Tectonometamorphic evolution of a long-lived crystalline basement: the northern Dora-Maira Massif in the Germanasca &#8211; Pellice Valleys (Western Alps)
Authors: Dana Davide , De Cesari Francesco , Montomoli Chiara , Iaccarino Salvatore , Rubatto Daniela , Lenci Simone , Corno Alberto , Carosi Rodolfo 
Published: August 2024

Recent investigations in the northwestern part of the Dora-Maira Massif (Nosenzo et al., 2024 and references therein) shed new light on the structural architecture and metamorphism of its tectonic units, with the discovery of a new UHP unit. Despite these efforts, many open questions remain regarding the structural architecture and tectono-metamorphic evolution of this basement. In this contribution, we present preliminary data from an area located between the Tredici Laghi and Conca Cialancia natural park (Germanasca - Pellice Valleys), a so far poorly explored mountainous region. This area consists of a polycyclic basement composed of micaschist, orthogneiss, paragneiss, marble and metabasite. The structural setting of the area has been reconstructed using a new structural map and geological cross-sections carried out in the framework of the CARG mapping project (Sheet 172 &#8211;&#8220;Pinerolo&#8221;). Microtectonics studies and preliminary P-T-t data have been integrated to tentatively provide a more complete picture of the tectono-metamorphic evolution of the studied area.Geochronological analyses (U-Pb dating on zircon) allow the recognition of several generations of orthogneiss, with locally preserved overlapping relationships in the field, whose ages range from Early to Late Ordovician. The Alpine structural evolution of the area has been deduced from the correlation of the P-T path with the microstructures. The S1 foliation, rarely preserved in microlithons, developed during prograde P-T conditions and is associated with the syn-kinematic recrystallization of phengite, paragonite, chloritoid, garnet, rutile and probably sodic amphibole (currently pseudomorphsed by albite and chlorite). A subsequent S2 foliation (defined by a second generation of phengite, paragonite, chloritoid, garnet with epidote, ilmenite, albite and minor chlorite) developed along E-W trending lineation-parallel folds. D2 deformation is very heterogeneous: a mylonitic fabric is present in high-strain domains, whereas local pre-Alpine features are preserved in low-strain domains (as already documented elsewhere by Nosenzo et al., 2022). The D3 event is associated with the development of a local S3 foliation, parallel to the axial planes of open NW-SE trending folds and deforms all the previous structures. The S3 foliation is associated with metamorphic re-equilibration in greenschist facies. Several examples of superimposed D2 and D3 folds are documented at various scales. The axial planes of the D3 folds are bended by the final doming of the Dora-Maira nappe stack (D4), associated with late metamorphic conditions.This research has been supported by the funds of the CARG &#8211; Project &#8211; Geological Map of Italy 1:50,000&#160;Nosenzo, F., Manzotti, P., Poujol, M., Ball&#232;vre, M., &amp; Langlade, J. (2022). A window into an older orogenic cycle: P&#8211;T conditions and timing of the pre&#8208;Alpine history of the Dora&#8208;Maira Massif (Western Alps). Journal of Metamorphic Geology, 40(4), 789-821.Nosenzo, F., Manzotti, P., Krona, M., Ball&#232;vre, M., &amp; Poujol, M. (2024). Tectonic architecture of the northern Dora-Maira Massif (Western Alps, Italy): field and geochronological data. Swiss Journal of Geosciences, 117(1), 6.