Gondwana accretion tectonics and implications for the geodynamic evolution of eastern Arabia: first structural evidence of the existence of the Cadomian Orogen in Oman (Jabal Akhdar Dome, Central Oman Mountains)

Abstract

The present work describes two early Cambrian folding events within Cryogenian to earliest Cambrian rocks of the western Jabal Akhdar Dome (Central Oman Mountains). This sequence is truncated at an angular unconformity and topped by Permo-Mesozoic sedimentary shelf strata. The Permo-Mesozoic is brittlely deformed and largely unfolded. This differs in style and intensity of deformation with the refolded underlying Neoproterozoic-Cambrian rocks. Evidences for an older Paleozoic deformation (D1) have been identified within limestone of the Hajir Formation. Tight to close inclined folds (F1) reflect the ductile deformation affecting Neoproterozoic-Cambrian rocks. The folds yield 5-50m amplitudes, with a short-overturned limb, sub-horizontal to gently plunging fold axes and moderately to sub-horizontally inclined axial surfaces. A younger event (D2) has refolded the F1 folds. F2 folds are open to close with amplitudes and wavelengths from several hundred meters to 3 and 5km respectively. The F2 folds display sub-vertical to steep axial planes dipping towards NNW, and fold axes plunging either ENE-wards with ∼50°, or SW-wards with ∼30°, at the northern and southern side of the Jabal Akhdar Dome, respectively. F2 folds have been mentioned by previous authors as possibly Hercynian in age, while the occurrence of F1 folds is here firstly presented, revealing a uniform NW-vergence of F1 folds after restoration at pre D2 geodynamic conditions.We present in this work the first structural evidence related to the D1 Cadomian event which occurred in eastern Arabia between ∼542 and 525 ±5Ma, due to the convergence between Arabia and microcontinents and/or oceanic subduction of the Proto-Tethys Ocean. The two deformation events, D1 (Cadomian Orogeny) and D2 (Angudan Orogeny), are related to NE-SW and ∼NW-SE main compressional directions, respectively. The evidence arising from the present research study directly challenges former accounts of a “Hercynian Orogeny” in eastern Arabia.