华南湘中南地区中生代构造变形特征及深部过程
投稿时间:2016-07-20  最后修改时间:2016-07-20  点此下载全文
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作者单位E-mail
李 勇 北京大学中国地质科学院 colyly@163.com 
董树文 中国地质科学院  
韩宝福 北京大学  
张岳桥 中国地质科学院地质力学所  
中文摘要:华南板块地处西太平洋俯冲构造域与特提斯构造域的交汇地带,经历了三叠纪特提斯洋关闭导致的陆-陆碰撞和古太平洋板块俯冲的大地构造过程。然而,关于华南板块内部复杂变形和丰富岩浆作用的构造属性,对应古特提斯和古太平洋构造体制转换的记录等仍然存在着严重的分歧。本文通过华南中部湘中南地区发育的大型叠加褶皱系统的构造解析、相关断层滑动矢量构造反演,结合同构造岩浆岩年代学研究,恢复两期褶皱的变形样式和叠加机制,建立华南中部早中生代两期重要的构造-岩浆事件及其构造应力场。其中,鉴别出两期叠加构造中早期E-W/WNW向褶皱与三叠纪岩浆系统,受控于NE-SW向挤压应力场,与三叠纪华南南部与印支地块碰撞、北部与华北地块碰撞事件相协调;晚期近NE/NEN向褶皱近直交地叠加在近早期褶皱之上,形成穹-盆(dome-basin)样式的大型叠加褶皱系统,这期褶皱受控于NWW-SEE向的挤压应力场,结合卷入变形的地层关系和岩浆岩年代学数据,确定了大致形成与中-晚侏罗世,对应古太平洋板块俯冲事件。大型叠加褶皱样式的建立和两期褶皱变形事件的鉴别,对华南陆内复杂变形的过程和动力学背景的解释提出重要的时空约束,对理解华南陆内造山作用乃至中国东部的早中生代构造序列具有重要的参考价值。 通过穿越骑田岭岩体的78km高精度人工地震剖面,本文揭示了郴州-临武断裂深部特征和地壳结构。郴州-临武断裂整体倾向NW,地震反射清晰,断裂由地表延伸到骑田岭岩体下部,推测一直可延伸到莫霍面。在地震剖面中莫霍面在骑田岭岩体下部出现了不连续,由深部向上一直到地表出现了无地震反射的纵向透明通道,并穿过郴州-临武断裂。结合地表地质,得到郴州-临武断裂是一条先存断裂在中生代活化,后经历了多期运动。在华南中生代陆内变形过程具有非常重要的意义,是中生代雪峰-江南造山带挤压隆升时的东边界大型逆冲断层。
中文关键词:叠加褶皱  构造应力场  郴州-临武断裂  人工地震剖面  华南板块
 
Episodic Mesozoic constructional events of central South China: constraints from lines of evidence of superimposed folds, fault kinematic analysis, magma geochronology and seismic-reflection profiling
Abstract:The South China block (SCB), located in the convergence zones of the western Pacific subduction tectonic domain and Tethyan tectonic domain, has experienced complex tectonic processes, including the continent–continent collision caused by the closure of the Palaeo-Tethys Ocean, and the subduction of the Palaeo-Pacific plate. However, due to complex intracontinental deformation and abundant magmatism, there are serious divergences in the corresponding records of the tectonic transformation from Palaeo-Tethys to Palaeo-Pacific. We have analysed the map-scale superimposed fold system developed in central SCB and also inverted the palaeo-stress field based on the fault–slip vectors. On this basis, the deformation styles and superposition mechanism of two-stage folds were recovered to establish the tectonic stress field in early Mesozoic and tectono-magmatic events by combining the chronology of the accompanying syntectonic magma. The early E–W/WNW-trending folds and Triassic magmatic system were identified; these were controlled by the NE–SW-trending compressive stress field, to coordinate with the collisions between the SCB and the Indochina block in the southwest, and the North China block in the north. The late NE/NNE-trending folds superimposed on the early folds in an orthogonal way to form a large-scale dome-basin superimposed fold system, which were controlled by the WNW–ESE-trending compressive stress field. According to the strata relations involved in deformation and the chronology data of magmatic rocks, it could be determined that NE/ENE-trending folds would be formed during the Mid- to Late Jurassic, corresponding to the westward subduction events of the Palaeo-Pacific plate. The establishment of the large-scale superimposed fold styles and the identification of fold deformation in the Triassic and Jurassic are important for understanding the early Mesozoic tectonics of South China, and even for all East Asia continent. In particular, it can provide important temporal and spatial constraints to explain the complex deformation process and geodynamic settings of South China in the early Mesozoic. We present results of a 78-km-long high-resolution seismic reflection profile across Qitianling granite. For the first time, its reveals deep crustal characteristics of Chenzhou-Linwu fault. The Chenzhou-Linwu fault tending NW in the clearly seismic reflection profile, from ground to the deeper of the Qitianling pluton, and suggesting that has been extended to the Moho. The Moho, in the lower of Qitianling granite, is discontinuous. Combined with surface geology, the seismic reflection profile shows that the Chenzhou-Linwu fault was a pre-existing fault and multi-reactivating in Mesozoic, displayed boundary fault of the Xuefeng-Jiangnan orogenic belt upliftting in intracontinental deformation process of the SCB.
keywords:Superimposed fold  tectonic stress field  Chenzhou-Linwu fault  seismic reflection profile  South China.
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