What is Dyke (geology)?
[[File:Gangar.jpg|thumb|upright=1.35|View of the Kattsund-Koster dyke swarm in the [[Koster Islands]], western [[Sweden]]]] [[Image:Mackenzie dike swarm.png|thumb|Map of the Mackenzie dike swarm in [[Canada]]. This is the largest dike swarm known on Earth ]] [[Image:Matachewan and Mistassini dike swarms.png|thumb|right|Map of the Matachewan and Mistassini dike swarms in Canada]] [[File:Dike diabase AZ.jpg|thumb|A [[diabase]] dyke crosscutting horizontal [[limestone]] beds in Arizona.]] [[File:Geological Dike Cross-Island Trail Alaska.jpg|thumb|A dyke on the [[Baranof Cross-Island Trail]], [[Alaska]].]] A '''dyke''' (or [[dike (geology)|dike]]) is when later molten [[lava]] pushes up between older rock layers. This produces later [[vertical]] rock between older layers of rock. Technically, it is any geologic body which cuts across: a) flat wall rock structures, such as [[strata|bedding]]. b) massive rock formations, usually [[igneous]] in origin. Dykes can therefore be either pushed in between ([[Intrusion (geology)|intrusive]]) or laid down ([[sediment]]ary) in origin. The most usual thing that happens is that later [[volcanic]] activity pushes [[lava]] through strata which were laid down earlier in a [[sedimentary]] fashion, or through earlier igneous rocks. On the [[Isle of Arran]], for example, there are hundreds of igneous dykes. This gives rise to the term '''dyke swarm'''. Alternatively, sedimentary rocks can be laid down in vertical gaps between strata. Or, after underwater [[earthquakes]], gaps caused by the earthquake can be filled in with [[breccia]], that is, broken rocks. Dykes are a common, almost universal, feature of the older [[Palaeozoic]] rocks. Another type of [[Intrusion (geology)|intrusion]] is the [[Sill (geology)|sill]], where later rock is formed between older layers, not through them. So dykes are vertical intrusions, and sills are horizontal intrusions. Many magmatic events produce both vertical and horizontal intrusions. Dyke swarms can be seen on other planets.<ref> Ernst R.E;