Speaker – Alan Whittington, Volcanology, The University of Texas at San Antonio (host – Arianna Soldati) Zoom

Seminar Title – Space lava! Adventures beyond the terrestrial T-X limits of igneous petrology

Abstract – As planetary geology reaches the edges of the solar system and prepares for the leap to exoplanets, we should be ready to encounter igneous processes occurring over a much wider range of T-X space than is familiar to terrestrial petrologists.

Volcanism on Earth is typically restricted to compositions that can be generated by partial melting of the Earth’s mantle and/or crust, and through subsequent modifying processes such as magma mixing, assimilation, and fractional crystallization. This leads to the familiar range of terrestrial lava compositions, limited at the present day to foidites (e.g. Nyiragongo, DRC) at the low-SiO2 end, and high-silica rhyolites (e.g. Obsidian Dome, USA) at the other. Carbonatites represent a rare departure from silicate volcanism on Earth. At much lower temperatures, cryovolcanism is the probable mechanism for the extrusion of sodium carbonate-rich domes on Ceres. Sulfate, chloride and carbonate-rich brines are likely cryovolcanic materials at Europa, Enceladus, and other ocean worlds.

Impact melts are composed primarily of target material, whose composition is dictated by surface processes that extend beyond the realm of igneous petrology. Consequently they span a much wider range. On terrestrial bodies with primary crusts, such as the anorthositic lunar highlands, impact melts can resemble monomineralic melts, which could never form by any other mechanism. Where impacts remelt secondary crusts, for example the lunar maria, the same magma could be reborn but at a much higher temperature than during initial formation and emplacement. These superheated sheets of lava have tremendous erosive power, both thermal and mechanical, until they cool below their liquidus.

Finally, in situ resource utilization (ISRU) on the Moon or Mars will likely require melting to produce glass and ceramics for construction and technical applications. Energy requirements can be minimized by using starting materials with a glassy component, sourced from volcanic or impact melt deposits (including micron-scale agglutinates). The tendency for finer grained lunar regolith to also be more feldspathic and glassy raises the possibility that physical sorting by size can also sort for composition and crystallinity, facilitating brick/ ceramic production in locations where the bulk regolith is less suitable.