Abstract
The Angudan Orogeny affected Cryogenian to earliest Cambrian sedimentary rock formations of the Jabal Akhdar Dome of the Oman Mountains. These rocks were folded and cleaved at 525 ± 5 Ma. We studied the Cambro-Ordovician (Terreneuvian to Darriwillian) Amdeh Formation of the neighboring Saih Hatat Dome to see whether this formation was also affected by the Angudan Orogeny. The Angudan deformation within the Jabal Akhdar Dome is known for its folds and cleavage. Due to age considerations (see above), we studied the folds and cleavages within the two oldest members of the Amdeh Formation (Am 1 and Am 2) in order to compare them with the ones that are known from the Jabal Akhdar Dome to possibly detect Angudan-related deformation in Am 1 and Am 2. Angudan folds of the Jabal Akhdar Dome display fold axes that are oriented NE/SW, but the two lowest members of the Amdeh Formation reveal one set of folds with subhorizontal fold axes that trend NW-NNW/SE-SSE. The lack of Angudan-related folds suggests that the lowest Amdeh Member (Am 1) postdates the Angudan Orogeny. The age of Am 1 is uncertain. Based on our structural results, we consider an upper Terreneuvian age (late stage 2) for Am 1. The folds in Am 1 and 2 are related to the Late Cretaceous–Cenozoic Semail Orogeny (term introduced here). The observed fold vergences (mainly to the W and SW) were caused by shear deformation during descent into the subduction zone by simple shear. The contact between the stratigraphically underlying Hiyam Formation and the Amdeh Formation is generally considered to be an unconformity. We observed a distinct NW/SE-striking deformation zone along the contact of both formations which is located in proximity to the largest observed fold. Tectonically, this contact is defined by the sinistral Wadi Amdeh Fault (name introduced here). The unconformity should be present in the subsurface of the southwestern fault block. Near the contact between the Hiyam and the Amdeh formations, a 20 cm thick unit of reddish cataclasite/tectonic breccia occurs within the basal part of Am 1 which represents a deformed acidic layer or sill. This rock unit could be the first evidence for Cambrian igneous activity.
Highlights
Geosciences2019, 9, x FORinPEER REVIEWRecent work the Jabal Akhdar of 23Dome (Figure 1) has demonstrated two Early Cambrian2folding events within Cryogenian to earliest Cambrian rocks [1]
The study area occupies a structural position within the upper limb of a regional recumbent isoclinal fold, distant from the fold closure which is located to the NE ([4], their Figure 2)
Since there is evidence for two Early Cambrian folding events in the Jabal Akhdar area [1] and the possibility of a lower Cambrian age of the Amdeh Formation (Figure 2) [5], we want to determine whether the two oldest Amdeh members show the same fold pattern as the Cryogenian to earliest
Summary
Dome (Figure 1) has demonstrated two Early Cambrian2folding events within Cryogenian to earliest Cambrian rocks [1]. Inexhibit the course of with shallow, gently dipping slaty cleavage fold during axial planes, the Angudan a steeply the Orogeny, the. Cadomian folds display amplitudes of to m andyounger low-dipping planes (10–30°). Vertical axial planes striking ENE and fold axes that plunge either ∼50 to the ENE or ∼30 to the hundred meters to 3 and 5 km, respectively. These younger folds exhibit steeply dipping to vertical. Correlation of the oldest (Am is less certain than for the other (Figure 2) This member may or may not partly correspond to the Fortunian (Lower Terreneuvian).
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