Structural geometry, style and timing of deformation in the Hawasina Window, Al Jabal al Akhdar and Saih Hatat culminations, Oman Mountains

ABSTRACT The Al Jabal al Akhdar and Saih Hatat culminations in the central Oman Mountains expose the complete mid-Permian to Late Cretaceous (Cenomanian) passive shelf and margin carbonate sequence beneath the allochtonous slope (Sumeini Group), basin (Hawasina complex), distal ocean-trench (Haybi complex) facies rocks, and the Semail ophiolite thrust sheets that were emplaced from NE to SW during the Late Cretaceous. Reconstruction of the pre-thrust sequences shows that time-equivalent rocks occur in successively stacked thrust sheets from shelf to slope to basin. The Al Jabal al Akhdar structure is a 60 km wavelength anticline plunging to the northwest beneath the Hawasina Window and with a fold axis that curves from WNW-ESE (Jabal Shams) to NNE-SSW (Jabal Nakhl). The structure shows little internal deformation except for minor intra-formational thrust duplexing within the Cretaceous shelf stratigraphy along the northern margin. The upper structural boundaries around the flanks of the shelf carbonate culminations have been re-activated as late stage normal faults. The Semail thrust formed a passive roof fault during late-stage culmination of al Al Jabal al Akhdar such that the ophiolite rests directly on Wasia Formation top-shelf with the entire Sumeini, Hawasina and Haybi thrust sheets displaced around the margins. NE-directed backthrusting and intense folding in the northern part of the Hawasina Window affects all allochtonous units and is related to a steep ramp in the Late Cretaceous shelf margin at depth. The Saih Hatat culmination is another 40 km half-wavelength anticline in the central Oman Mountains, but shows extreme deformation in the form of recumbent folds, sheath folds with NNE-trending axes and thrusting along the northern margin. High-pressure carpholite, blueschist and eclogite facies rocks are exposed at successively deeper structural levels, separated by high-strain normal sense shear zones. There is no evidence for a separate ‘North Muscat microplate’ or an intra-continental subduction zone, as previously proposed; all high-pressure units can be restored to show their pre-deformation palaeographic positions along the northern margin of the Arabian Plate. Both Al Jabal al Akhdar and Saih Hatat are Late Cretaceous culminations, folded after obduction of the Hawasina, Haybi and Semail ophiolite thrust sheets from northeast to southwest during the period Turonian to Campanian-Lower Maastrichtian. Maximum compressive stress along the central Oman Mountains was oriented NE-SW, parallel to the ophiolite emplacement direction, but a second compressive stress axis was oriented WNW-ESE, either concurrently or slightly later in time, resulting in a dome and basin structural geometry. The biaxial fracture pattern in the foreland, southwest of the Oman Mountains could be explained as a result of the WNW-directed emplacement of the Masirah ophiolite belt and Batain mélange during the Campanian-early Palaeocene. Both Al Jabal al Akhdar and Saih Hatat were positive topographic features at the end of the Cretaceous with Upper Maastrichtian and Palaeogene sediments onlapping both flanks. In Jabal Abiad, these Palaeogene sediments have been uplifted by at least 2 km since the Late Miocene-Early Oligocene associated with minor NNE-SSW compression. Tertiary shortening, folding and thrusting increases to the north in the Musandam peninsula where the first effects of the Arabian Plate-Eurasian Plate (Zagros belt) continent-continent collision are seen.

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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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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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Structural and tectonic evolution of the Jabal Sumeini – Al Ain – Buraimi region, northern Oman and eastern United Arab Emirates

GeoArabia ◽

10.2113/geoarabia1401115 ◽

2009 ◽

Vol 14 (1) ◽

pp. 115-142 ◽

Cited By ~ 7

Author(s):

Michael P. Searle ◽

Mohammed Y. Ali

Keyword(s):

United Arab Emirates ◽

Late Cretaceous ◽

Foreland Basin ◽

Arabian Plate ◽

Asmari Formation ◽

Crustal Shortening ◽

Oman Mountains ◽

Al Ain ◽

Carbonate Slope ◽

Semail Ophiolite

ABSTRACT Four main Late Cretaceous and Tertiary phases of crustal shortening and thrust-related deformation are recognised in the northern Oman Mountains, each phase ending with a regional unconformity throughout the Oman Mountains and the UAE foreland. The earliest is the major thrust emplacement of the Semail Ophiolite, and underlying Haybi, Hawasina and Sumeini duplexes from NE to SW onto the depressed northeastern continental margin of the Arabian Plate during the Cenomanian to Campanian-early Maastrichtian (D1). A prominent widespread unconformity that places Maastrichtian Qahlah Formation laterite, sandstones and conglomerates and Simsima Formation rudist - Acteonellid gastropod limestones over all underlying allochthonous units is recognised throughout the Oman Mountains. SW-verging folds and thrusts in Triassic to Cretaceous carbonate slope facies rocks exposed in Jabal Sumeini (Sumeini Group and Hamrat Duru Group) have been emplaced over uppermost Cretaceous Juweiza Formation conglomerates at the highest level of the Aruma foreland basin. These Sumeini D1 structures are abruptly truncated by an unconformity, above which are Middle Maastrichtian beds showing up to 95% ‘death assemblage’ rudists and gastropods just below the Cretaceous – Tertiary boundary (top of Simsima Formation). A second deformation event (D2) affected the Simsima Formation and underlying Sumeini Group, Hamrat Duru complex and Semail Ophiolite rocks. This phase shows gentle folding about NW-SE fold axes (e.g. Jabal Rawdah), along a similar trend to the Late Cretaceous D1 event. This trend is also parallel to a regional set of NW-SE aligned fractures in the UAE foreland. A major angular unconformity occurs beneath the Upper Palaeocene – Eocene shallow-marine limestones (Umm Er Radhuma, Rus and Dammam formations). Many foreland jabals in eastern Abu Dhabi (Jabals Qatar, Malaqet, Mundasa) show gentle post-Eocene folding formed during the third stage of crustal shortening (D3). The large pericline of Jabal Hafit is a double-plunging, east-verging box fold that formed after deposition of the Oligocene Asmari Formation limestones and Miocene Fars Formation gypsum and clays, the youngest beds affected by the fold. This Late Miocene – Pliocene phase of crustal shortening (D4) is the youngest phase of deformation in the eastern Al Ain-Buraimi region.

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Ductile-brittle shear zone in a listwaenite body, within the Frontal Range Fault of the Oman Mountains (Sultanate of Oman)

10.5194/egusphere-egu2020-12672 ◽

2020 ◽

Author(s):

Andreas Scharf ◽

Frank Mattern ◽

Paul Mattern

Keyword(s):

Shear Zone ◽

Oceanic Lithosphere ◽

Late Eocene ◽

Age Dating ◽

Deformation Pattern ◽

Sultanate Of Oman ◽

Brittle Deformation ◽

Northern Margin ◽

Oman Mountains ◽

Semail Ophiolite

Listwaenite (fully serpentinized and carbonatized/silicified ultramafic rock) is common within the Oman Mountains near Fanja. The Oman Mountains formed during the late Cretaceous obduction of the Semail Ophiolite. Eventually, major exhumation and associated extensional shearing formed the Saih Hatat Dome during the latest Cretaceous to Paleocene. This dome displays rocks of the Arabian platform, framed by the Hawasina Allochthonous and the Semail Ophiolite. Postobductional rapid exhumation/cooling of the Saih Hatat Dome is reflected by a major extensional shear zone at the northern margin of the dome (Frontal Range Fault, FRF; Mattern and Scharf, 2018). Shearing along the FRF with a throw of few to several kilometers, occurred within two intervals. The major first event occurred during the latest Cretaceous to Paleocene while the minor second event lasted probably from the late Eocene to Oligocene (Mattern et al., 2019). Along and within the FRF, major tabular listwaenite bodies occur displaying a lateral extend from few meters to hundreds of meters and a thickness of up to a few to tens of meters. According to Scharf et al. (2020), the listwaenite dates as latest Cretaceous to Paleocene.Most of the numerous SiO2-rich listwaenite bodies near Fanja preserve a brittle deformation pattern, indicating that the temperature during and after formation was less than 250&#176;C. As an exception, we found one unusually well-developed, intensely foliated and wide strike-slip ductile-brittle shear zone at the surface, exhibiting a width of 5m and a length of a few tens of meters within a large listwaenite body near the community of Sunub. The foliation of the shear zone dips to the SW with about 50-80&#176;. The shear zone intersects at a high angle with the FRF (strike SW-NE) and the listwaenite unit it contains. The shear movement is unrelated to that of the FRF. Approximately 6km WNW of the sheared listwaenite, a mafic dike of Lutetian age (42.7&#177;0.5Ma; Mattern et al., 2019) intruded Cenozoic limestone. Intrusion is associated with the second shearing interval of the FRF. Because listwaenite bodies usually display brittle deformation, we tentatively conclude that the ductile-brittle shear zone formed during the late Eocene because of mafic intrusions. We assume that another mafic body is located near the shear zone and provided the heat for the ductile-brittle deformation conditions.&#160;References:Mattern, F., Scharf, A., 2018. Postobductional extension along and within the Frontal Range of the Eastern Oman Mountains. Journal of Asian Earth Sciences 154, 369-385, doi: 10.1016/j.jseaes.2017.12.031.Mattern, F., Sudo, M., Callegari, I., Pracejus, B., Bauer, W., Scharf, A., 2019. Late Lutetian 40Ar/39Ar Age Dating of a Mafic Intrusion into the Jafnayn Formation and its Tectonic Implications (Muscat, Oman). AAPG Event, 2nd Edition, Structural styles of the Middle East, 9th-11th December 2019, Muscat, Oman.Scharf, A., Mattern, F., Bolhar, R., Bailey, C.M., Ring, U., 2020. U-Pb dating of postobductional carbonate veins in listwaenite of the Oman Mountains near Fanja. International Conference on Ophiolites and the Oceanic Lithosphere: Results of the Oman Drilling Project and Related Research, 12-14th January, 2020, Sultan Qaboos University, Muscat, Sultanate of Oman.

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Kinematic interpretation and structural evolution of North Oman, Block 6, since the Late Cretaceous and implications for timing of hydrocarbon migration into Cretaceous reservoirs

GeoArabia ◽

10.2113/geoarabia110197 ◽

2006 ◽

Vol 11 (1) ◽

pp. 97-140 ◽

Cited By ~ 8

Author(s):

Jacek B. Filbrandt ◽

Salah Al-Dhahab ◽

Abdullah Al-Habsy ◽

Kester Harris ◽

John Keating ◽

...

Keyword(s):

Late Cretaceous ◽

Seismic Velocity ◽

Horizontal Stress ◽

Arabian Plate ◽

Late Cenozoic ◽

Oblique Collision ◽

Oman Mountains ◽

Structural Style ◽

Platform Margin ◽

Maximum Horizontal Stress

ABSTRACT On the basis of structural style and differences in Late Cretaceous evolution, the carbonate platform in northern Oman and the allochthonous wedge comprising deepwater sediments and oceanic crust in the Oman Mountains form distinct structural domains. Imbrication associated with the emplacement of the Semail Ophiolite and predominantly SW-verging thrusting of the Arabian Platform margin culminated in the late early Campanian. The structural grain of NW-trending thrust faults and contractional folds contrasts markedly with the style and grain of the region immediately south of the Oman Mountains (our study area) and implies strong strain partitioning. Kinematic indicators from subsurface data, combined with the age of growth faulting, provide the basis for the interpretation that maximum horizontal stress was oriented NW-SE in this foreland region rather than NE-SW during the Campanian. The dominant tectonic control on the formation of faults is believed to have been an oblique “collision” of the Indian Continent with the Arabian Plate during the Santonian-Campanian. Deformation in this domain was dominated by distributed strike-slip and normal faulting. This period of faulting was significant for two reasons: (1) The faults both enhanced existing structures and formed new traps. They also allowed vertical migration of hydrocarbons from Palaeozoic reservoirs (e.g. Haushi clastic accumulations) into Shu’aiba and Natih carbonates above. Until that time, some 75 Ma ago, oil was retained in Late Palaeozoic and older traps. This period of deformation is a “Critical Event” within the context of Oman’s hydrocarbon distribution.(2) Faults with NNW and WNW orientations that developed at that time appear to be directly associated with important fracture systems that affect the productivity of several giant fields comprising Natih and Shu’aiba carbonate reservoirs (e.g. Lekhwair, Saih Rawl). Following this tectonic event, late Maastrichtian to Palaeocene uplift and erosion in excess of 1,000 m, is recorded by truncation of the Aruma Group and Natih Formation, as well as part of the Shu’aiba Formation below the base Cenozoic unconformity. Seismic velocity and porosity anomalies from Lekhwair field in the northwest to the Huqf-Haushi High in the southeast, provide additional support for the areal distribution of this event. Around the Lekhwair and Dhulaima fields, the circular to elliptical subcrop pattern below this unconformity does not support the notion of a peripheral bulge related to the emplacement of the allochthon. The stress field changed during the late Cenozoic with the opening of the Red Sea and Gulf of Aden, and the collision of the Arabian Plate with the Iranian Plate. NE-SW-oriented maximum horizontal stress during the late Cenozoic led to the formation of major folds resulting in, for example, the surface anticlines over the Natih and Fahud fields as well as causing inversion along the Maradi Fault Zone. This may also have led to the uplift of the Oman Mountains. The regional northerly subsidence caused by crustal loading of the Arabian Plate gently tilted traps during the Pliocene-Pleistocene from Lekhwair to Fahud.

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Structural Style and Stratigraphy of the Huwayyah Anticline: an Example of an Al-Ain Tertiary Fold, Northern Oman Mountains

GeoArabia ◽

10.2113/geoarabia0503387 ◽

2000 ◽

Vol 5 (3) ◽

pp. 387-402 ◽

Cited By ~ 4

Author(s):

M. Atef Noweir ◽

Abdulrahman S. Alsharhan

Keyword(s):

Late Cretaceous ◽

Middle Eocene ◽

Fold Axis ◽

The North ◽

Oman Mountains ◽

Structural Style ◽

Dammam Formation ◽

Al Ain ◽

Mountain Front ◽

Semail Ophiolite

ABSTRACT Detailed field mapping and structural studies in the Jebel Auha-Jebel Huwayyah area northeast of Al-Ain indicate that folding of neoautochthonous sedimentary rocks produced the north-northwest-trending Huwayyah Anticline. The anticline at the surface is composed of the Maastrichtian Qahlah and Simsima formations unconformably overlain by shallow-marine carbonate rocks that are correlated on faunal grounds with the Middle Eocene Dammam Formation. The investigation of the Huwayyah Anticline has identified three microfacies of bioclastic packstone, nummulitic packstone, and nummulitic packstone-grainstone in the local Dammam Formation. Diagenesis in the form of silicification, cementation, recrystallization, dissolution, compaction and neomorphism is widespread. The Huwayyah Anticline is a fault-propagation fold above a thrust ramp. The ramp developed from a pre-existing Late Cretaceous basal thrust within the Semail Ophiolite on the Oman Mountain Front. The anticline was formed as a result of regional compressive deformation due to rejuvenation of the Late Cretaceous thrust in post-Middle Eocene times. Westward-directed high-angle reverse faults of Jebel Auha trend parallel to the fold axis of the anticline. The Auha faults probably originated as west-dipping thrusts on the western flank of the anticline and were subsequently rotated to their present attitude as the flank of the anticline became steeper due to compression from the east.

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Alkaline peridotite, pyroxenite, and gabbroic intrusions in the Oman Mountains, Arabia

Canadian Journal of Earth Sciences ◽

10.1139/e84-043 ◽

1984 ◽

Vol 21 (4) ◽

pp. 396-406 ◽

Cited By ~ 18

Author(s):

Michael P. Searle

Keyword(s):

Continental Margin ◽

Late Cretaceous ◽

Volatile Components ◽

Titanium Oxides ◽

Structural Mapping ◽

Oman Mountains ◽

Intrusive Rocks ◽

Alkaline Magmas ◽

High Level ◽

Semail Ophiolite

High-level intrusions of highly undersaturated alkalic ultrabasic and gabbroic rocks occur in four areas of the Oman Mountains. They all intrude either the Haybi volcanic – Oman Exotic limestone (Permo-Triassic) thrust slice immediately beneath the Semail Ophiolite (Cenomanian) or the uppermost thrust slice of the underlying Hawasina (Permian to Cenomanian) Tethyan sediments. Detailed structural mapping indicates that the sills were all emplaced prior to the Late Cretaceous thrusting of the Oman allochthon onto the Mesozoic continental margin of Arabia, and therefore in an oceanic setting. These differentiated sills consist of biotite wehrlites at the base and kaersutite-bearing jacupirangites above, with kaersutite gabbros at the top. Olivine occurs only at the base. Titanaugite, kaersutite, titanium phlogopite, apatite, and opaque iron–titanium oxides are common mineral phases.Fractional crystallization and gravity differentiation processes and a rapid increase in volatile components at decreasing pressures all played a part in the petrogenesis of these uncommon intrusive rocks. K–Ar ages on biotites span the mid-Jurassic to Cenomanian, and in the northern Oman Mountains kaersutite jacupirangites are incorporated into the Cenomanian–Turonian amphibolite facies metamorphic sheet beneath the Semail Ophiolite. Alkaline magmas were present at depth along the passive continental margin, right up until Cenomanian times when northeast subduction was initiated and compressional tectonics began. Alkaline volcanism of Cenomanian age in the Dibba Zone indicates that tensional rifting processes were operative along the continental margin at the same time as compressional thrusting was occurring outboard. The alkaline rocks are unrelated to the ophiolite but are artifacts of Mesozoic rifting events in Tethys now preserved in footwall thrust slices beneath the ophiolite.

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Evidence of postobductional, brittle and transtensional deformation: the lineamentary Issmaiya Fault Zone – insights from kinematic analyses and remote sensing data interpretation (Semail Ophiolite near Ibra, Oman Mts., Sultanante of Oman)

10.5194/egusphere-egu2020-12472 ◽

2020 ◽

Author(s):

Ivan Callegari ◽

Alvar Braathen ◽

Andreas Scharf ◽

Frank Mattern ◽

Ekkehard Holzbecher ◽

...

Keyword(s):

Fault Zone ◽

Late Cretaceous ◽

Sedimentary Rocks ◽

Acute Angle ◽

Field Analysis ◽

Arabian Plate ◽

Deformation Model ◽

Tectonic Event ◽

Southwestern Margin ◽

Semail Ophiolite

The main Meso-Cenozoic tectonic event that affected northern Oman was the obduction of allochthonous Hawasina Basin-derived sedimentary and volcanic rocks as well as the Semail Ophiolite during the Late Cretaceous. The allochthonous units were thrust onto the passive Arabian margin and platform. Obduction was followed by immediate uplift (doming) of the Saih Hatat Dome in the Southeastern Oman Mountains. The present work relates to the postobductional tectonic development of the Semail Ophiolite in the Ibra region southwest of the Saih Hatat Dome. The main aim of this work is to develop a regional brittle deformation model using structural field data comparing with borehole wireline log structural data from the Oman Drilling Project (ODP) wells sites, drilled in the same area for the investigation of active serpentinization in the peridotite aquifers. The study area of ~100 km2 contains a brittle fault zone of ~3 km kilometers in width and ~30 km in length herein called the &#8220;Issmaiya Fault Zone (IFZ)&#8221;. Along the IFZ, a structural field analysis and eleven structural survey stations using the 1-D scanline method for the kinematics elements were realized. In particular, the structural stations were chosen close to the ODP wells sites location, in order to compare the field survey with the borehole logging data.The IFZ is characterized by sub-vertical faults within the mantle part of the Semail Ophiolite which also partially affected latest Cretaceous to Paleocene/early Eocene sedimentary rocks. The latter are also mapped within a structural basin, 25 km NE of Ibra (the so called &#8220;Ibra Basin&#8221;). Our field work and satellite imagery interpretations demonstrate that most faults are within the Semail Ophiolite and few affecting the postobductional sedimentary rocks. This indicates that the ILS was mostly active immediately after the Late Cretaceous emplacement of the Semail Ophiolite. The IFZ strikes NW and forms an acute angle of ~30&#176; with the southwestern margin of the Saih Hatat Dome which strikes WNW-ESE. The LFZ is a transtensional fault zone as indicated by the coexistence of sub-vertical fault planes, with mainly sinistral strike-slip kinematic indicators, and from medium to high angle fault planes with dip-slip movement. The IFZ seems to end towards the NW at the tectonic contact with the Mesozoic sedimentary rocks of the Arabian Plate (Hajar Supergroup). The southwestern margin of the Saih Hatat Dome is marked by a major sinistral transtensional fault (Wadi Mansah Fault Zone; Scharf et al., 2019). This shear zone was active during the Eocene to Miocene and postdates the IFZ.This work provides key insights on the effect of the fault zone to the hydrogeology of the ODP multi-borehole site, in terms of anomalies in the hydrogeochemical log and intervals of high transmissivity.

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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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Deformation of the Cambro-Ordovician Amdeh Formation (Members 1 and 2): Characteristics, Origins, and Stratigraphic Significance (Wadi Amdeh, Saih Hatat Dome, Oman Mountains)

Geosciences ◽

10.3390/geosciences10020048 ◽

2020 ◽

Vol 10 (2) ◽

pp. 48 ◽

Cited By ~ 1

Author(s):

Frank Mattern ◽

Andreas Scharf ◽

Pu-Jun Wang ◽

Ivan Callegari ◽

Iftikhar Abbasi ◽

...

Keyword(s):

Late Cretaceous ◽

Simple Shear ◽

Late Stage ◽

Deformation Zone ◽

Sedimentary Rock ◽

Rock Unit ◽

Oman Mountains ◽

Fault Block ◽

Rock Formations ◽

Igneous Activity

The Angudan Orogeny affected Cryogenian to earliest Cambrian sedimentary rock formations of the Jabal Akhdar Dome of the Oman Mountains. These rocks were folded and cleaved at 525 ± 5 Ma. We studied the Cambro-Ordovician (Terreneuvian to Darriwillian) Amdeh Formation of the neighboring Saih Hatat Dome to see whether this formation was also affected by the Angudan Orogeny. The Angudan deformation within the Jabal Akhdar Dome is known for its folds and cleavage. Due to age considerations (see above), we studied the folds and cleavages within the two oldest members of the Amdeh Formation (Am 1 and Am 2) in order to compare them with the ones that are known from the Jabal Akhdar Dome to possibly detect Angudan-related deformation in Am 1 and Am 2. Angudan folds of the Jabal Akhdar Dome display fold axes that are oriented NE/SW, but the two lowest members of the Amdeh Formation reveal one set of folds with subhorizontal fold axes that trend NW-NNW/SE-SSE. The lack of Angudan-related folds suggests that the lowest Amdeh Member (Am 1) postdates the Angudan Orogeny. The age of Am 1 is uncertain. Based on our structural results, we consider an upper Terreneuvian age (late stage 2) for Am 1. The folds in Am 1 and 2 are related to the Late Cretaceous–Cenozoic Semail Orogeny (term introduced here). The observed fold vergences (mainly to the W and SW) were caused by shear deformation during descent into the subduction zone by simple shear. The contact between the stratigraphically underlying Hiyam Formation and the Amdeh Formation is generally considered to be an unconformity. We observed a distinct NW/SE-striking deformation zone along the contact of both formations which is located in proximity to the largest observed fold. Tectonically, this contact is defined by the sinistral Wadi Amdeh Fault (name introduced here). The unconformity should be present in the subsurface of the southwestern fault block. Near the contact between the Hiyam and the Amdeh formations, a 20 cm thick unit of reddish cataclasite/tectonic breccia occurs within the basal part of Am 1 which represents a deformed acidic layer or sill. This rock unit could be the first evidence for Cambrian igneous activity.

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