[meteorite-list] Silicated Iron vs. Winonaite (Part 2)

From: cdtucson at cox.net <cdtucson_at_meteoritecentral.com>
Date: Mon, 29 Mar 2010 13:43:58 -0400
Message-ID: <20100329134358.ORVR7.264098.imail_at_fed1rmwml45>

Bernd, All,
Thank you for this info brend. Glad you are back.
This is very interesting. It is yet another case where O-isotopes rule!
Even though by definition these Winonaites are the same as silicated irons, the O-Isotopes move them up to a higher status as Winonaites.
This was also done on the very unique meteorite Graves Nunatak 06128 and 06129. (GRA 06128 and 9).These were determined to be Brachinites based on their O-isotopes as well. Even though they had nothing else in common with other Brachinites or any other meteorite yet known.

http://www.psrd.hawaii.edu/Feb09/asteroidalMagmas.html

Furthermore this info seems to suggest that since there are winonaites without any silicate material IAB Irons, then there should also be Winonaites devoid of iron?
So, Question here . Are there any known Winonaites without the IAB metal phase?
In addition this variation in silicate and metal would also seem to significantly change the average Specific gravity of these rocks. So, a specific gravity test might tell us something even prior to cutting and looking inside. More metal would raise the density more silicate would lower the density.

--
Carl or Debbie Esparza
Meteoritemax
---- bernd.pauli at paulinet.de wrote: 
> Hello again Jeff, Jason, and List!
> 
> Further, more specific information culled from the Benedix et al.
> article in MAPS about IAB, IIICD inclusions and winonaites.
> 
> Cheers,
> 
> Bernd
> 
> ------------------------------------------------------------------------------------
> 
> BENEDIX G.K. et al. (2000) A petrologic study of the IAB iron meteorites:
> Constraints on the formation of the IAB-Winonaite parent body
> (MAPS 35-6, 2000, pp. 1127-1141):
> 
> 1) most IAB and IIICD inclusions are roughly chondritic in mineralogy and composition
> 
> 2) most IAB and IIICD inclusions have nonchondritic, recrystallized textures,
>    similar to winonaites in O-isotopic and mineral compositions
> 
> 3) seemingly contradictory presence of relatively primitive silicate inclusions embedded
>    in dense metal that was presumably molten at the time of mixing
> 
> 4) three models for the formation of these inclusions:
> 
>    - formation by impact-induced large-scale selective melting and
>      mixing in the megaregoliths on a chondritic parent body
> 
>    - formation by parent-body-wide partial melting and fractional
>      crystallization during formation of a S-rich core
> 
>    - inhomogeneous segregation of silicates and metal
> 
> 5) petrologic, textural, and isotopic evidence suggest formation from heterogeneous chondritic
>    precursor materials by partial melting, brecciation, and metamorphism (Benedix et al., 1998).
> 
> 6) mineralogies and mineral compositions of silicates overlap between
>    winonaites and silicate inclusions in IAB iron meteorites
> 
> 7) most textures of the IAB and IIICD chondritic clasts
>    are nearly identical to the textures of winonaites
> 
> 8) different cosmic-ray exposure ages for winonaites (0.02-0.08 Ga) and IAB iron
>    meteorites (0.4-1.0 Ga) reflect liberation from the parent body in different events.
> 
> 9) same parent body for IAB iron-winonaite meteorites *and* IIICD iron meteorites?
> 
>    - oxygen-isotopic compositions of silicates from inclusions in IAB and
>      IIICD iron and winonaite meteorites are essentially indistinguishable
> 
>    - inclusions broadly similar in mineralogy to those in IIICD iron
>      meteorites are found among the IAB iron-winonaite meteorites
> 
> But important differences exist in mineral compositions:
> 
>    - higher Fs contents of the pyroxene compositions of inclusions in IIICD meteorites
>    - plagioclase compositions more albitic* than those in IAB iron-winonaite meteorites
> 
> *albite = the sodium end-member of the plagioclase series (NaAlSi3O8).
>   anorthite = the calcium end-member of the plagioclase series (CaAl2Si2O8).
> 
> Benedix et al. state there is a strong link between IAB iron and winonaite meteorites
> but question such a strong link exists between IAB iron and winonaite meteorites and
> IIICD iron meteorites.
> 
> But they also advise caution because these apparent differences might simply be
> sampling biases so that further recoveries of additional meteorites are necessary
> to exlude or include the IIICD iron meteorites.
> 
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Received on Mon 29 Mar 2010 01:43:58 PM PDT