Keywords
Post-obductional E/W-shortening; wrench-fault assemblage; reactivation of basement faults; strike-slip tectonics
1. Introduction
During the Late Cretaceous, northeastern Oman was overthrust from the NE by the iconic Semail Ophiolite, including tectonically underlying nappes of Neo-Tethyan sedimentary rocks (e.g., Glennie et al., 1974). N/S-shortening was recorded in the Oman Mountains during the Cenozoic due to the Arabia-Eurasia convergence (e.g., Fournier et al., 2006; Hansman et al., 2017; Levell et al., 2021). In addition, the Oman Mountains, especially their southeastern part, underwent post-mid-Eocene ~E/W-shortening (e.g., Mann et al., 1990; Wyns et al., 1992; Fournier et al., 2006). This study focuses on timing and cause of this shortening.
Numerous N/S-striking post-mid-Eocene compressional structures of the eastern Oman Mountains are documented in maps and other publications (Table 1). However, these structures have never been examined in detail with respect to a common genetic context. Furthermore, major ~N/S-striking compressional structures of Oligocene to early-mid-Miocene age also occur on the western flank of the northern Oman Mountains (prominent ~N/S-oriented Hagab Thrust in the Musandam Peninsula and the NNW/SSE-trending Jabal Hafit Anticline; Fig. 1; Table 1). Besides ~N/S-oriented compressional features, abundant relevant post-mid-Eocene sinistral ~NW-striking faults are common in the eastern Oman Mountains, too.
At a local scale, Mann et al. (1990) recognized open N-trending folds in the Rusayl Embayment (Fig. 1), affecting mid-Eocene rocks. They related these folds to exhumation and gravitational collapse of the nearby Saih Hatat and Jabal Akhdar domes (Fig. 1), causing extensional transport to the NW from Saih Hatat Dome and to the NE from the Jabal Akhdar Dome. The converging rock masses produced N-trending folds. For the Rusayl Embayment, this would be a suitable geometric explanation. However, similarly aged N-trending compressive structures also exist beyond the Rusayl Embayment (i.e., Hagab Thrust, Jabal Hafit, Qalhat Fault; Fig. 1), where the formation of such structures must have a different cause.
At a large regional scale, Fournier et al. (2006) identified two compressional events in the Oman Mountains, which started during the late Oligocene or early Miocene with E/W to NE/SW-directed shortening (Fig. 2). They did not identify the actual causes of the defomation but pointed out that the origin of E/W to NE/SW-shortening is “not entirely clear and could result from the interaction between the Arabian and Indian plates”. Gaina et al. (2015) suggested minor E/W-shortening between Arabia and India from 40 Ma to the present (their Fig. 7). The strike of NW-striking faults varies in the eastern Oman Mountains, ranging from WNW to NNW. For simplification, we will refer to them as “NW-striking”. Such faults are known from the Rusayl Embayment in the NW, the southern margin of the Saih Hatat Dome, the Salma Plateau, the inverted Abat Basin and the Jabal Ja’alan area in the SE (Figs. 2 and 3; Table 1).
Table 1. Documented N/S to NW/SE-oriented post-obductional compressive structures and sinistral NW-striking faults of the Oman Mountains with focus on the eastern Oman Mountains. Listed in appearance from the NW (Musandam Peninsula) to the SE (Jabal Ja’alan/Batain area).