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).
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