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

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