Cone sheet
Type of igneous intrusion of subvolcanic rock
A cone sheet is a type of high-level igneous intrusion of subvolcanic rock, found in partly eroded central volcanic complexes. Cone sheets are relatively thin inclined sheets, generally just a few metres thick, with the geometry of a downward-pointing cone. Viewed from above, their outcrop is typically circular to elliptical. They were originally described from the Ardnamurchan, Mull and other central complexes of the British Tertiary Volcanic Province (now recognised as part of the North Atlantic Igneous Province).
01Occurrence
Cone sheets are widely distributed at the lower levels of volcanic complexes.
| Name | Location | Age | Dominant rock type | Reference |
|---|---|---|---|---|
| Ardnamurchan | Scotland | Paleogene | dolerite | |
| Tejeda | Gran Canaria | Miocene | trachyte, phonolite | |
| Vallehermoso | La Gomera | Miocene | trachyte, phonolite | |
| Jabal Arknu | Libya | Tertiary | ||
| Otoge | Japan | Miocene | alkali basalt, trachyandesite | |
| Zarza | Mexico | Cretaceous | gabbro | |
| Houshihushan | China | Cretaceous | granite porphyry | |
| Boa Vista | Cape Verde | Miocene | phonolite | |
| Ruri Hills | Kenya | Miocene | carbonatite | |
| Bagstowe | Queensland | late Paleozoic | rhyolite | |
| Thverartindur | Iceland | Pliocene | ||
| Tehilla | Sudan | Cambrian, Ordovician | granite, monzonite |
02Formation
Soon after cone sheets were first described, their formation was explained in terms of intrusion along conical fractures extending from the top of an intrusive body into the overlying rocks, caused by high magmatic pressure.
Sources and credits
This article is adapted from the Wikipedia article “Cone sheet”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Cone Sheet Mingary Ardnamurchan 01.jpg by Anne Burgess https://www.geograph.org.uk/profile/139, CC BY-SA 2.0
- Cone sheet at Mingary - geograph.org.uk - 4378.jpg by Anne Burgess, CC BY-SA 2.0
- Presa del Parralillo on Gran Canaria in Canary Islands 2011.jpg by Cristian Bortes, CC BY 2.0
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