Suizhou-Zaoyang area is located in the southern Qinling-Tongbai-Dabie Orogen, China. A combined research on U-Pb ages and Lu-Hf isotopes for detrital zircons from three meta-sedimentary rocks in the Wudang Group is re...Suizhou-Zaoyang area is located in the southern Qinling-Tongbai-Dabie Orogen, China. A combined research on U-Pb ages and Lu-Hf isotopes for detrital zircons from three meta-sedimentary rocks in the Wudang Group is reported. The upper Wudang Group has a major age population of ca. 750 Ma and a sub-major of ca. 860 Ma. But the lower part only yields one age peak at ca. 2.03 Ga. In situ Lu-Hf analyses of the young age group of ca. 750 Ma for zircons from the upper Wudang Group yield an average εHt(t) value of -8.6 and two-stage Hf model ages (TDM2) from 1837 to 2230 Ma, respectively. However, zircons from the lower Wudang Group give an average εHf(t) value of 4.5 and TDM1 of 2220±22 Ma, close to the timing of zircon crystallization. Thus, it is suggested that, in the study area, the continental crust grew during the middle Paleoproterozoic and reworked during the middle Neoproterozoic, which shows the affinity to the Dabie Orogen. In addition, in the lower Wudang Group, two metamorphic zircon ages of 1992±91 and 1999±61 Ma are consistent with that of the middle Paleoproterozoic metamorphism event in the northern Yangtze Block, which may represent the assemblage of the Columbia Supercontinent. On the basis of the U-Pb ages and Hf isotopes, it is proposed that Suizhou-Zaoyang area was involved in the subduction-collision event in the middle Paleoproterozoic and the Yangtze Block was one of the components of the Paleo-Mesoproterozoic supercontinent.展开更多
The Shigujian pluton is a gneissic quartz monzonite located in Tiantangzhai area in central part of the Dabie orogen.Anisotropy of magnetic susceptibility(AMS) data show that most magnetic foliations dip steeply to so...The Shigujian pluton is a gneissic quartz monzonite located in Tiantangzhai area in central part of the Dabie orogen.Anisotropy of magnetic susceptibility(AMS) data show that most magnetic foliations dip steeply to southeast.About 85% of sampling points dip from 40° to 90°.Magnetic foliations are generally parallel to the foliations measured in the field.The pluton has NWW-SEE trending lineations in the southeast and NE-SW trending lineations in central part and north,but the lineations plunge to SW in central part and to NE in the north.All plunges are moderate.The anisotropy degree(P) is between 1.065 and 1.532 and the shape parameter(T) is between 0.005 and 0.694.A Flinn diagram of the magnetic fabrics shows that the value of K is less than 1.The analysis of AMS suggests that the pluton was emplaced and deformed under a SE-NW compressional stress regime.The analysis of quartz C-axis fabrics indicates that the pluton was deformed under compressional stress and deformation temperatures range from 400 to 500℃.Microstructures indicate that the pluton is deformed in near solidus conditions and the pluton is a synkinematic intrusion.The emplacement of the Shigujian granite is inferred to have taken place syntectonically.The zircon U-Pb dating of the granite suggests that the pluton was intruded at 141±2.3 Ma.By synthesizing all data,it seems that the Shigujian pluton was emplaced in a compressional environment and the transformation time of the Dabie orogen from compression to extension took place after 141 Ma.The structural evolution of the Dabie orogen was controlled by the Pacific tectonic domain when the Shigujian pluton was emplaced,whereas the adjacent Tiantangzhai complex massif is the result of an extensional environment.展开更多
Foliated garnet-bearing granite,usually associated with high pressure and ultrahigh-pressure(UHP) metamophic rocks,is a particular rock-type extensively exposed in the Mesozoic Dabie-Sulu orogenic belt of China.This s...Foliated garnet-bearing granite,usually associated with high pressure and ultrahigh-pressure(UHP) metamophic rocks,is a particular rock-type extensively exposed in the Mesozoic Dabie-Sulu orogenic belt of China.This study focuses on deformation features and SHRIMP zircon dating of foliated garnet granite in a high-pressure metamorphic unit from Huwan,western Dabie Mountains in order to resolve discrepancies in current versions of its petrogenesis and structural evolution.SHRIMP dating reveals a zircon age of 762 ± 15 Ma(MSWD=1.7) for Huwan granites,representing the Middle to Late Neoproterozoic age of intrusion and crystallization.Field and microstructural studies show that the Huwan granite body underwent multiple-stage deformation.The deformation was manifested by an early stage of rootless folding and imposition of relict foliation(S1);an Indosinian main stage marked by imposition of north-dipping penetrative gneissosity(S2) and development of ductile shear zones under NNE-SSW directed compression;and a final Indosinian stage of southward thrusting of the Huwan high-pressure unit.Shallow level extension prevailed after the Late Triassic,giving rise to south-dipping thrust faults and north-dipping normal faults.展开更多
基金supported by the National Natural Sciences Foundation of China(Grants Nos.41172189,40972137,and 41402179)
文摘Suizhou-Zaoyang area is located in the southern Qinling-Tongbai-Dabie Orogen, China. A combined research on U-Pb ages and Lu-Hf isotopes for detrital zircons from three meta-sedimentary rocks in the Wudang Group is reported. The upper Wudang Group has a major age population of ca. 750 Ma and a sub-major of ca. 860 Ma. But the lower part only yields one age peak at ca. 2.03 Ga. In situ Lu-Hf analyses of the young age group of ca. 750 Ma for zircons from the upper Wudang Group yield an average εHt(t) value of -8.6 and two-stage Hf model ages (TDM2) from 1837 to 2230 Ma, respectively. However, zircons from the lower Wudang Group give an average εHf(t) value of 4.5 and TDM1 of 2220±22 Ma, close to the timing of zircon crystallization. Thus, it is suggested that, in the study area, the continental crust grew during the middle Paleoproterozoic and reworked during the middle Neoproterozoic, which shows the affinity to the Dabie Orogen. In addition, in the lower Wudang Group, two metamorphic zircon ages of 1992±91 and 1999±61 Ma are consistent with that of the middle Paleoproterozoic metamorphism event in the northern Yangtze Block, which may represent the assemblage of the Columbia Supercontinent. On the basis of the U-Pb ages and Hf isotopes, it is proposed that Suizhou-Zaoyang area was involved in the subduction-collision event in the middle Paleoproterozoic and the Yangtze Block was one of the components of the Paleo-Mesoproterozoic supercontinent.
基金supported by National Natural Science Foundation of China (Grant Nos. 40972137,41172189)
文摘The Shigujian pluton is a gneissic quartz monzonite located in Tiantangzhai area in central part of the Dabie orogen.Anisotropy of magnetic susceptibility(AMS) data show that most magnetic foliations dip steeply to southeast.About 85% of sampling points dip from 40° to 90°.Magnetic foliations are generally parallel to the foliations measured in the field.The pluton has NWW-SEE trending lineations in the southeast and NE-SW trending lineations in central part and north,but the lineations plunge to SW in central part and to NE in the north.All plunges are moderate.The anisotropy degree(P) is between 1.065 and 1.532 and the shape parameter(T) is between 0.005 and 0.694.A Flinn diagram of the magnetic fabrics shows that the value of K is less than 1.The analysis of AMS suggests that the pluton was emplaced and deformed under a SE-NW compressional stress regime.The analysis of quartz C-axis fabrics indicates that the pluton was deformed under compressional stress and deformation temperatures range from 400 to 500℃.Microstructures indicate that the pluton is deformed in near solidus conditions and the pluton is a synkinematic intrusion.The emplacement of the Shigujian granite is inferred to have taken place syntectonically.The zircon U-Pb dating of the granite suggests that the pluton was intruded at 141±2.3 Ma.By synthesizing all data,it seems that the Shigujian pluton was emplaced in a compressional environment and the transformation time of the Dabie orogen from compression to extension took place after 141 Ma.The structural evolution of the Dabie orogen was controlled by the Pacific tectonic domain when the Shigujian pluton was emplaced,whereas the adjacent Tiantangzhai complex massif is the result of an extensional environment.
基金Supported by the National Natural Science Foundation of China (Grant Nos.40802046 and 40334037)the Project of Science & Technology Research and Development from Sinopec (Grant No.P02009)
文摘Foliated garnet-bearing granite,usually associated with high pressure and ultrahigh-pressure(UHP) metamophic rocks,is a particular rock-type extensively exposed in the Mesozoic Dabie-Sulu orogenic belt of China.This study focuses on deformation features and SHRIMP zircon dating of foliated garnet granite in a high-pressure metamorphic unit from Huwan,western Dabie Mountains in order to resolve discrepancies in current versions of its petrogenesis and structural evolution.SHRIMP dating reveals a zircon age of 762 ± 15 Ma(MSWD=1.7) for Huwan granites,representing the Middle to Late Neoproterozoic age of intrusion and crystallization.Field and microstructural studies show that the Huwan granite body underwent multiple-stage deformation.The deformation was manifested by an early stage of rootless folding and imposition of relict foliation(S1);an Indosinian main stage marked by imposition of north-dipping penetrative gneissosity(S2) and development of ductile shear zones under NNE-SSW directed compression;and a final Indosinian stage of southward thrusting of the Huwan high-pressure unit.Shallow level extension prevailed after the Late Triassic,giving rise to south-dipping thrust faults and north-dipping normal faults.