Abstract:
We report an anomalous present day crustal thickness
of 43–52 km beneath the 3.4–3.0 Ga mid-Archean
segment of the western Dharwar craton (WDC) undisturbed
by Proterozoic events. In contrast, adjoining
late-Archean (2.7–2.5 Ga) eastern Dharwar craton
(EDC) has a 33–40 km crustal thickness similar to the
Archean global average. Considering that mineral
assemblages in the central part of the WDC crust
(amphibolite grade metamorphics) equilibrated at a
depth of 15–20 km, we argue that the western Dharwar
crust 3.0 Ga ago must have been at least 60–
80 km thick. Both segments of Dharwar craton crust exhibit Poisson’s ratio of 0.24–0.28 suggesting felsic
to intermediate average crustal composition. The
thickest crust beneath WDC has also underlying highvelocity
thicker lithosphere compared to EDC, inferred
from faster arrivals of teleseismic P and S wave.
The contact between WDC and EDC is marked as
gradational thinning of crust (42–36 km) from Chitradurga
thrust to the western part of Closepet granite.
In WDC, the crustal thickness increases in step fashion
towards the oldest crustal block. These details suggest terrain accretion in Dharwar craton during 3.4 to 2.5 Ga through subduction related process
