Uplift estimated from remanent magnetization: Munro area of Superior Province since 2150 Ma ago

1981 ◽  
Vol 18 (7) ◽  
pp. 1164-1173 ◽  
Author(s):  
Kenneth L. Buchan ◽  
Erik J. Schwarz
Keyword(s):  
Remanent Magnetization ◽  
Country Rock ◽  
Canadian Shield ◽  
Magnetic Component ◽  
Superior Province ◽  
Ambient Temperatures ◽  
Different Ages ◽  
Depth Of Burial ◽  
Erosion Surface

A method for determining depth of burial from remanent magnetization was applied to three igneous contacts of two different ages in Munro Township of the Superior Province of the Canadian Shield. Sampling profiles perpendicular to the contact of a 2150 Ma diabase dike, one collected in an older (2690 Ma) diabase dike and a second in gabbro country rock, yielded ambient temperatures for the present erosion surface at the time of dike emplacement of 219 ± 23 and 181 ± 7 °C, respectively. A third sampling profile perpendicular to a 2690 Ma dike failed to provide a usable magnetic contact zone.A secondary magnetic component with shallow inclination and easterly declination was detected in individual samples collected from both dikes as well as from the surrounding country rock. Converging remagnetization circles indicate that this component, acquired some time after emplacement of the younger (2150 Ma) dike, has the direction D = 70°, I = −39° and corresponding paleopole 39°E, 4°S.

Post-Aphebian uplift deduced from remanent magnetization, Yellowknife area of Slave Province

1985 ◽  
Vol 22 (12) ◽  
pp. 1793-1802 ◽  
Author(s):  
Erik J. Schwarz ◽  
Kenneth L. Buchan ◽  
Alain Cazavant
Keyword(s):  
Host Rock ◽  
Remanent Magnetization ◽  
Probable Error ◽  
Slave Province ◽  
Rock Temperature ◽  
Individual Specimen ◽  
Depth Of Burial ◽  
Paleogeothermal Gradient ◽  
Structural Zones ◽  
Erosion Surface

Remanent magnetization in five Indin, three Dogrib, two Archean, and one Mackenzie dyke contact zone(s) from the Yellowknife area of the Canadian Precambrian Shield has been studied in order to establish the ambient temperature of the host rock and the depth of burial of the present erosion surface at the time of intrusion. A positive baked-contact test for an Aphebian Indin dyke demonstrates the primary nature of the dyke magnetization. From this contact, eight individual specimen determinations of the ambient host-rock temperature at the time of intrusion yield an average of 211 °C, with a standard deviation of 18 °C and probable error of ± 36 °C. Assuming a paleogeothermal gradient of 44 °C/km (± 30%) the estimated depth of burial of the present erosion surface is [Formula: see text]. None of the remaining contacts yield estimates of the depth of burial. However, the results from the three Dogrib contacts illustrate complications such as chemical overprinting that must be considered when analysis is made of magnetization in igneous contact zones. Thus, only one spot reading of the depth of burial of the area has been obtained. Correlation of the Indin result with a result from the Matheson area of Ontario and with stratigraphic indicators is uncertain because of large intervening distances and the occurrence of younger structural zones.

Some new measurements of heat flow in the Superior Province of the Canadian Shield

1987 ◽  
Vol 24 (7) ◽  
pp. 1486-1489 ◽  
Author(s):  
Malcolm Drury ◽  
Alan Taylor
Keyword(s):  
Standard Deviation ◽  
Heat Flow ◽  
Canadian Shield ◽  
Superior Province ◽  
Flow Measurements ◽  
Radiogenic Heat ◽  
Radiogenic Heat Production ◽  
Climatic Variations ◽  
The Mean ◽  
A Site

Borehole heat-flow measurements are reported from six new sites in the Superior Province of the Canadian Shield. Values adjusted for glaciation effects, but not for Holocene climatic variations, range from 42 to 56 mW/m2. When these new values are combined with 21 previously published borehole values the mean is 42 mW/m2 with a standard deviation of 11 mW/m2. The data for a site on the Lac du Bonnet batholith suggest that the batholith has a thin veneer, less than 3 km, of rock of high radiogenic heat production at the surface.

Carbon-isotope systematics of Archean Au–Ag vein deposits in the Superior Province

1990 ◽  
Vol 27 (1) ◽  
pp. 40-56 ◽  
Author(s):  
R. Kerrich
Keyword(s):  
Hydrothermal Fluids ◽  
Superior Province ◽  
Ambient Temperatures ◽  
Rayleigh Fractionation ◽  
Clastic Sediments ◽  
Isotopic Equilibration ◽  
Vein Deposits ◽  
Carbonaceous Rocks ◽  
Isotope Systematics ◽  
Main Population

Abundant carbonate is a characteristic feature of most Archean mesothermal Au–Ag vein deposits, but the source of the C is controversial. For Superior Province deposits collectively, the maximum variation of average δ13C values is from −9.0 ± 0.7‰ (1σ, n = 19; Darius) to −0.6 ± 1.6‰ (1σ, n = 7; Cochenour–Willians), and limiting δ13C values are−13.6 and + 1.3‰. At the deposit scale, Fe dolomites in nongraphitic lithologies are for the most part isotopically uniform, where δ13C = −3.4 ± 0.4 (1σ) (Hollinger), −3.2 ± 0.3 (McIntyre), −4.7 ± 1.7 (Dome), −2.8 ± 0.6 (Buffalo Ankerite), −3.6 ± 0.5 (Macassa), −3.2 ± 0.3 (Bousquet), −5.4 ± 0.9 (Lamaque), and −5.3 ± 0.5‰ (Hasaga): the restricted individual ranges of δ13C values imply a corresponding uniformity to the ambient temperature and δ13CΣC of the ore-forming fluids.Within individual deposits, small systematic variations of δ13C carbonate arise from (i) interaction of hydrothermal fluids with carbonaceous rocks, (ii) immiscible separation of CO2 + CH4, or (iii) Rayleigh fractionation effects. Positive shifts in δ13C result from buffering of the fluid to lower Eh by reaction with reduced C, whereas negative shifts reflect partial isotopic equilibration between 13C-depleted C (δ13C ≈ −26‰) and aqueous hydrothermal C species. Transient immiscibility of CO2 + CH4 acts to precipitate carbonates enriched relative to the main population of Fe dolomites. The δ13C values of carbonates in unmineralized alteration halos (−2.2 ± 1.1‰, n = 42) at the McIntyre deposit are enriched in 13C relative to the main gold-bearing vein systems (δ13C = −3.2 ± 0.3‰): the enrichment is attributed to a Rayleigh fractionation accompanying progressive consumption of CO2 as hydrothermal fluids infiltrate laterally from veins into wall rocks. Fe dolomite and calcite are variably enriched in 18O with respect to equilibrium quartz-carbonate fractionations for ambient temperatures of 270–340 °C. Carbonate δ18O values diminish in an irregular manner with depth, converging on values of ~11‰ (Fe dolomite, 6800 ft (2073 m), McIntyre). Variable degrees of oxygen-isotope disequilibrium represent overprinting of carbonates by post-Archean brines in the Canadian Shield.Synvolcanic vesicle calcite in three groups of metabasalts (δ13C = −4.3 ± 2.1; −2.8 ± 1.5; −2.7 ± 1.3‰) and calcite in two groups of clastic sediments (−6.4 ± 1.8; −4.6 ± 2.5‰) remote from deposits are systematically depleted of 13C relative to average Precambrian limestones (~0 ± 1‰), owing to the involvement of CO2 derived from 13C-depleted organic matter. Consequently, calcite in greenstone belt supracrustal rocks is not restricted to approximately 0‰. The total spread of average δ13CFe dol values (−9.0 ± 0.7 to −0.6 ± 0.6‰) in the Au deposits, which goes in hand with a geographical provinciality in O-, Sr-, and Pb-isotope compositions of the ore-forming fluids, is too large to be accounted for by mantle CO2 (−6 ± 2‰) or magmatic CO2 (−6 ± 2‰) alone but rather is interpreted as reflecting generation of hydrothermal fluids in crustal or subcreted rocks heterogeneous in terms of the distribution of 13C-enriched (carbonate) and 13C-depleted (reduced C) lithologies.

Paleomagnetism of the 1.1 Ga Lackner Lake Complex and tectonics of the Kapuskasing Structural Zone

1989 ◽  
Vol 26 (9) ◽  
pp. 1778-1783 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
Fault Zone ◽  
Canadian Shield ◽  
Superior Province ◽  
Thermal Demagnetization ◽  
Abitibi Subprovince ◽  
Reversed Polarity ◽  
Middle Proterozoic

The Middle Proterozoic Lackner Lake Complex is a circular alkalic syenite–carbonatite stock with a diameter of about 5.5 km. It intrudes granulite-rank Archean gneisses in the Kapuskasing Structural Zone of the Wawa Subprovince in the Superior Province of the Canadian Shield. It adjoins the Ivanhoe Lake fault zone, which forms the boundary with the Abitibi Subprovince and is the probable locus of maximum motion between the subprovinces. Specimens from 18 sites in the complex were analyzed paleomagnetically by alternating-field and thermal demagnetization and by saturation isothermal remanence tests. Large, recent viscous remanence components required removal before a stable remanence with a mean direction of 305.4°, 64.1 °(α95 = 5.2°) was isolated. Its pole of 53.7°N, 156.5°W (dp = 6.7°, dm = 8.3°) indicates emplacement at 1108 ± 10 Ma during a brief normal interval in a predominantly reversed-polarity time. This study indicates that there has been no postintrusion tilting of the Kapuskasing Structural Zone and that postintrusion uplift by unroofing did not exceed about 8 km.

A detailed 40Ar/39Ar age study of an Abitibi dike from the Canadian Superior Province

1979 ◽  
Vol 16 (5) ◽  
pp. 1060-1070 ◽  
Author(s):  
J. A. Hanes ◽  
Derek York
Keyword(s):  
Canadian Shield ◽  
Superior Province ◽  
Low Grade ◽  
Polar Wander ◽  
Mafic Mineral ◽  
Fine Grained ◽  
Apparent Polar Wander Path ◽  
Step Heating ◽  
Apparent Age ◽  
Hydrothermal Event

40Ar/39Ar step-heating analyses were performed on 11 felsic and mafic mineral separates from a 90 m wide Precambrian diabase dike of the Abitibi swarm in the Superior Province of the Canadian Shield. Deuterically altered minerals from the dike interior define a primary age of 2150 ± 25 Ma. Updated ages, obtained from felsic separates within 30, and mafic within 1.5 m of the dike border, are evidence of a previously undetected 'Hudsonian' (1.7–1.8 Ga) hydrothermal event in the area. It is possible to distinguish the deuteric from the later hydrothermal alteration by both dating and petrographic methods. The data from this study demonstrate the successful application of 40Ar/39Ar dating to early Proterozoic dikes which have suffered low grade metamorphism. The ages support a north to south sense of motion of the Track 5 apparent polar wander path (APWP). A monotonic decrease in apparent age of felsic spectra indicates reactor induced recoil effects which are correlated with the fine-grained saussurite in the feldspar.

THE MAGNETIZATION OF A ROCK CONTAINING MAGNETITE AND HEMOILMENITE

Geophysics ◽  
1964 ◽  
Vol 29 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Charles M. Carmichael
Keyword(s):  
Remanent Magnetization ◽  
Magnetic Moments ◽  
Canadian Shield ◽  
Titanium Oxides ◽  
Aeromagnetic Anomalies ◽  
X Ray ◽  
Lake Region ◽  
Unusual Occurrence

In areas such as the Canadian Shield, rocks often contain iron and titanium oxides with a remanent magnetization. These rocks can produce aeromagnetic anomalies that are positive, negative, or nonexistent depending on the magnitude and direction of the remanent component relative to that of the induced. In the Allard Lake region of Quebec there is a deposit containing up to 20 percent oxide that produces no anomaly detectable by either the airborne or ground magnetometer. Analyses of the rock by microscopic, magnetic, and X‐ray techniques have shown that it contains separate crystals of an almost pure magnetite and of exsolved hemoilmenite. The magnetite crystals are magnetized normally and the hemoilmenite crystals inversely. They are present in quantities such that their magnetic moments cancel and so produce no anomaly. While this is probably an unusual occurrence it shows that considerable care must be taken in regions where minerals having an inverse remanent magnetization may be present.

Horizontal shortening of upward-facing greenstone structures in the southern Superior Province, Canadian Shield

1984 ◽  
Vol 21 (5) ◽  
pp. 611-615 ◽  
Author(s):  
Graham John Borradaile ◽  
W. M. Schwerdtner
Keyword(s):  
Compressive Strain ◽  
Canadian Shield ◽  
Superior Province ◽  
Maximum Value

Metavolcanics and clastic metasediments in parts of the Wabigoon and Shebandowan–Wawa subprovinces have been folded into tight upward-facing structures. Although the principal compressive strain is locally greater than 70%, the maximum value obtained for the overall horizontal shortening in a north–south direction is in the range of 40–60%. The actual horizontal shortening may be much less than this range unless there are large reverse faults or thrusts that have not been recognized to date.

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