| 摘要: |
| 冲绳海槽是新月形的弧后扩张盆地，强烈的构造活动和广泛的火山作用是海槽重要的特征。本文作者主要借助对海槽火山岩的常量元素、微量元素、Sr-Nd 同位素和年龄数据分析，结合火山的时空分布及相关构造地质条件，揭示了海槽火山作用的演化过程及其与本地区构造活动的关系，以便更好地了解海槽和沟-弧-盆体系的形成演化历史。作者通过研究得出:①海槽的火山岩石地球化学特征表明岩石属钙碱性系列，主要包括玄武岩、玄武质安山岩和流纹岩，岩石组成具双峰结构。②在海槽的不同区段内，火山作用具有一定的差异。海槽不同区段内火山带岩浆源区深度的差异，是造成海槽不同区段火山活动性质变化的原因，而岩浆源深度受俯冲带形态和地壳厚度控制。海槽北、中段火山岩以流纹岩和安山岩为主，流纹岩分布在海槽盆地内，形成时代较新( <1Ma)，安山岩大部分分布在岛弧火山带中，形成时代是中、晚中新世。海槽南段火山岩由玄武岩和玄武质安山岩组成，从老到新分布在琉球火山弧(大约13Ma)、台北火山带(3Ma～现代)和南段中央凹陷(晚第四纪)中。③琉球火山弧形成于中、晚中新世(17～6Ma)。但大约12Ma发生的吕宋弧与欧亚板块的碰撞作用改变了本地区的动力条件，而宫古断裂对此次改变起了阻断作用，使海槽南段的张裂要晚于北、中段。另外，中新世琉球岛弧南段的形成确定了海槽南段的弧后盆地性质。
冲绳海槽是年轻的弧后盆地，其岩浆、构造活动发育。对海槽岩浆作用的研究可上溯至20世纪50年代，但由于海水及恶劣气候等条件的制约，几十年来对海槽研究程度仍很有限，且在不同区段有很大差异。特别是对区内岩浆作用的研究，极大地受到样品采集偶然性的限制。作者收集前人资料综合对比海槽不同区段内火山活动的异同，了解海槽火山活动研究中的成就与问题， 为进一步开展此项研究打下基础。 |
| 关键词: 冲绳海槽 火山 形成演化 |
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| 基金项目:中国科学院知识创新工程重点方向项目(LZCX3-SW-223)资助和国家自然科学基础研究发展规划项目(G2000046703)。 |
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| Magmatism and Evolution of Okinawa Trough and Adjacent Areas |
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HUANG Peng1,2, LI Anchun1, XIAO Shangbin1,2, XU Zhaokai1,2
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1.Institute of Oceanology, The Chinese Academy of Sciences;2.Graduate School of the Chinese Academy of Sciences
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| Abstract: |
| The Okinawa Trough (OT) is a new moon-like back-arc rifting basin, in tense tectonic activity and drastic magmatism are main characteristics for it and adjacent areas. In this paper, according to major, trace elements, Sr-Nd isotopic and age data of volcanic rocks, volcanic properties and distribution as w ell as their link with geological background and evolution were discussed in order to understand the development of magmatism and tectonics on the OT and adjacent areas, deeply. The main conclusions are as follow: (1) Geochemic data show that volcanic rocks from the basin-arc system belong to cal-alkali rock groups, including basalts, basaltic andesites, and rhyolites. The magmatism is bimodal. (2) Rock compositions are different in different parts of the study area. Depth variation of magma source can be though t as a major factor to lead these differences. In middle and northern study area, volcanic rocks are mostly andesites and ryolites. The former mainly located in middle and northern trough, and was juvenile rocks (<1Ma); The latter outcropped in the arc and formed during Miocene. Volcanic rocks in southern study area mostly contain basalts and basaltic andesites. From old to young, they located at Ryukyu arc (RA , 6～18Ma), Northern Taiwan Volcanic Zone(NTVZ, from
3M a-present), and central grabens (Quaternary). (3) Ryukyu volcanic arc (including the southern arc) have been formed since middle and late Miocene (8～6M a). The continental extension behind RA caused the Northern and middle OT opening about 6M a ago, but the collision between Luson Arc and Eurasian plate changed geodynamical conditions in this region about 12Ma ago and led that southern OT opening was later than middle and northern OT. This kinetic change hasn't affected on middle and northern OT, because Keram a Gap stopped the effect of the event. In addition, southern OT should belong to the back-arc basin, because southern RA has been formed about 13Ma ago. |
| Key words: the Okinawa Trough magmatism and evolution |
