Geodynamic implications of "subduction related" magmatism, insights from the Tyrrhenian-Apennines region

The location and age of potassic and ultra-potassic magmatism, mostly recognized as derived from mantle sources hybridized by subducted crustal rocks, in the Tyrrhenian-Apennines system do not show any plausible causal relationship with the evolutionary history of subduction processes, reconstructed from the time pattern of accretionary activity in the Apenninic belt. On the other hand, since magmatism in the study area was always associated in space and time with major phases of crustal stretching, one could think that the uprise of magmas through the uppermost lithosphere is strictly conditioned by the occurrence of extensional tectonics and, in particular, by the formation of significant fractures in the upper brittle crust. This would imply that using the distribution of "subduction related" magmatism for recognizing the timing and location of paleosubduction processes could be misleading. The geochemical features of these magmas can provide information on the kind of tectonophysical processes which took place in the mantle during the previous evolution but, as far as we know, the delay between mantle hybridization and magmatic activity cannot easily be assessed. (C) 2000 Elsevier Science B.V. All rights reserved.