Studies of tectonic mélanges provide constraints on the evolution of active plate margins. However, resolving the pressure‐temperature trajectories of these deformed rocks, which are exhumed from low‐temperature conditions, can be challenging. We analyzed a Late Miocene‐Early Pliocene tectonic mélange formed in a shear zone in the southern Apennines (Basilicata, Italy), located in the hanging wall of a regional thrust, to provide estimates of temperature, pressure and strain. The mélange comprises slates with a finegrained phyllosilicate matrix embedding larger porphyroclasts with relict S0 bedding. Electronic microscope analysis revealed a disjunctive cleavage (S1), partially to fully transposed by a top‐to‐the‐E/SE crenulation cleavage (S2) marked by white mica and chlorite. A late weak cleavage (S3) is not accompanied by newly formed minerals. Kinematic vorticity analysis indicates a range of 20%–35% coaxial strain, whereas 3D strain analysis of deformed clasts suggests oblate strain. X‐Ray Powder Diffraction analysis of grains <2 μm indicates anchimetamorphic conditions between 200 and 250°C, with temperatures increasing by 50°C toward the thrust contact. Multi‐equilibrium modeling of coarser S1‐S2 grains ranges from 300 to 380°C, independent of their position in the shear zone. We attribute the low‐temperature range of finer grains to Apennine anchimetamorphism, whereas grains >2 μm are likely detrital and record higher pressure‐temperature conditions. Assuming a regional paleogeothermal gradient of 20°C/km, we estimate a maximum burial depth of about 12 km and a pressure of 0.32 GPa. This approach can be applied to similar contexts worldwide, providing a tool for regional tectonic reconstruction and process‐oriented studies.
The Anchimetamorphic Tectonic Mélange of Tempa Roccarossa (Southern Apennines, Italy): Insights on the Kinematic and Thermobaric Evolution of the Upper Miocene‐Pliocene Orogenic Wedge
Jacopo Natale;
2025-01-01
Abstract
Studies of tectonic mélanges provide constraints on the evolution of active plate margins. However, resolving the pressure‐temperature trajectories of these deformed rocks, which are exhumed from low‐temperature conditions, can be challenging. We analyzed a Late Miocene‐Early Pliocene tectonic mélange formed in a shear zone in the southern Apennines (Basilicata, Italy), located in the hanging wall of a regional thrust, to provide estimates of temperature, pressure and strain. The mélange comprises slates with a finegrained phyllosilicate matrix embedding larger porphyroclasts with relict S0 bedding. Electronic microscope analysis revealed a disjunctive cleavage (S1), partially to fully transposed by a top‐to‐the‐E/SE crenulation cleavage (S2) marked by white mica and chlorite. A late weak cleavage (S3) is not accompanied by newly formed minerals. Kinematic vorticity analysis indicates a range of 20%–35% coaxial strain, whereas 3D strain analysis of deformed clasts suggests oblate strain. X‐Ray Powder Diffraction analysis of grains <2 μm indicates anchimetamorphic conditions between 200 and 250°C, with temperatures increasing by 50°C toward the thrust contact. Multi‐equilibrium modeling of coarser S1‐S2 grains ranges from 300 to 380°C, independent of their position in the shear zone. We attribute the low‐temperature range of finer grains to Apennine anchimetamorphism, whereas grains >2 μm are likely detrital and record higher pressure‐temperature conditions. Assuming a regional paleogeothermal gradient of 20°C/km, we estimate a maximum burial depth of about 12 km and a pressure of 0.32 GPa. This approach can be applied to similar contexts worldwide, providing a tool for regional tectonic reconstruction and process‐oriented studies.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
