Metamorphic History of the Precambrian Rocks of the Narmada Section, Southwest of Jabalpur, M.P.

The Precambrian rocks of the Narmada section, southwest of Jabalpur, which bear imprint of several periods of deformation, are found to have undergone Barrovian type of regional metamorphism with garnet-staurolite-sillimanite assemblages in the higher grades. An increase in the metamorphic grade is indicated by successive development of a higher grade mineral assemblage, as also a coarser metamorphic fabric, as the rocks are followed to the east. Textural evidence is given to show that metamorphism in the area has been a polyphase event, the main episodes of crystallisation having occurred before, during and after the second (F₂) fold phase. The metamorphic climax, marked by the development of sillimanite, is shown to have occurred after the second fold movement. That higher temperatures prevailed in the Tilwaraghat section through successive metamorphic episodes is shown by the development of higher grade minerals and a coarser rock fabric in the above area than anywhere to the west of it. Retrogression was negligible in this area, while extensive retrogression occurred in the western part, particularly between the water falls and Lamhetaghat.