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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Towards a lower mantle reference temperature and composition
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Towards a lower mantle reference temperature and composition

机译：朝向较低的地幔参考温度和成分

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We aim to constrain the lower mantle geotherm and average composition from 1D seismic models and experimental mineralogy data, explicitly accounting for possible sources of uncertainty. We employ an isentropic third-order Birch–Murnaghan equation of state, which is in excellent agreement with recent ab initio calculations of density and bulk modulus for Mg-perovskite. Furthermore, ab initio and experimental data are reasonably consistent with each other. Modelling the shear modulus is not as straightforward, but is needed because density and the bulk modulus alone do not sufficiently constrain temperature and composition. To correctly predict ab initio calculations for the shear modulus of Mg-perovskite, we needed to prescribe a cross-derivative at zero pressure, which we determined by trial and errors. Unless this ad hoc cross-derivative is confirmed by further experimental results, there seems to be an inconsistency between ab initio and experimental data. Purely experimental data most likely require a non-adiabatic temperature profile, but it is difficult to infer the number and location(s) of the non-adiabatic increase(s). If ab initio data are used, at least one thermal boundary layer seems reasonable, but its location depends on the modelling of the iron content. A strong chemical density contrast in the mid-mantle (≥2%) is not supported by ab initio data, but is possible with experimental data. Other major sources of uncertainty are the trade-off between thermal and compositional effects, the possible influence of aluminium perovskite, and poorly understood frequency effects.
机译：我们旨在通过一维地震模型和实验矿物学数据来约束下地幔地热和平均成分，从而明确考虑不确定性的可能来源。我们采用了等熵的三阶Birch-Murnaghan状态方程，该方程与镁钙钛矿的密度和体积模量的最近从头算的计算非常吻合。此外，从头算和实验数据彼此之间合理地一致。剪切模量的建模不是那么简单，但是因为密度和体积模量本身不足以限制温度和组成，所以需要建模。为了正确地预测镁钙钛矿的剪切模量的从头算，我们需要规定零压力下的交叉导数，我们通过反复试验确定该导数。除非进一步的实验结果证实了这种特殊的交叉导数，否则从头算数据和实验数据之间似乎不一致。纯粹的实验数据很可能需要非绝热温度曲线，但是很难推断出非绝热升高的次数和位置。如果使用从头算数据，则至少一个热边界层似乎是合理的，但其位置取决于铁含量的模型。从头算数据不支持中幔中强烈的化学密度对比（≥2％），但实验数据可能支持。其他不确定性的主要来源是热效应和成分效应之间的权衡，钙钛矿铝的可能影响以及对频率效应的了解不足。

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