Seismic imaging of crust beneath the Dharwar Craton, India, from ambient noise and teleseismic receiver function modelling

We use cross-correlation of continuous 18 months (2009 February to 2010 August) ambient noise data recorded over 35 broad-band seismographs in the Archean Dharwar Craton and the adjoining granulite terrain to generate Rayleigh-wave group velocity maps in the period 5-28 s. This is supplemented with longer period data (40-70 s) from earthquake source. Combined group velocity measurement was inverted jointly with the teleseismic receiver functions obtained at 50 stations (includes 15 stations operated during 1998-2002) to produce shear velocity image of the crust. The velocity image reveals thinner crust (34-38 km) in the late Archean (similar to 2.7 Ga) Eastern Dharwar Craton (EDC), while all other terrains (mid-Archean and Proterozoic) have crustal thickness from 40 to over 50 km. The mid-Archean (3.36 Ga) greenstone belt of the Western Dharwar Craton (WDC) has the thickest crust (similar to 50 km). The average crustal V-s beneath the EDC is similar to 3.70-3.78 km s(-1) as compared to 3.80-3.95 km s(-1) beneath the WDC. We observe significant lateral variation in the thickness of lower crust (V-s similar to 3.8-4.2 km s(-1)): similar to 10-15 km in the EDC compared to similar to 20-30 km in the WDC. The lowermost part of the crust (V-s >= 4.0 km s(-1)) is thin (< 5 km) beneath the EDC in contrast to more thickness (10-27 km) beneath the WDC. Our analysis suggests intermediate composition for the crust beneath the EDC similar to those for other cratons. In contrast, the mid-Archean exposed WDC crust has more mafic composition and exceptional thickness-a scenario at variance with the global observations. We interpret this thick mafic crust to represent undeformed geological segment of 3.36 Ga. The EDC with a nearly flat Moho, felsic to intermediate composition of crust and thin basal layer may represent a reworked terrain during the late-Archean.