班公湖—怒江结合带安多—丁青蛇绿岩地球化学特征及构造演化研究

发布时间：2018-08-04 19:14

【摘要】：班公湖—怒江结合带(班—怒带)对研究青藏高原的构造演化具有重要意义。然而,该带中东段安多、丁青蛇绿岩所代表特提斯洋的发育时限和构造演化模式等还存在激烈的争论;此外,该带还缺乏对俯冲消减比较敏感的岛弧型火山岩的报道。本研究选择安多、丁青蛇绿岩和相关的岛弧型火山岩为研究对象,对其开展详细的野外地质调查和室内矿物学、岩石学研究。运用LA-ICP-MS锆石U-Pb定年、锆石原位Hf同位素测试、全岩主微量元素分析和Sr-Nd同位素示踪等手段,结合区域地质成果,探讨安多、丁青蛇绿岩的时空格架和构造环境,揭示岛弧型火山岩对班—怒洋壳俯冲消减的制约意义。论文取得了以下主要认识:(1)安多蛇绿岩中辉绿岩锆石U-Pb年龄为183.4±2.5Ma,丁青蛇绿岩中辉长岩和淡色辉长岩锆石U-Pb年龄分别为175.3±2.5Ma、163.1±1.8Ma,表明班—怒特提斯洋安多—丁青段主要发育时限为中—晚侏罗世。(2)丁青地区发现一套洋岛组合,其地球化学特征与典型的洋岛玄武岩相似,Sr-Nd同位素表明其岩浆来源于亏损地幔。结合区域资料推测其形成时代很可能为早白垩世,表明特提斯洋丁青段在早白垩世并未闭合。(3)安多、丁青蛇绿岩元素地球化学特征显示出SSZ型特征,Sr-Nd同位素和锆石原位Hf同位素组成表明安多、丁青基性岩的岩浆来源于亏损地幔。(4)安多地区的中酸性火山岩地球化学特征为岛弧型,Sr-Nd同位素和锆石原位Hf同位素表明其岩浆来源于岩石圈地幔。英安岩锆石U-Pb年龄为179.7±4.4Ma,为班公湖—怒江特提斯洋在早侏罗世向北俯冲消减提供了直接的火山岩证据。(5)达如错接奴群火山岩通过元素地球化学特征识别出了一套高镁安山岩,高镁安山岩锆石U-Pb年龄为163.3±1.7Ma,为班公湖—怒江特提斯洋在中—晚侏罗世向南俯冲消减提供了直接的火山岩证据。(6)班公湖—怒江特提斯洋在侏罗纪(~190-163Ma)洋壳发生洋内俯冲,在晚侏罗世—早白垩世(~163-108Ma)洋壳双向俯冲。
[Abstract]:The Bangong Lake-Nujiang belt is of great significance for the study of the tectonic evolution of the Qinghai-Xizang Plateau. However, in the middle and eastern part of the belt, there are still heated arguments about the development time limit and tectonic evolution model of the Tethys Ocean represented by the Dingqing ophiolite, and there are no reports of the island arc volcanic rocks which are sensitive to subduction and subduction. In this study, Ando, Dingqing ophiolite and related island arc volcanic rocks were selected as the research objects, and detailed field geological survey and indoor mineralogical and petrological studies were carried out. By means of LA-ICP-MS zircon U-Pb dating, zircon in-situ HF isotopic testing, whole-rock principal trace element analysis and Sr-Nd isotope tracing, combined with regional geological results, the temporal and spatial framework and tectonic environment of Ando and Dingqing ophiolite are discussed. It is revealed that the island arc volcanic rocks restrict the subduction and subduction of Ban-Nu oceanic crust. The main results are as follows: (1) the zircon U-Pb age of diabase in Ando ophiolite is 183.4 卤2.5 Ma. the U-Pb age of zircon of gabbro and pyroxene in Dingqing ophiolite is 175.3 卤2.5 Ma and 163.1 卤1.8 Marespectively, which indicates that Ban-Nuttiando-Dingqing member is the main source of hair. The breeding time is middle to late Jurassic. (2) A set of oceanic island assemblages was discovered in the Dingqing area. Its geochemical characteristics are similar to those of typical oceanic island basalts, indicating that the magma originated from the depleted mantle. Based on the regional data, it is suggested that the age of formation is probably early Cretaceous, indicating that the Dingqing member of Tethys Ocean was not closed in the early Cretaceous. (3) Ando, The elemental geochemical characteristics of the Dingqing ophiolite show the SSZ type characteristics of Sr ND isotope and zircon in situ HF isotopic composition indicating Ando. The magma of Dingqing basic rock is derived from depleted mantle. (4) the geochemical characteristics of intermediate-acid volcanic rocks in Ando area are island arc type Sr-Nd isotope and zircon in-situ HF isotope, indicating that the magma originated from lithospheric mantle. The zircon U-Pb age of dolomite is 179.7 卤4.4 Ma, which provides direct evidence of volcanic rocks for northward subduction and subduction of Bangonghu-Nujiang Tethys ocean in the early Jurassic. (5) A set of high-mafic andesite has been identified by elemental geochemical characteristics of the Dagujienu volcanic rocks. The zircon U-Pb age of high-mafic andesite is 163.3 卤1.7 Ma, which provides direct volcanic evidence for the subduction of Bangong Lake to Nu River Tethys ocean in the Middle-Late Jurassic. (6) the Bangong Lake and the Tethys Ocean of the Nujiang River occurred intraoceanic subduction during the Jurassic period (190-163Ma). During the late Jurassic to early Cretaceous (163-108 Ma), the oceanic crust subducted in both directions.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P587;P583

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