[meteorite-list] NWA 5400: Earth-Related Meteorite

From: Alan Rubin <aerubin_at_meteoritecentral.com>
Date: Thu, 10 Jun 2010 10:15:33 -0700
Message-ID: <EDF9DB83C644455FA266094E77EBBC25_at_igpp.ucla.edu>

        Oxygen isotopes are a good classificatory parameter. Silicate
inclusions within irons have been analyzed for O isotopes and in some cases,
seem to point to particular chondrite groups as possible progenitors of the
irons (e.g., IIE irons and H chondrites; the Guin iron and L or LL
chondrites; IAB irons and winonaites). [I know winonaites are not
chondrites, but they are chondritic in bulk composition.] Enstatite
chondrites and aubrites are not alike texturally, but they are similar in
mineralogy and both have the same O-isotopic compositions. We don't know
that Earth and chondrites are unrelated. The Earth accreted from chondritic
planetesimals and/or from differentiated planetesimals that were themselves
initially chondritic. It derived its original O-isotopic composition from
the average of these accreting bodies (which melted and homogenized).

        Because meteorites have a large range in O-isotopic compositions and
presumably were derived from different regions of the solar system, many
researchers believe that there were "reservoirs" in the solar system that
had distinct O-isotopic compositions. Materials derived from a particular
reservoir are assumed to have formed in relatively close proximity. Of
course, we don't know how big these reservoirs were, or even if they really
existed. As far as the Moon is concerned, there are several possibilities
allowed even if we accept the impact-derivation hypothesis. The Mars-size
impactor could have formed near the Earth and thus had the same O-isotopic
composition to begin with. Thus, the Moon would end up with the same
O-isotopic composition as Earth and the impactor regardless of how much
material was derived from each body. Alternatively, the impactor had a
different O-isotopic composition than the Earth and that this enormous
impact caused mixing of the materials; in that event, the Earth and Moon may
be homogenized mixtures of two initially distinct O-isotopic compositions.

Alan Rubin
Institute of Geophysics and Planetary Physics
University of California
Los Angeles, CA 90095-1567
phone: 310-825-3202
e-mail: aerubin at ucla.edu
website: http://cosmochemists.igpp.ucla.edu/Rubin.html


----- Original Message -----
From: <cdtucson at cox.net>
To: <meteorite-list at meteoritecentral.com>; "Greg Hupe" <gmhupe at htn.net>;
"Richard Kowalski" <damoclid at yahoo.com>; "Alan Rubin" <aerubin at ucla.edu>;
"Stuart McDaniel - Action Shooting Supply" <actionshooting at carolina.rr.com>
Sent: Thursday, June 10, 2010 9:54 AM
Subject: Re: [meteorite-list] NWA 5400: Earth-Related Meteorite


> Alan, Sterling, list,
> Thank you for these very informative reviews.
> There are three things that still puzzle me. One is the lack of
> Plagioclase. Neither you or Sterling mentioned it.
> It seems to me anything even remotely related to the Earth-Moon should
> have plagioclase.
> The second question I have is: wouldn't this meteorite have a combination
> of O-isotopes between the impactor and the impactee? and not match Earth?
> This seems to be the same problem I have believing the Moon was caused by
> a collision with Theia.
> What are the odds of Theia having the same O-isotopes as Earth? Which
> would have to be the case in order for the Earth-Moon O-isotopes to match
> each other. Wouldn't it?
> And the third question is;
> Knowing what we know about O-isotopes and how even enstatite chondrites
> and a few other types including at least one iron match that of Earth. Why
> do we place so much importance on O-isotopes. I mean surely we know
> chondrites and Earth are not related and yet they sometimes have the same
> O-isotopes. Doesn't that tell us that O-isotopes are not definitive of
> anything? And therefore useless in determining origin? Or at least
> semi-useless.
> Seriously. How is it that we ignore this fact?
> Seems to me if we know for a fact that these things are not related
> because of lithology differences. What makes us think O-isotopes amount to
> anything more than a simple observation?
> Carl
> --
> Carl or Debbie Esparza
> Meteoritemax
>
>
> ---- Alan Rubin <aerubin at ucla.edu> wrote:
>> I think that the speculation is getting way out of hand. It seems very
>> unlikely to me that the meteorite is a piece of Earth, proto-Earth or of
>> the
>> Mars-size planet that is inferred to have smacked the Earth 4.5 billion
>> years ago to form the Moon. The meteorite has a basically chondritic
>> bulk
>> composition and, prior to terrestrial weathering, had fresh metal. It is
>> therefore probably not from a differentiated body. The only chondrites
>> we
>> know that have terrestrial-like O-isotope compositions are enstatite
>> chondrites and CI chondrites. CI chondrites are essentially all matrix
>> and
>> are probably unrelated to NWA 5400. And, of course, enstatite chondrites
>> are far more reduced than NWA 5400. Nevertheless, at least one enstatite
>> chondrite has been oxidized after having been impact-heated and partly
>> melted in proximity to oxidized material. That would be Galim. I
>> haven't
>> studied NWA 5400 (although I would like to), but I'm guessing that its
>> origin is more likely to be that of an enstatite chondrite that was
>> altered
>> by aqueous fluids and impacts than as some early progenitor of Earth.
>>
>>
>> Alan Rubin
>> Institute of Geophysics and Planetary Physics
>> University of California
>> Los Angeles, CA 90095-1567
>> phone: 310-825-3202
>> e-mail: aerubin at ucla.edu
>> website: http://cosmochemists.igpp.ucla.edu/Rubin.html
>>
>>
>> ----- Original Message -----
>> From: "Richard Kowalski" <damoclid at yahoo.com>
>> To: "Greg Hupe" <gmhupe at htn.net>; <meteorite-list at meteoritecentral.com>;
>> "Stuart McDaniel - Action Shooting Supply"
>> <actionshooting at carolina.rr.com>
>> Sent: Wednesday, June 09, 2010 8:34 PM
>> Subject: Re: [meteorite-list] NWA 5400: Earth-Related Meteorite
>>
>>
>> >I don't want to speak for Greg, but yes, that is one possible origin.
>> > It could be from the proto-Earth, the Mars sized impactor that stuck
>> > the
>> > proto-Earth, (this is the impact that formed the moon) or the remnants
>> > of
>> > that event.
>> >
>> > No matter which, it is an awesomely exciting meteorite!
>> >
>> > --
>> > Richard Kowalski
>> > Full Moon Photography
>> > IMCA #1081
>> >
>> >
>> > --- On Wed, 6/9/10, Stuart McDaniel - Action Shooting Supply
>> > <actionshooting at carolina.rr.com> wrote:
>> >
>> >> From: Stuart McDaniel - Action Shooting Supply
>> >> <actionshooting at carolina.rr.com>
>> >> Subject: Re: [meteorite-list] NWA 5400: Earth-Related Meteorite
>> >> To: "Greg Hupe" <gmhupe at htn.net>, meteorite-list at meteoritecentral.com
>> >> Date: Wednesday, June 9, 2010, 5:30 PM
>> >> So this could be a piece of Earth
>> >> before Earth was Earth??
>> >>
>> >>
>> >> Stuart McDaniel
>> >> Lawndale, NC
>> >> Secr., CCAS
>> >> ----- Original Message ----- From: "Greg Hupe" <gmhupe at htn.net>
>> >> To: <meteorite-list at meteoritecentral.com>
>> >> Sent: Tuesday, June 08, 2010 7:31 PM
>> >> Subject: [meteorite-list] NWA 5400: Earth-Related
>> >> Meteorite
>> >>
>> >>
>> >> > Dear List Members,
>> >> >
>> >> > I would like to announce an important new meteorite
>> >> that has been under intense analysis over the last two years
>> >> by a select group of scientists from around the world...
>> >> >
>> >> > NWA 5400: Earth-Related Ungrouped Meteorite
>> >> >
>> >> >
>> >> > Northwest Africa 5400 may be a sample from a large
>> >> asteroid or dwarf planet, which accreted in the early solar
>> >> nebula in the vicinity of proto-Earth or Theia. NWA 5400 has
>> >> oxygen isotope ratios indistinguishable from those of rocks
>> >> from the Earth and the Moon, which plot on the TFL
>> >> (Terrestrial Fractionation Line). A precise formation age
>> >> has not yet been measured, but it cannot be older than 4.54
>> >> billion years, which likely makes NWA 5400 anomalously young
>> >> among primitive achondritic objects from the early Solar
>> >> System. It is generally accepted that the Earth-Moon system
>> >> was created when Theia collided with proto-Earth about 4.3
>> >> billion years ago. Is it possible that NWA 5400 is somehow
>> >> related to this phenomenal event?
>> >> >
>> >> >
>> >> >
>> >> > NWA 5400 adds valuable understanding of events that
>> >> took place in the early evolution period of the Solar
>> >> System. After two years of intense analysis, scientists at
>> >> prominent institutions from around the world continue to
>> >> diligently study this 'stand-alone' meteorite, which will
>> >> add to the already incredible information NWA 5400 has to
>> >> offer.
>> >> >
>> >> >
>> >> >
>> >> > Link to 2009 LPSC abstract on NWA 5400:
>> >> >
>> >> > http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2332.pdf
>> >> >
>> >> >
>> >> >
>> >> > Link to 2010 LPSC abstract on NWA 5400:
>> >> >
>> >> > http://www.lpi.usra.edu/meetings/lpsc2010/pdf/1492.pdf
>> >> >
>> >> >
>> >> >
>> >> > NWA 5400 has a Total Known Weight of 4.818 kg in a
>> >> single stone that was discovered in Northwest Africa in
>> >> 2008. The chocolate-brown mottled matrix takes an extremely
>> >> nice polish, which reveals the dazzling olivine crystals
>> >> exhibited in this scientifically important new meteorite!
>> >> >
>> >> >
>> >> >
>> >> > Cross-polarized light optical thin section image of
>> >> NWA 5400 (width of field = 1.2mm):
>> >> >
>> >> > http://www.lunarrock.com/NWA5400/nwa5400xpl.jpg
>> >> >
>> >> >
>> >> >
>> >> > Image of 58.9-gram complete slice with hologram-like
>> >> olivine crystals that dance across the polished surface when
>> >> tilted from side to side:
>> >> >
>> >> > http://www.lunarrock.com/NWA5400/nwa5400slice.jpg
>> >> >
>> >> >
>> >> > Best regards,
>> >> > Greg
>> >> >
>> >> > ====================
>> >> > Greg Hupe
>> >> > The Hupe Collection
>> >> > NaturesVault (eBay)
>> >> > gmhupe at htn.net
>> >> > www.LunarRock.com
>> >> > IMCA 3163
>> >> > ====================
>> >> > Click here for my current eBay auctions:
>> >> > http://search.ebay.com/_W0QQsassZnaturesvault
>> >> >
>> >> > ______________________________________________
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>> >> >
>> >>
>> >>
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>> >
>> >
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Received on Thu 10 Jun 2010 01:15:33 PM PDT