Vaddineni, Venkata A., Singh, Satish C. and Grevemeyer, Ingo (2018) Tomographic study of oceanic lithosphere from 0 to 25 Ma in the Equatorial Atlantic Ocean using wide angle OBS data. [Poster] In: AGU Fall Meeting 2018. , 10.-14.12.2018, Washington, D.C., USA .

Abstract

The global Mid-Ocean Ridge system is a 65000 km long continuous mountain range and is a central part of the plate tectonic theory. New oceanic lithosphere is continuously being generated at these centers of magma upwelling and then propagated away from the ridge axis by the forces of ridge push and slab pull. Though these processes of crustal generation and propagation are well studied at spreading ridges, much less is known about how crustal accretion changed over time and how the crust and lithosphere evolve with age. Also, the Lithosphere-Asthenosphere Boundary (LAB), which occurs around Moho near the ridge axis, deepens with age and is poorly defined in terms of depth and thickness. To quantify the variation of velocity structure in the crust and lithosphere and to image the LAB from 0 to 50 Ma using wide-angle reflections, LITHOS experiment was conducted in late 2017 near the equatorial Mid-Atlantic Ridge on R/V Maria S. Merian. A total of 71 Ocean Bottom Seismometers (OBS) and hydrophones were deployed to acquire refraction and wide angle reflection data with an average spacing of 15 km along 1100 km long seismic transect coincidental with a deep seismic reflection profile acquired in 2015 using a 12 km long streamer. The OBS profile runs across the Mid-Atlantic Ridge covering 75 km on the South American plate and the rest of 1025 km lies on the African plate over 0 to approximately 50 Ma old lithosphere. In this study we analyze 600 km long profile in the western part of the seismic transect crossing the ridge-axis with age variation from 0 to 25 Ma. The OBS data was band pass filtered between 3 and 30 Hz and predictive deconvolution was applied. Pn arrivals were observed till offsets of up to 150 km on some OBS stations away from ridge axis. We present the velocity structure of the crust and upper mantle down to a depth of 10 km from seafloor by using first arrival travel time tomography. We also observe secondary arrivals on most of the OBS stations starting from offsets around 35 - 40 km and ongoing analysis will determine the nature of such events. Detailed analysis of velocity structure and heat flow data will shed light on the effect of cooling of lithosphere with age on the crustal and mantle velocities and presence of hydrothermal circulation near the ridge axis.

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