[meteorite-list] Lunar origin of tektites

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Sat Mar 26 11:00:26 2005
Message-ID: <42458435.33135571_at_bhil.com>

Hi, Marc, List,

    Tektites are glass but comparing them to obsidian is very misleading. If
tektites decayed in terrestrial environs like obsidian, then there would be a
small number of tektites found in various stages of decay, especially
bediasites and georgiaites which are the oldest tektites.
    I've never heard of a degraded bediasite or georgiaite being found. (We
should ask Norm Lehrman; he would know.) The reason I'm pretty sure that
they've never been found is that any collector of tektites who finds any
tektite with any unusual characteristic will talk about its unique
attributes... forever. You should hear me go on about why my half-button
australite is not the same as half of a button australite!
    While obsidian is a glass, it is formed at much lower temperatures. It
is a "wet" glass with high water content, lots of dissolved gasses, and
partially melted xenoclasts. Moreover, obsidian is often layered, which
contributes to rapid breakdown. Even so, there's plenty of 15-25 million
year old obsidian in pristine condition to be found.
    Tektites are the driest mineral known, with water content far lower than
nuclear bomb glass, the next driest item on the list. That tektites were
formed at extremely high temperatures is evidenced by the fact that the
Martha's Vineyard tektite, a rare and precious one and only outlyer of the
North American field, contains a zircon crystal that is partially melted. I
could go and look up the melting point of zircon because I can't remember it,
but it's very very high (3400 degrees?).
    Someone else mentioned in a post to the List that there are bubbles in
tektites, thinking that they had terrestrial atmosphere in them. Not so.
The bubbles in tektites either leaked (have atmosphere in them) or they
didn't, in which case they have a high class vacuum in the bubble with
pressures about equal to 40 km into space. The only recovered gas is
Argon40, presumably from potassium decay, although there is one report of
helium detected in an intact bubble. Helium? Captured solar wind?

Sterling Webb
-------------------------------------------
Marc Fries wrote:

> Howdy
>
> Let me point something out here... The following email mentions the
> lack of tektites around the world relative to the number of impact
> craters. That's to be expected. Tektites are glass, which doesn't
> survive very long in your typical wet terrestrial environment (maybe
> 100 million years?). Other glasses like obsidian meet the same fate -
> they devitrify, or turn into a fine powdery crystalline phase. If
> you've ever seen snowflake obsidian, you've seen this process in
> action.
> That's why there are many more impact craters than tektite fields. We
> will only see tektites from the handful of craters in the past 100 mA
> or so that had the right conditions to produce tektites. Exactly what
> those conditions were is still up to debate. One thing worth noting -
> each of the suspected source craters may have been underwater at the
> time of impact. However, other craters were created underwater (i.e.
> Wetumpka) but didn't seem to produce tektites. As an added twist,
> tektites contain no water whatsoever themselves.
>
> Cheers,
> MDF
>
> > 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 ===
> >
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>
> --
> Marc Fries
> Postdoctoral Research Associate
> Carnegie Institution of Washington
> Geophysical Laboratory
> 5251 Broad Branch Rd. NW
> Washington, DC 20015
> PH: 202 478 7970
> FAX: 202 478 8901
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Received on Sat 26 Mar 2005 10:48:05 AM PST