Magmatism in the context of "Acasta Gneiss"

Magma (from Ancient Greek μάγμα (mágma) 'thick unguent') is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as lava) is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural satellites. Besides molten rock, magma may also contain suspended crystals and gas bubbles.

Magma is produced by melting of the mantle or the crust in various tectonic settings, which on Earth include subduction zones, continental rift zones, mid-ocean ridges and hotspots. Mantle and crustal melts migrate upwards through the crust where they are thought to be stored in magma chambers or trans-crustal crystal-rich mush zones. During magma's storage in the crust, its composition may be modified by fractional crystallization, contamination with crustal melts, magma mixing, and degassing. Following its ascent through the crust, magma may feed a volcano and be extruded as lava, or it may solidify underground to form an intrusion, such as a dike, a sill, a laccolith, a pluton, or a batholith.

Rockall (/ˈrɒkɔːl/) is a 17.15-metre-high (56 ft 3 in), uninhabitable granite islet in the North Atlantic Ocean. It is 301 kilometres (187 statute miles; 163 nautical miles) west of Soay, St Kilda, Scotland; 423 kilometres (263 statute miles; 228 nautical miles) north-west of Tory Island, Ireland; and 700 kilometres (430 statute miles; 380 nautical miles) south of Iceland. The nearest permanently inhabited place is in North Uist, 370 kilometres (230 mi; 200 nmi) east in Scotland's Outer Hebrides.

Rockall was formed during the Paleogene period, by magmatism as part of the North Atlantic Igneous Province. Rockall and Hasselwood Rock, 200 metres north, are the only emergent parts of Helen's Reef and the Rockall Plateau. Twenty-nine-metre waves just east of Rockall were reported in 2006 as the largest ever recorded by scientific instruments in the open ocean. Rockall's first named geographic location and only occupiable area is Hall's Ledge.

Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology.

In general, strata are primarily igneous or sedimentary relating to how the rock was formed. Sedimentary layers are laid down by deposition of sediment associated with weathering processes, decaying organic matter (biogenic) or through chemical precipitation. These layers are often distinguishable as having many fossils and are important for the study of biostratigraphy. Igneous layers occur as stacks of lava flows, layers of lava fragments (called tephra) both erupted onto the Earth's surface by volcanoes, and in layered intrusions formed deep underground. Igneous layers are generally devoid of fossils and represent magmatic or volcanic activity that occurred during the geologic history of an area.

The Izanagi plate (named after the Shinto god Izanagi) was an ancient tectonic plate, which began subducting beneath the Okhotsk plate 130–100 Ma (million years ago). The rapid plate motion of the Izanagi plate caused northwest Japan and the outer zone of southwest Japan to drift northward. High-pressure metamorphic rocks were formed at the eastern margin of the drifting land mass in the Sanbagawa metamorphic belt, while low-pressure metamorphic rocks were formed at its western margin in the Abukuma metamorphic belt. At approximately 55 Ma, the Izanagi Plate was completely subducted and replaced by the western Pacific plate, which also subducted in a northwestern direction. Subduction-related magmatism took place near the Ryoke belt. No marked tectonics occurred in the Abukuma belt after the change of the subducted plate.

The discovery of an extinct Jurassic–Cretaceous spreading system in the northwest Pacific led to the introduction of the extinct Kula plate in 1972. The Izanagi plate was subsequently introduced in 1982 to explain the geometry of this spreading system. Knowledge of the former Izanagi plate is limited to Mesozoic magnetic lineations on the Pacific plate that preserve the record of this subduction.

In geology, anorogenic magmatism is the formation, intrusion or eruption of magmas not directly connected with orogeny (mountain building). Anorogenic magmatism occurs, for example, at mid-ocean ridges, hotspots and continental rifts. This contrasts with orogenic magmatism that occurs at convergent plate boundaries where continental collision, subduction and orogeny are common.

The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 80 to 70 million years ago, and ended 55 to 35 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute. The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this orogeny was deep-seated, thick-skinned deformation, with evidence of this orogeny found from Canada to northern Mexico, with the easternmost extent of the mountain-building represented by the Black Hills of South Dakota. The phenomenon is named for the Laramie Mountains of eastern Wyoming. The Laramide orogeny is sometimes confused with the Sevier orogeny, which partially overlapped in time and space.

The orogeny is commonly attributed to events off the west coast of North America, where the Kula and Farallon Plates were sliding under the North American Plate. Most hypotheses propose that oceanic crust was undergoing flat-slab subduction, that is, subduction at a shallow angle. As a consequence, no magmatism occurred in the central west of the continent, and the underlying oceanic lithosphere actually caused drag on the root of the overlying continental lithosphere. One cause for shallow subduction may have been an increased rate of plate convergence. Another proposed cause was subduction of thickened oceanic crust.