Turkish Journal of Earth Sciences (Turkish J. Earth Sci.), Vol.S. ADAMIA 20, 2011, ET pp. AL. 611–628. Copyright ©TÜBİTAK doi:10.3906/yer-1005-12 First published online 02 February 2011 Great Caucasus (Cavcasioni): A Long-lived North-Tethyan Back-Arc Basin SHOTA ADAMIA1, VICTOR ALANIA1, ALEKSANDRE CHABUKIANI1, ZURAB KUTELIA2 & NINO SADRADZE1,3 1 M. Nodia Institute of Geophysics, 1/1 M. Alexidze str.,0171, Tbilisi, Georgia (E-mail: [email protected]) 2 Mining Geologic Project Ltd, 87a Paliashvili str., 0162 Tbilisi, Georgia 3 Al. Janelidze Institute of Geology, 1/9 M. Alexidze str., 0193, Tbilisi, Georgia Received 15 May 2010; revised typescripts receipt 15 December 2010 & 14 January 2011; accepted 02 February 2011 Abstract: Th e Great Caucasus is a northwest−southeast-directed mountain range more than 1100 km long, located between the Black Sea and Caspian Sea. It represents an intracontinental tectonic system resulting from the Late Cenozoic structural inversion of a Palaeozoic−Mesozoic−Early Cenozoic back-arc basin (Dizi basin) in response to the convergence of the Africa-Arabian and Eurasian lithospheric plates. It is bounded to the south by the Transcaucasian massif, a palaeo-island-arc, and to the north by the Scythian platform. Th e Great Caucasus fold-and-thrust mountain belt is characterized by complete, intensive folding, mainly south vergent imbricated thrusting, close-joint cleavage etc. Structural relationships of the Great Caucasian fold-and-thrust mountain belt with the Transcaucasian massif and Scythian platform are, as a rule, tectonic overthrusts, but in some places the contacts are transitional. Th e Great Caucasus basin has developed, at least from Devonian, throughout Palaeozoic and Mesozoic to Early Cenozoic, as established by marine palaeontological data. Late Palaeozoic (Variscan) metamorphic and magmatic events, folding and topographic inversion are not observed in the Southern Slope Zone of the Great Caucasus. Variscan and Early Mesozoic (Old Cimmerian) orogenic events did not lead to closure of the Dizi back-arc basin. Th e mountainous Crimea (Triassic−Liassic Tauric series) represents a similar basin of continuous deposition with no Variscan and Old Cimmerian orogenic events and is generally considered to be the western extension of the Great Caucasian basin. East of the Caucasus, such a basin characterized by continuous Triassic−Jurassic marine sandy-argillaceous sedimentation is the Great Balkans (Transcaspian), which was continuously developing since the Palaeozoic. Th roughout the whole Mesozoic, Palaeocene and Eocene, the Great Caucasus represented a domain accumulating thick terrigenous, carbonate, and volcanogenic marine deposits and only in Oligocene−Miocene it was transformed into a mountainous edifi ce between the Black Sea and Caspian Sea basins. At present, the Black Sea and Caspian Sea basins unconformably overlie diff erent structures of adjacent land; their shoreline cuts several main tectonic units of the Caucasus and Crimea. Key Words: Great Caucasus, Cavcasioni, Transcaucasus, pre-Caucasus, Tethys, back-arc Büyük Kafk aslar: Kuzey Tetis’in Uzun Süreçli Yay-ardı Havzası Özet: Büyük Kafk aslar, Karadeniz ile Hazar Denizi arasında kuzeybatı−güneydoğu yönünde 1100 km uzanan bir dağ silsilesidir. Bu dağ kuşağı Paleozoyik−Mesozoyik−Erken Tersiyer yaşlı bir yay-ardı havzanın (Dizi havzası) Geç Tersiyer’de Afrika-Arabistan ile Avrasya levhalarının yakınlaşması ve çarpışmasına bağlı olarak yapısal terslenmesi ile oluşmuştur. Büyük Kafk aslar kıvrım-bindirme kuşağı yoğun kıvrımlanma, genellikle güneye verjanslı bindirmeler ve sık eklem klivajı ile tanımlanır; güneyde eski bir ada-yayını temsil eden Transkafk asya masifl eri, kuzeyde ise İskit Platformu ile sınırlanır. Büyük Kafk as kıvrım-bindirme kuşağının Transkafk asya masifl eri ve İskit Platformu ile olan dokanakları genellikle bindirmeli fakat bazı bölgelerde geçişlidir. Paleontolojik verilere göre Büyük Kafk asya havzası gelişmesine Devoniyen’de veya öncesinde başlamış, tüm Geç Paleozoyik, Mesozoyik ve Erken Tersiyer’de devam etmiştir. Büyük Kafk asların güney zonunda (Southern Slope Zone) Geç Palaeozyik’te (Variskan) metamorfi k ve magmatik olaylar, kıvrımlanma ve yükselme gözlenmez. Daha kuzeydeki gözlenen bu Variskan ve Erken Mesozoyik (eski Kimmeriyen) olayları güney zondaki Dizi yay-ardı havzasının kapanmasına yol açmamıştır. Dağlık Kırım bölgesi de (Triyas−Liyas Tavrik serisi) Variskan ve erken Kimmeriyen olaylarının gözlenmediği, sürekli çökelim gösteren benzer bir havza oluşturur ve genellikle Büyük Kafk aslar havzasının batıya doğru devamını oluşturduğu kabul edilir. Büyük Kafk asların doğusunda benzer bir havza Triyas−Jura süresince 611 GREAT CAUCASUS sürekli kumlu-kili yaşlı sedimentasyonla tanımlanan, Paleozyik’te beri sürekli gelişim gösteren Büyük Balkan (Transcaspian) havzasıdır. Tüm Mesozoyik, Palaeosen ve Eosen boyunca Büyük Kafk aslar kalın kırıntılı, karbonat ve volkanik malzemenin depolandığı bir havza oluşturur, Oligo−Miyosen’de bu havza Karadeniz ve Hazar denizi havzaları arasında yükselen bir dağ kuşağına dönüşür. Günümüzde Karadeniz ve Hazar Denizi çökelleri Büyük Kafk asların değişik birimlerini ve yapılarını uyumsuzlukla üzerlemektedir. Anahtar Sözcükler: Büyük Kafk aslar, Transkafk asya, pre-Kafk asya, Tetis, yay-ardı Introduction and Early Cenozoic ages. Th e oldest deposits of the Cavcasioni (Bolshoi Kavkaz in Russian and Great Dizi series, dated as Devonian–Triassic, are exposed Caucasus in English) is a NW–SE-directed mountain within the Southern Slope Zone (Figure 1). range more than 1100 km long, located between the Black Sea and Caspian Sea. It represents an Th e Palaeozoic–Triassic Formations intracontinental fold-and-thrust mountain system Th e Palaeozoic–Triassic sediments crop out within resulting from the Late Cenozoic syn- and post- three regions of the Southern Slope Zone of the Great collisional structural inversion of a Palaeozoic– Caucasian fold-and-thrust mountain belt. Th ey are: Mesozoic–Early Cenozoic pre-collisional back- (1) the Mzimta gorge located within the western arc basin (Khain 1974; Adamia et al. 1977, 1981; Southern Slope Zone, (2) Svaneti – within the central Dercourt et al. 1985; Stampfl i et al. 2001) in response Southern Slope Zone (Dizi series), and (3) Speroza – to convergence of the Africa-Arabian and Eurasian within the eastern Southern Slope Zone. lithosphere plates (Figure 1). It is bounded to the south by the Transcaucasian massif, which is a Palaeozoic–Early Cenozoic island-arc, and to the Th e Dizi Series north by the Scythian young platform (Figure 2). Th e Dizi series crops out in the cores of two (Enguri At present, this is a fold-and-thrust mountain belt and Tskhenistskali) alpine antiforms (Figure 5). Th e characterized by intensive tight and subisoclinal core of the former is more eroded; exposed formations folding, mainly south-vergent imbricated thrusting, range in age from Lower–Middle Devonian to close-joint cleavage etc (Figures 3 & 4). Structural the uppermost Triassic. Th ickness of the series, as relations of the Great Caucasian fold-and-thrust reported by various authors, is 1.5–2.0 km. Present mountain belt with the Transcaucasian massif and knowledge on its stratigraphy is mainly based on the Scythian platform are, as a rule, tectonic overthrusts, palaeontological data (corals, foraminifers, crinoids) however, in some places the contacts are transitional described or reported by Sh. Adamia, G. Agalin, A. (Milanovsky & Khain 1963; Gamkrelidze 1964; Belov, G. Chikhradze, V. Kazmin, Z. Kutelia, V. Slavin, Shardanov & Borukaev 1968; Grigoriants et al. 1972; and M. Somin. Lately, radiolarians and conodonts Gamkrelidze & Gamkrelidze 1977; Adamia et al. were found in this series (Z. Kutelia, I. Barskov) that 1987a; Giorgobiani & Zakaraia 1989; Kengerli 2005). promoted a better understanding of the stratigraphic Th e crust of the Great Caucasus is continental, setting of the series and changed existent notions on up to 55–60 km thick; it covers an area up to 60–75 its structure. km wide. Th e ‘granite’ layer of the Great Caucasus Th e Dizi series is rather monotonous. Th e is exposed within its Main Range Zone forming the presence of Lower–Middle Devonian, Upper crystalline core of the fold-and-thrust mountain Devonian and Lower–Middle Carboniferous, and belt. Sedimentary cover of the Great Caucasian Triassic anchimetamorphic deposits (phyllites, fold-and-thrust mountain belt, which is widespread slates) is proved on the basis of palaeontological within the Main Range Zone and Southern Slope fi ndings. Th e deposits are represented mainly by fi ne- Zone, is dominated by deep marine terrigenous grained terrigenous and hemipelagic formations, and hemipelagic deposits of Palaeozoic, Mesozoic, characterized by an irregular alternation of siltstones, 612 S. ADAMIA ET AL. a P R E CAU CAS U S CAS PIAN B L A C K S E A S E A GR EA Azov-Kuban TC Scythian AU CA 37 00’o 41o 00’ STAVROPOL AK Ku ba n S U SC b Sp Kz 2 Bechasin S ST Sp Kz2 PcMz- Kz1 Terek-Caspian BLACK SEA Pc Kz1 o 44 00’ GC PcMz- Kz1 Pc Mz Be 45o 00’ Ch Pc Mz Laba-MalkaMain Range BPC-Pz Scythian Pc Mz-Kz 1 FR Pc Pz TK GROZNI La MR Chugush Pc Kz1 Bu BPC-Pz TC Pc Mz-Kz 1 Laba Di SC Great Caucasus Pc Pz Pc Mz 49o 00’ Pc Mz-Kz1 Ka KAZBEGUI 3a Pc Kz1 Transcaucasus i GR R ion R o ’ E CASPIAN 42 00 Fore Range Dizi Sz AT Sp Kz2 Pc Mz 3b SEA Buulgen Kassar Aragvi K CAU Al GD 4 Al Rioni az Gussar-Devichi a C A S USp KSz2 Kura ni Speroza TC SS Alazani Pc -Kz1 Transcaucasus BAKI 40o00’ Southern Slope MAIN TECTONIC UNITS TECTONOSTRATIGRAPHIC UNITS Neogene-Quarternary subaerial volcanic area B PC- Pz pre-Cambrian-Palaeozoic basement Scythian Platform (SC) Pc Pzpre - collisional , Palaeozoic fold-and-thrust mountain belt: Great Caucasus (GC) Pc Mzpre - collissional , Mesozoic foredeeps: Azov-Kuban (AK), Stavropol High (ST), Pc Mz-Kz1 pre - collissiona ,l Mesozoic-Early Cenozoic Terek-Caspian (TC), Gussar-Devichi (GD). Pc Kzpre - collissional , Early Cenozoic Transcaucasian massif (TC), foredeeps: Rioni (R), 1 Kura (K), Alazani (Al). Sp Kz2 syn-, post-collisional , Late Cenozoic location of the cross-sections: 3a, 3b and 4.