發(fā)布時間：2018-03-21 04:02

  本文選題：羌塘　切入點：龍木錯-雙湖縫合帶　出處：《中國地質(zhì)大學(xué)(北京)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：研究區(qū)位于羌塘中部南羌塘的瑪依崗日地區(qū)和雪水河地區(qū),構(gòu)造位置位于龍木錯—雙湖縫合帶中段,主要地層為早古生代俄久賣巖組(E1-2),石炭—二疊系岡塘錯巖組((C-P2)g)、石炭—二疊系雪水河巖群((C-P2)x)、中晚三疊統(tǒng)瑪依崗日巖組(T2-3m)。本文對增生雜巖帶內(nèi)沉積地質(zhì)體四條巖性剖面進行實測分析、并對玄武巖、砂巖采用巖石礦物學(xué)和地球化學(xué)等方法進行詳細(xì)分析,結(jié)果表明:瑪依崗日巖組和岡塘錯巖組源巖沉積環(huán)境為海底扇沉積,雪水河巖群為半深海-深海相沉積,早古生代巖群俄久賣巖組為濱、淺海環(huán)境沉積。雪水河附近玄武巖Ti O2、P2O5含量高,稀土總量高,輕重稀土強烈分餾的特點,富集大離子親石元素Ba、Rb和高場強元素Zr、Th、Hf,地球化學(xué)特征和稀土微量元素分布形式均與標(biāo)準(zhǔn)洋島型玄武巖相似。地球化學(xué)判別圖解顯示為板內(nèi)洋島環(huán)境,巖漿上涌過程中受到了來自于地殼物質(zhì)的混染,但混染程度不深�，斠缻徣丈皫r稀土元素總量較高,其稀土配分與Bhatia提出的大洋島弧雜砂巖相近,明顯的輕稀土富集特征,無明顯的Eu負(fù)異常,不具有Ce異常,而不同于大陸島弧和活動陸緣雜砂巖。在構(gòu)造背景判別圖解中,顯示出物源構(gòu)造背景相對比較復(fù)雜,大部分屬于大洋島弧環(huán)境,其次為大陸島弧環(huán)境。通過對岡塘錯巖組和瑪依崗日巖組砂巖重礦物分析,其物源母巖可能是一個不穩(wěn)定的造山帶甚至為火山弧。通過增生雜巖帶內(nèi)的幾個主要沉積地質(zhì)體分析,并結(jié)合前人研究資料,增生雜巖帶演化產(chǎn)物主要為:晚石炭世—早二疊世時期,堆晶輝長巖和二疊系的蛇綠巖即代表了古特提斯洋初始張開的產(chǎn)物;早二疊世,古特提斯洋開始俯沖,雪水河洋島型玄武巖即是古特提斯洋俯沖消減的殘余地質(zhì)體;中晚三疊世時期,古特提斯洋已經(jīng)開始發(fā)生俯沖消減,并伴隨著變質(zhì)巖和島弧火山巖的形成,至晚三疊世中晚期,俯沖作用完成,古特提斯洋閉合,羌南和羌北兩地塊發(fā)生碰撞,形成了典型的造山帶增生雜巖。
[Abstract]:The study area is located in the Maygang and Xueshui River areas in the southern Qiangtang area of the central Qiangtang, and the tectonic position is located in the middle section of the Longmujia-Shuanghu suture zone. The main strata are early Paleozoic E1-2G, Carboniferous-Permian Gangtang dislocation formation, Carboniferous-Permian Xueshuihe Group, Carboniferous-Permian Xueshuihe Group, Middle and late Triassic Mayigang Ri formation, T2-3m.The four lithologic profiles of sedimentary geological bodies in the accretive complex are presented in this paper. Surface measurement and analysis, The basalt and sandstone are analyzed in detail by means of petro-mineralogy and geochemistry. The results show that the source rock sedimentary environment of Mai Gangri formation and Gangtang fault rock formation is submarine fan deposition, and Xueshuihe rock group is semi-deep-sea and deep-marine sedimentary. The early Paleozoic Ejiushiyan formation is a shoreline and shallow sea sedimentary environment. The basalt near Xueshui River is characterized by high content of TIO _ 2O _ 2P _ 2O _ 5, high amount of rare earth, and strong fractionation of heavy and heavy rare earths. The geochemical characteristics and the distribution of rare earth elements are similar to those of standard oceanic island basalts, and the geochemical discriminant diagram shows that the geochemical discriminant diagram is an intraplate oceanic island environment. In the process of magma upwelling, it was mixed by crustal materials, but the degree of mixed contamination was not deep. The total amount of rare earth elements in Mai Gangri sandstone is relatively high, its rare earth distribution is close to that of oceanic island arc complex sandstone proposed by Bhatia, and the enrichment characteristics of light rare earth elements are obvious. There is no obvious negative EU anomaly and no ce anomaly, which is different from continental island arc and active continental margin complex sandstone. In the distinguishing diagram of tectonic background, it shows that the provenance tectonic background is relatively complex, most of which belong to the oceanic island arc environment. Secondly, the continental island arc environment. Based on the analysis of sandstone heavy minerals in Gangtang fault rock formation and Mayiganri formation, The source rock may be an unstable orogenic belt or even a volcanic arc. The evolution products of the accretive complex are: during the late Carboniferous to early Permian, the heaped gabbro and the Permian ophiolite represented the initial opening of the PaleoTethys Ocean, and the PaleoTethys Ocean began to subduction in the early Permian. The islet basalt of Xueshuihe Ocean is the residual geological body of the subduction of the PaleoTethys ocean, which began to subduction in the middle and late Triassic, and was accompanied by the formation of metamorphic rocks and island arc volcanic rocks until the middle and late Triassic. The subduction was completed, the paleoTethys ocean was closed, and the southern Qiang and the northern Qiang landmasses collided, forming a typical orogenic belt accretive complex.
【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】：2015
【分類號】：P512.2;P548

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