北京密云条带状铁建造的锆石SHRIMP U-Pb年龄及其地质意义

发布时间：2018-01-05 14:29

本文关键词：北京密云条带状铁建造的锆石SHRIMP U-Pb年龄及其地质意义　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】：前寒武纪条带状硅铁建造(BIF)是全球范围内重要的铁矿资源类型,在世界上分布广泛。BIF作为一种早前寒武纪特殊化学沉积建造类型,其在形成的过程中经历了复杂的变质变形作用,在反演地球早期构造(地幔柱与早期板块构造)演化方面有重要作用。北京密云地区位于华北克拉通北缘,该区在古太古代到早中元古代经历了复杂的构造变质事件,在此过程中形成了大量的大中型沉积变质铁矿床。本文主要通过对该区冯家峪铁矿、沙厂铁矿和放马峪铁矿等典型BIF型铁矿床的磁铁石英岩及其附近含铁岩系共4件样品进行SHRIMP锆石U-Pb测年研究,得到的年龄数据如下:(1)冯家峪铁矿的含云母闪石类磁铁石英岩(MF01)的变质锆石207Pb/206Pb年龄主要集中在1777±9 Ma和2456±8 Ma;(2)沙厂铁矿的透闪石化磁铁石英岩(MY01)的变质锆石定年结果为1806±13 Ma和2469±21 Ma,碎屑锆石的207Pb/206Pb年龄为2517±12 Ma。侵入矿体中的长英质辉石角闪岩(SY01)的变质锆石207Pb/206Pb年龄为1798±15 Ma,具有明显韵律环带的捕获锆石的年龄为2531±7 Ma。从而限定首云铁矿BIF建造的沉积时代为可能2469±21 Ma到2517±12 Ma之间;(3)放马峪铁矿的含磁铁矿石榴子石二长片麻岩(MFM01)的变质锆石测年结果分别为1817±13 Ma和2456±6 Ma,碎屑锆石207Pb/206Pb年龄为2529±8 Ma。由此间接限定了放马峪条带状铁建造的形成时代约为2456±6 Ma到2529±8 Ma,根据前人研究,最可能为太古代晚期。密云BIF型铁矿指示了该区在华北克拉通新太古代晚期的一次重要的BIF成矿事件。由年龄数据结合其野外勘查情况及样品岩相学和锆石阴极发光图表明该区两组变质锆石年龄即分别代表了该区条带状铁建造的变质年龄,这两期变质年龄时间基本上与之前已提出的华北克拉通在古元古代时期的两次变质事件(2.44Ga和1.82 Ga)相一致。因此我们推测该区BIF的变质成矿作用与整个华北克拉通东部陆块在古元古代发生的两次大的构造热事件有密切成因关系,二者在时间上是一个连续的过程。结合华北克拉通的构造演化史,我们推测密云地区BIF建造可能形成于岛弧构造环境。
[Abstract]:The Precambrian banded iron formation (BIF) is an important type of iron ore resources in the global scope, wide distribution of.BIF as an early Precambrian sedimentary formation of special chemical type in the world, it has experienced complex metamorphic deformation in the process of formation, in the early tectonic inversion (mantle plume and ball the early plate tectonics) plays an important role in evolution. Beijing Miyun area is located in the northern margin of the North China Craton, the area in the Archean to early Proterozoic metamorphic complex experienced tectonic events, formed in this process a large number of large and medium-sized sedimentary metamorphic iron deposit. This paper is mainly based on the study of the Fengjiayu iron ore, iron ore sand plant and the Fangmayu iron mine and other typical BIF type iron ore deposits of magnetite quartzite and nearby iron rocks a total of 4 samples of SHRIMP zircon U-Pb dating, the age data obtained are as follows: (1) oxybiotite Feng Jiayu ore Amphibole magnetite quartzite (MF01) metamorphic zircon 207Pb/206Pb age mainly concentrated in the 1777 + 9 and 2456 + 8 Ma Ma; (2) sand plant iron ore flash Petrochemical magnetite quartzite (MY01) metamorphic zircon dating results for 1806 Ma + 13 and 2469 + 21 Ma, detrital zircon 207Pb/206Pb years at the age of 2517 + 12 Ma. intrusive orebody in felsic pyroxene amphibolite (SY01) metamorphic zircon 207Pb/206Pb age of 1798 + 15 Ma, zircon has obvious oscillatory zoning at the age of 2531 + 7 Ma. to limit the deposition time of Shouyun Iron Mine BIF built for 2469 + 21 to 2517 + 12 Ma Ma between; (3) magnetite garnet gneiss containing two Fangmayu iron mine (MFM01) of the metamorphic zircon dating results were 1817 + 13 and 2456 + 6 Ma Ma, detrital zircon 207Pb/206Pb age of 2529 + 8 Ma. indirectly defines Ma Yu banded iron formation formation era about 2456 + 6 Ma 2529 + 8 Ma, according to previous research, most likely for the late Archean Miyun. BIF type iron ore indicates an important BIF mineralization events in the region through late Neoarchean in the North China Craton. Exploration and sample petrography and zircon cathodoluminescence shows that the metamorphic age of the metamorphic zircon age is two group on behalf of the banded iron formation by age data combined with the field, the two metamorphic age time basically and has been proposed before the North China Craton in the two Paleoproterozoic metamorphic event period (2.44Ga and 1.82 Ga) are consistent. So we speculate that the metamorphic mineralization in this region has a close genetic BIF the relationship with the two major tectonic thermal events throughout the eastern North China Craton landmass in the early Proterozoic occurred, the two is a continuous process in time. The combination of the North China Craton tectonic evolution history, we speculate that the Miyun. The formation of BIF in the region may be formed in the island arc tectonic environment.

【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;P618.31

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