Structure of the Rajnagar marble band and its bearing on the early Precambrian stratigraphy of central Rajasthan, Western India

Abstract

The marble band of supposedly Raialo (Precambrian) age around Rajnagar in the Udaipur district of Rajasthan represents a large isoclinal fold with the two limbs coalesced and with the terminations marking the sharp hinges. The arcuate map pattern is due to coaxial refolding of the axial surface of the isoclinal fold, on which open, NNE-trending upright folds have been overprinted. The isoclinal folds of small scale are reclined or inclined in style and plunge gently westward where not involved in the upright folding. The axes of the isoclinal folds have been scattered by superposed folding, so that some of the isoclinal folds now plunge even to the south. The plunge of the upright folds is gentler and steeper in the limb zones of reclined and inclined isoclinal folds respectively. Subvertical upright folds occur only in the hinges of the westerly trending reclined folds. Interference patterns of dome-and-basin type and mirror-image type have formed in zones where both hinges and limbs of the early folds have been affected by upright folding. The structure of the marble band, the stratigraphic relations that the marble bears with the supposedly older Aravalli mica schists and migmatites of the Banded Gneissic Complex engulfing it, and the stratigraphic findings in adjacent terrains indicate that the Banded Gneissic Complex represents migmatized portions of the metasediments of the Aravalli and the Raialo groups, and is not the basement rock in central Rajasthan. Evidence for granitic rocks of at least two generations in the Early Precambrians of central Rajasthan is adduced.