北祁连古大洋俯冲带碎屑锆石年代学及构造意义

发布时间：2018-02-15 03:19

本文关键词： 北祁连造山带古生代沉积岩碎屑锆石U-Pb定年物源分析　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

【摘要】：北祁连造山带地处青藏高原东北缘,其构造演化是在新元古代Rodinia超大陆汇聚和裂解的基础上,又经历了早寒武纪古祁连洋发育、奥陶纪洋壳俯冲、志留纪平稳过渡,以及泥盆纪碰撞造山过程。目前,对于北祁连造山带洋壳俯冲阶段尚存颇多争议,对高压变质带中沉积岩的物源归属尚欠深入研究。本文选择北祁连高压变质带沉积岩为研究对象,在野外地质调查基础上,采用碎屑岩锆石年代学研究方法,对奥陶纪之后沉积岩的物源进行了深入研究;结合前人取得的区域构造演化认识,探讨了北祁连造山带洋-陆汇聚至隆升造山阶段周边陆块属性、岩浆活动等关键性地质问题。洋-陆汇聚阶段形成沉积岩组合:样品Q15-04(磨拉石)、Q15-124(变质杂砂岩)、Q15-129(蓝片岩相变质杂砂岩)和Q15-165(变质粉砂岩)的碎屑锆石U-Pb年龄谱图揭示北祁连造山带沉积岩的物源时代横跨太古代-早古生代,峰值年龄为:2.5Ga、1.7Ga、1.4Ga、1.0Ga、0.76Ga和0.47Ga。与相邻板块构造岩浆热事件对比分析表明:太古代碎屑锆石主要源自北部的阿拉善地块变质基底杂岩;晚元古代-新元古代碎屑锆石主要来源于南部、具扬子属性的中祁连地块变质结晶岩系;早古生代碎屑锆石来源于北祁连岛弧火山岩。年龄谱中明显存在0.76Ga峰值年龄,与前人研究提出本区因Rodinia超大陆裂解发育的裂谷火山岩年龄一致,显示这一时期祁连洋初始拉张已形成。样品Q15-80(细砂岩)、Q15-98(变质砂岩)和Q15-102(蓝片岩相变质杂砂岩)的碎屑锆石U-Pb年龄谱图显示:碎屑锆石主要来源于北祁连岛弧火山岩、蛇绿岩以及俯冲杂岩,指示了岛弧火山岩的活动时限540~430Ma,其与前人研究古北祁连洋洋壳的俯冲时限基本一致。陆-陆碰撞造山阶段形成沉积岩组合:样品Q15-78(三叠纪砂岩)和Q15-79(二叠纪砂岩)的碎屑锆石年龄谱图揭示沉积岩的物源主要来自阿拉善地块、北祁连岛弧以及东昆仑地区。综合以上分析,北祁连造山带高压变质带沉积岩中的碎屑物质主要来源于相邻的中祁连地块前寒武系变质结晶基底、阿拉善地块前寒武系变质结晶基底以及北祁连岛弧,后期造山阶段有东昆仑地区的物源混入,整体具有亲扬子板块的基本属性。
[Abstract]:The North Qilian orogenic belt is located in the northeastern margin of the Qinghai-Xizang Plateau. Its tectonic evolution is based on the convergence and fragmentation of the Neoproterozoic Rodinia supercontinent, and experienced the early Cambrian Paleo-Qilian ocean development, the Ordovician oceanic crust subduction, and the steady transition of Silurian. And the Devonian collision orogenic process. At present, there are still many controversies about the subduction stage of the oceanic crust in the North Qilian orogenic belt. The provenance of sedimentary rocks in the high-pressure metamorphic zone is not well studied. In this paper, the sedimentary rocks of the North Qilian high-pressure metamorphic belt are selected as the research objects. Based on the field geological survey, the zircon chronological study method of clastic rocks is used. The provenance of sedimentary rocks after Ordovician is studied in depth, and the attributes of the continental block around the ocean-land convergence to uplift orogenic stage of the North Qilian orogenic belt are discussed in combination with the understanding of the regional tectonic evolution obtained by the predecessors. Key geological problems such as magmatic activity. Sedimentary rock assemblage in ocean-continental convergence stage: sample Q15-04( molashizhizhuo Q15-124 (metamorphic complex sandstone) Q15-129 (blueschist metamorphic complex sandstone) and Q15-165 (metamorphic siltstone) zircon U-Pb age map unraveled. The provenance of sedimentary rocks in the northern Qilian orogenic belt spans the Archean and early Paleozoic. The peak age is 1. 7Ga1. 7Ga1. 4Ga1. 0. 76Ga and 0. 47Ga. the results show that the Archean clastic zircon is mainly derived from the metamorphic basement complex of the Alashan block in the north, and the late Proterozoic-Neoproterozoic clastic zircon is mainly from the south. The metamorphic crystalline rocks of the Middle Qilian block with Yangtze attribute, the early Paleozoic clastic zircon derived from the North Qilian island arc volcanic rocks, and the peak age of 0.76 Ga obviously exist in the age spectrum. The age of rift volcanic rocks developed by Rodinia supercontinent in this area is the same as that of previous studies. The U-Pb age spectra of the detrital zircons from samples Q15-80 (fine sandstone, Q15-98 (metamorphic sandstone) and Q15-102 (blue-schist facies metamorphic complex sandstone) show that the clastic zircons are mainly derived from the northern Qilian island arc volcanic rocks. Ophiolite and subduction complex, The time limit of activity of island arc volcanic rocks is 540 ~ 430 Ma, which is basically consistent with the subduction time limit of oceanic crust of Paleo Northern Qilian. Sedimentary rock assemblage formed during the continental-continental collision orogenic stage: samples Q15-78 (Triassic sandstone) and Q15-79 (Permian sandstone). The age spectrum of detrital zircon reveals that the source of sedimentary rocks mainly comes from the Alashan massif. Based on the above analysis, the clastic material in the sedimentary rocks of the high pressure metamorphic belt of the North Qilian orogenic belt is mainly derived from the Precambrian metamorphic crystalline basement of the adjacent Middle Qilian block. The Precambrian metamorphic crystalline basement and the northern Qilian island arc in the Alashan massif are mixed with the East Kunlun area in the late orogenic stage, and the whole has the basic attributes of the pro-Yangtze plate.
【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】：2017
【分类号】：P597.3;P542

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