Highlands of tesserae terrain and ridge belt Tectonic activity
[Computer generated, based on Magellan radar data] Impact Craters Sequence of surface units
Resurfacing models: Crater distribution Turcotte et al. (1998)
Resurfacing models: Mean surface age Crater frequencies on Venus are low compared with those on the surface of the Moon and Mars. This shows that the surface is young, perhaps no older than a mean of 500 Myr (estimates of the crater production rate predict ages between 190-800 Myr)
The spatial and hypsometric distribution of craters cannot be distinguished from a random distribution. The random crater distribution is independent of size. The density of small craters declines with decreasing diameters due to atmospheric filtering. The spectrum of crater modification differs greatly from that of other planets: 62-84% are pristine, 2.5-4% are embayed by lavas, aprox. 8.5% are slightly fractured, and only 3.5% (aprox.) are highly fractured. The lava embayed craters are concentrated in zones of recent volcanism, and the highly fractured craters are associated with the equatorial rift systems. Resurfacing models: Constraints [Schaber et al. 1992; Strom et al. 1994]
Resurfacing models: Global vs Regional Global resurfacing: Catastrophic burial associated with instantaneous overturn of the lithosphere and intense volcanic and tectonic activity about 300-500 Myr ago which ended abruptly. Regional resurfacing: Progressive burial of small areas at a time as new volcanic centers developed. Requires a constant rate and spatially random distribution of volcanism. Ultimately, the whole planet would be resurfaced, albeit over a longer time period.
Global vs Regional resurfacing: Simulations Strom et al. 1994
Bullock&Grinspoon 1993 Global vs Regional resurfacing: Simulations Equilibrium regional scenario. 30% partially embayed craters, substantially greater than observed. Equilibrium number significantly less than observed. Catastrophic, global scenario. 950 surviving craters 5% partially embayed craters. Competing processes of constant rate impact cratering and volcanism. Initially crater-free surface. Resurfacing age uniquely determined by number of observed surviving and partially embayed craters.
Global vs Regional resurfacing: Conclusions Objections to regional resurfacing models : Simulations result in about 17 times/15% more embayed craters than observed. Simulations result in unobserved nonrandom crater distributions for resurfacing areas between 0.03% and 100% of the planet’s surface. Models not consistent with the number and nonrandom distribution of volcanoes and the nonrandom distribution of embayed and heavily fractured craters. Global resurfacing models are consistent with : The spatially random crater distribution and its diameter independence. The random hypsometric crater distribution. The very low abundance of embayed craters and fractured craters. The concentration of embayed and highly fractured craters at zones of recent volcanism and tectonism. [Bullock&Grinspoon 1993; Strom et al. 1994]
References Basilevsky, A. T. & McGill, G. E. 2013. Surface Evolution of Venus, in Exploring Venus as a Terrestrial Planet (eds L. W. Esposito, E. R. Stofan and T. E. Cravens), American Geophysical Union, Washington, D.C. Bullock, M. A., D. H. Grinspoon, & J. W. Head III 1993. Venus resurfacing rates: Constraints provided by 3-D Monte Carlo simulations, Geophys. Res. Lett., 20(19), 2147–2150. Herrick, Robert R. 1994. Resurfacing history of Venus. Geology, vol. 22, no 8, p. 703-706. Saunders, R. S., Arvidson, R. E., HEAD, J. W., Schaber, G. G., Stofan, E. R., & Solomon, S. C. 1991. An overview of Venus geology. Science, 252(5003), 249-252. Strom, R. G., G. G. Schaber, & D. D. Dawson 1994. The global resurfacing of Venus, J. Geophys. Res., 99(E5), 10899–10926. http://en.wikipedia.org/wiki/Geology_of_Venus http://csep10.phys.utk.edu/astr161/lect/venus/surface.html http://ircamera.as.arizona.edu/NatSci102/NatSci102/text/venusgeol.htm http://geology.about.com/od/venus/a/aa_venus.htm http://www.harmonicamundi.org/HGS/atmos_proj/resurfacing.html http://explanet.info/Chapter07.htm http://www.geol.umd.edu/~jmerck/geol212/lectures/12.html http://global.britannica.com/EBchecked/topic/625665/Venus/54191/Interior-structure-and-geologic- evolution http://global.britannica.com/EBchecked/topic/625665/Venus/54191/Interior-structure-and-geologic- evolution http://geology.about.com/gi/o.htm?zi=1/XJ&zTi=1&sdn=geology&cdn=education&tm=8923&f=10&tt =14&bt=8&bts=1&zu=http%3A//www.lpi.usra.edu/publications/slidesets/venus.html http://geology.about.com/gi/o.htm?zi=1/XJ&zTi=1&sdn=geology&cdn=education&tm=8923&f=10&tt =14&bt=8&bts=1&zu=http%3A//www.lpi.usra.edu/publications/slidesets/venus.html