Tectonic evolution of the Tethys and the boundary between the Gondwanaland and the Eurasia during the Carboniferous and Permian remain hotly debated. Qiangtang region in the Qinghai-Tibet Plateau may be a key place to...Tectonic evolution of the Tethys and the boundary between the Gondwanaland and the Eurasia during the Carboniferous and Permian remain hotly debated. Qiangtang region in the Qinghai-Tibet Plateau may be a key place to study these problems. A paleomagnetic study was conducted on the Late Paleozoic rocks in the northern Qiangtang region （33.7°N, 86.7°W）, Tibet. Two sites （21 samples） in the Upper Carboniferous, eleven sites （101 samples） in the Permian, and two sites （16 samples） in the Lower Triassic were investigated. The rock magnetic data revealed hematite and magnetite as the main magnetic carders. In stepwise thermal demagnetization and/or combined alternating field （AC） demagnetization, two characteristic components in the majority of the samples were identified as （1） the Low-temperature Component （LTC）, characterized by northerly decli- nation and moderate to steep inclination, corresponding to a pole position overlay with the present North Pole. A minority of the samples present single component, and their directions are the same as （2） the High-temperature Component （HTC） of double components. The combined single-component and HTC data of the Permian can pass the R-test at 95% level and the F-test at 99% level, as well as the BC-test. The pole position from the Late Carboniferous is at 31.8°S, 45.7°E with dp=2.1, dm=3.9, that from the Early and Middle （Late） Permian is at 31.7°S, 46.8°E with @=9.2, dm=16.9 （34.4°N, 54.1°E with dp=6.9, dm=1 2.5） respectively, and that from the Early Triassic is at 16.9°S, 22.5°E with dp=4.9, dm=9.2. These pole positions are different from the other poles for the Qiangtang Block, which suggests the single-component and HTC directions are probably a primary magnetization and the northern Qiangtang Block was paleogeographically situated at low latitudes in the Northern Hemisphere in the Late Paleozoic.展开更多
基金supported by the China Geology Survey Bureau Program (Grant No. 1212010610102)the National Natural Science Foundation of China (Grant No. 41074045)the Special Key Subject Funds of Colleges and Universities in Shaanxi Province (Grant No. 081802)
文摘Tectonic evolution of the Tethys and the boundary between the Gondwanaland and the Eurasia during the Carboniferous and Permian remain hotly debated. Qiangtang region in the Qinghai-Tibet Plateau may be a key place to study these problems. A paleomagnetic study was conducted on the Late Paleozoic rocks in the northern Qiangtang region （33.7°N, 86.7°W）, Tibet. Two sites （21 samples） in the Upper Carboniferous, eleven sites （101 samples） in the Permian, and two sites （16 samples） in the Lower Triassic were investigated. The rock magnetic data revealed hematite and magnetite as the main magnetic carders. In stepwise thermal demagnetization and/or combined alternating field （AC） demagnetization, two characteristic components in the majority of the samples were identified as （1） the Low-temperature Component （LTC）, characterized by northerly decli- nation and moderate to steep inclination, corresponding to a pole position overlay with the present North Pole. A minority of the samples present single component, and their directions are the same as （2） the High-temperature Component （HTC） of double components. The combined single-component and HTC data of the Permian can pass the R-test at 95% level and the F-test at 99% level, as well as the BC-test. The pole position from the Late Carboniferous is at 31.8°S, 45.7°E with dp=2.1, dm=3.9, that from the Early and Middle （Late） Permian is at 31.7°S, 46.8°E with @=9.2, dm=16.9 （34.4°N, 54.1°E with dp=6.9, dm=1 2.5） respectively, and that from the Early Triassic is at 16.9°S, 22.5°E with dp=4.9, dm=9.2. These pole positions are different from the other poles for the Qiangtang Block, which suggests the single-component and HTC directions are probably a primary magnetization and the northern Qiangtang Block was paleogeographically situated at low latitudes in the Northern Hemisphere in the Late Paleozoic.
