Superior craton - AbsoluteAstronomy.com

The Superior craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

(or Superior Province

Geologic province

A geologic or geomorphic province is a spatial entity with common geologic or geomorphic attributes. A province may include a single dominant structural element such as a basin or a fold belt, or a number of contiguous related elements...

) forms the core of the Canadian Shield

Canadian Shield

The Canadian Shield, also called the Laurentian Plateau, or Bouclier Canadien , is a vast geological shield covered by a thin layer of soil that forms the nucleus of the North American or Laurentia craton. It is an area mostly composed of igneous rock which relates to its long volcanic history...

at the heart of the North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

n continent. It extends from Quebec

Quebec

Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....

in the east to eastern Manitoba

Manitoba

Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...

in the west. The western margin extends from northern Minnesota through eastern Manitoba to northwestern Ontario.

The formation of the Superior craton is best explained within the context of 2.72-2.68 Ga accretion of small continental plates and trapped oceanic terrane

Terrane

A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...

s in a tectonic regime resembling that of today's rapidly changing southwestern Pacific Ocean. The craton is made up of a collage of small continental fragments of Mesoarchean

Mesoarchean

The Mesoarchean is a geologic era within the Archean, spanning 3200 Ma to 2800 Ma . The period is defined chronometrically and is not referenced to a specific level in a rock section on Earth. Fossils from Australia show that stromatolites have lived on Earth since the Mesoarchean. The Pongola...

age and Neoarchean

Neoarchean

The Neoarchean is a geologic era within the Archaean. It spans the period of time from —the period being defined chronometrically and not referenced to a specific level in a rock section on Earth...

oceanic plates and tracts of oceanic crust that consists of the following domains: Northern Superior, North Caribou, Winnipeg River, Marmion, Minnesota River Valley, Opatica, and Goudalie. These domains are generally separated by greenstone-granite terranes with long strike lengths that record various geodynamic environments, including oceanic floor, plateau, island arc and back-arc settings. Examples include the Oxford-Stull terrane in the north, the western Wabigoon in the west, and the Wawa-Abitibi subprovince in the southeastern Superior Province. A suite of Neoarchean monzodiorite intrusion

Intrusion

An intrusion is liquid rock that forms under Earth's surface. Magma from under the surface is slowly pushed up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years. As the rock slowly...

s from greenstone belt

Greenstone belt

Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies....

s of the western Superior province have been termed "sanukitoid

Sanukitoid

Sanukitoids are a variety of high-Mg granitoid found in convergent margin settings. The term "sanukitoid" was originally used to define a variety of Archean plutonic rock, but now also includes younger rocks with similar geochemical characteristics...

" because of their similarity in bulk chemical composition to high-magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

andesite

Andesite

Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...

from Japan known as "sanukite

Sanukitoid

."

Neoarchean volcano-plutonic rocks of arc affinity dominate the oceanic margins of the Superior craton and indicate that there was widespread subduction

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

prior to the 2.72-2.68 Ga collisional events that amalgamated the present-day Superior craton. However, during the amalgamation-collisions, five discrete orogenies are recognized. In the western and southern Superior province, the orogenies resulting from these collisional events all have the following common elements: 1) widespread calc-alkaline arc magmatism on the upper plate preceding collision; 2) deposition, rapid burial and deformation of syn-orogenic sediments (conglomerate, greywacke) in suture zones over strike lengths of >1000 km; 3) high-temperature, low-pressure regional metamorphism over broad regions; 4) steep foliation and orogen-parallel strike-slip faults attributed to transpressive deformation; 5) emplacement of mantle-derived, post-orogenic plutons of the sanukitoid suite; 6) widespread emplacement of late granitic plutons of crustal derivation; and 7) rapid post-orogenic uplift and cooling. (Percival, 2003).

Sedimentary rocks as old as 2.48 Ga unconformably overlie Superior Province granites indicating that most erosion had occurred prior to ca. 2.5 Ga. Younger metasedimentary belts separate some of the continental and oceanic domains and extend across the entire province. These 50–100 km wide belts of metagreywacke, migmatite and derived granite appear to represent thick syn-orogenic sequences that were deposited, deformed and metamorphosed during collisional orogeny. Faults developed in association with several distinct tectonic events host a variety of orogenic gold deposits across the province. (Percival, 2006).

The Superior craton has a lithosphere thickness of at least 250 km beneath the craton, and possibly as much as 350 km. The Kapuskasing uplift represents a 500-km long fault-bounded structure that divides the Superior Province into eastern and western halves. 2.765-2.66 Ga mid to lower crustal levels of the Abitibi-Wawa and Quetico belts contain amphibolite- to granulite-facies tonalite gneiss, paragneiss, mafic gneiss and anorthosite exposed through east-directed thrusting and sinistral transcurrent motion during the Paleoproterozoic. Recent work suggests that the Kapuskasing structure accommodated a 20-degree counterclockwise rotation of the western Superior with respect to the east. (Percival, 2006).

Archean Superior proto-craton

The planet's oldest continental crust

Crust (geology)

In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

(up to 3.7 Ga) occurs in the Northern Superior superterrane and the Inukjuak domain of the northeastern Superior province. A large region of the ca. 3.0 Ga North Caribou terrane, extending into northern Quebec, has been interpreted as a continental nucleus (or proto-craton) during assembly of the Superior Province. Farther south the Winnipeg River and Marmion terranes are relatively small continental fragments dating back to 3.4 and 3.0 Ga, respectively. In the far south, the Minnesota River Valley terrane contains remnants of crust as old as ca. 3.6 Ga (Percival, 2006). Crustal evolution in the western Superior province occurred at 3.4, 3.0, and 2.7 Ga. The 2.7 Ga crustal additions were contaminated by crustal material subducted into the region or by intrusions into the sanukitoids.

U-Pb

Radiometric dating

Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...

geochronology

Geochronology

Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...

mapping with SHRIMP

SHRIMP

The sensitive high resolution ion microprobe is a large-diameter, double-focusing secondary ion mass spectrometer sector instrument produced by Australian Scientific Instruments in Canberra, Australia...

results support a ca. 3.0 Ga Superior proto-craton

Craton

A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

extending across Hudson Bay

Hudson Bay

Hudson Bay , sometimes called Hudson's Bay, is a large body of saltwater in northeastern Canada. It drains a very large area, about , that includes parts of Ontario, Quebec, Saskatchewan, Alberta, most of Manitoba, southeastern Nunavut, as well as parts of North Dakota, South Dakota, Minnesota,...

into the North Caribou Terrane

Terrane

of northwestern Ontario. Remnants of a 3.0-2.8 Ga proto-craton

Craton

extend from Manitoba to Ungava with mainly TTG

Tonalite-Trondhjemite-Granodiorite

Tonalite–trondhjemite–granodiorite series are an aggregation of rocks that are formed by melting of hydrous mafic crust at high pressure. It is widely accepted that most Archaean granite–greenstones are dominated by TTG, although Late Archaean terranes, such as in the Yilgarn Craton, are dominated...

and volcanic

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

septa overlain locally by remnants of a komatiite

Komatiite

Komatiite is a type of ultramafic mantle-derived volcanic rock. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content...

-quartzite

Quartzite

Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...

-carbonate

Carbonate

In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....

rift

Rift

In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....

sequence

Sequence

In mathematics, a sequence is an ordered list of objects . Like a set, it contains members , and the number of terms is called the length of the sequence. Unlike a set, order matters, and exactly the same elements can appear multiple times at different positions in the sequence...

. Juvenile volcanic

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

rocks >2.8 Ga may have been incorporated into the proto-craton

Craton

prior to establishment of Andean

Andes

The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...

arcs on its margins (2.75-2.70 Ga), docking (2.71-2.69 Ga) of blocks of 2.75-2.70 Ga juvenile crust and subsequent seaward arc migration through the accreted

Accretion (geology)

Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...

terranes (2.69-2.68 Ga). (Percival, 2006a).

Plate tectonic activity in Superior province is rooted in the granite-greenstone and metasedimentary belts of the southern part of the craton. The northeastern domain of the Minto block evolved during 3.1-2.8, 2.725, and 2.69 Ga events. Western and eastern proto-cratons (3.1-2.8 Ga) rifted about 2.79 Ga to produce an ocean basin that was consumed by subduction at 2.725 Ga. The Leaf River plutonic suite of calc-alkalic

Calc-alkaline

The calc-alkaline magma series is one of two main magma series in igneous rocks, the other magma series being the tholeiitic. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it...

hornblende

Hornblende

Hornblende is a complex inosilicate series of minerals .It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole....

, biotite

Biotite

Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula . More generally, it refers to the dark mica series, primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous endmembers...

, orthopyroxene

Pyroxene

The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...

, and clinopyroxene

Pyroxene

granodiorite

Granodiorite

Granodiorite is an intrusive igneous rock similar to granite, but containing more plagioclase than orthoclase-type feldspar. Officially, it is defined as a phaneritic igneous rock with greater than 20% quartz by volume where at least 65% of the feldspar is plagioclase. It usually contains abundant...

represent magma

Magma

Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

tic arc

Volcanic arc

A volcanic arc is a chain of volcanoes positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic island arc. Generally they result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench...

s built on the protocratons. The intervening Goudalie domain contains fault-bounded fragments of rifted continental crust, rift volcanics, primitive oceanic crust, 2.724 Ga island arc

Volcanic arc

rocks, and a ca. 2.7 Ga back-arc assemblage that marks a suture. Terminal collision at 2.7 Ga led to thickening and crustally-derived granitoid magmatism. A northern proto-Superior craton had continental magmatic arcs built on its eastern and southern flanks in response to west-northwest-directed subduction. Orthogonal convergence in the east produced wide plutonic arcs, in contrast to terrane-accretion tectonics along the southern margin. (Begin et al., 1994)

The microcontinental fragments and juvenile oceanic terranes were amalgamated into a composite Superior superterrane

Terrane

in a series of orogenic events

Orogeny

Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...

between 2.72 and 2.68 Ga and are remnants of the ancient Kenorland

Kenorland

Kenorland was one of the earliest supercontinents on Earth. It is believed to have formed during the Neoarchaean Era ~2.7 billion years ago by the accretion of Neoarchaean cratons and the formation of new continental crust...

(also known as Algoman Orogeny

Algoman orogeny

During the Late Archaen Eon repeated episodes of continental collisions, compressions and subductions generated a mountain-building episode known as the Algoman orogeny; it is known as the Kenoran orogeny in Canada. The Superior province and the Minnesota River Valley microcontinent collided about...

) supercontinent orogeny (~2.7-2.5 Ga). Ca. 2.5 Ga K-Ar

Potassium-argon dating

Potassium–argon dating or K–Ar dating is a radiometric dating method used in geochronology and archeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium into argon . Potassium is a common element found in many materials, such as micas, clay minerals,...

ages from the Superior, Slave

Slave craton

The Slave craton is a Canadian geological formation located in the Northwest Territories and Nunavut. This craton is approximately in size and forms part of the Canadian Shield. It is dominated by ca. 2.73-2.63 Ga greenstones and turbidite sequences and ca. 2.72-2.58 Ga plutonic rock, with large...

, Churchill

Churchill craton

The Churchill craton is the northwest section of the Canadian Shield and stretches from southern Saskatchewan and Alberta to northern Nunavut. It has a very complex geological history punctuated by at least seven distinct regional tectonometamorphic intervals, including many discrete accretionary...

and Nain Provinces, represent coincidental cooling within individual craton

Craton

s carrying separate and distinct accretion

Accretion (geology)

Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...

histories that were not amalgamated until the Paleoproterozoic

Paleoproterozoic

The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...

.

Major metasedimentary

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

belts represent collisional flysch

Flysch

Flysch is a sequence of sedimentary rocks that is deposited in a deep marine facies in the foreland basin of a developing orogen. Flysch is typically deposited during an early stage of the orogenesis. When the orogen evolves the foreland basin becomes shallower and molasse is deposited on top of...

basins

Sedimentary basin

The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification...

fed by detritus

Detritus

Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...

eroded from rising arc and cratonic highlands which were rapidly deformed and metamorphosed

Metamorphic rock

Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

. By 2.670 Ga major tectonic

Tectonics

Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...

activity including strike-slip faulting had waned. However, renewed high temperatures are indicated by Superior-wide leucogranite

Leucogranite

In geology, leucogranites are amongst the youngest intrusions related to anatexis of continental crust anywhere in the world. Leucogranites are commonly found in deformed metapelitic/metagraywacke sequences that have been thrusted over basements during crustal thickening associated with continental...

plutonism and metamorphism

Metamorphism

Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...

(2.66-2.64 Ga), as well as regional deep crustal metamorphism

Metamorphism

and ductile

Ductility

In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized...

, orogen

Orogeny

-parallel flow, correlated with ubiquitous subhorizontal reflectivity. The late activity marks thermal flux

Heat flux

Heat flux or thermal flux is the rate of heat energy transfer through a given surface. The SI derived unit of heat rate is joule per second, or watt. Heat flux is the heat rate per unit area. In SI units, heat flux is measured in W/m2]. Heat rate is a scalar quantity, while heat flux is a vectorial...

possibly related to asthenospheric

Asthenosphere

The asthenosphere is the highly viscous, mechanically weak and ductilely-deforming region of the upper mantle of the Earth...

replacement of gravitationally unstable lithosphere

Lithosphere

The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...

. Seismic

Seismology

Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...

profiles show a mosaic of accretionary

Accretion (geology)

Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...

, magma

Magma

tic and late collapse-related structures. Although similar growth stages are recognized in Proterozoic

Proterozoic

The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...

and Phanerozoic

Phanerozoic

The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...

orogens

Orogeny

, remnants of the rift

Rift

In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....

ogenic

Orogeny

phases of the Wilson cycle

Supercontinent cycle

The supercontinent cycle describes the quasi-periodic aggregation and dispersal of Earth's continental crust. There are varying opinions as to whether the amount of continental crust is increasing, decreasing, or staying about the same, but it is agreed that the Earth's crust is constantly being...

are very poorly preserved in Archean

Archean

The Archean , also spelled Archeozoic or Archæozoic) is a geologic eon before the Paleoproterozoic Era of the Proterozoic Eon, before 2.5 Ga ago. Instead of being based on stratigraphy, this date is defined chronometrically...

cratons. (Percival, 2006)

Northern Superior province

The 3.9-2.8 Ga Northern Superior superterrane (NSS) is at the northern fringe of the Superior Province and is dominated by granitic and gneissic rocks. It consists of an arcuate

River delta

A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...

belt extending from Assean Lake in Manitoba to Porpoise Cove in northern Quebecb (Percival, 2003). Supracrustal

Supracrustal rock

Supracrustal rocks are rocks that were deposited on the existing basement rocks of the crust, hence the name. They may be further metamorphosed from both sedimentary and volcanic rocks....

units in the Assean Lake complex of Manitoba include greywacke with detrital zircon ages up to 3.9 Ga, iron formation and mafic to intermediate volcanic rocks. The ancient rocks have been strongly reworked by granitoid magmatism at 3.2-3.1, 2.85-2.81 and 2.74-2.71 Ga, representing evolution in a continental magmatic arc setting, followed by amphibolite-facies metamorphism at 2.68 and 2.61 Ga that may have resulted from collisions during tectonic assembly. The NSS merged with the North Caribou terrane (3.0-2.8 Ga) at 2.72 Ga. The NSS is bounded to the south by the North Kenyon fault, which juxtaposes it with the Oxford-Stull terrane. Correlation is uncertain between the NSS and units of similar antiquity in the Inukjuak domain of northern Quebec. (Percival, 2006).

It is here that very recently the oldest rocks on earth have been found.

Northern Superior province, Oxford-Stull Lake domain

The Oxford-Stull Lake domain in the northwest contains some of the largest greenstone belts in the province, including the Knee Lake-Gods Lake and Stull Lake belts of Manitoba. Mainly basaltic rocks of the Hayes River assemblage have been dated locally in the 2.83 Ga range, and volcanic rocks of the Oxford Lake assemblage fall between 2.729 and 2.719 Ga. The occurrence of coarse clastic sediments and alkaline volcanic rocks along some faults suggests that they were active during deposition of the Oxford Lake assemblage. Mafic intrusions are common in some belts such as at Big Trout Lake, and have some Nickel-Platinum group potential. Plutons of tonalite, granodiorite and granite underlie large parts of the terrane and yield ages between 2.83 and 2.69 Ga. Isotopic data suggest that the Oxford-Stull terrane evolved in an oceanic setting, possibly on the edge of thinned North Caribou crust until ca. 2.71 Ga, when it was juxtaposed with the NSS along the North Kenyon fault. It is bounded by the Gods Lake Narrows shear zone in the south, bordering the North Carribou terrane. (Percival, 2006).

Northern Superior province, Minto Block

The early Archaean Minto Block of northern Quebec includes the following domains from west to east: the Inukjuak, Tikkerutuk, Lac Minto

Lake Minto

Lake Minto is a lake on western Ungava Peninsula, Nunavik, Quebec, Canada. It has a total surface area of and a net area of ....

, Goudalie Utsalik and the Douglas Harbour Domains. The Inukjuak Domain is distinguished from the domains to the east by significantly older neodymium

Neodymium

Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...

] isotopic ages that range from 4.0-3.0 Ga. The change in isotopic compositions from the Tikkerutuk and Inukjuak Domains is abrupt and not entirely coincident with the suggested aeromagnetic

Magnetometer

A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...

boundary between the two domains. There also appears to be very little addition of juvenile Kenoran

Kenorland

crust (ca. 2.7 Ga) in this domain. This places the Inukjuak domain on par with such old domains such as Assean Lake in northern Manitoba and the Northern Superior Super Terrane (NSS) in northwestern Ontario.

The Inukjuak domain in the west hosts the ancient (ca. 3.825 Ga) Nuvvuagittuq greenstone belt

Nuvvuagittuq greenstone belt

Nuvvuagittuq greenstone belt, also called the Porpoise Cove greenstone belt, is a greenstone belt on the eastern shore of Hudson Bay in northern Quebec, Canada. With an age of about 4.28 billion years, it is the only portion of the Earth's crust known to have formed during the Hadean...

and ca. 3.65 Ga tonalitic gneisses but is dominated by younger plutonic rocks (2.84-2.69 Ga). To the east, the Tikkerutuk domain consists of pyroxene-bearing plutonic rocks, 3.02-2.71 Ga, that merge into the Bienville domain to the south, which is characterized by 2.71-2.69 Ga granite and granodiorite. Farther east, Lac Minto domain contains metasedimentary and derived migmatitic rocks, in addition to 2.76-2.70 Ga pyroxene-bearing plutonic rocks. The Goudalie domain forms a central spine consisting of relatively large volcano-sedimentary belts (2.88-2.71 Ga) with sparse 3.0 Ga tonalite and abundant pyroxene-bearing plutons (2.73-2.68 Ga). In the east-central Minto, the Utsalik domain consists of highly magnetic, 2.74-2.69 Ga pyroxene-bearing plutonic rocks with model ages in the 3.0 Ga range. To the northeast, Douglas Harbour domain consists of two large charnockitic massifs (2.74-2.73 Ga) within an older (2.88-2.75 Ga) tonalitic complex. Deformation and high-grade metamorphism in the western Minto block is attributed to collisional processes. (Percival, 2006).

The Minto block is dominated by mantle-derived, crustally contaminated granitoid

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

-charnockitic

Charnockite

Charnockite is applied to any orthopyroxene-bearing granite, composed mainly of quartz, perthite or antiperthite and orthopyroxene , as an end-member of the charnockite series.-Charnockite series:...

massif

Massif

In geology, a massif is a section of a planet's crust that is demarcated by faults or flexures. In the movement of the crust, a massif tends to retain its internal structure while being displaced as a whole...

s separated by sinuous greenstone belt

Greenstone belt

s that preserve a record of ocean

Ocean

An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

ic (2.84-2.77 Ga) and continent

Continent

A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...

al (2.76-2.70 Ga) volcanism

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

, sedimentation

Sedimentary rock

and pluton

Intrusion

ism. In the northeastern Superior portion of the Minto Block this is interpreted as Andean

Andes

marginal roots and ocean

Ocean

ic arcs

Volcanic arc

with terrane assembly between ~2.73 and 2.69 GA. The tonalite

Tonalite

Tonalite is an igneous, plutonic rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase with 10% or less alkali feldspar. Quartz is present as more than 20% of the rock. Amphiboles and pyroxenes are common accessory minerals.In older references tonalite is...

-trondjhemites are aged at 3 GA. (Bedard, 2001). Granitoid rocks are emplaced in continental arc settings and juxtaposed during a ca. 2.7 Ga arc - continent collision. Regional metamorphism related to emplacement of a hot arc terrane had minor effect on the anhydrous

Anhydrite

Anhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...

(charnockitic) plutons. Archean

Archean

tonalite

Tonalite

-trondjhemites, enderbite

Enderbite

In geology, enderbite is primarily an igneous rock of the charnockite series, consisting essentially of quartz, antiperthite , orthopyroxene and magnetite, and is equivalent to an orthopyroxene bearing tonalite. It is named for its occurrence in Enderby Land, Antarctica.-References:Classification...

s, granodiorite

Granodiorite

granite

Granite

s, and clinopyroxene

Pyroxene

or orthopyroxene

Pyroxene

-bearing hornblende

Hornblende

Hornblende is a complex inosilicate series of minerals .It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole....

-tonalite

Tonalite

(most retain igneous microtextures). Outcrop-scale structures such as melt-filled shear zones and deformed intraplutonic dikes imply that deformation was synmagmatic. The multiple embayments are interpreted as magmatic resorption structures. Since epidote and muscovite stabilities are pressure dependent, these resorption structures suggest that magmas ascended as crystal-charged mushes. Amphibolite

Amphibolite

Amphibolite is the name given to a rock consisting mainly of hornblende amphibole, the use of the term being restricted, however, to metamorphic rocks. The modern terminology for a holocrystalline plutonic igneous rocks composed primarily of hornblende amphibole is a hornblendite, which are...

-grade supercrustal rocks are associated with tonalite-trondhjemite or granite-granodiorite plutons, while granulite-grade belts are associated with enderbite and clinopyroxene or orthopyroxene-bearing tonalite. This dichotomy suggests that metamorphism of supercrustal rocks reflects localized equilibration with adjacent plutons rather than orogenesis. (Bedard, 2003).

According to a study by Percival and Skulski (2006): Rare older pluton

Intrusion

ic bodies (3.12-2.87 Ga), coupled with inherited zircon

Zircon

Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...

and low epsilon

Epsilon

Epsilon is the fifth letter of the Greek alphabet, corresponding phonetically to a close-mid front unrounded vowel . In the system of Greek numerals it has a value of 5. It was derived from the Phoenician letter He...

Nd values in younger pluton

Intrusion

s, attest to the presence of sial

Sial

In geology, the sial is the upper layer of the Earth's crust made of rocks rich in silicates and aluminium minerals. It is sometimes equated with the continental crust because it is absent in the wide oceanic basins, but "sial" is a geochemical term rather than a plate tectonic term.Geologists...

ic crust

Crust (geology)

In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

inferred to have been juxtaposed with oceanic assemblages ca. 2.77 Ga. Continent

Continent

al calc-alkaline

Calc-alkaline

magma

Magma

tism produced granodiorite

Granodiorite

batholith

Batholith

A batholith is a large emplacement of igneous intrusive rock that forms from cooled magma deep in the Earth's crust...

s ca. 2.72 Ga, followed by widespread deformation, metamorphism

Metamorphism

and crustal

Crust (geology)

In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

magma

Magma

tism at 2.70-2.69 Ga. Early (ca. 2.81 Ga) deformation is recorded locally in ocean

Ocean

ic assemblages, but the main polyphase regional events postdate deposition

Deposition (geology)

Deposition is the geological process by which material is added to a landform or land mass. Fluids such as wind and water, as well as sediment flowing via gravity, transport previously eroded sediment, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of...

of unconformable

Unconformity

An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...

conglomerate-greywacke

Greywacke

Greywacke or Graywacke is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found...

+/- iron formation sequences loosely constrained at <2.77, <2.75 and <2.72 Ga. Both basement and cover sequences were deformed into steeply-dipping, NW-trending belts, metamorphosed to low-P amphibolite

Amphibolite

facies

Facies

In geology, facies are a body of rock with specified characteristics. Ideally, a facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment....

, and variably affected by open E-W cross-folds. Monazite

Monazite

Monazite is a reddish-brown phosphate mineral containing rare earth metals. It occurs usually in small isolated crystals. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:...

U-Pb

Radiometric dating

ages of upper amphibolite

Amphibolite

to granulite

Granulite

Granulites are medium to coarse–grained metamorphic rocks that have experienced high temperature metamorphism, composed mainly of feldspars sometimes associated with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure...

facies

Facies

gneiss

Gneiss

Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...

es record metamorphism

Metamorphism

at 2.70-2.67 Ga, indicating protracted metamorphism

Metamorphism

accompanying plutonism

Plutonism

Plutonism is the geologic theory that the rocks forming the Earth were formed in fire by volcanic activity, with a continuing gradual process of weathering and erosion wearing away rocks, which were then deposited on the sea bed, re-formed into layers of sedimentary rock by heat and pressure, and...

, whereas those in lower-grade schist

Schist

The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...

s range from 2.69 to 2.62 Ga, possibly reflecting continued monazite

Monazite

growth during late structural events. Late, possibly hydrothermal, disturbances are also indicated in lower-T isotopic

Isotope

Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

systems, including U-Pb

Radiometric dating

titanite

Titanite

Titanite, or sphene , is a calcium titanium nesosilicate mineral, CaTiSiO5. Trace impurities of iron and aluminium are typically present...

(2.68-2.56 Ga), Ar/Ar

Radiometric dating

hornblende

Hornblende

Hornblende is a complex inosilicate series of minerals .It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole....

(2.64 Ga) and rutile

Rutile

Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...

(2.50 Ga)

The main collisional-metamorphic

Metamorphic rock

event (ca. 2.70 Ga) in the Minto block coincides with the initiation of 2.70-2.69 Ga accretionary

Accretion (geology)

Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...

events recognized in the southwestern Superior province. Similarly, post-amalgamation events observed in the western Superior (2.68-2.63 Ga deep-crustal metamorphism

Metamorphism

and leucogranite

Leucogranite

plutonism

Plutonism

) are evident in the Minto block as protracted metamorphism

Metamorphism

and deformation, isotopic

Isotope

resetting and renewed mantle-derived (alkalic) magma

Magma

tism, suggesting a pan-Superior extent, possibly driven by foundering of mantle

Mantle (geology)

The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....

lithosphere

Lithosphere

on the 1000 km scale." (Percival and Skulski, 2006)

Western Superior province, Inukjuak domain

The Inukjuak domain is the western-most domain in the Superior province. It is distinguished from the domains to the east by its significantly older Nd

Neodymium

isotopic

Isotope

compositions of 4.0-3.0 Ga. The change in isotopic compositions from the Tikkerutuk and Inukjuak Domains is abrupt and is not entirely coincident with the suggested aeromagnetic

Magnetometer

A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...

boundary between the two domains. There appears to be an addition of juvenile Kenoran

Kenorland

crust (ca. 2.7 Ga) in this domain. This places the Inukjuak domain on par with the Assean Lake domain in northern Manitoba

Manitoba

and the Northern Superior super terrane in northwestern Ontario (Stevenson, 2003). The orogenic framework for the western Superior Province appears to continue northeastward into the Minto block. In particular, the Uchian orogeny (2.70 Ga) of high-grade metamorphism in the western Minto block is comparable to that of Alpine-style mountain belts in the northeast.

Tikkerutuk domain

The Tikkerutuk domain represents a north-trending, 50-km wide calc-alkaline

Calc-alkaline

magma

Magma

tic arc with ages between 2.71 and 2.70 Ga, that extends southward into the Bienville subprovince on the basis of aeromagnetic anomalies

Magnetometer

A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...

and geochronology

Geochronology

. Zircon

Zircon

inheritance ages indicate that the Tikkerutuk area was built upon antecedent arcs of 2.84, 2.77 and 2.725 Ga. (Percival et al., 2001).

Goudalie and Qualluviartuuq domains

A tonalitic

Tonalite

rock from the southern Goudalie domain with an age of 2.833 Ga supports a linkage to 2.84-2.83 Ga units of the Qalluviartuuq domain along the strike

Strike and dip

Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented...

to the north. (Percival et al., 2001).

Utsailk domain

The Utsailk domain is made up of pyroxene

Pyroxene

and hornblende

Hornblende

Hornblende is a complex inosilicate series of minerals .It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole....

-bearing Leaf River pluton

Intrusion

s with consistent 2.725-2.723 Ga ages and local inheritance of 2.82 and 2.77 Ga. However, the southern extension of Utsalik domain contains pyroxene-bearing granodiorite

Granodiorite

s both older (2.762 Ga) and younger (2.692 Ga) than the Leaf River suite. (Percival et al., 2001).

Northeast Superior province, Douglas Harbour domain

The Douglas Harbour domain is the eastern-most domain in the northeast Superior province (3.1 to 2.7 Ga) and lies east of Hudson and James Bays. It is dominated by 2.78-2.69 Ga plutonic rocks emplaced into older crust (3.8-2.83 Ga). U-Pb

Radiometric dating

ages obtained through SHRIMP

SHRIMP

analyses of zircon

Zircon

samples reveal a history of successive

Succession (geology)

A succession, in geology, is a group of rock units or strata that succeed one another in chronological order. Rock successions are often easily seen on exposed sections of a geological column or wall.Based on uncomfortable or comfortable succession....

magma

Magma

tism between 3.07 and 2.70 Ga, followed by metamorphism

Metamorphism

, emplacement

Intrusion

of crustally

Crust (geology)

In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

-derived granite

Granite

s (2.702-2.685 Ga), and late hydrothermal

Hydrothermal circulation

Hydrothermal circulation in its most general sense is the circulation of hot water; 'hydros' in the Greek meaning water and 'thermos' meaning heat. Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust...

events (ca. 2.65 Ga). In the northeastern Minto block of the Douglas Harbour domain, dated localities to the northeast are 2.87 Ga. The Leaf River suite

Suite

In music, a suite is an ordered set of instrumental or orchestral pieces normally performed in a concert setting rather than as accompaniment; they may be extracts from an opera, ballet , or incidental music to a play or film , or they may be entirely original movements .In the...

is dated at 3.01 Ga and the tonalitic

Tonalite

crust

Crust (geology)

In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

contains 2.734-2.725 Ga granodioritic

Granodiorite

pluton

Intrusion

s. (Percival et al., 2001).

To the east of the Douglas Harbour domain are the Utsalik, Goudalie, Lac Minto and Tikkerutuk Domains that yield almost exclusively late Archean

Archean

ages of 3.0 to 2.7 Ga. This range of ages is evidence for recycling of earlier crustal lithologies

Petrology

Petrology is the branch of geology that studies rocks, and the conditions in which rocks form....

by younger orogenic

Orogeny

events and reflects melting of mid-Archean lithologies during the emplacement of juvenile late Archean magma

Magma

s.

The Douglas Harbour Domain includes two TTG suites: the Faribault-Thury West and the Faribault-Thury East. Both contain embedded KT greenstone belts. The tonalities

Tonalite

display elevated La/Yb ratios and are enriched in LILE (Ba-Rb-K-Cs-U-Th-Pb) with Sr-Pb anomalies and B Nb-Ta-Ti anomalies. This implies melting rates of subducted oceanic crust, but could also be the result of melting at the base of a basaltic plateau in the presence of garnet

Garnet

The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...

and rutile

Rutile

Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...

. Trace element models collectively imply that the evolution of trondhjemitic tonalite resulted from hornblende-dominated crystallization and is probably not caused by variable rates of partial melting in the subducted oceanic crust. The repetitive process of catalytic delamination explains the synchronous genesis of Archean crust and mantle, explains progressive crustal maturation (tonalite to granite transition), and simplifies tectonic models because all Archean magmatic suites can be generated in a single environment. (Bedard, 2005).

Eastern Superior province, Abitibi subprovince

The Abitibi subprovince tectono-stratigraphic evolution is explained in terms of oceanic geodynamic settings from plateau, to arc and rift environments. The Abitibi subprovince has been subdivided into three domains with overlapping tectonostratigraphic histories. In the northern Abitibi, volcanic assemblages are mainly 2.735-2.72 Ga and associated with layered intrusions, whereas volcanic rocks of 2.71-2.695 Ga are restricted to the southern Abitibi. The southern Abitibi has relatively young sedimentary-volcanic deposits including ca. 2.69 Ga greywackes of the Porcupine Group and 2.677-2.673 Ga conglomeratic and alkaline volcanic rocks of the Timiskaming Group. The central zone is dominated by plutonic rocks.

The Opatica belt in the south divides the Abitibi belt to the north and consists of units ranging from 2.82 Ga tonalite, through 2.77-2.70 Ga. tonalite-granodiorite, to 2.68 Ga granite and pegmatite. Polyphase deformation includes early, west-verging shear zones (<2.72 Ga), overprinted by 2.69-2.68 Ga south-vergent structures.

The Opinaca belt is characterized by metagreywacke, derived migmatite and granite. Polydeformed schists occur at the belt margins, whereas the interior portions are metamorphosed to amphibolite and granulite facies. These rocks are cut by the 2.67 Ga Broadback River granite. (Percival, 2006).

Western Superior province, North Caribou terrane

The North Caribou terrane is the largest domain of the Superior Province. The North Caribou terrane sustained protracted reworking that culminated with 2.7 Ga Kenoran Orogeny. Prior to the 2.99 Ga Balmer volcanism, the North Caribou protocraton comprised a 3.02 Ga island arc mafic-felsic volcanic crust and a 3.01 to 3.0 Ga tonalitic crust. The Balmer volcanic-plutonic substrate is a voluminous mafic-ultramafic submarine sequence with intercalated komatiite and basalt that has been interpreted to be the product of a mantle plume in which the hot, deep, mantle-derived axis produced komatiite magma that mixed with asthenospheric mantle to produce tholeiitic basalt magma. The north trending calc-alkalic volcanic centers may reflect a contiguous continental arc built during eastward subduction below the western margin of the North Caribou terrane at ca. 2.94 to 2.92 Ga. At ca. 2.9 Ga volcanism was widespread across the North Caribou terrane. (Parker, 2001).

The following study is mostly from Percival (2006): The basement consists of ca. 3.0 Ga tonalitic

Tonalite

and juvenile plutonic and minor volcanic belts, upon which were deposited early rift-related (2.98-2.85 Ga) and younger (2.85-2.71 Ga) arc sequences. It was severely reworked by continental arc magmatism at 2.75-2.70 Ga. The terrane has wide transitional margins in both the north and south and an unconformable

Unconformity

platform/rift succession of quartzite

Quartzite

, carbonate

Carbonate rock

Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite and dolostone, which is composed of the mineral dolomite .Calcite can be either dissolved by groundwater or precipitated by...

, banded iron formation

Banded iron formation

Banded iron formations are distinctive units of sedimentary rock that are almost always of Precambrian age. A typical BIF consists of repeated, thin layers of iron oxides, either magnetite or hematite , alternating with bands of iron-poor shale and chert...

and komatiite

Komatiite

Komatiite is a type of ultramafic mantle-derived volcanic rock. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content...

. The unconformity

Unconformity

is exposed between the tonalitic basement and the overlying Lewis-Storey rift assemblage, where tectonically

Tectonics

juxtaposed mafic

Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...

volcanic

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

rocks are a common feature.

The core of the North Caribou terrane lies to the north and consists of a 2.745-2.69 Ga Neoarchean

Neoarchean

pluton

Intrusion

called the Berens River Plutonic Complex. It is intruded by widespread tonalitic, dioritic, granodioritic and granitic plutons at depths ranging from 18 to 10 km. Remnants of ca. 3.0 Ga tonalite and supracrustal rock

Supracrustal rock

Supracrustal rocks are rocks that were deposited on the existing basement rocks of the crust, hence the name. They may be further metamorphosed from both sedimentary and volcanic rocks....

s are sporadically preserved through the younger magmatism. Within the greenstone belts, thin packages of quartz arenite-carbonate-komatiite have variably been interpreted as platformal cover strata and plume-related rift deposits. Evidence of early (>2.87 Ga) deformation is recorded in the North Caribou greenstone belt.

In the north, the Munro Lake and Island Lake terranes are inferred to have been formed on thinned crust of the North Caribou terrane. These regions are dominated by plutonic rocks with several small supracrustal belts. In the Ponask Lake area near the Ontario-Manitoba border, detrital zircons from a quartzite-komatiite sequence indicate a depositional age of <2.865 Ga that infer a breakup at the northern North Caribou margin. The main phase of plutonism was followed by localized strain and shear-zone-hosted gold mineralization, particularly in the Little Stull Lake area near the Ontario-Manitoba border.

The North Caribou terrane collided with the Northern Superior superterrane (NSS) between 2.72 and 2.71 Ga on the north, and the Winnipeg River terrane to the south, trapping the English River flysch belt in between at 2.70 and 2.69 Ga. Docking of the juvenile western Wabigoon subprovince occurred at a similar time, followed by collision of the Abitibi-Wawa subprovince and syntectonic Quetico sedimentation (2.698-2690 Ga).

The western margin of the North Caribou terrane and the Superior province is the ~3.0 Ga Lewis-Storey rift

Rift

In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....

assemblage, a sedimentary

Sedimentary rock

-volcanic

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

sequence

Sequence (geology)

A sequence in geology refers to a sequence of geological events, processes, or rocks, arranged in chronological order.A rock stratigraphical sequence is a geographical, or lithostratigraphic, discrete unit greater than a group or supergroup rank, and traceable over large areas of a continent...

in eastern Lake Winnipeg

Lake Winnipeg

Lake Winnipeg is a large, lake in central North America, in the province of Manitoba, Canada, with its southern tip about north of the city of Winnipeg...

. The East Shore Plutonic Complex, adjacent and east of the Lewis-Storey rift

Rift

In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....

, contain two enclave

Enclave and exclave

In political geography, an enclave is a territory whose geographical boundaries lie entirely within the boundaries of another territory.An exclave, on the other hand, is a territory legally or politically attached to another territory with which it is not physically contiguous.These are two...

s of fine-grained

Granularity

Granularity is the extent to which a system is broken down into small parts, either the system itself or its description or observation. It is the "extent to which a larger entity is subdivided...

schist

Schist

ose sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

and quartz diorite

Quartz diorite

Quartz diorite is an igneous, plutonic rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase with 10% or less potassium feldspar. Quartz is present at between 5 to 20% of the rock. Biotite, amphiboles and pyroxenes are common dark accessory...

porphyroclast

Porphyroclast

thumb|350px|right|A [[mylonite]] showing a number of porphyroclasts: a clear red [[garnet]] left in the picture while smaller white [[feldspar]] porphyroclasts can be found all over...

ic gneiss

Gneiss

within hornblende

Hornblende

Hornblende is a complex inosilicate series of minerals .It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole....

tonalite

Tonalite

that may represent remnants of an ancient supracrustal sequence. These rocks are similar to the 3.0-2.92 Ga quartzite, iron-formations, and komatiite at Wallace Lake and predate the emplacement of the East Shore Plutonic Complex. (Percival, 2006).

The southern margin of the North Caribou terrane is the Uchi subprovince. Aeromagnetic trends show the complex structural configuration of supracrustal rocks in a chain of greenstone belts separated by large lobes of plutonic material. The stratigraphic record preserved in the Rice Lake, Wallace Lake, Red Lake, Confederation Lake, Meen-Dempster, Pickle Lake and Fort Hope greenstone belts reflects a history of rifting beginning ca. 2.99 Ga, followed by a protracted history of continental arc magmatism at 2.94-2.91, 2.90-2.89, 2.85 and 2.75-2.72 Ga. Several deformation episodes are recognized within the greenstone belts, including pre-2.74, 2.73, 2.72 and 2.70 Ga events that have produced composite, steep, east-trending fabrics. Coarse clastic sedimentary rocks generally represent the youngest strata along the southern margin of the North Caribou terrane. These sequences contain detrital zircons as young as 2.703 Ga, and may be facies equivalents of the marine greywacke turbidites of the English River subprovince to the south. (Percival, 2006).

The Gray Point sequence at the south margin, along Wanipigow Lake, is a basalt

Basalt

Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

~1000 meter thick unit of aphyric

Phenocryst

thumb|right|300px|[[Granite]]s often have large [[feldspar|feldspatic]] phenocrysts. This granite, from the [[Switzerland|Swiss]] side of the [[Mont Blanc]] massif, has large white [[plagioclase]] phenocrysts, [[triclinic]] [[mineral]]s that give [[trapezium|trapezoid]] shapes when cut through)...

, nonvesicular

Vesicular texture

Vesicular texture is a volcanic rock texture characterised by a rock being pitted with many cavities at its surface and inside. The texture is often found in extrusive aphanitic, or glassy, igneous rock...

pillow

Pillow lava

Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in...

basalt and basaltic andesite

Andesite

flows with some hyaloclastite

Hyaloclastite

Hyaloclastite is a hydrated tuff-like breccia rich in black volcanic glass, formed during volcanic eruptions under water, under ice or where subaerial flows reach the sea or other bodies of water. It has the appearance of angular flat fragments sized between a millimeter to few centimeters...

, overlain by 700–1200 meters of massive porphyritic

Porphyry (geology)

Porphyry is a variety of igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a fine-grained feldspathic matrix or groundmass. The larger crystals are called phenocrysts...

basalt (pyroxene-plagioclase-phyric

Phenocryst

) and basaltic andesite flows. Using N-MORB

Mid-ocean ridge

A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...

compositional data and Th/Nb

Radiometric dating

ratios, the Gray Point sequence represents an oceanic plateau

Oceanic plateau

An oceanic plateau is a large, relatively flat submarine region that rises well above the level of the ambient seabed. While many oceanic plateaus are composed of continental crust, and often form a step interrupting the continental slope, some plateaus are undersea remnants of large igneous...

setting. (Balles, 2001)

The Trout bay assemblage of the Red Lake greenstone belt at the south margin of the North Caribou terrane may represent a back arc or oceanic plateau crust, tectonically juxtaposed with the North caribou terrane between 2.853 and 2.735 Ga. A final phase of ca. 2.73 Ga Andean-style arc magmatism is recorded at Red Lake by the Grave sequence and throughout the Berens arc. At ca. 2.718, continued subduction in the Red Lake and Birch-Uchi belts culminated in collision of the Winnipeg River terrane during the Uchian phase of the Kenoran Orogeny. This was a protracted event involving brittle-ductile reworking during extensive hydrothermal alteration and metamorphism that ultimately led to syn- to late-tectonic precipitation of gold to form one of Canada's foremost gold mining camps. (Parker, 2001).

Northwestern Superior Province, English River subprovince

The English River subprovince (ERS) is thought to mark the suture between the North Caribou and Winnipeg River terranes. The English River-Winnipeg River boundary separates dominantly metasedimentary rocks of the English River subprovince from mainly metaplutonic rocks of the Winnipeg River subprovince to the south. The east-trending Sydney Lake-Lake St. Joseph fault (450 km strike length) separates rocks of the North Caribou margin to the north from metasedimentary schists and migmatitic rocks of the English River subprovince to the south. The ERS also displays high metamorphic grade, and a prominent east-west structural grain.

Between the two subprovinces lies the metavolcanic Bird River subprovince in eastern Manitoba, with mafic intrusion-hosted Cr deposits, and its narrow eastward extension, the Separation Lake belt. These belts consist dominantly of largely juvenile mafic rocks with ages of ca. 2.78 to 2.73 Ga. Depositional contacts have been inferred between English River clastic rocks and both volcanic strata of the Separation Lake belt and gneissic tonalitic basement to the east. The Separation Lake belt appears to be in tectonic and intrusive contact with granitic rocks of the Winnipeg River subprovince to the south. The boundary zone is a focus for emplacement of ca. 2.646 Ga rare metal pegmatites, including the Tanco and Separation Rapids fields. (Percival, 2006).

Based on the turbiditic nature of its chemically immature greywackes, the setting of the English River has traditionally been considered a fore-arc basin or accretionary prism. Detrital zircon studies indicate that the sediments were deposited after arc activity in adjacent volcanic belts and close to the time of collisional orogeny, thereby implying an origin as a syn-orogenic flysch basin. The small Melchett Lake greenstone belt in the central English River subprovince comprises a juvenile, ca. 2.723 Ga calc-alkaline volcanic sequence, possibly correlative with the Lake St. Joseph assemblage to the north. Metamorphic conditions in the English River range from middle amphibolite facies near the margins, to low-pressure granulite facies, coinciding with widespread generation of migmatite and diatexite at 2.691 Ga. The main tectonothermal event was followed by a second thermal pulse at 2.669 Ga, intrusion of ca. 2.65 Ga pegmatites, and growth of hydrothermal minerals. (Percival, 2006).

Northwestern Superior Province, Winnipeg River terrane

The following study is from Percival (2006): The Winnipeg River terrane is a collective term used to describe the plutonic domain exposed north and east of the western Wabigoon subprovince. It consists of two main elements: 1) the Winnipeg River subprovince proper, a >500 km long terrane composed of Mesoarchean metaplutonic rocks variably intruded by Neoarchean plutons; and 2) a largely Neoarchean plutonic domain, formerly referred to as the central Wabigoon granitoid complex and Wabigoon diapiric axis, that contains scattered remnants of Mesoarchean crust. The 3.4 Ga Winnipeg River terrane stands apart from the Northern Superior and North Caribou terranes to the north and the Marmion domain to the south. It also carries a distinct record of magmatic and structural events, typically characterized by amphibolite to granulite facies metamorphism.

The Mesoarchean tonalitic rocks are the oldest units recognized, and include both 3.32-3.05 Ga gneissic and 3.04 Ga foliated varieties. Similar isotopic signatures characterize younger (2.88, 2.84 and 2.83 Ga) tonalitic rocks, reflecting the antiquity of the basement. Mafic volcanic belts older than ca. 3.0 Ga and ca. 2.93-2.88 Ga volcanic rocks in the eastern Savant-Sturgeon greenstone belt are also considered part of the Winnipeg River terrane. Significant pulses of Neoarchean tonalite-granodiorite magmatism occurred at 2.715-2.705 Ga followed by emplacement of granites at ca. 2.70-2.69 Ga. A complex Neoarchean structural-metamorphic history began with deposition of metasedimentary rocks after 2.72 Ga. The supracrustal rocks and older gneisses were folded between 2.717 and 2.713 Ga, prior to syntectonic injection of 2.713-2.707 Ga tonalite and granodiorite sheets accompanying horizontal extensional deformation. Upright folding during deformation took place after 2.705 Ga, and younger upright folds indicate a period of north-south compression associated with emplacement of 2.695-2.685 Ga granite and granodiorite. Late pegmatites and granites intruded during a dextral transpressive regime.

The eastern Winnipeg River terrane hosts east-trending greenstone belts including the Caribou Lake, Obonga, Garden Lake and Heaven Lake belts that have ages >3.075 to 2.703 Ga . Dated granitoid units have ages in the range 3.075-2.680 ga and some of the oldest rocks have eNd values of -1 to + 1, suggesting derivation from even older crustal sources. At least five generations of Neoarchean structures have been recognized in complex tonalitic gneisses. The Marmion domain, formerly included as part of the south-central Wabigoon subprovince, is now recognized to consist of 3.01-2.999 Ga tonalite, upon which the Steep Rock, Finlayson Lake and Lumby Lake greenstone belts formed between 2.99 and 2.78 Ga.

A period of continental arc magmatism in the Winnipeg River subprovince (2.72-2.70 Ga) is attributed to north- and eastward subduction of oceanic rocks followed by 2.708-2.701 Ga deformation. Post-2.704 Ga regional deformation across the Wabigoon outlasted deposition of syncollisional coarse clastic sedimentary overlap sequences. Late faults with both strike-slip and dip-slip motion define the present subprovince boundary.

Northwestern Superior province, Wabigoon-Winnipeg River superterrane

Amalgamation of the Wabigoon subprovince (2.77-2.72 Ga) with Winnipeg River (3.5-2.8 Ga) subprovince in the western Superior province occurred ca. 2.715 Ga. During the Uchian orogeny (ca. 2.70 Ga) the Wabigoon-Winnipeg River superterrane collided with and was subducted beneath the active southern margin of the composite Superior superterrane (CSS), resulting in deposition and burial of the English River turbidite wedge. Collision between the largely juvenile Abitibi-Wawa subprovince and its subduction beneath the CSS resulted in the 2.69 Ga Shebandowanian orogeny, including deposition and burial of the Quetico turbiditic prism. The final, ca. 2.68 Ga Minnesotan orogeny is responsible for collision and underthrusting of the Minnesota River Valley terrane (3.6-2.7 Ga) beneath the CSS. This orogeny was accompanied by the intrusion of alkalic suites that range in composition from syenite

Syenite

Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or...

to nepheline

Nepheline

Nepheline, also called nephelite , is a feldspathoid: a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites...

syenite

Syenite

and rare carbonitic compositions, and their parental magmas formed by smaller degrees of partial melting of a large-ion lithophile

Lithophile

Lithophiles are micro-organisms that can live within the pore interstices of sedimentary and even igneous rocks to depths of several kilometers....

elements (LILE)-enriched upper mantle

Mantle (geology)

. The involvement of a deeper asthenospheric

Asthenosphere

The asthenosphere is the highly viscous, mechanically weak and ductilely-deforming region of the upper mantle of the Earth...

source in the petrogenesis

Petrogenesis

Petrogenesis, also known as petrogeny, is a branch of petrology dealing with the origin of igneous rocks. Petrology is the branch of geology dealing with the origin, occurrence, structure and history of igneous, metamorphic, and sedimentary rocks....

of these late mantle-derived magmas has been inferred by many workers. The involvement of a sublithospheric

Lithosphere

source is indicated by the Beaverhouse Lake intrusion, which is distinct in its lack of negative Nb-Ta anomalies in primitive-mantle-normalized diagrams. Instead, its chemical characteristics resemble those of present-day ocean-island basalts and imply that it is related to hotspots

Hotspot (geology)

The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...

. The upwelling of asthenospheric mantle could have provided heat for extensive magmatism in southwestern Superior province by melting of metasomatized lithospheric mantle." (Hattori, 2001).

Southwestern Superior province, Wabigoon subprovince

The following study is from Percival (2006): The Wabigoon subprovince has long been recognized as a composite terrane comprising volcanic-dominated domains and consists of distinct western and eastern segments. The Western Wabigoon subprovince is dominated by mafic volcanic rocks with large tonalitic plutons. Volcanic rocks range in composition from tholeiitic to calc-alkaline, and are interpreted to represent ocean floor or plateau and arc environments, respectively. Most of the preserved volcanic rocks were deposited between ca. 2.745 and 2.72 Ga, with rare older rocks, such as the 2.775 Ga Fourbay assemblage of oceanic plateau affinity and minor younger (2.713-2.70 Ga) volcanic-sedimentary sequences. Plutonic rocks range from broadly synvolcanic batholiths composed of tonalite-diorite-gabbro (ca. 2.735-2.72 Ga) to younger granodiorite batholiths and plutons (ca. 2.710 Ga), monzodiorite plutons of sanukitoid affinity (ca. 2.698-2.690 Ga), and plutons and batholiths of monzogranite (2.69-2.66 Ga). Immature clastic metasedimentary sequences are preserved in narrow belts within volcanic sequences. They are commonly younger than the volcanic rocks with local unconformable relationships and geochronological constraints indicating deposition between ca. 2.711 and <2.702 Ga. Detrital zircons >3 Ga indicate old components in source regions. At least two phases of deformation affected supracrustal rocks of the western Wabigoon subprovince, with apparent diachroneity in the onset of deformation from ca. 2.709 Ga in the Lake of the Woods area, to ca. 2.700 Ga in the Sioux Lookout-Savant area in the east. These events involved at least local tectonic inversion, through thrust imbrication and possible formation of nappe-like structures.

The Sturgeon-Savant greenstone belt consists of several tectonostratigraphic

Tectonostratigraphy

In geology, tectonostratigraphy refers either to rock sequences in which large-scale layering is caused by the stacking of thrust sheets or nappes in areas of thrust tectonics or the effects of tectonics on lithostratigraphy.-Tectonically formed stratigraphy:...

packages, including the previously described Jutten assemblage, the ca. 2.775 Ga Fourbay assemblage, and 2.745-2.735 Ga sequence, the Handy Lake and South Sturgeon assemblages. The 2.735 Ga Lewis Lake batholith may have provided the heat source for seawater convection and massive sulfide mineralization. Younger (ca. 2.718 Ga), high Fe, Ti basalt and minor dacite of the central Sturgeon assemblage represent a rifted arc sequence. Associated sedimentary rocks contain both arc (2.745-2.730 Ga) and continental (3.1-2.8 Ga) detritus. Two younger sedimentary sequences complete the stratigraphic record: 1) greywacke-iron formation (ca. 2.705 Ga) of the Warclub assemblage; and 2) sandstone and arkose (<2.698 Ga) of the syn-orogenic Ament Bay assemblage. Two sets of ductile structures postdate <2.704 Ga rocks: 1) north-trending upright folds; and 2) east-trending upright folds and penetrative foliation. Pre-D1 folds have been inferred locally.

The Eastern Wabigoon subprovince is a composite terrane with greenstone belts and intervening granitoid plutons that show variable Mesoarchean (Winnipeg River and Marmion) and oceanic affinity. In the northwest part of the belt the 3.0-2.92 Ga Toronto and Tashota assemblages may represent a continental margin sequence built on the Winnipeg River terrane. Calc-alkaline rocks of the 2.74 Ga Marshall assemblage have small massive sulfide deposits. The central part of the belt is dominated by rocks of oceanic affinity including tholeiitic juvenile pillowed basalt of the 2.78-2.738 Ga Onaman and Willet assemblages and the overlying calc-alkaline 2.725-2.715 Ga Metcalfe-Venus assemblage. Parts of these assemblages contain widespread hydrothermal alteration and host small massive sulfide deposits. Across the southern part of the eastern Wabigoon domain, the 2.78-2.74 Ga calc-alkaline Elmhirst-Rickaby assemblage is possibly built on Marmion-age substrate. Unconformably overlying clastic rocks (Albert-Gledhill and Conglomerate assemblages) were deposited after ca. 2.71 Ga. At least two deformation events affected the eastern Wabigoon domain: east-striking structures (<2.706 Ga) and east-striking, dextral transpressive shear zones. The 2.694 Ga Deeds Lake pluton provides a lower limit on the age of D2 deformation.

Southwestern Superior province, Quetico subprovince

The Quetico-western Wabigoon boundary is well defined as the Seine River-Rainy Lake fault. The Wabigoon-Quetico interface is also marked sporadically by <2.692 Ga coarse clastic rocks of the Seine assemblage that were deposited in transtensional basins or delta fan environments.

The following study is from Percival (2006): The Quetico subprovince consists dominantly of greywacke, derived migmatite and granite. No stratigraphic sequence has been established within the steeply dipping, polydeformed and variably metamorphosed sedimentary succession; however, younging directions are dominantly to the north. Depositional age constraints indicate slightly older ages for the northern Quetico (<2.698>2.696 Ga) than for the south (<2.692 Ga).

Several plutonic suites cut metasedimentary units, including early (2.696 Ga) tonalite. An early deformation event predated emplacement of a chain of Alaskan type mafic-ultramafic intrusions in the northern Quetico. They are associated with alkaline plutons including nepheline syenite and carbonatite with ages in the range 2.69-2.68 Ga and geochemical affinities with the Archean sanukitoid suite. Two subsequent deformation events were followed by low-pressure, high-temperature metamorphism that reached upper amphibolite and local granulite facies at ca. 2.67-2.65 Ga in the central region and greenschist facies at the margins Coeval, crust-derived granitic plutons and pegmatites, including ca. 2.67 Ga peraluminous granite and ca. 2.65 Ga biotite granite have sporadic rare-element mineralization.

Tectonic models for the Quetico subprovince have favoured forearc settings. Depositional ages of ca. 2.698 to 2.690 Ga overlap those of late arc magmatism in the Wabigoon. The dominantly sanukitoid plutons of this age may have been triggered by slab breakoff.

The southern Quetico boundary separates metasedimentary rocks from the dominantly volcano-plutonic Wawa-Abitibi subprovince to the south. Stratigraphic linkages between subprovinces are evident in some areas, although at ca. 2.685 Ga dextral transpressive shear zones are common.

Southwestern Superior province, Wawa subprovince

The Wawa and Abitibi subprovinces correlate across the transverse Kapuskasing uplift. Within the Wawa subprovince, volcanism appears to have begun with the 2.89-2.88 Ga Hawk assemblage. The 2.775 Ga Hemlo-Black River, 2.745 Ga Wawa and 2.72 Ga Greenwater and Manitouwadge assemblages indicate an oceanic setting, the latter contains significant massive sulfide mineralization. There is a variety of oceanic magma types from the Schreiber belt, and interpreted the belt as a tectonic mélange. Late-stage volcanism occurred at ca. 2.695 Ga. Subsequent calc-alkalic to alkalic magmatism (ca. 2.689 Ga) and associated coarse clastic sedimentation was followed by emplacement of sanukitoid plutons (2.65-2.68 Ga) and dextral transpressive deformation.

The Great Lakes tectonic zone is the unexposed boundary between the Minnesota River Valley terrane and Wawa subprovince and is identified from aeromagnetic images. It is inferred to dip northward based on the presence of isotopic inheritance in plutons of the Vermilion district of the southern Wawa-Abitibi subprovince. (Percival, 2006).

Southwestern Superior province, Quetico Subprovince

The Quetico Subprovince of the western Superior province has several alkalic intrusions emplaced 2.696 Ga into turbiditic metasedimentary rocks and are cut by granite dykes

Dike (geology)

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...

ranging from 2.67-2.66 Ga. The intrusions consist of four main rock types: undersaturated mafic rocks, hornblendite

Hornblendite

Hornblendite is a plutonic rock consisting mainly of the amphibole hornblende. Hornblende rich ultramafic rocks are rare and when hornblende is the dominant mineral phase they are classified as hornblendites with qualifiers such as garnet hornblendite identifying a second abundant contained...

and hornblende

Hornblende

Hornblende is a complex inosilicate series of minerals .It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole....

-pyroxenite

Pyroxenite

Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite and diopside, hypersthene, bronzite or enstatite. They are classified into clinopyroxenites, orthopyroxenites, and the websterites which contain both pyroxenes...

, alkali

Alkali

In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...

syenite

Syenite

, and silico

Silicon

Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

carbonatite

Carbonatite

Carbonatites are intrusive or extrusive igneous rocks defined by mineralogic composition consisting of greater than 50 percent carbonate minerals. Carbonatites may be confused with marble, and may require geochemical verification....

and carbonatite

Carbonatite

. These rocks share much of the same characteristics as the Neoarchean shonitic rocks from other western Superior province greenstone belts, such as high Al2O3, high total alkalis, high large-ion lithophile

Lithophile

Lithophiles are micro-organisms that can live within the pore interstices of sedimentary and even igneous rocks to depths of several kilometers....

elements (LILE), and low high-field strength elements (HFSE). The Gheen intrusion near Linden, Minnesota ranges in composition from pyroxenite

Pyroxenite

to monzosyenite and are rich in hornblende. the common occurrence of hornblende suggests that the magma was hydrous and crystallized at low temperatures, although water might have been introduced at shallow levels. (Hattori, 2001).

Southeastern Superior province

The southeast part of the Superior province is divided into the following subdivisions: to the north is the E-W oriented Opinaca subprovince located between the La Grande and Ashuanipi, and to the south is the Opatica Subprovince.

Detrital zircon

Zircon

s from the Opinaca metasediments give ages between 3.3 and 2.7 Ga indicating that they were deposited prior to 2.7 Ga. To the east is the Hublet Group composed of detritic metasediments and some metavolcanic rocks. The Hublet Group is a lateral equivalent of the Rossignol-Laguiche Group to the west. The Joubert Suite to the east is dated at 2.7 Ga. The Gamart suite, composed of monzogranite, is dated at 2.647 Ga. The Lataignant Suite is composed of megaporphyric

Porphyry (geology)

granite

Granite

and dated at 2.645-2.638 Ga. The Opinaca/Ashuanipi contact is constrained by the Nichicun Fault, presenting a mylonite

Mylonite

Mylonite is a fine-grained, compact rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. It is classified as a metamorphic rock...

zone that reveals a southward vergence

Vergence (geology)

In structural geology, the vergence of a fold is the direction in which an antiform is inclined or overturned. The term vergence comes from the German vergenz, which means "overturn"....

of Ashuanipi. The LaGrande/Opinaca contact is marked by the Dalmas Fault. The Duhesme Group is located near this contact and consists of tholeiitic and calc-alkaline volcanic rocks and polygenic conglomerate

Conglomerate (geology)

A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...

s deposited during a period of extension on the sides of a volcanic arc that was formed around 2.735 Ga. They are thought to represent the base of the Opinaca now interpreted like a large sedimentary basin

Sedimentary basin

deposited in a rift

Rift

In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....

environment. (Caderon, 2000).

Southern Superior province

The Southern Superior province is of Late Archean

Archean

origin: 2.75-2.65 Ga. There were two primary volcanic

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

associations: the tholeiitic basalt

Basalt

-komatiite

Komatiite

Komatiite is a type of ultramafic mantle-derived volcanic rock. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content...

and the tholeiitic to calc-alkaline

Calc-alkaline

bimodal

Bimodal distribution

In statistics, a bimodal distribution is a continuous probability distribution with two different modes. These appear as distinct peaks in the probability density function, as shown in Figure 1....

basalt

Basalt

-rhyolite

Rhyolite

This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...

. The tholeiitic basalt-komatiite association is "characterized by near-flat REE

Rare earth element

As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...

patterns and complex Th-U-Nb

Radiometric dating

-LREE

Rare earth element

As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...

systematics; rare transitional to alkaline basalts and Al-depleted komatiites have fractional crystallization REE patterns and OIB-like trace element signatures. This is interpreted as representing an oceanic plateau

Plateau

In geology and earth science, a plateau , also called a high plain or tableland, is an area of highland, usually consisting of relatively flat terrain. A highly eroded plateau is called a dissected plateau...

derived from a heterogeneous mantle plume

Mantle plume

A mantle plume is a hypothetical thermal diapir of abnormally hot rock that nucleates at the core-mantle boundary and rises through the Earth's mantle. Such plumes were invoked in 1971 to explain volcanic regions that were not thought to be explicable by the then-new theory of plate tectonics. Some...

. The latter bimodal

Bimodal distribution

In statistics, a bimodal distribution is a continuous probability distribution with two different modes. These appear as distinct peaks in the probability density function, as shown in Figure 1....

association has fractionated REE

Rare earth element

As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...

patterns and negative Nb

Niobium

Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...

, Ta

Tantalum

Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as tantalium, the name comes from Tantalus, a character in Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory...

, P

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

, and Ti

Thallium

Thallium is a chemical element with the symbol Tl and atomic number 81. This soft gray poor metal resembles tin but discolors when exposed to air. The two chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861 by the newly developed method of flame spectroscopy...

anomalies typical of arc magma

Magma

s. Turbidite

Turbidite

Turbidite geological formations have their origins in turbidity current deposits, which are deposits from a form of underwater avalanche that are responsible for distributing vast amounts of clastic sediment into the deep ocean.-The ideal turbidite sequence:...

s plot on mixing hyperbola

Hyperbola

In mathematics a hyperbola is a curve, specifically a smooth curve that lies in a plane, which can be defined either by its geometric properties or by the kinds of equations for which it is the solution set. A hyperbola has two pieces, called connected components or branches, which are mirror...

e between mafic

Mafic

and felsic

Felsic

The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....

end members. This association is interpreted as an arc-trench

Trench

A trench is a type of excavation or depression in the ground. Trenches are generally defined by being deeper than they are wide , and by being narrow compared to their length ....

system. Tonalite

Tonalite

pluton

Intrusion

s derived from partial melting of subducted

Subduction

ocean

Ocean

ic slab

Plate tectonics

Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

s intrude

Intrusion

the subduction

Subduction

-accretion

Accretion (geology)

Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...

complex as the magmatic arc axis migrated towards the trench....The variability of the mantle mineral ratios in these oceanic plateau basalts is interpreted in terms of recycling variable quantities of ocean

Ocean

ic crust

Crust (geology)

In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

processed through a subduction

Subduction

zone (high Nb/U, Nb/Th)

Radiometric dating

, and complementary arc crust

Crust (geology)

In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

(low Nb/U, Nb/Th)

Radiometric dating

into the source of the plumes. Collectively, these events are interpreted as a part of a late Archean

Archean

supercontinent

Supercontinent

In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...

cycle, involving accretion

Accretion (geology)

Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...

of oceanic plateau

Plateau

s, island arcs

Volcanic arc

, continental fragments, closure of ocean basins, rift

Rift

In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....

ing of magmatic arcs, and plume arc interactions." (Polat et al., 2001).

The Southern province consists of the following early Paleoproterozoic

Paleoproterozoic

The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...

thick cover sequence: from west to east there is the Animikie Group, Marquette Range Supergroup, Huronian Supergroup-Whitewater Group and Mistassini-Otish Mountains Group. Glacial

Glacier

A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

diamictite

Diamictite

Diamictite : through and µεικτός : mixed) is a poorly or non-sorted conglomerate or breccia with a wide range of clasts, up to 25% of them gravel sized...

s characterize the Southern province sequence All of the successions are characterized by deep-water marine deposits, Fe-formation and mafic volcanic rocks above the quartzarenite

Quartzarenite

A quartz arenite or quartzarenite is a sandstone composed of greater than 90% detrital quartz, with limited amounts of other framework grains and matrix...

s. Above the deep-water deposits is a ca. 1.95-1.85 Ga upward-coarsening succession thought to have been formed during collisional orogeny

Orogeny

during the formation of Laurentia

Laurentia

Laurentia is a large area of continental craton, which forms the ancient geological core of the North American continent...

. (Rainbird, 2004).

The 1.85 Ga Sudbury Intrusive Complex is situated on the southern edge of the Superior Province and represents one of the most richly mineralized bodies of the Canadian Shield. Current thinking regards the gabbro-noritic intrusion to have been generated in response to meteorite impact. (Percival, 2006).

Southern Superior province, Schreiber-Hemlo greenstone belt

The Late Archean

Archean

(2.7 Ga) Schreiber-Hemlo greenstone belt

Greenstone belt

in the Wawa Subprovince is located just north of Lake Superior and is characterized by lithologically

Petrology

Petrology is the branch of geology that studies rocks, and the conditions in which rocks form....

and geochemically diverse convergent margin igneous rock

Igneous rock

Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...

s. Supracrustal assemblages of the Schreiber-Hemlo greenstone belt (ca. 2.75-2.69 Ga) are composed of tectonically juxtaposed fragments of oceanic plateau

Oceanic plateau

s, oceanic island arcs

Volcanic arc

, and siliciclastic

Siliciclastic

Siliciclastic rocks are clastic noncarbonate sedimentary rocks that are almost exclusively silica-bearing, either as forms of quartz or other silicate minerals. All siliciclastic rocks are formed by inorganic processes, or deposited through some mechanical process, such as stream deposits that are...

arc-derived trench

Oceanic trench

The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor....

turbidite

Turbidite

s. Bedrock exposure of the Schreiber-Hemlo greenstone belt is of intermediate and mafic metavolcanic rocks. These rocks are generally pillowed or massive to foliated flows, and or fragmental tuffs and breccias. This is the classic locality of the Gunflint Chert where ~1.88 Ga cyanobacteria and other microfossils were first discovered in the 1950s. Paleoproterozoic Gunflint Chert rests unconformably on the 2.7 Ga pillow basalts (see photos:http://www.cretaceousfossils.com/scenic_geology/ontario_canada.htm)

According to a study by Kerrich and Polat (1999): The late Archean (ca. 2.75-267 Ga) Schreiber-Hemlo greenstone belt, is composed of tectonically juxtaposed fragments of oceanic plateaus, oceanic island arcs, and siliciclastic trench turbidites. Following this juxtaposition, these diverse lithologies were collectively intruded by synkinematic, ultramafic to felsic

Felsic

The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....

dyke

Dike (geology)

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...

s, and Tonalite

Tonalite

-Trondhjemite

Trondhjemite

Trondhjemite is a leucocratic intrusive igneous rock. It is a variety of tonalite in which the plagioclase is mostly in the form of oligoclase. Trondhjemites are sometimes known as plagiogranites....

-Granodiorite

Granodiorite

TTG

Tonalite-Trondhjemite-Granodiorite

pluton

Intrusion

s (ca. 2.72-2.69 Ga) and ultramafic to felsic dikes and sills (ca. 2.69-2.68 Ga) with subduction zones. Overprinting relations between different sequences of structures suggest that this greenstone belt underwent at least three phases of deformation:

During the first phase (2.695-2.685 Ga) oceanic plateau basalts and associated komatiites, arc-derived trench turbidites, and oceanic island arc sequences were all tectonically juxtaposed as they were incorporated into the accretionary complex. Fragmentation of these sequences resulted in broken formations and a tectonic mélange assemblage.

During the second phase (ca. 2.685-2.680 Ga), oceanic island arc sequences, with right-lateral transpressional

Transform fault

A transform fault or transform boundary, also known as conservative plate boundary since these faults neither create nor destroy lithosphere, is a type of fault whose relative motion is predominantly horizontal in either sinistral or dextral direction. Furthermore, transform faults end abruptly...

deformation; further fragmentation and mixing of ocean plateau fragments; synkinematic dikes and sills; arc-derived trench turbidites; and arc-derived mafic to felsic igneous rocks with associated komatiites, and further development of the broken formations, suggest that the tectonic mélange formation continued. The oceanic island arc sequences were all tectonically juxtaposed and incorporated into the accretionary complex. The phase one to phase two transition is interpreted in terms of a trenchward migration of the magmatic arc axis due to continued accretion and underplating.

During this second sequence the strike-slip faults in the fore-arc region of the Schreiber-magma

Magma

tic arc may have provided conduits for uprising melts from the descending slab

Subduction

, and induced decompressional partial melting in the sub-arc mantle

Mantle (geology)

wedge. This yielded the syn-kinematic ultramafic to felsic and gabbro

Gabbro

Gabbro refers to a large group of dark, coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt. The rocks are plutonic, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline mass....

ic intrusion

Intrusion

s. A similar close relationship between orogen

Orogeny

-parallel strike-slip faulting and magmatism has been recognized in several Phanerozoic

Phanerozoic

transpressional orogenic belt counterparts, including the North American Cordillera

Cordillera

A cordillera is an extensive chain of mountains or mountain ranges, that runs along a coastline . It comes from the Spanish word cordilla, which is a diminutive of cuerda, or "cord"...

, Japanese island arcs

Volcanic arc

, and British Caledonides, suggesting that the orogen-parallel strike-slip faulting in the Schreiber-Hemlo greenstone belt played an important role in magma emplacement and lateral crustal accretion. It is suggested that subduction

Subduction

-accretion, with associated mélange formation and magmatism, was an important mechanism of continental growth in the late Archean southern Superior Province. (Kerrich and Polat, 1999)

In a further analyses of the belt by Polat (1999), the Schreiber-Hemlo greenstone belt includes mafic to intermediate tholeiitic flows, mafic to intermediate calc-alkaline

Calc-alkaline

flows, felsic calc-alkaline flows, syn-kinematic ultramafic (picritic

Picrite basalt

Picrite basalt, picrobasalt or oceanite is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts and black to dark brown pyroxene, mostly augite....

) to felsic dykes, and high-Al TTG

Tonalite-Trondhjemite-Granodiorite

plutons. All these suites share positively fractionated REE

Rare earth element

As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...

patterns, and negative anomalies of Nb and Ti....Fractionated REE patterns, negative Nb and Ti anomalies, and transition metal contents are all consistent with a metasomatized

Metasomatism

Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...

mantle wedge source for the tholeiitic and calc-alkaline volcanic

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

suites, and ultramafic to intermediate dykes. The geochemical characteristics of mafic to intermediate tholeiitic and calc-alkaline flows suggest a deeper and more primitive mantle source compositions for the calc-alkaline suite than the tholeiitic counterpart. Felsic flows and dykes, and TTG plutons are all defined by the enrichment of LREE

Rare earth element

As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...

, Th, and Zr, and by the depletion of Nb, Ti, Cr, Sc abundances. High Al₂O₃/TiO₂, Zr/Y, Sr/Y, La/Yb, and Gd/Yb ratios for felsic rocks are consistent with slab melting and garnet

Garnet

-amphibole

Amphibole

Amphibole is the name of an important group of generally dark-colored rock-forming inosilicate minerals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures.-Mineralogy:...

-clinopyroxene

Pyroxene

residue in the source. The existence of overlapping fields between mafic, intermediate, and felsic suites on trace element ratios suggest that processes controlling the production of these arc rocks were more complex than simple slab and/or wedge melting. This complexity may have resulted from a mixture of slab and wedge melts, second stage melting, magma mixing, fractional crystallization, partial equilibration with sub-arc wedge peridotite

Peridotite

A peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron...

, crustal contamination, or some combination.

Economic Geology

The Superior Province is the mining heartland of Canada with major mining camps in the Abitibi district of Ontario-Quebec and Red Lake region of western Ontario. The Sudbury structure located on the southeastern edge of the Superior Province is one of the world's largest nickel producing regions. The Big Trout Lake belt and others have nickel and platinum group elements (PGE) potentials. (Percival, 2006).

The Northern Superior Superterrane (NSS) hosts diamondiferous kimberlite at the Victor pipe in the Attawapiskat area. Additional exploration targets have been identified through kimberlite indicator minerals in the Ontario-Manitoba border region, the Wemindgi and Otish Mountains in Central Quebec, the Wawa region in south Ontario, and the Timiskaming/Temagami areas in southeastern Ontario near the border of Quebec. Production at Victor project is planned for 2008.

Twenty-five percent of Canadian gold production has come from the Schreiber-Hemlo Greenstone Belt in the Wawa subprovince in the south Ontario. The Shebandowan-Schreiber mineral belt hosts important gold, iron, volcanic-hosted massive sulfide and intrusion-hosted Ni deposits (Percival, 2006). The most significant is the Hemlo gold camp. At present, three mines exploit the Hemlo gold deposit (Williams, Golden Giant, and David Bell mines). The world-class Hemlo deposit was a major gold discovery in Canada during the 1980s and contains ~22 million ounces (680 t) of gold. Average gold grade for the main deposit (84 Mt of ore, 21 Moz Au) is 7.7 g/t. (Bodycomb, 2000). The Uchi subprovince of the North Carribou terrane hosts some of the largest mineral deposits of the western Superior region, including the Red Lake gold camp. These rocks host both world-class gold deposits and massive sulfide mineralization. Iron formations in the central North Caribou terrane host the Musselwhite lode gold deposit. The Quetico-western Wabigoon Seine River-Rainy Lake fault is an area known for numerous gold showings. Small deposits East of Lake Nipigon hosts the Long Lac vein gold deposits. (Percival, 2006).

The Abitibi subprovince in the east hosts some of the richest mineral deposits of the Superior Province, including the giant Kidd Creek massive sulfide deposit and the large gold camps of Ontario and Quebec. The northern Abitibi belt is best known for the Matagami-Chibougamau mineral belt, characterized mainly by Cu-Zn massive sulfide deposits, Cu-Zn vein deposits and some lode gold deposits. The central zone has massive sulfides as well as vein gold deposits. The southern Abitibi belt hosts the Timmins-Val d'Or mineral belt, known for its numerous gold deposits, major Cu-Zn massive sulfide deposits, komatiite and intrusion-related Ni deposits, some pegmatite-hosted deposits and minor porphyry type mineralization. The richly gold-mineralized Cadillac-Larder Lake break forms the southern boundary of the belt. The Abitibi belt also has some of the largest massive sulfide deposits in the province. (Percival, 2006).

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