[meteorite-list] Richat Dome (Structure) PhD Dissertation Available Online

From: Paul H. <oxytropidoceras_at_meteoritecentral.com>
Date: Thu, 18 Aug 2011 12:23:17 -0500
Message-ID: <20110818132317.RQBXK.1445436.imail_at_eastrmwml37>

Dear Friends,

Dr. Guillaume Matton?s PhD dissertation about the Richat
Dome is available online as a PhD file. It is:

Matton, G., 2008, The Cretaceous Richat Complex (Mauritania);
a peri-Atlantic alkaline. Unpublished PhD. dissertation,
Universite du Quebec a Chicoutimi, Chicoutimi, Quebec, Canada.
http://gradworks.umi.com/NR/47/NR47231.html

PDF file at http://bibvir.uqac.ca/theses/030084214/030084214.pdf
or PDF file at http://www.archipel.uqam.ca/1201/1/D1684.pdf

The Richat Dome (Richat Structure) is a large, 40 km in diameter,
remarkably symmetrical, deeply eroded, dome, which is found in
west ? central Mauritania. The sedimentary rocks exposed in this
dome range in age from Neoproterozoic Era within the dome?s
center to Ordovician Period around its periphery. The sedimentary
strata dip at 10 to 20 degrees away from the center of this structure.
Erosion resistant strata, primarily quartzites, form circular cuestas
of high relief.

A variety of variety of igenous rocks have intruded the uplifted
sedimentary strata comprising the Richat Dome. These igneous
rocks include en-echelon carbonatite dikes andl sills, two
subvertical gabbro ring dikes, kimberlitic plug and sills, and
extrusive felsic rocks. The felsic rocks consist of hydrothermally
altered conglomeratic, tuffaceous, and other rocks filling a
diatreme pipe. They might represent a deeply eroded volcanic
maar. The carbonatite rocks have been dated as having cooled
between 94 to 104 million years ago. These intrusive igneous
rocks are interpreted as indicating the presence of a large
alkaline igneous intrusion within Precambrian strata that
underlie the Richat Dome.

Because of its circular form, The Richat Dome has been
hypothesized to be an extraterrestrial impact structure. It has
been intensively studied in the field along with samples from it
in the laboratory. Despite this research, a complete lack of any
evidence for shock metamorphism or any type of deformation
from a hypervelocity extraterrestrial impact has been found.
Further study of coesite reported from the Richat Dome found
it to be barite. Prominent breccias mapped within its center
are currently regarded to be hydrothermal karst. Furthermore,

the Richat Dome lacks the annular depression that is typically
in impact structures of this size. Finally, the sedimentary strata
comprising this structure is remarkably intact and "orderly"
and lacking in overturned, steeply-dipping strata or disoriented
blocks.

Its location is Lat. 21.126148 degrees N, Long. 11.400369 degrees W

Some other references are:

Dietz, R. S., R. Fudali, and W. Cassidy, 1969, Richat and
Semsiyat Domes (Mauritania): Not Astroblemes. Geological
Society of America. vol. 80, no. 7, pp. 1367-1372.
http://gsabulletin.gsapubs.org/content/80/7/1367.short

Fudali, R. F., 1969, Coesite from the Richat Dome, Mauritania:
A Misidentification. Science. vol. 166, no. 3902, pp. 228-230.
http://www.sciencemag.org/content/166/3902/228.abstract

Master, S., and J. Karfunkel, 2001, An alternative origin for coesite
from the Richat Structure, Mauritania. Meteoritics & Planetary
Science. vol. 36, no. 9, Suppl., p. A125.
http://www.lpi.usra.edu/meetings/metsoc2001/pdf/5237.pdf

Matton, G., M. J?brak and J. K.W. Lee, 2005, Resolving the Richat
enigma: Doming and hydrothermal karstification above an
alkaline complex. Geology. vol. 33, no. 8, pp. 665-668.
http://geology.geoscienceworld.org/cgi/content/abstract/33/8/665
http://geology.gsapubs.org/content/33/8/665.abstract

Netto, A. M., J. Fabre, J., G. Poupeau, and M. et Champemmois,
1992, Datations par traces de fissions de la structure circulaire
des Richats. Comptes Rendus de l'Acad?mie des Sciences.
vol. 314, pp. 1179-1186.

Woolley, A. R., 2001, Alkakline Rocks and Carbonities of the
World, Part3: Africa. The Geological Society of London,
London, United Kingdom.

Woolley, A. R., A. H. Ramkin, C. J. Elliott, A. C. Bishot, and
D. Niblett, 1985, Carbonatite dykes from the Richat Dome,
Mauritania and the genesis of the dome. Indian Mineralogist.
vol. 22, no. 2, pp. 189-207.

Some web pages are

Richat Structure, Mauritania
http://earthobservatory.nasa.gov/IOTD/view.php?id=2561

Earth?s Bulls-Eye, the Eye of Africa, Landmark for Astronauts
http://www.lovethesepics.com/2011/04/earths-bulls-eye-the-eye-of-africa-landmark-for-astronauts-14-pics/

Richat Structure
http://en.wikipedia.org/wiki/Richat_Structure

Best wishes,

Paul H.
Received on Thu 18 Aug 2011 01:23:17 PM PDT