Analysis of the geologic structure and compilation of the geologic map of the northern part of planet Venus

Based on an analysis of the images of the Venusian surface obtained by the side-looking radar of the Magellan orbiter, a geologic map of the northern part of Venus (the region extending to the north of the 35 degreesN latitud e) at 1 : 10000000 scale is compiled. The map of this vast territory, compr ising one-fifth of the planet surface, was compiled using only 12 geologic units, which implies a uniform character of terrains and landforms on the i nvestigated territory and, therefore, the uniformity of geologic processes that occurred on this planet. These units are the products of four main gro ups of geologic processes that occurred on Venus during the last 0.5-1 Myr: (1)basaltic volcanism; (2) tectonic compression and tensile deformation; ( 3) impact cratering; and (4) wind-related mobilization, transportation, and deposition of loose fine grained materials. Basaltic volcanism is the main process that supplies new material on the surface of Venus. Tectonic defor mation structures, superposed on the material of different geologic units, determined the morphology of the units and formed the surfaces of unconform ity between neighboring units. Ten of 12 geologic units form an age sequenc e that is virtually identical over the entire mapped territory of the plane t. The possible inconsistency of this sequence caused by anomalous relation s existing between smooth plains (Ps) in the southeastern part of Lakshmi P lenum and wrinkle ridged plains (Pwr) in the northern part of Sedna Planiti a does not destroy this sequence as a whole. The results of our mapping sup port the model of global stratigraphy of Venus proposed by Basilevsky and H ead (1995-1998) and provide evidence of the quasi-synchronous character of single-type geologic units on different areas of Venus rather than of the a bsence of synchronism. An analysis of the distribution of impact craters on different geologic units has shown the proximity of mean absolute ages of the material of the surface of Pwr plains, of the entire studied territory, and of the entire Venusian surface. The results of our analysis suggest th at, within the area under study, the intensity of the leading geologic proc esses at the beginning of the studied segment of the geologic history was r elatively high but decreased dramatically later.