Sill (geology) - Citizendia

In geology, a sill is a tabular pluton that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit A pluton in Geology is an Intrusive Igneous rock body that crystallized from a Magma slowly cooling below the surface of the Earth In Geology, an intrusion is a body of Igneous rock that has Crystallized from molten Magma below the surface of the Earth. In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Plate tectonics and hotspots Divergent plate boundaries At the Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures Tuff (from the Italian "tufo" is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change The term sill is synonymous with concordant intrusive sheet. This means that the sill does not cut across preexisting rocks, in contrast to dikes, which do cut across older rocks. A dike or dyke in Geology is a type of Sheet intrusion referring to any geologic body that cuts Discordantly ' across planar

Illustration showing the difference between a dike and a sill.

Sills are always parallel to beds (layers) of the surrounding country rock. Usually they are in a horizontal orientation, although tectonic processes can cause rotation of sills into near vertical orientations. They can be confused with solidified lava flows; however there are several differences between them. Intruded sills will show partial melting of and incorporation of the surrounding country rock. Country rock is a geological term meaning the rock native to an area On both the "upper" and "lower" contact surfaces of the country rock into which the sill has intruded, evidence of heating will be observed (contact metamorphism). Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i Lava flows will show this evidence only on the lower side of the flow. In addition, lava flows will typically show evidence of vesicles (bubbles) where gases escaped into the atmosphere. Vesicular texture is a Volcanic rock texture characterised by or containing many vesicles An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " Because sills generally form at depth (up to many kilometers), the pressure of overlying rock prevents this from happening much, if at all. Lava flows will also typically show evidence of weathering on their upper surface, whereas sills, if still covered by country rock, typically do not. Weathering is the decomposition of earth rocks, Soils and their Minerals through direct contact with the planet's Atmosphere.

Salisbury Crags in Edinburgh, Scotland, a sill partially exposed during the ice ages

Certain ultramafic to mafic layered intrusions are a variety of sill that often contain important ore deposits. Holyrood Park (also called Queen's Park, and formerly King's Park) is a royal park in central Edinburgh, Scotland. Edinburgh ( ˈɛdɪnb(ərə Dùn Èideann) is the Capital of Scotland and is its second largest city after Glasgow. Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets Ultramafic to mafic layered intrusions are found in typically ancient Cratons and are rare but worldwide in distribution An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining Precambrian examples include the Bushveld, Insizwa, and the Great Dyke complexes of southern Africa, the Duluth intrusive complex of the Superior District, and the Stillwater igneous complex of the United States. The Precambrian ( Pre-Cambrian) is an informal name for the supereon comprising the eons of the Geologic timescale that came before the current The Bushveld Igneous Complex (or BIC) is a large Igneous Intrusion within the Earth's crust which has been tilted and eroded and now The Great Dyke is a linear geological feature that trends nearly north-south through the center of Zimbabwe passing just to the west of the capital Harare. The Duluth Complex, the related Beaver Bay Complex (often treated as part of the Duluth Complex and the associated North Shore Volcanic Group are rock formations The Stillwater igneous complex is a large ultramafic to mafic layered intrusion located in southern Montana in Stillwater, Sweet Grass and The United States of America —commonly referred to as the Phanerozoic examples are usually smaller and include the Rùm peridotite complex of Scotland and the Skaergaard igneous complex of east Greenland. The Phanerozoic (occasionally Phanaerozoic) Eon is the current eon in the Geologic timescale, and the one during which abundant animal life has existed Rùm (rˠuːm a Scottish Gaelic name often Anglicised to Rum) is one of the Small Isles of the Inner Hebrides, in the district of A peridotite is a dense coarse-grained Igneous rock, consisting mostly of the minerals Olivine and Pyroxene. Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. The Skaergaard Intrusion is a layered Gabbro complex in East Greenland, located at. Greenland (Kalaallit Nunaat meaning "Land of the Greenlanders" Grønland is a self-governing Danish Province located between the These intrusions often contain concentrations of gold, platinum, chromium, and other rare elements. In Geology, an intrusion is a body of Igneous rock that has Crystallized from molten Magma below the surface of the Earth. Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24

See also