Project Details
Projekt
Behavior of refractory metals during metal-silicate segregation in a multi-metal system.
Applicant
Dr. Daniel Schwander
Subject Area
Mineralogy, Petrology and Geochemistry
Astrophysics and Astronomy
Palaeontology
Astrophysics and Astronomy
Palaeontology
Term
from 2015 to 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 277008682
Submicrometer-sized highly siderophile metal (HSE) alloy nuggets have been found in quenched materials from experiments conducted at reducing conditions with the aim to understand the core- mantle segregation process on Earth and also inside Ca-Al-rich inclusions (CAIs) from meteorites as well as in cosmic spherules. In the former case - where mostly one metal was set in equilibrium with the silicate - the metal-nuggets have formed by precipitation. In the latter cases multi-metal-nuggets have been commonly thought to have formed by direct gas-solid condensation from a solar composition gas. When the topic was pursued further, it became clear that there is more complexity in the elemental patterns and appearance of refractory metal nuggets (RMNs; HSE-nuggets) from CAIs than previously realized. Detailed chemical, petrological, metallurgical and structural investigations on RMNs point against a condensation origin and suggest formation by precipitation from a silicate-liquid instead. I conducted experiments and showed that Os-Ir-Mo-Ru-Re-Pt-Fe-Ni-nuggets (RMNs) precipitated from an artificial CAI-liquid and showed features just as observed in the meteoritic CAIs. This new approach in understanding the origin of RMNs is evidence for a precipitation origin of the meteoritic RMNs from CAI-liquids. It follows that CAIs with embedded RMNs can be considered a natural source of HSE-nuggets. Thus, these CAIs provide important information about the solubility, partitioning and fractionation behavior of HSE in silicate/CAI liquids in a multi metal system. Consequently, in both cases, CAIs - the oldest and highly primitive materials of the Solar System - and synthesized mantle-like materials, the nuggets appear to have formed by precipitation from a melt under reducing conditions. The aim of the proposed project is to search for a connection between the occurrence of nuggets in CAIs, cosmic spherules and the laboratory studies and to investigate the partitioning and fractionation behavior of siderophile elements relevant in silicate- / CAI- liquids under realistic conditions. This includes, e.g., use of a realistic multi-element mixture of highly siderophile elements in experiments rather than individual elements only as in most previous work and the comparison of experimental studies with observations on (probably) quenched meteoritic material (CAIs). For this purpose I will conduct melting experiments in which up to eight refractory metals will be equilibrated with each other and a CAI/ silicate-liquid at fixed temperatures between 1400 and 1800°C (given degree of polymerization of the melt). Varying run times, quench and cooling rates of the run products will further help in understanding nugget-formation. Both, run products and meteoritic CAIs will be analyzed by EDX for single nugget-compositions and by LA-ICP-MS for bulk metal contents of the quenched silicate liquids and CAIs.
DFG Programme
Research Grants
International Connection
Hungary
