Geology of the southern Dora-Maira Massif: insights from a sector with mixed ophiolitic and continental rocks (Valmala tectonic unit, Western Alps)

Figures & data

Figure 1. Tectonic map of the Western Alps (modified after Balestro et al., 2015). The red square indicates the study area.

Figure 2. Field images of different lithologies exposed in Valmala: (a) mylonitic augen gneiss (Rocca Solei Unit, N of Vacot, 44°33′33, 7°21′22); (b) stratigraphic contact relationships (dashed white line) between the garnet- and chloritoid-bearing mica schist (Dm) and the fine-grained massive metabasite (Db) (Dronero Unit, N of Santuario di Valmala, 44°31′7, 7°20′31); (c) layer of leucogneiss (lg) interbedded in micro-augen gneiss (ag) (Dronero Unit, S of Chiot del Bosco, 44°31′57, 7°20′46); (d) grayish mica schist with millimeters-thick quartz veins (Valmala Tectonic Unit, Bric Guardia, 44°32′50, 7°19′35); (e) massive meta-quartzdiorite with centimeters-thick mafic enclave (me) and acidic dyke (ad) (Valmala Tectonic Unit, Comba di Valmala, 44°32′54, 7°20′27); (f) carbonate-rich calcschist (Valmala Tectonic Unit, W of Perotto, 44°32′34, 7°20′17); (g) banded metabasite showing the S1 foliation (dashed white lines) deformed by D2 folds (Valmala Tectonic Unit, E of Rora, 44°32′56, 7°20′54); (h) carbonate-bearing serpentinite (Valmala Tectonic Unit, W of Botto, 44°32′53, 7°19′52).

Figure 3. Images of different field-scale structures: (a) D2 crenulation cleavage (dashed black lines) in garnet- and chloritoid-bearing mica schist (Dronero Unit, N of Santuario di Valmala, 44°31′7, 7°20′35); (b) D2 folds deforming the contact between metabasite (Db) and leucogneiss (Dg) (Dronero Unit, E of Santuario di Valmala, 44°30′48, 7°21′2); (c) D3 extensional shear planes (dashed red lines) dragging the S2 foliation (dashed white lines) in mylonitic dioritic gneiss (Valmala Tectonic Unit, Comba di Valmala, 44°32′48, 7°20′30). (d–h) Equal-area lower-hemisphere stereographic projections of different structures (n: number of data; counting method: Fisher distribution): (d) poles of S1 foliation; (e) poles of D2 axial plane (AP2); (f) D2 axes (A2); (g) poles of S2 foliation; (h) D2 stretching lineations (L2).

Balestro, G., Festa, A., Dilek, Y., & Tartarotti, P. (2015). Pre-Alpine extensional tectonics of a peridotite localized oceanic core complex in the late Jurassic, high-pressure Monviso ophiolite (Western Alps). Episodes, 38(4), 266–282. https://doi.org/10.18814/epiiugs/2015/v38i4/82421

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