Hawasina Basin Research Articles

New constraints on the Neoproterozoic geological evolution of the SE corner of the Arabian Plate (NE Oman)

The Saih Hatat Dome is a tectonic window in northeastern Oman with a NW–SE extent of c. 95 km and an east–west extent of c. 50 km, rimmed by the allochthonous Samail Ophiolite and the tectonically underlying nappes composed of sedimentary rocks from the Neo-Tethyan Hawasina Basin. Rocks within the window were affected by high pressure/low-temperature metamorphism during the latest Cretaceous. Stratigraphically, the Saih Hatat Dome contains a basal, several kilometre thick sequence, made up of low-grade metamorphic volcanosedimentary rocks (Hatat Formation). U–Pb zircon laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) data from a quartzdiorite dyke, intruding the basal part of the Hatat Formation yielded a crystallization age of 845 +2/−4 Ma, whereas zircons from a quartz keratorphyre have ages of 870 ± 5 Ma. Thus, the basal schists of the Hatat Formation are Tonian in age, similar to Tonian felsic volcanic rocks and a granodioritic intrusion in the Huqf area, 300 km to the south. Detrital zircons from the Hatat Formation show an age peak of 837 Ma with some Neoarchean and Paleoproterozoic grains, which have no potential source in the Arabian–Nubian Shield. Based on the new results, we propose that the Hatat Formation signifies a Tonian back-arc basin, contemporaneous with calc-alkaline igneous intrusions in the Jabal Ja'alan region. Similar calc-alkaline intrusions of comparable ages have been identified in the Mirbat area of Dhofar and the Huqf region in central eastern Oman. We interpret these outcrops as components of a cohesive island arc, characterized by calc-alkaline volcanic rocks and volcanosedimentary back-arc sedimentation. Our model situates these regions off the coast of NW India during the Tonian.

Origin of the Cretaceous olistostromes in the Oman mountains (Sultanate of Oman): Evidence from clay minerals

Mid- to Late Cretaceous olistostrome generation ensued sequentially, linked to progressive southwest-directed thrusting of the Semail Ophiolite towards and over Arabia – at first in the northeastern part of the oceanic Hawasina Basin (Umar Sub-Basin) and then in its southwestern part (Hamrat Duru-Sub-Basin). Thrusting steepened slopes, causing seismic tremors, which destabilized slope sediments and triggering olistostrome formation. Ophiolite thrusting over Arabia created the Aruma Foreland Basin. Olistostrome formation in the foredeep ensued last and on the flank of the uplifting forebulge.As olistoliths, Olistostrome 1 contains radiolarian limestone, plain micrite, allodapic limestone, basalt, amygdaloidal basalt, radiolarian chert and coarse, massive limestone with crystalline texture (Oman Exotics). These olistoliths “float” in shale, containing illite/muscovite, vermiculite and kaolinite. Olistostrome 1 formed in the Umar Sub-Basin.Olistostrome 2 is associated with the Late Albian to Coniacian Nayid Formation of the Hamrat Duru Sub-Basin. It is characterized by olistoliths of graded limestones (calc-turbidites) with angular shelfal limestone lithoclasts. The olistoliths are embedded in shale with unidentifiable clay minerals. Olistostrome 2 formed in the Hamrat Duru Sub-Basin, postdating Olistostrome 1.Olistostrome 3 is associated with the Upper Cretaceous Aruma Foreland Basin and characterized by olistoliths, like lithoclastic packstone (calcarenite), dolomitic limestone, and sandstone with carbonate lithoclasts. The matrix of the olistoliths is a pyrophyllite- and kaolinite-bearing shale. Olistostrome 3 formed in the foredeep as the youngest olistostrome.The different clay mineralogy of Olistostrome 1 and Olistostrome 3, reflects their different basinal origin. Shale samples taken from conventional sediments (no olistostromes) of the syn-tectonic and post-tectonic Aruma units show some resemblance in their clay mineralogy as they contain detritus from the Oman Mountains. Olistolith types of both Hawasina olistostromes differ significantly.The reviewed and novel data may serve as a guideline for future olistostrome studies in the Oman Mountains and may be particularly helpful in identifying the basinal origin of olistostromes in case of fault-bounded olistostromes, unexposed olistostrome contacts and inconclusive olistoliths. Evaluating matrix shales of olistostromes leads to important decision criteria, such as color, oxygenation state and clay mineralogy, to determine the paleogeographic basin position.

A NEW OIL SEEPAGE IN THE OMAN MOUNTAINS AND ITS GEOLOGICAL, GEOCHEMICAL AND PETROLEUM SYSTEMS CONTEXT

A minor natural oil seepage is described from an unlikely setting in the Oman Mountains. The host rocks are fractured pelagic limestones of the lower member of the Triassic – Lower Jurassic Matbat Formation of the Hamrat Duru Group in the lower part of the allochthonous Hawasina Complex. This paper summarises Oman's established oil families and documents previously recorded oil seepages as context for describing the new seepage, its geochemistry, and possible source rock. The seep oil is different to those known from Oman's oil fields and probably derived from a poor quality, Mesozoic clastic source rock containing a mix of terrigenous and marine organic matter. The most likely source appears to be the Toarcian turbiditic upper member of the Matbat Formation, equivalent to the clastic Mafraq Formation of the Arabian Platform. The occurrence of source rocks in the allochthonous sediments of the NeoTethyan Hawasina Basin has been suspected previously, though their commercial significance remains to be established.

Chapter 5 Tectonic evolution of the Oman Mountains

Abstract The tectonic evolution of the Oman Mountains as of the Neoproterozoic begins with a major extensional event, the Neoproterozoic Abu Mahara rifting. It was followed by the compressional Nabitah event, still during the Neoproterozoic, in Oman but possibly not in the study area. During the earliest Cambrian, the Jabal Akhdar area was affected by the Cadomian Orogeny, marked by NE--SW shortening. It is unclear, whether the Saih Hatat area was exposed to the Cadomian deformation, too. Still during the lower Cambrian, the Angudan Orogeny followed, characterized by NW--SE shortening. An episode of rifting affected the Saih Hatat area during the mid-Ordovician. During the mid-Carboniferous, both dome areas were deformed by tilting and large-scale open folding in the course of the ‘Hercynian’ event. As a consequence, a major unconformity formed. As another Late Paleozoic event, the Permian break-up of Pangaea and subsequent formation of the Hawasina ocean basin, are recorded in the Southeastern Oman Mountains. As a result, a passive margin formed which existed until the mid-Cretaceous, characterized by deposition of mostly shelfal carbonates. This interval of general tectonic quiescence was interrupted during the early Jurassic by uplift and tilting of the Arabian Platform. The platform collapsed during the late Cretaceous, related to the arrival of the obducted allochthonous nappes including the Semail Ophiolite, transforming the passive margin to an active margin. The Semail Ophiolite formed most likely above a subduction zone within the Neo-Tethys Ocean during the Cenomanian while parts of the Arabian Plate were subducted to the NE. Formation of oceanic lithosphere and SW-thrusting was broadly coeval, resulting in ophiolite obduction onto the Hawasina Basin. The Semail Ophiolite and the Hawasina rocks combined were thrust further onto the Arabian Plate. Their load created a foreland basin and forebulge within the Arabian Platform. Once the continental lithosphere of the Arabian Platform was forced into the subduction zone, a tear between the dense oceanic lithosphere and the buoyant continental lithosphere developed. This led to rapid uplift and exhumation of subducted continental lithosphere of the Saih Hatat area, while obduction was still going on, causing in multiple and intense folding/thrusting within the eastern Saih Hatat Dome. Exhumation of the Saih Hatat Dome was massive. The emplacement of the ophiolite was completed during the Campanian/Maastrichtian. For completeness, we also present alternative models for the developmental history of the Semail Ophiolite. Immediately after emplacement, the Arabian lithosphere underwent intense top-to-the-NE extensional shearing. Most of the Saih Hatat Dome was exhumed during the latest Cretaceous to Early Eocene, associated with major extensional shearing at its flanks. Further convergence during the late Eocene to Miocene resulted in exhumation of the Jabal Akhdar Dome and some gentle exhumation of the Saih Hatat Dome, shaping the present-day Southeastern Oman Mountains. In the coastal area, east and SE of the Saih Hatat Dome, some late Cretaceous to present-day uplift is evident by, e.g., uplifted marine terraces. The entire Oman Mountains are uplifting today, which is evident by the massive wadi incision into various rock units, including wadi deposits which may form overhangs.

Late Jurassic to Cretaceous evolution of the eastern Tethyan Hawasina Basin (Oman Mountains)

AbstractRemnants of a Mesozoic continental margin can be studied today in the nappe pile of the Oman Mountains. Successions of the Arabian carbonate platform and the adjacent deep Hawasina Basin are preserved in the nappe pile and in the foothills of this Mountain range. The Jurassic–Cretaceous sediment successions of the Hawasina Basin (Sumeini and Hamrat Duru Group) are focus of this study. These basinal archives contain information on the response of an eastern Tethyan equatorial ocean system to multiple perturbations of the carbon cycle and of climate during the Cretaceous. Turbiditic continental slope and basinal successions formed near the Calcite Compensation Depth are difficult to date with biostratigraphy and sequence stratigraphy. The available stratigraphic framework for the Hawasina successions was not sufficient for tracing palaeoceanography through the time window of interest in this study. Therefore, existing sequence stratigraphy and biostratigraphy are complemented by additional biostratigraphic data and with a newly established carbon and strontium isotope chemostratigraphy. The Hawasina Basin was affected by sea‐level variations, by changes in oceanography and also by regional tectonics. A first major modification of oceanography occurred at the end of the Jurassic when pelagic Maiolica‐type sediments were accumulated in the deep basin and on adjacent submarine highs (Lower Member of Huwar and Sid'r formations). Pelagic to hemipelagic conditions existed until the Valanginian, marked by a major carbon isotope excursion. Pelagic sediments were replaced afterwards by a succession of fine to coarse‐grained turbidites of Hauterivian to Aptian age. The transition into the mid‐Cretaceous is marked by a sudden shift to fine‐grained siliceous or chert deposits, at a time when sediments enriched in organic carbon were accumulated in the western Tethys and Atlantic Oceans. The continental slope as well as the Hawasina Basin seemed to have been well‐ventilated during Early and mid‐Cretaceous time. Siliceous limestones and chert are indicators of well‐mixed and nutrient‐rich surface water, while the absence of black shales suggests young and oxygenated deep water with a possible source on the vast Arabian platform. These peculiar oceanographic conditions were most pronounced during the onset of the extreme greenhouse episodes of the Oceanic Anoxic Event 1a.

Evolution of the Arabian continental margin of the northern Dibba Zone, eastern United Arab Emirates and Oman

The southern margin of the Musandam Mountains (UAE and northern Oman) preserves a Late Permian to Late Cretaceous Neo-Tethyan platform margin sequence that provides important insights into the switch from deposition in shallow shelf to deeper-water margin slope environments. New biostratigraphic dating resolves ambiguities in previous works and better constrains the timing of the stages in the development of the south Musandam platform margin and their link to the wider Oman tectonic framework. The accumulation of Late Permian to Late Triassic mainly dolomitised shelf carbonates along this sector of the nascent Neo-Tethyan margin was ended by a phase of margin-edge collapse linked to the onset of a major phase of Neo-Tethyan rifting and extension, and deposition of a fore-reef talus assemblage. This is newly dated as also being Late Triassic (Norian-Rhaetian) and termed the Kharas Formation. Following non-deposition, or possible erosion of Early Jurassic deposits, differential subsidence in the Middle Jurassic led to deposition of on-lapping deeper-shelf/slope facies peri-platform lime mudstones, fine grained turbidites and minor, channelised coarser-grained graded conglomerates and packstones (Sumeini Group) along the southern side of the Musandam platform. In the west, oolitic peloidal packstone and grainstone shoals were deposited, here termed the Jarief Formation. Their Bathonian-Callovian age is coeval with the regional development of oolitic facies on the carbonate platform, linked to a mid-Jurassic sea-level highstand, and their redeposition into the adjacent Hawasina Basin as turbidites of the Guwayza Formation of the Hamrat Duru Group. Uplift and destabilisation of the margin of the carbonate platform throughout Oman in the Late Jurassic during a mild compressional regime cut off the coarser sediment supply to the Jarief Formation, which was superseded by deposition of Sumeini Group slope-facies lime mudstones with numerous intraformational truncation surfaces. Slope facies sedimentation then persisted along the length of the southern edge of the Musandam platform as the margin relaxed and subsided until the end of the Early Cretaceous. Uplift of the margin edge, related to changing regional compressive stresses as seafloor spreading increased in the South Atlantic and intra-oceanic subduction in Neo-Tethys initiated creation of the Semail Ophiolite, led first to collapse along the shelf edge, generating the thick and highly channelised post Aptian Ausaq Formation mega-breccias. This marked the end of the passive margin as a thick, Late Cretaceous predominantly shale and chert succession was deposited as the margin subsided with continent-ward migration of the foredeep that developed ahead of final emplacement of the Neo-Tethyan Hawasina Nappes and Semail Ophiolite during the Santonian.

Chemostratigraphy of the Upper Albian to mid‐Turonian Natih Formation (Oman) – how authigenic carbonate changes a global pattern

AbstractThe Oman Mountains preserve a Cretaceous continental margin transect with the proximal Arabian carbonate shelf and the adjacent deep Hawasina Basin. Today, the sediments from the Arabian Platform outcrop in the Oman Mountains (Jabal Akdhar and Saih Hatat) and in the Adam Foothills. The western part of the Adam Foothills provides insight into the evolution of a Late Cretaceous intra‐platform basin with organic‐rich sediments in the central part of this basin. The aims of this study are (a) to establish a biostratigraphy and chemostratigraphy of the Natih Formation and (b) to reconstruct depositional conditions of organic‐rich sediments in an intra‐platform basin during Cenomanian–Turonian times. The hypothesis that local black shale formation is an expression of global perturbations of the global carbon cycle will be tested. Reconstruction of the depositional history of the Arabian Platform and its intra‐platform basin within a global palaeoclimatic framework requires an accurate time frame. The Upper Albian to mid‐Turonian biostratigraphy of the Natih Formation has resulted in controversial age models that will be integrated into a solid chemostratigraphic framework with additional biostratigraphic data. A major positive δ13C excursion (+4·6‰) has been identified as of Middle Cenomanian age, which is confirmed by an ammonite datum. A second positive δ13C excursion (+4·5‰) following a major negative excursion (−1·0‰) confirms the existence of the Cenomanian/Turonian Boundary Event. The accurate chemostratigraphy and biostratigraphy confirms that major source rocks in the Mishrif‐Natih Basin precede OAE2. Low δ13C values measured in the sediments of the Natih B member are considered a consequence of diagenetic alteration. Elevated organic carbon contents and argillaceous sediments alternating with limestones resulted in diagenetic conditions favouring formation of authigenic calcite depleted in C‐13.

New hybodontiform and neoselachian sharks from the Lower Triassic of Oman

Elasmobranchs are reported for the first time from Lower Triassic deposits in Oman. The well-preserved remains consist of isolated teeth, dermal denticles and fin spines, recovered from conodont residues. The low-palaeolatitude sections consist of Lopingian–Olenekian shallow and pelagic carbonates in exotics, olistoliths and breccia blocks that have been redeposited in younger allochthonous strata of the Hawasina Basin throughout the Oman Mountains at Jabal Safra (olistoliths within the Jurassic Guwayza Formation, Olenekian), as well as at Wadi Alwa (exotic Alwa Formation, Lopingian–Olenekian) and Wadi Wasit Block (slope breccia in the Al Jil Formation, Induan), both of which occur in the Ba'id region. The recovered fauna contains a small number of pre-existing genera, but is mainly composed of new hybodont and neoselachian taxa. They are identified as: Omanoselache halli Koot & Cuny sp. nov., cf. Omanoselache sp., Safrodus tozeri Koot & Cuny gen. et sp. nov. and Polyfaciodus pandus Koot & Cuny gen. et sp. nov., based on the majority of the recovered dental remains. Spine fragments are identified as cf. Amelacanthus sp. This fauna represents the second published record of neoselachian teeth from the Induan and the most extensive record from the Lower Triassic in terms of abundance and diversity. The fauna is dominated by Neoselachii, whereas other Early Triassic faunas are hybodont-dominated, and histological study of the neoselachian enameloid significantly adds to our knowledge of the early stages of their evolution. All described taxa are new to the Oman fossil record and that of western Neotethys, apart from Omanoselache and Amelacanthus, which have been recognized from Wordian deposits, and Omanoselache is the second genus from Oman known to have survived the late Permian mass extinction. The level of faunal diversity recognized here is comparable to other Early Triassic faunas but is much reduced compared to the Wordian pre-extinctions fauna.http://zoobank.org/urn:lsid:zoobank.org:pub:E82E8BC2-1743-4883-B27B-3564DAAF2DF1

The Buday’ah Formation, Sultanate of Oman: A Middle Permian to Early Triassic oceanic record of the Neotethys and the late Induan microsphere bloom

The Middle Permian to Lower Triassic Buday’ah section, exposed in the Oman Mountains, is the first deep-sea section to be described in the Neotethys. The oceanic sediments were deposited along the southern Tethys margin in the newly formed Hawasina Basin. It is one of the few places where true Tethyan Permian radiolarites are exposed that allow the documentation of CCD evolution through time. The succession begins as oceanic crust pillow basalt with red ammonoid-rich pelagic limestone occurring both above and within inter-pillow cavities; the new occurrence of Clarkina postbitteri hongshuiensis indicates a late Capitanian age for the carbonate. The sharp change to overlying late Capitanian to Changhsingian radiolarite reflects rapid subsidence about 10 Myrs after initial continental breakup that resulted in the formation of the Neotethys Ocean. New conodonts indicate that the Permian–Triassic boundary succession occurs in the first platy lime mudstone beds above a Changhsingian siliceous to calcareous shale unit. The platy lime mudstone beds include an Upper Griesbachian bloom of calcite filled spheres (radiolarians?) that marks a potential world-wide event. New conodonts indicate an early Olenekian age for overlying grey papery limestone that are devoid of both macrofossils and trace fossils indicating that recovery from the Late Permian extinction has not yet progressed within this deep-water environment. δ 13C org, isotope values have not been disturbed and they show a negative shift just below the Permian–Triassic transition and a second one at the parvus zone level above. The Buday’ah succession may represent the most distal and probably deepest Permian and Lower Triassic depositional sequence within the basin.

Facies architecture of an isolated carbonate platform in the Hawasina Basin: The Late Triassic Jebel Kawr of Oman

In the oceanic realm of the southern Tethys, carbonate production of isolated platforms ceased after the end-Permian mass extinction and did not recover until the Late Triassic. The Misfah Formation (MF) at Jebel Kawr in the Oman Mountains is interpreted as a relic of such an isolated Late Triassic platform of the Hawasina Ocean, a part of the Neo-Tethys. Correlation of three sections at Jebel Kawr points to a sequence architecture with four third-order sequences (MF1–MF4). The maximum flooding surface (mfs) of MF3 can be correlated to the attached Arabian platform. The shallow-water carbonates of Jebel Kawr comprise a platform rim reef facies and bedded inner-platform facies characterized by stacked high-frequency cycles with subtidal to intertidal carbonate sequences. The depositional profile of this Late Triassic isolated platform evolved during Carnian and Norian time from a low-relief carbonate bank to a high-relief platform rimmed by reefs. The onset of the carbonate sedimentation is characterized by an initial phase with volcaniclastic interruptions, followed by a carbonate bank stage with a shallow subtidal to peritidal interior and marginal oolite shoals. In the Norian vertical accumulation caused an increase of the platform height and developed a relief along the margins that progressively increased through the aggrading reef stage. The possibility that a reef rim existed and was later removed by erosion is suggested by the Sint reef and olistoliths of similar reef limestones in the surrounding areas.

The Tethyan plume: geochemical diversity of Middle Permian basalts from the Oman rifted margin

According to palinspastic reconstructions, the Neo-Tethys opening took place during the Permian between the Cimmerian fragments in the north and the Indo-Arabian margin in the south. Igneous remnants of this opening are exposed in Oman within either the Hawasina nappes or the para-autochtonous Arabian platform exposed in the Saih Hatat tectonic window. They consist predominantly of pillowed basaltic flows among which three groups have been distinguished. Group 1 is tholeiitic and characterized by low TiO2 and incompatible trace element contents, and a large range of εNdi values. Group 1 basalts are associated with distal sediments and plot near the boundary of or within the MORB field in the Pb–Pb correlation diagrams and between the MORB and Bulk Silica Earth (BSE) fields in εNdi–(206Pb/204Pb)i diagram. Group 2 basalts are alkaline and differ from Group 1 ones by their higher TiO2, La and Nb contents, and lower and more homogeneous εNdi values (+3 to +5). Group 2 volcanics are similar to alkali basalts from oceanic islands and share with Group 1 similar initial Pb ratios. Group 3 consists of tholeiitic and alkali basalts which are interbedded either with carbonate-platform sediments from the Saih Hatat window or with distal sediments from the Hawasina Nappes. This group differs from Groups 1 and 2 by its low to negative εNdi (+1.6 to −2). Group 1 likely derived from the mixing of depleted and enriched sources while Group 2 derived exclusively from an enriched source. There is no indication that continental crust was involved in the genesis of both Groups 1 and 2. In contrast, the low to negative εNdi values of Group 3 suggest that the magmas of this group were contaminated by the Arabian continental crust during their ascent. The geochemical features of the Middle Permian plume-related basalts suggest thus that the basement of the Hawasina basin was not genuine oceanic crust but either the thinned Arabian rifted continental margin or the continent–ocean transition zone of the Neo-Tethys.

The Tethyan plume: geochemical diversity of Middle Permian basalts from the Oman rifted margin

According to palinspastic reconstructions, the Neo-Tethys opening took place during the Permian between the Cimmerian fragments in the north and the Indo-Arabian margin in the south. Igneous remnants of this opening are exposed in Oman within either the Hawasina nappes or the para-autochtonous Arabian platform exposed in the Saih Hatat tectonic window. They consist predominantly of pillowed basaltic flows among which three groups have been distinguished. Group 1 is tholeiitic and characterized by low TiO 2 and incompatible trace element contents, and a large range of εNd i values. Group 1 basalts are associated with distal sediments and plot near the boundary of or within the MORB field in the Pb–Pb correlation diagrams and between the MORB and Bulk Silica Earth (BSE) fields in εNd i–( 206Pb/ 204Pb) i diagram. Group 2 basalts are alkaline and differ from Group 1 ones by their higher TiO 2, La and Nb contents, and lower and more homogeneous εNd i values (+3 to +5). Group 2 volcanics are similar to alkali basalts from oceanic islands and share with Group 1 similar initial Pb ratios. Group 3 consists of tholeiitic and alkali basalts which are interbedded either with carbonate-platform sediments from the Saih Hatat window or with distal sediments from the Hawasina Nappes. This group differs from Groups 1 and 2 by its low to negative εNd i (+1.6 to −2). Group 1 likely derived from the mixing of depleted and enriched sources while Group 2 derived exclusively from an enriched source. There is no indication that continental crust was involved in the genesis of both Groups 1 and 2. In contrast, the low to negative εNd i values of Group 3 suggest that the magmas of this group were contaminated by the Arabian continental crust during their ascent. The geochemical features of the Middle Permian plume-related basalts suggest thus that the basement of the Hawasina basin was not genuine oceanic crust but either the thinned Arabian rifted continental margin or the continent–ocean transition zone of the Neo-Tethys.

Eoalpine (Cretaceous) evolution of the Oman Tethyan continental margin: insights from a structural field study in Jabal Akhdar (Oman Mountains)

ABSTRACT A structural study in Jabal Akhdar (an autochthonous window in the Oman Mountains) shows that the thrusts and imbrications, mapped in the Permian-Cretaceous formations of the Arabian Platform, have a vergence top to the north-northeast and are associated with a regional cleavage resulting from a ductile shear deformation of the same vergence. This deformation affects the entire autochthonous unit, from the southwestern edge of Jabal Akhdar to the northeastern edge of Saih Hatat, with an increasing strain intensity towards the northeast. The same domain is also affected by a HP/LT metamorphism with a northeastward increase from chlorite facies to blueschist and eclogite facies, i.e. characteristic of a northeast-dipping subduction. However, the retrograde character of the metamorphic parageneses associated with the ductile shear, as well as its north-northeast vergence, indicate that this deformation is linked to the exhumation of the autochthon during the Campanian. These observations have been synthesised in a new lithospheric-scale interpretation of the geodynamic development of the North Oman continental margins during the middle to late Cretaceous. The sequential evolution along a transect passing from southwest of Jabal Akhdar to northeast of Muscat can be summarised as follows: An intra-continental subduction zone affected the autochthon of the Arabian Platform with a basal rupture lying in the proximal part of the continental margin, to the south of the northern edge of the carbonate platform. A North Muscat microplate was created between the intra-continental subduction zone and the intra-oceanic subduction that gave rise to the Samail Ophiolite; this microplate includes the outer part of the Arabian Platform, the continental slope and the entire Hawasina Basin. From Early Turonian to Late Santonian the obduction and the intra-continental subduction were coeval and parallel. The northeast edge of the North Muscat microplate plunged below the Samail Nappe whilst the emergent southwest part overthrust the innermost parts of the Arabian Platform. The leading edge of the Samail and Hawasina Nappes advanced across the southwestern border of the North Muscat microplate just before obduction and intra-continental subduction ceased at the Santonian–Campanian boundary. Towards the end of the intra-continental subduction, the lower part of the crust of the subducted autochthon delaminated the upper part, marking the first stage of the metamorphic rocks exhumation. From Early Campanian to Early Maastrichtian, the North Muscat microplate moved to the northeast, its northeastern edge sinking by gravity into the asthenosphere. The subducted autochthon rose up, and came into contact with the base of the obducted units. The resulting uplift of the ophiolite nappes produced its emergence and partial erosion. Local crustal thickening, related to the lithospheric delamination, caused doming at Saih Hatat and subsequent erosion that locally extended to the pre-Permian sedimentary basement during the Early Maastrichtian. The present day domal shape of Jabal Akhdar is however related to Tertiary tectonic events.

Middle Permian plume‐related magmatism of the Hawasina Nappes and the Arabian Platform: Implications on the evolution of the Neotethyan margin in Oman

Permian pillow basalts are commonly found in Oman either at the base of the Hawasina Nappes or within the Arabian Platform successions exposed in the Saih Hatat tectonic window. There is an ongoing debate on whether these lavas include normal mid‐oceanic ridge basalts (NMORB) witnessing the Permian opening of the Neotethys or if they are plume‐related magmas that are emplaced either on the Arabian Platform or on its thinned continental margin. We sampled these lavas from several paleontologically dated middle Permian sites. Four of them (Buday'ah, Rustaq, Al Ajal, and Wadi Wasit) are located within the Hawasina Nappes and are exposed as thrust slices overlain by the Samail Nappe, and one (Wadi Aday) is within the Arabian Platform units and is exposed in the Saih Hatat window. These lavas are associated with marine sediments deposited in environments ranging from proximal (Saih Hatat, Wadi Wasit, and base of the thrust pile of Al Ajal) to distal (Buday'ah, Rustaq, and top of the Al Ajal pile) with respect to the Arabian Platform. Major and trace element features of the basalts allow two groups to be recognized. Enriched high‐Ti basalts similar to alkali basalts from intracontinental traps, rifted continental zones, and oceanic islands are exposed in Wadi Aday, Wadi Wasit, and at the structural base of the Al Ajal pile. Moderately enriched to slightly depleted low‐Ti tholeiitic basalt magmas resembling the low‐Ti flood basalts and those from seaward dipping reflector sequences are represented in Wadi Al Hulw in Saih Hatat, Buday'ah, Rustaq, and at the top of the Al Ajal thrust pile. Both groups show distinct plume‐related trace element signatures, and they do not include typical NMORB. Although emplaced in shallow to deep submarine environments, these basalts provide no direct evidence for a Neotethyan seafloor‐spreading event in the Hawasina Basin. Instead, they were likely erupted through the crust of the already rifted and drowned Arabian continental margin. Thus, despite their characteristic plume‐related geochemical signatures, the middle Permian basalts from Oman were not likely emplaced during the evolution of a typical volcanic rifted margin. We suggest that they originated from a mantle plume which ascended beneath the Arabian passive margin well after the initiation of seafloor spreading of the Neotethys.

A unique Permian–Triassic boundary section from the Neotethyan Hawasina Basin, Central Oman Mountains

In the Wadi Wasit area (Central Oman Mountains), Dienerian breccias are widespread. These breccias consist mostly of Guadalupian reefal blocks, often dolomitised, and some rare small-sized blocks of lowermost Triassic bivalve-bearing limestones. A unique block, with a size of about 200 m 3, including Permian and earliest Triassic faunas has been studied in detail. The so-called Wadi Wasit block consists of three major lithological units. A basal unstratified grey limestone is rich in various reef-building organisms (rugose corals, calcareous sponges, stromatoporoids) and has been dated as Middle Permian. It is disconformably overlain by well- and thin-bedded light grey to yellowish coloured limestones rich in molluscs. Two major lithologies (Coquina Limestone respectively Bioclastic Limestone unit) characterise the shelly limestones, their contact seems gradual. These two units are well-dated; they are of Griesbachian age and contain three conodont zones, the Parvus Zone, the Staeschei Zone and the Sosioensis Zone, and two ammonoid zones, the Ophiceras tibeticum Zone and an ‘unnamed interval’. The third unit consists of a grey marly limestone containing Neospathodus kummeli (basal Dienerian). It is the first record of well-dated basal Triassic sediments in the Arabian Peninsula. The Coquina Limestone is dominated by the bivalve Promyalina with some Claraia and Eumorphotis. This bivalve association is interpreted as a pioneering opportunistic assemblage. Towards the top of the Bioclastic Limestone unit, the faunal diversity increases and contains probably more than 20 taxa of bivalves, microgastropods, crinoids, brachiopods, ammonoids, echinoid spines, ostracods and conodonts. The generic diversity of this biofacies exceeds by far any other Griesbachian assemblage known. Our data give new evidence for the geodynamical history for the distal carbonate shelf bordering the Hawasina Basin. A break in the sedimentation characterises the Late Permian. The basal Triassic shows a steady transgression and the breccias may record a distinct gravitational collapse of platform margins linked with sea-level low stand at the end of Induan time (late Dienerian–basal Smithian). δ 13C carb isotopic analyses were performed and yield typical Permian values of around 4‰ for the Reefal Limestone, with a strong negative shift across the Permian–Triassic boundary. During the Griesbachian values shift positively from 0.5 to 3.1‰ parallel to an increase in faunal diversity and probably primary productivity. The detailed faunal analysis and the discovery of an unexpected diversity give us a new understanding of the recovery of the Early Triassic marine ecosystem.

The break-up of East Gondwana along the northeast coast of Oman: evidence from the Batain basin

Recent detailed studies on the Batain nappes (northeast coast of Oman), which represent a special part of the so-called ‘Oman Exotics’, have led to a better understanding of the Neotethyan geo-dynamic evolution. The Batain Exotics bear witness to volcanic activity, sea-level changes, tectonic instability, rifting and oceanization along the Eastern Oman margin during Late Palaeozoic and Mesozoic times. They allow definition of the Batain basin as an aborted Permian branch of Neotethys. This marine basin was created in Early Permian times extending southward to the East African/ Madagascar region and was linked to the Karoo rift system. The presented revised classification of the Batain nappes considers the Batain basin to be no longer a part of the Hawasina basin and the Neotethyan margin proper. We attribute the Batain basin to a Mozambique–Somali–Masirah rift system (Somoma). This system started in Early Permian, times, creating a marine basin between Arabia and India/Madagascar; rifting in the Late Triassic and oceanization during Late Jurassic times led to the separation of East Gondwana.

Detrital chromites in metasediments of the East-Arabian continental margin in the Saih Hatat area: constraints for the palaeogeographic setting of the Hawasina and Semail basins (Oman Mountains)

In Oman, the convergence between Arabia and Eurasia resulted in the Late Cretaceous overthrusting of oceanic crust and mantle lithosphere onto the Arabian continental margin. During this compressional event, a part of the continental plate was subducted to a depth of more than 60 km (0.5 GPa, 250–350 °C to more than 2.0 GPa, 550 °C) resulting in progressive metamorphism of the continental margin sediments, well exposed in the Saih Hatat tectonic window, northeastern Oman Mountains. We attempt to constrain the possibility of one continuous history of extension (starting along the east Arabian continental margin in the Permian) that was followed by one continuous history of convergence starting at 90 Ma near a dead oceanic ridge. This compression resulted in the observed progressive metamorphism by ophiolite overthrusting onto the continental margin. Constraining arguments are the palaeogeographic setting before ophiolite obduction of the As Sifah units and the Hawasina Complex near Ghurba. Detrital chromites in the Triassic–Cretaceous metasediments of the Hawasina Complex are compared with magmatic Semail chromites, and the whole-rock chemistry of these metasediments and associated metabasites are investigated. In contrast to former hypotheses, differences in the chemical composition between detrital and magmatic chromites, and the probable origin of all detrital chromites in the Hawasina Basin from Permian age oceanic rocks, suggest that the high-pressure metamorphic sediments of As Sifah can be considered as part of the basal deposits of the Hawasina Basin.

West‐northwest directed obduction of the Batain Group on the eastern Oman continental margin at the Cretaceous‐Tertiary boundary

The Batain coast area in eastern Oman is dominated by allochthonous Permian to Late Maastrichtian sedimentary and volcanic rocks (Batain Group), unconformably overlain by neoautochthonous Tertiary sediments. The allochthonous rocks of the Batain coast were previously attributed to the Hawasina complex, the Permian to Coniacian/Santonian sedimentary infill of the neo‐Tethyan Hawasina basin off northern Oman. Previous structural interpretations suggested that the Batain Group, along with the Hawasina complex and the Semail ophiolite, was obducted in the Coniacian to Campanian from NE to SW onto the northern Oman continental margin. Results of our work in the Batain area differ from previous interpretations, with most significant differences concerning timing and direction of obduction. Our results show that WNW directed tectonic movements formed a fold‐and‐thrust belt and led to the obduction of allochthonous rocks onto the east Oman continental margin during latest Maastrichtian/earliest Paleocene times. This is coeval with emplacement of ophiolitic fragments along the eastern coast of Oman (eastern ophiolite belt) but is about 15–20 Myr later than emplacement of Hawasina complex and Semail ophiolite in northern Oman. Postemplacement structural evolution during the Tertiary involved intraplate extension, possibly reflecting the Red Sea/Gulf of Aden opening, and late Tertiary shortening related to convergence between Arabia and Eurasia. Late Tertiary contractional deformation resulted in refolding of the Batain nappes and in folding of the overlying Tertiary sediments. A palinspastic reconstruction of the Batain area indicates that the Permian to Upper Cretaceous sediments were formerly deposited in the Batain basin, a part of the proto‐Indian Ocean, along the present‐day eastern Oman margin. This leads us to propose that Permian breakup of Gondwanaland created both continental margins of Oman and led to the opening of two major basins: the neo‐Tethyan Hawasina basin in the north and the proto‐Indian Ocean Batain basin in the east, the latter separating Arabia from greater India.

Upper Triassic reefs of the Oman Mountains: Data from the South Tethyan margin

The Upper Triassic reefal limestones of the Oman Mountains were investigated with respect to their microfacies, palaeontology and community structure. The reef fauna described and figured for the first time occurs in parautochthonous slope deposits of the Arabian platform (Sumeini Group) and in allochthonous reefal blocks (‘Oman Exotics’, Hawasina Complex). The ‘Oman Exotics’ are tectonically dislocated blocks, derived from isolated carbonate platforms on seamounts in the Hawasina basin or in the South Tethys Sea.

Geochemistry of metamorphosed mafic rocks from Saih Hatat: pre-obduction history of NE Oman

Field and petrological data, combined with major, trace and rare earth element analysis of mafic rocks that structurally underlie the Semail ophiolite in Saih Hatat, have led to their subdivision into five groups: (a) crossite-bearing mafic schists that represent metamorphosed within-plate alkali basalts, erupted in a Proterozoic continental rift or ocean basin setting; (b) greenschists, blueschists, garnet-blueschists, clinopyroxene-rich layers and eclogites, representing metamorphosed Permian basaltic flows and tuffs with enriched-MORB affinities; (c) crossite-bearing metavolcanics, representing alkali basalts, trachyandesites and dacites erupted on oceanic islands in a small ocean basin or through rifted continental crust during the late Permian; (d) lawsonite- and pumpellyite-bearing metavolcanic blocks incorporated in a Cretaceous tectonic melange, and originally erupted as alkali basalts on oceanic islands in the Hawasina basin; and (e) unmetamorphosed tholeiites formed at a spreading centre in the Hawasina basin and preserved in the Hawasina thrust sheets. A reconstruction of the tectonic history of Saih Hatat based on these data suggests that continental rifting took place in the Permian, developing two distinct basins separated by rifted continental material. Some of the basaltic blocks that formed in the outboard Hawasina basin were tectonically dislocated and incorporated into a tectonic melange formed in a foredeep during the early stages of obduction. Emplacement of the Semail ophiolite onto the continental margin resulted in high-pressure, low-temperature metamorphism of this melange and the underlying units.