2002-2003 Science Planning Summary

Geology & Geophysics

Dr. Scott Borg
Program Manager

GO-089-M

NSF/OPP 99-09603
Station: McMurdo Station
RPSC POC: Joni English
Research Site(s): TAMCAMP, deep field

A broadband seismic experiment to investigate deep continental structure across the East-West Antarctic boundary
Dr. Douglas A. Wiens
Washington University
Department of Earth and Planetary Sciences
doug@kermadec.wustl.edu
http://epsc.wustl.edu/seismology/Tamseis
Dr. Andy Nyblade
Pennsylvania State University

Deploying Team Members: Noel Barstow . Bruce C Beaudoin . Margaret H Benoit . Jesse L Fisher . Alexander Gerst . Audrey Huerta . Andy Nyblade . Sara Pozgay . Patrick J Shore . Timothy Watson
Research Objectives: Antarctica's outline shape looks generally like Australia, though half again as large. However beneath its enormous ice sheet lies evidence of its origin. East Antarctica has a bedrock continent-like foundation, while the ice sheet over West Antarctica -- a third the area -- in fact covers a series of "islands." West Antarctica shares a geologic history with the South American Andes Mountains, the result of plates colliding and subducting. East Antarctica is more like a large coherent chunk that broke free of the supercontinent, Gondwanaland, and drifted to a new position at the bottom of the world. The boundary between these two regions (with their disparate geologic pedigrees) is called the east-west antarctic boundary. The crust and upper mantle here reveals many important and interesting distinctions which tells the basic story of the tectonic development of Antarctica.

In November 2000 this group began making seismic measurements using three arrays and a total of 44 seismic stations, all geared to evaluating geodynamic models of the evolution of Antarctica that rely on data about the crust and upper mantle. To analyze the data, researchers use a variety of proven modeling techniques, including body- and surface-wave tomography, receiver function inversion, and shear-wave splitting analysis.

One basic question is, "How were the Transantarctic Mountains formed?" Though widely considered a classic example of rift-flank uplift, there is little consensus about the uplift mechanism. Many theories have been proposed ranging from delayed phase changes to transform-flank uplift. All make various assumptions about upper mantle structure beneath and adjacent to the rift-side of the mountain front.

Another focus will be the structure of the east antarctic craton, the highest ice block in the world. Was this anomalous elevation a prime driver in the onset of glaciation there? More to the point, how did it arise? Proposed models include isostatic uplift from thickened crust, anomalously depleted upper mantle, and thermally modified upper mantle, as well as dynamic uplift. How far the old continental lithosphere extends is also uncertain. In particular, it is unknown whether the old lithosphere extends to the western edge of East Antarctica beneath the crustal rocks deformed during the Ross Orogeny (formation).

When completed and analyzed, this comprehensive set of data and theory testing will enable new maps of the variation in crustal thickness, upper mantle structure, anisotropy, and mantle discontinuity topography across the boundary of East and West Antarctica, providing a much enhanced foundation for understanding the geodynamics of the antarctic.


Field Season Overview:
Project team members will travel by helicopter and Twin Otter aircraft to install new broadband seismic stations and upgrade existing stations at several locations near McMurdo Station. Some team members will remain in McMurdo while others travel by LC-130 aircraft to the TAMSEIS (Trans-Antarctic Mountain Seismic) field camp and from there by Twin Otter to the seismic stations.

Later in the field, project team members will return to Antarctica to revisit and service the seismic stations. These team members will also provide training to the winter-over science technician. During the austral-winter season, the science technician will download data and make repairs as necessary to the seismic station installed at McMurdo.