This dataset contains bulk geochemical data of variably altered mafic rocks (basalt and diabase) from the Langseth Ridge and Afanasenkov Seamount, two volcanic centers on the ultraslow-spreading Gakkel Ridge, Arctic Ocean. The samples were collected during R/V Polarstern Expeditions PS78 and PS101 and USCGC HEALY Expedition HLY0102. Compositions were obtained via X-ray fluorescence and inductively coupled plasma-mass spectrometry. Details on the analytical procedure can be found in Albers et al. (2024).