HR: 0830h
AN: P41A-0399    [PDF]
TI: Spherical Harmonic Analysis of Mountain and Volcanic Center Distributions on Io
AU: * Kirchoff, M R
EM: kirchoff@levee.wustl.edu
AF: Washington University, Dept. of Earth and Planetary Sci. One Brookings Hall, St. Louis, MO 63130 United States
AU: McKinnon, W B
EM: mckinnon@levee.wustl.edu
AF: Washington University, Dept. of Earth and Planetary Sci. One Brookings Hall, St. Louis, MO 63130 United States
AU: Schenk, P
EM: schenk@lpi.usra.edu
AF: Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058 United States
AB: Mountains and volcanic centers on Io are broadly zonally concentrated and the two distributions are anticorrelated (e.g., Schenk et al. 2001, {\it JGR 106}, 33,201-33,222). The mountains are tectonic in origin and the interplay between volcanism and tectonism is key to understanding their origin (McKinnon et al. 2001, {\it Geology 29}, 103-106; McEwen et al. 2003, in press in {\it Jupiter - The Planet, Satellites and Magnetosphere}). Here we extend previous analyses of these distributions beyond simple (but informative!) smoothing by means of counting circles. We initially assign equal weighting to each mountain ({\it n} = 115) and volcanic center ({\it n} = 541) in the global data sets. Spectral power analysis for the mountains shows a strong peak at {\it l} = 2 and a smaller one at {\it l} = 1, little power at {\it l} = 3, and the rest of the spectrum is "white" (flat). The volcanic center distribution shows an even stronger {\it l} = 2 peak, a modest peak at {\it l} = 1, and low spectral power for {\it l} $>$3. The result is that two concentrations of mountains are located at $\sim$ $30\deg$ N, $80\deg$ W and $30\deg$ S, $260\deg$ W, with the first being substantially larger. The two volcanic center concentrations are more nearly equatorial and quite close to the sub- and antijovian points, at $\sim$ $5\deg$ N, $170\deg$ W and $15\deg$ S, $345\deg$ W, again with the first being larger. We also weighted the mountains by mountain length, length x width, polygonal area (footprint), and area x height (a proxy for volume). For weighting by length, the peak at {\it l} = 1 increased slightly and the peak at {\it l} = 2 decreased, but both remained statistically significant compared with a random distribution. Power spectra of the distributions weighted by length x width or polygonal area lose much of their statistical significance at {\it l} = 1 and 2, however, due to several mountains of large areal extent outside the regions of concentration above. Nevertheless, mountain concentration positions (summing low degree terms) remain virtually the same for all weightings. Volume weighting is corrupted by the large fraction of mountains for which there are no height constraints. Lastly, a subset of only paterae (calderas) was created from the volcanic center catalog. This set of 387 paterae compares well to the 417 counted by Radebaugh et al. ({\it JGR 106}, 33,005-33,020, 2001). Each patera was given equal weight, and the spectral power distribution is similar to that for the full volcanic center data set. A strong peak at {\it l} = 2 is present, with a smaller peak at {\it l} = 1, and the two concentration positions are shifted slightly to the east. However, a minor, but statistically significant peak, is found at degree 6. This causes regions of small, dense concentrations at the equator with longitudes $\sim$ $140\deg$ W and $325\deg$ W surrounded by small, less dense concentrations and sparse areas. We will discuss the degree of correlation of the mountain and volcanic center distributions.
DE: 5475 Tectonics (8149)
DE: 5480 Volcanism (8450)
DE: 6200 PLANETOLOGY: SOLAR SYSTEM OBJECTS (New field)
DE: 6218 Jovian satellites
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting