STRUCTURAL GEOLOGY AND KINEMATIC HISTORY OF THE LACHESIS TESSERA QUADRANGLE (V-18), VENUS

The Lachesis Tessera V-18 quadrangle (25^o-50^oN, 300^o-330^oE) includes parts of Sedna and Guinevere Planitiae; regional plains cover ~80% of the quadrangle. A linear grouping of a prominent structural belt, coronae, and coronae-like structures are located oriented NW to SE in the southern half of the quadrangle. Important individual structural features include radar-bright lineaments, graben, wrinkle ridges, and broader ridges, all of which are abundant and pervasive.

Wrinkle ridges range in length from a few to scores of kms, and are generally >1 km in width. The greatest abundance occurs to the NE in Sedna Planitia, where they define a wavy E-W trend. To the SW, in Guinevere Planitia, wrinkle ridges are much less abundant. This distribution coincides approximately with local topography. There are also broader ridges scattered around the quadrangle that may be isolated inliers within younger regional plains or else local folds involving regional plains.

Many of the radar-bright, straight to arcuate linear features are inferred to be small faults or extensional fractures, although most are too narrow to define their geometries. Individual lineaments range in length from the limit of detection (1-2 km) to 100s of km. In places, there are 2 trends of straight linear features at high angle to each other, defining a “grid” pattern. Where wrinkle ridges cross plains with gridded lineaments it is clear that the wrinkle ridges are younger.

Deformation belts vary widely in trend with respect to each other, even exhibiting significant variations within individual belts. Shishimora Dorsa is the largest and most clearly defined ridge belt, with ~250 km within V-18. The belt trends NE and is somewhat elevated relative to adjacent regional plains. Although dominated by ridges, the belt also includes radar-bright lineaments with two distinct azimuths that define a grid pattern.

Breksta Linea is the largest fracture belt in V-18, at about 500 km long. It consists of closely spaced fractures and graben, most of which trend with about the same azimuth as the belt itself. The fractures appear to be younger than the regional plains adjacent to Breksta Linea, as they crosscut the contact between regional plains units in about the center of the belt. Breksta Linea is elevated relative to adjacent regional plains.