Collaborative Research: A Broadband Seismic Investigation of Deep Continental Structure Across the East-West Antarctic Boundary

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9909603WiensThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a project to evaluate geodynamic models for the tectonic development of Antarctica by investigating crust and upper mantle structure beneath the East-West Antarctic boundary. This experiment will use a focused broadband seismograph deployment to address two outstanding problems concerning the tectonic development of the Antarctic continent. (1) The origin of the Transantarctic Mountains.Even though the Transantarctic Mountains are widely considered a classic example of rift flank uplift, there appears to be little consensus about the exact uplift mechanism. Many mechanisms have been proposed, ranging from delayed phase changes to transform-flank uplift, all of which make various assumptions about upper mantle structure beneath and adjacent to the rift-side of the mountain front. (2) The structure of the East Antarctic Craton.East Antarctica displays the greatest modal elevation of any major cratonic block when corrected for glacial loading. The anomalous elevation of East Antarctica may have been an important factor in the onset of continental glaciation. However, the support mechanism for this anomalous topography is unknown; possible models include isostatic uplift from (a) thickened crust, (b) anomalously depleted upper mantle, and (c) thermally modified upper mantle, as well as dynamic uplift. The lateral extent of the very old continental lithosphere 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.To examine details of the crust and upper mantle structure across the East-West Antarctic boundary, this passive seismic experiment is comprised of three elements:(1) A 1400 km linear array of 17 broadband seismic stations extending from the high central regions of the East Antarctic craton to the Transantarctic Mountains (Array 1).(2) An intersecting 400 km linear array of 16 broadband seismic stations extending from the coast across the Transantarctic mountains nearly perpendicular to the strike of the range in the dry valleys region (Array 2).(3) An array of 11 broadband stations in coastal regions around Ross Island and Terra Nova Bay (Array 3).This experiment will be conducted over a three-year period, to allow sufficient data collection from naturally occurring earthquakes, and will begin in November 2000. Airborne surveys for surface elevation and ice thickness will be completed in support of this work. If feasible, aerogravity and aeromagnetics data will also be collected. Data will be analyzed using a variety of proven modeling techniques, including body and surface wave tomography, receiver function inversion, and shear wave splitting analysis. The results of these analyses will be maps of the variation in crustal thickness, upper mantle structure, anisotropy, and mantle discontinuity topography across the boundary of East and West Antarctica. These results will provide a solid foundation for understanding the geodynamics of the Antarctic continent.