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.

Tectonic development of the Bransfield Basin and its prolongation to the South Scotia Ridge, northern Antarctic Peninsula

“…It resulted from tectonic interaction between the structures related to the Scotia/Antarctic plate boundary in the western South Scotia Ridge, the subduction zone of the South Shetland Trench, and the extinction of the PhoenixAntarctic Ridge in Pliocene times (about 3.3 Ma, Fig. 11; Livermore et al, 2000) related to the opening of the backarc Bransfield Basin (Figs. 1, 2 and 11).…”

“…Subduction of Phoenix Plate oceanic crust along the Pacific margin of the Antarctic Peninsula came to an end progressively towards the NE as a result of ridgetrench collisions. Sandwell and Smith (1997) Continued subduction at the South Shetland Trench, with roll-back of the subducting slab, then led to the rifting and separation of a sliver of the Antarctic Peninsula margin, the South Shetland Block, carrying the South Shetland Islands, and to the opening of the NE -SW elongated Late Plioceneto-recent anomalous backarc Bransfield Basin (Pelayo and Wiens, 1989;Gamboa and Maldonado, 1990;Larter and Barker, 1991;Maldonado et al, 1994;Aldaya and Maldonado, 1996;Galindo-Zaldívar et al, 1996;Jabaloy et al, 1997;Barker and Austin, 1998;Livermore et al, 2000). In addition, it has been proposed that the rift of the Bransfield Basin merges eastwards into an active transcurrent fault zone within the South Scotia Ridge (Aldaya and Maldonado, 1996;Galindo-Zaldívar et al, 1996;González-Casado et al, 2000).…”

“…1 and 2), two extinct spreading ridges, the West Scotia and the Phoenix -Antarctic, have been identified. Their activity ended, respectively, after magnetic chron C5A (6 Ma), and chron C2A (3.3F0.2 Ma) (Lawver et al, 1992;Livermore et al, 2000;Maldonado et al, 2000). Subduction of Phoenix Plate oceanic crust along the Pacific margin of the Antarctic Peninsula came to an end progressively towards the NE as a result of ridgetrench collisions.…”

Chemistry and microstructures of clay particles in smectite-rich shelf sediments, South Shetland Islands, Antarctica

“…The arc was active from the Late Jurassic until the Tertiary, during the subduction of the Phoenix plate beneath the Antarctic plate, with pulses of volcanism and related plutonic activity lasting until the Oligocene. Subduction in the South Shetland Trench ceased at about 4 Ma (Livermore et al, 2000).…”

Insights about the structure and evolution of the Scotia Arc from a new magnetic data compilation

“…The Phoenix Plate underwent subduction below the Antarctic Plate during the late Mesozoic and Cenozoic (Dalziel, 1984;Barker et al, 1991;Eagles et al, 2004Eagles et al, , 2009). The subduction continued at the South Shetland Trench due to roll-back processes at the subduction hinge and produced active spreading in Bransfield Strait (Maldonado et al, 1994;Livermore et al, 2000;Maurice et al, 2003).…”