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Volatiles in chainpur chondrules
Author(s) -
Grossman Jeffrey N.,
Kracher Alfred,
Wasson John T.
Publication year - 1979
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl006i007p00597
Subject(s) - chondrule , kamacite , geology , chondrite , volatiles , redistribution (election) , metamorphic rock , mineralogy , meteorite , chemical physics , geochemistry , analytical chemistry (journal) , chemistry , astrobiology , environmental chemistry , physics , politics , political science , law
A study of individual chondrules in the Chainpur (unequilibrated) LL3 chondrite revealed order‐of‐magnitude variations in volatile element concentrations, with maxima ∼2X and minima ∼0.1X whole‐rock concentrations. In no chondrule were concentrations of all volatiles lower than 0.5X bulk values; only one volatile, Ge, had an observed chondrule/bulk ratio lower than 0.15. Volatile elements differing in geochemical behavior tended to vary randomly; correlated variations were observed only for those elements inferred to occupy similar mineral sites. Although metamorphic redistribution could produce similar observations, variations in Co and Ni in kamacite show that metal in chondrule interiors have not approached equilibrium, and it appears that postformational elemental redistribution has mainly altered siderophile concentrations in surface metal grains, and has probably left ionic species relatively unaltered. Etching to remove 3–5% of the chondrule mass selectively dissolved siderophiles; the volatiles Zn and Na were enhanced by small factors relative to nonvolatile Cr in the etch, but a large enhancement of Cd involved about 20% of total Cd. This portion of the Cd may have been present as a late nebular condensate. If metamorphic redistribution of nonsiderophile volatiles was negligible, their high concentrations are inconsistent with chondrule formation by direct condensation. Models involving sudden melting of preexisting solids can explain the observations but require rapid cooling to prevent volatile loss.