[meteorite-list] Pseudocraters Never Die (Phillips County, Montana)

[Paul H.]

On the Internet, known pseudocraters ( craterwrongs ) 
never seem to die. They seem to get endlessly recycled 
as seen in a rambling article, “The Younger Dryas Impact 
Event and the Cycles of Cosmic Catastrophes,” reprinted 
by RH on July 5, 2012 at:
http://nexusilluminati.blogspot.com/2012/07/younger-dryas-impact-event-and-cycles.html

This web page cites 

Geologists may have found 'new' meteor crater – Montana
by Annette Hayden, Havre Daily News, June 11, 2007.
http://sinkholeswww.sott.net/articles/show/134335-Geologists-may-have-found-new-meteor-crater-Montana

This circular feature is located at Latitude: 47.804896°: 
Longitude: -108.631878° in Phillips County, Montana,
about 14.5 km southwest of Zortman, Montana.

as can be seen at:
http://maps.google.com/maps?f=q&hl=en&q=montana&ie=UTF8&ll=47.827793,-108.679848&spn=0.071453,0.150719&t=h&z=13&iwloc=addr&om=1
and http://www.sott.net/image/image/1705/NewMeteorCraterMinn.gif

Unfortunately, these circular features are not impact craters. 
These features, which partially surround the Little Rocky 
Mountains, are eroded surfaces of circular structural domes 
created by the uplift of sedimentary strata overlying laccolithic 
intrusions composed of syenite porphry.

These laccoliths are discussed in "Geology and Physiography
of Fort Belknap" at:
http://serc.carleton.edu/research_education/nativelands/ftbelknap/geology.html

A geologic cross section of these circular features can 
be found at:
http://serc.carleton.edu/images/research_education/nativelands/ftbelknap/crosssection.gif

According to the above web page, a laccolith is a “concordant 
igneous intrusion that has domed the overlying rocks and has 
a known or assumed flat floor and a postulated dikelike 
feeder beneath its thickest point. It is roughly circular in plan, 
less than five miles in diameter, and from a few feet to several 
hundred feet in thickness.”

The geology of these features is illustrated by:

Porter, K. W., and E. M. Wilde, 2001, Geologic map of the 
Zortman 30' x 60' quadrangle, eastern Montana, Montana 
Bureau of Mines and Geology. Open-File Report 438, 
16 p., 1 sheet(s), 1:100,000.
http://www.mbmg.mtech.edu/mbmgcat/public/ListCitation.asp?selectby=series&series_type=MBMG&series_number=438&series_sub=&

This report is available from:
http://www.mbmg.mtech.edu/pdf_100k/zortman-text.pdf

The 4.2 MB PDF file of the geologic map is available from:
http://www.mbmg.mtech.edu/pdf_100k/zortman.pdf

Publications about these circular geologic structures are:

Collier, A. J., and S. H. Cathcart, 1922, Possibility of finding 
oil in laccolithic domes south of the Little Rocky Mountains, 
Montana. Bulletin 736-F (pp. F171-F178) United States
Geological Survey, reston, Virginia.
http://pubs.usgs.gov/bul/0736f/report.pdf
http://ngmdb.usgs.gov/Prodesc/proddesc_93198.htm

Knechtel, M. M., 1944, Oil and gas possibilities of the plains 
adjacent to the Little Rocky Mountains, Montana. Oil and Gas 
Investigations Map no. OM-4, scale 1:48000, U.S. Geological 
Survey, Reston, Virginia.
http://ngmdb.usgs.gov/Prodesc/proddesc_32205.htm

Knechtel, M.M., 1959, Stratigraphy of the Little Rocky 
Mountains and encircling foothills, Montana. Bulletin 
no. 1072-N, U.S. Geological Survey, Reston, Virginia. 
http://pubs.usgs.gov/bul/1072n/report.pdf
http://ngmdb.usgs.gov/Prodesc/proddesc_20726.htm

Web pages:

Laccolith - http://en.wikipedia.org/wiki/Laccolith
2. What's a laccolith? - http://formontana.net/2a.html

Syenite - http://en.wikipedia.org/wiki/Syenite

I survived Hurricane Isaac without any damage. My 
power was off from about noon August 29th to about 
10:30 PM, August 30th. So we were extremely lucky. 
However, there are thousand of people, who were
badly hurt by Hurricane Isaac and can use any help
and prayers that can be given them.

American Red Cross – Louisiana
http://www.arcno.org
http://www.batonrouge.redcross.org

Best wishes,

Paul H.