An experimental investigation of the stability of majoritic garnet in the Earth’s mantle and an improved majorite geobarometer
An experimental investigation of the stability of majoritic garnet in the Earth’s mantle and an improved majorite geobarometer
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DOI：
10.1007/s00410-016-1255-7
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发表时间：
2016-05
影响因子：
3.5
通讯作者：
C. H. Wijbrans;A. Rohrbach;S. Klemme
中科院分区：
文献类型：
--
作者：
C. H. Wijbrans;A. Rohrbach;S. Klemme
实验研究了高温高压下石榴石中镁橄榄石成分的稳定性，重点考察了石榴石的体相组成和温度对其稳定性的影响。高压实验是在多顶锤装置上进行的，压力范围为6~14.5 Gpa，温度范围为1400~1700℃。实验范围为SiO_2-Al_2O_3-Cr_2O_3-CaO-MgO系，具有不同的铬/(铬+铝)比。随着压力的增加，石榴石中镁橄榄石的含量逐渐增加，石榴石的成分，特别是铬/(铬+铝)比值对镁橄榄石的取代作用有显著影响。我们没有发现温度的显著影响。利用实验结果，结合文献资料，推导出两个经验地质压力计，可用于测定橄榄岩和榴辉岩块体成分的天然主晶石榴石的平衡压力。橄榄岩成分的晴雨表为IS，榴辉岩成分的晴雨表为P=-29.6+11.8×Si+7.81×Na+4.49×加州。
The stability of the majorite component in garnet has been experimentally investigated at high pressure and high temperature, focusing on the effect of bulk composition and temperature. High-pressure experiments were performed in a multi-anvil apparatus, at pressures ranging from 6 to 14.5 GPa, and temperatures between 1400 and 1700 °C. Experiments were performed in a range of bulk compositions in the system SiO2–Al2O3–Cr2O3–CaO–MgO with varying Cr/(Cr + Al) ratios. The majorite content of garnet gradually increases with pressure, and the composition of the garnet, specifically the Cr/(Cr + Al) ratio, exerts a significant effect on the majorite substitution. We found no significant effect of temperature. We use the experimental results in combination with the literature data to derive two empirical geobarometers, which can be used to determine the equilibration pressure of natural majoritic garnets of peridotitic and eclogitic bulk compositions. The barometer for peridotitic compositions isAnd the barometer for eclogitic compositions is P = - 29.6 + 11.8 × Si + 7.81 × Na + 4.49 × Ca .