西藏班公湖蛇绿混杂岩中火山岩锆石U-Pb年代学及地球化学特征  

Zircon U-Pb Geochronology and Geochemical Characteristics of Volcanic Rocks in the Ophiolite Mélange at the Bangong Lake,Tibet

作　　者：周涛[1,2] 陈超[1,2] 梁桑[1,2] 陈桂凡[1,2] 李华亮[1,2] 李德威[1,2,3] 

机构地区：[1]中国地质大学(武汉)地质调查研究院,湖北武汉430074 [2]中国地质大学(武汉)地球科学学院,湖北武汉430074 [3]中国地质大学(武汉)青藏高原研究中心,湖北武汉430074

出　　处：《大地构造与成矿学》2014年第1期157-167,共11页Geotectonica et Metallogenia

基　　金：中国地质调查局西藏1:5万聂拉木等4幅区域地质调查(项目编号:1212011121242)及西藏1:5万日土县卡易错地区4幅区域地质调查(项目编号:1212011121246)

摘　　要：班公湖地区位于班公湖-怒江缝合带西段,蛇绿岩出露完整,火山岩类型多样,但一直缺少高精度年龄约束。本文报道了西藏班公湖地区卜垄蛇绿混杂岩中火山岩的岩石学、年代学和地球化学数据。研究结果表明:火山岩中锆石结构和Th/U比值都显示其为岩浆成因,锆石U-Pb年龄163.9±0.7 Ma(MSWD=1.06)代表火山岩形成时代。岩石亏损轻稀土元素,暗示岩浆源于亏损地幔;同时显示富集K、U、Th、Ba、Pb等大离子亲石元素及亏损Nb、Ta等高场强元素的岛弧火山岩地球化学特征,与形成于活动大陆边缘之上伸展环境的岩浆岩类似。结合区域构造背景研究,认为火山岩形成于弧间盆地或弧前盆地,岩浆起源于亏损地幔,一定程度上受到板片俯冲脱水和陆壳的影响;蛇绿岩属于SSZ型蛇绿岩,是中晚侏罗世班公湖-怒江洋盆北向俯冲的产物。The Bangong Lake region is situated in the western part of the Bangong-Nujiang Suture Zone. The Bangong Lake ophiolite outcrops a complete profile and contains various volcanic rock types, however, it lacks high-precision age constraint. This paper reports petrological, geochronological, and geochemical data for the volcanic rocks of ophiolite m＆#233;lange in Pulong, the Bangong region of Tibet. The zircons from the volcanic rock show structure and Th/U ratios of magmatic origin, and yield a zircon U-Pb age of 163.9±0.7 Ma （MSWD=1.06）. The volcanic rocks have geochemical characteristics similar to magmatic rocks occurring in extensional environment of the active continental margin, such as enriched in K、U、Th、Ba、Pb and other LILE elements, depleted in LREE and high field strength elements, derived from an enriched depleted mantle source. Combined with the regional tectonic setting, we suggest that the volcanic rocks were formed in the inter-arc basin or forearc basin originated from the depleted mantle that influenced by subduction dehydration and continental crust, while the ophiolite belongs to SSZ-type produced during the northward subduction of the Bangong-Nujiang oceanic basin at the mature period in the Late Jurassic.

关 键 词：火山岩 锆石U-PB年代学 弧间盆地或弧前盆地 蛇绿岩 班公湖 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]