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arXiv 2004.10932physics.geo-ph
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lower mantle矿物地震性质对LLSVP成分和温度的约束

Constraints on the composition and temperature of LLSVPs from seismic properties of lower mantle minerals

Kenny Vilella, Thomas Bodin, Charles-Edouard Boukaré, Frédéric Deschamps, James Badro, Maxim Ballmer, Yang Li

摘要:

在这里,我们提供了一个潜在的LLSVP组合物的基础上改进的矿物模型,包括,例如,氧化铝的影响重新评估。我们还系统地研究了六个参数的影响:FeO和Al $_{2}$ O $_{3}$含量,比例的CaSiO $_{3}$和bridgmanite(使铁方镁石的比例隐含调查),Fe $^{3+}$ / $\sum$ Fe和温度之间的差异远场地幔和LLSVP。在研究的8100万个案例中,只有79000个案例解释了地震观测。然而,这些成功的情况涉及大范围的参数,例如,FeO含量在12- 25重量%之间,Al $_{2}$ O $_{3}$含量在3- 17重量%之间。然后,我们应用主成分分析(PCA),这些情况下,并找到两个强大的结果:(i)铁方镁石的比例应该是低的($<$ 6体积\%);(ii)形成的Fe $^{3+}$轴承bridgmanite比其他含铁相更有利。根据这些结果,我们确定了两个端员组合物,丰富的Bm和CaPv丰富,并讨论了它们的特点。最后,我们讨论了LLSVP形成的不同方案,并建议调查每个方案产生的矿物比例是评估其相关性的最佳方法。例如,原始岩浆海洋的凝固可能产生FeO和Al $_{2}$ O $_{3}$含量与我们的分析所建议的相似。然而,这种水库的矿物比例并没有很好的约束,可能包含更大比例的铁方镁石比我们的研究结果所允许的。

英文摘要:

Here, we provide a reappraisal of potential LLSVPs compositions based on an improved mineralogical model including, for instance, the effects of alumina. We also systematically investigate the effects of six parameters: FeO and Al$_{2}$O$_{3}$ content, proportion of CaSiO$_{3}$ and bridgmanite (so that the proportion of ferropericlase is implicitly investigated), Fe$^{3+}$/$\sum$Fe and temperature contrast between far-field mantle and LLSVPs. From the 81 millions cases studied, only 79000 cases explain the seismic observations. Nevertheless, these successful cases involve a large range of parameters with, for instance, FeO content between 12--25~wt\% and Al$_{2}$O$_{3}$ content between 3--17~wt\%. We then apply a principal component analysis (PCA) to these cases and find two robust results: (i) the proportion of ferropericlase should be low ($<$6vol\%); (ii) the formation of Fe$^{3+}$-bearing bridgmanite is much more favored than other iron-bearing phases. Following these results, we identify two end-member compositions, Bm-rich and CaPv-rich, and discuss their characteristics. Finally, we discuss different scenarios for the formation of LLSVPs and propose that investigating the mineral proportion produced by each scenario is the best way to evaluate their relevance. For instance, the solidification of a primitive magma ocean may produce FeO and Al$_{2}$O$_{3}$ content similar to those suggested by our analysis. However, the mineral proportion of such reservoirs is not well-constrained and may contain a larger proportion of ferropericlase than what is allowed by our results.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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