# Slave Craton

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{{short description|Area of ancient rocks in northwest Canada}}
thumb|Geological map of north-western Canada. Slave Craton is marked with A.
right|thumb|Palaeomap of North American and Scandinavian cratons, basement rocks, and orogenic belts (ages in billions of years)
The '''Slave craton''' is an [Archaean](/source/Archean) [craton](/source/craton) in the north-western [Canadian Shield](/source/Canadian_Shield), in [Northwest Territories](/source/Northwest_Territories) and [Nunavut](/source/Nunavut).  The Slave Craton includes the 4.03&nbsp;Ga-old [Acasta Gneiss](/source/Acasta_Gneiss) which is one of the [oldest dated rocks](/source/oldest_dated_rocks) on Earth.<ref>{{Harvnb|Stern|Bleeker|1998|loc=Summary}}</ref><ref name="Bleeker-2004-Basement">{{Harvnb|Bleeker|Davis|Ketchum|Stern|2004|loc=Basement complex, p. 1}}</ref>
Covering about {{Convert|300000|km2|abbr=on}}, it is a relatively small but well-exposed craton dominated by ~2.73–2.63&nbsp;Ga (billion years-old) [greenstones](/source/greenstone_belt) and [turbidite](/source/turbidite) [sequences](/source/sequence_(geology)) and ~2.72–2.58 Ga [plutonic](/source/plutonic) rocks, with large parts of the craton underlain by older [gneiss](/source/gneiss) and [granitoid](/source/granitoid) units.<ref>{{Harvnb|Bleeker|Stern|Sircombe|2000|loc=Slave Craton and previous investigations, pp. 2–3}}</ref>
The Slave Craton is one of the blocks that compose the Precambrian core of North America, also known as the palaeocontinent [Laurentia](/source/Laurentia).<ref name="Helm-Geolset">{{Harvnb|Helmstaedt|2009|loc=Geological setting, pp. 1056–1057}}</ref>

The exposed portion of the craton, called the Slave Province, comprises {{Convert|172500|km2|abbr=on}} and has an elliptical shape that stretches {{Convert|680|km|abbr=on}} NNE from Gros Cap on the [Great Slave Lake](/source/Great_Slave_Lake) to Cape Barrow on the [Coronation Gulf](/source/Coronation_Gulf) and {{Convert|460|km|abbr=on}} EW along latitude 64°N.<ref name="Helm-Geolset" />  It covers about {{Convert|700x500|km|abbr=on}} and is bounded by Palaeoproterozoic belts to the south, east, and west, while younger rocks cover it to the north.<ref name="Davis-2003-GeolBG">{{Harvnb|Davis|Jones|Bleeker|Grütter|2003|loc=Geological background}}</ref>

The Slave Craton is divided into a west-central basement complex, the Central Slave Basement Complex, and an eastern province, named the Hackett River Terrane or the Eastern Slave Province. These two domains are separated by a 2.7&nbsp;Ga-old [suture](/source/Suture_(geology)) defined by two isotopic boundaries running north to south over the craton.<ref>{{Harvnb|Jones|Garcia|2006|loc=Geological setting, pp. 126–127}}</ref>

== Subdivisions ==
=== Central Slave basement complex ===
thumb|A 4.03&nbsp;Ga sample from the small Acasta River
The Central Slave basement complex (CSBC) is the [basement](/source/basement_(geology)) under the central and western part of the craton. The CSBC's eastern extent is unknown, as its disappearance is marked by Nd and Pb isotopic boundaries.<ref name=":5" /> The CSBC dips to the east and underlies at least the central part of the craton. Along the Acasta River the CSBC includes the [Acasta Gneiss](/source/Acasta_Gneiss)es with a [protolith](/source/protolith) age of about 4.03&nbsp;Ga, one of the oldest dated rock units on Earth.  These [gneiss](/source/gneiss)es are [polymetamorphic](/source/Metamorphic_rock) and have a [tonalitic](/source/tonalite) and [gabbro](/source/gabbro)ic composition. The rest of the CSBC is younger with a central core <3.5&nbsp;Ga and the remaining craton with [detrial](/source/Detritus_(geology)) and protolith ages ranging from 3.4 to 2.8&nbsp;Ga.<ref name="Bleeker-2004-Basement" />
The basement complex is overlain by Neoarchaean [supracrustal](/source/Supracrustal_rock) [sequences](/source/Sequence_(geology)) and intruded by [pluton](/source/pluton)ic suites.<ref>{{Harvnb|Bleeker|2011}}</ref>
The Acasta gneisses are geochemically similar to other Archaean complexes but, four billion years old, they contain even older zircon cores. These cores indicate that the parental magmas of such complexes formed by interaction between the zircon-bearing crust and mantle-derived melts. No such older Acasta gneisses have been discovered yet, but the zircon cores indicate they could exist.<ref>{{Harvnb|Bowring|Williams|1999|loc=Implications of zircon data, pp. 14–15}}</ref>

=== Back River volcanic complex ===
The [Back River volcanic complex](/source/Back_River_volcanic_complex) is an Archaean [stratovolcano](/source/stratovolcano) preserved in an upright position surrounded by four sedimentary sequences reflecting the volcano's magmatic history.  An exposed dome in the southern half of the complex is interpreted to be the eroded portion of the volcano.  In contrast to the remaining craton, the complex has only undergone a low degree of deformation.<ref>{{Harvnb|Villeneuve|Lambert|van Breemen|Mortensen|2001|loc=Introduction, p. 2}}</ref>

=== Yellowknife Supergroup ===
The Yellowknife Supergroup, also known as the [Yellowknife greenstone belt](/source/Yellowknife_greenstone_belt), was deposited over 300 million years from ca. 2.9-2.6 Ga, and directly overlies the CSBC including much of the Eastern Slave Province.<ref name=":2">{{cite journal |last=Bleeker |first=W. |last2=Davis |first2=B. |last3=Ketchum |first3=J. |last4=Stern |first4=R. |last5=Sircombe |first5=K. |last6=Waldron |first6=J. |year=2004 |title=The Slave Craton From On Top: The Crustal View |journal=Geological Survey of Canada}}</ref><ref name=":5">{{Cite journal|last1=Heaman|first1=Larry M.|last2=Pearson|first2=D. Graham|date=2010-04-01|title=Nature and evolution of the Slave Province subcontinental lithospheric mantle|url=http://cjes.geoscienceworld.org/content/47/4/369|journal=Canadian Journal of Earth Sciences|language=en|volume=47|issue=4|pages=369–388|doi=10.1139/E09-046|issn=0008-4077|bibcode=2010CaJES..47..369H|url-access=subscription}}</ref> The CSBC and the Yellowknife greenstone belt are separated by a distinct unconformity that is laterally continuous over hundreds of kilometres.<ref name=":3">{{Cite book|title=Why the Slave Province, Northwest Territories, got a little bigger.|last1=Bleeker |first1=W. |last2=Stern |first2=R. |last3=Sircombe |first3=K. |publisher=Natural Resources Canada, Geological Survey of Canada|year=2000|isbn=978-0660180212|oclc=932794624}}</ref> The Yellowknife Supergroup has been exposed to major metamorphism around 2605 Ma resulting in a range of [greenschist](/source/greenschist) to lower [amphibolite](/source/amphibolite) facies.<ref name=":4">{{Cite journal|last1=Isachsen|first1=C. E.|last2=Bowring|first2=S. A.|date=1994-10-01|title=Evolution of the Slave craton|url=http://geology.geoscienceworld.org/content/22/10/917|journal=Geology|language=en|volume=22|issue=10|pages=917–920|doi=10.1130/0091-7613(1994)022<0917:EOTSC>2.3.CO;2|bibcode=1994Geo....22..917I |issn=0091-7613|url-access=subscription}}</ref> The Supergroup contains at least four distinct sequences representing different tectonic environments, deposited in separate intervals.<ref name=":4" /> The four main sequences include from oldest to youngest, the Central Slaver Cover Group, Kam Group, Banting Group, and Jackson Lake Formation.<ref name=":4" /> The Yellowknife Supergroup has been used to represent the general stratigraphy of the greenstone belts in the Slave Craton, including belts in the Eastern Slave, in order to interpret the processes involved in the evolution of the Slave Craton.<ref name=":4" />

==== Central Slave Cover Group ====
The Neoarchean supracrustal sequence known as the Central Slave Cover Group (informally Dwyer Group) is a 2.9–2.8 Ga package of [fuchsitic](/source/fuchsite) quartzites overlain by [banded iron formation](/source/banded_iron_formation)s.<ref name=":2" /> This fuchisitic quartziite sequence seems to be characteristic of many other cratons between about 3.1 and 2.8 Ga and marks a global peak in quartzite production.<ref name=":4" /><ref name=":3" /> The Central Slave Cover Group is typically 100 to 200 meters thick.<ref name=":2" /> A quartz pebble conglomerate found at the base of the Central Slave Cover Group marks a distinct unconformity that is laterally continuous over much of the CSBC.<ref name=":3" /> This quartz pebble conglomerate layer has been found as far northwest as the 4.03 Ga Acasta Gneiss Complex.<ref name=":3" /> The Central Slave Cover Group is autochthonous and represents a single continuous cover sequence, that links the basement complex in the northwest with the basement in the south-central Slave Province.<ref name=":3" /> Uniform, laterally continuous deposition implies that the CSBC was previously a part of a single ancient craton that existed as early as 2.85 Ga.<ref name=":3" />

==== Kam Group ====
The Kam Group is a 0.3–6 kilometre thick sequence that overlies banded iron formations of the Central Slave Cover Group.<ref name=":2" /> The contact between these two groups is not well preserved due to the intrusion of gabbro sills and moderate shearing.<ref name=":4" /> The Kam group is separated into a lower and upper group based on the existence of a thin felsic volcaniclastic layer (Ranney Chert) dated at 2722 Ma.<ref name=":4" /> The lower Kam group consists of the Chan Formation which contains flows of pillowed basalts intruded by a series of gabbroic sills and dikes that were produced in an extensional back-arc basin setting.<ref name=":4" /> Sedimentary rocks exposed in the northern part of the formation are between 2.84 and 2.80 Ga.<ref name=":4" /> The Upper Kam Group contains three formations deposited between 2772 and 2701 Ma.<ref name=":4" /> It is composed mainly of intermediate and basaltic volcanic rocks with thin intercalated rhyolite tuff layers and minor [komatiite](/source/komatiite) flows.<ref name=":4" /><ref name=":2" /> Rocks in this formation were seemingly formed in an arc environment and may be a result of rifting of basement rocks due to increased mantle plume activity.<ref name=":4" /><ref name=":2" />

==== Banting Group ====
The Banting group is a north-striking sequence that is faulted overtop of the older Kam Group and younger Jackson Lake Formation.<ref name=":4" /> The contact between the lower units and the Banting Group is a disconformity that represents a ~40 million year gap in deposition.<ref name=":4" /> The Banting Group contains siliceous to intermediate volcanic rocks that are typically calk-alkalic.<ref name=":4" /><ref name=":0" /> The Banting Group formation is largely a result of post 2.7 Ga volcanism and sub-volcanic activity.<ref name=":2" /> A series of 2658 Ma quartz-feldspar intrusions are found throughout the underlying Kam group that are related to the post 2.7 Ga volcanism found in the Banting Group.<ref name=":4" /><ref name=":5" />

==== Jackson Lake Formation ====
Deposition of the Jackson Lake Formation began at 2605 Ma.<ref name=":4" /> The formation is a high energy sedimentary deposit that overlies the volcanic rocks of the Kam Group. The deposit consists of polymict conglomerates and fluvial sandstones that have been subjected to a major metamorphic event as evident by similarly oriented vertical dips and lineations found in older groups.<ref name=":4" />

== Evolution of Slave Craton ==
=== Earliest formation ===
Information on the earliest formation of the Slave Craton may be found in the Acasta Gneiss Complex, but due to the complex history, poor preservation, and lack of exposure, much is still unknown about crustal forming processes in the Hadean and early Archean. [Xenocryst](/source/Xenocryst)s found within 3.94 Ga [tonalitic](/source/tonalite) gneisses of the Acasta Gneiss Complex have U–Pb dates of 4.2 Ga.<ref name=":0">{{Cite journal|last1=Iizuka|first1=Tsuyoshi|last2=Horie|first2=Kenji|last3=Komiya|first3=Tsuyoshi|last4=Maruyama|first4=Shigenori|last5=Hirata|first5=Takafumi|last6=Hidaka|first6=Hiroshi|last7=Windley|first7=Brian F.|title=4.2 Ga zircon xenocryst in an Acasta gneiss from northwestern Canada: Evidence for early continental crust|journal=Geology|volume=34|issue=4|doi=10.1130/g22124.1|year=2006|page=245|bibcode=2006Geo....34..245I}}</ref> These [zircon](/source/zircon) xenocrysts originally crystallized in a granitic magma of crustal origin.<ref name=":0" /> Further evidence suggests that the 3.94 Ga tonalitic gneisses are at least partly derived from this 4.2 Ga granite magma, which indicates that crustal reworking was an important process in the [Eoarchean](/source/Eoarchean).<ref name=":0" /> Zircons from this granite protolith shows similarities to [zircons](/source/Jack_Hills) from the [Yilgarn craton](/source/Yilgarn_craton) in Western Australia, and may be evidence for continental crust forming in the [Hadean](/source/Hadean) Eon.<ref name=":0" /> However, it is suggested that these two cratons have never been directly connected, which may indicate that the early Hadean crust was primarily continental granite.<ref name=":1">{{Cite journal|last=Bleeker|first=Wouter|date=2003-12-01|title=The late Archean record: a puzzle in ca. 35 pieces|journal=[Lithos](/source/Lithos_(journal))|series=A Tale of Two Cratons: The Slave-Kaapvaal Workshop|volume=71|issue=2–4|pages=99–134|doi=10.1016/j.lithos.2003.07.003|bibcode=2003Litho..71...99B}}</ref><ref name=":0" /> Trace isotope analysis show that these early granite rocks originated from a highly depleted mantle and suggest that large scale differentiation occurred before ~4.0 Ga.<ref name=":0" /> These zircon crystals may be important in furthering the understanding of the earliest crustal formation processes, as little is yet known.<ref name=":0" />

=== Craton stabilization ===
The overall stability of a craton is highly correlated to the presence of a strong and deep [continental lithospheric mantle](/source/Subcontinental_lithospheric_mantle) because it protects the crust from thermal erosion and mitigates the effects of tectonism.<ref name=":5" /> The Slave Craton shows a long history of continental lithospheric mantle formation. Diamond formation is relatively extensive throughout the Slave Craton and requires a thick cratonic root.<ref name=":4" /> The oldest diamonds derived from the mantle were between 3.5 and 3.3 Ga, which suggest that the Slave Protocraton would have formed a thick crustal root by this time.<ref name=":4" /> The main stabilization of the Slave craton occurred in the Neoarchean at ~2.75 Ga as noted by an abundance of peridotite formation<ref name=":5" /> The [Kaapval](/source/Kaapvaal_craton) Craton showed a similar peak age of growth which may suggest that much of the earth's continental lithospheric mantle was formed in the Neoarchean<ref name=":4" /> The formation and stabilization of the continental lithospheric mantle and the evolution of the crust are closely related during the period between 2.8 and 2.0 Ga.<ref name=":4" />
=== Tectonic history ===
thumb|276x276px|Cross-section of the Slave Province including Slave Craton. SRT: Snare River Terrane, CSST: Central Slave Superterrane, CT: Contwoyto Terrane, HRT: Hackett River Terrane.
Attempts to reconstruct the craton's tectonic history have focused extensively on the east–west asymmetry. The presence of a collisional [suture](/source/Suture_(geology)) suggests the CSBC collided with an [island arc](/source/island_arc) [terrane](/source/terrane) along a boundary directed north–south before 2.69&nbsp;Ga. Alternatively, the Eastern Slave may be an attenuated and modified Mesoarchaean lithosphere which developed during rifting at 2.85–2.70&nbsp;Ga. The mantle lithosphere under the western Slave can be 400&nbsp;Ma older than that underlying the eastern Slave.<ref name="Davis-2003-GeolBG" /><ref>{{Harvnb|Davis|Jones|Bleeker|Grütter|2003|loc=Fig. 1, p. 576}}</ref> Furthermore, rifting is backed up by the existence of younger arc or back-arc rocks that overly the CSBC, but make up most of the Eastern Slave.<ref name=":2" /> However, whether the Eastern Slave was the result of rifting or the accretion of another terrane is still up for debate.

Following the 2.7 Ga rifting or accretion event, the Slave underwent large scale extension at 2680 Ma resulting in the formation of the > 400x800 km Burwash Basin, widespread mafic sills, and other younger turbidites along the northwestern margin.<ref name=":7">{{Cite journal|last1=Ferguson|first1=Mark E|last2=Waldron|first2=John WF|last3=Bleeker|first3=Wouter|title=The Archean deep-marine environment: turbidite architecture of the Burwash Formation, Slave Province, Northwest Territories|journal=Canadian Journal of Earth Sciences|volume=42|issue=6|pages=935–954|doi=10.1139/e04-070|year=2005|bibcode=2005CaJES..42..935F}}</ref><ref name=":2" /> The Burwash Basin consists of metamorphosed turbiditic sandstones and slates interspersed with thin felsic tuff layers.<ref name=":7" /> At 2634 Ma the Slave switched to a compressional regime and the Burwash Basin started to close, possibly due to shallow subduction from the NW or SE.<ref name=":2" /><ref name=":7" /> By 2.6 Ga the Slave had collided with the much larger [Sclavia](/source/Sclavia_craton), resulting in shortening and cross-folding over the craton.<ref name=":1" /><ref name=":2" /> The presence of three rifted margins around the Slave, as well as similarly aged 3.3–3.5 Ga basement rocks, fuchsitic quartzite, and 2.9 Ga tonalites, suggest that the [Dharwar](/source/Dharwar_craton), [Zimbabwe](/source/Zimbabwe_craton), and [Wyoming](/source/Wyoming_craton) cratons were also part of Sclavia.<ref name=":1" /> The Slave broke off of Sclavia between 2.2 and 2.0 Ga, as noted by a host of [dyke swarm](/source/dyke_swarm)s at its margins.<ref name=":1" /> The Slave Craton drifted for approximately 200 million years before its accretion with the [Rae Craton](/source/Rae_craton) around 2.0–1.8 Ga in the Taltson–Thelon orogeny.<ref name=":1" /><ref name=":6">{{Cite book|url=https://books.google.com/books?id=iamPDAAAQBAJ&q=collision+of+Rae+and+Slave&pg=PA337|title=GEOLOGY- Volume IV|last1=Vivo|first1=Benedetto De|last2=Grasemann|first2=Bernhard|last3=Stüwe|first3=Kurt|date=2009-12-11|publisher=EOLSS Publications|isbn=9781848260078|language=en}}</ref> The orogenic belt accreted smaller exotic terranes before the Slave was eventually subducted eastward under the Rae, resulting in a continental magmatic arc known as the [Taltson magmatic zone](/source/Taltson_magmatic_zone).<ref name=":6" /><ref>{{Cite journal|last1=Tirrul|first1=Rein|last2=Grotzinger|first2=John P.|date=1990-10-01|title=Early Proterozoic Collisional Orogeny along the Northern Thelon Tectonic Zone, Northwest Territories, Canada: Evidence from the foreland|journal=Tectonics|language=en|volume=9|issue=5|pages=1015–1036|doi=10.1029/TC009i005p01015|issn=1944-9194|bibcode=1990Tecto...9.1015T}}</ref> Continual eastward movement of the Slave province, along with collision of the [Hottah terrane](/source/Hottah_terrane) on the western margin of the Slave,  lead to intense deformation of the Taltson magmatic zone.<ref name=":6" /> The Hottah terrane accreted with the Slave during the [Wopmay orogen](/source/Wopmay_orogen)y at 1.88 Ga, shortly after the Thelon orogeny.<ref name=":6" /> This event produced another continental magmatic arc on the Slave's western margin, the [Great Bear magmatic zone](/source/Great_Bear_magmatic_zone), as well as the Wopmay fault zone.<ref name=":1" /><ref name=":6" /> The Wopmay fault zone consists of thin skinned thrust belts that mark the suture between the Hottah terrane and Slave Craton.<ref name=":6" /> These two orogenies have emplaced the Slave Craton within [Laurentia](/source/Laurentia), where it is still found today.

== See also ==
{{Portal|Geology|Canada}}
* [Geology of Canada](/source/Geology_of_Canada)
* [Canadian Shield](/source/Canadian_Shield)
* [Flin Flon greenstone belt](/source/Flin_Flon_greenstone_belt)
* [Hearne Craton](/source/Hearne_craton)
* [Wyoming Craton](/source/Wyoming_craton)

{{clear}}

== References ==
{{reflist}}

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Category:Cratons
Category:Historical geology
Category:Economic geology
Category:Structural geology
Category:Precambrian Canada
Category:Geology of the Northwest Territories

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