Lancaster, Michael Gavin; (1994) Flood lava flow fields on the plains of Venus. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The Magellan spacecraft has mapped nearly 99% of the surface of Venus with high resolution synthetic aperture radar (SAR) images, radiometry and altimetry. These data are used to study the characteristics and distribution of volcanic deposits on Venus, specifically the large flood-type lava flow fields, and their relationship to tectonic features. Regional stratigraphy and the nature of plains formation are also investigated. A set of fifty flood-type lava flow fields on Venus with total areas greater than 50,000 km2 (great flow fields) are analysed. These fields have typical lengths of several hundred kilometres and estimated volumes of 103 to 104 km3. The fields have been classed into five morphological types, with the basic distinction being drawn between sheet-like and digitate morphologies. The sheet flow fields may represent single massive volume limited eruptions from laterally extensive fissures, while the digitate fields were formed by the repeated eruption of individual lobate flows. Six eruptive episodes are identified in Mylitta Fluctus, which is studied in detail. Most of the great flow fields may be characterised by extremely smooth pavement-like surface textures, with some occurrences of aa. First order estimates of eruption rate of between 105 and 106 m3s-1 have been made for typical flow units within the digitate fields. Most of the great flows are associated with zones of lithospheric extension and thinning, and represent comparatively recent volcanism. However, a population of indistinct flows on the plains may represent an extended period of plains resurfacing. The great flow fields are considered to be Venusian analogues of terrestrial flood basalt provinces. A specific regional study of Rusalka Planitia and Atla Regio has indicated three main phases in the geological history of that area, including early tessera formation, widespread plains formation and the burial of tessera, and later mantle upwelling and the formation of coronae, large volcanoes and rift zones.

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