Effect of temperature on shock metamorphism of single-crystal quartz.

Features characteristic of shock metamorphism in target rocks are the main diagnostic tool for recognizing impact phenomena on the Earth and other planetary bodies, 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, all available calibration data are based on experiments performed with the targets at room temperature. Observations at Vredefort and at the Sudbury impact structure indicate, however, that considerable shock stresses occur in deep-seated crystal 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 degree Celsius, which show that the physical pro perties of shocked quartz (refractive indices, lattice parameters, amorphization, type and frequency of planar deformation features) depend strongly on the pre-shock temperature.