The dolerite dyke swarm of Mongo, Guéra Massif (Chad, Central Africa): Geological setting, petrography and geochemistry

Open Geosciences. 2017;9(1):138-150 DOI 10.1515/geo-2017-0012

 

Journal Homepage

Journal Title: Open Geosciences

ISSN: 2391-5447 (Online)

Publisher: De Gruyter

LCC Subject Category: Science: Geology

Country of publisher: Poland

Language of fulltext: English

Full-text formats available: PDF

 

AUTHORS

Nkouandou Oumarou Faarouk (Faculty of Science, Department of Earth Science, University of Ngaoundéré, Ngaoundéré, Cameroon)
Bardintzeff Jacques-Marie (Univ Paris-Sud, Sciences de la Terre, Volcanologie, Planétologie, UMR CNRS 8148 GEOPS, bât. 504, Université Paris-Saclay, F-91405 Orsay, France)
Mahamat Oumar (Faculty of Science, Department of Earth Science, University of Ngaoundéré, Ngaoundéré, Cameroon)
Fagny Mefire Aminatou (Faculty of Science, Department of Earth Science, University of Ngaoundéré, Ngaoundéré, Cameroon)
Ganwa Alembert Alexandre (Faculty of Science, Department of Earth Science, University of Ngaoundéré, Ngaoundéré, Cameroon)

EDITORIAL INFORMATION

Blind peer review

Editorial Board

Instructions for authors

Time From Submission to Publication: 15 weeks

 

Abstract | Full Text

Dolerite dykes are widespread in the Mongo area within the granitic Guéra Massif (Chad, Central Africa). Dykes are several hundred metres to several kilometres long, a metre to decametre thick, and vertical, crosscutting the Pan-African granitic basement rocks. They are controlled by major Pan-African NNE-SSW, NE-SW and ENE-WSW faults. Rocks constituting the dykes exhibit typical doleritic textures (i.e. intergranular, ophitic or subophitic). They are mainly composed of phenocrysts, microcrysts and microlites of clinopyroxene, amphibole, plagioclase, alkali feldspar and Fe-Ti oxides. Mongo dolerites are classified into two groups: Group 1 of basalt and trachybasalt and Group 2 of basaltic trachyandesite, which follow a trend with continental tholeiite affinities, and are differentiated through fractional crystallization. Trace element enrichment and REE contents show the high melting degree at shallow depths of enriched sub-continental lithospheric mantle, whose composition is intermediate between OIB and MORB, contaminated by small amounts of sediment during older subduction. Mongo dolerites are interpreted as imprints of either the final stage of stabilization of ancient continental crust, or the initiation of tectonic activity related to Pan-African mobile belts.