2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 2
Presentation Time: 1:45 PM


HANSEN, Vicki L., Department of Geological Sciences, University of Minnesota Duluth, Duluth, MN 55812, vhansen@d.umn.edu

Perhaps the most surprising result of NASA's Magellan mission was ~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. 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. Catastrophic resurfacing and global stratigraphy, although initially compelling, do not stand up to the rigors of ~15 years of Magellan data analysis. Geologic mapping indicates that thin, rather than thick, flows cover hypothesized pre-flood surfaces. In addition, the ~8% of the surface hypothesized as ancient pre-flood remnants, preserved in elevated plateaus, does not correlate spatially with Venus' oldest surfaces as indicated by crater density and morphology; and extensive lowland regions, representative of hypothesized flooded surfaces, correlate with some of the oldest surfaces, contrary to hypotheses' predictions.

The SPITTER hypothesis postulates SPatially Isolated Time-Transgressive Equilibrium Resurfacing during a time of a globally thin lithosphere; near steady-state impact crater formation and destruction resulted from spatially and temporally punctuated formation of ancient crustal plateaus. SPITTER does not depend on a particular mechanism of plateau formation (whether by mantle downwelling, mantle plume, or impact-induced lava-pond), but rather focuses on the elements common to all plateau hypotheses: plateaus evolved spatially and temporally separately on thin lithosphere; formation of each plateau obliterated craters across an ~3x106 km2. Secular change to thick lithosphere ceased crater destruction, resulting in crater accumulation. Local young surfaces reflect volcanotectonic burial of craters. The emerging view provides tantalizing evidence that Venus' surface records a long rich history of terrestrial planet evolution, rather than ~500 m.y. as widely assumed.