Geology of the Colle di Tenda – Monte Marguareis area (Ligurian Alps, NW Italy)

Abstract

The 1:25,000 geological map of the Colle di Tenda-Monte Marguareis area covers an area of about 130 km 2 in the Italian Ligurian Alps, between the Vermenagna and Tanaro valleys. It is a detailed geological map of a sector of the Ligurian Alps of renewed scientific interest, and represents the eastern continuation of a recently published geological map of the Entracque-Colle di Tenda area. In addition to the increased detail and scale, the more relevant new contents of this map are represented by: (1) a map of all the tectonic elements making up the Limone-Viozene Zone and the Refrey Unit, which represent the southeastern portion of a major regional transfer zone developed at the southern termination of the Western Alps arc; (2) the representation of km-scale Cretaceous palaeoescarpments previously overlooked or interpreted as Alpine faults; (3) a new interpretation of some dark shales with interbedded sandstones, which were previously mapped as Helminthoides Flysch tectonic remnants, as belonging to the Annot Sandstone unit, the uppermost term of the Alpine Foreland Basin succession; and (4) a map legend designed following the same criteria of the 1:250,000 Map of the Piemonte Region.

Structural relationships between Helminthoid Flysch and Briançonnais Units in the Marguareis Massif: A key for deciphering the finite strain pattern in the external southwestern Alps

“…Referring to theoretical model of transtensional tectonics (Dooley & Schreurs, 2012; Naylor, Mandl, & Sijpesteijn, 1986), the geometrical pattern of the faults belonging to three systems depicts a map‐scale Riedel system coherent with a roughly E‐W‐direct dextral shear deformation. In contrast with recent interpretations (Bertok et al, 2018; d'Atri et al, 2016), these brittle deformations are not able to deeply modify the pre‐existing structural setting of the study area, as detectable in the tectonic map (see Figure 2a), thus played not significant role during the structural evolution of the Marguareis Massif. The age of the post‐stacking structures is scarcely constrained.…”

“…One of these areas is located at the boundary between the Maritime and Ligurian Alps, in the southwestern termination of the Western Alps (Figure 1a,b). In this area, despite the available scientific contributions (e.g., Bertok, Musso, d'Atri, Martire, & Piana, 2018; Brizio et al, 1983; d'Atri, Piana, Barale, Bertok, & Martire, 2016; Lanteaume, 1968; Maino & Seno, 2016; Mueller, Maino, & Seno, 2020; Piana et al, 2009; Vanossi, 1972), the geometry and structural evolution of nappes stacking, remains a matter of debate. Facing these contradictions and improving the understanding of finite strain pattern and tectonic evolution of this sector of the Alpine collisional belt, requires reliable stratigraphic and structural constraints.…”

Crystallographic and Seismic Anisotropies of Calcite at Different Depths: A Study Using Quantitative Texture Analysis by Neutron Diffraction

“…It consists of Jurassic limestone strongly deformed during Alpine thrusting of the external part of the chain [44]. According to [45,46] the External Briançonnais units equilibrated at a pressure not exceeding 5 kbar, corresponding to depths <15 km, and T = 300-350 • C. Moreover, overall simple shear kinematics is constrained by map-to micro-scale indicators, extensively described in the area [47][48][49]; however, the studied sample does not show clear microstructures that could be uniquely related to a simple shear geometry (Figure 2). • P1 was collected in the well-known Carrara marbles quarries.…”

Deciphering large-scale superposed fold systems at shallow crustal levels in collision zones: insights from the Marguareis Massif (southwestern Alps)

“…The fault system cuts at highangle all the previously described structures and only locally juxtaposes different tectonic units. In contrast with Bertok et al (2018), we retain that the reworking caused by the fault-network did not substantially modify or obscure the previous structural configuration.…”

“…A different interpretation was proposed by Bertok et al (2018). The authors describe an intricate highangle fault-network separating different tectonic units showing different P-T conditions (Piana et al, 2014).…”