The eight glass samples analysed by means of the fission-track method were recovered from deep-sea dredge sites 314D, 316D, 323D and 325D in the SW Pacific. The bulk uranium contents of the fresh remnants of unweathered glasses range between 51 ppb and 108 ppb. One glass from site 316 D with a U-content of 227 ppb might be part of a dike intrusion. The basalts from all four sites are altered to various extents. Ambient temperatures prevailing during these alteration processes are estimated to have been 1–5°C at sites 314 D and 325 D; about 10°C at site 323 D; but 40–110°C at site 316 D. The measured fission-track ages of sites 314 D, 323 D and 325 D scatter between 34 Ma in the north and 20 Ma in the south. At site 316D, they are exceedingly low, being from, 4.4 to ⩽ 0.7 Ma. All these ages are thermally lowered and required correction. The ages corrected for thermally induced partial track-loss converge to 56.0±4.9 Ma at site 314 D; 53.3±5.8 Ma at site 323 D; and 36.4± 5.2 Ma at site 325 D. Site 316 D has a minimum age of 37±12 Ma. From these ages and the site positions, a spreading rate of 0.61 + 1.27−0.24 cm a −1 is deduced for the northern part of the North Loyalty Plateau, which comes close to values estimated for slow-spreading ridges.