Shock Compression of Crustal Rocks: Data for Quartz, Calcite, and Plagioclase Rocks

ttugoniot data in the 4to 250-kb stress range were obtained for quartzite and novaculite, sandstones of varying porosity, single-crystal calcite, marble, porous and nonporous limestone, several plagioclases of varying composition, and a basalt. Conventional plane-wave, in-contact explosive assemblies were used; the shock state was computed from measured shock velocities; particle velocities are inferred from either specimen or driver plate free-surface motion. Impedence-match solutions were obtained for porous rock. I-Iigh values of the I-Iugoniot elastic limit were observed in nonporous rocks--approximately 40 to 90 kb in quartzite and novaculite, 40 to 50 kb in the plagioclase rocks, and 15 to 25 kb in calcite and marble. Reduced values were found for porous rocks, approximately 5 kb in sandstone and limestone. Phase transitions are inferred at 30, 45, and 95 kb in calcite, and 22, 45, and 90 kb in marble and limestone. For calcite these are indicated by multiple shock fronts. Anomalously low volumes achieved by sandstone shocked to above approximately 40 kb, and high calculated shock temperatures, suggest partial conversion to coesite or stishovite. High-pressure states observed in basalt and plagioclase agree with previously reported states for gabbro [Hughes and McQueen, 1958] above 300 kb when both data are plotted in terms of relative volume. The previously observed slope-change of the gabbro I-Iugoniot is believed to result from an elastic wave of perhaps 50-kb amplitude which is overdriven at 300 kb. Introduction. The constitutive relation represented by the locus of shock-stress and compressed-volume states obtained in shock-wave experiments, the Itugoniot, describes material behavior over a wide pressure and temperature range. Determination of the maximum attainable longitudinal elastic-wave amplitude provides an intrinsic measurement of the strength of rocks under an extremely high (possibly maximum) loading rate. Shock-wave experimentation permits certain phenomena such as elastic-wave stress relaxation [Duvall and Fowles, 1963, p. 270] to be studied. Indirect observation of polymorphism in crustal materials appears possible in certain cases; thus interest is renewed in the study of the Itugoniots of crustal rocks, particularly as a result of the recent suggestions [Ringwood, 1962] concerning a series of reactions and phase changes occurring in the earth's mantle at a combination of pressures and temperatures higher than that obtainable in static laboratory apparatus. Additional interest stems from the application of these data to calculations describing stress-wave propagation in the vicinity of intense energy sources, such as underground explosions and meteorite impacts. The materials here studied are polycrystalline quartz (in the form of quartzite and novaculite), sandstones of varying porosity, singlecrystal calcite, marble, porous and nonporous limestone, several plagioclases of varying composition, and a basalt. These were chosen on the basis of the following criteria: (1) extreme crustal abundance; (2) mineralogically simple rocks and chemically simple minerals; (3) materials for which reasonably uniform specimens are obtainable; and (4) mediums for which little or no previous data are reported. Particular emphasis has been placed on studying monomineralogic mediums, since these individually display a host of new and interesting phenomena under shock compression. After these have been examined, the shock compression behavior of more complex rocks with their infinite possible variety of compositions and structures may be understood and perhaps, eventually, predicted.