HR: 11:05h
AN: P31C-04    [PDF]
TI: Wrinkles on the Crust of Venus
AU: * McGill, G E
EM: gmcgill@geo.umass.edu
AF: Department of Geosciences,, University of Massachusetts,, Amherst,, MA 01003 United States
AB: Wrinkle ridges are very abundant on the plains of Venus, and thus they constitute an important source of kinematic information. Wrinkle ridges generally are inferred to be related to thrust or reverse faults. We can address some of the kinematic issues with a set of questions: Can the presence of wrinkle ridges be used to define stratigraphic material units? Can the formation of wrinkle ridges be used as a rough time line? Can wrinkle ridges define kinematics by determining temporal sequences of stress states? Intersection relationships of wrinkle ridge sets with each other and with other structures, and the ages of wrinkle ridge sets relative to the impact crater population provide the data needed. The area studied includes the 20 quadrangles bounded by 60 west and 90 east longitude, 50 north and south latitude, slightly less than one-third of the total surface area of Venus, and it includes 314 impact craters, slightly less than one-third of the total global population. Throughout most of the area studied wrinkle ridges occur as 2 or more sets with different orientations. Wrinkle ridges can be used to define a stratigraphic material unit only if it can be shown that wrinkle ridge formation was coeval with the processes forming the material unit. Relationships with older fracture fabrics and with the impact crater population effectively rule out formation of wrinkle ridges coeval with material emplacement. In the area studied, east-west trending wrinkle ridges appear to be the oldest set, and these probably formed quickly enough to define a regional time line. If one can unequivocally determine the relative ages of wrinkle ridge sets, the temporal sequence of stress states in the plains can be determined. Commonly, the earliest structures to form after plains emplacement are radar-bright lineaments inferred to be fractures or small faults. East-west wrinkle ridges formed after these lineaments, and after formation of a small but significant fraction of the impact crater population. A larger fraction of the impact crater population formed before wrinkle ridges with other orientations, and these commonly terminate at intersections with east-west wrinkle ridges. Thus at least a regional scale north-south contraction of plains materials was followed by rotation of the maximum contraction direction into various other directions, depending on locality.
DE: 5475 Tectonics (8149)
DE: 6295 Venus
DE: 8010 Fractures and faults
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting