Intracrystalline nucleation during the post-garnet transformation under large overpressure conditions in deep subducting slabs
Intracrystalline nucleation during the post-garnet transformation under large overpressure conditions in deep subducting slabs
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深俯冲板片大超压条件下石榴石相变过程中的晶内成核
DOI：
10.1029/2012gl053915
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发表时间：
2012
影响因子：
5.2
通讯作者：
et al.
中科院分区：
文献类型：
--
作者：
Nishi;et al.
在∼31-43 GpA的大超压条件下，用烧结式金刚石砧座多砧装置研究了天然单晶热释石石榴石中石榴石的后石榴石转变机制。在35-38 GPa时，晶内形核占主导地位，而在较低压力下，只有晶界形核起主导作用。此外，天然热解石榴石在38 GPa以上未分解为多相，而转变为单一的钙钛矿相。在大的超压条件下，石榴石后相变的晶内形核和多晶性生长都将极大地提高相变动力学。因此，后石榴石相变可能在∼950公里附近的俯冲板块中迅速蔓延，从而导致俯冲板块的显著流变性减弱。亚稳的后石榴石相变也可能导致900-1080公里深度的地震不连续，在一些俯冲带下确实可以观察到这种不连续。
The mechanism of the post‐garnet transformation in natural single‐crystalline pyropic garnet has been examined under large overpressure conditions of ∼31–43 GPa using the multianvil apparatus with sintered diamond anvils. Intracrystalline nucleation was found to be dominant above 35–38 GPa, while only grain‐boundary nucleation is responsible at lower pressures. In addition, natural pyropic garnet transformed to a single phase of perovskite without decomposing to multiple phases above 38 GPa. Both intracrystalline nucleation and polymorphic growth of the post‐garnet transformation under large overpressure conditions would strongly enhance the transformation kinetics. Consequently, the post‐garnet transformation may pwroceed rapidly in the subducting slab at depths near ∼950 km, which would cause substantial rheological weakening of the subducting slab. The metastable post‐garnet transformation may also cause the seismic discontinuities at a depth of 900–1080 km depth, which is indeed observed beneath some subduction zones.