云南兰坪盆地晚白垩世云龙组物源分析及其构造意义

发布时间：2018-02-25 21:41

  本文关键词： 物源分析 碎屑锆石U-Pb年龄 兰坪盆地 云龙组　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】：东南亚地区发育许多具有蒸发岩系的白垩纪陆内盆地,盆地中又分布着众多不同类型的蒸发岩矿床。其中几个较大的盆地包括呵叻盆地、万象盆地、勐赛盆地、思茅盆地以及兰坪盆地。之前的研究发现呵叻、勐赛、思茅含盐层的碎屑物具有一定的联系,之间存在着碎屑沉积物的沟通,即沉积物从思茅往呵叻流,指示晚白垩纪时期两者是相互贯通的。兰坪盆地位于思茅北部,其古新统是中生代盆地末期于干燥条件下沉积形成的红色含盐碎屑岩系,含膏盐地层称之为云龙组;位于兰坪盆地南端的思茅盆地勐野井组地层发育一套相同的蒸发岩系,两者岩性组合可对比。前人对思茅盆地勐野井组碎屑物源研究发现其存在不同的物质来源,而对兰坪盆地云龙组的碎屑沉积物的来源问题并没有进行过详细的研究,因而对北部兰坪盆地物源分析,能很好的将盆地之间的物源关系做进一步的补充,可以恢复当时的古地理环境及古水系的大致展布。本文在前人研究的基础上,结合砂岩岩相学及地球化学方面的证据,利用碎屑锆石LA-ICP-MS U-Pb测年方法,探讨了兰坪盆地云龙组碎屑物源属性问题。前人砂岩岩石地球化学研究表明,碎屑物主要来自长英质岩源区,且源区具有被动大陆边缘构造环境特征。本次研究中,用于定年的砂岩经过碎屑组分投图,其结果显示均在旋回造山带区域,表明碎屑沉积物在造山带演化过程中经过了旋回沉积。本文对盆地不同地区采集的7个砂岩样品进行了碎屑锆石U-Pb年龄及锆石微量元素分析。其中,锆石微量元素研究表明锆石主要来源于岩浆成因,与岛弧或造山有关的活动构造背景有关。另外,碎屑锆石测年550颗,共获得502个有效的单颗粒碎屑锆石年龄。结果显示,盆地中碎屑锆石年龄最老为2733 Ma,最年轻为105 Ma。根据碎屑锆石年龄谱段的结果可以分为3个主要的年龄段:古元古代-新太古代(2733~2384 Ma、2057~1531 Ma),新元古代(1011~558 Ma),奥陶纪-三叠纪(493~371 Ma、340~203 Ma)。每一个年龄段都对应在盆地的周缘存在一个或多个潜在的源区。经分析,古元古代-新太古代的锆石主要来自秦岭造山带和扬子板块。而扬子板块的旋回沉积物可能为新元古代的锆石提供了物源。临近造山带的沉积物最有可能为三叠-奥陶纪的锆石提供碎屑沉积物。此次研究揭示了兰坪盆地的碎屑主要来自扬子板块,然后碎屑沉积物再被搬运至思茅地区,最后流到呵叻。证实了晚白垩世存在着向南或向西南方流向的古河流。
[Abstract]:Many Cretaceous intracontinental basins with evaporite series are developed in Southeast Asia, and many different types of evaporite deposits are distributed in the basins. The Simao basin and the Lanping basin. Previous studies have found that there is a certain connection between the clastic materials of Khorat, Mengsai, and Simao salt beds, and there is a communication between the clastic sediments, that is, the sediment flows from Simao to Kala. The Lanping basin is located in the northern part of Simao, and its Paleocene is a red salt clastic series formed in the late Mesozoic basin under dry conditions, which is called Yunlong formation. The formation of Mengye well formation in Simao basin, located at the southern end of Lanping basin, developed a set of identical evaporative rock series, and the two lithologic combinations can be compared. The previous studies on the clastic material sources of Mengye well formation in Simao Basin have found that there are different material sources. However, the origin of clastic sediments of Yunlong formation in Lanping Basin has not been studied in detail. Therefore, the analysis of provenance in the northern Lanping Basin can make a further supplement to the relationship between the two basins. The paleogeographic environment and the distribution of paleogeographic system can be restored. Based on the previous studies, combined with the evidence of sandstone lithology and geochemistry, the LA-ICP-MS U-Pb dating method of clastic zircon is used in this paper. The characteristics of clastic source of Yunlong formation in Lanping Basin are discussed. The previous study of sandstone rock geochemistry shows that the clastic material mainly comes from the source area of felsic rocks, and the source area has the characteristics of passive continental margin tectonic environment. The sandstones used for dating have passed through the clastic composition chart, and the results show that they are all in the region of the cyclic orogenic belt. The results show that clastic sediments have been cyclically deposited during orogenic evolution. Seven sandstone samples collected from different areas of the basin were analyzed for zircon U-Pb age and trace elements of zircon. The trace element study of zircon indicates that the zircon is mainly derived from magmatic origin and is related to the active tectonic setting related to island arc or orogenic. In addition, the dating of 550 detrital zircons has obtained 502 effective single-grain zircon ages. The age of detrital zircon in the basin is 2733 Ma and the youngest is 105 Ma. according to the results of the age spectrum of clastic zircon, it can be divided into three main ages: Paleoproterozoic, NeoArchaean (2733) 2384 Ma2057531 Ma, Neoproterozoic 101111558 Ma, Ordovician Triassic. Each age age corresponds to the existence of one or more potential sources around the basin. The zircon from Paleoproterozoic to NeoArchean mainly came from the Qinling orogenic belt and Yangtze plate. The cyclic sediments of Yangtze plate may provide material source for Neoproterozoic zircon. The sediments near the orogenic belt are most likely to be Triassic. -zircon from the Ordovician provides clastic sediments. This study reveals that the debris in the Lanping basin is mainly from the Yangtze plate. Then the detrital sediments were transported to Simao area and finally flowed to Khorat confirming the existence of ancient rivers flowing southward or southward in the late Cretaceous.
【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;P534.53
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本文编号：1535260