Sill (geology)

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Sill (geology)

In geology

Geology

Geology is the science and study of the solid and liquid matter that constitute the Earth. The field of geology encompasses the study of the composition, structural geology, physical properties, dynamics, and History of the Earth of Earth materials, and the processes by which they are formed, moved, and changed....
, a sill is a tabular pluton

Pluton

A pluton in geology is an intrusive igneous rock body that crystallized from a magma slowly cooling below the surface of the Earth. Plutons include batholiths, dike , Sill , laccoliths, lopoliths, and other igneous bodies....
that has intruded between older layers

Stratum

In geology and related fields, a stratum is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers....
of sedimentary rock

Sedimentary rock

Sedimentary rock is one of the three main Rock types . Sedimentary rock is formed by deposition and consolidation of mineral and organic material and from precipitation of minerals from solution....
, beds of volcanic lava

Lava

Lava is molten Rock expelled by a volcano during an eruption. When first expelled from a volcanic vent, it is a liquid at temperatures from 700 ?C to 1,200 ?C ....
or tuff

Tuff

Tuff is a type of Rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is also sometimes called tufa, particularly when used as construction material....
, or even along the direction of foliation

Foliation (geology)

Foliation is any penetrative planar Fabric present in Rock . Foliation is common to rocks affected by regional metamorphism compression typical of orogeny....
in metamorphic rock

Metamorphic rock

Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form"....
. The term sill is synonymous with concordant intrusive sheet. This means that the sill does not cut across preexisting rocks, in contrast to dikes

Dike (geology)

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In geology

Geology

Pluton

Stratum

In geology and related fields, a stratum is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers....
of sedimentary rock

Sedimentary rock

Lava

Lava is molten Rock expelled by a volcano during an eruption. When first expelled from a volcanic vent, it is a liquid at temperatures from 700 ?C to 1,200 ?C ....
or tuff

Tuff

Foliation (geology)

Foliation is any penetrative planar Fabric present in Rock . Foliation is common to rocks affected by regional metamorphism compression typical of orogeny....
in metamorphic rock

Metamorphic rock

Dike (geology)

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
, which do cut across older rocks.

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 and incorporation of the surrounding country rock

Country rock (geology)

Country rock is a Geology term meaning the rock native to an area. It is similar and in many cases interchangeable with the terms basement and wall rocks....
. 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

Metamorphism is the solid-state Crystallization of pre-existing Rock due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids....
. Lava flows will show this evidence only on the lower side of the flow. In addition, lava flows will typically show evidence of vesicles

Vesicular texture

Vesicular texture is a volcanic Rock texture characterised by, or containing, many vesicles. The texture is often found in extrusive aphanite, or glassy, igneous rock....
(bubbles) where gases escaped into the atmosphere

Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low....
. 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

Weathering

Weathering is the decomposition of earth Rock , soils and their minerals through direct contact with the planet's atmosphere. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, wind, and gravity....
on their upper surface, whereas sills, if still covered by country rock, typically do not.

Certain ultramafic to mafic layered intrusions

Ultramafic to mafic layered intrusions

Ultramafic to mafic layered intrusions are found in typically ancient cratons and are rare but worldwide in distribution. The intrusive complexes exhibit evidence of Fractional crystallization and crystal segregation by settling or floating of minerals from a melt....
are a variety of sill that often contain important ore

Ore

An ore is a type of Rock that contains minerals such as gemstones and metals that can be extracted through mining and refined for use. Samples of ore in the form of exceptionally beautiful crystals, exotic layering visible when sectioned or polished or metallic presentations such as large nuggets or crystalline formations of metals suc...
deposits. Precambrian

Precambrian

The Precambrian is an informal name for the supereon comprising the eon of the geologic timescale that came before the current Phanerozoic eon....
examples include the Bushveld

Bushveld igneous complex

The Bushveld Igneous Complex is a large igneous intrusion within the Earth's Crust which has been tilted and erosion and now outcrops around what appears to be the edge of a great Basin ....
, Insizwa, and the Great Dyke

Great Dyke

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....
complexes of southern Africa

Africa

Africa is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km? including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area....
, the Duluth intrusive complex

Duluth Complex

The Duluth Complex, the related Beaver Bay Complex , and the associated North Shore Volcanic Group are rock formations which comprise much of the Basement bedrock of the Geology_of_Minnesota#Northeast_Minnesota:_ancient_bedrock of the U.S....
of the Superior District, and the Stillwater igneous complex

Stillwater igneous complex

The Stillwater igneous complex is a large Ultramafic to mafic layered intrusions located in southern Montana in Stillwater County, Montana, Sweet Grass County, Montana and Park County, Montana....
of the United States

United States

The United States of America is a Federal government constitutional republic comprising U.S. state and a federal district. The country is situated mostly in central North America, where its Contiguous United States and Washington, D.C., the Capital districts and territories, lie between the Pacific Ocean and Atlantic Oceans, Borders of the U...
. Phanerozoic

Phanerozoic

The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 545 million years and goes back to the time when diverse hard-shelled animals first appeared....
examples are usually smaller and include the Rùm

Rûm

R?m, also Roum or Rhum , is a very indefinite term used at different times in the Muslim world to refer to the Balkans and Anatolia generally, and for the Byzantine Empire in particular, for the Seljuk Sultanate of R?m in Asia Minor, and for Greeks inhabiting Ottoman Empire or modern Turkey territory as well as for Greek Cypriots....
peridotite

Peridotite

A peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic and ultrabasic, as the rock contains less than 45% silica....
complex of Scotland

Scotland

conventional_long_name = ScotlandAlba|common_name= Scotland|image_flag = Flag of Scotland.svg|flag_width = 130px...
and the Skaergaard igneous complex

Skaergaard intrusion

The Skaergaard intrusion is a layered gabbro complex in East Greenland, located at .Discovered by Lawrence Wagerin 1931 during the British Arctic Air Route Expedition led by Gino Watkins, the intrusion has been important to the development of key concepts in igneous rock petrology, including magma differentiation...
of east Greenland

Greenland

Greenland is a member country of the Kingdom of Denmark located between the Arctic Ocean and Atlantic Oceans, east of the Canadian Arctic Archipelago....
. These intrusion

Intrusion

In geology, an intrusion is a body of igneous rock that has crystallized from molten magma below the surface of the Earth. Bodies of magma that solidify underground before they reach the surface of the earth are called plutons, named for Pluto , the Roman mythology of the underworld....
s often contain concentrations of gold

Gold

Gold is a chemical element with the symbol Au and atomic number 79. It is a highly sought-after precious metal, having been used as money, as a store of value, in jewelry, in sculpture, and for ornamentation since the beginning of recorded history....
, platinum

Platinum

Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is in Group 10 of the periodic table of elements....
, chromium

Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is a steely-gray, Lustre , hard metal that takes a high polish and has a high melting point....
, and other rare elements.

Sill (geology)

See also