Mehmood, Mubashir (2025) Crustal Shortening Mechanisms and Accretionary Prism Architecture in the Southern Apennines (Cilento–Mt Sirino), Italy. [Tesi di dottorato]

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Abstract

This study investigates the orogenic evolution of some key areas in the southern Apennines. The work focused on three key geological units: (i) the Lagonegro unit in the Mt. Sirino area (Basilicata region); (ii) the oceanic wedge of Ligurian Accretionary Complex (LAC); and (iii) the Cilento Group deposited in a wedge-top basin above the LAC. The latter are both studied in the Cilento area (Campania region). The Lagonegro unit exposed in the Tempa Roccarossa area hosts a tectonic mélange, formed in a shear zone associated with a regional thrust, that exhibits multiple deformation stages, including brittle and ductile shear, with a burial temperature range of 200°C-250°C (anchimetamorphism), corresponding to depths of 10–13 km. Kinematic vorticity and strain analyses indicate a dominant simple shear component with a secondary pure shear deformation, and a general flattening strain. The LAC shows polyphase deformation, characterized by veins, stylolites, cleavages, folds and faults. Thermal analysis using the Kubler Index (KI) and Raman spectroscopy indicates temperatures of 250-280°C (anchimetamorphism) and pressures of 0.3–0.4 GPa, corresponding to a burial depth of 11–15 km. This suggests a geothermal gradient of 17–25°C/km. Kinematic and strain analyses indicate similar features of the LAC deformation. In the Cilento Group basin, paleocurrent analysis reveals complex turbidite current flow directions, with sediment sources including the LAC, the overriding plate (Calabria-Peloritani Terrane), and volcaniclastics from synorogenic volcanic arcs. The study reconstructs the tectonic collapse of the Ligurian Accretionary Complex and the development of the wedge-top basin, indicating a transition from compressional to extensional tectonics. The integration of structural, petrographic, and geothermometric data provides new insights into the thermal history, deformation mechanisms, and sedimentary evolution of the Cilento region in the southern Apennines, contributing to a broader understanding of accretionary wedge formation at active plate margins. These findings enhance our understanding of the region's tectono-metamorphic and deformational evolution and provide a framework for understanding the interaction among fluid migration, shear zone dynamics, and sedimentation during orogenic processes. By applying these results to other active tectonic settings, the study offers a tool for regional tectonic reconstruction and helps clarify the processes governing accretionary wedge and orogenic mechanisms.

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