Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmmr14a..06w&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #MR14A-06
Physics
[8115] Tectonophysics / Core Processes
Scientific paper
Planetary cores comprise major portions of the bodies they inhabit, yet little geochemical evidence can be gained from geophysical observations of them. This is true of even the heavily studied core of the Earth. Fortunately, some iron meteorites likely sample planetesimal cores, and so provide important insights to the chemical processes involved in core formation and crystallization. Applicability of information gleaned from iron meteorites, which come from relatively small bodies, to understanding the cores of larger planetary bodies that likely segregated at much higher pressures and temperatures, may be limited. Nevertheless, some of the chemical characteristics of the cores of the larger bodies could have been established in smaller bodies that accreted to form the larger bodies. As has been long known, iron meteorite groups are chemically diverse, and therefore sample bodies that formed from diverse materials, under different conditions. Tungsten isotopic study has shown that most irons that sample cores formed within the first several million years of solar system history. Consequently, the compositions of iron meteorite must reflect chemical heterogeneities present in the early solar system when planetary embryos, the building blocks of the terrestrial planets were beginning to form. Siderophile elements are particularly useful for characterizing differences in parent body compositions, as cores contain >90% of the total siderophile element mass balance of the body. Estimations of the parent body compositions of siderophile elements suggest rather diverse compositions in which relative abundances of even refractory elements were strongly fractionated compared to chondritic references in some bodies. Such fractionated compositions, therefore, could be characteristic of the cores of larger planetary bodies, so assumptions regarding the chondritic relative abundances of siderophile elements in planetary cores may not be valid. Such fractionations may affect models proposed for detecting core-mantle interactions on Earth. Crystallization processes for cores sampled by different iron groups also varied considerably. Solid metal-liquid metal distribution coefficients for siderophile elements in iron systems are strongly affected by elements, such as S, P and C.
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