View source for Jormua Ophiolite

{{short description|Remnant of ancient oceanic lithosphere near Jormua, Finland}}
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{{Location map~|Finland|lat=64.316667|long=27.866667 |label=Jormua Ophiolite|position=right|mark=Red pog.svg}}
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The '''Jormua Ophiolite''' ([[Finnish language|Finnish]]: ''Jormuan ofioliitti'') is a [[Ophiolite|remnant]] of ancient [[Oceanic crust|oceanic]] [[lithosphere]] near the village of [[Jormua]] close to the geographical centre of [[Finland]]. The rocks of the Jormua Ophiolite formed about 1,950 million years ago in the [[Paleoproterozoic|Paleoproteozoic Era]]. The conditions under which the ocean crust rocks of Jormua formed was likely similar to present-day [[Red Sea]]. Thus, a linear sea of this type is thought to have existed between two [[Continental crust|continental]] landmasses in Finland. At some point this sea closed and the ophiolite was [[Obduction|obducted]].  The Jormua ophiolite is the best preserved one along a larger chain of ophiolites that occur within the Kainuu Schist Belt.

The Jormua Ophiolite is broken into 4 geographical blocks termed as the: eastern block, central block, northern block, and western block. The eastern and northern blocks are most similar to one another containing mantle peridotites intruded by gabbro stocks and basaltic sheeted dikes. These are overlaid by a metabasaltic pillow lava layer which is directly overlain by black turbitic shales. These are best associated with an extrusive seafloor sequence. The central block lacks extrusive rocks, gabbro rocks and dikes but otherwise resembles the eastern and northern blocks. The main difference being EMORB dikes. The western block resembles the central block except its bounded by older archean basement rocks and its mantle peridotites are in general less depleted.<ref>Peltonen, P., & Kontinen, A. (2004). The Jormua Ophiolite: A Mafic-Ultramafic Complex from an Ancient Ocean-Continent Transition Zone. In ''Developments in Precambrian Geology'' (Vol. 13, pp. 35–71). Elsevier. {{doi|10.1016/S0166-2635(04)13001-6}}</ref>

In review, the crustal rocks of the ophiolite include [[pillow lava]], [[hyaloclastite]], [[Sheeted dyke complex|sheeted dykes]], [[gabbro]], [[plagiogranite]] and [[ultramafic]] [[cumulate rock]]. [[Mantle (geology)|Mantle]] rocks exposed in the ophiolite are the [[peridotite]] varieties of [[lherzolite]], [[harzburgite]] and [[dunite]]. 

[[File:JormuaOphiolite01.jpg|thumb|250px|right|[[glacial striation|Glacier-polished]] [[outcrop]] of the Jormua Ophiolite.]]

==References==
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[[Category:Geology of Finland]]
[[Category:Ophiolites]]
[[Category:Paleoproterozoic magmatism]]
[[Category:Paleoproterozoic volcanism]]
[[Category:Suture zones]]


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