Jadeite formation in shocked ordinary chondrites
Jadeite formation in shocked ordinary chondrites
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DOI：
10.1016/j.epsl.2013.04.023
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发表时间：
2013-07-01
影响因子：
5.3
通讯作者：
Hirao, Naohisa
中科院分区：
文献类型：
--
作者：
Miyahara, Masaaki;Ozawa, Shin;Hirao, Naohisa
从静态高压和高温合成实验中回收的受冲击的普通方解石（Yamato 791384 L6和Yamato 75100 H6）和钠长石中的钠长石（Kubo等人，2010）进行了研究，用透射电子显微镜（TEM）后，传统的显微拉曼光谱分析，以澄清在高压和高温条件下的钠长石解离反应。当硬玉由钠长石形成时，SiO_2相作为钠长石分解反应的残留相，从化学计量学上来说应该伴随硬玉。然而，钠长石中和附近的冲击熔融脉的冲击辉石解离成硬玉+残留的非晶（或不良结晶）的材料具有不同的化学成分之间的硬玉和SiO2相。通过对静态高压高温合成实验中回收的钠长石和钠长石的TEM观察，发现硬玉的结晶是由钠长石（或钠长石）的晶粒细化引发的。成核作用发生在钠长石细晶组合的沿着晶界或三结点处。翡翠晶体从晶核开始通过晶界扩散生长。考虑到受冲击的辉石岩的冲击熔融脉记录的压力条件，斯氏石英最有可能是伴随硬玉的残留SiO2相。高温高压条件下诱发的一次动力学事件是非常短暂的。与硬玉相比，由于成核速率较慢，难以通过动力学过程形成，导致钠长石分解反应不均匀和不完全，钠长石分解为硬玉+残余非晶物质。(C)2013 Elsevier B.V.保留所有权利。
Albitic feldspar in shocked ordinary chondrites (Yamato 791384 L6 and Yamato 75100 H6) and albite recovered from static high-pressure and high-temperature synthetic experiments (Kubo et al., 2010) were investigated with a transmission electron microscope (TEM) subsequent to a conventional micro-Raman spectroscopy analysis to clarify albite dissociation reaction under high-pressure and high-temperature condition. When jadeite forms from albite, SiO2 phase as a residual phase of albite dissociation reaction should accompany jadeite from the stoichiometry. However, albitic feldspar in and adjacent to shock-melt veins of the shocked chondrites dissociates into jadeite+residual amorphous (or poorly-crystallized) material having varied chemical compositions between jadeite and SiO2 phase. TEM observations of albitic feldspar in the shocked chondrites and albite recovered from the static high-pressure and high-temperature synthetic experiments show that jadeite crystallization is initiated by grain refinement of albite (or albitic feldspar). Nucleation occurs along grain-boundaries or at triple-junctions of the fine-grained albite crystal assemblage. Jadeite crystal starts to grow from the nucleus through grain-boundary diffusion. Considering pressure condition recorded in the shock-melt veins of the shocked chondrites, stishovite is the most likely as a residual SiO2 phase accompanying jadeite. High-pressure and high-temperature condition induced by a dynamic event is very short. Stishovite would be hardy formed through a dynamic event due to sluggish nucleation rate of stishovite compared with that of jadeite, thus leading to induce heterogeneous and incomplete albite dissociation reaction; albite dissociates into jadeite+residual amorphous material. (C) 2013 Elsevier B.V. All rights reserved.