How long does the signature of tectonic events last in the landscape? Topographical analysis of Jebel Akhdar dome and surrounding Semail Ophiolite in the Al-Hajar Mountains (northern Sultanate of Oman)

Earth’s surface undergoes significant modifications due to tectonic events, which occur at different spatial and temporal scales with various deformation magnitudes and rates. Surface processes respond to these topographic modifications, striving to achieve a state of equilibrium. Active tectonic processes leave intense signals on the landscape, and, after their cessation, the responses become more litho-structurally and climatic controlled. Thus, understanding the overprint of tectonics on the topography and the preservation of this record is crucial to comprehend and describe how surface processes shape landscapes. Morphometric analysis and field survey were employed to investigate the Jebel Akhdar dome (JAK) and surrounding ophiolites in the Al-Hajar Mountains (Sultanate of Oman). This orogenic belt, located in the NEArabian plate, is renowned for hosting the Semail Ophiolite, one of the most complete obducted ophiolite sequences globally (Searle, 2007). The obduction occurred during the Late Cretaceous, resulting in the emplacement of ophiolites over JAK autochthonous units, composed by pre-Permian sedimentary and volcanic sequence and Permian-Late Cretaceous carbonate platforms. The Late Cretaceous and subsequent Cenozoic tectonics have resulted in the doming of JAK and the deformation of its rock sequences by predominantly transtensional structures (Searle, 2007). Field survey shows that river networks, structural elements, and karst systems heavily influenced the topographic evolution. This has been confirmed by morphometric indices, such as terrain ruggedness index (TRI), topographic position index (TPI), hypsometric integral (HI), and swath profiles. At regional scale, TRI, HI, and swath profiles show higher values for JAK and lower ones for Semail Ophiolite, emphasizing tectonic windows in JAK with intermediate-lower values. At a more detailed scale, escarpments, faults, and canyons are underlain by differences in values of TPI and TRI. In this way, morphometric results permit to quantify the topographic evolution, suggesting the influence of multiple factors at the local scale, including litho-structural setting, karst, (neo)tectonic activity and base-level variations. The combination of field observations and geomorphometry permits to understand the evolution of the topography, controlled by litho-structural setting, that played an important role in the drainage and karstic network development, leading to the formation of narrow and incised canyons in JAK, and larger and dendritic valleys in the Semail Ophiolite. Furthermore, the results indicate that the regional landscape evolution may be influenced by ongoing geological processes, such as uplift related to rebound processes of the Arabian crust, overlapping the offshooting effects of JAK doming and orogenic collapse that have not yet reached a topographic equilibrium, while the Semail Ophiolite may have reached equilibrium because not involved in the doming processes