3.9.3 Joint Zone (Sprekksone)
3.9.3.1 A joint zone is a structural unit composed of several adjacent joints. These may be genetically related to one another, but this is not a prerequisite (Fig. 17).
3.9.3.2 Joint zone ranks next above joint.
3.9.3.3 A joint zone crops out within a long, narrow geographical area. The breadth of the zone is defined by the outermost joints in the zone. No other limitations are placed on the extent of the zone.
3.9.3.4 The structure is mappable at the surface and/or traceable in the subsurface with the help of geomorphological, geological or geophysical methods. The degree of detail in the cartographical presentation of a joint zone will depend upon the map scale and the knowledge available.
3.9.3.5 A joint zone will often be characterized by irregular landscape features, and frequently coincides with valleys and depressions.
3.9.3.6 A joint zone is given a formal or an informal name in accordance with the "general rules for naming and defining geological units" (Chap. 2) and the provisions of Section 3.9.1. The proper name (Section 2.2.2) is placed between the words "the ... Joint Zone" (formal) in the compound name.
3.9.3.7.a A joint (sprekk, sprekkflate) is a fracture surface in the rock along which no displacement has taken place. Joints are usually smooth and planar.
3.9.3.7.b A joint set (sprekksett) is a group of more or less parallel, closely spaced joints assumed to have been formed during the same deformation event (Fig. 17).
3.9.3.7.c A joint system (sprekksystem) is composed of two or more intersecting joint sets assumed to have been formed during the same deformation event (Fig. 17).
3.9.3.7.d A joint complex (sprekk-kompleks) is composed of two or more intersecting joint sets formed during different deformation events, or having unknown age relationships (Fig. 17).
3.9.3.7.e A fissure (spalte) is an open joint or crack, or one which clearly has been open but which has subsequently become filled with mineral growth (e.g. quartz-filled feather joints).
3.9.3.7.f A fissure system (spaltesystem) comprises several parallel, closely spaced fissures assumed to be of the same age (Fig. 17).
3.9.3.7.g Structural features b-f should preferably be given informal names (Section 2.3).
3.9.3.8 Examples: There are no examples of named joint structures in Norway. The formation of certain joints and their influence on the pattern of fjords in western Norway has been much discussed (e.g. O. Holtedahl 1956, H. Holtedahl 1967, Nilsen 1973, Roberts 1973).
3.9.3.9 Key references: Hobbs (1911), Anderson (1951), Price (1968).
