祁连山中段门源盆地新构造运动的阶段划分

门源盆地是祁连山中段的山间盆地，南北边缘均为断裂控制，发育古近系白杨河组、第四纪冰碛物和冰水堆积物。地层变形、地貌发育和断裂活动分期的差异显示新生代以来门源盆地经历了4个构造运动阶段。新生代最早的构造运动开始于渐新世中期（约30MaB．P．），Ⅰ级夷平面解体，盆地断陷形成并接收了白杨河组砂砾石沉积。第二阶段始于渐新世末期一中新世初（约23MaB．P．），盆地结束了沉降过程，白杨河组褶皱变形，这一过程持续至中更新世初期。第三阶段始于中更新世中期（约460kaB．P．），新的边界断裂形成，盆地再次断陷，堆积了厚度大于400m的冰碛或冰水堆积物，边缘断裂强烈活动，这一过程持续到晚更新世晚期（约30kaB．P．）。最新阶段始于30kaB．P．，盆地和两侧的山地整体抬升，盆地面由此前的加积过程转变为侵蚀切割过程，北缘断裂的活动由含走滑分量的逆冲性质转变为走滑性质，但走滑速率明显降低。

STAGES OF THE NEOTECTONIC MOVEMENT OF THE MENYUAN BASIN IN THE MIDDLE SEGMENT OF THE QILIAN MOUNTAINS

The Menyuan Basin is an intermontane basin in the central segment of the Qilian Mountains,bounded by boundary faults on the north and south.The basin is filled with the Paleogene Baiyanghe Formation and Quaternary tills and glaciofluvial deposits.The differences in rock deformation,geomorphological evolution and fault movement phases show that the Menyuan Basin underwent four stages of tectonic movements since the Cenozoic.The earliest Cenozoic tectonic movement began in the middle Oligocene(30 Ma B.P),when the I-order planation surface was disintegrated and basin was downfaulted and received sandy gravel deposits of the Baiyanghe Formation.The second stage occurred from the end of the Oligocene to the beginning of the Miocene(25 Ma to 460 ka B.P) and was characterized by the end of the basin subsidence,termination of Tertiary deposition and folding of the Baiyanghe Formation.This process continued to the initial middle Pleistocene.The third stage started in the middle part of the middle Pleistocene(460 ka B.P) and ended at 30 ka B.P.During the stage new boundary faults formed, the basin was again downfaulted and received >400 m thick tills and glaciofluvial deposits,and boundary faults were very active.This process lasted till the late part of the late Pleistocene(30 ka B.P).The latest stage began at 30 ka B.P,which was marked by the wholesale uplift of the basin and mountains at both sides of the basin and transition of the basin surface process from deposition to incision and erosion.The fault movement changed from thrusting with a strike-slip component to strike-slip movement,but the strike-slip rate decreased significantly.