A Late Cretaceous Contamination Episode of the European-Mediterranean Mantle

One of the most debated issues about the Tertiary-Quaternary alkaline magmatism of the Euro- Mediterranean region is the assessment of both the nature of its mantle source and the mechanism responsible for the common HIMU-like (High μ=high 238U/204Pb) character of erupted lavas, enduring over about 100 million years in diverse tectonic environments. We reconcile here geochemistry, timing and locations of the main Na-rich alkaline volcanic centers, seismic tomography and plate kinematics. We propose that the common component of the Euro-Mediterranean mantle derives from a contamination episode triggered by the rise of the Central Atlantic Plume (CAP) head. Highly incompatible element ratios and Sr-Nd-Pb isotope compositions indicate a common source for Na-rich alkali basalts of NE Atlantic, Europe and North Africa. Plate reconstruction shows that at Late Cretaceous-Paleocene time the oldest magmatic centers of the Euro-Mediterranean region were shifted more than 2000 km SW of their present day position, close to the CAP hot spot location, where seismic tomography detects a broad low seismic velocity region in the lower mantle. Thus, a possible common source for the Cenozoic Euro-Mediterranean volcanism could refer to this geographical area, representing both its Cretaceous paleo-position and geochemical endmember. The north-eastward migration of the Eurasian and African plates involved also the CAP contaminated mantle, which moved in the same direction coupled to the lithospheric plate, explaining the presence of geochemically-uniform material in the sub-lithospheric mantle. During the Tertiary, regional-scale convection and related processes such as rifting, back-arc spreading, slab detachment/windows, may have favored upwelling and partial melting of the frayed plume head material via adiabatic decompression, shaping the discontinuous spatial and temporal distribution of HIMU-like volcanics. The growing supply of subducted lithosphere may explain as well the increase of crustal isotopic signatures of alkaline magmas with time.