Geochronology and Sr–Nd–Hf isotope constraints on the petrogenesis of teschenites from the type-locality in the Outer Western Carpathians

Abstract

The Teschenite Association Rocks (TAR) in the Outer Western Carpathian (OWC) flysch form a classic suite of alkaline intrusions where teschenite and picrite were first defined. They represent continental intraplate volcanism that produced a wide range of melano- to mesocratic rocks emplaced during the Early Cretaceous rifting within the southern margin of the European Plate. Geochemical modelling indicates that they may be a product of ~2–5 % partial melting of the metasomatised, asthenospheric mantle. The variations in REE (low / heavy REE content, LaN/YbN = 11–34) are consistent with deep melting of garnet peridotite. Initial ε(Nd)i = 5.0–6.3 and ε(Hf)i = 4.9–10.0 preclude the significant mature crust involvement. Instead, a linear array formed by the 143Nd/144Nd and 176Hf/177Hf isotopic ratios points to a genesis from the mixed, HIMU–OIB source with the more depleted, MORB-type component. Mantle metasomatism was most likely caused by the Variscan subduction–collision processes as indicated by the depleted mantle Nd model ages. The isotope and trace element ratios of the TAR resemble the European Asthenospheric Reservoir (EAR) — the common mantle end-member for the widespread Cenozoic volcanic rocks in Europe. This confirms a long-term existence of the EAR mantle component beneath the Central Europe, at least since the Early Cretaceous. In situ laser-ablation ICP-MS U–Pb dating of titanite indicates short duration of mafic alkaline magmatism in the OWC, lasting from 123.7 ± 2.1 to 117.9 ± 1.8 Ma. Emplacement of the TAR is correlated with the maximum lithospheric thinning that triggered adiabatic decompression and partial melting of the upwelling asthenospheric mantle. Magmatism ceased most likely due to transition to the dominantly compressive regime associated with the major stress field reorganization directly preceding the Carpathian– Alpine Orogeny.

Keywords

• mafic alkaline magmatism
• teschenite
• picrite
• Outer Western Carpathians
• laser ablation U–Pb titanite dating