Paleomagnetic Results Of Late Paleozoic Rocks From QT Basin In Qinghai-Tibet Plateau

Qiangtang Basin is a petroliferous basin in Tethyan tectonic domain, where nature and evolution has become the investigative highlight of scholars in China and abroad. Especially, the investigation on boundaries of the Gondwana and Eurasian continent has always been a hot issues for several decades, as Qiangtang region is the key to solve the above problem. From the perspective of both rock magnetism and paleomagnetic studies, this paper gives a detailed interpretation on the rocks derived from the Late Paleozoic strata of the Norther Qiangtang-Qamdo-Simao stratigraphic and Southern Qiangtang-Baoshan districts.Rock magnetic experiments have been conducted in representative samples from all rock units of Northern and Southern Qiangtang respectively (for instance, the measure of Saturation IRM acquisition, thermal demagnetization of the Armand Magnetic susceptible variation with the temperature).The results show that: In Northern Qiangtang samples, the main magnetic minerals is hematite and magnetite, but on the aspects of magnetite and hematite content, there exist relatively differences in different lithology samples. In part, few pyrrhonist or goethite exist. The magnetic feature of samples from collecting area in Southern QiangTang Basin is relatively complex, for almost every sort of samples in all kinds of layers contains certain amount of Pyrrhotite. Besides, samples in different kinds of lithology in the distinct layers contain magnetite or hematite, and the Goethite is found in part ones.The paleo-magnetic investigation on 136 samples, which are derived from 15 sites of the Late Paleozoic strata in Northern Qiangtang Basin show that: obviously double magnetic components can be separated from most samples. The low temperature component is extremely close to the present geocentric axial dipole field direction (PEF) in geograghic coordinates, which are probably viscid remains of the current magnetic field. Part samples represented single magnetic component, which seems close to the high temperature component of the double components samples. The high temperature component were decomposed from 18 samples from 2 sites of the Late Carboniferous strata, which results in the average: D=213.8°, I=24.6°, K=52.5,α₉₅=4.9°. The corresponding position of paleomagnetic pole is atΦp=-33.4°N,λp=46.2°E, (dp=5.3, dm=2.8); The average high temperature component on 46 samples of 5 sites from the Early Middle Permian strata is: D=214.3°, I=27.4°, K=25.4,α₉₅=15.5°.the corresponding paleomagnetic pole is atΦp=-31.7°N,λp=46.8°E(dp=16.9, dm=9.2); while that of 30 samples of 5 sites from the Late Permian strata is: D=207.5°, I=28.8°, K=45.9,α₉₅=11.4°. The corresponding paleomagnetic pole situates at:Φp=-34.4°N,λp=54.1°E (dp=12.5, dm=6.9); The high temperature component on 15 samples of 2 sites from the Early Triassic strata . A tilt-corrected formation mean direction is: D=241.2°, I=20.6°, K=20,α₉₅=8.8°.the corresponding paleomagnetic pole is atΦp=-16.9°N,λp=22.5°E (dp=9.2, dm=4.9); The High temperature component of all Triassic samples can pass through the Fold test at 99% confidence level and Reversal test at 95% confidence level Baked Contact Test, which probably interpreted that of original components. The paleomagnetic investigation on 159 samples of 16 sites from the Late Paleozoic strata in Southern Qiangtang Basin showed a complex result. Therefore, a further investigation on its formation reason is to be completed.This paper selectsΦ=33.7°N,λ=86.7°E as the reference of northern QiangTang Block. The corresponding paleo-altitudes in geological age is calculated as following results: Late Carboniferous strata:.Φ_古=12.9°; Middle Permian strata:Φ_古=14.5°; Late Permian strata:Φ_古 =15.4°; Early Triassic strata:Φ_古 =10.6°. These all suggest that the major northern QiangTang Block is situated in the Low-latitude regions of northern hemisphere in the Late Paleozoic age.