Kontakthof (geology)

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The contact zone (also contact aureole or contact zone ) is in geology the transition zone between an igneous intrusion and the surrounding rock ( secondary rock ). Depending on the size of the intrusion, the dimensions of the contact zone vary from a few millimeters for small corridors to several kilometers for large plutons . In the area of ​​the contact area, the adjacent rock is metamorphically shaped by heating and, in some cases, chemical interactions with hot solutions . One speaks of a contact metamorphosis or contact metasomatosis . Depending on the distance from the pluton, the type of protolith and possibly the chemical composition of the magma, either certain minerals are converted into others, new minerals are formed, or the rock structure is only changed through recrystallization. Due to the decreasing temperature towards the outside, a contact zone is often zoned.

Typical rocks of the inner hotter zones of the contact zone of plutons are massive rocks such as horn rock (among others with mudstone , marl and basic volcanites as protoliths), marble (with relatively pure carbonate protoliths), skarn (with metasomatosis of carbonate protoliths), quartzite (with relatively pure quartz sandstone or silica slate as protolith) and anthracite (with coal as the starting material). Recrystallization is incomplete in the outer zones, so that the primary stratification or cleavage of claystones is retained. A typical rock in these zones is the fruit slate .

literature

  • Martin Okrusch, Siegfried Matthes: Mineralogy - An introduction to special mineralogy, petrology and deposit science. 8th edition, Springer Verlag, 2010, ISBN 978-3-540-78200-1 , chapter Metamorphic Rocks (pp. 379-432)
  • Wolfhardt Wimmenauer: Petrography of igneous and metamorphic rocks. Enke-Verlag, Stuttgart 1985, ISBN 3-432-94671-6 , pp. 255 ff.