Blueschist facies metamorphism in Nordenskiöld Land of west‐central Svalbard

Abstract

Abstract Recent fieldwork in Nordenskiöld Land, Svalbard's Southwestern Basement Province, has established the presence of high‐pressure ( HP ) lithologies. They are strongly retrogressed blueschists consisting mainly of garnet and Ca‐amphibole with remnants of ferroglaucophane and phengite. The pressure–temperature ( P–T ) conditions were estimated using phase equilibrium modelling in the NCKFMM n ASHTO system. P–T estimates based on the garnet, phengite and ferroglaucophane compositional isopleths and modelled paragenetic assemblage indicate peak metamorphism at 470–490 °C and 14–18 kbar. These data fall close to the 7–8 °C km −1 geotherm, which is similar to that from Motalafjella, the only previously known occurrence of blueschists in Svalbard's Caledonides. The newly discovered blueschists could have formed during the early stage of the Caledonian Orogeny and may represent a vestige of missing marginal basins of the western Iapetus developed at the onset of subduction. The likely counterpart to Svalbard's blueschists is the ophiolitic sequence in the Pearya Terrane of northern Ellesmere Island.