Scotia Arc Research Project

Project Description

Antarctica is the Earth's most isolated continent. It is surrounded by
actively spreading ridges except in the South American sector. The
motion of South America with respect to Antarctica is latitudinal and
left-lateral at approximately 22 mm per year and is distributed along
the boundaries of the intervening Scotia plate. A prominent but
discontinuous bathymetric high known as the Scotia Ridge surrounds the
Scotia plate on three sides. This feature includes some continental
material detached from the South American and Antarctic continents,
but its eastern closure is a volcanically and seismically active group
of islands, the South Sandwich arc, that is separated from the Scotia
plate by a vigorously spreading back-arc ridge. The entire
east-closing, locally emergent bathymetric feature joining the two
continents, is known as the Scotia arc. The D-shaped Sandwich plate
and arc appear to be moving rapidly east with respect to both South
America and Antarctica, thereby for the first time introducing a
subduction system into the otherwise rift-bounded South Atlantic Ocean
basin. This motion may constitute the best evidence for mantle return
flow from the closing Pacific Ocean basin to the expanding Atlantic
Ocean basin. The Scotia arc is nonetheless one of the most poorly
constrained of the major tectonic systems on Earth, yet it is a
critical and enigmatic link in global plate-motion circuits.

Our proposed ScArc GPS Project (SCARP) will use the Global Positioning
System (GPS) to measure the plate motions between South America,
Antarctica and Africa, and around the Scotia arc using a newly
developed geodetic strategy known as a multimodal occupation strategy
(MOST). This involves setting up permanent GPS receivers at a small
number of sites in South America and Antarctica, and using additional
receivers to position numerous stations relative to this continuously
operating network. Two seasonally occupied stations in the South
Sandwich islands will be tied to permanent GPS sites in South America,
Antarctica and Africa, and to intervening stations in the Falkland,
South Georgia and South Orkney islands that will be occupied on an
occasional basis by British collaborators. During the initial three
years the South Sandwich arc motion will be easily resolved, and using
roving stations in the Antarctic Peninsula-South Shetland Islands
area, we should be able to determine if extension is occurring across
Bransfield Strait. We also propose to construct a relatively dense
subnetwork in Patagonia/Tierra del Fuego, and a moderately dense
subnetwork in the Antarctic Peninsula. While we do not expect to
achieve sub-millimeter/year velocity resolution in the initial three
year project with these subnetworks, this project will establish the
baseline necessary for a follow-on suite of measurements in perhaps
six to eight years. The follow-on project will allow us to
characterize the slow motions and deformations that occur across and
within the boundaries of the Scotia plate. The deformation at the
South Sandwich Trench and seafloor spreading behind the arc will be
investigated by marine geophysics while GPS measurements are be
undertaken on the islands.

The objectives of SCARP are to determine:

1. the relative motions of the Antarctic, South American, Scotia and
South Sandwich plates;

2. the rate of rollback of the South Sandwich Trench in a South
American-African framework;

3. strain partitioning within the South America-Scotia plate boundary
zone, Tierra del Fuego;

4. the rate of extension across the volcanically active Bransfield
trough and the present rate of uplift or subsidence of the extinct
South Shetland Islands volcanic arc.

These objectives in turn will allow us to:

1. Evaluate what the South Sandwich trench rollback tells us about
mantle flow and the potential for transforming a passive rifted ocean
basin into a subducting or disappearing ocean basin. This also
requires shipboard work that will allow us to investigate deformation
of the South American plate as it is subducted at the South Sandwich

2. Test for motion between East and West Antarctica postulated as a
source of error in global plate circuits

3. Determine why there is transpression along the northern boundary of
the Scotia plate and transtension along its southern boundary; and

4. Contribute to a geodetic assessment of the elastic displacement
field associated with extension in Bransfield Strait and the
accumulation or loss of ice on the Antarctic continent.