Lessons from Venus for understanding mantle plumes on Earth

Mantle plumes are important in the magmatic and tectonic history for both Earth and Venus. The expression of plumes is distinctive on Venus and complementary to that on Earth; therfore, a cross-comparison is useful for better understanding plume magmatism on both planets. In contrast to the Earth, Venus has no observed record of plate tectonics, a low degree of surface erosion, and an apparently short duration for the formation of the present planetary surface. The absence of plate tectonics indicates that all magmatism is 'intraplate' and is generated beneath a stagnant lithospheric lid. A low degree of surface erosion preserves the surface structures and short-wavelength topography. The short duration of preserved magmatic activity suggests a global resurfacing event. Magmatic elements include: (a) individual volcanoes with diameters ranging up to 1000 km, which represent hotspots; (b) annular structures termed coronae with diameters averaging 300km, but ranging up to 2600km, and which appear to lack terrestrial (i.e. Earth) analogues; (c) radiating graben-fissure systems extending up to >2000 km in radius, some of which are purely uplift-related while others mark the plumbing system (dyke swarms) of volcanic systems; (d) lava flow fields of scale comparable to terrestrial flood basalts (large igneous provinces (LIPs)); and (e) regions of small shield volcanoes representing shallow-source melting. There are several hierarchies of magmatic events on Venus, ordered in terms of increasing scale and significance: (1) isolated coronae, volcanoes, flow fields, and radiating graben systems; (2a) individual and small clusters of volcanoes and coronae associated with topographic swells, geoid highs, and triple-junction rifting; these are most clearly indicative of terrestrial-type plumes originating from the deep mantle; (2b) coronae distributed along rifts (chasmata); these are the clearest examples of melt generation associated with rifting; (3) regional concentration of activity in the Beta-Atla-Themis (BAT) region; this is the closest example of a plume cluster event, sometimes termed a 'superplume event'; and (4) global volcanic resurfacing of the volcanic plains; no terrestrial analogue is confirmed, although the global burst of terrestrial plume activity in the Neoarchean is a possible analogue. Crown Copyright (C) 2004 Published by Elsevier B.V. All rights reserved.