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

Abstract

Joint inversion of magnetic isochron and fracture zone data from the extinct Antarctic^Phoenix spreading system in SW Drake Passage yields seven new finite reconstruction poles. The inversion results are very well constrained for such a short length of plate boundary. Although this is partly because the finite poles are located close to the reconstructed region, the optimum use of fracture zone identifications from satellite-derived free-air gravity data is also important^as the stability of stage poles throughout the short intervals in the model affirms. The model results describe a well-organised spreading system since magnetic anomaly chron C5AD (V15 Ma) in which the Phoenix plate rotated about stage poles nearby to the southwest. Stage pole locations are broadly consistent with a hypothesis of pivoting subduction as the driving force of Phoenix plate movement, and there is some evidence in the progression of stage poles for late stage movement of the subduction pivot in response to the changing azimuth of the subduction zone at which the Phoenix plate was being consumed. The model kinematics alone provide no unequivocal support for previous interpretations of disruption of the subducted part of the Phoenix plate. The very latest stages of spreading saw falling spreading rates between magnetic anomaly chrons C4 (V8.1 Ma) and C2A (V3.3 Ma) when the Antarctic^Phoenix Ridge became extinct. This is consistent with an increase in shear stress across the plate bounding Shackleton Fracture Zone due to a plate reorganisation in the neighbouring Scotia Sea following the cessation of spreading on the West Scotia Ridge. ß

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.…”

Eocene to Miocene geometry of the West Antarctic Rift System

“…This system of gravity anomaly lineations is aligned in direct northward prolongation of the eastern West Antarctic Rift System axis through the Bentley Subglacial Trough and the Byrd Subglacial Basin (Figure 2). Geophysical data and detailed plate-kinematic reconstructions have shown that these lineations are primarily associated with the eastern boundary of the former Bellingshausen Plate and tectonic events resulting from a plate reorganisation in the South Pacific around chron C27o (61 Ma) Eagles 2004). The Bellingshausen Plate existed from about 80 to 61 Ma with a strike-slip and transpressional eastern plate boundary at the location of the Bellingshausen Gravity Anomaly (Figures 2, 4).…”

Giant mounded drifts in the Argentine Continental Margin: Origins, and global implications for the history of thermohaline circulation

“…15 Ma), which is coeval with Discontinuity M in the Indian Ocean (Niemi et al, 2000), and an unconformity in the South Pacific Ocean (Carter et al, 2004). Several important events occurred in southern South America after 15 Ma, coeval with the re-opening and deepening of the Drake Passage, after 15 Ma (Lagabrielle et al, 2009): first, the margin underwent a massive aggradational phase, which could be associated with major regional subsidence and global third-order highstand intervals in the middle Miocene (Van Andel et al, 1977;Kennett, 1982;Haq et al, 1987;Malumian and Olivero, 2005); second, the end of the compressional tectonics in the Patagonian Cordillera (Barreda and Palamarczuk, 2000); third, a marked rise in sea level over the South American continent (Aceñolaza, 2000); and last, widening of the Drake Passage due to active oceanic spreading along the Phoenix-Antarctic Ridge, from 15 to 8e3 Ma (Livermore et al, 2000;Eagles, 2003), and along the East Scotia Ridge, since 20 Ma (Eagles et al, 2005).…”