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Creating three-dimensional (3D) models to replicate geological structures is crucial in discerning the geometry and kinematics of an orogen. The Jabal Hafit anticline, in the foreland of the Al Hajar Mountains, extends through Oman and the United Arab Emirates and is a relatively simple and well exposed structure. Surprisingly, previous studies of this anticline have presented conflicting interpretations regarding the strain field and the timing of deformation. In this study a structural 3D geological model of the Jabal Hafit anticline is constructed and demonstrates that the anticlines geometry can be reproduced by a two-phase model: (1) flexural slip folding, followed by (2) trishear fault-propagation folding. The trishear mode occurred due to a west-dipping backthrust that propagated from the decollement, to accommodate WSW–directed shortening. The different geometries of the various biostratigraphic layers indicate that anticline growth occurred during the late Oligocene to early–middle Miocene. This timing supports the recently established age for uplift of the Al Hajar Mountains.

We reconstruct the three-dimensional (3D) geometry of the Naxos detachment fault and quantify E–W shortening associated with strong N–S extensional deformation. In addition, 3D reconstruction of the detachment indicates how it interacted with the underlying metamorphic sequence, as well as a set of concentric metamorphic isograds that formed during extensional deformation. For doing so, we used the software MOVE™ (Midland Valley Ltd.) to develop a 3D model of the Naxos metamorphic core complex (NCC) and the Naxos detachment fault. The model is constrained by structural data, metamorphic isograds, and fission-track ages from the footwall of the NCC. Our analysis shows that greater minimum amounts of E–W shortening correlate with higher metamorphic grade, ranging from 6 to 10% outside the migmatite dome and up to 17% within the migmatite dome. The metamorphic isograds around the migmatite dome are less intensely folded by E–W shortening than the lithologic layering. We conclude that this is because the isograd surfaces “froze-in” after folding had already started. Our model indicates that the isograds are cut by the brittle detachment, demonstrating that the final stages of top-to-the-NNE extension outlasted the formation of the metamorphic dome and the isograds. Despite some limitations of the 3D model, the outlined geometric reconstruction of a major extensional fault system in the central Aegean highlights: (1) the interplay between large-scale extension and temperature-dependant shortening perpendicular to the extension direction, (2) the evolution of metamorphism and migmatization, (3) the formation of metamorphic isograds, and (4) granitoid intrusions during extension and exhumation.

Direct dating of brittle structures is challenging, especially absolute dating of diagenesis followed by a series of superimposed brittle deformation events. We report 22 calcite U-Pb ages from tec ...

Bolin Centre for Climate Research; Royal Swedish Academy of Sciences [GS2015-0002]; Stiftelsen Lars Hiertas Minne [FO2015-0130]; Swedish Foundation for International Cooperation in Research and Higher Education [IB2015-6002]; Stiftelsen Anna-Greta och Holger Crafoords fond; Stockholm University

The Saih Hatat Dome in the Al Hajar Mountains provides an outstanding opportunity to study subduction/exhumation processes coeval with obduction of the Semail Ophiolite. The exceptionally good outcrop conditions offer a unique opportunity to constrain the geometry of this subduction/obduction complex. In this review, the metamorphic, structural, and tectonic evolution of the Oman high-pressure complex in the Saih Hatat Dome is discussed. New structural cross-sections are developed and are used to interpret a geometrically feasible tectonic model for the Saih Hatat Dome. Our review highlights the importance of two major tectonic boundaries: (1) The As Sheik Shear Zone which separates the high pressure rocks of the As Sifah Unit (1.7–2.3 GPa and 510–550 °C) from the overlying Hulw Unit (1.0–1.2 GPa and 250–300 °C), and was active at ~79–76 Ma; and (2) the Upper Plate–Lower Plate Discontinuity, which forms a major surface in the landscape and developed by ~76–74 Ma, cutting through structures of the HP rocks in the lower plate (footwall). This discontinuity is associated with a pronounced strain gradient, notably in its upper plate (hanging wall), and separates rocks that have markedly different deformation geometry. The Upper Plate–Lower Plate Discontinuity initiated with a modest dip angle, making it a neutral structure in terms of crustal shortening vs extension. As a result, there is no discernable break in P-T conditions across it. The upper plate is dominated by the Saih Hatat Fold Nappe, forming between ~76 and 70 Ma. Subsequently, the upper plate has been dissected by a number of NNE-dipping thrusts at ~70–66 Ma, followed by normal faults at