The Tuscany Province

Abstract

The Tuscany Magmatic Province consists of various intrusive and extrusive bodies ranging in composition from mafic to felsic and from calcalkaline to ultrapotassic lamproitic. Rock age ranges from about 8 to 0.3 Ma, and decreases eastward from the Tuscan Archipelago to the Southern Tuscany mainland. An isolated sill from Sisco (Alpine Corsica, 14.5 Ma) is also included in the Tuscany Province. Silicic magmas make up several granitoid bodies and minor lavas. They are polygenetic and have been formed by crustal melting, mixing between crustal anatectic and minor amounts of mafic melts, and fractional crystallisation or AFC of intermediate-mafic parents. Except for the Capraia Island stratovolcano, mafic-intermediate rocks mostly occur as small subvolcanic and extrusive bodies, and as mafic enclaves in the silicic rocks. Mafic magmas originated within the upper mantle but have striking crustal-like trace element and radiogenic isotope signatures, resembling closely some upper crustal rocks such as metapelites. The coexistence of both crustal and mantle signatures in these magmas reveals an origin from anomalous sources, consisting of a mélange of mantle and crustal rocks. Such a particular type of source in Tuscany probably formed during the Late Cretaceous to Eocene subduction of the European plate beneath the African margin. Partial melting of subduction mélange took place much later, during the Miocene to present opening of the northern Tyrrhenian Sea behind the west dipping and eastward retreating Adriatic subducting slab. Age polarity of Tuscany magmatism reflects the timing of backarc extension that migrated from west to the east.