Geology of the Simlipal Volcano-sedimentary Basin of Singhbhum Revisited: A Simplistic Interpretation

The status of the Proterozoic volcano-sedimentary Simlipal complex (covering latitudes 21 degrees 14 '-22 degrees 20 ' N and longitudes 86 degrees 03 '-86 degrees 35 ' E) of Singhbhum, eastern India remains unclear till date. The Simlipal complex has classically been designated to represent three layers of alternate spilitic volcanics and quartzite deposited in a geosyncline that unconformably overlies the meta-sedimentary Singhbhum Group of rocks. The study of the authors (entailing digital elevation map) bring out that the concentric ring-like outcrop pattern of Simlipal complex is only topography-controlled and repetitive bands of quartzite and volcanics do not exist. Further, it has been documented that the Simlipal complex comprises basemental weakly metamorphosed quartzite-phyllite (similar to 450m thick) heterolith unit (proposed Lulung Formation), which is followed upward by fresh, sub-horizontal (similar to 250m thick) volcanic unit (proposed Barehipani Formation) with local presence of peridotite-gabbro, and finally to quartz arenite unit (similar to 150m thick) as the topmost layer (proposed Jurunda Formation). The heterolith unit (proposed Lulung Formation) has been envisaged as a part of the older Singhbhum Group. The basaltic rocks (Barehipani Formation) correspond to calc-alkaline tectonic affinity based on geochemistry. We propose an arc-subduction related setting for the Simlipal complex which may be further confirmed through detailed major/trace elements and isotopic studies.