Geochemistry and zircon U–Pb geochronology of the ultramafic and mafic rocks emplaced within the anatectic series of the Variscan Pyrenees: The example of the Gavarnie–Heas dome (France)

Abstract

International audienceThe origin and evolution of ultramafic (UM), mafic (M) and intermediate rocks emplaced within the metamorphic and anatectic series of the middle crust of the Variscan segment of the Pyrenees are defined in the light of new isotopic data U–Pb zircon ages, and Sr, Nd isotopic ratios. In the Gavarnie–Heas dome (central Pyrenees), ultramafic, mafic and intermediate rocks form three massifs several kilometers in size emplaced within the anatectic series: (i) the Gloriettes massif, which mostly consists of norites with enclaves of ultramafic rocks; (ii) the Troumouse massif, which comprises intermediate rocks (gabbro-diorite and diorite) with norite enclaves, and (iii) the Aguila massif, which consists of intermediate rocks with hornblendite enclaves. U–Pb zircon geochronology (first data for these rock types in the Axial Zone of the Pyrenees) revealed an age of 294 Ma for the diorite crystallization and correlatively for the crystallization of the anatectic granite. This new radiometric age allows us to suggest that the Variscan orogeny continued at least until the Early Permian and spread over around 30 Ma. The Nd and Sr isotopic compositions of all UM and M samples plot within the field of the continental crust. Two scenarios can explain the genesis and the emplacement of the components of the magmatic suite: i) evolution of mantle melts and contamination (AFC); ii) evolution of melts originating from a heterogeneous source (mantle + crust) at the local or regional scale. The strong crustal affinity of all UM and M rock types from Gavarnie–Heas leads us to favor the second scenario

Vertical strain partitioning in hot Variscan crust: Syn-convergence escape of the Pyrenees in the Iberian-Armorican syntax

“…For that, an additional asthenospheric heat source is required in a context of attenuated or missing lithospheric mantle (Sandiford and Powell, 1991;Chardon et al, 2009). The switch from crustal to mantle and hybrid sources of 310-290 Ma plutonism in the Pyrenees (e.g., Kilzi et al, 2016) is in agreement with such a lithospheric configuration that enhances mantle-crust interactions. This switch, which is also documented across both limbs of the syntax after ca.…”

“…2) intruding the roof of the infrastructure at 307 ± 3 Ma and 300 ± 2 Ma, and suggested that the first group dated metamorphism and the second pluton crystallization. Recently, Kilzi et al (2016) obtained an age of 294 ± 1 Ma by LA-ICPMS on zircons in a mantle-derived dioritic sill hosted by migmatites of the Gavarnie massif (Fig. 2).…”

Origin and duration of late orogenic magmatism in the foreland of the Variscan belt (Lesponne — Chiroulet — Neouvielle area, French Pyrenees)

“…Up to now, only few geochronological constraints are available on migmatites, anatectic granites and mafic to intermediate magmatic bodies in the Pyrenees. Recent works suggest that magmatic activity lasted until the middle Permian (Aguilar et al, 2014;Esteban et al, 2015;Kilzi et al, 2016). We present new geochronological data on migmatites and magmatic rocks from the Lesponne and Chiroulet gneiss domes and the Neouvielle pluton, in the western Axial Zone (figure 1b).…”

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

“…10: Maps of Early Permian (Autunian, 290-260 Ma) sedimentary basins and volcanics compiled from Trümpy and Dösseger (1972), Lorenz and Nicholls(1976) , Feys (1989), Châteauneuf (1989), Burg et al (1994) and Cassinis et al (2012). 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;…”