Map of the strain and reaction-rate partitioning in the Mombarone – Mt. Mucrone area (Sesia Lanzo Zone, Italian Western Alps)

Francesco Delleani (a), Michele Zucali (a,b), M. Iole Spalla (a,b) & Guido Gosso (a,b)
(a) Dipartimento di Scienze della Terra "A. Desio", Università degli Studi di Milano, via Mangiagalli, 34, 20133 Milano, Italy. E-mail: francesco.delleani@unimi.it (b) CNR-IDPA, via Mangiagalli, 34, 20133 Milano, Italy

The Mt. Mucrone – Mt. Mars – Mombarone area includes several Permian intrusive bodies and metasediments preserving granulitic to amphibolitic pre-Alpine metamorphism widely re-equilibrated under eclogite-facies conditions during the Cretaceous. They are now part of the Eclogitic Micaschists Complex of the Sesia-Lanzo Zone in the Alpine HP metamorphic belt of the Western Alps. During the field structural analysis, seven groups of ductile structures were recognized as having evolved as follows: the D1 – D3 fabrics took place under eclogite-, D4 under blueschist- and D5 to D7 under greenschist-facies conditions, respectively. Combined structural and petrologic studies generated maps that correlate the degree of fabric evolution and metamorphic transformation at map scale and allow to conclude that, over a critical threshold of fabric reworking, the accomplishment of metamorphic transformations increase proportionally with the degree of fabric evolution. Such map-scale counterpart of outcrop-size deformation zones makes strain-partitioning a critical factor controlling reaction progress.

Deformation metamorphism relationships, Degree of fabric evolution, Eclogitic Micaschists Complex