[meteorite-list] Estherville Mesosiderite

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Wed May 5 13:20:08 2004
Message-ID: <DIIE.0000001A0000213A_at_paulinet.de>

Hello Anne, Adam, Dave, Mark and List,

> quite a few vesicles in the darker ?melt? pockets some of them quite
> big bubbles, what are the implications for this? Does this mean it's just
> odd impact melt or would you normally expect vesicles on a core-mantle
> sample??

My 5.6-gram Estherville slice shows such vesicular areas too. Maybe they
originated when the differentiated parent body of the mesosiderites was
disrupted and reaccreted. These vesicles may have been created when
the hot and cold clasts, breccias, and melts of the Estherville mesosiderite
were thermally equlilibrated. This may also have happened during later
catastrophic events. See David Weir's website for excellent details!

> from the crust of an achondrite body. What is noticeably
> missing from the mesosiderites is olivine..."

Well, this is obviously untrue as most mesosiderites have at least
minor amounts of olivine. Estherville is known to even have more
olivine than the average mesosiderite.

> Well, I have a 180+ thick slice of Estherville and I can assure you
> that there are olivine xls present - you can shine a torch thru them!

This would solve a long-standing problem of the impact origin theory:
If the mesosiderites really represent material from the mantle of a
differentiated, there should be much more olivine!
 
> So I would like to assume that a mesosiderite is not a core-mantle
> sample (like a Pallasite) but the smushed up surface of a well pounded
> asteroid.

On the other hand: while the abundance of pyroxene and plagioclase should
be lower in surficial material, it actually shows twofold enrichments relative to
ordinary chondrites.

Mittlefehldt (1980) states that "olivine may be much more abundant in some multi-
kilogram samples as centimeter-sized olivine clasts appear to be relatively common
in several mesosiderites and Mount Padbury contains olivine crystals and dunite clasts
that are 10 cm in length (McCall, 1966)."

Best wishes,

Bernd
Received on Wed 05 May 2004 01:20:06 PM PDT