Seismo-Tectonics, Crustal Velocity Structure and Moho Depth Beneath the Dharwar Craton, India

Abstract

Ravi Ande

The cross-correlation of continuous ambient noise data gathered from 35 broad-band seismographs over 18 months (February 2019 to August 2021), we produce Rayleigh-wave group velocity maps in the 5–28 s range. We supplement this with longer period data (40–70 s) from the earthquake source. Combining combined group velocity measurements with the tele-seismic receiver functions gathered at 50 stations—15 of which were operational from 1998 to 2012—was necessary to construct a shear velocity image of the crust. The crustal thickness of the late Archean (2.7 Ga) Eastern Dharwar Craton (EDC) is 34–38 km, but the crustal thickness of the mid-Archean and Proterozoic terrains is 40–50 km. The Western Dharwar Craton (WDC) is located 50 km away in the mid-Archean (3.36 Ga) greenstone region, which has the thickest crust. The average crustal velocity beneath the EDC is 3.70–3.78 km s-1, while the Moho depth and average crust velocity beneath the WDC are 3.80–3.95 km s-1. The thickness (Vs 3.8-4.2 km s1) of the lower crust varies significantly lateral, ranging from 10-15 km in the EDC to 20-30 km in the WDC. The lowest part of the crust (Vs 4.0 km s1) is thin (5 km) beneath the EDC, in contrast to the WDC, where the crust is thicker (10–27 km). We anticipate an intermediately composed crust beneath the EDC, akin to those of other cratons. The exposed WDC crust from the mid-Archean exhibits an unusual thickness and a greater mafic composition, in contrast to worldwide observations. We interpret this significant mafic crust as an undeformed geological section dating to 3.36 Ga. The EDC's very flat Moho, felsic to intermediate crust composition, and thin basal layer suggest that it was a reworked terrain during the late Archean.

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