Abstract

The chemical compositions of initial flood basalts that were extruded into rift basins related to the break-up of Pangea are distinguished from secondary Pangean flows that quickly followed. Mesozoic Pangean flows are found in eastern North America (Watchungs), Morocco (High Atlas), Portugal (Algarve), South Africa (Karroo), Brazil (Parana) and Siberia (Norilsk). Initial Pangean flows are characterized by a virtually identical composition that is absent, or rarely found in flood basalt provinces not associated with Mesozoic rifting. They contain lower concentrations of high field strength elements (HFSE) than non-Pangean flood basalts and have isotopic ratios consistent with a subcontinental lithospheric keel source. They may be the product of unusually strong (Pangean) tensional forces, low degrees of partial melting of a homogeneous mantle source and rapid penetration through the lithosphere near new major plate boundaries or failed boundaries at locations beyond the compositional influence of OIB type plumes.

In contrast, overlying secondary Pangean basalts are compositionally diverse, ranging from distinct incompatible element depletion to compositions typical of non-Pangean flood basalt.