[meteorite-list] Armored chondrules -- how?

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Fri Jan 7 08:43:03 2005
Message-ID: <DIIE.0000003500003077_at_paulinet.de>

On Friday Dec 24, 2004,
Darren Garrison wrote:

> I'm wondering what the theory is on how "armored" chondrules get
> their coating? Does the nickel/iron accrete around the chondrules,
> or is there some melting event where liquid metal flows around them?

VOGEL N. et al. (2004) Noble gases in chondrules and associated
metal-sulfide-rich samples: Clues on chondrule formation and the
behavior of noble gas carrier phases (MAPS 39-1, 2004, 117-135).

Excerpts:

"Chondrules are small silicate spherules in primitive meteorites that show
evidence for a once molten stage. Although they are common in most chondrite
groups, their formation mechanism(s) and environment(s) are uncertain. The
two main theories are nebular chondrule formation by melting of dust ball
precursors and chondrule formation in a planetary environment."

"The study also includes metal-sulfide (MS*)-rich coatings of chondrules, MS
droplets within chondrules, and MS-rich patches in the matrix that are also
genetically related to chondrules. We assume that, during chondrule formation,
small MS droplets segregated from the silicate melt, migrated to the chondrule
margins, and were eventually expelled."

"Expelled droplets formed coatings around chondrules or were completely separated
from their host chondrules and are now present as isolated MS-rich patches within the
matrices of primitive chondrites. It is also possible that MS evaporated from, and
subsequently recondensed back onto, chondrule surfaces. Alternatively, Kojima et al.
(2003) discuss the extraction of chondrule MS and the formation of the coatings during
later impact events on the parent bodies to which the chondrules first assembled."

*MS = metal-sulfide


Best wishes,

Bernd
Received on Fri 07 Jan 2005 08:43:01 AM PST