Structural and geomorphological framework of the upper Maira Valley (Western Alps, Italy): the case study of the Gollone Landslide

An interdisciplinary study has been adopted to investigate the upper Maira Valley (Western Alps, Italy). A geological map of an unmapped area, of about 12 km2, at scale 1:10.000, has been realized. The combination of field surveys, GIS database creation, aerial photo observation, local archival data consultation, geo-structural analysis and drillholes re-interpretation outlined a relationship between structures and landforms. A ductile and brittle deformation history with the definition of four discontinuity systems (F1-F4) has been detected. Where the fracturation is intense, rock-falls and topplings are triggered. In area associated with a homogeneous presence of weathered cover, debris flows were identified. The geo-structural pattern obtained from the surveys in the upper Maira Valley allowed characterizing detachment zones of the slope overlooking Acceglio town. The Gollone Landslide is an excellent case study to unravel the structural-morphological interaction and the kinematic evolution due to its framework

Comparison between 2D and 3D microstructures and implications for metamorphic constraints using a chloritoid–garnet-bearing mica schist

Despite the fact that rock textures depend on the 3D spatial distribution of minerals, our tectono-metamorphic reconstructions are mostly based on a 2D visualisation (i.e. thin sections). This work compares 2D and 3D investigations of petrography and microstructures, modal abundances, and local bulk rock composition and their implication for P–T estimates, showing the pros and cons and reliability of 2D analysis. For this purpose, a chloritoid–garnet-bearing mica schist from the Dora-Maira Massif in the Western Alps has been chosen. In particular, for 2D a thin section scan has been combined with chemical X-ray maps, whereas for 3D the X-ray computerised axial microtomography (µCT) has been applied. Two-dimensional investigations are readily accessible and straightforward but do not consider the entire rock volume features. Conversely, the rise of 3D techniques offers a more comprehensive and realistic representation of metamorphic features in the 3D space. However, they are computationally intensive, requiring specialised tools and expertise. The choice between these approaches should be based on the research aims, available resources, and the level of detail needed to address specific scientific questions. Nevertheless, despite differences in the modal distribution, the estimated bulk rock compositions and relative thermodynamic modelled phase fields show similarities when comparing the 2D and 3D results. Also, since different thin section cut orientations may influence the results and consequent interpretations, three different cuts from the 3D model have been extrapolated and discussed (i.e. XZ, YZ, and XY planes of the finite-strain ellipsoid). This study quantitatively corroborates the reliability of the thin section approach for tectono-metamorphic reconstructions, still emphasising that 3D visualisation can help understand rock textures.</p

Deformation and temperature variation along thrust-sense shear zones in the hinterland-foreland transition zone of collisional settings: A case study from the Barbagia Thrust (Sardinia, Italy)

In the Internal Zone of a continental collisional orogen, first-order contractional shear zones accommodate crustal shortening. Structural investigations at different scales, flow kinematics, and finite strain analyses are fundamental tools to determine how deformation is accommodated and partitioned. Spatial temperature vari-ations can be responsible for the dynamic weakening and strain localization in the crust, therefore understanding the thermal conditions of shearing and deformation is critical. We integrate field observations, meso-and microstructural analyses, kinematic vorticity estimations, and finite strain data with a quantitative thermometric analysis by Raman spectroscopy on carbonaceous material along a ductile shear zone: the Barbagia Thrust (BT) in the hinterland-foreland transition zone of the Sardinian Variscan belt. These analyses, performed in two different parts of the shear zone, yield similar finite strain gradients, albeit with an increasing component of simple shear with increasing temperature, highlighting the feedback between temperature and vorticity. Our results best fits with a tectonic scenario with shear heating, where higher magnitude gradients correspond to higher vorticity and finite strain values, which indicate greater shear and heating values. The heating quantified along the BT (~50C) is compared favorably to numerical and mechanical models. We demonstrate how the BT represents a major tectonic boundary separating the internal sector belonging to the metamorphic core of the belt from the external one involved in the orogenic wedge system