本文選題：輝長巖　切入點(diǎn)：鋯石U-Pb年代學(xué)　出處：《大地構(gòu)造與成礦學(xué)》2017年05期 　論文類型：期刊論文

【摘要】：班公湖-怒江中特提斯洋的俯沖極性和俯沖時(shí)間一直存在爭議。作者通過野外地質(zhì)調(diào)查、巖相學(xué)、鋯石U-Pb年代學(xué)及巖石地球化學(xué)研究,從西藏班公湖蛇綠混雜巖帶中識別出一套早白堊世SSZ型蛇綠巖,巖石組合上主要由輝長巖和玄武巖組成,還有少量的硅質(zhì)巖和超基性巖。本文對輝長巖進(jìn)行了全巖主、微量元素地球化學(xué)及LA-ICP-MS鋯石U-Pb年代學(xué)研究。地球化學(xué)組成特征顯示,輝長巖富集輕稀土元素,重稀土元素平坦,相對富集大離子親石元素,高場強(qiáng)元素存在一定虧損;Th/Ta比值與島弧玄武巖相似(Th/Ta1.6),Ta/Hf比值較高(0.1),顯示其既保留了俯沖環(huán)境的地球化學(xué)特征,也提供了伸展構(gòu)造環(huán)境的信息。輝長巖中鋯石U-Pb加權(quán)平均年齡為129.2±0.4 Ma(MSWD=0.36),該年齡是班公湖-怒江縫合帶中迄今報(bào)道的最年輕蛇綠巖年齡。結(jié)合區(qū)域地質(zhì)背景,認(rèn)為這套蛇綠巖形成于班公湖-怒江古洋盆西段向南俯沖形成的弧前盆地,而班公湖-怒江古洋盆北向俯沖可能始于早侏羅世,晚侏羅世形成雙向俯沖格局,直到早白堊世洋盆關(guān)閉,晚白堊世進(jìn)入陸內(nèi)構(gòu)造環(huán)境。
[Abstract]:The subduction polarity and subduction time of the Tethys ocean in the Bangong Lake-Nujiang River have always been controversial. The authors studied the geochemistry and geochemistry of zircon by means of field geological survey, petrography, zircon U-Pb geochronology and geochemistry. A set of early Cretaceous SSZ ophiolite was identified from the Bangonghu ophiolite melange belt in Tibet. The rock assemblage consists mainly of gabbro and basalt, and a small amount of siliceous and ultrabasic rocks. Trace element geochemistry and LA-ICP-MS zircon U-Pb geochronology. Geochemical composition features show that gabbro is rich in light rare earth elements, heavy rare earth elements are flat, and relatively rich in large ion lithophile elements. The Th / Ta ratio of the high field strength elements is similar to that of the island arc basalts, and the ratio of Th / Ta / Ta / HF is higher than that of the island arc basalts, indicating that it retains the geochemical characteristics of the subduction environment. The U-Pb weighted mean zircon age in gabbro is 129.2 鹵0.4 Mai MSWDU 0.36, which is the youngest ophiolite age reported to date in the Bangong Lake-Nujiang suture zone, in combination with the regional geological background, and the zircon U-Pb weighted mean age is 129.2 鹵0.4 Mai, which is the youngest ophiolite age ever reported in the Bangong Lake-Nujiang suture zone. It is considered that the ophiolite was formed in the forearc basin which subducted southward in the western section of Bangong Lake-Nujiang ancient ocean basin, while the northward subduction of Bangong lake-Nujiang ancient ocean basin probably began in the early Jurassic and formed a bidirectional subduction pattern in the late Jurassic. The oceanic basin was closed until the early Cretaceous, and the late Cretaceous entered the continental tectonic environment.
【作者單位】： 南方石油勘探開發(fā)責(zé)任有限公司;中國地質(zhì)大學(xué)(武漢)地質(zhì)調(diào)查研究院;中國地質(zhì)大學(xué)(武漢)地球科學(xué)學(xué)院;中國地質(zhì)大學(xué)(武漢)青藏高原研究中心;
【基金】：中國地質(zhì)調(diào)查局西藏1∶50000聶拉木等4幅地質(zhì)圖區(qū)調(diào)(1212011121242) 1∶50000日土縣卡易錯(cuò)地區(qū)4幅地質(zhì)圖區(qū)調(diào)(1212011121246) 油氣資源與探測國家重點(diǎn)實(shí)驗(yàn)室開放基金(KFKT2010-5)聯(lián)合資助
【分類號】：P542;P588.124
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本文編號：1622626