SAPPHO PATERA, VENUSMapping
Geologic mapping is a fundamental part of any attempt to understand the crustal history of a planet. Venus quadrangles are mapped at 1:5,000,000, but there is a great deal of data impossible to map at this scale. The work proposed here is to map the area north of Sappho Patera at the full Magellan image resolution of 75 m/pxl using FMAP tiles. By determining the relative ages of the structures and units, a history the orientations of the principal stresses during the formation of the local regional plains, as well as Eistla Regio, can be assumed. Since most tectonic models for Venus predict some specific sequence of stress orientations, this analysis can be expected to help constrain the various existing tectonic models.
The V20 quadrangle [McGill, 2000] shows that the regional plains around Eistla Regio and Sappho Patera are deformed by Guor and Badb Lineae (two major extensional fault zones), as well as by multiple sets of wrinkle ridges and extensional lineation fabrics, but not every small structure could be included. The area immediately north of Irnini Mons is complex and interesting. McGill [2000] shows a shield plains unit younger than the regional plains, flows from Irnini Mons that are also younger than the plains, and a smooth plains unit that is younger than the flows. Small-scale structures include two sets of wrinkle ridges, two overlapping sets of radar-bright lineations, and grabens related to Badb Linea.
The shield plains unit is abundantly covered with small domes. Although it is crossed by wrinkle ridges, they are not necessarily oriented in the same manner as the wrinkle ridges on the background regional plains. Grabens associated with Badb Linea cut through the shield material. It overlies a lineated plains material, interpreted as being a relatively old, deformed plain of volcanic rocks [McGill, 2000]. The Irnini flows are described by McGill [2000] as two units. The first is interpreted as basaltic lava flows, while the second is basaltic lava overlain by a thin pyroclastic veneer. Both units are free of wrinkle ridges, but do show fabrics of lineations and grabens. They seem to overlie every unit save the smooth plains. The smooth plains unit is superposed over all other units and most of the structures [McGill, 2000]. There are no wrinkle ridges, but there are small domes and some lineations are visible, though apparently covered. The most interesting of the lineation fabrics appear on the regional plains between the shield material and the Irini flows. Two sets of lineations appear to be overlapping in the area. Further complicating the immediate region are grabens associated with Badb Linea and closely spaced wrinkle ridges. Small domes are also present.
Numerical Modeling
Understanding some of the more curious structural features surrounding Sappho Patera can be aided by three-dimensional numerical modeling. There are many complex intersections between grabens and other linear features. Numerical modeling can determine which set of lineations is older. Also, modeling of grabens and lineations radial to volcanic peaks can determine if the volcano formed before, during or after wrinkle ridge formation.