岛弧火山岩成因和地球化学特征

岛弧火山岩主要为俯冲带的俯冲板片脱水形成的富大离子亲石元素流体交代地幔楔,并使其发生部分熔融,产生岛弧岩浆作用而形成的,岩石组合通常为玄武岩—安山岩—英安岩—流纹岩及相应侵入岩组合。它以Al2O3、K2O高,低Ti O2,且K2ONa2O为特征,相对富集LILE,亏损HFSE,特别是Ti、Nb、Ta等。本文主要从岛弧岩浆作用的起因着手,分析流体和熔体对地幔楔的交代作用,以及岛弧岩浆作用过程,进而分析岛弧火山岩的地球化学特征。

The Origin and Geochemical Characteristics of Island Arc Volcanic Rocks

Island arc volcanic rocks were formed by the island arc magmatism, which was generated by partial melting of the subsiding oceanic crust and mantle wedge beneath the island arc. Besides the interaction of fluid derived from the dehydration of subducted slab with the mantle wedge peridotites, the interaction of slab-derived melt with over lying mantle has also been found in the subduction zone. The fluid brought LILE from subsiding oceanic crust and remained HFSE, which made that island arc volcanic rocks enriched LILE and lost HFSE, particularly for Ti, Nb, Ta and so on. The combination of this rock is mainly composed of basalts andesites rhyolites dacites, belonging to some instrusive rock combinations. The paper is mainly about the subduction between oceanic crust and continental crust, talks the origin of island arc magmatism, analyzes slab-deriving fluid in mantle wedge, and learns the characteristics of island arc volcanic rocks.