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Author: Chris Stassen
Subject: FAQ: Evaluation of ICR Grand Canyon Research Project [DRAFT]
Updated: 02/27/92
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NOTE: Austin has promised to publish all of his data at some point, and
this work cannot really be completed until that happens.
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The Grand Canyon looks something like this:
Grand Plateau
Canyon
\ ________________
_\ /________________
__| /_________________
___\ /__________________ <-- Paleozoic rocks
____| |___________________
_____\__/ ___________________
...\ \ \ \ \ \ .... <-- Angular unconformity
.....\ \ \ \ \ ......
.......\ \ \ ............
.........\ .................. <-- Metamorphic rocks
Steve Austin of the ICR wrote _Impact #224_, claiming that he
has derived a Rb/Sr isochron age for lava flows on the Uinkaret
Plateau in excess of 1.3 billion years (several of these flows
spill into the canyon). The Cardenas Formation, a tilted layer
at the bottom of the canyon (below the angular unconformity) is
generally accepted as being about 1.1 billion years in age.
Clearly, something is wrong here. Lava flows which spill off
the plateau into the canyon cannot be older than the canyon
itself. The canyon can't be older than the rocks that it is
cut into. The flat sediments can't be older than those below
the angular unconformity (as they were deposited on top).
Austin's apparent thesis: Rb/Sr dating of the feature which
must be the youngest gives a value older than that which must
be the oldest, therefore the method does not work. (Of course,
then, all radiometric results can safely be ignored.)
I received a description of the data from Steve Austin (a
little more than what was published in _Impact_, but not nearly
enough to really know what is going on, unfortunately). I
forwarded the data to Dr. G. Brent Dalrymple of the U.S.
Geological Survey. He has apparently received many questions
on Austin's work, and sent me a short article that he had
written on the subject. I am in the process of getting
permission to give out copies of this report; please send
contact me (stassen@alc.com) if you are interested in getting a
copy (I can probably get copying done for free, but you may
have to cover the postage).
A few excerpts:
"Trying to prove that some methodology does not work by
focusing on a small percentage of anomalous data, while
ignoring a much larger percentage of concordant data is
not a productive exercise because it will prove nothing
except that the method did not work *in those particular
instances* [underlined in original -CS]. It is even
less meaningful if one seeks to perform an experiment
under circumstances that are known beforehand to be
inappropriate, and this is precisely what Steven Austin
is doing. He has set up an experiment that will fail
because he has chosen circumstances that guarantee the
outcome. So what is being tested--radiometric dating
methods or Steve Austin's knowledge and objectivity?"
Commenting on the fact that Austin has published three *different*
alleged isochron dates for the Cenozoic lava flows:
"These differences [changes in various measurements for
certain samples! -CS] explain the change in Steven's
``isochron age'' from 2.07 Ga to 1.39 Ga (or vice versa),
but we do not know why the analytical data changed so
radically from one table (and one diagram) to the other,
why one sample was omitted from the second table, or why
Steven selects just a few of the many available hawaiite
flows for his project."
Summary:
"In summary, I can't really tell what Steven Austin is
doing with his western Grand Canyon data. They keep
changing and he never provides enough information to do
an independent evaluation of important things like the
isochron fit. In addition, he is ignoring what I and
others have told him about using lava flows that are
demonstrably not cogenetic, and he is ignoring Leeman's
data, which clearly indicates that the rough correlation
between the Rb and Sr isotopic ratios reflects time-
integrated radioactive decay in the source rock(s), and
not in the lava flows."
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This is some additional material, which I put together at a later
date.
David M.V. Utidjian writes, in :
> But isn't the K-Ar method of radiometric dating the apropriate method
> for dating igneous rocks like lava flows? Please correct me if I am
> wrong.
The K-Ar dating method is probably the most _popular_ method
for dating lava flows. Since it involves relatively few
measurements, and they are relatively straightforward, it is
also one of the cheapest methods. Jim Lippard was kind enough
to look up and copy for me a technical paper on the topic of
K-Ar dating the Grand Canyon lava flows (McKee et. al, 1968).
It gives K-Ar dates for laval flows associated with the
Toroweap fault (~1.2 million years). Austin references this
paper (Austin, 1992, 1988), so it seems that these are the same
flows that he is "dating."
Despite its popularity, the K-Ar method is not the most
_reliable_ dating method. Since it is not an isochron method,
there is no built-in check for contamination (that is, in the
event of contamination it will yield an incorrect date -- while
an isochron method under the same conditions will usually yield
no date at all). Since argon is an inert gas, later heating
events can permit it to escape, and partially or completely
reset the "clock." Since there is excess argon associated with
the lava source, its method of cooling must be such that the
initial argon could escape.
This does not mean that the K-Ar method is useless; it only
means that it must be used with caution -- on samples that have
the right sort of history and properties. In fact, this case
(plateau lava flows) appears to be one where K-Ar yields the
right age and proper use of Rb/Sr dating yields no age at all.
If we plot all of the Rb/Sr data which Austin has ever
published (in three different places) for "Western Grand
Canyon" lava flows, you will see why I say "no age at all":
Sr-87/Sr-86
| (5)
0.711 +
=====
0.708 +
|
| (D)
0.707 + (4) (f)
| (C)
|
0.706 + (3)
|
|
0.705 + (2) (e)
| (1) (d)
|
0.704 + (b)
| (c)
| (B)
0.703 + (Aa)
|
|
0.702 +-------+-------+-------+-------+-------+-------+-------+-------+
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Rb-87/Sr-86
Lowercase letters (e.g., "(a)") are from Austin 1988. Uppercase
letters (e.g., "(A)") are from Austin, No Date. Numbers (e.g.,
"(1)") are from Austin, 1992. Warning: All data points were
"eyeballed" from published diagrams. ["(Aa)" is "(A)" and "(a)"
relatively close together.]
In Austin's diagrams, A-B-C-D fall relatively close to a line.
a-b-c-d-e-f also fall relatively close to a line. 1-2-3-4-5-6
fit very well to a single line. However, you can see that there
is quite a bit of scatter when all of the data is plotted
together.
I've been told that Austin has in the past used a computer
program that discards data that do not lie near a line. If that
is what he is doing here (it has that appearance, but I really
don't have enough information to be sure), it is no surprise
that he is ending up with data points that fall on or near a
line.
It is also no surprise that the resulting "age" is not
meaningful. In ignoring data points away from the line, one
would be ignoring data points which indicate that the "line"
does not represent an isochron. Here are two reasons why there
is the appearance that this is what is going on:
In Austin 1988 (lowercase letters above), he presents data from
Leeman, 1974. He uses samples "U-33, U-35, U-59, U-24, U-43,
and U-58." He does not explain why he chooses only these data
points. Leeman's diagram shows considerable scatter to the
data. From Leeman's diagram, it is clear that no Rb/Sr age can
be calculated. Austin has chosen only a few of the data points,
and these happen to fall near a line (however, the appearance
is that even these are not close enough to a line to be
considered a valid isochron date).
For another example, the most recent data (Austin, 1992)
appears in two forms. In an as-yet-unpublished paper (maybe a
chapter from a forthcoming book), Austin produces an isochron
that gives an "age" of 2.07 Ga, from samples "QU-1, QU-2, QU-3,
and QU-5."
In a report on the progress of the "Grand Canyon Research
Project," Austin notes that there was a problem with some of
the measurements, that an incorrect value resulted, but that
the sample is now correctly dated. (The project is running a
little behind for this reason.)
The _Impact_ article uses the some of the same sample numbers
as the other isochron, however (as Dalrymple notes) some of the
isotope concentration values have changed. (I suspect that this
is a result of the correction of the lab results.) However, the
_Impact_ isochron uses samples "QU-1, QU-2, QU-5 and QU-14."
Sample QU-3 is missing. Its previous position would be well off
the line.
Only ICR folks know why sample QU-3 was dropped, why sample
QU-4 has never been used, and where samples QU-6 through QU-13
are. Until they publish _all_ of the lab results and _all_ of
the data points, it will be difficult to assess exactly what
has been going on.
The appearance at the moment is that their results are not the
major blow against isochron methods that they are claiming.
Until they are more open with their results (ALL of their
results), that will have to suffice.
> It also appears that K-Ar methods would be more accurate for the
> apparent ages of these samples than the Rb-Sr method because the of
> their respective halflives of 1.25 x 10^9 for K-Ar and 4.88 x 10^10
> for Rb-Sr, respectively. That is to say the error bars for the Rb-Sr
> method may be an order of magnitude larger than the ones for the K-Ar
> method in my amateur evaluation of the two techniques.
It is true that the decay rate has some influence on the size
of the errors. However, the disagreement in this case cannot
be explained merely by measurement error. It is still
important to understand where the two methods agree or do not
agree (and why).
References:
Austin, Steve, 1992, "Excessively Old ``Ages'' For Grand Canyon Lava
Flows", _Impact_, Number 224, February.
Austin, Steve, 1988, "Grand Canyon lava flows: A survey of isotope
dating methods", _Impact_, Number 178, April.
Austin, Steve, No Date, "Grand Canyon dating project: A proposal for
research".
Leeman, 1974, "Late Cenozoic Alkali-Rich Basalt from the Western Grand
Canyon Area, Utah and Arizona: Isotopic Composition of Strontium", in
_Geological Society of America Bulletin_, Vol. 85, November, pp. 1691-1696.
McKee, E., D., et al., 1968, "K-Ar Age of Lava Dam in Grand Canyon",
in _Geological Society of America Bulletin_, Vol. 79, January, pp. 133-136.
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