Partial Melting of Ordinary Chondrite: Implications for Siderophile Behavior During Early Differentiation

Details Partial Melting of Ordinary Chondrite: Implications for Siderophile Behavior During Early Differentiation Partial Melting of Ordinary Chondrite: Implications for Siderophile Behavior During Early Differentiation

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.v52d..05r&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #V52D-05

Physics

1015 Composition Of The Core, 1050 Marine Geochemistry (4835, 4850), 3630 Experimental Mineralogy And Petrology, 3640 Igneous Petrology, 3672 Planetary Mineralogy And Petrology (5410)

Scientific paper

Core formation scenarios in growing planetesimals include a variety of possible physical mechanisms such as segregation in a solid or partially molten silicate body or whether or not the body was actively deforming. The resulting geochemical composition of the metal and silicate phases will also be a function of bulk composition, percent of metal melted and oxygen fugacity. To explore the relationship between physical core formation scenarios and geochemistry, deformation experiments have been conducted on a H6 ordinary chondrite at different stages of melting. Deformation experiments provide a dynamic component that allows liquid metal to segregate from solid silicate, or from matrices containing various amounts of silicate melt. Geochemical analyses of metal quench in several experimental charges and on metal grains in the Kernouve H6 starting material have been performed by LA-ICP-MS (Hummayun &\ Campbell, EPSL, 2002; Rushmer et.al., Geochem. Cosmochem. Acta, Goldschmidt Conf. Abs,, 2002). Below the silicate solidus (KM-10, 1.0 GPa, 925°C, 1x10-5 s-1), analyses of compatible (Re, Os) and incompatible (Pd, Au) siderophiles in residual, strained Fe-Ni metal and unmodified metal show little variation. These data suggest even though metamorphosed, siderophile abundances are not strongly modified by shearing. At higher temperatures, (KM-17, 1.2 GPa, 940°C, 10-6 s-1) data from metal quench representing early formed liquid (S-rich and possibly O-rich) and of residual Fe-Ni metal have been plotted on a Fe, H-chondrite normalized plot with starting Kernouve metal and bulk H4-6 metal compositions. The quench metal resembles liquid, being depleted in compatible siderophiles, e.g., Re, Os, Ir, and enriched in Ni, Pd. Residual metal mirrors the quench metal and is enriched in compatible elements and depleted in the incompatibles when compared with bulk H metal. Ga and Ge show slight fractionation. Ga, Ge, Co and Ir vs. Ni plots show quench metal compositions are similar to natural IIE iron meteorites, providing some support for the hypothesis that these irons come from an H-chondrite like precursor. Partitioning data collected from these charges also suggest deformation may play an important role in enhancing kinetics during partial melting.

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