Structural and petrographic map of the Sassa gabbro complex (Dent Blanche nappe, Austroalpine tectonic system, Western Alps, Italy)

Abstract

The Sassa gabbro complex outcrops in the upper Valpelline and is part of the Permian gabbros of the CollonMatterhorn group, set in the Dent Blanche nappe of the Western Austroalpine tectonic system. This 1:2500-scale map was constructed through the synergic use of meso-and microscopic analysis of fabrics to identify the relationships of the superposed foliations with the growth of equilibrium mineral assemblages. Throughout the foliation trajectories, a mosaic of rock volumes, in which strain is differently partitioned, is highlighted on the map for all the successive deformation stages. Therefore, this mosaic shows deformation gradients spanning from unstrained or weakly strained domains, where the primary magmatic features are still well preserved, to domains in which the Alpine fabrics are pervasive and obliterate the previous structures. The preAlpine history is characterized by the polyphasic emplacement of the Sassa gabbro and by a coronitic growth of successive mineral assemblages during crustal thinning-related exhumation. The Alpine history is characterized by multistage heterogeneous deformation consisting of a first D1 stage developed in blueschist facies conditions followed by D2 and D3 stages developed in greenschist facies conditions. In summary, by applying this analytical method, the geologic traces of the pre-Alpine lithospheric thinning and Alpine subduction histories have been separated.

U–Pb geochronology of the Sondalo gabbroic complex (Central Alps) and its position within the Permian post-Variscan extension

“…Late Carboniferous and Early Permian gabbros and granulites exhumed by tectonic activity or Tertiary to Quaternary volcanoes are indicated with: 1 -Iberian margin (ODP Site 1069; Manatschal et al 2001); 2 -Spanish Central System (Fernández-Suárez et al 2006;Villaseca et al 2007); 3 -Gavarnie-Héas dome (Kilzi et al 2016);4 -Ursuya massif, Pyrenees (Vielzeuf 1984;Vielzeuf and Kornprobst 1984); 5 -Quérigut massif, Pyrenees (Roberts et al 2000); 6 -Treilles norite, Pyrenees (Vielzeuf and Pin 1991); 7 -Ceret gabbro, Pyrenees (Aguilar et al 2014); 8 -Calabria (Schenk 1980;Caggianelli et al 2013); 9 -Santa Lucia massif, Corsica (Paquette et al 2003;Rossi et al 2006); 10 -Bocca di Tenda gabbro, Corsica (Cocherie et al 2005;Tribuzio et al 2009); 11 -Puy Beaunit, French Massif Central (Downes et al 1991;Costa and Rey 1995;Féménias et al 2003); 12 -Bournac, French Massif Central (Rossi et al 2006); 13 -Eiffel massif, Germany (e.g. Loock et al 1990); 14 -Monte Ragola, Appenines (Meli et al 1996); 15 -Ivrea zone, Southern Alps (Pin 1986;Vavra et al 1999;Quick et al 2003;Peressini et al 2007); 16 -Sassa, Sermenza and Mont Collon, Western Alps (Bussy et al 1998;Monjoie et al 2007;Baletti et al 2012): 17 -Gruf complex, Central Alps (Galli et al 2012); 18 -Malenco nappe, Eastern Alps (Hansmann et al 2001;Hermann and Rubatto 2003); 19 -Sondalo gabbroic complex (Bachmann and Grauert 1981;Tribuzio et al 1999; this study). See…”

Superposed syn-metamorphic structures of the Alpine and pre-Alpine convergent cycles in the Southalpine basement of the Orobic Alps (Northern Italy)

“…The chosen representation allows the visualisation of different episodes of the thermomechanical evolution through the use of different symbols and colours. Following methods used in mineral prospections (Johnson & Duncan, 1992) and already used in metamorphic terrains in the Alps (Baletti, Zanoni, Spalla, & Gosso 2012;Delleani, Spalla, Castelli, & Gosso, 2013;Di Paola & Spalla, 2004;Spalla et al, 2000;Zucali et al, 2002), it is therefore possible to recognise tectonic contacts, even when they are partially obliterated, sutured and polydeformed, individuating also the structural level at which coupling between tectonic units took place, thanks to the information on the metamorphic environment of fabrics development.…”

Deciphering orogeny: a metamorphic perspective. Examples from European Alpine and Variscan belts

“…Since 2004, some significant new data have been obtained in different tectonic units, as (i) the Austro-Alpine continental crust [Rebay and Messiga, 2007;Roda and Zucali, 2008;Gosso et al, 2010;Zucali and Spalla, 2011;Baletti et al, 2012;Roda et al, 2012;Delleani et al, 2012;Delleani, 2013], (ii) the ophiolites and Schistes Lustrés units [Federico et al, 2004[Federico et al, , 2009Guillot et al, 2004;Bucher et al, 2005;Bousquet, 2008;Li et al, 2008;Angiboust et al, 2009Angiboust et al, , 2012Groppo et al, 2009;Zanoni et al, 2011;Malatesta et al, 2012;Rebay et al, 2012;Debret et al, 2013], (iii) the Internal Crystalline massifs and the Briançonnais domain [Brouwer et al, 2004;Ganne et al, 2005Ganne et al, , 2007Le Bayon and Ballevre, 2006;Lapen et al, 2007;Beltrando et al, 2008;Gabudianu-Radulescu et al, 2009;Gasco et al, 2011Gasco et al, , 2013Lanari et al, 2012], (iv) the Valaisan domain [Masson et al, 2008;Mugnier et al, 2008;Beltrando et al, 2012], and (v) the External Crystalline massifs from the Dauphinois domain [Corsini et al, 2004;Leloup et al, 2005;Challandes et al, 2008;Rolland et al, 2008;…”