|
|||||
|
|
The Mesozoic to Early Cenozoic Magmatism of the Benue Trough (Nigeria); Geochemical Evidence for the Involvement of the St Helena Plume |
|
| Authors: | COULON C; VIDAL P; DUPUY C; BAUDIN P; POPOFF M; MALUSKI H; HERMITTE D |
| Institution: | 1PTROLOGIE MAGMATIQUE URA 1277, CEREGE, BP 80, 13545 AIX EN PROVENCE CEDEX 4, FRANCE 2CENTRE DE RECHERCHES VOLCANOLOGIQUES URA 10, 63038 CLERMONT FERRAND CEDEX, FRANCE 3CENTRE GOLOGIQUE ET GOPHYSIQUE CNRS, PLACE BATAILLON, 34095 MONTPELLIER CEDEX, FRANCE 4INSTITUT DE GODYNAMIQUE URA 1279, UNIVERSIT DE NICE—SOPHIA ANTIPOLIS, AVENUE EINSTEIN, 06560 VALBONNE, FRANCE 5LABORATOIRE DE GOGHRONOLOGIE—GEOCHIMIE URA 1763, PLACE BATAILLON, 34095 MONTPELLIER CEDEX, FRANCE |
| Abstract: | The Benue Trough is a continental rift related to the openingof the equatorial domain of the South Atlantic which was initiatedin Late Jurassic-Early Cretaceous times. Highly diversifiedand volumetrically restricted Mesozoic to Cenozoic magmaticproducts are scattered throughout the rift. Three periods ofmagmatic activity have been recognized on the basis of 40 Ar-39Ar ages: 147–106 Ma, 97–81 Ma and 68–49 Ma.Trace element and Sr, Nd and Pb isotope determinations, performedon selected basaltic samples, allow two groups of basaltic rocksto be identified: (1) a group with a tholeiitic affinity, withZr/Nb=7–11.1; La/Nb = 0.77–1; 87Sr/86Sr; =0.7042–0.7065143Nd/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 leadto the conclusion that three types of mantle sources were involvedin the genesis of the Mesozoic to Cenozoic basaltic rocks ofthe Benue, without significant crustal contamination: (1) anenriched subcontinental lithospheric mantle from which the tholeiiticbasalts were derived; (2) a HIMU-type (plume) component fromwhich the alkaline basalticrocks originated; (3) a depletedasthenospheric mantle (N-MORB-type source), which was involvedin the genesis of the alkaline basaltic magmas. According to(1) the postulated location of the St Helena hot spot in theEquatorial Atlantic at about 130 Ma and (2) the isotopic compositionof the alkaline basaltic rocks of the Benue Trough and theirgeochemical similarity with the basalts of St Helena, we concludethat the St Helena plume was involved in the genesis of thealkaline magmatism of the Benue at the time of opening of theEquatorial Atlantic. Moreover, the geochemical similarity betweenthe alkaline magmatism of the Benue Trough and that of the CameroonLine suggests that both magmatic provinces were related to theSt Helena plume. Finally, the temporal change of the mantlesources observed in the Benue Trough can be accounted for bythe recent models of plume dynamics, in the general frameworkof opening of the Equatorial Atlantic. KEY WORDS: Benue Trough; Mesozoic to Cenozoic magmatism; Equatorial Atlantic; mantle sources; St Helena plume *;Corresponding author. |
| Keywords: | |
| 本文献已被 Oxford 等数据库收录！ | |