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Authors
Affiliations
1 Department of Geological Sciences, Gauhati University, Guwahati - 781 014, Assam, AF
2 Department of Geological Sciences, Gauhati University, Guwahati - 781 014, Assam, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 68, No 6 (2006), Pagination: 1100-1108
Abstract
Conglomerates deserve a unique status in the tectonostratigraphic history of the intracratonic Proterozoic Shillong basin of Assam Meghalaya plateau (erstwhile Shillang plateau). Stratigraphic positions of these conglomerates are ascertained with the help of field and laboratory observations along with a correlation to structure and tectonics of the basin. Quantitative strain analyses of the pebbles and whole rocks have been carried out to determine finite strain Variation in the strain rate is discussed. Tectonostratigraphic study reveals that the Nongkhya conglomerate is a continuation of Summer conglomerate of interformational status and is tectonicaily attenuated, shifted and emplaced over the Basement Gneissic Group (BGG) as tectonic melange and thus acts as basal conglomerate of Shillong Group. Relatively small and discontinuous Nongbri conglomerate bears the evidences of sillimanite fibrolite, which separates the BGG of amphibolite-Granulite transitional facies from that of greenschist-amphibolite transitional facies of Shillong Group Laitsopliah conglomerate overlie the highly deformed Shillong Group of rocks and separates the unmetamorphosed but moderately deformed Cretaceous-Tertiary rock sequences. Thus the NE-SW trending intracratonic Shillong basin can be divisible into two broad blocks-north-western block and south eastern block, the former block belongs to Lower Metapelitic Formation (LMF) and the latter belongs to Upper Quartzitic Formation (UQF) of Shillong Group (SG) respectively,both being separated by a long, persistent, partly faulted, Nongkhya-Summer-Mawmaram interformational conglomerate.
Keywords
Tectonostratigraphy, Conglomerates, Strain, Shillong Group, Meghalaya.