西太平洋雅浦海沟弧前辉长岩的成因及其地质意义:来自矿物地球化学的制约  

Genesis and geological significance of the Yap forearc gabbro in the western Pacific:Constraints from mineral geochemistry

作　　者：王政刚 陈灵 唐立梅 田原[2] Wang Zhenggang;Chen Ling;Tang Limei;Tian Yuan(Key Laboratory of Submarine Geosciences,Second Institute of Oceanography,MNR,Hangzhou 310012;Ocean College,Zhejiang University,Zhoushan,Zhejiang 316021)

机构地区：[1]自然资源部海底科学重点实验室,自然资源部第二海洋研究所,杭州310012 [2]浙江大学海洋学院,浙江舟山316021

出　　处：《地质科学》2024年第6期1708-1721,共14页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金面上项目(编号:41976072)资助。

摘　　要：俯冲带是连接地表和深部地球之间物质循环的关键纽带。目前对俯冲带演化过程及内部物质传递机制认识还不够清晰,其中一个难点在于缺乏记录早期弧岩浆过程的载体。雅浦俯冲带被广泛认为代表着俯冲带体系演化过程的早期阶段,目前针对雅浦俯冲带的地球化学研究相对不足,尤其缺乏针对矿物地球化学的研究。本文利用电子探针(EMPA)和激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)分析了来自雅浦岛弧南部弧前区域的5块辉长岩的斜长石和单斜辉石的主、微量元素组成,发现相较于岛弧和弧后盆地的样品,雅浦辉长岩的单斜辉石和斜长石稀土元素更加亏损,尤其亏损轻稀土元素,同时亏损Zr、Hf等高场强元素并富集大离子亲石元素;雅浦辉长岩的斜长石表现出高Al2O3和高An的特征,An值高达92.51,显著高于弧后盆地的辉长岩。结合前人工作基础,我们进一步确定了这些辉长岩的岩浆源自弧前环境,可能为亏损地幔部分熔融的产物。弧前深成侵入岩(辉长岩)的出露进一步证实了卡罗琳洋脊与雅浦岛弧碰撞造成了强烈的构造侵蚀,而这些辉长岩可能记录了俯冲带初始阶段的关键信息。Subduction zones are the key link between the surface and the deep earth.The evolution of subduction zones and the internal material transfer mechanism are not clear enough.One of the difficulties is the lack of carriers to record the early arc magmatic process.The Yap subduction zone is widely believed to represent the early stage of the evolution of the subduction zone system.At present,the geochemical research on the Yap Island arc is relatively insufficient,especially the lack of research on mineralogy and single mineral geochemistry.This work analyzes the major and trace element compositions of plagioclase and clinopyroxene from five gabbro in the southern forearc area of the Yap Island arc based on EMPA and LA-ICP-MS.Compared with samples from arcs and back-arc basins,the clinopyroxene and plagioclase of the gabbro in this study are more depleted in rare earth elements(REE),especially in light REE,while also depleted in high field strength elements(HFSE)such as Zr and Hf and enriched in large ion lithophile elements(LILE).The plagioclase in the gabbro shows high Al2O3 and high An contents,with an An value as high as 92.51,significantly higher than that of the back-arc basins.Combined with the previous work,we further determined that the magma of these gabbro originated from the forearc environment and may be the product of partial melting of the depleted mantle.The exposure of these forearc plutonic intrusive rocks(gabbro)further verifies the intense tectonic erosion process caused by the collision between the Caroline ridge and the Yap Island arc,and the gabbro may record key information on the initial stage of the subduction zone.

关 键 词：雅浦海沟 俯冲带 辉长岩 岛弧演化 

分 类 号：P575[天文地球—矿物学] P588.1[天文地球—地质学] P59