Structural Framework of Deolapar Area, Central India and its Implications for Proterozoic Nappe Tectonics

A controversial ‘nappe-like’ structure (‘Deolapar Nappe’) in the intensely deformed and polymetamorphosed Precambrian rocks of the Sausar Fold Belt around the Deolapar area of Central India has remained the subject of a long- standing, unresolved debate. While some workers interpreted it as the inverted limb of a large-scale recumbent fold which has been thrusted onto the adjoining part of the supracrustal sequence (Sausar Group), others discounted the very existence of the nappe because of the lack of structural evidence in favour of the recumbent fold-thrust structure. Recent structural study by the present authors around the Deolapar area and also in the adjoining parts of the Sausar Fold Belt has looked back into the controversy surrounding the Deolapar Nappe. The study reveals that the Deolapar Nappe is constituted of an allochthonous block of metasedimentary rocks and crystalline gneiss-migmatites, placed over the metacalcareous rocks (Lohangi Formation) of the Sausar Group along a low angle thrust plane, marked by a sheared fibrolite-biotite schist. The whole thrust sheet has been folded by later (F2) upright folds. However, careful structural mapping confirmed that there is no evidence of any map-scale F1 recumbent fold in the whole area, although small-scale, thrust-related reclined (F1) folds are occasionally found. Also, there is not enough field evidence suggesting regional inversion of stratigraphic succession so as to indicate the lower limb of a recumbent fold. The Deolapar Nappe can therefore be best interpreted as a thrust-nappe. Details of the existing controversy, the new observations and a new tectonic model of the Deolapar Nappe is presented here.