Late mantle evolution of the Pyrenean sub-continental lithospheric mantle in the light of new 40Ar–39Ar and Sm–Nd ages on pyroxenites and peridotites (Pyrenees, France)

In-situ U–Pb zircon ages for Early Ordovician magmatism in the eastern Pyrenees, France: the Canigou orthogneisses

“…Furthermore, the age coincides with an ancient melting event in the mantle at 462±20 Ma, re-corded in garnet-bearing pyroxenites from the North Pyrenean Zone (Henry et al 1998). It can also be tentatively related to an Ordovician rifting event reported in volcano-sedimentary series of the southern French Massif Central (Pin and Marini 1993;Delaperrière and Respaut 1995).…”

Mineralogical and geochemical constraints on the shallow origin, ancient veining, and multi-stage modification of the Lherz peridotite

“…1), which marks the meeting of the Iberian plate to the south and European plate to the north (e.g., Choukroune, 1992). The peridotite-pyroxenite assemblage of Lherz covers a wide-range of major-, minor-, and trace-element abundances (e.g., Bodinier et al, 1988;Burnham et al, 1998;Le Roux et al, 2007), and lithophile-element isotope compositions of this body overlap the spectrum of 147 Sm/ 144 Nd, 87 Sr/ 86 Sr, and PbPb isotopic values reported in mantle peridotites worldwide (Polvé and Allègre, 1980;Downes et al, 1991;Mukasa et al, 1991;Zanetti et al, 1996;Henry et al, 1998;Le Roux et al, 2009). Within the Lherz massif harzburgites distal from cross-cutting veins are isotopically enriched with high 87 Sr/ 86 Sr (0.70475 ± 4), high 87 Rb/ 88 Sr ($0.0075), low eNd ($+0.6), and contrast to lherzolites that commonly display low 87 Sr/ 86 Sr (0.70202 ± 2 to 0.70274 ± 4), low 87 Rb/ 88 Sr (0.0011-0.0042), and high eNd (+7.2 to +11.9); these isotopic characteristics are not the result of melt extraction processes alone (Downes et al, 1991;Le Roux et al, 2009).…”

“…Two contrasting petrogenetic models may account for the compositional diversity of the Lherz massif; (1) harzburgites and lherzolites may result from variable degrees of ancient melt extraction, and isotope systems based on incompatible lithophile-elements may record later events linked to thermal perturbation and/or incompatible-element modification by moderate amounts of exotic melts and/or fluids (e.g., Burnham et al, 1998;Henry et al, 1998); or (2) Le Roux et al (2007Roux et al ( , 2008Roux et al ( , 2009) recently proposed that the peridotite-pyroxenite assemblage of Lherz could reflect refertilisation of ancient depleted peridotites by substantial volumes of percolating basaltic melt (30-60 wt.% websterite, where these authors view websterites as frozen melt-fronts) during the Variscan orogeny. It is important to distinguish between these models as recent suggestions of Variscan-age igneous refertilisation may cast doubt on the significance of osmium model-age determinations for the Lherz massif and other global peridotite suites.…”

High-temperature metamorphism during extreme thinning of the continental crust: a reappraisal of the North Pyrenean passive paleomargin

“…In addition, absolute ages are available on Cretaceous magmatic rocks, with a spread from 113 to 85 Ma ( Fig. 3; Golberg et al, 1986;Montigny et al, 1986;Henry et al,1998). Some authors distinguish an early phase of intrusive magmatism followed by a paroxysm from the Cenomanian to the end of the Turonian (Debroas and Azambre, 2012).…”

“…Some manifestations of the Cretaceous alkaline magmatism have also been recognized within the peridotite bodies of the NPZ, where they appear as dykes of amphibole-bearing pyroxenites and hornblendes ("ariégites à amphiboles" and "lherzites" of Lacroix 1917) considered to represent trans-mantellic melt conduits for the Cretaceous alkaline magmatism (Bodinier et al, 1987;Conquéré 1971;Vétil et al, 1988). Radiometric dating of these rocks gave ages around 100 Ma (Vershure et al, 1967;Golberg et al, 1986;Henry et al, 1998). The peridotite bodies of Tuc de Desse, Arguenos-Moncaup, Montaut and Turon de la Técouère also contain gabbroic intrusions that present chilled margins along their contacts, indicating that some of the mantle rocks were already cooled during the emplacement of the magmatic rocks (Azambre and Monchoux, 1998).…”