Enstatite chondrites: Trace element clues to their origin

Title Enstatite chondrites: Trace element clues to their origin
Author: Hertogen, Jan; Janssens, Marie-Jos\'{e}e; Takahashi, H; Morgan, John W & Anders, Edward
Geochimica et Cosmochimica Acta, 1983
More details: We have analyzed by \{RNAA\} 3 \{EH\} and 3 \{EL\} chondrites for 20 trace elements. Interelement correlations were examined visually and by factor analysis, to assess the effects of nebular fractionation and metamorphism. Refractory siderophiles (Ir, Os, Re) correlate with ?«£normal siderophiles?�? (Ni, Pd, Au, Sb, and Ge) in EL's but not EH's; presumably these two element groups originally condensed on separate phases (CAI and metal), but then concentrated in metal during metamorphism. Sb and Ge are more depleted than the other three elements of the ?«£normal?�? group, presumably by volatilization during chondrule formation. Volatiles are consistently more depleted in EL's than EH's, by factors \>10?� for the more volatile elements. Some of the stronger correlations are found for In-Tl, Tl-Bi, and Zn-Cd-In. These correlations are about equally consistent with predicted condensation curves for the solar nebula (especially for host phases with negative heats of solution, or for P .1?��1 atm) and with volatilization curves for artificially heated Abee, as determined by M E. Lipschutz and coworkers at Purdue. No decisive test between these alternatives is available at present, but the close correlation of Zn, Cd, In may eventually provide a crucial test. Factor analysis shows that 3 factors account for 93\% of the variance; they seem to reflect volatile (F1), siderophile (F2), and chalcophile (F3) behavior. The element groupings agree largely with those recognized visually; they are listed with the inferred host phases. \{F1\} (minor sulfide, probably ZnS): Zn, Cd, In, Br; \{F2\} (CAI, later metal): Ir, Os. Re; F1, \{F2\} (metal): Ni, Pd, Au, Ge, Sb; F3, \{F1\} (FeS): Se, Te, Bi, Tl. These correlations differ to some extent from those obtained by Shaw (1974) in an earlier factor analysis, presumably because the new data are more homogeneous and extensive, especially for siderophiles. The new correlations also show that the cosmochemical behavior of some volatiles in E-chondrites differs from that predicted for ordinary chondrites, so that condensation curves for the latter are not strictly applicable.

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