[meteorite-list] Chelyabinsk - IMB or SMB? The nomenclature of Melts.

From: Jeff Kuyken <info_at_meteoritecentral.com>
Date: Thu, 25 Apr 2013 12:53:19 +1000
Message-ID: <000901ce4160$0cd2a3c0$2677eb40$_at_meteorites.com.au>

Definitely IMB although you will find variations within different stones.
Some will be shocked to the point of melt and others will not quite get
there. Personally I think IMB and SMB are the exact same terms as both are
"melt breccias" and shock is derived from impact.

The official classification of Chely states: "A significant portion (1/3) of
the stones consist of a dark, fine-grained impact melt containing mineral
and chondrule fragments."

http://www.lpi.usra.edu/meteor/metbull.php?code=57165

I personally don't think "nodules" is really the correct terminology either.
They are just individuals / fragments of the same material shocked to a
higher degree in the parent body. For example... compare it to Gao. We don't
call the IMB pieces, nodules. They are IMB individuals. The term "nodules"
would seem to me to be better reserved for things like "iron nodules" in a
stony Mesosiderite or a "Troilite nodule" in an iron meteorite.

Good question Mike.

Cheers,

Jeff

-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of Galactic
Stone & Ironworks
Sent: Thursday, 25 April 2013 10:42 AM
To: Meteorite List
Subject: [meteorite-list] Chelyabinsk - IMB or SMB? The nomenclature of
Melts.

Hi List,

We keep hearing about the "IMB nodules" that have been recovered -
these have an all-black lithology with no chondrules, shock veins, or
grey matrix material.

However, these nodules were not created on impact. Had there been
such an impact, we would have a visible crater and the nodules would
be located in a radius directly adjacent to the crater amidst the
ejecta. Instead, these nodules were apparently created during the
fragmentation events that took place while the body was still in
atmospheric flight.

If this is true, shouldn't these nodules be called "shock melt" and
not "impact melt" ?

Is there any distinction in the official nomenclature between an
impact melt and a shock melt?

Is it correct to continue using IMB in reference to these Chelyabinsk
specimens?

Best regards,

MikeG

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Received on Wed 24 Apr 2013 10:53:19 PM PDT