Metastable transformations of eclogite to garnetite in subducting oceanic crust
Metastable transformations of eclogite to garnetite in subducting oceanic crust
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DOI：
10.2465/jmps.080929
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发表时间：
2008-12
影响因子：
0.7
通讯作者：
M. Nishi;T. Kubo;Takumi Kato
中科院分区：
文献类型：
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作者：
M. Nishi;T. Kubo;Takumi Kato
在11 GPa和1000 - 1550 ° C条件下，以合成的多晶榴辉岩为原料，进行了榴辉岩-石榴子石转变实验。榴辉岩-石榴子石的转化过程分为两个阶段：（1）单斜辉石沉淀出镁橄榄石石榴石;（2）单斜辉石吸附镁橄榄石形成镁橄榄石石榴石。在1000 ° C下进行180分钟的转化中的第一阶段，然而，即使在相同时间尺度上在1550 ° C的高温下也没有观察到第二阶段。动力学的差异是由于单斜辉石和石榴石之间的对比扩散系数。这种动力学效应将改变MORB的矿物学和岩石微结构，通过改变密度和粘度关系，为俯冲洋壳动力学提供重要的意义。
The eclogite-garnetite transformation experiments were conducted at 11 GPa and 1000-1550 °C using synthesized polycrystalline eclogite with MORB composition as a starting material. We found that the eclogite-garnetite transformation proceeds by two stages, (1) precipitation of majoritic garnet from clinopyroxene and (2) formation of majoritic garnet from original pyropic garnet by absorption of clinopyroxene. The 1st stage in the transformation proceeds at 1000 °C for 180 minutes, however the 2nd stage was not observed even at the high temperature of 1550 °C on the same time scale. The differences in kinetics are due to contrasting diffusivities between clinopyroxene and garnet. The kinetic effect would modify the mineralogy and rock microstructures in MORB, which provides important implications for dynamics of subducting oceanic crust by changing the density and viscosity relation.