Emplacement of the Arzachena Pluton (Corsica–Sardinia Batholith) and the geodynamics of incoming Pangaea

The assembly of the Corsica–Sardinia Batholith (C–SB) coincides with final shaping of the Variscan belt and represents a key structure to unravel the feedbacks between partial melting, rheology and the evolution of collisional orogens. This paper presents a model for the genesis of the Arzachena pluton (AZN), one of the major calc-alkaline massifs of the C–SB, based on U–Pb zircon dating, thermobarometry and structural analysis. Major and trace element compositions indicate that AZN has hybrid characteristics between that of typical S- and I-type granites, that could be explained in terms of incremental melting of a heterogeneous crustal source made of metatexites and Ordovician calc-alkaline granitoids. Growth of the pluton started around 320–315 Ma with the emplacement at middle crustal level (0.37–0.4 GPa) of granodioritic melts within narrow, conjugate, NW–SE sinistral and E–W dextral shear zones. The main growth stage (311 + 6/− 4 Ma) is marked by emplacement of large volumes of monzogranitic melts that induced a local decrease of the crustal strength expressed by horizontal channel flow driven by the gravity. Finally (307.6 ± 3.5 Ma), leucogranites emplaced within radial and peripheral dilatant fractures developed during the cooling of the main body. The transition from magmatic to sub-magmatic and HT-solid state fabric observed throughout AZN indicates that deformation plays a non-trivial role during the growth of the magmatic system. Restoring the position of the Corsica–Sardinia block to early Permian coordinates allow to recast the birth of the C–SB in a consistent geodynamic framework that conciliates the development of conjugates strike-slip structures, the oroclinal bending of the chain and the thermal relaxation. This study indicates that the C–SB had an active role during post-orogenic extension rather than being just a consequence of it.

► The Corsica–Sardinia Batholith emplaced during late-Variscan strike-slip tectonics.
► The Arzachena Pluton is bracketed between 320 and 308 Ma by U–Pb zircon dating.
► Magmatic to solid-state fabrics record the emplacement-related stress field.
► Fast growth of the magmatic system weakened the crust.
► Melt-induced softening caused rotation of the local stress tensor favoring collapse.