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Mu Ramkumar - One of the best experts on this subject based on the ideXlab platform.
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high ba sr adakitic charnockite suite from the nagercoil block southern india vestiges of paleoproterozoic arc and implications for columbia to gondwana
Geoscience frontiers, 2021Co-Authors: Pin Gao, M Santosh, Sanghoon Kwon, Chengxue Yang, Mu RamkumarAbstract:Abstract The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane (SGT) in India and is mainly composed of charnockitic rocks and felsic gneisses (charnockite suite). In this study, we present petrologic, geochemical, zircon U–Pb, REE, and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block. Based on field investigations and petrologic studies, the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene. The charnockites and leucogneiss show transition from Adakites to non-adakitic magmatic rocks, with enrichment in LREEs (light rare earth elements) and LILEs (large ion lithophile elements), and depletion in HREEs (heavy rare earth elements) and HFSEs (high field strength elements). Some of the charnockites and the leucogneiss show typical HSA (high silica Adakite) characters, (high SiO2, Al2O3, Ba–Sr, La/Yb, and Sr/Y). The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge. The high Ba–Sr features were possibly inherited from subducted oceanic crust melting under high thermal gradient during Precambrian. The magmas were underplated and subjected to fractional crystallization. Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims. Magmatic zircon grains from the charnockites show ages ranging from 1983 ± 8.8 Ma to 2046 ± 14 Ma, and the metamorphic domains show an age range of 502 ± 14 Ma to 547 ± 8.7 Ma. Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860 ± 20 Ma and 575.6 ± 8.8 Ma. Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma. The REE data of the zircon grains show LREE depletion and HREE enrichment, with the metamorphic grains showing more depletion in HREE. Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yielded eHf(t) values from −1.17 to 0.46 with TDM and TDMC and age peaks at 2392 Ma and 2638 Ma, suggesting Neoarchean to Paleoproterozoic juvenile sources. We suggest that the high Ba–Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent, and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic–Cambrian. Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.
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high ba sr adakitic charnockite suite from the nagercoil block southern india vestiges of paleoproterozoic arc and implications for columbia to gondwana
Geoscience frontiers, 2020Co-Authors: Pin Gao, M Santosh, Sanghoon Kwon, Chengxue Yang, Mu RamkumarAbstract:Abstract The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane (SGT) in India and is mainly composed of charnockitic rocks and felsic gneisses (charnockite suite). In this study, we present petrologic, geochemical, zircon U–Pb, REE, and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block. Based on field investigations and petrologic studies, the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene. The charnockites and leucogneiss show transition from Adakites to non-adakitic magmatic rocks, with enrichment in LREEs (light rare earth elements) and LILEs (large ion lithophile elements), and depletion in HREEs (heavy rare earth elements) and HFSEs (high field strength elements). Some of the charnockites and the leucogneiss show typical HSA (high silica Adakite) characters, (high SiO2, Al2O3, Ba–Sr, La/Yb, and Sr/Y). The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge. The high Ba–Sr features were possibly inherited from subducted oceanic crust melting under the high thermal gradient condition during Precambrian. The magmas were underplated and subjected to fractional crystallization. Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims. Magmatic zircon grains from the charnockites show ages ranging from 1983 ± 8.8 Ma to 2046 ± 14 Ma, and the metamorphic domains show an age range of 502 ± 14 Ma to 547 ± 8.7 Ma. Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860 ± 20 Ma and 575.6 ± 8.8 Ma. Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma. The REE data of the zircon grains show LREE depletion and HREE enrichment, with the metamorphic grains showing more depletion in HREE. Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yielded eHf(t) values from −1.17 to 0.46 with TDM and TC DM and age peaks at 2392 and 2638 Ma, suggesting Neoarchean to Paleoproterozoic juvenile sources. We suggest that the high Ba–Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent, and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic–Cambrian. Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.
M Santosh - One of the best experts on this subject based on the ideXlab platform.
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high ba sr adakitic charnockite suite from the nagercoil block southern india vestiges of paleoproterozoic arc and implications for columbia to gondwana
Geoscience frontiers, 2021Co-Authors: Pin Gao, M Santosh, Sanghoon Kwon, Chengxue Yang, Mu RamkumarAbstract:Abstract The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane (SGT) in India and is mainly composed of charnockitic rocks and felsic gneisses (charnockite suite). In this study, we present petrologic, geochemical, zircon U–Pb, REE, and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block. Based on field investigations and petrologic studies, the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene. The charnockites and leucogneiss show transition from Adakites to non-adakitic magmatic rocks, with enrichment in LREEs (light rare earth elements) and LILEs (large ion lithophile elements), and depletion in HREEs (heavy rare earth elements) and HFSEs (high field strength elements). Some of the charnockites and the leucogneiss show typical HSA (high silica Adakite) characters, (high SiO2, Al2O3, Ba–Sr, La/Yb, and Sr/Y). The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge. The high Ba–Sr features were possibly inherited from subducted oceanic crust melting under high thermal gradient during Precambrian. The magmas were underplated and subjected to fractional crystallization. Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims. Magmatic zircon grains from the charnockites show ages ranging from 1983 ± 8.8 Ma to 2046 ± 14 Ma, and the metamorphic domains show an age range of 502 ± 14 Ma to 547 ± 8.7 Ma. Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860 ± 20 Ma and 575.6 ± 8.8 Ma. Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma. The REE data of the zircon grains show LREE depletion and HREE enrichment, with the metamorphic grains showing more depletion in HREE. Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yielded eHf(t) values from −1.17 to 0.46 with TDM and TDMC and age peaks at 2392 Ma and 2638 Ma, suggesting Neoarchean to Paleoproterozoic juvenile sources. We suggest that the high Ba–Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent, and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic–Cambrian. Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.
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high ba sr adakitic charnockite suite from the nagercoil block southern india vestiges of paleoproterozoic arc and implications for columbia to gondwana
Geoscience frontiers, 2020Co-Authors: Pin Gao, M Santosh, Sanghoon Kwon, Chengxue Yang, Mu RamkumarAbstract:Abstract The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane (SGT) in India and is mainly composed of charnockitic rocks and felsic gneisses (charnockite suite). In this study, we present petrologic, geochemical, zircon U–Pb, REE, and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block. Based on field investigations and petrologic studies, the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene. The charnockites and leucogneiss show transition from Adakites to non-adakitic magmatic rocks, with enrichment in LREEs (light rare earth elements) and LILEs (large ion lithophile elements), and depletion in HREEs (heavy rare earth elements) and HFSEs (high field strength elements). Some of the charnockites and the leucogneiss show typical HSA (high silica Adakite) characters, (high SiO2, Al2O3, Ba–Sr, La/Yb, and Sr/Y). The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge. The high Ba–Sr features were possibly inherited from subducted oceanic crust melting under the high thermal gradient condition during Precambrian. The magmas were underplated and subjected to fractional crystallization. Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims. Magmatic zircon grains from the charnockites show ages ranging from 1983 ± 8.8 Ma to 2046 ± 14 Ma, and the metamorphic domains show an age range of 502 ± 14 Ma to 547 ± 8.7 Ma. Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860 ± 20 Ma and 575.6 ± 8.8 Ma. Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma. The REE data of the zircon grains show LREE depletion and HREE enrichment, with the metamorphic grains showing more depletion in HREE. Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yielded eHf(t) values from −1.17 to 0.46 with TDM and TC DM and age peaks at 2392 and 2638 Ma, suggesting Neoarchean to Paleoproterozoic juvenile sources. We suggest that the high Ba–Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent, and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic–Cambrian. Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.
Robert Kerrich - One of the best experts on this subject based on the ideXlab platform.
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geochemical sr nd pb and zircon hf o isotopic compositions of eocene oligocene shoshonitic and potassic Adakite like felsic intrusions in western yunnan sw china petrogenesis and tectonic implications
Journal of Petrology, 2013Co-Authors: Robert Kerrich, Campbell Mccuaig, Craig J R Hart, Peter A Cawood, Zeng Qian Hou, Leon Bagas, John B Cliff, E A Belousova, Suo Han TangAbstract:Coeval potassic Adakite-like and shoshonitic felsic intrusions in the western Yunnan province of SW China are spatially and temporally associated with Eocene^Oligocene shoshonitic mafic volcanic rocks. The shoshonitic syenite and quartz monzonite intrusions are characterized by high K2O contents (4·9^6·8 wt %) and K2O/Na2O ratios (1·1^1·7), high Y (1·7^34·8 ppm) and Yb (1·50^3·16 ppm) contents, nearly flat heavy rare earth element (HREE) patterns and moderate Eu anomalies (Eu/Eu*1⁄4 0·65^0·78).The potassic Adakite-like granite and quartz monzonite intrusions are characterized by enrichment in light rare earth elements (LREE), depletion in HREE and fractionated HREE patterns, high Sr (328^1423 ppm), Sr/Y (38^243) and La/Yb (23^62), and low Y
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precambrian arc associations boninites Adakites magnesian andesites and nb enriched basalts
Developments in Precambrian Geology, 2004Co-Authors: Ali Polat, Robert KerrichAbstract:Publisher Summary This chapter reviews the field and geochemical characteristics of recently recognized Precambrian boninites, Adakites, MA, NEB, and related arc volcanic rocks. Boninites of Phanerozoic age occur in ophiolites or intra-oceanic island arcs, such as the Izu-Bonin-Mariana arc system. These primary liquids are interpreted as second-stage high-temperature, low-pressuremelting of a depleted refractorymantle wedge fertilized by fluids and/or melts, above a subduction zone. Recent geochemical investigations of Precambrian orogenic belts have documented a great compositional diversity in subduction-related volcanic rocks. The association of Adakite, MA, and NEB flows with tholeiitic to calc-alkaline basaltsandesites in intra-oceanic arcs has recently been recognized in two 2.7 Ga greenstone belts of the Superior Province. The original stratigraphic relations between mafic and ultramafic units have been disrupted, and no primary volcanic textures such as spinifex have so far been recognized in ultramafic units. The sedimentary units consist mainly of banded iron formations, cherts, siliciclastic turbidites, and conglomerates.
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nd isotope systematics of 2 7 ga Adakites magnesian andesites and arc basalts superior province evidence for shallow crustal recycling at archean subduction zones
Earth and Planetary Science Letters, 2002Co-Authors: Ali Polat, Robert KerrichAbstract:Abstract An association of Adakite, magnesian andesite (MA), and Nb-enriched basalt (NEB) volcanic flows, which erupted within ‘normal’ intra-oceanic arc tholeiitic to calc-alkaline basalts, has recently been documented in ∼2.7 Ga Wawa greenstone belts. Large, positive initial ϵNd values (+1.95 to +2.45) of the Adakites signify that their basaltic precursors, with a short crustal residence, were derived from a long-term depleted mantle source. It is likely that the Adakites represent the melts of subducted late Archean oceanic crust. Initial ϵNd values in the MA (+0.14 to +1.68), Nb-enriched basalts and andesites (NEBA) (+1.11 to +2.05), and ‘normal’ intra-oceanic arc tholeiitic to calc-alkaline basalts and andesites (+1.44 to +2.44) overlap with, but extend to lower values than, the Adakites. Large, tightly clustered ϵNd values of the Adakites, together with Th/Ce and Ce/Yb systematics of the arc basalts that rule out sediment melting, place the enriched source in the sub-arc mantle. Accordingly, isotopic data for the MA, NEBA, and ‘normal’ arc basalts can be explained by melting of an isotopically heterogeneous sub-arc mantle that had been variably enriched by recycling of continental material into the shallow mantle in late Archean subduction zones up to 200 Ma prior to the 2.7 Ga arc. If the late Archean Wawa Adakites, MA, and basalts were generated by similar geodynamic processes as their counterparts in Cenozoic arcs, involving subduction of young and/or hot ocean lithosphere, then it is likely that late Archean oceanic crust, and arc crust, were also created and destroyed by modern plate tectonic-like geodynamic processes. This study suggests that crustal recycling through subduction zone processes played an important role for the generation of heterogeneity in the Archean upper mantle. In addition, the results of this study indicate that the Nd-isotope compositions of Archean arc- and plume-derived volcanic rocks are not very distinct, whereas Phanerozoic plumes and intra-oceanic arcs tend to have different Nd-isotopic compositions.
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magnesian andesites nb enriched basalt andesites and Adakites from late archean 2 7 ga wawa greenstone belts superior province canada implications for late archean subduction zone petrogenetic processes
Contributions to Mineralogy and Petrology, 2001Co-Authors: Ali Polat, Robert KerrichAbstract:Magnesian andesites (MA) occur with 'normal' tholeiitic to calc-alkaline basalt-andesite suites in four greenstone belts of the 2.7 Ga Wawa subprovince, Canada. Collectively, the magnesian andesites span ranges of SiO2=56–64 wt%, Mg-number=0.64–0.50, with Cr and Ni contents of 531–106 and 230–21 ppm, respectively. Relative to 'normal' andesites, the magnesian andesites form distinct trends on variation diagrams, with relatively high Th and LREE contents, uniform Yb over a range of MgO, more fractionated HREE, and lower Nb/Thpm and Nb/Lapm ratios. Niobium-enriched basalts and andesites (NEBA; Nb=7–16 ppm), and an Al-enriched rhyolite (Adakite) suite are associated in space and time with the magnesian andesites. Nb-enriched basalts and andesites are characterized by high TiO2, P2O5, Th, and Zr contents, variably high Zr/Hf (36–44) ratios, and more fractionated HREE (Gd/Ybcn=1.3–4.1) compared to the 'normal' tholeiitic to calc-alkaline basalt-andesite suites. The Adakite suite has the high Al (Al2O3=16–18 wt%), high La/Ybcn (21–43), and low Yb (0.4–1.2 ppm) of Archean tonalite-trondhjemite-granodiorite (TTG) suites and Cenozoic Adakites, indicative of liquids derived mainly from slab melting. The basalt-andesite suites are not characterized by normal tholeiitic or calc-alkaline fractionation trends of major or trace elements. Rather, compositional trends can be accounted for by some combination of fractional crystallization and variable degrees of metasomatism of the source of basalt and/or andesites by adakitic liquids. The occurrence of magnesian andesites, Nb-enriched basalts/andesites, and Adakites has been described from certain Phanerozoic arcs featuring shallow subduction of young and/or hot oceanic lithosphere. Adakites likely represent slab melts, magnesian andesites the product of hybridization of Adakite liquids with mantle peridotite, and Nb-enriched basalts/andesites melts of the residue from hybridization. Geological similarities between the late-Archean Wawa greenstone belts and certain Cenozoic transpressional orogens with the MA-NEBA-Adakite association suggest that subduction of young, hot oceanic lithosphere may have played an important role in the production of this arc-related association in the late Archean.
Pin Gao - One of the best experts on this subject based on the ideXlab platform.
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high ba sr adakitic charnockite suite from the nagercoil block southern india vestiges of paleoproterozoic arc and implications for columbia to gondwana
Geoscience frontiers, 2021Co-Authors: Pin Gao, M Santosh, Sanghoon Kwon, Chengxue Yang, Mu RamkumarAbstract:Abstract The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane (SGT) in India and is mainly composed of charnockitic rocks and felsic gneisses (charnockite suite). In this study, we present petrologic, geochemical, zircon U–Pb, REE, and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block. Based on field investigations and petrologic studies, the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene. The charnockites and leucogneiss show transition from Adakites to non-adakitic magmatic rocks, with enrichment in LREEs (light rare earth elements) and LILEs (large ion lithophile elements), and depletion in HREEs (heavy rare earth elements) and HFSEs (high field strength elements). Some of the charnockites and the leucogneiss show typical HSA (high silica Adakite) characters, (high SiO2, Al2O3, Ba–Sr, La/Yb, and Sr/Y). The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge. The high Ba–Sr features were possibly inherited from subducted oceanic crust melting under high thermal gradient during Precambrian. The magmas were underplated and subjected to fractional crystallization. Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims. Magmatic zircon grains from the charnockites show ages ranging from 1983 ± 8.8 Ma to 2046 ± 14 Ma, and the metamorphic domains show an age range of 502 ± 14 Ma to 547 ± 8.7 Ma. Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860 ± 20 Ma and 575.6 ± 8.8 Ma. Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma. The REE data of the zircon grains show LREE depletion and HREE enrichment, with the metamorphic grains showing more depletion in HREE. Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yielded eHf(t) values from −1.17 to 0.46 with TDM and TDMC and age peaks at 2392 Ma and 2638 Ma, suggesting Neoarchean to Paleoproterozoic juvenile sources. We suggest that the high Ba–Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent, and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic–Cambrian. Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.
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high ba sr adakitic charnockite suite from the nagercoil block southern india vestiges of paleoproterozoic arc and implications for columbia to gondwana
Geoscience frontiers, 2020Co-Authors: Pin Gao, M Santosh, Sanghoon Kwon, Chengxue Yang, Mu RamkumarAbstract:Abstract The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane (SGT) in India and is mainly composed of charnockitic rocks and felsic gneisses (charnockite suite). In this study, we present petrologic, geochemical, zircon U–Pb, REE, and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block. Based on field investigations and petrologic studies, the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene. The charnockites and leucogneiss show transition from Adakites to non-adakitic magmatic rocks, with enrichment in LREEs (light rare earth elements) and LILEs (large ion lithophile elements), and depletion in HREEs (heavy rare earth elements) and HFSEs (high field strength elements). Some of the charnockites and the leucogneiss show typical HSA (high silica Adakite) characters, (high SiO2, Al2O3, Ba–Sr, La/Yb, and Sr/Y). The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge. The high Ba–Sr features were possibly inherited from subducted oceanic crust melting under the high thermal gradient condition during Precambrian. The magmas were underplated and subjected to fractional crystallization. Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims. Magmatic zircon grains from the charnockites show ages ranging from 1983 ± 8.8 Ma to 2046 ± 14 Ma, and the metamorphic domains show an age range of 502 ± 14 Ma to 547 ± 8.7 Ma. Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860 ± 20 Ma and 575.6 ± 8.8 Ma. Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma. The REE data of the zircon grains show LREE depletion and HREE enrichment, with the metamorphic grains showing more depletion in HREE. Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yielded eHf(t) values from −1.17 to 0.46 with TDM and TC DM and age peaks at 2392 and 2638 Ma, suggesting Neoarchean to Paleoproterozoic juvenile sources. We suggest that the high Ba–Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent, and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic–Cambrian. Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.
Qiang Wang - One of the best experts on this subject based on the ideXlab platform.
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genesis of pristine adakitic magmas by lower crustal melting a perspective from amphibole composition
Journal of Geophysical Research, 2017Co-Authors: Derek A Wyman, Qiang Wang, Sunlin Chung, Gongjian Tang, Hongyi Chen, Zhenhua ZhaoAbstract:Genesis of Adakites in arc and nonarc tectonic settings plays an important role in magmatic processes and material recycling along convergent margins. However, little is known about characteristics of pristine adakitic melts due to late stage magma evolutionary processes that dilute or obscure primary melt features, and thus, the genesis of Adakites remains controversial. Here we present a detailed analysis of amphibole composition from Early Permian Awulale postcollisional adakitic diorite and granodiorite porphyries in the core of Tianshan Orogen, the central Asian orogenic belt. Two distinct populations of amphiboles, with markedly different aluminum contents, are observed in the adakitic rocks. These are (1) high-Al amphiboles, crystallizing as an early mineral phase at about 1 GPa, and (2) low-Al amphiboles, as a late mineral phase at 220–400 MPa, estimated on the basis of experimental phase equilibria data. Trace element modeling indicates that melts in equilibrium with the high-pressure amphiboles are of adakitic composition, suggesting that the Awulale pristine magmas already had an adakitic nature before the amphibole crystallization. This is consistent with the mafic lower crustal melting model, rather than a high-pressure basaltic melt fractionation, for Adakite petrogenesis. Our results lend new insights into how amphibole composition can be used to constrain the geochemical characteristics of pristine adakitic magmas.
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triassic nb enriched basalts magnesian andesites and Adakites of the qiangtang terrane central tibet evidence for metasomatism by slab derived melts in the mantle wedge
Contributions to Mineralogy and Petrology, 2008Co-Authors: Qiang Wang, Feng Zi, Ziqi Jiang, Derek A Wyman, Chaofeng Li, Jifeng Xu, Zhenhua Zhao, Yanhui DongAbstract:New chronological, geochemical, and isotopic data are reported for Triassic (219–236 Ma) Adakite-magnesian andesite-Nb-enriched basaltic rock associations from the Tuotuohe area, central Qiangtang terrane. The Adakites and magnesian andesites are characterized by high Sr/Y (25–45), La/Yb (14–42) and Na2O/K2O (12–49) ratios, high Al2O3 (15.34–18.28 wt%) and moderate to high Sr concentrations (220–498 ppm) and eND (t) (+0.86 to +1.21) values. Low enrichments of Th, Rb relative to Nb, and subequal normalized Nb and La contents, and enrichments of light rare earth elements combine to distinguish a group of Nb-enriched basaltic rocks (NEBs). They have positive eND (t) (+2.57 to +5.16) values. Positive correlations between Th, La and Nb and an absence of negative Nb anomalies on mantle normalized plots indicate the NEBs are products of a mantle source metasomatized by a slab melt rather than by hydrous fluids. A continuous compositional variation between Adakites and magnesian andesites confirms slab melt interaction with mantle peridotite. The spatial association of the NEBs with Adakites and magnesian andesites define an “adakitic metasomatic volcanic series” recognized in many demonstrably subduction-related environments (e.g., Mindanao arc, Philippines; Kamchatka arc, Russia; and southern Baja California arc, Mexico). The age of the Touhuohe suite, and its correlation with Triassic NEB to the north indicates that volcanism derived from subduction-modified mantle was abundant prior to 220 Ma in the central Qiangtang terrane.
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partial melting of thickened or delaminated lower crust in the middle of eastern china implications for cu au mineralization
The Journal of Geology, 2007Co-Authors: Qiang Wang, Derek A Wyman, Zhenhua Zhao, Ping JianAbstract:Abstract Field relations, isotope systematics, and plate tectonic reconstructions require that felsic Adakites in the Yangtze Block and the Dabie Orogen, eastern China, were not derived from a subducting slab, despite the signature of a mantle component in the contemporaneous mafic Adakite hosts of Cu‐Au deposits in the same areas. The apparently contradictory requirements are accounted for by (a) a deep crustal melting origin for barren Adakites and (b) a crustal delamination origin, followed by ascent through lithospheric mantle, for Adakites associated with mineralization. The crustal delamination process associated with the prospective porphyries duplicates the metallogenically essential aspects of the subduction environment. The importance of adakitic magmas in the genesis of porphyry‐style Cu‐Au deposits is affirmed by these findings, but the range of prospective tectonic environments is extended to include an important intraplate, postsubduction setting. The porphyries of eastern China demonstrate ...
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petrogenesis of carboniferous Adakites and nb enriched arc basalts in the alataw area northern tianshan range western china implications for phanerozoic crustal growth in the central asia orogenic belt
Chemical Geology, 2007Co-Authors: Qiang Wang, Derek A Wyman, Zhenhua Zhao, Xiaolin Xiong, Zhenghua Bai, Tongmo Dai, Zhuyin ChuAbstract:Abstract Carboniferous volcanic rocks in the Alataw area, Northern Tianshan Range (Xinjiang), consist of early Carboniferous (ca. 320 Ma) Adakites and Nb-enriched arc basalts and basaltic andesites (NEBs), and late Carboniferous (ca. 306–310 Ma) mainly high-K calc-alkaline andesites, dacites and rhyolites. The Adakites are calc-alkaline, and characterized by high Na2O/K2O (1.52–3.32) ratios, negligible to positive Eu anomalies, strong depletion of heavy rare earth elements (e.g., Yb = 0.74–1.47 ppm) and Y (6.7–14.9 ppm), positive Sr and Ba but negative Nb and Ti anomalies, and relatively constant eNd(T) values (+ 3.4–+ 6.6) and (87Sr/86Sr)i ratios (0.7035–0.7042). Some andesitic and dacitic Adakite samples exhibit high MgO contents similar to magnesian andesites. The NEBs are sodium-rich (Na2O/K2O = 2.03–8.06), and differ from the vast majority of arc basalts in their higher Nb, Zr, TiO2 and P2O5 contents and Nb/Th, Nb/La and Nb/U ratios, and minor negative to positive anomalies in Ba, Nb, Sr, Zr and Ti. They have the highest eNd(T) values (+ 6.4–+ 11.6) but varying (87Sr/86Sr)i ratios (0.7007–0.7063). The high-K calc-alkaline suite is similar to typical ‘normal’ arc volcanic rocks in terms of moderately fractionated rare earth abundance and distinctly negative Eu, Nb, Sr and Ti anomalies. They have eNd(T) values (+ 1.2–+ 6.4) and (87Sr/86Sr)i ratios (0.7018–0.7059). Geochemically, they are similar to coeval I-type granitoids in the Alataw area. Given the presence of early Carboniferous ophiolites in the Northern Tianshan Range, and the isotopically inappropriate compositions of Proterozoic metamorphic basement in the Alataw area, we argue that the Alataw Adakites were most probably related to the melting of young subducted crust of the Northern Tianshan Ocean. The NEBs likely originated from mantle wedge peridotites metasomatized by Adakites and minor slab-derived fluids. The later high-K calc alkaline suite was generated by AFC processes that acted on melts derived from a mantle wedge metasomatized by hydrous fluids. The larger range of isotopic compositions exhibited by both the NEB and high-K suite, relative to the Adakites, suggests that the mantle wedge was heterogeneous prior to slab- or fluid-mediated metasomatism. Continental crustal growth of the Central Asian orogenic belt was dominated by contributions of the juvenile materials from the depleted mantle prior to 270 Ma and possibly afterwards. The results of this study suggest that other Carboniferous Nb-enriched basalts in the Tianshan Range were generated by subduction processes rather than by intraplate tectonics as previously proposed.
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extremely high na Adakite like magmas derived from alkali rich basaltic underplate the late cretaceous zhantang andesites in the huichang basin se china
Geochemical Journal, 2003Co-Authors: Xiaolin Xiong, Jifeng Xu, Qiang Wang, Zhenhua Zhao, Xianhua Li, Wuxian Li, Xiaoming ChenAbstract:The Zhantang andesites, which erupted in the Late Cretaceous Huichang Basin of SE China interior, were associated with the Late Mesozoic lithospheric extension and basaltic underplating. They are high-Na (6.59-8.46 wt% Na2O), high-Al trondhjemitic rocks with high Sr and Ba, low Y and HREE, and high Sr/Y and La/Yb ratios, similar to modern Adakites. However, they are much higher in Na2O but lower in CaO than Adakites. Their eNd(T) values of -2.3 to -3.8 and initial 87Sr/86Sr ratios of 0.707 to 0.708 are also significantly different from those of Adakites with MORB-like isotopic compositions. These chemical and isotopic features, along with the tectonic setting, suggest that they were not produced by partial melting of subducting slab. The Zhantang Adakite-like magmas may be derived from underplated basaltic lower crust, but require a compositionally peculiar basaltic protolith to account for their extremely high-Na and low-Ca feature. They are compositionally comparable to the experimentally produced partial melts of alkali-rich basalt. We therefore interpret them as the products of melting of an alkali-rich basaltic rock.