[meteorite-list] Portales Valley: Not Just Another OrdinaryChondrite

From: moni Waiblinger-Seabridge <moni2555_at_meteoritecentral.com>
Date: Wed Oct 5 12:51:08 2005
Message-ID: <BAY103-F33B57F2EAA64FA4D312270CD820_at_phx.gbl>

Hi All,

I can see why this is confusing!
Wasn't there another meteorite where people had discussions of what kind of
meteorite it was?
Here in the US.
I can not remember which one.
Maybe Gold Basin and Hualapai Wash stones?

Sternengruss, Moni

>From: M come Meteorite Meteorites <mcomemeteorite2004_at_yahoo.it>
>To: Meteorite Mailing List <meteorite-list_at_meteoritecentral.com>
>Subject: Re: [meteorite-list] Portales Valley: Not Just Another
>OrdinaryChondrite
>Date: Wed, 5 Oct 2005 18:22:54 +0200 (CEST)
>
>Another....the probably H7, Metallic Melt Breccia
>(Primitive Achondrite) classification its for the
>pieces with metal veins...but for the normaly portales
>valley without any veins the classification its a H6?
>The matrix its paired to a normaly ordinary chondrite.
>
>Matteo
>
>--- Frank Cressy <fcressy_at_prodigy.net> ha scritto:
>
> > Matteo and all,
> >
> > I believe it is now classified as a "Metallic-melt
> > Meteorite Breccia".
> >
> > Cheers,
> > Frank
> >
> > M come Meteorite Meteorites
> > <mcomemeteorite2004_at_yahoo.it> wrote:
> > ok...in conclusion what new classification is
> > portales
> > valley?
> >
> > Matteo
> >
> > --- Ron Baalke ha
> > scritto:
> >
> > >
> > >
> >
>http://www.psrd.hawaii.edu/Sept05/PortalesValley.html
> > >
> > > Portales Valley: Not Just Another Ordinary
> > Chondrite
> > > Planetary Science Research Discoveries
> > > September 30, 2005
> > >
> > > --- A melted meteorite gives a snapshot of the
> > heat
> > > and shock that
> > > wracked an asteroid during the first stages of
> > > differentiation.
> > >
> > > Written by Alex Ruzicka and Melinda Hutson
> > > Department of Geology, Portland State University
> > >
> > > Soon after the Portales Valley meteorite fell in
> > > 1998, it was classified
> > > as one of the most common types of meteorites, an
> > H6
> > > ordinary chondrite.
> > > Although researchers quickly recognized that
> > > Portales Valley is not a
> > > typical H6 chondrite, there was little agreement
> > > about how the meteorite
> > > formed. A recent study of Portales Valley by
> > Ruzicka
> > > and colleagues
> > > suggests that the textures, mineralogy, and
> > > chemistry of the meteorite
> > > are best explained as the first good example of a
> > > metallic melt breccia.
> > > This meteorite represents a transitional stage
> > > between chondrites and
> > > various classes of differentiated meteorites, and
> > > offers clues as to
> > > how differentiation occurred in early-formed
> > > planetary bodies.
> > >
> > > Reference:
> > >
> > > * Ruzicka, A., Killgore, M., Mittlefehldt, D.W.
> > > and Fries, M.D
> > > (2005) Portales Valley: Petrology of a
> > > metallic-melt meteorite
> > > breccia. Meteoritics & Planetary Science, v. 40,
> > p.
> > > 261-295.
> > >
> > >
> >
>------------------------------------------------------------------------
> > >
> > > Differentiation: a widespread but
> > poorly-understood
> > > process
> > >
> > > Most solar system material underwent
> > > differentiation, a process
> > > involving melting and separation of liquids and
> > > solids of varying
> > > density and chemical composition. However,
> > > chondritic meteorites escaped
> > > this process and are believed to be pieces of
> > > undifferentiated
> > > asteroids. All other meteorites, and probably all
> > > rocks from planets and
> > > large moons, melted when the parent bodies
> > > differentiated to form cores,
> > > mantles, and crusts. The heat source for
> > > differentiation is uncertain,
> > > as are the exact physical processes and conditions
> > > that allowed
> > > differentiation to proceed in small planetary
> > bodies
> > > with weak gravity.
> > > Proposed sources of heat include
> > > internally-generated heat from
> > > short-lived radioactive materials such as
> > > aluminum-26 (26Al), external
> > > heating from our young active Sun, and heating
> > > resulting from collisions
> > > between planetary bodies (shock heating). A
> > detailed
> > > study of the
> > > Portales Valley meteorite suggests that
> > > differentiation of small
> > > planetary bodies involved a combination of an
> > > internal heat source and
> > > shock. Shock heating was not the major heat source
> > > involved in
> > > differentiation, but the stress waves associated
> > > with even modest shock
> > > events played a critical role in helping materials
> > > to separate and
> > > reconfigure during differentiation.
> > >
> > > illustration of differentiation by Granshaw
> > >
> > > A sequence of images showing stages in the
> > > differentiation of a
> > > planetesimal, an early-formed planetary body. The
> > > image in the left hand
> > > side shows a chondritic planetesimal becoming hot
> > > enough for melting to
> > > begin. The middle image shows that the heavier
> > > metallic liquid sinks
> > > toward the center, while the less dense rocky
> > > material rises toward the
> > > surface. The result is a differentiated object
> > with
> > > a crust, mantle and
> > > core, as shown in the image in the right hand
> > side.
> > > (Images created by
> > > Frank Granshaw of Artemis Software for the
> > Cascadia
> > > Meteorite
> > > Laboratory, Portland State University.)
> > >
> > >
> >
>------------------------------------------------------------------------
> > >
> > > Not an ordinary H6 ordinary chondrite
> > >
> > > Three features link Portales Valley to H-group
> > > ordinary chondrites.
> > > These are (1) the presence of rare chondrules with
> > a
> > > rather typical
> > > chondritic texture present in silicate-rich areas,
> > > (2) the compositions
> > > of most minerals, and (3) the
> > > bulk oxygen isotopic composition of the meteorite.
> > > Nonetheless, Portales
> > > Valley contains unusual features that distinguish
> > it
> > > from any other
> > > ordinary chondrite. Even in a cut section, the
> > > differences between
> > > Portales Valley and a typical H-chondrite are
> > > readily apparent (see
> > > figures below).
> > >
> > > comparison to H chondrite
> > >
> > > A comparison of a typical H-chondrite and Portales
> > > Valley. Bright areas
> > > are mainly metallic; dark areas are mainly
> > > silicates. Left: A slice of a
> > > meteorite that is paired with the Franconia (H5)
> > > chondritic meteorite.
> > > The small lines on the ruler are one millimeter
> > > apart. Right: A slice of
> > > the Portales Valley meteorite showing that the
> > > chondritic, silicate-rich
> > > material occurs as angular clasts floating in
> > > metallic veins. Tiny
> > > bright spots in silicate-rich clasts consist of
> > > troilite (FeS) and
> > > smaller amounts of fine-grained metal. A large
> > > graphite nodule is visible.
> > >
> > > Besides the obvious differences between Portales
> > > Valley and a typical H
> > > chondrite, Portales Valley is also unusual in
> > > several other ways. It is
> > > the only known ordinary chondrite that contains
> > > coarse (cm-sized)
> > > graphite nodules as well as metal that shows a
> > > Widmanstätten texture (an
> > > intergrowth of high- and low-Ni metal, see left
> > > image below), both of
> > > which are common in iron meteorites. Another
> > notable
> > > feature is that
> > > different sections of Portales Valley vary widely
> > in
> > > their proportion of
> > > metal, ranging from silicate-rich areas almost
> > > devoid of metal to areas
> >
>=== message truncated ===
>
>
>M come Meteorite - Matteo Chinellato
>Via Triestina 126/A - 30030 - TESSERA, VENEZIA, ITALY
>Email: mcomemeteorite2004_at_yahoo.it
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Received on Wed 05 Oct 2005 12:51:06 PM PDT