Geology, Structural Architecture and Tectonic Framework of the Rocks of Southern Lalitpur District Uttar Pradesh, India: An Epitome of the Indian Peninsular Shield

Abstract

The southern part of Lalitpur district exposes several lithostratigraphic units that are typically represented in the peninsular shield. Towards south these are crystalline-metamorphic rocks of the Bundelkhand Gneissic Complex (BGC) in the northern part, the Bijawar Group in the central part and the Vindhyan Supergroup in the southern part. A few outcrops of the Deccan Trap are also exposed at the southern fringe of the area. A tectonically sandwiched unit, named as Mahrauni Group, exists between the BGC to the north and the Bijawar Group to the south. The BGC is represented by a variety of granitoids, gneisses and schists together with mylonitised granite gneisses, migmatites and amphibolite schists. The Bijawar Group exposes a sedimentary sequence mainly including carbonate rocks, shales and sandstones. These rocks occasionally show very low degree of metamorphism. The Vindhyan Supergroup (Meso-Neoproterozoic) is dominantly constituted of sandstone and shales and is represented by the Semri Group overlain by the Kaimur Group. Structurally, the area can be divided into three domains. The northern domain with BGC rocks does not show any major structure excepting a dominating south-dipping foliation. The central domain is dominated by the Bijawar Group of rocks that folded into an anticline to the south and a corresponding syncline to the north. Both these folds show an approximately E-W to ENE-WSW trending axial trace. The southern domain exposes the rocks of the Vindhyan Supergroup that shows a simple dipping structure with southward dipping strata. Mesoscopic structures are rather sporadically distributed and are confined to the rocks of the BGC and the Bijawar Group. The minor folds show three generations of folding. The first generation (F₁) folds are tight recumbent isoclinals; the second generation (F₂) folds are generally coaxial to F₁ but are more open and asymmetrical that the F₁ folds; the third generation (F₃) folds are rare and occur as open folds with high wavelength-amplitude ratios. In the area, the BGC appears to bear a thrust contact with the Bijawars, which appear to bear a faulted contact with the Vindhyans. This type of tectonic framework appears to be specific of this area as compared to several other areas of the peninsular shield and this can be explained in terms of repeated tectonic reactivation of the area during the Proterozoic to Neoproterozoic times. With the typical geological set up of the area, the southern Lalitpur district can be described to epitomize the Indian peninsular shield in general.