Тектоностратиграфиялық террандар: Қыбыршақталған қыртыс фрагменттері

Fragment of crust formed on one tectonic plate and accreted to another

In geology, a terrane (/t//ə/'/r//eɪ//n//, /'/t//ɛr//eɪ//n/; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (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 deposit that buries the contact of the terrane with adjacent rock is called an overlap formation. An igneous intrusion that has intruded and obscured the contact of a terrane with adjacent rock is called a stitching pluton. The older usage of terrane described a series of related rock formations or an area with a preponderance of a particular rock or rock group.

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 that 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 they are old island arcs formed at some distant subduction zones. 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, it must be demonstrable that the geologic evolutions are different and incompatible. There must be an absence of intermediate lithofacies that could link the strata. The concept of tectonostratigraphic terrane developed from studies in the 1970s of the complicated Pacific Cordilleran orogenic 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 fetch up, crumpled, against an exotic shore. Such terranes were dubbed "accreted terranes" by geologists. When terranes are composed of repeated accretionary events, and hence are composed of subunits with distinct history and structure, they may be called superterranes.

McPhee, John (1981). Basin and Range. New York: Farrar, Straus and Giroux. McPhee, John (1983). In Suspect Terrain. New York: Farrar, Straus and Giroux. McPhee, John (1993). Assembling California. New York: Farrar, Straus and Giroux.