Strutture deformative nel plutone delle Vedrette di Ries: una chiave d'interpretazione della cinematica oligocenica delle Alpi Orientali.

Deformation in plutons intruded at crustal depth shallower than that of brittle-ductile rheological boundary develops through a brittle-ductile-brittle sequence and brings to the development, respectively, of joint- mylonites-faults and cataclasites (+ pseudotachylites). These plutons can also record the stress field of a restricted range of time equivalent to their cooling time (which is equal maximum to some million year). The composite Rieserferner pluton represents one of the very few magmatic bodies worldwide that intruded at deep crustal level (brittle-ductile transition, 12-15km) and that are easily accessible and analyzable. The aim of this work is to verify the uniformity of the deformative sequence both across the different magmatic suites of this pluton and between Rieserferner pluton and other shallower granitoid bodies (Adamello, Tauern Window, Sierra Nevada). Furthermore it’s interesting to verify if the cinematic record is comparable to the one found in neighboring areas already studied and that is characterized by σ1 striking NNW and σ3 vertical. My thesis was focused on four outcrop areas composed of the first and second magmatic suite. I carried out a structural survey of the outcrops, particularly focused on joints, mylonites and quartz-mylonites, faults and fractures, cataclasites and pseudotachylites; I recorded the GPS coordinates and spatial orientation of them, the movement type and the relationships with the surroundings structures. The obtained data were inserted in an ArcGIS project and analyzed by the use of WinTensor software. Moreover I collected some samples in order to perform an optical microscope analysis of the geometry and cinematic of the deformative structures. The aim was to find out qualitative data about T-P conditions at the time of their formation by the quartz deformation study. Thanks to that kind of analysis I recognized the same deformative story made of a brittle-ductile-brittle sequence in all of the examined areas. The control of the brittle joint precursors, formed during the first brittle stage, on the formation and development of ductile structures was confirmed too. Regional stress field is coherent with that of Adamello massif and Tauern Window and characterized by a N-S shortening direction. Finally, the study of mylonites and quartz-mylonites revealed the occurrence of an E-W direction extensional phase coeval with the N-S compression. The origin of this movement was probably a tectonic unroofing process similar to that recorded by the Tauern Window.