Thermo-mechanical structure of the Indian continental lithosphere

Thermo-mechanical properties of the rocks constituting the lithosphere control the nature of lithospheric deformation at multi-scales. The oceanic lithosphere, being simple in terms of the crustal structure, composition, and the thermal structure, in general has a fairly well defined thermo-mechanical structure. Significant variations in the crustal thickness and composition, complex evolutionary history, and variations in the composition and viscosity of the mantle part of the lithosphere due to varying degree of depletion of incompatible elements lead to a very complex mechanical structure of the continental lithosphere. This paper presents a brief review of the modeling studies carried out to estimate the mechanical/thermo-mechanical properties and structure of the Indian continental lithosphere. A synthesis of the results obtained by various approaches reveals two major inferences and the discrepancies in the estimates of the mechanical strength of the Indian continental lithosphere. First inference is that the Indian shield can be broadly sub-divided into the northern and the southern segments based on the mechanical strength of the lithosphere, with the Central Indian Tectonic Zone forming the contact between the two segments. Second inference is that there are variations in the mechanical strength of the northern Indian shield along the strike of the Himalayan collision belt. The observations of the lowest surface heat flow in the Archaean western Dharwar craton implying the thickest lithosphere in this region and the low effective elastic thickness for the southern shield obtained by the admittance and coherence analyses present an exciting paradoxical scenario having implications for the tectonic deformation of the Indian continental lithosphere in response to the plate boundary forces. An integration of the new geophysical images of the Indian continental lithosphere and thermo-mechanical modeling can help in resolving the discrepancy.