The early Mesozoic granodiorites (ca.165 Ma) in the northeastern Hunan Province (NEH) have SiO2=65.4-69.65%, K2O/Na2O=0.95-1.38 and K2O+Na2O>6%, A/CNK=0.96-1.13 and belong to metaluminous high-K calc-alkaline serie...The early Mesozoic granodiorites (ca.165 Ma) in the northeastern Hunan Province (NEH) have SiO2=65.4-69.65%, K2O/Na2O=0.95-1.38 and K2O+Na2O>6%, A/CNK=0.96-1.13 and belong to metaluminous high-K calc-alkaline series. They are characterized by LREE and LILEs enrichment, and HFSE depletion with slightly negative Eu anomalies (Eu/Eu*=0.62-0.90). The initial 87Sr/86Sr ratios are in range from 0.711458 to 0.717461, and εNd values vary from -9.4 to -12.3, distinct from those of the contemporaneous granodiorites mantle-derived from the Southeastern Hunan Province (SEH) (87Sr/86Sr(i)=0.707962～0.710396, εNd(t)=-6.98～-2.30). By contrast, such signatures are roughly similar to those of the neighboring other Mesozoic granitic plutons (Eu/Eu*=0.30-0.70; 87Sr/86Sr >0.710; εNd = -12 to -16) in South China Block (SCB), which have been interpreted as the remelting products of Precambrian basement. The Proterozoic lower-middle crust is an important contributor to the petrogenesis of these early Mesozoic granodiorites in the NEH. An intracontinental extension setting is present in the northeastern Hunan Province at that time due to the demand of enough thermal transfer.展开更多
The SHRIMP zircon U-Pb geochronology ofthree typically Indosinian granitic plutons with peralumi-nous and potassium-rich affinities (Tangshi ultraunit forWeishan and Baimashan, and Longtan ultraunit forGuandimiao) is ...The SHRIMP zircon U-Pb geochronology ofthree typically Indosinian granitic plutons with peralumi-nous and potassium-rich affinities (Tangshi ultraunit forWeishan and Baimashan, and Longtan ultraunit forGuandimiao) is presented in Hunan Province, South China.The analyses of zircons from biotite monozonite granites forWeishan, Baimashan and Guandimiao plutons show the sin-gle and tight clusters on the concordia, and yield theweighted mean 206Pb/238U ages of 244±4, 243±3 and 239±3Ma, respectively, representing the crystallized ages of theseIndosinian granites. These data suggest that the Indosiniangranitic plutons as previously thought formed at a narrowage span. In combination with other data, it is inferred thatthe Indosinian granites within the South China Block proba-bly distributed in Hunan, Jiangxi, Guangxi and Guangdongprovinces as planar shape, and were the derivation of thecrustal materials in the intracontinental thickening setting.These precisely geochronological data provide importantconstraints for better understanding the spatiotemporal pat-tern of the Indosinian peraluminous granites and earlyMesozoic tectonic evolution of the South China Block.展开更多
The Late Paleozoic layered or stratoid-layered basalts in western Guangxi have similar elemental and isotopic compositions to Emeishan high-Ti basalts. Whole-rock ^40Ar/^39Ar and SHRIMP zircon U-Pb dating were carried...The Late Paleozoic layered or stratoid-layered basalts in western Guangxi have similar elemental and isotopic compositions to Emeishan high-Ti basalts. Whole-rock ^40Ar/^39Ar and SHRIMP zircon U-Pb dating were carried out for the representative basalt samples in three typical profiles in the area. Three basalts from the upper segment of Yangxu profile and lower segment of Yufeng and Min'an profiles yield the 4^40Ar/^39Ar plateau ages of 253.6±0.4 Ma (20BS-71),255.4±0.4 Ma (20BS-99) and 256.2±0.8 Ma (20BS-119), respectively. Twenty-three analyses on 23 zircons of the basalt from the upper segment of Yangxu profile give a weighted mean ^206Pb/^238U age of 253.7±6.1 Ma with an MSWD=2.8.These new and published geochronological data for Emeishan large igneous province (LIP) indicate that the Emeishan LIP was initiated at -260 Ma, voluminously erupted between 253 and 256 Ma, and possibly ended at -251-253Ma: The age (251-260Ma) is generally consistent with that of the associated environmental deterioration and mass extinction events at the end-Guadalupian and Permo-Triassic boundary. These precise geochronological data provide important constraints on the dominantly eruptive time of the Emeishan LIP and understanding of the distribution of Emeishan high-Ti basalts and its mantle plume dynamics.展开更多
Yunkaidashan, located at the southern South China block (SCB) and closely adjacent to the Indochina block, is an ideal region for better understanding the temporal and spatial framework of tectonothermal overprinting ...Yunkaidashan, located at the southern South China block (SCB) and closely adjacent to the Indochina block, is an ideal region for better understanding the temporal and spatial framework of tectonothermal overprinting at the southern SCB since Mesozoic. Apatite and zircon fission track thermochronology of various-type rocks from Yunkaidashan is presented in this paper. The results show, no matter what rocks are, the apparent ages of zircon fission track range from 97.4 to 133.0 Ma, and those of apatite fission track from 43.2 to 68.4 Ma. The length of apatite fission track yields an average confined track length of ～13 μm and shows normal distribution of unimodal frequency. It is inferred that the uplifting amplitude has been more than 5 km in Yunkaidashan since late Mesozoic. The difference of fission track apparent ages at different locations in Yunkaidashan suggests a paleophysiognomic scenario of the heterogeneous uplift/denudation. These data of the fission track thermochronology provide new constraints for better understanding the tectonophysiognomic pattern of the SCB since late Mesozoic.展开更多
基金This project was jointly supported by China National Natural Science Foundation(Grant No.40334039)CAS Knowledge Innovation Project(Grant No.KZCX1-102)CAS Key Laboratory ofIsotope Geochronology and Geochemistry(Grant No.GIGCX-03-01)
文摘The early Mesozoic granodiorites (ca.165 Ma) in the northeastern Hunan Province (NEH) have SiO2=65.4-69.65%, K2O/Na2O=0.95-1.38 and K2O+Na2O>6%, A/CNK=0.96-1.13 and belong to metaluminous high-K calc-alkaline series. They are characterized by LREE and LILEs enrichment, and HFSE depletion with slightly negative Eu anomalies (Eu/Eu*=0.62-0.90). The initial 87Sr/86Sr ratios are in range from 0.711458 to 0.717461, and εNd values vary from -9.4 to -12.3, distinct from those of the contemporaneous granodiorites mantle-derived from the Southeastern Hunan Province (SEH) (87Sr/86Sr(i)=0.707962～0.710396, εNd(t)=-6.98～-2.30). By contrast, such signatures are roughly similar to those of the neighboring other Mesozoic granitic plutons (Eu/Eu*=0.30-0.70; 87Sr/86Sr >0.710; εNd = -12 to -16) in South China Block (SCB), which have been interpreted as the remelting products of Precambrian basement. The Proterozoic lower-middle crust is an important contributor to the petrogenesis of these early Mesozoic granodiorites in the NEH. An intracontinental extension setting is present in the northeastern Hunan Province at that time due to the demand of enough thermal transfer.
基金supported by the National Natural Science Foundation of China(Grant Nos.40334039,40421303 and 40473019)the Chinese Academy of Sciences(Grant No.KZCX2-102)
文摘The SHRIMP zircon U-Pb geochronology ofthree typically Indosinian granitic plutons with peralumi-nous and potassium-rich affinities (Tangshi ultraunit forWeishan and Baimashan, and Longtan ultraunit forGuandimiao) is presented in Hunan Province, South China.The analyses of zircons from biotite monozonite granites forWeishan, Baimashan and Guandimiao plutons show the sin-gle and tight clusters on the concordia, and yield theweighted mean 206Pb/238U ages of 244±4, 243±3 and 239±3Ma, respectively, representing the crystallized ages of theseIndosinian granites. These data suggest that the Indosiniangranitic plutons as previously thought formed at a narrowage span. In combination with other data, it is inferred thatthe Indosinian granites within the South China Block proba-bly distributed in Hunan, Jiangxi, Guangxi and Guangdongprovinces as planar shape, and were the derivation of thecrustal materials in the intracontinental thickening setting.These precisely geochronological data provide importantconstraints for better understanding the spatiotemporal pat-tern of the Indosinian peraluminous granites and earlyMesozoic tectonic evolution of the South China Block.
文摘The Late Paleozoic layered or stratoid-layered basalts in western Guangxi have similar elemental and isotopic compositions to Emeishan high-Ti basalts. Whole-rock ^40Ar/^39Ar and SHRIMP zircon U-Pb dating were carried out for the representative basalt samples in three typical profiles in the area. Three basalts from the upper segment of Yangxu profile and lower segment of Yufeng and Min'an profiles yield the 4^40Ar/^39Ar plateau ages of 253.6±0.4 Ma (20BS-71),255.4±0.4 Ma (20BS-99) and 256.2±0.8 Ma (20BS-119), respectively. Twenty-three analyses on 23 zircons of the basalt from the upper segment of Yangxu profile give a weighted mean ^206Pb/^238U age of 253.7±6.1 Ma with an MSWD=2.8.These new and published geochronological data for Emeishan large igneous province (LIP) indicate that the Emeishan LIP was initiated at -260 Ma, voluminously erupted between 253 and 256 Ma, and possibly ended at -251-253Ma: The age (251-260Ma) is generally consistent with that of the associated environmental deterioration and mass extinction events at the end-Guadalupian and Permo-Triassic boundary. These precise geochronological data provide important constraints on the dominantly eruptive time of the Emeishan LIP and understanding of the distribution of Emeishan high-Ti basalts and its mantle plume dynamics.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.40334039,40421303 and 40473019)the Chinese Academy of Sciences(Grant Nos.KZCX2-SW-117 and GIGCX-03-0l).
文摘Yunkaidashan, located at the southern South China block (SCB) and closely adjacent to the Indochina block, is an ideal region for better understanding the temporal and spatial framework of tectonothermal overprinting at the southern SCB since Mesozoic. Apatite and zircon fission track thermochronology of various-type rocks from Yunkaidashan is presented in this paper. The results show, no matter what rocks are, the apparent ages of zircon fission track range from 97.4 to 133.0 Ma, and those of apatite fission track from 43.2 to 68.4 Ma. The length of apatite fission track yields an average confined track length of ～13 μm and shows normal distribution of unimodal frequency. It is inferred that the uplifting amplitude has been more than 5 km in Yunkaidashan since late Mesozoic. The difference of fission track apparent ages at different locations in Yunkaidashan suggests a paleophysiognomic scenario of the heterogeneous uplift/denudation. These data of the fission track thermochronology provide new constraints for better understanding the tectonophysiognomic pattern of the SCB since late Mesozoic.
