Discovery and implication of P2₁/n crystal structure on a nano-scale in single jadeite crystals

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• 作者：Wu ; Xiuling ; Han ; Yujing ; Meng ; Dawei ; Li ; Douxing
• 关键词：jadeite ; omphacite ; equilibrium ; transmission electron microscope ; Dabie Mountains
• 刊名：Earth and Planetary Science Letters
• 出版年：2002
• 期刊代码：18_0012821x
• 类别：ph
• 出版时间：April 15, 2002
• 卷：197
• 期：3-4
• 页码：165-169
• 文件大小：618 K

摘要

We present the results of high-resolution transmission electron microscope (HRTEM) studies on jadeite crystals of jadeite quartzite from the Dabie ultra-high-pressure (UHP) metamorphic terrane, China. Although jadeite is known to have only C2/c crystal structure, [100], [110], [112], [010] diffraction patterns and HRTEM images reveal C2/c and P2₁/n structures in 500 nm microdomains of single jadeite crystals, that we recognized in all the above four orientations. The cell parameters of C2/c crystal structure correspond to those of jadeite, whereas the cell parameters of P2₁/n structure are equivalent to those of omphacite. The presence of the P2₁/n structure shows that jadeite partially changed into omphacite on a nano-scale during retrograde metamorphism and that this reaction failed to reach equilibrium. It suggests uplift of the host rock during exhumation accompanied by complex non-equilibrium retrogressive process in the jadeite, with significant implications for the derivation of P–T paths and tectonic interpretation of the Dabie UHP metamorphic terrane.