AN EXAMINATION OF FOUR VENUSIAN SHIELD FIELDS

Small shields represent perhaps the most dominant manifestation of volcanism on Venus. Defined as volcanic constructs <20 km in diameter and <<1 km in height, many small shields (or shields) typically occur in fields that are either associated with a larger volcanic edifice (e.g. a corona) or as isolated clusters. Although much work has examined the physical characteristics of shields and the timing relations of shield fields with surrounding units, the origin and history within individual shield fields remains unclear. With the goal of better understanding the geologic history recorded within Venusian shield fields, we have examined shield clusters in four regions using Magellan Synthetic Aperture Radar (SAR) imagery (~75 m/pixel): 1) Chernava Colles (335^oE, 10^oN), 2) Ran Colles (162^oE, 0^oN), 3) Llorona Planitia (146^oE, 4^oN), and 4) Jurate Colles (156^oE, 55^oN). Chernava Colles is a ~164,000 km² shield field with predominantly cone-shaped edifices ~1-2 km in diameter. Llorona Planitia hosts a ~185,000 km² field; the average edifice diameter is ~4 km with constructs displaying morphologies ranging from a flat, pancake like shape to cone-like edifices. Ran Colles measures ~643,000 km² and hosts edifices ~6 km in diameter with a large width:height ratio where shields are mostly defined by circular changes in backscatter. Jurate Colles, is ~617,000 km² with edifices ~3 km in diameter; Jurate’s shields are the most defined of the examined fields where they typically occur as steep-sided conical edifices with visible summit pits. Although an array of edifice morphologies may be present within a single field, one type of edifice morphology typically dominates over others within each field (e.g., cone-shaped edifices in Jurate vs. flatter edifices at Ran). This intra-field dominance of one edifice type may reflect magma viscosity variations and/or eruption rate/style at each field – factors possibly influenced by each field’s surrounding geology, suggesting that each field should be put into a regional context when interpreting its evolution. Shield-sourced flow material within a field typically blends with surrounding edifices and deposits making intra-field timing relations difficult to decipher through geologic mapping at Magellan SAR resolution meaning additional means of examining shield fields may be required.