Chemical fractionations in meteorites--III. Major element fractionations in chondrites

Details Chemical fractionations in meteorites--III. Major element fractionations in chondrites Chemical fractionations in meteorites--III. Major element fractionations in chondrites

Mar 1970

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1970gecoa..34..367l&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 34, Issue 3, pp.367-387

Computer Science

69

Scientific paper

Some 20 elements, including the major constituents of chondritic matter, are fractionated among the several chondrite classes. We have tried to explain these fractionations on the assumption that they occurred in the solar nebula, starting from material of carbonaceous chondrite composition. 1. (1) Lithophile elements (Al, Ca, Cr, Hf, Mg, Sc, Si, Th, Ti, U, Y, Zr, and lanthanides) may have been fractionated at 1300-1350°K by partial loss of an early condensate, consisting of minerals such as MgAl 2 O 2 , Mg 2 SiO 4 , CaTiO 3 , Ca 2 Al 2 SiO 7 , etc. 2. (2) Siderophile elements (Fe, Co, Ni, etc.) apparently were fractionated between 680 and 1050°K, by partial separation of metal and silicate. Redox conditions at this stage seem to have varied from class to class, as indicated by the Fe 2+ / Mg 2+ ratio in the silicates during fractionation: 0.14 ±0.02 for ordinary, 0.00 ± 0.07 for enstatite, and 0.14 ± 0.08 or 0.08 ± 0.07 for carbonaceous chondrites. This fractionation may have been based on the ferromagnetic properties of the metal, since it apparently took place below the Curie point. 3. (3) Chondrule formation does not seem to have been causally related to either of these fractionations. It may have occurred at ~700°K during or after metal-silicate fractionation, presumably by partial remelting of the dust. It was followed by further condensation of volatiles and accretion.

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