Drip Magmatism: Intra-Plate Volcanism and Its Importance to the Early Earth and Other Terrestrial Planets

Abstract:

In the present neither Mars nor Venus has Earth-like plate tectonics, though both are likely still volcanically active. Volcanism on Mars and Venus most resembles intra-plate volcanism on Earth, where magmatism occurs through intact lithospheric plates, away from plate boundaries. On Earth intra-plate magmatism has long been proposed to be the result of lithospheric thinning through delamination or ductile dripping. Exactly how these processes create volcanism, however, has remained obscure; particularly in the case of ductile dripping, which does not produce significant topography in the lithosphere-asthenosphere boundary.

Though its fall may not trigger significant asthenospheric upwelling, the sinking drip itself will heat conductively as it enters the asthenosphere, and may itself melt, depending upon its solidus temperature and the temperature of the asthenosphere. We refer to this as “drip magmatism,” following the hypothesis of Elkins-Tanton (2007). This model produces testable predictions for the resulting magmatic compositions. Drip magmatism was tested by Ducea (2013) for the Altiplano Plateau in the central Andes, by Holbig and Grove (2008) for magmas from Tibet, by Elkins-Tanton (2014) for the Sierra Nevada, and by Furman et al. (2014) for the central African rift; geochemistry in all these localities confirm drip magmatism.

Drip magmatism provides a quantifiable mechanism for slow but regular recycling of volatiles into a planetary atmosphere. Further, it could be driven primarily by carbon, or halogens, or other incompatible and volatile elements, in addition to water. Thus, volcanism on one-plate planets, or during a putative “hot” or “slow” tectonics phase on the early Earth, may provide sufficient volatile recycling for habitability.