| 大陆俯冲过程中的流体 |
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| 引用本文： | 李曙光,侯振辉.大陆俯冲过程中的流体[J].地学前缘,2001,8(3):123-129. |
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| 作者姓名： | 李曙光 侯振辉 |
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| 作者单位： | 中国科学技术大学地球和空间科学系 |
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| 基金项目： | 国家重点基础研究发展规划项目 (G19990 75 5 0 3)，国家自然科学基金项目 ( 498730 0 6)，中国科学院知识创新重点资助项目 (KZCXZ 10 7) |
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| 摘 要： | 含水矿物矿物稳定性的实验研究和超高压岩石的同位素地球化学研究表明 ,大陆地壳在俯冲过程中 ,随着变质程度的升高和部分含水矿物的相继分解 ,会有流体释放出来。当俯冲深度接近5 0km ,俯冲陆壳岩石中大量低级变质含水矿物 (如绿泥石、绿帘石、阳起石 )会脱水并从俯冲陆壳逸出形成流体流。这一流体流可溶解带走俯冲陆壳内已从云母类矿物逸出的放射成因Ar及部分U、Pb ,并导致w(U) /w(Pb)升高。这一阶段逸出的流体有可能交代、水化仰冲壳楔 ,为其发生部分熔融形成同碰撞花岗岩或加速山根下地壳的榴辉岩化创造条件。在俯冲深度为 5 0～ 10 0km ,变镁铁质岩石中的角闪石相继分解并释放出H2 O。由于变镁铁质岩石在陆壳中所占比例较少 ,因此 ,这一阶段释放的水不能形成大规模的流体流 ,因而不能使体系内的过剩Ar大量散失 ,但足以形成局部循环 ,加速变镁铁质岩石及其互层或邻近围岩的榴辉岩化变质反应。在俯冲深度 >10 0km的超高压变质阶段 ,仅有少量的含水矿物分解 ,而多硅白云母仍保持稳定。这时俯冲陆壳内只可能有少量粒间水存在 ,从而导致俯冲陆壳与周围软流圈地幔不能发生充分的相互作用。
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| 关 键 词： | 大陆俯冲 流体 超高压变质作用 |
| 文章编号： | 1005-2321(2001)03-0123-07 |
| 修稿时间： | 2001年5月25日 |
FLUID DURING CONTINENTAL SUBDUCTION |
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| LI Shu-guang,HOU Zhen-hui.FLUID DURING CONTINENTAL SUBDUCTION[J].Earth Science Frontiers,2001,8(3):123-129. |
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| Authors: | LI Shu-guang HOU Zhen-hui |
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| Abstract: | Experimental studies of stability of hydrous mineral and isotopic geochemical studies of ultra-high pressure rocks show that the hydrous minerals in subducted continental crust will progressively dehydrate along with increase of pressure and temperature, which results in a separate aqueous fluid. When the subduction depth is near 50km, the voluminous lower grade metamorphic hydrous minerals(e.g. chlorite, epidote, actinolite)undergo dehydration forming an aqueous fluid flux. The dissolved radiogenic Ar from micas and U, Pb in the subducted continental crust are more readily transported by this fluid flux, which may result in the elevation of U/Pb ratio of the rocks at the subducted continental crust. This aqueous fluid rising through the subduction channel as well as diffusing into the overlaying crustal wedge can induce partial melting of the crust wedge to produce syncollisional granites, or eclogitization of lower continental crust in the thickened mountain root. The amphiboles in meta-mafic rocks dehydrate at the depth between 50～100 km. Because of the lower proportion of meta-mafic rocks in subducted continental crust, the devolatilization of meta-mafic rocks at this depth can not generate a large scale aqueous fluid flux, thus the excess Ar in the system can not be significantly lost. However, the aqueous fluid released from the meta-mafic rocks may move in local cycle, so that it can markedly enhance the reaction rates of eclogite-facies metamorphism in the meta-mafic rocks and metapelite interbeded with them, or adjacent wall rocks. Only minor H 2O -bearing minerals dehydrate, but phengite keeps stable during ultrahigh pressure metamorphic stage (subduction depth >100km). Thus only a little pore fluid could exit between minerals during this stage, which impedes the interreaction between the subducted continental crust and mantle. |
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| Keywords: | continental subduction fluid ultrahigh-pressure metamorphism |
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