Observations of stratigraphy and volcanism from guinevere and sedna planitiae, venus

Detailed mapping, using recently acquired full resolution photo-products and synthetic stereo data from the Magellan spacecraft, is used to investigate the stratigraphy and formation of landforms observed on Venus. The research focuses on two large contiguous plains, Guinevere and Sedna Planitiae. It has been suggested that distinct volcanic and deformational processes have operated throughout Venus within specific time periods. For example tesserae are considered to have only formed relatively early on in the visible venusian rock record. New observations of volcanic landforms within Guinevere and Sedna Planitia support a non-directional stratigraphy. Contrary to earlier models for the evolution of coronae, those in the study area have had a protracted history. Both Idem-Kuva and Heng-o display multiple phases of annulus formation (previously thought to occur during a specific stage of corona formation). Furthermore, annulus formation and rim topography formation do not necessarily coincide in space and time, as seen at Idem-Kuva, indicating that both large and small-scale deformational processes at coronae can be protracted. The amount and style of volcanism associated with the coronae studied here varies considerably. Predicted early stage volcanism is not observed at Idem-Kuva, Nissaba or Silvia Coronae, while Benten Corona shows multiple phases of volcanism which decrease in volume over time. A study of Sif and Gula Montes shows the two large shield volcanoes have a different overall morphology, summit structure and associated flow fields. Sif Mons is approximately circular in plan view, with a prominent summit caldera, with morphologically varying flow fields. In contrast, Gula Mons in elongate in plan view, surmounted by a rift joining two modified calderas, and is surrounded by more sinuous flows. Using terrestrial volcanoes as analogies, especially Mt. Etna, it is shown that the morphological differences between the two volcanoes may be a consequence of different internal and surrounding stress regimes.