Thickness, composition, and evolution of the Indian Precambrian crust inferred from broadband seismological measurements

We present seismological constraints to model the evolution of Indian Precambrian crust through receiver function analysis of teleseismic waveforms, recorded on 22 broadband seismographs along a N–S corridor, from southern granulite terrain to Delhi, on the Aravalli craton. Archean terrains (Eastern Dharwar, Bastar, Bundelkhand and Aravalli cratons) are underlain by crust with felsic-intermediate composition (Vp/Vs ∼ 1.65–1.75) in contrast to mafic composition (Vp/Vs > 1.78) of crust beneath Vindhyan basin, Godavari basin, and the Narmada-Son Lineament (NSL) of Proterozoic age. The Moho depth varies between 33 and 43 km with no definite relationship with age of the crust. Duplex Moho with highly mafic underplated lower crust is characteristic feature of the NSL, signifying its paleo-rift character. Present day felsic character of the Indian Archean crust could be a consequence of post-formation modification of the initial mafic lower crust through the process of lithospheric delamination. This major tectonic event also created layered lithosphere beneath parts of India imprinted as positive velocity contrast at a depth of ∼80 km, usually referred to as Hales discontinuity. The upper part of the lithosphere has shear velocity (Vs) ∼4.52 km/s and the lower one ∼4.77 km/s. We speculate that such a layered lithosphere could be due to a low-density, depleted spinel peridotite (with Archean affinity) lying over higher density fertile garnet peridotite of Proterozoic age.