Crustal evolution of the southwestern Kuril Arc, Hokkaido Japan, deduced from seismic velocity and geochemical structure
Crustal evolution of the southwestern Kuril Arc, Hokkaido Japan, deduced from seismic velocity and geochemical structure
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DOI：
10.1016/j.tecto.2008.03.003
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发表时间：
2009-07
期刊：
影响因子：
2.9
通讯作者：
A. Nakanishi;E. Kurashimo;Y. Tatsumi;H. Yamaguchi;S. Miura;S. Kodaira;K. Obana;N. Takahashi;T. Tsuru;Y. Kaneda;T. Iwasaki;N. Hirata
中科院分区：
文献类型：
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作者：
A. Nakanishi;E. Kurashimo;Y. Tatsumi;H. Yamaguchi;S. Miura;S. Kodaira;K. Obana;N. Takahashi;T. Tsuru;Y. Kaneda;T. Iwasaki;N. Hirata
西南千岛弧不受一系列吸积碰撞作用的影响，是世界弧沟系统中研究弧壳演化的最重要的试验点之一。已发表的岩石学和地震研究表明，在北海道中南部，千岛弧形地壳的上部向西向上推进，而下部则向下朝同一方向下降。在陆壳形成的几种假说中，我们根据地球化学和地震速度结构模型讨论了岛弧下地壳拆沉的作用。地震速度结构是在西南千岛弧海沟系统进行的陆上-海上地震调查中获得的。弧后地区的构造表现为古近纪的吸积碰撞作用形成的厚实的增生杂岩。根据已发表的地震结果，这种增生杂岩被认为在陆地上延续到在东高带观察到的白垩纪增生杂岩。千岛弧构造以上地壳安山岩(6.0~6.2公里/S)和厚中下地壳(6.5~7.3公里/S)为特征。在已发表的地球化学研究的基础上，我们考虑了一个简单的地壳演化的地球化学模型，解释了千岛弧安山岩的形成机制。根据地球化学模型估算的安山岩、玄武岩和镁铁质层的每个体积与从地震速度模型获得的体积一致。根据千岛弧火山岩的地球化学模型和主量元素化学估算的地壳成分表明，机械拆沉作用不足以使大洋岛弧地壳演化为陆壳。
The southwestern Kuril Arc, which is not affected by a series of accretion and collision processes, is one of the most important experimental sites among the world arc–trench systems for investigating the evolution of arc crust. Published petrological and seismic studies have shown that, in south-central Hokkaido, the upper part of the Kuril Arc crust is thrusting upward toward the west while the lower part is descending downward in the same direction. Among several hypotheses for formation of continental crust, we discuss the role of delamination of the island arc lower crust based on geochemical and seismic velocity structure models. Seismic velocity structure is obtained from an onshore–offshore seismic survey across the southwestern Kuril Arc–Trench system. The structure in the back-arc area shows a thick accretionary complex formed by Paleogene accretion and collision. Based on published seismic results, this accretionary complex is considered to continue on land to the Cretaceous accretionary complex observed in the Hidaka Belt. The structure of the Kuril Arc appears characteristic of upper crustal andesitic rocks (6.0–6.2 km/s) and thick middle to lower crust (6.5–7.3 km/s). Based on published geochemical study, we consider a geochemical model of simple crustal evolution explaining the mechanism of generation of andesitic rocks on the Kuril Arc. Each volume of andesitic, basaltic, and mafic layers estimated from the geochemical model is consistent with those obtained from the seismic velocity model. Crustal composition estimated from the geochemical model and major-element chemistry of the volcanic rocks in the Kuril Arc indicate that mechanical delamination is insufficient to cause the oceanic island arc crust to evolve into continental crust.