Shirley fracture zone possible ridge jumps

ID: 3-22

Ocean: Pacific
Spreading center type: Segment-scale ridge jumps
Time of cessation: 25 Ma, C7A (Lonsdale, 2005)
Subsequent active spreading centre: Guadalupe microplate

Review of previous studies:

The extinct spreading ridge segments referred to as the Shirley ridge jumps are situated offshore the west coast of North America, around 400 km west of the Guadalupe extinct ridge and microplate. They are located between the Shirley fracture zone and the eastern end of the Molokai fracture zone. Lonsdale (2005), identified the segments in a detailed synthesis of shiptrack magnetic and swath bathymetry data and seismic traces. Lonsdale (2005) primarily reports on the timing and processes that are preserved from fragmentation of the Farallon plate, that resulted in the formation of a large-scale spreading centre between the newly formed Nazca and Farallon plates. The Shirley ridge-jumps are oriented perpendicular to the major plate fracture that defines the Nazca-Cocos spreading centre and are likely to have developed in a secondary reorganization related to that episode of plate fragmentation.

Observations and comments:

Due to their short length these proposed extinct ridge segments were ranked in our tertiary tier and not included in the statistical analysis.


Lonsdale, P., 2005. Creation of the Cocos and Nazca plates by fission of the Farallon plate. Tectonophysics, 404, pp. 237-264.

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