Phase transitions of α‐quartz at elevated temperatures under dynamic compression using a membrane‐driven diamond anvil cell: Clues to impact cratering?

Abstract

Coesite and stishovite are high‐pressure silica polymorphs known to have been formed at several terrestrial impact structures. They have been used to assess pressure and temperature conditions that deviate from equilibrium formation conditions. Here we investigate the effects of nonhydrostatic, dynamic stresses on the formation of high‐pressure polymorphs and the amorphization of α‐quartz at elevated temperatures. The obtained disequilibrium states are compared with those predicted by phase diagrams derived from static experiments under equilibrium conditions. We analyzed phase transformations starting with α‐quartz in situ under dynamic loading utilizing a membrane‐driven diamond anvil cell. Using synchrotron powder X‐ray diffraction, the phase transitions of SiO2 are identified up to 77.2 GPa and temperatures of 1160 K at compression rates ranging between 0.10 and 0.37 GPa s−1. Coesite starts forming above 760 K in the pressure range between 2 and 11 GPa. At 1000 K, coesite starts to transform to stishovite. This phase transition is not completed at 1160 K in the same pressure range. Therefore, the temperature initiates the phase transition from α‐quartz to coesite, and the transition from coesite to stishovite. Below 1000 K and during compression, α‐quartz becomes amorphous and partially converts to stishovite. This phase transition occurs between 25 and 35 GPa. Above 1000 K, no amorphization of α‐quartz is observed. High temperature experiments reveal the strong thermal dependence of the formation of coesite and stishovite under nonhydrostatic and disequilibrium conditions.

Experimental impact cratering: A summary of the major results of the MEMIN research unit

“…Within MEMIN, the formation of high‐pressure phases of α‐quartz was studied under dynamic and nonhydrostatic conditions in a novel approach utilizing membrane‐driven diamond anvil cells at pressures up to 66 GPa, at ambient temperature, and at different loading rates (Carl et al. ), and up to 70 GPa at high temperatures (Carl et al. Forthcoming).…”

“…At elevated temperatures and under nonhydrostatic and disequilibrium conditions, the phase transition from α‐quartz to coesite, and the transition from coesite to stishovite were initiated (Carl et al. Forthcoming).…”

Apollo 15 regolith breccia provides first natural evidence for olivine incongruent melting

“…Therefore, we expect that incongruent melting boundaries derived by static high-pressure experiments can be used to confidently estimate the P-T conditions reached during the shock event recorded the studied section. We also acknowledge that recent advances in dynamic compression experiments could allow the investigation of the effects that nucleation and growth kinetics have on the phase boundaries (Jenei et al 2019;Méndez et al 2020), thus providing a tool to better interpret high-pressure mineralogy in shocked materials (e.g., Carl et al 2017Carl et al , 2018Černok et al 2017;Sims et al 2019;Husband et al 2021).…”

New dynamic diamond anvil cells for tera-pascal per second fast compression x-ray diffraction experiments

“…More recently, it was realized that this technique can also be used to study compression processes on the atomistic scale that occur during meteorite impacts on the surface of the Earth or other planetary bodies. [8][9][10][11] Time-resolved x-ray diffraction experiments have been reported; most of these experiments follow the crystal structure evolution of materials along a defined compression pathway in dynamically driven DACs. [12][13][14][15] These experiments have mostly been confined to lower compression rates since neither the intensity of the incident beam at 3rd generation light sources nor the repetition rate and sensitivity of the available detectors have been sufficient to offer the time resolution required at higher compression rates.…”