Earth and Planetary Science Letters 462 (2017) 1–14 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Possible magmatic underplating beneath the west coast of India and adjoining Dharwar craton: Imprint from Archean crustal evolution to breakup of India and Madagascar Utpal Saikia ∗ , Ritima Das, S.S. Rai Department of Earth and Climate Science, Indian Institute of Science Education and Research Pune, Dr. Homi Bhabha Road, Pune, 411008, India a r t i c l e i n f o a b s t r a c t Article history: Received 15 August 2016 Received in revised form 5 January 2017 Accepted 6 January 2017 Available online xxxx Editor: P. Shearer Keywords: Dharwar craton India–Madagascar separation Western Ghat receiver function joint inversion lower crust The shear wave velocity of the crust along a ∼660 km profile from the west to the east coast of South India is mapped through the joint inversion of receiver functions and Rayleigh wave group velocity. The profile, consisting of 38 broadband seismic stations, covers the Archean Dharwar craton, Proterozoic Cuddapah basin, and rifted margin and escarpment. The Moho is mapped at a depth of ∼40 km beneath the mid-Archean Western Dharwar Craton (WDC), Cuddapah Basin (CB), and the west and east coasts formed through the rifting process. This is in contrast with a thin (∼35 km) crust beneath the late- Archean Eastern Dharwar Craton (EDC). Along the profile, the average thickness of the upper, middle and lower crust is ∼4 km, 12 ± 4 km and 24 ± 4 km respectively. Above the Moho, we observe a high-velocity layer (HVL, Vs > 4 km/s) of variable thickness increasing from 3 ± 1 km beneath the EDC to 11 ± 3 km beneath the WDC and the CB, and 18 ± 2 km beneath the west coast of India. The seismic wave velocity in this layer is greater than typical oceanic lower crust. We interpret the high-velocity layer as a signature of magmatic underplating due to past tectonic processes. Its significant thinning beneath the EDC may be attributed to crustal delamination or relamination at 2.5 Ga. These results demonstrate the dual signature of the Archean Dharwar crust. The change in the geochemical character of the crust possibly occurred at the end of Archean when Komatiite volcanism ceased. The unusually thick HVL beneath the west coast of India and the adjoining region may represent underplated material formed due to India–Madagascar rifting, which is supported by the presence of seaward dipping reflectors and a 85–90 Ma mafic dyke in the adjoining island.  2017 Elsevier B.V. All rights reserved. 1. Introduction The growth of continental crust and its deformation history through time are recorded in the chemical and physical proper- ties of the crust. Most of our present understanding of the nature of the deeper portion of the continental crust is derived normally based on the velocities of seismic waves. Global compilations of seismic velocity structure with depth show significant variability in the composition of continental crust with tectonics and thermal regimes (Christensen and Mooney, 1995; Rudnick, 1995). The con- tinental crust with a global average thickness of 34 km to 40 km is usually divided into upper, middle and lower crust with charac- teristic shear wave velocity of <3.5 km/s, 3.5–3.8 km/s and greater than 3.8 km/s respectively. The thickness of the layers is approx- imately 11–12 km each. Compositionally the upper crust is felsic * Corresponding author. E-mail address: ngriutpal@gmail.com (U. Saikia). with over 66% SiO 2 dominated by granite/granodiorite. The middle crust contains rocks in the amphibolite facies with lower SiO 2 and K 2 O and higher FeO, MgO than the upper crust. It is widely agreed that felsic to mafic granulites of igneous origin dominate the lower crust with the corresponding mean SiO 2 varying from 69 to 48% and the P-wave velocity from 6.7 to 7.2 km/s (Rudnick and Foun- tain, 1995). By contrast, Rudnick and Gao (2003) and Hacker et al. (2011) demonstrate that the lower crust might not be mafic. The composition and physical properties of the upper and mid- dle crust are better understood, but the nature of lower crust and its seismic signature are more difficult to determine and have been the subject of numerous studies (Rudnick and Fountain, 1995; Rudnick and Gao, 2003; Hacker et al., 2011; Huang et al., 2013). Although, the average velocity of crust increases with the depth, the increase is primarily confined to the lower crust. The average velocity of the upper crust does not vary with the crustal thickness (Drummond and Collins, 1986). It is, therefore, a reasonable propo- sition that the lower crust participates in the processes responsible http://dx.doi.org/10.1016/j.epsl.2017.01.004 0012-821X/ 2017 Elsevier B.V. All rights reserved.