Geochemical characteristics and origin for the Cenozoic adakitic rocks in Java and Kalimentan (Indonesia), and comparison of tectonic setting to the nearby area
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摘要: 本文根据文献上的新生代岩浆岩岩石化学数据,确定印尼爪哇岛和加里曼丹岛中部等地存在埃达克质岩存在的证据和成因,判别其地球化学-构造环境,将其与印支板块东北侧的同时代埃达克质岩以及南苏门答腊楠榜省第四纪埃达克质岩的构造环境进行对比。本区新生代埃达克质岩形成于活动大陆边缘火山弧,可以划分为两种类型:C-型(大陆型)和O-型(岛弧型)埃达克岩,其La/Yb比值变化于3.47~28之间,比阿留申群岛的典型埃达克岩的La/Yb比值(>20)变化范围更大,其成因是由俯冲板片部分熔融,地幔楔混染和上地壳的结晶分离作用(AFC)而成。Zr/Nb-MgO和Zr/Nb-Zr图解以及Zr/Hf和Nb/Ta比值证明了本区大多数火山岩的岩浆作用和岩浆岩源区与地幔楔混染有关。Abstract: Based on the published magmatic lithogeochemical data, this paper conforms the evidence for the existing of Cenozoic adakitic rocks in Java island and Kalimantan island (Indonesia), presents a lots of geo-chemical-tectonic setting discrimination diagrams, and discusses their tectonic setting comparison to adakitic rocks of the same ages at the north-east part of the Indochina Plate as well as the Quaternary adakitic rocks in Lampung Province of Southern Sumatra. The Cenozoic adakitic rocks in this area, which formed in the vol-canic arc at active continental margin, may be classified into two types of adakitic rocks:C-type (continental) and O-type ( island arc), with La/Yb ratio widely varying in 3.47~28, compared to that of the typical adakites (>20 ) in Allusion Archipelago. The origin of these adakitic rocks may be resulted by partly melting of sub-ducted oceanic plate, the assimilation of mantle wedge plus the fractional crystallization (AFC) within upper crust. The Zr/Nb-MgO and Zr/Nb-Zr diagrams as well as Zr/Hf and Nb/Ta ratios indicate that the magmatism and its provenances in this area were related to the assimilation of mantle wedge.
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