Volcanic complexes on Venus: Distribution, age, mechanisms of origin, and evolution

Abstract

The paper addresses the morphology and age relations of plain terrains on Venus. The stratigraphically oldest and strongly tectonized complexes of this planet are remnants of plains made up of tessera-forming tectonic structures. This suggests that tessera terrains were formed mostly by eruptions of low-viscosity (likely basaltic) lavas. The stratigraphically oldest units, in which volcanic activity played a leading role, are shield plains, whose morphology testifies that they were produced by numerous but relatively weak eruptions of basaltic material from likely shallow-sitting chambers. The only Venusian landforms whose shapes suggest eruptions of high-viscosity lavas are festoons and steep-sided domes. The great majority of the domes is spatially and stratigraphically related to the shield plains, and this testifies that the type of volcanism during the origin of the plains was unusual and favorable for the local derivation of highly viscous lavas. The mechanisms that could possibly form the steep-sided domes suggest that the domes were most likely produced by eruptions of silica-enriched (and hence, more viscous) melts that had been generated by crystallization differentiation in chambers. The surface topography of the younger regional plains suggests that these plains were produced by large-volume but brief eruptions of basaltic (or perhaps, also komatiitic) lavas (lava flooding). The surface areas and possible volumes of the regional plains are more consistent with their generation via melting portions of mantle material that had replaced delaminated blocks of lithospheric roots. The morphology, character of spatial distribution, and typical associations of the lobate plains suggest that they were formed during melting of the head portions of mantle diapirs. The morphologic parameters of the dominant volcanic complexes on Venus (shield, regional, and lobate plains) and their unvarying stratigraphic relations highlight a clearly pronounced character of the evolution of volcanic activity in the geological history of Venus.