Geo log i cal Quar terly, 2020, 64 (2): 288–303 DOI: http://dx.doi.org/10.7306/gq.1530 New ev i dences of Ho lo cene tec tonic and vol ca nic ac tiv ity of the west ern part of Lake Sevan (Ar me nia) Ara AVAGYAN1, *, Lilit SAHAKYAN1, Khachatur MELIKSETIAN1, Arkadi KARAKHANYAN 1, Vasily LAVRUSHIN2, Tatul ATALYAN1, Hayk HOVAKIMYAN1, Seda AVAGYAN1, Petros TOZALAKYAN1, Evgenia SHALAEVA2, Chris tine CHATAINGER3, Sergey SOKOLOV2, Arkadi SAHAKOV1 and Gagik ALAVERDYAN1 1 Acad emy of Sci ences of Ar me nia, In sti tute of Geo log i cal Sci ences, Baghramyan 24a, 0019 Yerevan, Ar me nia 2 Geolog i cal In sti tute of the Rus sian Acad emy of Sciences (RAS), 7 Pyzhevsky, Mos cow 119017, Russia 3 Archeorient UMR 5133 CNRS, Mai son de l’Orient et de la Mediterranee, Jean Pouilloux, 7 rue Raulin, 69365 Lyon, France Avagyan, A., Sahakyan, L., Meliksetian, K., Karakhanyan, A., Lavrushin, V., Atalyan, T., Hovakimyan, H., Avagyan, S., Tozalakyan, P., Shalaeva, E., Chatainger, C., Sokolov, S., Sahakov, A., Alaverdyan, G., 2020. New evi dences of Ho locene tec tonic and vol ca nic ac tiv ity of the west ern part of Lake Sevan (Ar me nia). Geo log i cal Quar terly, 64 (2): 288–303, doi: 10.7306/gq.1530 The purpose of this pa per is to pres ent new data on active geo log i cal pro cesses in the Lake Sevan Ba sin and to show its multidisciplinary as pects. The in ves ti ga tions of its struc tures, recent lake sed i ments, and lake floor gas emis sion al low a better under stand ing of the his tory of geolog i cal de vel op ment and the recent tec tonic and vol ca nic ac tiv ity of the basin. This pa per sum ma rizes un der wa ter in ves ti ga tions of ac tive geo log i cal fea tures of Lake Sevan, under taken for the first time in Ar me nia. More than 30 aligned un derwa ter-source related gas emis sion points were discov ered. The gas con tains car bon di ox ide of vol ca nic or volcanogenic-metamorphogenic ori gin and can be re lated to un load ing of deep fluid systems. This al lows de fin ing the Noratus-Kanagegh Fault seg ment trace be low the recent Lake Sevan floor sed i ments. The dis cov - ery of the sub aque ous seg ment of ac tive fault shows the pres ence of an other natu ral haz ard of lake tsu nami re lated to pos - si ble fu ture co-seis mic rup ture. The recent sed i ments of the north western Lake Sevan coast line are sandwiched be tween two blocky lava flows. The radio car bon dat ing of bones of bo vine mam mals (with en tire skull), found ~15 cm from the cover of the lake sed i ments, sug gests that the up per blocky basaltic -ande site layer can be a result of erup tion younger than ~3400 years BP. About 80 m of the Noratus se quence sed i ments have been sam pled for palaeomagnetic study and the age of 3.1–2.3 Ma for the lower part (42 m) is ob tained. The up per and post-Gelasian ac tiv ity of the Noratus-Kanagegh Fault is proven by a cross-cutscoria layer of 2.30 ±0.15 Ma K/Ar age. Key words: ac tive fault, gas emis sion, lake sed i ments, palaeomagnetism, lake tsu nami. INTRODUCTION wide spread land us age. The study of the area is im por tant for the meth od olog i cal point of view be cause of pos si ble in ter ac tion be tween vol ca nic and tec tonic ac tiv i ties and lake tsu nami. The study area is sit u ated in the cen tral part of the Ara - The ac tive nor mal and oblique slip faults are well-expressed bia-Eur asian con ti nen tal col li sion zone and is char ac ter ized by in the crest area and on the east ern slope of the Gegham Volca - com plex ge ol ogy (Fig. 1) and dense con cen tra tion of ac tive nic High land (Milanovsky, 1952, 1968; Karakhanyan et al., faults (Fig. 2A). A study of intra-block ac tive faults have a fun da - 2004, 2016; Avagyan et al., 2005, 2010) lim it ing the south west - men tal im por tance for ac cess ing seis mic haz ards and risks ern part of Lake Sevan of vol cano-tec tonic or i gin. par tic u larly for small coun tries with rel a tively dense pop u la tion The aim of the pa per is to ev i dence re cent tec tonic and vol - such as the Re pub lic of Ar me nia. These faults can be of rel a - ca nic ac tiv ity in the west ern part of the Lake Sevan Basin with tively low and me dium mag ni tude po ten tial. How ever, the study studying the lake sed i ments, struc tures and ge ol ogy, using of nat u ral haz ard be comes im por tant, be cause of high pop u la - multidisciplinary ap proaches in clud ing un der wa ter in ves ti ga - tion den sity (the pop u la tion in the Sevan Ba sin area reaches tions to shows multi-haz ard as pects of the ba sin. 280,000 peo ple in 92 com mu ni ties, of which five are ur ban) and GEOLOGICAL SETTING The mid dle east-Ar me nian High land area is char ac ter ized by * Corresponding author, e-mail: [email protected] two dis tinct su ture zones: the North ern Tethyan suture zone of Received: November 20, 2019; accepted: February 19, 2020; first published online: May 4, 2020 Izmir-An kara-Erzincan-Amasia-Sevan-Hakari (IAEASH), and New evi dences of Ho lo cene tec tonic and vol ca nic ac tiv ity of the west ern part of Lake Sevan (Ar me nia) 289 the South ern Tethyan suture zone of Misis-Andirin-Bitlis -Zagros with Eur asia oc curred in the Late Cre ta ceous (e.g., Sosson et al., (MABZ). They formed from the clo sure of the Palaeo tethys 2010; Rolland, 2017), and the Ara bia-Eur asia (with SAB in the Ocean (north ern branch of the Neotethys to the north, and the south) col li sion in the Late Eocene -Oligocene ac cord ing to most south ern branch of the Neotethys to the south; e.g., Sosson et au thors (e.g., Homke et al., 2010; Rolland et al., 2012). The sum - al., 2010; Rolland, 2017; Bar rier et al., 2018). The clo sure of the ma rize ar ti cles of the geodynamic evo lu tion of the Cau ca sus north ern branch and col li sion of the Gond wana-de rived South Moun tain belt from the Pa leo zoic to pres ent, and the his tory of Ar me nian Block (SAB cor re lated to the Taurides-Anatolides) Ju ras sic to Eocene subduction, obdu ction, and con ti nent-con ti - Fig. 1. Geolog i cal map of the Lake Sevan Ba sin (lo ca tion is in di cated in Fig. 2) mod i fied from Kharazyan (2005) As ter isks (1, 2) show un der wa ter sam pling sites 290 Ara Avagyan et al. nent col li sion be tween Eur asia and Ara bia is pre sented by Avagyan et al. (2005, 2010), Galoyan (2008), Sosson et al. (2010) and Rolland (2017), with ref er ences therein. Dur - ing Eo cene times, in tense mag matic and vol - ca nic phases took place to the north of the MABZ su ture zone, con nected with a north - -dip ping south ern Neotethys sub duction, in an exten sio nal (back-arc) en vi ron ment of oro genic belts, sug gest ing the Ara bia–Eur - asia col li sion af ter this mag matic event (Saha kyan et al., 2017). The low est part of the Sevan Basin is oc cu pied by Sevan Lake di vided into two sub- bas ins (Big and Small Sevan bas ins). The geo log i cal struc tures of the north east - ern part of Lake Sevan are well-stud ied. Here, the Mid dle Ju ras sic and Early Creta - ceous ophiolite su ture zone (Sevan-Hakari) is sit u ated to the NNE of Lake Sevan (e.g., Ga loyan, 2008; Sosson et al., 2010; Asatryan et al., 2010; Avagyan, 2013) con - trolled by the Pambak-Sevan-Sunik active fault (Fig. 2). Due to the south ern Neotethys clo sure, the Sevan-Hakari ophiolitic su ture zone was re ac ti vated by some ma jor thrusts and strike - slip faults (Avagyan et al., 2005, 2010). NW–SE com pres sion was dom i nant be tween the Paleogene and late Early Mio- cene, and NE–SW com pres sion has re - vealed be tween the Late Mio cene and Qua - ter nary (Avagyan et al., 2010). The W, SW and S parts of the Sevan Ba- sin are rep re sented by the Gegham and Vardenis vol ca nic high lands, re spec tively.