Ir, Ru, Pt, and Pd in basalts and komatiites: new constraints for the geochemical behavior of the platinum-group elements in the mantle
Ir, Ru, Pt, and Pd in basalts and komatiites: new constraints for the geochemical behavior of the platinum-group elements in the mantle
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DOI：
10.1016/s0016-7037(99)00219-7
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发表时间：
1999-11
影响因子：
5
通讯作者：
M. Rehkämper;A. Halliday;J. Fitton;Der-Chuen Lee;M. Wieneke;N. Arndt
中科院分区：
文献类型：
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作者：
M. Rehkämper;A. Halliday;J. Fitton;Der-Chuen Lee;M. Wieneke;N. Arndt
铂族元素（PGE）Ir，Ru，Pt和Pd的浓度测定在18个幔源玄武岩从各种构造环境和6个科马提岩从三个位置。所有分析均使用同位素稀释、Carius管消化和多收集器电感耦合等离子体质谱法的精确技术进行。对两个样品的多次分析表明，基于单独溶出度，在ppt至ppb浓度范围内的外部重现性约为2-9%。大洋中脊玄武岩从Kolbeinsey海岭，拉斑玄武岩从冰岛和碱性玄武岩从喀麦隆线定义三个独立的样品套，其特征在于不同的主要，微量元素和铂族元素系统学。所有三个样品套件显示PGE与MgO、Ni和Cr的相关性。新的分析结果被用来约束PGE在幔源熔体形成和分异过程中的地球化学行为。PGE在硫化物-硅酸盐熔体分配系数约为101 × 104时，与硫化物相容。地幔熔体的分馏PGE模式的结果Pd在非硫化物相的不相容性，而Ir和Ru必须在至少一个其他地幔相兼容。模型计算表明，PGE合金或尖晶石可能是负责后者的元素在部分熔融过程中的较高的兼容性。这进一步表明，熔融制度的形状有深刻的影响，地幔岩浆的铂族元素系统。PGE对Ni和Cr的图中的三个样品套件的系统趋势是岩浆分异过程的结果，该过程涉及硅酸盐矿物的分离结晶和不混溶的硫化物液体的同时分离。岩浆分异过程中PGE的行为表明，分离的硫化物可能与>90%的硅酸盐岩浆平衡，硫化物对PGE的清除最好用分批和分步平衡分配相结合来描述。
The concentrations of the platinum-group elements (PGE) Ir, Ru, Pt, and Pd were determined in 18 mantle-derived basalts from a variety of tectonic settings and six komatiites from three locations. All analyses were performed using isotope dilution, Carius tube digestion, and the precise technique of multiple collector inductively coupled plasma mass spectrometry. Multiple analyses of two samples indicate external reproducibilities, based upon separate dissolutions, of approximately 2–9% in the ppt to ppb concentration range. Mid-ocean ridge basalts from the Kolbeinsey Ridge, tholeiites from Iceland and alkali basalts from the Cameroon Line define three individual sample suites that are characterized by distinct major, trace, and platinum-group element systematics. All three-sample suites display correlations of the PGE with MgO, Ni, and Cr. The new analytical results are employed to constrain the geochemical behavior of the PGE during the formation and differentiation of mantle–derived melts. The PGE are inferred to be compatible in sulfides during partial melting with sulfide-silicate melt partition coefficients of ∼1 × 104. The fractionated PGE patterns of mantle melts are a consequence of the incompatibility of Pd in nonsulfide phases, whereas Ir and Ru must be compatible in at least one other mantle phase. Model calculations indicate that PGE alloys or spinel may be responsible for the higher compatibility of the latter elements during partial melting. It is further demonstrated that the shape of the melting regime has a profound effect on the PGE systematics of mantle magmas. The systematic trends of the three sample suites in plots of PGE against Ni and Cr are the result of magma differentiation processes that involve fractional crystallization of silicate minerals and the concurrent segregation of an immiscible sulfide liquid. The behavior of the PGE during magma fractionation indicates that the segregated sulfides probably equilibrate with >90% of the silicate magma and that PGE scavenging by sulfides is best described by a combination of batch and fractional equilibrium partitioning.