CERAMIC VOLCANISM ON REFRACTORY WORLDS: THE CASES OF IO AND CHONDRITE CAIs

Background/Overview: Most differentiated rocky worlds in our Solar System have mantles of olivine, pyroxene, spinel, and calcic plagioclase (or equivalent high-pressure phase assemblages). Earth’s mantle peridotite and similar rocks in other silicate planets and asteroids normally melt to form basaltic magma, komatiite, or other olivinenormative melts. Details of planetary mantle compositions and magma petrogenesis may lead to departures of magma compositions from olivinenormative liquids, e.g., the silicic trend of magmas derived from Earth’s subduction-watered mantle. However, magma genesis on inner Solar System bodies produces melts that are generally less refractory (in melting and volatility senses) than the mantle source was to begin with. There are hints that a very different process might occur on Io and some asteroids, resulting in ultrarefractory, silicadeficient Ca-Al-rich lava compositions that would make a ceramic engineer proud. In the extreme, volatilization of very hot lavas could produce unsilicated, nonmagnesian, non-ferroan residues of simple refractory oxides.