The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform
Yuan-bao Wu - One of the best experts on this subject based on the ideXlab platform.
-
LA-ICP-MS monazite U-Pb age and trace element constraints on the Granulite-Facies metamorphism in the Tongbai orogen, central China
Journal of Asian Earth Sciences, 2014Co-Authors: Yuan-bao Wu, Hao Wang, Zhaochu Hu, Hujun GongAbstract:Abstract Granulite-Facies metamorphic rocks in the Tongbai orogen have great implications for the evolution of the whole Qinling–Tongbai–Dabie orogenic belt. However, the age and tectonic setting of the Granulite-Facies metamorphism have not been well constrained yet. In this contribution, BSE imaging, trace element analysis and U–Pb dating of monazite were undertaken for three felsic Granulites, a gneiss and a leucosome from the Tongbai orogen. Most monazite grains from the Granulite and gneiss samples exhibit no zoning, relatively low Th/U ratios, significant depletion in HREEs and Y, and negative Eu anomalies, indicating their formation under Granulite-Facies metamorphic conditions. Their formation ages range from 423 ± 2 to 430 ± 3 Ma with a weighted mean of 426 ± 5, which is taken as the timing of the peak Granulite-Facies metamorphism. In the leucosome sample, the monazite shows a euhedral to subhedral shape, coupled with a core and rim structure. Besides being depleted in HREEs and Y, both of them have significantly negative Eu anomalies and variable U contents (1220–13323 ppm) and Th/U ratios (7.2–136.7). This suggests that their formation was coeval with the crystallization of feldspar, metamorphic zircon, and garnet. The monazites yield a weighted mean age of 426 ± 3 Ma, suggesting nearly coeval partial melting during Granulite-Facies metamorphism. The relationship between metamorphic monazite and zircon within the same metamorphic sample is complex as revealed by metamorphic monazite and zircon U–Pb ages for the gneiss, Granulite and leucosome samples. In the other two Granulite samples, the monazite yields U–Pb ages of 423 ± 2 and 425 ± 3 Ma, whereas only little overgrowth or recrystallization of metamorphic zircon. This indicates that monazite is more sensitive than zircon in recording of metamorphic age even at the Granulite-Facies conditions. Combined with previous metamorphic zircon U–Pb age results, the prograde, peak, and retrograde stages of the Granulite-Facies metamorphism in the Tongbai orogen can be constrained at ca. 440, 426, and 415 Ma, respectively. Therefore, the Granulite-Facies metamorphism would have lasted for more than 20 Myr. The prolonged Granulite-Facies metamorphism might result from the continuous northward subduction of the Paleotethyan oceanic crust beneath the North Qinling terrane.
-
silurian Granulite Facies metamorphism and coeval magmatism and crustal growth in the tongbai orogen central china
Lithos, 2011Co-Authors: Hao Wang, Yuan-bao Wu, Hujun Gong, Hongfei Zhang, Min Peng, Jing Wang, Honglin YuanAbstract:Abstract It is intriguing whether the formation of Granulite in an orogenic belt is related to magmatism and crustal growth. The Tongbai orogen is one of the particular areas in the Qinling–Tongbai–Dabie–Sulu orogen that contains both Granulites and associated arc magmatic rocks, and thus is an optimal place to address this issue. However, the formation age and genesis of the Granulites and their relations to the magmatic rocks have not yet been well constrained. In situ LA (MC)-ICPMS U–Pb dating, and trace element and Lu–Hf isotope analyses were undertaken on zircon grains from gneiss, Granulite, gabbro and granodiorite samples. Most zircons in three Granulite samples and a gneiss sample have core–rim structures. The cores have oval or rounded shapes, oscillatory zones, high Th/U ratios and variable U–Pb ages, suggesting a detrital genesis. The youngest group of the detrital zircons yields a weighted mean 206 Pb/ 238 U age of 450 ± 5 Ma, which is interpreted as the maximum depositional age of their protoliths. A major age cluster is ca. 450–490 Ma, corresponding to prolonged arc magmatism in the northern Tongbai and Qinling orogens. Another group of ages range from 660 to 950 Ma, implying that the Qinling Group of the Tongbai orogen belongs to the South China Block (SCB). Metamorphic zircons in the Granulites have weak or no zoning, low Th/U ratios and REE contents, negative Eu anomalies, and relatively flat HREE patterns, which indicate that they formed contemporaneously with garnet and plagioclase, and thus under Granulite-Facies metamorphic conditions. Their weighted mean age of 424 ± 4 Ma is taken as the best estimated age of the Granulite-Facies metamorphism. Zircons in a leucosome sample have significant negative Eu anomalies and relatively flat HREE patterns with a formation age of 428 ± 4 Ma, indicating partial melting coeval with the Granulite-Facies metamorphism. Metamorphic zircons in the gneiss show apparently negative Eu anomalies, and variable Th/U ratios and HREE contents. They yield a weighted mean 206 Pb/ 238 U age of 438 ± 4 Ma, which was suggested to record the timing of the prograde metamorphism. Zircon grains in a gabbro and a granodiorite yield U–Pb ages of 432 ± 4 and 424 ± 4 Ma, respectively, which are interpreted as their formation ages and identical to the ages of the Granulite-Facies metamorphism. They have positive e Hf ( t ) values of up to 5.1, showing clear evidence for crustal growth during their formation. The appearance of the Silurian Granulite-Facies metamorphism and magmatism in the Tongbai orogen provides a good paradigm of coeval Granulite-Facies metamorphism, magmatism and crustal growth in an arc-continent collision orogenic belt.
Charlotte Moller - One of the best experts on this subject based on the ideXlab platform.
-
late sveconorwegian grenville high pressure Granulite Facies metamorphism in southwest sweden
Journal of Metamorphic Geology, 1991Co-Authors: Leif Johansson, Anders Lindh, Charlotte MollerAbstract:Mafic Granulite, garnet amphibolite and charnockite occur in the southwest Swedish part of the Baltic Shield. This part is generally considered to be the continuation of the Grenville collisional belt in Canada. The area with Granulite Facies rocks, the Southwest Swedish Granulite Region (SGR), is considerably larger than previously thought. The SGR is bounded to the east and west by two major tectonic zones. The first quantitative age data and P–T determinations for the high-grade metamorphism in the SGR are presented. Conventional geothermobarometry was applied to mafic Granulites from five localities. The estimated P–T conditions for the peak of metamorphism range from 705°C and 8.1 kbar at Hallandsas in the south, to 770°C and 10.5 kbar at Ullared in the north (medium- to high-P Granulite Facies conditions). Sm–Nd geochronology on minerals from the mafic Granulites at Hallandsas and Ullared give late Sveconorwegian (Grenville) ages of 907 ± 12 and 916 ± 11 Ma for the high-grade metamorphism, which is considerably younger than previously thought. Our results stress the hitherto underestimated importance of the late Sveconorwegian high-grade metamorphism in the southwestern part of the Baltic Shield.
-
Late Sveconorwegian (Grenville) high‐pressure Granulite Facies metamorphism in southwest Sweden
Journal of Metamorphic Geology, 1991Co-Authors: Leif Johansson, Anders Lindh, Charlotte MollerAbstract:Mafic Granulite, garnet amphibolite and charnockite occur in the southwest Swedish part of the Baltic Shield. This part is generally considered to be the continuation of the Grenville collisional belt in Canada. The area with Granulite Facies rocks, the Southwest Swedish Granulite Region (SGR), is considerably larger than previously thought. The SGR is bounded to the east and west by two major tectonic zones. The first quantitative age data and P–T determinations for the high-grade metamorphism in the SGR are presented. Conventional geothermobarometry was applied to mafic Granulites from five localities. The estimated P–T conditions for the peak of metamorphism range from 705°C and 8.1 kbar at Hallandsas in the south, to 770°C and 10.5 kbar at Ullared in the north (medium- to high-P Granulite Facies conditions). Sm–Nd geochronology on minerals from the mafic Granulites at Hallandsas and Ullared give late Sveconorwegian (Grenville) ages of 907 ± 12 and 916 ± 11 Ma for the high-grade metamorphism, which is considerably younger than previously thought. Our results stress the hitherto underestimated importance of the late Sveconorwegian high-grade metamorphism in the southwestern part of the Baltic Shield.
Hao Wang - One of the best experts on this subject based on the ideXlab platform.
-
LA-ICP-MS monazite U-Pb age and trace element constraints on the Granulite-Facies metamorphism in the Tongbai orogen, central China
Journal of Asian Earth Sciences, 2014Co-Authors: Yuan-bao Wu, Hao Wang, Zhaochu Hu, Hujun GongAbstract:Abstract Granulite-Facies metamorphic rocks in the Tongbai orogen have great implications for the evolution of the whole Qinling–Tongbai–Dabie orogenic belt. However, the age and tectonic setting of the Granulite-Facies metamorphism have not been well constrained yet. In this contribution, BSE imaging, trace element analysis and U–Pb dating of monazite were undertaken for three felsic Granulites, a gneiss and a leucosome from the Tongbai orogen. Most monazite grains from the Granulite and gneiss samples exhibit no zoning, relatively low Th/U ratios, significant depletion in HREEs and Y, and negative Eu anomalies, indicating their formation under Granulite-Facies metamorphic conditions. Their formation ages range from 423 ± 2 to 430 ± 3 Ma with a weighted mean of 426 ± 5, which is taken as the timing of the peak Granulite-Facies metamorphism. In the leucosome sample, the monazite shows a euhedral to subhedral shape, coupled with a core and rim structure. Besides being depleted in HREEs and Y, both of them have significantly negative Eu anomalies and variable U contents (1220–13323 ppm) and Th/U ratios (7.2–136.7). This suggests that their formation was coeval with the crystallization of feldspar, metamorphic zircon, and garnet. The monazites yield a weighted mean age of 426 ± 3 Ma, suggesting nearly coeval partial melting during Granulite-Facies metamorphism. The relationship between metamorphic monazite and zircon within the same metamorphic sample is complex as revealed by metamorphic monazite and zircon U–Pb ages for the gneiss, Granulite and leucosome samples. In the other two Granulite samples, the monazite yields U–Pb ages of 423 ± 2 and 425 ± 3 Ma, whereas only little overgrowth or recrystallization of metamorphic zircon. This indicates that monazite is more sensitive than zircon in recording of metamorphic age even at the Granulite-Facies conditions. Combined with previous metamorphic zircon U–Pb age results, the prograde, peak, and retrograde stages of the Granulite-Facies metamorphism in the Tongbai orogen can be constrained at ca. 440, 426, and 415 Ma, respectively. Therefore, the Granulite-Facies metamorphism would have lasted for more than 20 Myr. The prolonged Granulite-Facies metamorphism might result from the continuous northward subduction of the Paleotethyan oceanic crust beneath the North Qinling terrane.
-
silurian Granulite Facies metamorphism and coeval magmatism and crustal growth in the tongbai orogen central china
Lithos, 2011Co-Authors: Hao Wang, Yuan-bao Wu, Hujun Gong, Hongfei Zhang, Min Peng, Jing Wang, Honglin YuanAbstract:Abstract It is intriguing whether the formation of Granulite in an orogenic belt is related to magmatism and crustal growth. The Tongbai orogen is one of the particular areas in the Qinling–Tongbai–Dabie–Sulu orogen that contains both Granulites and associated arc magmatic rocks, and thus is an optimal place to address this issue. However, the formation age and genesis of the Granulites and their relations to the magmatic rocks have not yet been well constrained. In situ LA (MC)-ICPMS U–Pb dating, and trace element and Lu–Hf isotope analyses were undertaken on zircon grains from gneiss, Granulite, gabbro and granodiorite samples. Most zircons in three Granulite samples and a gneiss sample have core–rim structures. The cores have oval or rounded shapes, oscillatory zones, high Th/U ratios and variable U–Pb ages, suggesting a detrital genesis. The youngest group of the detrital zircons yields a weighted mean 206 Pb/ 238 U age of 450 ± 5 Ma, which is interpreted as the maximum depositional age of their protoliths. A major age cluster is ca. 450–490 Ma, corresponding to prolonged arc magmatism in the northern Tongbai and Qinling orogens. Another group of ages range from 660 to 950 Ma, implying that the Qinling Group of the Tongbai orogen belongs to the South China Block (SCB). Metamorphic zircons in the Granulites have weak or no zoning, low Th/U ratios and REE contents, negative Eu anomalies, and relatively flat HREE patterns, which indicate that they formed contemporaneously with garnet and plagioclase, and thus under Granulite-Facies metamorphic conditions. Their weighted mean age of 424 ± 4 Ma is taken as the best estimated age of the Granulite-Facies metamorphism. Zircons in a leucosome sample have significant negative Eu anomalies and relatively flat HREE patterns with a formation age of 428 ± 4 Ma, indicating partial melting coeval with the Granulite-Facies metamorphism. Metamorphic zircons in the gneiss show apparently negative Eu anomalies, and variable Th/U ratios and HREE contents. They yield a weighted mean 206 Pb/ 238 U age of 438 ± 4 Ma, which was suggested to record the timing of the prograde metamorphism. Zircon grains in a gabbro and a granodiorite yield U–Pb ages of 432 ± 4 and 424 ± 4 Ma, respectively, which are interpreted as their formation ages and identical to the ages of the Granulite-Facies metamorphism. They have positive e Hf ( t ) values of up to 5.1, showing clear evidence for crustal growth during their formation. The appearance of the Silurian Granulite-Facies metamorphism and magmatism in the Tongbai orogen provides a good paradigm of coeval Granulite-Facies metamorphism, magmatism and crustal growth in an arc-continent collision orogenic belt.
Honglin Yuan - One of the best experts on this subject based on the ideXlab platform.
-
silurian Granulite Facies metamorphism and coeval magmatism and crustal growth in the tongbai orogen central china
Lithos, 2011Co-Authors: Hao Wang, Yuan-bao Wu, Hujun Gong, Hongfei Zhang, Min Peng, Jing Wang, Honglin YuanAbstract:Abstract It is intriguing whether the formation of Granulite in an orogenic belt is related to magmatism and crustal growth. The Tongbai orogen is one of the particular areas in the Qinling–Tongbai–Dabie–Sulu orogen that contains both Granulites and associated arc magmatic rocks, and thus is an optimal place to address this issue. However, the formation age and genesis of the Granulites and their relations to the magmatic rocks have not yet been well constrained. In situ LA (MC)-ICPMS U–Pb dating, and trace element and Lu–Hf isotope analyses were undertaken on zircon grains from gneiss, Granulite, gabbro and granodiorite samples. Most zircons in three Granulite samples and a gneiss sample have core–rim structures. The cores have oval or rounded shapes, oscillatory zones, high Th/U ratios and variable U–Pb ages, suggesting a detrital genesis. The youngest group of the detrital zircons yields a weighted mean 206 Pb/ 238 U age of 450 ± 5 Ma, which is interpreted as the maximum depositional age of their protoliths. A major age cluster is ca. 450–490 Ma, corresponding to prolonged arc magmatism in the northern Tongbai and Qinling orogens. Another group of ages range from 660 to 950 Ma, implying that the Qinling Group of the Tongbai orogen belongs to the South China Block (SCB). Metamorphic zircons in the Granulites have weak or no zoning, low Th/U ratios and REE contents, negative Eu anomalies, and relatively flat HREE patterns, which indicate that they formed contemporaneously with garnet and plagioclase, and thus under Granulite-Facies metamorphic conditions. Their weighted mean age of 424 ± 4 Ma is taken as the best estimated age of the Granulite-Facies metamorphism. Zircons in a leucosome sample have significant negative Eu anomalies and relatively flat HREE patterns with a formation age of 428 ± 4 Ma, indicating partial melting coeval with the Granulite-Facies metamorphism. Metamorphic zircons in the gneiss show apparently negative Eu anomalies, and variable Th/U ratios and HREE contents. They yield a weighted mean 206 Pb/ 238 U age of 438 ± 4 Ma, which was suggested to record the timing of the prograde metamorphism. Zircon grains in a gabbro and a granodiorite yield U–Pb ages of 432 ± 4 and 424 ± 4 Ma, respectively, which are interpreted as their formation ages and identical to the ages of the Granulite-Facies metamorphism. They have positive e Hf ( t ) values of up to 5.1, showing clear evidence for crustal growth during their formation. The appearance of the Silurian Granulite-Facies metamorphism and magmatism in the Tongbai orogen provides a good paradigm of coeval Granulite-Facies metamorphism, magmatism and crustal growth in an arc-continent collision orogenic belt.
R J Hart - One of the best experts on this subject based on the ideXlab platform.
-
evolution of the amphibolite Granulite Facies transition exposed by the vredefort impact structure kaapvaal craton south africa
The Journal of Geology, 2003Co-Authors: Rebecca M Flowers, D E Moser, R J HartAbstract:Abstract Geological mapping is integrated with high‐precision U‐Pb zircon and monazite geochronology to document in detail the nature and temporal evolution of the amphibolite‐Granulite Facies boundary exposed in the Vredefort impact structure of the central Kaapvaal Craton. Our study has revealed that the preimpact configuration of the amphibolite‐Granulite Facies boundary is best preserved in panels between impact‐related brittle faults and that past concepts of the boundary must be revised. A regional lithologic transition exists between amphibolite Facies Outer Granite Gneiss (3.084–3.09 Ga) and a heterogeneous assemblage of Granulite Facies gneisses (ca. 3.1–3.3 Ga). Tabular deformed quartz syenite bodies, dated at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cy...
-
Evolution of the Amphibolite‐Granulite Facies Transition Exposed by the Vredefort Impact Structure, Kaapvaal Craton, South Africa
The Journal of Geology, 2003Co-Authors: Rebecca M Flowers, D E Moser, R J HartAbstract:Abstract Geological mapping is integrated with high‐precision U‐Pb zircon and monazite geochronology to document in detail the nature and temporal evolution of the amphibolite‐Granulite Facies boundary exposed in the Vredefort impact structure of the central Kaapvaal Craton. Our study has revealed that the preimpact configuration of the amphibolite‐Granulite Facies boundary is best preserved in panels between impact‐related brittle faults and that past concepts of the boundary must be revised. A regional lithologic transition exists between amphibolite Facies Outer Granite Gneiss (3.084–3.09 Ga) and a heterogeneous assemblage of Granulite Facies gneisses (ca. 3.1–3.3 Ga). Tabular deformed quartz syenite bodies, dated at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cy...
-
Archean age for the Granulite Facies metamorphism near the center of the Vredefort structure, South Africa
Geology, 1999Co-Authors: R J Hart, D E Moser, Marco A.g. AndreoliAbstract:Granulite Facies metamorphic assemblages in rocks exposed near the center of the 2.02 Ga Vredefort impact structure previously have been interpreted either as Early Proterozoic, genetically related to the 2060 Ma Bushveld Complex, or as Archean, and representative of lower crust that rebounded to upper crustal levels following an impact event. Zircon and monazite recovered from the Granulite Facies rocks record high-grade metamorphism at 3107 ± 9 Ma and a primary age of ≥ 3425 Ma for detrital zircon. A shock-deformed, but otherwise pristine, dolerite dike that intrudes the Granulite terrane yields a U-Pb zircon age of ≥ 2560 Ma, providing a minimum age for the metamorphism. These isotopic age data are difficult to reconcile with a regional high-grade metamorphic event in the crust beneath Vredefort at 2060 Ma. Instead, the preimpact, high-temperature metamorphic history observed in the Vredefort lower crustal rocks indicates an enigmatic high-temperature event during the stabilization of diamondiferous Archean tectosphere.
