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Friday, 19 August 2011

Richat Dome (Structure) PhD Dissertation Available Online


Richat Dome (Structure) PhD Dissertation Available Online


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 Unpublished PhD.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. Jébrak 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'Académie 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.

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