水与地幔的部分熔融

发布时间：2018-01-17 01:04

本文关键词：水与地幔的部分熔融　出处：《中国科学:地球科学》2016年03期 　论文类型：期刊论文

【摘要】：水对于地幔的部分熔融发挥了关键作用.地幔岩浆作用主要发生在板块边界(俯冲带和洋中脊)和若干板内热异常区域.在大洋俯冲带,俯冲板片释出的水可以诱发上覆地幔楔甚至板片自身发生熔融,导致弧岩浆作用,也有可能形成超临界流体.板片熔融和产生超临界流体的物理化学条件仍存在争议.在洋中脊和板内热异常区域,水和CO_2使上涌地幔发生熔融的起始深度增加,熔融比例增大.在地球深部层圈边界可能发生低程度的地幔熔融,如岩石圈和软流圈边界、上地幔和过渡带边界、过渡带和下地幔边界等,其成因一般认为与边界两侧矿物储水能力的差异有关.水可以促进地幔岩石熔融的根本原因在于水是一种不相容组分,强烈倾向于富集在硅酸盐熔体相(矿物-熔体的水分配系数远小于1),从而令其吉布斯自由能降低.前人对水在橄榄石、辉石和石榴石等地幔矿物与熔体之间的分配行为已经研究得比较充分,但水对硅酸盐熔体密度和迁移性质的影响还需要更进一步的高温高压实验和计算制约.
[Abstract]:Water plays a key role in the partial melting of the mantle. Mantle magmatism occurs mainly in plate boundaries (subduction zones and mid-ocean ridges) and several intraplate thermal anomalies, as well as in oceanic subduction zones. The water released from the subduction plate can induce the melting of the overlying mantle wedge or even the plate itself resulting in arc magmatism. It is also possible to form supercritical fluids. The physicochemical conditions for plate melting and supercritical fluid production are still controversial. Water and CO_2 increase the initial melting depth and melting ratio of upwelling mantle. Low degree mantle melting may occur at the deep boundary of the Earth's stratosphere, such as lithosphere and asthenosphere boundary. Upper mantle and transition zone boundary, transition zone and lower mantle boundary, etc. Its genesis is generally considered to be related to the difference in the water storage capacity of minerals on both sides of the boundary. The fundamental reason why water can promote the melting of mantle rocks lies in the fact that water is an incompatible component. It is strongly inclined to concentrate in silicate melt phase (the water partition coefficient of mineral-melt is much less than 1), which makes its Gibbs free energy lower. The distribution behavior between mantle minerals and melts, such as pyroxene and garnet, has been well studied, but the influence of water on the density and migration properties of silicate melts requires further high temperature and high pressure experiments and calculations.
【作者单位】：中国科学院壳幔物质与环境重点实验室中国科学技术大学地球和空间科学学院;
【基金】：国家自然科学基金项目(批准号:41590622,41473058) 高等学校学科创新引智计划项目中央高校基本科研业务费专项项目中组部“青年千人计划”项目资助
【分类号】：P542.5
【正文快照】： 国家自然科学基金项目(批准号:41590622,41473058)、高等学校学科创新引智计划项目、中央高校基本科研业务费专项项目和中组部“青年千人计划”项目资助1引言地幔岩石中通常含有一定数量的水,其丰度以H2O质量分数形式表示一般仅为50~1000ppm(Bell和Rossman,1992;Michael,1995;

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