Terrane

The terrane concept, in structural geology, describes how continents grow by the accretion of distinct fragments of crust, called terranes, each bounded by faults and each carrying a geological history (a distinct rock sequence, fossil record or paleomagnetic signature) different from the region it has become attached to, showing it formed elsewhere, often on a separate tectonic plate, before being carried by plate motion and welded onto a continental margin at a convergent boundary. The framework for recognizing and mapping exotic or suspect terranes developed substantially during the 1970s and 1980s, with geologists Peter Coney, David Jones and James Monger publishing an influential 1980 paper identifying and mapping dozens of distinct terranes making up the North American Cordillera, the mountain belt running along western North America. Their work, and related studies elsewhere, showed that large sections of continental crust once assumed to have formed in place were in fact assembled over hundreds of millions of years from many separate fragments, including former island arcs, submerged seamounts and small microcontinents, each accreted onto the growing continental margin in turn. The terrane concept substantially reshaped understanding of continental crust formation, showing that continental growth at convergent margins proceeds through the piecemeal accretion of separate terranes rather than only through the gradual, in-place buildup of new crust.