Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Abstract

The basement consisting of banded to streaky gneisses with inclusion of migmatites, schist, quartzite, amphibolites, mafics/ultramafics, BIF and metasedimentaries are exposed around Kuraicha, Mauranipur and adjoining areas. These Pre-Bundelkhand rocks were deformed during three phases of folding (F₁-F₃) under the influence of three tectonic episodes (D₁-D₃). The granitic rocks mainly comprise of large batholithic massif of medium to coarse grained pink granite along with a few lensoidal bodies of porphyritic pink and grey biotite granites.

The F₁ folds exhibiting tight to isoclinal geometries are characterized by IC, 4, and 1A types of fold style. The increasing trend of flattening (30-90%) and quarter wavelength/Amplitude (w/4/A) ratio (0.43-0.56) exhibited by F₁ folds exposed close to the shear zone, while away from the shear zone the definite decrease (10-60%) in these values is marked. Similar relationship is also noticed in F₂ and F₃ folds exposed at proximal and distal parts of the shear zone. It reveals that the flattening percentage and W/4/A ratio have inverse relationship with the distance from the shear zone.

The kinematic indicators viz. mylonitic foliation, stretching lineation, asymmetric and rotated porphyroclasts, sheath folds and S-C fabrics observed on mesoscopic scale, strongly support the existence of brittle-ductile shear zone in the study area. These observations also infer that the fabrics in this brittle ductile shear zone, deformed due to moderate to high shear strain under the predominance of nonaxial strain and extensional tectonics in D₄ phase of deformation.

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