Petrogenesis of dolerites from Suriname, Ivory Coast and Burkina Faso. A magmatic connection between South America and West Africa preceding the initial opening of the Central Atlantic Ocean

Abstract

The Central Atlantic Magmatic Province (CAMP), representing one of most extensive flood basalt regions of all time, is linked to the opening of the Atlantic Ocean at the Triassic-Jurassic transition ca. 200 Ma ago. CAMP rocks from Suriname and West Africa, two areas on opposite sides of the present-day Atlantic, were studied to examine magma evolution in a regional context and to explore the extent to which they have a common petrogenetic heritage. A detailed petrographic and geochemical investigation was performed on dolerites from Suriname, the Ivory Coast and Burkina Faso with the objective of characterizing their sources. Dykes in Suriname and the Ivory Coast are mainly tholeiitic basalts, while sills in Burkina Faso are mostly basaltic-andesites with tholeiitic as well as calc-alkaline affinities. The Suriname rocks are slightly more evolved (Mg#=34-46) than the Ivory Coast dolerites (Mg#=43-51), whereas the Burkina Faso dolerites include the least evolved compositions (Mg#=45-66). Petrographic and geochemical observations suggest that moderate crustal contamination could have occurred during magma evolution. A geographic subdivision into high-Ti (1.93-3.70 wt.% TiO2) and low low-Ti (0.91-1.18 wt.%) dolerites is consistent with a similar compositional grouping in other parts of the CAMP. However, overall geochemical characteristics tend to be distinct. The Suriname and Ivory Coast dolerites fall in a narrow zone of high-Ti magmatism along the margins of the present-day Atlantic Ocean, where preferential upwelling shortly before initial rifting has been proposed. According to trace-element signatures and results from partial melting models, the mantle sources of the Suriname and Ivory Coast dolerites were different from those of the Burkina Faso rocks. Minor differences in trace-element signatures point to inhomogeneity of sources and variations in melting conditions on regional as well as local scales. Relatively deep melting of a garnet-rich source with primitive-mantle like composition is inferred for the Suriname and Ivory Coast dolerites, whereas the Burkina Faso dolerites originated by shallower melting of a more spinel-rich source that might have been affected by subduction-type enrichment. Chemostratigraphic criteria, used in correlations of northern CAMP basalts, are not directly applicable to southern counterparts on both sides of the Atlantic Ocean.