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In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a plate tectonics (or broken off from it) and accreted or "sutured" to crust lying on another plate. The crustal block or fragment preserves its distinctive geologic history, which is different from the surrounding areas—hence the term "exotic" terrane. The suture zone between a terrane and the crust it attaches to is usually identifiable as a fault. A sedimentary rock deposit that buries the contact of the terrane with adjacent rock is called an overlap formation. An igneous rock intrusion that has intruded and obscured the contact of a terrane with adjacent rock is called a stitching pluton.
There is also an older usage of the term terrane, which described a series of related rock formations or an area with a preponderance of a particular rock or rock group.
A tectonostratigraphic terrane is a fault-bounded package of rocks of at least regional extent characterized by a geologic history that differs from that of neighboring terranes. The essential characteristic of these terranes is that the present spatial relations are incompatible with the inferred geologic histories. Where terranes that lie next to each other possess strata of the same age, they are considered separate terranes only if it can be demonstrated that the geologic evolutions are different and incompatible. There must be an absence of intermediate facies that could link the strata.
The concept of tectonostratigraphic terrane developed from studies in the 1970s of the complicated Pacific Cordilleran Orogeny margin of North America, a complex and diverse geological potpourri that was difficult to explain until the new science of plate tectonics illuminated the ability of crustal fragments to "drift" thousands of miles from their origin and attach themselves, crumpled, to an exotic shore. Such terranes were dubbed "accreted terranes" by . Geologist J. N. Carney writes:
When terranes are composed of repeated accretionary events, and hence are composed of subunits with distinct history and structure, they may be called superterranes. "Terranes" University of British Columbia website
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