[meteorite-list] GRA 06128/9 = brachinite

From: Randy Korotev <korotev_at_meteoritecentral.com>
Date: Thu, 28 Feb 2008 10:18:39 -0600
Message-ID: <200802281618.m1SGIKY06238_at_levee.wustl.edu>

The confusion here is that the original O-isotope data, the data
published in the original announcement, are NOT consistent with
brachinites, whereas newer data in the Rumble et al. abstract (#1974)
and Zeigler et al. (#2456) abstract that Adam mentions below ARE
consistent with brachinites.

One of several peculiar things about GRA 06128/9 is a high abundance
of calcium phosphate minerals (chlorapatite, Na-merrillite) that are
heterogeneously scattered about the stones. The original
announcement did not mention these, apparently because there were no
phosphates in the thin sections first examined. As I understand it,
high phosphate abundance can cause an error in oxygen isotope
measurements if the sample is not first treated properly. The sample
analyzed by Doug Rumble for abstracts #1974 & #2456 was treated with
acid to dissolve the phosphates, so we think the resulting O isotope
data are more accurate. Of the various abstracts about this
meteorite, only the two mentioned in Adam's message below had access
to Doug Rumble's new-and-improved data, so these are the only two
that make the brachinite connection.*

Earth's moon has a feldspathic crust because feldspar floated to the
top of the lunar magma ocean after much of the olivine and pyroxene
crystallized and sunk. We argue in Zeigler et al. that GRA 06128/9
is from the heretofore unseen feldspathic (oligoclase) crust
("flotation cumulate") of the brachinite parent body.

To me, the lesson for finders and collectors is that had this
meteorite not had a fusion crust, only the most astute would have
recognized it as a meteorite, given the bizarre mineralogy.

Randy Korotev


* For scientists, the Lunar & Planetary Science Conference and the
Annual Meeting of the Meteoritical Society are the equivalent of the
Tucson G&M Show. We keep our little secrets to ourselves until we
submit the abstracts so that we can scoop our colleagues.



At 23:52 27-02-08 Wednesday, you wrote:
>Hi Sterling and List,
>
>This abstract clearly states that GRA 06128/9 oxygen
>isotopes plot with the Brachinites:
>
>http://www.lpi.usra.edu/meetings/lpsc2008/pdf/2456.pdf
>
>This abstract actually has a nice plot clearly showing
>GRA 06128/9 plotting dead center with the Brachinites:
>
>http://www.lpi.usra.edu/meetings/lpsc2008/pdf/1974.pdf
>
>I understand that the mineralogy is different from
>Brachinites, but its parent body group been identified
>as far as I am concerned.
>
>NWA 3133 was instrumental in demonstrating that
>finding groups for orphaned stones using oxygen
>isotope plotting for parent-body provenance purposes
>is feasible. This is the only reason why I can see the
>metachondrite issue coming up in the case of GRA
>06128/9 which seems to be more evolved. A neat stone,
>yes, but the outrageous claims that it is more
>fantastic than other equally interesting meteorites
>holds no water with me. Whatever is claimed for the
>parent body for this stone also applies to
>Brachinites.
>
>Just my thoughts,
>
>Best Regards,
>
>Adam
>
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Received on Thu 28 Feb 2008 11:18:39 AM PST