Structural map of Ligurian Briançonnais sheath folds (Pamparato-Murialdo unit, Bormida valley, Liguria, Italy)

Matteo Maino (a), Lorenzo Bonini (a), Giorgio Dallagiovanna (a) & Silvio Seno (a)
(a) Department of Earth Sciences and Environmental Sciences , University of Pavia, via Ferrata, 1 -27100 Pavia, Italy. E-mail: matteo.maino@unipv.it

We performed a careful geometric analysis of minor structural details of curvilinear hinge geometries exposed in blueschist rocks from the Pamparato-Murialdo unit of the central Ligurian Alps. The data collection resulted in a new structural map and related cross-sections, which elucidate the relationships and evolution of the associated large-scale sheath folds of the Ligurian Briançonnais. We measured and collected the geometric parameters of minor fold shape, vergence, lineation obliquity and structural facing pattern, in order to define the large-scale fold structure. The synthesis of the small-scale data results in a coherent structure showing several orders of magnitude of parasitic folds. The meticulous definition of the relationships between facing and fold hinge/lineation obliquity at small scales is the only tool to reconstruct the large-scale structure and to define the sheath fold vergence and transport direction. On the whole, the new map and related cross-sections supply new insights on the three-dimensional structure and evolution of sheath folds generated by the ductile deformation of the Briançonnais rocks during the Alpine subduction.

Sheath fold, structural map, Briançonnais, Ligurian Alps