Specific Features of the Distribution Pattern of Detrital Zircon Age in the Epi-Hercynian Molasse of the Greater Caucasus (Lower Permian Aksaut Formation)

Abstract Results of the U‒Pb isotope dating of detrital zircon grains from sandstones in the typical section of the Lower Permian Aksaut Formation on the northern slope of the Greater Caucasus are presented. This formation represents a structural element of the Hercynian molasse that completes the Hercynide section in the Greater Caucasus. Results of the U‒Pb dating of detrital zircons from the Aksaut Formation sandstones are compared with the previously published similar data on metasedimentary rocks of various ages within the Hercynides of the Greater Caucasus, as well as with the date intervals of crystalline complexes that comprise the Hercynian basement of the Greater Caucasus. Prominent age peaks at about 309 and 385 Ma on the probability density curve characterizing the distribution of detrital zircon dates from sandstones of the Aksaut Formation are related to the widespread development of granite magmatism and metamorphism in the central part of the Greater Caucasus with dates closely corresponding to the above age peaks. The presence of numerous zircon groups with ages of 450‒750 Ma in the Aksaut sandstones is associated with: (1) erosion products of magmatic manifestations in the Cadomide blocks (peri-Gondwanan terranes) participating in the structure of Hercynides in the Greater Caucasus, (2) recycling detrital zircons from igneous complexes of the peri-Gondwanan terranes and/or rocks of Upper Precambrian and Lower Paleozoic sequences composed of erosion products of the peri-Gondwanan terranes into the Late Paleozoic Aksaut Formation rocks.