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Huaning Qiu - One of the best experts on this subject based on the ideXlab platform.
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constraints on Retrograde Metamorphism of uhp eclogites in north qinling central china from 40ar 39ar dating of amphibole and phengite
Gondwana Research, 2020Co-Authors: J R Wijbrans, Fraukje M Brouwer, Xiujuan Bai, Huaning QiuAbstract:Abstract Coesite- and microdiamond- bearing ultra-high pressure (UHP) eclogites in the North Qinling terrane have been widely retrogressed to amphibolites. Previous geochronological studies on these UHP rocks mainly focused on the timing of peak eclogite facies Metamorphism. The Kanfenggou UHP metamorphic domain is one of the best-preserved coesite-bearing eclogite occurrences in the North Qinling terrane. In this study, mafic amphibolites and host schists from this domain were collected for 40Ar/39Ar dating to constrain their Retrograde evolution. Two generations of amphibole are recognized based on their mineral parageneses and 40Ar/39Ar ages. A first generation of amphibole from garnet amphibolites yielded irregularly-shaped age spectra with anomalously old apparent ages. Isochron ages of 484–473 Ma and initial 40Ar/36Ar ratios of 3695–774 are obtained from this generation of amphibole, indicating incorporation of excess argon. Second generation amphibole occurs in epidote amphibolites yielded flat age spectra with plateau ages of 464–462 Ma without evidence for excess argon. These ages suggest that the amphibolite-facies Metamorphism has taken place as early as 484 Ma and lasted until 462 Ma for the North Qinling UHP metamorphic rocks. Phengite from the country-rock schists yielded 40Ar/39Ar plateau ages of 426–396 Ma, with higher phengite Si contents associated with the older the plateau ages. Based on our new 40Ar/39Ar ages and previous zircon U Pb geochronological data, we construct a new detailed pressure-temperature-time (P-T-t) path illustrating the Retrograde Metamorphism and exhumation rate of the North Qinling eclogites and host schists. The P-T-t path suggests that these UHP metamorphic rocks experienced initial medium-to-high exhumation rates (ca. 8.7 mm/yr) during the Early Ordovician (489–484 Ma), which was mainly derived from buoyancy forces. Subsequently, the exhumation rate decreased gradually from ~0.8 to 0.3 mm/yr from 484 to 426 Ma, which was probably governed by extension and/or erosion.
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Constraints on Retrograde Metamorphism of UHP eclogites in North Qinling, Central China, from 40Ar/39Ar dating of amphibole and phengite
Gondwana Research, 2020Co-Authors: Jan Wijbrans, Xiujuan Bai, Fraukje M Brouwer, Huaning QiuAbstract:Abstract Coesite- and microdiamond- bearing ultra-high pressure (UHP) eclogites in the North Qinling terrane have been widely retrogressed to amphibolites. Previous geochronological studies on these UHP rocks mainly focused on the timing of peak eclogite facies Metamorphism. The Kanfenggou UHP metamorphic domain is one of the best-preserved coesite-bearing eclogite occurrences in the North Qinling terrane. In this study, mafic amphibolites and host schists from this domain were collected for 40Ar/39Ar dating to constrain their Retrograde evolution. Two generations of amphibole are recognized based on their mineral parageneses and 40Ar/39Ar ages. A first generation of amphibole from garnet amphibolites yielded irregularly-shaped age spectra with anomalously old apparent ages. Isochron ages of 484–473 Ma and initial 40Ar/36Ar ratios of 3695–774 are obtained from this generation of amphibole, indicating incorporation of excess argon. Second generation amphibole occurs in epidote amphibolites yielded flat age spectra with plateau ages of 464–462 Ma without evidence for excess argon. These ages suggest that the amphibolite-facies Metamorphism has taken place as early as 484 Ma and lasted until 462 Ma for the North Qinling UHP metamorphic rocks. Phengite from the country-rock schists yielded 40Ar/39Ar plateau ages of 426–396 Ma, with higher phengite Si contents associated with the older the plateau ages. Based on our new 40Ar/39Ar ages and previous zircon U Pb geochronological data, we construct a new detailed pressure-temperature-time (P-T-t) path illustrating the Retrograde Metamorphism and exhumation rate of the North Qinling eclogites and host schists. The P-T-t path suggests that these UHP metamorphic rocks experienced initial medium-to-high exhumation rates (ca. 8.7 mm/yr) during the Early Ordovician (489–484 Ma), which was mainly derived from buoyancy forces. Subsequently, the exhumation rate decreased gradually from ~0.8 to 0.3 mm/yr from 484 to 426 Ma, which was probably governed by extension and/or erosion.
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amphibolite facies Retrograde Metamorphism of the zhujiachong eclogite se dabieshan 40ar 39ar age constraints from argon extraction using uv laser microprobe in vacuo crushing and stepwise heating
Journal of Metamorphic Geology, 2010Co-Authors: Huaning Qiu, J R Wijbrans, Fraukje M Brouwer, J B Yun, Linghao ZhaoAbstract:The Zhujiachong eclogite in the south-eastern Dabieshan ultra-high-P terrane has been overprinted during Retrograde Metamorphism, with the development of garnet-amphibolite mineral assemblages in most rocks in the outcrop. This study is focused on providing age constraints for the Retrograde amphibolite facies and greenschist facies mineralogy by 40 Ar ⁄ 39 Ar dating. By applying a novel approach of combining three different techniques for extracting argon: laser stepwise heating of single grains and small separates, a spot fusion technique by UV-laser ablation microprobe on polished sections and an in vacuo crushing technique for liberating radiogenic argon from fluid inclusions, it is demonstrated that an internally consistent thermal history can be derived. The 40 Ar ⁄ 39 Ar ages indicate that phengite formed before 265 Ma, probably during the ultra-high-P event. Ages associated with amphibolite facies Retrograde Metamorphism range from 242 to 217 Ma by the analyses of amphibole. Ages of c. 230 Ma were found for the symplectite matrix that formed during retrogression from eclogite pyroxene. Late stage hydrothermal activity leading to the formation of coarse-grained paragonite and fluid inclusions in vein amphibole was dated at c. 200 Ma. These age results agree well with the mineral crystallization sequence observed from thin-sections of the Retrograded eclogite: phengite fi paragonite and amphibole in matrix fi amphibole in the corona.
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Amphibolite facies Retrograde Metamorphism of the Zhujiachong eclogite, SE Dabieshan: 40Ar/39Ar age constraints from argon extraction using UV‐laser microprobe, in vacuo crushing and stepwise heating
Journal of Metamorphic Geology, 2010Co-Authors: Huaning Qiu, J R Wijbrans, Fraukje M Brouwer, J B Yun, Linghao ZhaoAbstract:The Zhujiachong eclogite in the south-eastern Dabieshan ultra-high-P terrane has been overprinted during Retrograde Metamorphism, with the development of garnet-amphibolite mineral assemblages in most rocks in the outcrop. This study is focused on providing age constraints for the Retrograde amphibolite facies and greenschist facies mineralogy by 40 Ar ⁄ 39 Ar dating. By applying a novel approach of combining three different techniques for extracting argon: laser stepwise heating of single grains and small separates, a spot fusion technique by UV-laser ablation microprobe on polished sections and an in vacuo crushing technique for liberating radiogenic argon from fluid inclusions, it is demonstrated that an internally consistent thermal history can be derived. The 40 Ar ⁄ 39 Ar ages indicate that phengite formed before 265 Ma, probably during the ultra-high-P event. Ages associated with amphibolite facies Retrograde Metamorphism range from 242 to 217 Ma by the analyses of amphibole. Ages of c. 230 Ma were found for the symplectite matrix that formed during retrogression from eclogite pyroxene. Late stage hydrothermal activity leading to the formation of coarse-grained paragonite and fluid inclusions in vein amphibole was dated at c. 200 Ma. These age results agree well with the mineral crystallization sequence observed from thin-sections of the Retrograded eclogite: phengite fi paragonite and amphibole in matrix fi amphibole in the corona.
Linghao Zhao - One of the best experts on this subject based on the ideXlab platform.
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amphibolite facies Retrograde Metamorphism of the zhujiachong eclogite se dabieshan 40ar 39ar age constraints from argon extraction using uv laser microprobe in vacuo crushing and stepwise heating
Journal of Metamorphic Geology, 2010Co-Authors: Huaning Qiu, J R Wijbrans, Fraukje M Brouwer, J B Yun, Linghao ZhaoAbstract:The Zhujiachong eclogite in the south-eastern Dabieshan ultra-high-P terrane has been overprinted during Retrograde Metamorphism, with the development of garnet-amphibolite mineral assemblages in most rocks in the outcrop. This study is focused on providing age constraints for the Retrograde amphibolite facies and greenschist facies mineralogy by 40 Ar ⁄ 39 Ar dating. By applying a novel approach of combining three different techniques for extracting argon: laser stepwise heating of single grains and small separates, a spot fusion technique by UV-laser ablation microprobe on polished sections and an in vacuo crushing technique for liberating radiogenic argon from fluid inclusions, it is demonstrated that an internally consistent thermal history can be derived. The 40 Ar ⁄ 39 Ar ages indicate that phengite formed before 265 Ma, probably during the ultra-high-P event. Ages associated with amphibolite facies Retrograde Metamorphism range from 242 to 217 Ma by the analyses of amphibole. Ages of c. 230 Ma were found for the symplectite matrix that formed during retrogression from eclogite pyroxene. Late stage hydrothermal activity leading to the formation of coarse-grained paragonite and fluid inclusions in vein amphibole was dated at c. 200 Ma. These age results agree well with the mineral crystallization sequence observed from thin-sections of the Retrograded eclogite: phengite fi paragonite and amphibole in matrix fi amphibole in the corona.
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Amphibolite facies Retrograde Metamorphism of the Zhujiachong eclogite, SE Dabieshan: 40Ar/39Ar age constraints from argon extraction using UV‐laser microprobe, in vacuo crushing and stepwise heating
Journal of Metamorphic Geology, 2010Co-Authors: Huaning Qiu, J R Wijbrans, Fraukje M Brouwer, J B Yun, Linghao ZhaoAbstract:The Zhujiachong eclogite in the south-eastern Dabieshan ultra-high-P terrane has been overprinted during Retrograde Metamorphism, with the development of garnet-amphibolite mineral assemblages in most rocks in the outcrop. This study is focused on providing age constraints for the Retrograde amphibolite facies and greenschist facies mineralogy by 40 Ar ⁄ 39 Ar dating. By applying a novel approach of combining three different techniques for extracting argon: laser stepwise heating of single grains and small separates, a spot fusion technique by UV-laser ablation microprobe on polished sections and an in vacuo crushing technique for liberating radiogenic argon from fluid inclusions, it is demonstrated that an internally consistent thermal history can be derived. The 40 Ar ⁄ 39 Ar ages indicate that phengite formed before 265 Ma, probably during the ultra-high-P event. Ages associated with amphibolite facies Retrograde Metamorphism range from 242 to 217 Ma by the analyses of amphibole. Ages of c. 230 Ma were found for the symplectite matrix that formed during retrogression from eclogite pyroxene. Late stage hydrothermal activity leading to the formation of coarse-grained paragonite and fluid inclusions in vein amphibole was dated at c. 200 Ma. These age results agree well with the mineral crystallization sequence observed from thin-sections of the Retrograded eclogite: phengite fi paragonite and amphibole in matrix fi amphibole in the corona.
Marty Grove - One of the best experts on this subject based on the ideXlab platform.
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growth conditions of symplectic muscovite quartz implications for quantifying Retrograde Metamorphism in exhumed magmatic arcs
Geology, 2010Co-Authors: Emily M. Peterman, Marty GroveAbstract:Symplectic intergrowths are important markers of incomplete Retrograde Metamorphism. Because they represent arrested reactions that were limited by diffusion, these textures provide constraints on how pressure and temperature varied following peak-grade Metamorphism. For example, symplectic intergrowths of muscovite + quartz that formed in upper amphibolite facies sillimanite + K-feldspar wall rocks permit assessment of the thermal history of a magmatic arc post-intrusion. Wall rocks surrounding the last plutons to be emplaced within the Peninsular Ranges batholith, (Southern California, USA, to Baja California, Mexico), present an ideal setting to investigate Retrograde textures that elucidate arc evolution. During intrusion, wall rocks reached 625 ± 25 °C and exceeded muscovite + quartz stability. Post-intrusion, muscovite + quartz symplectites grew at the expense of K-feldspar in response to falling temperature. Ti-in-quartz measurements reveal that symplectic quartz grew at ≥375 °C, which reflects temperatures as much as 250 °C lower than peak-grade Metamorphism. This result has significant implications for the mechanical and thermal evolution of Peninsular Ranges batholith arc crust.
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Growth conditions of symplectic muscovite + quartz: Implications for quantifying Retrograde Metamorphism in exhumed magmatic arcs
Geology, 2010Co-Authors: Emily M. Peterman, Marty GroveAbstract:Symplectic intergrowths are important markers of incomplete Retrograde Metamorphism. Because they represent arrested reactions that were limited by diffusion, these textures provide constraints on how pressure and temperature varied following peak-grade Metamorphism. For example, symplectic intergrowths of muscovite + quartz that formed in upper amphibolite facies sillimanite + K-feldspar wall rocks permit assessment of the thermal history of a magmatic arc post-intrusion. Wall rocks surrounding the last plutons to be emplaced within the Peninsular Ranges batholith, (Southern California, USA, to Baja California, Mexico), present an ideal setting to investigate Retrograde textures that elucidate arc evolution. During intrusion, wall rocks reached 625 ± 25 °C and exceeded muscovite + quartz stability. Post-intrusion, muscovite + quartz symplectites grew at the expense of K-feldspar in response to falling temperature. Ti-in-quartz measurements reveal that symplectic quartz grew at ≥375 °C, which reflects temperatures as much as 250 °C lower than peak-grade Metamorphism. This result has significant implications for the mechanical and thermal evolution of Peninsular Ranges batholith arc crust.
Fraukje M Brouwer - One of the best experts on this subject based on the ideXlab platform.
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constraints on Retrograde Metamorphism of uhp eclogites in north qinling central china from 40ar 39ar dating of amphibole and phengite
Gondwana Research, 2020Co-Authors: J R Wijbrans, Fraukje M Brouwer, Xiujuan Bai, Huaning QiuAbstract:Abstract Coesite- and microdiamond- bearing ultra-high pressure (UHP) eclogites in the North Qinling terrane have been widely retrogressed to amphibolites. Previous geochronological studies on these UHP rocks mainly focused on the timing of peak eclogite facies Metamorphism. The Kanfenggou UHP metamorphic domain is one of the best-preserved coesite-bearing eclogite occurrences in the North Qinling terrane. In this study, mafic amphibolites and host schists from this domain were collected for 40Ar/39Ar dating to constrain their Retrograde evolution. Two generations of amphibole are recognized based on their mineral parageneses and 40Ar/39Ar ages. A first generation of amphibole from garnet amphibolites yielded irregularly-shaped age spectra with anomalously old apparent ages. Isochron ages of 484–473 Ma and initial 40Ar/36Ar ratios of 3695–774 are obtained from this generation of amphibole, indicating incorporation of excess argon. Second generation amphibole occurs in epidote amphibolites yielded flat age spectra with plateau ages of 464–462 Ma without evidence for excess argon. These ages suggest that the amphibolite-facies Metamorphism has taken place as early as 484 Ma and lasted until 462 Ma for the North Qinling UHP metamorphic rocks. Phengite from the country-rock schists yielded 40Ar/39Ar plateau ages of 426–396 Ma, with higher phengite Si contents associated with the older the plateau ages. Based on our new 40Ar/39Ar ages and previous zircon U Pb geochronological data, we construct a new detailed pressure-temperature-time (P-T-t) path illustrating the Retrograde Metamorphism and exhumation rate of the North Qinling eclogites and host schists. The P-T-t path suggests that these UHP metamorphic rocks experienced initial medium-to-high exhumation rates (ca. 8.7 mm/yr) during the Early Ordovician (489–484 Ma), which was mainly derived from buoyancy forces. Subsequently, the exhumation rate decreased gradually from ~0.8 to 0.3 mm/yr from 484 to 426 Ma, which was probably governed by extension and/or erosion.
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Constraints on Retrograde Metamorphism of UHP eclogites in North Qinling, Central China, from 40Ar/39Ar dating of amphibole and phengite
Gondwana Research, 2020Co-Authors: Jan Wijbrans, Xiujuan Bai, Fraukje M Brouwer, Huaning QiuAbstract:Abstract Coesite- and microdiamond- bearing ultra-high pressure (UHP) eclogites in the North Qinling terrane have been widely retrogressed to amphibolites. Previous geochronological studies on these UHP rocks mainly focused on the timing of peak eclogite facies Metamorphism. The Kanfenggou UHP metamorphic domain is one of the best-preserved coesite-bearing eclogite occurrences in the North Qinling terrane. In this study, mafic amphibolites and host schists from this domain were collected for 40Ar/39Ar dating to constrain their Retrograde evolution. Two generations of amphibole are recognized based on their mineral parageneses and 40Ar/39Ar ages. A first generation of amphibole from garnet amphibolites yielded irregularly-shaped age spectra with anomalously old apparent ages. Isochron ages of 484–473 Ma and initial 40Ar/36Ar ratios of 3695–774 are obtained from this generation of amphibole, indicating incorporation of excess argon. Second generation amphibole occurs in epidote amphibolites yielded flat age spectra with plateau ages of 464–462 Ma without evidence for excess argon. These ages suggest that the amphibolite-facies Metamorphism has taken place as early as 484 Ma and lasted until 462 Ma for the North Qinling UHP metamorphic rocks. Phengite from the country-rock schists yielded 40Ar/39Ar plateau ages of 426–396 Ma, with higher phengite Si contents associated with the older the plateau ages. Based on our new 40Ar/39Ar ages and previous zircon U Pb geochronological data, we construct a new detailed pressure-temperature-time (P-T-t) path illustrating the Retrograde Metamorphism and exhumation rate of the North Qinling eclogites and host schists. The P-T-t path suggests that these UHP metamorphic rocks experienced initial medium-to-high exhumation rates (ca. 8.7 mm/yr) during the Early Ordovician (489–484 Ma), which was mainly derived from buoyancy forces. Subsequently, the exhumation rate decreased gradually from ~0.8 to 0.3 mm/yr from 484 to 426 Ma, which was probably governed by extension and/or erosion.
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amphibolite facies Retrograde Metamorphism of the zhujiachong eclogite se dabieshan 40ar 39ar age constraints from argon extraction using uv laser microprobe in vacuo crushing and stepwise heating
Journal of Metamorphic Geology, 2010Co-Authors: Huaning Qiu, J R Wijbrans, Fraukje M Brouwer, J B Yun, Linghao ZhaoAbstract:The Zhujiachong eclogite in the south-eastern Dabieshan ultra-high-P terrane has been overprinted during Retrograde Metamorphism, with the development of garnet-amphibolite mineral assemblages in most rocks in the outcrop. This study is focused on providing age constraints for the Retrograde amphibolite facies and greenschist facies mineralogy by 40 Ar ⁄ 39 Ar dating. By applying a novel approach of combining three different techniques for extracting argon: laser stepwise heating of single grains and small separates, a spot fusion technique by UV-laser ablation microprobe on polished sections and an in vacuo crushing technique for liberating radiogenic argon from fluid inclusions, it is demonstrated that an internally consistent thermal history can be derived. The 40 Ar ⁄ 39 Ar ages indicate that phengite formed before 265 Ma, probably during the ultra-high-P event. Ages associated with amphibolite facies Retrograde Metamorphism range from 242 to 217 Ma by the analyses of amphibole. Ages of c. 230 Ma were found for the symplectite matrix that formed during retrogression from eclogite pyroxene. Late stage hydrothermal activity leading to the formation of coarse-grained paragonite and fluid inclusions in vein amphibole was dated at c. 200 Ma. These age results agree well with the mineral crystallization sequence observed from thin-sections of the Retrograded eclogite: phengite fi paragonite and amphibole in matrix fi amphibole in the corona.
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Amphibolite facies Retrograde Metamorphism of the Zhujiachong eclogite, SE Dabieshan: 40Ar/39Ar age constraints from argon extraction using UV‐laser microprobe, in vacuo crushing and stepwise heating
Journal of Metamorphic Geology, 2010Co-Authors: Huaning Qiu, J R Wijbrans, Fraukje M Brouwer, J B Yun, Linghao ZhaoAbstract:The Zhujiachong eclogite in the south-eastern Dabieshan ultra-high-P terrane has been overprinted during Retrograde Metamorphism, with the development of garnet-amphibolite mineral assemblages in most rocks in the outcrop. This study is focused on providing age constraints for the Retrograde amphibolite facies and greenschist facies mineralogy by 40 Ar ⁄ 39 Ar dating. By applying a novel approach of combining three different techniques for extracting argon: laser stepwise heating of single grains and small separates, a spot fusion technique by UV-laser ablation microprobe on polished sections and an in vacuo crushing technique for liberating radiogenic argon from fluid inclusions, it is demonstrated that an internally consistent thermal history can be derived. The 40 Ar ⁄ 39 Ar ages indicate that phengite formed before 265 Ma, probably during the ultra-high-P event. Ages associated with amphibolite facies Retrograde Metamorphism range from 242 to 217 Ma by the analyses of amphibole. Ages of c. 230 Ma were found for the symplectite matrix that formed during retrogression from eclogite pyroxene. Late stage hydrothermal activity leading to the formation of coarse-grained paragonite and fluid inclusions in vein amphibole was dated at c. 200 Ma. These age results agree well with the mineral crystallization sequence observed from thin-sections of the Retrograded eclogite: phengite fi paragonite and amphibole in matrix fi amphibole in the corona.
J R Wijbrans - One of the best experts on this subject based on the ideXlab platform.
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constraints on Retrograde Metamorphism of uhp eclogites in north qinling central china from 40ar 39ar dating of amphibole and phengite
Gondwana Research, 2020Co-Authors: J R Wijbrans, Fraukje M Brouwer, Xiujuan Bai, Huaning QiuAbstract:Abstract Coesite- and microdiamond- bearing ultra-high pressure (UHP) eclogites in the North Qinling terrane have been widely retrogressed to amphibolites. Previous geochronological studies on these UHP rocks mainly focused on the timing of peak eclogite facies Metamorphism. The Kanfenggou UHP metamorphic domain is one of the best-preserved coesite-bearing eclogite occurrences in the North Qinling terrane. In this study, mafic amphibolites and host schists from this domain were collected for 40Ar/39Ar dating to constrain their Retrograde evolution. Two generations of amphibole are recognized based on their mineral parageneses and 40Ar/39Ar ages. A first generation of amphibole from garnet amphibolites yielded irregularly-shaped age spectra with anomalously old apparent ages. Isochron ages of 484–473 Ma and initial 40Ar/36Ar ratios of 3695–774 are obtained from this generation of amphibole, indicating incorporation of excess argon. Second generation amphibole occurs in epidote amphibolites yielded flat age spectra with plateau ages of 464–462 Ma without evidence for excess argon. These ages suggest that the amphibolite-facies Metamorphism has taken place as early as 484 Ma and lasted until 462 Ma for the North Qinling UHP metamorphic rocks. Phengite from the country-rock schists yielded 40Ar/39Ar plateau ages of 426–396 Ma, with higher phengite Si contents associated with the older the plateau ages. Based on our new 40Ar/39Ar ages and previous zircon U Pb geochronological data, we construct a new detailed pressure-temperature-time (P-T-t) path illustrating the Retrograde Metamorphism and exhumation rate of the North Qinling eclogites and host schists. The P-T-t path suggests that these UHP metamorphic rocks experienced initial medium-to-high exhumation rates (ca. 8.7 mm/yr) during the Early Ordovician (489–484 Ma), which was mainly derived from buoyancy forces. Subsequently, the exhumation rate decreased gradually from ~0.8 to 0.3 mm/yr from 484 to 426 Ma, which was probably governed by extension and/or erosion.
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amphibolite facies Retrograde Metamorphism of the zhujiachong eclogite se dabieshan 40ar 39ar age constraints from argon extraction using uv laser microprobe in vacuo crushing and stepwise heating
Journal of Metamorphic Geology, 2010Co-Authors: Huaning Qiu, J R Wijbrans, Fraukje M Brouwer, J B Yun, Linghao ZhaoAbstract:The Zhujiachong eclogite in the south-eastern Dabieshan ultra-high-P terrane has been overprinted during Retrograde Metamorphism, with the development of garnet-amphibolite mineral assemblages in most rocks in the outcrop. This study is focused on providing age constraints for the Retrograde amphibolite facies and greenschist facies mineralogy by 40 Ar ⁄ 39 Ar dating. By applying a novel approach of combining three different techniques for extracting argon: laser stepwise heating of single grains and small separates, a spot fusion technique by UV-laser ablation microprobe on polished sections and an in vacuo crushing technique for liberating radiogenic argon from fluid inclusions, it is demonstrated that an internally consistent thermal history can be derived. The 40 Ar ⁄ 39 Ar ages indicate that phengite formed before 265 Ma, probably during the ultra-high-P event. Ages associated with amphibolite facies Retrograde Metamorphism range from 242 to 217 Ma by the analyses of amphibole. Ages of c. 230 Ma were found for the symplectite matrix that formed during retrogression from eclogite pyroxene. Late stage hydrothermal activity leading to the formation of coarse-grained paragonite and fluid inclusions in vein amphibole was dated at c. 200 Ma. These age results agree well with the mineral crystallization sequence observed from thin-sections of the Retrograded eclogite: phengite fi paragonite and amphibole in matrix fi amphibole in the corona.
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Amphibolite facies Retrograde Metamorphism of the Zhujiachong eclogite, SE Dabieshan: 40Ar/39Ar age constraints from argon extraction using UV‐laser microprobe, in vacuo crushing and stepwise heating
Journal of Metamorphic Geology, 2010Co-Authors: Huaning Qiu, J R Wijbrans, Fraukje M Brouwer, J B Yun, Linghao ZhaoAbstract:The Zhujiachong eclogite in the south-eastern Dabieshan ultra-high-P terrane has been overprinted during Retrograde Metamorphism, with the development of garnet-amphibolite mineral assemblages in most rocks in the outcrop. This study is focused on providing age constraints for the Retrograde amphibolite facies and greenschist facies mineralogy by 40 Ar ⁄ 39 Ar dating. By applying a novel approach of combining three different techniques for extracting argon: laser stepwise heating of single grains and small separates, a spot fusion technique by UV-laser ablation microprobe on polished sections and an in vacuo crushing technique for liberating radiogenic argon from fluid inclusions, it is demonstrated that an internally consistent thermal history can be derived. The 40 Ar ⁄ 39 Ar ages indicate that phengite formed before 265 Ma, probably during the ultra-high-P event. Ages associated with amphibolite facies Retrograde Metamorphism range from 242 to 217 Ma by the analyses of amphibole. Ages of c. 230 Ma were found for the symplectite matrix that formed during retrogression from eclogite pyroxene. Late stage hydrothermal activity leading to the formation of coarse-grained paragonite and fluid inclusions in vein amphibole was dated at c. 200 Ma. These age results agree well with the mineral crystallization sequence observed from thin-sections of the Retrograded eclogite: phengite fi paragonite and amphibole in matrix fi amphibole in the corona.
