The northern Indian Ocean has been widely recognized as an area of broadly distributed deformation within the composite India‐Australia‐Capricorn plate, hosting several diffuse boundary zones and a diffuse triple junction. The occurrence, along reactivated fracture zones, of the exceptionally large (Mw=8.6 and Mw=8.2) 2012 Wharton Basin strike‐slip earthquakes, however, questions whether this composite plate is breaking apart along a discrete boundary. Using recent bathymetric and seismic data, we analyze the most prominent fracture zone (F6a), whose structural trace is particularly well‐expressed. We identify sixty kilometric‐scale pull‐apart basins with geometric properties (length/width ratios) similar to those observed along continental strike‐slip plate boundaries. Four of the pull‐aparts formed above narrow, sub‐vertical faults extending into the oceanic crust. Within the broad Wharton deformation zone, the significant slip rates (0.8 to 2.5 mm/yr) and unusually large co‐seismic displacements recorded along F6a suggest that it may be a nascent plate boundary.

Plain Language Summary

Oceanic plates are usually rigid and aseismic, except along their boundaries. In 2012, two extraordinary earthquakes with magnitudes M>8, typical of plate boundary events, occurred in the Wharton Basin, inside the India‐Australia‐Capricorn plate, slicing the seafloor along straight, old fracture zones bearing evidence of active tectonic deformation. Using submarine relief and seismic data, we study the freshest fracture zone (F6a) to examine whether it might qualify as a nascent plate boundary between India and Australia. We find that localized cracks along it and narrow rectangular basins (pull‐aparts) resemble those along large continental strike‐slip boundary faults, supporting the inference that the composite Indo‐Australian plate is breaking apart.

Key Points

Sixty kilometric‐scale, pull‐apart basins show aspect ratios similar to those observed along crustal‐scale strike‐slip faults

At least four deep pull‐aparts rooted into lithospheric faults illustrate a progressive localization of deformation along F6a

Sinistral slip rates < 2 mm/yr and exceptionally large 2012 co‐seismic slip support the evolution of F6a into a nascent plate boundary