Anatomy of the Zhangshudun ophiolitic melange in the northeastern Jiangxi and its enlightenment to the evolution of Neoproterozoic South China Ocean basin
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摘要:
赣东北蛇绿构造混杂岩是江南造山带最典型的地质实体之一，对其开展以大比例尺岩性填图+构造解析为核心的露头解剖。查明岩块类型包括0.9~1 Ga的洋壳残片蛇绿岩岩块和0.8~1 Ga的岛弧火山-沉积岩块，基质类型包括约1 Ga的蛇绿岩组分基质、0.9~1 Ga的洋盆沉积物基质和830~1000 Ma的碎屑复理石基质。混杂岩总体呈北东向延伸的网结状构造，就位期构造变形表现为自北西向南东的韧塑性逆冲剪切变形，并受到后期推-滑覆和走滑构造的叠加改造。综合解剖性填图认识和区域资料，认为赣东北樟树墩蛇绿构造混杂岩是弧后洋盆闭合至弧-陆碰撞等一系列洋-陆转换过程的产物，华南洋盆最终闭合的时间在780 Ma之后。研究成果丰富了蛇绿构造混杂岩专题填图方法，对认识华南新元古代洋盆演化及造山过程具有重要的意义。
Abstract:The northeastern Jiangxi ophiolitic melange is one of the most typical geological entities in Jiangnan orogenic belt.Through the anatomy of outcrop of Zhangshudun ophiolite melange with large-scale lithologic mapping plus structural analysis, it was confirmed that the blocks includes 0.9~1 Ga ophiolite of oceanic crust fragment and 0.8~1 Ga island arc volcanic-sediments.The matrix includes about 1 Ga ophiolite component, 0.9~1 Ga ocean basin sediments and 830~1000 Ma clastic flysch matrix.The melange generally presents a network structure trending northeast.The structural deformation was characterized by ductile-plastic thrust-shear deformation from northwest to southeast in the emplacement period, and was superimposed by late thrust-sliding nappe and strike-slipping structures.Based on the understanding of anatomical mapping and regional data, the Zhangshudun ophiolitic melange is considered to be the product of ocean-continent conversion processes from the closure of the back arc ocean basin to the arc-continent collision, and the final closure time of the South China Ocean basin was 780 Ma.These achievements enrich the thematic mapping method of ophiolitic melange, and are of great significance for understanding the evolution of ocean basin and orogenic process.
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