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

AbstractDolerite 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 (

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Petrology and Geochemistry of Hama Koussou Dolerite Dyke Swarms (North Cameroon, Central Africa)

Journal of Geography Environment and Earth Science International ◽

10.9734/jgeesi/2019/v23i330170 ◽

2019 ◽

pp. 1-19

Author(s):

Fagny Mefire Aminatou ◽

Bardintzeff Jacques-Marie ◽

Nkouandou Oumarou Faarouk ◽

Lika Gbeleng Thomas D’Aquin ◽

Ngougoure Mouansie Samira

Keyword(s):

Central Africa ◽

Alkali Feldspar ◽

Rift System ◽

Spinel Lherzolite ◽

Dolerite Dyke ◽

Pan African ◽

Tholeiite Basalt ◽

Petrology And Geochemistry ◽

African Rift ◽

Geochemical Analyses

The Pan African granitoid basement of Hama Koussou Cretaceous half basin in North Cameroun (Central Africa) is transected by near N-S, NE-SW and ENE-WSW giant doleritic dykes trending along the same Pan African directions. Hama Koussou dolerites are compliant with the regional distension that occurred after the Pan African basement consolidation prior to the development of West and Central African Rift System at Late Jurassic-Early Cretaceous times. Studied lavas are composed of large clinopyroxene oïkocrysts, plagioclase and alkali feldspar laths and oxides phenocrysts exhibiting ophitic, sub-ophitic and intercertal textures. Microprobe chemical analyses carry out on the main mineral phases show that clinopyroxenes are diopside and augite, plagioclases are labradorite, andesine, oligoclase and albite and alkali feldspars are mainly sanidine with a few percent of orthoclase. ICP-MS and ICP-AES geochemical analyses of Hama Koussou lavas exhibit basalt, basaltic trachyandesite and trachyandesite compositions of continental tholeiite features. Tholeiite basalts of Hama Koussou are the results of high partial melting of E-MORB mantle source of spinel lherzolite composition, located at 65-55 km depth. More evolved tholeiite lavas of Hama Koussou basin are the products of tholeiite basalt differentiation trough assimilation and fractional crystallization coupled with fluids circulation.

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Occurrence of a sheeted dolerite dyke complex in the Ballantrae ophiolite, Scotland

Geological Magazine ◽

10.1017/s0016756898001162 ◽

1998 ◽

Vol 135 (4) ◽

pp. 509-517 ◽

Cited By ~ 10

Author(s):

G. J. H. OLIVER ◽

R. R. McALPINE

Keyword(s):

Dyke Swarm ◽

Dolerite Dyke ◽

Early Ordovician ◽

Marginal Basin ◽

Geological Setting ◽

Back Arc

A sheeted dolerite dyke swarm has been discovered at Duniewick Fort, Ballantrae. It forms part of the Early Ordovician Ballantrae Complex of Ayrshire, southwest Scotland. Asymmetric chilled margins, parallel to sub-parallel dykes and multiple dykes (dykes within dykes) are found. Although the mineralogy has been altered by metamorphism, the geochemistry is comparable with modern day back-arc marginal basin basalt. Cross-cutting sills have the chemistry of within-plate basalt. The regional geological setting suggests that an ophiolite sequence has been dismembered and incorporated into a serpentinite mélange. This is the first description of a 100% sheeted dyke complex (senso stricto) from the Ballantrae ophiolite.

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