Experimental grain growth of forsterite and nickel in melt-free and melt-bearing systems: implications for meteorite parent-body processes

Details Experimental grain growth of forsterite and nickel in melt-free and melt-bearing systems: implications for meteorite parent-body processes Experimental grain growth of forsterite and nickel in melt-free and melt-bearing systems: implications for meteorite parent-body processes

Oct 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011epsc.conf..730g&link_type=abstract

EPSC-DPS Joint Meeting 2011, held 2-7 October 2011 in Nantes, France. http://meetings.copernicus.org/epsc-dps2011, p.730

Computer Science

Scientific paper

The grain growth kinetics and microstructural evolution of olivine (forsterite) and metal (nickel) have been experimentally quantified in the presence and absence of a silicate melt. Experiments of variable duration have been performed at 1bar pressure, a temperature of ~1440°C, and an oxygen fugacity (ƒO2) approximately 3.5 log units below the NiNiO buffer. In melt-free systems, grain growth was measured for four binary mixtures, containing 95, 80, 30, and 10 vol% Ol, covering geometries for each phase varying from an interconnected matrix to isolated grains. In all aggregates, the grain growth exponent n is found to have a value of 4-5. Despite this common value, consideration of the distribution of grain sizes points to variable grain growth mechanisms, from grain boundary migration for forsterite and nickel when they form an interconnected matrix, to grain growth by coalescence for nickel when the latter occurs as isolated grains. For melt-bearing systems a fixed Fo/Ni ratio was used (95:5) to which 5 and 20 vol% of melt was added. Five olivine-saturated liquid compositions from the forsterite-anorthite-diopside ternary were tested (liquids containing 0 to 24 wt% Al2O3). In all cases, grain growth of both Fo and Ni is faster than under "dry" conditions. Grain growth of Fo is controlled by Ostwald ripening (n~2-3) while that of Ni appears to remain controlled by coalescence (n~4-5). For 20% melt, an effect of melt composition is also observed. Finally, comparisons between experimental data and natural observations (in chondrites and achondrites) have been made with the aim of constraining the thermal history of their parent bodies.

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