New geological map and 3D section of the Loki crystalline massif and surrounding area (the Caucasus)

The Loki crystalline massif and adjacent territories are exposed in South Georgia within the northern marginal part of the Beiburt-Sevan terrane. It is part of the Loki-Karabakh tectonic zone. The Loki massif is a large anticlinal structure with a pre-Alpine crystalline basement exposed in the core surrounded by a Mesozoic-Cenozoic sedimentary cover. According to the complex study of the massif, it was established that it is composed of autochthonous Upper Devonian gneissose quartz-diorites, allochthonous pre-Late Paleozoic Moshevani and Sapharlo-Lok-Jandari overthrust sheets of metasediments, Precambrian Lower Gorastskali ofiolite sheet and Upper Gorastskali mélange sheet. All these rocks are cut by Late Paleozoic, Jurassic and Cretaceous intrusions. All sheets, except for ophiolite one, were metamorphosed during the Caledonian orogeny and then were overthrust during Bretonian and Early Cimmerian orogenies. The Loki massif is a part of the northern active continental margin of the Paleotethys oceanic basin, where supra-subduction regional metamorphism and granite formation occurred during Variscan orogeny. During the Late Bretonian orogeny, the obduction of Precambrian ophiolite rocks and the overthrusting of Paleozoic metamorphic sheets onto the continental margin took place. Later they were intruded by granites. Along the entire perimeter, the crystalline basement and granites are transgressively covered by Mesozoic-Cenozoic deposits. On the basis of detailed studies of terrigenous deposits in the section of the r. Gorastskali gorge on nanoplankton new age data have been obtained. Based on these data, for three lithostratigraphic units – Moshevani (conglomerates and quartz sandstones), Lokchay (mica sandstones) and Jandari (argillites) suites, the following ages were established: Norian - Rhaetian, Hettangian - Low Pliensbachian and Upper Pliensbachian - Aalenian, respectively. Triassic deposits were discovered in this area for the first time. With the accumulation of new data on the Loki massif and surrounding area, a new corrected digital geological map, lithostratigraphic column and 3D section were compiled.