本文選題：蛇綠巖 + 蛇綠混雜巖帶��； 參考：《中國地質(zhì)大學(xué)(北京)》2017年碩士論文

【摘要】：研究區(qū)位于內(nèi)蒙古自治區(qū)中部,大地構(gòu)造位置上位于華北板塊與西伯利亞板塊之間的興蒙造山帶中東部地區(qū)。研究區(qū)內(nèi)存在三條蛇綠混雜巖帶,由北向南分別是賀根山蛇綠混雜巖帶、迪彥廟—達(dá)青牧場(chǎng)蛇綠混雜巖帶、西拉木倫蛇綠混雜巖帶。本文通過野外地質(zhì)調(diào)查,重點(diǎn)區(qū)域地質(zhì)樣品采集及室內(nèi)分析,并結(jié)合前人對(duì)興蒙造山帶內(nèi)蛇綠巖的研究成果,運(yùn)用區(qū)域大地構(gòu)造學(xué)、沉積學(xué)、巖石學(xué)、巖石地球化學(xué)、年代學(xué)等方法進(jìn)行研究,發(fā)現(xiàn)興蒙造山帶中東部在晚古生代時(shí)期具有多期次的構(gòu)造活動(dòng)特征。賀根山蛇綠混雜巖帶中存在兩種構(gòu)造環(huán)境中形成的玄武巖,一種為變質(zhì)玄武巖,稀土和微量元素具有IAT和N-MORB特征,為賀根山蛇綠巖的組成成分,其形成年齡為403Ma-354Ma,該時(shí)期并沒有島弧巖漿記錄,因此推測(cè)其形成于洋中脊環(huán)境,受到早期古亞洲洋俯沖板片的影響而具有島弧的性質(zhì)。另一種玄武巖的稀土元素特征為輕稀土富集的右傾型,該特征類似于陸殼型(C-crust型)玄武巖。因此表明其形成大陸裂谷環(huán)境。其形成年齡約為300Ma-292Ma。迪彥廟—達(dá)青牧場(chǎng)蛇綠混雜巖帶中,迪彥廟蛇綠巖具有IAT和N-MORB型的特征,并且發(fā)現(xiàn)有玻安巖的存在,推測(cè)其形成于島弧環(huán)境,根據(jù)本文采集的迪彥廟堆晶輝長(zhǎng)巖所測(cè)得的年齡為345.6±2.3Ma,結(jié)合前人的研究成果,推測(cè)迪彥廟蛇綠巖的形成時(shí)代為早石炭世早期—早石炭世晚期(356Ma-320Ma)。達(dá)青牧場(chǎng)蛇綠巖中具有兩種類型的玄武巖:一種為枕狀玄武巖,其巖石地球化學(xué)特征類似于N-MORB。另一種為片理化玄武巖,其玄武巖中REE總量極低,微量元素特征類似于陸殼型(C-crust型)玄武巖,推測(cè)其形成于大陸裂谷環(huán)境。西拉木倫蛇綠混雜巖帶中,小葦塘蛇綠巖的蝕變玄武巖具有N-MORB型玄武巖的特征,上覆巖系中含有放射蟲硅質(zhì)巖,推測(cè)小葦塘蛇綠巖形成于洋中脊環(huán)境。硅質(zhì)巖中發(fā)現(xiàn)有中二疊世的放射蟲化石及伴生的牙形石,因此推測(cè)該區(qū)蛇綠巖形成時(shí)代應(yīng)該在早—中二疊世。興蒙造山帶中東部三條蛇綠混雜巖帶中蛇綠巖的年齡由北向南具有依次變年輕的特征,可能代表了興蒙造山帶中東部由北向南,大洋依次開合的過程。
[Abstract]:The study area is located in the central part of Inner Mongolia Autonomous region, and the tectonic position is located in the central and eastern part of the Xingmeng orogenic belt between the North China Plate and the Siberian Plate. There are three ophiolite melange belts in the study area, from north to south, they are Hegen Mountain ophiolite melange, Diyanmiao Dachingshan ophiolite melange and Xilamurun ophiolite melange. Based on the field geological survey, the collection and laboratory analysis of geological samples in key regions, and the previous research results on ophiolite in the Xingmeng orogenic belt, this paper applies regional geotectonics, sedimentology, petrogeochemistry, etc. By means of chronology and other methods, it is found that the central and eastern part of the Xingmeng orogenic belt is characterized by multiple tectonic activities in the late Paleozoic. There are two kinds of basalts formed in the Hegenshan ophiolite melange belt, one is metamorphic basalt, rare earth and trace elements have IAT and N-MORB characteristics, and they are the composition of Hegenshan ophiolite. The age of its formation is 403Ma-354Ma.There is no island arc magma recorded in this period, so it is assumed that it formed in the middle ridge environment of Yu Yang and was influenced by the early paleo-Asian ocean subduction plate and has the character of island arc. Another type of basalt is characterized by LREE enriched right-dip type, which is similar to the continental crust type (C-crust type) basalt. Therefore, it shows that it formed a continental rift environment. The age of formation is about 300Ma-292Ma. In the Dianmiao-Dachingshan ophiolite melange belt, the ophiolite has the characteristics of IAT and N-MORB type, and the existence of Boyanite is found, which is supposed to be formed in the island arc environment. According to the age of 345.6 鹵2.3 Ma. obtained from the Diyan Miao crystal gabbro collected in this paper, combined with the previous research results, it is inferred that the age of formation of the ophiolite is 356Ma-320Maan in the early Carboniferous to the late early Carboniferous. There are two types of basalts in the ophiolite of Dachingchang: one is pillow basalt, and its geochemical characteristics are similar to those of N-MORB. The other is schistatic basalt, in which the total amount of REE is very low, and the trace element characteristic is similar to that of continental crust type (C-crust) basalt, which is supposed to be formed in the continental rift environment. In the Xilamurun ophiolite melange, the altered basalts of the ophiolite in Xiaolitang have the characteristics of N-MORB type basalts, and the overlying rocks contain radiolarian siliceous rocks. It is inferred that the ophiolite formed the Yu Yang middle ridge environment. There were radiolarian fossils and conodonts associated with the Middle Permian in siliceous rocks, so it is assumed that the ophiolite was formed in the early and Middle Permian. The ages of ophiolite in the three ophiolite melange belts in the central and eastern part of the Xingmeng orogenic belt are younger from north to south, which may represent the process of opening and closing from north to south in the central and eastern part of the Xingmeng orogenic belt.
【學(xué)位授予單位】：中國地質(zhì)大學(xué)(北京)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P587

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