THE HERCYNIAN CHAIN IN SARDINIA (ITALY)

A new geodynamic model for the Sardinian segment of the Hercynian chai n is presented. The improvement of knowledge regarding several geologi cal, metamorphic, magmatic and geochronological aspects of the Sardini an Palaeozoic basement, mainly achieved in the last few years, allows us to propose a more complete picture of its evolution. The occurrence of remnants of an oceanic suture along a major tectonic lineament in northern Sardinia, as well as the products of Ordovician calc-alkaline magmatism, testifies to the presence, during the Lower Paleozoic, of an ancient (Precambrian- Cambrian) oceanic domain and its consumption along an Andean- type subduction zone. The following Carboniferous con tinental collision caused crustal stacking with Barrovian metamorphism and southward-migrating deformation from the suture zone toward the f oreland. Early Carboniferous Culm-type facies sediments, deposited in the outermost zone of the chain, imply that continental collision took place earlier in the internal zone, from Late Devonian or Early Carbo niferous. The collisional orogenic wedge experienced ductile extension during the Late Carhoniferous as a result of gravitational collapse o f the thickened continental crust. Extensional tectonism enhanced the uplift of the chain and some regions underwent tectonic denudation or LP/HT metamorphism and somewhere anatexis. The emplacement of calc-alk aline batholiths and the development of Late Carboniferous - Early Per mian molasse basins occurred during extension that prolonged throughou t the Permian.