| Ocean: | Pacific |
| Spreading center type: | Large-scale extinct MOR |
| Time of cessation: | Ca. 15 Ma, chron C5AD (Meschede et al., 1998) |
| Subsequent active spreading centre: | Cocos-Nazca present-day spreading system |
| Later deformation or volcanism: | Anderson et al. (1976) argued that some extrusive activity may have continued after the ridge migration on the basis of heat flow patterns. |
Anderson et al. (1976), reviewed heat flow measurements in combination with bathymetry and geophysical data from the eastern Pacific Ocean, in order to assess the status of mid-ocean ridge segments in the region of the Galapagos (Cocos-Nazca) spreading centre. They proposed that a region of low-heat flow, defined by a rift-valley and with thin sediment cover suggested a fossil ridge (Anderson et al., 1976). They place the inferred extinct ridge adjacent to the Costa Rica rift and suggest that is formed an earlier plate boundary between the recently formed Nazca and Cocos plates.
Meschede et al. (1998), suggested that two ridge-jumps occurred before the ridge relocated to the present-day Cocos-Nazca spreading centre, with both leaving distinct extinct spreading centres. They argued that grabens on the Cocos Ridge suggested an axial structure oriented northeast to southwest, oblique to the present-day east-west trending spreading centre (Meschede et al., 1998). Meschede et al., (1998) also identified symmetric magnetic anomalies about the inferred extinct spreading centres, with the youngest identified as chron C5ADr.
A major change in spreading direction is proposed at around 19 Ma, which is suggested as a possible contributing factor for the spreading centre becoming unstable (Meschede et al., 1998). The Galapagos plume is also suggested as possible influence in the region according to Anderson et al. (1976) and from the iron-content of lavas, according to Wilson and Hey (1995).
Anderson, R.N., Moore, G.F., Schilt, S.S., Cardwell, R.C., Tréhu, A. and Vacquier, V., 1976, Heat flow near a fossil ridge on the north flank of the Galapagos Spreading Center, Journal of Geophysical Research, v. 81, no. 11, p. 1828-1838.
Meschede, M., Barckhausen, U. and Worm, H.-U., 1998, extinct spreading on the Cocos Ridge, Terra Nova, v. 10, p. 211-216.
Wilson, D.S. and Hey, R.N., 1995, History of rift propagation and magnetization intensity for the Cocos‐Nazca spreading center, Journal of Geophysical Research: Solid Earth, v. 100, no. B6, p. 10041-10056.
