Formation of Pancake Domes on Venus as Viscous Flows Over an Elastic Lithosphere

Abstract

Venus' steep-sided domes are circular volcanoes ∼10s of km wide and ∼1 km tall, which are known for their characteristic flat tops and steep sides. However, their composition remains mysterious. These “pancake” domes are likely formed by a high-viscosity lava, and other studies have predicted a range of compositions, from rhyolite to basalt. In this study, we build on previous work modeling pancake domes as spreading viscous gravity currents. However, previous models of dome formation assumed that they form over a rigid lithosphere. We previously found signatures of lithospheric flexure at 14 out of 75 pancake domes and therefore built a new model of dome formation over a bending elastic lithosphere. We found that flexure during formation can influence the shape of the resulting pancake dome. Our results also support the idea that pancake domes continue to spread for a long time after their emplacement. In comparing our model to the topography of a real pancake dome (Narina Tholus), we find a range of high, though variable, lava viscosities. Our range of lava viscosities is related to the size of the observed dome, and our results for a large dome agree with those of other studies. We test different lava densities and find that a lava density of ∼2,400–2,700 kg/m³ best reproduces the flexural signatures observed at Narina Tholus. Low-density lava (∼1,500 kg/m³) does not reproduce the flexural signatures, implying that dome-forming lava is not highly vesiculated.