Alexander Terrane
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) |
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]
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
[edit]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 the ancient Siberian or Arctic continents.[2]
Development
[edit]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]
References
[edit]- 1 2 3 4 5 6 Gehrels, George E.; Saleeby, Jason B. (1987). "Geologic framework, tectonic evolution, and displacement history of the Alexander Terrane". Tectonics. 6 (2): 151–173. doi:10.1029/TC006i002p00151.
- 1 2 Israel, Steve; Bernanek, Luke P.; Friedman, Richard M.; Crowley, James L. (2014). "New ties between the Alexander terrane and Wrangellia and implications for North America Cordilleran evolution". Lithosphere. 6 (4): 270–276. doi:10.1130/L364.1.
- ↑ Gehrels, G. E. (2001). "Geology of the Chatham Sound region, southeast Alaska and coastal British Columbia". Canadian Journal of Earth Sciences. 38 (11): 1579–1599. doi:10.1139/e01-040.
- ↑ Beranek, Luke P.; van Staal, Cees R.; McClelland, William C.; Israel, Steve; Mihalynuk, Mitch G. (2013). "Baltican crustal provenance for Cambrian–Ordovician sandstones of the Alexander Terrane, North American Cordillera: evidence from detrital zircon U–Pb geochronology and Hf isotope geochemistry". Journal of the Geological Society. 170 (1): 7–18. doi:10.1144/jgs2012-070.
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