Bird's feather lineation - discovery of a new type of linear structure in calc-silicate rocks of Sheopura-Kesarpura mine area near Beawar, Rajasthan, India

摘要

The present correspondence reports an unusual type of lineation recently discovered in complexly deformed calc-silicate rocks in the eastern part of Sheopura-Kesarpura limestone mine near Beawar, Rajasthan (Figure 1). The linear structure resembles abird's feather spread in a well-oriented fashion with the longest dimension aligned strictly parallel to the lineation (Figure 2), particularly mullions parallel to the axis of a set of folds in the area. The linear structure observed in the study area can be compared in shape and genesis with the lineation formed by the elongate mineral aggregates. Geologically, in the Sheopura-Kesarpura area the linear bands of medium-grained calc-silicate and dolomitic marble are enclosed in the muscovite-biotite schist of Beawar Formation of the Kumbhalgarh Group/Raialo Series/ Raialo Group of the Mesoproterozoic Delhi Supergroup of rocks resting uncon-formably on the Archaean basement, i.e. the Banded Gneissic Complex. The rocks of the area are intruded by small bodies, i.e. dykes, veins and veinlets of pegmatite, possibly of the Erinpura age (-850 Ma). With respect to deformation the Delhi Supergroup of rocks exhibit four phases of folding episodes.