本文選題：年代學(xué) + 地球化學(xué)��； 參考：《中國地質(zhì)大學(xué)(北京)》2017年博士論文

【摘要】：拉薩地體是歐亞大陸最南緣的構(gòu)造單元,是青藏高原的重要組成部分之一。研究拉薩地體前碰撞的構(gòu)造演化,不僅可以更好理解印度-歐亞大陸的碰撞過程,還可以對(duì)青藏高原成礦作用提供重要的基礎(chǔ)資料。然而,對(duì)于該演化歷史,學(xué)術(shù)界一直存在爭議;對(duì)拉薩地體南緣新生地殼的增生機(jī)制亦缺乏足夠的認(rèn)識(shí)。在此背景之下,本文對(duì)拉薩地體南緣早侏羅世火山巖和白堊紀(jì)碎屑沉積巖進(jìn)行了全面的年代學(xué)和地球化學(xué)研究,意在為拉薩地體在中生代的構(gòu)造和地殼生長機(jī)制提供新的約束。拉薩地體南緣早侏羅世火山巖主要分布于葉巴組和桑日群之中。葉巴組火山巖主要包括同期噴發(fā)的玄武巖、玄武安山巖、英安巖和流紋巖,構(gòu)成雙峰式火山巖組合,噴發(fā)年齡為183-174Ma。近同期噴發(fā)的桑日群火山巖包括玄武巖、玄武安山巖和安山巖�；曰鹕綆r(包括葉巴組和桑日群的玄武巖、玄武安山巖)具有富集大離子親石元素、輕稀土元素,虧損高場強(qiáng)元素,和虧損的Sr-Nd-Hf同位素特征,暗示了巖石源于俯沖物質(zhì)交代的地幔楔部分熔融作用。中酸性火山巖(葉巴組英安巖、流紋巖,桑日群安山巖)與基性火山巖之間無成因聯(lián)系,其中酸性火山巖為新生下地殼與變質(zhì)硬砂巖混合源區(qū)在高溫低壓條件下部分熔融成因;中性火山巖具有鎂安山巖的特征,是板片熔體與上覆地幔楔橄欖巖的反應(yīng)的產(chǎn)物。綜合已有資料對(duì)比結(jié)果顯示拉薩地體南緣早侏羅世玄武巖應(yīng)是新特提斯洋北向俯沖體系構(gòu)造背景的弧后巖漿作用產(chǎn)物。拉薩地體南緣白堊系沉積地層主要形成于大陸邊緣弧的弧后盆地環(huán)境之中。下白堊統(tǒng)楚木龍組的沉積時(shí)限約為121-112Ma,物源多來自中北部拉薩地體物質(zhì)的再循環(huán);上白堊統(tǒng)設(shè)興組沉積時(shí)限約為88-70Ma,物源多數(shù)來自拉薩地體南緣弧巖漿巖的風(fēng)化剝蝕。碎屑沉積巖的巖石地球化學(xué)數(shù)據(jù)分析再現(xiàn)了白堊紀(jì)時(shí)期拉薩地體南緣的構(gòu)造環(huán)境,早白堊世拉薩地體總體呈現(xiàn)北高南低的低緩地勢,氣候濕熱;晚白堊世地體南緣發(fā)生了快速的地殼隆升和剝蝕。結(jié)合區(qū)域資料,本文首次提出了拉薩地體南緣從三疊紀(jì)新特提斯洋開始俯沖至古近紀(jì)印度-歐亞大陸碰撞之間經(jīng)歷了多期“弧盆系統(tǒng)”的構(gòu)造演化和拉薩地體南緣地殼生長的“弧后增生”模型。拉薩地體南緣在三疊紀(jì)發(fā)育基本無酸性巖的不成熟島弧體系,到侏羅紀(jì)弧盆系統(tǒng)有中酸性巖漿巖出現(xiàn),直至白堊紀(jì)巖漿活動(dòng)大爆發(fā)發(fā)育各種類型巖漿巖。在地殼伸展階段,幔源巖漿不斷注入弧后區(qū)域并引發(fā)地殼的部分熔融,形成普遍具有高溫低壓成因的酸性巖類;隨后的擠壓階段新生組分被深埋入地下,免受俯沖帶侵蝕;而俯沖板片的后撤又引發(fā)了新一期的弧后伸展作用。在多階段伸展、擠壓、伸展的構(gòu)造體制轉(zhuǎn)換下,新生地殼組分在弧后區(qū)域被不斷增生至拉薩地體南緣,最終的新特提斯洋盆閉合、印度歐亞大陸碰撞,使得這些新生組分得以保留至今。
[Abstract]:The Lhasa ground body is the southernmost tectonic unit of the Eurasian continent and one of the important components of the Qinghai Tibet Plateau. To study the tectonic evolution of the pre collision in Lhasa, it is not only better to understand the collisions between India and Eurasia, but also provide important basic data for the mineralization of the Qinghai Tibet plateau. There has been a lot of controversy, and there is no sufficient understanding of the proliferation mechanism of the new crust in the southern margin of Lhasa. Under this background, this paper carried out a comprehensive chronological and geochemical study of the early Jurassic and Cretaceous sedimentary rocks in the southern edge of the Lhasa geo body, which is intended to be the Mesozoic tectonic and crustal growth mechanism of the Lhasa geo body. The early Jurassic volcanic rocks in the southern margin of the Lhasa terrain are mainly distributed in the Ye Ba group and the sangday group. The volcanic rocks of the leaf bar group mainly include basalt, basaltic andesite, angianite and rhyolite, which constitute the Shuangfeng type volcanic rock assemblage, and the eruption age of the volcanic rocks of the sangsun group, which is 183-174Ma. near the same period of eruption, includes basalt. Rock, basaltic andesite and andesite. Basic volcanic rocks (including basalt and basaltic andesite of the leaf bar group and Sansun group, basaltic andesite) are rich in large ion stone elements, light rare earth elements, loss of high field and strong elements, and loss of Sr-Nd-Hf isotopes, suggesting that the rocks originated from the partial melting of the mantle wedge in the subduction of the subduction material. There is no genetic connection between the rock (EANA group, rhyolite, andesite) and basic volcanic rocks, and the acid volcanic rocks are the cause of partial melting of the nascent lower crust and the metamorphic hard sandstone under the condition of high temperature and low pressure, and the neutral volcanic rocks are characterized by magnesium andesite, which is the reaction between the sheet melt and the overlying mantle wedge peridotite. The results of the comprehensive data show that the early Jurassic basalt in the southern margin of the Lhasa terrain should be the product of the post arc magmatism in the tectonic setting of the North subduction system of the new Tethys ocean. The Cretaceous sedimentary strata in the southern margin of the Lhasa terrestrial body are mainly formed in the back arc basin environment of the continental margin arc. The limit is about 121-112Ma, and the source is mostly from the recirculation of the Lhasa ground substance in the middle and northern part of the middle part of the upper Cretaceous. The sedimentary time of the upper Cretaceous setting up group is about 88-70Ma. Most of the source of the material comes from the weathering and erosion of the arc magma of the southern margin of the Lhasa ground. The analysis of the rock geochemical data of the clastic sedimentary rocks reproduces the tectonic setting of the southern margin of the Cretaceous period of Lhasa, early white The Lhasa ground body in the Cretaceous generally presents low North High South low low terrain, the climate is damp and hot, the late Cretaceous Earth Body south margin of rapid crustal uplift and denudation. Combined with regional data, this paper first proposed that the southern margin of the Lhasa ground body began to subduction from the Triassic new Tethys ocean to the Paleogene India Eurasian collision. The tectonic evolution of the system and the "post arc proliferation" model of the crustal growth in the southern margin of Lhasa, the immature island arc system of the basic acidity of the Triassic in the southern margin of the Lhasa ground body, the emergence of intermediate acid magmatic rocks in the Jurassic arc basin, and the large eruption and development of various types of magmatic rocks in the Cretaceous magmatism. The mantle derived magma continuously injected into the post arc region and triggered partial melting of the crust, forming an acid rock generally having high temperature and low pressure. The subsequent extrusion stage was deeply buried under the subduction zone from the subduction zone, while the withdrawal of subduction plates triggered a new period of post arc extension. Under the transformation of structural system, the new crustal components in the back arc region are constantly proliferated to the southern edge of the Lhasa earth body, and the final new Tethys ocean basin is closed and the India Eurasian continent collide, which makes these new groups so far as retained.
【學(xué)位授予單位】：中國地質(zhì)大學(xué)(北京)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：P548;P534.5

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