Pre-Alpine Illitization Ages From the Palaeozoic Sequences of the Tauride Belt, Southern Turkiye: New Data for a Late Palaeozoic Event in Northern Gondwana

Abstract

Due to the effects of the Alpine orogeny, it is extremely difficult to obtain age data for pre-Alpine geological events for northern Gondwana. This study aims to study the metamorphism in Precambrian (Ediacaran) metaclastic rocks of the Geyik Dagi unit and re-evaluate the geodynamic models of the northern Gondwana-margin based on the geochronology of illite diagenesis in the Late Silurian to Carboniferous shales of the Aladag and Geyik Dagi units of the Taurides, in southern Turkiye. The average illitization (diagenesis) ages of similar to 275 Ma and similar to 165 Ma correspond to the periods of main unconformities between the Middle Carboniferous and the Late Permian and the Triassic and the Late Jurassic. The fossil records from below and above the unconformity plane between the Middle Carboniferous and the Late Permian indicate a gap of > 70 Ma. Mineralogical and organic matter reflectance data indicate a temperature difference of similar to 50 degrees C between Permian and Carboniferous units indicating different thermal gradients below and above the hiatus. This thermal event coincides with the maximum burial depth resulting from the Palaeozoic subsidence curve of the Geyik Dagi Unit. Mineral and organic petrography-based thermal indicators indicate a pre-Alpine (Variscan) regional tectonic event, confirmed here for the first time by combined mineralogical, organic-petrographic, and isotopic age data. The new data may have the potential to re-evaluate geodynamic models of the northern Gondwana-margin during the Late Palaeozoic. The illitization ages associated with the Alpine metamorphism are ascribed to ophiolite emplacement during the Cretaceous and to tectonic events during the Eocene compressional period, which led to the present nappe structure of the Taurides.