HR: 17:00h
AN: T14A-05    [Abstracts]
TI: Do the Volcanic Rocks Erupted in the West Antarctic Rift System Beneath the West Antarctic Ice Sheet (WAIS), Interpreted From Aeromagnetic Surveys, Define a Large Igneous Province?
AU: * Behrendt, J C
EM: behrendj@colorado.edu
AF: U.S. Geological Survey, Federal Center, Denver, CO 80225 United States
AU: Finn, C A
EM: cfinn@usgs.gov
AF: U.S. Geological Survey, Federal Center, Denver, CO 80225 United States
AU: Blankenship, D D
AF: UTIG, University of Texas, Austin, TX 78759-8500 United States
AU: Morse, D
AF: UTIG, University of Texas, Austin, TX 78759-8500 United States
AU: Bell, R A
AF: LDEO, Columbia University, Palisades, NY 10964 United States
AB: Aeromagnetic and radar ice sounding surveys over the West Antarctic Ice Sheet (WAIS) made in the 1990s allow a recalculation of the estimate of the volume of late Cenozoic volcanic magmatic rocks erupted in the West Antarctic rift system. In the late 1950s and early 1960 widely spaced aeromagnetic profiles acquired over the WAIS area revealed numerous high amplitude ($>$100 nT) short-wavelength anomalies interpreted as evidence of volcanic rocks beneath the ice. By the late 1970s a 50-100-km-spaced grid of aeromagnetic and radar ice sounding profiles over the WAIS combined with the earlier survey flights allowed a fairly accurate delineation of the area covered by the high amplitude anomalies with sources inferred at the base of the ice. The Central West Antarctica (CWA) aerogeophysical survey of the 1990s consists of 5-km-spaced orthogonal aeromagnetic, radar ice sounding and aerogravity profiles. This survey, particularly the aeromagnetic data, defined the character in detail of the volcanic centers defining the late Cenozoic magmatic activity interpreted as associated with the West Antarctic rift system. In a 1994 paper, using a preliminary part of the total CWA survey we estimated $>$500,000 square km areal extent of the high amplitude, shallow source volcanic anomalies corresponding to a volume of $>$one million cubic km magmatic rocks beneath the ice. We interpreted this as evidence of a large igneous province. Now that the CWA survey is complete, we are better able to use the accurately estimated extent of the volume of volcanic centers (subglacial volcanic intrusions) in the CWA area and indirectly (using the widely spaced profiles in the WAIS area surrounding the CWA survey) to infer the extent of the late Cenozoic volcanism throughout the WAIS. During the same period, geologists have better dated volcanic exposures throughout the West Antarctic rift area, which appears to extend the period of volcanism from present to as far back as 48 Ma. We present these revised estimates, which indicate that the interpretation of a large igneous province would be correct if the bulk of the volcanic eruptions beneath the WAIS occurred during a shorter period of time than the apparent maximum age range of 48 m.y. We are unable to estimate a mode age of the volcanic activity, because the great volume of the magmatic rocks beneath the WAIS has not been sampled.
DE: 9310 Antarctica
DE: 8107 Continental neotectonics
DE: 8123 Dynamics, seismotectonics
DE: 8158 Plate motions--present and recent (3040)
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting