Structural analysis of the north-eastern margin of the Tertiary intrusive stock of Biella (Western Alps, Italy)

A new form surface map has been synthesised From structural and petrographic fieldwork, performed along the Northeastern margin of the Tertiary intrusive complex of Biella. The interpretative structural map shows the relative chronology of superposed foliations and the different degree of transformation induced by contact metamorphism on different country rocks of the Sesia-Lanzo Zone. The contours of the contact aureole of the Biella pluton are here reconstructed studying the structural and metamorphic evolution along the north-eastern boundary; a shallow crustal level emplacement (contact metamorphism peak conditions: 550 degrees <= T <= 700 degrees C, P <= 0.2-0.3 GPa) and the separation of the pre- from the post-intrusive tectonic evolution are inferred.