FN Archimer Export Format PT J TI Is there a Nascent Plate Boundary in the Northern Indian Ocean? BT AF Coudurier‐Curveur, A. Karakaş, Ç. Singh, S. Tapponnier, P. Carton, H. Hananto, N. AS 1:1,2;2:1,3;3:1,2;4:1,4;5:2;6:5; FF 1:;2:;3:;4:;5:;6:; C1 Earth Observatory of Singapore Nanyang Technological University, Singapore Equipe de Géosciences Marines, Institut de Physique du Globe de Paris (CNRS, Paris Diderot, Sorbonne Paris Cité), 1 rue Jussieu Paris Cedex 05, France Schlumberger Research Center, Risabergvegen 3 Stavanger, Norway Institute of Crustal Dynamics, China Earthquake Administration, Haidian Beijing ,China Research Center for Oceanography, Indonesian Institute of Sciences Jakarta Utara ,Indonesia C2 UNIV TECH NANYANG, SINGAPORE IPGP, FRANCE SCHLUMBERGER RESEARCH CENTER, NORWAY CHINA EARTHQUAKE ADM, CHINA LIPI, INDONESIA IF 4.72 TC 13 UR https://archimer.ifremer.fr/doc/00614/72646/71645.pdf https://archimer.ifremer.fr/doc/00614/72646/71646.pdf https://archimer.ifremer.fr/doc/00614/72646/71647.xlsx LA English DT Article CR MD 204 / MIRAGE-1 MD 210 / MIRAGE 2 BO Marion Dufresne DE ;Wharton Basin;reactivated fracture zones;nascent plate boundary;pull-apart basins;intraplate deformation AB 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 PY 2020 PD APR SO Geophysical Research Letters SN 0094-8276 PU American Geophysical Union (AGU) VL 47 IS 7 UT 000560367600014 DI 10.1029/2020GL087362 ID 72646 ER EF