Geology of the Variscan basement of the Laconi-Asuni area (central Sardinia, Italy): the core of a regional antiform refolding a tectonic nappe stack

Abstract

The study area extends in central Sardinia between the coordinates 8°56′00″/39°55′00″ (NW corner) and 9°03′00″/39°50′00″ (SE corner). It forms part of the Sardinian Variscides that are characterized here by the western-most aspect of a regional structure known as the Flumendosa Antiform, which runs ENE-trending for more than 50 km along its axis. It represents the envelopment of several, upright km-scale minor folds that refold the different tectonic units of the Variscan Nappe zone characterized by a number of isoclinal folds, with axial plane foliation and thick ductile shear zones. The antiform is in turn deformed by late-orogenic extensional structures, namely asymmetric folds and narrow, low angle ductile shear zones that generally reactivate earlier collisional structures.

The 1:12,500 scale map completes the mapping of this important regional structure, meaning that a detailed survey of the entire mega-structure is now available. This enables more detailed structural analyses of poly-deformed areas in low-grade metamorphic conditions to be conducted, given the robust knowledge available of the lithostratigraphic succession and the geometric and kinematic outlines.

Keywords:

• Variscan orogenesis
• north-Gondwana
• regional antiform
• Nappe zone
• polyphasal deformation
• structural map

Acknowledgements

This research has been partially funded by the Regione Autonoma della Sardegna (L.R. n.7, grant to A.L.). A.F. thanks L. Carmignani, P.C. Pertusati and G. Oggiano who 20 years ago introduced him to the mapping of metamorphic basement, often recalling the necessity to return to map the Laconi area. G. Cornamusini, H. Apps and R. Carosi are thanked for their constructive review of the submitted manuscript.