GIANT CIRCUMFERENTIAL MAFIC DYKE SWARMS ON EARTH, MARS AND VENUS

Giant mafic dyke swarms (>300 km long) generally have radiating or linear geometry and are a key component of large igneous provinces (LIPs) on Earth. Both geometric types of swarms (recognized by their surface expression as graben-fissure systems) are also present on Mars and Venus.

Another class of giant dyke swarms, with an arcuate to sub-circular geometry, is recognized on Mars and Venus, (as graben-fissure systems), and more speculatively on Earth (Ernst & Buchan 1998 29^thLPSC abstr. no. 1021). Major circumferential systems on Mars, typically 400-600+ km in diameter, are associated with volcanic edifices in the Tharsis and Elysium regions (Montési 2001 GSA SP352 p. 165; Ernst et al. 2001 Ann. Rep. Earth Planet. Sci. 29: 489). On Venus, circumferential systems of comparable scale (e.g. Ernst et al. 2003 Icarus 164: 282) help characterize circular tectono-magmatic features termed coronae (e.g. Grindrod & Hoogenboom 2006 Astron. Geophys. 47: 3.16-3.21).

An example of similar scale on Earth is the arcuate Kochikha swarm, 300 km long, that partially circumscribes the Siberian Trap plume center (Ernst & Buchan 2001 GSA SP352 p. 247). A second is the recently-recognized Lake Victoria swarm in East Africa that has a diameter of c. 500 km and spans at least 180 degrees of arc (Mäkitie et al. 2014 J. Afr. Earth Sci. 97: 273), and is linked to mantle plume activity during the 1380 Ma Kunene-Kibaran LIP event. A third possible example is the arcuate, 700 km long, c. 945 Ma Blekinge-Dalarna swarm which partially circumscribes the Rogaland massif in southern Scandinavia (Ernst & Buchan 1998).

Giant circumferential swarms on Mars, Venus and Earth are typically several hundred km in diameter, and linked to underlying mantle plume or diapir activity. Some magmatic centers exhibit both radiating and circumferential swarms, suggesting there are complex spatial and/or temporal stress regime differences driving the observed variations. Giant circumferential swarms have been linked to stress effects from underlying intrusive bodies and/or volcanic edifice construction.

Recognition of giant circumferential systems on Mars and Venus, as well as terrestrial examples associated with Ni-Cu-PGE-mineralization (e.g. Siberian Trap and Kunene-Kibaran LIPs), motivates further study of this enigmatic class of giant dyke swarms.