The Lanzo massif consists of a 150 km2 body of plagioclase Iherzolite, situated along the inner arc of the Alps, at the triple junction of the Ivrea zone, the Sesia-Lanzo zone, and the Pennine zone, Geophysical models show that the massif is probably still rooted in the mantle. A reliable study of field structures, rock structures, and mineral preferred orientations is interpreted in terms of plastic flow during the solid-state emplacement of the peridotite. The kinematics of the massif are related to the relative displacement of the South Alpine and European plates during Cretaceous time. During its solid-state emplacement, the peridotite underwent a gabbroic partial melting episode that produced dikes and lenses whose orientations are related to the flow structures. The petrology of the lherzolite and gabbros indicates that the peridotite mass originated as deep as 100 km in the mantle and crossed the lherzolite solidus at about 15 to 20 km and 1250 °C during its ascent. The pyroxenitic layering is considered from a structural and petrological point of view. The observed clinopyroxene preferred orientation is assumed to be of magmatic origin and not transposed by plastic flow.

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