西藏改则地区拉果错蛇绿岩地球化学特征及成因

拉果错蛇绿岩位于西藏改则县南侧,是班公湖-怒江缝合带南侧蛇绿岩带中发育最完整的蛇绿岩之一,可能形成于晚侏罗世-早白垩世,主要由地幔橄榄岩、堆晶岩、枕状熔岩、岩墙、斜长花岗岩及放射虫硅质岩等构造单元组成.微量元素分析结果表明该蛇绿岩中的中基性岩富集Sr、Rb等大离子亲石元素,亏损Nb、Ta等高场强元素,具有岛弧型火山岩的特点,其在稀土元素球粒陨石标准化配分图解中主要显示平坦型曲线,它们可能是由消减板片流体交代的地幔楔源区的部分熔融形成.拉果错蛇绿岩可能形成于弧间盆地环境,代表了班公湖.怒江缝合带南侧弧-弧碰撞的产物.

Geochemistry and genesis of Lhaguo Tso ophiolite in south of Gerze area-Center Tibet

Lhaguo Tso ophiolite, which is geographically located in south of Gerze county, Tibet, is one of the most completed ophiolites preserved on the south side of the Bangong-Nujiang suture zone. It was probably generated during Jurassic to Cretaceous and mainly consists of mantle peridotites,cumulates,pillow lavas,dykes,plagiogranites and radiolarian siliceous rocks units. Trace elements analyses indicates that mafic-intermediate rocks in the ophiolite are enriched in LILE,such as Sr,Rb, depleted in HFSE, such as Nb, Ta,clearly displaying compositional characteristicsof island-arc volcanic rocks, and their rare earth elements also mainly show a flat pattern. We suggest that these rocks be produced by partial melting of a mantle wedge metasomatized by the fluid released in the slab dehydration. Lhaguo Tso ophiolite likely occurred and developed in an inter-arc basin, representing the product of arc-arc collision on the south side of the Bangong-Nujiang suture zone.