Thinned continental crust intruded by volcanics beneath the northern Bay of Bengal

• Published in: Marine and Petroleum Geology
• Main Authors: Sibuet, Claude, Klingelhoefer, Frauke, Huang, Yuan-Ping, Yeh, Yi-Ching, Rangin, Claude, Lee, Chao-Shing, Hsu, Shu-Kun
• Other Authors: Institute of Applied Geophysics, National Taiwan Ocean University, 44 rue du Cloître, 29280 Plouzané, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Unité Géosciences Marines (GM), Department of Atmospheric Sciences Taoyuan City, National Central University Taiwan (NCU), Taiwan Ocean Research Institute, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UniCA)-Université Côte d'Azur (UniCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD France-Sud )
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Antarc*; Antarctica
• Online Access: https://hal.science/hal-01744829; https://doi.org/10.1016/j.marpetgeo.2016.07.006

International audience Since the early Cretaceous, the Bay of Bengal was formed during rifting between India and Antarctica and then by subsequent seafloor spreading. The nature of the crust underlying the Bay of Bengal is oceanic south of 15°N, but remains unknown (thinned continental crust, serpentinized mantle or oceanic crust) north of this limit. In order to better define the nature of the crust in the northern Bay of Bengal, three wide-angle reflection seismic and refraction profiles were acquired during the multichannel seismic reflection Bengal cruise. Nine ocean-bottom seismometers were deployed alternatively on three profiles. A seismic source consisting of 64 air guns with a volume of 6180 in3 was used simultaneously with a 10.05-km long streamer to acquire both seismic reflection and refraction data. Tomographic and forward modelings of the three refraction profiles reveal a 20-km thick crust north of the Bengal delta front beneath a minimum of 13 km thick sedimentary cover. The crust thins to about 10 km immediately south of the EW trending delta front and the thickness of sediments reaches a minimum of 7 km. Crustal velocities and velocity gradients are consistent with a continental origin of the crust in this area. At the base of the crust, high seismic velocities (>7.2 km/s) are interpreted as magmatic underplating. Wide-angle seismic reflection and refraction data cannot resolve the nature of the upper 4–5 km of crust (oceanic crust, exhumed mantle or thinned continental crust). But coincident seismic reflection profiles show the emplacement of a volcanic intrusion, sills and some seaward dipping reflectors (SDRs) located close to the northern prolongation of the Ninety East ridge before 70 Ma (Maastrichtian). However, most of the fan-shaped reflectors identified in the northern Bay of Bengal are synrift features. We conclude that the crust in the northern Bay of Bengal is thinned continental crust intruded by volcanic products with the presence of a minor amount of underplating material at ...