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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 layered intrusion is a large sill-like body of igneous rock which exhibits vertical layering or differences in composition and texture. These intrusions can be many kilometres in area covering from around 100 km 2 (39 sq mi) to over 50,000 km 2 (19,000 sq mi) and several hundred metres to over one kilometre (3,300 ft) in thickness. [1]
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.
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 ...
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 ...
Basic types of intrusions: 1. Laccolith 2. Small dike 3. Batholith 4. Dike 5. Sill 6. Volcanic neck, pipe 7. Lopolith As a general rule, in contrast to the smoldering volcanic vent in the figure, these names refer to the fully cooled and usually millions-of-years-old rock formations, which are the result of the underground magmatic activity shown.
The Henry Mountains of Utah, US, are an example of a mountain range composed of exposed laccoliths. It was here that geologist Grove Karl Gilbert carried out pioneering field work on this type of intrusion. Laccolith mountains have since been identified in many other parts of the world. Basic types of intrusions: