[meteorite-list] NWA 7325 - Mercurian or not?

From: Gary Fujihara <fujmon_at_meteoritecentral.com>
Date: Wed, 20 Mar 2013 09:02:05 -1000
Message-ID: <22DE1CE1-A7B7-4389-8D06-CBBBBCFCEA59_at_mac.com>

Mahalo Melinda for your recap of discussions regarding NWA 7325 at LPSC. It is of great benefit to me and others who cannot attend, but are interested in this meeting's proceedings in general, and of meteoritical topics in particular.

gary

On Mar 20, 2013, at 8:36 AM, Melinda Hutson <mhutson at pdx.edu> wrote:

> Tony Irving has presented an abstract at the Lunar and Planetary
> Science Conference, describing NWA 7325 and suggesting it MAY be
> Mercurian. Chemically speaking, NWA 7325 is more plausible than
> the angrites (which Tony argued were Mercurian a few years ago) as a
> meteorite from Mercury, although there are some apparent mismatches.
> During the Q & A, Tim McCoy got up and argued the "con" position,
> stating that there are other more likely origins for this unusual
> meteorite. One big problem is the apparent crystallization age.
> There is some preliminary data (and I didn't get the isotopic system)
> suggesting the rock formed from a melt 4.5 billion years ago. That
> argues against Mercury and for an asteroidal parent body. McSween and
> others used the young crystallization ages of the SNC meteorites to
> argue they were Martian before we had proof in the form of trapped
> Martian atmosphere. Mercury is larger than the Moon, and its surface
> looks somewhat younger than the older portions of the Moon. Rocks
> from the Moon do not have the 4.5 billion year old crystallization
> ages we see in asteroidal samples. Highlands rocks are generally
> 4.2-4.3 billion years old, and maria samples are distinctly younger.
> There is one old lunar rock, but the error bars are large on that
> date. Mercurian rocks should have crystallized at or later than lunar
> highland rocks, and definitely later than asteroidal. So maybe
> somewhere in the 4-4.3 billion year range would be expected.
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Gary Fujihara
Big Kahuna Meteorites
PO Box 4175, Hilo, HI 96720
(808) 640-9161
http://bigkahuna-meteorites.com/
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Received on Wed 20 Mar 2013 03:02:05 PM PDT