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.

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.

scholarly journals Geology, Red Lake greenstone belt, western Superior Province, Ontario

2004 ◽  
Author(s):  
M Sanborn-Barrie ◽  
T Skulski ◽  
J Parker
Keyword(s):  
Greenstone Belt ◽  
Superior Province ◽  
Red Lake

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.

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.

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.

Age structure and orogenic significance of the Berens River composite batholiths, western Superior Province

1998 ◽  
Vol 35 (10) ◽  
pp. 1089-1109 ◽  
Author(s):  
Fernando Corfu ◽  
Denver Stone
Keyword(s):  
Age Structure ◽  
Greenstone Belt ◽  
Biotite Granite ◽  
Superior Province ◽  
Northwestern Ontario ◽  
Peraluminous Granites ◽  
Granitic Intrusions ◽  
Age Patterns ◽  
Greenstone Belts ◽  
Intrusive Activity

The Berens River area of northwestern Ontario is underlain mainly by Archean felsic plutonic rocks, which enclose minor supracrustal and gneissic enclaves and merge with the greenstone-belt-rich Uchi Subprovince to the south. U-Pb geochronology using zircon and monazite shows that the batholiths evolved mainly between 2750 and 2690 Ma by sequential and essentially continuous intrusive activity into an older substratum composed of 3000-2800 Ma volcanic and tonalitic crust. There is a broad, but not strict, compositional transition from early biotite tonalite and hornblende tonalite, progressing with time towards a greater abundance of hornblende granodiorite to granite, and finally to late biotite granite, rare peraluminous granites, and sanukitoid (dioritic, monzodioritic to granitic) plutons. The tonalite suites were predominantly synvolcanic. The late granitic intrusions postdated volcanism, but were largely synchronous with the main compressional events that caused widespread sedimentation, deformation, and metamorphism in other parts of the region. The age patterns and compositional features of the batholiths and the spatial and temporal links between their evolution and those of the supracrustal sequences in the greenstone belts of the region are consistent with mechanisms of magma generation and emplacement at converging plate margins.

scholarly journals Geology, Red Lake greenstone belt, western Superior Province, Ontario

2004 ◽  
Author(s):  
M Sanborn-Barrie ◽  
T Skulski
Keyword(s):  
Greenstone Belt ◽  
Superior Province ◽  
Red Lake

First U–Pb zircon ages of granitoid plutons from the La Grande greenstone belt, James Bay area, New Quebec

1989 ◽  
Vol 26 (5) ◽  
pp. 1068-1073 ◽  
Author(s):  
Karen St. Seymour ◽  
Andrew Turek ◽  
Ronald Doig ◽  
Stephen Kumarapeli ◽  
Robert Fogal
Keyword(s):  
Greenstone Belt ◽  
The Other ◽  
Superior Province ◽  
Present Level ◽  
James Bay ◽  
Zircon Age ◽  
Maximum Deformation ◽  
The Third ◽  
Bay Area ◽  
Greenstone Belts

Zircon ages from three granitoid plutons are the first to be reported from the La Grande greenstone belt. Two of the dated samples are from highly tectonized, early tectonic plutons that at the present level of erosion are just outside the greenstone belt proper. Their zircon ages of ca. 2740 Ma are emplacement ages or alternatively represent the age of maximum deformation of the greenstone belt. The third sample is from a mildly deformed late tectonic pluton within the greenstone belt. Its zircon age of ca. 2670 Ma probably represents the emplacement age. The above dates and the relationships of the dated plutons to the greenstone belt as a whole suggest that the bulk of the volcanism in the La Grande belt is older than 2.7 Ga. This limiting age indicates that the age of the La Grande "supracrustals" is similar to those of the other greenstone belts in the Superior Province.

The Western Superior Province Lithoprobe and NATMAP transects: introduction and summary

2006 ◽  
Vol 43 (7) ◽  
pp. 743-747 ◽  
Author(s):  
John A Percival ◽  
Herwart Helmstaedt
Keyword(s):  
Continental Crust ◽  
Greenstone Belt ◽  
Wide Spectrum ◽  
Superior Province ◽  
Western Region ◽  
Research Projects ◽  
Special Issue ◽  
Multidisciplinary Research ◽  
Red Lake ◽  
History Of

The Special Issue on the Western Superior Province Lithoprobe and NATMAP transects presents a wide spectrum of contributions from coordinated, multidisciplinary research projects on the western region of Earth's largest Archean craton. Articles include aspects of the geophysical, stratigraphic, geochemical, geochronological, petrological, and structural evidence bearing on the accretionary history of this classic, well-exposed piece of ancient continental crust, as well as analyses of the prospectivity and seismic character of the gold-rich Red Lake greenstone belt.

A Discussion on the evolution of the Precambrian crust - The evolution of the early Precambrian crust of Southern Africa

1973 ◽  
Vol 273 (1235) ◽  
pp. 359-388 ◽  
Keyword(s):  
Southern Africa ◽  
Greenstone Belt ◽  
Sedimentary Basins ◽  
Granitic Rocks ◽  
Evolutionary Development ◽  
Geochemical Data ◽  
Island Arcs ◽  
Early Precambrian ◽  
Greenstone Belts ◽  
Middle Proterozoic

The early Precambrian granite-greenstone basement complex of Rhodesia and South Africa constitutes one of the oldest known fragments of the Earth’s crust. Scattered within the expanse of granitic rocks are numerous greenstone belts some approaching, or even possibly exceeding, ages of about 3400 Ma. These ancient greenstone belt remnants represent the earliest clearly decipherable geological events on the Earth’s surface, and any evidence concerning the nature and evolutionary development of the primitive crust must be sought largely from an examination of their lithologies. The stratigraphy of the early greenstone occurrences in southern Africa is described with particular emphasis being given to the geological record established in the well-preserved Barberton Mountain Land of the Transvaal. The evidence for a primitive sialic versus simatic crust is reviewed and reference is made to the reported pre-greenstone belt basement remnants found in Rhodesia as well as in Swaziland. Comparisons are drawn between the early greenstone belts and modern island arcs, use being made of available geochemical data from the two environments. It is concluded that the early crust in southern Africa had analogies with the present-day abyssal regions of the oceans. Progressive transformation, involving island arc-like development and protocontinental nucleation, resulted from processes involving partial melting of the primitive lithosphere coupled with the secular mixing of mantle derived, granitic additions. The early thin, unstable, primordial crust underwent progressive thickening processes and, about 3000 Ma ago, stabilized sufficiently to permit the development of the first interior or cratonic-type sedimentary basins. Increases in the areal extent of the developing basins are briefly traced and the more significant events, from the earliest Precambrian to middle Proterozoic times (ca. 1700 Ma ago), are contrasted and summarized.

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