【摘要】：當(dāng)前公認(rèn)青藏高原是印度板塊和歐亞板塊持續(xù)匯聚的產(chǎn)物,為全球造山過(guò)程的研究提供了一個(gè)天然實(shí)驗(yàn)室。藏北羌塘地區(qū)廣泛發(fā)育不同系列的新生代火山巖,但對(duì)其時(shí)空分布與地球化學(xué)特征的認(rèn)識(shí)還比較匱乏,也不清楚不同巖石系列之間的聯(lián)系以及與巖石圈構(gòu)造演化過(guò)程之間的關(guān)系,因此本文選取研究程度較低的扎美仁地區(qū)新生代鉀質(zhì)火山巖作為研究對(duì)象,開(kāi)展巖石學(xué)、礦物學(xué)、年代學(xué)和地球化學(xué)的研究工作,結(jié)合羌塘地區(qū)新生代火山巖的研究成果,試圖探討羌塘地區(qū)巖石圈新生代構(gòu)造演化過(guò)程,為青藏高原的形成演化過(guò)程的研究提供新的科學(xué)依據(jù)。扎美仁地區(qū)新生代火山巖以粗面安山巖和堿玄質(zhì)響巖為主,形成于漸新世(26-33Ma)。火山巖貧硅、富鉀和低鎂,稀土總量(∑REE)較高,輕、重稀土分異明顯,稀土配分曲線總體呈右傾型,無(wú)明顯負(fù)銪異常(0.79-0.88)。巖石總體呈現(xiàn)富集Rb、Th、Ba、Sr等大離子親石元素,相對(duì)虧損Nb、Ta、P、Ti等高場(chǎng)強(qiáng)元素。火山巖具有較高的87Sr/86Sr比值、206Pb/204Pb、207Pb/204Pb、208Pb/204Pb比值以及較低143Nd/144Nd比值,以上特征指示火山巖的巖漿源區(qū)與EM II型富集地幔有關(guān),其成因機(jī)制受幔源巖漿分離結(jié)晶作用所控制,具有板內(nèi)堿性火山巖和活動(dòng)陸緣、島弧火山巖的雙重地球化學(xué)與構(gòu)造環(huán)境屬性。利用火山巖中的單斜輝石斑晶估算出扎美仁火山巖的形成的深度大約在48公里左右,結(jié)晶溫度為1146-1297℃。綜合對(duì)比藏北羌塘地區(qū)新生代火山巖的巖石系列、時(shí)代變化、空間分布以及地球化學(xué)等特征,指出羌塘地區(qū)出現(xiàn)的一系列新生代火山巖,是受印度板塊向歐亞大陸的俯沖和碰撞所引起的俯沖板片斷離作用以及軟流圈上涌和擾動(dòng)的影響而形成的。
[Abstract]:At present, Qinghai-Xizang Plateau is recognized as the product of continuous convergence of Indian plate and Eurasian plate, which provides a natural laboratory for the study of global orogenic process. Different series of Cenozoic volcanic rocks have been widely developed in Qiangtang area, northern Tibet, but their spatio-temporal distribution and geochemical characteristics are still poorly understood. It is also not clear that the relationship between different lithological series and lithospheric tectonic evolution process, so this paper selects the Cenozoic potash volcanic rocks in Zameiren area as the research object, and develops petrology and mineralogy. Combined with the research results of Cenozoic volcanic rocks in Qiangtang area, this paper attempts to explore the Cenozoic tectonic evolution process of the lithosphere in Qiangtang area, which provides a new scientific basis for the study of the formation and evolution process of the Qinghai-Tibet Plateau. The Cenozoic volcanic rocks in the Zameiren area were mainly composed of coarse andesite and alkaline-syenite, and formed in the Oligocene (26-33Ma). The volcanic rocks are poor in silicon, rich in potassium and low in magnesium. The total amount of rare earth (鈭，

本文編號(hào)：2329338