Oman

Western Neotethys subduction system

104

±

1

Ma

New destructive boundary

B2000O

Schematic tectonic reconstruction of the Oman SZI event (modified from van Hinsbergen et al., 2019a,b). Shown are the new subduction zone (pink line), other active subduction zones (solid purple lines), and transform faults (red dashed lines).

The Oman subduction zone, together with the Anatolian subduction zone, formed the Western Neotethyan subduction system. The Oman SZI event was widely thought to have initiated along, or in the vicinity of, a Neotethyan mid-oceanic ridge (e.g., Boudier et al. 1988; Nicolas et al., 2000; Duretz et al., 2016). Recently, it has been suggested that the subduction zone initiated along a fracture zone, located parallel to the Arabian continent (van Hinsbergen et al., 2019a; Maffione et al., 2017).

The subduction zone seems to have initiated at 104 Ma (e.g., Guilmette et al., 2018) within Neotethyan oceanic lithosphere, similar to the Anatolia SZI (see Anatolia SZI event in the SZI database), but with the opposite vergence (van Hinsbergen et al., 2019a). At the time of SZI, both the downgoing and overriding plates were oceanic lithosphere of the Neotethys. In the case of Oman (and in contrast to the Anatolian subduction zone), the ‘Anadolu plate’ (Gürer et al., 2016) subducted below the Africa-Arabia continental plate (i.e., ‘Greater Adria’ of Gaina et al., 2015 and van Hinsbergen et al., 2019a,b). The subduction zone later terminated and resulted in widespread ophiolite obduction onto the Arabian continental margin in the Late Cretaceous at 70 ± 5 Ma, represented by the Semail ophiolite of Oman, the Kermanshah and Neyriz ophiolites of Iran, the Baer Bassit ophiolite of Syria, the Hatay ophiolites of SE Turkey, and the Troodos ophiolite of Cyprus (Koop and Stoneley, 1982; Searle and Cox, 1999; Nicolas et al., 2000; Al-Riyami et al., 2002; Searle et al., 2004; Dilek and Furnes, 2009; Homke et al., 2009; Agard et al., 2011).


The oldest subduction-related products in Oman are represented by the plutonic section of the Semail ophiolite, which indicates that the ophiolitic crust formed at a fast spreading ridge in less than 1 Myr in the Late Cretaceous (zircon U–Pb ages of ~96–95 Ma; Rioux et al., 2016). Boninites are found in the Alley unit (also called V2) and are interbedded with tholeitic lavas (which have similarities with the Izu-Bonin-Mariana Early basalts). The age of the V2 unit is ~95 Ma (Rioux et al., 2016; Kusano et al., 2017). Basaltic andesites are also found in the Alley unit V2 (Alabaster et al., 1982), which are the products of the formation of the arc. Garnet Lu-Hf ages from the metamorphic sole constrain subduction-related prograde metamorphism to 104 Ma (Guilmette et al., 2018). The time lag between prograde metamorphism and the crystallisation of supra-subduction forearc crust argue for a horizontally-forced SZI event (Guilmette et al., 2018; van Hinsbergen et al., 2019a). The cause for this horizontally-forced SZI event within the western Neotethys remains speculative and matter of debate (Agard et al., 2007; van Hinsbergen et al., 2019a).


The model of Müller et al. (2016) does not implement this SZI event; instead, Oman is modelled as a passive margin during the Early Cretaceous, adjacent to a northeast-oriented transform (“Proto-Owen Fracture Zone”) running sub-parallel to the southeast margin of the Arabian subcontinent. From approximately 125 Ma, a southwest-facing intra-oceanic subduction zone (“Western Tethys intra-oceanic subduction zone”) began migrating toward the southwest from the southern margin of Eurasia (being separated from the latter by a backarc spreading system), and by ~85 Ma that intra-oceanic arc had collided with the passive margin of Oman. Following that collision, the margin of Oman remained passive until the Miocene, when it collided with the “Western Tethys subduction zone” along the southern margin of Eurasia.


The Arabia slab of the Atlas of the Underworld (van der Meer et al., 2017) has been identified to be related to the Oman SZI event, and its base age was recently updated to 105-102 Ma. This finding is supported in the vote maps, which shows a positive wavespeed anomaly consistently from 1100 km to 2000 km depth.

Seismic tomography VoteMap (Shephard et al., 2017) analysis of the Oman SZI event.

This SZI event is not implemented in the model of Müller et al. (2016).

Agard, P., Omrani, J., Jolivet, L., Whitechurch, H., Vrielynck, B., Spakman, W., Monié, P., Meyer, B., & Wortel, M.J.R., 2011, Zagros orogeny: a subduction-dominated process: Geological Magazine, v. 148, p. 692–725.


Alabaster, T., Pearce, J. A., & Malpas, J. (1982). The volcanic stratigraphy and petrogenesis of the Oman ophiolite complex. Contributions to Mineralogy and Petrology, 81(3), 168-183.


Al-Riyami, K., Robertson, A.H.F., Dixon, J.E., & Xenophontos, C., 2002, Origin and emplacement of the Late Cretaceous Baer–Bassit ophiolite and its metamorphic sole in NW Syria: Lithos, v. 65, p. 225–260.


Boudier, F., Ceuleneer, G., & Nicolas, A., 1988. Shear zones, thrusts and related magmatism in the Oman ophiolite: initiation of thrusting on an oceanic ridge. Tectonophysics 151, 275–296.


Dilek, Y., & Furnes, H. (2009). Structure and geochemistry of Tethyan ophiolites and their petrogenesis in subduction rollback systems: Lithosphere v. 113, p. 1–20.


Duretz, T., Agard, P., Yamato, P., Ducassou, C., Burov, E.B., & Gerya, T.V. (2016). Thermo-mechanical modeling of the obduction process based on the Oman Ophiolite case. Gondwana Res. 32, 1–10.


Gaina, C., van Hinsbergen, D.J.J., and Spakman, W. (2015), Tectonic interactions between India and Arabia since the Jurassic reconstructed from marine geophysics, ophiolite geology, and seismic tomography, Tectonics 34, p. 875-906.


Guilmette, C., Smit, M.A., van Hinsbergen, D.J.J., Gürer, D., Corfu, F., Charette, B., Maffione, M., Rabeau, O., & Savard, D. (2018). Forced subduction initiation recorded in the sole and crust of the Semail ophiolite, Oman, Nature Geoscience 11, p. 688-695.


Gürer, D., van Hinsbergen, D.J.J., Maţenco, L, Corfu, F., & Cascella, A. (2016). Kinematics of a former oceanic plate of the Neotethys revealed by deformation in the Ulukışla basin (Turkey), Tectonics 35, p. 2385-2416.


Homke, S., Verges, J., Serra-Kiel, J., Bernaola, G., Sharp, I.R., Garcés, M., Monetro-Verdu, I., Karpuz, R., & H, G.M. (2009). Late Cretaceous–Paleocene formation of the proto-Zagros foreland basin, Lurestan Province, SW Iran: Geological Society of America Bulletin, v. 121, p. 963–97.


Koop, W., & Stoneley, R. (1982). Subsidence history of the Middle East Zagros Basin: Permian to Recent: Philosophical Transactions of the Royal Society of London ser. A, v. 305, p. 149–168.


Kusano, Y., Umino, S., Shinjo, R., Ikei, A., Adachi, Y., Miyashita, S., & Arai, S. (2017). Contribution of slab-derived fluid and sedimentary melt in the incipient arc magmas with development of the paleo-arc in the Oman Ophiolite. Chemical Geology, 449, 206-225.


Maffione, M., van Hinsbergen, D. J., de Gelder, G. I., van der Goes, F. C., & Morris, A. (2017). Kinematics of Late Cretaceous subduction initiation in the Neo‐Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria. Journal of Geophysical Research: Solid Earth, 122(5), 3953-3976.


Nicolas, A., Boudier, F., Ildefonse, B., & Ball, E. (2000). Accretion of Oman and United Arab Emirates ophiolite–discussion of a new structural map. Mar. Geophys. Res. 21, 147–180.


Rioux, M., Garber, J., Bauer, A., Bowring, S., Searle, M., Kelemen, P., & Hacker, B. (2016). Synchronous formation of the metamorphic sole and igneous crust of the Semail ophiolite: new constraints on the tectonic evolution during ophiolite formation from high-precision U–Pb zircon geochronology. Earth Planetary Science Letters 451, 185–195.


Searle, M., & Cox, J. (1999). Tectonic setting, origin, and obduction of the Oman ophiolite. Geological Society of America Bulletin 111.


Searle, M., Warren, C., Waters, D., & Parrish, R. (2004). Structural evolution, metamorphism and restoration of the Arabian continental margin, Saih Hatat region, Oman Mountains. Journal of Structural Geology 26, 451–473.


Shephard, G.E., Matthews, K.J., Hosseini, K., & Domeier, M. (2017). On the consistency of seismically imaged lower mantle slabs. Scientific Reports 7.


van Hinsbergen, D.J.J., Maffione, M., Koornneef, L.M.T., & Guilmette, C. (2019a). Kinematic and paleomagnetic restoration of the Semail Ophiolite (Oman) reveals subduction initiation along an ancient Neotethyan fracture zone, Earth and Planetary Science Letters 518, p. 183-196.


van Hinsbergen, D.J.J., Torsvik, T.H., Schmid, S.M., Maţenco, L.C., Maffione, M., Vissers, R.L.M., Gürer, D., & Spakman, W. (2019b). Orogenic architecture of the Mediterranean region and kinematic reconstruction of its tectonic evolution since the Triassic, Gondwana Research, in press.

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