Graben–fissure systems in Guinevere Planitia and Beta Regio (264°–312°E, 24°–60°N), Venus, and implications for regional stratigraphy and mantle plumes

Detailed mapping in a 14,000,000 km2 area of northwestern Guinevere Planitia and northern Beta Regio bounded by 264°–312°E, 24°–60°N has revealed thousands of long extensional lineaments (graben, fissures and related fractures). These can be grouped into radiating, circumferential and linear systems. Thirty four radiating systems have been identified, of which 16 have radii greater than 300 km and eight have radii greater than 1000 km. Twenty six linear (straight) systems with a length greater than 300 km have been distinguished of which six have a length greater than 1000 km. Linear systems are generally associated with rifts, although some may represent distal portions of radiating systems. In addition, 19 circumferential systems, some associated with coronae, have been identified. The distribution of each system is compared with the host geology in order to place the graben–fissure systems in a regional stratigraphic framework. The majority of systems are: (1) younger than tesserae, ridge belts and densely fractured plains, (2) coeval with, and in many cases, define fracture belts, (3) partially flooded by wrinkle-ridged plains units, and (4) older than smooth and lobate plains units and young rifts. The inventory of radiating graben–fissure systems that we catalogue represents a database of tectono-magmatic centers that complements the centers defined using other criteria, e.g., large volcanoes, coronae, and shield fields. We have attempted to identify those systems that are underlain by dike swarms in order to evaluate their relationship to mantle plumes. At least 11 of the radiating systems extend well beyond any central topographic uplift and are therefore interpreted to be underlain by dike swarms.