Scandinavian CrustThis is an absolutely spectacular shot of several stages of crust formation from K

Scandinavian CrustThis is an absolutely spectacular shot of several stages of crust formation from Kosterhavet National Park in Sweden.The oldest rocks in this area are highly metamorphosed sedimentary rocks. They are the dark and white, wavy-interfingered rocks. Those rocks started off as sediments and then were caught up in one of several orogenies, or mountain building events, that occurred between 1 and 2 billion years ago.The sediments are 1.7 billion years old. They were deposited in a basin and then rapidly incorporated in a growing mountain range where they were buried and heated. The heat at the bottom of the mountain range was enough that the rocks began melting. The dark part is metamorphosed gneiss that reached the upper part of the amphibolite facies; the light part is felsic minerals that melted out of the sediments and basically formed a granite. This type of high grade metamorphic rock, heated to such a high grade that they begin melting, is called a migmatite.This migmatite is cross-cut by a dolerite dike. Dolerite is a term for a mafic, basaltic igneous rock that has slightly crystallized. Basalts are low viscosity and high temperature, so if basalt is trapped underground in a dike it starts to form tiny crystals. This slightly crystalline rock is called a dolerite, or a diabase elsewhere in the world.Sweden represents at least 2 characterized orogenies, the Gothian orogeny starting about 1.7 billion years ago and the Sveconorwegian Orogeny from about 1.3 to 0.9 billion years ago. These orogenies probably represent continued subduction along the coast of Baltica. This long-lived subduction built mountain ranges, sent magmatic rocks like the dolerite from the mantle up into the crust, and eventually culminated in the assembly of the supercontinent Rodinia.-JBBImage credit: Thomas Eliasson of Geological Survey of Swedenhttps://flic.kr/p/8PadbZReferences:http://foreninger.uio.no/ngf/ngt/pdfs/NGT_79_1_047-056.pdfhttp://bit.ly/2tgvk1y -- source link

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