The Great Caucasus Cavcasioni: Structure and Evolution

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1 This work was supported by Shota Rustaveli National Science Foundation (SRNSF). Grant Project title: Interactive Geological Map of Georgia, 1: scale The Great Caucasus Cavcasioni: Structure and Evolution Adamia, Sh., Chabukiani, A., Chkhotua, T., Mumladze, T, Sadradze, N., Shavishvili, I., Zakariadze, G. I.Javakhishvili Tbilisi State University, 1, Chavchavadze av., 0179, Tbilisi, Georgia. The Figure shows the main geomorphological units of the Caucasus: the Precaucasus, Cavcasioni (Bolshoy Kavkaz in Russian, Great(er) Caucasus in English), Transcaucasian lowlands and Lesser (Anti) Cavcasioni

2 The digital geological, tectonic zonality and physical maps of the Caucasus 2010, scale 1:

3 Southward of the Laba-Malka (LM pink) and Fore Range (FR light green) tectonic zones of the Scythian young platform (yellow) locate the Main Range (MRZ dark purple) and Southern Slope (SSZ dark green) Main Tectonic Units (MTU) of the Cavcasioni

4 There are reliable data concerning the evolution of the Cavcasioni from NeoProterozoic (?) -Early Paleozoic till present. The basement of the Cavcasioni includes regional intensively metamorphosed Early-Middle Paleozoic - Caledonian and late Paleozoic - Hercynian rock assemblages.

5 A B Caledonian and Hercynian basement complexes are widespread in FRZ and MRZ: a Geological sketch of the basement complexes of the Cavcasioni; b Lower Middle Paleozoic obducted metamorphic rocks and ophiolite allochthons within the FRZ (Zakariadze, et al., 2012)

6 CHUGUSH SOFIA TEBERDA-DIGORI The basement of the Cavcasioni was dismembered by Alpine tectonics into several megaslices salients, separated by Alpine (Jurassic) tectonic depressions: 1. Chugush salient; 2. Sofia salient and 3. Teberda-Digori salients separated by Arkhiz-Klich depression; 4. Shkhara-Adaikhokh salient separated from 5. Teberda -Digori salient by Shtulu-Kharesk depression

7 Cathodoluminescence image (a) and diagram with concordia (b) for zircons of the Azau orthogneiss, sample 0-29, Azau (Somin, 2011). Concordia diagram for metamorphic zircons of migmatized paragneiss zircons, sample 0-17, Condaray complex, Adyrsu River (Somin 2011) Varyscides Optical and (b) cathodoluminescence images of zircons from sample of orthogneiss, Makera complex, Cheget Mt. Numbers on (a) are age values, Ma. Scale bar 300 µm. (c) Concordia diagram (Somin, 2011) Caledonides Metamorphic basement of the Cavcasioni is composed mainly of complexes of continental crust, for example, the Makera, Gondoray, Azau, and Buron Formations (Snejko, 1968; Somin, 2011, and others). Isotopic geochronology dating of the oldest part of the basement yielded Early-Middle Paleozoic age (Caledonides), while its younger part (mainly granite and mica schist) late Paleozoic age (Varyscides).

8 MRZ contain numerous fragments of oceanic lithosphere. Accretional complex of basicultrabasic rocks are known along the southern margin of the range: Chugush, Laba, Buulgen, and Kassar metabasites and ultrabasites (A F) Buulgen group: (A) garnetite in plane-polarized light; (B) blastomylonite in plane-polarized light; (C) dunite in plane-polarized light; (D) dunite in crosspolarized light; (E) rodingite in plane-polarized light; and (F) rodingite in cross-polarized light. Abbreviations: garnet (Gr), amphibole (Amph), andalusite (And), kyanite (Ky), olivine (Ol), pyroxene (Pyr), grossular (Grs), epidotezoisite (Ep-Zo).

9 Crinoidea (Adamia et al. 1974) Crinoidea (Potapenko, Stukalina, 1971) Optical (a) and cathodoluminescence (b) images of detrital zircons from metapsammite of the Buulgen complex, sample P 93-3, Khetskvara riverhead. Numbers on (a) are ages in Ma. (c) Histogram of the ages and concordia diagram for zircon with mean at 486±2.6 Ma (Somin 2011). Lower-middle Paleozoic age of the Laba metabasites is appreciated by paleontological (Amphypora, Crinoidea, Blue-green algae; Kuznetsov & Miclukho-Maklay, 1955; Agalin, 1968, Potapenko & Stukalina, 1971; Adamia et al., 1974; Somin &Vidiapin, 1989 ) and geochronological data(gurbanov et al., 1995; Somin, 2011)

10 Lithostratigraphic columns of the Upper Palaeozoic units, Cavcasioni Main Range Zone (Belov et al. 1989). In the FRZ and MRZ, the late Paleozoic (Carboniferous - Permian) Triassic deposits are represented by continental and shallow marine molasse, limestones, middle Carboniferous and Permian island-arc type volcanics I-Khuko; II-Pseashkho; III-Kvishi; IV-Oseti

11 Conodonts Kutelia, Barskov 1983 Back-arc - to marginal sea type rocks occur in the Southern Slope zone - the Dizi series - a continuous section of Devonian to Triassic weakly metamorphosed (anchymetamorphic), homogeneous terrigenous turbidities -and bedded cherts (with radiolarians and conodonts), lenses of crinoidal and reef limestones, and thin volcanic admixture of intermediate (andesite, dacite) composition Generalized stratigraphic column of the Dizi series with the points of the paleontological findings

12 KP DZ SP Similar to the Dizi series nonmetamorphosed turbidities and carbonates within SSZ are known to the West (Krasnaya Poliana) and to the East (Speroza).

13 Mesozoic-early Cenozoic sedimentary cover of SSZ, which continuously follow Paleozoic-Triassic deposits, contain: olistostromes, black slates, terrigenous and carbonate turbidites, MORB and island-arc type volcanic formations

14 The sedimentary cover of the Cavcasioni strongly deformed. The basement was deformed together with sedimentary cover - thick-skinned structures

15 The Main Range Zone and Southern Slope Zone of the Cavcasioni are characterized by complete penetrative, intensive, linear, generally isoclinal folding with mainly south-vergent imbricated thrusting, close-joint cleavage and boudinage.

16 The Alpine Cavcasioni is a typical thick-skinned fold and thrust mountain belt located in-situ, not showing any large-scale horizontal displacement

17 Postcollisional formations of the central segment of MRZ and SSZ are represented mainly by Pleistocene subaerial volcanics of the Elbrus, Chegem, Mkinvartsveri (Kazbegui), Kabarjina, Keli etc extinct volcanoes.

18 The complex pattern of variations in the P and S velocities reveals a clear correlation between anomalous lower P and S velocities and the late Cenozoic fold and thrust mountain belts of the Cavcasioni. The lowest-velocity anomalies are characteristic of the areas affected by Neogene Quaternary volcanism, such as the Elbrus-Chegem, Kazbegui, and Keli. The Neogene Quaternary volcanism is associated with the locations of magma chambers within the upper mantle asthenosphere (Amanatashvili et al., 2012; Koulakov et al., 2012; Bewick, 2016).

19 Seismoactive structures of the Region, CauSIN 2011; R Racha, S - Şamaxı R S SEISMICITY MAP OF THE EMME PROJECT REGION EMME Mid-Term Assembly Meeting, 2011 Amman, JORDAN The Cavcasioni is an earthquake-prone region where devastating earthquakes have repeatedly caused significant loss lives and damage: the Mw 7.0 Racha earthquake 9 April 1991, in Georgia, took about 100 human lives. An event in 1668 near Sheki, Azerbaijan destroyed the city Şamaxı, killing c people.

20 Histogram of N=f1(h) relations for: 1 time period ; 2-time period ; 3 trend line that was drawn through the moving averaging by step 2 (of time period , Varazanashvili et al., 2011) Earthquake hypocenters in the western and central Cavcasioni are located mainly in the Upper Crust, (c km. Varazanashvili et al., 2011); However seismological data from the easternmost segment of the Cavcasioni and adjacent area of the Precaucasus and Caspian Sea reveal a deep-seated zone of stress and strain (Leonov et al., 2001), a zone of the lower crust-upper mantle-earthquake sources that dips beneath the eastern Caucasus (Kovachev et al., 2006). According to Mellors et al. (2012) the most likely explanation for the subcrustal earthquakes appears to be northward subduction of relict oceanic crust sinking below Eurasia, earthquake hypocenters yields evidence of a north-dipping subducted slab beneath the eastern Greater Caucasus [Mumladze et al., 2015]. But, there is no data in favor of Neogene-Quaternary oceanic crust, which could subduct. The extinct volcanoes locate more westwardly from Kazbegui till Elbrus. Configuration of the area of deep and superdeep earthquakes don t correlate with the configuration of subducted area.

21 Geological cross-section of the Cavcasioni fold-thrust mountain belt (LATE STAGE POP-UP) along the Georgian Military Road. 1-continental crust; 2-oceanic crust; 3-diabase dykes; 4-sediments (Field meeting, 1990) GPS horizontal velocities (in Eurasia-fixed reference frame) for the eastern Alpine-Himalayan belt (Vernant, 2003). The Caucasus region has been considered to be an example of indentation tectonics. The geometry of tectonic deformations in the Caucasus is largely determined by the configuration of the rigid Arabian block. Submeridional trough of the lithosphere of the Caspian Sea (FIRST POP-UP) may be a structure located at the borderland between the Arabian and Indian plates and resulted from the interference of lithospheric folding (Luth et al., 2010; Smith et al., 2013). Lower plate

22 Non-uniform lithosphere with suture zone, overlain by a 'mega syncline. Note the similarity with the South Caspian Basin (Smith et al., 2013 )