U–Pb LA–ICP–MS dating of zoned zircons from the Greater Caucasus pre-Alpine crystalline basement: Evidence for Cadomian to Late Variscan evolution

Abstract

Here we report U–Pb zircon age data, obtained using LA–ICP–MS, from a total of 14 rocks of the Pass and Elbrus sub-zones of the Main Range Zone of the Greater Caucasus, which differ quite significantly from each other in composition of sedimentary and igneous rocks. Both exotic (detrital) zircons, and those formed within the Greater Caucasus are revealed. The ages of detrital zircons range from 2981 to 668 Ma. On the basis of weighted mean age data among in situ zircons from meta-sedimentary rocks in both sub-zones figures of 626± 2 Ma and 627± 19 Ma were detected, which corresponds to the earliest – Cadomian stage of high temperature regional metamorphism. From meta-sedimentary rocks of the Elbrus sub-zone figures – 461±5.3 Ma, 457±12 Ma indicate manifestation of the Ordovician (tectonically associated with Caledonian orogeny) stage of high temperature prograde regional metamorphism. Figures from granitoid rocks of both sub-zones – 454±9 Ma, 468±5 Ma and 471.7±4.6 Ma were obtained, which also correspond to the Caledonian stage of synmetamorphic granitoid formation. Besides, figures from the meta-sedimentary rocks of the Pass sub-zone – 312.5±4 Ma, 317.0±8.3 Ma correspond to Late Variscan regressive regional metamorphism. In addition, figures obtained from the granitoid rocks of both sub-zones – 309±8 Ma, 310.9 Ma, 325±4 Ma, 311±5.9 Ma and 357±5.9 Ma correspond to the Late Variscan stage of synmetamorphic granitoid formation. These results are in good agreement with geological and petrological data for the Greater Caucasus.