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The gneisses and granitoids emplaced along E W sub vertical crustal shear zones are represented as important tectonic units in the Bundelkhand Craton. The tonalite trondhjemite granodiorite (TTG) gneisses (3.5 3.2 Ga; oldest unit), and streaky to mafic gneisses structurally deformed in D1 deformation. The gneisses, metabasic, felsic, banded iron formation (BIF) and metasedimentaries of greenstone complex exposed in central part, have characteristics of three sets of folding (F1 F3) generally evolved in D2 compressive phase, which are not occurring in northern part of craton. The K rich Neoarchean granitoids (2.6 2.49 Ga) were intruded as granitic complex (D3 magmatic phase) and the E W strike slip Raksa Garhmau shear zone reported as important tectonic unit, evolved in a syn to post tectonic D3 phase. The dolerite dykes (ca. 2.0 Ga) were emplaced along NW SE fractures in extension setting during D4 magmatic event and NE SW riedel shears occupied by giant quartz veins (reefs) evolved in Neoarchean Paleoproterozoic during D5 endogenic activity. The relationship between macro and microstructural fabrics has been documented by mylonitic foliation, stretching lineation, S C planes and rotated fabrics, reflect mesoscopic shear indicators, as noted in three types of mylonitic rocks. i) The rotated porphyroclasts of quartz, feldspars and asymmetric pressure shadows showing strong undulose extinction, deformation lamellae, and dynamic recrystallization are characteristic features of protomylonite where altered orthoclase and kinked plagioclase are noticed, ii) Mylonite, a distinct mylonitic foliation represented by parallel orientation of elongated quartz and feldspar with flakes of mica, iii) The ground matrix of recrystallized quartz with few protoliths of quartz and feldspar are observed, important features of ultramylonite. The asymmetric microstructures viz. σa and σb mantled porphyroclasts, other microstructures were progressively deformed by crystal plastic (non coaxial) strain softening process under low to moderate temperature conditions. The sinistral top to SW sense of shear movement was dominant. The microfractures/ microfaults, kinking and pull apart structures observed in K feldspars are indicative of overprinting of brittle deformation on ductile shearing.

Neoarchean crustal shear zones and implications of shear indicators in tectonic evolution of Bundelkhand craton, central India