Diapiric structures and regional compression in an Archean greenstone belt, Island Lake, Manitoba

1978 ◽  
Vol 15 (11) ◽  
pp. 1817-1825 ◽  
Author(s):  
W. K. Fyson ◽  
R. K. Herd ◽  
I. F. Ermanovics
Keyword(s):  
Greenstone Belt ◽  
Large Pressure ◽  
Archean Greenstone Belt ◽  
East West ◽  
Pressure Shadow ◽  
Regional Compression

The sequence of structures affecting rocks of the Island Lake greenstone belt suggests a progression from structures attributable to emplacement of granitic plutons to those that are of regional extent. Early homoclines (D0 deformation) and isoclinal folds (D1) are overturned or face away from marginal plutons which partly truncate the folds. Granitic offshoots display an S1 foliation. Syn-D1 emplacement of the granite is implied, and the pattern of homoclines and folds is consistent with deformation due to diapiric uplift.Later upright folds (D2) and a widespread subvertical schistosity S2 trend eastward throughout most of the region. S2 passes with little deflection into the granites. D1 folds are rotated towards S2 and clasts and volcanic vesicles are flattened, except within a zone of low strain extending 15 km east–west between two plutons. Evidently during D2 deformation the plutons acted as relatively rigid massifs between which a large 'pressure shadow' developed in response to regional north–south compression.

Geological evolution of the Manitouwadge greenstone belt and Wawa-Quetico subprovince boundary, Superior Province, Ontario, constrained by U-Pb zircon dates of supracrustal and plutonic rocks

1999 ◽  
Vol 36 (6) ◽  
pp. 945-966 ◽  
Author(s):  
Eva Zaleski ◽  
Otto van Breemen ◽  
Virginia L Peterson
Keyword(s):  
Hydrothermal Alteration ◽  
Greenstone Belt ◽  
Boundary Region ◽  
Detrital Zircons ◽  
Ductile Deformation ◽  
Superior Province ◽  
Geological Evolution ◽  
Hydrothermal Alteration Zones ◽  
Depositional Age ◽  
East West

Fifty million years of Archean evolution is recorded in the Manitouwadge greenstone belt and the Wawa-Quetico boundary region, from ca. 2720 Ma volcanism and subvolcanic plutonism associated with massive sulphide deposits and hydrothermal alteration zones, to 2689-2687 Ma and 2680-2677 Ma synkinematic plutonism. In the greenstone belt, greywackes were deposited after 2693 Ma, post-dating local volcanism by at least 25 Ma, and requiring that the volcanic-sedimentary contact is an unconformity or a fault. In migmatitic greywackes in the Quetico subprovince, detrital zircons limit the depositional age to <2690 Ma, permitting correlation of greywackes across the Wawa-Quetico subprovince boundary. Upward-facing inclined F2 folds that deform the volcanic-sedimentary contact are bracketed by the 2687 ± 2 Ma Loken Lake pluton, which shows strong D2 fabrics, and by 2680+4-3 Ma foliated granite which cuts D2 fabrics. Dextral transpression producing regional F3 folds and the overall east-west trends of the Wawa-Quetico boundary region post-dated the 2680 ± 2 Ma Nama Creek pluton. Field relationships and isotopic ages support correlation of greywackes across the subprovince boundary, and demonstrate that most or all of the ductile deformation post-dated sedimentation. Ductile structures, especially those associated with dextral transpression, are not directly related to juxtaposition of the Wawa and Quetico subprovinces, as these were already contiguous, either through sedimentation on a volcanic substrate or as a result of earlier cryptic structures. Our results imply that the belt-like configuration of the subprovinces, emphasized in accretionary models of the Superior Province, is a relatively late feature that overprints older, tectonically significant structures.

Skarn mineralization (Cr, Fe, Au) in an Archean greenstone belt, White River Property, Hemlo area, Ontario

1991 ◽  
Vol 86 (8) ◽  
pp. 1626-1645 ◽  
Author(s):  
Yuanming Pan ◽  
Michael E. Fleet ◽  
William E. Stone
Keyword(s):  
Greenstone Belt ◽  
White River ◽  
Archean Greenstone Belt

Sedimentology, Stratigraphy, and Crustal Evolution of the Archean Greenstone Belt near Sioux Lookout, Ontario

1973 ◽  
Vol 10 (6) ◽  
pp. 817-845 ◽  
Author(s):  
Colin C. Turner ◽  
Roger G. Walker
Keyword(s):  
Greenstone Belt ◽  
Large Scale ◽  
Depositional Environment ◽  
Final Section ◽  
Volcanic Rocks ◽  
Alluvial Fan ◽  
Facies Associations ◽  
Feature Based ◽  
Archean Greenstone Belt ◽  
Coastal Deposits

In the Archean greenstone belt at Sioux Lookout, N.W. Ontario, a lowermost belt of volcanic rocks is unconformably overlain by sediments of the Abram Group. Our mapping has subdivided the Abram Group into three formations. The lowest (Ament Bay Formation) consists of interbedded conglomerates and sandstones. The sandstones contain large-scale cross-stratification, and the conglomerates and sandstones both lack graded bedding. The depositional environment was a subaerial alluvial fan—this is the first description of such a feature based upon modern sedimentological work in Archean rocks. The Daredevil Formation conformably overlies the Ament Bay Formation, and is composed of felsic and basic tuffs, and some interbedded turbidites. The uppermost (Little Vermilion) Formation is composed entirely of turbidites.The petrography of the sand, and large clasts, in the Ament Bay Formation indicates derivation from a dominantly granodioritic terrain. Some granodiorite boulders contain greenstone xenoliths, implying intrusion of the granodiorite after formation of the lowermost belt of volcanic rocks.In a final section of the paper, we define two Archean facies associations—a Resedimented association containing turbidites, pebbly mudstones, resedimented conglomerates, and basinal black argillites; and a Continental association, containing alluvial fan deposits, and possible coastal deposits from South Africa and Australia. The facies sequence in the Sioux Lookout belt is Continental followed by Resedimented facies, the reverse of the normal geosynclinal flysch (resedimented) → molasse (continental) sequence.

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