Unveiling the Tectono-Metamorphic Framework of northern Dora-Maira Massif (Western Alps): new preliminary data from Pellice and Chisone valleys 

Abstract

Dora-Maira (DM) Massif plays a crucial role in understanding the geodynamics that shaped the Alpine belt. Extensive studies have been mostly conducted in the southern portion of DM (e.g., Chopin et al., 1991). Recent investigations (Manzotti et al. 2022; Nosenzo et al., 2024) have renewed interest in the northern portion of the massif. These authors provided new structural and metamorphic data on the area, particularly with the discovery of a new ultra-high-pressure unit (the Chasteiran Unit). Despite these significant contributions, there are many open questions at the scale of the entire DM. In this contribution we present new data collected within the framework of the CARG mapping project (Foglio 172-Pinerolo). Our aim is to shed light on the structural and metamorphic architecture in the Val Pellice and Val Chisone areas. We present a geological map with geological cross-sections, at a scale of 1:10,000, covering the region between Colle Lazzarà and Colle Vaccera. Additionally, we conducted preliminary microtectonic, petrographic, and geochronological studies to reconstruct the structural and metamorphic evolution of the investigated area. In this relatively unexplored part of DM, three distinct tectono-metamorphic units are exposed, which are (from bottom to top): Pinerolo-Sanfront Unit; Chasteiran Unit, and the poly-cyclic basement unit of the DM massif. Particular attention has been paid to mapping the tectonic contact related to the Chasteiran Unit, which is sandwiched between the other two tectono-metamorphic units. This contact has been traced further southward, up to Colle Vaccera, compared to previous investigations. To reconstruct the metamorphic history, we present preliminary P-T data obtained from ongoing analysis of the micaschist in the Pinerolo-Sanfront Unit. At least four deformation phases have been recognized: (i) the D1 phase, associated with the development of an S1 foliation preserved only within the microlithons; (ii) a second deformation phase, associated with the development of the main foliation (S2) characterized by an E-W trending lineation, (iii) the D3 deformation phase overprinting D2 structures; (iv) a D4 deformation phase that developed during the doming of the Dora-Maira Massif; and finally, (iv) a D4 deformational phase that developed during the doming of the Dora-Maira Massif. In addition, we present preliminary geochronological data performed on Freidour-type orthogneiss in the Pinerolo-Sanfront Unit, refining the Permian age obtained from previous studies (Bussy & Cadoppi 1996). This contribution has been performed whit the found of the CARG mapping project.