Metal-related mineral assemblages as probes into protoplanetary gas-solid interactions

• Applicant: Dr. Dennis Harries
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 248746696

At present, it is largely unknown how water, nitrogen compounds, and other volatile species interacted in the solar protoplanetary disk and, eventually, contributed to the terrestrial oceans and atmosphere. In this project we focus on the reactions of iron-rich metal grains with volatile species during the first ten million years of the Solar System. Due to their high reactivity, metals constitute ideal mineralogical probes into the protoplanetary processes involved. Typical reaction products observed in chondritic meteorites are iron-rich sulfides and oxides, such as pyrrhotite, pentlandite, and magnetite. We aim at deriving decisive criteria in order to differentiate between gas-solid interactions and liquid-water alteration as mechanisms for the origin of such metal-related mineral assemblages, and we aim at elucidating the involved volatile reservoirs. In particular, we will address the unresolved and eminent question whether evaporated multi-component (comet-like) ices played significant roles in protoplanetary gas-solid interactions. This is suggested by novel, nitride-bearing sulfide assemblages, pointing to the former presence of gaseous ammonia.We will test formation hypotheses by a dual approach: (i) By the reconstruction of physicochemical formation conditions from mineralogical and microstructural analysis of metal-related mineral assemblages in chondritic meteorites, (ii) by novel experimental investigation of gas-metal interactions in a low-pressure gas mixing furnace using mixtures of hydrogen, hydrogen sulfide, water, ammonia, and nitrogen. Transmission electron microscopy (TEM) will be a central analytical tool and will be supplemented by secondary ion mass spectrometry (SIMS) for isotopic analysis of oxygen, sulfur, and nitrogen.The results are expected to largely enhance our understanding of the protoplanetary interactions and reservoirs of volatile species. If it can be shown that evaporated multi-component ices were involved, the process and its physicochemical conditions will have important implications for the local redox state of the solar nebula and the evolution of primordial organic species, which were probably contained in such ices and could have been delivered to the early Earth along with other volatiles. If such a mechanism turns out to be unfeasible, the fluid-mediated alteration within meteoritic parent bodies was likely much more complex than currently thought and will require revision.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1385: The first 10 Million Years of the Solar System - A Planetary Materials Approach
• Participating Person: Professor Dr. Falko Langenhorst