Studio petrografico e minerochimico dell’orlo metasomatico presente a contatto tra il Massiccio Ultrabasico Di Lanzo e la Zona Sesia-Lanzo, (Balangero, TO, Italia).

The objective of this thesis is the characterization and classification of the onfacitites, and the different generations of veins that cut them, which are in contact with the ultrafemic rocks of the Ultrabasic Massif of Lanzo and the scales of the Sesia-Lanzo Area. The samples, already present in the collection of the Department, come from the former asbesto’s mine of Balangero. The work was divided into several phases: bibliographic research, macroscopic study and petrographic optical microscope of samples, SEM-EDS analysis of the most representative samples, processing and interpretation of data. The onfacitite has a milonitic fabric and is cut by several generations of veins: the older ones are constituted by garnet±onfacite and are cut from veins to garnet±diopside. The later veins are plagioclase±diopside±epidote±chlorite. This thesis work shows that: 1) the Ultrabasic Massif of Lanzo and the Sesia Lanzo Zone were already in contact when the high pressure paragenesis developed; 2) the contact was affected by intense and prolonged circulation of calcium-rich fluids during high-pressure subduction and subsequent exhumation.