Structural and Petrological Evolution of the Rocks around Jamua-Kakwara-Bhatia of Satpura Orogeny, Bhagalpur District, Bihar

The polyrnetamorphic sequence includes quartzites, mica-schists, calc-silicates, ortho-amphibolites, migmatites and granite gneisses with pegmatites, aplites and quartz veins. Diastrophic structures in the rocks indicate the presence of a series of buckled and flattened modified parallel or near similar folds of diverging trend and plunge. Structural analyses reveal a complex monoclinic squeezing along NW-SE initiating overturned isoclinal high plunging folds (F₁) with southerly dipping NE-SW axial plane (S₂), superposed with a probable time gap by steeply plunging disharmonic folds of second generation (F₂) with subvertical axial plane (S₃). Conjugate folds and kink bands with kink planes (S₄) striking NW-SE are related to F₃ fold of restricted nature.

The regional metamorphism (sillimanite-muscovite subfacies of almandine-amphibolite facies) is followed by syn- to late-kinematic (with reference to F₁ fold) in situ granitization, Geochemical changes in different rock types leading to in situ granitization have been traced on the basis of (a) petromineralogical study of representative samples, (b) systematic modal analyses, supported by analyses showing Na-K and trace element variations. Morphological and statistical analyses of zircon and authigenic tourmaline occurring in the area confirm a sedimentary parentage of the metamorphites. Stratigraphic position is fixed up above Kolhans.