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Toshiaki Tsunogae - One of the best experts on this subject based on the ideXlab platform.
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petrology phase equilibria modelling and zircon u pb geochronology of garnet bearing charnockites from the miyun area implications for microblock amalgamation of the north china craton
Lithos, 2019Co-Authors: Li Tang, M Santosh, Toshiaki TsunogaeAbstract:Abstract The North China Craton (NCC) was amalgamated through Late Neoarchean amalgamation of seven microblocks along zones of ocean closure represented by granite-greenstone belts (GGB). Typical basement rocks of the Zunhua GGB between the Qianhuai and Jiaoliao microblocks are exposed in the Miyun area of the NCC. Here we report petrology, mineral chemistry, metamorphic P–T estimation and zircon U-Pb geochronology of newly identified garnet-bearing charnockites from the Miyun area. The prograde mineral assemblages are composed of quartz + biotite + clinopyroxene + plagioclase occurring as inclusions in garnet. The peak metamorphic mineral assemblages are identified as garnet + clinopyroxene + orthopyroxene + quartz + plagioclase + K-feldspar + ilmenite ± hornblende whereas the retrograde assemblages are characterized by the breakdown of garnet and formation of quartz + biotite association, together with K-feldspar moats around garnet and magnetite in the matrix. The prograde metamorphic P–T Condition is defined at
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petrogenesis of incipient charnockite in the ikalamavony sub domain south central madagascar new insights from phase equilibrium modeling
Lithos, 2017Co-Authors: Takahiro Endo, M Santosh, Toshiaki Tsunogae, E Shaji, Roger A RambelosonAbstract:Abstract Incipient charnockites representing granulite formation on a mesoscopic scale occur in the Ambodin Ifandana area of Ikalamavony sub-domain in south-central Madagascar. Here we report new petrological data from these rocks, and discuss the process of granulite formation on the basis of petrography, mineral equilibrium modeling, and fluid inclusion studies. The incipient charnockites occur as brownish patches, lenses, and layers characterized by an assemblage of biotite + orthopyroxene + K-feldspar + plagioclase + quartz + magnetite + ilmenite within host orthopyroxene-free biotite gneiss with an assemblage of biotite + K-feldspar + plagioclase + quartz + magnetite + ilmenite. Lenses and layers of calc-silicate rock (clinopyroxene + garnet + plagioclase + quartz + titanite + calcite) are typically associated with the charnockite. Coarse-grained charnockite occurs along the contact between the layered charnockite and calc-silicate rock. The application of mineral equilibrium modeling on the mineral assemblages in charnockite and biotite gneiss employing the NCKFMASHTO system as well as fluid inclusion study on coarse-grained charnockite defines a P–T range of 8.5–10.5 kbar and 880–900 °C, which is nearly consistent with the inferred P–T Condition of the Ikalamavony sub-domain (8.0–10.5 kbar and 820–880 °C). The result of T versus H 2 O activity ( a (H 2 O)) modeling demonstrates that orthopyroxene-bearing assemblage in charnockite is stable under relatively low a (H 2 O) Condition of 0.42–0.43, which is consistent with the popular models of incipient-charnockite formation related to the lowering of water activity and stabilization of orthopyroxene through dehydration of biotite. The occurrence of calc-silicate rocks adjacent to the charnockite suggests that the CO 2 -bearing fluid that caused dehydration and incipient-charnockite formation might have been derived through decarbonation of calc-silicate rocks during the initial stage of decompression slightly after the peak metamorphism. The calc-silicate rocks might have also behaved as a cap rock that trapped CO 2 infiltrated from an external source. ‘CO 2 -rich fluid ponds’ formed beneath calc-silicate layers could have enhanced dehydration of biotite to orthopyroxene, and produced layers of coarse-grained charnockite adjacent to calc-silicate layers.
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petrology and zircon u pb geochronology of metagabbros from a mafic ultramafic suite at aniyapuram neoarchean to early paleoproterozoic convergent margin magmatism and middle neoproterozoic high grade metamorphism in southern india
Journal of Asian Earth Sciences, 2014Co-Authors: Tatsuya Koizumi, M Santosh, Toshiaki Tsunogae, Yukiyasu Tsutsumi, T R K Chetty, Yohsuke SaitohAbstract:Abstract Several mafic–ultramafic complexes occur within the Palghat-Cauvery Suture Zone (PCSZ) in southern India. The PCSZ is regarded in recent models as the zone along which crustal blocks were amalgamated during the Late Neoproterozoic–Cambrian (550–530 Ma) Gondwana assembly. Here we report petrologic and zircon U–Pb geochronologic data from gabbros associated with the Aniyapuram mafic–ultramafic suite in the central domain of the PCSZ. Geothermobarometry and pseudosection approach in the system NCFMASHTO for the metagabbro (Grt + Cpx + Opx + Hbl + Pl + Qtz + Ilm + Rt) yield peak P–T Condition of 9.8–10.6 kbar and 730–790 °C, which was followed by decompression to 6.5–8.0 kbar and ca. 750 °C as inferred from the formation of Opx + Pl symplectite around garnet, probably along a clockwise P–T path. Zircon U–Pb data analyzed by LA-ICP-MS plot along a well-defined discordia with upper and lower intercepts in the concordia at 2436 ± 22 Ma and 731 ± 11 Ma respectively, suggesting Neoarchean–Early Paleoproterozoic magmatic emplacement of the protolith and progressive Pb loss related to the Middle Neoproterozoic (Cryogenian) thermal event (or high-grade metamorphism). These results closely compare with the available Neoarchean magmatic ages of mafic–ultramafic complexes (e.g., Sittampundi, Devanur, Agali Hills, and Kanja Malai) and Middle Neoproterozoic magmatic event (e.g., Manamedu and Kadavur) in the PCSZ and adjacent granulite blocks. The 650 Ma concordia ages obtained from unzoned zircons might indicate the timing of high-grade metamorphism or post-peak hydration event. The P–T Conditions obtained from Aniyapuram are significantly lower than the high-pressure and ultrahigh-temperature Conditions of the 550–530 Ma final collisional event ( P > 14 kbar and T > 950 °C). The Middle Neoproterozoic (ca. 730 Ma or 650 Ma) high-grade metamorphism in Aniyapuram reported for the first time from the PCSZ is possibly associated with magmatism in arc tectonic setting.
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petrology fluid inclusions and metamorphic history of bhopalpatnam granulites central india
Journal of Asian Earth Sciences, 2006Co-Authors: M Santosh, Toshiaki Tsunogae, T Iki, S Vansutre, K R HariAbstract:Abstract The Bhopalpatnam granulite belt (BGB) flanks the Pranhita–Godavari (PG) rift basin with ages ranging from 1.6 to 1.9 Ga, representing a major Mesoproterozoic thermal regime in central India. We present here new results on the metamorphic P–T Conditions from garnet-bearing enderbitic charnockite and pelitic gneisses, and document the fluid regimes from detailed fluid inclusions studies in corundum and quartz in corundum-bearing gneiss and garnet–sillimanite–rutile gneiss, respectively, from this granulite belt. A peak pressure–temperature window of 8–9.5 kbar and 720–800 °C is defined by phase equilibrium considerations on garnet–clinopyroxene–plagioclase–quartz assemblages in garnet–bearing charnockite. The garnet–plagioclase–sillimanite–quartz assemblages in pelitic gneiss yield slightly lower P–T estimates of 660–720 °C at 4.7–6.5 kbar. Primary fluid inclusions in corundum comprise monophase carbonic inclusions with melting temperatures varying from −56.6 to −57.4 °C, indicating that the dominant part of the trapped fluid is pure CO 2 . The inclusions homogenize into the liquid phase at temperatures in the range of −18.5 to −5.9 °C (1.024–0.961 g/cm 3 ). Fluid inclusions in quartz from garnet–sillimanite–rutile gneiss correspond to two categories; Group I (primary) and Group II (pseudosecondary). Both the groups show melting temperatures in the range of −55.9 to −62.9 °C, suggesting the presence of traces of other volatiles (CH 4 /N 2 ) in addition to CO 2 . The homogenization temperature of Group I inclusions ranges from −46.3 to −0.1 °C, the extreme low homogenizations indicating very high-density (up to 1.140 g/cm 3 ) for the carbonic fluid. Group II inclusions show higher homogenization temperatures of up to 16.2 °C. The estimated CO 2 isochore for primary inclusions in corundum and quartz intersects the peak P–T Condition of the BGB derived from mineral phase equilibria. We therefore, infer that CO 2 was the dominant fluid species that was trapped at or near the peak metamorphic Conditions in BGB. The metamorphic and fluid regimes, as well as the exhumation history of this granulite belt are thus constrained from a combination of petrologic and fluid inclusion studies.
M Santosh - One of the best experts on this subject based on the ideXlab platform.
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petrology phase equilibria modelling and zircon u pb geochronology of garnet bearing charnockites from the miyun area implications for microblock amalgamation of the north china craton
Lithos, 2019Co-Authors: Li Tang, M Santosh, Toshiaki TsunogaeAbstract:Abstract The North China Craton (NCC) was amalgamated through Late Neoarchean amalgamation of seven microblocks along zones of ocean closure represented by granite-greenstone belts (GGB). Typical basement rocks of the Zunhua GGB between the Qianhuai and Jiaoliao microblocks are exposed in the Miyun area of the NCC. Here we report petrology, mineral chemistry, metamorphic P–T estimation and zircon U-Pb geochronology of newly identified garnet-bearing charnockites from the Miyun area. The prograde mineral assemblages are composed of quartz + biotite + clinopyroxene + plagioclase occurring as inclusions in garnet. The peak metamorphic mineral assemblages are identified as garnet + clinopyroxene + orthopyroxene + quartz + plagioclase + K-feldspar + ilmenite ± hornblende whereas the retrograde assemblages are characterized by the breakdown of garnet and formation of quartz + biotite association, together with K-feldspar moats around garnet and magnetite in the matrix. The prograde metamorphic P–T Condition is defined at
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petrogenesis of incipient charnockite in the ikalamavony sub domain south central madagascar new insights from phase equilibrium modeling
Lithos, 2017Co-Authors: Takahiro Endo, M Santosh, Toshiaki Tsunogae, E Shaji, Roger A RambelosonAbstract:Abstract Incipient charnockites representing granulite formation on a mesoscopic scale occur in the Ambodin Ifandana area of Ikalamavony sub-domain in south-central Madagascar. Here we report new petrological data from these rocks, and discuss the process of granulite formation on the basis of petrography, mineral equilibrium modeling, and fluid inclusion studies. The incipient charnockites occur as brownish patches, lenses, and layers characterized by an assemblage of biotite + orthopyroxene + K-feldspar + plagioclase + quartz + magnetite + ilmenite within host orthopyroxene-free biotite gneiss with an assemblage of biotite + K-feldspar + plagioclase + quartz + magnetite + ilmenite. Lenses and layers of calc-silicate rock (clinopyroxene + garnet + plagioclase + quartz + titanite + calcite) are typically associated with the charnockite. Coarse-grained charnockite occurs along the contact between the layered charnockite and calc-silicate rock. The application of mineral equilibrium modeling on the mineral assemblages in charnockite and biotite gneiss employing the NCKFMASHTO system as well as fluid inclusion study on coarse-grained charnockite defines a P–T range of 8.5–10.5 kbar and 880–900 °C, which is nearly consistent with the inferred P–T Condition of the Ikalamavony sub-domain (8.0–10.5 kbar and 820–880 °C). The result of T versus H 2 O activity ( a (H 2 O)) modeling demonstrates that orthopyroxene-bearing assemblage in charnockite is stable under relatively low a (H 2 O) Condition of 0.42–0.43, which is consistent with the popular models of incipient-charnockite formation related to the lowering of water activity and stabilization of orthopyroxene through dehydration of biotite. The occurrence of calc-silicate rocks adjacent to the charnockite suggests that the CO 2 -bearing fluid that caused dehydration and incipient-charnockite formation might have been derived through decarbonation of calc-silicate rocks during the initial stage of decompression slightly after the peak metamorphism. The calc-silicate rocks might have also behaved as a cap rock that trapped CO 2 infiltrated from an external source. ‘CO 2 -rich fluid ponds’ formed beneath calc-silicate layers could have enhanced dehydration of biotite to orthopyroxene, and produced layers of coarse-grained charnockite adjacent to calc-silicate layers.
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petrology and zircon u pb geochronology of metagabbros from a mafic ultramafic suite at aniyapuram neoarchean to early paleoproterozoic convergent margin magmatism and middle neoproterozoic high grade metamorphism in southern india
Journal of Asian Earth Sciences, 2014Co-Authors: Tatsuya Koizumi, M Santosh, Toshiaki Tsunogae, Yukiyasu Tsutsumi, T R K Chetty, Yohsuke SaitohAbstract:Abstract Several mafic–ultramafic complexes occur within the Palghat-Cauvery Suture Zone (PCSZ) in southern India. The PCSZ is regarded in recent models as the zone along which crustal blocks were amalgamated during the Late Neoproterozoic–Cambrian (550–530 Ma) Gondwana assembly. Here we report petrologic and zircon U–Pb geochronologic data from gabbros associated with the Aniyapuram mafic–ultramafic suite in the central domain of the PCSZ. Geothermobarometry and pseudosection approach in the system NCFMASHTO for the metagabbro (Grt + Cpx + Opx + Hbl + Pl + Qtz + Ilm + Rt) yield peak P–T Condition of 9.8–10.6 kbar and 730–790 °C, which was followed by decompression to 6.5–8.0 kbar and ca. 750 °C as inferred from the formation of Opx + Pl symplectite around garnet, probably along a clockwise P–T path. Zircon U–Pb data analyzed by LA-ICP-MS plot along a well-defined discordia with upper and lower intercepts in the concordia at 2436 ± 22 Ma and 731 ± 11 Ma respectively, suggesting Neoarchean–Early Paleoproterozoic magmatic emplacement of the protolith and progressive Pb loss related to the Middle Neoproterozoic (Cryogenian) thermal event (or high-grade metamorphism). These results closely compare with the available Neoarchean magmatic ages of mafic–ultramafic complexes (e.g., Sittampundi, Devanur, Agali Hills, and Kanja Malai) and Middle Neoproterozoic magmatic event (e.g., Manamedu and Kadavur) in the PCSZ and adjacent granulite blocks. The 650 Ma concordia ages obtained from unzoned zircons might indicate the timing of high-grade metamorphism or post-peak hydration event. The P–T Conditions obtained from Aniyapuram are significantly lower than the high-pressure and ultrahigh-temperature Conditions of the 550–530 Ma final collisional event ( P > 14 kbar and T > 950 °C). The Middle Neoproterozoic (ca. 730 Ma or 650 Ma) high-grade metamorphism in Aniyapuram reported for the first time from the PCSZ is possibly associated with magmatism in arc tectonic setting.
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petrology fluid inclusions and metamorphic history of bhopalpatnam granulites central india
Journal of Asian Earth Sciences, 2006Co-Authors: M Santosh, Toshiaki Tsunogae, T Iki, S Vansutre, K R HariAbstract:Abstract The Bhopalpatnam granulite belt (BGB) flanks the Pranhita–Godavari (PG) rift basin with ages ranging from 1.6 to 1.9 Ga, representing a major Mesoproterozoic thermal regime in central India. We present here new results on the metamorphic P–T Conditions from garnet-bearing enderbitic charnockite and pelitic gneisses, and document the fluid regimes from detailed fluid inclusions studies in corundum and quartz in corundum-bearing gneiss and garnet–sillimanite–rutile gneiss, respectively, from this granulite belt. A peak pressure–temperature window of 8–9.5 kbar and 720–800 °C is defined by phase equilibrium considerations on garnet–clinopyroxene–plagioclase–quartz assemblages in garnet–bearing charnockite. The garnet–plagioclase–sillimanite–quartz assemblages in pelitic gneiss yield slightly lower P–T estimates of 660–720 °C at 4.7–6.5 kbar. Primary fluid inclusions in corundum comprise monophase carbonic inclusions with melting temperatures varying from −56.6 to −57.4 °C, indicating that the dominant part of the trapped fluid is pure CO 2 . The inclusions homogenize into the liquid phase at temperatures in the range of −18.5 to −5.9 °C (1.024–0.961 g/cm 3 ). Fluid inclusions in quartz from garnet–sillimanite–rutile gneiss correspond to two categories; Group I (primary) and Group II (pseudosecondary). Both the groups show melting temperatures in the range of −55.9 to −62.9 °C, suggesting the presence of traces of other volatiles (CH 4 /N 2 ) in addition to CO 2 . The homogenization temperature of Group I inclusions ranges from −46.3 to −0.1 °C, the extreme low homogenizations indicating very high-density (up to 1.140 g/cm 3 ) for the carbonic fluid. Group II inclusions show higher homogenization temperatures of up to 16.2 °C. The estimated CO 2 isochore for primary inclusions in corundum and quartz intersects the peak P–T Condition of the BGB derived from mineral phase equilibria. We therefore, infer that CO 2 was the dominant fluid species that was trapped at or near the peak metamorphic Conditions in BGB. The metamorphic and fluid regimes, as well as the exhumation history of this granulite belt are thus constrained from a combination of petrologic and fluid inclusion studies.
Xu Chu - One of the best experts on this subject based on the ideXlab platform.
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phase equilibria modelling using major and trace element compositions of zoned garnet and clinopyroxene from southwestern tianshan eclogites china
Journal of Asian Earth Sciences, 2017Co-Authors: Lijuan Zhang, Xu Chu, Lifei ZhangAbstract:Abstract We present major and trace element zoning in clinopyroxene and garnet in the low-temperature eclogites from southwestern Tianshan ultrahigh-pressure metamorphic belt. The clinopyroxene crystals in the matrix exhibit three distinct growth zones, including the aegirine-rich core, a transition mantle and the omphacite rim. The aegirine core has weak Ce anomaly, flat light rare earth element pattern, and slightly enriched heavy rare earth element contents. The omphacite rim has lower trace element contents, and is depleted in large-ion lithospheric elements, light and heavy rare earth elements. The garnet zonation is featured by the core-to-rim increase in pyrope and grossular contents, and distinct rare earth element patterns: the core has left-leaning rare earth element patterns and the rim is depleted in both light and heavy rare earth elements. Phase equilibria modelling based on the phase assemblage and mineral zoning patterns reveal that the aegirine eclogite was heated and buried along the ca. 8 °C/km geotherm in the cold subduction zone, and reached the peak metamorphic Condition of 23–25 kbar, 540–560 °C. The jadeite content in the clinopyroxene increases along the prograde-to-exhumation P-T path (Jd: from 0.25 to 0.45), with the transitional mantle corresponds to the peak Conditions. The omphacite rim with the highest jadeite content (Jd ∼ 45) formed during decompression. For a Fe3+-rich clinopyroxene, the maximum in Jd component does not necessarily represent the peak pressure, so the conventional thermobarometers should be used with caution for mineral assemblages with such complicated zonation patterns. The variation of oxygen fugacity correlates with the changes in mineral assemblage, P-T Condition, and the bulk-rock Fe3+/FeT ratio. The oxygen fugacity is not always positively correlated with the Fe3+/(Fe3+ + Al) or Fe3+/FeT ratio in clinopyroxene. Rare earth element zoning garnet and clinopyroxene are modelled based on mass balance. The modelled growth zonation closely resembles the observed compositional profiles, suggesting that rare earth elements are passively distributed among phases near chemical equilibrium during the mineral growth.
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Phase equilibria modelling using major and trace element compositions of zoned garnet and clinopyroxene from southwestern Tianshan eclogites, China
JOURNAL OF ASIAN EARTH SCIENCES, 2017Co-Authors: Zhang Lijuan, Xu Chu, Zhang Lifei, Du JinxueAbstract:We present major and trace element zoning in clinopyroxene and garnet in the low-temperature eclogites from southwestern Tianshan ultrahigh-pressure metamorphic belt. The clinopyroxene crystals in the matrix exhibit three distinct growth zones, including the aegirine-rich core, a transition mantle and the omphacite rim. The aegirine core has weak Ce anomaly, flat light rare earth element pattern, and slightly enriched heavy rare earth element contents. The omphacite rim has lower trace element contents, and is depleted in large-ion lithospheric elements, light and heavy rare earth elements. The garnet zonation is featured by the core-to-rim increase in pyrope and grossular contents, and distinct rare earth element patterns: the core has left-leaning rare earth element patterns and the rim is depleted in both light and heavy rare earth elements. Phase equilibria modelling based on the phase assemblage and mineral zoning patterns reveal that the aegirine eclogite was heated and buried along the ca. 8 degrees C/km geotherm in the cold subduction zone, and reached the peak metamorphic Condition of 23-25 kbar, 540-560 degrees C. The jadeite content in the clinopyroxene increases along the prograde-toexhumation P-T path (Jd: from 0.25 to 0.45), with the transitional mantle corresponds to the peak Conditions. The omphacite rim with the highest jadeite content (Jd similar to 45) formed during decompression. For a Fe3+-rich clinopyroxene, the maximum in Jd component does not necessarily represent the peak pressure, so the conventional thermobarometers should be used with caution for mineral assemblages with such complicated zonation patterns. The variation of oxygen fugacity correlates with the changes in mineral assemblage, P-T Condition, and the bulk-rock Fe3+/Fe-T ratio. The oxygen fugacity is not always positively correlated with the Fe3+/(Fe3+ + Al) or Fe3+/Fe-T ratio in clinopyroxene. Rare earth element zoning garnet and clinopyroxene are modelled based on mass balance. The modelled growth zonation closely resembles the observed compositional profiles, suggesting that rare earth elements are passively distributed among phases near chemical equilibrium during the mineral growth.Major State Basic Research Development Program [2015CB856105]; National Natural Science Foundation [41330210, 41272069]SCI(E)ARTICLE,SI408-42314
J G Liou - One of the best experts on this subject based on the ideXlab platform.
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mineral evolution of a garnet pyroxenite nodule within eclogite eastern sulu ultrahigh pressure metamorphic terrane east china
Journal of Metamorphic Geology, 2005Co-Authors: T N Yang, L Zeng, J G LiouAbstract:Detailed microtextural observations and bulk chemical analysis were undertaken on a garnet-pyroxenite nodule within retrograde eclogites from the NE Sulu ultrahigh-pressure metamorphic (UHPM) terrane. The results suggest that the protolith was a cumulate from a gabbroic body. The nodule consists primarily of coarse clinopyroxene grains with a very high content of the Ca-Tschermakite molecule. Microscopic observations and back-scattered electron images (BSE) demonstrate a complicated intergrowth of clinopyroxene, garnet and ilmenite, which represents the peak metamorphic assemblage. The primary clinopyroxene grains are armoured with a thin garnet corona up to 0.5 mm wide that forms an interconnected network. Within the clinopyroxene grains, four sets of garnet lamellae are distributed along crystallographic planes; locally, a vermicular intergrowth of garnet and diopside is developed. Besides the garnet, parallel arrays of ilmenite blebs are common within the clinopyroxene. Hydrous minerals such as amphibole, zoisite and titanite formed at later stages, and replaced diopside, garnet and ilmenite respectively. The P-T Conditions determined for the formation of the garnet lamellae indicate that the garnet pyroxenite experienced UHP metamorphism at the same peak P-T Condition as its host eclogite. The very high Ca-Tschermakite content (31-34 mol.%) of the primary clinopyroxene indicates crystallization at about 9-17 kbar and 1250-1450 � C, and together with the microtextural observations, suggests that the protolith of the garnet pyroxenite was a cumulate from a former gabbroic body, in which case, the host eclogite might represent the gabbroic body.
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metamorphic evolution of kyanite staurolite bearing epidote amphibolite from the early palaeozoic oeyama belt sw japan
Journal of Metamorphic Geology, 2004Co-Authors: Tatsuki Tsujimori, J G LiouAbstract:Early Palaeozoic kyanite-staurolite-bearing epidote-amphibolites including foliated epidote-amphi- bolite (FEA), and nonfoliated leucocratic or melanocratic metagabbros (LMG, MMG), occur in the Fuko Pass metacumulate unit (FPM) of the Oeyama belt, SW Japan. Microtextural relationships and mineral chemistry define three metamorphic stages: relict granulite facies metamorphism (M1), high-P (HP) epidote-amphibolite facies metamorphism (M2), and retrogression (M3). M1 is preserved as relict Al-rich diopside (up to 8.5 wt.% Al2O3) and pseudomorphs after spinel and plagioclase in the MMG, suggesting a medium-P granulite facies Condition (0.8-1.3 GPa at > 850 � C). An unusually low-variance M2 assemblage, Hbl + Czo + Ky ± St + Pg + Rt ± Ab ± Crn, occurs in the matrix of all rock types. The presence of relict plagioclase inclusions in M2 kyanite associated with clinozoisite indicates a hydration reaction to form the kyanite-bearing M2 assemblage during cooling. The corundum-bearing phase equilibria constrain a qualitative metamorphic P-T Condition of 1.1-1.9 GPa at 550-800 � C for M2. The M2 minerals were locally replaced by M3 margarite, paragonite, plagioclase and ⁄ or chlorite. The breakdown of M2 kyanite to produce the M3 assemblage at < 0.5 GPa and 450-500 � C suggests a greenschist facies overprint during decompression. The P-T evolution of the FPMmay represent subduction of an oceanic plateau with a granulite facies lower crust and subsequent exhumation in a Pacific-type orogen.
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hydroxyl rich topaz in high pressure and ultrahigh pressure kyanite quartzites with retrograde woodhouseite from the sulu terrane eastern china
American Mineralogist, 2002Co-Authors: Ru Y Zhang, J G Liou, Jin F ShuAbstract:Hydroxyl-rich topaz was recognized in thick kyanite quartzites from both high-pressure (HP) and ultrahigh-pressure (UHP) belts of the Sulu terrane, China. These quartzites contain variable proportions of quartz, kyanite, and topaz, with minor phengite, pyrite, and rutile. Some topaz grains from the UHP belt contain abundant inclusions of oriented kyanite, whereas those from the HP belt are partially replaced by woodhouseite [CaAl 3 (PO 4 )(SO 4 )(OH) 6 ]. Most topaz crystals contain 9.5 to 13.5 wt% F [0.92–1.30 atoms per formula unit (apfu)], indicating 35–55% substitution of F by OH. Such naturally occurring, hydroxyl-rich topaz has not been previously reported. Some topaz grains from the HP belt show distinct zoning: (1) decreasing F content from narrow cores (13.3–16.5 wt%) to thick rims (9.5 wt%) or (2) oscillatory zoning (9.44–12.77 wt%). Unit-cell parameters of topaz show a positive linear correlation between the OH content and a and b as well as volume. Based on our petrologic data, the experimentally determined curve of Ky + H 2 O = topaz-OH at very high pressures, and calculated OH/(OH + F) isopleths of topaz at low pressures, the topaz with X OH ~ 0.35 from the UHP belt may have formed at P-T Conditions within the coesite stability field. The P-T Condition of HP topaz is less well constrained; its high X OH (0.40–0.55) may have been caused by lower metamorphic temperatures and higher initial X OH in comparison with UHP topaz. Hydroxyl-rich topaz together with other hydrous minerals in UHP rocks may be important carriers of H 2 O to mantle depths of 100–200 km during continental subduction.
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mineral inclusions in zircons of para and orthogneiss from pre pilot drillhole ccsd pp1 chinese continental scientific drilling project
Lithos, 2001Co-Authors: Fulai Liu, Ikuo Katayama, Jingsui Yang, Shigenori Maruyama, J G LiouAbstract:The pre-pilot drillhole CCSD-PP1, Chinese Continental Scientific Drilling Project (CCSD), with depth of 432 m, is located in the Donghai area in the southwestern Sulu terrane. The core samples are mainly comprised of paragneiss, orthogneiss and ultramafic rock with minor intercalated layers of eclogite and phengite-bearing kyanite quartzite. All analyzed paragneiss and orthogneiss samples were overprinted on amphibolite facies retrograde metamorphism. Coesite and coesite-bearing ultrahigh-pressure (UHP) mineral assemblages were identified by Raman spectroscopy and electron microprobe analysis as inclusions in zircons separated from paragneiss, eclogite and phengite-bearing kyanite quartzite samples. In the paragneiss samples, UHP mineral inclusion assemblages mainly consist of Coe+Omp+Grt+Phe, Coe+Jd+Phe+Ap preserved in the mantles (M) and rims (R) of zircons. These UHP mineral inclusion assemblages yield temperatures of 814–852 °C and pressures of ≥28 kbar, presenting the P–T Condition of UHP peak metamorphism of these country rocks. According to the mineral inclusions and cathodoluminescence images of zircons, the orthogneisses can be divided into two types: UHP (OG1) and non-UHP (OG2). In OG1 orthogneisses, low-pressure mineral inclusion assemblage, mainly consisting of Qtz+Phe+Ab+Ksp+Ap, were identified in zircon cores (C), while coesite or coesite-bearing UHP mineral inclusions were identified in the mantles (M) and rims (R) of the same zircons. These features suggest that the OG1 orthogneisses, together with the paragneisses, phengite-bearing kyanite quartzite and eclogite experienced widespread UHP metamorphism in the Sulu terrane. However, in the zircons of OG2 orthogneiss samples, no UHP mineral inclusions were found. Inclusions mainly comprised Qtz+Phe+Ap and were identified in cores (C), mantles (M) and rims (R) of OG2 zircons; the cathdoluminescence images of all analyzed zircons showed clear zonings from cores to rims. These features indicate that the OG2 orthogneisses in pre-pilot drillhole CCSD-PP1 did not experience UHP metamorphism. Therefore, we should not rule out the possibility that some orthogneisses in Sulu terrane might represent relatively low-pressure granitic intrusives emplaced after the UHP event.
Du Jinxue - One of the best experts on this subject based on the ideXlab platform.
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Phase equilibria modelling using major and trace element compositions of zoned garnet and clinopyroxene from southwestern Tianshan eclogites, China
JOURNAL OF ASIAN EARTH SCIENCES, 2017Co-Authors: Zhang Lijuan, Xu Chu, Zhang Lifei, Du JinxueAbstract:We present major and trace element zoning in clinopyroxene and garnet in the low-temperature eclogites from southwestern Tianshan ultrahigh-pressure metamorphic belt. The clinopyroxene crystals in the matrix exhibit three distinct growth zones, including the aegirine-rich core, a transition mantle and the omphacite rim. The aegirine core has weak Ce anomaly, flat light rare earth element pattern, and slightly enriched heavy rare earth element contents. The omphacite rim has lower trace element contents, and is depleted in large-ion lithospheric elements, light and heavy rare earth elements. The garnet zonation is featured by the core-to-rim increase in pyrope and grossular contents, and distinct rare earth element patterns: the core has left-leaning rare earth element patterns and the rim is depleted in both light and heavy rare earth elements. Phase equilibria modelling based on the phase assemblage and mineral zoning patterns reveal that the aegirine eclogite was heated and buried along the ca. 8 degrees C/km geotherm in the cold subduction zone, and reached the peak metamorphic Condition of 23-25 kbar, 540-560 degrees C. The jadeite content in the clinopyroxene increases along the prograde-toexhumation P-T path (Jd: from 0.25 to 0.45), with the transitional mantle corresponds to the peak Conditions. The omphacite rim with the highest jadeite content (Jd similar to 45) formed during decompression. For a Fe3+-rich clinopyroxene, the maximum in Jd component does not necessarily represent the peak pressure, so the conventional thermobarometers should be used with caution for mineral assemblages with such complicated zonation patterns. The variation of oxygen fugacity correlates with the changes in mineral assemblage, P-T Condition, and the bulk-rock Fe3+/Fe-T ratio. The oxygen fugacity is not always positively correlated with the Fe3+/(Fe3+ + Al) or Fe3+/Fe-T ratio in clinopyroxene. Rare earth element zoning garnet and clinopyroxene are modelled based on mass balance. The modelled growth zonation closely resembles the observed compositional profiles, suggesting that rare earth elements are passively distributed among phases near chemical equilibrium during the mineral growth.Major State Basic Research Development Program [2015CB856105]; National Natural Science Foundation [41330210, 41272069]SCI(E)ARTICLE,SI408-42314
