浙赣皖相邻区中生代推（滑）覆构造特征及其时序分析

There are both commonalities and differences on Mesozoic deformations like folds, thrust-nappe structures and extensional detachments between the junction region of Zhejiang-Jiangxi-Anhui (Zhe-Gan-Wan region), southeastern Yangtze Block, and the SE China. These multi-episodic nappe structures and extensional-sliding structures of different scales could be the new window to focus on the tectonic and geodynamic evolution of both the region and SE China. This study will perform field investigation on nappe structures in Zhe-Gan-Wan region, in order to understand their distribution, scale, geometry, kinematic and assemblage features. By establishing the effective index to distinguish different type faults, those group faults are assembled with same direction and same kinematic orientation. Both cross-cut relation between nappe structures and involved strata and magmatic rocks, and many type dating methods are used in an attempt to constrain the geochronology of these structures. On the basis of these new datasets, accompanied with both previous reported geochronology, geochemistry of magmatic rocks in the region and simulation experiment, this study will discuss the time sequence of the Mesozoic thrust-nappe structures, extensional-sliding structures and between magmatic activities, reestablish the tectonic evolution framework, and then probe into the response between tectonic-magmatic events and the subduction of the Pacific plate in the region and even SE China, and finally provide extra evidences for remodeling the tectonic and geodynamic evolution of SE China.

扬子地块东南段浙赣皖相邻区中生代时期逆冲推覆和伸展滑覆构造与华南内陆既有共性又有差别，开展研究区推（滑）覆构造及其形成机制的研究，是管窥和探讨华南中生代构造演化历史的新的窗口。查明研究区逆冲推覆和伸展滑覆构造的区域分布、产状、两盘地层或岩体、剖面结构等特征，分析断层的运动学特征，确立同类型断层的判别标志，按同方向、同性质归类组合。根据不同组合、不同方向断裂的交切关系、断层切割或覆盖断层的地层、贯穿断层或被断层破坏的岩浆岩等现象，以野外地质事实为依据，以便于测年的花岗岩、火山岩和易于识别的中生代红层为重要参考，判断逆冲推覆和伸展滑覆构造的先后时序，建立研究区时空构造格架。进行逆冲推覆和伸展滑覆构造与区域岩浆活动的联系、时序分析，探讨研究区中生代构造―岩浆事件与太平洋板块俯冲作用的响应关系，重塑构造演化史，进而为中国东南部花岗岩与大地构造环境的成因联系研究以及构建大陆动力学模型提供佐证。

浙赣皖相邻区至少存在两期侏罗纪–白垩纪逆冲推覆构造，第一期逆冲推覆构造发生于晚侏罗世末期，如朱溪铜钨矿床及五城–小溪逆冲推覆构造，以中侏罗世红层为底盘；第二期发生于白垩纪末期或中新生代之交，以晚白垩世红层为底盘，如歙县城北一带、赣东北婺源中云等地。研究区内第二期逆冲推覆方向大多具有北东或北北东走向，整体表现较为一致，但断层面倾向既有南东也有北西，以怀玉拗陷为中心，以北往南东推覆，以南往北西推覆，呈现出对冲构造样式；皖浙地区断层大多数由南东向北西逆冲，而皖赣交界樟公山地区、景德镇地区则由北西向南东逆冲。两期逆冲推覆构造期间，存在早白垩世早期开始的伸展作用，形成区域上近东西向分布的早白垩世A-型花岗岩、白垩纪红层盆地的边缘正断层等一系列伸展构造。同时，黄山红层盆地早白垩世徽州组下部发育伸展作用成因的生长地层，结合盆地中的火山岩接触关系和锆石U-Pb年龄，表明伸展作用开始于约140 Ma。.本项研究还对德兴—歙县断裂带北段三阳剪切带、中段江湾—黄山剪切带、白际—三阳剪切带、石耳山韧性剪切带开展了年代学、微观结构、矿物组构、3D应变椭球分析、有限应变及运动涡量计算等的综合研究，认为德兴—歙县断裂带右行剪切，白际—三阳剪切带左行剪切发生在465～430 Ma；石耳山剪切带可能形成于~430～400 Ma或更早，与早古生代江南造山带其它区域及华夏板块的褶皱、逆冲断裂和韧性剪切作用同期发生，揭示了该区域的压扭缩短变形。压扭过程中纯剪切分量导致鄣公—怀玉地区前寒武纪浅变质岩系区域性倒转向背斜构造及内部各种类型的小褶皱、逆冲构造以实现垂向增厚和水平缩短，剪切带的减薄，而单剪切分量使得白际—三阳、江湾—黄山、景德镇剪切带发生韧性剪切作用。研究认为，江南造山带东段早古生代构造变形是扬子和华夏板块斜向挤压的结果，驱动力可能和华南与澳大利亚西北缘碰撞的远程效应相关。