本文選題：青藏高原　切入點(diǎn)：拉薩地塊　出處：《中國(guó)科學(xué)院廣州地球化學(xué)研究所》2017年博士論文　論文類型：學(xué)位論文

【摘要】：近年來(lái),拉薩地塊新生代時(shí)期的高原隆升歷史和成礦作用研究已經(jīng)取得了一系列突破性進(jìn)展,但對(duì)中生代(尤其是晚三疊紀(jì)-晚侏羅紀(jì))所經(jīng)歷的大洋俯沖和陸/弧-陸碰撞過(guò)程,目前還存在很大爭(zhēng)議。重塑拉薩地塊中生代構(gòu)造演化歷史不僅是研究新生代碰撞作用的前提,更重要的是可以查明拉薩地塊發(fā)育的中生代時(shí)期的大型-超大型礦床形成的動(dòng)力學(xué)背景�；谝陨夏康�,本學(xué)位論文選取拉薩地塊南部和北部中生代侏羅紀(jì)代表性巖漿巖和蛇綠巖為研究對(duì)象,取得了如下的研究進(jìn)展:(1)位于拉薩地塊北部的達(dá)如錯(cuò)火山巖(~162 Ma)是班怒帶中段首次發(fā)現(xiàn)的侏羅紀(jì)火山巖,其地球化學(xué)組成具有高鎂安山巖的特征。此外,達(dá)如錯(cuò)火山巖還具有高的Th含量和(La/Sm)N比值,低的Ba/Th和Sr/Y比值以及富集的SrNd-Hf同位素組成,特別是其εNd(t)值與區(qū)域沉積物的εNd(t)值的一致,表明它們是沉積物融體與地幔楔反應(yīng)的產(chǎn)物,形成于高溫低壓的環(huán)境。野外考察表明,達(dá)如錯(cuò)火山巖是藏北湖蛇綠混雜巖的一部份,并不能作為班怒洋南向俯沖的證據(jù),結(jié)合區(qū)域上巖漿-構(gòu)造分布特征,其形成與班怒洋分支向北的初始俯沖有關(guān)。(2)首次確定位于拉薩地塊北部的永珠蛇綠巖中席狀巖墻群的鋯石年齡為~150 Ma,表明拉薩地塊內(nèi)部在晚侏羅紀(jì)時(shí)期存在海底擴(kuò)張。永珠鎂鐵質(zhì)巖石地球化學(xué)成分具有以E-MORB為主,P-和N-MORB次之,不具有Nb-Ta負(fù)異常等特征,暗示它們形成于洋中脊環(huán)境。永珠蛇綠巖中還含有斜方輝石為主的斜方輝石巖和二輝輝石巖,全巖和礦物成分表明它們?cè)磪^(qū)是一個(gè)高度虧損的地幔,由玻安巖類似的巖石堆晶形成。Re-Os同位素研究表明輝石巖源于經(jīng)歷過(guò)部分熔融后的殘余軟流圈地幔,而橄欖巖則源于古老的大陸巖石圈地幔,但它們是大陸裂解時(shí)同時(shí)拉出至地表的。結(jié)合區(qū)域地質(zhì)、橄欖巖、沉積等多方面的證據(jù),我們認(rèn)為永珠蛇綠巖代表了拉薩地塊大陸巖石圈裂解形成的初始洋盆,而不是前人所認(rèn)為的弧后盆地。(3)日喀則東嘎地區(qū)的角閃巖,閃長(zhǎng)巖等形成于早侏羅紀(jì)(~180 Ma),閃長(zhǎng)巖是源于流體交代地幔楔產(chǎn)生的富H2O巖漿結(jié)晶分異形成,而角閃巖是這些富H2O巖漿分異過(guò)程中由角閃石為主的礦物堆晶形成。由于它們與區(qū)域上同時(shí)期的長(zhǎng)英質(zhì)巖石有著相似的Sr-Nd同位素組成,結(jié)晶分異在這些長(zhǎng)英質(zhì)巖石的形成過(guò)程中起著十分重要的作用。盡管南拉薩地塊存在大規(guī)模的早侏羅紀(jì)巖漿作用,但拉薩市以西只有侵入巖出露,而以東則既有火山巖也有侵入巖出露。地球化學(xué)組成對(duì)比表明拉薩市以西的侵入巖比拉薩市以東的火山巖和侵入巖源區(qū)具有更高的H2O含量,可能和新特提斯洋北向俯沖差異有關(guān)。(4)結(jié)合前人研究,我們提出了一個(gè)新的拉薩地塊晚三疊紀(jì)-晚侏羅紀(jì)時(shí)期的構(gòu)造演化模式:新特提斯洋在晚三疊紀(jì)-早侏羅紀(jì)開(kāi)始向北俯沖,在南拉薩地塊形成了以葉巴組和桑日群為代表的火山巖及同時(shí)期的侵入巖;與此同時(shí),班公-怒江洋盆向北俯沖到羌塘地塊之下,但很可能并不存在南向俯沖;由于大洋俯沖的遠(yuǎn)程效應(yīng),拉薩中部大陸巖石圈開(kāi)始伸展和裂解,形成了獅泉河和拉果錯(cuò)等蛇綠巖。晚侏羅紀(jì)時(shí)期,新特提斯洋洋殼轉(zhuǎn)為平板俯沖,以及班公-怒江洋持續(xù)的向北俯沖,進(jìn)一步促進(jìn)了拉薩中部地塊巖石圈伸展和裂解,形成了以永珠蛇綠巖為代表的初始洋盆。
[Abstract]:In recent years, the Lhasa block Cenozoic uplift history research and mineralization has made a series of breakthroughs, but the Mesozoic (especially late Triassic to late Jurassic) oceanic subduction and continental / arc continental collision process, there are a lot of controversy. The Lhasa Mesozoic tectonic block remodeling history is not only the premise of Cenozoic collision, more important is to identify dynamic background of formation of large and super large deposits of Lhasa land development of the Mesozoic era. Based on the above purpose, this paper selects the Lhasa southern and Northern representative plots of the Mesozoic Jurassic ophiolite and magmatite as the research object, made research progress as follows: (1) is located in the northern part of the Lhasa block was wrong as volcano rock (~162 Ma) is a class of Middle Jurassic volcano rock anger first discovered, the geochemical composition. Have the characteristics of high Mg andesite. In addition, as if the wrong volcano rock also has a high content of Th and (La/Sm) N ratio, low Ba/Th and Sr/Y ratios and enriched SrNd-Hf isotopic composition, especially the epsilon Nd (T) value epsilon Nd and regional sediment (T) values, indicating that they is a product of sediment melt and mantle wedge formed in the reaction, high temperature and low pressure environment. The field survey, as if the wrong volcano rock is a part of Tibetan Lake OPHIOLITIC MELANGE, and cannot be used as evidence of the southward subduction of Bannu ocean, combined with regional magmatic tectonic characteristics, its formation and Bannu the initial subduction northward branch. (2) for the first time to determine the zircon age of sheeted dike swarms Yunzhug ophiolite is located in the northern part of the Lhasa block in ~150 Ma, showed that Lhasa block within the seafloor spreading in the late Jurassic period. Yunzhug mafic rocks have geochemical composition based on E-MORB Lord, P- and N-MORB, with Nb-Ta negative anomalies, suggesting that they form a ridge Yu Yang. Yunzhug ophiolite also contains orthopyroxene mainly orthorhombic pyroxenite and two are Shiyan, whole rock and mineral compositions show that they source region is a highly depleted mantle, from boninite similar rocks cumulate rock formation of residual.Re-Os isotope studies indicate that the pyroxenite derived from experienced partial melting of the asthenospheric mantle peridotite, and is derived from the ancient continental lithospheric mantle, but they are at the same time, cracking out to the surface. Combined with regional geology, sedimentary peridotite, etc. the evidence, we consider the initial ocean basin Yunzhug ophiolite represents the Lhasa massif of continental lithosphere cracking formation, rather than previously thought back arc basin. (3) Shigatse Dongga area of amphibolite, diorite formed in early Jurassic (~180 Ma), flash Long rock is derived from magmatic crystallization of H2O rich fluid metasomatized mantle wedge generated differentiation, and they are dominated by amphibole mineral these H2O rich magmatic differentiation during cumulate formation. Because of their area of the same period and felsic rocks have similar Sr-Nd isotopic composition, crystallization and differentiation in the formation process of these felsic rocks plays a very important role. Despite the massive early Jurassic magmatism in South Lhasa block, but only the west of the city of Lhasa invaded Iwade and East Lu, both volcano rocks have invaded Iwade Lu. Geochemical contrast group showed that the intrusive rocks west of the city of Lhasa with H2O the content of higher than the source rock in the East of the city of Lhasa volcano rocks and intrusive, and Neo Tethys northward subduction related differences. (4) based on previous research, we propose a new Lhasa block Late Triassic to late Jurassic During the period of tectonic evolution pattern: Ji Neo Tethys northward subduction began in the Late Triassic and early Jurassic, in South Lhasa block formed by the Yeba SANGRI group and as the representative of the volcano rocks and intrusive rocks of the same period; at the same time, the Bangong Lake Nu River basin subducting northward beneath the block, but probably not there is a southward subduction; because the remote effect of oceanic subduction, continental lithosphere in central Lhasa began to stretch and cracking, and formed the Shiquanhe Lagkor co ophiolite. Such as Jurassic period, Neo Tethys ocean crust to plate subduction, and the class public - Nu River Yang continued to further promote the northward subduction of lithospheric extension and central Lhasa block cracking, formed the initial ocean basin to the yonzhug ophiolite represented.

【學(xué)位授予單位】：中國(guó)科學(xué)院廣州地球化學(xué)研究所
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：P542
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本文編號(hào)：1596016