Ultraslow spreading mid-ocean ridges
At mid-ocean ridges, the lithospheric plates move apart at rates of 5-150 mm/y and new ocean lithosphere is formed continuously. At low spreading rates of less than 20 mm/y this engine sputters. Only very little melt is formed and this melt encounters difficulties to force its way through the cold and thick lithosphere to the seafloor. The generation of new ocean lithosphere at ultraslow spreading ridges therefore differs from all other ocean basins. Ultraslow spreading ridges form a class of mid-ocean ridges on their own making up for about 15% of all spreading axes globally. As ultraslow spreading ridges are situated in the Arctic Ocean and in the stormy Southwest Indian Ocean, the spreading processes of this class of mid-ocean ridges are still only poorly understood.
The Junior Research Group MOVE „Mid-Ocean Volcanoes and Earthquakes“ funded by the German Science Foundation analyses the active spreading processes oft he Arctic Ridge system and the Southwest Indian Ridge based on their earthquake activity. During several expeditions (AMORE • SWEAP • RHUM • AURORA) we collected a comprehensive data set of local earthquake records, the first ever at ultraslow spreading ridges. The earthquakes give information for example on unusual volcanic activity, as occurred on Gakkel Ridge in 1999-2001, on the thermal and mechanical state of the lithosphere and on pathways that magma uses to travel to the widely spaced volcanic centres of ultraslow spreading ridges.