The Eastern Ghats Mobile Belt, India: A collage of juxtaposed terranes (?)

Examination of Landsat TM images, reconnaissance field traverses and the published geological maps from the Eastern Ghats Mobile Belt (EGMB), India, reveal a network of major ductile shear zones both within and at the margins. These shear zones are characterized by mylonitic foliation, grain size reduction, metamorphic retrogression, stretching lineations and distinct signatures of alkaline, anorthositic and granitic magmatism. These shear zones divide the EGMB into distinct terranes, which are heterogeneously deformed with extensive tracts of foliated mylonitic gneisses and ultramylonites. The main gneissic foliation in all the terranes is refolded in near non-coaxial manner generally about the axis subparallel to the elongation of the terrane. Structural history in each terrane is distinct in the orientation of stretching lineations, attitude of gneissosity and early fold axial planes, lithological assemblages and available geochronological data. It is possible to recognise nine large terranes within the EGMB and the characteristics of each terrane have been described. The terrane distribution in the EGMB could well fit a thrust tectonic, allochthonous model of amalgamation and accretion. Different terranes could be different thrust nappes or allochthonous tectonic sheers representing tectono-stratigraphic terranes.