Geochronology of orthogneiss adjacent to the Archean Lake of the Woods greenstone belt, northwestern Ontario: a possible basement complex

1981 ◽  
Vol 18 (1) ◽  
pp. 94-102 ◽  
Author(s):  
G. S. Clark ◽  
R. Bald ◽  
L. D. Ayres
Keyword(s):  
Greenstone Belt ◽  
Canadian Shield ◽  
Amphibolite Facies ◽  
Isotopic Age ◽  
Basement Complex ◽  
Degree Of Deformation ◽  
Lake Of The Woods ◽  
The North ◽  
Northwestern Ontario

Deformed and recrystallized, amphibolite facies, trondhjemitic to granodioritic orthogneiss along the north margin of the Archean Lake of the Woods greenstone belt has an Rb–Sr isochron age of 2950 ± 150 Ma and an initial 87Sr/86Sr ratio of 0.7028 ± 0.0014. Preserved primary textures and complex internal intrusive relationships document the original plutonic nature of the orthogneiss. Based on isotopic age and degree of deformation and recrystallization, the orthogneiss is interpreted to be basement to the adjacent metavolcanic sequence of the greenstone belt. The contact between the orthogneiss and greenstone belt is the locus of deformation, but may be an unconformity. It is also the boundary between the English River subprovince on the north and the Wabigoon subprovince on the south.Similar orthogneiss ranging in age from 2800 to 3800 Ma is widespread in the Canadian Shield. It is basement to the 2650–2750 Ma Archean volcanism, at least in some areas, but is not necessarily basement to the older (2800–3000 Ma) volcanism. The orthogneisses are remnants of a once much more extensive sialic terrain, but the contemporaneity and extent of this sialic terrain are uncertain.

Orthoquartzite pebbles in Archean conglomerate, North Spirit Lake, northwestern Ontario

1977 ◽  
Vol 14 (9) ◽  
pp. 1980-1990 ◽  
Author(s):  
J. A. Donaldson ◽  
Richard W. Ojakangas
Keyword(s):  
Greenstone Belt ◽  
Sedimentary Rocks ◽  
Canadian Shield ◽  
Superior Province ◽  
Lake Area ◽  
Definite Evidence ◽  
The North ◽  
Northwestern Ontario ◽  
Form Part ◽  
Quartz Grains

An Archean conglomerate in the North Spirit Lake area of northwestern Ontario contains rare orthoquartzite pebbles. Detailed study of these pebbles shows that mineralogically they are very mature, consisting of as much as 99.8 percent quartz and a heavy mineral suite of zircon, tourmaline, and apatite. Textures are typically bimodal, characterized by rounded sand-sized quartz grains set in a 'matrix-cement' of thoroughly recrystallized finer quartz grains. These orthoquartzite pebbles provide the first definite evidence for local tectonic stability of the Canadian Shield before deposition of the immature sedimentary rocks that form part of an Archean (>2.6 Ga) greenstone belt of the Superior Province.

Trondhjemitic basement enclave near the Archean Favourable Lake volcanic complex, northwestern Ontario, Canada

1980 ◽  
Vol 17 (5) ◽  
pp. 652-667 ◽  
Author(s):  
E. M. Hillary ◽  
L. D. Ayres
Keyword(s):  
Partial Melting ◽  
Amphibolite Facies ◽  
Volcanic Complex ◽  
Volcanic Event ◽  
Major Phase ◽  
Trout Lake ◽  
The North ◽  
Northwestern Ontario ◽  
Quartz Monzonite ◽  
Facies Metamorphism

A 15 km2 foliated to gneissic trondhjemite enclave (2.91 Ga) in the Archean North Trout Lake batholith is a metamorphosed remnant of prevolcanism sialic basement. The basement is separated from the nearby Archean Favourable Lake volcanic complex by younger plutons, but was a source of detritus for some of the sedimentary formations in the volcanic complex. The trondhjemite is only a small remnant of an originally more extensive basement.Primary plutonic features can be readily recognized in the trondhjemite in spite of amphibolite facies metamorphism. The basement underwent at least two deformational events: (1) syn-emplacement deformation that produced foliation and gneissosity, and brecciated and deformed early dikes and xenoliths and (2) later recrystallization. The recrystallization was caused by strain and heat produced by emplacement of the North Trout Lake batholith. Emplacement of successive batholith phases progressively heated the basement and elevated it from its originally deeper level. Metamorphism culminated with emplacement of the youngest major phase of the batholith. The intensity of recrystallization and the habit and abundance of late leucocratic quartz monzonite sills and dikes are zoned with respect to this youngest phase.The high Al2O3 trondhjemitic magma probably formed by partial melting of amphibolite at relatively shallow depths. The parent amphibolite probably represents a still earlier volcanic event.

Overburden geochemical signature of the Lac des Iles platinum group element deposit, northwestern Ontario, Canada

2007 ◽  
Vol 44 (8) ◽  
pp. 1151-1168 ◽  
Author(s):  
Peter J Barnett
Keyword(s):  
Mineral Exploration ◽  
Shallow Groundwater ◽  
Soil System ◽  
Near Surface ◽  
Rock Fragments ◽  
The North ◽  
Northwestern Ontario ◽  
Airborne Contamination ◽  
The Many ◽  
Lac Des Iles

Many previously published studies of the behaviour of Pt and Pd in till and soils have been done in areas of complex stratigraphy or very thin overburden cover, making the interpretation of soil results difficult because of the many variables associated with these settings. At the Lac des Iles mine site in northwestern Ontario, there are excellent exposures of the overburden in a series of exploration trenches. Glacial dispersal trains can be observed in till (C horizon) geochemistry (e.g., Ni, Cr, Cu, and Co). Regional geochemical dispersal trains of elements, such as Ni, Cr, Mg, and Co associated with the North Lac des Iles intrusion, can be detected for about 4 km beyond the western margin of the Mine Block intrusion. Entire dispersal trains range from 5 to 7 km in length and about 1 to 2 km in width. The dispersal of North Lac des Iles intrusion rock fragments tends to mask the response of the Mine Block intrusion. Dispersal trains of Pt and Pd are not well defined and tend to be very short, <1 km in length, due to the initial low concentrations of these elements in C-horizon till samples from the Lac Des Iles area. An exception to this is the Pd dispersal train originating from the high-grade zone that is up to 3 km long. Pd, Pt, Ni, and Cu appear to be moving both within and out of the soil system downslope into surface and shallow groundwater. It is suggested that these elements, to varying degrees, are moving in solution. Airborne contamination from mine operations of the humus has adversely affected the ability to determine the effectiveness of humus sampling for mineral exploration at Lac des Iles. The airborne contamination likely influences the geochemical results from surface water, shallow groundwater, and near-surface organic bog samples, particularly for the elements Pd and Pt.

Overview of regional geophysical studies in Manitoba and northwestern Ontario

1982 ◽  
Vol 19 (11) ◽  
pp. 2049-2059 ◽  
Author(s):  
D. H. Hall ◽  
W. C. Brisbin
Keyword(s):  
Greenstone Belt ◽  
Seismic Velocities ◽  
Crustal Layer ◽  
Northwestern Ontario ◽  
Reflection And Refraction ◽  
Gravity And Magnetic ◽  
Winnipeg River ◽  
Lower Crustal ◽  
Gravity And Magnetic Anomaly

This paper presents an overview of six geophysical projects (seismic reflection and refraction, gravity and magnetic anomaly interpretation, specific gravity and magnetic property measurements) carried out in an area in Manitoba and northwestern Ontario bounded by 93 and 96°W longitude, and 49 and 51°N latitude.The purpose of the surveys was to define crustal structure in the Kenora–Wabigoon greenstone belt, the Winnipeg River batholithic belt, the Ear Falls – Manigotagan gneiss belt, and the Uchi greenstone belt. The following conclusions emerge.In all of the belts, a major discontinuity divides the crust into the commonly found upper and lower crustal sections. At the top of the lower crust, a seismically distinct layer (the mid-crustal layer) occurs. Seismic velocities in this layer suggest either intermediate to basic igneous rocks or metamorphic rocks of the amphibolite facies.Crustal geophysical characteristics vary sufficiently among the four belts to justify the classification of all four as distinct subprovinces of the Superior Province.Cet article présente une vue générale sur six projets de géophysique (réflexion et réfraction sismique, interprétation d'anomalies de gravité et magnétiques, déterminations de densité et de propriétés magnétiques) réalisés dans une région du Manitoba et du nord-ouest de l'Ontario encadrée par les longitudes 93 et 96°O et les latitudes 49 et 51°N.

scholarly journals Structural and geochronological constraints on the evolution of the Juréia Massif, Registro Domain, State of São Paulo, Brazil

2007 ◽  
Vol 79 (3) ◽  
pp. 441-455 ◽  
Author(s):  
Cláudia R. Passarelli ◽  
Miguel A.S. Basei ◽  
Hélcio J. Prazeres-Filho ◽  
Oswaldo Siga-Jr. ◽  
Gergely A.J. Szabó ◽  
...  
Keyword(s):  
Shear Zone ◽  
Sao Paulo ◽  
Amphibolite Facies ◽  
Metamorphic Event ◽  
São Paulo ◽  
Paulo State ◽  
The North ◽  
Domain State ◽  
Geochronological Constraints ◽  
Shear System

The Juréia Massif, southeastern São Paulo State (Brazil), is part of the Registro Domain, limited to the north by the Cubatão-Itariri Shear System and to the south by the Serrinha Shear Zone. Mostly composed of migmatitic granitegneiss rocks, represents a Paleoproterozoic terrane (1.9-2.2 Ga) strongly deformed during the Neoproterozoic (750-580 Ma). The present tectonic scenario was established at the end of the Neoproterozoic, as a result of collages associated with the formation of Western Gondwana. The Ponta da Juréia, our study area within the Juréia Massif, is constituted by paragneisses (garnet-muscovite-biotite gneisses). The monazite U-Pb age of 750 Ma is related to a main regional metamorphic event that reached the high amphibolite facies, recorded in rocks from the Itatins Complex and Cachoeira Sequence as well, which also belongs to the Registro Domain. The paragneissic rocks of this study are affected by the E-W-trending Serrinha Shear Zone, registering a predominantly dextral movement. Biotite K-Ar ages of 482 ± 12 Ma may represent later movements and reflect the younger ages of reactivation of the major lineaments and juxtaposition of the tectonic blocks involved.

scholarly journals Mapping in the Fiskefjord area, southern West Greenland

1982 ◽  
Vol 110 ◽  
pp. 55-57
Author(s):  
A.A Garde ◽  
V.R McGregor
Keyword(s):  
Granulite Facies ◽  
Amphibolite Facies ◽  
Isotopic Age ◽  
Supracrustal Rock ◽  
Granulite Facies Metamorphism ◽  
West Greenland ◽  
Facies Metamorphism ◽  
Geological Work ◽  
Age Determinations

Previous geological work on the 1:100000 map sheet 64 V.l N (fig. 15) includes published maps of smaller areas by Berthelsen (1960, 1962) and Lauerma (1964), mapping by Kryolitselskabet Øresund A/S (Bridgwater et al., 1976) and mapping by GGU geologists for the 1:500000 map sheet Frederikshåb Isblink - Søndre Strømfjord (Allaart et al., 1977, 1978). The Amltsoq and Niik gneisses and Malene supracrustal rock units south and east of Godthåbsfjord have not so far been correlated with rocks in the Fiskefjord area. Godthåbsfjord separates the granulite facies gneisses in Nordlandet from amphibolite facies Nûk gneisses on Sadelø and Bjørneøen; the granulite facies metamorphism occurred at about 2850 m.y. (Black et al., 1973), while no published isotopic age determinations from the Fiskefjord area itself are available.

Age and Geochemical Studies of the Snyder Breccia, Coastal Labrador

1975 ◽  
Vol 12 (3) ◽  
pp. 361-370 ◽  
Author(s):  
Jackson M. Barton Jr. ◽  
Erika S. Barton
Keyword(s):  
Trace Element ◽  
North Atlantic ◽  
Layered Intrusion ◽  
Basement Complex ◽  
Fine Grained ◽  
The North ◽  
Isotopic Analyses ◽  
The Matrix ◽  
The North Atlantic ◽  
Geochemical Studies

The Snyder breccia is composed of angular to subrounded xenoliths of migmatites and amphibolites in a very fine grained matrix. It is apparently intrusive into the metasediments of the Snyder Group exposed at Snyder Bay, Labrador. The Snyder Group unconformably overlies a migmatitic and amphibolitic basement complex and is intruded by the Kiglapait layered intrusion. K–Ar ages indicate that the basement complex is Archean in age (> 2600 m.y. old) and that the Kiglapait layered intrusion was emplaced prior to 1280 m.y. ago. Major and trace element analyses of the matrix of the Snyder breccia indicate that while it was originally of tonalitic composition, later it locally underwent alteration characterized by loss of sodium and strontium and gain of potassium, rubidium and barium. Rb–Sr isotopic analyses show that this alteration occurred about 1842 m.y. ago, most probably contemporaneously with emplacement of the breccia. The Snyder Group thus was deposited sometime between 2600 and 1842 m.y. ago and may be correlative with other Aphebian successions preserved on the North Atlantic Archean craton.

Mid-Ordovician subduction, obduction, and eduction in western Newfoundland; an eclogite problem

2021 ◽  
Author(s):  
J.F. Dewey ◽  
J.F. Casey
Keyword(s):  
Subduction Zone ◽  
Shear Zone ◽  
Continental Margin ◽  
Amphibolite Facies ◽  
Island Arcs ◽  
Early Ordovician ◽  
The North ◽  
Shelf Slope ◽  
Major Strike ◽  
Laurentian Margin

Abstract. The narrow, short-lived Taconic-Grampian Orogen occurs along the north-western margin of the Appalachian-Caledonian Belt from, at least, Alabama to Scotland, a result of the collision of a series of early Ordovician oceanic island arcs with the rifted margin of Laurentia. The present distribution of Taconian-Grampian ophiolites is unlikely to represent a single fore-arc from Alabama to Scotland colliding at the same time with the continental margin along its whole length; more likely is that there were several Ordovician arcs with separate ophiolites. The collision suture is at the thrust base of obducted fore-arc ophiolite complexes, and obduction distance was about two hundred kilometres. Footwalls to the ophiolites are, sequentially towards the continent, continental margin rift sediments and volcanics and overlying rise sediments, continental shelf slope carbonates, and sediments of foreland flexural basins. The regionally-flat obduction thrust complex between the ophiolite and the rifted Laurentian margin is the collision suture between arc and continent. A particular problem in drawing tectonic profiles across the Taconic-Grampian Zone is several orogen-parallel major strike-slip faults, both sinistral and dextral, of unknown displacements, which may juxtapose portions of different segments. In western Newfoundland, most of the Grenville basement beneath the Fleur-de-Lys metamorphic complex (Neoproterozoic to early Ordovician meta-sediments) was eclogitised during the Taconic Orogeny and separated by a massive shear zone from the overlying Fleur-de-Lys, which was metamorphosed at the same time but in the amphibolite facies. The shear zone continued either to a distal intracontinental “subduction zone” or to the main, sub-fore-arc, subduction zone beneath which the basement slipped down to depths of up to seventy kilometres at the same time as the ophiolite sheet and its previously-subcreted metamorphic sole were being obducted above. Subsequently, the eclogitised basement was returned to contact with the amphibolite-facies cover by extensional detachment eduction, possibly enhanced by subduction channel flow, which may have been caused by slab break-off and extension during subduction polarity flip. Although the basal ophiolite obduction thrust complex and the Fleur-de-Lys-basement subduction-eduction surfaces must have been initially gently-dipping to sub-horizontal, they were folded and broken by thrusts during late Taconian, late Ordovician Salinic-Mayoian, and Acadian shortening.

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