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首页> 外文期刊>Contributions to Mineralogy and Petrology >Compositional effects on element partitioning between Mg-silicate perovskite and silicate melts
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Compositional effects on element partitioning between Mg-silicate perovskite and silicate melts

机译：成分对镁硅酸盐钙钛矿和硅酸盐熔体之间元素分配的影响

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High-pressure melting experiments were performed at ~26 GPa and ~2,200–2,400°C on synthetic peridotite compositions with varying FeO and Al2O3 contents and on a synthetic CI chondrite analogue composition. Peridotite liquids show a crystallisation sequence of ferropericlase (Fp) followed down temperature by Mg-silicate perovskite (MgPv) + Fp, which contrasts a sequence of MgPv followed by MgPv + Fp observed in the chondritic composition. The difference in crystallisation sequence is a consequence of the different bulk Mg/Si ratios. MgPv/melt partition coefficients for major, minor and trace elements were determined by electron microprobe and secondary ion mass spectrometry. Partition coefficients of tri- and tetravalent elements increase with increasing Al concentration in MgPv. A lattice strain model indicates that Al3+ substitutes predominantly onto the Si-site in MgPv, whereas most elements substitute onto the Mg-site, which is consistent with a charge-compensating coupled substitution mechanism. MgPv/melt partition coefficients for Mg (D Mg) and Si (D Si) are related to the melt Mg/Si ratio such that D Si becomes lower than D Mg at low Mg/Si melt ratios. We use a crystal fractionation model, based on upper mantle refractory lithophile element ratios, to constrain the amount of MgPv and Ca-silicate perovskite (CaPv) that could have fractionated during a Hadean magma ocean event and could still be present as a chemically distinct heterogeneity in the lower mantle today. We show that a fractionated crystal pile composed of 96% MgPv and 4% CaPv could comprise up to 13 wt% of the entire mantle.
机译：在具有变化的FeO和Al2 O3 含量的合成橄榄岩成分和合成的CI球粒陨石类似成分上，在〜26 GPa和〜2,200–2,400°C的温度下进行了高压熔融实验。橄榄岩液体显示了铁镁硅酸盐酶（Fp）的结晶顺序，随后是镁硅酸盐钙钛矿（MgPv）+ Fp的结晶顺序，这与在软骨组织中观察到的MgPv随后是MgPv + Fp的顺序形成对比。结晶顺序的差异是由于不同的Mg / Si体积比造成的。主要，次要和痕量元素的MgPv /熔体分配系数通过电子探针和二次离子质谱法测定。三价和四价元素的分配系数随MgPv中Al浓度的增加而增加。晶格应变模型表明Al3 +主要取代了MgPv中的Si位，而大多数元素取代了MgPv中的硅，这与电荷补偿耦合取代机理一致。 Mg（D Mg ）和Si（D Si ）的MgPv /熔体分配系数与熔体Mg / Si比相关，从而D Si 变得低于D Mg 在低Mg / Si熔融比下。我们使用基于上地幔难处理的亲石元素比例的晶体分馏模型来限制MgPv和钙硅酸盐钙钛矿（CaPv）的量，这些量在哈德岩浆海洋事件中可能已经分馏，并且仍可能以化学上独特的异质性存在在今天的下地幔中。我们表明，由96％MgPv和4％CaPv组成的分级晶体堆可以占整个地幔的13％。

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