Late Eocene Uplift of the Al Hajar Mountains, Oman, Supported by Stratigraphy and Low‐Temperature Thermochronology

Abstract

Uplift of the Al Hajar Mountains in Oman has been related to either Late Cretaceous ophiolite obduction or the Neogene Zagros collision. To test these hypotheses, the cooling of the central Al Hajar Mountains is constrained by 10 apatite (U‐Th)/He (AHe), 15 fission track (AFT), and four zircon (U‐Th)/He (ZHe) sample ages. These data show differential cooling between the two major structural culminations of the mountains. In the 3 km high Jabal Akhdar culmination AHe single‐grain ages range between 39 ± 2 Ma and 10 ± 1 Ma (2σ errors), AFT ages range from 51 ± 8 Ma to 32 ± 4 Ma, and ZHe single‐grain ages range from 62 ± 3 Ma to 39 ± 2 Ma. In the 2 km high Saih Hatat culmination AHe ages range from 26 ± 4 to 12 ± 4 Ma, AFT ages from 73 ± 19 Ma to 57 ± 8 Ma, and ZHe single‐grain ages from 81 ± 4 Ma to 58 ± 3 Ma. Thermal modeling demonstrates that cooling associated with uplift and erosion initiated at 40 Ma, indicating that uplift occurred 30 Myr after ophiolite obduction and at least 10 Myr before the Zagros collision. Therefore, this uplift cannot be related to either event. We propose that crustal thickening supporting the topography of the Al Hajar Mountains was caused by a slowdown of Makran subduction and that north Oman took up the residual fraction of N‐S convergence between Arabia and Eurasia.

Multiphase Structural Evolution of a Continental Margin During Obduction Orogeny: Insights From the Jebel Akhdar Dome, Oman Mountains

“…Alternatively, cooling could also be related to initial folding under ductile conditions of the Jebel Akhdar Dome and subsequent exhumation thereafter. Cooling to temperatures below 110°C was recorded by apatite fission track data at 55 ± 5 Ma and 48 ± 7 Ma (four samples, Poupeau et al, ) and between 51 ± 8 Ma and 32 ± 4 Ma (seven samples, Hansman et al, ). The first ones have been interpreted as rejuvenation of the basal blind thrust related to ongoing doming and exhumation of the Jebel Akhdar (Saddiqi et al, ).…”

Cenozoic Exhumation and Foreland Basin Evolution of the Zagros Orogen During the Arabia‐Eurasia Collision, Western Iran

“…In addition to the SSZ exhumation shown in this study, Late Eocene deformation within the Eurasian upper plate has been demonstrated by structural, stratigraphic, and thermochronometric studies across central and north Anatolia (Ballato et al, 2018;Darin et al, 2018;Fayon et al, 2001), Caucus Mountains (Cowgill et al, 2016), Talesh Mountains (Vincent et al, 2005), Alborz Mountains (Paolo Ballato et al, 2011), and central Iran (Morley et al, 2009). Similarly, Late Eocene shortening in the Arabian lower plate has been documented on the basis of growth strata in the Anti-Lebanon Mountains, Syrian Arc, and Palmyride fold-thrust belt (Chaimov et al, 1992;Guiraud & Bosworth, 1997;Hancock & Atiya, 1979), stratigraphic and thermochronometric data from the border fold region of SE Turkey (Cater & Gillcrist, 1994;Perincek, 1980), stratigraphic relationships in the Abd al Aziz Mountain along the Iraq-Syria border (Kent & Hickman, 1997), syncontractional sedimentation in Iraqi Kurdistan (Numan et al, 1998), progressive unconformities in the HZ of Iran in Lorestan and Fars (Farzipour-saein et al, 2009;Hessami et al, 2001), and thermochronometric and structural analysis of the Al Hajar Mountains (Hansman et al, 2017). These regional timing constraints on suture zone lithologies and coeval shortening within the lower and upper plates provide compelling evidence for the onset of continental collision between Arabia and Eurasia by Late Eocene time.…”

Jurassic to Early Cretaceous basin configuration(s) in the Fingerdjupet Subbasin, SW Barents Sea

“…The Rusayl Formation consists of lagoonal to offshore transition limestones (Nolan et al, 1990;Racey, 1995; Beavington-Penney, Wright and Racey, 2006;Dill et al, 2007;Özcan et al, 2015). The Lutetian-Barthonian Seeb Formation has been interpreted as an open-shelf carbonate with little terrigenous input and few evidences for subaerial exposure; it has thus been suggested that the Saih Hatat window was submerged by mid-Eocene (Skelton, Nolan and Scott, 1990;Hansman et al, 2017). This implies post-mid Eocene uplift of the Oman Mountains to their current elevation (up to 3 km a.s.l).…”

“…This implies post-mid Eocene uplift of the Oman Mountains to their current elevation (up to 3 km a.s.l). The precise timing and cause of the uplift is debated; suggestions for timing range from late Eocene to Oligocene (Würsten et al, 1991;Mount, Crawford and Bergman, 1998;Gray et al, 2006;Saddiqi et al, 2006;Hansman et al, 2017).…”