Tectonics of the 'Marble Rocks' of Jabalpur, Madhya Pradesh

The' Marble Rocks' of the Narbada gorge, Jabalpur, Madhya Pradesh, appear to have a polyphase structural history. Of the three fold phases (F₁ - F₃) recognised in the metamorphic rocks of the Narbada section, west-southwest of Jabalpur town, only two are distinguishable in the Bhera ghat section-an early phase of tight folding on roughly easterly trending axes and a late phase of gentle folding on axes oriented transverse to the earlier fold trend. The early and late folds are, related to second (F₂) and third (F₃) fold phases respectively, in the region as a whole. Basic dykes cutting the marbles of Bhera ghat are shown to belong to two different ages-one highly metamorphosed and deformed and considered to be syntectonic with the early fold phase, and the other, practically unaltered and undeformed, of a post-tectonic, post-metamorphic age. Emplacement of quartz veins associated with the marbles is shown to have begun sometime during the early fold phase, continued through the late fold phase and outlasted it. Special features of the above rocks and those of the Sausar group are compared.