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Igneous intrusions may form from a single magmatic event or several incremental events. Recent evidence suggests that incremental formation is more common for large intrusions. [34] [35] For example, the Palisades Sill was never a single body of magma 300 meters (980 ft) thick, but was formed from multiple injections of magma. [36]
For example, the alkali feldspar in plutonic rocks is typically orthoclase, while the higher-temperature polymorph, sanidine, is more common in volcanic rock. The same distinction holds for nepheline varieties. Leucite is common in lavas but very rare in plutonic rocks. Muscovite is confined to intrusions. These differences show the influence ...
A feeder dike is a dike that acted as a conduit for magma moving from a magma chamber to a localized intrusion. For example, the Muskox intrusion in arctic Canada was fed by a large dike, with a thickness of 150 meters. [10] A sole injection is a dike injected along a thrust fault plane, where rock beds were fractured and thrust up over younger ...
The change of rock composition most responsible for the creation of magma is the addition of water. Water lowers the solidus temperature of rocks at a given pressure. For example, at a depth of about 100 kilometres, peridotite begins to melt near 800 °C in the presence of excess water, but near or above about 1,500 °C in the absence of water ...
Linear infrastructure intrusions may cause landslides and soil erosion, particularly on steep and mountainous terrain. In southeast Asian tropical forests, roads on steep terrain contribute the largest surface erosion and landslide losses (per unit area disturbed) compared to other land uses.
The principle of intrusive relationships concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock. There are a number of different types of intrusions, including stocks, laccoliths, batholiths, sills ...
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Certain layered intrusions are a variety of sill that often contain important ore deposits. Precambrian examples include the Bushveld, Insizwa and the Great Dyke complexes of southern Africa; and the Duluth intrusive complex along Lake Superior, and the Stillwater igneous complex of the United States.