See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/249546472 Structure of the Musandam Culmination (Sultanate of Oman and United Arab Emirates) and the Straits of Hormuz Syntaxis 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 © 1988 Geological Society of London Journal of the Geological Society, London, Vol. 145, 1988, pp. 831-845, 11 figs. Printed in Northern Ireland 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-south- west 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