The Batang Group in the Zhaokalong area not only hosts an important Fe-Cu polymetallic deposit but also reveal important insights for the Late Triassic tectonism in the northern Sanjiang region. In order to delineate ...The Batang Group in the Zhaokalong area not only hosts an important Fe-Cu polymetallic deposit but also reveal important insights for the Late Triassic tectonism in the northern Sanjiang region. In order to delineate the tectonic setting and evolutionary process of the paleo arc-basin system, geochemical studies on the Batang Group strata have been carried out. The results suggest that andesite in the Zhaokalong area mainly belongs to the tholeiite series and is characterized by obvious fractionation of LREE and HREE, enrichment in LILE and depletion in HFSE, and a distinctly elevated δ^（34）SCDT average of 10.5‰. The sandstone is classified as lithic sandstone, which is also characterized by obvious fractionation of LREE and HREE, as well as weak negative Ce and Eu anomalies. The limestone displays positive Eu anomalies, with δ^（13）CPDB ranging from-1.3‰ to 4.4‰ and δ^（18） OSMOW ranging from 14.6‰ to 22.5‰. These results indicate that the andesite has a dual signature of both arc andesite and rift volcanic rocks, whereas the sandstone may be formed in an active continental margin, and the limestone could be deposited in a weak oxidizing shallow sea. The sandstone in the Zhaokalong area represents sedimentation in a platform slope facies, corresponding to the main stage of the Jinshajing oceanic basin subduction during the middle period of Late Triassic. The continental arc volcanic activity resulted from subsequent strengthened subduction, forming the andesite in the North Qiangtang backarc basin. Afterwards, the limestone was formed after the cessation of magmatic activity. The information gleaned from the Batang Group strata helped constrain the evolution of the paleo-Jomda island arc and Jinshajiang oceanic subduction in the Late Triassic.展开更多
The shape,texture,content and REE characteristics of zircons from the O2tnd-1,O3tnd-2,O3tnd-3pyroclastic rock of Tanjianshan Group on the north margin of Qaidam Basin indicate that the O2-3tndis the product of volcani...The shape,texture,content and REE characteristics of zircons from the O2tnd-1,O3tnd-2,O3tnd-3pyroclastic rock of Tanjianshan Group on the north margin of Qaidam Basin indicate that the O2-3tndis the product of volcanism during the transitional period from ocean-land interim crust to oceanic crust.The U-Pb surface ages obtained from O3tnd-2and O3tnd-3can be divided into 9 groups,every age group coincides with the period when significant tectonic-heat event took place at Oulongbuluke micro-continental base of northern Qaidam,suggesting that the base rocks have provided materials for the formation of sedimentary and volcanic rock in O2-3tnd.The volcanic rocks of O3tnd-3formed at 440 Ma,with time gap 46 Ma to those of O1tna-1and O3tnd-3may represent the minor period that Xitieshan back-arc extension have lasted,the scale of back-arc basin that formed in Xitieshan extension may approach to 1 400 km.Based on the test of ithochemistry data for major elements and analysis of Sr isotope geochemistry for the clastic sedimentary rock in O1tna-2and O3tnd-2,the authors get the conclusion that the O1tna-2and O3tnd-2of Tanjianshan Group may form in back-arc basin environment,while the lithology difference between these two formations may reflect the changes of geodynamic processes as the diagenesis tectonic environment transformed from continental margin depression to adjacent sea basin.展开更多
The thermal history of the Jiaodong region and adjacent provinces （Shandong and northem Jiangsu） have been extensively studied, particularly by apatite fission track （AFT） dating. However, the AFT ages from surfac...The thermal history of the Jiaodong region and adjacent provinces （Shandong and northem Jiangsu） have been extensively studied, particularly by apatite fission track （AFT） dating. However, the AFT ages from surface outcrops range broadly and do not show an apparent relationship between age and elevation. This work provides a multiple low temperature thermochronological dataset including zircon and apatite （U-Th）/He ages （ZHe and AHe）, and AFT ages from a 1000-m-deep borehole at the Jiaojia goldfield in the northwest of Jiaodong Peninsula. ZHe, AFT and AHe ages range from -100-70, -85-50 and -65-50 Ma, respectively. These data conform to the principles of age vs. closure temperature and age vs. elevation and thus can be employed to estimate the exhumation history. Based on the density histogram of fission track length calculation, thermal history modeling, and previously published AFT ages from the Chinese Continental Science Drill program, this work concludes that compared to the AFT ages from surface outcrops, the low temperature thermochronological ages from the boreholes show a better relationship between age, elevation and closure temperature, and the age becomes younger with increasing depth. In addition, the exhumation history in the Jiaodong and adjacent areas can be divided into two distinct stages： a short, rapid tectonic exhumation （-100-95 Ma） and a long, slow exhumation since 95 Ma. The rate and amount of tectonic exhumation since 95 Ma are inferred as -30 m Ma-1 and -3 km, respectively.展开更多
基金co-financed by the Fundamental Research Funds for the Central Universities,China University of Geosciences(Wuhan)(Grant No.CUG150612)the National Natural Science Foundation of China(Grant No.41502067,41172087)
文摘The Batang Group in the Zhaokalong area not only hosts an important Fe-Cu polymetallic deposit but also reveal important insights for the Late Triassic tectonism in the northern Sanjiang region. In order to delineate the tectonic setting and evolutionary process of the paleo arc-basin system, geochemical studies on the Batang Group strata have been carried out. The results suggest that andesite in the Zhaokalong area mainly belongs to the tholeiite series and is characterized by obvious fractionation of LREE and HREE, enrichment in LILE and depletion in HFSE, and a distinctly elevated δ^（34）SCDT average of 10.5‰. The sandstone is classified as lithic sandstone, which is also characterized by obvious fractionation of LREE and HREE, as well as weak negative Ce and Eu anomalies. The limestone displays positive Eu anomalies, with δ^（13）CPDB ranging from-1.3‰ to 4.4‰ and δ^（18） OSMOW ranging from 14.6‰ to 22.5‰. These results indicate that the andesite has a dual signature of both arc andesite and rift volcanic rocks, whereas the sandstone may be formed in an active continental margin, and the limestone could be deposited in a weak oxidizing shallow sea. The sandstone in the Zhaokalong area represents sedimentation in a platform slope facies, corresponding to the main stage of the Jinshajing oceanic basin subduction during the middle period of Late Triassic. The continental arc volcanic activity resulted from subsequent strengthened subduction, forming the andesite in the North Qiangtang backarc basin. Afterwards, the limestone was formed after the cessation of magmatic activity. The information gleaned from the Batang Group strata helped constrain the evolution of the paleo-Jomda island arc and Jinshajiang oceanic subduction in the Late Triassic.
基金Supported by the National Natural Science Foundation of China(No.41172087)the Fundamental Research Funds for the Central Universities(No.CUG090102)
文摘The shape,texture,content and REE characteristics of zircons from the O2tnd-1,O3tnd-2,O3tnd-3pyroclastic rock of Tanjianshan Group on the north margin of Qaidam Basin indicate that the O2-3tndis the product of volcanism during the transitional period from ocean-land interim crust to oceanic crust.The U-Pb surface ages obtained from O3tnd-2and O3tnd-3can be divided into 9 groups,every age group coincides with the period when significant tectonic-heat event took place at Oulongbuluke micro-continental base of northern Qaidam,suggesting that the base rocks have provided materials for the formation of sedimentary and volcanic rock in O2-3tnd.The volcanic rocks of O3tnd-3formed at 440 Ma,with time gap 46 Ma to those of O1tna-1and O3tnd-3may represent the minor period that Xitieshan back-arc extension have lasted,the scale of back-arc basin that formed in Xitieshan extension may approach to 1 400 km.Based on the test of ithochemistry data for major elements and analysis of Sr isotope geochemistry for the clastic sedimentary rock in O1tna-2and O3tnd-2,the authors get the conclusion that the O1tna-2and O3tnd-2of Tanjianshan Group may form in back-arc basin environment,while the lithology difference between these two formations may reflect the changes of geodynamic processes as the diagenesis tectonic environment transformed from continental margin depression to adjacent sea basin.
基金sponsored by the Fundamental Research Funds for the Central Universities,China University of Geosciences(Wuhan)(Grant Nos.CUG090102&CUG150612)National Natural Science Foundation of China(Grant Nos.41672074&41502067).
文摘The thermal history of the Jiaodong region and adjacent provinces （Shandong and northem Jiangsu） have been extensively studied, particularly by apatite fission track （AFT） dating. However, the AFT ages from surface outcrops range broadly and do not show an apparent relationship between age and elevation. This work provides a multiple low temperature thermochronological dataset including zircon and apatite （U-Th）/He ages （ZHe and AHe）, and AFT ages from a 1000-m-deep borehole at the Jiaojia goldfield in the northwest of Jiaodong Peninsula. ZHe, AFT and AHe ages range from -100-70, -85-50 and -65-50 Ma, respectively. These data conform to the principles of age vs. closure temperature and age vs. elevation and thus can be employed to estimate the exhumation history. Based on the density histogram of fission track length calculation, thermal history modeling, and previously published AFT ages from the Chinese Continental Science Drill program, this work concludes that compared to the AFT ages from surface outcrops, the low temperature thermochronological ages from the boreholes show a better relationship between age, elevation and closure temperature, and the age becomes younger with increasing depth. In addition, the exhumation history in the Jiaodong and adjacent areas can be divided into two distinct stages： a short, rapid tectonic exhumation （-100-95 Ma） and a long, slow exhumation since 95 Ma. The rate and amount of tectonic exhumation since 95 Ma are inferred as -30 m Ma-1 and -3 km, respectively.
