Question

Write Notes on Sausar Group.

Answer 1

The Precambrian rocks of the Mansar area, Nagpur district, Maharashtra, belong to the Sausar Group and the Tirodi Gneiss. Both these lithological units show an unconformable relation in the area, marked by a conglomerate at the base of the Sausar Group. The metasediments of the Sausar Group bear imprints of polyphase deformation. The folds of the first generation (F1) are isoclinal with high amplitude to wavelength ratios and pervasive axial planar cleavage (S1). The structures of the second generation are represented by WNW-ESE trending upright isoclinal folds (F2) and axial planar crenulation cleavage (S2). Gentle upright folds with NE-SW striking axial planes represent structures of the third generation (F3) Superposition of F2 folds on F1 folds is marked by mushroom shaped interference pattern in small-scale. Because of upright isoclinal nature of F2 folds on WNW-ESE striking axial planes, the metasedimentary bands extend in E-W direction. Slight arcuate geometry of the metasedimentary bands is the result of superposition of F3 folds on F1/F2 folds.

Answer 2

The Precambrian rocks of the Sausar Group are exposed in an arcuate belt on the southern flank of the Satpura Mountain belt. Rocks of this belt show superposed deformations of three generations in large-scale. Dominant E-W to ENE-WSW alignment of the Sausar belt was developed during the pervasive second deformation represented by isoclinal folds with upright to steeply inclined axial surfaces with ~E-W strike. Complex (mirror-image type) map patterns in the region have resulted from the interference of the second generation upright isoclinal folds at high angles to the axial surfaces and fold axes of equally pervasive early isoclinal folds with axial planar cleavage. The basement, Tirodi Gneiss, and the cover rocks, the Sausar Group, show such interference patterns at several places of the region. Mapping and identification of well-preserved basement-cover contact in the eastern and central parts of the belt lead to reexamine the stratigraphic succession proposed for the Sausar Group by the early workers. Presence of a horizon of paleosol, a polymictic conglomerate at the contact of the Tirodi Gneiss with the Sausar Group, synsedimentary volcanism in the basal part of the Sausar Group and glaciogenic unit with a 'cap carbonate' have been recorded from many places in the Sausar belt. Critical analyses of relationship between deformation and metamorphism in the rocks of the Sausar Group and adjacent gneiss-migmatite terrane have shown that the dominant fabric of the region having EW strike (/ trend), which was considered by the previous workers to be the earliest fabric in the region, represents structural features of second generation in the Sausar Group. Therefore, the P-T-t path of the region and the tectonic model proposed by the earlier workers do not stand critical scrutiny.