P. BAUDIN

Laboratoire Magmas et Volcans

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C. Coulon

Center for Northern Studies

Michel R. Popoff

Institut Pasteur

Henri Maluski

Géosciences Montpellier

Philippe Vidal

Identités et Différenciation de l'Environnement des Espaces et des Sociétés

Daniel Hermitte

Centre de Recherche et d’Enseignement de Géosciences de l’Environnement

C. Dupuy

Groupe de Recherche en Économie Théorique et Appliquée

Cooperative Institutions

Centre National de la Recherche Scientifique

Université Paris Cité

Sorbonne Université

Université de Montpellier

Observatoire des Sciences et des Techniques

Université Toulouse-I-Capitole

Center for Northern Studies

Université Laval

International Water Management Institute

Hôpital de la Croix-Rousse

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⁴⁰ Ar/ ³⁹ Ar chronology, petrology and geodynamic setting of Mesozoic to early Cenozoic magmatism from the Benue Trough, Nigeria

Journal of the Geological Society (1995)

Henri Maluski C. Coulon Michel R. Popoff P. BAUDIN

The Benue Trough is a continental-scale intraplate tectonic megastructure which is part of Mid-African Rift System. This rift, initiated in the latest Jurassic, was related to the opening of the Central and South Atlantic oceans. Mesozoic to early Cenozoic magmatism accompanied this evolution. Two principal magmatic domains are evident, the Northern and Southern Benue. In the northern domain, magmatism is characterized by transitional alkaline basalts and transitional tholeiitic basalts. Acidic magmatism of peralkaline nature is also present. In the Southern Benue, several magmatic districts exhibit alkaline or tholeiitic affinities. A detailed chronology of emplacement of this volcanism has been established using the 40 Ar/ 39 Ar radiometric method which lead to recognition of three periods of magmatic activity: (1) 147–106 Ma, well expressed in the Northern Benue represefited by transitional basaltic types; (2) 97–81 Ma, occurring only in the Southern Benue, represented exclusively by alkaline intrusive rocks; (3) 68–49 Ma, restricted also to the Southern Benue, with alkaline intrusions followed by tholeiitic subvolcanic rocks. In the light of the general geodynamic evolution, a scenario is proposed, supported by the three chronological periods. The late Jurassic to Albian magmatism occurred when the Equatorial Atlantic was still closed, contemporaneous with the NE Brazilian magmatism. Both magmatism could represent the forerunners of opening of the Equatorial Atlantic. This activity occurred under a general extensional regime during which crustal strike-slip faults gave rise to the emplacement of transitional alkaline basalts. Transitional tholeiitic basalts erupted along normal faults. The second period of activity, Cenomanian to Santonian, restricted to the Southern Benue, occurred after the opening of Atlantic Ocean during a period of decreasing extension. This period ended with a Santonian compressional episode. The last period of activity, from late Maastrichtian to Eocene, is characterized by subsidence, generated as an isostatic response to the Early Cretaceous crustal thinning and post-rift thermal relaxation of the lithosphere, expressed by Tertiary E–W extension.

Trough (economics)

Chronology

10.1144/gsjgs.152.2.0311

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The Mesozoic to Early Cenozoic Magmatism of the Benue Trough (Nigeria); Geochemical Evidence for the Involvement of the St Helena Plume

Journal of Petrology (1996)

C. Coulon Philippe Vidal C. Dupuy P. BAUDIN Michel R. Popoff

The Benue Trough is a continental rift related to the opening of the equatorial domain of the South Atlantic which was initiated in Late Jurassic-Early Cretaceous times. Highly diversified and volumetrically restricted Mesozoic to Cenozoic magmatic products are scattered throughout the rift. Three periods of magmatic activity have been recognized on the basis of 40 Ar-39 Ar ages: 147–106 Ma, 97–81 Ma and 68–49 Ma. Trace element and Sr, Nd and Pb isotope determinations, performed on selected basaltic samples, allow two groups of basaltic rocks to be identified: (1) a group with a tholeiitic affinity, with Zr/Nb=7–11.1; La/Nb = 0.77–1; 87Sr/86Sr; =0.7042–0.7065 143Nd/144Nd;i = 0.5125–0.5127; 206Pb/204Pbi = 17.59–18.48; (2) a group with an alkaline affinity, with Zr/Nb = 3.6–6.8; La/Nb=0.53–0.66; 87Sr/86 Sri=0.7029–0.7037; 143Nd/144Ndi=0.5126–0.5129; 206Pb/204Pbi = 18.54–20.42. The geochemical data lead to the conclusion that three types of mantle sources were involved in the genesis of the Mesozoic to Cenozoic basaltic rocks of the Benue, without significant crustal contamination: (1) an enriched subcontinental lithospheric mantle from which the tholeiitic basalts were derived; (2) a HIMU-type (plume) component from which the alkaline basalticrocks originated; (3) a depleted asthenospheric mantle (N-MORB-type source), which was involved in the genesis of the alkaline basaltic magmas. According to (1) the postulated location of the St Helena hot spot in the Equatorial Atlantic at about 130 Ma and (2) the isotopic composition of the alkaline basaltic rocks of the Benue Trough and their geochemical similarity with the basalts of St Helena, we conclude that the St Helena plume was involved in the genesis of the alkaline magmatism of the Benue at the time of opening of the Equatorial Atlantic. Moreover, the geochemical similarity between the alkaline magmatism of the Benue Trough and that of the Cameroon Line suggests that both magmatic provinces were related to the St Helena plume. Finally, the temporal change of the mantle sources observed in the Benue Trough can be accounted for by the recent models of plume dynamics, in the general framework of opening of the Equatorial Atlantic.

Mantle plume

Trough (economics)

Primitive mantle

10.1093/petrology/37.6.1341

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Citations (100)