Scientific article

Permian post-collisional basic magmatism from Corsica to the Southeastern Alps

Published inLithos, vol. 376-377, no. 105733
Publication date2020

Post-Variscan Early Permian magmatism is widespread from Corsica to the Eastern Alps. After the formation of the Variscan orogenic belt between Laurussia and Gondwana, felsic and mafic bodies were emplaced during an extensional tectonic phase. This study focuses on a mafic dyke swarm that intruded in the region of Ajaccio (Corsica, France) and on a gabbroic intrusive complex outcropping in the Eastern Alps (Bressanone/Brixen, South Tyrol, Italy) both of which were emplaced during this extensional event. New U-Pb data from zircon show that both of these intrusions were emplaced at ca. 282 Ma. Most Ajaccio dykes display a calc-alkaline affinity and are characterized by enrichment of LILE (Large Ion Lithophile Elements) and LREE over HREE (Light and Heavy Rare Earth Elements) and HFSE (Nb, Ta, Hf, Zr; High Field Strength Elements). Two dykes show tholeiitic affinity and are characterized by marked LREE and Th-U depletion and by minor negative Nb-Ta anomalies on multielement diagrams,which is typical forwithin-plate basalts. Bressanone/Brixen gabbros display similar geochemical features to the Ajaccio calc-alkaline samples with LREE enrichment over MREE (Medium Rare Earth Elements) and HREE, and HFSE depletion. Such characteristics are also confirmed by trace element data obtained by LA-ICP-MS on clinopyroxene and plagioclase crystals. The calc-alkaline to tholeiitic dykes are characterized by enriched to depleted Sr-Nd-Pb isotopic compositions, respectively. Some Ajaccio dykes and the Bressanone/Brixen gabbros are clearly affected by crustal contamination. However, the combination of trace element and isotopic variations suggests that mantle source heterogeneities were also involved. Isotopic compositions of the Ajaccio dykes reveal the presence of two distinct mantle source signatures: an enriched mantle (EM) component, which dominates the composition of the calc-alkaline-like suite, while a DMM (Depleted MORB Mantle) component dominates the source of the tholeiitic suite. The EM mantle source likely formed during Variscan subduction, however the composition of the tholeiitic suite requires a source composed dominantly of depletedmantle,with aminor contribution from both the subducting slab and supra-subduction mantle wedge. The mantle source of the tholeiitic magmas possibly originated from greater depths (compared to the calc-alkaline-like suite) during the post-orogenic extensional phase potentially due to break-off and/or roll-back of the Variscan slab ormantle flow fromthe front or margins of the subducted slab. Notably, coeval Permianmafic intrusive bodies fromthroughout Corsica (Bocca di Tenda, Porto, Pila Canale) and from the Australpine and Southalpine Alps intruded at a similar time and have geochemical features that are very similar to the Ajaccio dyke swarm and Brixen gabbro. This indicates that a widespread Permianmagmatic province developed in a post-orogenic extensional tectonic setting at the margin of the former Variscan belt. During the Middle-Late Triassicmagmatism with similar enriched geochemical signatures occurred in the Southern Alps,Dinarides, Australpoine domains and at the end of the Triassic over central Pangea (Central Atlantic Magmatic Province). Thiswould highlight the importance that the Variscan orogeny had in the development of a more fertile mantle.

  • Permian
  • Post-collisional magmatism
  • Corsica
  • Alps
  • Variscan orogeny
  • Zircon
Citation (ISO format)
BOSCAINI, Andrea et al. Permian post-collisional basic magmatism from Corsica to the Southeastern Alps. In: Lithos, 2020, vol. 376-377, n° 105733. doi: 10.1016/j.lithos.2020.105733
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Article (Published version)
ISSN of the journal0024-4937

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