Chemistry of grain boundaries in mantle rocks

被引：65

作者：

Hiraga, T ^{[1
]}

Anderson, IM

Kohlstedt, DL

机构：

[1] Univ Minnesota, Dept Geol & Geophys, Minneapolis, MN 55455 USA

[2] Oak Ridge Natl Lab, Met & Ceram Div, Oak Ridge, TN 37831 USA

来源：

AMERICAN MINERALOGIST | 2003年 / 88卷 / 07期

关键词：

D O I：

10.2138/am-2003-0709

中图分类号：

P3 [地球物理学]; P59 [地球化学];

学科分类号：

0708 ; 070902 ;

摘要：

The compositions of olivine grain boundaries have been analyzed with scanning transmission electron microscopy (STEM) via energy dispersive X-ray (EDX) spectrum profiling in three specimens: a peridotite ultramylonite, olivine phenocrysts in a basaltic rock, and synthesized compacts of olivine + diopside. Composition profiles across grain boundaries in both natural and synthetic samples exhibit a characteristic width of 5 nm and a depletion of Mg and concomitant enrichments of Ca, Al, Ti, and Cr. Chemical segregation is known to affect grain boundary processes such as brain boundary diffusion, sliding, fracture, and migration, all of which influence the theological properties of polycrystalline aggregates. Also, because grain boundaries are enriched in trace elements, the boundaries can be important storage sites for such elements in mantle rocks. Mantle-derived melts with unusual compositions, such as those rich in Ca and/or Ti, might be explained by preferential melting of olivine grain boundaries enriched in these elements. The common chemical signatures at grain boundaries in all samples indicate that chemical segregation is an energetically favorable phenomenon and thus should occur elsewhere in Earth's mantle. Segregation of trace elements to grain boundaries may play an important role in dynamical and geochemical processes in Earth's mantle.

引用

页码：1015 / 1019

页数：5

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