Most highlands on Venus have summit areas that display low radiothermal emissivity. This is thought to result from weathering of primary rock, which at high altitudes (relatively low temperatures) produces a distinctive pyrite-bearing high-dielectric-constant mineral asemblage. This paper treats exceptions to the rule, high-emissivity peaks at high altitudes and low-emissivity domes at low altitudes, which are related to volcanism on Venus. Low-emissivity plains domes tend to be spatially correlated with volcanoes having high-emissivity summits. Both phenomena are interpreted to be manifestations of relatively recent volcanism: the volcano summits display high emissivity because flows on them are too young to have had time to weather to the low-emissivity mineral assemblage, and nearby small volcanic domes on the plains are still seeping volcanic gases which, permeating the pore space of the plains soil layer, make the high-dielectric-constant pyritic mineral assemblage stable at the higher temperatures of plains altitudes. Of the volcanoes studied, Maat Mons has undergone the most recent major episode of volcanic activity. © 1993 by Academic Press, Inc.
