South Rennell Trough possible extinct ridge

ID: 4-24

Ocean: Marginal basin
Spreading center type: Large-scale MOR
Time of cessation: Ca. 28 Ma (Mortimer et al., 2014)
Subsequent active spreading center: No subsequent spreading center evident in region of proposed extinct ridge

Review of previous studies:

The South Rennell Trough is a prominent oceanic structure that is situated in the north east of the Coral Sea and west of the North Fiji Basin. It has a NE-SW trend and cross-cuts the Santa Cruz Basins and the western edge of the D'Entrecasteaux Basin.

Recent sampling of volcanic rocks from across the South Rennell Trough has revealed that both sides have a similar age and geochemical signature that is indicative of an enriched-mid-ocean ridge basalt (E-MORB), suggesting a possible back-arc basin influence (Mortimer et al., 2014). This suggests that the structure may represent a former back-arc basin spreading centre, as was proposed by Mortimer et al. (2014).


Profiles across the inferred axis show that the trough has a largely symmetric form, with bathmetric relief of ca. 2000 m, between the flanks and central trough. Each segment has a prominent and symmetric negative free-air grativy anomaly that is within thone standard deviation of the primary tier mean of well-defined extinct ridges. We think that it is likely that the South Rennell Trough represents an extinct spreading axis.


Mortimer, N., Gans, P. B., Palin, J., M., Herzer, R. H., Pelletier, B. and Monzier, M., 2014, Eocene and Oligocene basins and ridges of the Coral Sea-New Caledonia region: Tectonic link between Melanesia, Fiji, and Zealandia, Tectonics, v. 33, p. 1386–1407, doi:10.1002/ 2014TC003598.

Maps showing the location of extinct ridge segments

Depth profiles across the axes of extinct ridge segments

Gravity profiles across the axes of extinct ridge segments