Sub-crustal LVZ below Dharwar craton, India: An evidence for mantle metasomatism and tectonothermal activity in the Archean crust

Improved knowledge of seismic structure of the continental crust provides deep insights into the mechanism of the crustal growth since the Archean times. Reprocessing of deep seismic sounding data, acquired over western Dharwar craton, India, reveals presence of (i) a high velocity magmatic layer (7.30 km/s) at the base of the crust, (ii) a higher Pn velocity (8.35 km/s) at a deeper depth of 45 km than in an usual Archean crust and (iii) an unusually low velocity layer (7.40 km/s) at a depth range of 48-60 km in the upper mantle. Such shallow subcrustal lithospheric LVZs are rarely found in a stable Archean craton, which is associated with low surface heat flow and devoid of recent tectonic activities. Considering various geological, tectonic and geothermal scenarios, occurrence of such a low velocity zone has been ascribed to chemical alteration caused by mantle metasomatism, rather than mafic partial melts or high temperature sub-solidus. The derived velocity structure and distribution of volcanic rocks of different ages in the studied area indicate multiple crust-mantle thermal interaction in the Archean crust. (C) 2012 Elsevier B.V. All rights reserved.