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USGS CMG InfoBank: Nonconformity

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Comment: 19:30 - 20:30 (01:00)
Source: Annenberg/CPB Resources - Earth Revealed - 8. Earth's Structures
Keywords: "Dee Trent", nonconformity, unconformity, "geologic structure", erosion, "sea level change", "tectonic activity", deposition, "metamorphic rock", "igneous rock", "sea level change", erosion, "sedimentary rock", contact

Our transcription: Another kind of unconformity is a nonconformity.
This is the one that represents the greatest lapse of time between the formation of the underlying rocks and the overlying rocks.
Nonconformities are those in which crystalline rocks, either metamorphic or igneous rocks, primarily plutonic rocks, are overlain by sedimentary rocks.
Plutonic rocks and metamorphic rocks form deep in the Earth 10, 15 kilometers deep.
And in order for them to be at the surface, there has to have been the removal of all the overlying rocks.
So this takes many millions of years, and maybe tens of millions of years, and eventually those rocks reach a surface where they're exposed to erosion.
Then, a return of the oceans will result in sedimentary rocks being deposited on top of them.
So the time lapse there is immense, and the advance in the number of events that have occurred are really phenomenal.
Whole mountain ranges are built, and then worn away, and then covered over.

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