Authigenesis of amphibole and its relationship to the diagenetic evolution of lower cretaceous sandstones of the Potiguar rift basin, northeastern Brazil

Authigenic amphibole occurs in the fan-delta-front arkoses and lithic sandstones of the Neocomian Pendência Formation in the Potiguar rift basin, northeastern Brazil as overgrowths, fracture-healing and replacement of detrital amphibole. The amphibole, which is closely associated with diagenetic albite, chlorite and sphene, has precipitated from K-Na-Cl brines enriched in Ti-Fe-Mg, at temperatures ≤100°C. These ions were derived from the diagenetic alteration of detrital amphibole and pyroxene, chloritization of volcaniclastic sediments at the base of the formation, and from brines that ascended along faults from the underlying basement.