[meteorite-list] Breccia formation

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 09:55:43 2004
Message-ID: <3C3A07C6.C5F03894_at_lehrer1.rz.uni-karlsruhe.de>

Dave Harris wrote:

> So, can I assume that the meteorite, prior to ejection from the parent
> asteroid was already a brecciated rock lying on the surface or embedded in
> the lithosphere, or does brecciation occur when the regolith is pounded by
> an impact, fusing together all the different rocks lying around on the
> surface of the planetoid?

Hello again,

JÄCKEL A. et al. (1998) Textural and mineralogical differences
between LL-chondritic fragmental and regolith breccias
(Meteoritics 33-4, 1998, A077, excerpts):

"Essentially, two different types of breccias can be distinguished:
regolith breccias and the more abundant fragmental breccias. Regolith
breccias derive from the uppermost surface material of the parent
bodies, and contain significant concentrations of solar-wind-implanted
noble gases as well as preirradiated mineral grains. Fragmental breccias
represent material that was shielded from irradiation, and do not
contain solar-wind-implanted noble gases."

"The chemical compositions of the matrix olivines in regolith breccias
vary, unlike the composition of matrix olivines in fragmental breccias.
The occurrence of clasts showing different olivine compositions
indicates that equilibrated and unequilibrated lithologies were mixed
together by impact events after the equilibrated and recrystallized
fragments were formed by thermal metamorphism."


Best wishes,

Bernd
Received on Mon 07 Jan 2002 03:40:38 PM PST