羌塘岩带碰撞后超钾质火山岩地球化学特征及成因探讨

GEOCHEMICAL CHARACTERISTICS AND PETROGENESIS OF THE POST COLLISION ULTRAPOTASSIUM VOLCANIC ROCKS IN QIANGTANG ROCK ZONE

羌塘超钾质火山岩为板块碰撞后的产物,地球化学特征表明,其同时具有板内火山岩和俯冲带岛弧火山岩的双重地球化学特性。化学组成上富含轻稀土和大离子亲石元素而亏损Cr、Ni等相容元素。在成因上受分离结晶作用和源区混合作用共同制约。源区为受古俯冲上地壳物质和下地幔上升流体交代混合的EMII型富集地幔端元,可能富含角闪石和金云母等矿物。

The ultrapotassium volcanic rocks result from the collision between the India plate and Asia plate in the Qiangtang rocks zone, their geochemical characteristics imply that they have the characteristics of the K rich volcanic rocks of internal plate and island arc occuring in the subducted belt. They are rich in LREE and LILE, while depleted in incompatibility elements (Cr, Ni, etc.). The petrogenesis is restricted by fractional crystallization and the provenance contamination by the upper crust in source. The source of the rocks belongs to the EMII type enriched mantle resulted from the metasomatism between upper mantle and the fluids coming from lower mantle or the upper crust dipping into the mantle by subduction, maybe contains abundantly hornblende and phlogopite etc.