Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996lpi....27.1007p&link_type=abstract
Lunar and Planetary Science, volume 27, page 1007
Astronomy and Astrophysics
Astrophysics
Episodic Evolution, Global Resurfacing, Lithosphere Stability, Venus
Scientific paper
Impact craters on Venus are consistent with a surface age of 300-500 Myr and their distribution on the surface is indistinguishable from a random one. Despite the relatively young age and volcanic origin of the surface, remarkably few craters are obviously flooded by volcanic deposits. The simplest interpretation is relatively rapid global resurfacing about 300-500 Myr ago. Mechanisms that could cause catastrophic and perhaps episodic global scale mantle overturn with consequent decompression melting and volcanic resurfacing are thus important to understanding the evolution of Venus. The age at which the lithosphere contains zero net buoyancy is a function of mantle potential temperature since this controls the crustal thickness. The calculated maximum age of zero net buoyancy is about 300 Myr for a mantle potential temperature of about 1500 degrees C corresponding to a crustal thickness of about 40 km. It must be regarded as a concidence that this age concides almost exactly with lower bounds for the estimated age of the Venusian surface. The calculated age depends at least weakly on parameters such as the melting model, which is not precisely known for Venus. This simple anaylsis does show that the buoyancy of the crust and depleted mantle layer are sufficient to keep the lithosphere buoyant for time scales at least comparable to the present age the Venusian surface. Relative to the much younger age of zero net buoyancy of the terrestrial oceanic lithosphere, this is accomplished by having a thicker crust. Gravitaitonal instability of dense granulite or eclogite may limit the crustal thickness to about 40 km.
Head James W.
Hess Paul C.
Parmentier Marc E.
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