Permian magmatism and metamorphism in the Dent Blanche nappe: constraints from field observations and geochronology

Paola Manzotti,Daniela Rubatto,Martin Engi,Michel Ballèvre,Afifé El Korh,Bénédicte Cenki-Tok,Michele Zucali

doi:10.1007/s00015-017-0284-1

Abstract

In the Dent Blanche Tectonic System, the Mont Morion biotite-bearing granite is a km-scale intrusion preserved in a low-strain volume. Zircon saturation thermometry suggests that it crystallised from a melt that reached about 800 °C. U–Pb zircon and allanite geochronology indicates crystallization of the magma in the Permian (290 ± 3 Ma; 280 ± 8 Ma, respectively). Migmatitic biotite-gneiss and amphibolite are found as xenoliths within the Mont Morion granite and constitute its country-rocks. In two samples of migmatitic biotite-gneiss zircon has metamorphic overgrowths that yield U–Pb ages of 285 ± 3 Ma and 281 ± 4 Ma, and are thus contemporaneous with the intrusion of the granite. The Mont Morion granite with its country-rocks of migmatitic biotite-bearing gneiss and amphibolite was thus emplaced at middle crustal levels while amphibolite facies metamorphism affected its country rocks. The magmatic and metamorphic record in the Mont Morion area reflects the high-temperature regime and lithospheric thinning of the Adriatic continental margin during Permian.

Highlights

The high thermal regime that characterised the European Alpine region during the Permian was responsible for diffuse magmatism with gabbroic and granitic intrusives at all crustal levels (e.g., Paquette et al 1989; Bussy et al 1998; Monjoie et al 2007; Cenki-Tok et al 2011; Miller et al 2011) and explosive, acid volcanism at the surface (e.g., Quick et al 2009)
The Mont Morion granite with its country-rocks of migmatitic biotite-bearing gneiss and amphibolite was emplaced at middle crustal levels while amphibolite facies metamorphism affected its country rocks
In the Dent Blanche Tectonic System (DBTS) (Fig. 1), the Arolla Series is classically considered as a slice (*50 9 5 km) of Permian upper continental crust (e.g., Argand 1911; Diehl et al 1952; Dal Piaz et al 1972, 2015; Manzotti et al 2014a)

Summary

Introduction

The high thermal regime that characterised the European Alpine region during the Permian was responsible for diffuse magmatism with gabbroic and granitic intrusives at all crustal levels (e.g., Paquette et al 1989; Bussy et al 1998; Monjoie et al 2007; Cenki-Tok et al 2011; Miller et al 2011) and explosive, acid volcanism at the surface (e.g., Quick et al 2009) This igneous activity was associated with high temperature medium/low pressure metamorphism in the lower and middle continental crust (e.g., Rivalenti et al 1984; Sinigoi et al 1994; Peressini et al 2007; Manzotti et al 2012; Zanetti et al 2013; Klotzli et al 2014). These data allow discussing the age and characteristics of the high temperature metamorphism for the migmatitic biotite-gneiss

Methods

Findings

Discussion

Conclusion