[meteorite-list] Portales Valley

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:01:31 2004
Message-ID: <3CFE7FEE.BF03AD65_at_lehrer1.rz.uni-karlsruhe.de>

Rhett Bourland wrote:

> My 8 cents

Hello Rhett and List,

Those 8 cents are well spent :-)

> I also know there are large sections of iron in this chondrite that are
> unlike any other meteorite out there. These large sections of irons will
> display a Widmanstatten like most iron meteorites when etched. To be able
> to form the necessary bands in the pattern would require that this meteorite
> was formed deep within the asteroid so that there would be plenty of
> insulation (in the form of rock) to keep the heat in the inside of the
> asteroid so that the kamacite and taenite would have the needed time
> to grow large enough to show up when etched.

> Early in the H parent body's history a pretty good sized impact happens
> on the H parent body. Its powerful enough to disrupt the asteroid to its
> center but not necessarily powerful enough to break up the asteroid.
> When it does this, some of the free metal in this region pools together
> to form the large metal veins.


KRING D.A., HILL D.H., GLEASON J.D., BRITT D.T. et al. (1999)
Portales Valley: A meteoritic sample of the brecciated and metal-veined
floor of an impact crater on an H-chondrite asteroid (MAPS 34-4, 1999,
663-669):

Summary of the authors' conclusions:

01) Portales Valley has unusually large veins of metal and pockets of
     metal produced by intersecting veins.

02) Provenance of these veins:

a) produced by an impact event on the original H-chondrite parent body,

or

b) a large asteroid produced from the fragmentation of that parent body.

03) Cooling rate about a few to perhaps tens of degrees per million
     years for the products of that shock metamorphism.

04) The meteorite was deep within the H-chondrite body at the time of
     the large impact event.

05) The crater diameter was >= 20 km in diameter (about 10% of the
     original H-chondrite parent body).

06) The impact event probably occurred about 4.4 or 4.5 Ga, soon after
     accretion from the solar nebula.


Best regards,

Bernd
Received on Wed 05 Jun 2002 05:17:34 PM PDT