Protolith ages and Indosinian deformation mechanism of metamorphic rocks in the Zhangbaling uplift segment of the Tan-Lu Fault Zone are important, unsolved problems. Our LA-ICP-MS zircon dating work indicates that pro...Protolith ages and Indosinian deformation mechanism of metamorphic rocks in the Zhangbaling uplift segment of the Tan-Lu Fault Zone are important, unsolved problems. Our LA-ICP-MS zircon dating work indicates that protolith ages of the greenschist-facies Zhangbaling Group are 754–753 Ma, and those of the amphibolite-facies Feidong Complex are 800–745 Ma. These rocks belong to the earliest cover of the Yangtze Plate. Their ages and metamorphic features suggest that the rocks did not come from the Dabie Orogen. The Indosinian structures in the Zhangbaling Group and lower Sinian strata formed in a flatlying ductile detachment zone with a shear sense of top-to-the-SSW whereas those in the underlying Feidong Complex are characterized by ENE-WSW inclined folds developed under a ductile regime. It is suggested therefore that the sinistral Tan-Lu Fault Zone of the Indosinian period is buried under the Hefei Basin west of the Zhangbaling uplift segment and the uplift segment is a displaced block neighboring the fault zone. Detachment deformation between the upper rigid and lower ductile crust during displacement of the Zhangbaling uplift segment resulted in the formation of the flat-lying ductile detachment zone and its underlying drag fold zone of a ductile regime. The protolith ages and deformation mechanism in the Zhangbaling uplift segment further prove sinistral origination of the Tan-Lu Fault Zone during the continent-continent collision of the North China and Yangtze plates and support the indentation model for the two-plate collision that considers the Tan-Lu Fault Zone as an oblique convergence boundary.展开更多
Intensive mid-Neoproterozoic magmatism is the salient feature of the Yangtze Block,preserving abundant information about crustal reworking and growth.Zircon U-Pb-Lu-Hf isotope analysis was performed on material from t...Intensive mid-Neoproterozoic magmatism is the salient feature of the Yangtze Block,preserving abundant information about crustal reworking and growth.Zircon U-Pb-Lu-Hf isotope analysis was performed on material from the Feidong Complex(FDC)and Zhangbaling Group(ZBLG)of the Zhangbaling Uplift,in order to determine the age and magmatic source of the Neoproterozoic igneous rocks as well as the detrital provenance for the sedimentary rocks,to further provide important data for understanding the mid-Neoproterozoic crustal evolution of the Northeast Yangtze Block.The amphibolite and gneissic granites in the Feidong Complex(FDC)gave similar protolith ages of 782-776 Ma.The synmagmatic zircons exhibited variable negativeεHf(t)values of-26.9 to-8.3.Early(ca.2.4 Ga)to late Paleoproterozoic(ca.2.0-1.9 Ga)inherited zircons were found in the gneissic monzogranite,with negativeεHf(t)values of-11.2 to-7.2,indicating strong reworking of the ancient crustal materials of the Northeast Yangtze Block.Whereas the amphibolites represent minor crustal growth through emplacement of continental rifting-related mafic magmas.The quartz-keratophyres in the Xileng Formation of the ZBLG in contrast systematically yield young protolith crystallization ages of 754-727 Ma with highεHf(t)values of-2.0 to+5.6,indicating their derivation from the reworking of juvenile crustal materials.The detrital zircons from the metasiltstone in the Beijiangjun Formation yield variable^(206)Pb/^(238)U ages(871-644 Ma)with a peak age at 741±11 Ma andεHf(t)values of-4.3 to+5.3,which is consistent with those of the Xileng Formation,but distinct from the FDC,indicating that the provenance of the metasiltstone is primarily the underlying Xileng Formation.The mid-Neoproterozoic igneous and sedimentary rocks of the Zhangbaling Uplift were products from continental rifting zones along the northern margin of the Yangtze Block,situated in different positions from the Susong Complex and the Haizhou Group.The transition from ancient to juvenile crustal sources for fels展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.41072162,91214301)
文摘Protolith ages and Indosinian deformation mechanism of metamorphic rocks in the Zhangbaling uplift segment of the Tan-Lu Fault Zone are important, unsolved problems. Our LA-ICP-MS zircon dating work indicates that protolith ages of the greenschist-facies Zhangbaling Group are 754–753 Ma, and those of the amphibolite-facies Feidong Complex are 800–745 Ma. These rocks belong to the earliest cover of the Yangtze Plate. Their ages and metamorphic features suggest that the rocks did not come from the Dabie Orogen. The Indosinian structures in the Zhangbaling Group and lower Sinian strata formed in a flatlying ductile detachment zone with a shear sense of top-to-the-SSW whereas those in the underlying Feidong Complex are characterized by ENE-WSW inclined folds developed under a ductile regime. It is suggested therefore that the sinistral Tan-Lu Fault Zone of the Indosinian period is buried under the Hefei Basin west of the Zhangbaling uplift segment and the uplift segment is a displaced block neighboring the fault zone. Detachment deformation between the upper rigid and lower ductile crust during displacement of the Zhangbaling uplift segment resulted in the formation of the flat-lying ductile detachment zone and its underlying drag fold zone of a ductile regime. The protolith ages and deformation mechanism in the Zhangbaling uplift segment further prove sinistral origination of the Tan-Lu Fault Zone during the continent-continent collision of the North China and Yangtze plates and support the indentation model for the two-plate collision that considers the Tan-Lu Fault Zone as an oblique convergence boundary.
基金supported by funds from the Natural Science Foundation of China(41772228)。
文摘Intensive mid-Neoproterozoic magmatism is the salient feature of the Yangtze Block,preserving abundant information about crustal reworking and growth.Zircon U-Pb-Lu-Hf isotope analysis was performed on material from the Feidong Complex(FDC)and Zhangbaling Group(ZBLG)of the Zhangbaling Uplift,in order to determine the age and magmatic source of the Neoproterozoic igneous rocks as well as the detrital provenance for the sedimentary rocks,to further provide important data for understanding the mid-Neoproterozoic crustal evolution of the Northeast Yangtze Block.The amphibolite and gneissic granites in the Feidong Complex(FDC)gave similar protolith ages of 782-776 Ma.The synmagmatic zircons exhibited variable negativeεHf(t)values of-26.9 to-8.3.Early(ca.2.4 Ga)to late Paleoproterozoic(ca.2.0-1.9 Ga)inherited zircons were found in the gneissic monzogranite,with negativeεHf(t)values of-11.2 to-7.2,indicating strong reworking of the ancient crustal materials of the Northeast Yangtze Block.Whereas the amphibolites represent minor crustal growth through emplacement of continental rifting-related mafic magmas.The quartz-keratophyres in the Xileng Formation of the ZBLG in contrast systematically yield young protolith crystallization ages of 754-727 Ma with highεHf(t)values of-2.0 to+5.6,indicating their derivation from the reworking of juvenile crustal materials.The detrital zircons from the metasiltstone in the Beijiangjun Formation yield variable^(206)Pb/^(238)U ages(871-644 Ma)with a peak age at 741±11 Ma andεHf(t)values of-4.3 to+5.3,which is consistent with those of the Xileng Formation,but distinct from the FDC,indicating that the provenance of the metasiltstone is primarily the underlying Xileng Formation.The mid-Neoproterozoic igneous and sedimentary rocks of the Zhangbaling Uplift were products from continental rifting zones along the northern margin of the Yangtze Block,situated in different positions from the Susong Complex and the Haizhou Group.The transition from ancient to juvenile crustal sources for fels
