Depositional features and sedimentary model of Buqu Stage in Mid-Jurassic in Qangtang Basin, Xizang (Tibet), China

The largest Mesozoic northward transgression in Qangtang Basin of Qinghai-Xizang (Tibet) Plateau occurred during the Buqu Stage, Middle Jurassic. Mainly filled with carbonate rocks, the whole basin is composed of transgression-regression sedimentary cycle. Field outcrops and indoor analysis revealed 8 types of sedimentary facies markers in this region. 4 types of sedimentary facies have been recognized: platform facies, platform marginal facies, foreslope facies and basin facies. Influenced by the northern Lazhuglung-Jinshajiang suture zone, central uplift region and southern Bangongco-Nujiang suture zone, these facies belts extended east-west. The sedimentary model was established based on observed depositional features. From their biological features and sedimentary characteristics, it is suggested that the paleoclimate was warm and humid at that time. The Buqu Formation is a promising target for oil and gas exploration in Shuanghu-Duoyong area in future.

PRESENT-DAY CRUSTAL MOVEMENT OF NORTH-EASTERN QINGHAI-TIBET PLATEAU

GPS observations of CMONOC and other network reveal that, relative to Dingxin fiducial station in Alashan block, the crustal movements of north eastern Qinghai Tibet plateau and its adjacent regions have the following characteristics:(i)The western part of Qilian block is shortening and moving mainly northeastward, the 8 mm/a motion of southern margin of Qaidam basin is almost completely absorbed by compressed subsidence of Qaidam basin and uplift of Qilian mountain; (ii) Eastern part of Qilian block manifests itself mainly as block like rotation or extrusion along Haiyuan left lateral fault,with an angular velocity of 0.135 /Ma; (iii) Due to the clockwise rotation of the eastern Qilian sub block in the NW Liupanshan range, Ordos block shows a slight anticlockwise rotation; (iv) Haiyuan left lateral fault and northern edge thrust fault of Qilian mountain jointly constitute the major northeastern boundary of Qinghai Tibet plateau judging from the present day crustal movement.

The Rotational Structure along the Eastern Segment of the Altyn Tagh Fault and Its Implications in Dynamics

As a result of the left-lateral strike-slipping of the Altyn Tagh fault in Neotectonic period, a contra-rotational structure, namely the Zhaobishan vortex structure, has developed at the juncture of the main Altyn Tagh fault and the northern fringe fault of the Qilian Mountains. Preliminary analysis on the deformation and evolution of the Zhaobishan vortex structure. In combination with the previous data, suggests that the tectonic transform between the Altyn Tagh fault and the northern fringe fault of the Qilian Mountains attributes to the deformation of the rotational structure. The existence of a series of rotational structures along the Altyn Tagh fault and on the northeastern edge of the Qinghai-Xizang(Tibet) plateau indicate that as the substance in the northern Qinghai-Xizang (Tibet) plateau moves clockwise around the eastern tectonic knot of the Himalayas, rotational structures become the principal mode on the northern marginal zone of the Plateau of transforming and absorbing tectonic deformation.