GENGE M.J. and GRADY M. (1999) The fusion crusts of stony meteorites: implications for the atmospheric reprocessing of extra- terrestrial materials (MAPS 34-3, 1999, 341-356):
a) Fusion crusts develop on *all* meteorites during their passage of the atmosphere ... b) Most chondrite fusion crusts are porphyritic and dominated by olivine, glass and accessory magnetite whereas those of the achondrites are mainly glassy. c) Chondrite fusion crusts contain sulphide droplets with high-Ni contents (>55 wt%). d) The partially melted substrate of OCs, underlying the outer melted crusts, are dominated by silicate glass and composite metal, sulphide and Cr-bearing Fe-oxide droplets that form as coexisting immiscible liquids. e) Enstatite chondrite substrates contain Cr- and Mn- bearing sulphides. f) The substrates of the CCs comprise a sulphide-enriched layer of matrix. The compositions of melted crusts are similar to those of the bulk meteorite. Differences from whole rock, however, suggest that three main processes control their chemical evolution: 1) the loss and reaction of immiscible Fe-rich liquids, 2) mixing between substrate partial melts and bulk melts of the melted crust, 3) the loss of volatile components by evaporation and degassing. Conclusions, p. 356: The fusion crusts of stony meteorites exhibit considerable variation with meteorite type and compositions and textures that are largely dependent on the bulk chemical and mineralogical properties of the meteorite. Four processes are important in the chemical evolution of fusion crusts: 1) the separation and reaction of Fe-rich sulphide, metal, and oxide liquids, 2) reaction with atmospheric O, 3) mixing of incompatible element-rich partial melts from the substrate with bulk melted crust liquid, 4) the loss of volatile elements by e v a p o r a t i o n and d e g a s s i n g. Best wishes, Bernd ______________________________________________ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
