Wow... thanks for all of those references and for the info below Jason. And
thanks also to everyone else who replied both on and off list with their
helpful input.
It's very much appreciated!
Thanks,
Jeff
----- Original Message -----
From: "Jason Utas" <[email protected]>
To: "Meteorite-list" <[email protected]>; "Jeff Kuyken"
<[email protected]>
Sent: Tuesday, July 20, 2010 1:54 PM
Subject: Re: [meteorite-list] Acapulcoite/Lodranite Parent-body
Hello Jeff,
There is a great deal of literature online that addresses this topic
-- in addition to the McCoy research.
The general consensus is that the Acapulcoite/Lodranite parent body
was heterogeneously metamorphosed (impact-melted or
partially-differentiated, depending on which paper you read) and was
then largely broken up by an impact(s) nearly 4.6 billion years ago.
Lodranites and Acapulcoites have been differentiated in the past
almost solely based on structural observations/grain size.
The trouble is that the cutoff between the two has traditionally been
determined by grain size and is not clearly defined - check out the
discussion section of this paper (also in the list of sources below)
for a good summary:
http://www.lpi.usra.edu/meetings/LPSC98/pdf/1237.pdf
Here's the meat of it:
"Acapulcoites experienced only low degrees of Fe,Ni-
FeS cotectic melting and have maintained essentially
chondritic troilite and plagioclase abundances, whereas
lodranites experienced higher degrees of melting that
included partial silicate melting with subsequent loss of
troilite and/or plagioclase fractions."
If you keep reading through the discussion, you'll find that the
authors call at least a few of McCoy's analyses into question because
they haven't been as mineralogically metamorphosed as their large
grain size would seemingly suggest. In other words, they're
"large-grained acapulcoites." Or maybe they're transitional. It just
depends on how you want to break things up.
It's another example of how meteoritics is still a science begging for
a better classification system. Do we use the degree of metamorphosis
or grain size to determine the class?
Who knows...
Here are some related docs about the classes and parent body - the
first one [ending with 1237.pdf] was the one I noted above:
http://www.lpi.usra.edu/meetings/LPSC98/pdf/1237.pdf
http://www.lpi.usra.edu/meetings/metsoc97/pdf/5200.pdf
http://aaa.wustl.edu/Work/pub_files/acapulcoite_lodranite.html
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V66-3SVR613-1M&_user=10&_coverDate=02%2F28%2F1997&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=eaea4c9e7fbd30d2ba053bedb0883412
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060024503_2006090520.pdf
http://adsabs.harvard.edu/abs/2009M%26PS...44.1151C
http://cat.inist.fr/?aModele=afficheN&cpsidt=16823360
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-45FCNK6-5&_user=10&_coverDate=11%2F30%2F2000&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=7f6c0ded981b140af26e95baafd2d055
http://www4.nau.edu/meteorite/Meteorite/Book-PrimitiveAchond.html
Regards,
Jason Utas
On Mon, Jul 19, 2010 at 8:15 PM, al mitt <[email protected]> wrote:
Hi Jeff,
Here is what McSween has to say about these two classes. Distinct in
appearance but form a coherent group with continuously varying
characteristics. They share simular mineralogies, both being composed
largely of olivine and pyroxene, with minor plagioclase, iron-nickel
metal,
and troilite. They have similar oxygen isotopic composition, however they
don't define a clear mass-fractionation line.
He states that Tim McCoy and colleges shown that the acapuloite-lodranite
achondites represent sesidues from varying degrees of partial melting of
chondrites, ranging from less than 1% to as great as 25%. It is thought
that
the lodranite material formed deeper in the parent body, and rising melts
generated from them passed through fractures in the overlying acapulites
on
the way to the surface.
An age of 4.56 billion years has been determained for the
Acapulco-lodranite
parent body from percise lead isotop chronometer. Partial melting occured
shortly after accretion.
Spectra of acapulcoites are similar to those of ordinary chondrites and
lodranites have spectra similar to a variety of "S" subtype asteroids,
suggestions include S(III), S(IV), and S(V) depending on the amount of
melt
extracted.
--AL Mitterling
----- Original Message ----- From: "Jeff Kuyken"
To: "Meteorite List"
Sent: Monday, July 19, 2010 7:23 AM
Subject: [meteorite-list] Acapulcoite/Lodranite Parent-body
Hi all,
Does anyone know enough about the Acapulcoite/Lodranite Parent-body to
know what the main differences between the classifications are? Is it
just
the grain size or is there a composition difference etc too? Any paper
references would be appreciated.
Thanks,
Jeff
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