[meteorite-list] Ensisheim as an IMB?

From: j.divelbiss_at_att.net <j.divelbiss_at_meteoritecentral.com>
Date: Thu Apr 22 10:13:10 2004
Message-ID: <20030425203940.637285397D_at_pairlist.net>

Martin,

I just read a section on breccias in Norton's book(pg 96-99). It makes it
pretty clear that all breccias are from impacts...and for the most part, most
chondrites have some evidence of brecciation (evidence of impact). As you know
the list of breccia variations is a bit confusing. Application to Chondrites
versus Achondrites is probably a little different...not sure. I'll give it a
try for chondrites, please correct where needed.

Monomict - A mixing of the same textures and compositions (ie. L6 with L6 for
chondrites)

Polymict - A mixing of different textures but the same compositions (L5 light
with L6 dark)

Genomict - A mixing of different petrologic stages of same composition (L3.8
and L6)

Regolith - Mixing of different compositions and/or petrologic stages with a
fine matrix at the surface of an asteroid, or moon, etc. Measurement of solar
radiation is involved to show surface exposure implying multiple events at
surface. (H3-6 Zag!)

Impact Melt - Large energy impacts causing great shock and mixing of materials
to create materials of different shades (darker material for melts). The
changing of minerals...olivine to spinel, etc. (Park Forest? L6 IMB ?)

The answer is yes about Ensisheim, I think...but when does a chondrite become
a breccia or even an impact melt breccia? And can there be just impact melts
(Chico L6 IM)...impact without brecciation????

That clears it up,

John

John
> Hello All,
>
> I was looking at my slice of Ensisheim, and it looks to me like there is
> little river of lighter material with some islands of darker breccia flowing
> through it?
>
> It sure looks like at least an melt breccia, but how else besides impact
> would a chondrite become melted?
>
> Here is a pic of what I am talking about:
>
> http://aristotle.isu.edu/ensisheim.jpg
>
> As before, the blue cube is 1cm^3.
>
> Cheers,
>
> Martin
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Received on Fri 25 Apr 2003 04:39:39 PM PDT