Describe the Tectonic Activities That Continues to Impact the Arabian Peninsula
Introduction
F.M. Gradstein , in The Geologic Time Scale, 2012
1.6 Stratigraphic Charts and Tables
The plethora of names for time and time-rock units in local regions lends itself to the production of wall charts and stratigraphic lexicons that visualize the links between regional schemes and the standard scale. The international standard was developed by the International Commission on Stratigraphy (ICS), and in 2000 and 2004 was formally published in conjunction with the International Geological Congress (Remane, 2000; Gradstein et al., 2004). The Commission for the Geological Map of the World (CGMW) in Paris and the ICS closely collaborated on the map, and the color coding of chronostratigraphic units on the standard chart. The updated charts in PDF format are freely available from websites https://engineering.purdue.edu/Stratigraphy/ , and http://www.nhm2.uio.no/stratlex/stratlexgts.html , and also are distributed by CGMW.
Nearly all nations, states, and/or continents have compiled regional chronostratigraphic charts or lexicons of regional stratigraphy, a majority calibrated to GTS2004. Attractive wall chart examples using the GTS2004 standard are from India (Raju et al., 2005), Australia, the British Isles and other regions (see https://engineering.purdue.edu/Stratigraphy/tscreator/datapack/ ). Offshore Norway lithostratigraphic charts may be obtained from http://www.nhm2.uio.no/norlex .
An Australian Phanerozoic Timescale (Young and Laurie, 1996) is an erudite and well-illustrated standard work covering that part of the world. Detailed explanatory notes make this study a valuable compendium of bio-, magneto-, and chronostratigraphic information. There is a wealth of data on Australian biostratigraphy in particular, that is well documented in many charts and in a wall chart linking local and standard zonations in one scheme.
In 1998, a team of specialists led by J. Hardenbol (Exxon) published a set of eight, large-format charts summarizing the Mesozoic–Cenozoic correlations and ages of biostratigraphic (dozens of types), sequence stratigraphic, geomagnetic and other events through the Mesozoic and Cenozoic Eras of the past 250 million years (Hardenbol et al., 1998). These charts were scaled to the numerical age scale of 1995 (Berggren et al., 1995; Gradstein et al., 1995). The detailed calibrations of fossil events and zonal units are particularly valuable, since they involve many classical localities, classical taxa, and classical zones in European basins.
Based on a suggestion by Gabi Ogg, James Ogg with assistance of colleagues in the ICS set out in 2004 to produce an interactive, digital version of the international, standard Cenozoic–Mesozoic–Paleozoic bio-magneto-sequence time scale charts of Exxon. A sophisticated, albeit easy, time scale graphics interface was put in place, coded masterfully in Java by Adam Lugowski. The popular program called TSCreator with its large and integrated data set is freely available from the Purdue University website ( https://engineering.purdue.edu/Stratigraphy/tscreator/ ). Now there are more than 20 000 Cambrian through Holocene biostratigraphic, sea-level, magnetic and geochemical events in the database, all calibrated to GTS2012. Retro-calibration to GTS2004 (or GTS2008) is a simple internal conversion procedure. Cross-correlations are in place for trilobites, conodonts, graptolites, ammonoids, fusulinids, chitinozoans, megaspores, nannofossils, foraminifers, dinoflagellates, radiolarians, diatoms, strontium-isotope, C-org and oxygen curves, etc. Scalable vector graphics output is an easy option. A majority of linear scale drawings including calibrated event and zonal data discussed in this GTS2012 book were initiated in TSCreator before being drafted.
In 2002, the Stratigraphic Table of Germany 2002 (Deutsche Stratigraphische Kommission, 2002) saw the light. The wall chart is well laid out and documents the interrelation of regional German rock units through Precambrian and Phanerozoic time. Chronostratigraphic units of the standard reference scale have the suffix -ium (in English -ian, and in French -ien); this is elegant and deserves consideration in other Germanic, including Nordic, languages where orthographic principles have occasionally "muddied" stage, series, and system nomenclature. Linear time scale modifications for parts of Paleozoic and Mesozoic are documented summarily. The discrepancy between U-Pb TIMS and HR-SIMS dates in the Devonian–Carboniferous is resolved by taking the youngest possible estimate of age dates with the former method and the oldest possible estimate of age dates with the latter one. Essentially, a regression line is forced through the opposite extremes of error bar values for successive age dates to interpolate stages.
In 2005, a new time scale was developed for the "Stratigraphische Tabelle von Deutschland 2002", with Devonian, Triassic and Late Jurassic scales being newly created (Menning, 2005; Menning et al., 2005a, b). It is a good thing that error bars on boundary ages are relatively large, since limited external error analysis was performed on radiogenic isotope data. It was erroneously reported by Menning that GTS2004 used the maximum likelihood method for error analysis on ages of stage boundaries, rounded off to mostly 0.1 Ma/myr. In the final stage of GTS2004 analysis, Ripley's Maximum Likelihood fitting of a Functional Relationship (MLFR) algorithm was indeed used for error estimation, but final error bars on stage boundary ages are an order of magnitude larger than mentioned by Menning. The value of this German multi-author 2005 compilation is in the correlation tables which link a great many regional lithostratigraphic and chronostratigraphic units for Central Europe. Once that framework of regional correlation is in place, an effort must be made to calibrate it to the standard international geologic time scale, as was done successfully for example in New Zealand (see above), and in Arabia through the outstanding geoscience journal 'GeoArabia'.
The sequel of publications on Arabian Plate Sequence Stratigraphy ( Sharland et al., 2004; Haq and Al-Qahtani, 2005; Simmons et al., 2007), are a combination of mega-style Wheeler diagrams, maximum flooding horizon charts for Arabian petroleum basins, and eustatic cycle charts with linkage to reference outcrop and well sections. The author teams detail the ability to recognize and correlate third order depositional sequences across Arabia and between Arabia and other plates, and indicate that these sequences are driven by synchronous eustatic sea-level change. Mostly missing from the studies is the extensive biostratigraphic documentation that initially went into the analysis. The Simmons et al. (2007) study recommends that stage boundaries should be related to correlative conformities of sequence boundaries; GSSPs should be placed in the conformable setting of third order sequences. In the words of the authors;
'this closely links chronostratigraphy with sequence stratigraphy and honors the original concepts upon which many stages were first described in the 19th Century.'
It might be mentioned here that the ICS undoubtedly would be pleased to see auxiliary GSSP sections created in conformable stratigraphic settings with (third order) sequence boundaries. At the same time, the commercially driven sequence stratigraphic literature should create a database with systematic listings of the semi-regional sequentially numbered sequence boundaries, calibrated with high-resolution biostratigraphy. Making such a data set publicly available would be a big help with advocating the GSSPs for sequences concept, and make it easier to formally link sequences and stages.
That eustatic sea level, together with subsidence, controls the sediment accommodation in a basin is well understood. Cataloguing the semi-regional sequence stratigraphic interpretations in terms of predictive orbital-forcing theory and its effect on eustatics, is still in its infancy. Although it has long been hypothesized that Milankovitch type cyclicity and sequences are linked at the 405 000 y resolution, few published studies actually try to empirically link sequences and cycles. Good examples are by Gale et al. (1996, 1999) for the Cenomanian–Turonian cyclic record along continental margins, by P. Heckel in Strasser et al. (2006) on Carboniferous cyclothems, and by Boulila et al. (2011). More information on this subject may be found in Chapter 13 on sequence stratigraphy and sea-level change.
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Volume 4
Mark B. Allen , in Encyclopedia of Geology (Second Edition), 2021
Iranian Plateau
The tectonic boundary to the Arabian plate and the Zagros range is formed by the Main Zagros Reverse Fault, to the north of which lie once-fragmented microcontinents of Gondwanaland origin. Deformation of these Eurasian plate components before and during the Arabia-Eurasia collision has resulted in the high, wide and topographically subdued area known as the Iranian Plateau ( Allen et al., 2004). The Iranian Plateau is part of a larger zone within the collision, known as the Turkish-Iranian Plateau. The Iran-Turkey border region very roughly marks a transition from the Iranian scenario of thick crust and mantle lithosphere, with widespread but scattered volcanoes, to the Turkish (east Anatolian) counterpart where both crust and mantle lithosphere are thinner, and late Cenozoic magmatism is far more abundant (Fig. 8; Priestley et al., 2012). Therefore similarities in present-day regional elevation (commonly 2 km above sea level) and subdued relief mask very different crustal and sub-crustal structures.
Fig. 8. Syn-collision magmatism of the Arabia-Eurasia collision.
From Kaislaniemi L, van Hunen J, Allen MB and Neill I (2014) Sublithospheric small-scale convection-A mechanism for collision zone magmatism. Geology 42: 291–294.Regionally-widespread Eocene volcanics have been interpreted as the result of back-arc extension, immediately before the initial Arabia-Eurasia collision (Vincent et al., 2005), accompanied by core complex formation (Verdel et al., 2007). These rocks are followed by continental clastics, known in Iran as the Lower Red Formation, which pass into the Oligo-Miocene Qom Formation. The Qom Formation consists mainly of shallow marine carbonates, which are at first sight an oddity for models of the collision which suggest an Oligocene or even Late Eocene age for initial collision. Why should such rocks be deposited within a collision zone, on crust that was presumably of near-normal thickness, given that it was submerged? Bottrill et al. (2012) provided an explanation, in a scenario where the elevation of the overriding plate was bought down by the underthrust plate during the early stages of collision.
In the Late Miocene, the Qom Formation was succeeded by non-marine clastics of the Upper Red Formation, which indicates convergence and uplift across the Iranian Plateau (Mouthereau et al., 2012). Succeeding formations are coarser and reflect continued uplift (Ballato et al., 2017).
In terms of active tectonics, it is possible to use the distribution of thrust seismicity to define margins for the Iranian Plateau, as noted above for the Zagros: thrust earthquakes of M > 5 are rare above the regional 1250 m elevation contour (Nissen et al., 2011) (Fig. 7). Most of the area to the north of this contour has a relatively sparse seismicity record, at least by Iranian standards, and large thrust earthquakes appear again within the Alborz and Kopeh Dagh ranges at the north side of the plateau (next section). This sparse seismicity record matches the GPS-derived velocity field for the Iranian Plateau, which shows internal deformation taking place at rates of 2 mm/year or less (Vernant et al., 2004)—i.e., somewhat close to the error limits of the measurements. Most of the active faults present within the plateau are strike-slip structures, but even these have a low historical and instrumental seismicity record, matching the low rates of strain recorded in the GPS data.
Note that this working definition of the active plateau margins, using the cut-offs of thrust seismicity, does not match the bedrock geology limit of the Zagros. Higher elevation regions of the Zagros are behaving like elevated counterparts north of the suture, in that they clearly have shortened and thickened crust from Cenozoic collision tectonics, but seismogenic thrusting is not going on now. Nissen et al. (2011) and Allen et al. (2013) expressed this pattern in terms of southwards growth or expansion of the Iranian Plateau, suggesting that as regions of the Zagros crossed a crustal thickness threshold equivalent to the 1250 elevation contour they ceased to be part of the seismogenic fold-and-thrust belt and instead acted as part of the plateau region (Fig. 7). A dynamic explanation is that thickened and elevated crust possesses greater gravitational potential energy than adjacent, unthickened and low elevation regions, and resists further shortening and thickening. In this way deformation not only migrates southwards over time, into previously undeformed parts of the foreland, but also shuts off in the hinterland of the fold-and-thrust belt.
Many parts of the High Zagros are marked by internal drainage, or systems close to reaching this point, where sediment derived from further north becomes trapped in synclinal valleys between the main anticlines (Ramsey et al., 2008). A geomorphic consequence is that relief becomes more subdued with time, as the valleys become filled in and the anticlinal crests of folds are not only subject to erosion but burial.
North of the Zagros suture, major structures within the Iranian Plateau include a series of right-lateral strike-slip faults that trend WNW-ESE or NW-SE. These include (from west to east) the Kashan, Deshir, Anar, Rafsanjan and Kuh Banan faults (Nazari et al., 2009; Fattahi et al., 2011). To the east, fault strike is more north-south, and these particular faults are dealt with in a later section. To the west, individual faults become shorter and less distinct. Although there is little evidence for rapid active slip or major earthquakes on these faults, they appear to have been active in the late Cenozoic, on the basis of offsets of Tertiary strata and volcanics (Allen et al., 2011). Some of the strike-slip faults interact with Cenozoic folds within the Plateau interior, including hydrocarbon-bearing structures in the Qom region in the center of the plateau.
Strike-slip faulting to the north of this right-lateral array is left-lateral, on NE-SW structures, principally the Doruneh Fault (Farbod et al., 2011). The Doruneh Fault has undergone a reversal in strike-slip sense in the Tertiary, dated as post Middle Miocene (Javadi et al., 2013). Like their counterparts to the south, these left-lateral faults may accommodate a fraction of the overall convergence by clockwise vertical axis rotation (Mattei et al., 2020), although the rates involved must currently be small, given the low degree of active slip on the structures.
The western side of the Iranian Plateau contains NW-SE striking right-lateral strike-slip faults which are active, notably the Tabriz Fault (Fig. 2), which has slip rate estimated to be as high as 7–8 mm/year (Rizza et al., 2013). These structures continue to the northwest into the territory of Turkey and Armenia. They have been interpreted by Copley and Jackson (2006) as an array which rotates anticlockwise, permitting greater plate convergence in the east than to the west, and consistent with the GPS-based observation that active strain in the eastern Greater Caucasus is faster than further west (Reilinger et al., 2006). These ideas build on an earlier interpretation that the NW-SE strike-slip faults combine with NE-SW directed thrusting across the Greater Caucasus, to produce overall north-south convergence (Jackson, 1992).
Late Cenozoic magmatism is a distinct feature of the Iranian Plateau (Fig. 8; Chiu et al., 2013); this magmatism continues to the northwest into Armenia and Azerbaijan (Neill et al., 2015) and merges with the more concentrated centers in eastern Anatolia (e.g., Keskin et al., 1998; Yilmaz et al., 1998). There are numerous volcanic centers ranging in size from isolated cinder comes to giant composite volcanoes. Sahand and Sabalan are tens of kilometers across, whilst Damavand reaches an altitude of > 5500 m, by virtue of being established over the elevated Alborz range at the north side of the plateau. Whilst there has been intermittent magmatism across Iran after the onset of collision (using the broad 25–35 Ma framework adopted here), there seems to have been an upsurge in the last few millions of years. Precise age estimates are still being established for many centers, but there does not seem to be a systematic pattern to the onset of magmatism. Instead, centers switch on seemingly randomly, but typically spatially distinct from previous late Cenozoic centers. Structural control plays a factor at least in some centers (Shabanian et al., 2012) but has not been universally recognized. Magmatism at an individual center lasts for no more than a couple of million years before it dies out (Neill et al., 2015). The detailed chemistry and causes of this magmatism are beyond the scope of this study, but in Iran it is confined to the Eurasian side of the Zagros suture, strongly implicating pre-collision hydration and fertilization of the lithospheric mantle as a source. Some references for specific centers in Iran are: Kheirkhah et al. (2009); Pang et al. (2012, 2016). Some of the older centers are important sites of mineralization, especially for copper (e.g., Zarasvandi et al., 2015).
The precise trigger for melting is a subject of active study. Large-scale lithospheric delamination has been proposed (e.g., Pearce et al., 1990), as has break-off of the subducted Tethyan slab (e.g., Keskin, 2003; Hafkenscheid et al., 2006). The problem with the former mechanism is the apparent presence of an intact mantle lithosphere beneath Iran (Priestley et al., 2012). Slab break-off might be expected to produce a linear belt of magmatism above the break-off point, if at all: this is not observed. Kaislaniemi et al. (2014) produced a numerical model of small-scale, sub-lithospheric convection triggered by drips of hydrated lithosphere in the collision zone. Resultant convection produced melting on the length-scales and time-scales appropriate to the observed volcanic centers in Iran and adjacent areas, suggesting that this is a plausible explanation for the collision zone magmatism.
Slab break-off may have played a role in the present-day elevation of the plateau, which is suspected to have a component of dynamic support from the underlying mantle, given that the elevations (commonly ~ 2 km asl) seem high for the crustal thickness (~ 45 km, Paul et al., 2010). The argument runs that mantle flow induced by slab break-off supports the overriding plate (Bottrill et al., 2012).
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Tectonic and Structural Framework of the Zagros Fold-Thrust Belt
Wathiq Abdulnaby , in Developments in Structural Geology and Tectonics, 2019
Conclusion
Iraq is located at the NE margin of the Arabian plate near the suture zone of collision with the Eurasian plate. Structural and neotectonics studies of Iraq are important to shed more light on the tectonic evolution, stratigraphy, and distribution of natural resources in the NE margin of the Arabian plate. This chapter was written to fulfill this purpose.
There are various tectonic divisions of Iraq; the most recent one was chosen and compared with others. Based on this division, the NE part of Iraq is located within the Arabian outer platform, whereas the SW part is located within the Arabian inner platform. The Anah-Abu Jir-Euphrates fault zone represents the boundary between these two platforms. The outer platform consists of the Zagros fold–thrust belt and the Mesopotamia foredeep, whereas the inner platform within Iraq is occupied by the western desert.
The outer platform has different types of neotectonic evidence, such as continuous folding and faulting, seismic activity, abandoned river channels, shifting of river courses, and active and inactive alluvial fans. Neotectonic evidence cannot be seen on the inner platform within Iraq. Therefore, the outer and inner platforms are described as active and stable platforms, respectively.
More structural and neotectonic studies need to be carried out to obtain a clearer view of the geology of Iraq in general and tectonic setting in particular.
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AN INTRODUCTORY OVERVIEW
A.S. ALSHARHAN , A.E.M. NAIRN , in Sedimentary Basins and Petroleum Geology of the Middle East, 2003
GEOLOGIC SETTING
In plate-tectonic terms, the area lies within the Arabian Plate. It covers the Republic of Yemen, Oman, Saudi Arabia, the U.A.E., Qatar, Bahrain, Kuwait, Jordan, the fertile crescent of Syria and Iraq, southeastern Turkey, and southwestern Iran during the Paleozoic and earliest Mesozoic. The generalized geologic map ( Fig. 1.5) and illustrative cross sections (Fig. 1.6) are simplifications of the combined results of field research by governments, academic institutes and detailed hydrocarbon exploration by the petroleum industry. Excluded from consideration here are the continental part of the Levantine Plate and Sinai, that is the areas west of the Levantine Fracture System (Dead Sea Rift).
Fig. 1.5. Generalized geologic map of the Middle East, with lines of section of Fig. 1.6.
(modified from CGMW-UNESCO, 1985: USGS-ARAMCO, 1963, Beydoun, 1988) Copyright © 1988 
Fig. 1.6. Northeast-southwest and northwest- southeast schematic geological cross sections of the Middle East. The locations of the cross sections and references are indicated on Fig. 1.5.
As Beydoun (1988) pointed out, the Middle East, as defined here, formed part of the African Plate throughout the greater part of the Phanerozoic. Breakup began during the early Mesozoic with the opening of Neotethys, as a result of which the Iranian segment split off. This was followed during the late Tertiary by the development of a spreading ridge that propagated from the Indian Ocean, forming the Gulf of Aden and the beginning of spreading along the Red Sea Rift (Figs. 1.2 and 1.3). Together, these form the southeastern and southwestern boundaries of the Middle East area. Both are very young features, and as a result, the development of a coastal plain in both regions is minimal. The agreement of the geological features on both sides of the Gulf of Aden and the Red Sea, which show concordant geological structures, indicates that separation in a geologically very recent time was accompanied by a small, but significant, transcurrent displacement. It is the onshore continuation of shear fractures associated with the opening of the Red Sea, passing up the Gulf of Aqaba and forming the Dead Sea Rift, to abut against the Taurus Mountains in the north, that complete the periphery of the Middle East. Along the eastern shores of the Red Sea, uplifted Precambrian rocks and their sedimentary and volcanic cover provide greater relief than is seen on the western side; and, in the Asir Mountains of Yemen, elevations of more then 3,700 m (11,840 ft) are reached. This elevation gradually declines to the north and east. The western side of the Jordan rift is overlooked by the Levant uplands, completing the elevated rim of the area.
An indication of the underlying geological basis for the limits to the Middle East is shown by the distribution of seismicity (Fig. 1.7). It particularly is marked along the mountain fronts and, to a lesser extent, along the ridge-rift system that forms the southwestern and northwestern limits, lines that are essentially plate boundaries (Figs. 1.2 and 1.3). In the western part of the Arabian Plate, young volcanics are abundant; they occur as the Trap Series in Yemen, where they form the "harrats," and extend into Saudi Arabia. They also crop out extensively in Jordan, Syria and Turkey. Thus, the Red Sea and the Gulf of Aden are young ocean basins of the type with which the Neotethys, formed by separation between central Iran and Arabia during the Late Triassic, can be compared.
Fig. 1.7. General distribution of earthquakes in the Middle East in the pre-instrumental period (to 1899) plotted as triangles, and events of magnitude 5 or greater, from 1899-1992, plotted as open circles.
(after Ambraseys et al., 1994, by kind permission of Cambridge University Press) Copyright © 1994Geologically, the principal features defining the area can be assigned to three causes (Beydoun, 1988): extensional events in southern and eastern Arabia that result from seafloor spreading in the Gulf of Aden and the Red Sea with the generation of incipient ocean basins; compressional folding in the north and northeast in the Taurus-Zagros-Oman Orogenic Zone consequent upon continent-continent collision; and strike-slip faulting along the Dead Sea Rift or Levant Fracture Zone (Figs. 1.2 and 1.3). The ability to recognize such features, which were the result of similar events in the geological past, provides the key to understanding the geological evolution of the region. This recognition is made difficult by the tendency for such events to coincide with, or to be close to, zones of present activity, as, for example, the late Paleozoic to Cenozoic history of the Zagros Crush Zone with the opening and subsequent closure of the Neotethys. The Arabian Peninsula forms the nuclear region for the Middle East. It is generally separated into the exposed Precambrian part or shield, and the sediment-covered platform. The Precambrian basement generally dips gently to the north-northeast and east, as the sediment cover thickens progressively from less than 1,500 m (4,920 ft) to more than 10,940 m (35,883 ft) in the vicinity of the Arabian Gulf (Fig. 1.8), to more than 12,500 m (41,000 ft) in southwestern Iran and northeastern Iraq. This thickness varies over structures such as the Qatar-South Fars Arch, a result of Hercynian upwarping during the late Paleozoic. The erosion that followed the uplift led to the removal of considerable thicknesses of the Paleozoic sequence. Although there are many geological complications associated with the Iranian area east of the Zagros, beginning in the latest Paleozoic and continuing through the Mesozoic, during the early Paleozoic, the geological history of the whole region so closely parallels that of the Arabian Peninsula that it is reasonable to assume it formed an integral part of the Arabian Platform (sensu stricto) for most of the Paleozoic.
Fig. 1.8. Isopach contour map of the total Phanerozoic sedimentary cover in the Middle East, with contour interval in thousands of feet.
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Earthquakes and Coseismic Surface Faulting on the Iranian Plateau
Manuel Berberian , in Developments in Earth Surface Processes, 2014
9.4.1.1 The Zāgros Fold-and-Thrust Mountain Belt
Nearly half of the GPS-derived convergence rate between the Arabian plate and the Central Iran (10 ± 4 mm/year) is accommodated in the Zāgros by north–south crustal shortening and strike-slip faults oblique to the strike of the belt (Figure 9.4). The main shortening direction ranges from N7°E in the southeast to N3°W in the northwest. The convergence rate is decreasing from 9 ± 2 mm/year in the southeastern Zāgros to 7 ± 2 mm/year near the longitude of Kāzerun in central Zāgros and to 4.5 ± 2 mm/year in the northwest (Tatar et al., 2002; Nilforoushan et al., 2003; Vernant et al., 2004). Slip vector directions derived from the focal mechanism data of the Zāgros thrust earthquakes show an angle of 35–40° to the east of the GPS-derived vectors, suggesting partitioning of strain between reverse and strike-slip faults in the Zāgros (Jackson, 1992; Berberian, 1995; Maggi et al., 2000a,b; Talebian and Jackson, 2002).
The Zāgros Main Recent fault (Tchalenko and Braud, 1974; Tchalenko et al., 1974b; Berberian, 1976a, 1995) is an active right-lateral strike-slip fault of about 640 km length, which more or less follows the NW–SE trend of the Main Zāgros reverse fault (the Neo-Tethyan geosuture) separating the Central Iranian range-and-basin province to the northeast from the Zāgros fold-and-thrust belt to the southwest (Figure 9.1). It marks an abrupt cut-off of intense seismic activity of the Zāgros (Figure 9.3) adjacent to the less seismic Sirjān belt of the southwestern Central Iran (Berberian, 1995; Maggi et al., 2000a,b; Talebian and Jackson, 2002). A right-lateral offset of a geological marker bed along the Nahāvand and Dorud segments of the Zāgros Main Recent Fault was reported by Gidon et al. (1974). Later, Talebian and Jackson (2002) reported a right-lateral offset of 50–70 km and estimated a horizontal slip rate of 10–17 mm/year. By using GPS data, Vernant et al. (2004), arrived at slip rate of 3 ± 2 mm/year. Walpersdorf et al. (2006) suggested a horizontal slip rate of 4–6 mm/year with 3–6 mm/year perpendicular shortening. Later, based on his three-dimensional mechanical modeling using GPS data, Nankali (2011) arrived at 2.3 mm/year horizontal slip rate. Finally, Alipoor et al. (2012) suggested a slip rate of 1.6–3.2 mm/year horizontal slip rate based on 16-km displacement along the fault.
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Volume 3
Vincent S. Cronin , in Encyclopedia of Geology (Second Edition), 2021
Example 1: An RRR Triple Junction
The Afar triple junction between the Nubian, Somalian, and Arabian plates ( Fig. 1, #37) provides an example of a ridge-ridge-ridge triple junction whose finite evolution we can simulate (Fig. 6). In the NNR-MORVEL56 reference frame published by Don Argus, Richard Gordon, and Charles DeMets in 2011, each of the three plates moves in an anti-clockwise or right-handed manner around an axis extending from Earth's center to the pole of rotation listed in Table 3. Negative latitudes are south latitudes, and negative longitudes are west longitudes.
Fig. 6. (A) Three rift boundaries (black lines) converge at the Afar (NB-SM-AR) triple junction today, simplified from Bird (2003). Arrows indicate direction each plate is moving relative to the NNR reference frame of Argus et al. (2011). (B) Current plate boundaries (colored lines) and predicted location of the triple junction (black lines) after 3 Myr of displacement. Base maps are from GeoMapApp.org.
Table 3. Input data for finite modeling of Afar triple junction.
| Poles of rotation, NNR-MORVEL56 model | |||
|---|---|---|---|
| Plate Name | Pole latitude (°N) | Pole longitude (°E) | Angular speed (°/Myr) |
| Nubia | 47.68 | − 68.44 | 0.292 |
| Somalia | 49.95 | − 84.52 | 0.339 |
| Arabia | 48.88 | − 8.49 | 0.559 |
| Reference points | ||
|---|---|---|
| Description | Latitude (°N) | Longitude (°E) |
| Triple junction | 11.317 | 41.442 |
| On Nubia-Somalia rift | 9.446 | 40.107 |
| On Somalia Arabia rift | 12.013 | 43.650 |
| On Arabia-Nubia rift | 13.209 | 40.091 |
The model whose results are shown in Fig. 6 held the pole location and angular speed constant for each of the three plates, as resolved in an NNR reference frame. Each of the three rift axes are represented by a great circle defined by a single point away from the triple junction and the triple-junction point. (A "straight line" on the surface of a sphere is a segment of a great circle.)
The angle between the modeled Arabia-Nubia rift and the Nubia-Somalia rift today is 110.0° (Fig. 6A); 143.2° between the Nubia-Somalia and Somalia-Arabia rifts; and 106.7° between the Somalia-Arabia and Arabia-Nubia rifts. Moving the three plates around their rotational axes for 3 Myr while symmetric spreading is occurring would cause these inter-ridge angles to change to 109.5°, 143.8°, and 106.8°, respectively. The specific angles are not as important as noting that the angles between the rifts do not remain constant given symmetric spreading over a finite time interval.
Moving the three plates around their rotational axes for 3 Myr while symmetric spreading is occurring would cause the triple-junction to move ~123 km northeast (Fig. 6B) as observed in the NNR reference frame. The observation that both the location of the triple junction and the inter-ridge angles vary during a finite time interval is not unique to the choice of reference frame. Similar observations would result from using other recently published external reference frames developed for use in plate tectonics.
The rifts between each plate pair must propagate toward the triple junction during finite displacement. One might assume that if the new alignment of the rift is constrained to be half-way between the previous edge of each plate as they diverge, all three rift lines (great circles) should meet at a common point—at the triple junction. In modeling the Afar triple junction, the three rift great-circles do not intersect at a single point as soon as finite displacement has occurred. Similar results have been noticed when modeling other RRR triple junctions, including synthetic triple junctions in which the rift great circles were chosen so that instantaneous motion across the rift was perfectly perpendicular to the rift axis. It is perhaps not surprising that small microplates are found within several RRR triple junctions. The Galapagos and Juan Fernandez microplates are examples.
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Tectonic Geomorphology
L.M. Schoenbohm , in Treatise on Geomorphology, 2013
5.3.4.1 Overview of Geology and Geomorphology
Along the Alpine–Himalayan chain to the east, the Arabian plate (rifted from the African margin) is colliding with Eurasia, causing widespread deformation, extrusion of continental crust along strike–slip faults, and the formation of the Anatolian and Central Iranian plateaus ( Figure 7). After a series of small accretion events, final closure of the Neo-Tethys and collision between Arabia and Eurasia began in the Middle to Late Miocene (10–12 Ma; Dewey et al., 1986; McQuarrie et al., 2003), although other authors have argued for closure as early as the Late Cretaceous (Agard et al., 2005). Collision initiated shortening, uplift, and mountain building in the Zagros Mountains adjacent to the Persian Gulf and in the Caucasus, Talash, Alborz, and Kopet-Dag mountains wrapping around the Black and Caspian seas (Figure 7; e.g., Stöcklin, 1968; Falcon, 1974; Berberian and King, 1981; Berberian et al., 1982; Berberian, 1983, 1995; Şengör et al., 1985; Alavi, 1994).
Figure 7. Turkish–Iranian Plateau region (Allen et al., 2004). (a) Simplified tectonic map of the Arabia–Eurasia collision zone. Area above 1000 m elevation shown by light shading. NAF, North Anatolian fault; EAF, East Anatolian fault; MRF, Main Recent Fault. (b) Crustal cross section along A–A′ shown in (a).
Modern and historical seismicity and GPS data suggest that the intervening region, including the Turkish and Central Iranian plateaus, largely behaves as a series of rigid blocks, with relatively minor internal deformation (e.g., Jackson and McKenzie, 1984; Vernant et al., 2004). Although shortening is active along the flanks of the Central Iranian Plateau (the Bitlis-Zagros fold-thrust belt to the south and the Caucasus Mountains to the north), the plateau itself undergoes almost exclusively strike–slip and normal faulting (Copley and Jackson, 2006). The region experienced a transition from collision to escape with the initiation of the East and North Anatolian strike–slip faults (Figure 7) around 5–7 Ma, which accommodate westward extrusion of the Anatolian Plate (e.g., Şengör, 1979; Westaway, 1994, 2003; Armijo et al., 1999). The Main Recent fault (Figure 7) to the east of the Anatolian plateau in Iran accommodates significant strike–slip movement as well. Strike–slip and normal faults on the Turkish–Iranian plateau appear to have originated at around the same time (5±2 Ma; Copley and Jackson, 2006). The modern convergence rate between Arabia and Eurasia is 22±2 mm yr−1 (Vernant et al., 2004). The Anatolian plateau has been volcanically active since 6–8 Ma (Innocenti et al., 1976a, 1976b; Pearce et al., 1990). The crust beneath the Anatolian plateau is a relatively thin 38–50 km, based on receiver function data (Zor et al., 2003), and seismic data indicate that the mantle lithosphere is entirely absent (Gok et al., 2007).
The Anatolian and the Central Iranian plateaus (Figure 7) are arid and partly internally drained, with an average elevation of ∼2000 m. Geographically, these plateaus are not as striking as their counterparts in Tibet or the central Andes, but they are of relatively low relief, consistent elevation, and are partially internally drained, particularly in Turkey. The central part of the Anatolian plateau is characterized by a number of large basins, including Lake Van, and the Erzurum, Pasinler, Mus, and Ararat basins and active volcanism in the Kars volcanic plateau (e.g., Dhont and Chorowicz, 2006). Although rare, glaciers were present during the Last Glacial Maximum in some parts of the region (Erol, 1991).
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THE GEOLOGICAL HISTORY AND STRUCTURAL ELEMENTS OF THE MIDDLE EAST
A.S. ALSHARHAN , A.E.M. NAIRN , in Sedimentary Basins and Petroleum Geology of the Middle East, 2003
Phase 6: The Cenozoic Events
Neotethys closed during the Cenozoic with the collision of the Afro-Arabian Plate with the Eurasian Plate, as the continued subduction of the Afro-Arabian Plate brought the two continental units into contact. The first clear indication of this was the obduction of the Late Cretaceous ophiolite bodies (80-90 Ma) onto the Arabia Plate in Oman, Iran (Kermanshah of Neyriz) and Turkey ( Alavi, 1994) (Fig. 2.14A-C). The principal zones of the Zagros part of the Zagros-Taurus Fold Belt are shown on Fig. 2.14E, with an outline of the stages in closure in Fig 2.14D. Although the limit of the Zagros traditionally is set at the Sanandaj-Sinjar Zone, the Arabian continental crust continues beneath that zone, as the Arabian crust descends below the magmatic, ensialic arc, the Urumieh-Dokhtar magmatic assemblage. The southwestern limit of the Sanandaj-Sirjan Zone does not coincide with the Main Zagros Thrust, but lies some kilometers to the west.
Fig. 2.14A-F. Tectonics of the Zagros Orogenic Belt of Iran. A-C=schematic cross sections illustrating pre-obductional and obductional initial collision steps in the Zagros Collision Zone; D=schematic cross-sectional view of the Zagros Orogen, where syn-collisional thrusts have complicated the picture; E=location and simplified Zagros subdivision.
(after Alavi, 1994) Copyright © 1994The Sanandaj-Sirjan consists of numerous overlapping nappes, which have transported various rock sequences southwestwards from the suture zone (Fig. 2.14A-D). These rock units consist of epicontinental, passive continental and shelf facies rocks, which differ only from the lithologies of the units in the Simple Fold Belt in that the Middle Triassic to Lower Jurassic beds show a dramatic change from marine carbonates to non-marine shale and graywacke. A few of the Sanandaj thrust sheets contain pyroclastic and volcaniclastic rocks and minor andesites from forearc sediments formed on the now-destroyed margin of the Iranian Plate. There are several generations of imbricated sheets and both small and large-scale duplexes.
The same continuing convergence and associated orogenic events in the Taurus Mountains region of Anatolia (Southeast Turkey) have been documented by Yilmaz (1990), as the ocean that formerly existed along the northern margin of the Arabian Plate was progressively eliminated. During that process, convergence initially led to the collision of an island arc and continent (the Yuksekova Complex and Taurides) at the end of the Early Eocene. This deformed package during the late Middle Eocene to Late Eocene collided with the Arabian Platform. The allochthon, as a package, was then thrust over the autochthon at a later stage in the orogeny in the late Early Miocene. Subsequent post-collisional convergence in post-Middle Miocene time was accommodated along east-west strike-slip faults reactivating earlier thrusts and by their dissection by high-angle faults.
The final phase in the Zagros of Iran involved epeirogenic uplift of the southern and central parts of the folded mountain belt, with the development of gravity-slump features west of the mountain belt in the present-day foreland. Thus, in the Arabian Gulf area, the orogenic events are most apparent and led to the development of structures later tapped for hydrocarbons. The result of these compressional events in the Arabian Gulf Basin was to restrict the basin and shift the trough axis toward the southwest.
In recent years, the assumption that the cover sequence of the Simple Fold Belt was detached from basement along a surface formed by the Hormuz evaporites or, to some extent, over the younger Phanerozoic evaporites has been called into question by a re-evaluation of the role of basement tectonics (Ameen, 1991a, b, 1992; McQuillan, 1991). While not questioning the decollement over the Hormuz evaporites in southwestern Zagros in northeastern Iraq, where evidence of diapiric structures is lacking, their extension is not known, and basement block faulting is regarded as a critical factor in the development of the fold belt (Ameen, 1992). Here, a distinction can be made between the northern area (Iraq, Turkey), where basement reactivation is important, and the southern Zagros, where salt decollement plays the larger role.
Along the Taurus-Zagros range, Ameen (1992) defines a number of blocks separated from one another by NE-SW lines, which, in the case of the Mosul and Kirkuk blocks, is a fault zone along the line of the Greater Zab River (Fig. 2.15a, b). Each block is divided into a number of zones parallel to the trend of the mountains, but which show changes from block to block. The separation of the two blocks has been determined from the shape and values of the contour lines, surface structural trends, major lineaments recognized on Landsat images and gravity anomalies (Ameen, 1992, Figs. 2 a, b and 3). The boundaries of the blocks were regarded as the surface expression of faults or fault zones in the basement. Expanding this idea, Ameen (1991a) introduced the idea of geowarping for open or gentle composite flexures or folds composed of lesser folds. The geowarps find geomorphological expression and tend to be more intense in the high mountains than in the foothills regions. They are related to the orogenic, crustal movements that led to greater lateral shortening and crustal thickening in the zones closer to the suture between colliding plates and are contemporaneous with the fold belt itself. The relative geowarps provide the conditions favorable to the development of forced folds or buckle folds, which require coherent contact between a thin (less than 10 km), sedimentary cover and a low-temperature, low-pressure environment.
Fig. 2.15a, b. The regional basement tectonic pattern of northern Iraq showing the borders of the Mosul and Kirkuk blocks and the longitudinal and transverse faults that break the blocks into smaller sub-blocks (lines 1-8). Notice that other longitudinal and transverse faults apart from those shown on the map do occur.
(after Ameen, 1992, and reproduced by kind permission of AAPG) Copyright © 1992Although in southwestern Iran, emergent salt plugs exhibit alignment patterns, McQuillan (1991) shows that the alignment is not that of the Zagros Fold Belt, but considers it to be controlled by basement lineaments, which manifest older, more north-south trends. Thus, recent findings relating to investigations of hydrocarbon accumulations have served to emphasize the importance of basement structure, whether by directly influencing Cenozoic sedimentation, as in northeastern Iraq, or indirectly, as in the northern Arabian Gulf.
A further result of the Neogene compression in the northern part of the Middle East was the inversion of the Syrian and northwest Iraqi Palmyra and Sinjar depressions (Fig. 2.16), with the formation in the north of broad, open anticlines that become tighter southward, developing into typical ramp anticlines overturned to the south (Lovelock, 1984). Erosion has cut deeper into the anticlines in the south than in the north, exposing Triassic rocks, in contrast to the north, where only Cretaceous horizons are exposed. In depth, detachment occurs in these folds at the level of the Triassic and Jurassic evaporites. Associated with these structures in central Syria is a major NE-SW–trending fault zone with the Abba and al Furat faults at the northeastern end of the zone (Fig. 2.16) (Lovelock, 1984). The Abba Fault appears to form the western end of the Sinjar Trough, continuing southward to terminate along its southern margin. The al Furat Fault appears to be a flower structure associated with the strike- slip zone. The Euphrates Graben (Fig. 2.16) is offset by the east-west–trending Anah Graben. Both of these grabens, which began to subside during the Late Cretaceous, were inverted during the Miocene. The Abu Jir Fault Zone, which can be traced 600 km running parallel to the main Zagros Thrust, extends southeastward from the Euphrates Graben into southern Iraq (Fig. 2.16).
Fig. 2.16. Generalized structural sections across the Palmyra and Sinjar zones, al Furat Transcurrent Fault and Euphrates Graben in Syria and Iraq, and reproduced by kind permission of Geological Magazine.
(modified from Lovelock, 1984) Copyright © 1984In the southwestern and western parts of the Middle East, sandwiched between the two main phases of orogenic activity during the Paleocene-Eocene and the late Miocene-Pliocene, and in part contemporaneous with them, is the evidence of extension most apparent in the Gulf of Aden and the Red Sea, particularly during the Paleogene (Burek, 1969, 1970). The first indications of significant movement in the Gulf of Aden-Red Sea-Arabian Sea area is of Late Cretaceous uplift (Table 2.9). The doming of the Arabo-Nubian Shield, which was followed by rifting in the Gulf of Aden and the Red Sea, culminated near the close of the Eocene (Lowell and Genik, 1972; Peterson and Wilson, 1986). Reactivation of the Hadhramout Arch is dated as beginning in the early Paleocene, with the arch, and the Rub al Khali Depression north of it, reaching their present form by the end of the Eocene. Separation of Arabia from Somalia as a result of rifting of what had been a local depression (Beydoun, 1966; Azzarolli, 1968; Closs, 1939) began in the late Eocene, accompanied by widespread volcanism in the Gulf of Aden. Vertical faulting and uplift of the rift walls by as much as several thousand meters occurred and is recorded on both sides of the rift. This activity continued through the Oligocene, and by the early Miocene, the Red Sea margins had attained essentially their present form. Baker (1970), however, concluded that the main phase of development occurred during the early Miocene with the deposition of early Miocene marine sediments in the proto-gulf, followed in the late Miocene and Pliocene by phases of faulting and seaward warping of Neogene sediments. The currently active zone of rifting passes through the Gulf of Tadjura into the Afar. This Gulf of Aden Rift and transform spreading links with the 2,000 km Owen Fracture Zone, which is aligned approximately parallel to the continental margin of the Indian Ocean (Beydoun, 1982). McElhinny (1970) concluded from his interpretation of paleomagnetic data that during the early Tertiary, the fracture zone was a sinistral transform fault separating Arabia-Somalia from India, and Whitmarsh (1979) described the northern part of the transform zone as a relict of earlier sea-floor spreading before the opening of the Gulf of Aden. There are two possible models of Late Cretaceous-Early Tertiary sea-floor spreading involving the Owen Fracture Zone (Whitmarsh, 1972). One, a three-plate model, gives the best fit of the paleomagnetic data from Africa, Madagascar and India, and involves the separation of Madagascar and India near the end of the Cretaceous. The second model, which shows a migration northward of the spreading ridge with respect to Africa, requires India and the anomalies north of the ridge to spread at twice the speed of the ridge.
Table 2.9. Time constraints and nature of crust in the evolution of the Red Sea, Gulf of Aden and Afar depressions
| Area | Age of Initiation of Rifting | Initiation of Seafloor Spreading | Nature of Crust |
|---|---|---|---|
| Gulf of Suez |
| No development of spreading axis |
|
| Gulf of Aqaba |
| No development of spreading axis | continental crust |
| Red Sea |
| Late Miocene (9 Ma) |
|
| Gulf of Aden |
|
|
|
| Afar |
| Development of axial volcanic range 1-2 Ma | Continental to transitional crust, except in the Erta Ala spreading axis. |
(compiled from Behre, 1986).
Copyright © 1986
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Tectonic and Structural Framework of the Zagros Fold-Thrust Belt
Iraj AbdollahieFard , ... Bilal U. Haq , in Developments in Structural Geology and Tectonics, 2019
Conclusions
This study shows that tectono-sedimentary evolution of the NE margin of the Arabian Plate results from variations in vectors and rates of displacement for hosting and neighboring plates. Major changes in displacement rates and vectors of the African–Indian plates reflect tectonically active periods (e.g., Berriasian, Valanginian, Turonian, Maastrichtian, and Oligocene) with reactivation of the deep-seated faults in the Zagros Basin. On the other hand, steady movement of the plates without major changes in rates and directions of motion, indicate quiescence periods (e.g., Aptian, Cenomanian), in which sedimentary processes governed Zagros Basin evolution. Consequently, Zagros source and reservoir rock distribution pattern is variable depending on these different periods. In reference to our observation, the concentration of exploration activities around deep-seated faults is recommended during tectonically active periods, whereas, constructional highs close to intrashelf basins should be the main focus during tectonically calm periods.
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Application of NDSHA at regional and local scale in Iran
Habib Rahimi , Mehdi Rastgoo , in Earthquakes and Sustainable Infrastructure, 2022
1 Introduction
The Iranian plateau within the Alpine–Himalayan orogenic belt is located between the Arabian plate in the southwest and the Eurasian plate in the northeast ( Fig. 29.1). Its tectonic situation is the result of the convergence of Arabian and Eurasian plates at a rate of 22 ± 2 mm/year (Vernant et al., 2004a), which controls various tectonic processes in Iran, like (a) continental collision in Alborz, Zagros, Kopeh Dagh, and Talesh mountains and (b) subduction of oceanic lithosphere in Makran region. On the other side, central Iran and the south Caspian basin are regarded as relatively rigid and aseismic blocks (Vernant et al., 2004a). Based on the reported historical earthquakes and paleoseismology studies, in the Alborz mountain range (49°E–56°E), great earthquakes are inevitable in the future. Alborz in the north of Iran is a relatively narrow V-shaped deformation belt, which has surrounded the south of the rigid south Caspian basin. It seems to involve oblique left-lateral shortening (Jackson et al., 2002). The north–south shortening rate across the Alborz is 5 ± 2 mm/year and the east-west left-lateral shear motion along the Alborz occurs at 4 ± 2 mm/year (Vernant et al., 2004b). Folds and faults of Alborz have NW–SE trend in the west and NE–SW trend in the east. The highest peak of the Alborz mountain range is Damavand, which reaches about 5671 m above sea level (Jackson et al., 2002), as the highest peak in Iran and a potentially active volcano. Based on the stratigraphy studies (Allen et al., 2003), the youngest (Paleocene-Eocene formations) and the oldest rocks are dominant in the south and in the north of Alborz, respectively.
Figure 29.1. Seismicity map of Iran including the reported historical earthquakes before 1900 (Ambraseys and Melville, 1982; Berberian, 1994) and recorded instrumental earthquakes in 1900/01–2020/06 based on the global earthquake catalog of NEIC (2020).
Alborz region as a seismically and tectonically active mountain range (Fig. 29.2) includes a considerable population of Tehran metropolitan area (the capital of Iran) with more than 8.5 million population. It is located at the foothill of the southern slopes of the Alborz mountain range. It is, therefore, crucial to have a realistic assessment of seismic Hazard in Tehran before the next great earthquake occurs. The results of probabilistic seismic hazard assessment (PSHA) in Iran are neither always realistic nor reliable because of the limitation of the recorded earthquake data that undermines the empirical peak ground acceleration (PGA) attenuation relationship and subsequently any statistical seismic analysis. In fact, some destructive earthquakes have occurred in the regions of Iran, which were not considered as the ones with high seismic regions in the PSHA maps, such as the 2003 Bam earthquake with MW = 6.5 and ~26,000 fatalities (in the southeast of Iran), the 2012 Ahar-Varzaghan earthquake with MW = 6.5 and ~300 fatalities (in the northwest of Iran), and the 2017 Sarpol Zahab earthquake with MW = 7.3 and ~600 fatalities (in the west of Iran).
Figure 29.2. Seismicity of the Alborz region including instrumental earthquakes (ISC catalog, 2014), historical earthquakes (Ambraseys and Melville, 1982; Berberian, 1994), and focal mechanisms. Black beach balls: Global Centroid Moment Tensor catalog (Dziewonski et al., 1981; Ekstrom et al., 2012); Gray beach balls: Regional Moment Tensor Catalog of the Swiss Seismological Service (SRMT Catalog, 2006; Rastgoo et al., 2018).
In view of the scarcity of the recorded earthquake data, neo-deterministic seismic hazard assessment (NDSHA) including the physics-based earthquake simulation is preferred (Panza and Bela, 2019). The synthetic seismograms can be computed through the knowledge of the earthquake generation process and of the seismic wave propagation in an anelastic medium. The results of such research projects can be used by civil engineers, as the input data for designing new sustainable structures against the strong earthquakes and reinforcement of the existing structures (Rugarli et al., 2019).
To simulate the strong ground motion at a regional scale due to the seismic wave propagation from source to site bedrock, the modal summation method (Panza, 1985; Florsch et al., 1991) is used for modeling of seismic source and the path structure so that the synthetic seismograms can be computed for maximum cut-off frequency 1 Hz. At the local scale, the lateral heterogeneity and sloping layers of the sedimentary structures can cause some effects on seismic wave amplitude and duration, such as excitation of local surface waves, focusing, and variable resonances (Fah et al., 1994). Numerical methods such as the finite difference method (Alterman and Kara, 1968; Boore, 1972) are capable to estimate the amplification effects in sedimentary structures. These methods are restricted in the size of structural models so that the source cannot be included. Therefore, a hybrid method combining modal summation and the finite difference methods has been developed (Fah et al., 1990; Fah, 1992; Fah et al., 1993a,b) to take into account the source, path, and local site effects. In such a way, the synthetic seismograms are computed using the regional 1D structural model by modal summation method and then they are numerically propagated through the local 2D sediment structure based on the finite difference scheme. On this basis, the synthetic seismograms can be computed for a maximum cut-off frequency of 10 Hz.
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