Late Cenozoic Tectonic Landform Analysis And Dynamic Mechanism Of Xidatan Basin,Eastern Kunlun

The mountains around the Tibetan Plateau uplifts are significant geology events during the late Cenozoic time. The tectonic study of the mountains should be helpful to understand the dynamics of the uplift and expand of the plateau. The Eastern Kunlun Mountains lies on the northern margin of the Tibetan Plateau, forming the geographical barrier between the Chaidamu Basin to the north and the surface of the plateau to the south. There is a huge left-lateral strike-slip active faults zone just on the southern margin of the mountains named the Eastern Kunlun Active Faults Zone(EKAFZ). The Xidatan left-lateral strike-slip active fault(XAF) is a part of the EKAFZ, controlling the tectonic geomorphology development of the Xidatan Basin(XB).The XB lies on the southern part of the Eastern Kunlun Mountains, which is a small long and narrow valley, extend from east to west with late Quaternary glacial drifts filling in it.This article study the kinematics of the active faults at the inner areas and the boundary of the XB, based on the field survey and the geometry measure. The XAF lies in the central of the XB, while a series of active normal faults with high dip angles lie on both boundaries, dipping to the central of the XB, forming the slops of the XB with their clear triangular facets. Together with the left-lateral strike-slip fault(XAF) in the central XB, these ladder-like normal faults form a negative flower shaped structure in section, implying there are extensional deformations in XB. There are always many tectonic transform deformations during the movement of strike-slip faults, for example, the pull-apart basin can be found in the fault bending areas or the adjoin areas of two strike-slip faults. The XB is a long narrow small basin with a length-width ratio >7:1, and there is no obvious bending of the XAF, so the XB should not be a pull-apart basin. It is considered that the negative flower shaped structure of the XAF reflects the transtensional rather than transpressional strain state of the areas of the XB, closely related to the rigid deformation of the upper crust and the plastic flow of the weak lower crust of the Tibetan Plateau.The article indicates that the tectonic-landform development of the XB was driven by the plateau lower crust channel flow during the late Cenozoic time.According to the previous studies, the initial time of the transtensional deformationmay began at least before 7Ma or 10±2Ma, with more activity at 3.6Ma when the Kunlun Pass downfaulted basin developed, and reached the climax at 0.6Ma during the Kunlun-Yellow River tectonic movement, when the XB shaped its tectonic-landform.