Mont Blanc Massif southeast flank (Monte Bianco Massif southeast flank), Courmayeur, Aosta Valley, Italyi

Regional Level Types
Mont Blanc Massif southeast flank (Monte Bianco Massif southeast flank)	Massif
Courmayeur	Commune
Aosta Valley	Autonomous Region
Italy	Country

The Mont Blanc southeastern flank represents the left side of the Veny Valley and the right side of the Ferret Valley.

Between the Mont Blanc de Courmayeur and the Grandes Jorasses the southeastern flank of the range is impressively steep (average slope of 35° from the top of the Mont Blanc de Courmayeur to the Veny Valley over 3000 m below). It is marked by several steeply northward dipping thrust faults. The southernmost thrust brings the Mont Blanc granite on top of the Jurassic-Cretaceous sedimentary series (e.g., Baggio, 1964; Antoine et al., 1975; Guermani & Pennacchioni, 1998). Northeast of Courmayeur, near Pra Sec in Ferret Valley, the thrust dips 55° to the NW, is marked by a ca. 2 m thick fault breccia and brings the granite on top of black schists and Cretaceous sandy limestones. Farther NW, below the Boccalatte refuge and near the Mont Frety the contact dips 50–65° to the NW and brings the granite on top of overturned Liassic slates. These series probably correspond to the roots of the Helvetic nappes in the hanging wall of the Val Ferret thrust but overturned below a counter thrust: the so-called Mont Blanc back thrust. The contact is well exposed on the trail to the Boccalatte refuge where it corresponds to a ca. 50 m thick granite cataclasite layer. West of Mont Frety, within the granite numerous greenschist shear zones anastomose around less deformed lenses (Guermani & Pennacchioni, 1998). Most mylonitic shear zones trend N16° to N52° and display shear criteria suggesting top to the SE (dip slip) thrusting. However, given the common absence of stretching lineations and the strong influence of preexisting brittle faults on the shear zones geometry (Guermani & Pennacchioni, 1998), the precise direction of thrusting is difficult to constrain. The brittle faults that affect the granite show chlorite crystallization, are mostly parallel to the Mont Blanc back thrust and often show dip slip motions. Northwest of Courmayeur, near Peuterey village, the fault contact strikes N36°, is nearly vertical and shows evidence for upward motion of the northwestern (Mont Blanc) unit. Within the granite, ca. 2 km away from the main contact, two major shear zones straddle the Aiguille de la Brenva and probably merge at depth to form the major NW dipping shear zone found in the Mont Blanc tunnel 3.5 km from the Italian entrance. Then northernmost shear zone outcrops near the Helbronner cable car station and exhibits a clear morphological trace through the Peuterey and Rey passes, at the base of the highest part of the Mont Blanc massif. In the deformed sedimentary series of the Veny Valley, few brittle faults that reactivate schistosity planes show dextral motion (Leloup et al., 2005).

Fossils

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Other Databases

Wikipedia:	https://en.wikipedia.org/wiki/Mont_Blanc_massif
Wikidata ID:	Q671343

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References