西秦岭地区东昆仑-秦岭断裂系晚新生代左旋走滑历史及其向东扩展

要通过在TM遥感图像解译和野外观测的基础上,描述了东昆仑断裂带东段活动形迹的组成和活动断层地貌特征,阐述了甘南高原西秦岭地区新近纪拉分盆地的沉积-构造特征,提出了该区东昆仑-秦岭断裂系晚新生代左旋走滑伸展-走滑挤压-走滑伸展的3个阶段的构造变形模式。指出,中新世晚期至上新世早期,东昆仑-秦岭断裂系以左旋走滑伸展活动为主,伴随着西秦岭地区拉分盆地的形成和超基性火山岩群的发育。这期左旋走滑伸展活动向东扩展导致了渭河盆地新近纪引张应力方向由早期的NE-SW向转变为晚期的NW—SE向。上新世晚期以来(约3．4Ma以前),东昆仑-秦岭断裂系以左旋走滑挤压活动为主,导致早期拉分盆地的轻微褶皱变形,走滑挤压活动主要集中在东昆仑东段玛沁-玛曲主断裂带上。该期构造变动持续到早更新世,它的向东扩展产生了广泛的地壳形变效应,包括青藏东缘岷山隆起带的快速崛起、华北地区汾-渭地堑系的形成和发展以及郯庐断裂带右旋走滑活动等。中、晚更新世时期,断裂系以走滑伸展变形为主,主要集中在东昆仑断裂带东段3个分支上,地块向东挤出伴随着顺时针旋转。

Late Cenozoic Left-Slip Faulting Process of the East Kunlun-Qinling Fault System in West Qinling Region and Its Eastward Propagation

Based on TM imagery interpretation and field observations, this paper has described the distribution and morphostructural features of main active faults in East Kunlun, analyzed tectono-sedimentary characteristics of the Neogene pull-apart basins in West Qinling region, and proposed a 3-stage evolutionary model for the East Kunlun-Qinling fault system in Late Cenozoic. It is pointed out that the East Kunlun-Qinling fault system behaved as transtensional strike-slip faulting from Late Miocene to Early Pliocene, with the development of pull-apart basins and ultrabasic volcanic activities along the fault zones. The onset of this faulting stage was concomitant with the change in the direction of extension from NE-SW to NW-SE in Weihe graben. Beginning from Late Pliocene (about 3.4 Ma ago), the kinematics of the East Kunlun-Qinling fault system changed into transpressional strike-slip faulting, which caused gentle deformation of the Neogene pull-part basins. This deformation stage lasted till Early Pleistocene. Its eastward propagation caused widespread effect of crustal deformation, which included the initiation and development of the N-S trending Minshan uplift in the eastern margin of Tibetan plateau, the Fen-Wei graben system in North China and the right-lateral strike-slip motion along the Tan-Lu fault zone. During Middle and Late Pleistocene, the fault system was active left-laterally with a normal slip component, mostly localized along the three bifurcated fault zones in East Kunlun.