Terrane

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A terrane in paleogeography is an accretion that has collided with a continental nucleus, or "craton" but can be recognized by the foreign origin of its rock strata. The boundaries of a terrane are usually represented by crustal faults. In the lithospheric scheme of plate tectonics, a terrane is not a microplate, but a piece of crust "riding" atop another plate. It can accrete to another piece of crust when the plate of which it is a part collides with the plate associated with the other crust.

The concept of terranes developed from studies in the 1970s of the complicated Western or Canadian Cordilleran ("backbone") orogenic margin of North America, a virtual geological lasagna that had remained an inexplicable apparent "irreducible complexity", until the new science of plate tectonics illuminated the ability of crustal fragments to "drift" thousands of miles from their origin and fetch up, crumpled, against an exotic shore. Such terranes are dubbed accreted terranes by geologists.

"It was soon determined that these exotic crustal slices had in fact originated as "suspect terranes" in regions at some considerable remove, frequently by thousands of kilometers, from the orogenic belt where they had eventually ended up. It followed that the present orogenic belt was itself an accretionary collage, composed of numerous terranes derived from around the circum-Pacific region and now ‘welded’ together along major faults. These concepts were soon applied to other, older orogenic belts, e.g. the Appalachian belt of North America.... Support for the new hypothesis came not only from structural and lithological studies, but also from studies of faunal biodiversity and palaeomagnetism." (Carney et al.)

For an example of a terrane, see Avalonia.