發(fā)布時間：2018-05-24 07:04

  本文選題：獨居石 + 碎屑鋯石�。� 參考：《中國地質(zhì)大學(北京)》2017年碩士論文

【摘要】：中元古代長城系為華北克拉通第一套蓋層沉積,代表中元古代的開始,對其沉積時代和物質(zhì)來源進行深入研究具有十分重要的地質(zhì)意義。本文對采自北京十三陵地區(qū)長城系串嶺溝組底部沉積巖中的獨居石及碎屑鋯石進行了SHRIMP及LA-ICP-MS U-Pb年代學研究。由下向上按層位分別采樣MC1~MC5,對5件樣品進行了詳細的能譜分析,于樣品MC1中發(fā)現(xiàn)了大量的獨居石顆粒,最大粒徑88μm,背散射圖像顯示獨居石邊緣不平整,形狀不規(guī)則,呈現(xiàn)出“魚形”、“鳥形”、“花形”、“蟲形”等各種形狀。大量的觀察發(fā)現(xiàn)獨居石絕大多數(shù)都分布在石英脈或赤鐵礦細脈里,遠離脈的地方幾乎沒有獨居石的分布。對獨居石進行初步的SHRIMP U-Pb原位定年,獲得的年齡為152±11 Ma,結(jié)合其低U、Th含量及其特征的產(chǎn)狀和礦物組合,表明這些獨居石顆粒并非成巖期形成,而為次生獨居石,其形成與后期的熱液事件有關。5件樣品中的碎屑鋯石年齡譜圖顯示ca.2.5 Ga的主峰和ca.2.0 Ga的次峰,表明串嶺溝組碎屑沉積巖物源主要來自以新太古代晚期陸殼物質(zhì)為主構(gòu)成的華北克拉通基底及研究區(qū)西南的中部造山帶。本次研究中發(fā)現(xiàn)的最年輕碎屑鋯石年齡為1673±44 Ma,由此限定串嶺溝組沉積巖沉積的下限年齡為1673±44 Ma。從MC1到MC3,碎屑鋯石的年代范圍由窄變寬,認為串嶺溝組在MC3層位時曾發(fā)生一次海侵,海水將大量ca.2.0 Ga的碎屑物質(zhì)從研究區(qū)西南的陸地帶到海洋接受沉積,導致其沉積物中有大量ca.2.0 Ga的碎屑物質(zhì)加入。從MC4到MC5,巖性由碎屑巖過渡為碳酸鹽巖,說明海水由淺變深;年齡譜圖顯示MC5比MC4物源更廣,推測在MC5層沉積時也發(fā)生了一次海侵事件。本文對長城系串嶺溝組碎屑鋯石的研究表明其物質(zhì)來源具有隨地層變新越來越廣泛的趨勢,靠上部層位有顯著的ca.2.0 Ga的年輕物質(zhì)加入。
[Abstract]:The Mesoproterozoic the Great Wall system is the first set of cover deposits in the North China Craton, which represents the beginning of the Middle Proterozoic. It is of great geological significance to study the sedimentary age and material source of the Mesoproterozoic system. In this paper, the SHRIMP and LA-ICP-MS U-Pb chronology of monazite and clastic zircon collected from the bottom sedimentary rocks of the Great Wall series of Chuanling Gou formation in the Ming Tombs area of Beijing have been studied. MC1 / MC5 was sampled from the bottom up and the five samples were analyzed by energy spectrum in detail. A large number of monazite particles were found in the sample MC1, with a maximum diameter of 88 渭 m. The backscatter images showed that the edge of monazite was uneven and the shape of monazite was irregular. It presents various shapes, such as fish, bird, flower, worm and so on. A large number of observations show that most of the monazite are distributed in quartz veins or hematite veins, and there is almost no monazite distribution far away from the veins. The primary SHRIMP U-Pb dating of monazite is obtained at 152 鹵11 Ma. combined with its low U ~ (2 +) Th content and its characteristic occurrence and mineral assemblage, it is shown that these monazite particles were not formed in diagenetic stage, but were secondary monazite. The zircon ages of 5 samples are related to the late hydrothermal events, which show the main peaks of ca.2.5 Ga and the secondary peaks of ca.2.0 Ga. The results show that the clastic sedimentary rocks of the Chuanling Gou formation are mainly derived from the North China craton basement and the central orogenic belt in the southwest of the study area, which are mainly composed of the late NeoArchean continental crust. The youngest zircon age found in this study is 1673 鹵44 Ma, thus limiting the lower sedimentary age of the sedimentary rocks of the Chuanling formation to 1673 鹵44 Ma. From MC1 to MC3, the age range of detrital zircons has changed from narrow to wide. It is believed that a transgression occurred in the MC3 formation in the Chuanlinggou formation, and that the sea water brought a large amount of ca.2.0 Ga debris material from the land southwest of the study area to the ocean to receive sediments. A large amount of ca.2.0 Ga clastic material was added to the sediments. From MC4 to MC5, the lithology transition from clastic rock to carbonate rock indicates that the sea water has changed from shallow to deep, and the age spectrum shows that MC5 is more extensive than MC4 provenance, and a transgressive event occurred during the deposition of MC5 layer. In this paper, the study of the clastic zircon in the Great Wall series shows that the material source of the zircon is more and more new and widespread, and it is added by the young material with remarkable ca.2.0 Ga in the upper layer.
【學位授予單位】：中國地質(zhì)大學(北京)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P597.3;P588.2
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本文編號：1928145