The Mt.Gottero Unit (Internal Ligurid Units, Northern Apennines) displays a thick sedimentary sequence ranging in age from ?Late Jurassic to Paleocene p.p. interpreted as sedimentary cover of the Jurassic ophiolites. This unit is characterized by a complex structural history due to superposition of four folding phases (D1-D4) associated with minor brittle events. The deformational history can be connected with tectonic events related to Paleocene-Eocene intraoceanic subduction followed by Miocene thrusting on the Apennine continental margin. The structural evolution can be summarized as follows: Pretectonic parallel-bedding veins characterized by mosaic texture predate all the deformational phases. The D1 phase consists of strongly non-cylindrical folds with approximately similar geometry. Although characterized by scattered distribution, on the stereonet a N150°E/030°E trend of the A1 axis can be envisaged. In the shales the S1 foliation is classifiable as slaty cleavage with metamorphic mineral assemblage of quartz + chlorite + albite + white mica (illite). The illite crystallinity and vetrinite reflectance point to low grade metamorphism related to P/T conditions of 250°/350° C and 3/4 kb. Thrusts bounded by ultra- and cataclastic levels related to the latest stages of D1 phase are also recognized. The meso- and microstructural characteristics and the analyses of the syntectonic veins suggest a mainly non-coaxial deformation history related to high value of simple shear. The D2 phase is characterized by folds with approximately parallel geometry. The A2 axis shows a N130°E/180°E trend, while the N/NE vergence of D2 phase structures is well recognized. The axial plane foliation S2 is classifiable in the shaly lithologies as crenulation cleavage. Post-D2 phase a strike-slip fault system enhanced by block rotation and flower structures is also present in the Mt.Gottero Unit. The D3 and D4 phases are characterized by gentle folds with sub-vertical axial plane. The pre-Oligocene D1 and D2 phases are related to underplating and later uplift of the Mt.Gottero Unit in a subduction zone.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.