Regional Geologic and Morphologic Characterization of Rift Zones on Venus

Topographic and morphometric characteristics of rift zones and graben belts on Venus are analyzed. Venusian rift valleys extend from summit of large dome-shaped rises (domes) of Atla and Beta Regiones, while graben belts stretch out sideways from their feet and connect these domes. At the places where rift valleys intersect domes, the depth of rifts correlates with the height of domes; and the morphometric properties of rift valleys are controlled by the dome height. In Beta Regio, the width of the northern rift correlates with the height of the parent dome and reflects a degree of the rift opening as the dome increases, which probably indicates the continuing genesis of rifts. In Atla Regio, the tendency for decreasing depth of the south-western rift with increasing width has been revealed. This may be connected with the rift valley branching and dividing into separate smaller grabens. The absence of correlation between the width and the depth of structures in graben belts enables us to suppose them to be mature in morphology, which means that the increase in the width of a structure is not accompanied by the increase in its visible depth. Apparently, graben belts and rift valleys represent, respectively, the earlier and later phases of a single rifting process during the volcano-tectonic resurfacing regime on Venus. The characteristics of rift valleys in Beta Regio may be indicative of a currently ongoing process that forms extensional zones in this region.