东昆仑南缘东段可可尔塔地区蛇绿岩与相关火山岩地质特征、年代学及构造环境研究

发布时间：2018-10-19 10:31

【摘要】：阿尼玛卿—布青山构造混杂岩带夹持于东昆南构造带与巴颜喀拉造山带之间,其布青山段分布有不同岩石类型、不同时代、规模不一的构造岩块。通过可可尔塔路线地质剖面及禾日沟贡玛路线地质剖面对分布于布青山段可可尔塔地区的混杂岩块进行调查,从中厘定出了可可尔塔北蛇绿岩、可可尔塔南蛇绿岩和禾日沟贡玛玄武岩/安山岩,并对三者分别进行岩石学、地球化学、年代学及构造环境研究,取得了如下进展及成果:1、可可尔塔北蛇绿岩分布于可可尔塔地区禾日沟贡玛沟口,主要岩石类型包括蛇纹岩、片麻状辉长岩。蛇纹岩原岩为纯橄岩,岩石地球化学特征显示为高亏损的地幔残余,同时具富LREE流体/熔体交代特征。片麻状辉长岩表现为典型的堆晶辉长岩,其REE配分型式与MORB相似,并显示富LREE流体/熔体交代特征。片麻状辉长岩LA-ICP-MS锆石U-Pb年龄为467±4Ma。综合判断可可尔塔北蛇绿岩形成时代为中奥陶世,为MOR型蛇绿岩,侵位过程中受俯冲带改造,代表了俯冲背景下的原特提斯洋洋壳+上地幔残片。2、可可尔塔南蛇绿岩分布于可可尔塔沟中段及禾日沟贡玛沟脑一带,主要岩石类型为蛇纹岩、强蛇纹石化方辉橄榄岩、辉长岩、斜长岩。蛇纹岩(原岩为方辉橄榄岩)与强蛇纹石化方辉橄榄岩地球化学特征显示为较高程度部分熔融的地幔残余,并受俯冲带改造。辉长岩与斜长岩为同源岩浆岩,均表现为MORB型。辉长岩LA-ICP-MS锆石U-Pb年龄为457±2Ma;斜长岩LA-ICP-MS锆石U-Pb年龄为452±9Ma。综合判断可可尔塔南蛇绿岩形成时代为晚奥陶世—早志留世,为MOR型蛇绿岩,并受俯冲带改造,亦为俯冲背景下原特提斯洋的洋壳+上地幔残片代表。3、禾日沟贡玛玄武岩/安山岩产于禾日沟贡玛沟中段,主要岩性为片理化变玄武岩和片理化变安山岩,地球化学特征显示为典型的岛弧钙碱性玄武岩,结合区域岩浆岩分布特征判断其形成时代为中奥陶世—早中志留世,代表了该时期原特提斯洋向北俯冲形成的成熟岛弧。4、根据区域地质资料,结合本文研究结果,将阿尼玛卿—布青山构造混杂岩带早古生代的构造演化划分为四个阶段:晚震旦世—早寒武世初始大陆裂解阶段、早寒武世—晚寒武世原特提斯洋洋壳形成与扩张阶段、晚寒武世—晚志留世原特提斯洋俯冲消减与岛弧形成阶段、晚志留世末—泥盆纪原特提斯洋洋盆萎缩消亡阶段。
[Abstract]:The Animaching-Buqingshan tectonic melange belt is located between the Dongkunnan tectonic belt and the Bayan Kara orogenic belt. The Buqingshan section has different rock types, different ages and different scales of tectonic blocks. Based on the geological profile of the Keerta route and the geological section of the Heligou Gomma route, the mixed rock blocks distributed in the Kolta area of the Buqingshan section were investigated, from which the ophiolite was determined. The Kertanan ophiolite and the Heligou gongma basalt / andesite are studied in petrology, geochemistry, geochronology and tectonic environment respectively. The main results are as follows: 1. The ophiolite is distributed in Heligou gouge mouth in Kolta area. The main rock types include serpentine and schneiss gabbro. The ophiolite is a pure olivine. The geochemical characteristics of the ophiolite are high depleted mantle remnants and LREE rich fluid / melt metasomatism. The schneiss gabbro is a typical heap-grained gabbro, its REE distribution pattern is similar to that of MORB, and it is characterized by LREE rich fluid / melt metasomatism. The LA-ICP-MS zircon U-Pb age of the schneiss gabbro is 467 卤4Ma. It can be concluded that the ophiolite was formed in the Middle Ordovician and MOR type ophiolite during the emplacement, and was transformed by the subduction zone in the course of emplacement. It represents the remnants of the upper mantle of the original Tethys oceanic crust in the subduction background. (2) the Kertanan ophiolite is distributed in the middle section of the Coelta gully and the Gomagou area of the Heligou. The main rock types are ophiolite and strong serpentinized peridotite. Gabbro, plagioclase. The geochemical characteristics of ophiolite and strong serpentinized peridotite show that they are mantle remnants with high degree of partial melting and have been modified by subduction zone. Gabbro and plagioclase are homologous magmatic rocks, both of which are of MORB type. The LA-ICP-MS zircon U-Pb age of gabbro is 457 卤2Ma.The U-Pb age of LA-ICP-MS zircon is 452 卤9Ma. It is concluded that the formation age of the Kertanan ophiolite is late Ordovic-early Silurian and MOR type ophiolite, and has been transformed by subduction zone. It is also a representative of the upper mantle of the oceanic crust of the original Tethys ocean in the subduction background. 3. The gongma basalt / andesite of Hejigou occurs in the middle part of the Gongma gully. The main lithology is sheet physicochemical metamorphic basalt and schistatic altered andesite. Geochemical characteristics show that they are typical island arc calc-alkaline basalts, which are formed in the Middle Ordovician and early Middle Silurian combined with the regional magmatic distribution. It represents the mature island arc formed by the northward subduction of the original Tethys ocean during this period. According to the regional geological data, combined with the results of this paper, The tectonic evolution of the Arnimaqing-Buqingshan tectonic melange belt is divided into four stages: late Sinian to early Cambrian initial continental fragmentation stage, early Cambrian to late Cambrian primitive Tethys oceanic crust formation and expansion. The late Cambrian-late Silurian primitive Tethys ocean subduction and island arc formation stage, late Silurian-Devonian primitive Tethys ocean basin atrophy and extinction stage.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588

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