武陵-江南造山带中段地壳结构及其物质组成差异--基于地球化学和地球物理异常特征研究

Differences in Crustal Structure and Composition in Wuling-Middle Part of Jiangnan Orogenic Belt:Based on Geochemical and Geophysical Anomalies

区域深部结构和物质组成差异与成矿成藏及其保存具有密切关系。武陵—江南造山带中段区域西部地区是我国重要的含油气地区,中东部则以盛产铅锌等金属矿产为特征。本文通过对研究区地球化学和地球物理异常特征进行研究,探讨研究区地壳结构和物质组成差异的地球动力学背景。地球化学聚类分析结果表明武陵山—江南造山带中段不同块体之间在物质组成及元素富集规律上存在较大差异,推测与深部具有不同的构造特征有关。区域重、磁、震地球物理研究表明东部隔槽式褶皱断裂构造系统发育,且在中下地壳发育有大尺度叠瓦式逆冲断层;西部仅在上地壳尺度存在隔挡式褶皱。区内南北重力梯度带为纵贯中国南北的大兴安岭—太行山—武陵山重力异常梯度带的南段,它将华南陆块明显地分为东西两大部分。东西两部分的地质构造格局、地壳厚度以及地形地貌等方面都有巨大差别,地球物理属性差异揭示梯度带东侧构造演化主要受古太平洋西向俯冲及其远程应力作用影响,与中生代晚期古太平洋俯冲角度/方向和(或)后撤引发挤压-构造伸展体制转换有关。地球化学和地球物理综合研究表明不同块体的相互作用为湘西—鄂西成矿带成矿提供了有利条件,成矿带与齐岳山断裂和江南造山带边界交汇区域具有多处明显的化探高值异常,推测其具有进一步找矿前景。下一步,仍需加大地球化学和地球物理综合解释投入,为研究区域构造变形、演化及成矿过程提供进一步制约。

Regional deep structures and bulk crustal compositions are associated with mineralization and oil and gas accumulation and contribute to their preservation.The western part of the Wuling–Jiangnan orogenic belt represents an important petroliferous basin in China,while the central and eastern parts are characterized by an abundance of metals such as lead and zinc.Here,we investigate the geochemical and geophysical anomalies to elucidate the geodynamic background controlling the variation in crustal structure and composition of the Wuling–Jiangnan orogenic belt.We show substantial spatial variations in composition and element enrichment using geochemical cluster analysis and suggest that this may be related to certain structures deep in the crust.Regional geophysical studies(gravity,magnetic,and seismic)show a thrust-related chevron-type syncline zone in the east and a large-scale detachment in the middle and lower crust.While in the west,there are only thrust-related chevron-type anticlines in the upper crust.A north–south gravitational gradient belt is observed through the southeastern region,which divides the study area into two parts.There are substantial differences in crustal structure,thickness,composition,deformation,and topography.Variations in geophysical properties show that the tectonic evolution of the eastern side of the gravitational gradient belt is primarily affected by the westward subduction of the paleo-Pacific and its far-field stress,which is related to a geodynamic compressional–extensional background transition.This transition may be caused by the retreat and(or)change in the angle or direction of subduction during the Late Mesozoic.A comprehensive geochemical and geophysical study shows that the interaction of different geological units provides favorable conditions for forming the western Xiang(Hunan)-E(Hubei)metallogenic belt.High-value geochemical anomalies are distributed at the boundary of the metallogenic belt,where the Qiyueshan fault and Jiangnan orogenic belt are suggested as exploration prospects.Future studies will include continued investment in comprehensive geochemical and geophysical interpretation and provide further constraints for regional tectonic deformation,evolution,and metallogenic processes.