X-Ray investigations on the deformation of experimentally shock-loaded quartzes

Abstract

Quartz single crystals submitted to dynamic pressures higher than 200 kbar show intensive anisotropic postshock cell expansions and lattice disordering which gradually increase along with the degree of shock compression. Maximum expansion and lattice distortion occur parallel to [10.0] followed by [21.0] and [20.1], whereas the lowest expansion rates and comparatively little lattice damage can be observed parallel to [10.2] and [00.1]. [10.0], [21.0], and [20.1] represent short Burgers vectors within the quartz lattice. They are probably preferred directions of a structure-controlled deformation.

Annealing experiments carried out at 300, 605 and 900 ° C make the expanded cell parameters approach the values of unshocked quartz. Two different types of “recrystallization” can be observed:

• 1) No contraction of the α-constant but comparatively strong decrease of the c-parameter in samples shocked up to 260 kbar.

• 2) A strong or complete “recontraction” of both cell parameters α and c in highly shocked quartzes (260–300 kbar) if annealing to temperatures > 300 ° C.

The amount of solid-state (diaplectic) glasses within the shocked quartz samples was calculated by comparing average (“optical”) densities with X-ray densities. The content of the amorphous phase within the shocked quartz samples gradually increases with the degree of shock compression from 0 vol% at 150 kbar to >80 vol% at 300 kbar.

The degree of lattice expansion and the content of glass phase within the shocked sample was used for a petrologic subclassification of quartz-bearing rocks submitted to dynamic pressures from 100 to 380 kbar.