<b>Thick crust at Earth’s slowest spreading ridge: 3D gravity insights from Eurasian Basin, Arctic Ocean</b>

The Eurasian Basin of the Arctic Ocean opened by ultraslow spreading along the Gakkel Ridge, yet crustal thickness has remained poorly constrained due to sparse seismic data. We present a new basin-wide 3-D gravity model, updated by the most comprehensive sediment thickness and seismic observations, offering the first systematic view of crustal architecture. Since ~45 Ma, the western ridge, spreading at ~10-13 mm/yr, has produced generally thin (1-3 km) crust, with local mantle exhumation. In contrast, the slower eastern ridge (~6-10 mm/yr) generates robust volcanic crust 6-8 km thick. This “slower-yet-thicker” relationship challenges the classical spreading-rate paradigm, showing that mantle fertility, elevated temperatures, and active upwelling—not spreading rate alone—govern crustal production at ultraslow Gakkel ridges.