發(fā)布時間：2018-11-11 15:29

【摘要】：勐賽盆地位于老撾北部,主要被連續(xù)的中生代紅層充填;在地層及巖性組合特征方面與思茅盆地具有較高的對比性,因而是連接思茅盆地與老撾萬象盆地和泰國呵叻盆地的關(guān)鍵地帶。然而,目前對思茅盆地與老撾萬象盆地、泰國呵叻盆地是否具有相似的物源區(qū)以及古地理位置是否存在臨近等方面的問題仍存在較多爭論。因此,本文選擇勐賽盆地白堊紀(jì)中期的紅層作為研究對象,以沉積巖石學(xué)、地球化學(xué)和碎屑鋯石U-Pb年代學(xué)為主要研究手段,試圖揭示該盆地中生代地層砂巖樣品的碎屑成分及源區(qū)特征,明確樣品物源區(qū)風(fēng)化及沉積循環(huán)特征、地球化學(xué)物源特征和構(gòu)造環(huán)境,限定其地層的形成時代,得出勐賽盆地中生代地層的物源區(qū)及其來源特征,進(jìn)一步確定云南思茅盆地與老撾的萬象盆地以及泰國的呵叻盆地之間的古構(gòu)造位置關(guān)系。研究結(jié)論得出,這些沉積物主要來源于活動大陸邊緣或島弧的長英質(zhì)巖石及少量被動大陸邊緣的古旋回沉積物。碎屑鋯石U-Pb年齡表明,多數(shù)碎屑鋯石存在多個年齡峰值,分別是: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,最年輕年齡譜段的峰值為103Ma,將勐賽盆地中生代地層的時代限定為不早于晚白堊世。碎屑鋯石U-Pb年齡及微量元素數(shù)據(jù)并結(jié)合地球化學(xué)分析結(jié)果,表明前奧陶紀(jì)鋯石來源于揚(yáng)子板塊,最初來源于秦嶺造山帶。前人研究成果表明呵叻盆地白堊紀(jì)呵叻組地層中的碎屑鋯石顆粒來源于秦嶺造山帶。而通過對思茅盆地晚白堊世勐野井組的物源來源于揚(yáng)子板塊的古旋回沉積物,較年輕的鋯石來源于哀牢山斷裂縫合帶的巖漿巖。通過對比三者碎屑鋯石U-Pb年齡峰值,發(fā)現(xiàn)思茅盆地及呵叻盆地沉積物為同一物源:即416-466Ma和219-308Ma年齡的鋯石來源于哀牢山巖漿巖,長山帶和瀾滄地塊;101-110Ma和149-175Ma年齡的鋯石來自于華南板塊西南緣和越南北部。因此,勐賽盆地物源主要是來源于較遠(yuǎn)處再活化造山帶,而不是來源于區(qū)域造山帶隆起后再沉積。這些物源結(jié)果表明,呵叻盆地紅層的源巖主要是經(jīng)過大思茅盆地和越南北部進(jìn)入,而不是直接來源于揚(yáng)子板塊。
[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.
【學(xué)位授予單位】：中國地質(zhì)大學(xué)(北京)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P534.53

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