本文選題：比馬組 + 島弧火山巖��； 參考：《地球化學》2017年03期

【摘要】：拉薩地塊廣泛分布中生代巖漿巖,研究它們對于認識特提斯洋的演化和理解整個青藏高原的形成過程有著重要意義。本文首次對拉薩地塊南緣日喀則地區(qū)的比馬組火山巖進行了系統(tǒng)的鋯石SHRIMP U-Pb年代學、全巖主元素、微量元素及Sr-Nd同位素研究。結果表明,日喀則地區(qū)的比馬組火山巖主要為中基性巖(玄武巖)及酸性巖(粗面安山巖,英安巖),精確的SHRIMP U-Pb定年獲得了(177.9±2.5)Ma的年齡值,略晚于東部桑日縣地區(qū)比馬組火山巖。比馬組火山巖整體屬于低鉀拉斑系列巖石,稀土元素分布模式表現(xiàn)為輕稀土元素富集右傾型,Eu顯示弱的正異常,微量元素蛛網(wǎng)圖顯示巖石富集大離子親石元素Th、U、Sr等,虧損高場強元素Nb、Ta、Ti等。巖石具有相對低的Sr同位素組成和高的eNd(t)值,(~(87)Sr/~(86)Sr)i值為0.703767~0.704886,eNd(t)值為5.28~6.37,顯示典型的島弧火山巖特征。認為日喀則比馬組火山巖應為中生代時期新特提斯洋北向俯沖消減過程中導致虧損地幔楔部分熔融的產(chǎn)物,并受到了地殼的混染,形成時代上具有東早西晚的特點。
[Abstract]:Mesozoic magmatic rocks are widely distributed in Lhasa massif. It is of great significance to study the evolution of the Tethys ocean and to understand the formation of the whole Qinghai Tibet Plateau. In this paper, the systematic zircon SHRIMP U-Pb chronology, the main elements, trace elements and Sr-Nd of the whole rock of the volcanic rocks in the Shigatse region of the southern margin of the Lhasa massif have been carried out in this paper. The results show that the volcanic rocks in the Shigatse area are mainly middle base rock (Xuan Wuyan) and acid rock (Rough andesite, anganite). The accurate SHRIMP U-Pb years obtained the age value of (177.9 + 2.5) Ma, slightly later than the Pima group volcanic rocks in the eastern SANGRI county. The distribution pattern of stone and rare earth elements shows that the light rare earth elements are enriched right type, and Eu shows weak positive anomalies. The trace element cobweb map shows that the rocks are rich in large ion lithospheric elements Th, U, Sr, Nb, Ta, Ti and so on. The rock has relatively low Sr isotopic composition and high eNd (T) value, and (~ (87) Sr/~ (86) Sr) The Nd (T) value is 5.28~6.37, showing typical characteristics of island arc volcanic rocks. It is considered that the volcanic rocks in the Shigatse Bi Ma formation should be the product of partial melting of the depleted mantle wedge during the Mesozoic period of the North subduction subduction of the new Tethys ocean, and are contaminated by the crust, which has the characteristics of the late East early West.
【作者單位】： 桂林理工大學地球科學學院;中國科學院地球化學研究所礦床地球化學國家重點實驗室;中國科學院廣州地球化學研究所同位素地球化學國家重點實驗室;成都地質礦產(chǎn)研究所;
【基金】：國家自然科學基金(41003018,41463001) 中國地質調查局青藏高原地質研究中心開放課題(2014-02) 廣西八桂學者項目(2013許繼峰) 廣西礦冶與環(huán)境科學實驗中心資助項目(KH2011ZD002) 廣西自然科學基金(2016GXNSFAA380012;2014GXNSFAA118304)
【分類號】：P588.14

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