Continental collision, slab detachment and K-rich magmatism: central-southern Italy as a type example

Central-southern Italy offers a unique opportunity to investigate the relation between subduction zone evolution and post-collisional, K-rich volcanism. In our recent model for the geodynamic evolution of the region the process of slab detachment plays an important role (see Wortel and Spakman, Science, vol. 290, p. 1910-1917, 2000). The primary evidence for relatively recent (Late Miocene to Present) slab detachment in central Italy comes from seismic tomography studies but other geological, and numerical modeling studies have substantiated the inferences. We use our geodynamical model as a basis for the analysis of the relation between terminal stage subduction and post-collisional volcanism in central-southern Italy. In particular, we address the question to which extent the inferred geodynamic framework is capable of generating the typical characteristics of volcanism in the Roman Province. Slab detachment is not uniform along the plate boundary. Where it occurred, and where it occurred at mid-lithospheric depths, it strongly affected the thermal evolution of the plate boundary and it exposed crustal and lithospheric mantle to temperatures characteristic for upper mantle depths (> 100 km) . In addition, decompression of the asthenospheric material filling the gap upon shallow slab detachment contributed to the magma generation. As a whole, it is a naturally short-lived phenomenon. We conclude that the K-rich signature, the compositional diversity, and the spatial-temporal variations of the region’s magmatism are a natural consequence of the geodynamics as represented in our shallow slab detachment model. For several other regions (e.g. Northern Africa) suggestions have been made concerning the possible or likely relevance of the slab detachment (slab breakoff) process for the generation of post-collisional, K-rich volcanism. Our approach applied in this active region, where slab detachment is inferred to have taken place recently, has the advantage of implicitly incorporating enormous amounts of information acquired by geophysical and geological studies independent of petrological data. As such, our study may serve as a calibration of the relation between subduction zone evolution and post-collisional, K-rich volcanism and may shed light upon post-collisional magmatism in older regions of continental collision and suturing, among which the Tethyan-Himalayan suture zone is the most prominent one.