Joint (geology)
Clefts or fissure surfaces are fine dividing surfaces in the rock or in the mountains, caused by tectonic stress, but also by diagenetic processes or cooling ( contraction) of rocks. The magnitude of a gap is in the range of a few millimeters distance up to an extension of several meters. As a rule will be no displacement of the rocks separate the fissure surfaces. However, If larger movements along the fractures, so they develop into turmoil. With side opening of crevasses tear on columns.
The direction of incidence of fractures can be represented graphically in the so-called gap rose. Different, running almost parallel fractures are referred to as gap band. Joint sets form an important subject of investigation of the structural geology and geophysics. The direction of joint sets usually corresponds to the axis of compressive stress in a region, and in tectonically active regions often corresponds to its orientation to the fault planes of earthquakes.
As a leading expert in the Klufttektonik applies geophysicist Adrian Scheidegger ( Switzerland and Vienna). His research on the geomorphology of alpine landscapes and the statistics and dynamics of regional fractures provide strong evidence as the principal axes of geological stress and movement directions are inside the continental blocks. Where the local gap directions do not coincide with the continental directions, they often correspond to older tectonic phases (eg the Variscan ), which thus can be detected long after their decay. For example, shows the Diendorfer fault north of the Wachau (Lower Austria ) a clear connection with a strike-slip fault of the Danube, whose valley was offset by approximately 30 km to the northeast.
With the opening of a gap to a larger column can be deposited along the fissure surfaces by the circulation of groundwater or hydrothermal water divide minerals. Typical minerals are quartz, other variants of silica or calcite. In water-soluble rocks such as limestone, gypsum, and sandstones, the presence of fractures dissolves easily from the formation of karst caves. Larger, backfilled with rock crevices are called transitions or in case of noticeable metal content than ore veins.
On the Moon fractures can achieve greater proportions because they are not close by erosion or tectonics. They are signs of fossil voltages of the lunar crust and are classified by astronomers in the form of groups of Rupes ( ground levels ) and the Rimae ( grooves).