Geological and Geomorfological Investigations of the Javakheti Plateau (South Georgia)
Total Page:16
File Type:pdf, Size:1020Kb
saqarTvelos mecnierebaTa erovnuli akademiis moambe, t. 11, #4, 2017 BULLETIN OF THE GEORGIAN NATIONAL ACADEMY OF SCIENCES, vol. 11, no. 4, 2017 Geology Geological and Geomorfological Investigations of the Javakheti Plateau (South Georgia) Givi Maisuradze,* Tamaz Giorgobiani,* David Zakaraia,** Levan Basheleishvili* * Al. Janelidze Institute of Geology, Ivane Javakhishvili Tbilisi State University, Tbilisi, Georgia ** Caucasus Mining Group, LTD, Tbilisi, Georgia (Presented by Academy Member Mirian Topchishvili) ABSTRACT. In the article the territory of transport corridor on the Javakheti volcanic plateau (South Georgia) with its geological and geomorphologic structure and association of relief forms with young volcanism is considered. Neotectonic and morphotectonic structures, volcanic centers and modern exodynamic processes established by us in the region are characterized there. Volcanic activity in the study region was connected with interzonal and intrazonal deep faults. Volcanism was of subaerial type. Acid volcanism of Mio-Pliocene (Goderdzi suit) was replaced by heavy outpourings of basic lava in the Eopleistocene. Vast volcanic plateaus (sheets), stratovolcanoes and numerous small volcanic centers, extrusive cons, were formed. Among the outbursts of pulsation of volcanoes at the separate areas of land compensated troughs were formed in the lake basins. The second cycle that started, according to numerous isotopic, paleomagnetic and biostratigraphic evidence, about 3.5 Ma ago is characterized by outflow of huge masses of mafic lavas which formed extensive basaltic plateaus in South Georgia, West Armenia and East Anatolia. The centers of these basalts were mainly shield-shaped volcanoes of relative altitude 100-300 m. The most complete sections number up to 30 individual flows (5-15 m thick), with total thickness reaching 250-300 m. The uppermost flows are radiologically dated at 1.8-2.0Ma indicating their Eopleistocene age. Eopleistocene volcanism finished the relief planation in the areas of its spreading. © 2017 Bull. Georg. Natl. Acad. Sci. Key words: Goderdzi suit, Quaternary age, Eopleistocene, basaltic lava, volcanic cones Increasing scopes of international cooperation tion of construction of industrial and civilian ob- has given possibilities of effective use of the South jects and corresponding infrastructure in the zone. Caucasus and in particular Georgia, situated at the Transport corridor (railways, highways, product and intersection of the East-West and North-South power mains) and all accompanying industrial and transport corridor connecting different regions of civilian objects must be constructed in such a man- the Eurasian continent. Developing new transport ner to reduce possible risk caused by natural corridor will undoubtedly result in the intensifica- geodynamic processes. © 2017 Bull. Georg. Natl. Acad. Sci. Geological and Geomorfological Investigations of the Javakheti Plateau (South Georgia) 67 The territory of Javakheti plateau comprises con- parallel lava planes with thicknesses ranging from 1- siderable part of the volcanic highlands of Eastern 5cm to 10-30cm. Strike of bedding is sublatitudinal Anatolia and South Georgia. In the formation of the (azm. 260-270°), they are dipping north under the an- present-day relief and geological structure of these gle of 25-40°. In some exposures the zones of in- highland the main role belongs to neotectonic move- creased jointing are observed; they are 1m thick and ments and associated with them intensive effusive have a northwest strike (azm.315-320°) and south- subaerial volcanism – its products cover the greater west dip at an angle of 45-60°. To the north and east part of the vast region. Geological units exposed they are covered by younger lavas of the Akhalkalaki within the study area consist of Upper Tertiary (Mio- plateau and are exposed only in some erosion gorges Pliocene) volcanogenic continental rocks (tuff, tuff- of the rivers Kodala, Zagranichnaia etc. breccia, tuff-conglomerate, etc) and overlaying Qua- Nearly all the remaining part of the study area, ternary basaltic and andesite-basaltic lava flows that including the northern slopes of the Nialiskuri ridge, form the slightly undulated surface of the Kars and is covered by basaltic and andesite-basaltic lavas of Akhalkalaki plateaus. The volcanic rocks with total the Akhalkalaki suite (Eopleistocene). Similar lavas thickness exceeding 1000 m unconformably overlie are widely developed in Turkey in the Kars region. Paleogene-Cretaceous and older formations that are The absolute age of these rocks according to the not exposed within the study area. latest date, ranges between 2.5-0.8 Ma [1,2]. The geology of the Javakheti highland (within Petrographically, among the lavas of the Akhalkalaki the limits of the study area) consists of Neogen-Qua- suite, dominate olivine dolerites covering consider- ternary continental (subaerial) volcanogenic forma- able part of the study area. They are developed tions. Lithologically, piroclastic rocks and lava flows around Akhalkalaki, Diliska, Kulalisi and also cover of dacitic, andesite-dacitic, andesite-basaltic and ba- the Murakvali and Azmana ridges. From the village saltic composition represent them. These volcanic Dilifi to Akhalkalaki 3-5m thick alluvial-lacustrine rocks unconformably overlie intensely deformed sediments overlie these lavas. In the canyons of the marine Paleogene and Cretaceous sediments that form rivers Dilifi (Kirkhbulakh) and Paravani one can ob- the sublava substratum exposed locally in the Mtkvari serve 2-3 flows of olivine dolerites, each 3-5m thick. River gorge and encountered in some drill holes (in The flows are separated from one another by slaggy the villages Khertvisi and Nakalakevi). contact beds, 0.5-1.0 m thick. Outcrops of the volcanic rocks of the Goderdzi Olivine dolerites are developed around the vol- suite (Mio-Plioene) are observed in the western pe- cano (v) Kartsakhi (Ker-Ogly, 2213m) on the ripheral part of the Nialiskuri ridge (in the locality Murakvali ridge. Here, in outcrops occur several 1.5- Sakun); here they are represented by tuff-breccias, 2.0 m thick flows of dolerites; they are represented tuff-conglomerates and tuffs with interformational by dark-grey macroporous, full-crystalline rocks, in- flows of andesite-dacitic lava. Visible thickness of clined to southeast at an angle of <15-20°. The mount pyroclastic rocks reaches 300-400m. The suite is ter- Kartsakhi is a typical polygenic volcano that at first minated by andesite-dacitic and dacitic lavas (Lower erupted andesite-basalts and basalts and their Pliocene) that are widespread over the whole vol- breccias, and at the final stage - olivine dolerites. canic province of South Georgia and Eastern Anatolia. Besides the Kartsakhi volcano, there are some other These lavas are exposed on the northern slope of the volcanic centers in the axial zone of the Murakvali Nialiskuri (Geoktape) ridge, south of the Kartsakhi ridge that also produced olivine doleritic lavas. Lake. In andesites a well expressed stratification of A special interest represents 2 volcanic centers rocks is observed, they are presented by alternating located 4 km northwest of the railway line Mzechabuki Bull. Georg. Natl. Acad. Sci., vol. 11, no. 4, 2017 68 Givi Maisuradze, Tamaz Giorgobiani, David Zakaraia, Levan Basheleishvili (Didi Giuney – 2060m) and Mzekala (Patara Giuney – of total thickness up to 30m can be distinguished; 2034m). The dome-shaped uplifts, with diameter at small scarps separate them from one another. The the base reaching 2-2.5km and relative height of 200- uneven undulated surface formed by these lavas is 250m, rise sharply above the surrounding territory. characteristic of young volcanic formations. They are composed of tuff and scoria breccias, vol- Thus within the study area there is a great number canic bombs and sands. Dark-grey fine-crystalline (several dozens) of volcanic centers of Late Neogene basaltic lavas cover this clastic material. Such lavas and Eopleistocene age. Nearly all of them are located are widely developed south of village Vachiani, in along definite lines that, most probably, correspond the vicinity of villages Patara-Gondrio, Dadeshi, to faults and fault zones in the sublava substratum. Sulda, Bozali and Filipovka. South of Dilifi, these fine- Volcanic activity was of the aerial type and occurred grained basalts and dolerites overlie the erosion sur- in several phases of eruption separated by periods face of andesite-dacitic and dacitic lavas of the of relative calm that is evidenced by accumulation of Goderdzi suite. inter-lava alluvium and lacustrine sequences. In the closeness to the designed railway there are The territory of transport corridor in the Javakheti, several other volcanic centers – two-headed along the southwestern part of the Akhalkalaki lava Tsmindamta (Surp-Sar - 2001m), Kvatsihe (Tash-Kala plateau also embrace northern slopes of the Nialiskuri – 1983m) and Dadeshi (2021m). These cone-shaped (Geoktape) ridge extending in sublatitudinal (W-E) uplifts are built up of thick beds of red breccias con- direction. The Akhalkalaki plateau is a slightly un- taining fragments of pumice, scoria, lapilli, sand and dulating high-mountainous plain gently sloping to fine-grained doleritic lava. Dark-grey basalts and the north. Minimal elevations of the plateau within dolerites cover the tops of these volcanoes. the study area are observed near the village of Kulalisi Olivine dolerites and basalts in the central part of (1770-1800m),