Geometry and impact of transpressional faulting in polyphasic metamorphic orogenic belts: the Viù Deformation Zone (inner Western Alps)

Abstract

This paper describes the geometry, structural architecture of the Viù Deformation Zone (VDZ), a brittle-ductile to brittle structure affecting the metamorphic units of the inner Western Alps, and its role in modifying the preexisting syn-metamorphic structural setting. The VDZ reactivates and displaces the contact between two different oceanic units, the Lanzo Ultramafic Complex and the Lower Susa-Lanzo valleys Unit, characterized by a polyphasic syn-metamorphic deformation. It shows a strike-slip duplexes geometry, constituted by N-S reverse-dextral faults linked by NW-SE antithetical sinistral-reverse faults, and represents a contractional stepover zone along an N-S regional dextral-reverse structure, the Col del Lis-Trana Deformation Zone.The activity of these transpressional structures caused the steepening of the Lanzo Ultramafic Complex and drove the last stages of its exhumation. The 3D geometry of the VDZ seems to have been strongly controlled by the reactivation of different pre-existing anisotropies, like the buried western edge of the Ivrea body and the metamorphic foliations. Brittle reactivation also induced blocks rotation mechanism along this structure, causing anomalous kinematic relations between the VDZ associated faults.This study, hence, shows that in metamorphic orogens the mechanisms generating strike-slip duplexes may be different from those classically provided by literature, with brittle reactivation and blocks rotation strongly prevailing on newly formed faults. In such orogens, moreover, rotations induced by transpressional faulting may be sometimes mistaken with steep syn-metamorphic shear zones. Therefore, the overlook and the underestimation of the effects of the brittle deformations and of its associated rotations may cause erroneous interpretation in the tectonic reconstructions

New geomorphological and chronological constraints for glacial deposits in the Rivoli‐Avigliana end‐moraine system and the lower Susa Valley (Western Alps, NW Italy)

“…The Susa Valley is bordered at its western and eastern ends by two regional fault systems: (i) a longitudinal fault system (Barféty et al ., ; Sue and Tricart, ), characterized by an early phase of normal activity and subsequent right‐lateral reactivation during the Pliocene, and (ii) the Canavese Line and Col del Lys − Trana Deformation Zone, with dextral transtensive displacement, active since the Late Oligocene, and a last Plio‐Pleistocene reactivation, documented in the lower Susa Valley, which involved pre‐glacial continental successions (Balestro et al ., ; Perrone et al ., , ). A transverse fault system (Barféty et al ., ; Sue and Tricart, ) lies between these two N–S fault systems, corresponding to NE–SW trending normal faults with evidence of left‐lateral reactivation.…”

Pre-Alpine extensional tectonics of a peridotitelocalized oceanic core complex in the Late Jurassic, high-pressure Monviso ophiolite (Western Alps)

“…We think that inversion of extensional detachment faults into intraoceanic subduction zones under favorable geodynamic conditions provides a viable mechanism for basin collapse and closure without invoking other external driving forces in a given region. Acknowledgments Bigi et al, 1990;Bousquet et al, 2012;Fantoni et al, 2003Fantoni et al, , 2004Funicello et al, 1981;Ghibaudo et al, 2014;Ghielmi et al, 2013;Manzotti et al, 2014;Festa et al, 2015bFesta et al, , 2015cPerrone et al, 2015). (B) Tectonic cross-section across the Western Alps (modified from Lardeaux et al, 2006).…”