A regional perspective of the Quetico metasedimentary belt, Superior Province, Canada

1989 ◽  
Vol 26 (4) ◽  
pp. 677-693 ◽  
Author(s):  
John A. Percival
Keyword(s):  
Central Zone ◽  
Superior Province ◽  
Crustal Melting ◽  
Tectonic Feature ◽  
Polyphase Deformation ◽  
First Order ◽  
Mineral Assemblages ◽  
Tectonic Development ◽  
Accretionary Prisms ◽  
Volcanic Belts

Alternating greenstone–granite and metasedimentary gneiss belts are a first-order tectonic feature of the southern Superior Province. The tectonic development of the Quetico metasedimentary belt is reviewed with regard to depositional, structural, and metamorphic–plutonic history. Over its 1200 km length, the belt consists of marginal metasedimentary schists of turbiditic origin and interior metasedimentary migmatite and peraluminous leucogranite. Polyphase deformation has resulted in a steep easterly-striking foliation and regional, gently east-plunging stretching lineation. Metamorphic grade varies in a low-P facies series from greenschist at the belt margins to upper amphibolite and local granulite in the central migmatite – intrusive granite zone. Mineral assemblages in the central zone yield estimates of metamorphic pressure that increase systematically eastward over 800 km from about 250 MPa (2.5 kbar) near the Canada – United States border to 600 MPa (6 kbar) in granulites adjacent to the Kapuskasing structural zone.Geochronology suggests that sediments were deposited at approximately the same time as active volcanism in adjacent volcanic belts, although evidence of volcanic–sedimentary stratigraphic contiguity is weak as a result of later transcurrent movement parallel to major lithological boundaries. Adjacent belts are inferred to have been contiguous since common D2 deformation, 2689–2684 Ma ago. Major plutonism and associated metamorphism occurred in the Quetico Belt approximately 2670–2650 Ma ago, significantly later than major plutonism in the adjacent volcanic belts.The linear disposition of greywacke-rich sediments over 1200 km invites an analogy with modern accretionary prisms. However, the high-temperature, low-pressure metamorphism of the Quetico Belt is inconsistent with such a low-heat-flow environment, and a change in tectonic regime would be required to account for the metamorphism and intracrustal plutonism. Simple cessation of subduction beneath the thick sedimentary prism could have led to restoration of isotherms, with possible attendant crustal melting and isostatic recovery.

Review of crustal architecture and evolution in the Ungava Peninsula — Baffin Island area: connection to the Lithoprobe ECSOOT transect

2002 ◽  
Vol 39 (5) ◽  
pp. 589-610 ◽  
Author(s):  
M R St-Onge ◽  
D J Scott ◽  
N Wodicka
Keyword(s):  
Order Approximation ◽  
Close Correlation ◽  
Canadian Shield ◽  
Baffin Island ◽  
Aeromagnetic Data ◽  
Polyphase Deformation ◽  
First Order ◽  
Mineral Assemblages ◽  
First Order Approximation ◽  
Archean Basement

Within the Trans-Hudson Orogen in northern Quebec and southern Baffin Island, parautochthonous Archean basement and Paleoproterozoic cover, as well as allochthonous (accreted) Paleoproterozoic units, are exposed in a series of antiformal culminations and complementary synclinoria. The parautochthonous rocks of the Superior Province margin and two assemblages of accreted Paleoproterozoic units (Ungava and Meta Incognita crustal terranes) define a basic tripartite crustal architecture which is characterized by polyphase deformation and metamorphic histories. Early structures and mineral assemblages are recognized in all three crustal components and shown to be temporally distinct. The earlier structures and assemblages are overprinted by younger elements and mineral assemblages that are related to at least three regional contraction episodes and one thermal event that are common to all crustal components of the orogen. Close correlation of regional aeromagnetic data in northern Quebec and southern Baffin Island with the three crustal components offers a first-order approximation of the distribution of basement lithological units across Hudson Strait. Continuation of the aeromagnetic domains beneath Ungava Bay to northeastern Quebec and northern Labrador allows for the southward extrapolation of the tripartite Trans-Hudson Orogen crustal architecture into the Lithoprobe Eastern Canadian Shield Onshore–Offshore Transect area.

The Sedimentary Cycle on Early Mars

2019 ◽  
Vol 47 (1) ◽  
pp. 91-118 ◽  
Author(s):  
Scott M. McLennan ◽  
John P. Grotzinger ◽  
Joel A. Hurowitz ◽  
Nicholas J. Tosca
Keyword(s):  
Plate Tectonics ◽  
Sedimentary Rock ◽  
First Order ◽  
Sedimentary Environments ◽  
Source To Sink ◽  
Rock Record ◽  
Mineral Assemblages ◽  
Sedimentary Cycle ◽  
Early Mars ◽  
Over Time

Two decades of intensive research have demonstrated that early Mars ([Formula: see text]2 Gyr) had an active sedimentary cycle, including well-preserved stratigraphic records, understandable within a source-to-sink framework with remarkable fidelity. This early cycle exhibits first-order similarities to (e.g., facies relationships, groundwater diagenesis, recycling) and first-order differences from (e.g., greater aeolian versus subaqueous processes, basaltic versus granitic provenance, absence of plate tectonics) Earth's record. Mars’ sedimentary record preserves evidence for progressive desiccation and oxidation of the surface over time, but simple models for the nature and evolution of paleoenvironments (e.g., acid Mars, early warm and wet versus late cold and dry) have given way to the view that, similar to Earth, different climate regimes on Mars coexisted on regional scales and evolved on variable timescales, and redox chemistry played a pivotal role. A major accomplishment of Mars exploration has been to demonstrate that surface and subsurface sedimentary environments were both habitable and capable of preserving any biological record. ▪ Mars has an ancient sedimentary rock record with many similarities to but also many differences from Earth's sedimentary rock record. ▪ Mars’ ancient sedimentary cycle shows a general evolution toward more desiccated and oxidized surficial conditions. ▪ Climatic regimes of early Mars were relatively clement but with regional variations leading to different sedimentary mineral assemblages. ▪ Surface and subsurface sedimentary environments on early Mars were habitable and capable of preserving any biological record that may have existed.

ARCHAEAN VOLCANISM IN THE CANADIAN SHIELD

1965 ◽  
Vol 2 (3) ◽  
pp. 161-175 ◽  
Author(s):  
H. D. B. Wilson ◽  
Peter Andrews ◽  
R. L. Moxham ◽  
K. Ramlal
Keyword(s):  
Volcanic Rocks ◽  
Canadian Shield ◽  
Superior Province ◽  
Chemical Compositions ◽  
Volcanic Sequence ◽  
Southern Half ◽  
Orogenic Belts ◽  
Volcanic Belts

Chemical compositions of Archaean volcanic rocks in the Superior province of the Canadian shield have been determined from 261 new analyses from 10 volcanic belts. The analyses are compared with those of the various volcanic associations. This comparison shows that the volcanic rocks of all belts belong to the basalt andesite rhyolite association typical of continental orogenic belts or island are systems. A primitive continent with continental rocks must, therefore, have existed in early Archaean time.The Keewatin lava sequences in the various belts are remnants of a great volcanic sequence that covered the southern half of the Superior province of the Canadian shield.

Polyphase deformation and crustal evolution in the Pipestone Lake area of the Archean Wabigoon Subprovince, Superior Province, Canada

1999 ◽  
Vol 36 (3) ◽  
pp. 459-477 ◽  
Author(s):  
Garth R Edwards ◽  
Mel R Stauffer
Keyword(s):  
Shear Zone ◽  
Canadian Shield ◽  
Superior Province ◽  
Crustal Evolution ◽  
Lake Area ◽  
Polyphase Deformation ◽  
Crenulation Cleavage ◽  
East West

Archean supracrustal rocks in the western Wabigoon Subprovince, Superior Province, Canadian Shield, have undergone four phases of deformation, D1-D4. D1, confined to the oldest rocks, includes a large, refolded, reclined, isoclinal anticline (F1) with moderately developed axial-planar cleavage (S1). Rocks affected by D1 are overlain by a regional unconformity. D2 includes post-unconformity, steeply plunging, north-northeast-south-southwest-striking, isoclinal folds (F2) that are approximately coaxial with F1, but have contorted the F1 axial trace. D3 is represented by east-west-striking, steeply plunging folds at various scales (F3) which occur mainly in rocks near the regional Manitou Stretch - Pipestone Lake Shear Zone, also interpreted to be a D3 structure. D4 is represented by pervasive cleavage (S4), locally penetrative but mainly spaced, including crenulation cleavage, fractures, small faults, and brittle-ductile shears. S4 is parallel to the margin of the Jackfish Lake Pluton. D1-D3 are ascribed to convergence of the Wabigoon Subprovince with adjacent subprovinces, ending with formation of the Manitou Stretch - Pipestone Lake Shear Zone as a (presently) steep thrust and oblique-ramp structure. D4 is the result of either diapiric emplacement of the Jackfish Lake Pluton, or marginal strain intensification due to the rigidity of the older Ash Bay Dome during late north-south compression. Previously available zircon U-Pb geochronology provides a maximum age for D1 of 2728 Ma, and an approximate age for D4 of 2698 Ma. The unconformity developed between D1 and D2, 2725-2713 Ma.

Structural evolution of an early Proterozoic strata-bound Cu-Co-Zn deposit, Outokumpu, Finland

1981 ◽  
Vol 72 (2) ◽  
pp. 115-158 ◽  
Author(s):  
T. J. Koistinen
Keyword(s):  
Structural Evolution ◽  
Ocean Floor ◽  
Convective System ◽  
Mica Schist ◽  
Early Proterozoic ◽  
Polyphase Deformation ◽  
Mineral Assemblages ◽  
Show Evidence ◽  
Stratigraphic Position ◽  
Black Schist

ABSTRACTThe massive pyrite-pyrrhotite-chalcopyrite-sphalerite deposit of Outokumpu, comprising the Keretti and Vuonos orebodies, is a deformed and metamorphosed strata-bound mass associated with mineralised stockworks. Mobilisation of much of the ore followed formation of large recumbent isoclinal folds that are the major structures of the surrounding rocks and associated with the modification of originally flat saucer-shaped ore lenses into elongate ruler-shaped masses. Further modification of shape took place at the mobilisation stage with much of the pyrrhotitic ore, particularly, now occupying the thickest parts of the orebodies in the form of breccia or microbreccia. In many parts gross original characters still exist and the pyritic and pyrrhotitic constituents of the ore have survived as separate entities while locally the pyritic ore retains pre-deformational characteristics and consistent stratigraphic position within a thin horizon.Both ore and country rocks show evidence of extensive polyphase deformation with the effects of six fold phases shown in the ore. Mineral assemblages in the country rocks indicate a middle amphibolite facies peak of metamorphism. The serpentinite-black schist-carbonate-quartzite rock assemblage, with which the ore is associated, was tectonically incorporated within the regionally extensive mica schist by even earlier subhorizontal thrusting. This is related to the movement of a thrust nappe with the interdigitation of an ocean-floor ophiolite assemblage and flysch deposited during ocean closure associated with Svecokarelian tectonism.The original formation of the Keretti and Vuonos sulphide masses took place in a marine exhalative environment with a pyritic layer overlying a pyrrhotitic layer in each of the two c. 4 km diameter irregularly oval-shaped depressions whose centres were c. 8 km apart. The mineralised stockwork below each mass represents the upper parts of the conduit for metalbearing fluids in a convective system.

U–Pb geochronology of the central Uchi Subprovince, Superior Province

1993 ◽  
Vol 30 (6) ◽  
pp. 1179-1196 ◽  
Author(s):  
F. Corfu ◽  
G. M. Stott
Keyword(s):  
Large Scale ◽  
Regional Scale ◽  
Early Period ◽  
Superior Province ◽  
Northwestern Ontario ◽  
Granitoid Rocks ◽  
Age Patterns ◽  
Tectonic Development ◽  
Greenstone Belts ◽  
Multiple Episodes

U–Pb zircon and titanite ages for rocks of the central Uchi Subprovince in northwestern Ontario indicate a late Archean magmatic and tectonic development spanning over 200 Ma. An early period at 2900–2800 Ma formed volcano-plutonic complexes, presumably linked to 3.1–2.8 Ga terrains of the northwestern Superior Province. A later period of southward growth by magmatic and tectonic accretion occurred at 2750–2710 Ma and was concluded by large scale compression and plutonism at 2700 Ma.The oldest 2890–2860 and 2840–2820 Ma components occur in the Pickle Lake and Meen–Dempster greenstone belts and as gneisses in the Seach–Achapi and the Lake St. Joseph batholiths in northern and central sectors of the region. Together with distinct 2750–2740 Ma volcano-plutonic complexes they form a collage assembled by multiple episodes of tectonic juxtaposition and magmatic accretion. Plutons of 2730–2710 Ma age are intrusive into these older, northern domains, whereas their volcanic counterparts compose the Lake St. Joseph and Miminiska – Fort Hope greenstone belts to the south. Late-tectonic to posttectonic granitoid rocks intruded a region extending from the northern Berens River Subprovince to the southern English River Subprovince at 2700 Ma. These plutons were cut by regional scale faults formed by residual north-northwest directed shortening. The timing of this movement seems to be recorded by titanite ages of 2690–2670 Ma. Reactivation of the same faults may account for Proterozoic Pb loss observed in some of the zircon populations. The age patterns are consistent with crustal growth along a continental margin in a north-dipping subduction environment.

scholarly journals Mineralogical-geochemical features of corundum Miaskite-pegmatite from mine no. 210 (Ilmeny mountains, South Urals): preliminary results

2020 ◽  
pp. 38-54
Author(s):  
M.A. Rassomakhin ◽  
E.S. Sorokina ◽  
A.V. Somsikova
Keyword(s):  
Mineral Composition ◽  
Isotopic Ratio ◽  
Central Zone ◽  
South Urals ◽  
Zonal Structure ◽  
Accessory Minerals ◽  
Mineral Assemblages ◽  
Data Points ◽  
Formation Conditions ◽  
Compositional Changes

Miaskite-pegmatite of mine no. 210 exhibits an unusual mineral composition for the Ilmeny Mountains. It contains a signifcant amount of sapphire-like corundum (uncommon of nepheline-bearing pegmatites) and various Th-bearing minerals («thoro-aeschinite», pyrochlore, phosphates). Pegmatite has a zonal structure, in which the central nepheline and lateral feldspar zones difer in composition of rock-forming and accessory minerals. Corundum is found in all zones of pegmatite. Accessory minerals of the central, eastern, and western zones include (i) Ti-niobates (columbite, pyrochlore, srilankite), zircon, spinel and thorianite, (ii) columbite, pyrochlore and zircon, and (iii) columbite, «ilmenorutile», toro-aeschinite, monazite-La and Ce, and zircon, respectively. The calculations based on two-feldspar thermometer for diferent pegmatite zones show a decrease in temperature from the periphery toward the center, which is in agreement with the variability of mineral assemblages. Pegmatite is strongly altered, which is expressed in the formation of cancrinite and sodalite, hydration of pyrochlore of the central zone, and signifcant compositional changes of Ti-niobates in the lateral zones of pegmatite. The Rb-Sr age of corundum miaskite-pegmatite is ~275 Ma, but the Rb-Sr system is signifcantly destroyed. The initial 87Sr/86Sr(275) isotopic ratio and ?Nd(275) value of the mineral indicate its crustal formation conditions. The geochemistry of corundum points to its multistage crystallization. The data points on Fe vs. Ga / Mg and FeO – Cr2O3 – MgO – V2O3 vs. FeO + TiO2 + Ga2O3 plots correspond to both «magmatic» and «metasomatic» corundum.

Thermal evolution of two textural types of mafic granulites in the North China craton: evidence for both mantle plume and collisional tectonics

1999 ◽  
Vol 136 (3) ◽  
pp. 223-240 ◽  
Author(s):  
GUOCHUN ZHAO ◽  
SIMON A. WILDE ◽  
PETER A. CAWOOD ◽  
LIANGZHAO LU
Keyword(s):  
North China Craton ◽  
North China ◽  
Thermal Evolution ◽  
Central Zone ◽  
Magmatic Arc ◽  
The North ◽  
Final Assembly ◽  
Mineral Assemblages ◽  
History Of ◽  
Evolutionary Paths

Mafic granulites from the North China craton can be divided into two textural types, referred to as A- and B-types. A-type mafic granulites display garnet+quartz symplectic coronas, and outcrop in the eastern and western zones of the craton, whereas B-type mafic granulites exhibit orthopyroxene+plagioclase±clinopyroxene symplectites or coronas, and are mainly exposed in the central zone of the craton. Most A-type mafic granulites preserve the prograde (M1), peak (M2) and post-peak near-isobaric cooling (M3) assemblages, which are represented respectively by inclusions of hornblende+plagioclase+quartz, a peak mineralogy of orthopyroxene+clinopyroxene+plagioclase+quartz+garnet, and overprinted by garnet+quartz symplectic coronas. These mineral assemblages and their P–T (pressure-temperature) estimates define anticlockwise P–T evolutionary paths. The B-type mafic granulites preserve the peak (M1), post-peak near-isothermal decompression (M2) and cooling (M3) assemblages, which are represented by the peak assemblage of orthopyroxene+clinopyroxene+plagioclase+quartz+garnet±hornblende, post-peak orthopyroxene+plagioclase±clinopyroxene symplectites or coronas, and later hornblende+plagioclase+magnetite symplectites, respectively. These mineral assemblages and their P–T estimates define clockwise P–T paths.The anticlockwise P–T paths of the A-type mafic granulites in the eastern and western zones of the North China craton are consistent with a model of underplating and intrusion of mantle-derived magmas. In combination with lithological, structural and geochronological data, the eastern and western zones of the North China craton are considered to represent two continental blocks that developed through the interaction of mantle plumes with the lithosphere from the Palaeoarchaean to the Neoarchaean era. The B-type mafic granulites and associated rocks in the central zone represent a magmatic arc that was metamorphosed and deformed during amalgamation of the eastern and western continental blocks in the late Palaeoproterozoic era. The mineral reaction relations and clockwise P–T paths of the B-type mafic granulites from the central zone record the tectonothermal history of the collision that resulted in the final assembly of the North China craton at c. 1800 Ma.

Rb–Sr and U–Pb ages of volcanism and granite emplacement in the Michipicoten belt—Wawa, Ontario

1982 ◽  
Vol 19 (8) ◽  
pp. 1608-1626 ◽  
Author(s):  
A. Turek ◽  
Patrick E. Smith ◽  
W. R. Van Schmus
Keyword(s):  
Greenstone Belt ◽  
Granitic Rocks ◽  
Iron Formation ◽  
Superior Province ◽  
Initial Ratio ◽  
Metasedimentary Rocks ◽  
Granite Emplacement ◽  
Time Period ◽  
Metavolcanic Rocks ◽  
Volcanic Belts

The Michipicoten greenstone belt at Wawa, Ontario is typical of Archean volcanic belts in the Superior Province. The supracrustal rocks are divisible into lower, middle, and upper metavolcanic sequences, which are separated by iron formation and clastic metasedimentary rocks. These are intruded by granitic stocks and embayed by granitic batholiths.This study reports whole rock Rb–Sr and zircon U–Pb ages for the lower and upper metavolcanics, for the granitic rocks that are physically within the greenstone belt (internal granites), and for the granitic rocks that embay the greenstone belt (external granites). The apparent Rb–Sr ages for the lower metavolcanics are 2530 ± 90, 2285 ± 70, and 2680 ± 490 Ma. The U–Pb ages are 2749 ± 2 and 2744 ± 10 Ma. The internal granites give an Rb–Sr age of 2560 ± 270 Ma and a U–Pb age of 2737 ± 6 Ma. The external granite at Hawk Lake indicates an Rb–Sr age of 2550 ± 175 Ma and a U–Pb age of 2747 ± 7 Ma. It is possible that this unit contains elements older than 2812 Ma as it contains xenocrystic zircons. The upper volcanics give a U–Pb age of 2696 ± 2 Ma, which indicates that the belt evolved over a time period in excess of 53 Ma. The Rb–Sr ages are significantly younger than the U–Pb zircon ages and have very large uncertainties in age; hence it is unlikely that they have any stratigraphic significance. They probably reflect the Kenoran orogeny at about 2560 Ma. The 2285 ± 70 Ma Rb–Sr isochron age has an initial ratio of 0.7275 ± 0.0052, which is interpreted as a rotational isochron defining a younger post-Kenoran event in the area. The zircon ages appear to be correct chronostratigraphically. Furthermore, it appears that the granitic rocks are coeval and may also be cogenetic with the lower acid metavolcanic rocks.

Dual systems for all: Higher-order, role-based relational reasoning as a uniquely derived feature of human cognition

2019 ◽  
Vol 42 ◽  
Author(s):  
Daniel J. Povinelli ◽  
Gabrielle C. Glorioso ◽  
Shannon L. Kuznar ◽  
Mateja Pavlic
Keyword(s):  
Temporal Reasoning ◽  
Higher Order ◽  
Important Case ◽  
Human Cognition ◽  
Relational Reasoning ◽  
Dual Systems ◽  
First Order ◽  
Reasoning System ◽  
Role Based

Abstract Hoerl and McCormack demonstrate that although animals possess a sophisticated temporal updating system, there is no evidence that they also possess a temporal reasoning system. This important case study is directly related to the broader claim that although animals are manifestly capable of first-order (perceptually-based) relational reasoning, they lack the capacity for higher-order, role-based relational reasoning. We argue this distinction applies to all domains of cognition.

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