Basement (geology)

Basement ( basement english, french socle ) is the name for the geologically old, tectonically deformed ( folded ) crustal regions of a continent.

The term " basement " comes from the fact that the corresponding rocks below (hence basement, engl. For, basement ') of the deposits of geologically young sedimentary basins that have not been recorded and folded into a rule of a mountain formation and accordingly called overburden will be encountered. But this is only one of several geological contexts that speak from basement.

In addition, there is bedrock

  • Under relatively low powerful layers of sediment that were deposited on the tectonically stable areas of the continents during the past 500 million years. These areas are called " continental plates " or "continental platforms " means.
  • At the surface in the form of continental shields. These are also tectonically stable, very old basement complexes, however, were virtually since its formation ( one speaks in this context of " consolidation " ) never overlain by sediments (eg Canadian or Baltic Shield ).
  • At the surface in the form of prominent fault blocks whose overburden was removed again as a result of uplift (eg the Variscan basement, now, comes to light in Central Europe in the form of numerous low mountains, including the Vosges, Black Forest, Hunsrück, Taunus, resin, or Ore Mountains).
  • In the form of old rock complexes within geologically young fold mountains that were involved in the orogeny and partly today exposed by uplift and erosion (including the Mont Blanc massif in the Alps).

In the very young sedimentary basins whose origin is closely linked to the alpidischen orogeny, such as the Vienna Basin, can in principle also the geologically young, alpidisch folded rocks that underlie these basins are referred to as basement or basement.

The oldest basement complexes are the cores of the present continents, called cratons. In the Canadian Shield are rocks with ages of 4,280 mya known ( Nuvvuagittuq greenstone belt ) and in the Yilgarn Craton Western Australia that a zircon grain that is even 4,400 mya old. However, these are a so-called detrital zircon, ie, the rock, which it was taken is a sedimentary rock in which it was embedded after the erosion of its actual magmatic origin of rock on so-called "secondary deposit". So it is only an indirect indication that the Yilgarn Craton one of the oldest basement complexes of the earth.

Typical of a basement complex are a variety of folded and often metamorphic rocks, which are interspersed with plutonic rocks. Due to the relatively high silicon and aluminum contents this rock association was formerly known as " Sial " (as opposed to oceanic " Sima " crust ) refers.

Since they can contain references to " oil traps" in the outer layers, enjoy structure, slope and depth of the basement of sedimentary basins particular interest in the exploration of hydrocarbon deposits. The exploration can be done by Geoseismik and gravimetry, at shallow depths with Geoelectrics.