北京十三陵串岭沟组沉积岩中独居石和碎屑锆石的年代学研究

发布时间：2018-05-24 07:04

  本文选题：独居石 + 碎屑锆石　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：中元古代长城系为华北克拉通第一套盖层沉积,代表中元古代的开始,对其沉积时代和物质来源进行深入研究具有十分重要的地质意义。本文对采自北京十三陵地区长城系串岭沟组底部沉积岩中的独居石及碎屑锆石进行了SHRIMP及LA-ICP-MS U-Pb年代学研究。由下向上按层位分别采样MC1~MC5,对5件样品进行了详细的能谱分析,于样品MC1中发现了大量的独居石颗粒,最大粒径88μm,背散射图像显示独居石边缘不平整,形状不规则,呈现出“鱼形”、“鸟形”、“花形”、“虫形”等各种形状。大量的观察发现独居石绝大多数都分布在石英脉或赤铁矿细脉里,远离脉的地方几乎没有独居石的分布。对独居石进行初步的SHRIMP U-Pb原位定年,获得的年龄为152±11 Ma,结合其低U、Th含量及其特征的产状和矿物组合,表明这些独居石颗粒并非成岩期形成,而为次生独居石,其形成与后期的热液事件有关。5件样品中的碎屑锆石年龄谱图显示ca.2.5 Ga的主峰和ca.2.0 Ga的次峰,表明串岭沟组碎屑沉积岩物源主要来自以新太古代晚期陆壳物质为主构成的华北克拉通基底及研究区西南的中部造山带。本次研究中发现的最年轻碎屑锆石年龄为1673±44 Ma,由此限定串岭沟组沉积岩沉积的下限年龄为1673±44 Ma。从MC1到MC3,碎屑锆石的年代范围由窄变宽,认为串岭沟组在MC3层位时曾发生一次海侵,海水将大量ca.2.0 Ga的碎屑物质从研究区西南的陆地带到海洋接受沉积,导致其沉积物中有大量ca.2.0 Ga的碎屑物质加入。从MC4到MC5,岩性由碎屑岩过渡为碳酸盐岩,说明海水由浅变深;年龄谱图显示MC5比MC4物源更广,推测在MC5层沉积时也发生了一次海侵事件。本文对长城系串岭沟组碎屑锆石的研究表明其物质来源具有随地层变新越来越广泛的趋势,靠上部层位有显著的ca.2.0 Ga的年轻物质加入。
[Abstract]:The Mesoproterozoic the Great Wall system is the first set of cover deposits in the North China Craton, which represents the beginning of the Middle Proterozoic. It is of great geological significance to study the sedimentary age and material source of the Mesoproterozoic system. In this paper, the SHRIMP and LA-ICP-MS U-Pb chronology of monazite and clastic zircon collected from the bottom sedimentary rocks of the Great Wall series of Chuanling Gou formation in the Ming Tombs area of Beijing have been studied. MC1 / MC5 was sampled from the bottom up and the five samples were analyzed by energy spectrum in detail. A large number of monazite particles were found in the sample MC1, with a maximum diameter of 88 渭 m. The backscatter images showed that the edge of monazite was uneven and the shape of monazite was irregular. It presents various shapes, such as fish, bird, flower, worm and so on. A large number of observations show that most of the monazite are distributed in quartz veins or hematite veins, and there is almost no monazite distribution far away from the veins. The primary SHRIMP U-Pb dating of monazite is obtained at 152 卤11 Ma. combined with its low U ~ (2 +) Th content and its characteristic occurrence and mineral assemblage, it is shown that these monazite particles were not formed in diagenetic stage, but were secondary monazite. The zircon ages of 5 samples are related to the late hydrothermal events, which show the main peaks of ca.2.5 Ga and the secondary peaks of ca.2.0 Ga. The results show that the clastic sedimentary rocks of the Chuanling Gou formation are mainly derived from the North China craton basement and the central orogenic belt in the southwest of the study area, which are mainly composed of the late NeoArchean continental crust. The youngest zircon age found in this study is 1673 卤44 Ma, thus limiting the lower sedimentary age of the sedimentary rocks of the Chuanling formation to 1673 卤44 Ma. From MC1 to MC3, the age range of detrital zircons has changed from narrow to wide. It is believed that a transgression occurred in the MC3 formation in the Chuanlinggou formation, and that the sea water brought a large amount of ca.2.0 Ga debris material from the land southwest of the study area to the ocean to receive sediments. A large amount of ca.2.0 Ga clastic material was added to the sediments. From MC4 to MC5, the lithology transition from clastic rock to carbonate rock indicates that the sea water has changed from shallow to deep, and the age spectrum shows that MC5 is more extensive than MC4 provenance, and a transgressive event occurred during the deposition of MC5 layer. In this paper, the study of the clastic zircon in the Great Wall series shows that the material source of the zircon is more and more new and widespread, and it is added by the young material with remarkable ca.2.0 Ga in the upper layer.
【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;P588.2
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本文编号：1928145