Sill (geology)

A sill or sill is a layer- parallel penetrated in a rock rock body of igneous rock sedimentary rock or, less commonly (usually sandstone). In contrast to the storage aisle Dyke (also referred Dike ) a dyke that cuts the surrounding rock or crossed (vertical).

Features a storage aisle

The boundaries of a storage aisle are always parallel to the stratification, and therefore bearing courses may be confused at first glance with volcanic lava flows which are also parallel to the stratification by their deposition on the surface in most cases. However, there are several distinguishing features:

• Both at the base as well as at the top of the storage aisle shows the changes in the rock side of the high temperature of the intruding magma (contact metamorphosis fritting ), this is the case only at the bottom of lava
• Sills have no Entgasungsstrukturen as former gas cavities
• Show lava flows on its upper side often signs of weathering or soil formation, which are overlain by younger strata, this is never the case with sills
• The host rock may have been partially melted.

Since sills, depending on their thickness to cool slowly and solidify, they often show signs of gravitational differentiation. This fall ore minerals and other early formed minerals to the bottom of the storage aisle and form cumulates, which often form deposits of valuable ores (Layered Intrusions ).

Occurrence

Examples of sills or sill -like geological bodies are about the Precambrian Duluth Gabbrokomplex or the Stillwater Complex in southern Montana. In Scotland forms a bearing gear, the Salisbury Crags in Edinburgh. Numerous sills smaller scale are known in Germany as in the Lahn- Dill area in the Rhenish Slate Mountains, more can be found for example in the volcanic Eifel region or in the Seven Mountains ( Weilberg ).