江南造山带北缘鄣源构造带主要地质特征

鄣源构造带现今呈北东—南西向展布的混杂新元古代早期基性岩块以韧性变形构造为显著特点,并强烈叠加印支—燕山期逆冲-走滑脆性断裂的区域性超壳断裂带.构造带历经多期构造变形,主期构造变形以晋宁期弧-陆(扬子陆块)碰撞在地壳内部层圈结构相对薄弱部位形成的向南逆冲式韧性变形为特征.鄣源构造带中的蚀变枕状—块状基性熔岩、辉长岩、辉绿岩等基性岩块在空间上紧密相伴,形成于低速扩张的陆缘小洋盆扩张脊环境,具初始洋壳基性岩特征,属皖南伏川蛇绿岩西延组成部分.鄣源构造带及其两侧广布的新元古代早期火山-沉积建造体形成于大陆边缘与板块构造体制相关的构造-沉积环境,鄣源构造带南侧为裂解海盆沉积体系,北侧属于与大陆边缘火山弧有关的盆地沉积体系,鄣源构造带内显示深海—半深海沉积特征.鄣源构造带北东、南西向延伸分别与皖南伏川蛇绿混杂岩带及景德镇-宜丰深断裂带相接,是江南造山带北缘以皖南伏川蛇绿岩为代表的新元古代早期陆缘小洋盆俯冲-碰撞拼合带的重要组成部分.

Characteristics of Zhangyuan Structure Belt in the Northern Margin of Jiangnan Orogen

The Zhangyuan structure belt is a regional ultra-crust faulting belt intensely superimposed by Indosinian-Yanshanian thrust-strike slip brittle fault, characterized by NW-SW-trending ductile structural deformation mingled with Neoproterozoic mafic rocks.This structure belt experienced multiple deformations. The main event was the southward thrusting ductile deformation occurring in relatively weak position within internal layers of the Earth, which resulted from arc-continent (Yangtze Block) collision during Jinningian period. Mafic rocks in theZhangyuan structure belt, such as pillow-massive mafic lava, gabbro, diabase and etc.are associated closely in the space, and formed in a slowly spreading ridges environment of continental marginal ocean basin. They are characteristic of initial oceanic crust mafic rocks, suggesting that they are part of the western extension of ofFuchuanophiolite belt in southern Anhui province. The Zhangyuan structure belt and Neoproterozoicvolcano-sedimentation formation distributed on both sides of the belt formed in structure- sedimentary environment related to continental margin and tectonic plates. To the south was sedimentary system of rifting sea basin, and to the north was the sedimentary system related to the continental margin volcano arc. Therefore, the Zhangyuan structure belt is characteristic of abyssal-bathyal sedimentation. The Zhangyuan structure belt connects the Fuchuanophiolite belt in northeast and Jingdezhen-Yifeng deep-large fault in southwest, and constituted an important part of subduction- collision collaged belt of continental margin oceanic basinin the northern margin of Jiangnanorogenduring Early Neoproterozoic, which isrepresented by the Fuchuanophiolite belt.