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

From: MEM <mstreman53_at_meteoritecentral.com>
Date: Wed, 20 Mar 2013 19:45:47 -0700 (PDT)
Message-ID: <1363833947.61209.YahooMailNeo_at_web142401.mail.bf1.yahoo.com>

I can't speak to crystallization dates but I do have a theory about what one type of Veneusian or Mercurian meteorite might have petrologically speaking.? Because early mantles here on earth were 4-500? hotter than now, our early crust/mantle* was composed of a rock type called a "komatite"<http://en.wikipedia.org/wiki/Komatiite>? Komatite is very low in silica and theoretically washed over the crust like water in as shallow a dept of 10mm.?? Komatite is recognizable owing to its "spinafex texture"? This texture has acicular(needle-like) sprays of olivine? Some meta-komatites here on earth can have boughs of these extremely long yet thin olivine crystals(1m plus) dendritic chromite an sphericalclinopyrxene!.? Most of those early mantle extrusives/basalts have been recycled by weathering processes unlike those of Venus and Mercury which must have been left pertty much as they formed in a non-tectonic environment.


Now looking to images alleged to be from NWA 7325 <http://www.meteoritestudies.com/protected_NWA5790.HTM>? There is one view which approaches the description outwardly.

I haven't had an opportunity to research estimated mantle thermal histories - The inner planets should have been heated higher and lived in the komotite environment longer than we saw here on earth.? The link provided by Stephan regarding MESSENGER shows that there are several plots well within the basaltic komatite window. <http://www.sciencedirect.com/science/article/pii/S0012821X12007078>?


If anyone has the original classification paper--nakalite or not-- Please share.

Elton

* I call it "crust/mantle" because prior to weathering there wasn't much of a difference.

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.
>
Received on Wed 20 Mar 2013 10:45:47 PM PDT