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The alkaline intraplate volcanism of the Antalya nappes (Turkey): a Late Triassic remnant of the Neotethys

René C. Maury¹, Henriette Lapierre^2,, Delphine Bosch³, Jean Marcoux^4,, Leopold Krystyn⁵, Joseph Cotten¹, François Bussy⁶, Pierre Brunet⁷ and François Senebier²

¹ Laboratoire Domaines océaniques, UMR-CNRS 6538, Université de Bretagne occidentale, Place Nicolas Copernic, 29280 Plouzané, France. Email: maury{at}univ-brest.fr
² Laboratoire Géodynamique des Chaînes Alpines, UMR-CNRS 5025, Université J. Fourier, Maison des Géosciences, B. P. 53, 38041 Grenoble cedex, France.
³ Laboratoire Géosciences Montpellier, UMR-CNRS 5243, Equipe Manteau-Noyau, Université de Montpellier II, Place Eugène Bataillon, 34095 Montpellier cedex 05, France.
⁴ Institut de Physique du Globe de Paris, UMR-CNRS 7578, Université Paris VII, 4 Place Jussieu, 75252 Paris cedex 05, France.
⁵ Institute of Paleontology, Althanstr. 14, University of Vienna, 1090 Vienna, Austria.
⁶ Institute of Mineralogy and Geochemistry, BFSH-2 University of Lausanne, CH-1015 Lausanne, Switzerland.
⁷ Laboratoire Mécanismes de Transfert en Géologie, UMR-CNRS 5563, Université P. Sabatier, OMP, 14 Avenue E. Belin, 31400 Toulouse, France.

Late Triassic submarine alkali basalts and hawaiites were collected from two superimposed tectonic slices belonging to the Kara Dere – Sayrun unit of the Middle Antalya nappes, southwestern Turkey. New determinations on conodont faunas allow to date this sequence to the Lower Carnian (Julian). The volcanic rocks show rather homogeneous compositions, with high TiO₂ and relatively low MgO and Ni contents which suggest olivine fractionation. Their primitive mantle-normalised multi-elements plots show Nb and Ta enrichments relative to La, Pb negative anomalies and heavy rare earth element and Y depletions typical of intraplate ocean island basalts. These characteristics are consistent with the major and trace element compositions of their primary clinopyroxene phenocrysts, which do not show any feature ascribable to crustal contamination. The studied lavas display a restricted range of Nd (+4.6 to +5.2) which falls within the range of ocean island basalts. Their initial (¹⁴³Nd/¹⁴⁴Nd)i ratios are too low to be explained by a simple mixing line between depleted MORB mantle (DMM) and HIMU components. Their Pb and Nd isotopic compositions plot along a mixing line between HIMU component and an enriched mantle, the composition of which could be the result of the addition of about 5 to 8% of an EM2 component (recycled marine sediments) to DMM. The lack of evidence for any continental crustal component in their genesis could be consistent with their emplacement in an intra-oceanic setting.

Key Words: Alkali basalt • Intraplate volcanism • Triassic (Upper) • Neotethys • Turkey • Geochemistry