Shield (geology)
Large stable area of exposed Precambrian crystalline rock / From Wikipedia, the free encyclopedia
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This article is about the large-scale geological regions. For the volcano type, see shield volcano.
A shield is a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas.[1] These rocks are older than 570 million years and sometimes date back to around 2 to 3.5 billion years.[citation needed] They have been little affected by tectonic events following the end of the Precambrian, and are relatively flat regions where mountain building, faulting, and other tectonic processes are minor, compared with the activity at their margins and between tectonic plates. Shields occur on all continents.
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Extended | Oceanic crust: 0–20 20–65 >65 |