A new petro-structural map of the Monte Mucrone metagranitoids (Sesia-Lanzo Zone, Western Alps)

Abstract

The Mt. Mucrone metagranitoid is an extensively investigated intrusive Permian body, located in the Eclogitic Micaschists Complex of the Sesia-Lanzo Zone, within the high-pressure metamorphic belt of the Western Alps formed during the Alpine plate convergence. The structure of the northwestern sector of Mt. Mucrone, including both the metagranitoids and country rocks, has been mapped, although an integrated structural and petrological analysis is still lacking in its southwestern sector, a topic investigated in this contribution. During the field structural analysis, six groups of ductile structures were recognized to have evolved as follows: the D1 and D2 fabrics took place under eclogite-facies, D3 under blueschist-facies and D4 to D6 under greenschist-facies conditions, respectively. Foliation trajectories revealing the chronology of the superposed structures are represented in the analytical (drift and solid) and interpretative (solid) maps, both at a 1:10,000 scale, and a panel of structural cross-sections allows the 3D representation of the poly-deformed lithostratigraphy. The related metamorphism indicates the changes within the subduction-collision tectonic frame.

Analysis of fabric evolution and metamorphic reaction progress at Lago della Vecchia-Valle d’Irogna, Sesia-Lanzo Zone, Western Alps

“…In all rock types, blueschist-facies mineral assemblages (Table 3) define S2. This finding is in contrast with the nearby metaintrusive of M. Mucrone, where eclogitic mineral assemblages mark the pervasive fabric (Delleani et al, 2012;Delleani et al, 2013;Zucali et al, 2002). Thus, different FE and MT would have affected the retrograde blueschist re-equilibration and potentially generated km-scale heterogeneities within the EMC.…”

“…For instance, in the nearby area of M. Mucrone the correlation between FE and MT shows that the dominant tectono-metamorphic imprint is related to high degree of FE and MT (Delleani et al, 2012;Delleani et al, 2013;Zucali et al, 2002). Similar results have been also obtained in the Mont Morion complex of the Dent Blanche nappe (Roda & Zucali, 2008) and in the LanguardTonale unit in the central Austroalpine domain .…”

“…Eclogite-facies metamorphism is dated around 85-65 Ma (Cenki-Tok et al, 2011;Regis et al, 2014;Rubatto et al, 2011) and occurred at conditions of 13-20 kbar and 500-600°C (Compagnoni et al, 1977;Pognante, Talarico, Rastelli, & Ferrati, 1987;Zucali et al, 2002). Peak conditions were followed by retrogression under blueschist-facies conditions (Babist et al, 2006;Delleani et al, 2013;Giuntoli & Engi, 2016;Pognante, 1991;Spalla, De Maria, Gosso, Miletto, & Pognante, 1983;Spalla, Lardeaux, Dal Piaz, & Gosso, 1991;Zucali & Spalla, 2011) dated ∼60 Ma and occurred at P < 15 kbar and T = 450-550°C (Regis et al, 2014;Zucali, 2011;Zucali et al, 2002). Finally, the greenschist re-equilibration occurred at P < 8 kbar and T < 350°C before 30 Ma (Babist et al, 2006;Zanoni, Spalla, & Gosso, 2010;Zucali et al, 2002).…”

“…The Sesia-Lanzo Zone (SLZ) represents the largest portion ( ̴ 90 × 20 km) of Austroalpine continental crust that has been eclogized during the Alpine subduction and now exposed in the axial zone of the Western Alps (Babist, Handy, Konrad-Schmolke, & Hammerschmidt, 2006;Compagnoni et al, 1977;Dal Piaz, Hunziker, & Martinotti, 1972;Delleani et al, 2013;Lardeaux, 2014;Manzotti, Ballèvre, Zucali, Robyr, & Engi, 2014;Regis et al, 2014;Venturini, Martinotti, Armando, Barbero, & Hunziker, 1994;Zucali et al, 2002). The SLZ is bounded by rocks of the Penninic domain to the northwest, and the Canavese Line (Periadriatic Line (PL)) to the southeast, which separates the SLZ from the Southern Alps (Figure 1(A)).…”

“…In order to evaluate whether rock volumes record the same tectono-metamorphic history, mapping petro-structural heterogeneities in adjacent rock volumes is crucial (e.g. Delleani, Spalla, Castelli, & Gosso, 2012;Delleani, Spalla, Castelli, & Gosso, 2013;Gosso et al, 2015;Salvi et al, 2010;Zucali, Spalla, & Gosso, 2002). Since deformation heterogeneity commonly affects crystalline basements (e.g.…”