[meteorite-list] Irons and fusion crusts

[MexicoDoug]

Hi Gary,

Nice discussion!

I think there is a big difference between "fusion crust" for irons and just
a "thermally altered zone".

Fusion requires the crust to have been "fused".  At velocities over 3 km/s
the fusing material is the same material that is ablating, and as we know
very little remains stuck in flight.  (However a great amount can flow -
just look at aerodynamically sculpted iron meteorites!)  After slowing or
stopping some of the ablation melt is left and solidifies.  Thermal
alteration has never flowed to these high degrees and that is how I'd split
hairs; some level of structure is maintained at some levels - unlike the
ablativly free flowing fusion crust.

A while back when David Weir and I participated in this conservation, and
David posted a nice cross-section of a "typical" iron meteorite fusion
crust.  You can search the archives for the link if you don't have it.  It
was maybe two months ago?

Best health,
Doug

----- Original Message -----
From: "Gary K. Foote" <gary at webbers.com>
To: "Phil Morgan" <pkmorgan at ctcweb.net>;
<meteorite-list at meteoritecentral.com>
Sent: Monday, January 15, 2007 8:11 PM
Subject: Re: [meteorite-list] Irons and fusion crusts


> Hi Phil,
>
> I don't mean to split hairs, but what is the difference between a thermal
alteration zone
> and a fusion crust?  Is there a difference? Is not a fusion crust a
thermal alteration
> zone?
>
> Gary
>
> On 15 Jan 2007 at 19:07, Phil Morgan wrote:
>
> > I think we're seeing a thermal
> > alteration zone rather than anything that could be called a fusion
crust.
>
>
>
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