[meteorite-list] Re: [ I.M.C.A. ] FW: Lunar origin of tektites

From: Norman Lehrman <nlehrman_at_meteoritecentral.com>
Date: Fri Mar 25 22:50:22 2005
Message-ID: <20050326035020.41729.qmail_at_web81001.mail.yahoo.com>

Sterling,

Fabulous exposition! That one cost me some more
printer ink. I do have a few questions and comments.

No trace of terrestrial material? I'm not sure I
understand. If you mean no embedded clasts from the
target surface, I agree. That is very odd,
considering the obvious plastic deformation of the
"splatforms". But if you are talking composition, the
elemental and isotopic mix is (reportedly) quite
terrestrial looking. I'm not sure what else one could
hope for.

No matter where they came from, some should've skipped
around on top of the atmosphere and made their final
entry far from the main bulk of the fall. You have
cited some really interesting examples. Does your
emphasis on "antipodal points" have particular
significance? For example, if an object narrowly
misses re-entry angles is the next best shot
antipodal?

I am not at all content with the volume estimates for
the North American (Georgiaite/Bediasite) strewn
field. Since we can only see the eroded edges of the
host strata, our perspective is very limited. The
total recovered mass is trivial. Some monstrous
assumptions are involved in the oft-quoted estimates.

While on the subject of the North American tektites,
one of my favorite questions is why there is such a
marked difference between Georgiaites and Bediasites?
Some argue for melts sourced at different depths (and
target compositions) in the source crater, but this
doesn't strike a full chord with me.

Regarding Rayleigh Taylor instability, you are way
beyond me. But if I understand you (a little), part
of the problem is the lack of apparent mixing of the
target and impactor materials. I have never heard of
this lack. Tiny Ni-Fe beads are reported in a variety
of meteorites, and I have always believed (without
proof) that the inky blackness of all but the
moldavites might well be due to integration of
impactor Fe.

Your discussion involving the missing Australasian
crater is excellent. This thing cannot be easily
hidden. We should be able to still hear the earth
ringing with reverbrations. This is a huge problem.

I am also perplexed by the objects that I term
"splatforms"---tektites that have clearly "splatted"
while still significantly plastic. How far can a blob
of molten glass travel before it cools sufficiently
that it can no longer splat? tens of kilometers?
hundreds? Splatforms are found from south China
through Laos, Thailand, Vietnam---and of the
Tibetanites are real, Tibet. A huge area. Exactly
the same thing can be said for Muong Nongs. Same
areal distribution, no evidence of flight.

Further, if you want a full kilo specimen, you'll have
to go to the Philippines. The big ones flew a long
ways---but NOT to the far end of the strewn fiel like
most meteorites. Most Australites are relatively
tiny.

Antarctica. Not a small point by any means. Where
are the tektites?

Good stuff. Keep on ruminating!

Cheers,
Norm
http://taktitesource.com


 
--- "Sterling K. Webb" <kelly_at_bhil.com> wrote:

> Hi,
>
> Hey! If Rob says he can't figure out a way
> to get tektites
> shipped in from the Moon, it's good enough for
> me, But then, I
> never thought they came from the Moon. The
> lunar origin theory
> is an old one. In fact, all of the 40-odd
> theories of the origin
> of tektites are old (and most of them are odd,
> too).
> It might surprise meteorite fanciers to
> know that the
> argument over tektites goes back to the time
> when meteorites were
> still regarded as a myth or of being formed by
> thunder! The
> first speculation about tektite origins dates
> from 1793, more
> than a decade before the French Academy was
> persuaded by the
> L'Aigle fall that rocks really did fall from
> the sky.
> To those with long memories, I will recall
> to them the late
> List member Darryl Futrell, who supported the
> lunar origin
> theory, more from geological evidence than
> orbital
> considerations. I corresponded a lot with
> Darryl and I believe
> he did so more out of loyalty to the late John
> O'Keefe than being
> really convinced by the theory.
> Take a look at:
> <
>
>
http://six.pairlist.net/pipermail/meteorite-list/2001-May/024512.html
> >
> <
>
>
http://six.pairlist.net/pipermail/meteorite-list/2001-May/024513.html
> >
> <
>
>
http://six.pairlist.net/pipermail/meteorite-list/2001-March/022903.html
> >
>
> The current "orthodox" theory of tektite
> origin is the impact
> theory: that tektites are modified terrestrial
> surface rocks,
> modified by impact into molten drops, ejected
> into orbits above
> the atmosphere where they are rapidly cooled,
> which then re-enter
> the atmosphere at hypersonic velocities where
> they are re-heated
> and further modified in their descent to the
> surface of the
> Earth.
> It sounds perfectly reasonable. It
> powerfully explains the
> great variety of tektite shapes and many other
> characteristics of
> tektites, and the unique limited distributions
> of tektites. But
> there are problems -- huge problems -- with the
> theory. Here a
> few, for which there has never been any
> satisfactory answers.
>
> 1. There are only four tektite-producing
> events in the past
> forty million years. (Maybe a few more, if you
> accept some odd
> single potential tektites, irghizites, and
> Lybian Desert Glass as
> tektites.) A giant question looms. Since there
> many, many
> impacts in the last forty million years, why
> did only four of
> them produce tektites?
> The answer is not size: Botsumtwi (source
> of ivorites) is a
> tiny crater.
> The answer is not perfect matches to
> craters: where is that
> giant australite-producing crater?
> All of the "big four" tektite-producing
> coincide with a
> reversal of the Earth's magnetic field. Why?
> And why only these
> impacts, and not the dozens of other?
> How are they different?
>
> 2. If tektites are produced by earth
> impact, why do tektites
> contain no, not any, trace of terrestrial
> materials? That's
> right, boys and girls, there is no definitive
> trace of
> terrestrial origin in the composition of
> tektites. So how do you
> produce them from an earth impact without
> touching the earth?
> The quick ones among you will guess that
> they are made from
> the impacting body. Eergh! I'm sorry, wrong
> answer. They do
> not even vaguely resemble any extra-terrestrial
> material we know
> of. And the impact experts say that it's
> impossible anyway.
> If you plot the terrestrial surface
> compositions that matches
> the tektite bulk composition, the odds of four
> random impacts
> hitting only those spots on Earth are about 120
> to one. Do you
> feel lucky?
>
> 3. There are many oddities in the
> distribution of tektites,
> described as non elliptical geographically
> limited strewn
> fields. In the 1984 Shaw and Glassberg paper
> which is cited as
> the definitive proof of terrestrial origin
> (which it ain't), they
> cheerfully mention that one of the australites
> submitted for
> analysis (one that was recovered from the ocean
> off the
> australian coast), in not an australite at all.
> Nope, it's an
> ivorite.
> Now, the "source crater" for ivorites is
> almost exactly 180
> degrees in latitude and longitude from where
> this tektite was
> found, so either it is an "antipodal" tektite
> or it rolled along
> the ocean bottom for a million years and 15,000
> miles without
> abrading!
> And then in 1988, Alan Hildebrand published
> his analysis of
> two "tektites" found in a Mayan Temple at Tikal
> -- they are
> australites, perfectly ordinary australites in
> every way. And
> yes, Tikal is almost exactly 180 degrees in
> latitude and
> longitude from Australia.
> So did they crawl off Australia, cross the
> Pacific, climb up
> on the land and travel hundreds of miles across
> Guatemala to get
> to where the Mayan temple would be built in
> 793,000 years? Or
> did they fall from the sky and survive until
> they were brought to
> the priests as the mystery that they were (and
> are)? And if two
> tektites were brought to Tikal, wouldn't you
> guess a lot more
> than two fell?
> So, two of the four tektite fields are
> global, not limited in
> distribution. (The antipodal points for the
> other two craters are
> in deep ocean, S. Pacific and S. Indian.)
>
> It gets worse. There is no one impact
> theory. There is
> absolutely no agreement as to what the
> production mechanism is.
> Everyone supporting "impact" puts forward
> differing (and
> contradictory) mechanisms.
> The majority of impactists say surface
> jetting is the source
> of tektites, even though jetting in theoretical
> models of impact
> occurs from the body of the impactor rather
> than from the target
> material. This would be fine if they proposed
> silica impactors,
> but they emphatically do not. A large number of
> geochemists point
> to surface deposits as the only possible source
> for a tektite
> composition. The question is, why doesn't this
> happen with all
> (or most) impact events?
> Wasson's "atmospheric cratering event"
> proposes that there are
> no craters created in tektite producing events,
> which is curious
>
=== message truncated ===
Received on Fri 25 Mar 2005 10:50:20 PM PST


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