[meteorite-list] Largest Crater in the Sahara Desert and LDG

From: MexicoDoug_at_aol.com <MexicoDoug_at_meteoritecentral.com>
Date: Fri Mar 3 20:15:16 2006
Message-ID: <2c5.478baef.313a4414_at_aol.com>

Hola Norm, so it seems we actually agree on most of the points, including the
most important one: the subjectivity of the definition. You are just wanting
to be more liberal...and me more stoodgy...I wasn't dodging the layered
tektite issue when I said not to bring it up (which you unfortunately did:)).
Clearly layered tektites are closer to impact glasses in the continuum and I was
just trying to cleanly conceptualize. The definition of 'tektite' is a human
classification which like most, depends on a clear understanding of a concept,
not a recipe. The Muong Nong glasses (vs. tektites) as many experts also call
them deserve a category by themselves so if you want to point to experts
calling them tektites as support for calling the LDG's also tektites, all I can
say is we are pushing the concept even further. You do mention the meteoritic
content of Indochinites (=Australasian tektites). Yes a small component of
iron has been detected, but this is very rare, and no where near the content in
LDG which can approach a 0.5%.

You didn't mention that the partial pressure of the air in the bubbles of the
Indochinites corresponds to the upper atmosphere, and that in LDG I am
assuming it corresponds to the surface. This shouldn't be a surprise as the water
should not be linearly independent - thus they ought to track similarly.

Good point on the desert weathering, but is there a real strewn field defined
for LDG's, as we find with other conceptually true-to-form tektites (pun:))?
If any evidence could be found, your argument would be more solid, as a of
evidence isn't any proof of anything. Try checking nobel gas ratios and I bet
the tektite concept will be even further away...

Where I must really agree with you and put all grammatical gymnastics and
opinions aside, is where you make the best point of the whole discussion, imho.
That maybe our definition of tektites whatever that concept may be is based on
faulty ideas. With liberty taken, that maybe it will change as we learn
more. Yes, I buy that, I believe that is a distinct possibility. Things were so
much simpler when we all agreed they were blasted from the Moon and the
aerodynamic shapes and low water content actually meant something more to the
experts of that time. Gor the time being, I be conservative on the definitions for
the distinctions mentioned. Show me one aerodynamically shaped LDG besides
one sculpted by a Neanderthal, and I'll recommend you for a Harvey award which
would be quite fitting:), and definitely a nobel prize in the meteoritical
community...for the moment we think there is a crater now, well, we already called
them impact glasses, and now we have all these years of human transport
mucking it up for these highly prized special glasses.

Perhaps little Norm and little Doug in the 100th century will follow in our
footsteps. Norm will say, Doug, look at all the chondrites in the USA, and
there are none in the Sahara. Looks like the major strewn field is into North
America and then a minor one into Europe. And Doug will say, I don't know, they
weren't witnessed falls.... Jokes aside, the concepts are pretty clear ---
high energy, less meteoritic content, water content too low for earth's surface
under all available explanations, aerodynamic shapes, minimal nobel gas
concentration typical of higher atmosphere, upper atmosphere
pressures(=low)...where does LDG have a positive? A crater in the same environment///I'll sit this
one out on the fence...but note it duly with curiosity and opportunity...

Saludos, Doug


Norm L. wrote:
 
 <<Doug,
 
 Good points all, but if you want to raise the
 water/purity issue, you can't dodge the Muong Nong
 issue. (The best answer is that they shouldn't be
 called tektites, BUT, they ARE so called by all
 authorities).
 
 With LDG, it can be reasonably argued that
 flight-related morphology has been erased by
 ventifaction. In the area where this stuff is found,
 it is literally reasonable that ALL of the material
 has seen the wind and its entrained sand. LDG is
 pretty fine, clean glass, albeit with a higher water
 content. (So, here again, people have dodged the issue
 by calling them Muong Nongs---)
 
 As for inclusion of impactor material in LDG, you've
 got to remember that iron spherules are found in
 Australasian tektites. Good chance that's impactor
 condensate.
 
 I truly have no argument with the water content
 criterion. That's probably the best definitional
 parameter we have. But it makes me a bit nervous to
 turn the whole matter over to such a narrow
 definition. Are we positive, given all that we don't
 know about tektites, that there can't be any wet ones?
  Should we now start calling Pyrex another variety of
 tektite? Clearly, we are including some
 process-related factors (even if just inferred) in our
 definition.
 
 It is very much like the planet issue. I keep
 thinking that there have been a lot of grade-school
 kids that got marked down on tests for answering the
 question: "How many planets are in our solar system?"
 wrong according to the erroneous wisdom of a given
 time. How many tektite-producing impacts have there
 been? I get weary of qualifying my answers with,
 "Well, depending on whether or not you count LDG----"
 
 Cheers,
 Norm
 http://tektitesource.com>>
 
 
 --- MexicoDoug_at_aol.com wrote:
 
> Norm L. writes:
>
> << Where is the dividing line between impactite and
> tektite? I'd like to hear what others may
> understand,
> but my impression is that it fundamentally hinges
> on
> distance the glassy material is ejected from the
> crater. Material found only in and immediately
> around
> the source crater is impactite. Stuff blasted tens
> to
> hundreds of km or more crosses the definitional
> boundary into "tektites".
>
> If this is the criterion, LDG was already home free
> >>
>
> Hola Norm, yet again here's another one of those
> awkward definitions that
> when overyly analyzed starts falling apart. I think
> the distance criterion is
> not THE criterion, but rather a tektite differs from
> an impact glass in that the
> tektite has actually been exposed to general
> conditions of enough kinetic and
> thermal energy to create a greater melt uniformity
> where the original
> impactor has transmitted that energy "cleanly", and
> in such a great quantity that the
> energy is also enough to propel tektites into the
> upper atmosphere and have
> them re-enter ablating like meteorites.
>
> These are a bunch of hand-waving concepts, but as we
> know, it seems the one
> factor that really distinguishes "tektites" is the
> low water content. LDG's
> have at least 5 times the typical water content of
> the cleaner tektites, and
> they contain inclusions including those of the
> impactor, and aerodynamic shapes
> are not really known I believe.
>
> In fact the water content of LDG's at the low end of
> 5 times the amount of
> the cleaner tektites actually goes practically as
> high as obsidian. They don't
> usually look very aerodynamic and they have
> meteorites inside them. They
> deserve some distinction, they are dirty glass. Now
> all of this about water
> content might be just an academic distinction,
> except for one exception. One of
> the greatest mysteries of tektites is derived from
> the mystery of exactly what
> physical laws were twisted to get that low water
> content and this more than
> anything else is the criterion as much as the
> mystery. Plus they are generally
> clean (OK, they have smalled fused cuartz. etc., but
> there there tends to be a
> bimodal distribution between clean tektites and
> impact glasses as far as
> inclusions = so far you have clean ones and dirty
> ones) Please don't bring up
> layered tektites I don't want the definition system
> to fail even more...
>
> But practically speaking, you would have to be right
> that there is a
> continuum, just like in the definition of a planet,
> etc., the world tends towards
> complexity just when you get it all figured
> out...and soon we will come to know of
> the impektite that bridges tektites, water and all,
> with LDGs and other
> impact glasses. Better yet how about just saying
> they are all impact glasses -
> which they are no matter who starts talking about
> flying - and that tektites just
> had a higher energy/diffusion/flux melt event which
> is witnessed in the
> record by water content...If cats could only talk
> they could tell us how long we
> have erred on visible light as they see into the
> near UV, don't they? What's
> the use of going at it with a cat over the
> definition of "visible light"?:)
>
> My 2 centavos...Doug
> >>
Received on Fri 03 Mar 2006 08:15:00 PM PST