Geology of the Piemonte-Ligurian units of the Urtier area (Northwestern Alps-Italy)

Detailed geological mapping of the Urtier Valley in the Western Alps allowed to realize a new geological map 1:10.000 in scale. In the mapped area, a complete nappe stack of the axial part of the Alpine belt crops out. The study focused on the two units derived from the Piemonte-Ligurian oceanic domain, Broillot and Bardonney units, for which, in addition to the classic petrographic and structural considerations, a lithostratigraphic approach was applied. The lithostratigraphic approach, combined with structural analysis, led to reconstruct a nappe stacking significantly different from that generally proposed for the Western Alps. In the Urtier Valley in fact, the eclogite facies units are at the top of the nappe pile, overlapped on the blueschist facies units. This anomalous stacking order could be explained by interpreting the study area as an inverted limb of a regional fold with the eclogite facies units at the core.