Stress magnitudes in natural rock salt

Abstract

Subgrain sizes have been determined for Avery Island domal salt that was deformed experimentally at pressures in the range 3.4 to 20.7 MPa, temperatures from 100° to 200°C, and constant mean principal stress differences of from 2.0 to 20.3 MPa. The subgrain size decreases systematically with increasing stress, independent of temperature, according to the relation d = 190 σ−1, which is in substantial agreement with the work of others on single crystals and poly crystals of synthetic rocksalt. For two‐stage creep experiments it is observed that while subgrain size decreases upon increasing the stress, it does not increase upon lowering the stress. Thus the stresses deduced for seven naturally deformed bedded, domal, and anticlinal rocksalts, 0.5–1.1 MPa, reflect maximum stress differences experienced. The results are applied briefly to considerations of steady state flow during the growth of salt diapirs.