Low-angle normal faults record Early Permian extensional tectonics in the Orobic Basin (Southern Alps, N Italy)

Abstract

Well-preserved SSE-dipping low-angle normal faults (LANF) active during the Early Permian (Cisuralian) were recognized along the northern margin of the Orobic Basin (central Southern Alps, N Italy). These faults, which escaped most of the Alpine deformations, exhumed the Variscan basement during the deposition of the upper part of the Lower Permian succession (Pizzo del Diavolo Formation). Fault planes show evidence of frictional processes typical of the upper crust associated with hydrothermal circulation, responsible for the deposition of cm to m thick tourmalinite and Uranium mineralization.The recognized LANFs interacted with high-angle normal faults producing half grabens that stored the Lower Permian deposits, where synsedimentary fault activity in their hangingwall is testified by abrupt vertical and lateral facies changes, thickness variations and by soft-sediment deformations.Mesoscopic structures, exposed in the hangingwall of a major LANF (the Aga-Vedello Fault system) along a synthetic high-angle normal fault, include conjugate normal faults, horst-and-graben, domino-

Permian Hydrothermal Alteration Preserved in Polymetamorphic Basement and Constraints for Ore-genesis (Alpi Apuane, Italy)

“…At a larger scale, the present study reveals that the Alpi Apuane have recorded an hydrothermal post-Variscan event with similar features to those recognized in many ore districts in Europe (e.g., [77][78][79][80][81]85]). Further studies are needed to specify this scenario.…”

The Atlas-East Variscan -Elbe shear system and its role in the formation of the pull-apart Late Palaeozoic basins

“…Pohl et al (2018) and Zanchi et al (2019) evidenced pure extension in SSE-NNW direction instead of Permian dextral strike slip in the Central/Southern Alps. Zanchi et al (2019) inferred deformations at shallow crustal level which occurred during the Early Permian along high-angle normal faults soling into the Low Angle Normal Faults, forming the northern boundary of the Orobic Basin. Pohl et al (2018), however, highlighted the syn-kinematic emplacement of the Permian Val Biandino Quartz Diorite (287 Ma) with a D 2 mylonitic top-to-SE component of shear.…”

“…The NW-SE Carboniferous shortening direction (Neubauer and Handler 2000;Bouaziz et al 2002;Cassinis et al 2012;Padovano et al 2014) continued also in the Early Permian age (Stampfli et al 2000;Stampfli and Borel 2002;Beltrando et al 2007;Bergerat et al 2007;Muttoni et al 2009;Catalan et al 2011;Aubele et al 2012;Cassinis et al 2012;Bachtadse et al 2018). Pohl et al (2018) and Zanchi et al (2019) evidenced pure extension in SSE-NNW direction instead of Permian dextral strike slip in the Central/Southern Alps. Zanchi et al (2019) inferred deformations at shallow crustal level which occurred during the Early Permian along high-angle normal faults soling into the Low Angle Normal Faults, forming the northern boundary of the Orobic Basin.…”

Oncoids and groundwater calcrete in a continental siliciclastic succession in a fault-controlled basin (Early Permian, Northern Italy)

“…1), after the Variscan events, were affected in the Early Permian by extensional/ transtensional tectonics that produced an E-W alignment of fault-controlled continental basins. These basins, filled by volcanic and siliciclastic successions, were probably related to a wide wrench system, occurring in the low palaeolatitudes of Pangaea (Arthaud and Matte 1977;Muttoni et al 2003;Cassinis et al 2012), with some evidence of pure extension (Zanchi et al 2019). One of these basins is the Orobic Basin (De Sitter and De Sitter-Koomans 1949;Casati and Gnaccolini 1967;Cassinis et al 1988;Cadel et al 1996;Sciunnach 2001;Forcella et al 2001;Ronchi et al 2005;Berra and Felletti 2011;Berra et al 2016), about 60 km long in E-W direction and 15 km wide in N-S direction.…”