Submagmatic fabric in the 2.6 Ga Bundelkhand granitoid, India: Evidence from microstructure

Abstract

Primary foliations in igneous rocks are the key to understanding processes within the magma chamber, cooling history, paleostress regime and strain during emplacement of granitoid plutons. In the 2.6 Ga Bundelkhand granitoid rocks, weak to moderately strong regional fabric is the result of submagmatic grainsupported flow during syn-kinematic emplacement of the magma. Microstructural and outcrop-scale evidences provide an excellent record for interpreting the significance of this fabric development vis-à-vis rheological state during fabric formation. Preferentially oriented tabular feldspar phenocrysts in the granitoid show deformation such as reformed shape, marginal fragmentation and recrystallization, whereas the finer interstitial grains of quartz remain undeformed or mildly deformed. On the basis of the characteristic foliated structure of the Bundelkhand granitoid and the specific contrasting deformation characteristics of feldspar and quartz grains, we propose that the fabric is submagmatic in origin and perhaps formed during syn-emplacement deformation environment of the granitoid.