PGE (PLATINUM GROUP ELEMENTS) COSMOCHEMISTRY ON IRON

本文介绍了用电感耦合等离子体质谱（ICP-MS）进行的同位素测量，并提出了新的实验结果，旨在进一步发展同位素地球化学。通过激光烧蚀- icpms原位测量铂族元素（PGE）和Re，可以在宿主（卡玛长石）和富镍溶出相（带长石和硅长石）之间建立分异模式。对两颗IAB铁陨石（Canyon Diablo和Odessa）的测量表明，对于富镍相；a) Ru和Rh没有明显分馏，b) Pd富集，c) Ir、Os和Pt富集。我们认为，对于绢云母、带长石和硅长石，控制机理是离子大小，离子大小顺序由小到大依次为Ir-Os-Pt- (Re) - rh - ru - pd。这个级数在相对丰度分布与离子大小的关系图上画出一条光滑的曲线。铁陨石上的PGE和Re数据与CI球粒陨石上的更多ed数据的比较表明，元素之间很少或没有相对分异。唯一的例外是稀土，相对于球粒陨石，稀土明显富集于卡玛石中。这证实了早期观察到的大块IAB铁和CI值之间Re/Os的分馏。在Diablo峡谷IAB陨石中切割石墨包裹体的金属脉被解释为铁陨石的熔融部分。钾铁矿与金属脉之间的稀土元素（PGE）和稀土元素（Re）丰度比与钾铁矿与富镍相之间的丰度比相似。具有较大离子半径的元素（Rh， Ru和Pd）集中在金属脉中，这一事实增加了它们代表熔体分数的观点。我们对PGE和Re的原位测量表明，元素分馏发生在熔体偏析和固态扩散（析出）过程中。这些数据对Re/Os地球时计具有重要意义，并表明铁陨石中单个相的187Os/186Os比值测量可能提供潜在的矿物等时线。少

This paper describes in isotopic measurements that have been made with an inductively coupled plasma mass spectrometry (ICP-MS) and presentsresults of new experiments aimed at further progress of the isotope geochemistry. In situ measurement of the platinum group elements (PGE) and Re by laser ablation-ICPMS allows fractionation patterns to be established between host (kamacite) and Ni-rich exsolved phases (taenite and plessite). Measurements on two IAB iron meteorites (Canyon Diablo and Odessa) show that for the Ni-rich phases ; a) there is no significant fractionation for Ru and Rh, b) Pd is enriched and c) Ir, Os and Pt are strongly depleted. We suggest that in the case of kamacite, taenite and plessite, the controlling mechanism is ionic size with the order of ions (small to large) being Ir-Os-Pt- (Re) -Rh-Ru-Pd. This progression plots as a smooth curve on a diagram of relative abundance distribution versus ionic size. A comparison of PGE and Re data on iron meteorites with publish … More ed data from CI chondrites indicate that there is little or no relative fractionation between the elements. The exception is Re that is clearly enriched in kamacite relative to chondrites. This confirms earlier observations on the fractionation of Re/Os between bulk IAB irons and CI values. Metallic veins cutting graphite inclusions within the Canyon Diablo IAB meteorite are interpreted as a melt fraction from the iron meteorite. Abundance ratios for PGE and Re between kamacite and the metallic vein are similar to abundance ratios between kamacite and Ni-rich phases. The fact that those elements with large ionic radii (Rh, Ru and Pd) are concentrated in the metallic veins adds weight to the view that they represent a melt fraction.Our in-situ measurements of the PGE and Re demonstrate that elemental fractionation takes place both during melt segregation and solid state diffusion (exsolution). The data have important implications for the Re/Os geochronometer and indicate that measurements of 187Os/186Os ratios on individual phases within iron meteorites may provide a potential mineral isochron. Less