Paleomagnetic data from the Late Carboniferous-Late Permian rocks in eastern Tibet and their implications for tectonic evolution of the northern Qiangtang-Qamdo block  

作　　者：CHENG Xin WU HanNing DIAO ZongBao WANG HaiJun MA Lun ZHANG XiaoDong YANG Gang HONG JingJing JI WenHua LI RongShe CHEN ShouJian ZHAO ZhenMing 

机构地区：[1]State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University [2]Xi'an Branch, China Coal Research Institute [3]Xi'an Institute of Geology and Mineral Resource, China Geological Survey

出　　处：《Science China Earth Sciences》2013年第7期1209-1220,共12页中国科学（地球科学英文版）

基　　金：supported by the National Natural Science Foundation of China (Grant Nos.41074045 & 41174045);the China Geology Survey Bureau Program (Grant No.1212010610102);the Special Key Subject Funds of Colleges and Universities in Shaanxi Province (Grant No.081802)

摘　　要：We report paleomagnetic results from the Late Carboniferous-Late Permian strata in eastern Tibet (China), and aim to clarify the tectonic and paleogeographic evolution of the northern Qiangtang-Qamdo block, which is the key to the study of plate boundary between the Gondwanaland and the Eurasia during the late Paleozoic. Two hundred and nineteen samples-including limestone, muddy siltstone, basalt, lava, and tuff-were collected at 24 sites in the Upper Carboniferous and Middle-Upper Permian successions. A systematic study of rock magnetism and paleomagnetism yields three reliable paleomagnetic pole positions. Both hematite and magnetite occurred in the Late Carboniferous limestone samples. The demagnetization curve shows a characteristic double-component, with the remanent magnetization (ChRM) exhibiting a positive polarity (negative inclination). In the Late Permian limestone, tuff, and basalt, magnetic information were recorded primarily in magnetite, although a small fraction of them was found in hematite in basalt. The demagnetization curve illustrates a double or single component, with the ChRM showing a negative polarity (positive inclination), which has passed the classic fold test successfully. The single polarity features of the ChRM directions of the Late Carboniferous and Middle-Late Permian rocks are respectively related to the Kiaman positive and reversed polarities under the stratigraphic coordinates. This, in turn, indicates that both ChRMs directions represent the original remanence directions. By comparison with the previously published paleomagnetic results from the late Paleozoic rocks in the northern Qiangtang Range, we suggest that: (1) Qamdo and northern Qiangtang block were independent of each other during the Late Carboniferous to the Early Permian periods. The north Lancangjiang ocean basin between the two blocks may have closed before the Middle Permian and been involved in the continent-continent collision stage in the Late Permian-Early Triassic periods. (2) The northern Qiangtang-QamdWe report paleomagnetic results from the Late Carboniferous-Late Permian strata in eastern Tibet （China）, and aim to clarify the tectonic and paleogeographic evolution of the northern Qiangtang-Qamdo block, which is the key to the study of plate boundary between the Gondwanaland and the Eurasia during the late Paleozoic. Two hundred and nineteen samples--including limestone, muddy siltstone, basalt, lava, and tuff--were collected at 24 sites in the Upper Carboniferous and Middle-Upper Permian successions. A systematic study of rock magnetism and paleomagnetism yields three reliable paleomagnetic pole po- sitions. Both hematite and magnetite occurred in the Late Carboniferous limestone samples. The demagnetization curve shows a characteristic double-component, with the remanent magnetization （ChRM） exhibiting a positive polarity （negative inclina- tion）. In the Late Permian limestone, tuff, and basalt, magnetic information were recorded primarily in magnetite, although a small fraction of them was found in hematite in basalt. The demagnetization curve illustrates a double or single component, with the ChRM showing a negative polarity （positive inclination）, which has passed the classic fold test successfully. The single polarity features of the ChRM directions of the Late Carboniferous and Middle-Late Permian rocks are respectively related to the Kiaman positive and reversed polarities under the stratigraphic coordinates. This, in turn, indicates that both ChRMs directions represent the original remanence directions. By comparison with the previously published paleomagnetic results from the late Paleozoic rocks in the northern Qiangtang Range, we suggest that： （1） Qamdo and northern Qiangtang block were independent of each other during the Late Carboniferous to the Early Permian periods. The north Lancangjiang ocean basin between the two blocks may have closed before the Middle Permian and been involved in the continent-continent collision stage in the Late Permian-Early Triassic periods. （

关 键 词：PALEOMAGNETISM TETHYS Northern Qiangtang block PALEOZOIC North Lancangjiang belt 

分 类 号：P548[天文地球—构造地质学]