Cubic zirconia in >2370 °C impact melt records Earth's hottest crust

• Published in: Earth and planetary science letters Vol. 477; pp. 52 - 58
• Main Authors: Timms, Nicholas E., Erickson, Timmons M., Zanetti, Michael R., Pearce, Mark A., Cayron, Cyril, Cavosie, Aaron J., Reddy, Steven M., Wittmann, Axel, Carpenter, Paul K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2017
• Subjects: cubic zirconia; early Earth; impact melt; phase transformation; planetary evolution; zircon; early Earth; planetary evolution; cubic zirconia; zircon; impact melt; phase transformation
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2017.08.012

Bolide impacts influence primordial evolution of planetary bodies because they can cause instantaneous melting and vaporization of both crust and impactors. Temperatures reached by impact-generated silicate melts are unknown because meteorite impacts are ephemeral, and established mineral and rock thermometers have limited temperature ranges. Consequently, impact melt temperatures in global bombardment models of the early Earth and Moon are poorly constrained, and may not accurately predict the survival, stabilization, geochemical evolution and cooling of early crustal materials. Here we show geological evidence for the transformation of zircon to cubic zirconia plus silica in impact melt from the 28 km diameter Mistastin Lake crater, Canada, which requires super-heating in excess of 2370 °C. This new temperature determination is the highest recorded from any crustal rock. Our phase heritage approach extends the thermometry range for impact melts by several hundred degrees, more closely bridging the gap between nature and theory. Profusion of >2370 °C superheated impact melt during high intensity bombardment of Hadean Earth likely facilitated consumption of early-formed crustal rocks and minerals, widespread volatilization of various species, including hydrates, and formation of dry, rigid, refractory crust.
•Zircon has partially dissociated in impact melt rock from a Canadian impact crater.•Former presence of cubic ZrO2 is crystallographically encoded in reaction rims.•Cubic zirconia required >2370 °C melt, which is hottest recorded on Earth's surface.•Such superheated melt susceptible to devolatilization resulting in dry rigid crust.•Potential global effects for crustal evolution during bombardment of early Earth.