Effect of temperature on shock metamorphism of single-crystal quartz

Abstract

FEATURES characteristic of shock metamorphism in target rocks are the main diagnostic tool for recognizing impact phenomena on the Earth and other planetary bodies^1–4, and experimentally calibrated shock effects in silicate minerals have been important in elucidating the pressure histories of these rocks. Except for a few preliminary results for experimentally shocked pre-heated quartzites^5,6, all available calibration data are based on experiments performed with the targets at room temperature^7–11. Observations at Vredefort^12,13and at the Sudbury impact structure^14–16 indicate, however, that considerable shock stresses occur in deep-seated crustal rocks which are at elevated temperatures during large cratering events. High-temperature shock metamorphism must also have been of great importance in the collision history of meteorite parent bodies in the early Solar System. Here we report the results of shock experiments on single-crystal quartz heated to 630 °C, which show that the physical properties of shocked quartz (refractive indices, lattice parameters, amorphization, type and frequency of planar deformation features) depend strongly on the pre-shock temperature. We conclude that existing shock-wave barometers^1,8,9,11cannot be applied to high-temperature target rocks, and that new barometers independent of pre-shock temperature will be required to understand the shock pressure history of terrestrial and planetary impact formations.