老挝北部勐赛盆地白垩纪中期地层物源分析及其构造环境意义

发布时间：2018-11-11 15:29

【摘要】：勐赛盆地位于老挝北部,主要被连续的中生代红层充填;在地层及岩性组合特征方面与思茅盆地具有较高的对比性,因而是连接思茅盆地与老挝万象盆地和泰国呵叻盆地的关键地带。然而,目前对思茅盆地与老挝万象盆地、泰国呵叻盆地是否具有相似的物源区以及古地理位置是否存在临近等方面的问题仍存在较多争论。因此,本文选择勐赛盆地白垩纪中期的红层作为研究对象,以沉积岩石学、地球化学和碎屑锆石U-Pb年代学为主要研究手段,试图揭示该盆地中生代地层砂岩样品的碎屑成分及源区特征,明确样品物源区风化及沉积循环特征、地球化学物源特征和构造环境,限定其地层的形成时代,得出勐赛盆地中生代地层的物源区及其来源特征,进一步确定云南思茅盆地与老挝的万象盆地以及泰国的呵叻盆地之间的古构造位置关系。研究结论得出,这些沉积物主要来源于活动大陆边缘或岛弧的长英质岩石及少量被动大陆边缘的古旋回沉积物。碎屑锆石U-Pb年龄表明,多数碎屑锆石存在多个年龄峰值,分别是:2.50 2.47 Ga,1.85 1.83 Ga,858 730 Ma,466 416 Ma,308 219 Ma,175 149 Ma和110 101 Ma。其中,最年轻年龄谱段的峰值为103Ma,将勐赛盆地中生代地层的时代限定为不早于晚白垩世。碎屑锆石U-Pb年龄及微量元素数据并结合地球化学分析结果,表明前奥陶纪锆石来源于扬子板块,最初来源于秦岭造山带。前人研究成果表明呵叻盆地白垩纪呵叻组地层中的碎屑锆石颗粒来源于秦岭造山带。而通过对思茅盆地晚白垩世勐野井组的物源来源于扬子板块的古旋回沉积物,较年轻的锆石来源于哀牢山断裂缝合带的岩浆岩。通过对比三者碎屑锆石U-Pb年龄峰值,发现思茅盆地及呵叻盆地沉积物为同一物源:即416-466Ma和219-308Ma年龄的锆石来源于哀牢山岩浆岩,长山带和澜沧地块;101-110Ma和149-175Ma年龄的锆石来自于华南板块西南缘和越南北部。因此,勐赛盆地物源主要是来源于较远处再活化造山带,而不是来源于区域造山带隆起后再沉积。这些物源结果表明,呵叻盆地红层的源岩主要是经过大思茅盆地和越南北部进入,而不是直接来源于扬子板块。
[Abstract]:The Mengsai basin is located in the northern part of Laos and is mainly filled with continuous Mesozoic red beds. The characteristics of stratigraphic and lithologic assemblages are highly contrasted with that of Simao basin, so it is the key zone connecting Simao basin with Laotian Vientiane basin and Thai Bharat basin. However, there are still many controversies about whether Simao basin and Laotian Vientiane basin, Thailand Khorat basin have similar provenances and whether paleogeographic location is near or not. Therefore, the red beds in the middle Cretaceous period of Mengsai Basin are selected as the research objects, with sedimentary petrology, geochemistry and U-Pb chronology of clastic zircon as the main research methods. This paper attempts to reveal the clastic composition and source region characteristics of Mesozoic sandstone samples in the basin, determine the characteristics of weathering and sedimentary circulation, geo-chemical source characteristics and tectonic environment in the source area of the samples, and limit the formation time of the strata. The provenance and source characteristics of Mesozoic strata in Mengsai basin are obtained and the paleotectonic position relationship between Simao basin in Yunnan Province and Vientiane basin in Laos and Bharat basin in Thailand is further determined. It is concluded that these sediments are mainly derived from felsic rocks of active continental margin or island arc and a small amount of paleocycle sediments from passive continental margin. The U-Pb age of detrital zircon indicates that most of the zircons have multiple peak ages, which are 2.50 Ga,858 2.47 Ga,1.85 / 1. 83 Ga,858 / 730 Ma,466 / 416 Ma,308 / 219 Ma,175 / 149 Ma and 110 / 101 Ma., respectively. The peak value of the youngest age spectrum is 103 Ma. the Mesozoic strata in Mengsai Basin are limited to no earlier than the late Cretaceous. The U-Pb age and trace element data of detrital zircon and geochemical analysis indicate that the zircon of the pre-Ordovician originated from the Yangtze plate and originated from the Qinling orogenic belt. The results of previous studies indicate that the clastic zircon grains in the Cretaceous Kulak formation originated from the Qinling orogenic belt. The provenance of Mengye well formation in Simao Basin was derived from paleocycle sediments of Yangtze plate and younger zircon from magmatic rocks of Ailaoshan fault suture zone. By comparing the U-Pb age peaks of the three detrital zircons, it is found that the sediments of Simao basin and Bharat basin are the same material source: the zircon of 416-466Ma and 219-308Ma ages originated from the Ailaoshan magmatic rocks, Changshan belt and Lancang block; Zircon from 101-110Ma and 149-175Ma ages came from the southwestern margin of the South China plate and from northern Vietnam. Therefore, the provenance of Mengsai basin is mainly derived from the distant reactivated orogenic belt, not from the regional orogenic belt uplift and redeposition. The results of these sources indicate that the source rocks of the red beds in the Khorat basin are mainly entered through the Great Simao Basin and the northern part of Vietnam, rather than directly from the 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】：P534.53

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