| 义敦岛弧带弧后区板内岩浆作用的时代及意义 |
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| 引用本文： | 曲晓明,侯增谦,唐绍华.义敦岛弧带弧后区板内岩浆作用的时代及意义[J].岩石矿物学杂志,2003,22(2):131-137. |
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| 作者姓名： | 曲晓明 侯增谦 唐绍华 |
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| 作者单位： | 中国地质科学院,矿产资源研究所,北京,100037 |
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| 基金项目： | 原国家科委"九五"科技攻关资助项目(96-914-03-05) |
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| 摘 要： | 通过对义敦岛弧夏囊沟一带酸性火山岩的岩石地球化学和Rb-Sr同位素研究,首次在该岛弧弧后区确立了一条板内火山岩带.这些火山岩属钾玄岩系列,以高K2O,低CaO,富Nb、Ta、Zr、Hf,贫Sr、Eu为特点,具标准的"V"型稀土元素配分型式,构造环境判别图解显示其形成于板内裂陷环境.由4个全岩样品给出的Rb-Sr等时线年龄t=189.2±5.0 Ma,相关系数R=0.999?824,ISr=0.714?578.认为火山岩的成分分异受斜长石在岩浆源区熔融残留和岩浆形成后黑云母的结晶分离双重控制.位于该带东侧弧后扩张盆地中的晚三叠世勉戈组双峰火山岩的形成年龄为213.1 Ma,说明该岛弧仅仅在24 Ma左右时限内就完成了从俯冲造弧到板内裂陷的重大转换,由此可对该岛弧带的碰撞造山过程和演化时序做出精确约束.
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| 关 键 词： | 义敦岛弧 板内岩浆作用 Rb—Sr等时线 碰撞造山 演化时序 |
| 文章编号： | 1000-6524(2003)02-0131-07 |
| 修稿时间： | 2002年1月21日 |
Age of intraplate volcanism in the back-arc area of Yidun island arc and its significance |
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| QU Xiao_ming,HOU Zeng_qian and TANG Shao_hua.Age of intraplate volcanism in the back-arc area of Yidun island arc and its significance[J].Acta Petrologica Et Mineralogica,2003,22(2):131-137. |
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| Authors: | QU Xiao_ming HOU Zeng_qian and TANG Shao_hua |
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| Abstract: | Based on the study of the felsic volcanics in Xia'' nanggou district of Yidun island arc, the authors identified for the first time an intraplate volcanics belt in the back_arc region of the arc. These volcanic rocks are shoshonitic series and are geochemically characterised by K2O-, Nb-, Ta-, Zr-, Hf-enrichment and CaO-, Sr-,
Eu-depletion. They have a common V-type" REE chondrite-normalized pattern. Their Pearce'' s tectonic discrimination diagrams indicate a clear intraplate rifting formation setting. Four bulk-rock samples give a good Rb-Sr isochron witht=189.2±5 Ma, R=0.999 824, andISr=0.714 578. The chemical variation of the volcanics are controlled by both residual of plagioclase in the melting source area and crystal fractionation of biotite after magma formation. Considering the 213 Ma formation age of the Miange Formation bimodal volcanics in the back_arc basin east of the intraplate volcanic rock belt, it is held that the island arc completed the important transition from subduction arc-forming to intraplate rifting regime only within a period of 24 Ma, from which exact constraints on the arc evolution sequence have been obtained. |
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| Keywords: | Yidun island arc intraplate magmatism Rb_Sr isochron collision and orogeny evolulion sequence |
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