Central Superior Province geology: evidence for an allochthonous, ensimatic, southern Abitibi greenstone belt

1990 ◽  
Vol 27 (4) ◽  
pp. 582-589 ◽  
Author(s):  
S. L. Jackson ◽  
R. H. Sutcliffe
Keyword(s):  
Crustal Structure ◽  
Greenstone Belt ◽  
Superior Province ◽  
Low Grade ◽  
Simple Correlation ◽  
Abitibi Greenstone Belt ◽  
Structural Style ◽  
Metavolcanic Rocks ◽  
Crustal Model ◽  
Greenstone Belts

Published U–Pb geochronological, geological, and petrochemical data suggest that there are late Archean ensialic greenstone belts (GB) (Michipicoten GB and possibly the northern Abitibi GB), ensimatic greenstone belts (southern Abitibi GB and Batchawana GB), and possibly a transitional ensimatic–ensialic greenstone belt (Swayze GB) in the central Superior Province. This lateral crustal variability may preclude simple correlation of the Michipicoten GB and its substrata, as exposed in the Kapuskasing Uplift, with that of the southern Abitibi GB. Furthermore, this lateral variability may have determined the locus of the Kapuskasing Uplift. Therefore, although the Kapuskasing Uplift provides a useful general crustal model, alternative models of crustal structure and tectonics for the southern Abitibi GB warrant examination.Thrusting of a juvenile, ensimatic southern Abitibi GB over a terrane containing evolved crust is consistent with (i) the structural style of the southern Abitibi GB; (ii) juvenile southern Abitibi GB metavolcanic rocks intruded by rocks having an isotopically evolved, older component; and (iii) Proterozoic extension that preserved low-grade metavolcanic rocks within the down-dropped Cobalt Embayment, which is bounded by higher grade terranes to the east and west.

Precambrian Weathering in Acid Metavolcanic Rocks from the Superior Province, Villebon Township, South-Central Québec

1975 ◽  
Vol 12 (12) ◽  
pp. 2080-2085 ◽  
Author(s):  
D. E. Vogel
Keyword(s):  
Greenstone Belt ◽  
Depositional Environment ◽  
Superior Province ◽  
Shallow Marine ◽  
Abitibi Greenstone Belt ◽  
South Central ◽  
Metavolcanic Rocks

Chloritoid- and kyanite-bearing acid metavolcanic rocks of the Abitibi Greenstone belt have acquired an aluminum surplus by weathering prior to metamorphism. The weathering increases from the top of the volcanic unit downwards, as shown by increasing values for both Niggli-t and the Zr/P ratio. The depositional environment of these rocks is postulated to be either shallow marine or terrestrial.

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.

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.

Archean mafic metavolcanics from the Rouyn–Noranda district, Abitibi Greenstone Belt, Quebec. 1. Mobility of the major elements

1982 ◽  
Vol 19 (12) ◽  
pp. 2258-2275 ◽  
Author(s):  
Léopold Gélinas ◽  
Michel Mellinger ◽  
Pierre Trudel
Keyword(s):  
Greenstone Belt ◽  
Great Depth ◽  
Major Elements ◽  
Chemical Degradation ◽  
Type I ◽  
Calc Alkaline ◽  
Calcium Leaching ◽  
Abitibi Greenstone Belt ◽  
Metavolcanic Rocks ◽  
Metamorphic Facies

In a suite of Archean mafic pillows from the Rouyn–Noranda region of Quebec's Abitibi Greenstoné Belt, including both tholeiitic and calc-alkaline varieties spanning the prehnite–pumpellyite to upper greenschist metamorphic facies, three types of alteration can be defined: (I) chlorite–epidote–actinolite; (II) chlorite–epidote; and (III) chlorite ± sericite; the number of mineral phases decreases as a result of progressive hydration from type I to type III alteration. Albitization, resulting from substitution of [Formula: see text], in calcic plagioclase, is highly variable in type I alteration, but in types II and III the plagioclase is totally albitized and in some cases silicified. Chloritization is closely linked to increasing hydration and Ca leaching with MgO and FeO substituting for CaO in ferromagnesian minerals.Calcium was mobilized and carried by solutions, as evidenced by the variable concentration of epidote at the margins of pillows. This calcium leaching generated an excess of Al2O3 with respect to the combined molecular proportions of Na2O, K2O, and CaO, and is shown by the presence of corundum in CIPW norm calculations. In some pillows showing substitution of [Formula: see text], the fo2 of the invading fluid appears to have remained constant, being buffered by the pillow composition; this would be favored by a low water/rock mass ratio. As a result, the initial pillow Fe2O3/FeO ratio remained constant. In other pillows, the fo2 appears to have been imposed by the invading fluid rather than by the mineral assemblage: the FeO/MgO ratios are thus no longer representative of the magmatic composition whereas the ΣFeO/MgO is still representative of the pristine magmatic value.Two types of substitution of CaO by FeO and (or) MgO have been observed: (1) preferential substitution restricted to type I alteration, of FeO over MgO, similar to low-temperature substitution in modern-day sea-floor alteration; and (2) the more common substitution in type II and III alterations in which MgO predominates over FeO, similar to the high-temperature substitution taking place at great depth on the ocean floor.Although the samples were collected to test mineral heterogeneities caused by chemical degradation, more than 40% of the pillows sampled retained their pristine ΣFeO/MgO ratios. The various alteration patterns are independent of the initial tholeiitic or calc-alkaline lineage; this was confirmed using rare earth elements (REE) and inert trace elements such as Zr, Y, and Ti. The chemical changes in the mafic metavolcanic rocks do not obliterate their tholeiitic or calc-alkaline chemical affinities.

Variable unroofing in the western Superior Province - metamorphic evidence and possible origin

2006 ◽  
Vol 43 (7) ◽  
pp. 805-819 ◽  
Author(s):  
Andrew Hynes ◽  
Zixin Song
Keyword(s):  
Superior Province ◽  
Surface Distribution ◽  
Seismic Line ◽  
The North ◽  
Metavolcanic Rocks ◽  
Limited Support ◽  
Greenstone Belts ◽  
Rotation Motion ◽  
East West ◽  
Broad Region

Western Superior Lithoprobe seismic-reflection line 1 exhibits a broad region of northward-dipping reflectors in the Uchi subprovince, which gives way to southward-dipping reflectors farther north in the Berens River sub province. Mafic metavolcanic rocks across the region of northward-dipping reflectors exhibit a decline in metamorphic pressure, from pressures of 6 kbar (1 kbar = 100 MPa) in the south to only 2 kbar 80 km to the north. This indicates that the southern edge of the Uchi subprovince has undergone significantly more unroofing than regions farther north. The differential unroofing is not consistent with a doubly vergent thrusting origin for the northward- and southward-dipping reflector pattern. It could result from a crustal-scale synform, of which the region of northward-dipping reflectors would make up the southern limb. Metamorphic pressures from samples off the seismic line, however, provide only limited support for a regional synform, and suggest that much of the pressure variation may result from deformation associated with motion on late faults that are widespread in the western Superior Province. These faults occur in a WNW-striking set with dextral offsets and an ENE-striking set with sinistral offsets. They could result from north–south compression and east–west extension, provided the faults have rotated towards the east–west direction during deformation. Regional tilting and (or) jostling of crustal blocks is attributed to deformation associated with the fault rotation. Motion on the faults and the associated deformation of intervening fault blocks may be important contributors to the present crustal architecture of the western Superior Province, including the surface distribution and form of the greenstone belts.

Geodynamic setting, crustal architecture, and VMS metallogeny of ca. 2720 Ma greenstone belt assemblages of the northern Wawa subprovince, Superior Province

2015 ◽  
Vol 52 (3) ◽  
pp. 196-214 ◽  
Author(s):  
Robert W.D. Lodge ◽  
Harold L. Gibson ◽  
Greg M. Stott ◽  
James M. Franklin ◽  
George J. Hudak
Keyword(s):  
Trace Element ◽  
Greenstone Belt ◽  
Tectonic Setting ◽  
Geodynamic Setting ◽  
Trace Element Geochemistry ◽  
Superior Province ◽  
Suprasubduction Zone ◽  
Greenstone Belts ◽  
Arc Setting ◽  
Back Arc

The greenstone belts along the northern margin of the Wawa subprovince of the Superior Province (Vermilion, Shebandowan, Winston Lake, Manitouwadge) formed at ca. 2720 Ma and have been interpreted to be representative of a rifted-arc to back-arc tectonic setting. Despite a common inferred tectonic setting and broad similarities, these greenstone belts have a significantly different metallogeny as evidenced by different endowments in volcanogenic massive sulphide (VMS), magmatic sulphide, and orogenic gold deposits. In this paper, we examine differences in geodynamic setting and crustal architecture as they pertain to the metallogeny of each greenstone belt by characterizing the regional-scale trace-element and isotopic (Nd and Pb) geochemistry of each belt. The trace-element geochemistry of the Vermilion greenstone belt (VGB) shows evidence for a transition from arc-like to back-arc mafic rocks in the Soudan belt to plume-driven rifted arcs in the ultramafic-bearing Newton belt. The Shebandowan greenstone belt (SGB) has a significant proportion of calc-alkalic, arc-like basalts, intermediate lithofacies, and high-Mg andesites, which are characteristic of low-angle, “hot” subduction. Extensional settings within the SGB are plume-driven and associated with komatiitic ultramafic and mid-ocean ridge basalt (MORB)-like basalts. The Winston Lake greenstone belt (WGB) is characterized by a transition from calc-alkalic, arc-like basalts to back-arc basalts upward in the strata and is capped by alkalic ocean-island basalt (OIB)-like basalts. This association is consistent with plume-driven rifting of a mature arc setting. Each of the VGB, SGB, and WGB show some isotopic evidence for the interaction with a juvenile or slightly older differentiated crust. The Manitouwadge greenstone belt (MGB) is characterized by isotopically juvenile, bimodal, tholeiitic to transitional volcanic lithofacies in a back-arc setting. The MGB is the most isotopically juvenile belt and is also the most productive in terms of VMS mineralization. The Zn-rich VMS mineralization within the WGB suggests a relatively lower-temperature hydrothermal system, possibly within a relatively shallow-water environment. The Zn-dominated and locally Au-enriched VMS mineralization, as well as mafic lithofacies and alteration assemblages, are characteristic of relatively shallower-water deposition in the VGB and SGB, and indicate that the ideal VMS-forming tectonic condition may have been compromised by a shallower-water depositional setting. However, the thickened arc crust and compressional tectonics of the SGB suprasubduction zone during hot subduction may have provided a crustal setting more favourable for the magmatic Ni–Cu sulphide and relative gold endowment of this belt.

THE SHAPE AND THICKNESS OF AN ARCHAEAN GREENSTONE BELT BY GRAVITY METHODS

1965 ◽  
Vol 2 (5) ◽  
pp. 418-424 ◽  
Author(s):  
F. S. Grant ◽  
W. H. Gross ◽  
M. A. Chinnery
Keyword(s):  
Greenstone Belt ◽  
Granitic Rocks ◽  
Superior Province ◽  
Precambrian Shield ◽  
Maximum Thickness ◽  
Red Lake ◽  
Gravity Effects ◽  
Greenstone Belts

The Red Lake greenstone belt is Archaean in age (older than 2.5 billion years) and is located in the Superior province of the Canadian Precambrian Shield. It is a fairly typical greenstone belt, being composed of a complex assemblage of lavas, sediments, and intrusives. The belt is completely surrounded, and therefore is isolated from other greenstone belts, by granitic batholiths and acid paragneiss. Generally speaking, greenstones are more dense than the surrounding granitic rocks and they therefore give positive gravity effects, the amplitudes of which give some indication of their shape and overall thickness.At Red Lake, the greenstone belt is approximately 35 mi long by 18 mi wide. Gravity readings taken across the width of the belt indicate that the greenstones taper sharply in depth to a maximum thickness of approximately 25 000 ft. These results appear to confirm, as most geologists feel intuitively, that greenstone belts are basin-shaped and are underlain by granitic batholiths and gneiss.

Geochemical evolution in the Blake River Group, Abitibi Greenstone Belt, Superior Province

1980 ◽  
Vol 17 (9) ◽  
pp. 1292-1299 ◽  
Author(s):  
I. E. M. Smith
Keyword(s):  
Rare Earth ◽  
Volcanic Rock ◽  
Rare Earth Element ◽  
Greenstone Belt ◽  
Earth Element ◽  
Superior Province ◽  
Calc Alkaline ◽  
Abitibi Greenstone Belt ◽  
Rock Types ◽  
Element Fractionation

In well exposed, well developed greenstone belts of the Superior Province there is a clear progression from stratigraphically lower, geochemically primitive volcanic rock types (komatiites, tholeiites) to overlying geochemically evolved calc-alkaline volcanic rock types. In the western Blake River Group of the Abitibi Greenstone Belt the change from tholeiitic to calc-alkaline volcanics represents a geochemical discontinuity defined by an increase in incompatible elements and light/heavy rare-earth element fractionation in the overlying rocks. Quantitative modelling of the parameters of the discontinuity indicates that it can be explained by a change to very small amounts of melting of unmodified mantle lherzolite, although this is not a unique solution. In calc-alkaline suites showing high degrees of rare-earth element fractionation the calculated melt fraction required of unmodified mantle becomes unrealistically low and models involving a geochemically evolved source may have to be considered.

U–Pb zircon ages of volcanism and plutonism in the Mishibishu greenstone belt near Wawa, Ontario

1990 ◽  
Vol 27 (5) ◽  
pp. 649-656 ◽  
Author(s):  
A. Turek ◽  
R. Keller ◽  
W. R. Van Schmus
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Superior Province ◽  
Calc Alkaline ◽  
Metasedimentary Rocks ◽  
Metavolcanic Rocks ◽  
Volcanic Pile ◽  
Archean Greenstone Belt

The Mishibishu greenstone belt, located 40 km west of Wawa, is a typical Archean greenstone belt and is probably an extension of the Michipicoten belt. This belt is composed of basic to felsic metavolcanic rocks of tholeiitic to calc-alkaline affinity and of metasedimentary rocks ranging from conglomerate to argillite. Granitoids, diorites, and gabbros intrude and embay supracrustal rocks as internal and external plutons.Six U–Pb zircon ages have been obtained on rocks in this area. The oldest is 2721 ± 4 Ma for the Jostle Lake tonalite. The bulk of the volcanic rocks formed by 2696 ± 17 Ma, which is the age of the Chimney Point porphyry at the top of the volcanic pile. The Pilot Harbour granite has a similar age of 2693 ± 7 Ma. The age of the Tee Lake tonalite is 2673 ± 12 Ma, and the age of the Iron. Lake gabbro is 2671 ± 4 Ma. The youngest age for volcanics in this part of the Superior Province is 2677 ± 7 Ma, obtained from, the David Lakes pyroclastic breccia. these ages agree with those reported for the adjacent Michipicoten and Gamitagama belts.

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