Petrogenesis and stratigraphy of the high-Ti/Y Urubici magma type in the Parana flood basalt province and implications for the nature of 'Dupal'-typemantle in the South Atlantic region

The high-Ti/Y Urubici (or Khumib) magma type of the Parana-Etendeka large i gneous province has a restricted spatial extent, near the southeast Brazili an coast and in the northern Etendeka (Namibia). Urubici flows are interbed ded with low-Ti/Y Gramado flows. Flow correlations indicate that local topo graphic relief was important in controlling emplacement of flows, and that lavas near the coast have undergone up to 1 km of post-magmatic uplift rela tive to inland areas. Urubici magmas have undergone extensive fractional cr ystallization (MgO < 5.5 wt%). Stratigraphic variations highlight complexit ies of mixing and minor crustal assimilation indicative of open-system magm atic plumbing. The least contaminated samples have high La/Nb (similar to 1 .5) and (Tb/Yb)N(similar to 2.5), Sr-Nd isotopes close to Bulk Earth (Sr-87 /Sr-86(i) similar to 0.7050; epsilon(Ndi) - 2.7), and Dupal Pb isotopes wit h unradiogenic Pb-206/Pb-204 (similar to 17.6). These features are similar to those of the Walvis Ridge DSDP (Deep Sea Drilling Project) Site 525A bas alts that define the EM1 oceanic mantle component, and many are also shared with local Cretaceous alkalic magmas that are inferred to be lithospheric mantle melts. Low Pb-206/Pb-204 material found in the Urubici and Site 525A basalts is not seen as a mixing end-member within the modern Tristan plume system or in South Atlantic mid-ocean ridge basalt. An origin from lithosp heric mantle material, delaminated and dispersed within rite asthenosphere following continental break-zip, is preferred. Thus the South Atlantic Dupa l mantle anomaly cannot be considered as a single entity: Urubici flood bas alts and Walvis Ridge Site 525A basalts have a relatively shallow origin wi thin originally lithospheric mantle, whereas the Tristan plume is a deep ma ntle upwelling.