Tectonostratigraphy of the northern Monviso Meta-ophiolite Complex (Western Alps).

The Monviso Meta-Ophiolite Complex is a remnant of the Piedmont-Ligurian oceanic lithosphere stacked in the Western Alps, and consisting of dismembered HP meta-ophiolite sequences. In this work, focused on the northern sector of the Complex, we differentiate six tectonic units which structural, petrographic and stratigraphic characteristics are described in detail and discussed in the light of a comparison with the overall geology of the Monviso Meta-Ophiolite Complex. The structural evolution has been referred to i) an early syn-eclogitic deformation phase (D1), ii) a main deformation phase (D2) occurred in the blueschist- to greenschist-facies transition and characterized by the development of a regional foliation (S2) that is parallel to the tectonic contacts and to the axial plane of map-scale W-verging folds, and iii) a late-metamorphic deformation phase (D3) characterized by westward extensional tectonic. The northern Monviso Meta-Ophiolite Complex is characterized by a poor preservation of HP paragenesis and a widespread overprint of the blueschist- to greenschist-facies metamorphism, but the occurrence of garnet-, omphacite-, talc- and lawsonite assemblage in a Fe-Ti metagabbro indicates P-T eclogitic conditions (2.5-2.7 GPa for 550-570 °C) very similar to those calculated in the southern sector of the Complex. The stratigraphic characteristics of the meta-ophiolite sequences point out that, differently from the southern sector of the Complex where basalt-poor and basalt-rich oceanic units have been distinguished, in the northern Monviso Meta-Ophiolite Complex the different types of metasediments may be the key to restore the oceanic tectonostratigraphy, marked by gabbro and mantle peridotite exposition on a puzzle-like ocean floor where basalt effusion and different sedimentation processes took place.