Lineament architecture and fracure distribution in metamorphic and sedimentary rocks, with applications to Norway.
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With contributions from: H. Henriksen, A. Lothe, E. Midtbø, A.K. Midtgård, S. Berg, K. Lyslo & E. Skurtveit. Summary: Lineaments can be regarded as zones in the crust with enhanced fracture intensity (fracture zones) which have a distinct architecture. They can be divided into two main types: fault zones or joint zones. These structures are found both in metamorphic and sedimentary rocks, and have some common characteristics. The fracture distribution can be ascribed to: (i) The central part of the lineament, which consists of a dense network of short fractures, secondary minerals and fault rocks (sub-zones A-B), and (ii) the marginal part (sub-zones C-D),revealing lower fracture intensity, pronounced lineament-parallel fracturing, and absence of clogging minerals. (iii) Outside this, the distal part (sub-zone E; < 250 m) exhibits low fracture frequencies of variably oriented structures, grading outward into areas of (iv) general background fracturing. This lineament-parallel zonation is commonly symmetric around the central part of master joint zones and steep fault zones, whereas inclined fault zones generally have the highest strain in the hangingwall. There are some gereral differences between lineaments in metamorphic and sedimentary rocks. Typically, fracture zones in metamorphic rocks show more symmetric fracture distribution, more distinct zonation, and wider deformation zone than fracture zones in sedimentary rocks. Fracture systems have significant influence on conductivity in both metamorphic and sedimentary rocks, hence they are important for fluid extraction from wells and leakage in tunnels. The lineament-parallel symmetry of fracture sub-zones suggests that conductivity along the fracture zone in general is uniform, whereas lineament-normal conductivity is heterogeneous and controlled by impermeable sub-zone(s). Considerable variance in lineament architec