Imaging the lithosphere‐asthenosphere boundary of the Indian plate using converted wave techniques

Abstract

[1] The lithospheric structure of the Indian plate has been investigated using converted wave techniques (P and S receiver functions) and a novel stacking analysis technique (without using deconvolution) applied to a large seismological data set from permanent and temporary broadband seismic stations. We observe coherent energy from at least two seismic discontinuities, i.e., the crust-mantle (Moho) and lithosphere-asthenosphere boundary (LAB) in the uppermost mantle. Here we provide a novel seismic image of the Indian lithosphere showing definitive evidence of its flexure, which is interpreted to be primarily caused by the hard collision at~55 Myr resulting in the world's highest mountain chain-the Himalayas and the Tibetan plateau. Results from geoidal and gravity studies do suggest postcollisional flexuring of the Indian plate; however, the flexure lacks observational constraints. The observed wavelength of the flex is~1000 km with the thickness of the Indian shield lithosphere varying from~70 km to 140 km; such a low value for a continent implies that the Indian plate has been reworked in the past. The plate deepens in the Himalayan region to a depth of~170 km. Further, the converted phases are interpreted to be resulting from the bottom of the lithosphere. We clearly demonstrate that these are distinct and different from the midlithospheric discontinuity. For a large number of stations, the midlithospheric discontinuity and LAB are clearly separated in depth. Our observations suggest that the Archaean lithosphere is no longer intact and is prone to deformation.

Detailed Configuration of the Underthrusting Indian Lithosphere Beneath Western Tibet Revealed by Receiver Function Images

“…The recognized LABs in this research are denoted by the green dashed lines. The yellow and pink dashed lines (Figure 8a) mark the LABs from Kumar et al () and from Zhao et al () for reference, respectively. (c) Map of Sp piercing points at depths of 80 km (red pluses) and 200 km (blue pluses) along with the locations of the two CCP profiles.…”

The seismic mid-lithosphere discontinuity

“…Abt et al, 2010;Chen, 2009;Ford et al, 2010;Foster et al, 2014;Heit et al, 2007;Kumar et al, 2013;Savage and Silver, 2008;Sodoudi et al, 2013;Wittlinger and Farra, 2007;Wölbern et al, 2012). In some areas this seismic velocity decrease appears to be continuous between tectonically Rychert et al, 2007), Australia , South America (Heit et al, 2007), Africa (Hansen et al, 2009;Wölbern et al, 2012) and India (Kumar et al, 2013). Full coordinates are in the Supplementary Information.…”

Complex shallow mantle beneath the Dharwar Craton inferred from Rayleigh wave inversion

“…Their model also showed an increase in the S velocity at 75 km from 4.52 to 4.77 km s -1 . Using S receiver functions from three broad-band stations in the Dharwar Craton, Kumar et al (2007Kumar et al ( , 2013 suggested a velocity inversion at a depth of 80-100 km which they interpreted as the base of the lithosphere, but this result was criticized by Oreshin et al (2011) and Bodin et al (2013) as arising from an inappropriate analysis and modelling of the data. In a recent study, Bodin et al (2013) analysed data from the Geoscope station HYB in the north-central part of the Dharwar Craton using improved inversion methodology.…”