International Research Group Project SOUTH CAUCASUS GEOSCIENCES FINAL WORKSHOP October 25-27, 2017 Kiev, Ukraine The Workshop is organized by: CNRS, Université Côte d'Azur, UMR Geoazur UNS, Observatoire de la Côte d'Azur, IRD, Sophia Antipolis France S.I. Subbotin Institute of Geophysics, National Academy of Sciences of Ukraine, Kiev Ukraine INTERNATIONAL RESEARCH GROUP PROJECT Tethyan evolution and continental collision in SW Caucasus (Georgia and adjacent areas) © S. Adamia, V. Alania, A. Gventsadze, O. Enukidze, N. Sadradze, N. Tsereteli, G. Zakariadze, 2017 Tbilisi State University, M. Nodia Institute of Geophysics, Tbilisi, Georgia Georgia, the westernmost part of the and Transcaucasus-Pontian belts are of North southern Caucasus located at the junction Tethyan origin while Anatolia, Taurus, Iran, of European and Asiatic branches of the Al- and the southern Lesser Caucasus belong to pine-Himalayan orogenic belt represents an the South Tethys. area where the Tethys Ocean was completely The Arabia-Nubian Shield, at the end of closed only in the late Cenozoic as a result of the Proterozoic, experienced basement con­ prolonged convergence between the Eurasian solidation related to the final stages of the and Africa-Arabian plates. Pan-African cycle of tectogenesis. In contrast During the Neoproterozoic—early Ceno­ to the southern Lesser Caucasus (Daralagoz), zoic, the territory of Georgia and the adja­ the Transcaucasus did not undergo this pro­ cent area of the Black Sea-Caspian Sea region cess because it broke away from the Arabia- were parts of the Tethys Ocean and its north­ Nubia Shield and, during Cambrian—Devo­ ern and southern margins. The Prototethys- nian, drifted deep into the Prototethys toward Paleotethys-Tethys was not a single continu­ the northern (Baltica) continent. ous oceanic plate, but rather developed in During the early—middle Paleozoic in the branches separating continental terranes of wake of northward-migrating Gondwanian different sizes, which rifted and drifted away fragments, the Paleotethyan basin formed, from the Gondwana margin and eventually and, in the Ordovician, along its border with collided with Laurasia. Prior to the final col­ the Transcaucasus, subduction of oceanic lision in the late Cenozoic, the region hosted crust occurred, accompanied by suprasu- systems of island arc, intra-arc, and back-arc bduction volcanic eruptions. Northward mi­ basins located between the East European gration of the Transcaucasus throughout the (Baltica) continent and Gondwana. Integra­ Paleozoic caused narrowing of the Protote­ tive geological and paleogeographical stud­ thys and its transformation into an oceanic ies show a collage of several tectonic units back-arc (Dizi) basin. Fragments of paleoce- (terranes) in Georgia and adjoining areas anic crust are found along the southern bor­ that have distinctive geological histories with der of the Transcaucasus, within accretionary Tethyan, Eurasian, or Gondwanian affinities. complexes of the Lesser Caucasus ophiolite These include the Scythian platform, the Cav- suture, and in the Pontides, also in Iranian casioni (Great Caucasus), the Transcaucasus- Garadagh. During the late Paleozoic—early Pontides, and the Lesser Cavcasioni (Cauca­ Mesozoic, the oceanic basin separating the sus)—Alborz—West Iran regions. Their posi­ Africa-Arabian continent from the Taurus- tion between the Africa-Arabian and Eurasi- Anatolian-Iranian platformal domain gradu­ atic continents provides a reason for grouping ally extended. During this phase, only the them into the Northern Tethyan (Eurasian) Central Iranian terrain separated from Gond­ and Southern Tethyan (Gondwanian) do­ wana, drifted northward, and collided with mains. The Scythian platform, Caucasioni, the Eurasian continent in the Late Triassic. 78 Teo(pu3UHecKuû. xypnoA Ne 4, T. 39, 2017 SOUTH CAUCASUS GEOSCIENCES The Taurus-Anatolian terrane separated from Caucasioni; pre-Late Triassic obduction in Gondwana later, in the Early-Middle Jurassic. the Lesser Caucasus; and pre-Late Jurassic During the Mesozoic—Cenozoic, Daralagoz obduction during which ultrabasic rocks were represented the northwestern most margin of thrust over the continental unit of the Artvin- the Central Iranian platform and was sepa­ Bolnisi Block of the Somkhet-Garabagh zone. rated from the North Anatolian platform by an The metabasites apparently represent Paleo- oceanic or back-arc basin (Khoy basin), which tethyan fragments. within the modem structure is represented by During the Oligocene, marine Tethyan ba­ Mesozoic — Cenozoic ophiolites of Urumieh- sins were replaced by euxinic basins, which Khoy (Iran) and Van (Turkey). are considered to represent the beginning The Paleozoic-Eocene evolution of the of syncollisional development between Ara­ North Tethyan domain was marked by major bian and Eurasian plates in the region. On­ magmatic events corresponding to the Pacif­ going collision during Miocene—Quater­ ic-type and Mediterranean stages of Tethyan nary caused inversion of topography such development. The precollisional magmatic that fold-and-thrust mountain belts of the assemblages reflect a variety of paleotectonic Cavcasioni and Lesser Cavcasioni, and the environments. They are indicative of a west intermontane foreland basins in between Pacific-type oceanic setting in which a ma­ were formed. In the late Miocene, coeval with ture, Andean-type continental arc developed. molasse deposition in the foreland basins, There were several episodes of oceanic litho­ subaerial volcanic eruptions occurred, char­ spheric obduction onto the continental ter- acterized by intensively fractionated magma ranes of the region: the middle-late Paleozoic, of suprasubduction-type calc-alkaline series during which basite-ultrabasite complexes from basalts to rhyolites. were thrust over the island-arc system of the In addition to volcanism, earthquakes indi­ Transcaucasus and the Main Range zone of cate active tectonics in Georgia. Some of the 36°E 42°E 48°E 54°E 42°N 36°N ]Q mm/vr 95% confidence Fig. 1. Map showing global positioning system (GPS) velocities with respect to Eurasia and 95 % confidence ellipses for the eastern Black Sea—Caucasus—Caspian region [Vemant et al., 2013]. reo(pU3UHecxiiu xcypiiaA № 4, T. 39, 2017 79 INTERNATIONAL RESEARCH GROUP PROJECT major earthquakes have proven to be devas­ deformation of the crust and lithosphere of tating; i.e., the Racha earthquake of 29 April the region have taken place via compres­ 1991, with Ms=6.9, was the strongest ever re­ sional structures, as well as lateral tectonic corded in Georgia. The fault plane solution escape. The geometry of the topography and data for 130 earthquakes show that the terri­ tectonic features is largely determined by the tory of Georgia is currently under latitudinal wedge-shaped rigid Arabian block (indentor) compression, longitudinal extension, and an and by the configuration of the oceanic-sub- overall crustal thickening. A complex network oceanic lithosphere (buttresse) of the eastern of faults divides the region into a number of Black Sea and south Caspian Sea, all of which separate blocks. Three principal directions of cause bending of the main morphological and active faults compatible with the dominant, tectonic structures of the region around the near N-S compressional stress produced by strong lithosphere (Fig. 1). northward displacement of the Arabian plate Large-scale intraplate deformation of the can be distinguished: one longitudinal, trend­ lithosphere of the region as a result of the in­ ing WNW-ESE or W-E, and two transversal, dentation of Arabian and Indian plates result­ trending NE-SW and NW-SE. The first group ed in Late Cenozoic shortening and uplift of (WNW-ESE), the so-called «Caucasian» the mountain belts of the region, subsidence strike, is composed of compressional struc­ acceleration of the Black Sea—South Caspian tures, including reverse faults, thrusts, thrust crust, formation of submeridional, transversal slices, and strongly deformed fault-propa­ megastructure of the Caspian Sea that evi­ gation folds. The transversal faults are also dence for interference of lithospheric folding mainly compressional structures, but they contain considerable strike-slip components patterns induced by the Arabian and Indian as well. The tensional nature of submeridional collision with Eurasia [Smit et al., 2013]. faults is associated with intensive Neogene- Acknowledgements. This work was sup­ Quaternary volcanism in the Transcaucasus. ported by Shota Rustaveli National Science The NE-SW left-lateral strike-slip faults are Foundation (SRNSF), projects № 04-45 (GDRI the main seismoactive structures in the west­ — International Research Group: South Cau­ ern Transcaucasus, while right-lateral strike- casus GeoScience (Georgia — Eastern Black slip faults are developed in the southeastern Sea)) and № 217408 (Interactive Geological Transcaucasus. Considerable shortening and Map of Georgia, scale 1:200 000). References SmitJ. H. V., Cloetingh S. A. P. L., Burov E., Tesauro M., KarakhanianA.,AvagyanA., ErgintavS., DjamourY., Sokoutis D., Kaban M., 2013. Interference of litho­ Doerflinger E., RitzJ.-F., 2013. GPS constraints on spheric folding in western Central Asia by simulta­ continental deformation in the Black Sea, Caucasus neous Indian and Arabian plate indentation. Tecto- and Caspian region: Implications on geodynamics nophysics 602(Spec. is. Topo-Europe III), 176—194. and seismic hazard. Darius Programme (24—25June, https://doi.Org/10.1016/j.tecto.2012.10.032.