本文關(guān)鍵詞： 雅魯藏布江蛇綠巖帶 橄欖石組構(gòu) 就位機制 巖石地球化學 年代學　出處：《中國地質(zhì)大學(北京)》2016年博士論文　論文類型：學位論文

【摘要】：本論文選取雅魯藏布江蛇綠巖帶中西段日喀則—桑桑—薩嘎—仲巴一帶為研究靶區(qū),重點研究區(qū)為桑桑蛇綠巖區(qū)、薩嘎蛇綠巖區(qū)和仲巴蛇綠巖區(qū),研究對象為重點研究區(qū)內(nèi)蛇綠巖,重點關(guān)注研究區(qū)內(nèi)蛇綠巖的巖石地球化學、年代學、顯微構(gòu)造和地幔流變學研究,從而探究雅江蛇綠巖帶中西段的就位機制,并提出具有建設性意義的合理模型。雅魯藏布江蛇綠巖帶自桑桑蛇綠巖往西分成南北兩個亞帶。桑桑蛇綠巖序列中地幔橄欖巖、玄武巖和輝長巖均貧HFSE,玄武巖和輝長巖屬鈣堿性系列,發(fā)育堿性玄武巖,屬MORB型,桑桑所測基性巖鋯石U-Pb年齡為125±1.2Ma。薩嘎蛇綠巖南亞帶未發(fā)現(xiàn)蛇綠巖層序地層,北亞帶出露蛇綠巖層序地層,其中基性巖屬鈣堿性—低鉀系列,玄武巖普遍發(fā)育,并呈現(xiàn)邊緣亞堿性中間堿性的分布特征,發(fā)育貧硅富堿的富堿礦物,輝綠巖鋯石U-Pb年齡為125.6±2.7Ma,推測為洋內(nèi)俯沖帶之上(SSZ)的弧前-弧-弧后環(huán)境。仲巴蛇綠巖未發(fā)現(xiàn)地幔橄欖巖,其邊緣分布鈣堿性玄武巖,中部分布堿性玄武巖,具有典型洋島玄武巖組合特征,仲巴日瑪玄武巖鋯石U-Pb年齡為129.3±1.0Ma,推測形成于弧前拉張環(huán)境。日喀則白朗石榴輝石巖屬鈣堿性基性巖,年齡為149.0±3.1Ma,源于地幔,標志著新特提斯洋脊已俯沖消亡。選取薩嘎地幔橄欖巖進行橄欖石組構(gòu)分析,其EBSD解析結(jié)果是該橄欖石組構(gòu)屬“B”型橄欖石組構(gòu),主導滑移系為(010)[001],產(chǎn)生于高壓高應力環(huán)境,與俯沖帶之上(SSZ)關(guān)系密切,指示向南逆沖推覆,其結(jié)果與野外實際觀察的現(xiàn)象一致,橄欖巖中斜方輝石和單斜輝石也具有同樣的EBSD解析結(jié)果。根據(jù)研究資料,提出可能的運動學模型“俯沖面不均論”運動模型,通過研究區(qū)內(nèi)邊界處的線理和面理可以證實該模型有一定合理性。通過研究區(qū)內(nèi)玄武巖的研究,對研究內(nèi)蛇綠巖的構(gòu)造環(huán)境和動力學機制進行探究,推演出地幔流變學機制。大洋中脊是蛇綠巖形成的原始動力,由于地幔柱和熱點的推動力使得蛇綠巖中玄武巖復雜化,從而表現(xiàn)為經(jīng)歷了俯沖帶多階段多源區(qū)的改造,同時受到板內(nèi)裂谷作用的影響,形成具有復雜源區(qū)和復合地球化學特征的玄武巖組合。根據(jù)本文研究,提出了較為合理的適用于中西部蛇綠巖的“五段式”就位模型。
[Abstract]:This paper selects the Yarlung Zangbo River ophiolite zone in Western Shigatse - Saga - Sangsang - Zhongba area as the research target, the key research area for Sangsang ophiolite zone, Saga ophiolite zone and Zhongba ophiolite zone, the object of the study is the key research area within the ophiolite, geochemistry, focus in the research area of ophiolite Study on geochronology, microstructure and rheology of the mantle in place, so as to explore the mechanism of Yajiang ophiolite belt in the west, and put forward the reasonable constructive model. The Yarlung Zangbo River ophiolite zone is divided into West Sangsang ophiolite from north to South and two sub belts. The mantle peridotite Sangsang ophiolite sequence, basalt and gabbro are poor HFSE, basalt and gabbro of calc alkaline series, the development of alkaline basalts belong to MORB type, SinSin measured by mafic zircon U-Pb age of 125 + 1.2Ma. ophiolite belt in South Asia was not found in the saga ophiolite strata Sequence stratigraphy, northern belt exposed ophiolite sequence stratigraphy, the mafic rocks belong to the calc alkaline series, low potassium, widely developed basalt, distribution characteristics and presents the edge sub alkaline intermediate alkaline and alkali rich mineral development and poor silicon and alkali, diabase zircon U-Pb age of 125.6 2.7Ma, presumably above the ocean subduction zone (SSZ) the forearc island arc environment. Zhongba ophiolite was found in mantle peridotite, the marginal distribution of calc alkaline basalts, the central distribution of alkali basalts, with typical oceanic island basalt assemblage, zircon U-Pb age Rima basalt in Zhongba was 129.3 + 1.0Ma, presumably formed in the fore arc extensional environment. Shigatse white pomegranate pyroxenite calc alkaline rocks, age 149 + 3.1Ma, derived from the mantle, marking the new Tethys ocean ridge subduction and extinction. The saga of selected mantle peridotite olivine fabric analysis, the analytical result is the olivine EBSD Fabric is a "B" type of olivine fabric, the dominant slip system for [001] (010), resulting in high stress environment, and above the subduction zone (SSZ) closely, indicating southward thrusting, and the results of field observation of the phenomenon, peridotite in orthopyroxene and clinopyroxene also EBSD has the same analytical results. According to the research data, the kinematics model of "possible subduction of the uneven surface of the motion model of the study area within the boundary of the lineation and foliation can confirm that the model is reasonable. Through the study of basalt in the area, the tectonic environment of ophiolite and dynamics research to explore the mechanism, deduce the mantle rheology mechanism. The mid ocean ridge is the original power of the ophiolite formation, due to plume and hot force makes the ophiolite complex in basalt, which manifested as experienced multi stage multi subduction zone The transformation of the area is also influenced by the intraplate rift, forming a basalt combination with complex source area and complex geochemical characteristics. Based on this study, a more reasonable "five stage" positioning model suitable for Middle West ophiolite is proposed.

【學位授予單位】：中國地質(zhì)大學(北京)
【學位級別】：博士
【學位授予年份】：2016
【分類號】：P588

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