Shock experiments on feldspar crystals

Abstract

Single crystals of sanidine, orthoclase, microcline, oligoclase, and labradorite as well as polycrystalline bytownite were shocked from 10.5 to 45 GPa and recovered. The direction of shock wave propagation in single crystals was always parallel to the crystallographic a‐axis. Optical observations reveal a continuous sequence of shock effects: fracturing starts to develop at <10.5 GPa, planar elements develop at 10.5–14 GPa, mosaicism at 18–26 GPa, transformation of the crystal into diaplectic glass begins at 26–34 GPa, and formation of melt glass is observed at ∼42 GPa. Microcline, however, remains weakly birefringent even at 45 GPa. Refractive indices of diaplectic glass drop sharply at shock pressures between 30 and 40 GPa. Xray investigations reveal only a minor expansion of the unit cell of sanidine, whereas the other feldspars display no systematic change of lattice constants. The structural state (Al,Si‐distribution) of feldspars is not affected by shock. EPR analyses reveal the disordering of the crystal structure and the formation of a short‐range order phase in feldpars at pressures as low as 10.5–14 GPa. The beginning of the formation of diaplectic glass in the range from 18–22 GPa is evident from IR‐spectra of shocked samples. It is assumed that diaplectic glass is an arrangement of grossly unchanged crystalline material and a glassy phase that is structurally indistinguishable from fusion‐formed glass. The influence of the chemical composition and initial structural state of feldspars on the development of shock effects is believed to be less than the influence of exsolution lamellae and alteration products. Based on the results of these investigations, pressure ranges are given for the lower and upper boundary of the mixed‐phase regime of the pV Hugoniot (p = shock pressure; V = specific volume) for all samples. Two independent methods for the determination of shock pressures from residual shock effects are proposed based on optical and IR‐spectroscopic analyses.

Sodic plagioclase thermometry of type 6 ordinary chondrites: Implications for the thermal histories of parent bodies

“…As shown in Table I, the x-ray peaks of plagioclase from Owasco and Dhurmsala meteorites (S3 shock stage) are clearly broader than those of plagioclases from other very weakly shocked meteorites. The broadening of the x-ray peaks is due to the shock deformation of the plagioclase lattice (Ostertag, 1983). However, the temperatures obtained for Owasco (L6) take values similar to those for Holbrook (L6), which is assigned to S2 stage and shows sharp x-ray peaks of plagioclase.…”

Tsiolkovsky crater: A window into crustal processes on the lunar farside

“…Moderately shocked plagioclase, however, becomes disordered and loses this band, becoming featureless throughout the nearinfrared [Adams et al, 1979]. At higher shock pressures, plagioclase becomes diaplectic glass [Ostertag, 1983] with distinct but weak glass absorption features [Pieters, 1996]. Using high spectral resolution near-infrared telescopic spectra, shocked lunar anorthosites have previously been identified by spectra that are bright with no evidence of absorptions due to iron-bearing minerals [e.g., Pieters, 1986 …”

Shock experiments with the H6 chondrite Kernouvé: Pressure calibration of microscopic shock effects

“…1969;Sclar, 1969;Short, 1969;Hornernann and Muller, 1971;Stoffler. 1972;Stoffler and Hornemann, 1972;Horz and Quaide, 1973;Snce and Ahrens, 1975;Kieffer et al, 1976;Jeanloz et al, 1977;Reimold, 1977;Reimold and Stoffler, 1978;Horz, 1977, 1980;Bauer, 1979;Schaal et al, 1979;Jcanloz, 1980;Syono et al, 1981;Ostertag, 1981Ostertag, , 1983Langcnhorst, 1989;I luffmann et al, 1993;IIackbarth, 1993;tlackbarth et al, 1994). So far, only a few shock experiments with ordinary chondritcs were carried out (Fredriksson et al.…”