Extent and analogues of the Rangit window in the Sikkim Himalaya

摘要

Field identification and mapping of widespread occurrences of mudstone-dominated carbonate-free siliciclastic rock assemblages, frequently containing layers of matrix-supported sandy to pebbly mudstones, have helped to revise the extent, outline and tectonic setting of the Rangit window in the Sikkim Himalaya. The revisions raise doubts on validity of the tectonic interpretations that are based on the earlier maps. We have designated the siliciclastic assemblages as the Phong La Formation, which shows lateral passage, without any major tectonic break, into the carbonate-siliciclastic assemblages that were mapped by the earlier workers as the Baxa Group of rocks of the Rangit window zone. This conformable passage suggests that the Phong La Formation is a constituent unit of the Baxa Group. The facies assemblages of the Phong La Formation indicate its deposition by processes related to gravity-driven mass flow (turbidity current flow) in distal deep-water setting on the continental slope.