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)

Mohammad A. Kilzi, Michel Grégoire*, Valérie Bosse, Mathieu Benoît, Youssef Driouch, Michel de Saint Blanquat, Pierre Debat

*Corresponding author for this work

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

The 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.

Original languageEnglish
Pages (from-to)107-115
Number of pages9
JournalComptes Rendus - Geoscience
Volume348
Issue number2
DOIs
Publication statusPublished - 1 Feb 2016
Externally publishedYes

Keywords

  • Early Permian
  • Gavarnie-Heas dome
  • Geochemistry
  • Geochronology
  • Mafic to intermediate rocks
  • Ultramafic rocks
  • Variscan Pyrenees

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