¹Cassandra Seltzer,¹Hoagy O’Ghaffari,¹Matěj Peč
Journal of Geophysical Research (Planets) (in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008296]
¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
Published by arrangement with John Wiley & Sons

Icy moons in the outer Solar System likely contain rocky, chondritic interiors, but this material is rarely studied under confining pressure. The contribution of rocky interiors to deformation and heat generation is therefore poorly constrained. We deformed LL6 chondrites at confining pressures ≤100 MPa and quasistatic strain rates. We defined a failure envelope, recorded acoustic emissions (AEs), measured ultrasonic velocities, and retrieved static and dynamic elastic moduli for the experimental conditions. The Young’s modulus, which quantifies stiffness, of the chondritic material increased with increasing confining pressure. The material reached its peak strength, which is the maximum supported differential stress (σ1 − σ3), between 40 and 50 MPa confining pressure. Above this 40–50 MPa range of confining pressure, the stiffness increased significantly, while the peak strength dropped. Acoustic emission events associated with brittle deformation mechanisms occurred both during isotropic pressurization (σ1 = σ2 = σ3) as well as at low differential stresses during triaxial deformation (σ1 > σ2 = σ3), during nominally “elastic” deformation, indicating that dissipative processes are likely possible in the rocky interiors of icy moons. These events also occurred less frequently at higher confining pressures. We therefore suggest that the chondritic interiors of icy moons could become less compliant, and possibly less dissipative, as a function of the moons’ pressure and size.

¹Konstantin M. Ryazantsev,²Alexander N. Krot,³Chi Ma,¹Marina A. Ivanova,¹Cyril A. Lorenz,⁴Vasiliy D. Shcherbakov
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14238]
¹Vernadsky Institute of Geochemistry of the Russian Academy of Sciences, Moscow, Russia
²Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Mānoa, Honolulu, Hawai’i, USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
⁴Lomonosov Moscow State University, Moscow, Russia
Published by arrangement with John Wiley & Sons

Isolated corundum grains and corundum ± Mg-deltalumite [(Al,Mg)(Al,◻)2O4] ± hibonite assemblages were investigated in the CH3.0 metal-rich carbonaceous chondrite Sayh al Uhaymir (SaU) 290. Although very refractory inclusions containing abundant Zr- and Sc-rich oxides and silicates, hibonite, grossite, or perovskite have been previously described in CH chondrites, this is the first discovery of corundum and Mg-deltalumite in CHs and the first discovery of Mg-deltalumite in nature. Magnesium-deltalumite can be indexed by the Fd3m spinel-type structure and gives a perfect fit to the synthetic Al-rich spinel cells. Corundum-Mg-deltalumite grains, 5–20 μm in size, are occasionally rimmed by a thin layer of hibonite replacing corundum. Some corundum grains contain tiny inclusions of ultrarefractory Zr,Sc-rich minerals and platinum-group element (PGE) nuggets. All corundum, hibonite, and Mg-deltalumite grains studied have 16O-rich compositions (average Δ17O ± 2SD = −22 ± 3‰). Two corundum grains show evidence for significant mass-dependent fractionation of oxygen isotopes: Δ18O ~ +34‰ and ~ +19‰. We suggest that the SaU 290 corundum-rich objects were formed by evaporation and/or condensation in a hot nebular region close to the proto-sun where the ambient temperature was close to the condensation temperature of corundum. A corundum grain with tiny inclusions of Zr- and Sc-rich phases and PGE metal nuggets recorded formation temperatures higher than the condensation temperature of corundum. Two corundum-rich objects with highly fractionated oxygen isotopes must have crystallized from a melt that experienced evaporation. Corundum grains corroded by hibonite recorded gas–solid interaction in this region during its cooling. The Mg-deltalumite ± corundum ± hibonite objects were formed by rapid crystallization of high-temperature (>2000°C) refractory melts. The lack of minerals with condensation temperatures below those of corundum and hibonite in the SaU 290 corundum-rich objects suggests that after formation, these objects were rapidly removed from the hot nebular region by disk wind and/or by turbulent diffusion and disk spreading.