Hierarchical clustering of pit crater chains on Venus

Abstract

Composed of a series of circular to elliptical bowl-shaped depressions, pit crater chains are common on the surface of many of our solar system’s terrestrial planets and moons. Using Magellan synthetic aperture radar (SAR) images, four areas of Venus are examined in which a total of 354 pit crater chains are found: Ganiki Planitia (180°E–210°E, 25°N–50°N), Ulfrun Regio (200°E–240°E, 0°N–25°N), Themis Regio (270°E–300°E, 25°S–40°S), and Idunn Mons (205°E–225°E, 35°S–55°S). A study of the distribution of these pit crater chains at regional and local scales reveals hierarchical clustering. On a regional scale, pit crater chain clusters are associated with graben–fissure systems that are radiating (associated with volcano-tectonic features), circumferential (associated with coronae), and linear (with uncertain volcano-tectonic genesis). At a local scale, pit crater chains are found with marked restriction to particular portions of graben–fissure systems. We conclude that this hierarchical clustering is an indication that both an extensional process and a lithological control contribute to the formation of pit crater chains. Specifically, we propose that pit crater chain formation on Venus occurs in poorly welded volcaniclastic material (e.g., shield plains material unit) that has been crosscut by graben–fissure system(s). Only portions of the shield plains material unit may have sufficient thickness of volcaniclastic material, thus explaining the lack of a co-extensive relationship. Additionally, pit crater chains in other map units may be explained by shallow burial of the volcaniclastic material.