Towards a Li barometer for bimineralic eclogites: experiments in CMAS
Towards a Li barometer for bimineralic eclogites: experiments in CMAS
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DOI：
10.1007/s00410-009-0376-7
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发表时间：
2009-02
影响因子：
3.5
通讯作者：
M. Hanrahan;G. Brey;A. Woodland;R. Altherr;H. Seitz
中科院分区：
文献类型：
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作者：
M. Hanrahan;G. Brey;A. Woodland;R. Altherr;H. Seitz
榴辉岩气压计在研究上地幔过程和金刚石找矿中具有重要的应用价值。对天然样品中Li在单斜辉石（cpx）和石榴石（grt）之间分配的研究表明，这种特殊的元素对压力变化非常敏感，可以作为双矿物榴辉岩所需的气压计进行校准。在CMAS（CaO、MgO、Al 2 O3、SiO2）系统中，在4 - 13 GPa和1，100 - 1，400 °C下进行实验，Li以Li 3 PO 4形式添加，以将该压力依赖性量化到气压计中，该气压计以以下等式表示：P=（0. 00255 T-lnKd）/0.2351，其中P以GPa计，T以°C计，并且Kdis定义为Li在单斜辉石和石榴石之间的分配系数（以ppm计）。用此方程可将实验压力再现到± 0.38GPa（1σ）。此气压计仅严格适用于CMAS。在1，300 °C、8-12 GPa下的实验表明，在约0.01-1重量% Li的浓度范围内，Li在cpx和grt之间的分配满足亨利定律。直接将该方程应用于在1，300 °C从4到13 GPa的自然系统中进行的实验，始终高估了大约2 GPa的压力。
An eclogite barometer has profound importance in the study of upper mantle processes and potential application to diamond prospecting. Studies on the partitioning of Li between clinopyroxene (cpx) and garnet (grt) in natural samples have shown that this particular element is very sensitive to changes in pressure and could be calibrated as the barometer demanded for bimineralic eclogites. Experiments were performed from 4 to 13 GPa and 1,100–1,400°C in the CMAS (CaO, MgO, Al2O3, SiO2) system with Li added as Li3PO4to quantify this pressure dependence into a barometer expressed in the following equation:P= (0.00255T– lnKd)/0.2351 wherePis in GPa,Tis in °C andKdis defined as the partition coefficient of Li (in ppm) between clinopyroxene and garnet. The experimental pressures are reproduced to ±0.38 GPa (1σ) by this equation. This barometer is strictly applicable only to CMAS. Experiments at 1,300°C, 8–12 GPa showed that Henry’s Law is fulfilled for Li partitioning between cpx and grt in the concentration range of approximately 0.01–1 wt% Li. Direct application of the equation to experiments in natural systems performed at 1,300°C from 4 to 13 GPa consistently overestimates pressures by approximately 2 GPa.