Hi, Doug,
I am really not quite sure why Sterling
mentions the F and B assays would
tend to "identical" levels in tektites...
Both fluorine and boron, become volatile if
you heat them up enough. Fluorine's a gas but it
forms strong bonds and boron's much less volatile.
The point is that at any given high temperature,
you drive off more fluorine than boron. The virtue
of it is that the scale of the temperatures involved
is a long scale. It allows F/B ratios to function as
a kind of "thermometer" for very high temperature
events, a scale that covers tens of thousands of
degrees!
ALL terrestrial rocks have a F/B ratio greater
than 5.0 (often 20 or 30). but all impact glasses,
even the weakest dirtiest just barely melted impact
glasses have a F/B ratio less than 5.0 -- the result
of a few thousand degrees of heating.
I cannot fathom any mechanism that would insist
that tektites should have these levels "identical..."
I don't know the values for the Nubia Sandstone,
but the range of sandstones is fluorine 180 to 450
ppm and boron about 10 to 85 ppm. The figures
for LDG is fluorine 7 ppm and boron 7 ppm, so
you see how the ratios shift as the content drops.
As the temperature rises (microsecond by microsecond),
the fluorine content drops much faster than the boron
content. At some very high temperature (variable
for each source rock), both fluorine and boron
levels become the same, but at a higher level than
in the final product.
After that point, both are driven out of the melt
plasma at the same rate, their petty chemical
differences totally overwhelmed by the energy
available. So, fluorine goes faster until that point
is reached, after then, they drop together.
If the Nubia was 300 ppm fluorine and 30 ppm
boron, at some point, they might get to 20 and 20,
then 19 and 19, 18 and 18, until it's over...
Typical values for a indochinite are like 10 and 10.
Ditto for bediasites. Moldavites 30 and 30. Ivorites
25 and 25. At 7 and 7, the LDG was either formed
from very low boron content rock or, as I said,
"these puppies got really really hot."
As an example, the rock at the Darwin crater
has fluorine content of 389-769 ppm and boron
content of 19-35 ppm, ratios of 11.5 to 20.5. The
Darwin impact glass has fluorine content of
15-32 ppm and boron content of 9-13 ppm,
ratios of 1.2 to 3.6. You can see how much of
each element was lost, about 68% of the boron
but about 96% of the fluorine! The ratios indicate
a forming temperature that was very hot in some
spots (20,000 degrees?) and much cooler in
other places in the same event (5000 degrees?).
Darwin crater is small (smaller than the Arizona
Meteor Crater). The ratios of Darwin glasses
are about the same as Muong Nong tektites
(but they are much wetter than Muong's).
While impact glasses range up to nearly 5.0,
Muong Nong's never get up to 4.0, and "normal"
tektites never get above 1.5 and sometimes have
F/B ratios less than 1.0 (indicating fantastic temps),
like 0.4 which probably corresponds to 40 or 50
thousand degrees, or maybe 80,000 in some rock.
SUMMARY: F/B ratios are a thermometer
for measuring very high temperatures of formation.
Even hot lava has F/B ratios of 10.0 or more, so
you can see that this thermometer is ideally suited
for very energetic impact events.
It looks like LDG had a very hot forming event,
so the high water content is a real puzzle. Of course,
we all want to find a way to "save" our theories from
popping like soap bubbles on reality's sharp corners,
so here's one try... Geologically, in the era of the impact
and until the end of the Miocene, this area was lacrustine.
(My geologist-like talk courtesy of Ingrid's Rockin'
Dictionary at Uof AZ website; normally I'm limited
to English...) Means it was mostly under shallow
swamp and lake water. We know that submerged
tektites slowly increase in water content if they have
millions of years to do it in... Microtektites in the
ocean hydrate away completely. Tektite fragments
have high water content than whole tektites. So
water can be absorbed by tektites. Would 10 to
20 million years of glug-glug time in boggy swamps
wet up the LDG from 0.010% to 0.100% or more?
No problemo, to quote the redoubtable Awr-nauld.
Hey! I'm liking my new theory! I'm particularly
tickled by the notion of standing in the Lybian Desert
dune field at nigh noon and 58 degrees C in one of
the driest spots on Earth, holding a chunk of LDG,
and saying, "See, it's water content is high because
it spent millions of years right here, UNDERWATER."
It's here, where these deserts are now, that the
Great Swamps gave rise to the True Apes. Yes, the
first apes (as opposed to monkey-like lemuroids, and
such like) hung out (literally) in the trees above these
swamps, starting 32-34 million years ago. The Swamp
of the Lybian Desert, and the nasty things that hunted
in it, is what drove super-great-grand-daddy and
mommy up into the trees in the first place, and made
brachiators of us all.
I wonder what they thought when the sky dropped
millions of pieces of hot glass on them, to fall with a
sizzle into the still water below? "First, everything floods
and we have to move up into these stinking FEMA
treehouses, and now there's hot glass falling from the
sky... The world is going to hell."
Doug, did I answer your question?
Sterling K. Webb
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----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>;
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Sent: Saturday, March 04, 2006 4:05 PM
Subject: Re: [meteorite-list] Largest Crater in the Sahara Desert and LDG
Sterling W. writes:
<< Crustal rocks have 5 or 10 times
more fluorine than boron. Tektites should have a ratio of 1.0,
indicating that they were heated to temperatures high enough
to drive off most of the fluorine and leave the two halogens
at identical levels (however low the absolute amount), and indeed
tektites have values that "float" around 1.0 (like 0.8 to 1.2).
The tested LDG F/B ratio is 1.0. >>
Norm, Sterling, Mark, Tracy, list,
I'm still on the fence about Libyan Desert Glass and how it fits into the
puzzle and I wanted to thank Norm for the motivation to reconsider some of
it
based on the additional support that that LDG may have actually been
tossed a
significant (lateral?) distance to its resting point. Norm, my thoughts
on the
difference in the mechanism of formation here are basically along the
lines
pursued by Wasson, that Muong Nongs (and probably LDG's) result from a
different
conceptual and physical event: that while they may be clearly or partially
impacted and have received a portion of their formation from that, that
importantaly also: a major source of the energy that led to their
formation was being
broiled by an overhead explosion perhaps of a manyfold-Tunguska type, or
by the
same clould of incredible enery flux that formed some of the
"true-to-form"
tektites. This is why I am on the fence - because I feel more comfortable
with
that scenario to fall back upon.
Just want to hold on to a concept, of what tektite means to me as Norm
originally asked. While Norm argued to liberalize the definition to
include LDG's,
I'm playing the conservative interpretation here like Sterling is also
joining
to do. I don't disagree, just ask for one positive indication in my
preferred set of rules. Norm might just be right if we play by his rules
and accept
that LDG's were chucked a good distance and thus call them tektites based
on
that criterion. At minimumn LDGs are more important now as we glean more
information from them and maybe an additional piece of the endless puzzle.
I am really not quite sure why Sterling mentions the F and B assays would
tend to "identical" levels in tektites, and I while it may be my turn to
split
hairs, I think this is an interesting research point, but presented inside
out.
Yes, Fluorine is generally more volatile and probably preferentially
driven
off, though we should verify this is true for the source matrix solubility
before being 100% convinced. The major problem I have here is that there
is
nothing magic about having them with the same concentration level as you
imply, I
think this is just a coincidence on what has been looked at so far,
possibly
related to the temperatures and residence times (determined by physical
constraints) in the liquid state of formation too, yes, of course, but
that is as far
as I would go. That is why I think it is too great a leap of faith to
discuss why they would be "perfect tektites" based on these measurements.
Putting this [F]:[B] further under the microscope, it is also of academic
interest to compare this to the source rock - but I would never flip that
around
to discuss why [F] and [B] should be identical or at a particular ratio
without knowing the initial values in the source rock, since I cannot
fathom any
mechanism that would insist that tektites should have these levels
"identical",
and the range you quote and attribute some special meaning to, anyway for
tektites "floating" goes below 1.0 anyway, and as a matter of fact the
tektites
could easily have much lower values for this ratio than you quote, has Dr.
Koerbel and colleagues ever fired up their special Boron sensitive
electrode to
check these numbers for moldavites lately?
Basically, Sterling is making a big assumption by saying that the source
rocks of the sandstone are in the range of 5 - 10 for a [F]:[B] ratio, and
I think
frankly that is a poke in the dark or leap of faith at minimum. I would
much
rather see someone actually go measure the [F] and [B] numbers for
relatively
unaltered sandstone near the excitingly discussed crater just to check
that
the ratios didn't happen to start out at values much closer to equal ...
there
is significant variation on the earth.
The bottom line in my view is that the interpretation of the Fluorine and
Boron concentration numbers and ratios is meaningful for an apples to
apples
comparison when the situation of the crater is not known if and only if we
had
tektites (or some other glass type) formed from the LDG event then we
could
measure (at least Dr. Koerbel and his colleagues could) and compare the
tendencies
with the series (e.g.,LDG, hypothetical button, hypothetical
splashform,etc.)
which I consider the more appropriate interpretation of this. Not take it
out
of context and generalize for the whole planet and say "they should be
perfect tektites." So there are not enough numbers put on this pig, in my
opinion,
and wish my disagreement on that split hair point duly noted!
Eventually I feel comfortable that we have a good chance explaining all
the
curious forms of glass by considering what is jetted upwards to form
"tektites", what is heated below from explosions above, what receives the
good old
"one-two" punch on the ground in the form of energy transmitted by waves
propagated
as the impactor coalesces and subsequently scalded, and what gets scalded
alone by the jet of plasma like material sent upward. Given that an
impact isn't
an instantaneous event, there are many possibilities to work through here,
and each one imho probably leaves its unique signature in the glasses.
Saludos, Doug
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