Petrology, Geochemistry, and Geodynamic Implications of Basaltic DykeSwarms from the Southern Continental Part of the Cameroon VolcanicLine, Central Africa

摘要

Basaltic dyke swarms in the southern continental part of the Cameroon Volcanic Line (Bangangte, Dschang,Manjo areas) are tholeiitic in composition with 46 to 50 wt.% SiO2 and have moderate Mg-numbers (53–59), mediumTiO2 contents (1.48–2,05 wt.%), and flat to mildly enriched incompatible trace element patterns. Comparison with traceelement patterns of representative Cenozoic basaltic rocks of the Cameroon Volcanic Line (Bana anorogenic complex,Mt. Bambouto, Adamawa Plateau basalts) indicates that these dykes are less enriched in light REE and show differentincompatible trace element ratios (La/Yb: 5.7 to 8.6; Zr/Nb: 7.6 to 12.0; Ba/Th: 87.7 to 93.3). The trace element patternsof the dykes and their Sr- and Nd- isotope compositions, however, are similar to those of the pre-Cenozoic volcanic rocksof the Benue Trough in Nigeria. Our data therefore suggest that these dykes represent the magmatic history related to thebreak-up of Africa and South America and are unrelated to the Tertiary volcanism of the Cameroon Line.