GEOMETRY,KINEMATICS AND TECTONIC EVOLUTION OF KEPINGTAGE THRUST SYSTEM

In this paper we have discussed the stratigraphy, geometry, kinematics and tectonic evolution of Kepingtage thrust system based on a lot of outcrop geological surveys and comprehensive interpretation with seismic profiles, MT profiles and gravity data. Kepingtage thrust system consists of many arcuate thrust nappes thrusting-oblique thrusting from north to south with inversed multi-anticlines and their front thrust faults, which were formed by Cambrian—Quaternary sedimentary rocks. It is discovered that the Puchang fault was formed by unconnected thrusting-oblique thrusting segments divided by nappes rather than an integrate strike-slip fault. The front thrust faults of each nappe combined with the related segments of Puchang fault form the thrusting-oblique thrusting front faults of the nappes and the whole thrust system. The nappes to the west of Puchang basement uplift show the nose structures dipping to the west, and the nappes to the east of Puchang basement uplift show the nose structures dipping to the east. Puchang basement uplift is a part of Bachu uplift extending below the Kepingtage thrust system. The front faults of the nappes form an integrate detachment surface in the deep along the bottom of Cambrian with the shallower depth in the southeast and deeper depth in the northwest (for the region to the west of Puchang basement uplift) and with the shallower depth in the west and deeper depth in the east (for the region to the east of Puchang basement uplift)(6~10 km). Kepingtage thrust system was formed in Late Quaternary and is still active at present. We consider that the basement detachment and the inner Mesozoic—Cenozoic detachment faults could not have formed some integrate fault surfaces in the dipping end of nappes, so the earthquakes with the magnitude larger than 6 will occur in the near future in these area.