青藏高原东北缘弧形构造带新生代地层沉积序列及年代学研究进展

Stratigraphic sequence characteristics and geochronology research progress of the Cenozoic in the arcuate tectonic belt on the northeastern margin of the Tibet Plateau

青藏高原东北缘弧形构造带新生代的构造变形和沉积充填过程既受到了太平洋板块俯冲的远程效应影响,也受到了青藏高原北东向扩展的控制。确定新生代地层的沉积时代是深入理解青藏高原东北缘弧形构造带内构造变形和沉积充填过程的重要前提,但是目前弧形构造带内新生代地层序列和沉积时代仍存在诸多争议。文章系统研究了弧形构造带内古近纪至新近纪沉积序列和地层时代,结果显示弧形构造带内寺口子组、清水营组、彰恩堡组和干河沟组的沉积时代分别为中晚渐新世、晚渐新世—早中新世、中中新世—晚中新世和晚中新世—上新世。综合分析了古近纪至新近纪不整合界面的形成时代,重新厘定了古近纪—新近纪两期不整合及其大地构造意义,第一期不整合发育在清水营组与彰恩堡组之间,时代为早中新世,指示了青藏高原的北东向扩展到达弧形构造带;第二期不整合发育在彰恩堡组与干河沟组之间,时代为晚中新世,指示了青藏高原北东向扩展对弧形构造带的改造达到高峰。讨论了弧形构造带沉积充填过程与构造演化的耦合关系,新生代盆地的沉积演化过程主要经历了三个阶段:自中渐新世至早中新世,弧形构造带主要受控于早期的滨太平洋伸展构造体系域,处于伸展构造背景;早中新世至晚中新世,构造变形和盆地演化开始受到青藏高原北东向扩展的影响,处于挤压构造背景;晚中新世至上新世,弧形构造带持续快速隆升,并且走滑断裂体系的发育分割了新生代盆地。

The Cenozoic tectonic deformation and sedimentary processes in the arcuate tectonic belt along the northeastern margin of the Tibetan Plateau have been influenced by the remote effect of the subduction of the Pacific Plate as well as controlled by the northeastward extension of the Tibetan Plateau.Determining the sedimentary age of the Cenozoic strata is an essential prerequisite for understanding these tectonic deformation and sedimentary processes.However,the sequence and depositional age of the Cenozoic strata in the arcuate tectonic belt is still controversial.This paper systematically studied the Paleoproterozoic to Neoproterozoic sedimentary sequences and stratigraphic ages in the arcuate tectonic belt.The results show that the sedimentary ages of the Sikouzi Formation,the Qingshuiying Formation,the Zhang'enbao Formation,and the Ganhegou Formation in the arcuate tectonic belt are the Middle to Late Oligocene,the Late Oligocene-Early Miocene,the Middle Miocene-Late Miocene,and the Late Miocene-Pliocene,respectively.We systematically analyzed the two unconformities of the Paleocene to Neoproterozoic and refined their formation age as well as geotectonic significance.The first unconformity developed between the Qingshuiying Formation and the Zhang'enbao Formation in the Early-Middle Miocene,which indicates the appearance of the remote effect caused by the northeastward extrusion of the Tibet Plateau at about Early Miocene.The second unconformity developed between the Zhang'enbao Formation and the Ganhegou Formation,which implies the summit of tectonic activities caused by the northeastward extrusion of the Tibet Plateau at about the Late Miocene.It is concluded that the Cenozoic basins have evolved through three stages based on the coupling relationship between the sedimentary process and the tectonic evolution.From the Middle Oligocene to the Early Miocene,the tectonic stress field of the arcuate tectonic belt was controlled by extension under the remote effect of the rollback of the subducted Pacific Plate.The tectonic stress field changed into compression under the effect of the northeastward extrusion of the Tibet Plateau from the Middle to Late Miocene;Significant and sustainable tectonic uplift developed in the arcuate tectonic belt from the Late Miocene to Pliocene,and the Cenozoic basins were divided by the strike-slip fault systems.