Thermo-tectonic evolution of the North Singhbhum Mobile Belt (eastern India): A view from the western part of the belt

The arcuate North Singhbhum Mobile Belt (NSMB) comprises multiply-deformed greenschist-amphibolite facies phyllites and schists flanking the centrally-located belt of the Dalma meta-igneous suite of rocks. The NSMB is separated from the Archaean Singhbhum Craton in the south, and the suite of granulite-amphibolite facies gneisses and foliated granites of the Chotanagpur Gneissic Complex to the north, by ductile shear zones. Three fabrics (S-1S, S-2S and S-3S) formed due to D-1S, D-2S and D-3S deformation events and three metamorphic stages (M-1S: pre-S-2S; M-2S: syn-S-2S; and M-3S: syn/post-S-3S) were identified in phyllites and schists to the south of the Dalma meta-igneous in the NSMB. Reverse-sense transport along north-dipping imbricate thrusts (S3S) emplaced the high-grade garnet-kyanite-staurolite schists centrally located in the orogen over low-grade muscovite-biotite-chlorite schists in the foreland. The M-1S stage (similar to 1.5 Ga; EPMA monazite date) in the high-grade gneisses characterized by high P/T prograde metamorphism (P > 10 kbar) was followed sequentially by post-loading prograde heating (T-max similar to 650 degrees C) and exhumation - cooling at amphibolite facies (M-2S) and greenschist facies (M-3S: similar to 1.3 Ga; EPMA monazite date) conditions. In the northern part of the NSMB, mica schists fringing the CGC document a northward increase in strain (sequential cleavage formation) and temperature (greenschist to amphibolite facies). The strain-temperature spatial gradient is correlated with crustal shortening and heating (T similar to 620 degrees C, P similar to 7 kbar) synchronously with reverse-sense transport of schists along southerly-dipping thrust planes. The structural framework and thermal structure across the mobile belt is correlated with (a) collisional thickening of the orogen (>1.5 Ga), followed by convective removal of the lithospheric root resulting in post-burial heating and (b) syn-collision and exhumation of the orogen (similar to 1.3 Ga). The exhumation was caused by outward-directed extrusion of the crustal slices along imbricate foreland-vergent thrusts dipping towards the centre of the orogen. (C) 2007 Elsevier B.V. All rights reserved.