15.10). Combining these trace element features with the positive zircon εHf(t) values (+1.3 to +6.6), we propose that the mafic rocks were likely derived from partial melting of a previously metasomatized lithospheric mantle. In the primitive mantle-normalized diagram, the felsic rocks display uniform patterns enriched in LILE but depleted in Nb and Ta, similar to those of lower crust. Furthermore, their strongly fractionated REE ((La/Yb)N = 15.24-61.20), lower HREE concentrations (Yb = 0.47-1.65 ppm) and positive zircon εHf(t) values (+1.6 to +5.3) suggest that they were derived from partial melting of the lower crust with garnet in the residue. This coeval occurrence of metasomatized mantle-derived mafic magmas and potassic felsic magmas from different source regions reflects an intracontinental extensional setting during the late Neoarchean to earliest Paleoproterozoic following the cratonization of the NCC. Our new data, combined with previous published data, allow us to speculate that the intracontinental extensional regime might have prevailed in the NCC from late Neoarchean onwards.

  10. Formation and emplacement of two contrasting late-Mesoproterozoic magma types in the central Namaqua Metamorphic Complex (South Africa, Namibia): Evidence from geochemistry and geochronology

    NASA Astrophysics Data System (ADS)

    Bial, Julia; Büttner, Steffen H.; Frei, Dirk

    2015-05-01

    The Namaqua Metamorphic Complex is a Mesoproterozoic low-pressure, granulite facies belt along the southern and western margin of the Kaapvaal Craton. The NMC has formed between ~ 1.3 and 1.0 Ga and its central part consists essentially of different types of granitoids intercalated with metapelites and calc-silicate rocks. The granitoids can be subdivided into three major groups: (i) mesocratic granitoids, (ii) leucocratic granitoids and (iii) leucogranites. The high-K, ferroan mesocratic granitoids (54-75 wt% SiO2) have a variable composition ranging from granitic to tonalitic, and contain biotite and/or hornblende or orthopyroxene. They are strongly enriched in REE and LILE, indicating A-type chemical characteristics, and are depleted in Ba, Sr, Eu, Nb, Ta and Ti. The leucocratic granitoids and leucogranites (68-76 wt% SiO2) differ from the other group in having a granitic or slightly syenitic composition containing biotite and/or garnet/sillimanite. They have lower REE and MgO, FeOt, CaO, TiO2, MnO concentrations, but higher Na2O and K2O contents. Compositional variations in mesocratic granitoids indicate their formation by fractional crystallization of a mafic parental magma. Leucocratic granitoids and leucogranites lack such trends, which suggests melting of a felsic crustal source without subsequent further evolution of the generated magmas. The mineralogical and geochemical characteristics of the mesocratic granitoids are consistent magmatic differentiation of a mantle derived, hot (> 900 °C) parental magma. The leucocratic granitoids and leucogranites granites were formed from low-temperature magmas (< 730 °C), generated during fluid-present melting from metasedimentary sources. New U-Pb zircon ages reveal that both magma types were emplaced into the lower crust within a 30-40 million years interval between 1220-1180 Ma. In this time period the crust reached its thermal peak, which led to the formation of the leucocratic granitoids and leucogranites. A prolonged period of relatively high crustal temperatures is followed by a second heat pulse at ~ 1100 Ma, that was intense enough to facilitate zircon growth in the older plutons and it produced a younger granite suite. The crust cools down below amphibolite facies conditions after a further 100 million years. The prolonged high-temperature history is best compatible with steady and long-lasting heat transfer from mantle sources, suggesting a continental back-arc situation as the most likely setting of the NMC in the late Mesoproterozoic.

  11. Petrogenesis of granitoids in the eastern section of the Central Qilian Block: Evidence from geochemistry and zircon U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Li, Jiyong; Niu, Yaoling; Chen, Shuo; Sun, Wenli; Zhang, Yu; Liu, Yi; Ma, Yuxin; Hu, Zhenxing; Zhang, Guorui

    2017-02-01

    The Caledonian-age Qilian Orogenic Belt at the northern margin of the Greater Tibetan Plateau comprises abundant granitoids that record the histories of the orogenesis. We report here our study of these granitoids from two localities. The Qingchengshan (QCS) pluton, which is situated in the eastern section of the Central Qilian Block, is dated at 430-420 Ma. It has high-K calc-alkaline composition with high SiO2 (> 70 wt%), enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSEs), and varying degrees of negative Sr and Eu anomalies. The granitoids in the Tongwei (TW) area, 150 km east of the QCS, are complex, the majority of which are dated at 440 Ma, but there also exist younger, 230 Ma intrusions genetically associated with the Qinling Orogeny. The Paleozoic TW intrusions also have high SiO2, fractionated REE (rare earth element) patterns, but a negligible Eu anomaly. The whole rock Sr-Nd-Hf isotopic compositions suggest that all these Paleozoic granitoids are consistent with melting-induced mixing of a two-component source, which is best interpreted as the combination of last fragments of subducted/subducting ocean crust with terrigenous sediments. The mantle isotopic signature of these granitoids (87Sr/86Sri: 0.7038 to 0.7100, ɛNd(t): -4.8 to -1.3, ɛHf(t): -0.7 to +4.0) reflects significant ( 70 %) contribution of the ocean crust derived in no distant past from the mantle at ocean ridges with an inherited mantle isotopic signature. Partial melting of such ocean crust plus terrigenous sediments in response to the ocean closing and continental collision (between the Qilian and Alashan Blocks) under amphibolite facies conditions is responsible for the magmatism. Varying extents of fractional crystallization (±plagioclase, ±amphibole, ±garnet, ±zircon) of the parental magmas produced the observed QCS and TW granitoids. We note that sample HTC12-01 in the TW area shows an A-type or highly fractionated granite signature characterized by elevated abundances and a flat pattern of REEs, weak Nb-Ta anomaly, conspicuous negative Sr and Eu anomalies (Sr/Sr* = 0.09, Eu/Eu* = 0.22), and thus the high 87Sr/86Sr ratio (0.7851), and moderate ɛNd(t) (-4.9) and ɛHf(t) (-2.0), pointing to the significant mantle contribution. Compared with the Paleozoic granitoids, the 230 Ma granitoids in the TW area represented by sample JPC12-02 have higher initial 87Sr/86Sr (0.7073) and lower ɛNd(t) (-6.2) and ɛHf(t) (-4.5) values, offering an ideal opportunity for future studies on tectonic effects of juxtaposition of younger orogenesis on an older orogen.

  12. Geochronology and geochemistry of Eocene-aged volcanic rocks around the Bafra (Samsun, N Turkey) area: Constraints for the interaction of lithospheric mantle and crustal melts

    NASA Astrophysics Data System (ADS)

    Temizel, İrfan; Arslan, Mehmet; Yücel, Cem; Abdioğlu, Emel; Ruffet, Gilles

    2016-08-01

    40Ar-39Ar age, whole-rock chemical, and Sr-Nd isotope data are presented for the post-collisional, Eocene (51.3-44.1 Ma)-aged volcanic rocks from the Bafra (Samsun) area in the western part of the Eastern Pontides (N Turkey) aiming to unravel their sources and evolutionary history. The studied Eocene volcanic rocks can be divided into two groups: analcime-bearing (tephritic lava flows and dykes) and analcime-free (basaltic to trachytic lava flows and basaltic dykes). The analcime-bearing volcanic rocks have a fine-grained porphyritic texture with clinopyroxene phenocrysts, whereas analcime-free volcanic rocks show a variety of textures including hyalo-microlitic microgranular porphyritic, intersertal, trachytic, fluidal, and glomeroporphyritic. The volcanic rocks also show evidence of mineral-melt disequilibrium textures such as sieved, rounded, and corroded plagioclases, partially melted and dissolved clinopyroxenes and poikilitic texture. Petrochemically, the parental magmas of the volcanic rocks evolved from alkaline to calc-alkaline lava suites and include high-K and shoshonitic compositions. They display enrichments in light rare earth and large ion lithophile elements such as Sr, K, and Rb, as well as depletions in high field strength elements such as Nb, Ta, Zr, and Ti, resembling subduction-related magmas. The analcime-bearing and -free volcanic rocks share similar incompatible element ratios and chondrite-normalised rare rearth element patterns, indicating that they originated from similar sources. They also have relatively low to moderate initial 87Sr/86Sr (0.7042-0.7051), high positive εNd(t) values (+ 0.20 to + 3.32), and depleted mantle Nd model ages (TDM1 = 0.63-0.93 Ga, TDM2 = 0.58-0.84 Ga). The bulk-rock chemical and Sr-Nd isotope features as well as the high Rb/Y and Th/Zr, but low Nb/Zr and Nb/Y ratios, indicate that the volcanic rocks were derived from a lithospheric mantle source that had been metasomatised by slab-derived fluids. Trace element modelling suggests that the parental magma(s) of the volcanic rocks represent mixtures of melts derived by low-degree (~ 5-10%) partial melting of spinel-lherzolite (40-85%) and garnet-lherzolite (15-60%) mantle sources. Sr-Nd isotopic modelling also suggests that a 25-35% lower crustal component was added in the parental magmas; AFC modelling additionally indicates minor upper crustal contamination during the evolution of the volcanic rocks. In conclusion, integration of the geochemical, petrologic, and isotopic data with regional geology suggests that the analcime-bearing and -free volcanic rocks evolved from parental magma(s) derived from melts of a subcontinental lithospheric mantle and lower crustal sources.

  13. The Cenozoic volcanism in the Kivu rift: Assessment of the tectonic setting, geochemistry, and geochronology of the volcanic activity in the South-Kivu and Virunga regions

    NASA Astrophysics Data System (ADS)

    Pouclet, A.; Bellon, H.; Bram, K.

    2016-09-01

    The Kivu rift is part of the western branch of the East African Rift system. From Lake Tanganyika to Lake Albert, the Kivu rift is set in a succession of Precambrian zones of weakness trending NW-SE, NNE-SSW and NE-SW. At the NW to NNE turn of the rift direction in the Lake Kivu area, the inherited faults are crosscut by newly born N-S fractures which developed during the late Cenozoic rifting and controlled the volcanic activity. From Lake Kivu to Lake Edward, the N-S faults show a right-lateral en echelon pattern. Development of tension gashes in the Virunga area indicates a clockwise rotation of the constraint linked to dextral oblique motion of crustal blocks. The extensional direction was W-E in the Mio-Pliocene and ENE-WSW in the Pleistocene to present time. The volcanic rocks are assigned to three groups: (1) tholeiites and sodic alkali basalts in the South-Kivu, (2) sodic basalts and nephelinites in the northern Lake Kivu and western Virunga, and (3) potassic basanites and potassic nephelinites in the Virunga area. South-Kivu magmas were generated by melting of spinel + garnet lherzolite from two sources: an enriched lithospheric source and a less enriched mixed lithospheric and asthenospheric source. The latter source was implied in the genesis of the tholeiitic lavas at the beginning of the South-Kivu tectono-volcanic activity, in relationships with asthenosphere upwelling. The ensuing outpouring of alkaline basaltic lavas from the lithospheric source attests for the abortion of the asthenospheric contribution and a change of the rifting process. The sodic nephelinites of the northern Lake Kivu originated from low partial melting of garnet peridotite of the sub-continental mantle due to pressure release during swell initiation. The Virunga potassic magmas resulted from the melting of garnet peridotite with an increasing degree of melting from nephelinite to basanite. They originated from a lithospheric source enriched in both K and Rb, suggesting the presence of phlogopite and the local existence of a metasomatized mantle. A carbonatite contribution is evidenced in the Nyiragongo lavas. New K-Ar ages date around 21 Ma the earliest volcanic activity made of nephelinites. A sodic alkaline volcanism took place between 13 and 9 Ma at the western side of the Virunga during the doming stage of the rift and before the formation of the rift valley. In the South-Kivu area, the first lavas were tholeiitic and dated at 11 Ma. The rift valley subsidence began around 8-7 Ma. The tholeiitic lavas were progressively replaced by alkali basaltic lavas until to 2.6 Ma. Renewal of the basaltic volcanism happened at ca. 1.7 Ma on a western step of the rift. In the Virunga area, the potassic volcanism appeared ca. 2.6 Ma along a NE-SW fault zone and then migrated both to the east and west, in jumping to oblique tension gashes. The uncommon magmatic evolution and the high diversity of volcanic rocks of the Kivu rift are explained by varying transtensional constraints during the rift history.

  14. Zircon-apatite U-Pb geochronology, zircon Hf isotope composition and geochemistry of granite batholith in the northern Mexico: Implications for Tectonomagmatic evolution of southern Cordillera.

    NASA Astrophysics Data System (ADS)

    Mahar, M. A.; Goodell, P.

    2015-12-01

    We present the zircon-apatite U-Pb ages and zircon Hf isotope composition of the granite batholith exposed at the western boundary of Chihuahua. Granidiorite samples were analyzed from both, north and south of the Rio El Fuerte and Sinforosa Lineament. Based on previous studies, the WWN-EES trending Sinforosa Lineament is proposed as the manifestation of a terrane boundary between Seri in the north and Tahue terrane in the south. Zircon U-Pb data indicate that the magmatism spans a time period of 36 Ma from 89 to 53 Ma to the north of the Sinforosa Lineament while granodiorites in the south of the Sinforosa Lineament are dated at 59 Ma. The U-Pb apatite ages are variable in the north of the Sinforosa Lineament and range from 86-51 Ma. These apatite dates are 1-28 Ma younger than the corresponding zircon U-Pb crystallization ages. This indicates variable cooling rates and moderate to shallow emplacement. In contrast, in the south of the Sinforosa Lineament, the U-Pb apatite ages (64-59 Ma) are indistinguishable from the zircon U-Pb age (59 Ma), indicating rapid cooling and shallow emplacement. Zircon morphology and U-Pb dating revealed the absence of inherited component in the zircon ages, as no inheritance of any age has been observed. Most of the northwestern Mexico is underlain by Precambrian-Paleozoic-Jurassic basement. However, in the study area, U-Pb dating does not support the involvement of the older basement in generating the granite magmas. The weighted mean initial ɛHf (t) isotope composition of granodiorites on both sides of the Sinforosa Lineament varies from +2 to +5. However, Hf isotope composition in the south of the Sinforosa Lineament is more heterogeneous and relatively evolved with weighted Mean ɛHf (t) = +1.45. The Hf isotope composition is consistent with the previously reported near bulk silicate Sr-Nd isotope values. We suggest that the magmatic rocks in this region are not derived from melting of a felsic older crust beneath the batholith. Instead, the magmatism is related to the mildly radiogenic arc system in the northwestern Mexico. However, partial melting of sub continental mantle wedge cannot be ruled out. The difference in U-Pb ages and initial Hf isotope composition implies that the Sinforosa Lineament might be a refined boundary between the Seri and Tahue Terranes.

  15. Geochemistry and Geochronology of Eocene Plutons in Northeastern Washington: A Test of Farallon Slab Rollback as a Cause of the Challis Event

    NASA Astrophysics Data System (ADS)

    Caulfield, L.; Tepper, J. H.

    2015-12-01

    The causes of widespread magmatism and extension that affected the Pacific Northwest during the Eocene "Challis Event" are poorly understood. Two models that have been advanced to explain this activity are passage of a slab window (e.g., Haeussler et al., 2011) and rollback of the subducting Farallon slab following accretion of Siletzia (Schmandt and Humphreys, 2011). Both scenarios would have resulted in widespread magmatism but with different temporal patterns. Based on reconstructed plate motion vectors magmatism related to a slab window should produce a younging-to-the-NW pattern whereas magmatism associated with slab rollback should young to the S or SW. Existing dates on Eocene igneous units in NE Washington appear to show an overall younging to the SW, consistent with the slab rollback model. However, many of these dates (mainly K-Ar) have large uncertainties so we are conducting a U-Pb dating and geochemical survey of Eocene plutons across the region. An initial set of zircon U-Pb ages (by LA-MC-ICP-MS) from five intrusions in east-central WA range from 50.7 - 46.7 Ma and young to the SW, a trend similar to that observed among Eocene rocks in the Idaho Batholith (Gaschnig et al., 2013). To further investigate this pattern we are dating an additional ten plutonic units that define a ~100 km SW-NE transect through NE WA. From NE to SW the units in this transect are (with dates from WA DNR mapping) as follows: Sheppard granite (undated), Herron Creek intrusion (51.4 +/- 1.9 Ma), Mt. Bonaparte pluton (52.8 +/- 2.6 Ma), Daisy Trail granite (49.9 +/- 0.3 Ma), Swimptkin Creek pluton (48.2 +/- 1.2 Ma), Moses pluton (48.6 +/- 1.2 Ma), Keller Butte granite (52.9 +/- 0.4 Ma), Johnny George plutonic complex (49.9 +/- 0.45 Ma), Manilla Creek (undated), and Swawilla Basin pluton (58.8 +/- 2.2 Ma). Results of this study should lead to a better understanding of the cause(s) of Challis magmatism and specifically its relationship to the ~50-48 Ma accretion of Siletzia.

  16. Geochemistry and zircon geochronology of the Neoarchean volcano-sedimentary sequence along the northern margin of the Nilgiri Block, southern India

    NASA Astrophysics Data System (ADS)

    Samuel, Vinod O.; Santosh, M.; Yang, Qiong-Yan; Sajeev, K.

    2016-10-01

    The Nilgiri Block is one of the major Archean crustal blocks that define the tectonic framework of southern India. Here we report geologic, petrologic, geochemical, and zircon U-Pb, -REE, and -Lu-Hf data of a highly metamorphosed and disrupted sequence of amphibolite, meta-gabbro, websterite, volcanic tuff, meta-sediment, and banded iron formation (BIF) from the northern fringe of the Nilgiri Block. Geochemically, the amphibolite shows altered ocean floor basalt signature, whereas the meta-gabbro and the websterite samples form part of a volcanic arc. The metamorphosed volcanic tuff shows subalkaline rhyolitic signature. U-Pb isotope analysis of zircon grains from the volcanic tuff and meta-gabbro shows 207Pb/206Pb ages of 2490 ± 12 Ma and 2448 ± 16 Ma, respectively. Zircons from the meta-sediments show an age range of 2563 ± 33 Ma to 2447 ± 34 Ma. The dominantly positive εHf (t) values of the zircons in the analyzed rock suite suggest that the magmas from which the zircons crystallized evolved from a Neoarchean depleted mantle source. The Hf model ages (TDM) of volcanic tuff, meta-sediment and meta-gabbro samples are ranging between 2908-2706 Ma, 2849-2682 Ma, and 2743-2607 Ma, respectively. The ca. 2500 Ma ages for the arc-related magmatic rock suite identified along the northern periphery of Nilgiri Block suggest prominent Neoarchean arc magmatism and early Paleoproterozoic convergent margin processes contributing to the early Precambrian crustal growth in Peninsular India.

  17. Cretaceous subduction-related magmatism and associated porphyry-type Cu-Mo prospects in the Eastern Pontides, Turkey: New constraints from geochronology and geochemistry

    NASA Astrophysics Data System (ADS)

    Delibaş, Okan; Moritz, Robert; Ulianov, Alexey; Chiaradia, Massimo; Saraç, Cem; Revan, Kemal M.; Göç, Deniz

    2016-04-01

    This study focuses on the Elbeyli-Ordu, Emeksen-Giresun, Güzelyayla-Trabzon and Ulutaş-Ispir porphyry-type prospects located in the Eastern Pontides, Turkey. Our new LA-ICP-MS U-Pb zircon age data reveal that the Elbeyli-Ordu Mo-Cu mineralization is hosted by a 77.0 ± 1.3 Ma-old monzonite/monzodiorite with a shoshonitic character. The Emeksen Mo mineralization, located ~ 40 km southeast of the Elbeyli-Ordu prospect, consists of NW- and NE-striking quartz veins crosscutting a high-K calc-alkaline to shoshonitic granite dated at 78.5 ± 0.8 Ma, a granodiorite dated at 78.7 ± 0.5 Ma and porphyry granite dated at 77.7 ± 0.5 Ma. The Güzelyayla porphyry Cu-Mo prospect consists of a stockwork-type Cu-Mo mineralization crosscutting a calc-alkaline 81.4 ± 1.1 Ma-old dacite porphyry and Late Cretaceous calc-alkaline andesite. The Ispir-Ulutaş mineralization is hosted within a highly sericitized 131.1 ± 0.9 Ma-old quartz-porphyry that intruded into a 132.9 ± 0.6 Ma-old calc-alkaline granite porphyry. Our new U-Pb zircon ages, lithogeochemical and radiogenic isotopic data of the host rocks associated with the porphyry-type prospects in the Eastern Pontides indicate that they formed in an arc-related environment during Cretaceous subduction of the Neotethys Ocean, and the Ispir-Ulutaş prospect is attributed to the main stage of the northward subduction of the Neotethys during the Early Cretaceous. We conclude that the Güzelyayla and Emeksen hydrothermal systems were formed during a transitional compressional to extensional tectonic evolution, whereas the Late Cretaceous Elbeyli hydrothermal system was emplaced during an extensional arc magmatic event. Highly-oxidized, high-K calc-alkaline to shoshonitic magmas at Emeksen and Elbeyli were derived from a metasomatized, heterogeneous and enriched lithospheric mantle, with variable degrees of partial melting of the mantle wedge and variable crustal contamination. Mixing/mingling processes between mafic magmas derived from the lower crust and acidic magmas at upper crustal levels played an important role in the formation of Cu-Mo porphyry-type mineralization in the Eastern Pontides.

  18. Geochronology and geochemistry of Late Pan-African intrusive rocks in the Jiamusi-Khanka Block, NE China: Petrogenesis and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Yang, Hao; Ge, Wen-chun; Zhao, Guo-chun; Dong, Yu; Bi, Jun-hui; Wang, Zhi-hui; Yu, Jie-jiang; Zhang, Yan-long

    2014-11-01

    To constrain the early Paleozoic tectonic evolution of the Jiamusi-Khanka Block and its relationship to the Late Pan-African event in Gondwana, we undertook zircon U-Pb dating and geochemical analyses (major and trace elements, and Hf isotopic compositions) of early Paleozoic intrusive rocks in the Jiamusi-Khanka Block, NE China. LA-ICP-MS zircon U-Pb age data demonstrate that these intrusive rocks were emplaced at three stages during the Late Pan-African event, represented by ~ 540 Ma syenogranite, ~ 515 Ma quartz syenite, and ~ 500 Ma monzogranite and gabbro. Geochemically, the ~ 500 Ma gabbros in the Jiamusi-Khanka Block have low SiO2 (50.26-51.21 wt.%), relatively high MgO (4.08-5.67 wt.%), Ni (13.1-14.1 ppm) and Cr (28.4-56.0 ppm), and are slightly enriched in LILEs (e.g., Ba, K) and LREEs, and depleted in Zr, Hf, Nb, Ta and P. The εHf(t) values of zircons in the gabbro range from + 2.6 to + 6.4. All these geochemical features indicate that the gabbros were likely produced by the partial melting of a depleted mantle that had been metasomatized by fluids derived from a subducted slab. In contrast, the ca.540-500 Ma granites and quartz syenites contain high SiO2 (64.49-72.20 wt.%) and low MgO (0.40-0.75 wt.%), Cr (1.69-6.88 ppm) and Ni (1.26-3.26 ppm). They have relatively low 176Hf/177Hf ratios of 0.282247-0.282599 with Hf two-stage model ages of 1173-2280 Ma, and most of the magmatic zircons have positive εHf(t) values varying from + 0.2 - + 4.8, indicating that these granites and quartz syenites were probably derived from a dominantly Paleo-Mesoproterozoic "old" crustal source with possible different degrees of addition of juvenile materials. According to the geochemical data and global geological investigations, we propose that the 541-498 Ma intrusive rocks in the Jiamusi-Khanka Block formed in a post-collisional or post-orogenic extensional setting linked to the collapse of a Late Pan-African orogen associated within the Gondwana.

  19. Geochronology and geochemistry of Cretaceous Nanshanping alkaline rocks from the Zijinshan district in Fujian Province, South China: Implications for crust-mantle interaction and lithospheric extension

    NASA Astrophysics Data System (ADS)

    Li, Bin; Jiang, Shao-Yong

    2014-10-01

    In situ zircon U-Pb ages and Hf isotopic data, major and trace elements, and Sr-Nd-Pb isotopic compositions are reported for Nanshanping alkaline rocks from the Zijingshan district in southwestern Fujian Province (the Interior or Western Cathaysia Block) of South China. The Nanshanping alkaline rocks, which consist of porphyritic quartz monzonite, porphyritic syenite, and syenite, revealed a Late Cretaceous age of 100-93 Ma. All of the rocks show high SiO2, K2O + Na2O, and LREE but low CaO, Fe2O3T, MgO, and HFSE (Nb, Ta, P, and Ti) concentrations. These rocks also exhibit uniform initial 87Sr/86Sr ratios of 0.7078 to 0.7087 and εNd(t) values of -4.1 to -7.2, thus falling within the compositional field of Cretaceous basalts and mafic dikes occurring in the Cathaysia Block. Additionally, these rocks display initial Pb isotopic compositions with a 206Pb/204Pbi ratio of 18.25 to 18.45, a 207Pb/204Pbi ratio of 15.63 to 15.67, and a 208Pb/204Pbi ratio of 38.45 to 38.88. Combined with the zircon Hf isotopic compositions (εHf(t) = -11.7 to -3.2), which are different from those of the basement rocks, we suggest that Nanshanping alkaline rocks were primarily derived from a subduction-related enriched mantle source. High Rb/Sr (0.29-0.65) and Zr/Hf (37.5-49.2) but relatively low Ba/Rb (4.4-8.1) ratios suggest that the parental magmas of these rocks were most likely formed via partial melting of a phlogopite-bearing mantle source with carbonate metasomatism. The relatively high SiO2 (62.35-70.79 wt.%) and low Nb/Ta (10.0-15.3) ratios, positive correlation between SiO2 and (87Sr/86Sr)I, and negative correlation between SiO2 and εNd(t) of these rocks suggest that the crustal materials were also involved in formation of the Nanshanping alkaline rocks. Combined with geochemical and isotopic features, we infer magmatic processes similar to AFC (assimilation and fractional crystallization) involving early fractionation of clinopyroxene and olivine and subsequent fractionation of biotite-dominated assemblages coupled with a lesser amount of crustal contamination, thereby forming the Nanshanping alkaline rocks. The Nanshanping alkaline rocks appear to be associated with an extensional environment in the Cathaysia Block. This extensional regime could have resulted in the slab break-off and rollback of the subducting paleo-Pacific plate and the upwelling of the asthenospheric mantle, which induced partial melting of the enriched lithospheric mantle in the Cretaceous.

  20. Alpha / Mendeleev Ridge and Chukchi Borderland 40Ar/39Ar Geochronology and Geochemistry: Character of the First Submarine Intraplate Lavas Recovered from the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Mukasa, Samuel B.; Mayer, Larry A.; Aviado, Kimberly; Bryce, Julie; Andronikov, Alex; Brumley, Kelley; Blichert-Toft, Janne; Petrov, Oleg; Shokalsky, Sergey

    2015-04-01

    At least three episodes of magmatic activity have been recognized on the basis of 40Ar/39Ar age determinations in the submarine basaltic samples dredged, drilled or grabbed with a manipulation arm from Alpha / Mendeleev Ridge and Chukchi Borderland of the Arctic Ocean by US Coast Guard Icebreaker Healy, in August-September 2008, and Russian research vessel Captain Dranitsin in August-October 2012: ca. 112 Ma, ca. 100 Ma and ca. 85-73 Ma. Major-oxide and trace-element concentrations, and Pb, Sr, Nd, and Hf isotopic ratios of the recovered lavas provide important constraints on the composition and sources for the original melts. Lavas erupted at ca. 112 Ma (Group 1) have alkali basalt major-oxide compositions. Their low degree of rare-earth-element (REE) fractionation (CeN/YbN = 1.7-2.5), combined with high overall HREE (22-24 times chondrite) and Mg# ~54, suggest derivation from a garnet-free source followed by only minimal crystal fractionation for this group. Pb-Sr-Nd-Hf isotopic systematics of the lavas (206Pb/204Pb = 18.73-18.79; 207Pb/204Pb = 15.54-15.56; 208Pb/204Pb = 38.28-38.35; 143Nd/144Nd = 0.512594-0.512610; 87Sr/86Sr = 0.709458-0.709601; 176Hf/177Hf = 0.283224), together with ratios of highly incompatible trace elements (Th/Ce = 0.09-0.11; Ce/Nb = 2.58-3.09; Th/Nb = 0.24-0.33), point toward a lithospheric source for the magmas. Eruptions at ca. 100 Ma and 85-73 Ma produced two types of lavas: low-Ti tholeiitic basalts - LT, and high-Ti alkali basalts - HT, both assigned to Group 2. This distribution of low- and high-Ti lavas is common in continental flood basalt (CFB) provinces elsewhere, and has been attributed to plume activity in some studies. The trace-element abundance patterns for these Group 2 Arctic lavas are also very similar to those of CFBs elsewhere. Their low degrees of REE fractionation (CeN/YbN = 2.0-3.3) accompanied by progressively decreasing Mg#s (from 53 to 33) suggest a garnet-free source, with the derivative magmas experiencing significant crystal fractionation prior to eruption. Both LT and HT basalts have Sr, Nd and Hf isotope ratios that fall between MORB and Bulk Silicate Earth (143Nd/144Nd = 0.512669-0.512919; 87Sr/86Sr = 0.703820-0.704764; 176Hf/177Hf = 0.283128-0.283191), and are thus characterized as depleted, most likely originating in a subcontinental asthenospheric source. Contamination of these lavas with small amounts of lithospheric components is a distinct possibility. HT basalts, generally the younger of the two lava types in Group 2, are more depleted in their Nd and Sr isotopic compositions than the older LT basalts. Measured Pb-isotopic ratios plot mostly along and above the Northern Hemisphere Reference Line or NHRL (206Pb/204Pb = 18.59-19.37; 207Pb/204Pb = 15.55-15.60; 208Pb/204Pb = 38.31-38.99). Volume estimates between the Group 1 and Group 2 lavas are not yet possible to determine. However, the composition-time relationships for the lavas suggest inception of melting in the Amerasia Basin sub-continental lithospheric mantle (SCLM) - probably due to rift-related decompression - followed later (at 100 Ma and 85-73 Ma) by asthenospheric melting that may or may not be associated with a plume.

  1. Timing of the final closure of the Paleo-Asian Ocean in the Alxa Terrane: Constraints from geochronology and geochemistry of Late Carboniferous to Permian gabbros and diorites

    NASA Astrophysics Data System (ADS)

    Liu, Qian; Zhao, Guochun; Han, Yigui; Eizenhöfer, Paul R.; Zhu, Yanlin; Hou, Wenzhu; Zhang, Xiaoran

    2017-03-01

    Connecting the North China Craton to the east and the Tarim Craton to the west, the Alxa Terrane is a key place in investigating the timing of the final closure of the Paleo-Asian Ocean (PAO). New LA-ICPMS zircon U-Pb dating results reveal ca. 300-268 Ma gabbros and diorites in the Bayan Nuru area in the eastern part of the Alxa Terrane. The 300 Ma gabbros show plagioclase accumulations with anorthite compositions, arc-like geochemical affinities with relative enrichment in large ionic lithophile elements and depletion in high field strength elements (e.g., Ti, Nb and Ta), as well as negative εHf(t) and εNd(t) values and high initial 87Sr/86Sr ratios. These features indicate a magma source of an enriched lithospheric mantle metasomatized by high fluid activities. In comparison, the 280-268 Ma gabbros and diorites also have arc-like geochemical affinities but show increasingly evolved isotope compositions, implying more sediment inputs. Compiled zircon εHf(t) and whole-rock εNd(t) values of the magmatic rocks in the Alxa Terrane decrease from the Late Carboniferous to the Early Permian, and increase from the Middle Permian to the Triassic. The significantly large variation in zircon εHf(t) and whole-rock εNd(t) values at ca. 280-265 Ma likely reflects a tectonic switch from a subduction setting to a post-collisional setting, corresponding to the timing of the final closure of the PAO in the Alxa Terrane. Thus, the PAO progressively closed from west to east along the northern margin of the Tarim Craton, the Alxa Terrane, and then the northern margin of the North China Craton during Late Carboniferous to Middle Triassic time.

  2. Geochronology and geochemistry of mafic-intermediate intrusions in the Eastern Tianshan, NW China: Implications for a tectonic transition from subduction to post-collisional extension

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoran; Zhao, Guochun; Eizenhöfer, Paul R.

    2016-04-01

    This study presents new whole-rock geochemical, Sr-Nd and zircon U-Pb-Hf isotopic data for mafic-intermediate rocks from the Eastern Tianshan (NW China) to constrain the final closure of the Junggar Ocean between the Central Tianshan and Junggar terranes, which is essential in understanding the final assembly processes of the southern Central Asian Orogenic Belt. LA-ICP-MS U-Pb dating on selected igneous zircons yields well-constrained weighted mean 206Pb/238U ages of ca. 310 Ma and ca. 290 Ma, interpreted as the best estimates of the crystallization ages of the intrusions. Petrographic and geochemical analyses reveal that the Late Carboniferous samples are characterized by typical subduction-related signatures, low Sm/Yb (<2.0) but high Lu/Hf (≥0.2) ratios and positive ɛNd(t) (+1.2 to +3.1) and zircon ɛHf(t) (+4.1 to +7.8) values, suggesting that their parental magmas were most likely emplaced in a continental arc setting, genetically related to the partial melting of a metasomatized mantle wedge in the spinel stability field. This consideration agrees well with the findings of Carboniferous ophiolitic and arc-related granitoids in the region, most probably resulted from the southward subduction of the Junggar oceanic plate. In contrast, the Early Permian samples show high TiO2 (2.7-3.2 wt.%) contents with elevated Ti/V (86.0-115.1) and Zr/Y (4.9-9.3) ratios, OIB-like trace element patterns and high ɛNd(t) (+1.1 to +4.5) and zircon ɛHf(t) (+3.0 to +9.8) values, exhibiting close affinities to typical within-plate basalts. Combined with previous investigations, we suggest that the Early Permian mafic magmatism was most likely generated by the partial melting of an asthenospheric mantle source in the garnet stability field, plausibly triggered by upwelling of asthenosphere during the slab break-off of the Junggar oceanic plate, which is supported by the linear distributions of Permian post-collisional mafic-ultramafic rocks in the Eastern Tianshan. Therefore, our new data testify to a tectonic transition from Late Carboniferous oceanic subduction to Early Permian post-collisional extension in the Eastern Tianshan, probably as a result of the closure of the Junggar Ocean and subsequent arc-continent collision between the Central Tianshan and Junggar terranes that led to the final assembly of the Eastern Tianshan.

  3. Origin of the Wunugetushan porphyry Cu-Mo deposit, Inner Mongolia, NE China: Constraints from geology, geochronology, geochemistry, and isotopic compositions

    NASA Astrophysics Data System (ADS)

    Zhang, Fang-Fang; Wang, Yin-Hong; Liu, Jia-Jun; Wang, Jian-Ping; Zhao, Chun-Bo; Song, Zhi-Wei

    2016-03-01

    The Wunugetushan porphyry Cu-Mo deposit is located in the southeastern margin of the Mongol-Okhotsk Orogenic Belt and in the northwestern segment of the Great Xing'an Range, NE China. The orebodies of this deposit are mainly hosted in the monzogranitic porphyry stock and in contact with the granitic porphyry dyke and biotite granite batholith. The SHRIMP zircon U-Pb dating of the granitic porphyry dyke yielded ages of 201.4 ± 3.1 Ma (2σ, MSWD = 1.5). These results indicate that the magmatism in the Wunugetushan area might have occurred at ca. 201 Ma in the early Jurassic, and that the mineralization age (ca. 181 Ma) of this deposit is later than the age of intrusive granitic porphyry in the area. Geochemically, the Wunugetushan granitoids belong to high-K calc-alkaline and shoshonitic series, enriched in K, Rb, Nd, and Pb, and depleted in Sr, Nb, Ti and P, with negative Eu anomalies. In situ Hf isotopic analyses of zircons using LA-MC-ICP-MS indicate that the εHf(t) values for zircons from a granitic porphyry sample vary from +2.4 to +11.8 and that the corresponding crustal model ages (TDMC) vary from 483 to 1088 Ma. The least-altered monzogranitic porphyry, granitic porphyry and biotite granite yielded relatively uniform εNd(t) values from -1.0 to +0.6 and low (87Sr/86Sr)i ratios ranging from 0.704387 to 0.708385. The geochemical and Sr-Nd-Hf isotopic data for the granitoids indicate that the source magma for these rocks could be derived from a juvenile lower crust. The δ34S values of sulfides show a narrow range (+0.76‰ to +3.20‰) similar to those of magmatic sulfur, further implying a lower crust origin. Based on the results of this study and the regional geodynamic evolution, it is proposed that the formation of the Wunugetushan deposit and associated granitoids should be linked to the southeastward subduction of the Mongol-Okhotsk oceanic plate beneath the Erguna Massif during the early Jurassic, and that the monzogranitic porphyry intrusions in Wunugetushan area probably provided important ore metals responsible for the large-scale Cu-Mo mineralization.

  4. The Potassium-Argon Laser Experiment (karle): In Situ Geochronology for Planetary Missions

    NASA Technical Reports Server (NTRS)

    Cohen, B. A.

    2016-01-01

    Isotopic dating is an essential tool to establish an absolute chronology for geological events. It enables a planet's crystallization history, magmatic evolution, and alteration to be placed into the framework of solar system history. The capability for in situ geochronology will open up the ability for this crucial measurement to be accomplished as part of lander or rover complement. An in situ geochronology package can also complement sample return missions by identifying the most interesting rocks to cache or return to Earth. Appropriate application of in situ dating will enable geochronology on more terrains than can be reached with sample-return missions to the Moon, Mars, asteroids, outer planetary satellites, and other bodies that contain rocky components. The capability of flight instruments to conduct in situ geochronology is called out in the NASA Planetary Science Decadal Survey and the NASA Technology Roadmap as needing development to serve the community's needs. Beagle 2 is the only mission launched to date with the explicit aim to perform in situ K-Ar isotopic dating [1], but it failed to communicate and was lost. The first in situ K-Ar date on Mars, using SAM and APXS measurements on the Cumberland mudstone [2], yielded an age of 4.21 +/- 0.35 Ga and validated the idea of K-Ar dating on other planets, though the Curiosity method is not purpose-built for dating and requires many assumptions that degrade its precision. To get more precise and meaningful ages, multiple groups are developing dedicated in situ dating instruments.

  5. Development of the Potassium-Argon Laser Experiment (KArLE) Instrument for In Situ Geochronology

    NASA Technical Reports Server (NTRS)

    Cohen, Barbara A.; Li, Z.-H.; Miller, J. S.; Brinckerhoff, W. B.; Clegg, S. M.; Mahaffy, P. R.; Swindle, T. D.; Wiens, R. C.

    2012-01-01

    Absolute dating of planetary samples is an essential tool to establish the chronology of geological events, including crystallization history, magmatic evolution, and alteration. Traditionally, geochronology has only been accomplishable on samples from dedicated sample return missions or meteorites. The capability for in situ geochronology is highly desired, because it will allow one-way planetary missions to perform dating of large numbers of samples. The success of an in situ geochronology package will not only yield data on absolute ages, but can also complement sample return missions by identifying the most interesting rocks to cache and/or return to Earth. In situ dating instruments have been proposed, but none have yet reached TRL 6 because the required high-resolution isotopic measurements are very challenging. Our team is now addressing this challenge by developing the Potassium (K) - Argon Laser Experiment (KArLE) under the NASA Planetary Instrument Definition and Development Program (PIDDP), building on previous work to develop a K-Ar in situ instrument [1]. KArLE uses a combination of several flight-proven components that enable accurate K-Ar isochron dating of planetary rocks. KArLE will ablate a rock sample, determine the K in the plasma state using laser-induced breakdown spectroscopy (LIBS), measure the liberated Ar using quadrupole mass spectrometry (QMS), and relate the two by the volume of the ablated pit using an optical method such as a vertical scanning interferometer (VSI). Our preliminary work indicates that the KArLE instrument will be capable of determining the age of several kinds of planetary samples to +/-100 Myr, sufficient to address a wide range of geochronology problems in planetary science.

  6. Heavy mineral concentrations in the sandstones of Amij Formation with particular emphasis on the mineral chemistry and petrographic characteristics of monazite, western desert of Iraq

    NASA Astrophysics Data System (ADS)

    Kettanah, Yawooz A.; Ismail, Sabah A.

    2016-11-01

    The heavy minerals in the clastic unit of the Lower Jurassic Amij Formation exposed in the western desert of Iraq were studied. The uppermost part of the clastic unit contains thin, placer-like black sandstone horizons that are radioactive and abnormally rich in heavy minerals (0.6-56%), dominated by opaque (65%) and transparent (35%) heavy minerals. The minerals, in the order of decreasing abundance are pseudorutile, goethite, zircon, hematite, magnetite, monazite, rutile, leucoxene, tourmaline, ilmenite, chromite, and few others. Electron probe microanalysis (EPMA), microscopic and autoradiographic observations and analysis showed that the monazite is monazite-(Ce) type with an average composition of (Ce0.39Nd0.16La0.19Pr0.04Sm0.02Gd0.02Eu0.01Y0·04Th0·06U0·01Ca0·05Fe0.01)(P0·98Si0.03)O4. Monazite consists predominantly of REE-oxides (57.93%) and P2O5 (29.31%), with minor amounts of ThO2 (6.60%), Y2O3 (1.92%), UO2 (0.76%), CaO (1.14%), SiO2 (0.69%), and FeOt (0.17%). The dominant compositional substitution operating between REE and P were a mixture of the complex cheralite type substitution ([REE]-2 [Th][Ca]) and the coupled huttonite type substitution ([REE]-1 [P]-1 [Th][Si]). The chondrite-normalized REE distribution patterns of monazite show enrichment in LREE with positive Eu- and Pr-anomalies of 1.46 and 9.13, respectively. The median values of (La/Sm)CN and (La/Nd)CN ratios are 4.35 and 1.97, respectively. Zircon which is the dominant transparent mineral is Hf-rich that is composed of 30.61% SiO2, 57.58% ZrO2, 7.03% HfO2, 2.04% Y2O3, 0.56% ThO2, 0.19% UO2, and 0.19% Al2O3 corresponding to a formula (Zr0.909Hf0.065Th0·004U0·001Y0.031)Σ1.011(Si3·966Al0.028)Σ0.999O4. Rutile and tourmaline form 7% and 4% of the heavy minerals. Ilmenite which is one of the predominant heavy minerals forms 2.5% of the opaques because it is pervasively altered to Ti-Fe oxides. In addition of zircon and monazite, the chemical compositions of most of the other heavy

  7. Indus Basin sediment provenance constrained using garnet geochemistry

    NASA Astrophysics Data System (ADS)

    Alizai, Anwar; Clift, Peter D.; Still, John

    2016-08-01

    The chemical and mineralogical diversity of western Himalayan rivers is the result of each of them draining different tectonic and lithologic units, whose character is partly transferred to the sediments carried by those rivers. Garnet geochemistry was employed to discriminate provenance in the Indus River system. We characterized the geochemistry of garnet sediment grains from the modern Indus and all its major tributaries, as well as the related but ephemeral Ghaggar-Hakra River and dune sand from the Thar Desert. Garnet geochemistry displays a unique signature for the Himalayan rivers on the east of the Indus drainage compared to those in the western drainage. The trunk Indus remains distinct because of the dominant arc-type pyrope-garnet derived from Kohistan and the Karakoram. The Jhellum, which lies just east of the modern Indus has modest concentrations of arc-type pyrope garnets, which are more depleted in the other eastern tributaries. Their presence in the Jhellum reflects recycling of trunk Indus garnets through the Miocene Siwalik Group foreland sedimentary rocks. The Thar Desert dune sample contains significant numbers of grains similar to those in the trunk Indus, likely reworked by monsoon winds from the SW. Our data further indicate the presence of a Himalayan river channel east of the present Indus, close to the delta, in the Nara River valley during the middle Holocene. Sands from this channel cannot be distinguished from the Indus on the basis of their garnet geochemistry alone but we favour their sedimentation from an Indus channel rather than reworking of desert sands by another stream. The garnet geochemistry shows some potential as a provenance tool, but cannot be used alone to uniquely discriminate Indus Basin provenance.

  8. Petrology and geochemistry of Antarctic micrometeorites

    NASA Astrophysics Data System (ADS)

    Kurat, Gero; Koeberl, Christian; Presper, Thomas; Brandstätter, Franz; Maurette, Michel

    1994-09-01

    The petrology and geochemistry of twentythree chondritic dust particles with masses of 1-47 μg (sizes 100-400 μm) were recovered from blue ice near Cap Prudhomme, Antarctica, and studied by INAA, ASEM, EMPA, and optical microscopy. Sample selection criteria were irregular shape and (for a subsample) black color, with the aim of studying as many unmelted micrometeorites (MMs) as possible. Of thirteen unmelted MMs, six were phyllosilicate-dominated MMs, and seven were coarsegrained crystalline MMs consisting mainly of olivine and pyroxene. The remaining ten particles were largely melted and consisted of a foamy melt with variable amounts of relic phases (scoriaceous MMs). Thus, of the black particles selected, an astonishing portion, 40% (by number), consisted of largely unmelted MMs. Although unmelted, most phyllosilicate MMs have been thermally metamorphosed to a degree that most of the phyllosilicates were destroyed, but not melted. The original preterrestrial mineralogy is occasionally preserved and consists of serpentine-like phyllosilicates with variable amounts of cronstedtite, tochilinite-like oxides, olivine, and pyroxene. The crystalline MMs consist of olivine, low-Ca pyroxene, tochilinite-like oxides, and occasional Ni-poor metal. Relics in scoriaceous MMs consist of the same phases. Mineral compositions and the coexistence of phyllosilicates with anhydrous phases are typical of CM and CR-type carbonaceous chondrites. However, the olivine/pyroxene ratio (~ 1) and the lack of carbonates, sulfates, and of very Fe-poor, refractory element-rich olivines and pyroxenes sets the MMs apart from CM and CR chondrites. The bulk chemistry of the phyllosilicate MMs is similar to that of CM chondrites. However, several elements are either depleted (Ca, Ni, S, less commonly Na, Mg, and Mn) or enriched (K, Fe, As, Br, Rb, Sb, and Au) in MMs as compared to CM chondrites. Similar depletions and enrichments are also found in the scoriaceous MMs. We suggest that the

  9. Preliminary report on the geology and deposits of monazite, thorite and niobium-bearing rutile of the Mineral Hill district, Lemhi County, Idaho

    USGS Publications Warehouse

    Kaiser, Edward Peck

    1956-01-01

    Deposits of minerals containing niobium (columbium), thorium, and rare earths occur in the Mineral Hill district, 30 miles northwest of Salmon, Lemhi County, Idaho. Monazite, thorite, allanite, and niobium-bearing rutile form deposits in metamorphic limestone layers less than 8 feet thick. The known deposits are small, irregular, and typically located in or near small folds. Minor faults are common. Monazite generally is coarsely crystalline and contains less than one percent thorium. Rutile forms massive lumps up to 3 inches across; it contains between 5 and 10 percent niobium. Rutile occurs in the northwestern half of the district, thorite in the central and southeastern parts. Monazite occurs in all deposits. Allanite is locally abundant and contains several percent thorium. Magnetite and ilmenite are also locally abundant. A major thrust fault trending northwest across the map-area separates moderately folded quartzite and phyllitic rocks of Belt age, on the northeast, from more intensely metamorphosed and folded rocks on the southwest. The more metamorphosed rocks include amphibolite, porphyroblastic feldspar gneiss, quartzite, and limestone, all probably of sedimentary origin, and probably also of Belt (late Precambrian) age. The only rocks of definite igneous origin are rhyolite dikes of probable Tertiary age. The more metamorphosed rocks were formed by metasomatic metamorphism acting on clastic sediments, probably of Belt age, although they may be older than Belt. Metamorphism doubtless was part of the episode of emplacement of the Idaho batholith, but the history of that episode is not well understood. The rare-element deposits show no evidence of fracture-controlled hydrothermal introduction, such as special fracture systems, veining, and gangue material. They may, however, be of hydrothermal type. More likely they are metamorphic segregations or secretions, deposited in favorable stratigraphic and structural positions during regional metamorphism.

  10. Effects of Steam Environment on Creep Behavior of Nextel™610/Monazite/Alumina Composite at 1,100°C

    NASA Astrophysics Data System (ADS)

    Ruggles-Wrenn, Marina B.; Yeleser, Tufan; Fair, Geoff E.; Davis, Janet B.

    2009-12-01

    The tensile creep behavior of a N610™/LaPO4/Al2O3 composite was investigated at 1,100°C in laboratory air and in steam. The composite consists of a porous alumina matrix reinforced with Nextel 610 fibers woven in an eight-harness satin weave fabric and coated with monazite. The tensile stress-strain behavior was investigated and the tensile properties measured at 1,100°C. The addition of monazite coating resulted in ~33% improvement in ultimate tensile strength (UTS) at 1,100°C. Tensile creep behavior was examined for creep stresses in the 32-72 MPa range. Primary and secondary creep regimes were observed in all tests. Minimum creep rate was reached in all tests. In air, creep strains remained below 0.8% and creep strain rates approached 2 × 10-8 s-1. Creep run-out defined as 100 h at creep stress was achieved in all tests conducted in air. The presence of steam accelerated creep rates and significantly reduced creep lifetimes. In steam, creep strain reached 2.25%, and creep strain rate approached 2.6 × 10-6 s-1. In steam, creep run-out was not achieved. The retained strength and modulus of all specimens that achieved run-out were characterized. Comparison with results obtained for N610™/Al2O3 (control) specimens revealed that the use of the monazite coating resulted in considerable improvement in creep resistance at 1,100°C both in air and in steam. Composite microstructure, as well as damage and failure mechanisms were investigated.

  11. Pan-African metamorphic evolution in the southern Yaounde Group (Oubanguide Complex, Cameroon) as revealed by EMP-monazite dating and thermobarometry of garnet metapelites

    NASA Astrophysics Data System (ADS)

    Owona, Sebastien; Schulz, Bernhard; Ratschbacher, Lothar; Mvondo Ondoa, Joseph; Ekodeck, Georges E.; Tchoua, Félix M.; Affaton, Pascal

    2011-01-01

    Garnet-bearing micaschists and paragneisses of the Yaounde Group in the Pan-African Central African Orogenic Belt in Cameroon underwent a polyphase structural evolution with the deformation stages D 1-D 2, D 3 and D 4. The garnet-bearing assemblages crystallized in course of the deformation stage D 1-D 2 which led to the formation of the regional main foliation S 2. In XCa- XMg coordinates one can distinguish several zonation trends in the garnet porphyroblasts. Zonation trends with increasing XMg and variably decreasing XCa signalize a garnet growth during prograde metamorphism. Intermineral microstructures provided criteria for local equilibria and a structurally controlled application of geothermobarometers based on cation exchange and net transfer reactions. The syndeformational P- T path sections calculated from cores and rims of garnets in individual samples partly overlap and align along clockwise P- T trends. The P- T evolution started at ˜450 °C/7 kbar, passed high-pressure conditions at 11-12 kbar at variable temperatures (600-700 °C) and involved a marked decompression toward 6-7 kbar at high temperatures (700-750 °C). Th-U-Pb dating of metamorphic monazite by electron microprobe (EMP-CHIME method) in eight samples revealed a single period of crystallization between 613 ± 33 Ma and 586 ± 15 Ma. The EMP-monazite age populations between 613 ± 33 Ma enclosed in garnet and 605 ± 12 Ma in the matrix apparently bracket the high temperature-intermediate pressure stage at the end of the prograde P- T path. The younger monazites crystallized still at amphibolite-facies conditions during subsequent retrogression. The Pan-African overall clockwise P- T evolution in the Yaounde Group with its syndeformational high pressure stages and marked pressure variations is typical of the parts of orogens which underwent contractional crustal thickening by stacking of nappe units during continental collision and/or during subduction-related accretionary processes.

  12. Geochronological Constraints on Neoproterozoic Glaciations, the first appearance of Metazoans, and the Cambrian Explosion.

    NASA Astrophysics Data System (ADS)

    Bowring, S.; Condon, D.; Ramezani, J.; Myrow, P.; Landing, E.

    2004-05-01

    Studies of Neoproterozoic climate fluctuations, plate reconstructions, biological evolution and their interrelationships have been hindered by a lack of high-precision geochronological constraints. The correlation and estimates of duration for Neoproterozoic glaciations has relied on physical/chemo-stratigraphy, and thermal subsidence models respectively. New geochronological constraints from Neoproterozoic successions worldwide have sharpened the debate as to the number, synchroneity, and duration of glacial episodes and the relationship, if any, between Metazoan evolution and global glaciation(s). Crucial to the debate are correct interpretation of geochronological data that range from U-Pb zircon studies of intercalated volcanic ash-beds, U-Pb detrital zircon studies, Re-Os from black shales, Rb-Sr from clay-rich rocks, U-Pb and Pb-Pb from carbonates and phosphates, and Lu-Hf from phosphates. Development of a highly resolved Neoproterozoic timescale will require integration and cross-calibration of multiple dating techniques and consideration of what is actually being recorded by each chronometer. A review of available geological and geochronological data indicate that there were at least three and perhaps as many as five periods of Neoproterozoic glacial deposition including rocks from United States (Idaho and Virginia), Newfoundland and the Northwest Territories of Canada, Namibia, and Oman. What must be evaluated is how the paleogeographic distribution of glaciated regions varied with time during the Neoproterozoic. Do Neoproterozoic glacial successions distributed worldwide record a small number of globally synchronous, long-lived glaciations, or numerous diachronous glacial epochs, or a combination of both? At present, the duration of only one glacial deposit, the ca 581 Ma Gaskiers Formation (Newfoundland), is known and it is on the order of 1 Ma, at odds with a long-lived global glaciation predicted by the snowball Earth hypothesis. Other major issues are

  13. Cretaceous exhumation history of Cordillera Darwin, southern Patagonia, from patchily recrystallized garnet and U-Th-Pb monazite dating

    NASA Astrophysics Data System (ADS)

    Maloney, K. T.; Clarke, G. L.; Klepeis, K. A.; Fanning, C. M.; Wang, W.

    2010-12-01

    Garnet in amphibolite facies pelitic schists from Bahía Pia of Cordillera Darwin displays patchy textures whereby a single grain may have regions of turbid garnet with comparatively large inclusions of biotite, muscovite, plagioclase and quartz, juxtaposed against a region of clear, “ordinary” garnet. Clear areas with S1 inclusion trails are grossular rich, whereas post-S1 turbid areas are comparatively spessartine-pyrope rich. Raman spectroscopy identified the presence of an aqueous solution in turbid regions of garnet, lacking from clear areas. Turbid patches are associated with the growth of S2 kyanite and staurolite. Pseudosection modelling in Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3 (NCKFMASHTO) is consistent with garnet mode decreasing from c. 5% to less than 1% during exhumation of Cordillera Darwin, coinciding with the growth of S2 kyanite and staurolite at P≈9 kbar and T≈625°C. Turbid garnet in patchy and atoll-style textures is inferred to reflect recrystallization facilitated by fluid ingress whereby garnet cores, formed at higher P-T conditions than the rims, were preferentially recrystallised along grain cracks and boundaries. P-T paths inferred from the modelling indicate higher metamorphic conditions than previously documented, P conditions declining from 12 to 9 kbar over T= 610 to 630°C. U-Th-Pb dating of S2 monazite indicates that rapid exhumation was underway before 72.61±1.13 Ma, reflecting a tectonic shift from burial to uplift of Cordillera Darwin between c. 86 and c. 73 Ma. Sillimanite-bearing assemblages are restricted to contact aureoles associated with the intrusion of the Late Cretaceous Beagle Suite at shallower crustal conditions.

  14. Lu-Hf and Sm-Nd geochronology of garnet gneisses in the central Appalachians, U.S.: Implications for the timing and duration of Grenville Orogeny

    NASA Astrophysics Data System (ADS)

    Vervoort, Jeff; Ramsey, Molly; Mulcahy, Sean; Aleinikoff, John; Southworth, Scott

    2014-05-01

    The Grenville orogeny is one of the most significant geological events in Earth's history with remnants of this event prominent on virtually every continent. Constraining its timing and duration is important not only for understanding the tectonics of the Grenville itself, but also for understanding supercontinent cycles and other questions of Earth's evolution. In order to provide better constraints on the timing of Grenvillian metamorphism, we analyzed garnet-bearing Mesoproterozoic ortho and paragneisses, collected along a 150 km transect in the northern Blue Ridge Province, using combined Lu-Hf and Sm-Nd geochronology. The orthogneisses have U-Pb zircon crystallization ages of ~1140 and 1100 Ma. The paragneisses have maximum depositional ages ~1050 to 1020 Ma, based on the youngest detrital zircon populations. Zircon overgrowths and monazite ages suggest metamorphic events between ~1050 and 960 Ma. The Lu-Hf and Sm-Nd data for these samples both yield robust garnet ages with large spread of parent/daughter ratios, low age uncertainties, and low MSWD values. Lu-Hf ages define a narrow time span (1043±12 Ma to 1016±4 Ma; wtd. mean, 1024±7 Ma, 2σ). The Sm-Nd ages, determined on the same solutions as Lu-Hf, also define a narrow time range but are systematically younger (974±11 Ma to 932±5 Ma; wtd. mean, 957±10 Ma). The average difference between Lu-Hf and Sm-Nd ages is 67 Ma; the oldest Sm-Nd age is 40 Ma younger than the youngest Lu-Hf age. These large systematic differences in the ages are enigmatic. While Sm-Nd ages younger than Lu-Hf are not uncommon, these differences are typically small. There are, however, potential explanations for these differences. (1) Lu partitions strongly into garnet during growth resulting in high Lu/Hf ratios in the core and yielding ages weighted toward the beginning of growth (e.g., Skora, 2006); no similar partitioning exists in Sm/Nd and these ages reflect mean garnet growth. (2) Lu diffuses much faster than Hf at elevated

  15. The Chelyabinsk meteorite fall: Geochemistry and Mineralogy

    NASA Astrophysics Data System (ADS)

    Galimov, Eric

    suggestthat the Chelyabinsk meteorite parent body was affected by a major impact event at approximately 290 Ma; however, this event did not completely homogenize its Nd isotope composition. The Sr isotopic system was also not homogenized by this event. VH nuclei tracks of solar cosmic rays were detected in the meteorite; this indicates that a part of collected material could occur on the surface of the parent body. The results of the research were published in special issue of the Geochemistry journal (N6, 2013). The meteorite name was approved by the Meteoritical Society.

  16. Application of neogeographic tools for geochemistry

    NASA Astrophysics Data System (ADS)

    Zhilin, Denis

    2010-05-01

    edited manually. We would like to show some results of practical and scientific importance, obtained by non-experts. At 2006 our secondary school students investigated the distribution of snow salinity around Kosygina Street in Moscow. One can conclude that the distribution of salinity is reproducible and that the street influences the snow up to 150 meters. Another example obtained by our students is the distribution of electrical conductivity of swamp water showing extreme irregularity of this parameter within the small area (about 0.5x0.5 km) the electrical conductivity varied from 22 to 77 uS with no regularity. It points out the key role of local processes in swamp water chemistry. The third example (maps of electrical conductivity and pH of water on a large area) one can see at http://fenevo.narod.ru/maps/ec-maps.htm and http://fenevo.narod.ru/maps/ph-maps.htm. Basing on the map one can conclude mechanisms of formation of water mineralization in the area. Availability of GPS receivers and systems for easy measuring of chemical parameters can lead to neogeochemical revolution as GPS receivers have led to neogeographical. A great number of non-experts can share their geochemical results, forming huge amount of available geochemical data. It will help to falsify and visualize concepts of geochemistry and environmental chemistry and, maybe, develop new ones. Geophysical and biological data could be shared as well with the same advantages for corresponding sciences.

  17. Isotope and chemical age of the Greater Caucasus basement metamorphic rocks

    NASA Astrophysics Data System (ADS)

    Konilov, A. N.; Somin, M. L.; Mukhanova, A. A.

    2009-04-01

    complexes independently of baric type seem to be formed roughly synchronously during Variscan epoch. References: Gamkrelidze I.P., Shengelia D.M. ( 2005).The Precambrian-Paleozoic Regional Metamorphism, Granitoid Magmatism, and Geodynamics of the Caucasus. M: Nauchnyi Mir [in Russian]. Pyle J.M., Frank S. Spear F.S. et al. (2001). Monazite-Xenotime-Garnet Equilibrium in Metapelites and a New Monazite-Garnet Thermometer. Journal of Petrology, , 42, 2083-2107. Slagstad T. (2006).Chemical (U-Th-Pb) dating of monazite: Analytical protocol for a LEO 1450VP scanning electron microscope and examples from Rogaland and Finnmark, Norway. Norges geologiske undersøkelse Bulletin, 446, 11-18. Somin M.L. (2007a). Pre-Alpine basement of the Greater Caucasus: main features. In: Alpine history of the Greater Caucasus (Yu.G. Leonovб Ed.). GEOS. Moscow. P.15-38. Somin M.L., Lepekhina E.N., Konilov A.N. ( 2007b). Age of the High-Temperature Gneiss Core of the Central Caucasus. Doklady Earth Sciences, 415, 690-694. Somin M.L., Levchenkov O.A., Kotov A.B. et al. (2007c). The Paleozoic Age of High-Pressure Metamorphic Rocks in the Dakhov Salient, North-Western Caucasus: Results of U-Pb Geochronological Investigations. Doklady Earth Sciences, 416, 1018-1021. Suzuki K., Adachi M. (1991). Precambrian provenance and Silurian metamorphism of the Tsunosava paragneiss in South Kitakami terrane, northeast Japan, revealed by the chemical Th-U-total Pb isochron ages of monazite, zircon and xenotime. Journal of Geochemistry, 25, 357-376.

  18. Geochronological constraints (40Ar/39Ar and U/Pb) on the thermal history of the Tolumne Intrusive Suite (Sierra Nevada, California)

    NASA Astrophysics Data System (ADS)

    Mundil, R.; Nomade, S.; Paterson, S. R.; Renne, P. R.

    2004-12-01

    The Tuolumne Intrusive Suite (TIS) in the Eastern Sierra Nevada is considered a type example of a batholith and represents a spectacularly exposed, protracted record of internal differentiation and plutonic assembly in a large, open-system, continental arc magma chamber. One of the recent advances in our understanding of magmatic systems is the recognition that a substantial number are constructed episodically over timescales of up to millions of years for larger plutons. The main objective of this study is to investigate the episodic growth and evolution of magmatic systems by integrating thermal, geochronologic, geochemical, and crystal size distribution (CSD) studies with ongoing field studies of the TIS. Here we present high-resolution U/Pb and 40Ar/39Ar geochronology from the TIS (which was assembled between 93 and 85 Ma, Coleman et al., 2004) and adjacent older units in order to unravel the time scales of its assemblage and thermal history. 25 Samples were collected along a SW-NE corridor (ca 30 km) across the TIS, including older plutons to the SW (El Capitan) and the NE (Soldier Lake (SDL) and Green Lake plutons (GRL)). So far, conventional U/Pb single-zircon analyses yield weighted mean 206Pb/238U ages of 165.0 ± 0.3 Ma for the GRL and a preliminary age of ca. 95 Ma for the SDL, which are interpreted as emplacement ages (all uncertainties are given at the 2σ level). 40Ar/39Ar analyses were performed on two different biotite and hornblende grain size fractions (800-900μ m and 150-180μ m) from each sample. As expected, isotherms in the eastern pendant of the Sierra Nevada move towards the TIS as a result of its cooling between 85 to 80 Ma. The gradient of temperature at the time of the emplacement of the Cathedral Peak (CP) Pluton (U/Pb zircon age of ca 88 Ma, Coleman, 2004) was about 150° C to 200° C per 5 km. The western margin of the GRL (at 5 km distance from the TIS) is thermally affected by the TIS as indicated by biotite ages that are reset (ca

  19. Isotope systematics and shock-wave metamorphism: I. U-Pb in zircon, titanite, and monazite, shocked experimentally up to 59 GPa

    SciTech Connect

    Deutsch, A. ); Schaerer, U. )

    1990-12-01

    This study reports the first U-Pb isotope analyses on experimentally shocked zircon, titanite, and monazite extracted from Proterozoic granitoid rocks. In all three types of minerals, shock-waves produce drastic changes in the crystal lattices, causing strong lowering of birefringence, turbidization, and decolorization of the individual grains. Moreover, X-ray patterns indicate transition of the crystals into polycrystalline aggregates of <10{sup {minus}5} mm block-size. Precisely dated grains with concordant or nearly concordant ages were embedded in KBr and shocked at 35, 47.5, and 59 GPa. U-Pb isotope analyses on these grains show that shock metamorphism does not fractionate Pb isotopes within the analytical precision of {plus minus}0.1%. As far as chemical fractionation is concerned, there is no difference in degree of concordancy between shocked and unshocked monazite, and small degrees (<2%) of relative U/Pb fractionation in shocked zircon and titanite are due to time-integrated Pb-loss and not to the shock experiment. In consequence, the data document that shock-wave metamorphism alone does not measurably effect the U-Pb chronometer, questioning the view that lower intercept ages of discordant U-Pb data reflect shock-induced re-equilibration of the chronometer in moderately to highly shocked, rapidly cooling rocks.

  20. Fractionation of rare-earth elements in allanite and monazite as related to geology of the Mt. Wheeler mine area, Nevada

    USGS Publications Warehouse

    Lee, D.E.; Bastron, H.

    1967-01-01

    Rare-earth contents of 20 allanites and 13 monazites, accessory minerals from a restricted outcrop area of intrusive granitic rocks, are reported. A quantity called sigma (??), which is the sum of the atomic percentages of La, Ce and Pr, is used as an index of composition with respect to the rare-earth elements. Values of sigma vary from 61.3 to 80.9 at.% for these allanites and monazites, representing an appreciable range of composition in terms of the rare-earth elements. Degree of fractionation of rare earths varies directly with CaO content of the granitic rocks, which in turn depends largely on proximity of limestone. Four xenoliths included in the study suggest that spotty mosaic equilibria are superimposed on the regional gradients and that locally the degree of fractionation of rare earths responds to whole rock composition over distances of a few yards or less. The chemistry of the granitic rocks under study appears to be similar in some respects to that of alkalio rocks and carbonatites. Allanites from the most calcium-rich rocks show a pronounced concentration of the most basic rare earths, and whole-rock concentrations of such rare constituents as total cerium earths, Zr, F, Ti, Ba and Sr increase sympathetically with whole-rock calcium. The explanation for the concentration gradients observed in this chemical system must involve assimilation more than magmatic differentiation. ?? 1967.

  1. Sedimentary basin geochemistry and fluid/rock interactions workshop

    SciTech Connect

    1991-12-31

    Fundamental research related to organic geochemistry, fluid-rock interactions, and the processes by which fluids migrate through basins has long been a part of the U.S. Department of Energy Geosciences program. Objectives of this program were to emphasize those principles and processes which would be applicable to a wide range of problems associated with petroleum discovery, occurrence and extraction, waste disposal of all kinds, and environmental management. To gain a better understanding of the progress being made in understanding basinal fluids, their geochemistry and movement, and related research, and to enhance communication and interaction between principal investigators and DOE and other Federal program managers interested in this topic, this workshop was organized by the School of Geology and Geophysics and held in Norman, Oklahoma in November, 1991.

  2. Plutonium and Americium Geochemistry at Hanford: A Site Wide Review

    SciTech Connect

    Cantrell, Kirk J.; Felmy, Andrew R.

    2012-08-23

    This report was produced to provide a systematic review of the state-of-knowledge of plutonium and americium geochemistry at the Hanford Site. The report integrates existing knowledge of the subsurface migration behavior of plutonium and americium at the Hanford Site with available information in the scientific literature regarding the geochemistry of plutonium and americium in systems that are environmentally relevant to the Hanford Site. As a part of the report, key research needs are identified and prioritized, with the ultimate goal of developing a science-based capability to quantitatively assess risk at sites contaminated with plutonium and americium at the Hanford Site and the impact of remediation technologies and closure strategies.

  3. Petrography and Geochemistry of Lunar Meteorite Miller Range 13317

    NASA Technical Reports Server (NTRS)

    Zeigler, R. A.; Korotev, R. L.

    2016-01-01

    Miller Range (MIL) 13317 is a 32-g lunar meteorite collected during the 2013-2014 ANSMET (Antarctic Search for Meteorites) field season. It was initially described as having 25% black fusion crust covering a light- to dark-grey matrix, with numerous clasts ranging in size up to 1 cm; it was tenta-tively classified as a lunar anorthositic breccia. Here we present the petrography and geochemistry of MIL 13317, and examine possible pairing relationships with previously described lunar meteorites.

  4. Geochronological, geochemical and Sr-Nd-Hf isotopic constraints on the petrogenesis of Late Cretaceous A-type granites from the Sibumasu Block, Southern Myanmar, SE Asia

    NASA Astrophysics Data System (ADS)

    Jiang, Hai; Li, Wen-Qian; Jiang, Shao-Yong; Wang, He; Wei, Xiao-Peng

    2017-01-01

    The Late Cretaceous to Paleogene granitoids occur widespread in the Sibumasu block within Myanmar (SE Asia), which show a close association with tin-tungsten mineralization. However, the precise timing, petrogenesis and tectonic significance of these granitoids are poorly constrained so far. In this study, we present a detailed study on geochronology, elemental and Sr-Nd-Hf isotopic geochemistry for the Hermyingyi and Taungphila granites in southern Myanmar, with the aim of determining their petrogenesis and tectonic implications. LA-ICP-MS U-Pb dating of zircon grains from the two granites yield ages of 69-70 Ma, indicating a Late Cretaceous magmatic event. These granitic rocks are weakly peraluminous and belong to the high-K calc-alkaline series. They are both characterized by high SiO2, K2O + Na2O, FeOT/(FeOT + MgO) and Ga/Al ratios and low Al2O3, CaO, MgO, P2O5 and TiO2 contents, enriched in Rb, Th, U and Y, but depleted in Ba, Sr, P, and Eu, suggesting an A-type granite affinity. Moreover, they display prominent tetrad REE patterns and non-CHARAC trace element behavior, which are common in late magmatic differentiates with strong hydrothermal interaction or deuteric alteration. The granites belong to A2-type and probably formed at a high temperature and anhydrous condition. They have zircon εHf(t) values from - 12.4 to - 10.0 and whole-rock εNd(t) values from - 11.3 to - 10.6, with Paleoproterozoic TDM2 ages (1741-1922 Ma) for both Hf and Nd isotopes. Geochemical and isotopic data suggest that these A-type granites were derived from partial melting of the Paleoproterozoic continental crust dominated by metaigneous rocks with tonalitic to granodioritic compositions, without significant input of mantle-derived magma and followed by subsequent fractional crystallization. By integrating all available data for the regional tectonic evolution in SE Asia and adjacent regions, we attribute the formation of the Late Cretaceous A-type granites to a back-arc extension

  5. An integrative geologic, geochronologic and geochemical study of Gorgona Island, Colombia: Implications for the formation of the Caribbean Large Igneous Province

    NASA Astrophysics Data System (ADS)

    Serrano, Lina; Ferrari, Luca; Martínez, Margarita López; Petrone, Chiara Maria; Jaramillo, Carlos

    2011-09-01

    The genesis of the Caribbean Large Igneous Province (CLIP) has been associated to the melting of the Galapagos plume head at ~ 90 Ma or to the interaction between the plume and the Caribbean slab window. Gorgona Island, offshore western Colombia, is an accreted fragment of the CLIP and its highly heterogeneous igneous suite, ranging from enriched basalts to depleted komatiites and picrites, was assumed to have formed at ~ 89 Ma from different part of the plume. Here we present new geologic, geochronologic and geochemical data of Gorgona with significant implications for the formation of the CLIP. A new set of 40Ar- 39Ar ages documents a magmatic activity spanning the whole Late Cretaceous (98.7 ± 7.7 to 64.4 ± 5 Ma) followed by a shallower, picritic pyroclastic eruption in the Paleocene. Trace element and isotope geochemistry confirm the existence of an enriched (EDMM: La/Sm N ≥ 1 and ɛNd i of 5.7 to 7.8) and a depleted (DMM: La/Sm N < 1 and ɛNd i of 9.5 to 11.3) mantle sources. A progressive increase in the degree of melting and melt extraction with time occurred in both groups. Petrologic modeling indicates that low but variable degrees of wet melting (< 5%) of an EDMM can produce the LREE-enriched rocks. Higher degree of melting (> 10%) of a mixed DMM + EDMM (40 to 60%) may reproduce the more depleted rocks with temperatures in the range of ambient mantle in absence of plumes. Our results contradict the notion that the CLIP formed by melting of a plume head at ~ 90 Ma. Multiple magmatic pulses over several tens of Ma in small areas like Gorgona, also recognized in other CLIP areas, suggest a long period of diffuse magmatism without a clear pattern of migration. The age span of this magmatism is broadly concurrent with the Caribbean slab window. During this time span the Farallon oceanic lithosphere (later becoming the Caribbean plate) advanced eastward ~ 1500 km, overriding the astenosphere feeding the proto-Caribbean spreading ridge. This hotter mantle

  6. Automating U-Pb IDTIMS data reduction and reporting: Cyberinfrastructure meets geochronology

    NASA Astrophysics Data System (ADS)

    Bowring, J. F.; McLean, N.; Walker, J. D.; Ash, J. M.

    2009-12-01

    We demonstrate the efficacy of an interdisciplinary effort between software engineers and geochemists to produce working cyberinfrastructure for geochronology. This collaboration between CIRDLES, EARTHTIME and EarthChem has produced the software programs Tripoli and U-Pb_Redux as the cyber-backbone for the ID-TIMS community. This initiative incorporates shared isotopic tracers, data-reduction algorithms and the archiving and retrieval of data and results. The resulting system facilitates detailed inter-laboratory comparison and a new generation of cooperative science. The resolving power of geochronological data in the earth sciences is dependent on the precision and accuracy of many isotopic measurements and corrections. Recent advances in U-Pb geochronology have reinvigorated its application to problems such as precise timescale calibration, processes of crustal evolution, and early solar system dynamics. This project provides a heretofore missing common data reduction protocol, thus promoting the interpretation of precise geochronology and enabling inter-laboratory comparison. U-Pb_Redux is an open-source software program that provides end-to-end support for the analysis of uranium-lead geochronological data. The system reduces raw mass spectrometer data to U-Pb dates, allows users to interpret ages from these data, and then provides for the seamless federation of the results, coming from many labs, into a community web-accessible database using standard and open techniques. This EarthChem GeoChron database depends also on keyed references to the SESAR sample database. U-Pb_Redux currently provides interactive concordia and weighted mean plots and uncertainty contribution visualizations; it produces publication-quality concordia and weighted mean plots and customizable data tables. This initiative has achieved the goal of standardizing the data elements of a complete reduction and analysis of uranium-lead data, which are expressed using extensible markup

  7. In-situ Geochronology on the Mars 2020 Rover with KArLE (The Potassium-Argon Laser Experiment)

    NASA Technical Reports Server (NTRS)

    Cohen, Barbara A.; Li, Z. -H.; Miller, J. S.; Devismes, D.; Swindle, T. D.; Schwenzer, S. P.; Kelley, S. P.; Zacny, K. A.; Roark, S. E.; Hardaway, L. R.; Weinberg, J. D.

    2014-01-01

    A successful Mars exploration program has revealed chapters of Mars history, but in this book, the pages are ripped out of the binding and scattered across the surface. An examination of each page reveals interesting information, but there is no way to read the book in a logical order. Geochronology is the tool that puts page number onto the individual pages, and allows the book of Martian history to be read in its proper order. The KArLE experiment performs the first dedicated in situ geochronology investigation on Mars, bringing clarity to Mars 2020 samples and context to its landing site.

  8. Advanced Cyberinfrastructure for Geochronology as a Collaborative Endeavor: A Decade of Progress, A Decade of Plans

    NASA Astrophysics Data System (ADS)

    Bowring, J. F.; McLean, N. M.; Walker, J. D.; Gehrels, G. E.; Rubin, K. H.; Dutton, A.; Bowring, S. A.; Rioux, M. E.

    2015-12-01

    The Cyber Infrastructure Research and Development Lab for the Earth Sciences (CIRDLES.org) has worked collaboratively for the last decade with geochronologists from EARTHTIME and EarthChem to build cyberinfrastructure geared to ensuring transparency and reproducibility in geoscience workflows and is engaged in refining and extending that work to serve additional geochronology domains during the next decade. ET_Redux (formerly U-Pb_Redux) is a free open-source software system that provides end-to-end support for the analysis of U-Pb geochronological data. The system reduces raw mass spectrometer (TIMS and LA-ICPMS) data to U-Pb dates, allows users to interpret ages from these data, and then facilitates the seamless federation of the results from one or more labs into a community web-accessible database using standard and open techniques. This EarthChem database - GeoChron.org - depends on keyed references to the System for Earth Sample Registration (SESAR) database that stores metadata about registered samples. These keys are each a unique International Geo Sample Number (IGSN) assigned to a sample and to its derivatives. ET_Redux provides for interaction with this archive, allowing analysts to store, maintain, retrieve, and share their data and analytical results electronically with whomever they choose. This initiative has created an open standard for the data elements of a complete reduction and analysis of U-Pb data, and is currently working to complete the same for U-series geochronology. We have demonstrated the utility of interdisciplinary collaboration between computer scientists and geoscientists in achieving a working and useful system that provides transparency and supports reproducibility, allowing geochemists to focus on their specialties. The software engineering community also benefits by acquiring research opportunities to improve development process methodologies used in the design, implementation, and sustainability of domain-specific software.

  9. Stratigraphy and geochronology of pitfall accumulations in caves and fissures, Bermuda

    NASA Astrophysics Data System (ADS)

    Hearty, Paul J.; Olson, Storrs L.; Kaufman, Darrell S.; Edwards, R. Lawrence; Cheng, Hai

    2004-05-01

    Deep fractures ("fissures") and avens ("skylights") in limestone cave roofs create natural traps for sediments and biota. Fissures fill quickly with surface sediment and organisms soon after opening. Debris cones are formed as materials fall, wash, or drift on air through openings in cave skylights. Such deposits in Admiral's and Grand Canyon Cave, Bermuda contain distinct beds and are composed of mixtures of sediment and charcoal, together with fossils of land snails, crabs, birds, reptiles, and bats. The "pitfall" accumulations were periodically sealed over by calcite flowstone. A stratigraphic record of surface activity and fauna through both glacial and interglacial periods has been preserved. The succession also provides an ideal setting in which to compare several geochronological methods. Calibrated 14C ages on charcoal and shells provide dated horizons at 1600, 12,800, and about 35,000 14C yr BP. Thermal ionization mass spectrometric (TIMS) ages on several flowstone layers constrain the entire sequence in the Admiral's Cave sequence between 126,300±900 yr (Termination II) and historical times. A continuous relative-age record generated by amino acid epimerization (AAE) geochronology ( D-alloisoleucine/ L-isoleucine or aIle/Ile) on the pulmonate land gastropod Poecilozonites verifies the biostratigraphy, reveals a minimal degree of mixing between stratigraphic units, and establishes an independent temporal link between the subterranean and subaerial deposits of Bermuda. This convergence between stratigraphy and geochronology yields a precisely dated succession from the oceanic island of Bermuda, and thus presents a unique opportunity to assess the rates and processes of evolutionary and climate change during that interval.

  10. Algorithms and software for U-Pb geochronology by LA-ICPMS

    NASA Astrophysics Data System (ADS)

    McLean, Noah M.; Bowring, James F.; Gehrels, George

    2016-07-01

    The past 15 years have produced numerous innovations in geochronology, including experimental methods, instrumentation, and software that are revolutionizing the acquisition and application of geochronological data. For example, exciting advances are being driven by Laser-Ablation ICP Mass Spectrometry (LA-ICPMS), which allows for rapid determination of U-Th-Pb ages with 10s of micrometer-scale spatial resolution. This method has become the most commonly applied tool for dating zircons, constraining a host of geological problems. The LA-ICPMS community is now faced with archiving these data with associated analytical results and, more importantly, ensuring that data meet the highest standards for precision and accuracy and that interlaboratory biases are minimized. However, there is little consensus with regard to analytical strategies and data reduction protocols for LA-ICPMS geochronology. The result is systematic interlaboratory bias and both underestimation and overestimation of uncertainties on calculated dates that, in turn, decrease the value of data in repositories such as EarthChem, which archives data and analytical results from participating laboratories. We present free open-source software that implements new algorithms for evaluating and resolving many of these discrepancies. This solution is the result of a collaborative effort to extend the U-Pb_Redux software for the ID-TIMS community to the LA-ICPMS community. Now named ET_Redux, our new software automates the analytical and scientific workflows of data acquisition, statistical filtering, data analysis and interpretation, publication, community-based archiving, and the compilation and comparison of data from different laboratories to support collaborative science.

  11. Timing is Everything:The Boon and Bane of 14C Geochronology

    SciTech Connect

    Guilderson, T; Guilderson, T; Reimer, P J; Brown, T

    2004-10-29

    There are underappreciated limitations of the conversion of {sup 14}C-ages to the fixed, calendrical time-scale that bear directly upon our understanding of the dynamic climate system, or the relationship between the collapse of one civilization and it's neighbor's. In this paper we present a quantitative assessment of the limits of {sup 14}C-geochronology and calibration onto the absolute calendrical time-scale over the Holocene. We take into account not only the inherent limitations of the {sup 14}C-calendar calibration curve, but also analytical uncertainties.

  12. Monazite-type SrCrO4 under compression

    SciTech Connect

    Gleissner, J.; Errandonea, Daniel; Segura, A.; Pellicer-Porres, J.; Hakeem, M. A.; Proctor, J. E.; Raju, S. V.; Kumar, R. S.; Rodríguez-Hernández, P.; Munoz, A.; Lopez-Moreno, S.; Bettinelli, M.

    2016-10-20

    We report a high-pressure study of monoclinic monazite-type SrCrO4 up to 26 GPa. Therein we combined x-ray diffraction, Raman, and optical-absorption measurements with ab initio calculations, to find a pressure-induced structural phase transition of SrCrO4 near 8-9 GPa. Evidence of a second phase transition was observed at 10-13 GPa. The crystal structures of the high-pressure phases were assigned to the tetragonal scheelite-type and monoclinic AgMnO4-type structures. Both transitions produce drastic changes in the electronic band gap and phonon spectrum of SrCrO4. We determined the pressure evolution of the band gap for the low- and high-pressure phases as well as the frequencies and pressure dependencies of the Raman-active modes. In all three phases most Raman modes harden under compression, however the presence of low-frequency modes which gradually soften is also detected. In monazite-type SrCrO4, the band gap blueshifts under compression, but the transition to the scheelite phase causes an abrupt decrease of the band gap in SrCrO4. Calculations showed good agreement with experiments and were used to better understand the experimental results. From x-ray-diffraction studies and calculations we determined the pressure dependence of the unit-cell parameters of the different phases and their ambient-temperature equations of state. The results are compared with the high-pressure behavior of other monazites, in particular PbCrO4. A comparison of the high-pressure behavior of the electronic properties of SrCrO4 (SrWO4) and PbCrO4 (PbWO4) will also be made. Lastly, the possible occurrence of a third structural phase transition is discussed.

  13. Experimental determination of synthetic NdPO4 monazite end-member solubility in water from 21°C to 300°C: implications for rare earth element mobility in crustal fluids1 1Associate editor: D. J. Wesolowski

    NASA Astrophysics Data System (ADS)

    Poitrasson, Franck; Oelkers, Eric; Schott, Jacques; Montel, Jean-Marc

    2004-05-01

    The solubility of synthetic NdPO 4 monazite end-member has been determined experimentally from 21 to 300°C in aqueous solutions at pH = 2, and at 21°C and pH = 2 for GdPO 4. Measurements were performed in batch reactors, with regular solution sampling for pH measurement, rare earths and phosphorous analysis by inductively coupled plasma mass spectrometry (ICP-MS) coupled with a desolvation system. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to check that no reprecipitation of secondary phases occurred and that the mineral surfaces remained those of a monazite. Coupled with speciation calculations, measured solution compositions permitted the determination of NdPO 4 and GdPO 4 solubility products which are in general agreement with previous experimental determination on rhabdophane at 25°C, but showing that monazite is more than two orders of magnitude less soluble than inferred on the basis of previous thermodynamic estimates. The temperature evolution from 21 to 300°C of the equilibrium constant (K) of the NdPO 4 monazite end-member dissolution reaction given by: NdPO4( s) ⇆ Nd3++ PO43- can be described by the equation: -log K= 7.621+ 0.04163T+ 1785/T where T is in Kelvins. Integration of this expression permitted the determination of the enthalpy, free energy and entropy of dissolution and formation of the NdPO 4 monazite end-member. Solubility-speciation calculations show that the presence of aqueous ligands, notably fluoride, carbonate or hydroxide in water strongly affect monazite solubility, depending on pH and temperature. These calculations also show that monazite will exhibit retrograde solubility only under acidic conditions from 70°C to 300°C and to a lesser extent in neutral aqueous solutions from 150°C to 300°C. Solubility-speciation calculations performed on natural seafloor vent hydrothermal fluids and on thermal springwaters from granitic areas at aquifer temperature show that these fluids

  14. Episodic continental arc volcanism, tectonism and erosion recorded in stratigraphy and detrital zircon geochronology

    NASA Astrophysics Data System (ADS)

    Cao, W.; Paterson, S. R.

    2015-12-01

    Stratigraphic studies and detrital zircon geochronology of metamorphic host rock pendants of the Mesozoic Sierra Nevada arc in California show temporal correlations with episodic arc volcanism and tectonism, and have implications for our understanding of sources and sinks of recycled volcanic and sedimentary materials, as well as the paleo-geography and erosion history of an ancient continental arc. The Middle Triassic to Early Cretaceous stratigraphy of the metamorphic pendants shows alternating volcanic and sedimentary beds. The latter varies from rocks formed in high-energy terrestrial to low-energy shallow marine environments. Sedimentary textures also vary from poorly sorted volcanic-clast/breccia-rich to well-sorted fine-grained rocks and carbonates. We interpret these variations in stratigraphic records to reflect the waning and waxing of arc volcanism and tectonism, which controls erosion of source rocks, as well as elevation changes through isostastic balance. These in turn control the paleo-geography and depositional environments. Detrital zircon geochronology confirms our hypothesis. Detrital zircon ages of sedimentary rocks closely track the ages of volcanic/plutonic rocks formed immediately earlier and also include age signals of older igneous rocks and pre-arc basement, suggesting the erosion of igneous rocks of higher elevation during the magmatic flare-ups and deposition of these clasts afterwards. We conclude that episodic arc volcanism and tectonism play important roles on processes of surface erosion and sedimentation.

  15. Dating kimberlite emplacement with zircon and perovskite (U-Th)/He geochronology

    NASA Astrophysics Data System (ADS)

    Stanley, Jessica R.; Flowers, Rebecca M.

    2016-11-01

    Kimberlites provide rich information about the composition and evolution of cratonic lithosphere. Accurate geochronology of these eruptions is key for discerning spatiotemporal trends in lithospheric evolution, but kimberlites can sometimes be difficult to date with available methods. We explored whether (U-Th)/He dating of zircon and perovskite can serve as reliable techniques for determining kimberlite emplacement ages. We obtained zircon and/or perovskite (U-Th)/He (ZHe, PHe) dates from 16 southern African kimberlites. Most samples with abundant zircon yielded reproducible ZHe dates (≤15% dispersion) that are in good agreement with published eruption ages. The majority of dated zircons were xenocrystic. Zircons with reproducible dates were fully reset during eruption or resided at temperatures above the ZHe closure temperature prior to entrainment in the kimberlite magma. Not dating hazy and radiation damaged grains can help avoid anomalous results for more shallowly sourced zircons that underwent incomplete damage annealing and/or partial He loss during the eruptive process. All seven kimberlites dated with PHe yielded reproducible (≤15% dispersion) and reasonable results. We conducted two preliminary perovskite 4He diffusion experiments, which suggest a PHe closure temperature of >300°C. Perovskite in kimberlites is unlikely to be xenocrystic and its relatively high temperature sensitivity suggests that PHe dates will typically record emplacement rather than postemplacement processes. ZHe and PHe geochronology can effectively date kimberlite emplacement and provide useful complements to existing techniques.

  16. Geochronology and historical deposition of trace metals in three tropical estuaries in the Gulf of Guinea

    NASA Astrophysics Data System (ADS)

    Mahu, Edem; Nyarko, Elvis; Hulme, Samuel; Swarzenski, Peter; Asiedu, Daniel K.; Coale, Kenneth H.

    2016-08-01

    The depositional histories of trace metals (Pb, Cu, and Zn) in sediment cores from three Ghanaian estuaries were reconstructed using radioisotope-derived (210Pb and 137Cs) geochronologies. A core collected from each of the Amisa, Sakumo II and Volta estuaries was analyzed for trace metals and radionuclides. Lead-210 and 137Cs dating via gamma spectroscopy, and trace metal analysis via inductively coupled plasma mass spectrometry (ICP-MS) were used in deriving sedimentation rates, geochronologies and accumulation trends of trace metals. The sedimentation rates in all three estuaries (in the range of 0.54-0.83 cm yr-1) were greater than the predicted sea level rise (∼0.33 cm yr-1) for the Accra Coast of Ghana. The 210Pb depositional rates of 6.83 dpm cm-2 y-1, 2.74 dpm cm-2 y-1 and 1.75 dpm cm-2 y-1 estimated for the Amisa, Sakumo II and Volta estuaries, respectively, are higher than those recorded in other latitudes. Trace metal analysis revealed differences in the concentrations of Cu, Pb and Zn between deeper and surficial layers of each core to be in the range of 10-20%, which is well within the natural variations attributed to geochemical factors. Relative to the Amisa and Volta estuaries, the temporal profiles of Al-normalized metal concentrations and estimated fluxes suggest anthropogenic processes augmented the natural fluxes of trace metals, particularly Zn into the Sakumo II estuary during the last 7 years.

  17. Eruptive Style and Geochronology of the Initial Fases of Monogenetic Vulcanism of Southern Basis of Mexico

    NASA Astrophysics Data System (ADS)

    Jaimes, M. D.; Martin, A.; Layer, P. W.

    2013-05-01

    Monogenetic vulcanism in the central part of Mexico includes the Chichinautzin Monogenetic Volcanic Field, located at the front of the Transmexican Volcanic Belt (TMVB), 300 km from the Mesoamerican trench. At least 220 volcanoes formed during the Pleistocene and Holocene. Most are scoria cones with associated lava flows, small shield volcanoes and lava domes; and cover an área of 2400 km2 (Martin Del Pozzo, 1982; Wallace and Carmichael, 1999; Velasco-Tapia and Verma, 2001; Velasco-Tapia, 2003). Previous studies in the area (paleomagnetic, geomorphologic, vulcanologic and radiometric) indicate that volcanism is less than 0.79 Ma (Bloomfield, 1973; Mooser et al., 1974; Herrero and Pal, 1978; Martin Del Pozzo et al., 1997; Siebe et al., 2004a). Our field studies include mapping and sampling of 50 lava flows associated with scoria cones, phreatomagmatic structures (2), lava flows without cones (2) and lava domes (5). Geomorphologic analyses, whole rock chemical analyse (FRX), petrographic and geochronologic (Ar-Ar) were carried out. We identified three zones with different eruptive styles: strombolian and violent strombolian to the north and south; and phreatomagmatic style only in the north. Samples are basaltic andesites to dacites. Geochronologic data is consistent with some of the relative ages according to the geomorphologic data and corresponds to three age groups.

  18. Re-Os geochronology and coupled Os-Sr isotope constraints on the Sturtian snowball Earth.

    PubMed

    Rooney, Alan D; Macdonald, Francis A; Strauss, Justin V; Dudás, Francis Ö; Hallmann, Christian; Selby, David

    2014-01-07

    After nearly a billion years with no evidence for glaciation, ice advanced to equatorial latitudes at least twice between 717 and 635 Mya. Although the initiation mechanism of these Neoproterozoic Snowball Earth events has remained a mystery, the broad synchronicity of rifting of the supercontinent Rodinia, the emplacement of large igneous provinces at low latitude, and the onset of the Sturtian glaciation has suggested a tectonic forcing. We present unique Re-Os geochronology and high-resolution Os and Sr isotope profiles bracketing Sturtian-age glacial deposits of the Rapitan Group in northwest Canada. Coupled with existing U-Pb dates, the postglacial Re-Os date of 662.4 ± 3.9 Mya represents direct geochronological constraints for both the onset and demise of a Cryogenian glaciation from the same continental margin and suggests a 55-My duration of the Sturtian glacial epoch. The Os and Sr isotope data allow us to assess the relative weathering input of old radiogenic crust and more juvenile, mantle-derived substrate. The preglacial isotopic signals are consistent with an enhanced contribution of juvenile material to the oceans and glacial initiation through enhanced global weatherability. In contrast, postglacial strata feature radiogenic Os and Sr isotope compositions indicative of extensive glacial scouring of the continents and intense silicate weathering in a post-Snowball Earth hothouse.

  19. Developement of the Potassium-Argon Laser Experiment (KArLE) for In Situ Geochronology

    NASA Technical Reports Server (NTRS)

    Cohen, Barbara A.

    2012-01-01

    Absolute dating of planetary samples is an essential tool to establish the chronology of geological events, including crystallization history, magmatic evolution, and alteration. Thus far, radiometric geochronology of planetary samples has only been accomplishable in terrestrial laboratories on samples from dedicated sample return missions and meteorites. In situ instruments to measure rock ages have been proposed, but none have yet reached TRL 6, because isotopic measurements with sufficient resolution are challenging. We have begun work under the NASA Planetary Instrument Definition and Development Program (PIDDP) to develop the Potassium (K) - Argon Laser Experiment (KArLE), a novel combination of several flight-proven components that will enable accurate KAr isochron dating of planetary rocks. KArLE will ablate a rock sample, measure the K in the plasma state using laser-induced breakdown spectroscopy (LIBS), measure the liberated Ar using quadrupole mass spectrometry (QMS), and relate the two by measuring the volume of the abated pit using a optical methods such as a vertical scanning interferometer (VSI). Our preliminary work indicates that the KArLE instrument will be capable of determining the age of several kinds of planetary samples to 100 Myr, sufficient to address a wide range of geochronology problems in planetary science. Additional benefits derive from the fact that each KArLE component achieves analyses common to most planetary surface missions.

  20. Re-Os geochronology and coupled Os-Sr isotope constraints on the Sturtian snowball Earth

    PubMed Central

    Rooney, Alan D.; Macdonald, Francis A.; Strauss, Justin V.; Dudás, Francis Ö.; Hallmann, Christian; Selby, David

    2014-01-01

    After nearly a billion years with no evidence for glaciation, ice advanced to equatorial latitudes at least twice between 717 and 635 Mya. Although the initiation mechanism of these Neoproterozoic Snowball Earth events has remained a mystery, the broad synchronicity of rifting of the supercontinent Rodinia, the emplacement of large igneous provinces at low latitude, and the onset of the Sturtian glaciation has suggested a tectonic forcing. We present unique Re-Os geochronology and high-resolution Os and Sr isotope profiles bracketing Sturtian-age glacial deposits of the Rapitan Group in northwest Canada. Coupled with existing U-Pb dates, the postglacial Re-Os date of 662.4 ± 3.9 Mya represents direct geochronological constraints for both the onset and demise of a Cryogenian glaciation from the same continental margin and suggests a 55-My duration of the Sturtian glacial epoch. The Os and Sr isotope data allow us to assess the relative weathering input of old radiogenic crust and more juvenile, mantle-derived substrate. The preglacial isotopic signals are consistent with an enhanced contribution of juvenile material to the oceans and glacial initiation through enhanced global weatherability. In contrast, postglacial strata feature radiogenic Os and Sr isotope compositions indicative of extensive glacial scouring of the continents and intense silicate weathering in a post–Snowball Earth hothouse. PMID:24344274

  1. Paleontology and geochronology of the Long Beach core sites and monitoring wells, Long Beach, California

    USGS Publications Warehouse

    McDougall, Kristin; Hillhouse, John; Powell, Charles; Mahan, Shannon; Wan, Elmira; Sarna-Wojcicki, Andrei M.

    2012-01-01

    The U.S. Geological Survey's Focus on Quaternary Stratigraphy in Los Angeles (FOQUS-LA) project was a cooperative coring program between Federal, State, and local agencies. It was designed to provide a better understanding of earthquake potentials and to develop a stratigraphic model of the western Los Angeles Basin in California. The biostratigraphic, geochronologic, and paleoecologic analyses of eight wells drilled during the FOQUS-LA project are presented. These analyses are based on microfossils (benthic and planktic foraminifers), macrofossils, paleomagnetic stratigraphy, optically stimulated luminescence, thermoluminescence, radiocarbon dating, and tephrochronology. A geochronologic framework (incorporating paleomagnetism, luminescence, and tephrochronology) was used to calibrate the sequence stratigraphic units in the FOQUS-LA wells and also was used to calibrate the ages of the microfossil stage and zonal boundaries. The results of this study show that (1) the offshore California margin zones can be used in a nearshore setting, and (2) the California margin zonal scheme refines the chronostratigraphic resolution of the benthic foraminiferal biostratigraphic framework for the Pacific Coast. Benthic foraminiferal stages are modified by the recognition of an early Hallian substage, which is a faunal change recognized throughout the Los Angeles Basin. Although no detailed macrofossil zonations exist for the Quaternary of southern California, several species, whose distribution is regulated by the climatic conditions, are useful as secondary marker species in the shallower water deposits of the Los Angeles Basin.

  2. Paleomagnetic and 40Ar/39Ar geochronologic data from late Proterozoic mafic dikes and sills, Montana and Wyoming

    USGS Publications Warehouse

    Harlan, Stephen S.; Geissman, John William; Snee, Lawrence W.

    1997-01-01

    Paleomagnetic and 40Ar/39Ar results from mafic dikes and sills in northwestern Wyoming and western Montana yield similar virtual geomagnetic poles and isotopic dates. In combination with paleomagnetic and geochronologic data from elsewhere in the western Cordillera, these data provide evidence for a regional mafic magnetic event at 780 to 770 Ma that affected a large area of western North America.

  3. Continued Development of in Situ Geochronology for Planetary Using KArLE (Potassium-Argon Laser Experiment)

    NASA Technical Reports Server (NTRS)

    Devismes, D.; Cohen, B. A.

    2016-01-01

    Geochronology is a fundamental measurement for planetary samples, providing the ability to establish an absolute chronology for geological events, including crystallization history, magmatic evolution, and alteration events, and providing global and solar system context for such events. The capability for in situ geochronology will open up the ability for geochronology to be accomplished as part of lander or rover complement, on multiple samples rather than just those returned. An in situ geochronology package can also complement sample return missions by identifying the most interesting rocks to cache or return to Earth. The K-Ar radiometric dating approach to in situ dating has been validated by the Curiosity rover on Mars as well as several laboratories on Earth. Several independent projects developing in situ rock dating for planetary samples, based on the K-Ar method, are giving promising results. Among them, the Potassium (K)-Argon Laser Experiment (KArLE) at MSFC is based on techniques already in use for in planetary exploration, specifically, Laser-induced Breakdown Spectroscopy (LIBS, used on the Curiosity Chemcam), mass spectroscopy (used on multiple planetary missions, including Curiosity, ExoMars, and Rosetta), and optical imaging (used on most missions).

  4. Geochronological and lead-isotope evidences for rapid crust formation in middle-proterozoic time: The Labrador example

    NASA Technical Reports Server (NTRS)

    Schaerer, Urs

    1988-01-01

    Extensive U-Pb geochronological studies in the Grenville and Makkovik provinces have shown that eastern Labrador is underlain by two distinct crustal blocks. In order to substantiate the juvenile character of the middle-Proterozoic crustal block, the isotopic compositon of lead in leached k-feldspars from the same rocks were analyzed. The results of the analysis are briefly discussed.

  5. “AgeFinder”: A Mac OS X computer program to evaluate electron microprobe data of monazite for chemical age dating

    NASA Astrophysics Data System (ADS)

    Appel, Peter

    2010-04-01

    A computer program is presented that can be used to obtain ages of geological significance from compositional data of monazite. The program calculates dates and their errors from U, Th and Pb concentration data obtained with the electron microprobe. The results can be displayed in isochron and gauss curve diagrams. Subsets of the data can be selected and interactively evaluated with a user friendly graphical interface. For each selected data set a cumulative date, an isochron date, their errors and the mean squared weighted deviates (MSWD) are calculated and a chi-square test is performed. The diagrams can be saved to pdf and all calculated data can be exported to a text file or saved in native format. The software runs on any Apple Macintosh with Mac OS X Tiger or later versions.

  6. Lanthanide (Nd, Gd) compounds with garnet and monazite structures. Powders synthesis by "wet" chemistry to sintering ceramics by Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Potanina, Ekaterina; Golovkina, Ludmila; Orlova, Albina; Nokhrin, Aleksey; Boldin, Maksim; Sakharov, Nikita

    2016-05-01

    Complex oxide Y2.5Nd0.5Al5O12 with garnet structure and phosphates NdPO4 and GdPO4 with monazite structure were obtained by using precipitation methods. Ceramics Y2.5Nd0.5Al5O12 and NdPO4 were processed by Spark Plasma Sintering (SPS). Relative density more 98%, sintering time did not exceed 8 min, sintering temperature 1330-1390 °C. Leaching rates of elements from ceramics were 10-6-10-7 g/(cm2 d). The process of ceramics sintering has two-stage character: the first step of sintering-compaction process is related to the plastic flow of the material, the second step-to the process of grain boundary diffusion and grain growth.

  7. Linking bacterial diversity and geochemistry of uranium-contaminated groundwater.

    PubMed

    Cho, Kelly; Zholi, Alma; Frabutt, Dylan; Flood, Matthew; Floyd, Dalton; Tiquia, Sonia M

    2012-01-01

    To understand the link between bacterial diversity and geochemistry in uranium-contaminated groundwater, microbial communities were assessed based on clone libraries of 16S rDNA genes from the USDOE Oak Ridge Field Research Centre (FRC) site. Four groundwater wells (GW835, GW836, FW113-47 and FW215-49) with a wide range of pH (3 to 7), nitrate (44 to 23,400 mg L(-1)), uranium (0.73 to 60.36 mg L(-1)) and other metal contamination, were investigated. Results indicated that bacterial diversity correlated with the geochemistry of the groundwater. Microbial diversity decreased in relation to the contamination levels of the wells. The highly contaminated well (FW113-47) had lower gene diversity than less contaminated wells (FW215-49, GW835 and GW836). The high concentrations of contaminants present in well FW113-47 stimulated the growth of organisms capable of reducing uranium (Shewanella and Pseudomonas), nitrate (Pseudomonas, Rhodanobacter and Xanthomonas) and iron (Stenotrophomonas), and which were unique to this well. The clone libraries consisted primarily of sequences closely related to the phylum Proteobacteria, with FW-113-47 almost exclusively containing this phylum. Metal-reducing bacteria were present in all four wells, which may suggest that there is potential for successful bioremediation of the groundwater at the Oak Ridge FRC. The microbial community information gained from this study and previous studies at the site can be used to develop predictive multivariate and geographical information system (GIS) based models for microbial populations at the Oak Ridge FRC. This will allow for a better understanding of what organisms are likely to occur where and when, based on geochemistry, and how these organisms relate to bioremediation processes at the site.

  8. Hydroxamic acid interactions with solvated cerium hydroxides in the flotation of monazite and bastnäsite-Experiments and DFT study

    NASA Astrophysics Data System (ADS)

    Sarvaramini, A.; Azizi, D.; Larachi, F.

    2016-11-01

    Density functional theory (DFT) simulations and experiments were performed to clarify the interaction mechanisms between hydroxamic acid collectors and cerium hydroxides during the flotation of bastnäsite and monazite minerals. These minerals showed considerable floatability at moderately alkaline pH which was related to the adsorption of hydroxamic acids on their surfaces as confirmed by vibrational spectroscopic and zeta potential measurements. DFT simulations showed that at moderately alkaline pH, the interactions between solvated Ce(OH)2+ and Ce(OH)2+ and heptyl-hydroxamic acid (HHA) anions resulted in the formation of, respectively, [Ce(OH)(HHA)x(H2O)y]2-x (x[y = ] = 1[6],2[3],3[1]) and [Ce(OH)2(HHA)x(H2O)y]1-x (x[y = ] = 1[5],2[1],3[0]) complexes. The collector anions were found to interact directly through formation of two covalent bonds between their two polar-head oxygen atoms and cerium in the hydroxide complexes. However, formation of such new bonds resulted in breakage of a few covalent/electrostatic bonds between cerium and water molecules initially present in the first hydration shell of the rare-earth metal cation. Building up in the electric double layer of the semi-soluble minerals, these complexes, and by extension, those from other rare-earth elements belonging to monazite and bastnäsite, are speculated to play a role in the interactions between rare-earth minerals and hydroxamic acid collectors.

  9. Private Collection of Geochemistry and Oceanography Articles Available

    NASA Astrophysics Data System (ADS)

    Manheim, Frank T.

    2014-05-01

    It's time! I'm disposing of a 37-year career's worth of books and other scientific materials in geochemistry and oceanography. Ordinarily, reprints of articles have little value. However, in the course of my research, I assembled what may be the world's most comprehensive private collection of articles on marine ferromanganese deposits up to the late 1980s. It includes foreign language materials, especially Russian language articles. Soviet researchers played an active role in this field (I cooperated with them and was a guest of the Soviet Academy).

  10. The Apollo 16 Mare Component: Petrography, Geochemistry, and Provenance

    NASA Technical Reports Server (NTRS)

    Zeigler, R. A.; Haskin, L. A.; Korotev, R. L.; Jolliff, B. L.; Gillis, J. J.

    2003-01-01

    The A16 (Apollo16) site in the lunar nearside highlands is 220 km from the nearest mare. Thus it is no surprise that mare basalt samples are uncommon at the site. Here, we present the petrography and geochemistry of 5 new mare basalt samples found at the A16 site. We also discuss possible provenances of all A16 mare basalt samples using high-resolution global data for the distribution of Fe and Ti on the lunar surface derived from Clementine UV-VIS data [1-2].

  11. Infrared Spectroscopy and Stable Isotope Geochemistry of Hydrous Silicate Glasses

    SciTech Connect

    Stolper, Edward

    2007-03-05

    The focus of this DOE-funded project has been the study of volatile components in magmas and the atmosphere. Over the twenty-one year period of this project, we have used experimental petrology and stable isotope geochemistry to study the behavior and properties of volatile components dissolved in silicate minerals and melts and glasses. More recently, we have also studied the concentration and isotopic composition of CO2 in the atmosphere, especially in relation to air quality issues in the Los Angeles basin.

  12. Southern complex: geology, geochemistry, mineralogy, and mineral chemistry of selected uranium- and thorium-rich granites

    SciTech Connect

    Hoffman, M.A.

    1987-01-01

    Four major rock groups are defined in the Southern Complex: the Bell Creek Granite (BCG), the Clotted Granitoids (CGR), the Albite Granite (AGR), and the Migmatite Complex. Metatexites of the Migmatite Complex are the oldest rocks and include paleosome of a metasedimentary and metavolcanic protolith represented by Banded Iron Formation, Banded Amphibolite, and Banded Gneisses, and interlayered or crosscutting leucogranites. The CGR span the range from metatexite to diatexite and represent in-situ partial melting of metapelitic layers in the protolith during intrusion of the BCG. The BCG cuts the migmatites, is locally cut by the CGR, and was derived by partial melting of a dominantly metasedimentary protolith at some depth below the presently exposed migmatites during a regional tectonothermal event. The Albite Granite is a 2km diameter, muscovite-fluorite-columbite-bearing