北大别造山后伸展变形特征及其深部动力学意义  

Deformation Mechanism of Post-orogenic Extension and its Implications for Deep Dynamics in the Northern Dabie Orogenic Belt

作　　者：向必伟 陈林[2] 张强[2] 王志国[2] 高成 XIANG Biwei;CHEN Lin;ZHANG Qiang;WANG Zhiguo;GAO Cheng(School of Earth Sciences,East China University of Technology,Nanchang 330100,Jiangxi,China;The 7th Geological Brigade of Zhejiang Province,Lishui 323060,Zhejiang,China;State Key Laboratory Nuclear Resources and Environment,East China University of Technology,Nanchang 330100,Jiangxi,China)

机构地区：[1]东华理工大学地球科学学院,江西南昌330100 [2]浙江省第七地质大队,浙江丽水323060 [3]东华理工大学,核资源与环境国家重点实验室,江西南昌330100

出　　处：《大地构造与成矿学》2022年第5期867-883,共17页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(42162019、41472194、41002069)资助。

摘　　要：大别造山带位于华北板块南缘,其早白垩世伸展活动是华北克拉通伸展破坏活动的一部分。北大别穹隆是造山带伸展构造主要分布区域,其构造特征、岩石变形特征以及深部动力学对理解造山带伸展活动以及华北克拉通破坏具有重要意义。北大别穹隆内变形组构的构造归属及其所指示的岩石变形方式是研究穹隆伸展过程及深部动力学机制的基础。本次工作对北大别穹隆内发育不同倾伏方向拉伸线理的变形岩石开展了详尽的构造观察和锆石U-Pb年代学分析。年代学结果显示,6个样品的锆石边部给出了118~131Ma的年龄。结合实际构造观察与分析,我们认为这一变质年龄代表了拉伸线理的形成时间。北大别穹隆从边界剪切带到中部的垂向剖面上,变形组构分布指示边界剪切带以简单剪切为主的平面应变;随着深度增大,垂直剪切方向的主应变愈发显著,形成垂向上缩短,平行于剪切方向(上盘向NW)和垂直于剪切方向的伸长都不可忽略的三维变形。岩石变形特征及构造组合特征揭示,北大别穹隆总体上是以边界剪切带为拆离带的变质核杂岩,是古太平洋板块后撤的结果;拆离带以下的中-下地壳岩石发生的伸展,是加厚地壳受热活化后重力垮塌的结果。The Dabie orogenic belt, occurring along the southern margin of the North China Craton, experienced the Early Cretaceous extension triggered by the North China Craton thinning or destruction. The North Dabie Dome(NDD)is the major extensional structure in the Dabie orogenic belt. The tectonic processes, kinematics, and deep dynamics in the NDD are of great significance in understanding the extension of the orogenic belt and the destruction of the North China Craton. Field observations show that the plunging directions of the lineations near the center of the NDD are increasingly dispersive. When and how these lineations developed are critical issues for the study of the dome extension processes and deep dynamic mechanisms. In this contribution, zircon U-Pb dating was carried out on the deformed rocks.The rims of the zircon grains from six out of seven samples yield metamorphic ages of 118–131 Ma. Combined with the structures, we believe that these metamorphic ages represent the deformation time of the Early Cretaceous extension in the NDD. According to the distribution of the deformation fabrics, a pattern of the geology and kinematics of the extensional deformation in the middle-lower crust is established as follows. In the upper shear zone, the rock deformation was dominated by a simple shearing plane strain. With increasing depth, the principal strain perpendicular to NW(shear direction) increased and became mostly equivalent to the one along NW in the middle NDD. The structure assemblages of the NDD exhibit as a metamorphic core complex and a gravity collapse in the middle-lower crust. It can be inferred that the top to NW detachment of the metamorphic core complex was likely driven by the retreat of the Paleo-pacific plate, whereas the SE extension resulted from the gravity collapse because the thickened middle-lower crust was reheated.

关 键 词：北大别穹隆 造山后伸展 重力垮塌 构造年代学 侧向流变 

分 类 号：P542[天文地球—构造地质学]