Pressure solution compaction of sodium chlorate and implications for pressure solution in NaCl

Sodium chloride (NaCl) has been extensively used as a material to develop, test and improve pressure solution (PS) rock deformation models. However, u nlike silicate and carbonate rocks, NaCl can deform plastically at very low stresses (similar to 0.5 MPa). This could mean that NaCl is less suitable for use as an analogue for rocks that do not deform plastically at conditio ns where PS is important. In order to test the reliability of NaCl as a roc k analogue, we carried out a series of uniaxial compaction experiments on s odium chlorate (NaClO3) at room pressure and temperature (P-T) conditions a nd applied effective stresses of 2.4 and 5.0 Mpa. NaClO3 is a very soluble, elastic-brittle salt, that cannot be deformed plastically at room P-T cond itions. The results were compared with experiments on NaCl at similar condi tions and show that NaClO3 behaves in a strikingly similar way to NaCl, des pite its brittleness. Like NaCl, it most likely compacts by a grain boundar y diffusion controlled PS mechanism. Mechanical data were fitted to a power law in the form: (epsilon)over dot approximate to epsilon(-alpha)sigma(n)d (-m) (with volumetric strain rate epsilon(over dot), volumetric strain epsi lon, effective stress sigma and grain size d). A reasonable fit was obtaine d, with alpha = 2 to 4, n = 1.6 +/- 0.5, and m = 2.8 +/- 0.5. The similarit y in mechanical behaviour of the two materials (NaCl plastic, NaClO3 brittl e) suggests that plasticity does not play a key role in PS compaction defor mation of NaCl. This means that its plasticity is not a drawback for its us e as a PS analogue for rocks or for deriving PS creep laws for salt from co mpaction experiments. (C) 1999 Elsevier Science B.V. All rights reserved.