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

Abstract

The Monviso Meta-Ophiolite Complex is a remnant of the Piedmont-Ligurian oceanic lithosphere stacked in the Western Alps, andconsisting of dismembered HP meta-ophiolite sequences. In thiswork, focused on the northern sector of the Complex, we differen -tiate six tectonic units which structural, petrographic and stratigraphiccharacteristics are described in detail and discussed in thelight of a comparison with the overall geology of the MonvisoMeta-Ophiolite Complex. The structural evolution has been referredto i) an early syn-eclogitic deformation phase (D1), ii) a main deformationphase (D2) occurred in the blueschist- to greenschist-faciestransition and characterized by the development of a regional foliation(S2) that is parallel to the tectonic contacts and to the axialplane of map-scale W-verging folds, and iii) a late-metamorphicdeformation phase (D3) characterized by westward extensionaltectonic. The northern Monviso Meta-Ophiolite Complex is characterizedby a poor preservation of HP paragenesis and a widespreadoverprint of the blueschist- to greenschist-facies metamorphism,but the occurrence of garnet-, omphacite-, talc- and lawsoniteassemblagein a Fe-Ti metagabbro indicates P-T eclogitic conditions(2.5-2.7 GPa for 550-570 �C) very similar to those calculated in thesouthern sector of the Complex. The stratigraphic characteristics ofthe meta-ophiolite sequences point out that, differently from thesouthern sector of the Complex where basalt-poor and basalt-richoceanic units have been distinguished, in the northern MonvisoMeta-Ophiolite Complex the different types of metasedimentsmay be the key to restore the oceanic tectonostratigraphy, markedby gabbro and mantle peridotite exposition on a puzzle-like oceanfloor where basalt effusion and different sedimentation processestook place.