Atammik is a submarine volcano located in the Davis Strait 200 km west of Nuuk, at depths below sea level of 3690-4850 m. Drilling during hydrocarbon exploration revealed a 1.2 km thick sequence of alkaline volcanic and sedimentary rocks conical in shape, extending for 5x10 km. The lower sequence is tephri-phonolitic to phonolitic in composition from 4650-3950 m. The upper sequence is less alkaline, composed of phono-tephrite to basaltic trachy-andesite from 3950-3700 m, representing a higher degree of melting or lower degree of enrichment in the mantle source. Additionally, textural qualities such as the presence of “Pele’s tears” suggest that this unit was at least partially erupted sub-aerially. Quartzite xenoliths and quartz xenocrysts are commonly entrained within the volcanics, possibly skewing SiO2 higher in geochemical analysis. Hydrothermal alteration is common in both units, with K-feldspar commonly reprecipitated and vugs infilled with chlorite and illite. Petrography, bathymetry, and whole rock major and trace element data can be found in Knudsen et al. (2019).
KNUDSEN, C., GREGERSEN, U., KOKFELT, T.F., OLIVARIUS, M. & THOMSEN, T.B., 2019. A mid-Cretaceous alkaline volcano in the Davis Strait. Canadian Journal of Earth Sciences 57(1) pp 69-86