柴达木盆地大红沟剖面新生代地层磁组构特征及构造意义  

AN ANISOTROPY OF MAGNETIC SUSCEPTIBILITY STUDY OF THE CENOZOIC DAHONGGOU SECTION IN NORTHERN QAIDAM BASIN AND ITS TECTONIC IMPLICATIONS

作　　者：苏庆达 聂军胜[1] Joel E. Saylor Brian K. Horton Meredith A. Bush 陈文汉[1] 

机构地区：[1]兰州大学资源环境学院,西部环境教育部重点实验室,兰州730000 [2]Department of Earth and Atmospheric Sciences, University of Houston, Houston TX 77204- 5007, USA [3]Department of Geological Sciences and Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712, USA [4]Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712, USA

出　　处：《第四纪研究》2016年第4期859-869,共11页Quaternary Sciences

基　　金：国家自然科学基金优青项目（批准号：41422204）和国家自然科学基金面上项目（批准号：41172329）共同资助致谢感谢审稿专家和编辑部老师提出的建设性修改意见.

摘　　要：研究表明柴达木盆地新生代沉积物磁化率各向异性能够有效地记录印度-欧亚板块碰撞的应力场方向，然而过去对该盆地磁组构研究主要集中在始新世下干柴沟组和中新世下油砂山组，因此不能有效界定应力场方向发生变化的年代。本文对柴达木盆地北缘大红沟剖面沉积岩进行了详细的磁组构分析，获得了新生代较高分辨率（平均6~10m）的磁化率各向异性数据。结果表明，下干柴沟组、上干柴沟组、下油砂山组和上油砂山组及狮子沟组磁面理发育较为明显，磁化率椭球体呈压扁状，具有较强的压扁效应；而路乐河组磁线理发育更为明显，可能记录了较强的构造作用力。路乐河组和下干柴沟组磁组构指示构造应力的方向为近南北向；上干柴沟组和下油砂山组磁组构指示应力的方向为东北-西南向。因此，柴达木盆地由南北向挤压转变为东北-西南向挤压发生在始新世下干柴沟组和渐新世上干柴沟组之间，指示青藏高原北部应力场发生了变化。我们将青藏高原北部应力场的转变归因于阿尔金断裂的左旋走滑，而中晚中新世应力的进一步加强可能与下地壳流或昆仑山断裂开始走滑也有关系。这一研究加深了对青藏高原北部变形机制的理解。Anisotropy of magnetic susceptibility （AMS） of sediments is very sensitive to paleostress directions. Past studies demonstrate that AMS effectively records paleostress even where large-scale deformation structures are absent. Particularly, when deformation is weak, the intermediate AMS ellipsoid axis （K2） is parallel to the compression direction and the minimum ellipsoid axis （K3） is perpendicular to bedding. With increasing deformation, K3 begins to scatter away from the bedding pole, and results in a girdle oriented parallel to the maximum compressive strain. Past studies also demonstrate that it is the paramagnetic silicate minerals instead of ferrimagnetic minerals that control the magnetic fabrics of sediments. Here we present the results of strain analyses based on AMS results from a 6172m-thick Paleogene-Pliocene Dahonggou stratigraphic section （37°32＇55＂N, 95°09＇56＂E to 37°28＇42＂N, 95°07＇57＂E） in the northern Qaidam Basin to reconstruct the stress history within the northern Qaidam Basin. The Qaidam Basin is surrounded by the Altyn Shan to the west, the Qilian Shan to the east, and the Kunlun Shan to the south, and sits at an average elevation of 2500~3000m above sea level. The internally drained Qaidam Basin covers an area of more than 120000km2 and is a key region to test models about various uplift mechanisms of the Tibetan Plateau. The Dahongou section is divided into six formations： the Paleocene-Early Eocene Lulehe Formation, the Middle-Late Eocene Xiaganchaigou Formation, the Oligocene Shangganchaigou Formation, the Early Miocene Xiayoushashan Formation, the Late Miocene Shangyoushashan Formation, and the Pliocene Shizigou Formation. A total of 1327 oriented cylinder samples were collected with Portable Rock Core Drills at an average interval of 3~5m and were cut to a height of about 2.2cm in the laboratory. We measured AMS of 591 samples at an average interval of 6~10m using a MFK 1A with an automated sample handling system. The AMS data from the Paleocene

关 键 词：柴达木盆地 磁化率各向异性 阿尔金断裂 青藏高原 

分 类 号：P534.612[天文地球—古生物学与地层学] P318.4[天文地球—地质学]