Ductile wrench tectonics and exhumation of hercynian metamorphic basement in Sardinia: Monte Grighini Complex |
| |
Authors: | G Musumeci |
| |
Institution: | Dipartimento di Scienze della Terra, Via S. Maria 53, 56126 Pisa (Italia) |
| |
Abstract: | AbstractThe Monte Grighini Complex (Central-Western Sardinia) is a NW-SE trending metamorphic complex of Hereynian age made up of a medium grade Lower tectonic unit with mylonitie granitoids and a low grade Upper tectonic unit exposed in the westernmost and southernmost portions of this complex. The Lower Unit shows a prograde metamor phism from garnet to sillimanite zone and the transition from MP/MT to LP/HT metamorphism. The metamorphic climax was reached at the end of the main deformative phase 1)2 (600° C. 6 kbar). After the main tectonic and metamorphic phase. the Lower Unit was affected by a wide NW-SE trending ductile dextral wrench shear zone. Intrusive rocks emplaced within the shear zone yielded radiometric ages of 305-300 Ma. Shear deformation leads to low temperature C-S mylonites and retrograde phyllonitic rocks with subhorizontal NW-SE trending stretching lineations. Kinematic analysis of the shear zone points to a dextral sense of shear with an amount of ductile displacement of about 7 km. Later low angle N-S and E-W trending normal faults are associated with cataclastic zones separating the Lower Unit from the Upper one. These faults originated during a later evolutionary stage of the shear zone. This shows a progressive change of deformation regime from duetile wrenching to brittle normal faulting. The Monte Grighini Complex is a good example of ductile wrench tectonics. followed by uplift and extension in the Paleozoic basement of Sardinia. |
| |
Keywords: | Sardinia Hereynian orogenesis Wrench tec-tonies S-C mylonites Extensional tectonics |
|