The Meran-Mauls segment of the Periadriatic Fault System, Italy: pure thrusting across the brittle-plastic transition
Authors: Zanchi Andrea , Zanchetta Stefano , Montemagni Chiara , Mair Volkmar , Morelli Corrado , Mascandola Claudia 
Published: March 2022

&lt;p&gt;The Meran-Mauls Fault (MMF) connects the North Giudicarie Fault with the Pustertal segment of the Periadriatic Fault System (PFS), which separates the Southern Alps from the Europe-vergent Alpine collisional belt. Our study is based on detailed multiscale analyses carried out within the CARG project (National Italian Cartography) for the survey of the Meran (Bargossi et al., 2010), Sankt Leonhard and Sterzing geological sheets of the 1:50,000 geological map of Italy. In the frame of this project, we performed detailed geological mapping along key-sections, mesoscopic and microscopic structural analyses of fault rocks, vorticity analyses of mylonites, paleostress estimates and radiometric dating of pseudotachylytes. Although several models suggest that the PFS developed in a dextral transpressional regime during the Cenozoic, following the Adria-Europe collision, our analyses suggest that the Meran-Mauls Fault and related structures were active with a marked reverse kinematics (Viola et al., 2001), displaying several switches in the late stages between ductile and brittle deformation. Reverse motion is chiefly suggested by down-dip mineral lineations in early mylonites developed in greenschist-facies conditions within the Austroalpine units exposed along the hanging wall of the fault zone, as well as in the footwall within the Brixen Phyllites and in the Ifinger Permian intrusive, both belonging to the crystalline basement of the Southern Alps. SE-vergent thrusting was followed in time by a dextral reactivation in brittle conditions, which is evident especially in the eastern portion of the MMF starting from the Pennes Pass area. Our reconstruction is corroborated by the analyses of other important fault zones mainly developed in the Austroalpine thrust stack in the hanging wall of the MMF, showing a similar kinematic evolution. Strike-slip to normal faults with different trends ranging from NW-SE to NE-SW followed in time the dextral motion along the MMF, displacing previous structures. Paleostress reconstructions indicate a progressive switch of the main direction of compression from NW-SE to N-S, as previously suggested by us in the Central Alps (Agliardi et al., 2009).&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Agliardi F., Zanchi A., Crosta, G.B. (2009) &amp;#8211; Tectonics v. gravitational morphostructures in the central Eastern Alps (Italy): Constraints on the recent evolution of the mountain range. Tectonophysics, 474, 250-270.&lt;/p&gt;&lt;p&gt;Bargossi G.M., Bove G., Cucato M., Gregnanin A., Morelli C., Moretti A., Poli S., Zanchetta S. &amp; Zanchi A. (2010) - Note illustrative della Carta Geologica d&amp;#8217;Italia a scala 1:50.000 Foglio 013 Merano. CARG. ISPRA, 285 pp.&lt;/p&gt;&lt;p&gt;Viola G., Mancktelow N.S., Seward D. (2001) - Late Oligocene-Neogene evolution of Europe-Adria collision: New structural and geochronological evidence from the Giudicarie fault system (Italian Eastern Alps). Tectonics, 20, 999&amp;#8211;1020.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;