Structure of the Musandam Culmination (Sultanate of Oman and United Arab Emirates) and the Straits of Hormuz Syntaxis

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/249546472

Article in Journal of the Geological Society · October 1988 DOI: 10.1144/gsjgs.145.5.0831

CITATIONS READS 62 260

1 author:

M. P. Searle University of Oxford

372 PUBLICATIONS 19,731 CITATIONS

SEE PROFILE

Some of the authors of this publication are also working on these related projects:

ore deposits and tectonics of Myanmar View project

Tectonics of the Oman-UAE ophiolite View project

All content following this page was uploaded by M. P. Searle on 17 August 2017.

The user has requested enhancement of the downloaded file. Journal of the Geological Society

Structure of the Musandam culmination (Sultanate of Oman and United Arab Emirates) and the Straits of Hormuz syntaxis

M. P. SEARLE

Journal of the Geological Society 1988; v. 145; p. 831-845 doi:10.1144/gsjgs.145.5.0831

Email alerting click here to receive free email alerts when new articles cite this article service Permission click here to seek permission to re-use all or part of this article request Subscribe click here to subscribe to Journal of the Geological Society or the Lyell Collection

Notes

Downloaded by Michael Paul Searle on 23 January 2009

Structure of the Musandam culmination (Sultanate of Oman and United Arab Emirates) and the Straits of Hormuz syntaxis

M. P. SEARLE Department of Geology, University of Leicester, Leicester LE1 7RH, UK

Abstract: TheMusandam Mountains form alink, both in timeand space, between the late Cretaceous ophiolite obduction tectonics of the Oman Mountains and the late Tertiary continental collision tectonics of the Zagros Fold belt of Iran. Culmination of the Musandam shelf carbonates occurredafter the Turonian-Maastrichtian thin-skinned thrusting of theOman Mountains was completed. The basal Hagab thrust cuts up-section to the west from at least mid-Permian level up to thelate Cretaceous Aruma Group and breached up into the overlyingpreviously allochthonous (Cretaceous) Hawasina cherts. In the Hagil Window (Ras a1 Khaimah), the shelf carbonates show from 4 to 15 km of westward translation. Extrapolation of foreland sequences suggests that Upper Cretaceous Aruma Group and Hawasina complex sediments could occur in the subsurface along the footwall east of the mountain front. The Hagab thrust and Musandam structures plunge south-southwest at increasingly greater depth (and with decreasing amount of translation) and carry all overlying lateCretaceous thrust sheets of theOman Mountains in a piggy-back fashion.The Eocene-Lr. Oligocene Pabdeh foredeep developed as a result of loading in front of the Musandam thrust sheets wedging out to the south. The trailing (south-eastern) edge of the Musandam culmination is a hinged listric normal fault downthrowing to the south-east up to 2.5 km at Bayah and less than 500 m at the western end of Batha Mahani, and is interpreted as a dorsal culmination collapse feature.

The Musandam peninsula forms the northern extremity of Lees (1928)who first describedthe stratigraphy of the the Oman Mountains in eastern Arabia (Figs 1,2 & 3) and Musandam and Elphinstone beds. is separated from Qishm Island and SE Iran by the 50 km Geologists from Iraq Petroleum Company described the wide Straits of Hormuz. The Permian to Cenomanian shelf stratigraphy(Hudson & Chatton 1959; Hudson 1960) and carbonatesequence exposed in the Musandam peninsula structure of the Jebel Hagab area (Hudson et al. 1954). In (Ras a1 Khaimah and Oman) in the northern extremity of thewinters of 1966 and 1967geologists fromPetroleum theOman Mountains can be closely correlated with the Development (Oman) Ltdmade ahelicopter and foot Arabianplatform in the JebelAkhdar Massif (Central survey,and published mapa of the completeOman Oman) and in subsurface wells drilled in the foreland. The Mountains(Glennie et al. 1974). Elf Aquitaine(Oman) Musandam shelf carbonates are entirely allochthonous and a conductedmorea detailed survey of the Musandam series of huge domalstructures are hanging-wallculmina- peninsula and published a map (Biehler el al. 1975) and a tions. The tectonics of the Musandam form the link between report (Ricateau & Riche 1980). Alleman & Peters (1972) the lateCretaceous ophiolite obduction-related thrust also studiedthe southern part of theRuus a1 Jibaland tectonics of the Oman Mountains to the south and the later logged sections through the Musandam Group. Tertiary folding and thrusting of the Zagros Mountains in During three winterseasons the whole Musandam SE Iran to thewest. Along the eastern margin of Musandam peninsula and Dibba zone in both the United Arab Emirates amajor structural feature termed the ‘Oman Line’ (Lees (UAE) and Oman territory has been reinvestigated and the 1928;Stocklin 1968; White & Ross 1979) separatesa western parthas been mapped at l :20 000 scale. Three continent-continent collision boundary to the west (Zagros) balancedcross-sections have beenconstructed across the from a continent-ocean plate boundary to the east (Gulf of Musandammountains. Thesouthern section extends also Oman). across the Tethyan thrust sheets of the Dibba zone to the The geology, structureand evolution of theTethyan Semail ophiolite and Gulf of Oman. oceanicthrust sheets of theDibba zone separating the Musandam shelf carbonates from the Semail Ophiolite has recently been described by Searle (1988). This paper reviews Regional tectonics the regional tectonics of the Arabian Gulf-Gulf of Oman area and then defines the structural geometry and evolution of the Musandam mountains (Figs 3 & 4) and its links with Oman Mountains the tectonics of theOman Mountains to the SE andthe The Oman Mountains are composed of a series of thrust Zagros Mountains to the NW. sheets of (1) Sumeini Group shelf edgesediments (2) Pioneering geological visits tothe Ruus a1 Jibal or Hawasina complex distal slope and deep-sea sediments, (3) Musandamarea were made by Blandford (1872) tothe Haybi complex,comprising Permianand Triassic exotic ElphinstoneInlet or Khawr Khasaband in 1904-5by limestones (Oman Exotics), Triassic to Cretaceous volcanics Pilgrim (1908) who crossed from Dibba to Ras a1 Khaimah. (Haybi Volcanics) melanges and sub-ophiolitic metamorphic G. M. Lees and K. W. Gray studied some coastal sectionsof rocks,and (4) Semail ophiolitecomplex, an intact slab, the northern fjords and the Hagab frontal fold and it was approximately14kmthick of Cenomanian-Turonian 831 832 M. P. SEARLE

Fig. 1. LANDSAT composite photographof the Zagros fold belt (south Iran), Arabian Gulf, and the Straitsof Hormuz separating Qishm Island from the Musandam peninsula (Oman). The10-20 km half-wavelength Zagros folds are prominent and the circular dark patches are emergent HormuzSalt domes. The Zagros thrust and the Zendam fault define the probable limits of Arabian continental crust. BA, Bandar Abbas;M, the Musandam peninsula; D, the Dibba zone;S, the Semail Ophiolite complex of the northern Oman mountains. See Searle(1988, fig. 12) for a geological interpretation of this area. The dashed line offthe south coast of Iran marks the approximate southernlimit of Zagros folding and thrusting. Thecircles in the straits of Hormuz and south of Musandam show thelocalities of the two main transfer zonesdiscussed here. oceanic crust and mantle (Glennie et al. 1973, 1974; Searle foreland in apiggy-back manner.Some ‘out-of-sequence’ & Malpas 1980,1982). Palinspastic reconstruction of the thrusts andmore important late-stage ‘leap-frog’ or continental margin deducedfrom restoring balanced breakback thrusts have been described from culminations in cross-sectionsshows thatrocks spanning thesame time thenorthern and central Oman Mountains (Searle 1985; period (Permian to Cretaceous) occur in each major thrust Searle & Cooper 1986). sheetexcept the Semail ophiolite which is Cenomanian- Turonian age. More than 100Ma of stable sedimentary conditions on Gulf of Oman the passive continental margin of Arabia ended abruptly in The Gulf of Oman isfloored by oceaniccrust which is the Turonian with the emplacement of these thin-skinned subducting northward below Makran at a rate of about 5 cm Tethyan thrust sheets onto the Arabian shelf (Fig. 5). The a-’ (Jacob & Quittmeyer 1979). Uniformheat flow data foreland fold and thrust belt composed mainly of proximal suggest anage of 70-100 Mafor this oceanic crust Hawasina (Hamrat Duru GP. and Wahrah Fm.) sediments (Hutchison et al. 1981) making itsynchronous with the has been thrust at least 180 km south-westwards on top of spreadingevent that producedthe Semail ophiolite. the autochthonous shelf sequence of the foreland and the Large-scale sediment underplating offshore and onshore the late Cretaceous foredeep fill, the Aruma Group (Fig. 5). Makran continental margin (Platt et al. J985) suggests that a In generalterms the more distal thrustsheets were long-lived (lateCretaceous Holocene)to subduction/ emplacedover themore proximal ones, with thrusts accretionsystem hasbeen operative along thenorthern propagatingsequentially south-westwards towards the margin of the Gulf of Oman. The volcanic arc above this TH E MUSANDAM CULMINATION,MUSANDAMOMAN THE 833

subductionzone is represented by the andesiticvolcanic rocks along the Chagai Hills and Ras Koh, some 400 km north of theMakran coast westernin Baluchistan (Arthurton et al. 1985). Inthe westernpart of the Gulf of Oman, amajor structuralfeature termed the ‘Oman Line’ (Lees 1928; Stocklin 1968; White & Ross 1979) separates a continent- continent collision boundary to the west (Zagros) from a continent-ocean plate boundary to the east (Gulf of Oman). Just west of the‘Oman Line’ aNE-trending zone of earthquakes extends from the coast north of Qishm Island forover 100 km(Nowroozi 1976). This seismic belt coincides with the eastern limit of the Zagros fold belt, and atopographic surface escarpment visible onLANDSAT imagery (Kadinsky-Cade & Barazangi 1982).Multichannel seismic reflection and gravity profiles havedefined a subsurfacecontinuation of the Musandambasement high extending north beneath the Straits of Hormuz under the Iran coast (White & Ross 1979). They interpreted this as resulting from the underthrusting of a promontory of the Arabian shelf below Iran. TheZendan faultzone (Fig. 1) is characterized by high-angle, east-dipping reverse faults which affect Pliocene to Quaternarysediments (Shearman 1977). Several large- scale folds can be seen on LANDSAT photos with NW-SE axial traces between the coast and the Zendan fault (Fig. 1). There also appears to be some strike-slip component along the fault with dextral (right-lateral) sense of shear. Other major N-S faults showing dextral shear bound the western side of the Jaz Murian depression.

Zagros fold belt The Zagros Mountains in SW Iran are known as a classical fold mountain belt, formed as a result of collision of the Arabianplate with thecentral Iran microcontinent, along , the Zagros suture zone which has been modified by later reverseand strike-slip faulting. Collision and associated large-scalefolding hasbeen dated as late Miocene-early Pliocene (Berberian & King1981). Littleremains of the earlier,late Cretaceous, ophiolite abduction-related structures. At Neyriz andKermanshah, remnant ophiolites of late Cretaceous age with some associated radiolarian cherts i (Pichachun Fm.) were emplaced in pre-Maastrichtian times, and are now preservedimmediately south of theZagros suture zone (Stocklin1968, 1974; Wells 1969; Ricou 1971; Haynes & McQuillan 1974). In the high Zagros, reworked radiolarian chert material is found in the late Cretaceous- early Tertiary flysch deposits (R. J. Murris pers. comm.) The Zagros shelf sequence is clearly part of the Arabian - _____.._ __ - platform with continousdeposition from Cambrian to Pliocene (James & Wynd 1965), and shows a very similar Fig. 2. LANDSAT photograph of the Musandam peninsula, Mesozoic sedimentary history tothe UAE-Oman shelf northern Oman Mountains.The dark-coloured rocks southof Dibba are mainly mantle sequence harzburgites of the Semail sequence (Wilson 1969). Large-scale folding and thrusting of ophiolite complex. The lighter coloured rocks forming thebulk of thiscomplete Phanerozoic shelf sequenceoccurred in the the Musandam peninsula are the Musandam shelf carbonate Pliocene-Pleistocenefollowing continent-continent colli- sequence. The NE-SW-trending Dibba zone in the middle are the sion along the Zagros crush zone (Takin 1972; Colman-Sadd Tethyan oceanic thrust sheets (Hawasina and Haybi complexes). 1978; Koop & Stoneley 1982). Basal d6collement occurred North and eastward tilting of the Musandam penisula during along the Proterozoic Hormuz salt horizon and folding and Pleistocene and Recent time is evident from the spectacular thrusting affects thecomplete 12km thick Phanerozoic drowned fjords and ria coastlines along the north and east coast, sequence. where sea cliffs reach upto 800 m. R a1 K is Ras a1 Khaimah. Seismic activity in the Zagros Range is characteristically shallow (less than 40 km) and spread over a width of up to 300 km as far NE as the Zagros Thrust (Nowroozi1976; 834

Fig. 3. Geological map of the Musandam peninsula and Dibba zone, Sultanate of Oman-UAE. Inset box shows area of western Musandam shown in Fig. 9 and lines of cross-sections in Figs 4 and 6.

Jackson et al. 1981). Fault plane solutions show movement Rum a1 Jibal Group on high anglereverse faults dipping 40-50" NE. Jackson The Permian to middleTriassic sequence comprises three (1980) interpretsthese earthquakes asthe result of formations, the Bih, Hagil and Ghail formations which are reactivation of earlier normal faults as thrust faults. Some approximately 1500 m thick and are exposed mainly along thrusts may also be reactivated as strike-slip faults. the south-east coast of Musandam, and east of the Hagil Window (Fig. 3). The BihFormation isa very thick (c. Stratigraphy of the Musandam shelf carbonates 650 m),monotonous, sequence of cliff-forming, massive, The Musandam shelf carbonate sequence is clearly part of brown and grey dolomites and dolomitic mudstonesshowing the Arabian platform and the stratigraphy (Fig. 5) is closely fenestralstructures and rare foraminifera (Fusulinids) of comparable theto oil-well sections drilled in the Permian age (Hudson 1960). The overlying Hagil Formation UAE-Oman foreland (Glennie et al. 1973, 1974; Ricateau is c. 260m thick, equally monotonous, and contains a late & Riche 1980; Searle et al. 1983). Permianforaminiferal fauna, whilst the GhailFormation THECULMINATION, OMANMUSANDAM 835

Bukha Wad, Khasab Khawr Habalayn Ras Habalayn Khawr Khasab Wad, Bukha Secun

Nlad WNW l I I ESE I I I H.W..,". J

Jebel Rababah Rawdah Bih al Wad! Dawhat Sharyah I l

WNW

km 1

Fig. 4. Structural sections across the Musandam peninsula (lines of section shown in Fig.3) (a) along Wadi Khasab, (b) along Wadi Rahabah-Rawdah.

consists of c. 600m of massive cliff-forming, grey-brown, a very prominent 20 m marker bed of dark brown dolomite dolomites of Lower Triassic age (Hudson 1960). well-exposed nearthe summit of JebelHagab and very useful formapping purposes. Musandam units 2 and 3 (middle-upper Jurassic) consist of laminatedcarbonate Elphinstone Group sandsandmuds containing abundantan fauna of TheUpper Triassic-lowermost Jurassic consists of two gastropods, corals and bivalves including Lithiotis sp. Searle formations-the TriassicMilaha Formation (c. 180 m et al. (1983) recordedchangea in facies across the thickness) and the overlying Upper Triassic-lower Lias Musandam with reefal boundstones and fore-reef talusalong Ghalilah Formation (c. 250 m thick). The Milaha Formation BathaMahani in the south indicating the Jurassic-Lower consists of argillaceousdolomitized lime mudstones Cretaceous shelf edge. The Lower CretaceousMusandam containing thick-shelled lamellibranchs (Megalodon sp.) and unit 4 consists of whitish thin-beddedradiolarian lime Triassic microfauna (Hudson 1960; Ricateau & Riche 1980). mudstones with tintinnids, and grey mark and grainstones All Permianand Triassic bedsrecord deposition in an with rudists, gastropods, corals, bivalves and stromatopor- inter-tidal or supra-tidal, tectonicallyquiescent oids. This unit is equivalent to the Thammama Group in the environment. central Oman mountains. The six formations of the Lower The GhalilahFormation consists of distinctive orange- Cretaceous recognized in the subsurface from wells in the red shales and quartz sandstones, with buff grey mark and UAE-Omanforeland (from base: the Salil, Rayda, brachiopod and gastropod-rich thin limestones. It records a Habshan, Lekhwair, Kharaib and Shuaiba Formations) can marine regression atthe end of the Triassicwith a large becorrelated broadly with theLower Cretaceous Musan- clastic influx, andcorresponds in time tothe breakup of dam unit 4 in the mountains. Gondwana and the rifting of Tethys. Wasia Group Musandam Group The Middle Cretaceous Wasia Group isapproximately The Musandam Group is approximately 1500m thick and 650 m thick at Fahud in Oman and 450 m thick in the Jebel spans the Jurassic andLower Cretaceous (Hudson & Akhdar shelf sequencein the centralOman Mountains Chatton 1959). Following Glennie et al. (1974) it is divided (Glennie et al. 1973, 1974). In the Musandam peninsula the into four formations. Musandam unit 1 at the base contains Middle Cretaceous isdivided into two formations:the 836 M. P. SEARLE

Basin Seamount I Slop* -Proximal ~istal Haybl stage Shell (Sumelnl - Oman U.A E GP 1 Hawaslna Complex Complex

PLIOCENE Mlshan > MIOCENE Fors Fors a Asmorl 5 OLIGOCENE t- -- a U EOCENE t- JAHRUM PALAEOCENE GP GP

HETTANGIAN RHAETIAN l- ylv0 CARNIAN vvv “W 4 ~AYBI a c ANlSlAN VOLCANICS

TATARIAN

5 EL W a ARTINSKIAN L! Ordovlclan basement J Osmar

Fig. 5. Stratigraphic chart for the Oman mountains (compiled mainly from Glennie et al. 1973, 1974) including stratigraphy usedin the Oman part of the mountains and in the UAE-Musandam Peninsula. lower, Nahr Umr and upper, Mauddud Formations, which emplacedduring the Coniacian to EarlyMaastrichtian. rest disconformably on the Musandam limestones beneath. Stablesedimentation on the shelf (Musandam),slope The Nahr Umr shallow water carbonates contain abundant (Sumeini complex) and Tethyan basin (Hawasina and Haybi benthic foraminifera particularly Orbitolina sp. and record a complexes)ended after theCenomanian earliestor marineincursion during the Albian. The overlyinglate Turonian.The Turonian was a time of non-deposition in Albianto Cenomanian Mauddud Formation is laterally northernOman and the Emirates which Glennie et al. equivalentto the Natih limestones known fromJebel (1974) referto as the Wasia-Arumabreak. This Akhdar and the Oman foreland. In north-westem Oman the non-deposition is probablyrelated to the flexural bulge Mishrif Formationspans thelate Cenomanian and migrating westward in front of the advancing thrust sheets. conformablyoverlies theMauddud Formation (Harris & The thrust sheets of the Dibba zone form a tectonic wedge Frost 1984). The Middle Cretaceous shelf carbonates of the along the continental margin and the effect of their loading Mauddudand Mishrif Formationsform the major has causedthe deepening of theforeland basin andthe hydrocarbon reservoirs in northern Oman. inboardmigration of theforebulge. Two majorforeland basins can bedocumented, both associated with major phases of thrusting: the Aruma foredeep developed in front Age of deformation of the late Cretaceous Oman Mountains thrust-sheets, and The Semail ophiolite,the Haybi, Hawasina and Sumeini the Pabdeh foredeep or successor basin developed in front thrust sheets exposed in the Dibba zone (Fig. 6) were all of the lower-mid-Tertiary Musandam culmination. THEMUSANDAM CULMINATION. OMAN 831

Arabian Musandam Dibba Gulf of NW Gulf mountains 1 zone I Oman SE

I -- , ArumaGroup - Tertiarythrusts Shelf carbonates - Cretaceous thrusts m Sumeinlshelf edge Q. 6. Balanced cross-section across the Musandam Mountains, Dibba zone and Semail ophiolite from the Hagil Window in the NW to the Gulf of Oman at Ras Dadnah northof Khawr Fakkan in the SE.

Aruma Foredeep Campman-?Lower Maastrichtian sediments. TheAruma Group represents the infill of amajor basin In the SW part of the Dibba zone in the Haybi complex, developed along the margin of the shelf carbonates and into a thick sedimentary mklange sequence (Kub MBlange) has which theOman Mountainsthrust sheets were emplaced beendated as lateCretaceous and correlated as adistal (Glennie et al. 1973, 1974; Robertson 1987). Because of the equivalent of theAruma Group (Searle et al. 1983; later uplift and erosion of Musandam, the facies transition Robertson 1987; Searle 1988). It contains the huge olistolith from true shelf to oversteepened slope is superbly exposed of Jebel Qamar south (Jebel Ramaq of Glennie et al. 1974), along the south-eastern margin of the Musandam (Searle et a Permian-Triassic exotic limestone block underlain by an al. 1983). AlongBatha Mahani, north of Idhn(Fig. 3) Ordovician-Devonian clastic basement sequence (Searle & conglomerates and slope-facies debrisflows containing clasts Graham 1982). The Permo-Triassicexotic limestone as young as Aptian grainstones overlie a major unconfor- sequence, nowin the highest thrustsheet beneath the mity that progressively cutsout the whole Lower ophiolite is interpreted as a rifted horst block originallv part Cretaceous.Alleman & Peters (1972) termedthese of the platform sequence, now incorporated into the late conglomerates the Ausaq Formation and tentatively dated Cretaceous Aruma foredeep. them as Campanian. Searle et al. (1983) map these as partof The Aruma foredeephas an arcuate shape parallel to the theMuti Formation (ArumaGroup), and suggestedthat OmanMountains (Fig. 7a) with thedeepest axis roughly theseAruma sediments overlay shelf, slope and basin along the west andsouth-west margins of the mountains sedimentsand are now sandwichedbetween these thrust (Glennie et al. 1974; Murris 1980). The Muti Formation (c. slices, frequently having formedaneasy dkcollement 300 m thick Coniacian to Campanian age) contains clasts of horizon. Robertson (1987) included these rocks as the Sayja shelf carbonates and outcrops all around the Jebel Akhdar member of the Muti Formation and interpreted them as the shelf carbonate culmination in the central Oman Mountains product of theuplifted and flexurally downwarped forming the highest stratigraphic levelof the shelf sequence. Cretaceous platform edge. The bulk of theAruma Group in the Oman-UAE Aruma facies siltstones, finely laminated mudstones and foreland is the FiqaFormation (Coniacian to Campanian conglomeratesconformably overlie Mayhah Formation age)reaching a maximum thickness of over4000m (Sumeini Group)carbonates and are affected by the (13 124ft) in the A1 Ali no. 2 well SW of the Musandam west-facing recumbentfolds of severalSumeini culmina- ‘nose’ (Burmss et al. 1983), althoughthis may be tions, notably those at Wadi Ausaq and Jebel Agah in the structurallythickened by thruststacking. The Juweiza Dibbazone (Searle 1988). Thesethin Aruma shales are Formation(Campanian to Lower Maastrichtianage) is lateral equivalents of the Fiqa shales known from foreland 2920m thick in the Juweiza no. 1 well (Glennie et al. 1974) well data (Glennie et al. 1974). They are folded around the and forms the highest level of the Aruma foredeepdeposits. Sumeiniculminations and are sandwiched between them The Juweiza Formation contains clastsof ophiolitic material and the underlyingMusandam shelf carbonatesand also and Hawasina-derived cherts indicating thatby this time the between the Sumeiniand the overlying Hawasina thrust Oman Mountains thrust sheets were emplaced and available sheets. These syntectonic facies of the Mesozoic slope are forerosion. Deep bathyalconditions along theArabian included in the Qumayrah Member of the Muti Formation margin lasted about 15 Ma from Coniacian until the end of andhave been dated micropalaeontologically as Cenoma- the Campanian. nian to Campanian age (Alleman & Peters 1972; Robertson Following themajor emplacement of theOman 1987). Thrusting of thestructurally lowest Sumeinislope Mountains thrust sheets in the Coniacian-Lower Maastrich- carbonates must thereforehave occurred during the tianthin lateritic conglomerates (Qahlah Formation) Campman-Maastrichtianafter deposition of these indicate sub-aerial exposure. These orange-red beds overlap 838 P. M. SEARLE

(b) Palaeocene - L. Eocene PabdehBasin (0) LateCarnpanlan Aruma Basin

Fig. 7. Palaeogeographic facies maps for Oman and the Middle East (a) during the late Campanian showing extent of the Aruma foredeep, and (b) during Palaeocene to early Eocene showing extent of the Pabdeh foredeep deposits (after Murris 1980). Note the Palaeocene-Eocene Pabdeh deep open marine facies along the length of the Zagros Mountains in SW Iran and in the United Arab Emirates foreland, but shallowing and dying out to the south.

the mantle sequence harzburgites along the western edge of (Searle 1985). A schematicrestored sectionacross the the ophiolite south of the Dibba zone. Transgressive Upper Tethyanoceanic rocks of theDibba zone from the Maastrichtianshallow marine, rudist-bearing carbonates Musandam shelf to the Semail ophiolite is shown in Fig. 8. (Simsima Formation)unconformably overlap the alloch- This illustrates the pre-Turonianpalaeogeography and thonous rocks (Glennie et al. 1974; S. Nolan & P. Skelton shows the overall SW-propagation of major thrusts and the pers. comm.) These are well exposed at Jebel Faiyah in the thin-skinnednature of the Haybiand Hawasina thrust southern part of the UAE (Fig. 3) where they overlie the sheets. The Semail thrust wasactive fromthe mid- harzburgites and form awest-verging asymmetric fold. Stable Cenomanian when amphibolites were formed and accreted fossiliferous shelf carbonate sedimentation was resumed in ontothe footwall. Temperatureswere of theorder of theUpper Maastrichtianafter the catastrophictectonic 700-870 "C at 4 kbar pressure (Searle & Malpas 1980, 1982; events associated with obduction of the Semail ophiolite and Ghent & Stout 1981). Astemperature and pressure Tethyan thrust sheets (Searle & Stevens 1984). decreased, greenschists were accreted below the amphibolites. The Semail thrustchanged from deepa ductile detachmentzone associated with subductionJaccretion Late Cretaceous thrusting processes to a high-level brittle thrust with time (Fig. 8). LateCretaceous thrust tectonics deduced from mapping Promontoriesin the Sumeini shelf edgerocks caused windows through the Semail ophiolite have been described deeper level detachmentthrusts and resulted inthe by Glennie et al. (1973,1974), Searle & Malpas (1980, culminations of the Sumeini,Asjudi and Haybi-Hawasina 1982), Graham (1980a, 1980b),Searle & Graham (1982), Windows (Searle 1985; Searle & Cooper 1986). Fossiliferous Coleman (1981), Michard (1983), Michard et al. (1984) and neo-autochthonous Upper Maastrichtianand Lower Tert- Searle (1985, 1988). In the Oman Mountains emplacement iary limestonesunconformably overlie the allochthonon of the Semail ophiolite, Haybi, Hawasina and Sumeini thrust both sides of the mountain range. Tertiary rocks exposed in sheets occurred during the Coniacian to Lower Maastrich- the central and south-east Oman Mountains are only gently tian.Thrusting was dominantly a SW-directed piggy-back folded (showing a maximum of 10%shortening in Jebel sequence of thin-skinnedthrust sheets, althoughsome Awaynah) and much of this may be gravity-driven folding 'out-of-sequence'motion on thrusts has been documented associated with uplift or culmination collapse. THECULMINATION, OMANMUSANDAM 839

WNW Musandam Sumeini Hawasina Semail ESE shelf 1 slope 1 basin ophiolite

++++++++++++ + + + + + + + + + + + + +T++X:+;++++++++++? ++it+++++++++ ...... &+LIALLIII...... _

H.T. - Hagabthrustgs - Greenschistfacies

S.T. - Semailthrustam - Amphibolitefacies V=H - -isograds - Metamorphic

Fig. 8. Simplified schematic restored sectionacross the Musandam shelf and adjacent Tethyan oceanic rocks to the Semail Ophiolite in Cenomanian-Turonian time prior to development of the Aruma foredeep. Pz, Palaeozoic; Mz, Mesozic; H. T., Hagab thrust; S. T., Semail thrust; gs, greenschists; am, amphibolites. Positionof the major thrusts are shown and the bending of metamorphic isograds down the subduction zone, to explain the inverted metamorphism(dashed lines) along the base of the Semail ophiolite sequence.

Pabdeh basin thrustsheets over previously older,higher ones (Searle Along the Arabian (Persian) Gulf and the UAE foreland a 1985). Permian to Cenomanian shelf carbonates of the distinctive deep-water Palaeocene-Eocene facies shows an Arabiancontinental margin werethrust approximately elongate basinclosing southwards (Fig. 7b), infilled with 4-15 km westwards over allochthonous Hawasina cherts that thick pelagic lime mudstones, and abundant conglomerates werepreviously thrust ontop of themduring thelate in theEocene (Murris 1980). Silty limestonesand shales Cretaceous(Searle et al. 1983). A detailedmap of the with detritalchert (Hawasina), marine marls and ar- western part of the Musandam peninsula is given in Fig. 9 gillaceous limestones form the base of the Pabdeh Group, and four sections across the area in Fig. 10. andrecord a deepening event in thenorthern Emirates. The timing of thrust culmination of the Musandam shelf Lower Eoceneconglomerates contain clasts of Hawasina sequence is contentious. Previous reports of Middle Eocene cherts and shelf carbonates with reworked Cretaceous fossils foraminifera (A. T. S. Ramsay in Searle et al. 1983) from together with indigenous Tertiary foraminifera. The Middle imbricate slices in the footwall of the Hagab thrust, east of andUpper Eocene shows a typical flysch sequence with Dhayah village arenot correct. The sampleshave been abundantturbidite flows and high sedimentationrates. reanalysed and found to contain late Cretaceous foramini- Conglomerates again contain reworked Mesozoic faunas and fera (M. Hart & J. D. Smewing pers. comm. 1988). clasts were derived from the upper levels of the culminating Tightly foldedlimestone conglomerates and marls of Musandam shelf sequence(Mauddud and Nahr Umr probableEocene age outcrop just west of themountain Formations). front at Tawi a1 Harf, 4.5 km south of the entrance of Wadi The Lower Tertiary stratigraphy clearly indicates that a Bih (Fig. 9). These rocks occur on the frontal fold of the second,later foreland basin developed in front of the Hagabthrust whichis subsurface at this locality. Inthe rapidly uplifting and thrust-culminatingMusandam shelf Khasab no. 1 and Bukha no. 1 wells off the west coast of carbonates. The Musandam uplift was not a simple isostatic OmaniMusandam, the base of theTertiary onthe uplift related tothe load of Cretaceousthrust sheets autochthonousforeland is at 3200m depth(Ricateau & emplacedover it; it wasuplifted during compressional Riche 1980) and at Ras a1 Khaimah is at 4620 m. deformation as a series of hanging-wall anticlines above the Thrust culmination of the Musandam musthave Hagabthrust. The Palaeocene-EocenePabdeh basindies occurred after the late Cretaceous Aruma Group deposition out to the south of the Musandam and is not present in the sometime during theTertiary. seemsIt likely that central Oman foreland (Fig. 7b). culminationcoincided with flexural downwarping of the Palaeocene-Eocene Pabdeh foreland basin, and prior to the Miocene beds which unconformably overlie Tertiary thrust Musandam thrusting tip lines offshore in the Gulf (Ricateau & Riche 1980). Culmination of the Musandam shelf carbonates was a late-stagebreakback, rethrusting event, which occurred after the major late Cretaceous Oman Mountains thrusting. Late Tertiary Breakbackthrusts cut up-section througha previously The youngest marine faunas of the Lower and Mid-Tertiary assembled thrust stack putting previously younger, lower foreland basin are middleOligocene in the Khasabno. 1 Fig. 9. Geologic map of the western part of the Musandam Peninsula in Rasa1 Khaimah. Lines of cross-sections are given in Fig. 10. I A

\ B

sc.m

1 50.000 V.111S.l - hormonl.l sc.1.

Fig. 10. Four structural sections across the frontal fold and Hagab thrust system in Ras al Khaimah (lines of sections shown in Fig. 9). Sections are balanced for known stratigraphic thicknesses of Permian andMesozoic shelf carbonate units. 842 M. P. SEARLE

and Bukha no. 1 wells in the Straits of Hormuz (Ricateau & Straits of Hormuz. South of Wadi Bih (Fig. 9) Musandam Riche 1980), and in theUAE foreland (Dammam structures plungegently southward; progressively higher Formation). The Upper Oligocene shows an abrupt change levels are exposed along the western edge of the mountains to anevaporitic environment with a basalhalite and an going south to BathaMahani. The Musandamfolds and upperanhydrite unit (Lower Fars Formation). By the thrusts plunge SSEinto the UAE-North Oman foreland mid-Oligocene thePabdeh basinwas filled andthe carrying all earlier structures in the Oman Mountains in a Musandam shelf carbonates were emergent having ramped piggy-back style. Blind thrusts on the eastern side of Jebel westward overthe foreland succession, thinned Aruma Faiyah (Fig. 3) and the western side of Qarn Mulayh also Group and previously emplaced Hawasina complex. affect Eocene rocks. The large-scale folds of Jebel Faiyah, Seismic sections off thenorth coast of Musandamand Qarn Nizwa and Qarn Mulayh areinterpreted as through the Straits of Hormuz show Upper Miocene beds hanging-wall anticlines aboveshort displacement Tertiary drapedover the tip lines of Tertiarythrusts and normal thrusts. faults (Ricateau & Riche 1980). Thrust culmination of the Musandam must therefore have been post-late Cretaceous, Central Musandam Peninsula pre-lateMiocene. Upper Miocene to Recentsediments onlapboth the west andeast sides of the Musandam East of thefrontal foldsystem the shelf carbonatesare peninsula below sea level. conformable above the Hagab thrust and folded into a series Quaternaryto Recent north-eastward tilting of the of large-scaledoubly-plunging folds about N-S or Musandam peninsula is indicated by the presence of wadi NNE-SSW axes. A few steep east-dipping thrust faults with terraces and Quaternary raised beaches on the western (Ras onlyminor amounts of displacement, and N-S aligned a1 Khaimah)side and by thedrowned rias forming normal faults cut the succession (Fig. 4). spectacular 'fjords' along the north and east (Oman) coasts TheJebel Rahabah anticline axis is a 10 km half- (Fig. 2). Vita-Finzi in Cornelius et al. (1973) has recorded wavelengthfold in the north-westernpart of Musandam over 60 m of subsidence in the last 10 000 years along the (Fig. 4b).Its western limbis underlain by a steep thrust north and east coasts of the Musandam Peninsula. exposed in Wadi Rahabah (Fig. 9). The eastern limb is a gentle (20") dip slope west of the Oman border post in Wadi Bih and up which the new road to Khasabhas been Geometry of the Musandam thrust sheets constructed, following thedip slope of the Ghalilah Formation. TheRibat anticline in the north-east is a Two cross-sections across the Musandampeninsula are steep-limbed,box-folded, elongate dome with a doubly- shown in Fig. 4, their positions located on Fig. 3. Figure 9 plunging fold axis. shows a detailed map of the western part of the Musandam in theSheikdom of Ras a1 Khaimah (UAE).Four Steeply-dippingcontraction faults showonly minor cross-sections across the frontal fold and thrust system are amounts of displacement or throw. In the central part of the shownin Fig. 10balanced for the known stratigraphic Musandam peninsula these faults occur along the western thicknesses of the mid-Permian toCenomanian shelf shores of Khawr Habalayn, where Ghalilah Formation beds carbonates. are thrustover younger Musandam unit 1 beds with a downthrow of c. 100mto the west (Fig. 4a). The Wadi Ghail thrust and the Jebel Hagab thrust (Fig. 10d) are other Western leading edge examples of short-displacement contraction faults. Normal The western margin of Musandam shows a huge west-facing faultson NNE-SSW axes are widespreadand alsoshow frontal fold system with a series of major thrusts all showing only small amounts of throw. westwardmotion. These thrusts and folds affect the In the northern part of the Musandam peninsula, Biehler completemid-Permian to Cenomanian shelf sequence et al. (1975) map two small klippen of Hawasina radiolarian exposed,and presumably also affect the pre-Permian cherts in theQawah Sibi syncline axis resting ontop of basement. Further thrusts or steeply inclined, east-dipping Musandamunit 4. Ricateau & Riche (1980)also describe reversefaults probably also occur tothe west,buried some argillites with cobblesderived from Barremian to beneaththe coastal plain and offshore in the Gulf. The Cenomanian limestones which appear to be similar to the Hagabthrust shows the largestdisplacement and largest Dhera Formation in the Dibba zone (Glennie et al. 1974). amount of throw, and is exposed in the Hagil Window (Figs 9 & 10). Thrustgeometry varies considerably along strike.The South-eastern trailing edge frontal fold, exposed around the Hagil Window (Fig. 1Oc & The basal Hawasina/Sumeinithrust marking the northern d) is cut through by a major hanging-wall fault resulting in end of the Dibba zone (late Cretaceous in age) appears to the frontal fold wedge being overturned and squeezed out. cutupstratigraphic section towards the south-west. Behindthis wedge majora listric normalfault has Hawasina rocks are juxtaposed against Permian rocks north downthrown the completeJurassic-Cretaceous sequence of Dibba(Biehler et al. 1975) and Jurassic-Lower 400m to the east (Fig. 1Oc). These sections clarify how, on Cretaceous Musandam Group rocks at the western end of themap (Fig.9) this normal fault can be followedalong Batha Mahani. As thrust and fold vergence as well as minor strike into a thrust. kinematic indicators show thatthelate Cretaceous Major domal structures with gentle dips are centred on emplacement direction was towards the west or west-north- the SE corner of the Hagil Window and the eastern part of west inthe Dibba zone this would indicateeither (1) Wadi Sham (Fig. 9). North of Wadi Sham the Musandam westward tilting of the Musandam peninsula prior to late thrust sheets plunge gently northward; progressively higher Cretaceousthrusting of Dibbazone rocks, or (2) levels outcropnorth of AI Jeer towardsBukha and the post-emplacementnormal faultingalong thenorthern THECULMINATION, OMANMUSANDAM 843 margin of the Dibba zone, downthrowing Dibba zone rocks approximately 2.5 km to rest against PermianGhail Formation in the east near Bayah, and less than 500 m to rest againstMusandam unit 3 atthe western end of the Dibba zone. Faciesanalysis of the Lowerand Middle Cretaceous indicate that the shelf edge sloped south-east prior to nappe emplacementand did not tilt westward. The contact between the Dibba zone and the Musandam shelf is a late stage listric normalfault, caused by obliquedorsal culmination collapse during thrusting of the Musandam shelf sequence. It is interpreted here as a hinged listric normal fault showing a greater amount of throw in the north-east than in the south-west. There is little field evidence to suggest any major strike-slip faulting along the Dibba zone althoughsome dextral, right-lateral strike-slip faultingis presumed to havetaken place along the continent-ocean transform fault that parallels the Dibba zone, off the east coast of the Musandam peninsula. In the Sumeini, Hawasina and Haybi complexes, and the Semail ophiolite, almost all structures are related to thrust-emplacement.

Discussion: Straits of Hormuz syntaxis The dominantstructural feature of the Musandam peninsula-Straits of Hormuzarea is the 90" bend in the orogenicbelt from Iranto Musandamand thefurther arcuatebend of structuressouth of Musandam along the Oman Mountains. These orogenic syntaxes are perhaps best developed atthe western(Nanga Parbat Syntaxis) and Fig. 11. Palaeogeographic map of the Musandam-Straits of eastern(Namche Barwa Syntaxis) extremities of the Hormuz area showing the east-facing promontoryin the shelf Himalaya (Wadia 1931). Both these Himalayan syntaxes are carbonates prior to late Eocene-Oligocene thrustingof the Musandam. The shaded area shows the restored positionof the thought to result from a shear couple near a branch line shelf-slope break and arrows show emplacement vectors for the where the main E-W Himalayan thrusts join N-S thrusts or Dibba zone and Musandam thrusts. later strike-slip faults. The tectonics of the Musandam peninsula clearly form a link in bothtime and space between thelate Cretaceous ophiolite obduction tectonics of the Oman Mountains to the simple geometry of the Rocky Mountain examples, in that south-east and the late Tertiary Zagros fold and thrust belt the thrusts do not all join a basal dCcollement horizon and of SW Iran to the north-west. The folds and thrusts of the the major thrusts are also of different ages. Musandam peninsula are notlaterally-continuous, but Thetransfer zones showprogressively thicker-skinned plunge northwards below the Straits of Hormuzand tectonics fromOman to Iran, theybecome progressively south-south-westwards into the UAE-Oman foreland with younger from Oman to Iran and their timing correlates with decreasingamounts of shortening awayfrom the main collision of theArabian plate with the centralIran culmination of the Musandam. The amount of shortening microcontinentand the ensuing crustal-scale folding and andcrustal thickening inthe shelf carbonatesequence is thrusting of the Zagros orogeny. The Oman segment has yet much greaterMusandamin than in thesouthern to collide with Makran and Baluchistan thereby preserving Emirates-northern Oman area. The reason for this can only all the late Cretaceous ophiolite obduction tectonics seen in be explained by a major palaeogeographic promontory of the Oman Mountains, and the accretionary prism along the the shelf in the Musandam area, whereas to the south of the Makrancoast. The Musandam peninsula separatesthe Dibba zone was a major re-entrant (Fig. 11). continent-ocean collision belt of the Oman Mountains from Crustal shortening by thrust stacking is transferred from the continent-continent collision belt in theZagros. The the NE-SW Dibba zone to the N-S Musandam and across Zendan strike-slip fault is thought to mark the NE limit of theStraits of Hormuz to the NW-SE Zagrostrend by a the Arabian plate indentor. The Straits of Hormuz and the series of thrust transfer zones along branch lines at different western part of the Gulf of Oman are therefore unique and structural horizons. Dahlstrom (1970) implied the existence complex areas of plate segmentation associated with early of a basic transfer mechanism that enables adjacent, roughly stages of the collision of two continental plates. contemporaneousstructures totake over the shortening functions of thosethat die out. Using examples fromthe Canadian Rocky Mountains, Dahlstrom (1970) showed that Conclusions there the principal thrust-faults all join the underlying sole (1) Two foreland basinsaccumulating syn-orogenic flysch- thrust,and that all thesestructures developed simul- typesediments were developed along theUAE-north taneously. The thrust transfer zones in Musandam and the Omanplatform. The Coniacian-LowerMaastrichtian Straits of Hormuzare clearly more complicated thanthe Aruma basin foredeep developed in front of the main Oman M . P. SEARLE844 P. M. mountainsas a result of the loading of the Sumeini, (ed.) Trench-Forearc Geology. SpecialPublication of theGeological Hawasina,Haybi and Semailophiolite thrust sheets. The Society, London, 10, 373-85. Palaeocene-Eocene-LowerOligocene Pabdeh basin fore- BEWENAN,M. & KING,G. C. P. 1981.Towards a palaeogeography and tectonicevolution of Iran. CanadianJournal of EarthSciences, 18, deep developed in front of the culminating Musandam shelf 210-65. carbonates in the northern Emiratesdying out to the south. BIEHLER,J., CHEVALIER,C. & RICATEAU,R. 1975. Cartegeologique de la (2) TheHagab thrust shows 4-15 km of westward peninsula de Musandam. Edition B. R. G. M., Orleans, France. translation of the Musandam shelf sequence over previously BLANDORD,W. T. 1872. Notes on the geological formations seen along the coasts of Baluchistan and Persia from Karachi to the headof the Persian allochthonousHawasina cherts as a late-stage breaching Gulf and some Gulf Islands. Records of Geological Survey of India, 5, thrust.Extrapolation of foreland successions inRas a1 41-5. Khaimah andthe Arabian Gulfsuggest thatUpper Bumss, R. C., Cercone, K. R. & Harris,P. M. 1983.Fluid inclusion Cretaceous Aruma Group andHawasina complex sediments petrographyand tectonic burial history of the A1 AliNo. 2 well: could occur in the subsurface along the footwall east of the Evidence for the timing of diagenesis and oil migration, northern Oman Foredeep. Geology, 11, 567-70. mountain front. COLEMAN,R. G. 1981.Tectonic setting for ophiolite obduction in Oman. (3) The Hagab thrust and Musandam structures plunge Journal of Geophysical Research, 86, 2497-508. north from theHagil Window and Wadi Sham domes below COLMAN-SADD,S. P. 1978. Fold Development in Zagros Simply Folded Belt, theStraits of Hormuz.They also plunge SSW fromthe southwest Iran. American Association of Petroleum Geologists, Bulletin, 62, 984-1003. Hagil Window-Wadi Bih culmination into the UAE-north CORNELIUS, P. S.,F. FALCON, N.L., SO-, D. & VITA-FINIZI, C.1973. The Omanforeland, carrying ina piggy-back fashion, all MusandamExpedition 1971-2 scientific results. GeographicalJournal, overlying, earlier, late Cretaceous structures of the Oman l39, 400-25. Mountains. DAHLSTROM,C. D. A. 1970. Structural Geology in the eastern margin of the Canadian Rocky Mountains. BulletinCanadian Petroleum Geology, 18, (4) The trailing(south-east) edge of the Musandam 332-406. culmination is a hinged listric normalfault downthrowing GHENT,E. D. & STOUT,M. Z. 1981. Metamorphism at the base of the Samail Dibba zone rocks (late Cretaceous Sumeini, Hawasina and ophiolite,southeastern Oman Mountains. Journal of Geophysical Haybi thrust sheets) to thesouth-east 2.5 km at Bayah north Research, 86, 2557-71. GLENNIE,K. W., BOEUF,M. G. A., HUGHES CLARK,M. W., MOODY-STUART, of Dibba, and less than 500m at the western end of Batha M,, PILAAR,M. F. & REINHARDT, M. B. 1973. Late Cretaceous nappes in Mahani. Dorsal culmination collapse is responsible for the the Oman Mountains and their geologic evolution. American Association south-east-facing folds and rotated (inverted) thrusts in the of Petroleum Geologists, Bulletin, 57, 5-27. Dhera/Dibba Formations (Hawasina complex) adjacent to ---_-, , , , , & - 1974. Geology of rhe Oman Mountains. Verhandetingen van Ket Knoninktijk Nederlands geolgisch Minjbouw- the fault. kundig Genootschap. (5) A major north-east-projectingpromontory in the GRAHAM,G. M. 198Oa. Structureand sedimentology of theHawasina mid-Cretaceous shelf edgein the Musandam region was Window, Oman Mountains. PhD thesis, Open University, UK. responsible forthe subsequent thrust culmination of the - 1980b. Evolution of a passive margin and nappe emplacement in the shelf carbonates. It was bounded to the south by a major OmanMountains. In: PANAYIOTOU,A. (ed.) Proceedings of the International Ophiolite Symposium, Cyprus, 1979, 414-23. re-entrant with minor strike-slip lateral boundary faults in HARRIS,P. M. & FROST,S. H. 1984.Middle Cretaceous Carbonate the area of the Dibba zone. Reservoirs Fahud Field and Northwestern Oman. American Association (6) Crustal shortening by thrust stacking was transferred of Petroleum Geologists, Bulletin, 68, 649-58. duringprogressive continental collision fromthe NE-SW HAIAYNES,S. J. & MCQUILLAN,H. 1974. Evolution of the Zagros suture zone southern Iran. Bulletin of the Geological Society of America, 85, 739-40. Dibbazone (late Cretaceous thrusting) theto N-S HUDSON,R. G. S. 1960. The Permianand Trias of theOman Peninsula, Musandam(lower Tertiary thrusting) along aseries of Arabia. Geological Magazine, 97, 229-308. plunging branch lines and two major pivot points, one just - & CHA-ITON,M. 1959. TheMusandam Limestone (Jurassic to Lower south of the Musandam 'nose', the other in the Straits of Cretaceous) of Oman,Arabia. Notes etMemoires Moyen Orient, 7, Hormuz.The combination of thesemajor diachronous 69-93. -, MCGUIGAN,A. & MORTON,D. M.1954. The structure of the Jebel transfer zones defines a 90" orogenic bend in the Straits of Hagab area, Trucial Oman. Quaterly Journal of the Geological Society of Hormuz-Musandam area which alsodivides a continent- London, 110, 121-52. continentcrustal collision belt to the north-west(Zagros) HUTCHISON,I., LOUDEN,K. E., WHITE,R. S. & VON HERZEN,R. P. 1981. fromcontinent-oceanica plate collision belt tothe Heat flowand age of the Gulf of Oman. Earthand Planetary Science Letters, 56, 252-62. south-east (Oman). JACKSON,J. 1980. Reactivation of basement faults and crustal shortening in orogenic belts. Nature, 283, 343-6. Thiswork was funded by AmocoPetroleum Co. (International), -, FITCH,T. J. & MCKENIZE,D. P.1981. Active thrustingand the evolution of the Zagros Fold belt. In: MCCLAY, K. R. & PRICE, J. Amoco Oman and Amoco Sharjah Petroleum Co. Thanks are due N. (eds) Thrust and Nappe Tectonics. Special Publication of the Geological to Sheik Saqr of Ras a1 Khaimah and the Wali of Bayah (Oman Society, London, 9, 371-9. Musandam) for permission to work in the Musandam mountains. I JACOB,K. & QUITIMEYER,R. 1979. The Makran region of Pakistan and Iran: also thank S. O'Connor, T. Patton, I. Poyntz,J. Smewing, N. Trench-arcsystem with active plate subduction. In: FARAH,A. & James, T. Calon, P.Hancock, A. Robertson and D. Cooper for DEJONG,K. A.(eds) Geodynamics of Pakistan. GeologicalSurvey discussions. The Ministry of Petroleum and Minerals in Muscat and Pakistan, Quetta, Pakistan, 306-17. JAMES,G. A. & WYND,J. G. 1965. Stratigraphic nomenclatureof Iranian Oil Amoco Petroleum Co. (International) have kindly given permission ConsortiumAgreement Area. American Association of Petroleum for publication. Geologists, Bulletin, 49,2182-245. KADINSKY-CADE,K. & BARAZANGI,M.1982. Seismotectonics of Southern Iran: The Oman Line. Tectonics, 1, 389-412. References KOOP, W. J. & STONELEY, R.1982. Subsidence history of the Middle East ZagrosBasin, Permian to Recent. PhilosophicalTransactions of the ALLEMAN,F. & PETERS,TI. 1972. The Ophiolite-Radiolaritebelt of the Royal Society of London, AM5, 149-68. North Oman Mountains. Eclogue Geologicae Heluetiae, 65, 3, 657-97. LEES, G. M.1928. Thegeology and tectonics of Omanand of part of ARTHURTON,R. S., FARAH, A. & AHMED,W.1985. TheLate southeasternArabia. QuarterlyJournal of the Geological Society of Cretaceous-Cenozoichistory of westernBaluchistan Pakistan-the London, 84, 585-670. northern margin of the Makran subduction complex. In: LEGGEIT,J. K. MICHARD,A. 1983. Les nappes de Mascate (Oman), Rampe epicontinentale T H E MUSANDAM CULMINATION,MUSANDAMOMAN THE 845

d'obduction a facies schiste bleu, et la dualite apparente des ophiolites -& MALPAS,J. 1980. The structure and metamorphism of rocks beneath Omanaises. Bulletin des Sciences Geologiques, 36, 3-16. theSemail ophiolite of Omanand their significance inophiolite -, BOUCHEZ,J. L. & OUAZZANI-TOUHAMI,M. 1984. Obduction-related obduction. Tramactiom of the Royal Society of Edinburgh: Earth planarand linear fabrics in Oman. Journal of Struciural Geology, 6, Sciences, 71,213-28. 39-49. -& - 1982. Petrochemistry and origin of sub-ophiolitic metamorphic MURRIS,R. J. 1980. MiddleEast: Stratigraphic evolution and oil habitat. andrelated rocks in the Oman Mountains. Journal of the Geological American Association of Petroleum Geologirtr, Bulletin, 64,597-618. Society, London, W9,.235-48. NOWROOZI,A. 1976. Seismototectonicprovinces of Iran. Bulletin of the -& SEVENS, R. K. 1984, Obduction processes in ancient, modem and Seimological Society of America, 66, 1249-76. futureophiolites. In: GASS,I. G., LIPPARD, S. J. & SHELTON,A, W. PILGRIM,G. 1908. Geology of the Persian Gulfand adjoining portions of (eds) Ophiolites and Oceanic Lithmphere. SpecialPublication of the Persia and Arabia. Geological Imtiiute of India Memoir, 34, 4. Geological Society, London, W, 303-20. PLAIT,J. P,, LEGGETT,J. K., YOUNG,J., RA=, H. & ALAM,S. 1985. -, JAMES,N. P., CALON,T. J. & SMEWING,J. D. 1983. Sedimentological Large-scalesediment underplating in the Makran accretionary prism, andstructural evolution of theArabian continental margin in the southwest Pakistan. Geology, W, 507-11. Musandam Mountains and Dibba zone, United Arab Emirates. Bulletin RCATEAU,R. & R~E,P. H. 1980. Geology of theMusandam Peninsula of the Geological Society of America, 94, 1381-400. (Sultanate of Oman)and its surroundings. Journal of Petroleum SHEARMAN,D. J. 1977. Thegeological evolution of southernIran. Geology, 3, 139-52. Geographical JOUrMl, 142, 393-410. kcou, L. -E. 1971. Le croissantophiolitique pen-Arabe une ceinturede STOCKLIN,J. 1968. Structuralhistory and tectonics of Iran:A review. nappes mises en placeau Cretace superieur. Reuues Geographique American Association of Petroleum Geologists, Bulletin, 52, 1229-58. Physique et Geologique, W, 327-50. -1974. Possible ancient continental margins in Iran. In: BUM, C. L. & ROEIERTSON,A. H. F. 1987. The transition from apassive margin to an Upper DRAKE, C. L. (eds) The Geology of Continental Margins. Springer- Cretaceous foreland basin relatedto ophiolite emplacement inthe Oman Verlag, New York, 873-87. Mountains. Bulletin of the Geological Society of America, 99, 633-53. TAKIN,M. 1972. Iranian geology and continental drift in the Middle East. SEARLE, M.P. 1985. Sequence of thrusting and origin of culminations in the Nature, 235, 147-50. northern and central Oman Mountains.Journal of Structural Geology, 7, WADIA,D. N. 1931. The syntaxis of thenorth-west Himalay&its rocks, 129-43. tectonics and orogeny. India Geological Survey Recordr, 65, 189-220. -1988. Thrust tectonics of the Dibba zone and the structural evolutionof WELLS,A. J. 1969. The Crush zone of the Iranian Zagros Mountains and its the Arabian continental margin along the Musandam Mountains (Oman implications. Geological Magazine, 106, 385-94. and United Arab Emirates). Journal of the Geo[ogical Society, London, WHITE, R.S. &L Rms, D. A. 1979. Tectonics of the Western Gulf of Oman. 145,43-53. Journal of Geophysical Research, 84, 3479-89. - & COOPER,D. J. W. 1986. Structure of theHawasina Window WILSON,H. H. 1969. Late Cretaceous eugeosynclinal sedimentation gravity culmination,central Oman Mountains. Tramactions of the Royal tectonics,and ophiolite emplacement in the Oman Mountains, S. E. Society of Edinburgh: Earth Sciences, 77, 143-56. Arabia. American Association of Petroleum Geologim, Bulletin, 53, -& GRAHAM,G. M. 1982. 'Oman Exotics-Oceanic carbonate build-ups 626-71. associated with the early stagesof continental rifting. Geology, 10, 43-9.

Received 12 January 1988; revised typescript accepted 17 March 1988.

View publication stats