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Fractionation of refractory siderophile elements in metal from the Rose City meteorite
Author(s) -
Rubin Alan E.
Publication year - 1995
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1995.tb01145.x
Subject(s) - chondrite , vaporization , meteorite , refractory (planetary science) , shock metamorphism , refractory metals , geology , silicate , metal , mineralogy , volatiles , breccia , geochemistry , analytical chemistry (journal) , chemistry , materials science , metallurgy , astrobiology , environmental chemistry , physics , organic chemistry
— An ∼4 × 9 × 12‐mm concentration of metal (dubbed RC1) situated between silicate melt and a relict chondritic clast in the Rose City H5 impact‐melt breccia is compositionally heterogeneous. Approximately 65 wt% of RC1 is enriched in the refractory siderophile elements, Os and Ir, by 30–40% relative to bulk H chondrite metal; ∼20 wt% is depleted in these elements by 31–35%; and 15 wt% is depleted by a considerably greater amount (75%). Common and volatile siderophile elements are essentially unfractionated in all three regions; W is fractionated to only a moderate degree. The compositions of the different regions of RC1 are similar to those of previously analyzed metal nodules and veins in shocked but unmelted ordinary chondrites. All of these objects probably formed by a complex process involving vaporization of chondritic material, rapidly followed by oxidation of W to form volatile oxides, fractional condensation of refractory siderophile elements, transport of the residual vapor (containing common and volatile siderophile elements as well as W oxide) and condensation of this vapor in fractures and voids or on metallic liquid substrates. The common occurrence of vugs in shock‐heated chondrites and the pervasiveness of vaporization effects recorded in metal masses and veins underscores the important role of superheating in the formation of impact breccias.