Equation of state of spinel (MgAl2O4): constraints on self-consistent thermodynamic parameters and implications for elastic geobarometry of peridotites and chromitites
Equation of state of spinel (MgAl2O4): constraints on self-consistent thermodynamic parameters and implications for elastic geobarometry of peridotites and chromitites
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DOI：
10.1007/s00410-022-01975-w
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发表时间：
2022-11
影响因子：
3.5
通讯作者：
Yuuki Hagiwara;R. Angel;Junji Yamamoto;M. Alvaro
中科院分区：
文献类型：
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作者：
Yuuki Hagiwara;R. Angel;Junji Yamamoto;M. Alvaro
尖晶石是一种极具潜力的弹性地压测量矿物，但已有的尖晶石状态方程（EoS）存在较大的不确定性，阻碍了尖晶石弹性地压测量的应用。我们根据mgal2o4的体积、弹性和等压热容的文献数据，通过特别注意数据集中热弹性数据的一致性和反演度（i; (Mg1-iAli)[MgiAl2-i]O4）对物理性质的影响，确定了mgal2o4的EoS。经过适当的数据选择、归一化和校正后，得到的数据集被拟合为各种EoS。结合了三阶Birch-Murnaghan方程和mie - gren - neisen - debye方程的热压力方程最成功地解释了数据。分析得到6个EoS参数：V0= 39.78 cm3/mol（固定），KT0= 196.43(12) GPa, KT0= 4.37(4),θD0= 898(10) K,γ0= 1.136(11), q= 1.94(9)。室温条件下，EoS的α v = 1.6765（10） × 10 - 5k - 1, ks0 = 197.55(12) GPa。将我们的实验结果与已发表的实验结果相结合，发现来自尖晶石-辉沸石稳定场的橄榄石和正辉石中的mgal2o4包裹体在室温条件下应该始终具有正残余压力（Pinc）。这表明，利用这些寄主包裹体系统进行弹性地球压力测量有望成为估计含尖晶石橄榄岩深度物源的新方法。相比之下，mgal2o4中的橄榄石、正辉石和斜辉石包裹体只有在地热对应的地表热流分别低于50、60和70 mW/m2的地质环境中才能被捕获（或重新平衡）。
Spinel is potentially one of the best minerals for elastic geobarometry, but the large uncertainties in the published equation of state (EoS) of spinel prevent the application of elastic geobarometry using spinel. We have determined the EoS of MgAl2O4from literature data on the volume, elasticity, and isobaric heat capacity by paying particular attention to the consistency of the thermoelastic data within the dataset and the influence of the inversion degree (i; (Mg1-iAli)[MgiAl2-i]O4) on the physical properties. After appropriate data selection, normalization, and correction, the resulting dataset was fitted with various EoS. Thermal pressure EoS that combined the third-order Birch–Murnaghan EoS and the Mie–Grüneisen–Debye EoS explain the data most successfully. The analysis yielded the following six EoS parameters:V0= 39.78 cm3/mol (fixed),KT0= 196.43(12) GPa,K′T0= 4.37(4),θD0= 898(10) K,γ0= 1.136(11), andq= 1.94(9). The EoS has the properties at room conditions ofαV= 1.6765(10) × 10–5K–1andKS0= 197.55(12) GPa.Combining our EoS with the published EoS, it was found that MgAl2O4inclusions trapped in olivine and orthopyroxene derived from the spinel-lherzolite stability field should always have positive residual pressures (Pinc) at room conditions. This implies that elastic geobarometry using these host-inclusion systems can be expected to be new methods for estimating the depth provenance of spinel-bearing peridotites. In contrast olivine, orthopyroxene, and clinopyroxene inclusions in MgAl2O4are expected to havePinc> 0 only when trapped (or re-equilibrated) in geological environments with geotherms corresponding to surface heat flows below about 50, 60 and 70 mW/m2, respectively.