VOLCANISM AND TECTONICS ON VENUS

We review recent developments in the study of volcanism and tectonics on Venus. Venus's crust is basaltic, dry, and probably about 30 km thi ck. The mantle convects, giving rise to plumes, and has a similar comp osition and mean temperature (similar to 1300 degrees C), but a higher viscosity (similar to 10(20) Pa s), than that of the Earth. Inferred melt generation rates constrain the lithospheric thickness to between 80 and 200 km. The elastic thickness of the lithosphere is about 30 km on average. The present-day lack of plate tectonics may be due to str ong faults and the high viscosity of the mantle. Most of the differenc es between Earth and Venus processes can be explained by the absence o f water. Venus underwent a global resurfacing event 300-600 Ma ago, th e cause and nature of which remains uncertain. The present-day surface heat flux on Venus is about half the likely radiogenic heat generatio n rate, which suggests that Venus has been heating up since the resurf acing event.