Summary: | Labile trace elements are used to establish thermal histories and evolutionary episodes of meteorites. Fourteen trace elements--Ag, Au, Bi, Cd, Co, Cs, Ga, In, Rb, Sb, Se, Te, Tl, and Zn--covering most labile trace elements, were determined by radiochemical neutron activation analysis, in samples of C1-6 and unique carbonaceous (C) chondrites, mainly from Antarctica and a few non-Antarctic specimens, and in samples of dark matrix, and dark and light inclusions of the Fayetteville H chondrite regolith breccia. C chondrites: C1-normalized mean concentrations for the 9 most labile elements Ag $\to$ In are quite constant in most carbonaceous chondrites. Trace element contents in Antarctic and non-Antarctic carbonaceous chondrites are similar: they are essentially unaltered by weathering in Antarctica and by secondary metamorphism at $\geq$500$\sp\circ$C in an open-system. Concentrations of highly labile trace elements reveal a continuous distribution from 1.0 $\times$ C1 to 0.1 $\times$ C1 for C2-6 chondrites and unique carbonaceous chondrites, and there is considerable overlap between different petrographic types. Siderophile ratios (Ga/Co and Au/Co) exhibit trends similar to those of highly labile elements. The entire suite of carbonaceous chondrites do not seem to sample a few, compositionally-distinct parent materials but, rather, a compositional continuum in which parent materials forming under more oxidizing conditions incorporated lesser complements of volatiles, essentially unfractionated from cosmic composition. This may well reflect a continuum in formation conditions (temperature, duration, water/rock ratios) represented by oxygen isotope variations during preterrestrial genetic processes of parent materials. Fayetteville regolith breccia: Most dark inclusions had similar mean trace element concentrations as matrix but were compositionally more heterogeneous. Two dark inclusions were unique, one having apparently formed from impact-melted soil, the other being a mixture of 90% matrix--10% C2M chondrite. ...
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