Ultrapotassic volcanic centres as potential paleogeographic indicators: The Mediterranean Tortonian ‘salinity crisis’, southern Spain

Abstract

Dated peperites associated with ultrapotassic volcanic centres of the Neogene Volcanic Province of southeast Spain are of particular interest within the complex tectonomagmatic context of the Western Mediterranean because they show clear volcano-sedimentary interactions making them a valuable tool for correlating between Miocene sedimentary basins in the region. Detailed field mapping of two coeval, but geographically separate, ultrapotassic volcanic centres (Zeneta and La Aljorra), and comparison of sedimentary facies and radiometric ages with another at Fortuna, suggest that these centres apparently formed at approximately the same time, late Tortonian, by the same tectonomagmatic process, strike-slip, and in the same, shallow marine, paleogeographical context. Stratigraphic indicators in the Miocene basins suggest that basin-closure initiated in the region during the late Tortonian, prior to the main Mediterranean Messinian salinity crisis. Notably, many of the ultrapotassic volcanic centres are situated close to, and elongated along, the basin margins faults. We suggest, therefore, that movement of basin margin faults that closed the Miocene sedimentary basins causing drying out also facilitated the contemporaneous ascent of ultrapotassic magma. So, volcano-sedimentary interactions may be used to make inferences about both the tectonomagmatic and paleogeographic evolution of a region. In southeast Spain peperites provide evidence that the Tortonian ‘salinity crisis’ was geographically more widespread, extending to the southeast, than previously recognized.

Keywords

• Tortonian
• Peperites
• Lamproite
• Basin-closure
• Salinity crisis