中祁连西段托赖（岩）群的解体及其地质意义

发布时间：2018-06-06 04:24

本文选题：祁连地块 + 中新元古代　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：长期以来,人们对祁连地块基底物质组成和时代归属一直存在着不同的认识,对其大地构造属性及演化历史也存在有较大的分歧。笔者通过青海省1:5万上日木策尔等5幅区域地质调查发现,前人认为的“古元古代托赖岩群”实际是囊括了不同时代、性质和变质程度的岩石和地质体,因此,笔者,通过大比例尺填图、露头解剖和锆石U-Pb测年,将原“托赖岩群”解体成了托赖岩群、元古代片麻状花岗岩和变形的古生代侵入体三部分。其中重新厘定的托赖岩群,包括下岩组和上岩组两部分;侵入其中的元古代片麻状花岗岩主要为中粗粒黑云二长花岗片麻岩。为精确限定新厘定的托赖岩群的形成时代,本次工作分别在该岩群下岩组片麻岩、上岩组石英岩、含矽线石榴二云石英片岩和侵入其中的新元古代中粗粒黑云二长花岗片麻岩采集样品,进行了系统的LA-MC-ICP-MS锆石U-Pb测年。结果显示,下岩组片麻岩样品中最年轻的碎屑锆石年龄为1058Ma,上岩组石英岩样品最年轻的碎屑锆石为1149 Ma,含矽线石榴二云石英片岩中最年轻的碎屑锆石年龄为1178Ma,侵入该岩群的中粗粒黑云二长花岗片麻岩侵位年龄为897±4 Ma。这表明厘定后的托赖岩群的沉积时代至少应该晚于1178Ma、早于897Ma。值得注意的是,当前碎屑锆石样品的年龄谱其最大峰值在1700Ma附近,同时1200Ma和1400Ma左右有弱的峰值,2500~1900Ma则为明显的低频区。这表明当时源区存在多期强烈的古元古代及中元古代岩浆活动记录,且以古-中元古代之交的岩浆活动为主。同时其年龄谱系特征与华北克拉通有关研究结果具有较高的相似性,暗示中祁连地块可能与华北克拉通更具亲缘性,并可能共同见证了Columbia超大陆的聚合与离散;而该地块后期又被897±4Ma的晋宁期(格林威尔期)黑云二长花岗岩侵入,则表明新元古代时期的中祁连地块很可能参与了Rodinia超大陆的聚合;区内更晚的早中奥陶世岩浆侵入活动,则属于早古生代祁连洋消减-闭合阶段的相关记录。
[Abstract]:For a long time, people have different understanding of the material composition and age attribution of the basement of Qilian block, as well as the tectonic attributes and evolution history of Qilian block. According to the 5 regional geological surveys of 15: 50, 000 in Qinghai Province, it is found that the "Gu Yuan ancient Tolaiyan group" actually includes rocks and geological bodies of different ages, properties and degrees of metamorphism. Based on large scale mapping, outcrop anatomy and zircon U-Pb dating, the original "Torailite Group" was disintegrated into three parts: Tolaiyan Group, Proterozoic granitic granites and deformed Paleozoic intrusions. The newly determined Toraili group includes two parts: the lower rock formation and the upper rock formation, and the major intrusive granitic granites. In order to accurately define the formation time of the newly determined Torai rock group, the present work has been carried out in the lower part of the rock group, the gneiss of the rock formation, and the quartzite of the upper rock formation, respectively. LA-MC-ICP-MS zircon U-Pb dating was carried out on the samples collected from silicon-bearing pomegranate quartz schist and Neoproterozoic middle-coarse black cloud granitic gneiss. The results show that The youngest clastic zircon age of the gneiss samples of the lower formation is 1058Ma. the youngest of the quartzite samples of the upper rock formation is 1149 Ma. the youngest of the quartzite schist with silicon-line pomegranate is 1178Ma. it intruded into the rock group. The emplacement age of the granitic gneiss is 897 卤4 Ma. This indicates that the sedimentary age of the determined Torai rock group should be at least later than 1178 Maand 897Ma. It is worth noting that the maximum peak value of the current age spectrum of the clastic zircon samples is near 1700Ma, while the weak peak value of 1200Ma and 1400Ma is about 25000 ~ 1900 Ma, which is an obvious low-frequency region. This indicates that there were many strong records of Paleoproterozoic and Mesoproterozoic magmatism in the source area at that time, and the magmatic activity between Paleoproterozoic and Mesoproterozoic was dominant. At the same time, its age pedigree features are similar to those of the North China Craton, suggesting that the Central Qilian block may be more related to the North China Craton, and may witness the aggregation and dispersion of the Columbia supercontinent. The late stage of the block was invaded by the Jinning (Greenwell) bifeldite of 897 卤4Ma, indicating that the Neoproterozoic Middle Qilian massif was probably involved in the aggregation of the Rodinia supercontinent, and that the late early Middle Ordovician magmatic intrusion occurred in the area. It belongs to the early Paleozoic Qilian ocean subduction-closure stage.
【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】：2015
【分类号】：P588

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