P1: FUM March 19, 2001 21:23 Annual Reviews AR125-16 Annu. Rev. Earth Planet. Sci. 2001. 29:489–534 Copyright c 2001 by Annual Reviews. All rights reserved GIANT DIKE SWARMS: Earth, Venus, and Mars RE Ernst1, EB Grosfils2 andDMege` 3 1Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada, K1A 0E8 2Geology Department, Pomona College, Claremont, California, 91711 3Laboratoire de Tectonique, ESA CNRS 7072, case 129, Universite´ Pierre et Marie Curie, 4 place Jussieu, 75252 Paris cedex 05, France; e-mail:
[email protected], egrosfi
[email protected],
[email protected] Key Words mantle plume, rift, plate tectonics, graben, dike ■ Abstract Earth, Venus,and Mars all exhibit populations of giant (radiating, linear, and arcuate) mafic dike swarms hundreds to >2000 km in length. On Earth the dikes are exposed by erosion, while on Venus and Mars their presence is mainly inferred from associated volcanic morphology and surface deformation. The apparent absence of plate tectonics in the geologic record of Venus and Mars means that the observed population of swarms remains geometrically intact, while on Earth plate tectonics has fragmented swarms. About 30 giant radiating swarms have so far been identified on Earth, but with further study the number is expected to rise and may eventually coincide with the hundreds of mantle plume head events now being proposed. On Venus, at least 118 radiating swarms are distributed across the planet, and new high resolution mapping is revealing additional swarms. On Mars, up to 16 giant dike swarms are observed, most associated with the Tharsis region. INTRODUCTION On Earth, pioneering studies by Walter Fahrig and colleagues in the 1960s–1980s revealed the size (up to >2000 km), geometry (fanning, linear, and arcuate), age distribution (throughout the Proterozoic), and abundance (many 10s) of distinct large diabase dike swarms within the Canadian Shield including the huge fanning Mackenzie swarm (Figure 1a) (e.g.