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Tectonic Evolution of the Oman Mountains: an Introduction Downloaded from http://sp.lyellcollection.org/ by guest on October 2, 2021 Tectonic evolution of the Oman Mountains: an introduction H. R. ROLLINSON1*, M. P. SEARLE2, I. A. ABBASI3, A. I. AL-LAZKI4 & M. H. AL KINDI4 1School of Science, University of Derby, Derby DE22 1GB, UK 2Department of Earth Sciences, University of Oxford, South Parks Rd, Oxford OX1 3AN, UK 3Department of Earth Sciences, Sultan Qaboos University, P.O. Box 50, Muscat 123, Sultanate of Oman 4Exploration Department, Petroleum Development Oman, PO Box 81, Postal Code 100, Mina Al-Fahal, Oman *Corresponding author (e-mail: [email protected]) It is now more than 20 years since the Geological During the late 1970s and 1980s two major Society published The Geology and Tectonics of research teams from the USGS (led by Bob Coleman the Oman Region (Robertson et al. 1990) as one and Cliff Hopson) and the Open University, UK of its early special publications. That volume, the (led by Ian Gass, John Smewing and Steve Lip- ‘blue book’ as it became fondly known to multiple pard) conducted detailed geological surveys across generations of undergraduates, has been a major the ophiolite in the Muscat–Ibra transect (USGS) reference on the geology of Oman for many who and northern ophiolite (OU), respectively. Their work in the region. This present volume, more results were published in a Special Issue of the modest in its size compared to its illustrious prede- Journal of Geophysical Research (volume 86, cessor, is the fruit of a conference on The Geology editors Coleman & Hopson 1981) and the Geologi- of the Arabian Plate and the Oman Mountains cal Society of London Memoir no. 11 (Lippard et al. held in January 2012 at Sultan Qaboos University 1986). Major systematic mapping of the Oman in Muscat, organized by Professor Sobhi Nasir Mountains as well as the interior, Batain coast and with colleagues from Sultan Qaboos University, Dhofar region has been carried out by the Bureau the Oman Government and the Geological Society de Recherches Ge´ologiques et Minieres (BRGM), of Oman. Since the first comprehensive study of France, the Geological Survey of Japan and the the geology of the Oman Mountains during the University of Berne, Switzerland (see for example late 1960s and early 1970s by Ken Glennie and his Peters et al. (1991)) and the whole UAE part of the team from Shell, the Oman Mountains have been northern Oman Mountains was recently mapped by known to contain some of the most spectacular the British Geological Survey (UAE Ministry of and best-exposed geology not only in the Middle Energy Petroleum & Mineral Resources 2012). East but across the world. A summary of the geo- During the last 20 years major research groups logy and the lithostratigraphy is given in Figure 1. from France, Japan, USA and the UK have con- The publications of Glennie et al. (1973, 1974), ducted research projects in the country. Detailed building on many earlier Shell geologists’ internal field studies of the Oman Ophiolite have been reports (notably D. M. Morton, R. H. Tschopp, combined with geochemical and isotopic studies H. H. Wilson, B. M. Reinhardt and M. W. Hughes- to determine the tectonic setting and evolution of Clarke) set out the major stratigraphic framework the Late Cretaceous oceanic crust and upper mantle for the whole area, defined the major structures (Boudier & Juteau 2000). Field-based studies have and critically interpreted the Semail Ophiolite as a also been linked to ocean drilling sites, in particular thrust sheet of oceanic crust and upper mantle the East Pacific rise, to compare the ophiolite to emplaced onto the previously passive continental regions of active fast spreading. Key to the obduc- margin of Arabia. Since the Glennie et al. (1974) tion–emplacement story are the amphibolite and memoir was published, oil companies have carried greenschist facies rocks in the metamorphic sole out increasingly more intensive work comparing that record an inverted metamorphic field gradient well sections in the interior with the Permian– along the base of the ophiolite. The ophiolite has Mesozoic shelf carbonates so beautifully exposed been the source of recent detailed studies involving along numerous wadis cutting through the Jebel the possible sequestration of CO2 by the serpentini- Al-Akhdar and Saih Hatat massifs. zation reactions of ultramafic rocks. From:Rollinson, H. R., Searle, M. P., Abbasi, I. A., Al-Lazki,A.&Al Kindi, M. H. (eds) 2014. Tectonic Evolution of the Oman Mountains. Geological Society, London, Special Publications, 392,1–7. http://dx.doi.org/10.1144/SP392.1 # The Geological Society of London 2014. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on October 2, 2021 2 H. R. ROLLINSON ET AL. Fig. 1. (a) Structural map of Oman showing the main geological features and the subsurface oil and gas fields. Downloaded from http://sp.lyellcollection.org/ by guest on October 2, 2021 INTRODUCTION 3 Fig. 1. (b) The lithostratigraphy of Oman. After Forbes et al. (2010), used with permission from GeoArabia. Downloaded from http://sp.lyellcollection.org/ by guest on October 2, 2021 4 H. R. ROLLINSON ET AL. The Oman Mountains contain one of the best- imminent danger of destruction, such as the Wadi exposed and best-understood fold–thrust belts Mayh sheath fold, the As Sifah eclogites and anywhere on Earth; much research has focused on several important fossil localities (Jebel Sumeini, the structural evolution of the belt with major rudist reefs in the Huqf, etc.). The suggestion of phases of deformation during the Late Cretaceous establishing GeoParks in Oman has been around associated with ophiolite obduction and another for a long time but it is imperative now to get these major phase of folding and uplift during the Late sites fenced and protected in law. Elsewhere, in par- Palaeogene. Salt exposures have been recently ticular in the desert, the very isolation of some classic discovered in the core of a few of the large-scale localities means that they cannot be completely pro- culminations in the mountains. The Oman Moun- tected from ‘treasure hunters’, although protection tains have a unique belt of high-pressure eclogite, measures have recently been deployed in a number blueschist and carpholite-grade metamorphic rocks of geosites. An additional benefit of this paper, per- in northeastern Oman, a zone associated with haps an unintended consequence, is an excellent attempted subduction of the leading margin of Ara- ‘geotour’ through Oman’s classic geological sites. bian crust beneath the Semail Ophiolite–Gulf of Our first major section of this volume provides Oman oceanic crust. Oman also contains a unique new views on the Tectonics of the Arabian Plate. zone of me´lange, alkaline igneous rocks and Meso- Al-Lazki et al. (2014) use mantle tomographic zoic basinal sediments along the Batain me´lange methods to map out the eastern margin of the beneath the Masirah Ophiolite along the south Arabian Plate along the site of the Arabia–Eurasia coast of Oman. Outcrops of Proterozoic basement plate boundary. They find that in the NE the litho- occur in the Marbat region of south Oman. Com- spheric suture follows the Zagros Suture and that in bining field-based surveys in the mountains with the east the Makran region has the characteristics increasingly more detailed industry 2D and 3D of active subduction, while western Makran is seismic lines in the interior has led to the Oman– underlain by a low Pn velocity anomaly indicative UAE region being one of the most detailed and of hot and unstable upper mantle. Of particular comprehensively understood oil and gas provinces importance is the new finding that northern Oman known anywhere. is underlain by hot and possibly molten upper mantle. This anomaly is perhaps a remnant of the down-going oceanic slabs associated with the Present volume: Tectonic evolution of the Oman Ophiolite’s obduction process. Two papers Oman Mountains discuss the western margin of the plate. Al-Kwatli et al. (2014) discuss the link between tectonic style In the last 10 years groups from France, Germany, and Cenozoic magmatism from Syria in the north- Japan, USA and the UK as well as scientists from ern part of the Arabian Plate. Their new geochemical within Oman itself have continued to conduct sig- and geochronological data provide evidence for nificant research projects in the country, achieving magmatism related to extensional tectonics over results that move us on from the science of the the past 18 Ma, which is closely related to Red Sea 1990s and 2000s. It is therefore timely to provide rifting. Using a different information source (that a new summary of geological, geophysical and geo- of terrestrial and freshwater snails) from a more chemical data on the greater Oman region. Our southerly region of the Arabian Plate, Pickford volume is divided into three main sections which et al. (2014) also constrain the timing of the open- discuss the Tectonics of the Arabian Plate, the Pet- ing of the Red Sea. They show from their palae- rology of the Oman Ophiolite and the Sedimentary ontological evidence that the uplift of the Dhofar and Hydrocarbon Systems of Oman. The volume Plateau must have occurred later than the Early starts however with an impassioned plea from Oligocene. Searle (2014) for a fresh initiative towards geocon- The rocks of the Precambrian basement to the servation in Oman. He argues that in some parts Arabian Plate are rarely exposed in Oman. The of the country the pressure of development might new results of U–Pb zircon geochronology by overtake the need to conserve what are, in some Rantakokko et al. (2014) for the Marbat region in cases, world-class sites of scientific importance.
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