Tectonic Evolution of Babina–Prithvipur Crustal Shear Zones, Bundelkhand Craton, India: Implications of Shear Indicators

Abstract

The central Bundelkhand domains consisting of deformed gneisses and granitoids are delineated by E-W subvertical Neoarchean Babina–Prithvipur shear zone (~500 m wide). The tonalite-trondjhemite-granodiorite (TTG) gneisses (3.5–3.2 Ga), streaky to mafic gneisses, belonging to an oldest complex unit, and metabasic, banded iron formation (BIF), felsic volcanics, with metasedimentaries constituting greenstone complex were subjected to three sets of folding in D1 and D2 compressive phases. The S1 foliation trending ESE-WNW to E-W directions were developed in tight to isoclinals F1 folds during D1 phase. The F2 and F3 open folds generated in the D2 phase are characterized by S2 and S3 foliations. The NNE-SSW and NNW-SSE trends were observed in S2 and S3 foliations. The K-rich Neoarchean granitoids (2.6–2.49 Ga) intruded as large granitic complex were transected by E-W strike-slip Babina–Prithvipur shear zone (syn-to post-tectonic D3 phase). These sheared rocks are characterized by the E-W to ESE-WNW trending mylonitic foliation and stretching lineation. The mylonitic foliation, asymmetrical rotated porhyroclasts (σa and σb mantled clasts), asymmetrical pressure shadows and deformation lamellae were identified as macroscopic and microscopic shear indicators in protomylonite and mylonites. The minor folds and crinkles developed due to back rotation of axial plane and reorientation of fold axis during progressive shearing were found important features. The scattered few porphyroclasts of quartz and feldspar were examined in a recrystallized quartz matrix of ultramylonite. The sinistral top–to–SW sense of shear movement was exhibited by most of the asymmetrical porphyroclasts. The presence of undulose extinction deformation lamellae in asymmetrical fabrics reveals that the crystal plastic process was dominant during the evolution of mylonite under low to medium temperature conditions.