| Abstract Submission No. | ABS-1.2-0128 |
| Title of Abstract | Subsurface Anomalies beneath the Central Indian Ocean Basin |
| Authors | Amit Kumar*, Sanjay S. Negi, Lachit S. Ningthoujam, P. John Kurian |
| Organisation | National Centre for Polar and Ocean Research, Goa |
| Address | Marine Geoscience Division, NCPOR, Headland Sada, Vasco-Da-Gama, Goa, India Pincode: 403804 E-mail: amitkumar@ncpor.res.in |
| Country | India |
| Presentation | Oral |
| Abstract | The Indian plate has undergone a long tectonic journey since its separation from Gondwanaland. Its protracted rift-drift motion has rendered several enigmatic features in the Central Indian Ocean Basin (CIOB). In this study, we used Ocean Bottom Seismometers (OBS) and utilised the fundamental-mode Rayleigh wave group velocity, as it is generally well excited by shallow-focus earthquakes. We considered earthquake records with magnitude>4.5 that occurred at depth<50 km at regional/teleseismic distances. The fundamental model Rayleigh wave group velocity is observed over a period range of 12 to 300 s. The observation reveals a significant decrease in group velocity at an intermediate period (60-180 s) along the profiles beneath the CIOB. The inverted model shows a significant reduction in shear wave velocity underneath the base of the lithosphere (i.e. 22-24 km Lithosphere-Asthenosphere boundary). The anomalous low-velocity zone (LVZ) is observed at a depth interval of ~90 km to ~160 km. Quantitatively, a ~18% reduction in shear wave velocity is observed in the vicinity of the LVZ along the P2 (~3.7 km/s) and P3 (~3.73 km/s) profiles, compared to the velocity of the overlying lid. Our results suggest the possible presence of ~2% melt fraction, excess temperature of ~230�C, and maximum ~1% anisotropy in the CIOB, particularly beneath the Capricorn plate. However, the other profile reveals the relatively lesser melt fraction. The supplementary presence of extra melt fraction along the P2 and P3 profiles can be associated with an unextracted melt fraction, in conjunction with the northward movement of the Indian plate and appended by plume-lithosphere interaction, can account for the formation and persistence of an anomalous LVZ in the upper mantle beneath the CIOB region. Our result also favours the possibility of the west-to-east channel flow and strong anisotropy beneath the Capricorn plate. |
| Keywords | Ocean bottom seismometer, Surface wave, low-velocity zone and Mantle processes |