[meteorite-list] Estherville Mesosiderite

From: tracy latimer <daistiho_at_meteoritecentral.com>
Date: Wed May 5 15:00:29 2004
Message-ID: <Sea2-F38qjBEde3sswK0000593c_at_hotmail.com>

Hi, all!
Well this is a pretty kettle of fish! Most of the mesosiderites I have seen
are like Estherville, save that I don't recall any with such nice olivine
crystals, where the metallic component is arranged in a substantial web
through the rocky matrix, but is irregular in distribution, with somewhat
diffuse edges (blobby). Then you have anomalies like Portales Valley, where
the metal in larger pieces is in distinct veins with sharp edges.

We already assume that pallasites are from the core-mantle boundaries of
asteroids large enough to have undergone differentiation at one point in
their lives (before being turned into specimens in our collections!) What
other theories for the formation of mesosiderites, besides the mashing
together of a pallasite body and another rocky body, allow for the
incorporation of the occasional rogue olivine crystal? (Hmmmm, must consider
getting a piece of Estherville, if only for my personal edification...)

On a side note, how many meteorites incorporate dunite as part of their
makeup? The only place I remember hearing about dunite previously was in
Chassigny, since Chassigny is a Martian example of what would be called a
dunite on Earth.

Please forgive my ignorance, and thank you everyone who is willing to help
me fix that problem.
Tracy Latimer


>
>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)."
>

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Received on Wed 05 May 2004 03:00:23 PM PDT