本文關(guān)鍵詞： 物源分析 碎屑鋯石U-Pb年齡 蘭坪盆地 云龍組　出處：《中國地質(zhì)大學(xué)(北京)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：東南亞地區(qū)發(fā)育許多具有蒸發(fā)巖系的白堊紀陸內(nèi)盆地,盆地中又分布著眾多不同類型的蒸發(fā)巖礦床。其中幾個較大的盆地包括呵叻盆地、萬象盆地、勐賽盆地、思茅盆地以及蘭坪盆地。之前的研究發(fā)現(xiàn)呵叻、勐賽、思茅含鹽層的碎屑物具有一定的聯(lián)系,之間存在著碎屑沉積物的溝通,即沉積物從思茅往呵叻流,指示晚白堊紀時期兩者是相互貫通的。蘭坪盆地位于思茅北部,其古新統(tǒng)是中生代盆地末期于干燥條件下沉積形成的紅色含鹽碎屑巖系,含膏鹽地層稱之為云龍組;位于蘭坪盆地南端的思茅盆地勐野井組地層發(fā)育一套相同的蒸發(fā)巖系,兩者巖性組合可對比。前人對思茅盆地勐野井組碎屑物源研究發(fā)現(xiàn)其存在不同的物質(zhì)來源,而對蘭坪盆地云龍組的碎屑沉積物的來源問題并沒有進行過詳細的研究,因而對北部蘭坪盆地物源分析,能很好的將盆地之間的物源關(guān)系做進一步的補充,可以恢復(fù)當(dāng)時的古地理環(huán)境及古水系的大致展布。本文在前人研究的基礎(chǔ)上,結(jié)合砂巖巖相學(xué)及地球化學(xué)方面的證據(jù),利用碎屑鋯石LA-ICP-MS U-Pb測年方法,探討了蘭坪盆地云龍組碎屑物源屬性問題。前人砂巖巖石地球化學(xué)研究表明,碎屑物主要來自長英質(zhì)巖源區(qū),且源區(qū)具有被動大陸邊緣構(gòu)造環(huán)境特征。本次研究中,用于定年的砂巖經(jīng)過碎屑組分投圖,其結(jié)果顯示均在旋回造山帶區(qū)域,表明碎屑沉積物在造山帶演化過程中經(jīng)過了旋回沉積。本文對盆地不同地區(qū)采集的7個砂巖樣品進行了碎屑鋯石U-Pb年齡及鋯石微量元素分析。其中,鋯石微量元素研究表明鋯石主要來源于巖漿成因,與島弧或造山有關(guān)的活動構(gòu)造背景有關(guān)。另外,碎屑鋯石測年550顆,共獲得502個有效的單顆粒碎屑鋯石年齡。結(jié)果顯示,盆地中碎屑鋯石年齡最老為2733 Ma,最年輕為105 Ma。根據(jù)碎屑鋯石年齡譜段的結(jié)果可以分為3個主要的年齡段:古元古代-新太古代(2733~2384 Ma、2057~1531 Ma),新元古代(1011~558 Ma),奧陶紀-三疊紀(493~371 Ma、340~203 Ma)。每一個年齡段都對應(yīng)在盆地的周緣存在一個或多個潛在的源區(qū)。經(jīng)分析,古元古代-新太古代的鋯石主要來自秦嶺造山帶和揚子板塊。而揚子板塊的旋回沉積物可能為新元古代的鋯石提供了物源。臨近造山帶的沉積物最有可能為三疊-奧陶紀的鋯石提供碎屑沉積物。此次研究揭示了蘭坪盆地的碎屑主要來自揚子板塊,然后碎屑沉積物再被搬運至思茅地區(qū),最后流到呵叻。證實了晚白堊世存在著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.
【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】：P597;P534.53
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本文編號：1535260