Mathematics – Logic
Scientific paper
Oct 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.0101s&link_type=abstract
American Astronomical Society, DPS meeting #42, #1.01; Bulletin of the American Astronomical Society, Vol. 42, p.941
Mathematics
Logic
1
Scientific paper
Saturn's moon Iapetus is unique in that it has apparently despun while retaining a substantial equatorial bulge. Lineaments (linear surface features) on Iapetus were mapped, updated from Singer and McKinnon (LPSC XXXIX) to cover both bright and dark hemispheres. Lineament orientations are compared to model stress patterns predicted for spin-down from a rotation period of 16 hours, or less, to its present synchronous period, and for a range of lithospheric thicknesses. Many lineaments are straight segments of crater walls, which may be faults or joints reactivated during complex crater collapse. Most striking are several large troughs on the bright, trailing hemisphere. These troughs appear to be extensional and are distinctive because the interior floors and walls contain dark material. Globally, no specific evidence of strike slip or thrust offsets are seen, but this could be due to the age and degraded nature of any such features. Observed lineament orientations do not correlate with predicted patterns from despinning on either hemisphere (the equatorial ridge was excluded from this analysis). Modest evidence for preferred orientations 20-40° from north could be construed as consistent with respinning, but the latter is physically unlikely. Assuming the rigidity of unfractured ice, predicted maximum lithospheric differential stresses range from 1 MPa to 200 MPa for the elastic spheroid and thin lithosphere approximations, respectively (although it is only for thicker elastic lithospheres that we expect a nonhydrostatic state to be maintained over geologic time). The tectonic signature of despinning may have been obscured over time as the surface of Iapetus is very ancient, or the thick lithosphere may have inhibited its full expression. Several prominent lineaments strike E-W, and are thus parallel to the equatorial ridge (though not physically close to it), but a tectonic or volcanic origin for the ridge is highly problematic.
McKinnon William B.
Singer Kelsi
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