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

Abstract

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, highrelief 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.

Animated tectonic reconstruction of the Southern Pacific and alkaline volcanism at its convergent margins since Eocene times

“…All this time, and afterwards, accretion continued at the Antarctic-Phoenix Ridge, and the Phoenix plate continued to be subducted beneath the Antarctic Peninsula (Larter and Barker, 1991;Livermore et al, 2000;Eagles, 2003). This situation inevitably led to further ridge crest-trench collisions like those described southwest of the Tula Fracture Zone, but because of the long-offset on the Tula transform fault the first of these later collisions dates from around 20 Ma (Fig.…”

Tectonic evolution of the Antarctic–Phoenix plate system since 15 Ma

“…The last collisions occurred at V62 ‡S^63 ‡S on the margin around chron C3A (V6.5 Ma) [1]. Spreading on the Antarctic^Phoenix Ridge stopped around anomaly C2A (V3.3 Ma) [2], leaving only a small remnant of the Phoenix plate unsubducted, and this remnant was incorporated into the Antarctic plate.…”

“…The Phoenix plate has been treated in the past as a laboratory for the study of plate tectonic driving forces [1] via the study of sea£oor spreading rate changes revealed in magnetic anomaly pro¢les [1,2]. An inversion that ¢ts conjugate magnetic anomaly identi¢cations together is a powerful technique to identify discrepancies in identi¢cations of anomalies on pro¢les and generate estimates of spreading rates.…”

Opening history of Powell Basin, Antarctic Peninsula

“…Its interpretation as an extinct, buried spreading centre was con¢rmed by seismic pro¢ling (King et al, 1997). Although this generally has the character of a typical median valley, some pro¢les reveal the existence of basement highs of limited extent (King et al, 1997), which may represent late-stage eruptions rather like those inferred on segment P2 of the extinct Phoenix Ridge, southwest of the Shackleton Fracture Zone (Livermore et al, 2000). The ridge axis, as de¢ned by the gravity low, is linear, with no large o¡sets, although a small discontinuity at 62 ‡20PS, 49 ‡50PW is evident.…”