Models of fracture lineaments - Joint swarms, fracture corridors and faults in crystalline rocks, and their genetic relations

摘要

Fracture lineaments in crystalline andmetamorphic rocks of southern Norway can be subdivided into joint swarms, fracture corridors and faults, depending on displacement, the fracture mode and patterns, and the presence of fault rocks. Their physical appearance as lineaments seen by remote sensing is not discernible, as they define km-long and narrow tabular zones of high fracture intensity. Intrinsically, fracture zonation becomes better expressed from joint swarms to fracture corridors and especially faults as a consequence of increasing accumulate strain. Joint swarms and fracture corridors commonly reveal a symmetric fracture zonation on both sides of its core, whereas inclined extensional faults tend to have asymmetric patterns with enhanced strain and a wider damage zone in the hangingwall. Fracture lineament can bemapped in subzones A-B (core),which are typically some cm up to some tens of meters wide. Common structural elements are fault rocks/shear zones, lenses, and a network of fractures oftenwith very high fracture frequency. Secondaryminerals are common. Outside this, subzones C-D (damage zone) are commonly 20-50-m wide with lower fracture intensity of lineament-parallel fracturing, defining the topographic boundary of the lineament. Mineralisation is rarer. The transitional subzone E of multi-orientation fractures defines the transition to the background fracture system. We propose a model for the classification and development of fracture lineaments, applying their architecture (intrinsic geometry, spatial fracture pattern and spatial distribution of fault rocks) as tools for the systematic description. This links fault growth processes and mechanisms that can be ascribed to strain hardening and softening scenarios in a model of fault architecture.