Filling of flexural moats around large volcanoes on Venus: Implications for volcano structure and global magmatic flux

Abstract

The absence of topographic moats and concentric normal faulting around large volcanoes on Venus is attributed to filling of the annular flexural depression by lava flows from the central edifice. Large volcanoes on Venus are characterized by prominent, approximately conical edifices surrounded by relatively flat flow aprons. The surfaces of both of these constructional components consist dominantly of radially oriented flows. From analytic plate flexure models, we generate a synthetic stratigraphy for Venus volcanoes from which we calculate the volume of material filling the flexural moats to the level of the flow apron. The total volume of volcano-associated extrusive lavas, including moat fill, can be an order of magnitude greater than the volume of the edifice alone. Extended to all large volcanoes on Venus, this procedure yields estimates for magmatic flux on Venus comparable to the present terrestrial intraplate extrusive flux, but this scenario is nonetheless consistent with observations of areally limited resurfacing since the most recent global resurfacing event. The absence of flexure-related tectonic features around most large volcanoes, by the arguments advanced here, is attributable to masking by apron flows and low stresses in the apron moat fill. On Venus, a volcanic edifice and associated moat-filling material constitute a single structurally coherent unit. Large volcanoes on Venus thus appear to be structurally distinct from those on Earth and Mars. Copyright 1997 by the American Geophysical Union.