Chapter 1 Introduction and tectonic framework
Published:March 01, 2021
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Andreas Scharf, Frank Mattern, Mohammed Al-Wardi, Gianluca Frijia, Daniel Moraetis, Bernhard Pracejus, Wilfried Bauer, Ivan Callegari, 2021. "Chapter 1 Introduction and tectonic framework", The Geology and Tectonics of the Jabal Akhdar and Saih Hatat Domes, Oman Mountains, A. Scharf, F. Mattern, M. Al-Wardi, G. Frijia, D. Moraetis, B. Pracejus, W. Bauer, I. Callegari
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The extraordinary outcrop conditions provide a unique opportunity to study the geology and tectonics of the Oman Mountains, which record a geological history of more than 800 million years. We provide a summary of the geological evolution of the Oman Mountains with the emphasis on the Jabal Akhdar and Saih Hatat domes. This Memoir comprises seven chapters. This first chapter summarizes the former studies and the tectonic framework. This is followed by a comprehensive description of all geological formations/rock units (Scharf et al. 2021a, Chapter 2, this Memoir) including the famous Semail Ophiolite, the fault and fold pattern (Scharf et al. 2021b, Chapter 3, this Memoir) and the overall structure (Scharf et al. 2021c, Chapter 4, this Memoir). Chapter 5 (Scharf et al. 2021d) explains the varied tectonic evolution of the study area, ranging from the Neoproterozoic until present, while Chapter 6 (Scharf et al. 2021e) contains the conclusions and a catalogue of open questions. Finally, Chapter 7 (Scharf et al. 2021f) provides two over-sized geological maps (1 : 250 000 version available online) and a correlation chart, providing an overview of the geological units/formations. This volume is of interest for all geoscientists, geoscience students and professionals studying the Oman Mountains on the surface as well as in the subsurface because it represents a comprehensive and detailed reference.
The Oman Mountains at the northeastern margin of the Arabian Plate display an impressive geological record in terms of phenomenological diversity and significance since the Precambrian. This record includes (1) the ‘Snowball Earth’ glaciation (e.g. Leather et al. 2002; Kilner et al. 2005), (2) the Ediacaran ‘Shuram Excursion’ (e.g. Burns and Matter 1993; Le Guerroué et al. 2006a, 54C90b), (3) the enigmatic Hercynian Unconformity (‘Hercynian Orogeny’; e.g. Glennie et al. 1974; Beurrier et al. 1986b; Rabu et al. 1986; Faqira et al. 2009), (4) the Permo-Carboniferous glaciation (e.g. Heward and Penney 2014), (5) the Pangaea rifting and spreading of the Neo-Tethys Ocean during the Late Paleozoic (e.g. Blendinger et al. 1990; Béchennec et al. 1991), (6) the iconic obduction of the Semail Ophiolite (e.g. Glennie et al. 1974; Searle and Malpas 1980; Lippard et al. 1986; Goffé et al. 1988; Hacker and Mosenfelder 1996; Hacker et al. 1996; Cowan et al. 2014; Rioux et al. 2012, 2013, 2016), (7) high-pressure/low-temperature metamorphism of the continental margin (e.g. Lippard 1983; Le Métour et al. 1986b; Goffé et al. 1988; El-Shazly et al. 1990; Warren et al. 2003, 2005), (8) formation and exhumation of the large Jabal Akhdar Dome (JAD) and Saih Hatat Dome (SHD) which shape the Oman Mountains (e.g. Poupeau et al. 1998; Saddiqi et al. 2006; Hansman et al. 2017; Grobe et al. 2019), (9) Upper Cretaceous rudist limestones (e.g. Skelton et al. 1990; Wyns et al. 1992; Philip et al. 1995) and organic-rich intrashelf basin environments (e.g. van Buchem et al. 2002), (10) surface analogues of subsurface petroleum source and reservoirs rocks (Grantham et al. 1988; Koehrer et al. 2011; Pöppelreiter et al. 2011; Bendias et al. 2013; Heward and Penney 2014; Grobe et al. 2016), (11) Neogene to active tectonics (e.g. Fournier et al. 2006; Mattern et al. 2018; Moraetis et al. 2018) and (12) a palaeoclimate record for the past 325 ka based on speleothems from cave systems developed in Mesozoic carbonate formations (e.g. Burns et al. 1998, 2001). The Semail Ophiolite, as the world's largest and best preserved ophiolite (e.g. Searle and Cox 1999), and the Oman Mountains, as the unique case of an obduction orogen, have been the focus of much research interest from the international geoscientific community during the past decades (e.g. Nicolas et al. 1996, 2000).
Due to the massive improvement of Oman's road system during the last few decades and the excellent outcrops, the country became a field laboratory for tectonometamorphic, sedimentological and stratigraphic studies (e.g. Glennie et al. 1973, 1974; Robertson et al. 1990; Hacker et al. 1996; Saddiqi et al. 2006; Rollinson et al. 2014) with a research focus on ophiolites and ophiolite obduction (e.g. Lippard et al. 1986; Nicolas et al. 1996; Gregory et al. 1998; Searle and Cox 1999, 2002). We compiled these and many other studies to put forward an overview of the geology, tectonostratigraphy and tectonic evolution of the Oman Mountains, as well as a description of their large-scale structures. We concentrate on the eastern part of the Oman Mountains from the western tip of the JAD to the eastern end of the SHD (fig. A.1 (54C141Scharf et al. 2021f, Chapter 7, this Memoir)). To assist the international research community, we provide a newly compiled geological map of the eastern part of the Oman Mountains with the JAD and SHD in order to standardize the compiled tectonic units within a single map. This map is largely based on the geological maps of Oman at the scale of 1:250 000 (Béchennec et al. 1992a, 54C17b; Le Métour et al. 1992; Wyns et al. 1992). The map is accompanied by text which is an update on the geological knowledge of the Oman Mountains with some emphasis on the region's geodynamic history. Moreover, we provide a detailed topographic map and several simplified geological cross-sections, as well as an extensive tectonostratigraphic chart (fig. A.2 (54C141Scharf et al. 2021f, Chapter 7, this Memoir)).
The JAD consists of autochthonous rocks and is divided into the WNW-striking main dome (c. 85 km × 35 km) and NNE-oriented subdome attached to the NE of the main dome (25 km × 10 km; fig. 2.1 (54C136Scharf et al. 2021a, Chapter 2, this Memoir)). This NNE-oriented subdome is parallel to the Semail Gap and is known as the Nakhl Subdome (fig. A.1 in 54C141Scharf et al. 2021f, Chapter 7, this Memoir). In the NE, the Nakhl Subdome sharply bends towards the ESE and extends for c. 8 km until Fanja. The overall shape of the JAD is not circular, as expected for a tectonic dome, and may be attributed to the reactivation of faults within the subsurface during doming (see ‘Post-obduction deformation’ in Chapter 5 (54C139Scharf et al. 2021d)).
The SHD has an overall elongated shape and is aligned NW–SE from Fanja for c. 95 km towards the SE. The NE–SW extent ranges between 25 and 50 km. We define the SHD as the area consisting of (par-)autochthonous rocks that are surrounded by the Hawasina nappes and/or Semail Ophiolite to the NW and SW, as well as the ocean to the NE. Its southeastern margin is blanketed by Cenozoic shallow-marine sedimentary rocks near Tiwi (fig. A.1). The southeastern border or margin of the SHD is therefore not well defined. Between both domes near Fanja, a WNW–ESE-oriented structural and topographic depression is exposed (‘Fanjah Saddle’ of Coffield 1990). The autochthonous rocks west and east of the saddle rise 1.3 km above the saddle surface, which consists of allochthonous rocks. The fold axes of the JAD and SHD plunge below the 10-km-wide Fanjah Saddle at an angle of 20–40° (Coffield 1990). Roughly N–S-striking high-angle normal faults with dip directions towards the centre of the saddle cut the flanks of the JAD and SHD (Coffield 1990).
Lees (1928) introduced the Semail Nappe and recognized the allochthonous nature of the Hawasina nappes (see Heward 2016 for a summary of the pioneering expedition of Lees and others during the 1920s). The first descriptions of the Semail Ophiolite after the introduction of plate-tectonic theory were by Reinhardt (1969) and Allemann and Peters (1972).
The entire Oman Mountains were first mapped at a scale of 1:500 000 by Glennie et al. (1974). They introduced the main rock units of the Oman Mountains, the pre-Permian metasedimentary successions, the Arabian Platform sediments, the Hawasina nappes, the Semail Ophiolite and the post-obduction sedimentary rocks. Further mapping was carried out by the United States Geological Survey (USGS) in the vicinity of the SHD (Bailey 1981). Geologists of the Open University (UK) mapped the Semail Ophiolite (Lippard et al. 1986). French workers of the Bureau de Recherches Géologiques et Minières (BRGM) mapped the Central and Southeastern Oman Mountains at a scale of 1:100 000 (Béchennec et al. 1986a, 54C14b; Beurrier et al. 1986a, 54C21b; de Gramont et al. 1986; Hutin et al. 1986; Janjou et al. 1986; Le Métour et al. 1986a, 54C92b; Rabu et al. 1986; Villey et al. 1986a, 54C166b, 54C167c; Roger et al. 1991; Wyns et al. 1992). This map series was extended by the sheet of Ibra (Southeastern Oman Mountains) at a scale of 1:100 000 (Peters et al. 2005). Detailed mapping of the entire Semail Ophiolite was carried out and summarized by Nicolas et al. (2000). Eight geological maps of the Muscat-Seeb area have been published at a scale of 1:25 000 (Kajima and Ishii 2012; Kajima and Otake 2012; Kajima et al. 2012a, 54C78b, 54C79c, 54C80d, 54C81e, 54C82f).
Two important compilations of the subsurface stratigraphy and nomenclature were produced by Hughes Clarke (1988) and Forbes et al. (2010). The latter provided a comprehensive chart showing the subsurface stratigraphy of Oman (Forbes et al. 2010, their enclosure 1). Two Special Publications of the Geological Society of London (Robertson et al. 1990; Rollinson et al. 2014) represent significant advancements to the understanding of the geology and tectonics of the Oman Mountains. A summary booklet describing the geology and origin of the Oman Mountains was published by Glennie (1995). His work was the first step in understanding the geology of northern Oman for geologists, non-geologist scientists and engineers from the oil industry. This booklet became so famous and in such demand that a second edition was released (Glennie 2005). Searle (2007) wrote a review article about the Permo-Mesozoic evolution of the eastern Arabian Platform and margin with the adjacent Hawasina Basin. This work also targets the obduction of the Semail Ophiolite as well as the post-obduction evolution of parts of the Oman Mountains.
Many informative popular science and geoguide books, including the most recent and well-illustrated work of Al-Kindi (2018) and Searle (2019), have been published during the past decades, outlining the unique and spectacular geology of the Sultanate. With its description of numerous fascinating outcrops, the geological field guide of Hoffmann et al. (2016) could be used as a companion document to this book.
The formations at the surface in our study area may have different names to coeval deposits in the subsurface. The latter are commonly used by researchers in the oil industry (e.g. Hughes Clarke 1988; Sharland et al. 2004; Forbes et al. 2010). We use the surface names in our manuscript, but will also provide the subsurface names for clarity (Chapter 2 and fig. A.2 (54C136Scharf et al. 2021a,54C141f, Chapters 2 and 7, this Memoir)).
We first describe in detail all major geological formations and tectonic units (54C136Scharf et al. 2021a, Chapter 2, this Memoir), provide the regional fault and fold pattern (54C137Scharf et al. 2021b, Chapter 3, this Memoir) and characterize the large-scale structure of the study area (54C138Scharf et al. 2021c, Chapter 4, this Memoir). This is followed by a comprehensive description of the entire tectonic evolution of the Oman Mountains from the Neoproterozoic until present (54C139Scharf et al. 2021d, Chapter 5, this Memoir). This chapter includes a lithospheric scale series of cross-sections, depicting the kinematics and dynamics of the different deformation events with a tectono-metamorphic synthesis. The conclusions and a catalogue of open questions, based on the available literature complete this memoir (54C140Scharf et al. 2021e, Chapter 6, this Memoir). A compiled geological map at a scale of 1:250 000 and a tectonostratigraphic chart are enclosed in the appendix, providing a handy comprehensive overview (figs A.1 and A.2 (54C141Scharf et al. 2021f, Chapter 7, this Memoir). Note that in the literature the transcription of proper Arabic names into English commonly results in different spellings of the same feature; for example, the vowels in the name ‘Semail' as in ‘Semail Ophiolite' may be transcribed as ‘Samail' or ‘Sumail’.
The eastern part of the Arabian Peninsula (Fig. 1.1) was the site of several tectonic events. Recently, Callegari et al. (2020) documented the first evidence of the Cadomian Orogeny in northern Oman. This event is documented by tight to isoclinal folds with an amplitude of a few to tens of metres in the Hajir Formation of the JAD. The shortening direction during this event was NE–SW-aligned (in present coordinates). The age of deformation was at some time after deposition of the Fara Formation and before the Angudan event, that is, between c. 540 and 525 ± 5 Ma (Callegari et al. 2020; section ‘F1 folds’ in 54C137Scharf et al. 2021b, Chapter 3, this Memoir). The Cadomian Orogeny was followed (and probably overlapped) by the Neoproterozoic–Early Cambrian East African Orogeny (sensuStern 1994), resulting in the Angudan Unconformity that coincides with the final stage of the East African Orogeny (c. 550–510 Ma; Loosveld et al. 1996; Al-Husseini 2000; Immerz et al. 2000; Koopman et al. 2007; Forbes et al. 2010; Al-Kindi and Richard 2014; Droste 2014, fig. 6a). This orogeny is associated with the continent–continent collision of East and West Gondwana. Some authors use the term ‘Malagasy Orogeny’ in Arabia as a synonym for the latest part of the East African Orogeny (e.g. Collins and Pisarevsky 2005). We use the phrase ‘East African Orogeny’. We also use the name ‘Angudan Unconformity’ throughout the text.
The Hercynian Orogeny in Europe was caused by the convergence of Gondwana and Laurasia. The ‘Hercynian Orogeny’ in the northwestern Arabian Plate is manifested in the regional pre-Carboniferous uplift and erosion as well as arch formation (see Faqira et al. 2009). Additionally, Abbo et al. (2018) concluded that the ‘Hercynian’ event in the Arabian Plate was not a significant deformation event, but rather a thermal event. The same authors suggested that the large-scale Paleozoic arches and basins across NE Africa and Arabia formed due to a mantle disturbance. Terminologically, we are following Faqira et al. (2009) and use the term ‘Hercynian’ (in quotes), but we are not suggesting that the Hercynian Orogeny (sensu lato) and related deformation and/or folding took place in Oman; rather, it seems to have been a thermal event (Abbo et al. 2018). In the subsurface of Oman, a significant truncation of Lower Paleozoic strata below the mid-Carboniferous exists. This truncation is related to salt movements and reactivation of basement trends (Droste 1997, fig. 3; Konert et al. 2001; Svendsen 2004). The ‘Hercynian’ event in Oman is only evidenced by ‘Hercynian’ K/Ar crystallization ages in pre-Permian formations of the SHD at 327 ± 16 Ma (Glennie et al. 1974) and of the JAD at 329 ± 11 and 321 ± 10 Ma of chlorite samples from the Mu'aydin Formation. (Beurrier et al. 1986b). Moreover, pre-‘Hercynian’ rocks commonly display NE-trending fold axes in the JAD (Mann and Hanna 1990). The NE-trending folds are unconformably overlain by sedimentary rocks of the Haima Supergroup in the subsurface south of the Oman Mountains. The deformation is therefore Early Cambrian in age and not related to an ‘Hercynian’ event (Droste, H. 2018, pers. comm.). A pre-Amdeh age for the folding and thrusting in the Huqf area has been suggested by Le Métour et al. (1995). There is a major erosional gap with an angular unconformity between the pre-Permian rocks and the Permian Saiq Formation in the JAD and SHD (Le Métour et al. 1986b; Villey et al. 1986c). The age of the youngest rocks below the unconformity of the JAD and SHD is c. 540 Ma (Fara Formation) and c. 460 Ma (Amdeh Formation), respectively. These two aspects have been linked to the ‘Hercynian’ movements in the JAD area (Beurrier et al. 1986b, fig. 14; Rabu et al. 1986, fig. 16). Furthermore, block faulting has been attributed to the ‘Hercynian’ movements by Beurrier et al. (1986b), Le Métour et al. (1986b), Rabu et al. (1986) and Villey et al. (1986c). The trend of the aforementioned fold axes is in line with the trend of ‘Hercynian’ arches (Faqira et al. 2009, fig. 2). The ‘Hercynian Unconformity’ is also known as the ‘pre-Permian unconformity’ (e.g. Chauvet et al. 2009), the ‘mid-Carboniferous tectonic event’ (Al-Husseini 2004) and the ‘Pre-Unayzah unconformity’ in Saudi Arabia (Al-Husseini 2004; Fig. 1.1).
The ‘Hercynian’ event was followed by the break-up of Gondwana between Arabia and the Cimmerian continental blocks as well as between Arabian and India (e.g. Blendinger et al. 1990; Robertson and Searle 1990; Stampfli and Borel 2002; Chauvet et al. 2009; D4 in fig. A.2; fig. 5.18c). The timing of continental rifting is Late Carboniferous–Permian (see section on ‘Pangaea rifting and formation of the Neo-tethys Ocean and Hawasina Basin’ in Chapter 5 (54C139Scharf et al. 2021d)). The break-up of Gondwana resulted in the formation of the Batain Basin SE of Oman and the Hawasina Basin NE of Oman during the Early and mid-Permian, respectively (e.g. Béchennec et al. 1992a, 54C17b; Immenhauser et al. 2000; see also sections on ‘Hawasina nappes’ in Chapter 2 (54C136Scharf et al. 2021a) and ‘Pangaea rifting and formation of the Neo-Tethys Ocean and Hawasina Basin’ in Chapter 5 (54C139Scharf et al. 2021d)). Divergence between Arabia and the Cimmerian continental blocks continued to form the Neo-Tethys Ocean, while extension between Arabia and India aborted. Mostly deep-sea sediments with some limestone were deposited in the Hawasina Basin from the mid-Permian to the Late Cretaceous (e.g. Glennie et al. 1974). These rocks were thrust onto the Arabian margin and platform and were themselves overthrust by the Semail Ophiolite during the Late Cretaceous (e.g. Glennie et al. 1974; section ‘Intraoceanic thrusting, formation and obduction of the Semail Ophiolite’ in Chapter 5 of this Memoir (54C139Scharf et al. 2021d)).
Large-scale obduction of the prototypical Semail Ophiolite onto the Arabian passive margin during the Late Cretaceous, and the ophiolite sequence itself, have been well researched (e.g. Allemann and Peters 1972; Glennie et al. 1974; Searle and Malpas 1980; Coleman and Hopson 1981; Hacker et al. 1996; Searle and Cox 1999, 2002; Searle et al. 2004; Rioux et al. 2016; Soret et al. 2017; Guilmette et al. 2018). The recent analysis of Guilmette et al. (2018) advocates that initial intraoceanic subduction was induced at c. 104 Ma. At c. 96 Ma the subduction zone matured and a self-sustained subduction started with a supra-subduction zone spreading centre (e.g. Rioux et al. 2016). The newly formed oceanic lithosphere was coevally thrust (obducted) onto Arabian lithosphere. Thrusting lasted until c. 68 Ma (Lippard 1983; Goffé et al. 1988; Hacker et al. 1996; Searle and Cox 1999; El-Shazly et al. 2001; Warren et al. 2003, 2005; Rioux et al. 2016; section ‘Intraoceanic thrusting, formation and obduction of the Semail Ophiolite’ in Chapter 5 of this Memoir (Scharf et al. 2021d)). More than 400–450 km of obduction are considered for the extended part of the Arabian Crust (Cooper 1988; Searle 2007) and another 150 km for the Arabian Platform of more regular thickness as quantified by map analysis. The entire thrust range therefore amounts to > 550–600 km. Thrusting of the ophiolite ensued to the SW (Hacker et al. 1996). Today, the ophiolite covers an area of > 10 000 km2 and is c. 550 km long and c. 150 km wide (Searle and Cox 1999). The ophiolite measures several kilometres in thickness, which decreases towards the south (Al-Lazki et al. 2002; Aldega et al. 2017; Carminati et al. 2019). According to Reinhardt (1969), Glennie et al. (1974), Coleman (1981), Lippard et al. (1986), Nicolas (1989) and Searle and Cox (1999), the Semail Ophiolite is composed of c. 8–12 km of upper mantle peridotites (mainly harzburgite) and c. 2.5–8 km of oceanic crustal rocks; according to Rabu et al. (1986) and Villey et al. (1986b, c), the entire ophiolite thickness measures 8–9 km. Hacker and Mosenfelder (1996) provided an inferred pre-emplacement thickness of the Semail Ophiolite of 15–20 km.
Obduction is linked to plate convergence between Arabia and Eurasia and the closure of the intervening oceanic lithosphere (Dercourt et al. 1993; Stampfli and Borel 2002; Stampfli and Kozur 2006). Convergence was not only expressed by the obduction of the Semail Ophiolite. While the mantle and crust of the future Semail Ophiolite still formed in a supra-subduction zone spreading centre, the northeastern part of the Arabian passive margin was subducted to the NE beneath the future ophiolite (e.g. Lippard et al. 1986; El-Shazly and Coleman 1990; Searle et al. 1994; Searle and Cox 1999; Searle et al. 2004; Saddiqi et al. 2006; Rioux et al. 2012, 2013, 2016; Cowan et al. 2014; for more details on the direction of obduction and rotation during thrusting see van Hinsbergen et al. 2019 and section on ‘Intraoceanic thrusting, formation and obduction of the Semail Ophiolite’ in Chapter 5 of this Memoir (54C139Scharf et al. 2021d)). Eventually, the subducted plate segment was metamorphosed under high-pressure/low-temperature conditions (e.g. Lippard 1983; Le Métour et al. 1986b; Goffé et al. 1988; El-Shazly et al. 1990; Searle et al. 1994, 2004; Warren et al. 2003, 2005), and the Semail Ophiolite was thrust on the Arabian Plate (e.g. Searle et al. 2004). A slab break-off may have triggered rapid exhumation of the Arabian crustal slab with its blueschist and eclogite facies, exposed in the northeastern SHD (e.g. Searle et al. 2004).
A second ophiolite obduction affected the southeastern part of the Oman Mountains. The Masirah Ophiolite (or ‘Eastern Ophiolite Belt’ of Gnos et al. 1997; Immenhauser et al. 1998) is a fragment of oceanic lithosphere thrust onto the easternmost margin of Oman (e.g. Moseley and Abbotts 1979; Mountain and Prell 1990; Ries and Shackleton 1990; Shackleton and Ries 1990; Marquer et al. 1995; Schreurs and Immenhauser 1999; Immenhauser et al. 2000; Fig. 1.1). The sole of the ophiolite is not exposed, which makes it difficult to tectonically interpret its history of thrusting, emplacement and uplift. The Masirah Ophiolite derived from oceanic lithosphere of the ‘Somalia-Mozambique-Madagascar (SoMoMa) Ocean’ with a formation age of latest Jurassic to earliest Cretaceous (e.g. Smewing et al. 1991; Immenhauser 1995; Peters et al. 1995; Gnos et al. 1997; Marquer et al. 1998; Schreurs and Immenhauser 1999). Latest Jurassic ages (c. 150 Ma) are concluded based on U–Pb zircon studies and Ar/Ar dating on plagioclase of gabbro dykes (Peters et al. 1995), K–Ar ages on gabbros (Smewing et al. 1991) and dating of radiolarian cherts (Moseley 1990). The SoMoMa Ocean separated Gondwana into western (Africa and Arabia) and eastern (Madagascar and India) segments (fig. 5.18f). Formation of the ocean resulted in the gentle extension and uplift of the eastern Arabian margin and the Hawasina Basin (D5 in fig. A.2; Rabu 1987; Béchennec et al. 1992a, 54C17b; section ‘Arabian Platform’ in Chapter 5 (54C139Scharf et al. 2021d)). Geochemical analyses reveal that the ophiolite represents a young mid-ocean ridge that had formed during early drift between eastern and western Gondwana (Rollinson 2017). Later, the ocean basin underwent transpression as a result of convergence between India and Arabia, and was obducted and/or emplaced to the WNW for a few tens of kilometres as the ‘Masirah Ophiolite’ onto the easternmost tip of the Arabian Platform at the Cretaceous–Cenozoic boundary until the early Eocene (c. 65–55 Ma; Smewing et al. 1991; Peters et al. 1995; Gnos et al. 1997; Peters and Mercolli 1997; Marquer et al. 1998; Schreurs and Immenhauser 1999; Immenhauser et al. 2000; Gaina et al. 2015; fig. 5.18i). The Masirah Ophiolite therefore remained a part of the oceanic lithosphere for c. 80 Ma from its formation to its obduction (e.g. Rollinson 2017). The Hawasina and Haybi Complex were thrust along with the Semail Ophiolite during the Coniacian–Campanian from NE to SW. By contrast, the Masirah Ophiolite was thrust along with the Batain Mélange onto the eastern Oman margin during the Cretaceous–Cenozoic (Schreurs and Immenhauser 1999; Fig. 1.1). The Lower Permian to Upper Cretaceous sediments of the Batain Mélange derived from the Batain Basin, located east of Oman as part of the SoMoMa Ocean (Schreurs and Immenhauser 1999; Immenhauser et al. 2000). The Batain Basin is older (latest Carboniferous to Early Permian; Immenhauser et al. 2000) than the Hawasina Basin (Late Permian). Although the sediments of the Hawasina nappes and the Batain Mélange derived from different basins, the stratigraphy is similar (see Immenhauser et al. 1998, 2000).
The Semail and Masirah ophiolites differ in origin, tectonic setting, age of oceanic lithosphere formation (Neo-Tethys Ocean during the Cenomanian compared with SoMoMa Ocean during the latest Jurassic–earliest Cretaceous), time of obduction onto the Arabian Margin (late Cretaceous compared with latest Cretaceous–early Eocene) and direction of obduction (SW-ward compared with WNW-ward). Generation of the Semail Ophiolite is associated with a spreading centre in a supra-subduction zone setting with coeval formation and thrusting (e.g. Rioux et al. 2016), whereas the Masirah Ophiolite formed at a conventional mid-ocean ridge with its emplacement at c. 80 Ma after formation (see Rollinson 2017 for further comparison and discussion).
The Oligocene–Miocene to recent regional tectonic setting of the Arabian Plate is summarized in Figure 1.2. The northeastern plate margin corresponds to the Arabia–Eurasia collision zone, forming the Zagros and Makran mountains (e.g. Glennie et al. 1974; Robertson and Searle 1990; Loosveld et al. 1996; Immenhauser et al. 2000). Deformation in the Zagros Mountain Belt started before c. 25–23 Ma (e.g. Agard et al. 2011), amounts to 440 km of shortening (Monthereau 2011) and is still active (Vernant et al. 2004). Arabia is bounded in the west by the left-lateral Dead Sea Transform Fault that accommodated a displacement of 100–105 km (Walley 1998). The age of the fault is > 14 Ma (Bayer et al. 1988; Makris and Rihm 1991). The southwestern and southern margins of the Arabian Plate are defined by the spreading axes of the Red Sea and Gulf of Aden, respectively. Continental extension in the southern Red Sea area started during c. 27.5–23.8 Ma (Bosworth et al. 2005; Reilinger and McClusky 2011). Seafloor spreading between the Arabian and African plates (i.e. the Gulf of Aden) commenced at 20 Ma (Fournier et al. 2010). The southeastern boundary of Arabia is marked by the 8-Ma-old Owen Transform Fault. Dextral motion along this fault ensues at a rate of 3 ± 1 mm a−1 (Fournier et al. 2008).
AS: Conceptualization (lead), Writing original draft (lead), Visualization (lead), Supervision (lead), Investigation (lead); FM: Conceptualization (equal), Writing – review and editing (equal), Visualization (equal), Investigation (equal); MAW: Writing – review and editing (equal); GF: Writing – review and editing (equal); DM: Writing – review and editing (equal); BP: Writing – review and editing (equal); WB: Writing – review and editing (equal); IC: Writing – review and editing (equal).
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.
The Geology and Tectonics of the Jabal Akhdar and Saih Hatat Domes, Oman Mountains
CONTAINS OPEN ACCESS
The geology of the Oman Mountains, including the Jabal Akhdar and Saih Hatat domes, is extraordinarily well-exposed and diverse, spanning a geological record of more than 800 Ma. The area is blessed with first-class outcrops and is well known in the geological community for its ophiolite. The Oman Mountains have much more to offer; including, Neoproterozoic diamictites (“Snowball Earth”), fossil-rich Permo-Mesozoic carbonates and metamorphic rocks. The arid climate and deep incision of wadis allow for nearly complete rock exposure which can be investigated in all three dimensions. The diverse geology is also responsible for the breathtaking landscape. New roads and the nature of the friendly Omani people make fieldwork unforgettable.
This Memoir provides a thorough state-of-the-art overview of the geology and tectonics of the Southeastern Oman Mountains, and is accompanied by an over-sized geological map and a correlation chart.