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

Abstract

[1] 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 Copyright 2011 by the American Geophysical Union 1 of 24 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 reorganization of the fault system, and does not require any major kinematics change.Components: 11,900 words, 15 figures.

Mode of opening of an oceanic pull‐apart: The 20°N Basin along the Owen Fracture Zone (NW Indian Ocean)

“…Several fossil turbiditic channels coming from the Indus fan [ Rodriguez et al ., ] are observed at the seafloor on both sides of the 20°N Basin (i.e., west and east, Figure ). Assuming they were traveling in the abyssal plain, traces of their activity should predate the opening of the 20°N Basin and therefore give its maximal age.…”

“…A system of en echelon faults is observed on its southeastern side. An active turbiditic channel cuts through the arcuate fault system and feeds SB3, which has recorded the Indus deep‐sea fan activity since the opening of the basin [ Rodriguez et al ., ].…”

“…This raises the questions of how extensional deformation is distributed in a step over basin and what mechanism is responsible for the high amount of subsidence. Second, it remains unclear whether subbasins are still all active or not [ Rodriguez et al ., ]. The origin of transverse faults within pull‐apart basins, together with subsidence localization processes through times, are key processes in the structural evolution of pull‐apart basins [ Ten Brink and Ben Avraham , ; Ben Avraham and Ten Brink , ; Smit et al ., , ].…”

Mass wasting processes along the Owen Ridge (Northwest Indian Ocean)

“…Stratigraphic data from ODP Leg 117 are also used to assess the vertical distribution of MTDs. The tectonics of the Owen Fracture Zone is detailed in Rodriguez et al (2011), but where necessary we describe the relationship between the MTDs and the surface traces of the active faults. In the following, the term of open-slope type means that no topographic barrier obstructs Fig.…”

“…1; Rodriguez et al, 2011). This fault system connects the Sheba and Carlsberg ridges to the eastern end of the Makran subduction zone.…”