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Autopsy on a dead spreading center: The Phoenix Ridge, Drake Passage, Antarctica

¹ British Antarctic Survey, Cambridge CB3 0ET, UK
² Instituto Andaluz Ciencias de la Tierra, Universidad de Granada, 18002 Granada, Spain
³ Departamento de Geodinámica, Universidad de Granada, 18071 Granada, Spain
⁴ Instituto Tecnológico Geominero de España, Ríos Rosas, 23, 28003 Madrid, Spain
⁵ Facultad de Ciencias del Mar, Cádiz, Spain
⁶ Departamento de Geodinámica i Geofísica, Universitad de Barcelona, 08028 Barcelona, Spain
⁷ Departamento de Estratigrafía y Paleontología, Universidad de Granada, 18071 Granada, Spain

New bathymetric and magnetic anomaly data from the Phoenix Ridge, Antarctica, show that extinction of all three remaining segments occurred at the time of magnetic chron C2A (3.3 ± 0.2 Ma), synchronous with a ridge-trench collision south of the Hero Fracture Zone. This implies that the ultimate cause of extinction was a change in plate boundary forces occasioned by this collision. Spreading rates slowed abruptly at the time of chron C4 (7.8 ± 0.3 Ma), probably as a result of extinction of the West Scotia Ridge, which would have led to an increase in slip rate and transpressional stress across the Shackleton Fracture Zone. Spectacular, high-relief ridges flanking the extinct spreading center, mapped for the first time using multibeam swath bathymetry, are interpreted as a consequence of a reduction in spreading rate, involving a temporary magma oversupply immediately prior to extinction.

Key Words: Drake Passage • Phoenix Ridge • Antarctic plate • spreading centers

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