Geodynamics, seismicity, and seismic hazards of the Caucasus
Alik Ismail-Zadeh
a,b,
⁎
, Shota Adamia
c
, Aleksandre Chabukiani
c
, Tamaz Chelidze
c
,
Sierd Cloetingh
d
, Michael Floyd
e
, Alexander Gorshkov
b
, Alexei Gvishiani
f
, Tahir Ismail-Zadeh
g
,
Mikhail K. Kaban
h,i
, Fakhraddin Kadirov
g
, Jon Karapetyan
j
, Talat Kangarli
g
, Jemal Kiria
c
,
Ivan Koulakov
k,l
, Jon Mosar
m
, Tea Mumladze
c
, Birgit Müller
a
, Nino Sadradze
c
,Rafig Safarov
g
,
Frank Schilling
a
, Alexander Soloviev
b
a
Karlsruhe Institute of Technology, Institute of Applied Geosciences, Karlsruhe, Germany
b
Institute of Earthquake Prediction Theory and Mathematical Geophysics, Russian Academy of Sciences, Moscow, Russia
c
Javakhishvili Tbilisi State University, Nodia Institute of Geophysics, Tbilisi, Georgia
d
Utrecht University, Department of Earth Sciences, Utrecht, the Netherlands
e
Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, Cambridge, MA, USA
f
Geophysical Center, Russian Academy of Sciences, Moscow, Russia
g
Azerbaijan National Academy of Sciences, Institute of Geology and Geophysics, Baku, Azerbaijan
h
Helmholtz-Centre Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg, Potsdam, Germany
i
Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
j
National Academy of Sciences of the Republic of Armenia, Nazarov Institute of Geophysics and Engineering Seismology, Gyumri, Armenia
k
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
l
Novosibirsk State University, Novosibirsk, Russia
m
University of Fribourg, Department of Geosciences, Fribourg, Switzerland
ARTICLE INFO
Keywords:
Greater and Lesser Caucasus
Geological evolution
Geodesy
Gravity
Density
Deformation
Tectonic stresses
Seismic tomography
ABSTRACT
Being a part of ongoing continental collision between the Arabian and Eurasian plates, the Caucasus region is a
remarkable site of moderate to strong seismicity, where devastating earthquakes caused significant losses of lives
and livelihood. In this article, we survey geology and geodynamics of the Caucasus and its surroundings;
magmatism and heat flow; active tectonics and tectonic stresses caused by the collision and shortening; gravity
and density models; and overview recent geodetic studies related to regional movements. The tectonic devel-
opment of the Caucasus region in the Mesozoic-Cenozoic times as well as the underlying dynamics controlling its
development are complicated processes. It is clear that the collision is responsible for a topographic uplift /
inversion and for the formation of the fold-and-thrust belts of the Greater and Lesser Caucasus. Tectonic de-
formations in the region is influenced by the wedge-shaped rigid Arabian block indenting into the relatively
mobile region and producing near N-S compressional stress and seismicity in the Caucasus. Regional seismicity is
analysed with an attention to sub-crustal seismicity under the northern foothills of the Greater Caucasus, which
origin is unclear – whether the seismicity associated with a descending oceanic crust or thinned continental
crust. Recent seismic tomography studies are in favour of the detachment of a lithospheric root beneath the
Lesser and Greater Caucasus. The knowledge of geodynamics, seismicity, and stress regime in the Caucasus
region assists in an assessment of seismic hazard and risk. We look finally at existing gaps in the current
knowledge and identify the problems, which may improve our understanding of the regional evolution, active
tectonics, geodynamics, shallow and deeper seismicity, and surface manifestations of the lithosphere dynamics.
Among the gaps are those related to uncertainties in regional geodynamic and tectonic evolution (e.g., con-
tinental collision and associated shortening and exhumation, lithosphere structure, deformation and strain-stress
partitioning) and to the lack of comprehensive datasets (e.g., regional seismic catalogues, seismic, gravity and
geodetic surveys).
⁎
Corresponding author at: KIT-AGW, Adenauerring 20b, 76131 Karlsruhe, Germany.
E-mail address: alik.ismail-zadeh@kit.edu (A. Ismail-Zadeh).
1
http://doc.rero.ch
Published in "Earth-Science Reviews 207(): 103222, 2020"
which should be cited to refer to this work.
1. Introduction
Located between the Black Sea to the west and the Caspian Sea to
the east (Fig. 1), the Caucasus region links Asia with Europe. The region
is geographically subdivided into the North Caucasus known also as the
Ciscaucasus (i.e. the area north of the Greater Caucasus), and the South
Caucasus known also as Transcaucasus (i.e. the area south of the
Greater Caucasus). The region hosts the Greater and Lesser Caucasian
Mountains including Mount Elbrus, Europe's highest peak reaching
5642 m above sea level. According to Pliny the Elder (1855, p. 34),
Scythians called the Caucasus “Graucasis”, which means “white with
snow”.
The Caucasus region is a part of an ongoing continent-continent
collision of the Arabian and Eurasian (AR-EU) plates, which is often
compared to the collision zone between India and Eurasia during its
early stages of evolution (e.g., Şengör and Kidd, 1979). A wider plate
tectonic framework includes an active continental collision in eastern
Turkey, the Caucasus, and the westward extrusion of Anatolia
(McKenzie, 1970, 1972; Jackson and McKenzie, 1984, 1988; Philip
et al., 1989). Convergence of Arabia and Africa with Eurasia has been
occurring for more than 100 Ma. During this time span the Neotethys
Ocean lithosphere has been subducting beneath Eurasia (Dewey et al.,
1973; Khain, 1975; Adamia et al., 1977, 1981; Gamkrelidze, 1986).
Geological, geophysical, and geochemical studies add important
details to the regional plate tectonic characterization, including (i) the
westward movement of Anatolia accommodated by the North and East
Anatolian faults (Şengor et al., 1985), (ii) partitioning of crustal de-
formation in the eastern Turkey/Caucasus continental collision zone
(Jackson, 1992; Allen et al., 2004; Copley and Jackson, 2006), (iii) the
influence of slab detachment on uplift and volcanism of the Tur-
kish–Iranian plateau (e.g., Şengor et al., 2004; Barazangi et al., 2006),
and (iv) the incipient subduction of the South Caspian oceanic basin
beneath the North Caspian continental lithosphere along the Central
Caspian Seismic Zone – CCSZ (e.g., Jackson et al., 2002).
The Greater Caucasus is thought to have formed by tectonic inver-
sion of a former back-arc basin developed on continental crust, that
opened during the early Mesozoic above the north-dipping subduction
of the Neotethys (e.g., Adamia et al., 1981; Zonenshain and Le Pichon,
1986; Mosar et al., 2010). The eastern Black Sea and southern Caspian
Sea are remnants of oceanic basin developed in Cretaceous and Jurassic
times, respectively. Large foreland basins, such as the Kartli, Kuban,
Kura, Rioni, or Terek basins, develop during the orogenic process in
Tertiary times north and south of the Greater Caucasus range (e.g.,
Mosar et al., 2010). The Oligocene sedimentary fi
ll of the Kura basin
and
of
the Rioni basin is likely to be asymmetrical showing flexural
subsidence along its southern margin, arguably the result of tectonic
loading from the Lesser Caucasus (e.g., Nemčok et al., 2013 ).
Both the timing and spatial evolution of shortening and exhumation
remain uncertain, with preferred estimates of the timing being Late
Miocene to Early Pliocene (e.g., Kopp and Shcherba, 1985; Philip et al.,
1989; Avdeev and Niemi, 2011; Albino et al., 2014; Cavazza et al.,
2017, 2018). Meanwhile, using a thermochronological analysis, it was
shown that the topography of the western Greater Caucasus started to
grow during the Oligocene (Vincent et al., 2007, 2011). Total short-
ening across the Greater Caucasus is also uncertain with estimates
ranging from 150 to 400 km (e.g., McQuarrie and van Hinsbergen,
2013) and with an increase in total shortening from west to east at
present (e.g., Král and Gurbanov, 1996; Avdeev and Niemi, 2011; Forte
et al., 2012). The continued convergence generated a compressive
stress field reactivating the deformation and uplift of the Greater Cau-
casus in the Pliocene (e.g., Saintot and Angelier, 2002). Shallow seis-
micity is prevalent throughout the region, and sub-crustal earthquakes
occur in the eastern part of the Greater Caucasus, beneath the Middle
Caspian Sea, and along the edges of the south Caspian Sea beneath the
Kura basin fill (e.g., Godzikovskaya and Reysner, 1989 ; Triep et al.,
1995; Ulomov et al., 2007).
During the last several decades, significant research in regional
geology, geodynamics, geodesy and geophysics was conducted to
Fig. 1. Topographic map of the Caucasus and the surrounding area.
2
http://doc.rero.ch
understand the evolution of the Caucasus and the surrounding areas as
well as to elucidate the present tectonics, lithospheric deformation,
seismicity, and associated seismic hazards and risks. The research re-
sults are recorded in many research articles published in international
journals as well as in the journals published in the former Soviet Union,
Armenia, Azerbaijan, Georgia, and Russia. This paper overviews the
state-of-the-art knowledge in the geological and geophysical fields
(internationally and locally) addressing the gaps in knowledge, and
discusses the perspectives for future research combining expertise and
experience of Armenian, Azeri, Georgian, and Russian scientists and
their international colleagues. Doing so, we present a synthesis of the
current understanding of geodynamics and seismicity of the Caucasus,
highlighting different scientific views and trying to structure disjointed
and contradictory research works associated with the topics. We de-
scribe different models and compare them against the data available,
discuss still controversial points and possible ways to resolve them, and
conclude the paper presenting examples of desired scientific research in
the region.
2. Geology and geodynamics
The Caucasus located in the central part of the mobile Alpine-
Himalayan belt is the result of a continental collision between the AR-
EU plates (Dewey et al., 1973; Khain, 1975; Adamia, 1975; Dercourt
et al., 1986; Zonenshain and Le Pichon, 1986; Zonenshain et al., 1987;
Philip et al., 1989; Okay and Şahintürk, 1997; Allen et al., 2004;
Vincent et al., 2007; Zakariadze et al., 2007; Sosson et al., 2010a, 2017;
Adamia et al., 2011, 2017; Albino et al., 2014; Cavazza et al., 2017;
Alania et al., 2017). The ongoing interaction of these plates controls the
present geodynamics and the seismicity of the Caucasus (McKenzie,
1972; Jackson and McKenzie, 1988; Ambraseys and Jackson, 1998;
Berberian and Yeats, 1999; Allen et al., 2004; Panahi, 2006;
Karakhanyan et al., 2013, 2017; Şeşetyan et al., 2018). The region can
be sub-divided into several major tectonic units (Fig. 2a). It combines
(from the north to the south) the Scythian platform with the Stavropol
High and the Azov-Kuban and Terek-Kuma flexural foreland basins, the
Greater Caucasus Fold-and-Thrust Belt (GCFTB), the Rioni and Kura
basins superimposed mainly on the rigid platform blocks (e.g., the
Dzirula crystalline massif), the Achara-Trialeti (also known as Ajara-
Trialeti) and the Talysh fold-thrust belts (FTB), the Lesser Caucasus
FTB, the Sevan-Akera ophiolitic suture, the Lesser Caucasian part of the
Taurus-Anatolia-Central Iranian platform, and the Aras intermontane
basin (or the Aras flat).
The
Armenian and Javakheti highlands are
composed of Neogene–Quaternary continental volcanic formations, and
recent volcanoes of the Greater Caucasus are Elbrus, Chegem, Keli, and
Kazbegi (Adamia et al., 2011, 2017).
Integrative geological and paleobiogeographical studies show a
collage of several tectonic units in the Caucasus and adjoining areas
that have distinctive geological histories with marine Tethyan,
Eurasian, or Gondwanan affinities (Adamia et al., 2011, 2017). Their
position between the African-Arabian and Eurasian plates provides a
reason for grouping them into the North Tethyan (Eurasian) and South
Tethyan (Gondwanan) domains (Fig. 2b). The Scythian platform,
Greater Caucasus, and Lesser Caucasus - Transcaucasus-Pontian belts
originate from the North Tethyan, while Anatolia, Taurus, Iran, and the
southern Lesser Caucasus belong to the South Tethys (Stampfli et al.,
2001; Zakariadze et al., 2007, 2012). At the end of the Proterozoic, the
Arabia-Nubian shield experienced basement consolidation related to
the final stages of the Pan-African cycle of deformation (Zakariadze
et al., 2007, 2012). In contrast to the southernmost Caucasus (Dar-
alagöz, Fig. 2b), the Transcaucasus did not undergo this process, be-
cause it broke away from the Arabia-Nubia shield and drifted far in the
Prototethys toward the northern (Baltica) continent during Cam-
brian–Devonian times (Fig. 3a; Dercourt et al., 1986; Zonenshain et al.,
1987, 1990; Barrier and Vrielynck, 2008; Barrier et al., 2018). As a
consequence of northward-migrating Gondwanan fragments, the
Paleotethyan basin formed during the early–middle Paleozoic, and a
subduction of the oceanic lithosphere began along its border with the
Transcaucasus in the Ordovician, which was accompanied by volcanic
eruptions. Northward migration of the Transcaucasus throughout the
Paleozoic narrowed the Prototethys and transformed it into an oceanic
back-arc (Dizi) basin (Fig. 3b). An evidence for back-arc type of the
oceanic lithosphere beneath the Dizi basin comes from a Lower-Middle
Paleozoic basite-ultrabasite-tonalite metamorphic complex re-
presenting the northernmost strip of the mafic series along the northern
border of the basin. This complex is the largest pre-Upper Paleozoic
oceanic unit in the southern slope zone of the Greater Caucasus. It is
composed mainly of diverse tectonic slices of metamorphosed paleo-
oceanic lithosphere (Adamia et al., 2011, 2017b, 2017a; Zakariadze
et al., 2012).
During the late Paleozoic–Early Mesozoic, the oceanic basin separ-
ating the Africa-Arabian continent from the Taurus-Anatolian-Iranian
domain gradually extended. During this phase, only the Central Iranian
terrain separated from Gondwana, drifted northward, and collided with
the Eurasian continent in the Late Triassic (Fig. 3c). The Taurus-Ana-
tolian terrains separated from Gondwana later, in the Early–Middle
Jurassic. During the Mesozoic –Cenozoic (
Fig. 3d,e), Daralagöz (the
South Armenian Block – Nakhchivan)
represented
the northwestern-
most margin of the Central Iranian platform and was separated from the
North Anatolian platform by an oceanic or back-arc Khoy basin, which
in the recent structure is represented by Mesozoic–Cenozoic ophiolites
of Urumieh-Khoy and Van (Dercourt et al., 1986; Knipper et al., 1987;
Zonenshain et al., 1987). The structural relation of Daralagöz with re-
spect to the Central Iranian platform is still a matter of debates. Parti-
cularly, some regional paleo-reconstructions (e.g., Barrier and
Vrielynck, 2008; Barrier et al., 2018) suggest that during the Meso-
zoic–Cenozoic times, Daralagöz was a part of the Tauride-Anatolian
platform. The basement of the Khoy basin is considered to be a part of
the South Armenian Block, and the Khoy ophiolites to be obducted on
the block from the Sevan–Akera suture zone (e.g., Avagyan et al., 2016;
Sosson et al., 2016, 2019).
There were several episodes of oceanic lithospheric obduction onto
the continental terranes of the region. During the Middle–Late
Paleozoic obduction basite-ultrabasite complexes were thrust over the
Caucasus island-arc. During the pre–Late Triassic obduction in the
Lesser Caucasus (e.g., pre-Carnian breccia-conglomerates found in the
ophiolite mélange to the east of the Lake Sevan; Knipper, 1991) and the
pre–Late Jurassic obductions (e.g., the Oxfordian Tsopi suite in the
southern part of Georgia; Adamia et al., 1989), ultrabasic rocks were
thrust over the continental block of Daralagöz and the Artvin-Bolnisi
zone (Knipper et al., 1987; Sosson et al., 2010b; Adamia et al., 2011,
2017). Redeposited Albian-Cenomanian ophioclastics ( Knipper, 1975;
Sokolov, 1977) and the Cenomanian-Santonian ophiolitic complexes
(Gasanov, 1996) were found within the Sevan-Akera suture zone. The
obduction occurred during the Late Coniacian to Santonian was re-
sponsible for the widespread ophiolitic nappe outcrop in front of the
suture zone (Sosson et al., 2010b; Hässig et al., 2016, 2017).
The onset of the syn-collisional stage of the Caucasus tectonic evo-
lution is associated with Oligocene (e.g., Adamia et al., 2017-c). The
age of this continental collision has been the topic of much debates,
with proposed ages ranging from the Late Cretaceous to the Pliocene
(e.g., Hall, 1976; Berberian and King, 1981; Şengor et al., 1985;
Dercourt et al., 1986; Adamia et al., 1990; Yılmaz, 1993;
Alavi, 1994;
Okay and Şahintürk, 1997; Jolivet
and Faccenna, 2000; Stampfli,
2000;
Allen et al., 2004; Agard et al., 2005; Robertson et al., 2007; Allen and
Armstrong, 2008; Okay et al., 2010; Adamia et al., 2010b; McQuarrie
and van Hinsbergen, 2013; Cavazza et al., 2018). According to
McQuarrie and van Hinsbergen (2013), the Neotethys ocean's closure
north of the Arabian Plate occurred about 27 Ma, while ocean sub-
duction continues at present along the Hellenic and Cyprus trenches.
Cowgill et al. (2016) interpreted the AR-EU collision zone's re-
organization by the closure of the former rift basin (the southern slope
3
http://doc.rero.ch
of the Greater Caucasus mountains). However, Vincent et al. (2018)
argued that at least within the western Greater Caucasus, sedimento-
logical, provenance, and seismic data supports an earlier basin closure
age in Early Oligocene. Cowgill et al. (2018) suggested that the closure
of the basin initiated at about 35 My ago and ended at about 5 My ago
following the collision between the Lesser Caucasus and the Scythian
platform to form the Greater Caucasus. The basic underlying assump-
tion related to the collision is that the Greater Caucasus results from far-
field transmission of tectonic stresses from the Bitlis-Zagros collision
zone.
The final collision of the AR-EU plates and formation of the present
intracontinental mountainous edifice of the Caucasus occurred in the
Neogene–Quaternary (Cavazza et al., 2017, 2018, 2019). The collision
between the AR-EU plates caused a topographic uplift (inversion), and
the fold-and-thrust belts of the Greater and Lesser Caucasus were
formed (Mosar et al., 2010; Cavazza et al., 2019). Associated with the
orogenic climax during the Late Miocene (9–7 Ma) to Pleistocene (e.g.,
Adamia et al., 2010a, 2017), the central part of the region is subject to
Fig. 2. (a) Main tectonic units of the Caucasus. SASZ: the Sevan-Akera Suture Zone; TACIP: the Taurus-Anatolian-Central Iranian Platform; FD: foredeep; MCT: the
Main Caucasus Thrust; FTB: fold-and-thrust belt. (b) Correlation map of the main tectonic units of the Caucasus and adjacent areas (modified after Adamia et al.,
2011).
4
http://doc.rero.ch
Fig. 3. Paleotectonic reconstructions of the Caucasus and adjacent areas: (a) Early Middle Paleozoic; (b) Late Paleozoic; (c) Early Mesozoic; (d) Late Mesozoic; and (e)
Early Cenozoic (modified after Adamia et al., 2011).
5
http://doc.rero.ch
