Midcrustal shear zones in postorogenic extension: Example from the northern Tyrrhenian Sea

摘要: Metamorphic core complexes of the Aegean region have revealed midcrustal, shallow-dipping extensional shear zones. These zones display constant kinematic indicators over large regions (100–200 km). We analyze example northern Tyrrhenian Sea and then compare it to region. first summarize our observations on ductile extension metamorphic evolution in from Alpine Corsica Tuscany. (1) Extension migrated west east early Miocene Recent Apennines; (2) is accommodated by shallow dipping at depth brittle-ductile transition, Pliocene. (3) West normal faults accommodate eastern side volcanic arc. (4) preceded along convergence front formation a thrust wedge, where high-pressure low-temperature conditions are recorded; maximum PT decrease toward east, paths systematically very cold, suggesting that part exhumation occurred during synorogenic extension. discuss possible mechanisms account for sense domains. The model involves retreat slab migration Partially molten lower crust acts as low strength zone strain localized. Eastward motion upper mantle consequence induced component arc base stronger crust. In weak crust, arc, stresses not transmitted; this produces top-to-the-east migrates eastward, following migration.