[meteorite-list] New Australian fall

From: cdtucson at cox.net <cdtucson_at_meteoritecentral.com>
Date: Sat, 19 Sep 2009 13:00:01 -0700
Message-ID: <20090919160001.9K92Y.268724.imail_at_fed1rmwml44>

Sterling,
This may not surprise you but, I did not know that aubrites plotted on the same oxygen slope line as Earth and our Moon.
Does this mean that Aubrites could possibly be meteorites from Earth? I believe it was decided earlier they would be called "terrane"meteorites?
Has this previously been discussed here on this list?
I ask because don't we also apply a lot of weight to oxygen isotopes in determining if rocks indeed came from Mars? Sort of like if the glove fits? Or if it don't fit, you must acquit?
Carl E.

--
Carl or Debbie Esparza
IMCA 5829
Meteoritemax
---- "Sterling K. Webb" <sterling_k_webb at sbcglobal.net> wrote: 
> Hi, Jason, List
> 
>     The word "eucrite" comes from the Greek
> and means "easily recognized." It was coined
> to describe terrestrial basalts and only later
> was it applied to meteorites, and to the most
> common of achondrites. It is no longer used
> for Earthly rocks.
> 
>     They are basalts from lava flows on the
> surface of a differentiated body. They're just
> ordinary basaltic rocks, only from somewhere
> other than Earth.
> 
>     The oxygen data is tricky. You plot the slope
> of the ratios of O17 or O18 to O16 for each rock.
> Those that land on the same slope are not always
> from the same body, because different bodies may
> have the same oxygen ratios.
> 
>     For example, aubrites and lunar achondrites
> plot on the terrestrial ratio slope, meaning that
> the Earth and the Moon and the Wherever-the-
> aubrites-came-from all have the SAME oxygen
> ratios. Eucrites from Vesta plot along a slope
> all their own.
> 
>     I assume what the reporter said of what Bland
> said meant that this eucrite does not plot on the
> Vestan slope. We have no idea of what slope it
> plots on; as is usual with press reports, there is
> no usable information in them. What slope did
> it plot on? Who knows? Bland does; we're guessing
> without data. If he knew the body it came from,
> it would be big news and he would have told it.
> Shouted it, actually...
> 
>     So, it is a basalt lava flow from the crust of
> SOME other body than Vesta or a Vestoid, but
> otherwise not known. It's a breccia with clasts
> so that body has an impact-altered surface. We
> have exsolution so it was (once) a big enough body
> to have cooled slowly.
> 
>     Equally vague and useless are the press release
> level comments about "inner solar system" orbits.
> Numbers are the only thing with meaning. Semi-major
> axis in AU, please, eccentricity, etc. NOT knocking
> the scientist speaking, only the reporter listening to
> stuff he knows nothing about. It's like sending your
> five-year-old to talk to your Congressman, and then
> come back and tell you what he said about health
> care reform. Meaningless. The "Scientific" American
> article is, if anything, more vague.
> 
>     The mention of Bottke and SWR studies probably
> means the study that showed that many members
> of the inner asteroid zone were tossed there from the
> very "inner" solar system, <0.5 AU, particularly the
> big iron asteroids. This little eucrite could be a chunk
> of the largely battered-away former crust of Mercury,
> for example. Put a lander on Mercury and measure
> the oxygen ratios and we'll know.
> 
>     As usual, too little data for ANY conclusion. The
> connection with the Bottke study is likely purely
> hypothetical. In other words, a guess. There's nothing
> you can say about nothing.
> 
> 
> Sterling K. Webb
> --------------------------------------------------------------------------
> ----- Original Message ----- 
> From: "Jason Utas" <meteoritekid at gmail.com>
> To: "Meteorite-list" <meteorite-list at meteoritecentral.com>
> Sent: Friday, September 18, 2009 8:45 PM
> Subject: Re: [meteorite-list] New Australian fall
> 
> 
> Good point; and seeing as such meteorites haven't been
> reclassified/re-typed, it seems as though this brings up a very valid
> flaw in the classification system of basaltic achondrites.  Perhaps
> there are some scientists out there who can shed some light on why
> meteorites such as these are called Eucrites when they are apparently
> from different parent bodies.  I'd be curious of the general
> scientific opinion of the current classification scheme; is it
> adequate or should there be more, if not classes, at least meteorites
> deemed 'ungrouped.'
> Jason
> 
> On Fri, Sep 18, 2009 at 6:37 PM, Michael Fowler <mqfowler at mac.com> 
> wrote:
> >> And in case you didn't check the met-bull, the Bunburra Rockhole
> >> meteorite has been classified as a typical Eucrite.
> >> He stated that said meteorite is not from Vesta, but Eucrites are
> >> widely accepted to have come from Vesta.
> >> I suppose we don't have solid proof of that yet, but it is generally
> >> accepted to be true, based on reflected light analyses.
> >> Go figure.
> >> Jason
> >
> > Hi Jason,
> >
> > Sorry if I ruffled your feathers earlier.
> >
> > I did check the met bulletin, and it is described as: " meteorite is a
> > basaltic eucrite monomict breccia "
> >
> > http://tin.er.usgs.gov/meteor/index.php?code=48653
> >
> > However I note that many meteorites are not correctly classified on 
> > their
> > first appearance in the Met Bul, including of course Ibitria, which is
> > still listed as a Eucrite Monomict, even though we know it is not from
> > Vesta,
> >
> > http://tin.er.usgs.gov/meteor/index.php?sea=ibitira&sfor=names&ants=&falls=&valids=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=All&mblist=All&rect=&phot=&snew=0&pnt=no&code=11993
> >
> > However back to, Bunburra Rockhole, can someone comment or whether the
> > mineral composition as stated in the met bul is consistent, or 
> > anomalous for
> > a eucrite?
> >
> > Mineral compositions: Pyroxene, Fs62.5Wo3.6 (Fe/Mn-31.1) with augite
> > (Fs27.7Wo43.0) lamellae; plagioclase, An84.1 to An88.2.
> >
> > Of course, the final word is probably the O isotope work, which Dr 
> > Bland
> > says has already been done, although I couldn't find any additional
> > reference.
> >
> > Thanks,
> >
> > Mike
> >
> >
> >
> >
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Received on Sat 19 Sep 2009 04:00:01 PM PDT


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