From: Steven M Smith (smsmith@usgs.gov)
Date: Wed Oct 15 2003 - 19:39:28 EDT
Lest anyone accuse me of not admitting error, I issue the following
retraction.
In a reply to Allen Roy on the RATE thread I wrote:
>> Let me give another non-geological analogy. The Uinkaret basalts are
>> like a fruitcake (except that the fruitcake is probably older! <grin>).
>> Just like the fruit in the fruitcake, these basalts include pieces of
>> rock from other sources (known as xenoliths or literally "foreign
>> rocks"). According to the TalkOrigins FAQ, Austin has deliberately
>> chosen a sampling method that dates the fruit and then interpreted
>> that as the age of the cake.
Allen replied:
> Sorry: The T.O. FAQ says "phenocryst" not "xenolith"
Allen is correct. The T.O. FAQ does say phenocryst and not xenolith.
A careful check of the published literature on the Uinkaret Plateau basalts
revealed the following details.
According to Best & Brimhall, 1974, and Leeman, 1974, there is a "complete
absence of ultramafic inclusions in hawaiite and basaltic andesite"
although there is a "common occurrence of dense ultramafic inclusions in
many of the basanite and alkali-olivine basalt flows" from the western
Grand Canyon area. To translate the geologese, an 'ultramafic inclusion'
is a piece of mantle rock (a xenolith or fruit in my analogy above) that
was brought to the surface and included in a lava flow.
My fruitcake analogy was based upon the occurrence of ultramafic inclusions
in the lavas that Austin dated. However, according to ICR Impact Article
224 <http://www.icr.org/pubs/imp/imp-224.htm>, Steve Austin collected 4
whole rock samples and 1 crystal from HAWAIITE basalt flows. Therefore,
since the Grand Canyon Hawaiite basalt flows do NOT contain xenoliths, my
analogy above does not apply to the Grand Canyon Dating Project work of
Steve Austin. I mistakenly referred to the wrong Uinkaret Plateau basalt
flows.
I hereby retract my statement, "According to the TalkOrigins FAQ, Austin
has deliberately chosen a sampling method that dates the fruit and then
interpreted that as the age of the cake." and apologize to the ASA list,
Allen Roy, Steve Austin, and TalkOrigins FAQ author Chris Stassen.
However, I still stand by the other statements made in that ASA post and
will expand on the problems of Steve Austin's Grand Canyon Dating Project
(now apparently part of the RATE project) in the following post in the RATE
thread.
Sincerely
Steve
References:
Best, M.G., 1974, Late Cenozoic alkalic basaltic magmas in the Western
Colorado Plateau and the Basin and Range Transition Zone, U.S.A., and their
bearing on mantle dynamics, Geol. Soc. of America Bull., v. 85, p.
1677-1690.
Leeman, W.P., 1974, Late Cenozoic alkali-rich basalt from the Western Grand
Canyon area, Utah and Arizona: Isotopic composition of strontium, Geol.
Soc. of America Bull., v. 85, p. 1691-1696.
[Disclaimer: Opinions expressed herein are my own and are not to be
ascribed to my employer]
_____________
Steven M. Smith, Geologist, U.S. Geological Survey
Box 25046, M.S. 973, DFC, Denver, CO 80225
Office: (303)236-1192, Fax: (303)236-3200
Email: smsmith@usgs.gov
-USGS Nat'l Geochem. Database NURE HSSR Web Site-
http://pubs.usgs.gov/of/1997/ofr-97-0492/
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