伊朗扎格罗斯造山带Kermanshah蛇绿岩中韧性变形构造解析与地质意义

The mechanism and time of ductile deformation which occurred in ophiolitic melange are the key issues for ophiolite research. It is crucial for understanding the origin or emplacement of ophiolite and the tectonic evolution of the ocean marked by the ophiolite.Following these scientific problems, we will systematically anatomy the crucial geological units in Kermanshah ophiolitic melange, which are poorly constrained by tectonic property and timing, and build the fine structure process of the ductile deformation in ophiolitic melange and fully understand the orogenic process and associated geodynamic significance. Therefore, we will complete these issues from following points. Firstly, we will use petrology, geochemistry, metamorphic geology and chronology to define the tectonic property, the forming time and characteristics of ductile deformation occurred in mylonitic gabbro and peridotite. Secondly, we will combining the field mapping and geochemical and chronological analysis to decipher the tectonic setting, forming time and emplacement method of ophiolite. Finally, we will comparative study the documents published on Khoy and Neyriz ophiolie in Zagros orogenic belt, build the tectonic framework and discuss the tectonic evolution of the Zagros orogenic belt. The study will significantly contribute to the ophilite origin and emplacement study, and will develop and complete the tectonic evolution model of Tethys.

蛇绿岩中韧性变形机制与变形时代是蛇绿岩研究的关键问题，对理解蛇绿岩形成或就位机制及其所代表的大洋演化历史，具有决定性作用。本项目拟系统解剖伊朗扎格罗斯造山带Kermanshah蛇绿岩中韧性变形为切入点，查明它的变形、变质特征与形成机制及时代，全面探讨蛇绿岩中韧性变形发育的过程及其所蕴含的地球动力学意义。选择Kermanshah蛇绿岩中以糜棱岩化橄榄岩和辉长岩为标志的韧性变形带，开展详实的野外地质观测、室内显微镜观测、变质地质学与年代学分析，查明其几何学、运动学等构造变形特征、变质变形时代和变形机制；结合野外局部地区大比例地质填图、地球化学分析和年代学分析，解析蛇绿岩的形成构造背景、形成时代及方式；构建Kermanshah蛇绿岩从形成到就位的精细时空演化过程。综合对比分析扎格罗斯造山带上Khoy和Neyriz蛇绿岩资料，建立扎格罗斯蛇绿岩带的构造演化格架，发展和完善新特提斯洋的构造演化模式。

通过4年的研究，确定了伊朗特提斯构造域最年轻蛇绿岩形成时代为36 Ma，表明始新世末期新特提斯洋在扎格罗斯地区依然发育，且以现今慢速扩张的大西洋中脊拆离断层模式形成新生洋盆，从而推断新特提斯洋盆最终的闭合时代应晚于36 Ma。结合沉积岩碎屑锆石的U-Pb年龄谱系研究，认为阿拉伯-欧亚的陆陆初始碰撞时间在12-7Ma之间。研究成果改变了前人关于扎格罗斯蛇绿岩都在晚白垩世就位的认识，为解决伊朗地区新特提斯洋的最终闭合时限、阿拉伯与欧亚的碰撞时限等国际热点争议提供了有力证据。指出造山带中的蛇绿岩有相当一部分是古洋壳核杂岩，是洋底拆离断层作用形成的；蛇绿岩中的韧性变形带不一定都是就位在造山带时的变质底板成因，极有可能是初始形成洋中脊时的拆离断层成因。揭示了特提斯喜马拉雅构造带包含混杂岩结构组成，具有“基质+块体”的结构特征，统一的南向古水流物源、单一的欧亚大陆特征碎屑锆石年龄谱，均表明特提斯喜马拉雅应该是冈底斯弧前体系，在最终碰撞前具有欧亚大陆属性；提出特提斯提喜马拉雅是弧前增生杂言，而非印度板块北缘的被动陆缘的新认识。