123 Planetary Geology: Brother Mars, Sister Venus

Tuesday, 24 October 2006
8:00 AM - 12:00 PM

VENUS WAS NOT CATASTROPHICALLY RESURFACED

Paper number: 123-2
Program: Technical Sessions
Time: 8:15 AM – 8:30 AM

Authors

Abstract

Perhaps the most surprising result of NASA's Magellan mission was the existance of ~970 essentially pristine impact craters preserved in near-random distribution across Venus. Crater character and distribution are widely interpreted as evidence that Venus experienced near-global catastrophic resurfacing over 10-100 m.y., about 0.5-1 Ga. The catastrophic resurfacing hypothesis—which permeates textbooks, popular science, and is rarely questioned—emerged relatively early in Magellan data analysis; it calls for global volcanic burial of all craters formed prior to the massive outpouring of lava. The separate but related global stratigraphy hypothesis deems that catastrophic resurfacing involved emplacement of 1-3 km thick lava flows that buried pre-flood craters across ~80% of Venus, with high standing crustal plateaus, marked by ribbon-tessera fabrics preserving older terrain. Both of these hypotheses predict that ribbon-terrain, a unique tectonic fabric comprised of typically orthogonal folds and ribbons (marked by periodic ridges and troughs), predated, and therefore underlies, catastrophically emplaced plains material across Venus' lowlands. If these hypotheses are viable ribbon-terrain must be buried to a depth of >1 km globally.

We conducted global mapping of ribbon-terrain to test these hypotheses. Ribbon-terrain characterizes highland plateaus, but it also occurs in small to large kipuka scattered across much of the lowlands, with the exception of two regions in the southern hemisphere: 0-50S/160-240E and 50-82S/45E-360E. Data is lacking for ~82-90S. Within these two adjacent locations flood lava could be >1 km-thick. Elsewhere however, the distribution of ribbon-terrain, taken together with average slopes, disallows the occurrence of a globally extensive layer >1 km-thick—a minimum thickness required for proposed global-scale crater burial. These data present significant challenges for the global catastrophic resurfacing and the global stratigraphy hypotheses. Ribbon-terrain distribution, which is consistent with the SPITTER hypothesis (Spatially Isolated Time Transgressive Equilibrium Resurfacing), suggests that Venus' surface probably records a significantly longer history (>>1Ga) than previously appreciated, and that history does not include catastrophic volcanic resurfacing.