Magmatic and volcanological evolution of the Desertas rift zone (Madeira Archipelago, NE Atlantic)

Abstract

Volcanology, volcanic rift zones, Madeira, fluid inclusions, thermobarometry, geochemistry, geochronology. - Madeira and the Desertas Islands show two well-developed volcanic rift zones which intersect near the eastern tip of Madeira (São Lourenço peninsula). To examine a possible genetic link, volcanic structures, rock ages and rock compositions were investigated at the Desertas and São Lourenço. Barometric data derived from fluid inclusions and clinopyroxene-melt compositions indicate fractionation at multiple levels within the mantle beneath the rift zones, followed by temporary magma stagnation within the crust. Depths of crustal stagnation beneath São Lourenço and the Desertas differ significantly, and there is no evidence for a shallow magma reservoir feeding both rifts. This suggests that Madeira and the Desertas have separated magma supply systems. 40Ar/39Ar age determinations revealed that Desertas volcanism lasted from >5.1 to 1.9 Ma overlapping in age with the shield phase of Madeira. Eruptive quiescence between 4 and 2.5 Ma at São Lourenço coincides with the main period of volcanism on the Desertas. Major and trace elements and ...