Towards a paleogeography and tectonic evolution of Iran
01 Feb 1981-Canadian Journal of Earth Sciences (NRC Research Press Ottawa, Canada)-Vol. 18, Iss: 2, pp 210-265
TL;DR: In this paper, maps of the paleography of Iran are presented to summarize and review the geological evolution of the Iranian region since late Precambrian time on the basis of the data presented in this way reconstructions of the region have been prepared that take account of the known major movements of continental masses.
Abstract: Maps of the paleography of Iran are presented to summarize and review the geological evolution of the Iranian region since late Precambrian time On the basis of the data presented in this way reconstructions of the region have been prepared that take account of the known major movements of continental masses These reconstructions, which appear at the beginning of the paper, show some striking features, many of which were poorly appreciated previously in the evolution of the region They include the closing of the 'Hercynian Ocean' by the northward motion of the Central Iranian continental fragment(s), the apparently simultaneous opening of a new ocean ('the High-Zagros Alpine Ocean') south of Iran, and the formation of 'small rift zones of oceanic character' together with the attenuation of continental crust in Central IranWith the disappearance of the Hercynian Ocean, the floor of the High-Zagros Alpine Ocean started to subduct beneath southern Central Iran and apparently disappeared by Late Cretaceou
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TL;DR: In this article, the evolution of the Tethys belt from the Pliensbachian (190 Ma) to the Tortonian (10 Ma) is depicted at 1 20,000,000 scale.
1,574 citations
TL;DR: The Zagros orogenic belt of Iran is the result of the opening and closure of the Neo-Tethys oceanic realm, and consists, from northeast to southwest, of three parallel tectonic subdivisions: 1) the Urumieh-Dokhtar Magmatic Assemblage; 2. (2) the Sanandaj-Sirjan Zone; and 3. (3) the zagros simply folded belt.
1,382 citations
TL;DR: In this paper, the authors used 80 new fault plane solutions, combined with satellite imagery as well as both modern and historical observations of earthquake faulting, to investigate the active tectonics of the Middle East between western Turkey and Pakistan.
Abstract: Summary.
Over 80 new fault plane solutions, combined with satellite imagery as well as both modern and historical observations of earthquake faulting, are used to investigate the active tectonics of the Middle East between western Turkey and Pakistan.
The deformation of the western part of this region is dominated by the movement of continental material laterally away from the Lake Van region in eastern Turkey. This movement helps to avoid crustal thickening in the Van region, and allows some of the shortening between Arabia and Eurasia to be taken up by the thrusting of continental material over oceanic-type basement in the southern Caspian, Mediterranean, Makran and Black Sea. Thus central Turkey, bounded by the North and East Anatolian strike-slip faults, is moving west from the Van region and overrides the eastern Mediterranean at two intermediate depth seismic zones: one extending between Antalya Bay and southern Cyprus, and the other further west in the Hellenic Trench. The motion of northern Iran eastwards from the Van region is achieved mainly by a conjugate system of strike-slip faults and leads to the low angle thrusting of Iran over the southern Caspian Sea. The seismicity of the Caucasus shows predominantly shortening perpendicular to the regional strike, but there is also some minor elongation along the strike of the belt as the Causcasus overrides the Caspian and Black Seas.
The deformation of the eastern part of this region is dominated by the shortening of Iran against the stable borders of Turkmenistan and Afghanistan. The north-east direction of compression seen in Zagros is also seen in north-east Iran and the Kopet Dag, where the shortening is taken up by a combination of strike-slip and thrust faulting. Large structural as well as palaeomagnetic rotations are likely to have occurred in NE Iran as a result of this style of deformation. North-south strike-slip faults in southern Iran allow some movement of material away from the collision zone in NE Iran towards the Makran subduction zone, where genuinely intermediate depth seismicity is seen.
Within this broad deforming belt large areas, such as central Turkey, NW Iran (Azerbaijan), central Iran and the southern Caspian, appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200-300 km wide. The motion of these blocks can usefully be described by poles of rotation. The poles presented in this paper predict motions consistent with those observed and also predict the opening of the Gulf of Iskenderun NE of Cyprus, the change within the Zagros mountains from strike-slip faulting in the NW to intense thrusting in the SE, and the relatively feeble seismicity in SE Iran (Baluchistan). This description also explains why the north-south structures along the Iran-Afghanistan border do not cut the east-west ranges of the Makran.
Within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation, even though motions at the surface may be concentrated on faults. The evolution of fault systems within the active zones is controlled by geometric constraints, such as the requirement that simultaneously active faults do not, in general, intersect.
Many of the active processes discussed in this paper, particularly large-scale rotations and lateral movement along the regional strike, are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them.
1,130 citations
Cites background from "Towards a paleogeography and tecton..."
...aged by Bird, Toksoz & Sleep (1975) and Toksoz & Bird (1977). Finally, it should be noted that examination of the cumulative seismic moment from earthquakes recorded this century, reported by North (1974) and updated by Shoja-Taheri & Niazi (1981), indicates that less than 10 per cent of the predicted total motion between Arabia and Eurasia takes place seismically....
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TL;DR: A network of 27 GPS sites was implemented in Iran and northern Oman to measure displacements in this part of the Alpine-Himalayan mountain belt as mentioned in this paper, and the results of two surveys performed in 1999 September and 2001 October.
Abstract: SUMMARY A network of 27 GPS sites was implemented in Iran and northern Oman to measure displacements in this part of the Alpine‐Himalayan mountain belt. We present and interpret the results of two surveys performed in 1999 September and 2001 October. GPS sites in Oman show northward motion of the Arabian Plate relative to Eurasia slower than the NUVEL-1A estimates (e.g. 22 ± 2m m yr −1 at N8 ◦ ± 5 ◦ E instead of 30.5 mm yr −1 at N6 ◦ E at Bahrain longitude). We define a GPS Arabia‐Eurasia Euler vector of 27.9 ◦ ± 0.5 ◦ N, 19.5 ◦ ± 1.4 ◦ E, 0.41 ◦ ± 0.1 ◦ Myr −1 . The Arabia‐Eurasia convergence is accommodated differently in eastern and western Iran. East of 58 ◦ E, most of the shortening is accommodated by the Makran subduction zone (19.5 ± 2m m yr −1 ) and less by the Kopet-Dag (6.5 ± 2m m yr −1 ). West of 58 ◦ E, the deformation is distributed in separate fold and thrust belts. At the longitude of Tehran, the Zagros and the Alborz mountain ranges accommodate 6.5 ± 2m m yr −1 and 8 ± 2m m yr −1 respectively. The right-lateral displacement along the Main Recent Fault in the northern Zagros is about 3 ± 2m m yr −1 , smaller than what was generally expected. By contrast, large rightlateral displacement takes place in northwestern Iran (up to 8 ± mm yr −1 ). The Central Iranian Block is characterized by coherent plate motion (internal deformation < 2m m yr −1 ). Sites east of 61 ◦ E show very low displacements relative to Eurasia. The kinematic contrast between eastern and western Iran is accommodated by strike-slip motions along the Lut Block. To the south, the transition zone between Zagros and Makran is under transpression with right-lateral displacements of 11 ± 2m m yr −1 .
1,013 citations
Cites background from "Towards a paleogeography and tecton..."
...…climax of orogeny indicated by the Alborz and Zagros uplift and South Caspian subsidence took place during the late Neogene subsequent to the complete closure of the Neo-Tethyan ocean (e.g. Stöcklin 1968; Falcon 1974; Berberian & King 1981; Berberian et al. 1982; Berberian 1983, 1995; Alavi 1994)....
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...…Fault underlines an abrupt cut-off of seismic activity (Berberian 1995; Maggi et al. 2000), and is commonly considered as the northern limit of the Arabian Plate because it marks the northeastern limit of the thick infra-Cambrian Hormuz Salt Formation (Stöcklin 1968; Berberian & King 1981)....
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...The subsequent collision beginning in the Neogene between the Arabian Plate and the Iranian Block (e.g. Stöcklin 1968; Falcon 1974; Berberian & King 1981; Berberian et al. 1982; Berberian 1983, 1995; Alavi 1994)....
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TL;DR: In this paper, the main Zagros orogen is shown to be deeply rooted, possibly to Moho depths, and the suture zone effectively runs along the MZT.
Abstract: The Zagros orogen provides a unique opportunity within the Alpine system to evaluate the interplay between a young Tertiary collision and earlier subduction/obduction processes. Within the Crush zone and the Sanandaj–Sirjan (internal) zone separating the Zagros Fold belt from Central Iran, we document several major tectonic events taking place at the end of the Cretaceous, of the Eocene and from the Mio–Pliocene onwards (ca. <20–15 Ma). Contrary to recent interpretations, our data (cross-sections and description of the overall deformation style) strongly suggest that the Main Zagros Thrust (MZT) is deeply rooted, possibly to Moho depths, and that the suture zone effectively runs along the MZT. Field observations show that the final resorption of the oceanic domain took place slightly after 35 Ma and that collision must have started before ca. 23–25 Ma in northern Zagros. The shortening rate across the Crush zone since the Mid-Miocene (20–15 Ma) is estimated at a minimum 3–4 mm/year. Shear movements in the Crush zone during the Eocene–Oligocene period and extensional/strike-slip movements in the internal zones during the late Cretaceous point to an oblique setting early in the convergence history. A geotectonic scenario for convergence from the time of obduction to the present is finally proposed.
885 citations
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TL;DR: The structural development of the Iranian ranges has certain peculiarities which contradict the conventional geosynclinal theory of mountain building as mentioned in this paper, and the conventional tripartite division of Iran into an extensive median mass and two bordering ranges of geosyclinal origin (Zagros, Alborz) cannot be maintained.
Abstract: The structural development of the Iranian ranges has certain peculiarities which contradict the conventional geosynclinal theory of mountain building. Early orogenic movements resulted in the consolidation of the Precambrian basement and the formation of a vast Iranian platform considered to be an extension of the Arabian shield. Only epeirogenic movements affected the region during the Paleozoic, which is represented by typical platform deposits. However, most of Iran went through all stages of a complete Alpine orogeny in spite of the prevailing platform character in preorogenic time. Important trends in the Alpine structural plan clearly were inherited from Precambrian structures. Precursory Alpine movements in Mesozoic time were strongest in Central Iran, although this region and the closely related Alborz (Elburz) Mountain area generally retained their epicontinental character, allowing for only a rudimentary geosynclinal development. More clearly geosynclinal conditions developed in peripheral fold belts: the Zagros, the Kopet Dagh, and the East Iranian ranges. Strong folding and thrusting during the Alpine orogeny proper in Late Cretaceous-Tertiary time affected most of Iran except the rigid Lut block in the eastern part of the country. The conventional tripartite division of Iran into an extensive median mass and two bordering ranges of geosynclinal origin (Zagros, Alborz) cannot be maintained. The writer replaces this oversimplified interpretation by recognizing the existence of more structural zones which differ in structural development and present tectonic style.
1,749 citations
TL;DR: Two calc-alkaline plutonic complexes were intruded by the Rb-Sr whole-rock isochron method at 74 ± 2 and 24 ± 4.5 Ma, respectively.
Abstract: Two calc-alkaline plutonic complexes. Bazman and Natanz, intruded through the south-eastern active and south-western ancient continental margins of Central Iran, Have been dated by the Rb-Sr whole-rock isochron method at 74 ± 2 and 24 ± 4.5 Ma, respectively. Detailed trace element studies together with low 87 Sr/ 86 Sr initial ratios ( 87 Sr/ 86 Sr ratios and the gabbros, at least, were intruded some 10 Ma earlier.
424 citations
TL;DR: In this article, the authors examined the transition area between the Zagros continental collision zone and the Makran ocean-continent convergence zone (the ‘Oman Line’) and determined the depths of earthquakes along this seismic zone.
Abstract: Seismotectonic characteristics of the transition area between the Zagros continental collision zone and the Makran ocean-continent convergence zone (the ‘Oman Line’) are carefully examined. A northeast trending zone of earthquakes terminates the Zagros belt of seismicity just west of the Oman Line. This seismic zone extends northeastward beyond the Main Zagros Thrust and coincides with a surface escarpment clearly visible on LANDSAT imagery. Events with accurately determined depths along this seismic zone occurred in the upper 20 km of the crust and possibly show a shallow (<10°) northeastward dip. East of the Oman Line, the Zendan-Minab fault system is relatively aseismic. The Oman Line region may be characterized by underthrusting of a wedge of Arabian shelf edge beneath Iranian crust or by an indentation of Arabia into the Iranian crustal block as a promontory. Available seismological and geological data cannot uniquely distinguish between these two possible tectonic settings. The area located to the northwest of the Oman Line region, now a zone of continental collision, appears to have been characterized by an episode of Neogene subduction. A well-located, intermediate-depth earthquake occurred in this area to the northeast of the Main Zagros Thrust on November 9, 1970. It was accurately located at 107-km depth beneath a line of Quaternary volcanoes. Its focal mechanism may indicate downdip tension, with nodal planes that strike closely parallel to the trend of the Zagros arc. Comparison of this event and other neotectonic features in this part of Iran with those in other active convergent zones suggests that a descending oceanic lithosphere beneath the Zagros volcanic arc may still be attached to the colliding Arabian plate.
91 citations
TL;DR: In this article, the authors attempt to reevaluate depositional history, diastrophism, structure, and oil productivity in the greater Persian Gulf area, and to offer additional reasons for the great petroleum richness of this area.
Abstract: The writer attempts to reevaluate depositional history, diastrophism, structure, and oil productivity in the greater Persian Gulf area, and to offer additional reasons for the great petroleum richness of this area. Continuous subsidence and sedimentation through Phanerozoic time resulted in the deposition of maximum thicknesses of 25,000 ft, and possibly more than 30,000 ft under the present mountains and foothills of Iran. The zone of maximum thickness may best be regarded as one relatively thick prism within an immense compound prism of sedimentary rocks. The sedimentary prism also may be regarded as having been the site of persistent epicontinental conditions in a persistent platform environment. The center of the prism was not greatly uplifted until near the end of Tertiary time, when the geometry of the sediments was profoundly modified. The effect of uplift in the area of study was to deform basement into a relatively simple syncline with a slightly steeper northeastern flank. Overlying sediments perhaps glided down the asymmetrical flank of the syncline to form high-frequency folds, that is, the present fold belt of Iran. The fold belt and largely undeformed platform together constitute a synclinorium, a feature which the writer regards as the most prominent characteristic of the region. The region thus is called the "Persian Gulf synclinorium" in this paper. During the last two decades, a small amount of specific data relative to the synclinorium has been released. Nevertheless, an initial synthesis of the data into systemic isopach maps and a total-sedimentary-rock isopach map is attempted herein, with the aim of furthering a general understanding of the regional geology. Ordovician and especially Permian events appear to be important among the several marine transgressions. Thus the Permian Sea may have advanced southward from a Tethyan seaway into an ancestral Arabian Sea; this interpretation, which involves an ancestral Indian Ocean on the south, is as plausible as that of a supposed segment of Gondwanaland in the present Indian Ocean during Permian time. Ultimate producible reserves of crude oil in the Persian Gulf synclinorium are believed to exceed 250 billion bbl, which may mean that as much as 500 billion bbl of in-place oil accumulated in major structures. The main causes previously suggested for prolific reserves were continuity of sedimentation, great total sedimentary volume, good caprocks, rich source materials, and long anticlines. The writer stresses the importance of long anticlines and the presence within them of great reservoir pore volume confined within closure. The writer further stresses the intercalation of source materials and reservoir, and the early release of oil into the reservoir where its accumulation protected initial porosity from the adverse effects of diagenesis. The important sources of the Persian Gulf ynclinorium may not be those beds that now are obviously petroliferous.
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