Misplaced Pages

#934065

73-576: The exposed portion of the craton, called the Slave Province, comprises 172,500 km (66,600 sq mi) and has an elliptical shape that stretches 680 km (420 mi) NNE from Gros Cap on the Great Slave Lake to Cape Barrow on the Coronation Gulf and 460 km (290 mi) EW along latitude 64°N. It covers about 700 km × 500 km (430 mi × 310 mi) and

146-419: A Soviet Radar Ocean Reconnaissance Satellite , named Kosmos 954 , built with an onboard nuclear reactor fell from orbit and disintegrated. Pieces of the nuclear core fell in the vicinity of Great Slave Lake. Some of the nuclear debris was recovered by a joint Canadian Armed Forces and United States Armed Forces military operation called Operation Morning Light. In the late 2010s, many placenames within

219-435: A cumulate texture and morphology . The usual cumulate mineralogy is highly magnesium rich forsterite olivine, though chromian pyroxene cumulates are also possible (though rarer). Volcanic rocks rich in magnesium may be produced by accumulation of olivine phenocrysts in basalt melts of normal chemistry: an example is picrite . Part of the evidence that komatiites are not magnesium-rich simply because of cumulate olivine

292-574: A lava of at least 18 wt% magnesium oxide (MgO). It is classified as a 'picritic rock'. Komatiites have low silicon , potassium and aluminium , and high to extremely high magnesium content. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene . Komatiites are rare rocks; almost all komatiites were formed during

365-520: A collisional suture suggests the CSBC collided with an island arc terrane along a boundary directed north–south before 2.69 Ga. Alternatively, the Eastern Slave may be an attenuated and modified Mesoarchaean lithosphere which developed during rifting at 2.85–2.70 Ga. The mantle lithosphere under the western Slave can be 400 Ma older than that underlying the eastern Slave. Furthermore, rifting

438-439: A distinct unconformity that is laterally continuous over much of the CSBC. This quartz pebble conglomerate layer has been found as far northwest as the 4.03 Ga Acasta Gneiss Complex. 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. Uniform, laterally continuous deposition implies that

511-618: A form of sill-like conduit, where magma pools in a staging chamber before erupting onto the surface. The economic importance of komatiite was first widely recognised in the early 1960s with the discovery of massive nickel sulfide mineralisation at Kambalda, Western Australia . Komatiite-hosted nickel-copper sulfide mineralisation today accounts for about 14% of the world's nickel production, mostly from Australia, Canada and South Africa. Komatiites are associated with nickel and gold deposits in Australia, Canada, South Africa and most recently in

584-577: A granitic magma of crustal origin. 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 . Zircons from this granite protolith shows similarities to zircons from the Yilgarn Craton in Western Australia, and may be evidence for continental crust forming in

657-435: A highly magnesian melt. The rarely preserved flow top breccia and pillow margin zones in some komatiite flows are essentially volcanic glass, quenched in contact with overlying water or air. Because they are rapidly cooled, they represent the liquid composition of the komatiites, and thus record an anhydrous MgO content of up to 32% MgO. Some of the highest magnesian komatiites with clear textural preservation are those of

730-658: A komatiite will reflect the chemistry, which in turn represents an inference as to its volcanological facies and stratigraphic position. Typical metamorphic mineralogy is tremolite - chlorite , or talc -chlorite mineralogy in the upper spinifex zones. The more magnesian-rich olivine-rich flow base facies tend to be free from tremolite and chlorite mineralogy and are dominated by either serpentine - brucite +/- anthophyllite if hydrated, or talc- magnesite if carbonated. The upper flow facies tend to be dominated by talc, chlorite, tremolite, and other magnesian amphiboles ( anthophyllite , cummingtonite , gedrite , etc.). For example,

803-593: A maximum recorded depth in Christie Bay of 614 m (2,014 ft). On some of the plains surrounding Great Slave Lake, climax polygonal bogs have formed, the early successional stage to which often consists of pioneer black spruce . South of Great Slave Lake, in a remote corner of Wood Buffalo National Park , is the Whooping Crane Summer Range , a nesting site of a remnant flock of whooping cranes , discovered in 1954. The Slave River provides

SECTION 10

#1732845270935

876-406: A mean depth of 32.2 m (106 ft). To the east, McLeod Bay ( 62°52′N 110°10′W  /  62.867°N 110.167°W  / 62.867; -110.167  ( McLeod Bay, Great Slave Lake ) ) and Christie Bay ( 62°32′N 111°00′W  /  62.533°N 111.000°W  / 62.533; -111.000  ( Christie Bay, Great Slave Lake ) ) are much deeper, with

949-443: A real petrological source difference between the two types related to depth of melt generation. Al-depleted komatiites have been modeled by melting experiments as being produced by high degrees of partial melting at high pressure where garnet in the source is not melted, whereas Al-undepleted komatiites are produced by high degrees of partial melts at lesser depth. However, recent studies of fluid inclusions in chrome spinels from

1022-420: A rigid upper skin to the lava flows. Proximal volcanic facies are thinner and interleaved with sulfidic sediments, black shales, cherts and tholeiitic basalts . Komatiites were produced from a relatively wet mantle . Evidence of this is from their association with felsics , occurrences of komatiitic tuffs , niobium anomalies and by S- and H 2 O-borne rich mineralizations. A common and distinctive texture

1095-478: A similar peak age of growth which may suggest that much of the earth's continental lithospheric mantle was formed in the Neoarchean 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. Attempts to reconstruct the craton's tectonic history have focused extensively on the east–west asymmetry. The presence of

1168-685: A spinifex textured zone composed of bladed olivine and ideally a pyroxene spinifex zone and olivine-rich chill zone on the upper eruptive rind of the flow unit. Primary (magmatic) mineral species also encountered in komatiites include olivine, the pyroxenes augite , pigeonite and bronzite , plagioclase , chromite , ilmenite and rarely pargasitic amphibole . Secondary (metamorphic) minerals include serpentine , chlorite , amphibole, sodic plagioclase, quartz , iron oxides and rarely phlogopite , baddeleyite , and pyrope or hydrogrossular garnet . All known komatiites have been metamorphosed , therefore should technically be termed 'metakomatiite' though

1241-505: A thin felsic volcaniclastic layer (Ranney Chert) dated at 2722 Ma. 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. Sedimentary rocks exposed in the northern part of the formation are between 2.84 and 2.80 Ga. The Upper Kam Group contains three formations deposited between 2772 and 2701 Ma. It

1314-472: Is a 2.9–2.8 Ga package of fuchsitic quartzites overlain by banded iron formations . 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. The Central Slave Cover Group is typically 100 to 200 meters thick. A quartz pebble conglomerate found at the base of the Central Slave Cover Group marks

1387-520: 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. 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

1460-629: Is bounded by Palaeoproterozoic belts to the south, east, and west, while younger rocks cover it to the north. 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 Ga-old suture defined by two isotopic boundaries running north to south over

1533-444: Is composed mainly of intermediate and basaltic volcanic rocks with thin intercalated rhyolite tuff layers and minor komatiite flows. 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. The Banting group is a north-striking sequence that is faulted overtop of the older Kam Group and younger Jackson Lake Formation. The contact between

SECTION 20

#1732845270935

1606-603: Is extremely dense and unlikely to reach the surface, being more likely to pool lower within the crust. Modern (post-2004) interpretations of some of the larger olivine adcumulate bodies in the Yilgarn craton have revealed that the majority of komatiite olivine adcumulate occurrences are likely to be subvolcanic to intrusive in nature. This is recognised at the Mt Keith nickel deposit where wall-rock intrusive textures and xenoliths of felsic country rocks have been recognised within

1679-507: Is found in the Winnipegosis komatiite belt in Manitoba , Canada. Magmas of komatiitic compositions have a very high melting point , with calculated eruption temperatures up to, and possibly in excess of 1600 °C. Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C. The higher melting temperatures required to produce komatiite have been attributed to

1752-539: Is impacting the populations of these species. Copepoda are also prevalent in the lake. Rivers that flow into Great Slave Lake include (going clockwise from the community of Behchokǫ̀ ): Great Slave Lake has one ice road known as the Dettah ice road. It is a 6.5 km (4.0 mi) road that connects the Northwest Territories capital of Yellowknife to Dettah , a small First Nations fishing community also in

1825-426: Is interpreted to have the general form and structure of a shield volcano , typical of most large basalt edifices, as the magmatic event which forms komatiites erupts less magnesian materials. However, the initial flux of the most magnesian magmas is interpreted to form a channelised flow facie, which is envisioned as a fissure vent releasing highly fluid komatiitic lava onto the surface. This then flows outwards from

1898-471: Is known as spinifex texture and consists of long acicular phenocrysts of olivine (or pseudomorphs of alteration minerals after olivine) or pyroxene which give the rock a bladed appearance especially on a weathered surface. Spinifex texture is the result of rapid crystallization of highly magnesian liquid in the thermal gradient at the margin of the flow or sill . Harrisite texture , first described from intrusive rocks (not komatiites) at Harris Bay on

1971-426: Is produced by fluid-fluxed melting above a subduction zone . Boninites with 10–18% MgO tend to have higher large-ion lithophile elements (LILE: Ba , Rb , Sr ) than komatiites. The pristine volcanic mineralogy of komatiites is composed of forsteritic olivine (Fo90 and upwards), calcic and often chromian pyroxene , anorthite (An85 and upwards) and chromite . A considerable population of komatiite examples show

2044-582: Is relatively extensive throughout the Slave Craton and requires a thick cratonic root. 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. The main stabilization of the Slave craton occurred in the Neoarchean at ~2.75 Ga as noted by an abundance of peridotite formation The Kaapval Craton showed

2117-605: Is textural: some contain spinifex texture , a texture attributable to rapid crystallization of the olivine in a thermal gradient in the upper part of a lava flow. "Spinifex" texture is named after the common name for the Australian grass Triodia , which grows in clumps with similar shapes. Another line of evidence is that the MgO content of olivines formed in komatiites is toward the nearly pure MgO forsterite composition, which can only be achieved in bulk by crystallisation of olivine from

2190-409: Is very rare that no carbon dioxide is present in metamorphic fluids. At higher metamorphic grades, anthophyllite , enstatite , olivine and diopside dominate as the rock mass dehydrates. Komatiite tends to fractionate from high-magnesium compositions in the flow bases where olivine cumulates dominate, to lower magnesium compositions higher up in the flow. Thus, the current metamorphic mineralogy of

2263-742: The Archaean Eon (4.03–2.5 billion years ago), with few younger ( Proterozoic or Phanerozoic ) examples known. This restriction in age is thought to be due to cooling of the mantle, which may have been 100–250 °C (212–482 °F) hotter during the Archaean. The early Earth had much higher heat production, due to the residual heat from planetary accretion , as well as the greater abundance of radioactive isotopes, particularly shorter lived ones like uranium 235 which produce more decay heat . Lower temperature mantle melts such as basalt and picrite have essentially replaced komatiites as an eruptive lava on

Slave Craton - Misplaced Pages Continue

2336-489: The Barberton belt in South Africa, where liquids with up to 34% MgO can be inferred using bulk rock and olivine compositions. The mineralogy of a komatiite varies systematically through the typical stratigraphic section of a komatiite flow and reflects magmatic processes which komatiites are susceptible to during their eruption and cooling. The typical mineralogical variation is from a flow base composed of olivine cumulate, to

2409-458: The Hadean Eon. 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. 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. These zircon crystals may be important in furthering

2482-529: The Northern Plano tradition (8,000 years before present), Shield Archaic tradition (6,500 years), Arctic small tool tradition (3,500 years), and the Taltheilei Shale tradition (2,500 years before present). Each culture has left a distinct mark in the archaeological record based on type or size of lithic tools. Great Slave Lake was put on European maps during the emergence of the fur trade towards

2555-676: The Rae Craton around 2.0–1.8 Ga in the Taltson–Thelon orogeny. 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 . Continual eastward movement of the Slave province, along with collision of the Hottah terrane on the western margin of the Slave, lead to intense deformation of

2628-456: The A zone spinifex flows. In the distal thin flow facies, B zones are poorly developed to absent, as not enough through-flowing liquid existed to grow the adcumulate. The channel and sheeted flows are then covered by high-magnesian basalts and tholeiitic basalts as the volcanic event evolves to less magnesian compositions. The subsequent magmatism, being higher silica melts, tends to form a more typical shield volcano architecture. Komatiite magma

2701-415: The CSBC was previously a part of a single ancient craton that existed as early as 2.85 Ga. The Kam Group is a 0.3–6 kilometre thick sequence that overlies banded iron formations of the Central Slave Cover Group. The contact between these two groups is not well preserved due to the intrusion of gabbro sills and moderate shearing. The Kam group is separated into a lower and upper group based on the existence of

2774-502: The Central Slaver Cover Group, Kam Group, Banting Group, and Jackson Lake Formation. 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. The Neoarchean supracrustal sequence known as the Central Slave Cover Group (informally Dwyer Group)

2847-556: The Earth's surface. Geographically, komatiites are predominantly restricted in distribution to the Archaean shield areas, and occur with other ultramafic and high-magnesian mafic volcanic rocks in Archaean greenstone belts . The youngest komatiites are from the island of Gorgona on the Caribbean oceanic plateau off the Pacific coast of Colombia, and a rare example of Proterozoic komatiite

2920-463: The East Arm into McLeod Bay in the north and Christie Bay in the south. The lake is at least partially frozen during an average of eight months of the year. The main western portion of the lake forms a moderately deep bowl with a surface area of 18,500 km (7,100 sq mi) and a volume of 596 km (143 cu mi). This main portion has a maximum depth of 187.7 m (616 ft) and

2993-553: The East Arm is Łutselk'e, a hamlet of about 350 people, largely Chipewyan Indigenous peoples of the Dene Nation, and the abandoned winter camp and Hudson's Bay Company post Fort Reliance . Along the south shore, east of Hay River is the abandoned Pine Point Mine and the company town of Pine Point . Indigenous peoples were the first settlers around the lake after the retreat of glacial ice. Archaeological evidence has revealed several different periods of cultural history, including

Slave Craton - Misplaced Pages Continue

3066-457: The Northwest Territories were restored to their indigenous names. It has been suggested that the lake be renamed as well, particularly because of the mention of slavery. "Great Slave Lake is actually a very terrible name, unless you're a proponent of slavery," says Dëneze Nakehk'o, a Northwest Territories educator and founding member of First Nations organization Dene Nahjo. "It's a beautiful place. It's majestic; it's huge. And I don't really think

3139-528: The Northwest Territories. To reach the community in summer the drive is 27 km (17 mi) via the Ingraham Trail . From 2014 to 2016, Animal Planet aired a documentary series called Ice Lake Rebels . It takes place on Great Slave Lake, and details the lives of houseboaters on the lake. Komatiite Komatiite / k oʊ ˈ m ɑː t i ˌ aɪ t / is a type of ultramafic mantle -derived volcanic rock defined as having crystallised from

3212-656: The Slave Craton within Laurentia , where it is still found today. Great Slave Lake Great Slave Lake is the second-largest lake in the Northwest Territories of Canada (after Great Bear Lake ), the deepest lake in North America at 614 m (2,014 ft), and the tenth-largest lake in the world by area. It is 469 km (291 mi) long and 20 to 203 km (12 to 126 mi) wide. It covers an area of 27,200 km (10,500 sq mi) in

3285-750: The Taltson magmatic zone. The Hottah terrane accreted with the Slave during the Wopmay orogeny at 1.88 Ga, shortly after the Thelon orogeny. This event produced another continental magmatic arc on the Slave's western margin, the Great Bear magmatic zone , as well as the Wopmay fault zone. The Wopmay fault zone consists of thin skinned thrust belts that mark the suture between the Hottah terrane and Slave Craton. These two orogenies have emplaced

3358-527: The Yellowknife greenstone belt are separated by a distinct unconformity that is laterally continuous over hundreds of kilometres. The Yellowknife Supergroup has been exposed to major metamorphism around 2605 Ma resulting in a range of greenschist to lower amphibolite facies. The Supergroup contains at least four distinct sequences representing different tectonic environments, deposited in separate intervals. The four main sequences include from oldest to youngest,

3431-475: The basin with high nutrient levels; accordingly, coupled with a general absence of pollution and invasive species, the lake is rich in aquatic life relative to its biome. Fish species include lake whitefish , lake trout , inconnu , northern pike and walleye , cisco , burbot , ninespine stickleback , shiner , also longnose sucker . Lake whitefish enjoy the highest levels, followed by cisco and suckers. Climate change , specifically reduced ice coverage times,

3504-535: The craton. The Central Slave basement complex (CSBC) is the basement 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. 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 Gneisses with a protolith age of about 4.03 Ga, one of

3577-494: The craton. 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 , Zimbabwe , and Wyoming cratons were also part of Sclavia. The Slave broke off of Sclavia between 2.2 and 2.0 Ga, as noted by a host of dyke swarms at its margins. The Slave Craton drifted for approximately 200 million years before its accretion with

3650-422: The cumulate zones of komatiite flows have shown that a single komatiite flow can be derived from the mixing of parental magmas with a range of Al 2 O 3 /TiO 2 ratios, calling into question this interpretation of the formations of the different komatiite groups. Komatiites probably form in extremely hot mantle plumes or in Archaean subduction zones. Boninite magmatism is similar to komatiite magmatism but

3723-616: The current name on the map is fitting for that place." He has suggested Tu Nedhé, the Dene Soline name for the lake, as an alternative. Tucho, the Dehcho Dene term for the lake, has also been suggested. The Hay , Slave (which in turn includes the Peace ), Lockhart , and Taltson Rivers are its chief tributaries. It is drained by the Mackenzie River . Though the western shore is forested,

SECTION 50

#1732845270935

3796-522: 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. Xenocrysts found within 3.94 Ga tonalitic gneisses of the Acasta Gneiss Complex have U–Pb dates of 4.2 Ga. These zircon xenocrysts originally crystallized in

3869-558: The east shore and northern arm are tundra -like. The southern and eastern shores reach the edge of the Canadian Shield . Along with other lakes such as the Great Bear and Athabasca , it is a remnant of the vast glacial Lake McConnell . The lake has a very irregular shoreline. The East Arm of Great Slave Lake is filled with islands, and the area is within the proposed Thaidene Nene National Park Reserve . The Pethei Peninsula separates

3942-631: The essentially unaltered magma chemistry and not the result of crystal accumulation (as in peridotite ). Through a typical komatiite flow sequence the chemistry of the rock will change according to the internal fractionation which occurs during eruption. This tends to lower MgO, Cr, Ni, and increase Al, K 2 O, Na, CaO and SiO 2 toward the top of the flow. Rocks rich in MgO, K 2 O, Ba, Cs, and Rb may be lamprophyres , kimberlites or other rare ultramafic, potassic or ultrapotassic rocks. Komatiites often show pillow lava structure, autobrecciated upper margins consistent with underwater eruption forming

4015-569: The island of Rùm in Scotland , is formed by nucleation of crystals on the floor of a magma chamber . Harrisites are known to form megacrystal aggregates of pyroxene and olivine up to 1 metre in length. Harrisite texture is found in some very thick lava flows of komatiite, for example in the Norseman-Wiluna Greenstone Belt of Western Australia, in which crystallization of cumulates has occurred. Komatiite volcano morphology

4088-679: The komatiitic lava accumulated. Komatiite chemistry is different from that of basaltic and other common mantle-produced magmas, because of differences in degrees of partial melting . Komatiites are considered to have been formed by high degrees of partial melting, usually greater than 50%, and hence have high MgO with low K 2 O and other incompatible elements . There are two geochemical classes of komatiite; aluminium undepleted komatiite (AUDK) (also known as Group I komatiites) and aluminium depleted komatiite (ADK) (also known as Group II komatiites), defined by their Al 2 O 3 /TiO 2 ratios. These two classes of komatiite are often assumed to represent

4161-455: The low-strain contacts. The previous interpretations of these large komatiite bodies was that they were "super channels" or reactivated channels, which grew to over 500 m in stratigraphic thickness during prolonged volcanism. These intrusions are considered to be channelised sills , formed by injection of komatiitic magma into the stratigraphy, and inflation of the magma chamber. Economic nickel-mineralised olivine adcumulate bodies may represent

4234-480: The lower units and the Banting Group is a disconformity that represents a ~40 million year gap in deposition. The Banting Group contains siliceous to intermediate volcanic rocks that are typically calk-alkalic. The Banting Group formation is largely a result of post 2.7 Ga volcanism and sub-volcanic activity. A series of 2658 Ma quartz-feldspar intrusions are found throughout the underlying Kam group that are related to

4307-519: The metamorphic assemblage of a metakomatiite ( hereafter the prefix meta- is assumed ). The factor controlling the mineral assemblage is the partial pressure of carbon dioxide within the metamorphic fluid, called the XCO 2 . If XCO 2 is above 0.5, the metamorphic reactions favor formation of talc , magnesite (magnesium carbonate), and tremolite amphibole. These are classed as talc-carbonation reactions. Below XCO 2 of 0.5, metamorphic reactions in

4380-671: The northwest from Hudson Bay in the mid 18th century. The name 'Great Slave' came from the English-language translation of the Cree exonym , Awokanek ( Slavey ), which they called the Dene Tha. The Slavey people were Dene tribes living on the lake's southern shores at that time. As the French explorers dealt directly with the Cree traders, the large lake was referred to as "Grand lac des Esclaves" which

4453-507: The northwestern margin. The Burwash Basin consists of metamorphosed turbiditic sandstones and slates interspersed with thin felsic tuff layers. 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. By 2.6 Ga the Slave had collided with the much larger Sclavia , resulting in shortening and cross-folding over

SECTION 60

#1732845270935

4526-565: The oldest dated rock units on Earth. These gneisses are polymetamorphic and have a tonalitic and gabbroic composition. The rest of the CSBC is younger with a central core <3.5 Ga and the remaining craton with detrial and protolith ages ranging from 3.4 to 2.8 Ga. The basement complex is overlain by Neoarchaean supracrustal sequences and intruded by plutonic suites. 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

4599-426: 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. The Back River volcanic complex is an Archaean stratovolcano preserved in an upright position surrounded by four sedimentary sequences reflecting the volcano's magmatic history. An exposed dome in

4672-559: The post 2.7 Ga volcanism found in the Banting Group. Deposition of the Jackson Lake Formation began at 2605 Ma. 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. Information on

4745-473: The prefix meta is inevitably assumed. Many komatiites are highly altered and serpentinized or carbonated from metamorphism and metasomatism . This results in significant changes to the mineralogy and the texture. The metamorphic mineralogy of ultramafic rocks, particularly komatiites, is only partially controlled by composition. The character of the connate fluids which are present during low temperature metamorphism whether prograde or retrograde control

4818-464: The presence of water favor production of serpentinite . There are thus two main classes of metamorphic komatiite; carbonated and hydrated. Carbonated komatiites and peridotites form a series of rocks dominated by the minerals chlorite, talc, magnesite or dolomite and tremolite. Hydrated metamorphic rock assemblages are dominated by the minerals chlorite, serpentine - antigorite and brucite . Traces of talc, tremolite and dolomite may be present, as it

4891-688: The presumed higher geothermal gradients in the Archaean Earth. Komatiitic lava was extremely fluid when it erupted (possessing the viscosity close to that of water but with the density of rock). Compared to the basaltic lava of the Hawaiian plume basalts at ~1200 °C, which flows the way treacle or honey does, the komatiitic lava would have flowed swiftly across the surface, leaving extremely thin lava flows (down to 10 mm thick). The major komatiitic sequences preserved in Archaean rocks are thus considered to be lava tubes , ponds of lava etc., where

4964-413: 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. The Yellowknife Supergroup, also known as the 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. The CSBC and

5037-662: The southern part of the territory. Its given volume ranges from 1,070 km (260 cu mi) to 1,580 km (380 cu mi) and up to 2,088 km (501 cu mi) making it the 10th or 12th largest by volume. The lake shares its name with the First Nations peoples of the Dene family called Slavey by their enemies the Cree . Towns situated on the lake include (clockwise from east) Łutselk'e , Fort Resolution , Hay River , Hay River Reserve , Behchokǫ̀ , Yellowknife , Ndilǫ , and Dettah . The only community in

5110-475: The typical flow facies (see below) may have the following mineralogy; Komatiite can be classified according to the following IUGS geochemical criteria: When meeting the above, but the TiO 2 is more than 1 wt%, it is classified as meimechite . A similar high-Mg volcanic rock is boninite , having 52–63 wt% SiO 2 , more than 8 wt% MgO and less than 0.5 wt% TiO 2 . The above geochemical classification must be

5183-407: The understanding of the earliest crustal formation processes, as little is yet known. The overall stability of a craton is highly correlated to the presence of a strong and deep continental lithospheric mantle because it protects the crust from thermal erosion and mitigates the effects of tectonism. The Slave Craton shows a long history of continental lithospheric mantle formation. Diamond formation

5256-413: The vent fissure, concentrating into topographical lows, and forming channel environments composed of high MgO olivine adcumulate flanked by a 'sheeted flow facies' aprons of lower MgO olivine and pyroxene thin-flow spinifex sheets. The typical komatiite lava flow has six stratigraphically related elements; Individual flow units may not be entirely preserved, as subsequent flow units may thermally erode

5329-584: Was eventually translated into English as "Great Slave Lake". In the 1930s, gold was discovered on the North Arm of Great Slave Lake, leading to the establishment of Yellowknife which would become the capital of the NWT . In 1960, an all-season highway was built around the west side of the lake, originally an extension of the Mackenzie Highway but now known as Yellowknife Highway or Highway 3. On January 24, 1978,

#934065