同构造沉积分析反演逆冲构造变形过程——燕山东段凌源南部中生代逆冲构造变形过程研究

Syntectonic sedimentation analysis applied to the reconstructionof the thrusting deformation process: An example fromthe Mesozoic thrust tectonics in eastern Yanshan Orogenic Belt,south of Lingyuan City, western Liaoning Province

介绍了同构造沉积分析的基本概念、研究思路、主要研究方法及其在区域构造变形过程研究中的重要作用。基于对辽西凌源南部区域构造变形、晚侏罗世土城子组同构造沉积粗碎屑沉积物成分变化规律的研究 ,获得如下主要认识 :( 1)同构造沉积始于髫髻山组火山活动之后 ;沉积物成分变化及古水动力特征表明 ,同构造沉积物源区主体位于盆地西侧褶皱隆起区 ,而不是来自南东方向的大型逆冲断层上盘的前渊沉积 ;而且显示了正常层序的物源区倾斜岩层的剥蚀和揭顶过程 ;当时的剥蚀作用已达中元古界蓟县系雾迷山组上部。 ( 2 )分布于郭家店盆地和邓杖子盆地之间的中元古界长城系地层“残片” ,与其东侧北票组间为向SEE逆冲的断层接触 ,而西侧与土城子组 (原邓杖子组 )之间为不整合接触 ;在老虎沟东南长城系地层“残片”不复存在的区域 ,土城子组不整合于北票组之上。该“残片”很可能是髫髻山组火山活动之前指向SEE的逆冲构造变形形成的飞来峰构造的残余部分。( 3 )凌源南部中生代逆冲构造变形可以区分为 :早侏罗世北票组之前 (印支期 )由北向南的逆冲作用、北票组之后髫髻山组之前向SEE的冲断推覆、髫髻山组之后的逆冲褶皱变形与同构造沉积作用以及九佛堂组之后局部的逆冲作用。

The ideas and concepts regarding to the analysis of syntectonic sedimentation are briefly introduced together with the investigation approaches and its potential implications to the research of regional tectonic deformation processes. It was studied that the tectonic deformations together with the conglomerate composition variation within the Late Jurassic Tuchengzi Formation in south of Lingyuan City, western Liaoning Province, the following conclusions are reached. (1) The syntectonic/synkinematic sedimentation in the research area was commenced after the volcanism of the Tiaojishan Formation. The provenance area was located to the west of the synkinematic sedimentary basin—Dengzhangzi Basin, instead of the east side of the basin. Dengzhangzi Basin was not a foredeep sedimentary basin of the westward thrusting as it was thought to be by previous investigators. Variations of the conglomerates within the Tuchengzi Formation indicate an erosion and unroofing sequence of the tilted normal sequence of the provenance strata. The erosion reached the upper part of the Wumishan Formation of the Mesoproterozoic Jixian Group. (2) The contacts between the relic slices of Mesoproterozoic Changcheng Group, lying between the Niuyingzi-Guojiadian Basin and the Dengzhangzi Bansin, and the Beipiao group to the east is a major east southeast-ward thrust fault. To the northwest side, however, the Tuchengzi Formation lies unconformably on top of the relics of Changcheng Group. In the area SE of Laohugou where the Changcheng Group disappeared, the Tuchengzi Formation lies directly on top of the Beipiao Formation. The relics of Changcheng Group between the two basins aforementioned is interpreted to be a klippe formed during an extensive east-south-east thrusting events of prior to the volcanic activity of Tiaojishan formation. (3) The thrusting deformation sequence in the south of Lingyuan City, western Liaoning Province, could be identified as follows: starting from a southward thrusting prior to the Early Jurassic Beipiao Formation (the Indosinian), then to the east-south-east ward thrusting before Tiaojishan Formation followed by a thrusting and associated folding with vergence to the southeast after Tiaojishan Formation, finally to the ending of contraction deformation with local thrusting deformation within the Early Cretaceous Jiufotang Formation. About 35% shortening within the covering sequence was achieved during the east-south-east thrusting and folding in the study area.