Behavior of refractory metals during metal-silicate segregation in a multi-metal system.
Astrophysics and Astronomy
Palaeontology
Final Report Abstract
The behavior of the siderophile metals Fe, Ni, Mo, W, Pt, Os, Re, Ir and Ru within silicate systems in a cosmochemical setting related to RMNs were studied and discussed. The experiments show that nuggets mostly consisting of Mo, W, Fe and Ni but also of Pt, Ru, Ir, Os can form on a time scale between 5 seconds and 1 minute when a compact multi metal alloy stays in contact with silicate/CAI liquids at temperatures above the liquidus. This finding demonstrates an at least partial decomposition of the precursor alloys with a first loss of Mo and W. Siderophile element nuggets forming after metal oxidation, diffusion through the silicate and subsequent reduction will stay stable at peak temperature when silicate is in contact to one large metal object. If the silicate is enriched with small metal particles before heating, these particles will be distributed first and will subsequently coagulate to larger particles. At the same time pre-existing particles decompose while new particles form from metals that were previously oxidized, dissolved and reduced. Applied to a meteoritic environment, the results show that RMNs hosted by once (partially or completely) molten CAIs and chondrules cannot have retained their original composition. They were affected by oxidation and reduction processes as well as coagulation. RMNs as they are observed today therefore most likely formed from previously partially or completely decomposed condensed alloys by coagulation and/or crystallization during the melting episode of their host. Consistent with studies on cooling rates of chondrules, a time scale of a few seconds to a few minutes is enough for the formation and preservation of siderophile element nuggets. RMN bearing CAIs on the other hand should have experienced a dynamic cooling rate from extremely fast (few seconds) to very low (hours) to match studies on the crystallization behavior of both melilite and homogeneous RMNs.
Publications
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(2018) Defining the Potential of Nanoscale Re‐Os Isotope Systematics Using Atom Probe Microscopy. Geostand Geoanal Res (Geostandards and Geoanalytical Research) 42 (3) 279–299
Daly, Luke; Bland, Phil A.; Tessalina, Svetlana; Saxey, David W.; Reddy, Steven M.; Fougerouse, Denis; Rickard, William D.A.; Forman, Lucy V.; La Fontaine, Alexandre; Cairney, Julie M.; Ringer, Simon P.; Schaefer, Bruce F.; Schwander, Daniel
