Non-plume magmatism and rifting during the opening of the central Atlantic Ocean

Abstract

Major Early Jurassic basaltic magmatism accompanied Pangaean rifting during the formation of the central North Atlantic Ocean. Some geodynamic models attribute Early Mesozoic Atlantic rifting and magmatism to a large mantle plume. However, the central Atlantic basalts occur in overlapping provinces of distinct dike trends and compositional types, not as magmas generated from a single plume-style source. Continental rifting was active for 25 m.y. before and after the magmatic event, during which rifting and magmatism evolved into a spreading ocean crust. Rift basalts within the continents may be contemporaneous with a large basalt wedge that marks the eastern North American margin at the start of ocean-crust production, but there are no Jurassic hotspot tracks in the Atlantic Ocean crust, and the much younger alkalic ‘hotspots’ in the eastern Atlantic Ocean cannot be linked to the rift basalts. Thus, there is no physical evidence of a plume mechanism for Early Mesozoic Pangaean rifting and magmatism. Several convection cells beneath the rift zone may be responsible for both tectonic basins and basaltic magmas, as influenced by pre-existing lithospheric structures.