porphyritic? Are you sure? The meteorites cool down in a single stage, I believe. AA
----- Original Message ----- From: <[EMAIL PROTECTED]> To: <[email protected]> Sent: Thursday, March 22, 2007 5:35 PM Subject: [meteorite-list] Fusion crusts on stony meteorites > 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 > [email protected] > http://six.pairlist.net/mailman/listinfo/meteorite-list > ______________________________________________ Meteorite-list mailing list [email protected] http://six.pairlist.net/mailman/listinfo/meteorite-list
