Blueschist Facies Metamorphism in Daling Rocks from A Part of Kalimpong Hills, Eastern Himalayas

Blueschist facies assemblages are identified in the metagraywacke and associated metabasics occurring in the lower structural levels of the Daling-Darjeeling thrust block, which tectonically overlies the parautochthonous Gondwana-Buxa sequence. These rocks belong to an intermediate position between the pumpellyite-prehnite-quartz facies and the lawsonite-glaucophane-jadeite facies. A temporal and spatial relation of the blueschist facies metamorphism and the Barrovian regional metamorphism is demonstrated, and a transition from the blueschists to the greenschists from lower to higher structural levels is also indicated. The mineral paragenesis restrict the lower and upper limits of pressure-temperature magnitudes at about 300°C/5 kb and 400°C/7.5 kb respectively. The problem related to the age and geotectonic implications of blueschist metamorphism in these rocks are briefly discussed.