Can rock magnetic fabric reveal strain? Case studies of Early Triassic limestones from South China Block
岩石磁组构可以揭示应变吗 ——以华南地块早三叠世灰岩为例

It is generally regarded that magnetic fabrics can effectively reveal strain in rocks. In order to investigate the relationship between different magnetic fabric types and different stages of strain, we conducted a combined analysis of rock magnetics, magnetic fabrics and mesoscopic deformation features for Early Triassic limestones from two areas in the South China Block. Samples from the Tongshan county, Hubei province underwent three stages of deformation, which provided an ideal opportunity to test the relationship between magnetic fabric and multiple deformations. The minimum axes of AMS and AAR ellipsoids are normal to the bedding and the intermediate and maximum axes lie within the bedding, indicating deposition and compaction fabrics having not been affected by tectonic strain. Samples from the Lian county, Guangdong province experienced tectonic strain as evidenced by pervasive pressure solution seams and calcite veins. The principal directions of AMS are scattered, but those of AAR are well clustered, showing a triaxial fabric. The maximum axes of AAR are distributed around the maximum stress direction indicated by the geometry of calcite veins. The initial compaction fabric was replaced by tectonic strain. These results suggest: (1) AAR can better reflect pervasive strain than AMS; (2) Only under the condition that the scope of strain is less than that of the sample can magnetic fabric effectively reveal strain.