Abstract:
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 (∼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 (∼50 km). The average crustal Vs beneath the EDC is ∼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 (Vs ∼ 3.8–4.2 km s−1): ∼10–15 km in the EDC compared to ∼20–30 km in the WDC. The lowermost part of the crust (Vs ≥ 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.
