The Alexander Terrane (named for the Alexander Archipelago in Alaska) is a neoproterozoic continental fragment that originated far from its current location, before being transported and accreted to western North America in the Middle Jurassic. This terrane also forms part of the composite Wrangellia Terrane.
Rocks assigned to this terrane underlie much of Southeast Alaska, the north coast of British Columbia, and the Yukon southwest. The Alexander Terrane is intruded by Late Jurassic and Early Cretaceous plutons and is overlain to the east by Upper Jurassic through mid-Cretaceous clastic strata and mafic volcanic rocks.
In British Columbia, the terrane crops out primarily in the Coast Mountains, including the Kitimat Ranges, Chatham Sound, and Haida Gwaii, and continues to Klemtu.
The original location of the Alexander Terrane remains uncertain. Some evidence, including detrital zircon geochronology, suggests it may have formed along the margins of ancient Baltica or Laurentia, however, paleomagnetic, isotopic, and fossil data indicate a possible origin near the margins of the ancient Siberian or Arctic continents.
The terrane developed through three distinct phases: