Hales Discontinuity in the Southern Indian Continental Lithosphere: Seismological and Petrological Models

Abstract

A lithospheric discontinuity below the Moho was first observed in travel time data from the active seismic explosions in USA-Canada joint venture Project Early Rise at Lake Superior (R. Green & Hales, 1968). This was termed as the Hales discontinuity (Hales, 1969). This discontinuity was marked by a positive impedance contrast boundary at a depth of 84-94 km associated with increase in P wave velocity (V p) from 8.05 to 8.45 km s −1 (Mereu & Hunter, 1969). It was later shown to be associated with an increase in mean apparent reflection coefficient of 3.5% and an increase in S wave velocity (V s) of 3.8% (Revenaugh & Jordan, 1991). Since its discovery, the Hales discontinuity has been studied using various methods, which include active seismic travel time observations (

3D Shear‐Wave Velocity Structure of the Crust and Upper Mantle Beneath India, Himalaya and Tibet

“…Possible perturbations to this model have resulted from Proterozoic continental collision processes and accretion of subducted oceanic lithosphere. This lead to the growth of the sub-continental lithospheric mantle and formation of eclogite (metamorphosed oceanic crust with V s > 4.6 km s 1 ) embedded Journal of Geophysical Research: Solid Earth 10.1029/2023JB028292 with the mantle peridotite (Chaudhury et al, 2021;Karmalkar et al, 2009). Evidence of collisional processes is preserved within the suture zones between Cratons (Figure 1).…”