Neotectonics of the Owen Fracture Zone (NW Indian Ocean): Structural evolution of an oceanic strike-slip plate boundary

Abstract

The Owen Fracture Zone is a 800 km-long fault system that accommodates the dextral strike-slip motion between India and Arabia plates. Because of slow pelagic sedimentation rates that preserve the seafloor expression of the fault since the Early Pliocene, the fault is clearly observed on bathymetric data. It is made up of a series of fault segments separated by releasing and restraining bends, including a major pull-apart basin at latitude 20°N. Some distal turbiditic channels from the Indus deep-sea fan overlap the fault system and are disturbed by its activity, thus providing landmarks to date successive stages of fault activity and structural evolution of the Owen Fracture Zone from Pliocene to Present. We determine the durability of relay structures and the timing of their evolution along the principal displacement zone, from their inception to their extinction. We observe subsidence migration in the 20°N basin, and alternate activation of fault splays in the vicinity of the Qalhat seamount. The present-day Owen Fracture Zone is the latest stage of structural evolution of the 20-Myr-old strike-slip fault system buried under Indus turbiditic deposits whose activity started at the eastern foot of the Owen Ridge when the Gulf of Aden opened. The evolution of the Owen Fracture Zone since 3-6 Myr reflects a steady state plate motion between Arabia and India, such as inferred by kinematics for the last 20 Myr period. The structural evolution of the Owen Fracture Zone since 20 Myr- including fault segments propagation and migration, pull-apart basin opening and extinction - seems to be characterized by a progressive reorganisation of the fault system, and does not require any major kinematics change.