[meteorite-list] Re: Researcher Says... Tektite Events

From: Kelly Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:43 2004
Message-ID: <3AC030F8.EA80E843_at_bhil.com>

Hi, Jarmo and List,

Jarmo Moilanen wrote:

> Melosh doesn't mention anything about deeper excavation.

"Evidently, tektites originate from DEEPER WITHIN THE TARGET ROCKS..."
    -- quote from H.J.Melosh, "Impact physics constraints on the origin of
tektites", Meteoritics & Planetary Science Vol. 33, No 4 (Supplement),
1998. (Reprinted in Heinen, Tektites, 1998)
    The problem I have with this is, after the decompression by
rarefication waves and the silicate vapor and fluid phase is formed, that
this tektite source material, to get out of the bottom of the forming
crater, has to fight its way through the vaporized upper layers which are
already mixed with and contaminated by impactor material, then fight its
way through the even more thoroughly vaporized impactor which contains more energy (kinetic and thermal) than any of the target materials.
    If the tektite source vapor is expanding more slowly than the other
phases, it will never get out of the atmosphere. If the tektite source
vapor is moving at the same speed as the layers of vapor and liquid phases
above it, it will be in contact and they will mix. If the tektite source
vapor is moving faster than the other material, it will mix even better. So how does it escape without contact with the rest of the impact material
above it?
    Melosh doesn't say how much deeper his source layer has to be, but it
has to be below the lower limit of terrestrial material which gets
contaminated by impactor material (since it's not supposed to get
contaminated). I don't know how deep this would have to be (and Melosh
doesn't say) , but I do know that chemically resolvable traces of impactor
material can be found in the breccia lens left behind at the bottom of
recent craters. Where is this uncontaminated layer?

> He also doesn't mention rebound decompression but rarefaction waves (=
> release waves) which has a major role in tektite forming in his theory.
> Rebound decompression and rarefaction waves are, as far as I know,
> totally different things during cratering process.

    Whoops! Got me there. I was working from memory of the abstract. What
we have is a sudden drop in pressure which allows the superheated fluid to
transition to the vapor phase more or less instantly. Still, we have a few billion tons of silicate and iron vapor and another few billion tons of vaporized country rock churning around between the tektite vapor/liquid and the escape hatch.
    I can't help it; I see mixing as the likely outcome.

Kelly
Received on Tue 27 Mar 2001 01:19:37 AM PST