Late Paleozoic tectonic transition from subduction to collision in the Chinese Altai and Tianshan (Central Asia): New geochronological constraints
Late Paleozoic tectonic transition from subduction to collision in the Chinese Altai and Tianshan (Central Asia): New geochronological constraints
复制标题
中国阿尔泰和天山（中亚）晚古生代从俯冲到碰撞的构造转换：新的年代学约束
DOI：
10.2475/01.2021.05
复制
发表时间：
2021
影响因子：
2.9
通讯作者：
Pengfei Li;M. Sun;C. Yuan;F. Jourdan;Wan-Long Hu;Yingde Jiang
中科院分区：
文献类型：
--
作者：
Pengfei Li;M. Sun;C. Yuan;F. Jourdan;Wan-Long Hu;Yingde Jiang
中亚造山带（CAOB）是世界上最大的增生造山带，自新元古代以来经历了漫长的增生历史，并在晚古生代经历了与古亚洲洋闭合相对应的碰撞阶段。从俯冲到碰撞的构造转换的确切过程仍然缺乏约束。在这里，我们解决这个问题，通过研究晚古生代构造演化的中国阿尔泰和天山造山带在西部CAOB。我们提供了来自中国阿尔泰和天山造山带两个地区的新的年代学数据，这使我们能够将多期变形与造山过程联系起来。在中国阿尔泰造山带富蕴地区，我们对四个样品进行了独居石U-Pb测年，这些样品显示出普遍的叶理，最初呈近水平方向（DS 2/DQ 2）。独居石U-Pb年龄集中在284 ~ 281 Ma，代表近水平面理（DS 2/DQ 2）的形成时间，可能是阿尔泰造山带与东准噶尔地体碰撞的平行伸展作用的结果。在中国天山造山带的干沟地区，对一个中天山南右行剪切带中的云母片岩进行了白云母40 Ar/39 Ar坪年龄测定，结果为256.6 ± 0.6Ma。这一年龄证实了中国天山造山带二叠纪活动的右旋走滑变形（DCT 4）。而天山右行走滑剪切带中的3个糜棱岩片岩/花岗岩样品的40 Ar/39 Ar坪年龄分别为353.9 ± 1.9Ma（黑云母）、353.9 ± 1.5Ma（黑云母）和352.1 ± 0.7Ma（白云母）。我们解释这些早石炭世的年龄要么代表前二叠纪右旋剪切事件，或记录早石炭世的构造热事件与重结晶云母不重置在二叠纪走滑变形（DCT 4）。另一个280.9 ± 0.5Ma的40 Ar/39 Ar坪年龄（角闪石）来自横切中国南天山造山带宏观褶皱（DST 2）的基性岩墙（粗玄岩），为这些褶皱提供了最小的时间限制。这一时代支持中国天山造山带的褶皱变形（DST 2）与右行剪切（DCT 4）同时发生。结合全面综合现有的地质和年代学数据，我们认为，造山带平行伸展和压扭构造可能发挥了重要作用，晚古生代弧/大陆合并的西部CAOB。
The evolution of the largest accretionary orogen in the world, the Central Asian Orogenic Belt (CAOB), involved a prolonged accretion history since the Neoproterozoic, followed by a collisional phase in response to the closure of the Paleo-Asian Ocean in the latest Paleozoic. The exact process for the tectonic transition from subduction to collision is still poorly constrained. Here we address this issue by investigating the late Paleozoic tectonic evolution of the Chinese Altai and Tianshan orogens in the western CAOB. We provide new geochronological data from two areas of the Chinese Altai and Tianshan orogens, which allow us to link polyphase deformation with orogenic processes. In the Fuyun area of the Chinese Altai Orogen, we conducted monazite U-Pb dating on four samples that show pervasive foliations with the originally sub-horizontal orientation (DS2/DQ2). The monazite U-Pb ages cluster at ∼284 to 281 Ma, which interpreted to represent the time of sub-horizontal foliations (DS2/DQ2) that may result from orogen-parallel extension related to the collision of the Chinese Altai Orogen with the East Junggar Terrane. Farther south, in the Gangou area of the Chinese Tianshan Orogen, we obtained a muscovite 40Ar/39Ar plateau age of 256.6 ± 0.6 Ma for a mica schist from the dextral South Central Tianshan Shear Zone. This age confirms the Permian activity of dextral strike-slip deformation (DCT4) in the Chinese Tianshan Orogen. In contrast, three mylonitic schist/granitoid samples from the dextral Main Tianshan Shear Zone are characterized by 40Ar/39Ar plateau ages of 353.9 ± 1.9 Ma (biotite), 353.9 ± 1.5 Ma (biotite) and 352.1 ± 0.7 Ma (muscovite). We interpret these early Carboniferous ages to either represent a pre-Permian dextral shearing event, or to record an early Carboniferous tectono-thermal event with recrystallized micas not reset during the Permian strike-slip deformation (DCT4). An additional 40Ar/39Ar plateau age of 280.9 ± 0.5 Ma (hornblende) from a mafic dike (dolerite) that crosscuts macroscopic folds (DST2) in the southern Chinese Tianshan Orogen, provides a minimum time constraint for these folds. This age supports the simultaneous folding deformation (DST2) with dextral shearing (DCT4) in the Chinese Tianshan Orogen. Combined with a comprehensive synthesis of available geological and geochronological data, we argue that orogen-parallel extension and transpressional tectonics might have played a significant role in the late Paleozoic arc/continental amalgamation of the western CAOB.