Precise U–Pb zircon ages from the Gamitagama greenstone belt, southern Superior Province

1982 ◽  
Vol 19 (4) ◽  
pp. 859-867 ◽  
Author(s):  
T. E. Krogh ◽  
A. Turek
Keyword(s):  
Greenstone Belt ◽  
Sedimentary Cover ◽  
Lake Superior ◽  
Superior Province ◽  
Deep Zone ◽  
Abitibi Greenstone Belt

Volcanism in the Gamitagama Lake greenstone belt, 50 km south of Wawa, Ontario, on the east shore of Lake Superior, took place [Formula: see text] ago at the same time as similar volcanism in the much larger Abitibi greenstone belt to the east. Two post-orogenic intrusions in the metavolcanic–metasedimentary terrain are coeval at [Formula: see text] and [Formula: see text] and could very well be comagmatic as suggested by Ayres. A granitic sill in a metasedimentary–granitic migmatite terrain that borders the greenstone belt to the southwest has an age of 2615 ± 10 Ma and is much younger than the post-orogenic plutons to the northeast. This migmatite region represents either an uplifted deep zone that remained hot long after volcanism or a region that accumulated heat as a result of its sedimentary cover.

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.

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.

Orogen parallel and transverse shearing in the Opatica belt, Quebec: implications for the structure of the Abitibi Subprovince

1992 ◽  
Vol 29 (11) ◽  
pp. 2429-2444 ◽  
Author(s):  
Keith Benn ◽  
Edward W. Sawyer ◽  
Jean-Luc Bouchez
Keyword(s):  
Greenstone Belt ◽  
Regional Scale ◽  
Structural Evolution ◽  
Fault Zones ◽  
Crustal Thickening ◽  
Superior Province ◽  
Northern Margin ◽  
Abitibi Greenstone Belt ◽  
Ductile Shearing ◽  
Abitibi Subprovince

The late Archean Opatica granitoid-gneiss belt is situated within the northern Abitibi Subprovince, along the northern margin of the Abitibi greenstone belt. Approximately 200 km of structural section was mapped along three traverses within the previously unstudied Opatica belt. The earliest preserved structures are penetrative foliations and stretching and mineral lineations recording regional ductile shearing (D1). Late-D1 deformation was concentrated into kilometre-scale ductile fault zones, typically with L > S tectonite fabrics. Two families of lineations are associated with D1, indicating shearing both parallel and transverse to the east-northeast trend of the belt. Lineations trending east-northeast or northwest–southeast tend to be dominant within domains separated by major fault zones. In light of the abundant evidence for early north–south compression documented throughout southern Superior Province, including the Abitibi greenstone belt, D1 is interpreted in terms of mid-crustal thrusting, probably resulting in considerable crustal thickening. Movement-sense indicators suggest that thrusting was dominantly southward vergent. D2 deformation resulted in the development of vertical, regional-scale dextral and sinistral transcurrent fault zones and open to tight upright horizontal folds of D1 fabrics. In the context of late Archean orogenesis in southern Superior Province, the tectonic histories of the Abitibi and Opatica belts should not be considered separately. The Opatica belt may correlate with the present-day mid-crustal levels of the Abitibi greenstone belt, and to crystalline complexes within the Abitibi belt. It is suggested that the Abitibi Subprovince should be viewed, at the regional scale, as a dominantly southward-vergent orogenic belt. This work demonstrates that structural study of granitoid-gneiss belts adjacent to greenstone belts can shed considerable light on the regional structure and structural evolution of late Archean terranes.

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.

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