The Bell Lake group and Anton Complex: a basement – cover sequence beneath the Archean Yellowknife greenstone belt revealed and implicated in greenstone belt formation

1997 ◽  
Vol 34 (2) ◽  
pp. 169-189 ◽  
Author(s):  
C. E. Isachsen ◽  
S. A. Bowring
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Detrital Zircons ◽  
Iron Formation ◽  
Calc Alkaline ◽  
Banded Iron Formation ◽  
Slave Province ◽  
Extensional Setting

U–Pb zircon and monazite geochronology indicates the presence of a >2.93 Ga basement (Anton Complex) and >2.8 Ga cover sequence (Bell Lake group) beneath the 2.70 to >2.72 Ga Kam Group of the Yellowknife greenstone belt in the southern Slave Province. The Bell Lake group comprises remnants of a quartzite – rhyolite – banded iron formation succession. The ages of detrital zircons from the quartzite unit constrain its deposition to be younger than 2.92 and range up to 3.7 Ga. U–Pb ages for gneisses beneath the Bell Lake group are in excess of 2.93 Ga and they are locally overlain by the quartzite. The contact between the tholeiitic to calc-alkaline Kam Group and the Bell Lake group is poorly exposed and equivocal. Approximately 6 km higher in the section, the Ranney chert, a felsic volcaniclastic layer, separates 2.70 – 2.72 Ga tholeiitic to calc-alkaline upper Kam Group rocks from a lower tholeiitic section containing sheeted-dike complexes. Zircons from the Ranney chert yield Pb –Pb ages ranging from 2.72 to >2.8 Ga. The older ages suggest proximity of older basement during deposition of mostly tholeiitic lower Kam Group volcanic rocks in an extensional setting, followed by deposition of the upper Kam Group, which is more arc-like in character, on this earlier-formed tholeiitic crust beginning at 2.72 Ga.

The Central Slave Basement Complex, Part I: its structural topology and autochthonous cover

1999 ◽  
Vol 36 (7) ◽  
pp. 1083-1109 ◽  
Author(s):  
Wouter Bleeker ◽  
John WF Ketchum ◽  
Valerie A Jackson ◽  
Michael E Villeneuve
Keyword(s):  
Detrital Zircon ◽  
Hanging Wall ◽  
Volcanic Rocks ◽  
Iron Formation ◽  
Structural Topology ◽  
Banded Iron Formation ◽  
Basement Complex ◽  
South Central ◽  
Slave Province ◽  
Lake Formation

New field and geochronological data are used to define the distribution of Mesoarchean basement rocks in the south-central Slave Province. This distribution reflects a single contiguous basement terrane that we propose to call the Central Slave Basement Complex. It shows a structural topology that is internally consistent and compatible with known regional folding and faulting events. A sample of a proposed basement gneiss below the Courageous Lake greenstone belt, central Slave Province, has been dated by U-Pb methods and yields an age of 3325 ± 8 Ma, consistent with the new basement distribution. This sample also contains 2723 ± 3 Ma metamorphic zircon and ca. 2680 Ma titanite. The Central Slave Basement Complex is overlain by a thin, discontinuous, but distinctive cover sequence that includes minor volcanic rocks, clastic sedimentary rocks, and banded iron formation. All previously known and some new occurrences of this distinctive cover sequence occur in the immediate stratigraphic hanging wall of the Central Slave Basement Complex, locally overlying a preserved in situ unconformity. We propose to call this post-2.93 Ga cover sequence the Central Slave Cover Group. It is perhaps best typified by detrital chromite-bearing, fuchsitic quartzites. Formal formation names are proposed for the spatially separate occurrences of the Central Slave Cover Group. Detrital zircon ages are presented for one of the formations of the Central Slave Cover Group, the Patterson Lake Formation, which occurs on the western flank of a local basement culmination known as the Sleepy Dragon Complex. The detrital zircon data provide evidence for two discrete basement sources dated at ca. 2943 Ma and ca. 3147-3160 Ma. These detrital ages reinforce the depositional link between the Central Slave Cover Group and underlying crystalline rocks of the Central Slave Basement Complex.

The Central Slave Basement Complex, Part II: age and tectonic significance of high-strain zones along the basement-cover contact

1999 ◽  
Vol 36 (7) ◽  
pp. 1111-1130 ◽  
Author(s):  
Wouter Bleeker ◽  
John WF Ketchum ◽  
W J Davis
Keyword(s):  
High Strain ◽  
Volcanic Rocks ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Basement Complex ◽  
Maximum Displacement ◽  
Regional Deformation ◽  
Slave Province ◽  
Group A ◽  
Extensional Model

The basement-cover high-strain zone enveloping parts of the Sleepy Dragon Complex, northeast of Yellowknife, Slave Province, Canada, has been reinvestigated. Integrated stratigraphic, structural, and geochronological data show that the high-strain zone is of regional extent and is best interpreted as a décollement between crystalline, ca. 2.9-3.3 Ga rocks of the Central Slave Basement Complex and pre-2687 Ma cover rocks. Three temporally distinct mafic dyke swarms occur within the high-strain zone. The two oldest of these constrain the timing of the high-strain event to between 2734 ± 2 and 2687 ± 1 Ma. At the time of décollement development, the cover stratigraphy consisted of (i) the Central Slave Cover Group, a thin, pre-2734 Ma succession of mafic and ultramafic volcanic rocks, conglomerates, fuchsitic quartzites, minor rhyolites, and banded iron formation; and (ii) an overlying sequence of tholeiitic pillow basalts. The Central Slave Cover Group is considered to be autochthonous, whereas a variety of evidence suggests that the pillow basalts are parautochthonous to possibly allochthonous. The transport direction in the décollement was from northeast to southwest, and maximum displacement was probably on the order of 10 to several tens of kilometres. Presently, the décollement appears discontinuous due to younger intrusive and erosional events. Around most of the southern flanks of the Sleepy Dragon Complex, the crystalline core of the complex consists of post-décollement intrusive rocks and (or) is unconformably overlain by parts of the Yellowknife Supergroup that are younger than 2687 Ma. Lineation patterns in these younger rocks reflect regional deformation events that postdate and are unrelated to the décollement. The new data allow two tectonic models for development of the décollement: (i) a contractional thrusting model, involving collision of an eastern Slave Province arc terrane; or (ii) a syn-greenstone belt extensional model.

A new volcanic province: evidence from glacial erratics in western North Greenland

2000 ◽  
pp. 35-41 ◽  
Author(s):  
Peter R. Dawes ◽  
Bjørn Thomassen ◽  
T.I. Hauge Andersson
Keyword(s):  
Volcanic Rocks ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Common Component ◽  
Volcanic Province ◽  
North West ◽  
North East ◽  
The North ◽  
Surficial Deposits ◽  
North Greenland

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Dawes, P. R., Thomassen, B., & Andersson, T. H. (2000). A new volcanic province: evidence from glacial erratics in western North Greenland. Geology of Greenland Survey Bulletin, 186, 35-41. https://doi.org/10.34194/ggub.v186.5213 _______________ Mapping and regional geological studies in northern Greenland were carried out during the project Kane Basin 1999 (see Dawes et al. 2000, this volume). During ore geological studies in Washington Land by one of us (B.T.), finds of erratics of banded iron formation (BIF) directed special attention to the till, glaciofluvial and fluvial sediments. This led to the discovery that in certain parts of Daugaard-Jensen Land and Washington Land volcanic rocks form a common component of the surficial deposits, with particularly colourful, red porphyries catching the eye. The presence of BIF is interesting but not altogether unexpected since BIF erratics have been reported from southern Hall Land just to the north-east (Kelly & Bennike 1992) and such rocks crop out in the Precambrian shield of North-West Greenland to the south (Fig. 1; Dawes 1991). On the other hand, the presence of volcanic erratics was unexpected and stimulated the work reported on here.

scholarly journals Non-subduction petrological mechanisms for the growth of the neoarcheam continental crust of the Kola–Norwegian terrane, Fennoscandian shield: geological and isotope-geochemical evidence

2019 ◽  
Vol 27 (2) ◽  
pp. 161-186
Author(s):  
A. B. Vrevskii
Keyword(s):  
Continental Crust ◽  
Greenstone Belt ◽  
Geochemical Modeling ◽  
Volcanic Rocks ◽  
Fennoscandian Shield ◽  
Crustal Growth ◽  
Calc Alkaline ◽  
Geochemical Evidence

The paper reports new data on the composition and age of the Neoarchean calc-alkaline volcanic rocks of the Uraguba–Kolmozero–Voron’ya greenstone belt (UKV GB). Petrological-geochemical modeling indicates a polygenetic origin of primary melts of the basalt–andesite–dacite association and non-subduction geodynamic mechanisms for the crustal growth in the largest greenstone belt of the Kola–Norwegian Block of the Fennoscandian shield.

The application of the mise-a-la-masse electrical technique in Greenstone belt gold exploration

1989 ◽  
Vol 20 (2) ◽  
pp. 113
Author(s):  
L.G.B.T. Polomé
Keyword(s):  
Greenstone Belt ◽  
Electrical Potential ◽  
Gold Deposits ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Current Electrode ◽  
Barberton Greenstone Belt ◽  
A Current ◽  
Ore Zones ◽  
Gold Bearing

Most of the gold deposits in the Barberton Greenstone belt of South Africa are relatively small and in structurally complex geological areas.The mise-a-la-masse electrical technique, where a current electrode is earthed in a mineralised zone, was used on one of our exploration projects consisting of a sulphides/gold-bearing carbonaceous banded iron formation within a succession of mafic, ultramafic and sedimentary rocks. The technique was successful in delineating individual mineralised units within a broad lithological sequence. During the survey, electrical potential measurements were recorded on surface, in underground drives and in twenty five boreholes. Measurements were also repeated by earthing the mineralised zone in a number of boreholes. Major discontinuities were recognised within the ore zones and used to interpret geological structures. These were then used to define specific units for ore reserve calculations and the application of selected mining techniques.

scholarly journals Fractal Nature of the Band-Thickness in the Archean Banded Iron Formation in the Yellowknife Greenstone Belt, Northwest Territories, Canada

10.5772/55700 ◽  
2013 ◽  
Author(s):  
Nagayoshi Katsuta ◽  
Ichiko Shimizu ◽  
Masao Takano ◽  
Shin Kawakami ◽  
Herwart Helmstaedt ◽  
...  
Keyword(s):  
Northwest Territories ◽  
Greenstone Belt ◽  
Iron Formation ◽  
Fractal Nature ◽  
Banded Iron Formation

Geochemical Evolution of the Banded Iron Formation-Hosted High-Grade Iron Ore System in the Koolyanobbing Greenstone Belt, Western Australia

2012 ◽  
Vol 107 (4) ◽  
pp. 599-644 ◽  
Author(s):  
T. Angerer ◽  
S. G. Hagemann ◽  
L. V. Danyushevsky
Keyword(s):  
Western Australia ◽  
Greenstone Belt ◽  
Iron Ore ◽  
Iron Formation ◽  
Geochemical Evolution ◽  
High Grade ◽  
Banded Iron Formation

scholarly journals ORÓGENO ARAÇUAÍ: SÍNTESE DO CONHECIMENTO 30 ANOS APÓS ALMEIDA 1977

2013 ◽  
Author(s):  
Antônio Carlos Pedrosa-Soares ◽  
Carlos Maurício Noce ◽  
Fernando Flecha de Alkmim ◽  
Luiz Carlos da Silva ◽  
Marly Babinski ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Detrital Zircon ◽  
Volcanic Rocks ◽  
Oceanic Lithosphere ◽  
Continental Rift ◽  
Passive Margin ◽  
Iron Formation ◽  
Calc Alkaline ◽  
Magmatic Arc ◽  
Araçuaí Orogen

The Araçuaí Fold Belt was defined as the southeastern limit of the São Francisco Craton in the classicalpaper published by Fernando Flávio Marques de Almeida in 1977. This keystone of the Brazilian geologicliterature catalyzed important discoveries, such as of Neoproterozoic ophiolites and a calc-alkaline magmaticarc, related to the Araçuaí Belt and paleotectonic correlations with its counterpart located in Africa (the WestCongo Belt), that provided solid basis to define the Araçuaí-West-Congo Orogen by the end of the 1990thdecade. After the opening of the Atlantic Ocean in Cretaceous times, two thirds of the Araçuaí-West-CongoOrogen remained in the Brazil side, including records of the continental rift and passive margin phases ofthe precursor basin, all ophiolite slivers and the whole orogenic magmatism formed from the pre-collisionalto post-collisional stages. Thus, the name Araçuaí Orogen has been applied to the Neoproterozoic-Cambrianorogenic region that extends from the southeastern edge of the São Francisco Craton to the Atlantic coastlineand is roughly limited between the 15º and 21º S parallels. After 30 years of systematic geological mappingtogether with geochemical and geochronological studies published by many authors, all evolutionary stagesof the Araçuaí Orogen can be reasonably interpreted. Despite the regional metamorfism and deformation, thefollowing descriptions generally refer to protoliths. All mentioned ages were obtained by U-Pb method onzircon. The Macaúbas Group records rift, passive margin and oceanic environments of the precursor basinof the Araçuaí Orogen. From the base to the top and from proximal to distal units, this group comprises thepre-glacial Duas Barras and Rio Peixe Bravo formations, and the glaciogenic Serra do Catuni, Nova Auroraand Lower Chapada Acauã formations, related to continental rift and transitional stages, and the diamictitefreeUpper Chapada Acauã and Ribeirão da Folha formations, representing passive margin and oceanicenvironments. Dates of detrital zircon grains from Duas Barras sandstones and Serra do Catuni diamictitessuggest a maximum sedimentation age around 900 Ma for the lower Macaúbas Group, in agreement withages yielded by the Pedro Lessa mafic dikes (906 ± 2 Ma) and anorogenic granites of Salto da Divisa (875 ±9 Ma). The thick diamictite-bearing marine successions with sand-rich turbidites, diamictitic iron formation,mafic volcanic rocks and pelites (Nova Aurora and Lower Chapada Acauã formations) were depositedfrom the rift to transitional stages. The Upper Chapada Acauã Formation consists of a sand-pelite shelfsuccession, deposited after ca. 864 Ma ago in the proximal passive margin. The Ribeirão da Folha Formationmainly consists of sand-pelite turbidites, pelagic pelites, sulfide-bearing cherts and banded iron formations,representing distal passive margin to oceanic sedimentation. Gabbro and dolerite with plagiogranite veinsdated at ca. 660 Ma, and ultramafic rocks form tectonic slices of oceanic lithosphere thrust onto packagesof the Ribeirão da Folha Formation. The pre-collisional, calc-alkaline, continental magmatic arc (G1 Suite,630-585 Ma) consists of tonalites and granodiorites, with minor diorite and gabbro. A volcano-sedimentarysuccession of this magmatic arc includes pyroclastic and volcaniclastic rocks of dacitic composition datedat ca. 585 Ma, ascribed to the Palmital do Sul and Tumiritinga formations (Rio Doce Group), depositedfrom intra-arc to fore-arc settings. Detrital zircon geochronology suggests that the São Tomé wackes (RioDoce Group) represent intra-arc to back-arc sedimentation after ca. 594 Ma ago. The Salinas Formation, aconglomerate-wacke-pelite association located to northwest of the magmatic arc, represents synorogenicsedimentation younger than ca. 588 Ma. A huge zone of syn-collisional S-type granites (G2 Suite, 582-560Ma) occurs to the east and north of the pre-collisional magmatic arc, northward of latitude 20º S. Partialmelting of G2 granites originated peraluminous leucogranites (G3 Suite) from the late- to post-collisionalstages. A set of late structures, and the post-collisional intrusions of the S-type G4 Suite (535-500 Ma) andI-type G5 Suite (520-490 Ma) are related to the gravitational collapse of the orogen. The location of themagmatic arc, roughly parallel to the zone with ophiolite slivers, from the 17º30’ S latitude southwardssuggests that oceanic crust only developed along the southern segment of the precursor basin of the Araçuaí-West-Congo Orogen. This basin was carved, like a large gulf partially floored by oceanic crust, into the SãoFrancisco-Congo Paleocontinent, but paleogeographic reconstructions show that the Bahia-Gabon cratonicbridge (located to the north of the Araçuaí Orogen) subsisted since at least 1 Ga until the Atlantic opening.This uncommon geotectonic scenario inspired the concept of confined orogen, quoted as a new type ofcollisional orogen in the international literature, and the appealing nutcracker tectonic model to explain theAraçuaí-West-Congo Orogen evolution. 

scholarly journals The early Archaean to Proterozoic history of the Isukasia area, southern West Greenland

1986 ◽  
Vol 154 ◽  
pp. 1-80
Author(s):  
A.P Nutman
Keyword(s):  
Volcanic Rocks ◽  
Amphibolite Facies ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Stratigraphic Sequence ◽  
Supracrustal Belt ◽  
History Of ◽  
High Grade Metamorphism ◽  
Polyphase Metamorphism ◽  
Chemical Sediments

The c. 3800 Ma Isua supracrustal belt and associated smaller bodies of supracrustal rocks are intruded by >3600 Ma orthogneisses. A coherent stratigraphic sequence is recognised consisting of interlayered metabasic rocks, metasediments derived from volcanic rocks, chemical sediments, and metabasic and ultramafic intrusions. Despite repeated deformation and high-grade metamorphism sedimentary structures are locally preserved. The depositional environment was probably an immersed volcanic region remote from areas of significantly older crust. Conglomeratic structures in a metachert and banded iron formation unit suggest shoaling and shallow water conditions. Felsic sediments locally preserve evidence of deposition from turbidite flows. The Isua supracrustal rocks are regarded as thin fragments of a thicker, more extensive sequence. The orthogneisses that intrude the supracrustal rocks consist of 3750-3700 Ma multiphase tonalites (the grey gneisses) which were first intruded by the basic Inaluk dykes, then by abundant shallow-dipping swarms of c. 3600 Ma granite sheets (the white gneisses) and finally by c. 3400 Ma pegmatitic gneiss sheets. These early Archaean rocks were metamorphosed under amphibolite facies conditions and repeatedly deformed prior to intrusion of the Tarssartôq basic dykes in the mid Archaean. In the late Archaean (3100-2500 Ma) there was polyphase metamorphism up to amphibolite facies grade and two or more stages of deformation and local intrusion of granitic gneiss sheets and pegmatites. However, despite general strong deformation there is a large augen of low deformation preserved within the arc of the Isua supracrustal belt. During the Proterozoic there was intrusion of basic dykes, major faulting with associated recrystallisation under uppermost greenschist to lowermost amphibolite facies conditions, followed by heating and intrusion of acid dykes at c. 1600 Ma. No profitable mineralisations have been located.

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