冲绳海槽北、中段火山岩地球化学特征及其地质意义  

Geochemical features and their geological implications of volcanic rocks from the northern and middle Okinawa Trough.

作　　者：黄朋[1] 李安春[1] 蒋恒毅[1] 

机构地区：[1]中国科学院海洋研究所海洋地质科学重点实验室

出　　处：《岩石学报》2006年第6期1703-1712,共10页Acta Petrologica Sinica

基　　金：中国科学院知识创新工程重要方向项目(编号:KZCX3-SW-223);国家自然科学基金项目(批准号:40576032);国家重点基础研究发展规划项目(编号:G2000046703)共同资助.

摘　　要：为去除非火山物质对样品化学性质的影响,得到火山岩真实的地球化学及同位素组成数据,作者对采自冲绳海槽的酸性火山岩样品严格的前处理,其中海槽北段火山岩同位素数据以前还未见公开报道。根据所得U系同位素组成数据及其分布规律分辩混染物中俯冲板片的成分,结合Sr-Nd同位素组成,本文对海槽火山活动的岩石种类、物质来源和岩浆演化过程作了一些初步的讨论。结果表明,冲绳海槽酸性火山岩分布广泛,为钙碱性系列岩石,碱性弱(里特曼指数＜1．8);海槽岩浆主要源于地幔,源区同位素组成类似PREMA地幔,结晶分异作用是演化过程中最主要的地质作用,但岩浆也受到了不同程度地受到上地壳与/或俯冲板片物质的混入;根据混合模拟结果将海槽火山岩大致分成以上地壳物质混染为主和上地壳-俯冲板片混染两类,且认为上地壳混染发生在岩浆演化的晚期,此时岩浆体系SiO_2含量要高于混染物。In order to remove non-volcanic components from samples and gain the actual geochemical and isotopic compositions for volcanic rocks, authors deal these rocks sampling with strict pretreatment. The isotopic data about volcanic rocks from the northern Okinawa Trough have not been reported in previous works. Based on the data of the U-series isotopic compositions, we distinguished the mass of subduction plate （ Philippine sea plate ） from magna as a mixing component. Then, we take some works about the petrology, sources of magmas and magmatic evolution by U-series and Sr-Nd isotopic compositions of these rocks in the Okinawa Trough. The points are follow. Firstly, the Okinawa Trough held widely silicic volcanic activities, and the volcanic rocks belonged to cal-alkali group （ σ 〈 1.8 ）. Secondly, the magmas mainly came from mantle source area which has similar isotopic compositions to PREMA. The crystal fractionation was the most important geological process, but the magma also was contaminated with the mass from the upper crust and/or subduction plate. Finally, the volcanic rocks from the Okinawa Trough could be divided into two groups, which were contaminated by the upper crust and upper crust-subduction plate, based on the mixing model. Further, our studies indicated that contaminations occurred at the evening of magmatic evolution, in which SiO2 contents of magma system under the Trough were higher than exotic material.

关 键 词：冲绳海槽 同位素组成 岩浆演化 结晶分异作用 

分 类 号：P588.145[天文地球—岩石学]