Metamorphism and deformation at the northwest margin of the Ivrea zone, Val Loana (N. Italy).

The NW margin of the Ivrea zone is affected by three main deformational events, from the S end of Val Loana: 1) pre-Alpine deformation under conditions of upper amphibolite facies; 2) also pre-Alpine, but with continuously decreasing T from amphibolite to greenschist facies, indicating a continuous shear movement presumably related to upward thrusting of the Ivrea zone; and 3) pre-Alpine to Alpine deformation under very low-grade metamorphism causing a large isoclinal fold: the continuation of the Finero antiform. The Insubric line, the southern boundary of Alpine deformation and metamorphism at the S end of Val Loana, represents the S boundary of a broad mylonite zone related to the first Alpine deformation. Here, the Alpine deformation and upper greenschist-facies metamorphism began overprinting the pre-Alpine rocks. A third Alpine deformation event affected the mylonite of the Insubric line and produced distinct shear planes within the Ivrea rocks further SE.-W.S.