HR: 0800h
AN: T11A-1236    [Abstracts]
TI: Magnetic Depth Estimates and Their Potential for Constraining Crustal Composition and Heat Flow in Antarctica
AU: * Finn, C A
EM: cfinn@usgs.gov
AF: U. S. Geological Survey, MS 964, Denver Federal Center, Denver, CO 80225 United States
AU: Ravat, D
EM: ravat@geo.siu.edu
AF: Southern Illinois University, Depart. Geology, Southern Illinois University Carbondale, Carbondale, IL 62901 United States
AB: Crustal composition, temperature, and heat flow, key parameters in ice sheet and tectonic models, are difficult to measure in largely ice-covered Antarctica. Aeromagnetic data have been used on other continents to determine depths to the bottom of magnetic sources from which heat flow has been calculated. However, these depths can also reflect compositional variations, and the consistency of results from various depth determination methods has not been tested. Present spectral magnetic depth determination methods require 1) large window sizes (roughly 10 times the depth to the bottom of the magnetic layer), 2) statistical random or fractal behavior of sources, and 3) datasets free of intermediate to long-wavelength problems stemming from datum shifts or warping of surveys. Depths to both the top (Spector and Grant, 1970, as revised by Fedi et al., 1998) and bottom (Bhattachharyya and Leu, 1975; Shuey et al., 1977; Connard et al., 1983; Okubo et al., 1985; and Blakely, 1988) of magnetic units were calculated. Cross-checking the results by modeling the spectral slopes and locations of peaks ensures reasonable results. Consistency of results from the different methods leads to confidence in the derived estimates. Application of these methods helps determine depths to the top and bottom of magnetic units from several regions in east and west Antarctica using single surveys flown in short periods. Assuming the spectra are obtained from sufficiently large window sizes, comparison of the aeromagnetically-determined layer thicknesses and positions from those computed with other data yield information on crustal composition, and possibly, depth to the Curie isotherm and in turn, heat flow. For example, preliminary results show that a primary magnetic layer thins from ~15-20 km in inferred Precambrian crystalline shield beneath the polar plateau to ~7 km in reworked and juvenile crust of the central Transantarctic Mountains. If the 7 km depth represents the Curie isotherm, heat flow values of 100-200 mW/m2 would be expected, depending on the magnetic petrology of rocks. The lack of Cenozoic volcanic rocks in the region suggest that the heat flow is not this high; implying that the magnetic sources observed spectrally lie well above the Curie isotherm and that the thickness measurements reflect changes in crustal composition.
DE: 9310 Antarctica
DE: 8110 Continental tectonics--general (0905)
DE: 1517 Magnetic anomaly modeling
DE: 1540 Rock and mineral magnetism
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting