Tracking a common mantle plume, from Iberia to Canarias-Madeira

The origin, processes, and significance of intra-plate magmatism have long been debated, with the spotlight predominantly directed to oceanic volcanism. However, on continental margins the mechanisms that can generate or sustain prolonged magmatism throughout vast regions remains puzzling, with hotspot (s.s.), mantle plumes or edge-driven convection being invoked to explain these noteworthy manifestations.

Based on the age of emplacement and the present-day location of the magmatic occurrences, across the Central-East Atlantic Alkaline Province (CEAAP; Southwest Iberian Margin - SWIM, Morocco, Canarias and Madeira), the crustal paleogeographic location of emplacement was investigated. In parallel we analysed their relative motion paths relative to a stationary mantle reference and its associated tectonic plates.

Magmatism in this province, is revealed to be derived from a stationary super-plume ponded at the 660 km discontinuity at least since the late Cretaceous. Additionally, the recent discovery of new magmatic manifestation on the SWIM shows that magmatism in the region is more pervasive than anticipated. Our models indicate that this active mantle upwelling resulted in three main periods of activity and has been responsible for the irregular spatial-temporal distribution of magmatism. As tectonic plates wandered, alkaline magmatism that was initially emplaced within the Southwest Iberian Margin (103-70 Ma), was subsequently affecting continental Morocco (57-45 Ma), Canarias and Madeira (< 32 Ma), resulting in episodic and dispersed intra-plate magmatic activity, both on oceanic and continental crust. We estimate the position of the stationary mantle upwelling located between 20-30ºN and 10-20ºW.

Our models unravel prominent paleogeographic affinities of a common mantle source, linking late Cretaceous SWIM magmatism (e.g., Tore NW, Tore N, Ormonde, Sintra, Monchique) with present day Canarias and continental Morocco (e.g., Taourirt, Rekkame, Tamazert). Contrastingly, the motion paths from the occurrences on the SWIM (e.g., Torillon, Ampère and Unicorn), relate with the more recent magmatism at Madeira. Older magmatism from southern Canarias (e.g., Bisabuelas, Henry, Tropic) is revealed affine to the present-day location of the Sahara seamounts and Cape Verde. Younger magmatism in the High Atlas (e.g., Siroua, Sarrho, Oujda) appears to be as unrelated with the inherited SWIM mantle upwelling.

Results suggest that the intermittent emission of secondary mantle plumes (plumelets) ascended to the crust to form, as a whole, a cluster of dominantly non-aligned magmatism manifestations, including laccoliths, seamounts and volcanoes. Moreover, the spatial-temporal analysis of the magmatism on the CEAAP indicates a relative N-NW rejuvenation of emplacement. This is considered to have resulted from post-Cretaceous induced drag, as the plumelets progressively interacted with the base of the Nubian plate.

Acknowledgments: RP is supported Fundação para a Ciência e a Tecnologia, I.P. (FCT), Portugal, through the research unit UIDB/04035/2020 - GeoBioTec. JCD is supported by an FCT contract CEEC Inst. 2018, CEECINST/00032/2018/CP1523/CT0002.