Wrangellia Terrane

The Wrangellia terrane is a crustal fragment, or terrane, extending from south central Alaska along the coast of British Columbia, with some geologists arguing it continues as far south as Oregon, and it takes its name from the Wrangell Mountains of Alaska. Its rocks range in age from the Pennsylvanian through the Jurassic periods, but its defining feature is a thick sequence of Late Triassic flood basalts erupted around 230 million years ago over a span of about 5 million years. Geologists disagree on where Wrangellia originally formed: one hypothesis holds it accreted close to its present location as part of a back arc system of terranes dispersing westward from the ancient continent of Laurentia, joining the neighboring Alexander terrane by the late Carboniferous before docking with North America in the Middle Jurassic, while a rival hypothesis places its birth as island arcs and oceanic plateaus roughly 3,000 kilometers to the south, near present day Baja California, from where it migrated northeast and reached North America by Cretaceous time.