South Caspian Region Research Articles

Oroclinal bending, distributed thrust and strike-slip faulting, and the accommodation of Arabia-Eurasia convergence in NE Iran since the Oligocene

Regional shortening is accommodated across NE Iran in response to the collision of Arabia with Eurasia. We examine how N–S shortening is achieved on major thrust systems bounding the eastern branch of the Alborz (east of 57°E), Sabzevar and Kuh-e-Sorkh mountain ranges, which lie south of the Kopeh Dagh mountains in NE Iran. Although these ranges have experienced relatively few large earthquakes over the last 50 yr, they have been subject to a number of devastating historical events at Neyshabur, Esfarayen and Sabzevar. A significant change in the tectonics of the eastern Alborz occurs directly south of the Central Kopeh Dagh, near 57°E. To the east, shortening occurs on major thrust faults which bound the southern margin of the range, resulting in significant crustal thickening, and forming peaks up to 3000 m high. Active shortening dies out eastward into Afghanistan, which is thought to belong to stable Eurasia. The rate of shortening across thrust faults bounding the south side of the eastern Alborz north of Neyshabur is determined using optically stimulated luminescence dating of displaced river deposits, and is likely to be 0.4–1.7 mm yr^(−1). Shortening across the Sabzevar range 150 km west of Neyshabur has previously been determined at 0.4–0.6 mm yr^(−1), although reassessment of the rate here suggests it may be as high as 1 mm yr^(−1). Migration of thrust faulting into foreland basins is common across NE Iran, especially in the Esfarayen region near 57°E, where the northward deflection of the East Alborz range reaches a maximum of 200 ± 20 km (from its presumed linear E–W strike at the beginning of the Oligocene). West of 57°E, the tectonics of the Alborz are affected by the westward motion of the South Caspian region, which results in the partitioning of shortening onto separate thrust and left-lateral strike-slip faults north and south of the range. At the longitude of 59°E, published GPS velocities indicate that 50 per cent of the overall shortening across NE Iran is accommodated in the Kopeh Dagh. The remaining 50 per cent regional shortening must therefore be accommodated south of the Kopeh Dagh, in the eastern Alborz and Kuh-e-Sorkh ranges. Assuming present day rates of slip and the fault kinematics are representative of the Late Cenozoic deformation in NE Iran, the total 200 ± 20 km N–S shortening across the eastern Alborz and Kopeh Dagh mountains since the beginning of uplift of the Kopeh Dagh basin would be accommodated in 30 ± 8 Ma. Although this extrapolation may be inappropriate over such a long timescale, the age is nevertheless consistent with geological estimates of post Early-to-Middle Oligocene (<30 Ma) for the onset of Kopeh Dagh uplift.

The Early Mesozoic evolution of the Western Greater Caucasus (Russia): Triassic–Jurassic sedimentary and magmatic history

Abstract The Greater Caucasus (GC) forms a high Alpine fold-and-thrust belt on the southern margin of the East European Platform (EEP). The Triassic, and particularly, the Jurassic history of the Western Greater Caucasus region is important for our understanding of the palaeogeographic and tectonic evolution of the western Tethys area. In order to better constrain the nature and relevance of these events in the evolution of the region, which are classically described as the Late Triassic to Late Jurassic Cimmerian events, a field campaign in the Western Greater Caucasus was undertaken. Analysis of structural, sedimentological and petrological data from 41 sites in the Fore-Caucasus (Malaya Laba, Mount Tkhach-Belaya River), the Central Greater Caucasus (Georgievskoye, Otdaleni) and Southern Slope (Krasnaya Poliana) areas of the Western Greater Caucasus revealed that a broad asymmetric basin, with associated emergent volcanic islands, formed in the area in Jurassic times. Incipient back-arc rifting in Pliensbachian times was coeval with similar rifting episodes in the Pontides and South Caspian Sea areas. The synchroneity of these events may have been related to the renewal of the Tethys subduction to the south of the Eo-Cimmerian accretionary belt. Rift reactivation, with significant thinning of the continental lithosphere, occurred in the Aalenian. Despite the strong Alpine tectonic overprinting, some structural data confirms that the extension trend was east–west (almost parallel to the active margin) resulting in the formation of a series of pull-apart basins in the GC and the South Caspian region behind the Eastern Pontides–Lesser Caucasus subduction-related volcanic belt. In Bajocian times, subduction-related volcanic activity largely expanded from the Eastern Pontides–Lesser Caucasus to encompass the Transcaucasus, the southern part of GC and the Crimea region. Such widening of the volcanic arc was probably due to a shallowing of the northward subducting slab. In the back-arc GC region, this signalled the onset of the post-rift stage. The return of the slab to normal steepness resulted in subsidence in the back-arc region and in the GC with extensive accommodation space creation. This was subsequently filled by the Late Jurassic, Cretaceous and Cenozoic sedimentary successions.

Extrusion tectonics and subduction in the eastern South Caspian region since 10 Ma: COMMENT

[Hollingsworth et al. (2008)][1] proposed a “new” kinematic model for the complicated tectonic pattern in the eastern South Caspian Sea region. Our Comment is focused on the Ashkhabad fault and the Kopeh Dagh Mountains, examining the data and hypothesis used by the authors to support their model

Extrusion tectonics and subduction in the eastern South Caspian region since 10 Ma: REPLY

Extrusion tectonics and subduction in the eastern South Caspian region since 10 Ma: REPLY

Extrusion tectonics and subduction in the eastern South Caspian region since 10 Ma: COMMENT

[Hollingsworth et al. (2008)][1] propose that the westward motion of the South Caspian basin started 10 Ma ago. This is earlier than the ca. 5 Ma proposed by [Axen et al. (2001)][2] and [Allen et al. (2002)][3], and substantially earlier than the ca. 1.5 Ma proposed by [Ritz et al. (2006)][4]. This

Extrusion tectonics and subduction in the eastern South Caspian region since 10 Ma

We examine active deformation of the region surrounding the eastern South Caspian Sea using a combination of seismic, geological, geodetic, and geomorphological data. Global positioning system (GPS) velocities indicate a westward component of motion of the South Caspian basin, relative to Eurasia and central Iran. We identify major zones of shear (the Ashkabad and Shahrud fault zones) that accommodate this westward extrusion on either side of the South Caspian block. Estimates of total strike-slip motion could, at present-day slip rates derived from GPS observations, be achieved in ~10 m.y. Therefore, the northwest extrusion of the South Caspian region, which is accommodated by subduction beneath the North Caspian region (stable Eurasia) along the Apsheron-Balkan sill, may also date from that time. This suggests that the onset of subduction may be older than previous estimates (ranging from 1.8 to 5.5 Ma). Our results are summarized in a new kinematic model that significantly clarifies the active tectonics of this complicated region.

Concomitant Replacement of Language and mtDNA in South Caspian Populations of Iran

The Gilaki and Mazandarani occupy the South Caspian region of Iran and speak languages belonging to the North-Western branch of Iranian languages . It has been suggested that their ancestors came from the Caucasus region, perhaps displacing an earlier group in the South Caspian . Linguistic evidence supports this scenario, in that the Gilaki and Mazandarani languages (but not other Iranian languages) share certain typological features with Caucasian languages . We analyzed patterns of mtDNA and Y chromosome variation in the Gilaki and Mazandarani. Based on mtDNA HV1 sequences, the Gilaki and Mazandarani most closely resemble their geographic and linguistic neighbors, namely other Iranian groups. However, their Y chromosome types most closely resemble those found in groups from the South Caucasus. A scenario that explains these differences is a south Caucasian origin for the ancestors of the Gilaki and Mazandarani, followed by introgression of women (but not men) from local Iranian groups, possibly because of patrilocality. Given that both mtDNA and language are maternally transmitted, the incorporation of local Iranian women would have resulted in the concomitant replacement of the ancestral Caucasian language and mtDNA types of the Gilaki and Mazandarani with their current Iranian language and mtDNA types. Concomitant replacement of language and mtDNA may be a more general phenomenon than previously recognized.

Insights from the Talysh of Azerbaijan into the Paleogene evolution of the South Caspian region

Research Article| November 01, 2005 Insights from the Talysh of Azerbaijan into the Paleogene evolution of the South Caspian region Stephen J. Vincent; Stephen J. Vincent 1CASP, Department of Earth Sciences, University of Cambridge, 181a Huntingdon Road, Cambridge CB3 0DH, UK Search for other works by this author on: GSW Google Scholar Mark B. Allen; Mark B. Allen 1CASP, Department of Earth Sciences, University of Cambridge, 181a Huntingdon Road, Cambridge CB3 0DH, UK Search for other works by this author on: GSW Google Scholar Arif D. Ismail-Zadeh; Arif D. Ismail-Zadeh 2Geology Institute of the Azerbaijan Academy of Sciences, 29A H. Javid Ave., Baku, Az1143, Azerbaijan Search for other works by this author on: GSW Google Scholar Rachel Flecker; Rachel Flecker 3CASP, Department of Earth Sciences, University of Cambridge, 181a Huntingdon Road, Cambridge CB3 0DH, UK Search for other works by this author on: GSW Google Scholar Kenneth A. Foland; Kenneth A. Foland 4Department of Geological Sciences, Ohio State University, Columbus, Ohio 43210, USA Search for other works by this author on: GSW Google Scholar Michael D. Simmons Michael D. Simmons 5CASP, Department of Earth Sciences, University of Cambridge, 181a Huntingdon Road, Cambridge CB3 0DH, UK Search for other works by this author on: GSW Google Scholar GSA Bulletin (2005) 117 (11-12): 1513–1533. https://doi.org/10.1130/B25690.1 Article history received: 27 Jul 2004 rev-recd: 15 Mar 2005 accepted: 24 Mar 2005 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Stephen J. Vincent, Mark B. Allen, Arif D. Ismail-Zadeh, Rachel Flecker, Kenneth A. Foland, Michael D. Simmons; Insights from the Talysh of Azerbaijan into the Paleogene evolution of the South Caspian region. GSA Bulletin 2005;; 117 (11-12): 1513–1533. doi: https://doi.org/10.1130/B25690.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The age and mode of formation of the South Caspian Basin are disputed. An ∼10-km-thick, predominantly middle Eocene clastic and volcanic succession is exposed in the Talysh mountains of Azerbaijan at its western margin. Here, high-K alkali basalts pass laterally to the east and southeast into volcanogenic sandstone-dominated turbidity current and debris-flow deposits. These southeasterly directed depositional systems accumulated in water depths generally greater than 200 m and fed directly into the western South Caspian Basin. New Ar-Ar ages cluster around 39 Ma, with an upper, 1400-m-thick volcanic interval being deposited in 2.2 ± 0.2 m.y. We interpret that this rapid deposition and magmatism records a major back-arc extensional/transtensional event in the Talysh, north of the north-dipping Neotethyan subduction zone. This event is recognized across much of southwest Asia and may indicate a period of significant basin formation within the adjacent South Caspian Basin. A transition into Upper Eocene–Lower Oligocene strata, dominated by fine-grained turbidity current and hemipelagic sediments with slope instability features, is interpreted to mark the end of rifting and volcanism in the Talysh and the start of the Arabia-Eurasia collision. Overlying Oligocene coarse clastic rocks are interpreted as the erosional products of localized topography created by the further propagation of compressional deformation into the Talysh region. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Crustal-scale structure of the South Caspian Basin revealed by deep seismic reflection profiling

Two deep seismic reflection profiles from the South Caspian basin provide the first normal-incidence image of possibly the thickest sedimentary basin in the world. Significant features imaged with these seismic data are: (1) a series of high-amplitude folds, developed within a thick (>10 km) Neogene sedimentary section, bounded discordantly below by (2) a gently N-dipping, intermittent reflection at 14–20 km (8.0+ s), (3) a prominent deep reflector at 26–28 km depth (12.8–13.0 s) with a gentle northward dip, (4) an underlying layered interval with discernibly lower-frequency reflections down to ∼36–40 km (16.0–16.5 s), and (5) a noticeable decrease in reflectivity below ∼36–40 km. Based on the downward termination of fault-cored folds and their discordance with subhorizontal underlying reflections, the reflection at 14–20 km is interpreted to be the basal detachment for structures associated with the Absheron Ridge. The bright reflection at ∼26–28 km depth is interpreted as the basement/cover contact, and the underlying ∼10 km portion of the section is interpreted as crystalline basement. Downward diminution of reflectivity at ∼36–40 km is thought to represent the Moho despite the absence of a clearly reflective horizon. These interpretations are consistent with previous velocity models from both seismic refraction and teleseismic studies in the South Caspian region that suggested a minimum sedimentary thickness of 20 km and a crustal thickness of 35–40 km. Both the apparent lack of local structural relief on the basement reflector, and seismic velocities ( V p≈6.8 km/s) obtained from earlier studies suggest this crust is not thinned continental material. Although thicker than typical oceanic crust (6–8 km), the apparent ∼10 km thickness of the South Caspian crystalline crust is interpreted to be of oceanic affinity for this part of the basin. Active seismicity down to mantle depths (80 km) and gentle deepening of the crust from south to north suggest northward subduction of the South Caspian oceanic lithosphere beneath the continental lithosphere of the Central Caspian basin.

Late Cenozoic reorganization of the Arabia‐Eurasia collision and the comparison of short‐term and long‐term deformation rates

The Arabia‐Eurasia collision deforms an area of ∼3,000,000 km2 of continental crust, making it one of the largest regions of convergent deformation on Earth. There are now estimates for the active slip rates, total convergence and timing of collision‐related deformation of regions from western Turkey to eastern Iran. This paper shows that extrapolating the present day slip rates of many active fault systems for ∼3–7 million years accounts for their total displacement. This result means that the present kinematics of the Arabia‐Eurasia collision are unlikely be the same as at its start, which was probably in the early Miocene (16–23 Ma) or earlier. In some, but not all, active fault systems, short‐term (∼10 year) and long‐term (∼5 million year) average deformation rates are consistent. There is little active thickening across the Turkish‐Iranian plateau and, possibly, the interior of the Greater Caucasus. These are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening, and where there are structural and/or stratigraphic data for pre‐late Miocene deformation. We suggest that once thick crust (up to 60 km) built up in the Turkish‐Iranian plateau and the Greater Caucasus, convergence took place more easily by crustal shortening in less elevated regions, such as the Zagros Simple Folded Zone, the South Caspian region and foothills of the Greater Caucasus, or in other ways, such as westward transport of Turkey between the North and East Anatolian faults. The time and duration of this changeover are not known for certain and are likely be diachronous, although deformation started or intensified in many of the currently active fault systems at ∼5 ± 2 Ma.

Late Cenozoic deformation in the South Caspian region: effects of a rigid basement block within a collision zone

Active deformation in the South Caspian region demonstrates the enormous variation in kinematics and structural style generated where a rigid basement block lies within a collision zone. Rigid basement to the South Caspian Basin moves with a westward component relative both to stable Eurasia and Iran, and is beginning to subduct at its northern and western margins. This motion is oblique to the approximately north–south Arabia–Eurasia convergence, and causes oblique shortening to the south and northeast of the South Caspian Basin: thrusting in the Alborz and Kopet Dagh is accompanied by range-parallel strike–slip faults, which are respectively left- and right-lateral. There are also arcuate fold and thrust belts in the region, for two principal reasons. Firstly, weaker regions deform and wrap around the rigid block. This occurs at the curved transition zone between the Alborz and Talysh ranges, where thrust traces are concave towards the foreland. Secondly, a curved fold and thrust belt can link a deformation zone created by movement of the basement block to one created by the regional convergence: west-to-east thrusts in the eastern Talysh represent underthrusting of the South Caspian basement, but pass via an arcuate fan of fold trains into SSW-directed thrusts in the eastern Greater Caucasus, which accommodates part of the Arabia–Eurasia convergence. Each part of the South Caspian region contains one or more detachment levels, which vary dependent on the pre-Pliocene geology. Buckle folds in the South Caspian Basin are detached from older rocks on thick mid-Tertiary mudrocks, whereas thrust sheets in the eastern Greater Caucasus detach on Mesozoic horizons. In the future, the South Caspian basement may be largely eliminated by subduction, leading to a situation similar to Archaean greenstone belts of interthrust mafic and sedimentary slices surrounded by the roots of mountain ranges constructed from continental crust.

The Eagle Returns: Evidence of Continued Ismaili Activity at Alamut and in the South Caspian Region Following the Mongol Conquests

The catastrophic Mongol incursions into heart of Muslim world during thirteenth century left a path of death and destruction in their wake. Though assaults succeeded in vanquishing Baghdad, toppling Muslim caliph himself, it is notable that famous contemporary historian, 'Ata-Malik Juwayni, does not describe this as pinnacle of Mongol conquest. Rather, for this Sunni historian, zenith and culmination of Mongol invasion is obliteration of tiny rival enclave of Isma'ilis, a Shili sect centered at mountain fortress of Alamut. It is to this singular event that Juwayni dedicates concluding one-third of his History of World Conqueror. 3 Ibn al-Athir and later historians record a charming anecdote about this fortress. Apparently, Wahsudan b. Marzuban, one of Justanid rulers of Daylam, was on a hunting expedition when he saw a soaring eagle alight on a rock. Noticing how strategically ideal site was, ruler decided to build a castle there that was henceforth called Aluh amu[kh]t, which may mean the eagle's teaching, ta'lim al-'uqab in Ibn al-Athir's rendering. The name, later simplified to Alamut, is significant in at least two ways. As noticed by a number of historians, in traditional abjad system of alpha-numeric correspondence, name is a chronogram for year 483 A.H., corresponding to A.D. 1090, very year that Hasan Sabbah, champion of Nizari Isma'ili cause, came into possession of fortress. From them on, it became home of Nizaris, ta'limiyya, as they came to be known, reflecting their emphasis on need for authoritative instruction (ta'llm) and reminiscent of this delightful story about ta'lim al-'uqdb, eagle's teaching.4

Buried Gas Hydrates in the Deepwater of the South Caspian Sea, Azerbaijan: Implications for Geo-Hazards

Two multi-channel seismic reflection profiles in the deepwater of the South Caspian Sea, offshore Azerbaijan, document one of the first examples of buried gas hydrates. Based on their geophysical signature, these clathrates are characterized by (1) a depth-restricted, lenticular body well beneath the seafloor, (2) the apparent accumulation of free gas within the underlying sediment, and (3) evidence of associated recent slope failure in the overlying strata. The interpreted thickness and depth of gas hydrates in the South Caspian Basin fall within the hydrate stability field predicted from the rmobaric modelling of gas compositions identified from coring at the seafloor. Predicted minimum water depths (∼150 m) and maximum thicknesses (1,300 m) for hydrate stability are much shallower and considerably thicker in the South Caspian Sea than for other known hydrate occurrences. Accumulation of these hydrates near the base of the continental rise appears to control a large region (&gt; 200 km2) of shallow deformation, here named the Absheron allochthon. Such attributes make these gas hydrates important, and perhaps previously underestimated, geo-hazards of the South Caspian region. Primary among these hazards are (1) uncontrolled release of free gas trapped beneath the hydrate seal, (2) disruption of the gas hydrate stability field leading to either explosive dissociation of the gas hydrate, or (3) reduction in sediment strength, slope instability, and mass sediment transport. Documentation of the presence and distribution of gas hydrates, especially when concealed at depth in the subsurface, is a clear pre-requisite for exploration activities in the deepwater region of the South Caspian Sea.

The southern Caspian: A compressional depression floored by a trapped, modified oceanic crust"

The south Caspian intracontinental depression, floored by oceanic basement, is a relatively stable block, with minor deformation, surrounded by active fold-thrust belts of arcuate form (Talesh, Alborz, and Kopeh Dagh Mountains), which have undergone intense late Cainozoic crustal shortening. The basin is interpreted as a Neogene–Quaternary "compressional depression," bounded by multi-role mountain-bordering reverse faults, and apparently floored by a late Paleozoic – Triassic or late Mesozoic – early Tertiary "modified oceanic crust" trapped along an old geosuture. It may be a relic of an old (Paleozoic–Triassic) ocean, or else a marginal sea developed behind a Mesozoic–Paleogene ocean, and analysis of geological and geophysical data enables a scheme to be suggested. The general arcuate shape of the Alborz and the Talesh bordering mountain belts follows the pattern of the supposed rigid and thickened ocean crust of south Caspian depression.A tectono-sedimentary study of the south Caspian region, coupled with the body-wave modelling of a recent earthquake along one of the bordering faults, may suggest a possible flattening of the fault with depth (listric thrust), and that the estimate of the focal depth of the regional earthquakes based on teleseismic arrival time data is not accurate. The difference in elevation between the depression and the bordering active fold-thrust belts is caused by a difference in crustal structure and reverse faulting during a dominant compressional tectonic regime.The study may add support to the idea that old continental deep-seated multi-role faults, which have controlled the sedimentary facies and basins during different geological times and were responsible for the formation of the present physiographic feature, are the site of the present seismic activity in the orogenic belts.