Application of in situ zircon geochronology and accessory phase chemistry to constraining basin development during post-collisional extension: A case study from the French Massif Central

O. Bruguier, J. F. Becq-Giraudon, M. Champenois, E. Deloule, J. Ludden, D. Mangin

Research output: Contribution to journalArticle

37 Citations (Scopus)

Abstract

A series of five volcanic ash layers interbedded in Late Carboniferous sedimentary basins from the southern part of the French Massif Central (FMC, France) have been studied by ion-microprobe analyses of zircons in order to constrain the age of basin formation and sedimentation. Weighted mean 206Pb/238U ages for the five studied tuffs are indistinguishable at the 95% confidence level and range from 295.5 ± 5.1 Ma (Graissessac) to 297.9 ± 5.1 Ma (Roujan-Neffies). These U-Pb ages support the argument for intense magmatic activity in the southern part of the French Massif Central during the period 295-300 Ma. Inherited zircons were identified in two out of the five dated tuff horizons and indicate a anatexis of basement source rocks with ages of ca. 2400 (Jaujac basin), 1900 and 600 Ma (Graissessac basin). The Proterozoic components suggest a Gondwanan affinity for the deep-seated material. Chemical compositions of apatites and of one single zircon grain from the Roujan-Neffies bentonite further indicate magma generation mainly from anatexis of the continental crust and a rhyolitic affiliation. Conversely, the same minerals extracted from the Jaujac bentonite indicate involvement of a mantle component in the source of the magmas and a trachytic affiliation. The 295-300 Ma volcanic episode in the French Massif Central is contemporaneous with volcanic events identified in other parts of the Variscan Belt which suggests it was triggered by orogen-wide processes. Contemporaneous eruption of trachytic and rhyolitic magmas may be related to replenishment of magma chambers at depth by influx of mantle-derived magmas triggering the Late Carboniferous flare-up.

Original languageEnglish
Pages (from-to)319-336
Number of pages18
JournalChemical Geology
Volume201
Issue number3-4
DOIs
Publication statusPublished - 28 Nov 2003

Keywords

  • Apatite
  • Ash-fall tuffs
  • French Massif Central
  • Stephanian basins
  • Variscan orogen
  • Zircon

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

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