Structural evolution of Jabal Qumayrah: A salt-intruded culmination in the northern Oman Mountains

ABSTRACT The Jabal Qumayrah area of the northern Oman Mountains records the evolution and subsequent destruction of a Mesozoic passive continental margin in the Oman segment of the Neo-Tethys Ocean, followed by the re-establishment of a passive margin, punctuated by phases of Tertiary compression. Almost uniquely along the Oman Mountains, it also contains intrusions of salt. Detachment of oceanic sediments and volcanics during the early phases of NE-directed subduction beneath the nascent Semail Ophiolite created an in-sequence stack of imbricated thrust units comprising distal trench units (Haybi Complex), and deep-ocean and continental rise sediments derived from the Mesozoic Oman margin (the Hawasina Complex). These were emplaced onto the depressed margin beneath and ahead of the ophiolite during its obduction in the Cenomanian– Coniacian. The Mesozoic continental slope sediments of the Sumeini Group had already been largely over-ridden by the more distal thrust sheets when the Hawasina sole thrust propagated into those sediments. This detached a Sumeini Group thrust sheet, which was transported westward for at least 7 km, carrying with it the overlying Hawasina thrust stack. Structurally lower parts of the Hawasina thrust stack (Hamrat Duru Group) also extended ahead of the Sumeini Group thrust sheet, but they were not restacked with it, indicating motion continued along this part of the Hawasina sole thrust. Further footwall collapse detached at least one more imbricate within the Sumeini Group and the combined thrust stack was then folded along a N-S axis, possibly above a frontal ramp. This was associated with complex out-of-sequence forward and back-thrusting at the lower structural levels. A right-lateral scissors fault developed at right angles to the direction of nappe transport, associated with normal faulting down-to-south. Late-stage culmination within the nappe pile created an asymmetrical west-facing dome, around which the structurally overlying Hawasina thrust sheets are folded. Passive margin sedimentation was re-established in the Campanian–Maastrichtian following subsidence of the locally emergent nappe pile and was dominated by carbonate sedimentation with little clastic input from the ophiolite or Hawasina sediments. Stable sedimentation persisted until Oligocene–Miocene compression, synchronous with the Zagros compressional event in Iran, resulted in west-facing folding along the western side of the northern Oman Mountains and their subsequent uplift. The Jabal Qumayrah massif preserves a salt intrusion composed of gypsum and anhydrite, the top of which is now exposed in the centre of the culmination. The origin of the salt remains unclear and investigations continue. Possible sources include the extension of the major regional salt basins found in the foreland, in particular those at the Ediacaran/Cambrian boundary (Ara Group), beneath the Hawasina Nappes and Semail Ophiolite. Alternatively, evaporitic basins may have developed locally along the edge of the proto Neo-Tethyan margin during the earliest rifting phase, beneath what became the continental slope deposits, although there is little evidence for these elsewhere in the autochthonous shelf succession.

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Structure, strain and AMS of the Uzunakhmat thrust sheet (Talas Range, Kyrgyz North Tian Shan)

10.5194/egusphere-egu2020-726 ◽

2020 ◽

Author(s):

Anastasia Kushnareva ◽

Artem Moskalenko ◽

Alexander Pasenko

Keyword(s):

Cross Section ◽

Cross Sections ◽

Structural Evolution ◽

Middle Part ◽

Tien Shan ◽

Initial Shape ◽

Thrust Sheet ◽

Structural Style ◽

Thrust Sheets ◽

Tian Shan

The Talas Range forms the northwest part of the Caledonides of the Northern Tian Shan. Based on differences in the structural style, metamorphism and sedimentary successions, three thrust sheets have been identified &#8211; the Uzunakhmat, Talas, and Kumyshtag thrust sheets. The Talas and Kumyshtag thrust sheets consist of Neoproterozoic-Ordovician terrigenous and carbonate rock units, whereas the Uzunakhmat thrust sheet consists of Neoproterozoic terrigenous rocks metamorphosed up to greenschist facies. The Uzunakhmat thrust sheet is separated from the Talas and Kumyshtag thrust sheets by the southwest-dipping Central Talas thrust (CTT). The dextral strike-slip Talas-Fergana Fault bounds the Uzunakhmat thrust sheet in the southwest. The main deformation events occurred in the Middle-Late Ordovician.Structural and strain studies were done along profiles normal to the strike of folds and faults and located in the northwest and southeast parts of the Uzunakhmat thrust sheet. We also incorporate in our study structural profile in the central part of the Uzunakhmat thrust sheet, documented by Khudoley (1993) and Voytenko & Khudoley (2012).The main strain indicators were detrital quartz grains in sandstones. Rf/&#966; and Normalized Fry methods were used to identify the amount of strain. Oblate ellipsoids predominate with Rxz values varying mostly from 1,6 to 2,4. Long axes of strain ellipsoids are sub-horizontal with the southeast to east-southeast trend. Similar trends have long axes of the anisotropy magnetic susceptibility ellipsoid being parallel to fold axes, cleavage-bedding intersection and mineral lineation as well as the trend of the major thrusts, including CTT.The modern shape of the Uzunakhmat thrust sheet is similar to an elongated triangle, pinching out northwest and expanding southeast. Cross-section balancing corrected for the amount of strain shows along-strike decreasing of shortening in the southeast direction. Total shortening varies from 35% to 55% between sections located about 15 km from each other. Such significant variation in shortening corresponds to variation in structural style with much more tight folds and more numerous thrusts for cross-sections with a higher amount of shortening. However, the restored length of all cross-sections is quite similar pointing to the approximately rectangular initial shape of the Uzunakhmat thrust sheet. Our interpretation is that during the Caledonian tectonic events, the Uzunakhmat thrust sheet was displaced in the northwest direction with accompanied thrusting and folding of rock units within the thrust sheet. These deformations formed the modern shape of the thrust sheet in accordance with the amount of shortening detected by cross-section balancing. This interpretation also implies that modern erosion did not significantly affect shape of the Uzunakhmat thrust sheet formed after the Caledonian deformation.Khudoley, A.K., 1993. Structural and strain analyses of the middle part of the Talassian Alatau ridge (Middle Asia, Kirgiystan). J. Struct. Geol. 6, 693&#8211;706.Voytenko N.V., Khudoley A.K. Structural evolution of metamorphic rocks in the Talas Alatau, Tien Shan, Central Asia: Implication for early stages of the Talas-Ferghana Fault. // C. R. Geoscience. 2012. V. 344. P. 138&#8211;148.

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Chapter 5 Tectonic evolution of the Oman Mountains

Geological Society London Memoirs ◽

10.1144/m54.5 ◽

2021 ◽

Vol 54 (1) ◽

pp. 67-103

Author(s):

Andreas Scharf ◽

Frank Mattern ◽

Mohammed Al-Wardi ◽

Gianluca Frijia ◽

Daniel Moraetis ◽

...

Keyword(s):

Subduction Zone ◽

Late Cretaceous ◽

Tectonic Evolution ◽

Oceanic Lithosphere ◽

Passive Margin ◽

Arabian Plate ◽

Continental Lithosphere ◽

Oman Mountains ◽

Semail Ophiolite ◽

Arabian Platform

AbstractThe 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.

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Structure of the Hawasina Window culmination, central Oman Mountains

Transactions of the Royal Society of Edinburgh Earth Sciences ◽

10.1017/s0263593300010798 ◽

1986 ◽

Vol 77 (2) ◽

pp. 143-156 ◽

Cited By ~ 32

Author(s):

M. P. Searle ◽

D. J. W. Cooper

Keyword(s):

Structural Analysis ◽

Continental Margin ◽

Cross Sections ◽

Structural Evolution ◽

Complex Model ◽

Shelf Edge ◽

Oman Mountains ◽

Stacking Order ◽

Structural History ◽

Semail Ophiolite

ABSTRACTDetailed mapping, stratigraphic logging and structural analysis of the Hawasina Window culmination in the central Oman Mountains of Arabia reveals an extremely complex thrust geometry and structural history. The initial thrust sequence involved a southwestward propagating stacking during telescoping of the Arabian continental margin slope (Sumeini complex), and time-equivalent, more distal Tethyan basin (Hawasina and Haybi complexes) facies rocks. The Semail thrust, carrying the 12 km-thick ophiolite sequence, progressively overlaps Haybi and Hawasina duplexes towards the SW. Late stage “leap-frog” thrusts have punched Sumeini duplexes higher up into the earlier thrust stack locally reversing the normal stacking order. SW-directed thrusts and SW-facing folds in the SW and NE-directed backthrusts and NE-facing backfolds in the NE have created a fan structure cored by the Jebel Rais “pop-up” composed of Sumeini slope facies rocks.The palaeogeographic presence of a large NE-facing promontory in the Cretaceous shelf edge is inferred beneath the Window. The frontal ramp of this promontory was sufficiently large to inhibit the overthrusting of large volumes of Hawasina and Haybi complex rocks. The whole central part of the Window shows NE-facing and verging backfolds and backthrusts affecting all duplexes from the lowest Sumeini up to the Semail ophiolite. The promontory is bounded by major lateral ramps to the NW (Wadi Shafan area) and SE (Jebel Milh area). A map and four balanced cross-sections are presented here to promote a complex model for the structural evolution of the Hawasina Window.

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K—Ar ages of alkaline igneous rocks in the northern Oman mountains, NE Arabia, and their relations to rifting, passive margin development and destruction of the Oman Tethys

Geological Magazine ◽

10.1017/s0016756800026844 ◽

1982 ◽

Vol 119 (5) ◽

pp. 497-503 ◽

Cited By ~ 15

Author(s):

S. J. Lippard ◽

D. C. Rex

Keyword(s):

Upper Cretaceous ◽

Oceanic Lithosphere ◽

Passive Margin ◽

Igneous Rocks ◽

Oman Mountains ◽

Intrusive Rocks ◽

Igneous Activity ◽

Ophiolite Emplacement ◽

Alkaline Activity ◽

Semail Ophiolite

SummaryK–Ar ages of biotites from a variety of alkaline volcanics and minor intrusive rocks in the nothern Oman mountains allochthon give a range of ages from Triassic (230 Ma) to mid Cretaceous (92 Ma) and represent igneous activity on the Oman continental margin throughout the Mesozoic. This was a passive margin destroyed by the emplacement across it of a pile of nappes in the late Cretaceous, including a largely intact thrust sheet of Upper Cretaceous oceanic lithosphere (the Semail ophiolite). Biotite ankaramite dykes, cutting compositionally similar volcanics, in the thrust complex immediately beneath the ophiolite, give Triassic ages and are related to the rifting and break-up of the northeast Arabian margin at the beginning of formation of the Oman Tethys. Mid Cretaceous (Cenomanian–Turonian) ages are mostly recorded from the northern part of the mountains where there are alkaline tuffs in a sedimentary melange. They are approximately the same age as the ophiolite and may be related to tectonic instability of the Oman margin immediately prior to ophiolite emplacement. Alkaline sills, intrusive into a variety of rocks, including Triassic volcanics, give Jurassic and Cretaceous ages and are interpreted as periodic alkaline activity on the Oman margin throughout passive margin development.

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Origin of gypsiferous intrusions in the Hawasina Window, Oman Mountains: Implications from structural and gravity investigations

GeoArabia ◽

10.2113/geoarabia1902107 ◽

2014 ◽

Vol 19 (2) ◽

pp. 107-132

Author(s):

Mohammed Y. Ali ◽

David J.W. Cooper ◽

Michael P. Searle ◽

Ali Al-Lazki

Keyword(s):

Upper Cretaceous ◽

Country Rock ◽

Isotope Analysis ◽

Arabian Plate ◽

Fine Grained ◽

Oman Mountains ◽

South Central ◽

Thrust Sheets ◽

Semail Ophiolite ◽

Structural Levels

ABSTRACT Gypsiferous intrusions are exposed in road-cuts in the south-central Hawasina Window in the central Oman Mountains. They are located at lower structural levels in the allochthonous Hawasina Complex and lie along faults that cut Upper Cretaceous structures related to the obduction of the Semail Ophiolite and Hawasina Complex deep-water sediments onto the Arabian Plate. The intrusions form gypsiferous pods that are up to 200 m long, in which the gypsum occurs as a dark, fine-grained matrix that contains a pervasive network of anastomosing veins of gypsum and anhydrite. The intrusions contain abundant sub-angular to sub-rounded litharenites, and less common fragments of chert and fine-grained limestone. Although these clast types are undated, their petrographic characteristics suggest they originate from the local Hawasina (Hamrat Duru Group) country rock. Very well-rounded pebbles and cobbles of feldspathic litharenites, some of which show a well-developed cleavage, and rarer cobbles of well-rounded vein quartz appear to have come from the basement. Gravity investigations indicate salt diapirs are not present beneath the Hawasina Window. Instead, the gypsiferous intrusions are interpreted as having been brought up from depth during compression to form disconnected pods along deep-rooted faults, bringing with them small amounts of the basement country rock. Strontium isotope analysis and regional considerations, in particular the distribution, age and nature of other evaporite units on the eastern Arabian Plate, suggest the gypsum may have its origins in the Neoproterozoic (Ediacaran) to lower Cambrian Ara Group evaporites, perhaps from a previously unknown extension of the Fahud Salt Basin beneath the Hawasina thrust sheets.

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Salt intrusions in Jabal Qumayrah, northern Oman Mountains: Implications from structural and gravity investigations

GeoArabia ◽

10.2113/geoarabia1802141 ◽

2013 ◽

Vol 18 (2) ◽

pp. 141-176 ◽

Cited By ~ 1

Author(s):

David J.W. Cooper ◽

Mohammed Y. Ali ◽

Michael P. Searle ◽

Ali I. Al-Lazki

Keyword(s):

Late Cretaceous ◽

Host Rock ◽

Central Complex ◽

Salt Diapir ◽

Salt Intrusion ◽

Salt Domes ◽

The North ◽

Oman Mountains ◽

High Level ◽

Semail Ophiolite

ABSTRACT The Jabal Qumayrah area, 50 km ESE of Al Ain and Buraimi, preserves a culmination of Jurassic and Cretaceous continental slope deposits (Sumeini Group) that was emplaced during the Late Cretaceous onto the Oman margin with other Neo-Tethyan units and the Semail Ophiolite. Almost uniquely in the Oman Mountains, Jabal Qumayrah also contains outcrops of gypsum and anhydrite that occur as a central complex from which laterally discontinuous linear and arcuate outcrops extend up to 4 km to the northwest and south. The gypsum and anhydrite bodies contain sedimentary clasts and rafts, which show close affinities with the local Sumeini Group host rock. There are no sedimentary features that indicate the evaporites were deposited in situ, either as part of, or unconformably overlying the Sumeini Group. Boundaries with the host rock are either high-angle faults or steep and intrusive, with significant dissolution of host rock limestones. Two gravity transects across the area indicate the areas of gypsum and anhydrite lie on a gravity low, compatible with an elongated, high-level body concentrated along the main N-S axis of the Jabal Qumayrah dome. Taken together, these features point towards an intrusive origin for the evaporite bodies in Jabal Qumayrah. While the sub-surface is poorly constrained, the central complex is interpreted as representing the deeply weathered top of a salt diapir, whose emplacement had a strong tectonic fault-driven component. The smaller, discontinuous exposures to the northwest and south are interpreted as pods of gypsum and anhydrite that were injected along faults. The absence of other evaporite minerals, in particular halite, is attributed to deep weathering and dissolution similar to that seen at the surface-piercing salt domes of the Ghaba Salt Basin in central Oman. In the absence of unequivocal dating evidence, the regional context suggests the intrusion may be derived from evaporites within the Ediacaran–Early Cambrian Ara Group. These form large deposits in the Fahud and Ghaba salt basins to the southwest of the Oman Mountains and the Hormuz Salt Basin to the north. The Jabal Qumayrah area may represent another, smaller basin or an extension to the Fahud Basin. The Jabal Qumayrah intrusion does not contain rafts of Ara Group limestones, which characterise the salt diapirs of the Ghaba Salt Basin, but this is not considered diagnostic. Other regional evaporite units of Permian to Jurassic ages do not extend into the area of the Oman Mountains and are thus unlikely potential sources. There is no evidence to suggest the Jabal Qumayrah culmination was thrust over Cenozoic evaporites and this potential source is also discounted. The timing of intrusion is constrained by the boundary faults, which cut across and thus post-date structures related to the Late Cretaceous emplacement of the Sumeini Group of Jabal Qumayrah. There is no evidence of any movement since the unroofing and exposure of the salt intrusion, which began in the Late Miocene.

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The Caledonian thin-skinned thrust belt of Kronprins Christian Land, eastern North Greenland

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/geusb.v6.4817 ◽

2004 ◽

Vol 6 ◽

pp. 41-56 ◽

Cited By ~ 8

Author(s):

A.K. Higgins ◽

N.J. Soper ◽

M. Paul Smith ◽

Jan A. Rasmussen

Keyword(s):

Passive Margin ◽

Thrust Belt ◽

Thrust Sheet ◽

East Greenland ◽

Total Displacement ◽

Thrust Sheets ◽

Extreme North ◽

North Greenland

Kronprins Christian Land in the extreme north of the East Greenland Caledonides, exposes a thin-skinned thrust belt up to 50 km wide developed in Ordovician–Silurian platform limestones and dolostones of the Iapetus passive margin. This thrust belt is characterised by a series of SSW–NNE-trending and east-dipping Caledonian thrusts with westward displacements of generally a few kilometres each. It passes westwards into undisturbed autochthonous foreland. Based on a line and area restoration, total displacement along a well-exposed WNW–ESE section through the thrust belt amounts to 17.6 km, which represents a shortening of 45% in the line of section. Biostratigraphic control in the limestone and dolostone succession is based on conodonts and macrofossils. The alteration colours of the conodonts provide estimates of maximum burial temperatures, which show that the thickness of the overlying thrust sheets ranged from about 6 to 12.5 km from west to east across the thrust belt. Since the estimated former thickness of the Vandredalen thrust sheet above the thin-skinned parautochthonous thrust belt is insufficient to yield the temperatures attained, higher thrust sheets must once have extended across the region.

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Chapter 2 Tectonostratigraphy of the eastern part of the Oman Mountains

Geological Society London Memoirs ◽

10.1144/m54.2 ◽

2021 ◽

Vol 54 (1) ◽

pp. 11-47 ◽

Cited By ~ 1

Author(s):

Andreas Scharf ◽

Frank Mattern ◽

Mohammed Al-Wardi ◽

Gianluca Frijia ◽

Daniel Moraetis ◽

...

Keyword(s):

Deep Sea ◽

Upper Cretaceous ◽

Sedimentary Rocks ◽

Passive Margin ◽

Quaternary Deposits ◽

Oman Mountains ◽

Tethys Ocean ◽

Carbonate Formations ◽

Semail Ophiolite ◽

Stratigraphic Chart

AbstractThis chapter provides comprehensive descriptions of 52 numbered formations/rock units of the Southeastern Oman Mountains, based on available literature. The oldest eight siliciclastic and carbonate formations are positioned below the ‘Hercynian’ Unconformity. The overlying formation (9–16) mostly represent carbonates which accumulated in a passive margin platform setting during or after the opening of the Neo-Tethys Ocean. The passive margin slope and platform collapsed during the late Cretaceous because of the obduction of the Semail Ophiolite along with the deep marine Hawasina sedimentary rocks. The collapsing passive margin interval was recorded within the syn-obductional Aruma Group (17; Muti Formation). Above this formation are the allochthonous units (18–42) of the tectonically lower Hawasina deep-sea basin and the structurally overlying Semail Ophiolite. The former contains Permian to Upper Cretaceous formations, while the latter is Cenomanian in age. Above the allochthonous rocks, the Neo-autochthonous formations were deposited, starting with the post-obductional uppermost Cretaceous Aruma Group (43; Al-Khod Formation) until the Quaternary deposits (52). All these formations/rock units are depicted on an accompanying map and stratigraphic chart.

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Structural architecture of a thin-skinned imbricate fan: Evidence from Mesozoic deepwater sediments in the Jabal Wahrah area of the central Oman Mountains

GeoArabia ◽

10.2113/geoarabia160117 ◽

2011 ◽

Vol 16 (1) ◽

pp. 17-42

Author(s):

David J.W. Cooper

Keyword(s):

Leading Edge ◽

Trailing Edge ◽

Second Stage ◽

Oman Mountains ◽

Third Phase ◽

The Face ◽

Thrust Sheets ◽

Structural Architecture ◽

Semail Ophiolite ◽

Structural Levels

ABSTRACT In the central Oman Mountains, Mesozoic deepwater off-margin sediments of the Hawasina Complex were emplaced from the northeast onto the Oman continental margin during the Late Cretaceous obduction of the Semail Ophiolite. Detailed field mapping and structural investigation have shown that, in the area studied, margin-ward detachment of continental rise sediments (Hamrat Duru Group) created two major thrust units in the face of the advancing ophiolite and subduction zone wedge of sediments from more distal parts of the Hawasina Ocean. The upper unit is preserved in jabals Wahrah and Hurah as a wedge-shaped sheet, restoring to at least 60 km perpendicular to the line of emplacement but only about 500 m thick at its maximum. Its thinner leading edge (Jabal Wahrah) comprises a classic thin-skinned imbricate fan which is divided into five laterally continuous structural zones with finer-grained structures that are influenced by local stratigraphical variations in its Early Jurassic to Early Cretaceous section. The rear part of the thrust sheet (Jabal Hurah) behaved more rigidly, reflecting a thicker and more competent sedimentary sequence spanning the Early Triassic to ?mid Cretaceous. With the exception of a major duplex along its trailing edge, significant internal thrusts are rare and shortening is mostly accommodated by asymmetrical folding. This wedge was emplaced over the trailing edge of a lower thrust unit (Hammat Shulayshil), which formed through forward propagation of the Hawasina sole thrust and which was also deformed primarily through SW-directed folding with limited internal imbrication even after a translation during emplacement of at least 150 km. A second stage of thrusting after the main emplacement phase is linked to renewed locking of the lowest thrust planes in the imbricated Hawasina sediment wedge ahead of the Semail Ophiolite and late-stage motion transferring to higher structural levels closer to the ophiolite as movement of the latter gradually ceased. This resulted in out-of-sequence re-thrusting of higher thrust sheets over lower sheets along existing thrust planes. This was accompanied by the local rotation of parts of the Jabal Wahrah imbricate fan as an effect of the heterogeneous composition of the overlying thrust units, in particular the out-of-sequence emplacement of a mountain-sized thrust block of intra-oceanic reef limestone (Jabal Kawr) over the Hamrat Duru Group immediately to the east. A third phase of compression then folded and locally thrusted this re-thrust stack. The timing of this phase is not well constrained. It may represent the final effects of the Campanian emplacement; alternatively it may be tentatively linked to limited lateral motion (gravity sliding) of the thrust stack along the flanks of the Al Jabal al-Akhdar anticline during its main growth phase in the Oligocene.

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Tectonics of the Musandam Peninsula and northern Oman Mountains: From ophiolite obduction to continental collision

GeoArabia ◽

10.2113/geoarabia1902137 ◽

2014 ◽

Vol 19 (2) ◽

pp. 135-174

Author(s):

Michael P. Searle ◽

Alan G. Cherry ◽

Mohammed Y. Ali ◽

David J.W. Cooper

Keyword(s):

Continental Margin ◽

Granulite Facies ◽

Continental Collision ◽

Central Iran ◽

Early Miocene ◽

Late Cenozoic ◽

Shallow Marine ◽

Oman Mountains ◽

Thrust Sheets ◽

Semail Ophiolite

ABSTRACT The tectonics of the Musandam Peninsula in northern Oman shows a transition between the Late Cretaceous ophiolite emplacement related tectonics recorded along the Oman Mountains and Dibba Zone to the SE and the Late Cenozoic continent-continent collision tectonics along the Zagros Mountains in Iran to the northwest. Three stages in the continental collision process have been recognized. Stage one involves the emplacement of the Semail Ophiolite from NE to SW onto the Mid-Permian–Mesozoic passive continental margin of Arabia. The Semail Ophiolite shows a lower ocean ridge axis suite of gabbros, tonalites, trondhjemites and lavas (Geotimes V1 unit) dated by U-Pb zircon between 96.4–95.4 Ma overlain by a post-ridge suite including island-arc related volcanics including boninites formed between 95.4–94.7 Ma (Lasail, V2 unit). The ophiolite obduction process began at 96 Ma with subduction of Triassic–Jurassic oceanic crust to depths of > 40 km to form the amphibolite/granulite facies metamorphic sole along an ENE-dipping subduction zone. U-Pb ages of partial melts in the sole amphibolites (95.6– 94.5 Ma) overlap precisely in age with the ophiolite crustal sequence, implying that subduction was occurring at the same time as the ophiolite was forming. The ophiolite, together with the underlying Haybi and Hawasina thrust sheets, were thrust southwest on top of the Permian–Mesozoic shelf carbonate sequence during the Late Cenomanian–Campanian. Subduction ended as unsubductable cherts and limestones (Oman Exotics) jammed at depths of 25–30 km. The Bani Hamid quartzites and calc-silicates associated with amphibolites derived from alkali basalt show high-temperature granulite facies mineral assemblages and represent lower crust material exhumed by late-stage out-of-sequence thrusting. Ophiolite obduction ended at ca. 70 Ma (Maastrichtian) with deposition of shallow-marine limestones transgressing all underlying thrust sheets. Stable shallow-marine conditions followed for at least 30 million years (from 65–35 Ma) along the WSW and ENE flanks of the mountain belt. Stage two occurred during the Late Oligocene–Early Miocene when a second phase of compression occurred in Musandam as the Arabian Plate began to collide with the Iran-western Makran continental margin. The Middle Permian to Cenomanian shelf carbonates, up to 4 km thick, together with pre-Permian basement rocks were thrust westwards along the Hagab Thrust for a minimum of 15 km. Early Miocene out-of-sequence thrusts cut through the shelf carbonates and overlying Pabdeh foreland basin in the subsurface offshore Ras al Khaimah and Musandam. This phase of crustal compression followed deposition of the Eocene Dammam and Oligocene Asmari formations in the United Arab Emirates (UAE), but ended by the mid-Miocene as thrust tip lines are all truncated along a regional unconformity at the base of the Upper Miocene Mishan Formation. The Oligocene–Early Miocene culmination of Musandam and late Cenozoic folding along the UAE foreland marks the initiation of the collision of Arabia with Central Iran in the Strait of Hormuz region. Stage three involved collision of Arabia and the Central Iran Plate during the Pliocene, with ca. 50 km of NE-SW shortening across the Zagros Fold Belt. Related deformation in the Musandam Peninsula is largely limited to north and eastward tilting of the peninsula to create a deeply indented coastline of drowned valleys (rias).

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