STABILITY OF HIGH-DENSITY CLINOENSTATITE AT UPPER-MANTLE PRESSURES
STABILITY OF HIGH-DENSITY CLINOENSTATITE AT UPPER-MANTLE PRESSURES
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DOI：
10.1038/358322a0
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发表时间：
1992-07-23
期刊：
影响因子：
64.8
通讯作者：
ROSS, NL
中科院分区：
文献类型：
--
作者：
ANGEL, RJ;CHOPELAS, A;ROSS, NL
硅酸盐辉石是地球上地幔矿物学模型的主要组成部分1,2，链状硅酸盐辉石向更致密的石榴石结构的转变可能是400千米深处将上地幔与过渡带分开的地震不连续面的一个原因3。在较浅深度，含有两种辉石的组合是稳定的：钙和钠成分存在于透辉石 - 硬玉固溶体3中，而镁和铁形成第二种贫钙辉石。在缺乏实验数据的情况下，长期以来人们一直认为正顽火辉石是（镁，铁） - 辉石在上地幔整个区域的稳定多晶型物。然而，最近在压力超过8吉帕和温度超过900摄氏度的岩石学实验4,5提供了镁正辉石转变为单斜辉石相的证据。这个相的热力学和物理性质完全未知。在此我们报道一项高压单晶衍射研究的结果，该研究证实了在高压下MgSiO3的高单斜辉石相的稳定性，并能够初步估算与地球上地幔中正辉石组分转变相关的密度变化。
SILICATE pyroxenes are major components in mineralogical models of the Earth's upper mantle1,2, with the transformation of chain-silicate pyroxenes to denser garnet structures being a possible cause3 of the seismic discontinuity at 400 km depth that divides the upper mantle from the transition zone. At shallower depths assemblages containing two pyroxenes are stable: calcium and sodium components are accommodated in a diopside-jadeite solid solution3, while magnesium and iron form a second, calcium-poor pyroxene. In the absence of experimental data, orthoenstatite was long believed to be the stable polymorph of (Mg, Fe)-pyroxene over the entire upper mantle. More recently, however, petrological experiments4,5 at pressures and temperatures in excess of 8 GPa and 900-degrees-C have provided evidence for the transformation of Mg-orthopyroxene to a clinopyroxene phase. The thermodynamic and physical properties of this phase are completely unknown. Here we report the results of a high-pressure single-crystal diffraction study which confirm the stability of a high-clinopyroxene phase of MgSiO3 at high pressures, and allow an initial estimate to be made of the density changes associated with the transformation of the orthopyroxene component in the Earth's upper mantle.