扬子地块西南瓮安穹隆早古生代构造变形特征及其区域构造意义  

The Paleozoic deformational characteristics and tectonic significance of the Weng'an Dome in the Southwest Yangtze Block

作　　者：宋志冬 邱亮[1] 张岳[1] 张翼西[1] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地学前缘》2018年第1期14-32,共19页Earth Science Frontiers

基　　金：国家重点基础研究发展计划"973"项目(2014CB440903);国家自然科学基金项目(41372212;41672216)

摘　　要：扬子地块在前泥盆纪与泥盆纪之间发生了一次强烈且影响广泛的早古生代构造事件。前人对扬子地块早古生代构造事件存在3幕、2幕和古地理格局变迁等不同认识。文中选取扬子地块西南早古生代构造保存较完整的瓮安穹隆体,通过6条构造剖面详细的构造层划分和不同方向构造叠加关系与构造变形样式和序列的解析,综合构造年代学限定,认为瓮安穹隆本质上为一构造叠加穹隆,其自古生代以来至少发育两期主要构造变形,即D1期早古生代构造变形和D2期燕山期构造变形。D1期变形以东西向褶皱、右行走滑-逆冲断层和东西向近直立间隔劈理为代表,为近南北向纵弯挤压变形的结果。相比之下,区域上早古生代构造变形仅发育于寒武系—志留系构造层及其下伏构造层中。D1期变形形成的东西向构造普遍被D2期构造横跨和叠加改造,表明其形成于寒武系—志留系构造层与上覆泥盆系—中三叠统构造层角度不整合之前。根据碎屑锆石年龄分布统计结果,早古生代构造运动在瓮安地区发生时间约晚于438 Ma;结合地质关系分析和近年来区域上大量测年数据结果,进一步限定其早古生代构造事件发生的时间为438~390 Ma。从华南早古生代构造运动的时间来看,华南早古生代构造运动形成的时间从南向北从早到晚迁移变化。The Early Paleozoic, a key and widespread tectonic event, occurred between the Devonian and PreDevonian in the Yangtze Block. Different models on the event, such as the three episodes, two episodes and continued changing in paleogeographic patterns, have been proposed. This paper focuses on the Wengan Dome in the Southwest Yangtze Block, which has well preserved and exposed Early Paleozoic deformation. Six geologic crosssections of the Weng’an dome were used for the detailed divisions of the tectonic layers; analyses of structural styles, tectonic superposition and deformational sequence with chronological constraints were also performed. The results suggest that the Wengan Dome is essentially a tectonic superimposed dome. The dome experienced at least two deformations since the Paleozoic, namely the Early Paleozoic deformation D1 and Yanshanian deformation D2. The D1 deformation is represented by the EWtrending folds, strikeslip to thrust faults and EWtrending approximate to vertical interval cleavages—all resulted from SN vertical extrusion; it is seen in the CambrianSilurian and underlying tectonic layers. The EWtrending structures of the D1 deformation were intercepted and superimposed by the D2 deformation. This indicates that the D1 deformation formed before the angular unconformity between the tectonic layers of the CambrianSilurian and the Upper Devonian to Middle Triassic. According to the distribution of the detrital zircons, the Early Paleozoic era occurred later than ca. 438 Ma in the Wengan Dome. Geological investigation presented in this study, and numerous data published in recent years, further support the hypothesis that the Early Paleozoic tectonic deformation appeared first in the southern area of the South China Block before propagating to the north.

关 键 词：瓮安穹隆 早古生代构造事件 构造变形 角度不整合 碎屑锆石分析 

分 类 号：P542[天文地球—构造地质学]