New data on the Mesozoic magmatism of the Bechasyn zone, in the Greater Caucasus, and estimation of the age of the regional metamorphism

Abstract

The results of the local U–Th–Pb isotope dating of accessory zircons from gabbroic rocks of the Khasaut subvolcanic complex are considered. Dikes of gabbroic rocks, which were previously mapped as subvolcanic intrusions in the structure of the Precambrian metamorphic complex, were studied in the Bechasyn zone of the crystallinicum of the Greater Caucasus, in the riverbed of the Khasaut River (the left tributary of the Malka River). The U–Pb age of igneous zircons from these rocks of ~220 Ma does not support the Proterozoic age and is evidence of possible manifestation of Triassic magmatism in the Greater Caucasus. The recent data on the zircon age of the protolith of the Bechasyn complex indicate that some sedimentary rocks are younger than 440 Ma and the peak of regional metamorphism of greenschist facies in the Bechasyn zone, taking the thermochronological corrections into account, probably corresponded to 400–420 Ma.