Terrane

A terrane in geology, in full a tectonostratigraphic terrane is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate. The crustal block or fragment preserves its own distinctive geologic history, which is different from that of 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.

Older usage of terrane simply described a series of related rock formations or an area having a preponderance of a particular rock or rock groups.

A tectonostratigraphic terrane is not necessarily an independent microplate in origin, since it may not contain the full thickness of the lithosphere. It is a piece of crust which has been transported laterally, usually as part of a larger plate, and is relatively buoyant due to thickness or low density. When the plate of which it was a part subducted under another plate, the terrane failed to subduct, detached from its transporting plate, and accreted onto the overriding plate. Therefore, the terrane transferred from one plate to the other. Typically, accreting terranes are portions of continental crust which have rifted off another continental mass and been transported surrounded by oceanic crust, or old island arcs formed at some distant subduction zone.

A tectonostratigraphic terrane is a fault-bounded package of rocks of at least regional extent characterized by a geologic history which differs from that of neighboring terranes. The basic characteristics of these terranes is that the present spatial relations are not compatible with the inferred geologic histories. Where juxtaposed terranes processes coeval strata, it must be demonstrable that the geologic evolutions are different and incompatible, and there must be an absence of intermediate lithofacies which could link the strata

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