[meteorite-list] Fusion crusts on stony meteorites

From: Armando Afonso <armandoafonso_at_meteoritecentral.com>
Date: Thu, 22 Mar 2007 17:53:23 -0000
Message-ID: <004f01c76caa$fcc9eb40$62b0fea9_at_TOSHIBA>

porphyritic?
Are you sure?
The meteorites cool down in a single stage, I believe.
AA

----- Original Message -----
From: <bernd.pauli at paulinet.de>
To: <Meteorite-list at meteoritecentral.com>
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
>
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Received on Thu 22 Mar 2007 01:53:23 PM PDT