The Experts below are selected from a list of 117 Experts worldwide ranked by ideXlab platform
Mark D. Barton - One of the best experts on this subject based on the ideXlab platform.
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Mineralogical thallium geochemistry and isotope variations from igneous, metamorphic, and Metasomatic systems
Geochimica et Cosmochimica Acta, 2018Co-Authors: Shelby T. Rader, Frank K. Mazdab, Mark D. BartonAbstract:Abstract This study presents new thallium (Tl) concentration and isotopic composition data for potassium feldspar (K-feldspar), micas, sulfides, and other minerals using solution multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS). The samples studied represent a diverse set of igneous, metamorphic, and Metasomatic Rock types. Purified separates of minerals anticipated to be Tl-bearing were analyzed; in many cases coexisting minerals were measured to examine the distribution of Tl and its isotopes between coexisting phases. This study is the first of its kind to document mineralogical controls on Tl chemical and isotopic fractionation. Thallium contents in Rock-forming minerals and common sulfides vary from below detection limit (here, approximately 0.2 ppm Tl in the mineral utilizing an IsoProbe MC-ICP-MS) to 3200 ppm. In this present study, mica and feldspar samples can reach Tl concentrations well over 20 ppm, compared to only 0.7 ppm in average crust. In contrast, only 14 of 38 common sulfide samples contain Tl at levels above the detection limit. Measured Tl isotope ratios, reported as e205Tl relative to the NIST 997 standard solution, range from −12.1 ± 0.6 to +18.0 ±1.4 (2σ). Most samples analyzed fall within the published range of e205Tl (−20 to +15) (Nielsen et al., 2017). Although most sulfides show limited Tl enrichment, they display the highest e205Tl values among coexisting minerals, with Fe-rich micas having the lowest e205Tl values. The patterns in enrichment are best interpreted to reflect crystal chemical differences and the incompatible, dominantly lithophile nature of Tl. In turn, isotopic fractionation also reflects control by the bonding environment as well as redox conditions. The preferential distribution of Tl into micas and K-feldspar found here is consistent with the similarity in charge and ionic radius of Tl+ and K+. The higher e205Tl values in sulfides agree with previous observations and theoretical studies showing the tendency of covalent bonds, high bond strengths, and high oxidation states to favor heavy isotopes. This work highlights important areas for future research regarding the natural weathering of Tl-bearing substrates, understanding regional cycling of Tl, and potential bioremediation of Tl contamination.
Yu. V. Shchegol’kov - One of the best experts on this subject based on the ideXlab platform.
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Cation migration in hydrothermal clays: The problem of mineralization criteria in gas-hydrothermal fluids of hydrothermal fields in Southern Kamchatka
Journal of Volcanology and Seismology, 2012Co-Authors: S. N. Rychagov, R. G. Davletbaev, O. V. Kovina, M. S. Chernov, V. N Sokolov, A. V. Sergeeva, Yu. V. Shchegol’kovAbstract:Based on a comprehensive study of the hydrothermal clay layer that occurs in geothermal fields, the conditions of formation of cation composition in argillitized Rocks are discussed. Under the influence of gas-water fluids and pore solutions, micro- and nano-mineral mixtures are formed in hydrothermal clays; these mixtures include crystalline, amorphous, and transitional mineral phases. A considerable role in their composition belongs to cations of several metals (Fe, Al, Ti, Na, Mg, Ca, K, Mn, and Ba), as well as Si, C, N, S, and volatiles (F^− and Cl^−). The sources of cations and other elements are unaltered host Rocks, newly formed hydrothermal-Metasomatic Rocks, hydrothermal clays, salt deposits, siliceous, carbonate, and other sediments, as well as deep fluids. In the structures of geothermal anomalies and deposits the “hydrothermal Metasomatic Rock—gas-water fluid—newly formed mineral chemical compounds” united system is formed. Each of the elements of this system takes part in the transportation, accumulation, and redistribution of metals. This approach to studies of the geochemistry of present-day geothermal systems may serve as a foundation for developing criteria for the presence of mineralization in metasomatites, gas-hydrothermal fluids, and new mineral associations.
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Cation migration in hydrothermal clays: The problem of mineralization criteria in gas-hydrothermal fluids of hydrothermal fields in Southern Kamchatka
Journal of Volcanology and Seismology, 2012Co-Authors: S. N. Rychagov, R. G. Davletbaev, O. V. Kovina, M. S. Chernov, V. N Sokolov, A. V. Sergeeva, Yu. V. Shchegol’kovAbstract:Based on a comprehensive study of the hydrothermal clay layer that occurs in geothermal fields, the conditions of formation of cation composition in argillitized Rocks are discussed. Under the influence of gas-water fluids and pore solutions, micro- and nano-mineral mixtures are formed in hydrothermal clays; these mixtures include crystalline, amorphous, and transitional mineral phases. A considerable role in their composition belongs to cations of several metals (Fe, Al, Ti, Na, Mg, Ca, K, Mn, and Ba), as well as Si, C, N, S, and volatiles (F^− and Cl^−). The sources of cations and other elements are unaltered host Rocks, newly formed hydrothermal-Metasomatic Rocks, hydrothermal clays, salt deposits, siliceous, carbonate, and other sediments, as well as deep fluids. In the structures of geothermal anomalies and deposits the “hydrothermal Metasomatic Rock—gas-water fluid—newly formed mineral chemical compounds” united system is formed. Each of the elements of this system takes part in the transportation, accumulation, and redistribution of metals. This approach to studies of the geochemistry of present-day geothermal systems may serve as a foundation for developing criteria for the presence of mineralization in metasomatites, gas-hydrothermal fluids, and new mineral associations.
Toshiaki Tsunogae - One of the best experts on this subject based on the ideXlab platform.
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Fluid-induced high-temperature metasomatism at Rundvågshetta in the Lützow-Holm Complex, East Antarctica: Implications for the role of brine during granulite formation
Elsevier, 2018Co-Authors: Kazuki Takahashi, Toshiaki Tsunogae, Emmanuel Nwachukwu UgwuonahAbstract:We report new petrological, phase equilibria modeling, and fluid inclusion data for pelitic and mafic granulites from Rundvågshetta in the highest-grade region of the Neoproterozoic Lützow-Holm Complex (LHC), East Antarctica, and provide unequivocal evidence for fluid-Rock interaction and high-temperature metasomatism in the presence of brine fluid. The studied locality is composed dominantly of well-foliated pelitic granulite (K-feldspar + quartz + sillimanite + garnet + ilmenite) with foliation-parallel bands and/or layers of mafic granulite (plagioclase + orthopyroxene + garnet + ilmenite + quartz + biotite). The boundary between the two lithologies is defined by thin (about 1–20 cm in thick) garnet-rich layers with a common mineral assemblage of garnet + plagioclase + quartz + ilmenite + biotite ± orthopyroxene. Systematic increase of grossular and decrease of pyrope contents in garnet as well as decreasing Mg/(Fe + Mg) ratio of biotite from the pelitic granulite to garnet-rich Rock and mafic granulite suggest that the garnet-rich layer was formed by Metasomatic interaction between the two granulite lithologies. Phase equilibria modeling in the system NCKFMASHTO demonstrates that the metasomatism took place at 850–860 °C, which is slightly lower than the peak metamorphism of this region, and the modal abundance of garnet is the highest along the metapelite–metabasite boundary (up to 40%), which is consistent with the field and thin section observations. The occurrence of brine (7.0–10.9 wt.% NaCleq for ice melting or 25.1–25.5 wt.% NaCleq for hydrohalite melting) fluid inclusions as a primary phase trapped within plagioclase in the garnet-rich layer and the occurrence of Cl-rich biotite (Cl = 0.22–0.60 wt.%) in the Metasomatic Rock compared to that in pelitic (0.15–0.24 wt.%) and mafic (0.06–0.13 wt.%) granulites suggest infiltration of brine fluid could have given rise to the high-temperature metasomatism. The fluid might have been derived from external sources possibly related to the formation of major suture zones formed during the Gondwana amalgamation. Keywords: High-temperature metasomatism, Brine, Phase equilibrium modeling, Fluid inclusion, Gondwana, Lützow-Holm Comple
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Multiple magmatism in an evolving suprasubduction zone mantle wedge: The case of the composite mafic–ultramafic complex of Gaositai, North China Craton
Lithos, 2017Co-Authors: Fan Yang, Toshiaki Tsunogae, M. Santosh, Li Tang, Xue-ming TengAbstract:Abstract The suprasubduction zone mantle wedge of active convergent margins is impregnated by melts and fluids leading to the formation of a variety of magmatic and Metasomatic Rock suites. Here we investigate a composite mafic–ultramafic intrusion at Gaositai, in the northern margin of the North China Craton (NCC). The hornblende gabbro–serpentinite–dunite–pyroxenite–gabbro–diorite suite surrounded by hornblendites of this complex has long been considered to represent an “Alaskan-type” zoned pluton. We present petrologic, mineral chemical, geochemical and zircon U–Pb and Lu–Hf data from the various Rock types from Gaositai including hornblende gabbro, serpentinite, dunite, pyroxenite, diorite and the basement hornblendite which reveal the case of multiple melt generation and melt–peridotite interaction. Our new mineral chemical data from the mafic–ultramafic suite exclude an “Alaskan-type” affinity, and the bulk geochemical features are consistent with subduction-related magmatism with enrichment of LILE (K, Rb, and Ba) and LREE (La and Ce), and depletion of HFSE (Nb, Ta, Zr, and Hf) and HREE. Zircon U–Pb geochronology reveals that the hornblendites surrounding the Gaositai complex are nearly 2 billion years older than the intrusive complex and yield early Paleoproterozoic emplacement ages (2433–2460 Ma), followed by late Paleoproterozoic metamorphism (1897 Ma). The serpentinites trace the history of a long-lived and replenished ancient sub-continental lithospheric mantle with the oldest zircon population dated as 2479 Ma and 1896 Ma, closely corresponding with the ages obtained from the basement Rock, followed by Neoproterozoic and Phanerozoic zircon growth. The oldest member in the Gaositai composite intrusion is the dunite that yields emplacement age of 755 Ma, followed by pyroxenite formed through the interaction of slab melt and wedge mantle peridotite at 401 Ma. All the Rock suites also carry multiple population of younger zircons ranging in age from Paleozoic to Mesozoic, suggesting continuous mantle metasomatism through melts and fluids associated with prolonged subduction, which is also substantiated by the pervasive hydration of all the ultramafic units. Zircon Lu–Hf isotopic data from the basement Rock (hornblendite) on concordant grains yield eHf(t) values in the range of − 23.8 to − 5.2 with T DM of 1979–2424 Ma and T DM C between 2754 and 2899 Ma, suggesting Mesoarchean to Neoarchean reworked and juvenile sources. Concordant grains in the serpentinite also display a large range of eHf(t) values (− 5.0 to 5.8) suggesting multiple sources, whereas the concordant magmatic zircon grains in the dunite have a tight range of eHf(t) values between − 2.3 and 0.1 indicating primitive source. Those from the pyroxenite are characterized by highly negative eHf(t) values of − 21.5 to − 18.6 suggesting reworked ancient components. The diverse ages, lack of typical geochemical imprints, and magmas derived from multiple sources including Mesoarchean to Neoarchean reworked and primitive components within the same mafic–ultramafic complex exclude an “Alaskan-type” affinity and suggest multiple magmatism in an evolving and metasomatized suprasubduction zone mantle wedge. We correlate the tectonics with the prolonged subduction regime of the Paleo-Asian Ocean with melt–peridotite interaction and geologic history spanning through compression to extension.
Shelby T. Rader - One of the best experts on this subject based on the ideXlab platform.
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Mineralogical thallium geochemistry and isotope variations from igneous, metamorphic, and Metasomatic systems
Geochimica et Cosmochimica Acta, 2018Co-Authors: Shelby T. Rader, Frank K. Mazdab, Mark D. BartonAbstract:Abstract This study presents new thallium (Tl) concentration and isotopic composition data for potassium feldspar (K-feldspar), micas, sulfides, and other minerals using solution multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS). The samples studied represent a diverse set of igneous, metamorphic, and Metasomatic Rock types. Purified separates of minerals anticipated to be Tl-bearing were analyzed; in many cases coexisting minerals were measured to examine the distribution of Tl and its isotopes between coexisting phases. This study is the first of its kind to document mineralogical controls on Tl chemical and isotopic fractionation. Thallium contents in Rock-forming minerals and common sulfides vary from below detection limit (here, approximately 0.2 ppm Tl in the mineral utilizing an IsoProbe MC-ICP-MS) to 3200 ppm. In this present study, mica and feldspar samples can reach Tl concentrations well over 20 ppm, compared to only 0.7 ppm in average crust. In contrast, only 14 of 38 common sulfide samples contain Tl at levels above the detection limit. Measured Tl isotope ratios, reported as e205Tl relative to the NIST 997 standard solution, range from −12.1 ± 0.6 to +18.0 ±1.4 (2σ). Most samples analyzed fall within the published range of e205Tl (−20 to +15) (Nielsen et al., 2017). Although most sulfides show limited Tl enrichment, they display the highest e205Tl values among coexisting minerals, with Fe-rich micas having the lowest e205Tl values. The patterns in enrichment are best interpreted to reflect crystal chemical differences and the incompatible, dominantly lithophile nature of Tl. In turn, isotopic fractionation also reflects control by the bonding environment as well as redox conditions. The preferential distribution of Tl into micas and K-feldspar found here is consistent with the similarity in charge and ionic radius of Tl+ and K+. The higher e205Tl values in sulfides agree with previous observations and theoretical studies showing the tendency of covalent bonds, high bond strengths, and high oxidation states to favor heavy isotopes. This work highlights important areas for future research regarding the natural weathering of Tl-bearing substrates, understanding regional cycling of Tl, and potential bioremediation of Tl contamination.
Xue-ming Teng - One of the best experts on this subject based on the ideXlab platform.
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Multiple magmatism in an evolving suprasubduction zone mantle wedge: The case of the composite mafic–ultramafic complex of Gaositai, North China Craton
Lithos, 2017Co-Authors: Fan Yang, Toshiaki Tsunogae, M. Santosh, Li Tang, Xue-ming TengAbstract:Abstract The suprasubduction zone mantle wedge of active convergent margins is impregnated by melts and fluids leading to the formation of a variety of magmatic and Metasomatic Rock suites. Here we investigate a composite mafic–ultramafic intrusion at Gaositai, in the northern margin of the North China Craton (NCC). The hornblende gabbro–serpentinite–dunite–pyroxenite–gabbro–diorite suite surrounded by hornblendites of this complex has long been considered to represent an “Alaskan-type” zoned pluton. We present petrologic, mineral chemical, geochemical and zircon U–Pb and Lu–Hf data from the various Rock types from Gaositai including hornblende gabbro, serpentinite, dunite, pyroxenite, diorite and the basement hornblendite which reveal the case of multiple melt generation and melt–peridotite interaction. Our new mineral chemical data from the mafic–ultramafic suite exclude an “Alaskan-type” affinity, and the bulk geochemical features are consistent with subduction-related magmatism with enrichment of LILE (K, Rb, and Ba) and LREE (La and Ce), and depletion of HFSE (Nb, Ta, Zr, and Hf) and HREE. Zircon U–Pb geochronology reveals that the hornblendites surrounding the Gaositai complex are nearly 2 billion years older than the intrusive complex and yield early Paleoproterozoic emplacement ages (2433–2460 Ma), followed by late Paleoproterozoic metamorphism (1897 Ma). The serpentinites trace the history of a long-lived and replenished ancient sub-continental lithospheric mantle with the oldest zircon population dated as 2479 Ma and 1896 Ma, closely corresponding with the ages obtained from the basement Rock, followed by Neoproterozoic and Phanerozoic zircon growth. The oldest member in the Gaositai composite intrusion is the dunite that yields emplacement age of 755 Ma, followed by pyroxenite formed through the interaction of slab melt and wedge mantle peridotite at 401 Ma. All the Rock suites also carry multiple population of younger zircons ranging in age from Paleozoic to Mesozoic, suggesting continuous mantle metasomatism through melts and fluids associated with prolonged subduction, which is also substantiated by the pervasive hydration of all the ultramafic units. Zircon Lu–Hf isotopic data from the basement Rock (hornblendite) on concordant grains yield eHf(t) values in the range of − 23.8 to − 5.2 with T DM of 1979–2424 Ma and T DM C between 2754 and 2899 Ma, suggesting Mesoarchean to Neoarchean reworked and juvenile sources. Concordant grains in the serpentinite also display a large range of eHf(t) values (− 5.0 to 5.8) suggesting multiple sources, whereas the concordant magmatic zircon grains in the dunite have a tight range of eHf(t) values between − 2.3 and 0.1 indicating primitive source. Those from the pyroxenite are characterized by highly negative eHf(t) values of − 21.5 to − 18.6 suggesting reworked ancient components. The diverse ages, lack of typical geochemical imprints, and magmas derived from multiple sources including Mesoarchean to Neoarchean reworked and primitive components within the same mafic–ultramafic complex exclude an “Alaskan-type” affinity and suggest multiple magmatism in an evolving and metasomatized suprasubduction zone mantle wedge. We correlate the tectonics with the prolonged subduction regime of the Paleo-Asian Ocean with melt–peridotite interaction and geologic history spanning through compression to extension.