Delamination of the Continental Lithosphere and Magmatogenesis: Inferences from the Tyrrhenian Area

G. Lavecchia, F. Stoppa

On the basis of geologic and geophysical data, the Tyrrhenian rift zone is interpreted here as the result of an eastward-migrating process of delamination of the continental lithosphere. A fundamental consequence is the development of complex magmatogenetic processes within the crust, the lithosphere, and the asthenosphere.

Starting from this point of view, we have reclassified the Neogene-Quaternary Italian magmas by means of multivariate analysis and defined new homogeneous magmatic series whose spatial and temporal distributions have been compared with the tectonic and geophysical setting of the Tyrrhenian Sea and its margins. In such a way a magmatogenetic model has been defined that helps us explain globally the different aspects of Peri-Tyrrhenian magmatism and to insert them in the framework of a homogeneous geodynamic environment.

The delamination of the Tyrrhenian lithosphere is accompanied by partial melting of the asthenosphere due to rapid unloading that enables partial melting of the more volatile fraction of the mantle rocks. In such a way alkaline and/or carbonate magmas are produced. In the meantime the footwall rocks across the extending lithosphere are subject to many kilobars of pressure drops, producing subalkaline magmas by partial melting of the lithosphere. Crustal simple shear deformations, on the other hand, enable anatexis of the lower continental crust, producing at its bottom granitic magmas.

Thus, the Italian parent magmas are hypothesized to be produced by the above process, whereas the volcanic activity that takes place over the Peri-Tyrrhenian margins is supposed to be permitted by vertical deformations subsequent to the horizontal tension and caused by a sort of elastic rebound.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.