New investigations of the spreading of Earth's crust in Antarctica may change existing estimates of tectonic plate motion around the Pacific Ocean Basin.

Tectonic deformation in western Marie Byrd Land and the Ross Embayment area apparently occurs as the continent separates. Possible causes of the deformation include the separation and crustal uplift caused by isostatic rebound following the last glacial maximum, about 14,000 years ago. Isostatic adjustment is vertical movement caused when weight is added or subtracted from parts of the Earth's crust. When a glacier is at its heaviest, the crust falls; as it melts or moves from that part, the crust rises.

"It is widely accepted that the Ross Sea region is undergoing active deformation, but the rates and causes of deformation are essentially unknown. Tectonic extension may be occurring in the Ross Embayment during the current separation of West and East Antarctica," said Dr. Bruce Luyendyk, principal investigator and chair of the Geology Department, University of California Santa Barbara.

To measure isostatic rebound and tectonic deformation, researchers have installed three autonomous, continuously recording global positioning system (GPS) stations on outcrops in western Marie Byrd Land in concert with a series of stations in the Transantarctic Mountains. This enables scientists to collect data from a large area across the Ross Embayment. Data has been acquired since 1998 and will continue to be monitored for the next several years. Scientists plan site visits to evaluate and upgrade equipment and to collect data.

"So far, the data indicate that spreading is occurring across the Ross Embayment," said Dr. Andrea Donnellan, co- investigator of the project at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Future measurements will refine the number."

The joint JPL and UCSB project brings together experts in Antarctic geology and tectonics, tectonic geodesy, and lithospheric deformation. Funding is from the National Science Foundation Office of Polar Programs and NASA's Office of Earth Science Enterprise, Washington, D.C. Donnellan and Luyendyk are co-authors of a paper to be presented at the American Geophysical Union meeting in San Francisco on December 18. JPL is managed for NASA by the California Institute of Technology in Pasadena. More information is available at .

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