Reconstruction of igneous, tectonic and sedimentary events in the latest Carboniferous-Early Permian Seui basin (Sardinia, Italy), and evolutionary model

Based on a detailed geological mapping, drilling data and structural-petrological interpretations, the processes controlling the evolution of the latest Carboniferous-Early Permian Seui Basin (Sardinia) are reconstructed and interpreted in the post-Variscan geodynamic context. The basin represents a good exposure where the tectonic, sedimentary and igneous processes are recorded. The evolutionary picture is analogous to that occurring in many intramontane basins developed as a consequence of the transtensional and transpressional wrench tectonics active from the Maghrebides to a large part of Europe. The opening of the basin structure was associated with andesitic volcanism interlayered with detrital sedimentation in a fluviolacustrine to marsh environment. Abundant flora and repeated flows of rhyolitic pyroclastics from distal sources, probably to the NW, are recorded within the sedimentary succession. The basin was bounded to the N and to the W by morphological highs due to concomitant bowing of the metamorphic basement and intrusion of diorite dykes feeding dacite cryptodomes. The growth of the cryptodomes triggered the gravitational collapse of basement and cover slices. Contact metamorphism and hydrothermal processes along fractures also affected both basement and sediments. The andesites and the diorite-dacite suite, as well as the overlying rhyolitic ignimbrites have a common calc-alkaline signature, but different geochemical trends. Hybridisation of the magmas due to the complex interaction of mantle-derived and crustal melts, through different stages of assimilation, fractionation and mixing, probably accounts for the geochemical and petrographic characteristics.