Eocene high-K magmatic flare-up in a context of south dipping subduction and strike-slip tectonics: Insights from the Talysh Massif, NW Iran

[Display omitted] •In the Talesh Massif, we document an Eocene high-K volcanic flare-up.•A trachytic ignimbrite layer is dated at 43.17 ± 0.40 Ma.•Melting of previously metasomatized lithospheric mantle source has occurred.•Geodynamic scenario is south-dipping subduction and asthenospheric upwelling.•Efficient magma transfer occurred along strike-slip faults related to a step fault. The geodynamic significance of Cenozoic magmatism of the Central Tethyan orogenic belt linking the tectonic zones of Iran, South Armenian Block (Lesser Caucasus) and Turkey remains a subject of debate. This study is focused on the thick geological succession of high potassic magmatic rocks erupted in Talysh Massif, NW Iran. We report a comprehensive geochemical study that demonstrates that this succession is comprised of shoshonitic mostly basaltic and some rhyolitic pyroclastic rocks emplaced during an Eocene magmatic flare-up. Forsterite rich olivine (Fo 70–93), combined to high-Mg clinopyroxene (Mg# 0.6–0.8) and high-Ti calcic amphibole (magnesiohastingsite) are the dominant mafic minerals in these rocks. Mafic lavas are enriched in LILE and depleted in HFSE, with high Th/Yb, Ba/Th and Nb/Zr ratios, suggestive of an enriched mantle source following Tethys subduction history. Interlayered felsic lavas allowed to date the series by U-Pb on zircon at 43.17 ± 0.40 Ma, with one relict core displaying an inherited age of 580 Ma. eHfi CHUR of Eocene zircons range from 1.7 to −0.9 (with corresponding TDM ages around 1.0 Ga). The latter, along with the detection of a Neoproterozoic zircon xenocryst, indicates a crustal contamination by a Neoproterozoic (and older) lower crust. These data are in agreement with the partial melting of a subduction-modified subcontinental mantle. This magmatic flare-up could have been triggered by an Asthenosphere upwelling related to the onset of south-dipping subduction in the Transcaucasus region and transcrustal strike-slip faults with a more significant crustal contamination than in the Lesser Caucasus region.