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ABSTRACT

Small shield volcanoes with basal diameters <20 km represent the most abundant type of volcano on Venus. These shield volcanoes number >>106 in population and often occur in clusters known as shield fields, which have been interpreted to be analogous to basaltic volcanic fields on Earth. Despite previous work on shield fields, questions related to edifice morphology and magma viscosity, timing relations of events across an individual field, volume of erupted material, and the role of tectonic structures are still unresolved. Here, we address those questions through geologic mapping, volumetric calculations, and statistical analysis of possible edifice alignments in six venusian shield fields: Asherat Colles, Chernava Colles, Monoshi Tholus, Nordenflycht Patera, Ran Colles, and Urutonga Colles. Our results indicate that all of these shield fields and their associated deposits are younger than the surrounding units within the mapping areas, and each field displays overlapping temporal relations with local extensional and contractional structures. Each field also displays a lack of a consistent pattern in the temporal distribution of volcanism with regards to edifice type. Analyses of possible edifice alignments suggest edifice trends that are consistent with mapped tectonic structures within all studied fields except Asherat Colles. Comparison of these six venusian fields to terrestrial basaltic volcanic fields shows that venusian fields may be up to two to three orders of magnitude larger in their areal expanse and volume of erupted material. Our results are consistent with previous interpretations of venusian shield fields representing low rates (likely <5 × 10−4 km3/yr) of magma supply feeding these magmatic centers and highlight the effects of the resolution limit of the Magellan data set on interpreting fundamental geologic processes on the venusian surface.

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