Cenozoic motion between East and West Antarctica

Abstract

The West Antarctic rift system is the result of late Mesozoic and Cenozoic extension between East and West Antarctica, and represents one of the largest active continental rift systems on Earth. But the timing and magnitude of the plate motions leading to the development of this rift system remain poorly known, because of a lack of magnetic anomaly and fracture zone constraints on seafloor spreading. Here we report on magnetic data, gravity data and swath bathymetry collected in several areas of the south Tasman Sea and northern Ross Sea. These results enable us to calculate mid-Cenozoic rotation parameters for East and West Antarctica. These rotations show that there was roughly 180 km of separation in the western Ross Sea embayment in Eocene and Oligocene time. This episode of extension provides a tectonic setting for several significant Cenozoic tectonic events in the Ross Sea embayment including the uplift of the Transantarctic Mountains and the deposition of large thicknesses of Oligocene sediments. Inclusion of this East-West Antarctic motion in the plate circuit linking the Australia, Antarctic and Pacific plates removes a puzzling gap between the Lord Howe rise and Campbell plateau found in previous early Tertiary reconstructions of the New Zealand region. Determination of this East-West Antarctic motion also resolves a long standing controversy regarding the contribution of deformation in this region to the global plate circuit linking the Pacific to the rest of the world.

Cenozoic reconstructions of the Australia-New Zealand-South Pacific sector of Antarctica

“…An important aspect of the spreading history on the SEIR is that east of the Balleny Fracture Zone (FZ) (see Figure 1), anomalies older than anomaly 8 (26.6 Ma) are spreading faster than would be expected for Australia-East Antarctica spreading based on the rest of the SEIR [Stock and Molnar, 1982;Royer and Sandwell, 1989]. Cande et al [2000a] showed that these anomalies reflect Australia-West Antarctica spreading. The boundary between the Australia-East Antarctica and Australia-West Antarctica spreading, which lies east of the Balleny FZ, is shown by the line of dots south of the South Tasman Rise in Figure 2.…”

“…In the area immediately west of Tasmania, the oldest anomaly definitely identified by Royer and Ro/let (1997) was anomaly 18 (40 Ma). Similarly, although there are good constraints on the relative motion between East and West Antarctica back to Chron 20 [Cande et al, 2000a], and a rough estimate can be made for East-West Antarctic motion based on seafloor spreading constraints back to Chroo 27 [ Cande et al , 2000b], there are very few constraints on East-West Antarctica separation prior to Chron 27.…”

“…With the determination of a detailed global gravity field from satellite altimetry data ( Figure 1) [Sandwell and Smith, 1997), revealing the location of fracture zones and other tectonic features in the most remote portions of the oceans, and with the advent of GPS-navigated, swathmap bathymetry surveys, there has been considerable improvement in our understanding of the tectonics of the southern oceans. These developments include better constraints on the relative motion between the Pacific and Antarctic plates [Camie et al, 1995), a better understanding of the rifting and seafloor spreading history between the Pacific and Australia plates [Sutherland, 1995;Keller, 2003), marine magnetic anomaly constraints on the Cenozoic motion between East and West Antarctica [Cande et al, 2000a], and better constraints on the motion between the eastern and western portions of the South Tasman Rise [Royer and Rollet, 1997;Exon et al, 1996).…”

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

“…The Phoenix plate underwent subduction beneath the Antarctic Peninsula at its southeastern boundary, with which segments of the Antarctic-Phoenix ridge periodically collided leading to near-total destruction of the Phoenix plate (Larter and Barker, 1991). During much of Paleogene times, Antarctica underwent extension as the West Antarctic rift system slowly moved East Antarctica apart from West Antarctica, which we assume here included the Antarctic Peninsula (Behrendt et al, 1991;Cande et al, 2000). In addition to this, a complex of oceanic basins developed in the Scotia Sea at the region's eastern extremity, where west-directed subduction of the South American plate resulted in slow eastwards motion of an arc plate, as seen from Antarctica (Eagles et al, 2005).…”

Structure of the central Terror Rift, western Ross Sea, Antarctica

“…Tectonic models derived from global plate reconstructions and other data predict relative motion between East and West Antarctica (e.g., Cande et al, 2000) in the Cenozoic. Previous studies (Cooper et al, 1987, Salvini et al, 1997 identify the Terror Rift in the western Ross Sea as the zone of most recent deformation within the West Antarctic rift system (WARS), yet the magnitude, timing, or kinematics within the Terror Rift remain poorly constrained.…”