摘要
Optical, cathodoluminescence and transmission electron microscope (TEM)analyses were conducted on four groups of calcite fault rocks, a cataclastic limestone, cataclasticcoarse-grained marbles from two fault zones, and a fractured mylonite. These fault rocks showsimilar microstructural characteristics and give clues to similar processes of rock deformation.They are characterized by the structural contrast between macroscopic cataclastic (brittle) andmicroscopic mylonitic (ductile) microstructures. Intragranular deformation microstructures (i.e.deformation twins, kink bands and microfractures) are well preserved in the deformed grains inclasts or in primary rocks. The matrix materials are of extremely fine grains with diffusivefeatures. Dislocation microstructures for co-existing brittle deformation and crystalline plasticitywere revealed using TEM. Tangled dislocations are often preserved at the cores of highly deformedclasts, while dislocation walls form in the transitions to the fine-grained matrix materials andfree dislocations, dislocation loops and dislocation dipoles are observed both in the deformedclasts and in the fine-grained matrix materials. Dynamic recrystallization grains from subgrainrotation recrystallization and subsequent grain boundary migration constitute the major parts of thematrix materials. Statistical measurements of densities of free dislocations, grain sizes ofsubgrains and dynamically recrystallized grains suggest an unsteady state of the rock deformation.Microstructural and cathodoluminescence analyses prove that fluid activity is one of the major partsof faulting processes. Low-temperature plasticity, and thereby induced co-existence of macroscopicbrittle and microscopic ductile microstructures are attributed to hydrolytic weakening due to theinvolvement of fluid phases in deformation and subsequent variation of rock rheology. Duringhydrolytic weakening, fluid phases, e.g. water, enhance the rate of dislocation slip and climb, andincrease the rate of recovery of strain-hardened rocks, which accommodates fracturing.
Optical, cathodoluminescence and transmission electron microscope (TEM)analyses were conducted on four groups of calcite fault rocks, a cataclastic limestone, cataclasticcoarse-grained marbles from two fault zones, and a fractured mylonite. These fault rocks showsimilar microstructural characteristics and give clues to similar processes of rock deformation.They are characterized by the structural contrast between macroscopic cataclastic (brittle) andmicroscopic mylonitic (ductile) microstructures. Intragranular deformation microstructures (i.e.deformation twins, kink bands and microfractures) are well preserved in the deformed grains inclasts or in primary rocks. The matrix materials are of extremely fine grains with diffusivefeatures. Dislocation microstructures for co-existing brittle deformation and crystalline plasticitywere revealed using TEM. Tangled dislocations are often preserved at the cores of highly deformedclasts, while dislocation walls form in the transitions to the fine-grained matrix materials andfree dislocations, dislocation loops and dislocation dipoles are observed both in the deformedclasts and in the fine-grained matrix materials. Dynamic recrystallization grains from subgrainrotation recrystallization and subsequent grain boundary migration constitute the major parts of thematrix materials. Statistical measurements of densities of free dislocations, grain sizes ofsubgrains and dynamically recrystallized grains suggest an unsteady state of the rock deformation.Microstructural and cathodoluminescence analyses prove that fluid activity is one of the major partsof faulting processes. Low-temperature plasticity, and thereby induced co-existence of macroscopicbrittle and microscopic ductile microstructures are attributed to hydrolytic weakening due to theinvolvement of fluid phases in deformation and subsequent variation of rock rheology. Duringhydrolytic weakening, fluid phases, e.g. water, enhance the rate of dislocation slip and climb, andincrease the rate of recovery of strain-hardened rocks, which accommodates fracturing.
基金
partly financially supported by the State Education Commission and the NNSF(No.49872071).
