[meteorite-list] AD - Do you want a rareandimportantMetachondrite?

From: Jeff Kuyken <info_at_meteoritecentral.com>
Date: Wed Sep 28 20:57:16 2005
Message-ID: <006901c5c490$c1bcd580$96598b90_at_mandin4f89ypwu>

Hi List,

>The difference in oxygen records from other acapulcoites
>may be due to terrestrial alteration as the sample of
>NWA 1058 examined by us was substantially weathered (W3).

This is interesting as I've never heard this before. Can terrestrial
weathering really have a significant effect on oxygen results?

Thanks,

Jeff


----- Original Message -----
From: M come Meteorite Meteorites
To: Meteorite List
Sent: Thursday, September 29, 2005 5:03 AM
Subject: Re: [meteorite-list] AD - Do you want a
rareandimportantMetachondrite?


mmmmmm.....and why Andrea PATZER, Dolores H. HILL, and
William V. BOYNTON in the Evolution and classification
of acapulcoites and lodranites
from a chemical point of view say NWA 1058 its a
acapulcoite?

A detailed petrographic description was not available
at
the time this work was carried out. We, therefore,
include an
abbreviated description of its petrography and
mineralogical
composition. Interestingly, we found its texture and
composition to be similar to that of GRA 98028 and,
therefore, categorize it with the acapulcoites. The
difference
in oxygen records from other acapulcoites may be due
to
terrestrial alteration as the sample of NWA 1058
examined by
us was substantially weathered (W3).

NWA 1058

The petrographic investigation of NWA 1058 suggests
that this meteorite may belong to the group of
primitive
acapulcoites. Principally, its bulk elemental
composition
supports this assessment (Fig. 9). The lithophile
elements
show mostly ? chondritic concentrations. The
abundances of
siderophiles scatter around 2 ? CI. We encounter a
difference
from the primitive acapulcoite GRA 98028 only with
respect
to the contents of Sb, Se, and Zn. As a diagnostic
property,
GRA 98028 contains chondritic abundances of Sb and Se
and
considerably depleted Zn. NWA 1058 also reveals a
clear
fractionation of Se and Zn. However, its Se/Zn ratio
is even
~5? higher than that detected for GRA 98028. In
addition,
and more importantly, NWA 1058 exhibits a slight
depletion
of Se (~0.8 ? CI) and a low Sb concentration (~0.5 ?
CI). The
Sb value, especially, falls close to those determined
for the
typical acapulcoites (~0.4 ? CI). However, melting at
the Fe-
Ni-S eutectic and the extraction of sulfide phases as
experienced by the typical acapulcoites are primarily
indicated by clear depletions of Se (~0.3 ? CI). The
Se
concentration of NWA 1058 plots closer to the
chondritic
value. Therefore, we classify NWA 1058 as a primitive
acapulcoite with affinities to the typical
acapulcoites.


Matteo

--- David Weir <dgweir_at_earthlink.net> ha scritto:

> It's all according to which researcher you believe
> has it right. My
> webpage contains many of the disparate opinions, but
> I now believe the
> preponderance of the evidence points to the
> following:
>
> NWA 1058 is a chondrite, containing chondrules or
> relicts thereof, which
> originated within the regolith of the winonaite/IAB
> iron parent body.
> The term metachondrite is a particularly useful
> descriptor in this case.
>
> David
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list_at_meteoritecentral.com
>
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>


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Received on Wed 28 Sep 2005 08:57:21 PM PDT