关键词: 柯坪推覆构造, 晚第四纪, 变形样式, 缩短速率

Abstract: Less attention has been paid to the deformation pattern, shortening amount and shortening rate in late Quaternary across Kalpin thrust system. This paper tries to discuss them, mainly in the eastern part of the thrust system by doing field investigation along the faults and folds, measuring geomorphic deformation, excavating trenches in some important sites where young alluvial fans were displaced obviously and dating young deposits of alluvial terrace. There are two types of deformation in surface and near surface for the Kalpin thrust system in late Quaternary i.e. the movement of thrust faults at lower angles and bending of young folds. Both kinds of deformation are shown by shortening and uplifting of young geomorphic surfaces. The surface ages of 3 stages are concluded by dating 20 examples using TL method in the studying area and comparing the results of previous people on deposition and incision times of alluvial terraces in Tianshan mountain area, and they are 100ka, 33～18ka and 6.6～8.2ka, respectively, for large-scale deformed alluvial surfaces: T₃, T₂, and T₁ in kalpin region. Then, the 19 shortening amounts and rates are obtained in the 13 sites along 4 rows of anticlines in front of Kalpin thrust system and Piqian fold. The shortening amounts and rates show that there are two sections where deformation is stronger than others. The two sections consist of two arcs that is toward the south. Shortening rates near top of arcs are 1.32mm/a in the west and 1.39mm/a in the east across the thrust system, respectively. Besides, deformation on front rows is stronger than that behind for bifurcate folds.

Key words: Kalpin thrust system, late Quaternary, deformation pattern, shortening rate