| Calcite petrofabrics align easily with weak strains, possibly being the most sensitive classical petrofabric indicator. Thus, calcareous sediments may reveal stress trajectories in neotectonic environments. Calcite aligns by crystal-plastic deformation and pressure solution to produce corresponding alignments in accessory clay minerals and magnetite (possibly fossil-bacterial). Their alignments are rapidly and precisely detected by anisotropy of low field magnetic susceptibility (AMS). These net magnetic fabrics blend diamagnetic contributions from matrix calcite (diamagnetic bulk susceptibility kappa ∼ -14 muSI), accessory clay minerals (kappa = 100 to 500 muSI) and trace magnetite (kappa > 2 SI). Considering their relative abundances and different amsotropies, their orientation distributions of AMS axes are sensibly interpreted as paleostress trajectories in Neogene and Quaternary strata at the regional and sub-area level (each ∼400km2 and ∼30km2 respectively). The AMS axes may be correlated with the orientation of faults, plate-motion vectors and seismic solutions. (Abstract shortened by UMI.)... |
