The influence of melt composition on the partitioning of REEs, Y, Sc, Zr and Al between forsterite and melt in the system CMAS
The influence of melt composition on the partitioning of REEs, Y, Sc, Zr and Al between forsterite and melt in the system CMAS
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DOI：
10.1016/j.gca.2008.09.017
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发表时间：
2008-12-01
影响因子：
5
通讯作者：
Tuff, James
中科院分区：
文献类型：
--
作者：
Evans, Thomas M.;O'Neill, Hugh St. C.;Tuff, James
用激光烧蚀电感耦合等离子体质谱(LA-ICPMS)测定了1bar和1400℃时稀土元素(REE)、Y、Sc、Al和Zr在橄榄石(近端成员Mg2SiO4)和CaO-MgO-Al_2O_3-SiO_2(CMAS)系统10种熔体成分之间的分配系数，并用激光烧蚀电感耦合等离子体质谱(LA-ICP-MS)测量了橄榄石和熔体中的痕量元素。稀土和Sc的添加水平足以确保橄榄石中的浓度远远高于检测限值。REE分配系数(D-REE(ol/Melt))随熔体中SiO_2含量的增加而减小，表明REEO_(1.5)与熔体中的SiO_2之间存在较强的结合。D-REE(ol/熔体)随离子半径的变化可用Brice方程很好地描述，尽管这种变化有一小部分是由于熔体中REEO1.5-SiO_2相互作用强度随离子半径的增加所致。Sc的行为与稀土非常相似，但对所有10个熔体成分数据的全球拟合表明，D-Sc(ol/熔体)与REE和Y建立的抛物线有所偏离，这意味着Sc可能与稀土不同地代入橄榄石。与大三价阳离子的行为相反，橄榄石中铝的浓度与其在熔体中的浓度的平方根成正比，表明橄榄石中存在高度短程有序的偶合取代。橄榄石或熔体中的稀土分配系数与Al之间缺乏相关性，表明橄榄石中的稀土替代是由阳离子空位电荷平衡的。在橄榄石中高度不相容的四价微量元素Zr的分配系数取决于熔体中的CaO含量。皇冠版权所有(C)2008由爱思唯尔有限公司出版。保留所有权利。
Partition coefficients for a range of Rare Earth Elements (REEs), Y, Sc, Al and Zr were determined between forsteritic olivine (nearly end-member Mg2SiO4) and ten melt compositions in the system CaO-MgO-Al2O3-SiO2 (CMAS) at 1 bar and 1400 degrees C, with concentrations of the trace elements in the olivine and the melt measured by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The REEs and Sc were added at levels sufficient to ensure that concentrations in the olivine were well above the detection limits. The REE partition coefficients (D-REE(ol/melt)) decrease with increasing silica in the melt, indicating strong bonding between REEO1.5 and SiO2 in the melt. The variation of D-REE(ol/melt) as a function of ionic radius is well described by the Brice equation for each composition, although a small proportion of this variation is due to the increase in the strength of the REEO1.5-SiO2 interactions in the melt with ionic radius. Scandium behaves very similarly to the REEs, but a global fit of the data from all ten melt compositions suggests that D-Sc(ol/melt) deviates somewhat from the parabolas established by the REE and Y, implying that Sc may substitute into olivine differently to that of the REEs. In contrast to the behaviour of the large trivalent cations, the concentration of Al in olivine is proportional to the square root of its concentration in the melt, indicating a coupled substitution in olivine with a high degree of short-range order. The lack of any correlation of REE partition coefficients with Al in olivine or melt suggests that the REE substitution in olivine is charge-balanced by cation vacancies. The partition coefficient of the tetravalent trace element Zr, which is highly incompatible in olivine, depends on the CaO content of the melt. Crown copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.