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Resolving the Richat enigma; doming and hydrothermal karstification above an alkaline complex

Guillaume Matton, Michel Jebrak and James K. W. Lee
Resolving the Richat enigma; doming and hydrothermal karstification above an alkaline complex
Geology (Boulder) (August 2005) 33 (8): 665-668

Abstract

The Richat structure (Sahara, Mauritania) appears as a large dome at least 40 km in diameter within a Late Proterozoic to Ordovician sequence. Erosion has created circular cuestas represented by three nested rings dipping outward from the structure. The center of the structure consists of a limestone-dolomite shelf that encloses a kilometer-scale siliceous breccia and is intruded by basaltic ring dikes, kimberlitic intrusions, and alkaline volcanic rocks. Several hypotheses have been presented to explain the spectacular Richat structure and breccia, but their origin remains enigmatic. The breccia body is lenticular in shape and irregularly thins at its extremities to only a few meters. The breccia was created during karst dissolution and collapse. Internal sediments fill the centimeter- to meter-scale cavities. Alkaline enrichment and the presence of Cretaceous automorphous neoformed K-feldspar demonstrate the hydrothermal origin of these internal sediments and their contemporaneity with magmatism. A model is proposed in which doming and the production of hydrothermal fluids were instrumental in creating a favorable setting for dissolution. The circular Richat structure and its breccia core thus represent the superficial expression of a Cretaceous alkaline complex with an exceptionally well preserved hydrothermal karst infilling at its summit.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 33
Serial Issue: 8
Title: Resolving the Richat enigma; doming and hydrothermal karstification above an alkaline complex
Affiliation: University of Quebec at Montreal, Department of Earth and Atmospheric Sciences, Montreal, QC, Canada
Pages: 665-668
Published: 200508
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 20
Accession Number: 2005-048154
Categories: Structural geologyGeomorphology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. block diag., sketch maps
N21°10'60" - N21°10'60", W11°22'60" - W11°22'60"
Secondary Affiliation: Queen's University, CAN, Canada
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200517
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