Structural geology of the central Sesia Lanzo zone

Abstract

A synthesis of the metamorphic and structural history of the Central Sesia-Lanzo Zone. (Western Alps) is proposed, based upon detailed mapping. Four lithologic units are distinguished. The metamorphic history can be divided into a pre-Alpine amphibolite facies event, an early Alpine HP-LT event and a late Alpine greenschist facies event. Five generations of folds are distinguished. F0 is probably of pre-Alpine age. F1 produced isoclinal folds, part of the regional foliation and major shear zones along which the lithologic units are brought into their present relative positions. F2, F3 and F4 are subsequent phases of folding, each producing a locally developed foliation. Some F2 folds occur on a km scale and can be seen on the map. F4 might be related to a young, postulated major fold that trends NE-SW through the entire Sesia-Lanzo Zone. A detailed map and three-dimensional interpretation of the major structure in the central Sesia- Lanzo Zone are presented, including a new interpretation of the IIDK body at Mt. Nery..