摘要
西伯利亚板块与华北克拉通碰撞导致古亚洲洋闭合,形成了幅员辽阔的中亚造山带,该带内记录了丰富的板块碰撞信息,揭示深部缝合边界对于研究洋-陆俯冲到陆-陆碰撞的深部动力学过程具有重要的科学意义.本文对查干敖包—化德410km大地电磁测深(MT)剖面数据进行反演,获得二维电性结构,为研究西伯利亚板块与华北克拉通碰撞带深部构造形迹、碰撞边界问题提供地电结构的依据.结合人工反射地震及地质资料获得以下认识:(1)西伯利亚板块与华北克拉通碰撞带地壳存在多组"U"型低阻异常,多对应弧型、倾斜或"鳄鱼嘴"状反射界面.莫霍面存在两处错断现象,并与深部电性梯度带对应.岩石圈地幔除白乃庙岛弧呈低阻块体外,均为高阻块体,这些电性结构特征反映了南北汇聚所形成的构造形迹.(2)碰撞带可分为二连—贺根山和索伦—西拉木伦河两个不同时期的汇聚体系,晚泥盆世—晚石炭世早期形成的二连—贺根山汇聚体系由二连—贺根山增生杂岩带、宝力岛弧地体及断裂带组成,深部缝合边界位于二连浩特.而晚二叠—早三叠的索伦—西拉木伦河汇聚体系由二道井子增生杂岩带和温都尔庙增生杂岩带及断裂带组成,深部缝合边界位于苏尼特右旗.(3)在锡林浩特地区软流圈内部存在高阻异常,可能为俯冲消失的洋壳或碰撞造山后拆离的岩石圈残片.
The collision between the Siberia plate and the North China Craton led to the closure of the ancient Asian Ocean and the formation of a vast central Asian orogenic belt,which recorded abundant plate collision information and evidences that the deep suture boundary is of great significance to the study on the deep dynamic process from oceanic-continent subduction to continent-continent collision.To further address this issue,this paper presents an inversion of MT data along the 410 km-long Chagan Obo-Huade profile,thus to delineate a two-dimensional electrical structure beneath it.It provides evidence for the study of the deep structure and collision boundary between the Siberian plate and the North China Craton collision zone.Combining with seismic reflection and geological data we can obtain the following conclusions:(1)There are many groups of"U"-shaped low-resistance anomalies in the crust of the Siberian plate and the North China Craton collision zone which are correspond to arc-like and"crocodile mouth"-shaped reflection interfaces.Two dislocations on the Moho surface can be recognized,consistent with the deep electrical gradients.In addition to the low-resistivity blocks beneath the Bainaimiao island arc,the lithosphere of highresistivity.These physical characteristics reflect the structural traces formed by the north-south convergence.(2)The collision zone can be divided into two different converging systems:Erenhot-Hegenshan and Soren-Xilamulun.The Erenhot-Hegenshan convergence system which formed in the Late Devonian-Late Carboniferous is composed of the renhot-Hegenshan accretion complex belt,Baolidao Island arc geological body and fault zone,of which the deep suture boundary is located in Erenhot.And the Late Permian-Early Triassic Soren-Xilamulun convergence system consists of the Erdaojingzi accretional complex belt and the Wenduermiao accretion complex belt and the fault zone,of which the deep suture boundary is located in Sonid Zuoqi.(3)There are high resistivity anomalies in asthenosphere beneath the Xilinhaote area,which may be the fragments of subducted oceanic crust or detachment lithosphere after collision orogeny.