A review of flood lavas across the solar system
|Location||International Geological Congress,oslo 2008|
|Author||Keszthelyi, Laszlo۱; Jaeger, Windy۱; McEwen, Alfred۲; Self, Stephen۳; Thordarson, Thorvaldur۴|
|Holding Date||08 October 2008|
The goal of this presentation is to review the current understanding of flood lavas across the Solar System. Flood lavas are a major geologic component of the surfaces of all the larger silicate bodies in the Solar System. They play a key role in regulating the transfer of heat from the interior to the surface and have significant impact on the atmosphere. On Earth, they appear to have influenced mass extinctions. The vast majority of terrestrial flood lavas were emplaced as inflated pahoehoe flows, with eruption rates on the order of 1000-10 000 m3/s and eruption durations of order years to decades. These eruptions were fed from long fissure systems with episodic activity along different segments. Broad sheets of liquid lava moved underneath a thick insulating crust, allowing very extensive lava flow fields to be emplaced over an extended period of time. This was suggested to be the "Standard Way of Emplacing Long Lavas" or the "SWELL" hypothesis (Self et al., 1998, Annu. Rev. Earth Planet. Sci.).
Further insight has come from flood lavas in other parts of the Solar System. In particular, the active examples on Jupiter’s moon, Io, and young flood lavas on Mars show styles of emplacement not recognized in terrestrial studies alone. Io is home to the longest active lava flows in the Solar System. In general, isolated vents that have not moved for decades feed highly mafic lava through tubes at eruption rates of 100-1000 m3/s. A major exception is the 1997 Pillan eruption, which produced a new >5600 km2 sheet flow in a matter of months.
On Mars, the equatorial plains are covered by vast flood lavas that appear remarkably pristine, with the sparse craters suggesting ages <200 Ma and in some cases possibly <20 Ma. These lavas appear to have been emplaced as fast-moving flows with an unstable crust, forming a distinctive platy-ridged surface morphology. Upon comparison to Icelandic flows, the platy-ridged lavas were found to correspond to an enigmatic terrestrial lava type that has been named "rubbly pahoehoe". Rubbly pahoehoe is now inferred to be diagnostic of rapid emplacement and has been found in several different terrestrial flood basalt provinces.
It is the broad view across the Solar System that is allowing us to appreciate the wide range of emplacement styles that can produce long lava flows. The application of this understanding affects the interpretation of earlier data (such as the Apollo missions to the Moon) and should be considered in planning future planetary exploration.