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New paleomagnetic and magnetic fabric results for Early Cretaceous rocks from the Turpan intramontane basin,east Tianshan,northwest China

HUANG Baochun;WANG Yongcheng ZHU Rixiang Institute of Geology and Geophysics;Chinese Academy of Sciences;Beijing 100029;China

  In order to further constrain the tectonic configuration of the Tianshan fold belt and the blocks of its northern and southern sides prior to the Eocene India/Eurasia collision and to reveal their general kinematic characteristics after the collision,we carried out paleomagnetic study for Early Cretaceous rocks collected from the Turpan intramontane basin of east lianshan, northwest China.A high-temperature component(HTC) with dual polarities can be isolated from most samples after progressive thermal demagnetization.Thermal demagnetization behavior and some rock magnetic features of the samples indicate that this HTC resides mainly in hematite. The positive fold and reversal tests suggest that the HTC may be a primary magnetization acquired at or close to the time of formation of the rocks.Similar to previous results obtained from Cretaceous rocks in western China,paleomagnetic results from the Turpan intramontane basin retain also the inclination shallowing relative to stable Eurasia.However,the anisotropy of magnetic susceptibility(AMS) measurements showed weak anisotropy degrees for Early Cretaceous Shengjinkou sandstones from the Turpan Basin.These weak anisotropy degrees are independent of inclinations of the HTC,confirming that the effect of sedimentary compaction in most of these rocks can generally be neglected.Comparison of the Early Cretaceous results from Turpan with the coeval ones from Tarim,Junggar and stable Eurasia suggests that the Turpan intramontane basin displaced with no or slightly relative tectonic movement compared with Tarim but with a distinguishable latitudinal convergence relative to both Junggar and stable Eurasia since the India/Eurasia collision.……