High-pressure behavior of liebenbergite: The most incompressible olivine-structured silicate
High-pressure behavior of liebenbergite: The most incompressible olivine-structured silicate
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DOI：
10.2138/am-2019-6680
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发表时间：
2019-03
影响因子：
3.1
通讯作者：
Dongzhou Zhang;Yi Hu;Jingui Xu;R. Downs;J. Hammer;P. Dera
中科院分区：
文献类型：
--
作者：
Dongzhou Zhang;Yi Hu;Jingui Xu;R. Downs;J. Hammer;P. Dera
摘要镍是块状地球中丰富的元素，以镍为主的橄榄石是自然界中唯一发现的火成岩富镍硅酸盐。在这项研究中，我们使用高压单晶衍射法研究了合成锂贝母样品在常温下的压缩行为，其压力高达42.6 GPa.在所研究的压力范围内，锂贝母样品保持了正交晶系的Pbnm结构，没有观察到相变。用三阶Birch-Murnaghan状态方程拟合了晶胞体积、晶格参数、多面体体积和每个多面体内平均键长的压力行为。最适合的体积弹性系数KT0=163(3)Gpa及其压力导数KT0‘$\Begin{ARRAY}{}K{\Rm T}0}’\end{ARRAY}$=4.5(3)。我们发现Liebenbergite是迄今报道的最不可压缩的橄榄石族硅酸盐，Ni2+倾向于增加橄榄石和尖晶石结构的硅酸盐的等温体弹性系数。因此，在上地幔P-T条件下，富镍橄榄石的密度高于贫镍橄榄石；然而，地幔橄榄石中镍的富集度通常太低，不能使这种密度差异与分馏或浮力相关。
Abstract Nickel is an abundant element in the bulk earth, and nickel-dominant olivine, liebenbergite, is the only igneous nickel-rich silicate found in nature. In this study, we used high-pressure single-crystal diffraction to explore the compressional behavior of a synthetic liebenbergite sample up to 42.6 GPa at ambient temperature. Over the studied pressure range, the liebenbergite sample retains the orthorhombic Pbnm structure, and no phase transition is observed. A third-order Birch-Murnaghan equation of state was used to fit the pressure behavior of the unit-cell volume, lattice parameters, the polyhedral volume, and the average bond length within each polyhedron. The best-fit bulk modulus KT0 = 163(3) GPa and its pressure derivative KT0′$\begin{array}{} K_{{\rm T}0}' \end{array} $ = 4.5(3). We find that liebenbergite is the most incompressible olivine-group silicate reported thus far, and Ni2+ tends to increase the isothermal bulk modulus of both olivine- and spinel-structured silicates. Consequently, Ni-rich olivine has a higher density compared to Ni-poor olivine at the upper mantle P-T conditions; however enrichment of Ni in mantle olivine is generally too low to make this density difference relevant for fractionation or buoyancy.