Zircon typology, geochronology and whole rock Sr?Nd isotope systematics of the Mecsek Mountain granitoids in the Tisia Terrane (Hungary)

Abstract

Zircon typology and ages together with petrological data suggest similarities in the origin of the K–Mg-rich granitoids of the Mecsek Mountains (Moragy Unit, Tisia Terrane, S Hungary) and the durbachitic to K–Mg-rich rocks of the South and Central Bohemian Batholiths. Our investigations evidence a characteristic bimodal distribution of zircon types and ages. Zircons of “normal” magmatic habit and a typology around S24 show an age of 354±5 Ma. Zircons of tabular habit of subtype S4 indicate a possibly younger age of 339±10 Ma. The ages and typology of zircons from plutonic rocks in the Mecsek Mountains strongly resemble those from the Rastenberg granodiorite in the South Bohemian Batholith (Austria). This, as well as Rb/Sr and Sm/Nd isotope systematics, support the assumption of simultaneous formation and close spatial relationship between the Mecsek Mountain granitoids and the Rastenberg granodiorite. Thus, the Mecsek Mountains granitoids likely formed in a Late Palaeozoic palaeo-position S or SSW of the Rastenberg granodiorite. Having experienced a similar metamorphic and magmatic evolution during the Carboniferous, at least the northernmost part of the Tisia Terrane, the Moragy Unit, is therefore considered to represent a former part of the Helvetic-Moldanubian zone.