Phase Transitions of Fe‐, Al‐ and Ca‐Bearing Orthopyroxenes at High Pressure and High Temperature: Implications for Metastable Orthopyroxenes in Stagnant Slabs
Phase Transitions of Fe‐, Al‐ and Ca‐Bearing Orthopyroxenes at High Pressure and High Temperature: Implications for Metastable Orthopyroxenes in Stagnant Slabs
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DOI：
10.1029/2021jb023133
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发表时间：
2022-01
期刊：
影响因子：
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通讯作者：
Jingui Xu;D. Fan;Dongzhou Zhang;M. Ma;Yi Zhou;S. Tkachev;Wenge Zhou;P. Dera
中科院分区：
文献类型：
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作者：
Jingui Xu;D. Fan;Dongzhou Zhang;M. Ma;Yi Zhou;S. Tkachev;Wenge Zhou;P. Dera
The phase transitions of natural San Carlos Fe‐, Al‐ and Ca‐bearing orthopyroxene and two synthetic orthopyroxenes containing Al (up to 12 wt. % Al2O3) and Fe (up to 15 wt. % FeO) were investigated at high pressures and temperatures up to ∼30 GPa and 700 K using synchrotron‐based single‐crystal X‐ray diffraction. These orthopyroxenes undergo α‐opx → β‐opx → γ‐opx phase transitions with increasing pressure and temperature. We quantitatively described how the composition influences the pressures of the phase transitions. The results indicated that the variations in Mg, Fe, and Al contents do not significantly influence the pressure of the α‐opx → β‐opx transition (Pα‐β). For the β‐opx → γ‐opx phase transition, increasing Fe content decreases the Pβ‐γ while increasing Al content increases the Pβ‐γ. The incorporation of Ca increases the Pα‐β and decreases the Pβ‐γ. The thermal equations of states of α‐opx and β‐opx for these three orthopyroxenes were determined using the unit‐cell volume collected at high pressures and temperatures, which have been used to establish a density model to interpret the cold stagnant slabs. Our experimental results have indicated that β‐opx and γ‐opx are possible metastable phases of natural orthopyroxenes within cold stagnant slabs in the mantle transition zone.
