Other
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p41a0395b&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P41A-0395
Other
6295 Venus, 8010 Fractures And Faults, 8149 Planetary Tectonics (5475), 8164 Stresses: Crust And Lithosphere
Scientific paper
Flows and other deposits from Irnini Mons are superimposed on an older, regional plains material. Wrinkle ridges are generally abundant on this regional plains material and are present in at least two sets: one trending east-west and another concentric to Irnini Mons. Radial features on top of the Irnini flows are mapped as lineations or grabens, as resolution allows. High resolution mapping at 75 m/pixel also reveals ridges radial to Irnini Mons on top of the Irnini flows. These radial ridges are located from approximately N60E to N75E. Radial grabens around a volcano have been explained mathematically, with the magma chamber of a volcano simplistically described as a pressurized hole in an elastic plate. However, magma pressure alone can not explain the presence of radial ridges. The regional east-west trending wrinkle ridges imply a regional north-south compression affecting the Irnini Mons area. The regional stress field around an empty hole in an elastic plate is perturbed close to the hole, although it remains unperturbed at infinity; the change in material properties from the surrounding rock to a magma-filled chamber allows us to consider the chamber as "soft" and thus effectively empty. The perturbation of a uniaxial regional compressive stress around a pressurized hole is such that at angles of 90 and 270 degrees (east-west) the maximum principal stresses close to the hole are compressive, while at angles 0 and 180 degrees (north-south) the maximum principal stresses are tensile. The angle at which maximum principal stresses change from tension to compression depends upon the distance from the hole and the relative magnitudes of magma pressure and the regional compression. While in the simple model resultant stresses would be symmetric around the hole, structural complexities to the south and west of Irnini Mons restrict the predicted pattern of radial ridges as well as grabens to the region northeast of the volcano. Thus, the existence of radial ridges on the Irnini flows implies that the regional north-south compression that caused the east-west trending wrinkle ridges was still active during the formation of Irnini Mons. A rough timeline for events in the region could be: 1) formation of east-west wrinkle ridges on regional plains, 2) formation of graben radial to Irnini due to magma pressure coeval with formation of radial ridges due to a combination of magma pressure and ongoing regional compression, 3) cessation of magma pressure and formation of concentric grabens, and 4) formation of concentric wrinkle ridges, perhaps due to gravitational relaxation of the topographic rise.
Buczkowski Debra L.
Cooke Maren L.
McGill George E.
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