皖南地区新元古代浅变质岩系地层格架、沉积序列研究及其对构造演化模型的约束

Study on stratigraphy and sedimentary in orogenic belts, including determining stratigraphy sequence, founding sedimentary sequences, remolding tectonic paleogeography, and providing constraints on a tectonic model of the orogen belts, has been one of hot area of stratigraphy and sedimentology study in the world. South Anhui, where is located on the eastern of the Jiangnan orogenic belt, develops Neoproterozoic epimetamorphic rock series. In recent years, research on the petrology, provenance and tectonic geology of the series has made great progress, but there has been disagreement on understanding stratigraphy ages, sedimentary facies and environment of the series, which leads to it is difficult to build up a stratigraphy framework and tectonic evolution model of the series. This item will study Neoproterozoic epimetamorphic rock series in South Anhui. By detailly surveying on field stratigraphy sections and analyzing petrography characters, combining the analysis of detrital zircon chronology and heavy minerals, we will do division and correlation of the strata, determine their ages, and establish stratigraphy framework. We will make analysis of sedimentary facies, built up sedimentary system, and restore the filling sequences of the sedimentary basin. We will study components and their space-time changes of the sedimentary sequences, analysis the character of the source areas of the epimetamorphic rocks, remold tectonic paleogeography of the provenance and evolution history. The study result will support to determining the stratigraphy framework of the Neoproterozoic epimetamorphic rocks in the Jiangnan orogen belt, provide constraints to tectonic model of the orogen belt, and make contributions to dynamics study of the continental lithosphere of South China.

造山带地层学和沉积学研究，厘定造山带地层层序、建立地层沉积序列，恢复构造古地理，为造山带的构造演化模型提供约束，目前已经成为国际地层学和沉积学研究热点之一。皖南属于江南造山带东段，新元古代浅变质岩系地层发育，近年来对岩石学、物源区和构造地质学的研究取得了众多成果，但是，人们对地层时代归属、沉积相和沉积环境的认识还存在很大分歧，建立的地层格架和构造演化模型也是众说纷纭。本课题以皖南地区前寒武纪浅变质岩系为研究对象，通过野外剖面详细观察，岩相学分析，结合碎屑锆石年代学和重矿物分析，进行地层划分和对比，确定地层时代，建立地层格架；进行沉积相分析，确定沉积体系，建立盆地沉积充填序列；研究沉积层序的物质组成及其变化，确定物源区特征，重塑物源区构造古地理和演化历史。研究成果将为江南造山带前寒武纪地层格架厘定提供重要支撑，为新元古代构造演化模型建立提供重要约束，为华南大陆岩石圈动力学研究做出贡献。

江南造山带东段皖南地区新元古代浅变质岩系发育，厚达近万米，是研究江南造山带的经典地区，也存在着一些悬而未决问题，例如地层时代归属、沉积背景和板块汇聚时限等，约束了对华南大陆岩石圈构造演化的理解。我们通过野外剖面详细观察和岩相学、沉积学、岩石地球化学分析，特别是和碎屑锆石U-Pb年代学、Hf同位素相结合进行了研究。项目取得了如下主要成果。.1..厘定了浅变质岩系地层层序。浅变质岩系主要由杂砂岩、页岩、砾岩、石英砂岩和硅质岩组成，不存在大规模倒转层序，称为晋宁运动的角度不整合也未发现。26个碎屑锆石U-Pb样品限定了浅变质岩系地层时代为710.4 —802.3 Ma，属于Late Tonian到Early Cryogenian。重建皖南地区前寒武纪浅变质岩系地层格架，厘定了上溪群、歙县群和溪口群。.2..进一步确定了浅变质岩主要由海底扇沉积体系和浅海滨岸-陆棚沉积体系组成。海底扇沉积进一步分为内扇、中扇、外扇和海底平原沉积。浅变质岩系组成了由海侵和海退沉积序列构成的完整沉积旋回。浅变质岩形成于弧后盆地构造背景。.3..80个样品岩石地球化学数据、26件碎屑锆石年龄分析（1931个数据）和206个Hf同位素数据揭示物源主要来自江南造山带东段新元古代火山岩和侵入岩的长英质物源和基性岩，少量来自中元古代物源和古元古代-晚太古代扬子基底物源。新元古代物源区构造背景是具有过渡弧到切割弧的岩浆岛弧，不是裂谷火山岩。.4..限制了江南造山带东段扬子和华夏板块最终汇聚的时限为Cryogenian （大约710 Ma）。.5..结合前一个基金，对秦岭-大别造山带源汇系统进行了研究并且获得了新的认识。.6..发表论文8篇，其中SCI文章4篇。培养博士研究生2人，硕士研究生1人。.以上这些成果为江南造山带东段基础地质研究做出了新的贡献，将颠倒半个世纪的层序和时代纠正过来，否定了晋宁运动的角度不整合标志以及Rodinia超大陆裂解阶段的沉积记录，为华南板块最终汇聚提供了新的年代学约束。