40Ar/39Ar Incremental Release Ages of Biotite and Hornblende from Pre-Kenoran Gneisses between the Matagami-Chibougamau and Frotet-Troilus Greenstone Belts, Quebec

1974 ◽  
Vol 11 (11) ◽  
pp. 1586-1593 ◽  
Author(s):  
R. D. Dallmeyer
Keyword(s):  
High Temperature ◽  
Tectonic Evolution ◽  
Superior Province ◽  
High Grade ◽  
Continuous Increase ◽  
Thermal Event ◽  
Greenstone Belts ◽  
Orogenic Belts ◽  
Gas Fractions

Biotite and hornblende from high-grade, granitic gneisses exposed between the Matagami-Chibougamau and Frotet-Troilus greenstone belts in Quebec have been affected by Kenoran metamorphism. Biotites record total gas 40Ar/39Ar ages of 2308 ± 30 m.y. and 2338 ± 30 m.y. Incrementally released gas fractions yield similar plateau ages, suggesting that the biotites have been totally degassed as a result of the thermal event. The ages are interpreted as reflecting the time of post-metamorphic cooling when radiogenic 40Ar began to be retained within biotite. Hornblendes record total gas 40Ar/39Ar ages of 2517 ± 40 m.y. and 2610 ± 40 m.y. Incrementally released gas fractions show a wide deviation from the total gas ages, with a continuous increase in age from low to high temperature release fractions. This lack of correlation suggests that the hornblendes have been only partially degassed by Kenoran metamorphism. However, lack of a high-temperature release plateau indicates that original meramorphic crystallization was older than the ages recorded by the highest temperature release fractions (2599 ± 40 and 2801 ± 40 m.y.). Recognition of an older sialic terrain between these greenstone belts supports recent models proposed for the tectonic evolution of the supracrustal orogenic belts in the Superior Province.

Tectonic evolution of two greenstone belts from the Superior Province in Manitoba

1978 ◽  
Vol 15 (11) ◽  
pp. 1808-1816 ◽  
Author(s):  
R. G. Park ◽  
I. F. Ermanovics
Keyword(s):  
Tectonic Evolution ◽  
Superior Province ◽  
The North ◽  
Crenulation Cleavage ◽  
Facies Metamorphism ◽  
Tonalitic Gneiss ◽  
Uniform Stress Field ◽  
Greenstone Belts ◽  
East West ◽  
Lower Group

The Bigstone Lake and Stevenson Lake greenstone belts are two areas of supracrustal rocks surrounded by quartz diorite to granodiorite plutons and by small patches of tonalitic gneiss interpreted as basement to the greenstone belts. The supracrustal sequence is divided into a lower, mainly volcanic, group correlated with the Hayes River Group of Island Lake and an unconformable upper group with roughly equal proportions of sediments and volcanics correlated with the Island Lake 'Series'. The lower group consists of about 4600 m of basaltic and andesitic pillow lavas with minor greywackes and dacitic volcanics. It is partly replaced at the base by the bordering plutons and cut out at the top by the unconformable upper group, which consists of about 2300 m of greywackes, arkoses, and mudstones above a basal conglomerate containing boulders derived from the lower group and from the basement. A further 2100 m of volcanics overlies these sediments.The supracrustal rocks show three phases of deformation. The first, F1, produced major northeast–southwest and east–west synclines. S1 foliation was developed under greenschist facies to low amphibolite facies metamorphism. F2 produced smaller scale steep east–west folds with a crenulation cleavage. Subsequent deformation resulted in chevron folds and conjugate shear belts.The intrusion of the plutons commenced before the F1 deformation and partly controlled it, but a further period of plutonic intrusion occurred after F1 and before F2.The north–south compressive stress prevailing during F2 and later deformation under waning metamorphism implies that the batholiths in the vicinity of the greenstone belts had completely solidified and that the crust was rigid enough to transmit a uniform stress field. The dominance of east–west structural grain in this part of the Superior Province indicates that these conditions were general.

Rubidium–strontium ages from the Oxford Lake – Knee Lake greenstone belt, northern Manitoba

1980 ◽  
Vol 17 (5) ◽  
pp. 560-568 ◽  
Author(s):  
G. S. Clark ◽  
S.-P. Cheung
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Superior Province ◽  
Granitic Intrusion ◽  
Greenstone Belts ◽  
Archean Greenstone Belts

Rb–Sr whole-rock ages have been determined for rocks from the Oxford Lake – Knee Lake – Gods Lake greenstone belt, in the Superior Province of northeastern Manitoba.The age of the Magill Lake Pluton is 2455 ± 35 Ma (λ87Rb = 1.42 × 10−11 yr−1), with an initial 87Sr/86Sr ratio of 0.7078 ± 0.0043. This granitic stock intrudes the Oxford Lake Group, so it is post-tectonic and probably related to the second, weaker stage of metamorphism.The age of the Bayly Lake Pluton is 2424 ± 74 Ma, with an initial 87Sr/86Sr ratio of 0.7029 ± 0.0001. This granodioritic batholith complex does not intrude the Oxford Lake Group. It is syn-tectonic and metamorphosed.The age of volcanic rocks of the Hayes River Group, from Goose Lake (30 km south of Gods Lake Narrows), is 2680 ± 125 Ma, with an initial 87Sr/86Sr ratio of 0.7014 ± 0.0009.The age for the Magill Lake and Bayly Lake Plutons can be interpreted as the minimum ages of granitic intrusion in the area.The age for the Hayes River Group volcanic rocks is consistent with Rb–Sr ages of volcanic rocks from other Archean greenstone belts within the northwestern Superior Province.

Magmatic and tectonic emplacement of the Pukaskwa batholith, Superior Province, Ontario, CanadaThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.

2011 ◽  
Vol 48 (2) ◽  
pp. 187-204 ◽  
Author(s):  
Gary P. Beakhouse ◽  
Shoufa Lin ◽  
Sandra L. Kamo
Keyword(s):  
Partial Melting ◽  
Abrupt Change ◽  
Superior Province ◽  
Density Inversion ◽  
Tectonic Processes ◽  
Slab Breakoff ◽  
Greenstone Belts ◽  
Lower Crustal ◽  
Basaltic Crust ◽  
Structural Dome

The Neoarchean Pukaskwa batholith consists of pre-, syn-, and post-tectonic phases emplaced over an interval of 50 million years. Pre-tectonic phases are broadly synvolcanic and have a high-Al tonalite–trondhjemite–granodiorite (TTG) affinity interpreted to reflect derivation by partial melting of basaltic crust at lower crustal or upper mantle depths. Minor syn-tectonic phases slightly post-date volcanism and have geochemical characteristics suggesting some involvement or interaction with an ultramafic (mantle) source component. Magmatic emplacement of pre- and syn-tectonic phases occurred in the midcrust at paleopressures of 550–600 MPa and these components of the batholith are thought to be representative of the midcrust underlying greenstone belts during their development. Subsequent to emplacement of the syntectonic phases, and likely at approximately 2680 Ma, the Pukaskwa batholith was uplifted as a structural dome relative to flanking greenstone belts synchronously with ongoing regional sinistral transpressive deformation. The driving force for vertical tectonism is interpreted to be density inversion (Rayleigh–Taylor-type instabilities) involving denser greenstone belts and underlying felsic plutonic crust. The trigger for initiation of this process is interpreted to be an abrupt change in the rheology of the midcrust attributed to introduction of heat from the mantle attendant with slab breakoff or lithospheric delamination following the cessation of subduction. This process also led to partial melting of the intermediate to felsic midcrust generating post-tectonic granitic phases at approximately 2667 Ma. We propose that late density inversion-driven vertical tectonics is an inevitable consequence of horizontal (plate) tectonic processes associated with greenstone belt development within the Superior Province.

High-Temperature Metamorphism, Anataxis and Tectonic Evolution of a Mafic Granulite from the Eastern Himalayan Orogen

2018 ◽  
Vol 29 (5) ◽  
pp. 1010-1025 ◽  
Author(s):  
Zeming Zhang ◽  
Huixia Ding ◽  
Xin Dong ◽  
Zuolin Tian ◽  
Dongyan Kang ◽  
...  
Keyword(s):  
High Temperature ◽  
Tectonic Evolution ◽  
Mafic Granulite ◽  
Himalayan Orogen ◽  
High Temperature Metamorphism

The Pikwitonei Granulite Domain, Manitoba: a giant Neoarchean high-grade terrane in the northwest Superior ProvinceThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.N. Machado, T.E. Krogh, and W. Weber are deceased.

2011 ◽  
Vol 48 (2) ◽  
pp. 205-245 ◽  
Author(s):  
L. M. Heaman ◽  
Ch. O. Böhm ◽  
N. Machado ◽  
T. E. Krogh ◽  
W. Weber ◽  
...  
Keyword(s):  
Granulite Facies ◽  
Superior Province ◽  
High Grade ◽  
Metamorphic Zircon ◽  
Special Issue ◽  
Metamorphic History ◽  
Zircon Growth ◽  
The World ◽  
Northwestern Margin ◽  
History Of

The Pikwitonei Granulite Domain located at the northwestern margin of the Superior Province is one of the largest Neoarchean high-grade terranes in the world, with well-preserved granulite metamorphic assemblages preserved in a variety of lithologies, including enderbite, opdalite, charnockite, and mafic granulite. U–Pb geochronology has been attempted to unravel the protolith ages and metamorphic history of numerous lithologies at three main localities; Natawahunan Lake, Sipiwesk Lake, and Cauchon Lake. The U–Pb age results indicate that some of the layered enderbite gneisses are Mesoarchean (3.4–3.0 Ga) and the more massive enderbites are Neoarchean. The high-grade metamorphic history of the Pikwitonei Granulite Domain is complex and multistage with at least four episodes of metamorphic zircon growth identified: (1) 2716.1 ± 3.8 Ma, (2) 2694.6 ± 0.6 Ma, (3) 2679.6 ± 0.9 Ma, and (4) 2642.5 ± 0.9 Ma. Metamorphic zircon growth during episodes 2 and 3 are interpreted to be regional in extent, corresponding to M1 amphibolite- and M2 granulite-facies events, respectively, consistent with previous field observations. The youngest metamorphic episode at 2642.5 Ma is only recognized at southern Cauchon Lake, where it coincides with granite melt production and possible development of a major northeast-trending deformation zone. The timing and multistage metamorphic history recorded in the Pikwitonei Granulite Domain is similar to most Superior Province high-grade terranes and marks a fundamental break in Archean crustal evolution worldwide at the termination of prolific global Neoarchean greenstone belt formation.

A Discussion on natural strain and geological structure - Archaean deformation patterns in southern Africa

1976 ◽  
Vol 283 (1312) ◽  
pp. 313-331 ◽  
Keyword(s):  
Shear Zones ◽  
Geological Structure ◽  
Mobile Belt ◽  
Deformation Pattern ◽  
Strain Measurements ◽  
Regional Deformation ◽  
Greenstone Belts ◽  
Extension Direction ◽  
Orogenic Belts ◽  
Limpopo Belt

Strain measurements have been made to help quantify the intensity of deformation and amount of displacement across Archaean greenstone belts in Rhodesia and Botswana and across the gneisses of the Limpopo mobile belt. The area has been divided into three domains based on the orientation of the finite strain fabric and the orientation of the maximum extension direction in associated shear zones. The domains are considered to have different movement patterns and to be similar to small orogenic belts. Early deformation within the greenstone belts accompanied the intrusion of the diaipric granites, but there was also bulk translation and rotation of greenstone belt and gneiss leading to imbrication of the stratigraphic pile and the formation of large nappes of overturned rock. This was followed by regional phases of deformation which affected all the greenstone belts and the gneisses of the Limpopo belt. Detailed strain measurements show a variation in amount of shortening during this phase, from under 30 % across the Shabani-Bellingwe belt in central Rhodesia, to over 60 % across the Tati and Matsitama belts in northern Botswana. Many local variations in intensity of deformation occur within large ductile shear zones and deviations from plane strain may be partly due to such rotational deformation. The regional deformation pattern suggests that there was movement of the Rhodesian craton approximately 200 km to the southwest relative to the gneisses of the Limpopo belt, producing a dominantly flattening deformation in the southwest of Rhodesia, but dominantly simple shear with a nearly horizontal sinistral movement, in the southeast.

Relationships between distributed and localized shear in the tectonic evolution of a Caledonian fold and thrust zone, northwest Ireland

1994 ◽  
Vol 131 (1) ◽  
pp. 123-136 ◽  
Author(s):  
G. I. Alsop
Keyword(s):  
Tectonic Evolution ◽  
Large Scale ◽  
Structural Investigation ◽  
Localized Deformation ◽  
Large Magnitude ◽  
Structural Anisotropy ◽  
Transport Direction ◽  
Thrust Zone ◽  
And Migration ◽  
Orogenic Belts

AbstractBroad zones of distributed shear operating through mid-crustal regions of orogenic belts may incorporate narrow horizons of intense localized deformation culminating in discrete, large magnitude displacements. The relative importance and relationship between distributed and localized shear are influenced by a variety of factors including lithological variation, pre-existing structural anisotropy, strain rate and migration of fluids. Rigorous structural analysis of lower amphibolite facies Dalradian metasediments in northwestern Ireland demonstrates that an early (D1) discrete ductile detachment was subsequently reactivated during distributed non-coaxial D2 deformation operating in a broad zone through the structural pile. Regional shear was directed towards the southeast and resulted in the generation and translation of kilometre-scale, isoclinal, recumbent sheath folds which close and face towards the transport direction. The D1 detachment is clearly folded around the hinges of these major folds, whilst on fold limbs it was reactivated and acted as a local décollement within the zone of distributed shear. Shear criteria along the detachment indicate a southeast-directed translation of the major folds, in sympathy with regional shear. A broad zone of D3 translation operating through the nappe pile resulted in coaxial refolding of large scale F2 folds by the D3 Ballybofey Nappe producing a complex fold interference pattern. Non-coaxial D3 deformation resulted in continued reactivation of local decollements, together with the initiation of east-southeast directed oblique thrusts and partial dismemberment of D2 folds. Detailed structural investigation allows concepts of distributed and localized shear to be evaluated and models of crustal deformation to be assessed.

Where are the Eburnian–Transamazonian collisional belts?

1990 ◽  
Vol 27 (10) ◽  
pp. 1382-1393 ◽  
Author(s):  
Jean Michel Bertrand ◽  
Emmanuel Ferraz Jardim de Sá
Keyword(s):  
West African ◽  
High Grade ◽  
The West ◽  
West African Craton ◽  
Early Proterozoic ◽  
Late Proterozoic ◽  
Nappe Tectonics ◽  
Pan African ◽  
Orogenic Belts ◽  
Lower Crustal

The reconstruction of Early Proterozoic crustal evolution and geodynamic environments, in Africa and South America, is incomplete if cratonic areas alone are studied. If the presence of high-grade gneisses is considered as a first clue to past collisional behaviour, 2 Ga high-grade gneisses are more abundant within the Pan-African–Brasiliano mobile belts than in the intervening pre-Late Proterozoic cratons. The West African craton and the Guiana–Amazonia craton consist of relatively small Archaean nuclei and widespread low- to medium-grade volcanic and volcanoclastic formations intruded by Early Proterozoic granites. By contrast, 2 Ga granulitic assemblages and (or) nappes and syntectonic granites are known in several areas within the Pan-African–Brasiliano belts of Hoggar–Iforas–Air, Nigeria, Cameroon, and northeast Brazil. Nappe tectonics have been also described in the Congo–Chaillu craton, and Early Proterozoic reworking of older granulites may have occurred in the São Francisco craton. The location of the Pan-African–Brasiliano orogenic belts is probably controlled by preexisting major structures inherited from the Early Proterozoic. High-grade, lower crustal assemblages 2 Ga old have been uplifted or overthrust and now form polycyclic domains in these younger orogenic belts, though rarely in the cratons themselves. The Congo–Chaillu and perhaps the São Francisco craton are exceptional in showing controversial evidence of collisional Eburnian–Transamazonian assemblages undisturbed during Late Proterozoic time.

New high-precision U–Pb ages for the Island Lake greenstone belt, northwestern Superior Province: implications for regional stratigraphy and the extent of the North Caribou terrane

2006 ◽  
Vol 43 (7) ◽  
pp. 789-803 ◽  
Author(s):  
Jen Parks ◽  
Shoufa Lin ◽  
Don Davis ◽  
Tim Corkery
Keyword(s):  
Shear Zone ◽  
High Precision ◽  
Greenstone Belt ◽  
Superior Province ◽  
Geological History ◽  
Isotopic Data ◽  
Mapping Study ◽  
The North ◽  
Crustal Block ◽  
Greenstone Belts

A combined U–Pb and field mapping study of the Island Lake greenstone belt has led to the recognition of three distinct supracrustal assemblages. These assemblages record magmatic episodes at 2897, 2852, and 2744 Ma. Voluminous plutonic rocks within the belt range in age from 2894 to 2730 Ma, with a concentration at 2744 Ma. U–Pb data also show that a regional fault that transects the belt, the Savage Island shear zone, is not a terrane-bounding structure. The youngest sedimentary group in the belt, the Island Lake Group, has an unconformable relationship with older plutons. Sedimentation in this group is bracketed between 2712 and 2699 Ma. This group, and others similar to it in the northwestern Superior Province, is akin to Timiskaming-type sedimentary groups found throughout the Superior Province and in other Archean cratons. These data confirm that this belt experienced a complex geological history that spanned at least 200 million years, which is typical of greenstone belts in this area. Age correlations between the Island Lake belt and other belts in the northwest Superior Province suggest the existence of a volcanic "megasequence". This evidence, in combination with Nd isotopic data, indicates that the Oxford–Stull domain, and the Munro Lake, Island Lake, and North Caribou terranes may have been part of a much larger reworked Mesoarchean crustal block, the North Caribou superterrane. It appears that the Superior Province was assembled by accretion of such large independent crustal blocks, whose individual histories involved extended periods of autochthonous development.

Sign in / Sign up

Export Citation Format

Share Document