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USGS CMG InfoBank: How Far Did These Terranes Travel

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Comment: 17:18 - 18:25 (01:07)
Source: Annenberg/CPB Resources - Earth Revealed - 7. Mountain Building
Keywords: terrane, "exotic terrane", "suspect terrane", paleomagnetism, fossil, "oceanic crust", continent, accretion, mountain, "metamorphic rock", "igneous rock", "J. Lawford Anderson"

Our transcription: The notion that some terranes are exotic or suspect is controversial because it's unclear as to how far some of these terranes have traveled.
Some may be only locally derived. I mean let's say portions of Baja, California were offset and then rafted to the edge of California.
That would not be very far traveled.
But let's say portions of China traveled all the way across the Pacific Ocean, and they were rafted into the sides of Oregon; that would be far traveled.
It's clear from paleomagnetic evidence, fossil evidence, that some bits of material, some from the ocean crust and some from other parts of continents have been brought great distance, some thousands of kilometers and accreted to the edge of continents.
When we look at modern day mountain belts, we recognize there are really two portions, an interior portion of metamorphic rocks and igneous rocks that are intrinsic to that continent and then an outboard portion, an amalgamation of exotic or suspect terranes that have come from various distances and representing various ages of ancient rock.

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