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E‐CHONDRITES: SIGNIFICANCE OF THE PARTITION OF ELEMENTS BETWEEN ‘SILICATE’ AND ‘SULPHIDE’
Author(s) -
Easton A.J.
Publication year - 1985
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1985.tb00849.x
Subject(s) - chondrite , silicate , geology , geochemistry , chemical composition , mineralogy , phosphide , chemistry , analytical chemistry (journal) , meteorite , metal , environmental chemistry , astrobiology , physics , organic chemistry
Bulk chemical analyses of six E‐chondrites (Daniel's kuil, Khairpur, Kota Kota, Saint‐Sauveur, South Oman and St Mark's) are given, together with partial analyses of a further five (Blithfield, Hvittis, Indarch, Jajh deh Kot Lalu and Pillistfer). The distribution of some normally lithophile elements (Al, Ca, Cr, K, Mg, Na, P and Ti) between silicate and sulphide groups of minerals was determined using the selective attack by dry chlorine (350°C) on magnetically separated fractions. Subdivision of the E‐chondrites into types I and II (Yavnel;, 1963; Anders, 1964) is accepted and it is shown using chemical data that St Mark's and Saint‐Sauveur should be included in type I. Sulphides contribute an unexpectedly high proportion of several elements to the bulk: e.g. Ca (av. 88.5% type I, 66.3% type II); Ti(av. 77.1% type I, 84.8% type II) and P as phosphide (av. 44.4% type I, > 83.2% type II). The proportion of Ti contributed to the bulk composition by the sulphides in types I and II increases with increae in ‘thermal metamorphic effect’ (Easton, 1983b) within each type. There is marked variability in the relative abundances of metal, phosphide, silicate and sulphide among the members of each type in keeping with their aggregate nature. The chemical composition of the ‘silicate’ and ‘sulphide’ in type IE‐chondrites differs from that in type II (e.g. CaO in the silicates, Mg in the bulk sulphides) which therefore precludes the isochemical evolution of all E‐chondrites from a common parent material. Partition of Ti between silicate and sulphide groups of minerals indicates that types I and II E‐chondrites originated in separate, chemically distinct bodies.