One of the most controversial points regarding the Tertiary-Quaternary magmatism spread across the Euro-Mediterranean region consists in evaluating both the nature of its mantle source and the mechanisms responsible for the common HIMU-like character of erupted lavas. From a geochemical point of view, such a feature might be related to plume upwelling. However, the lack of peculiar characteristics typical of plume-related magmatism (i.e. large-scale doming, linear trends of volcanic centers in time and space, large volumes of erupted magmas) seems to be the main argument against the hypothesis of a standard hot-spot activity. We try to reconcile geochemical and geophysical data through a multidisciplinary investigation involving geochemistry, timing and locations of the main Na-rich alkaline volcanic centers, seismic tomography and plate kinematics. 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 (CEBRIA et alii, 2006). We propose that the geochemically uniform material presently located in the Euro-Mediterranean mantle derives from a contamination event triggered by the Central Atlantic Plume (CAP) on late Cretaceous-early Paleocene (PIROMALLO et alii, 2008). Plate reconstructions show that at this time the oldest magmatic centers were located SW of their present day position, in proximity of the CAP hot spot, on top of a low seismic velocity anomaly rising from the lower mantle. We suggest that the migration of the Eurasian and African plates north-eastwards involved also the plume head material, which moved in the same direction, being coupled to the lithospheric plate. The differential of velocity between the two plates with respect to the impinging CAP hot spot might have favored the detachment of the plume-head and the spreading of geochemically uniform material in the shallow sub-lithospheric Euro-Mediterranean mantle. Subsequent regional scale dynamics, such as local extensional activity (i.e. in the European Cenozoic Rift System, ZIEGLER, 1992) or slab vertical/horizontal tears (i.e. in the Veneto Volcanic Province, MACERA et alii, 2008; Roman Province, GASPERINI et alii, 2002; and Calabrian Arc, FACCENNA et alii, 2005), may have favored upwelling and partial melting of the frayed plume head material by adiabatic decompression, giving rise to the heterogeneous spatial and temporal distribution of HIMU-like volcanics. In our opinion, the Euro-Mediterranean upper mantle contamination might be ultimately related to a global event occurred during the Cretaceous as a consequence of a mantle avalanche caused by the Tethys closure (MACHETEL & HUMLER, 2003).
On a super plume origin for the Tertiary-Quaternary volcanism in the European and Mediterranean area
MACERA, PATRIZIA;
2008-01-01
Abstract
One of the most controversial points regarding the Tertiary-Quaternary magmatism spread across the Euro-Mediterranean region consists in evaluating both the nature of its mantle source and the mechanisms responsible for the common HIMU-like character of erupted lavas. From a geochemical point of view, such a feature might be related to plume upwelling. However, the lack of peculiar characteristics typical of plume-related magmatism (i.e. large-scale doming, linear trends of volcanic centers in time and space, large volumes of erupted magmas) seems to be the main argument against the hypothesis of a standard hot-spot activity. We try to reconcile geochemical and geophysical data through a multidisciplinary investigation involving geochemistry, timing and locations of the main Na-rich alkaline volcanic centers, seismic tomography and plate kinematics. 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 (CEBRIA et alii, 2006). We propose that the geochemically uniform material presently located in the Euro-Mediterranean mantle derives from a contamination event triggered by the Central Atlantic Plume (CAP) on late Cretaceous-early Paleocene (PIROMALLO et alii, 2008). Plate reconstructions show that at this time the oldest magmatic centers were located SW of their present day position, in proximity of the CAP hot spot, on top of a low seismic velocity anomaly rising from the lower mantle. We suggest that the migration of the Eurasian and African plates north-eastwards involved also the plume head material, which moved in the same direction, being coupled to the lithospheric plate. The differential of velocity between the two plates with respect to the impinging CAP hot spot might have favored the detachment of the plume-head and the spreading of geochemically uniform material in the shallow sub-lithospheric Euro-Mediterranean mantle. Subsequent regional scale dynamics, such as local extensional activity (i.e. in the European Cenozoic Rift System, ZIEGLER, 1992) or slab vertical/horizontal tears (i.e. in the Veneto Volcanic Province, MACERA et alii, 2008; Roman Province, GASPERINI et alii, 2002; and Calabrian Arc, FACCENNA et alii, 2005), may have favored upwelling and partial melting of the frayed plume head material by adiabatic decompression, giving rise to the heterogeneous spatial and temporal distribution of HIMU-like volcanics. In our opinion, the Euro-Mediterranean upper mantle contamination might be ultimately related to a global event occurred during the Cretaceous as a consequence of a mantle avalanche caused by the Tethys closure (MACHETEL & HUMLER, 2003).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
