# Alexander Terrane

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> Source: https://en.wikipedia.org/wiki/Alexander_Terrane
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{{more footnotes|date=January 2026}}
{{short description|Geological area in northwestern North America}}
{{Infobox landform
| name        = Alexander Terrane
| type        = physiographic section
| location    = [Alaska](/source/Alaska); [British Columbia](/source/British_Columbia); [Yukon](/source/Yukon)
| length_km   = 1000
| width_km    = 250
| coordinates = 
| part_of     = [Wrangellia Terrane](/source/Wrangellia_Terrane)
| range       = 
| pushpin_map = 
| map_caption = 
<!--      Geology     -->
| age         = 
| orogeny     = 
| formed_by   = 
| geology     = 
}}

The '''Alexander Terrane''' (named for the [Alexander Archipelago](/source/Alexander_Archipelago) in [Alaska](/source/Alaska)) is a [Neoproterozoic](/source/Neoproterozoic) [continental fragment](/source/continental_fragment) that originated far from its current location, before being transported and accreted to [western North America](/source/western_North_America) in the [Middle Jurassic](/source/Middle_Jurassic).<ref name="Gehrels">{{cite journal
| last1 = Gehrels
| first1 = George E.
| last2 = Saleeby
| first2 = Jason B.
| year = 1987
| title = Geologic framework, tectonic evolution, and displacement history of the Alexander Terrane
| journal = Tectonics
| volume = 6
| issue = 2
| pages = 151–173
| doi = 10.1029/TC006i002p00151
| url = https://doi.org/10.1029/TC006i002p00151
}}</ref>
This terrane also forms part of the composite [Wrangellia Terrane](/source/Wrangellia_Terrane).<ref name="Isreal">{{cite journal
| last1 = Israel
| first1 = Steve
| last2 = Bernanek
| first2 = Luke P.
| last3 = Friedman
| first3 = Richard M.
| last4 = Crowley
| first4 = James L.
| year = 2014
| title = New ties between the Alexander terrane and Wrangellia and implications for North America Cordilleran evolution
| journal = Lithosphere
| volume = 6
| issue = 4
| pages = 270–276
| doi = 10.1130/L364.1
| url = https://doi.org/10.1130/L364.1
}}</ref>

Rocks assigned to this [terrane](/source/terrane) underlie much of [Southeast Alaska](/source/Southeast_Alaska), the north [coast](/source/British_Columbia_Coast) of [British Columbia](/source/British_Columbia), and the [Yukon](/source/Yukon) southwest.<ref name="Gehrels"/>
The Alexander Terrane is intruded by [Late Jurassic](/source/Late_Jurassic) and [Early Cretaceous](/source/Early_Cretaceous) [plutons](/source/plutons) and is overlain to the east by [Upper Jurassic](/source/Upper_Jurassic) through [mid-Cretaceous](/source/mid-Cretaceous) [clastic](/source/clastic) strata and [mafic](/source/mafic) volcanic rocks.<ref>{{cite journal
 | last = Gehrels
 | first = G. E.
 | year = 2001
 | title = Geology of the Chatham Sound region, southeast Alaska and coastal British Columbia
 | journal = Canadian Journal of Earth Sciences
 | volume = 38
 | issue = 11
 | pages = 1579–1599
 | doi = 10.1139/e01-040
}}</ref>

In British Columbia, the terrane [crops out](/source/outcrop) primarily in the [Coast Mountains](/source/Coast_Mountains), including the [Kitimat Ranges](/source/Kitimat_Ranges), [Chatham Sound](/source/Chatham_Sound), and [Haida Gwaii](/source/Haida_Gwaii), and continues to [Klemtu](/source/Klemtu).<ref name="Gehrels"/>

==Origin==
The original location of the Alexander Terrane remains uncertain. Some evidence, including [detrital zircon geochronology](/source/detrital_zircon_geochronology), suggests it may have formed along the margins of ancient [Baltica](/source/Baltica) or [Laurentia](/source/Laurentia),<ref>{{cite journal
| last1 = Beranek
| first1 = Luke P.
| last2 = van Staal
| first2 = Cees R.
| last3 = McClelland
| first3 = William C.
| last4 = Israel
| first4 = Steve
| last5 = Mihalynuk
| first5 = Mitch G.
| year = 2013
| title = 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 = Journal of the Geological Society
| volume = 170
| issue = 1
| pages = 7–18
| doi = 10.1144/jgs2012-070
| url = https://doi.org/10.1144/jgs2012-070
}}</ref>
however, [paleomagnetic](/source/paleomagnetic), [isotopic](/source/Isohedral_figure), and [fossil](/source/fossil) data indicate a possible origin near the margins of the ancient [Siberian](/source/Siberian) or [Arctic](/source/Arctic) continents.<ref name="Isreal"/>

==Development==
The terrane developed through three distinct phases:

; [Late Cambrian](/source/Late_Cambrian) through [Early Devonian](/source/Early_Devonian) : During the initial phase, the terrane probably evolved along a convergent plate margin.<ref name="Gehrels"/>
; [Middle Devonian](/source/Middle_Devonian) through [Lower Permian](/source/Lower_Permian) : The second phase is marked by [strata](/source/strata) accumulated in [tectonically](/source/tectonically) stable [marine environments](/source/marine_environments).<ref name="Gehrels"/>
; [Triassic](/source/Triassic) : The third phase is marked by [volcanic](/source/volcanic) and [sedimentary](/source/sedimentary) rocks which are interpreted to have formed in a [rift](/source/rift) environment.<ref name="Gehrels"/>

==References==
{{Reflist}}

Category:Terranes
Category:Coast of British Columbia
Category:Triassic Alaska
Category:Triassic British Columbia
Category:Triassic Yukon
Category:Geology of Canada

{{BritishColumbia-geology-stub}}
{{plate-tectonics-stub}}

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Adapted from the Wikipedia article [Alexander Terrane](https://en.wikipedia.org/wiki/Alexander_Terrane) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Alexander_Terrane?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.