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

New bathymetric and magnetic anomaly data from the Phoenix Ridge, Antarctic a, show that extinction of all three remaining segments occurred at the tim e of magnetic chron C2A (3.3 +/- 0.2 Ma), synchronous with a ridge-trench c ollision south of the Hero Fracture Zone. This implies that the ultimate ca use 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, whic h would have led to an increase in slip rate and transpressional stress acr oss the Shackleton Fracture Zone. Spectacular, high relief ridges flanking the extinct spreading center, mapped for the first time using multibeam swa th bathymetry, are interpreted as a consequence of a reduction in spreading rate, involving a temporary magma oversupply immediately prior to extincti on.