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

1982 ◽  
Vol 119 (5) ◽  
pp. 497-503 ◽  
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.

Chapter 5 Tectonic evolution of the Oman Mountains

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.

Chapter 2 Tectonostratigraphy of the eastern part of the Oman Mountains

10.1144/m54.2 ◽  
2021 ◽  
Vol 54 (1) ◽  
pp. 11-47 ◽  
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.

Stratigraphy of the Mesozoic rocks above the Semail Ophiolite, Oman

1982 ◽  
Vol 119 (1) ◽  
pp. 67-76 ◽  
Author(s):  
N. H. Woodcock ◽  
A. H. F. Robertson
Keyword(s):  
Upper Cretaceous ◽  
Early Stages ◽  
Clastic Sediments ◽  
Sediment Cover ◽  
Ophiolite Emplacement ◽  
Semail Ophiolite

SummaryA revised stratigraphy is presented for the rocks which lie between the Upper Cretaceous Semail ophiolite and its post-emplacement sediment cover of uppermost Cretaceous to Tertiary age. Above the pelagic sediments of the ophiolite (Suhaylah Formation, Cenomanian–Turonian) occur ophiolite-derived clastic sediments (Zabyat Formation, ?Turonian–?Campanian) related to early stages of ophiolite emplacement. These formations are structurally overlain by the Batinah Complex, comprising Triassic to Cretaceous lithologies, all previously equated with the Hawasina rocks that now lie tectonically beneath the ophiolite. We recognize a lower melange unit to the complex, which demonstrably includes Hawasina lithologies. The melange formed by superficial rather than deep processes, but the mechanism by which Hawasina material was supplied to the ophiolite surface is unproven. The upper unit of the Batinah Complex shows a coherent stratigraphy which contrasts with that of the Hawasina. It comprises three main allochthonous tectonic sheets, within which we recognize three formations and one other informal unit. The upper Batinah Complex may have been tectonically derived not from the now subjacent Arabian margin but from another margin with a passive Mesozoic history.

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

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

<p>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.</p><p>Most of the numerous SiO<sub>2</sub>-rich listwaenite bodies near Fanja preserve a brittle deformation pattern, indicating that the temperature during and after formation was less than 250°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°. 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±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.</p><p> </p><p>References:</p><p>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.</p><p>Mattern, F., Sudo, M., Callegari, I., Pracejus, B., Bauer, W., Scharf, A., 2019. Late Lutetian <sup>40</sup>Ar/<sup>39</sup>Ar Age Dating of a Mafic Intrusion into the Jafnayn Formation and its Tectonic Implications (Muscat, Oman). AAPG Event, 2<sup>nd</sup> Edition, Structural styles of the Middle East, 9<sup>th</sup>-11<sup>th</sup> December 2019, Muscat, Oman.</p><p>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, 12-14<sup>th</sup> January, 2020, Sultan Qaboos University, Muscat, Sultanate of Oman.</p>

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

1984 ◽  
Vol 21 (4) ◽  
pp. 396-406 ◽  
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.

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

GeoArabia ◽  
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.

Structure and metamorphism of rocks beneath the Semail ophiolite of Oman and their significance in ophiolite obduction

1980 ◽  
Vol 71 (4) ◽  
pp. 247-262 ◽  
Author(s):  
M. P. Searle ◽  
J. Malpas
Keyword(s):  
Heat Source ◽  
Upper Cretaceous ◽  
Frictional Heating ◽  
Metamorphic Rocks ◽  
Polyphase Deformation ◽  
Oman Mountains ◽  
Wide Range ◽  
Semail Ophiolite ◽  
Low Pressures ◽  
Residual Heat

ABSTRACTMetamorphic rocks showing an inverted metamorphic zonation from upper amphibolite fades immediately beneath the peridotite to greenschist fades at lower levels, crop out discontinuously along the base of the Semail ophiolite thrust sheet in the Oman Mountains of eastern Arabia. These metamorphic rocks show polyphase deformation, mylonitic fabrics, and have been disrupted, folded and imbricated, and in places form tectonic inclusions in a serpentinite melange. In the more intact sequences, garnet-clinopyroxene amphibolites, with rare hornblende-bearing marbles and banded quartzites, occur at the higher levels, whilst a wide range of metasedimentary and metabasaltic rocks occur in the greenschist fades. Low glaucophane content of amphiboles and low jadeite content of clinopyroxenes suggest relatively low pressures of crystallisation. The distribution coefficient KD for co-existing garnet and clinopyroxene suggests a temperature range of 670 to 750°C. Residual heat from the recently formed ophiolite probably provided the dominant heat source for metamorphism, although frictional heating could have supplemented this. The metamorphic rocks were produced during Cenomanian-Turonian (late Cretaceous) times.The sub-ophiolite metamorphic rocks, together with basal serpentinite, Triassic alkaline and tholeiitic basalts (Haybi volcanic group), mountain-sized ‘exotic’ limestones and an upper Cretaceous sedimentary melange, comprise a distinct thrust slice termed the Haybi complex, which always overlies marine sediments of the allochthonous Hawasina complex and underlies the Semail ophiolite. The rocks of the Haybi complex are bounded by major thrust planes, the Semail thrust above and the Haybi thrust beneath, which truncate all schistosities, fold axes, imbricate thrusts and associated features. A model for ophiolite obducton is presented based on a palinspastic reconstruction of the allochthonous rocks on the Oman continental margin.

scholarly journals Structural and Stratigraphical Setting of the Faiyah Range, Northwestern Oman Mountain Front, United Arab Emirates

GeoArabia ◽  
1998 ◽  
Vol 3 (3) ◽  
pp. 387-398
Author(s):  
M. Atef Noweir ◽  
Abdulrahman S. Alsharhan ◽  
Mohamed A. Boukhary
Keyword(s):  
United Arab Emirates ◽  
Marine Environment ◽  
Upper Cretaceous ◽  
Sedimentary Rocks ◽  
Fold Axis ◽  
Oman Mountains ◽  
Mountain Front ◽  
Dextral Strike Slip Fault ◽  
Semail Ophiolite ◽  
Dextral Strike Slip

ABSTRACT The Faiyah Range belongs to a group of regional ridges that formed by post-obduction folding of the Upper Cretaceous-Tertiary sedimentary rocks exposed along the western margin of the Northern Oman Mountains. The Faiyah Anticline, generally trends north-northeast to south-southwest with thrust faults striking parallel to the fold axis. The anticlinal hinge was later displaced by a dextral strike-slip fault, named here as the Faiyah Fault, into two segments. The northeastern segment includes Jebels Rumaylah, Faiyah and Mulayhah, and the southwestern segment includes Jebels Buhays and Aqabah. The anticline is interpreted to result from northeast-southwest compression during the Tertiary. In the Faiyah Range the neoautochthonous sedimentary rocks are the Maastrichtian Qahlah and Simsima formations, and the Eocene Dammam Formation. Stratigraphic evidence shows that the lower part of the Qahlah was deposited in a non-marine environment while the upper part was deposited during a marine transgression. The Simsima was deposited in a shallow-marine environment. These units unconformably overlap the allochthonous Semail Ophiolite. The microfaunal content of the so-called Muthaymimah Formation (?Tertiary), of earlier authors, indicates that it is of Maastrichtian age in the Faiyah Range. This sequence is also conformable to the Simsima and therefore it is considered to be the upper member of the Simsima in this area.

scholarly journals Late Cretaceous–Early Eocene tectonic development of the Tethyan suture zone in the Erzincan area, Eastern Pontides, Turkey

2009 ◽  
Vol 146 (4) ◽  
pp. 567-590 ◽  
Author(s):  
SAMUEL P. RICE ◽  
ALASTAIR H. F. ROBERTSON ◽  
TIMUR USTAÖMER ◽  
NURDAN İNAN ◽  
KEMAL TASLI
Keyword(s):  
Subduction Zone ◽  
Late Cretaceous ◽  
Upper Cretaceous ◽  
Accretionary Prism ◽  
Oceanic Lithosphere ◽  
Suture Zone ◽  
Passive Margin ◽  
Early Eocene ◽  
Volcanic Arc ◽  
Eastern Pontides

AbstractSix individual tectonostratigraphic units are identified within the İzmir–Ankara–Erzincan Suture Zone in the critical Erzincan area of the Eastern Pontides. The Ayıkayası Formation of Campanian–Maastrichtian age is composed of bedded pelagic limestones intercalated with polymict, massive conglomerates. The Ayıkayası Formation conformably overlies the Tauride passive margin sequence in the Munzur Mountains to the south and is interpreted as an underfilled foredeep basin. The Refahiye Complex, of possible Late Cretaceous age, is a partial ophiolite composed of ~75% (by volume) serpentinized peridotite (mainly harzburgite), ~20% diabase and minor amounts of gabbro and plagiogranite. The complex is interpreted as oceanic lithosphere that formed by spreading above a subduction zone. Unusual screens of metamorphic rocks (e.g. marble and schist) locally occur between sheeted diabase dykes. The Upper Cretaceous Karayaprak Mélange exhibits two lithological associations: (1) the basalt + radiolarite + serpentinite association, including depleted arc-type basalts; (2) the massive neritic limestone + lava + volcaniclastic association that includes fractionated, intermediate-composition lavas, and is interpreted as accreted Neotethyan seamount(s). The several-kilometre-thick Karadağ Formation, of Campanian–Maastrichtian age, is composed of greenschist-facies volcanogenic rocks of mainly basaltic to andesitic composition, and is interpreted as an emplaced Upper Cretaceous volcanic arc. The Campanian–Early Eocene Sütpınar Formation (~1500 m thick) is a coarsening-upward succession of turbiditic calcarenite, sandstone, laminated mudrock, volcaniclastic sedimentary rocks that includes rare andesitic lava, and is interpreted as a regressive forearc basin. The Late Paleocene–Eocene Sipikör Formation is a laterally varied succession of shallow-marine carbonate and siliciclastic lithofacies that overlies deformed Upper Cretaceous units with an angular unconformity. Structural study indicates that the assembled accretionary prism, supra-subduction zone-type oceanic lithosphere and volcanic arc units were emplaced northwards onto the Eurasian margin and also southwards onto the Tauride (Gondwana-related) margin during Campanian–Maastrichtian time. Further, mainly southward thrusting took place during the Eocene in this area, related to final closure of Tethys. Our preferred tectonic model involves northward subduction, supra-subduction zone ophiolite genesis and arc magmatism near the northerly, Eurasian margin of the Mesozoic Tethys.

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