Extended Data Fig. 1: Bathymetric map and along-axis profiles of the Gakkel Ridge.
From: Highly variable magmatic accretion at the ultraslow-spreading Gakkel Ridge
a, Bathymetric map of the Gakkel Ridge. The full spreading rate of the Gakkel Ridge ranges from 12.7 mm year−1 near the Fram Strait to 7.3 mm year−1 close to the Laptev Sea margin. On the basis of the predominant types of rock sample obtained, the western Gakkel Ridge was divided into the Western Volcanic Zone (WVZ, basalts), the Sparsely Magmatic Zone (SMZ, peridotites) and the Eastern Volcanic Zone (EVZ, basalts)15. GRD, Gakkel Ridge Deep. b, Along-axis depth profiles of the seafloor (grey line) and the basement (black line). In the JASMInE zone, sediment thickness is constrained by sonobuoy data. West of the JASMInE zone, the sediment is assumed to be absent as extensive basalts and peridotites are directly exposed on the seafloor. Circles indicate the positions of seismometers on ice floes16. Most ice-floe seismometers were deployed above the deep part (water depth of 3.8–4.8 km) of the rift valley (that is, segment ends), at which the estimated average crustal thickness is roughly 2.7 km (ref. 16). Near a volcanic centre in the WVZ, the estimated crust thickness is 7 km (ref. 45). Thick grey lines indicate average values of the basement depth. c–f, Along-axis variations in the RMBA, Na8.0 composition of basaltic glasses, H2O in the mantle source and calculated Tp (ref. 26). The average values of each region are indicated by horizontal grey bars. The RMBA is a crude indicator of crustal thickness and/or mantle thermal structure. Black dots indicate data from samples obtained in this study. Na8.0 data suggest that the mantle beneath the Gakkel Ridge has a relatively low Tp and a reduced extent of partial melting15. Tp is calculated using the ReversePetrogen code29. H2O in source is calculated using the method PRIMELT3 MEGA.XLSM68.
