Alexander Terrane
Geological area in northwestern North America
From Wikipedia, the free encyclopedia
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.[1]
This terrane also forms part of the composite Wrangellia Terrane.[2]
Alexander Terrane | |
|---|---|
physiographic section | |
| Location | Alaska; British Columbia; Yukon |
| Part of | Wrangellia Terrane |
| Dimensions | |
| • Length | 1,000 km (620 mi) |
| • Width | 250 km (160 mi) |
Rocks assigned to this terrane underlie much of Southeast Alaska, the north coast of British Columbia, and the Yukon southwest.[1] 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.[3]
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.[1]
Origin
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,[4] however, paleomagnetic, isotopic, and fossil data indicate a possible origin near the margins of ancient Siberia or Arctic continents.[2]
Development
The terrane developed through three distinct phases:
- Late Cambrian through Early Devonian
- During the initial phase, the terrane probably evolved along a convergent plate margin.[1]
- Middle Devonian through Lower Permian
- The second phase is marked by strata accumulated in tectonically stable marine environments.[1]
- Triassic
- The third phase is marked by volcanic and sedimentary rocks which are interpreted to have formed in a rift environment.[1]
