Paleomagnetism, U–Pb geochronology, and geochemistry of Marathon dykes, Superior Province, and comparison with the Fort Frances swarm

1996 ◽  
Vol 33 (12) ◽  
pp. 1583-1595 ◽  
Author(s):  
Kenneth L. Buchan ◽  
Henry C. Halls ◽  
James K. Mortensen
Keyword(s):  
Major Element ◽  
Lake Superior ◽  
Magnetic Polarity ◽  
The Other ◽  
Dyke Swarm ◽  
Superior Province ◽  
Reverse Polarity ◽  
Element Geochemistry ◽  
Polar Wander ◽  
Collaborative Studies

We report the first detailed study of the paleomagnetism, U–Pb geochronology and major element geochemistry of Paleoproterozoic north-trending Marathon dykes north of Lake Superior. The paleomagnetic and geochemical results demonstrate that Marathon dykes can be divided into two subsets, one of normal magnetic polarity, the other of reverse polarity. Normal and reverse Marathon paleomagnetic poles, at 43°N, 196°E (dm = 9°, dp = 7°, number of dykes N = 16) and 51°N, 175°E (dm = 9°, dp = 6°, N = 12), respectively, are statistically distinct and may indicate different ages of normal and reverse dyke emplacement, A U–Pb baddeleyite age of [Formula: see text] Ma has been obtained at a normally magnetized Marathon paleomagnetic site. The reversely magnetized Marathon dykes are undated, but have a paleopole rather close to that of the reversely magnetized [Formula: see text] Ma Fort Frances dykes and major element geochemical signatures as portrayed on Jensen plots that are identical to those of the Fort Frances swarm. Therefore, reverse Marathon and Fort Frances dykes could define a giant radiating dyke swarm focused south of Lake Superior, supporting models that associate these dykes with Paleoproterozoic rifting along the southern margin of the Superior Province. The Marathon and Fort Frances paleopoles continue a northwesterly trend in southern Superior Province paleopoles, which has recently been defined by results for [Formula: see text] Ma Senneterre dykes and 2167 ± 2 Ma Biscotasing dykes. This trend contrasts with previous widely used polar wander paths for the same period that young in the opposite direction and illustrates the importance of collaborative studies of paleomagnetism and U–Pb geochronology.

Proterozoic reactivation of the southern Superior Province and its role in the evolution of the Midcontinent rift

1997 ◽  
Vol 34 (4) ◽  
pp. 562-575 ◽  
Author(s):  
Matthew L. Manson ◽  
Henry C. Halls
Keyword(s):  
Lake Superior ◽  
Dyke Swarm ◽  
Superior Province ◽  
Midcontinent Rift ◽  
Potential Field Data ◽  
Major Activity ◽  
The North ◽  
Western Lake ◽  
Narrow Belt ◽  
Radiometric Data

Major reverse faults associated with the late compressional phase of the 1.1 Ga Midcontinent rift in the western Lake Superior region appear to cut across the rift at the eastern end of the lake and join with reverse faults on the eastern shoreline, defined on the basis of geological and potential field data. The continuation of the faults across eastern Lake Superior is inferred on evidence drawn from nearshore shipborne magnetic surveys together with new interpretations of published bathymetric and GLIMPCE aeromagnetic data. In the Archean Superior Province about 100 km east of Lake Superior, paleomagnetic and petrographic data from the 2.45 Ga Matachewan dyke swarm show that the Kapuskasing Zone, a narrow belt of uplifted crust, can be extended to within 50 km of the Lake Superior shoreline and has bounding reverse faults that are almost continuous with two faults of similar dip and sense of displacement that define the inversion of the Midcontinent rift in the central and western parts of the lake. Since the Kapuskasing Zone is dominantly a Paleoproterozoic (about 1.9 Ga) structure, the continuity suggests that the Lake Superior faults, whose last major activity was during the Grenville Orogen, may represent reactivation of much older faults that were part of an extended Kapuskasing structure. Within the Superior Province to the north and east of Lake Superior, published radiometric data on biotites suggest a series of alternating crustal blocks of varying tectonic stability, separated by northeast-trending faults. The Lake Superior segment of the Midcontinent rift developed within the most unstable block, bounded by the Gravel River fault to the northwest and the Ivanhoe Lake fault (the eastern margin of the Kapuskasing Zone) to the southeast.

Broad-scale Proterozoic deformation of the central Superior Province revealed by paleomagnetism of the 2.45 Ga Matachewan dyke swarm

1991 ◽  
Vol 28 (11) ◽  
pp. 1780-1796 ◽  
Author(s):  
M. P. Bates ◽  
H. C. Halls
Keyword(s):  
Large Scale ◽  
Dyke Swarm ◽  
Superior Province ◽  
Polar Wander ◽  
The North ◽  
Paleomagnetic Study ◽  
Secondary Feature ◽  
Dual Polarity ◽  
Host Rocks ◽  
Broad Scale

An extensive paleomagnetic study of the 2.45 Ga Matachewan dyke swarm of the North American Superior Province suggests that the interior of an Archean shield can undergo broad-scale distortion as a result of later (Proterozoic) orogenic activity around the craton margins. Data collected from over 300 sites, of which 137 are reported here for the first time, reveal that the dykes contain a dual-polarity primary remanence that varies across the swarm in both inclination and declination. These regional variations are statistically significant at the 95% confidence level, and cannot be attributed to remagnetization or to magnetic anisotropy. Inclination variation is probably due to real or apparent polar wander during the emplacement of the swarm, and may in part explain the declination variation as well. However, for dykes within and northwest of the Kapuskasing Structural Zone (KSZ) a positive correlation is found between regionally averaged values of declination and dyke trend. Here the dykes appear to have suffered differential rotations about vertical axes of up to 40° since emplacement. The Matachewan swarm radiates northwards from a broad focus situated approximately in northern Lake Huron but the trend of the western half of the swarm follows a broad Z-shaped pattern where it crosses the KSZ. Our data suggest that this changing trend is a secondary feature and that the western dykes, like their eastern counterparts, originally had a more uniform trend. This large-scale distortion of the western Matachewan swarm and Archean host rocks within and north of the KSZ is probably the result of broad-scale deformation during the Trans-Hudson Orogeny at about 1.95 Ga, coeval with uplift along the KSZ.

Paleomagnetism and correlation of some Middle Keweenawan rocks, Lake Superior

1970 ◽  
Vol 7 (6) ◽  
pp. 1410-1436 ◽  
Author(s):  
H. C. Palmer
Keyword(s):  
Lake Superior ◽  
Pole Position ◽  
Magnetic Polarity ◽  
Secondary Component ◽  
Equal Weight ◽  
Reverse Polarity ◽  
North Shore ◽  
The North ◽  
Normal Polarity ◽  
The Mean

Paleomagnetic results from the Lake Superior region appear to indicate that Middle Keweenawan formations or magnetic divisions within formations can be correlated on the basis of magnetic polarity. The Logan sills, the volcanics of the Osler Group, the lava section at Alona Bay, the lower 6000 ft (1829 m) of North Shore volcanics, the lower 1000 ft (305 m) of Cape Gargantua volcanics and the lower 3000 ft (914 m) at Mamainse Point are of reverse polarity. Normal directions of magnetization, which differ from the reverse directions of magnetization by amounts ranging from 140° to 163° occur throughout the Michipicoten Island section, and in the upper parts of the North Shore, Cape Gargantua, and Mamainse Point sections. Provided part of the section at Mamainse Point has been repeated by faulting, these new results, together with data from the literature, are compatible with a single polarity reversal in Middle Keweenawan time separating older reverse polarity rocks from stratigraphically younger normal polarity rocks. The mean direction of magnetization from a conglomerate test is defined with higher precision than would be expected from a randomly distributed population. It is believed that this mean direction reflects a secondary component of magnetization which cannot be preferentially removed by alternating field demagnetization and which has caused the non anti-parallel alignment of normal and reverse populations of magnetization. An estimate of the pole position during Middle Keweenawan time can, however, be made by calculating a pole given equal weight to the mean normal and mean reverse pole. This is calculated to be 159° W, 42° N.

Paleomagnetism and U–Pb geochronology of the Lac de Gras diabase dyke swarm, Slave Province, Canada: implications for relative drift of Slave and Superior provinces in the PaleoproterozoicGeological Survey of Canada Contribution 20080350.

2009 ◽  
Vol 46 (5) ◽  
pp. 361-379 ◽  
Author(s):  
Kenneth L. Buchan ◽  
Anthony N. LeCheminant ◽  
Otto van Breemen
Keyword(s):  
Magnetic Polarity ◽  
Canadian Shield ◽  
Dyke Swarm ◽  
Superior Province ◽  
Igneous Complex ◽  
Contact Test ◽  
Slave Province ◽  
Formed Part ◽  
Dyke Swarms

Lac de Gras diabase dykes trend north to NNE across the central Slave Province of the Canadian Shield. U–Pb baddeleyite ages of 2023 ± 2 and 2027 ± 4 Ma are interpreted as dyke emplacement ages. These ages are similar to that of the Booth River igneous complex, exposed along the margins of Kilohigok Basin near the northern end of the dyke swarm. Ten paleomagnetic sites (from four to six dykes) yield a mean paleopole at 11.8°N, 92.1°W (dm = 8.4°, dp = 6.0°). A positive baked contact test where a Lac de Gras dyke crosscuts a NE-trending Malley dyke demonstrates that this pole is primary. It represents the first key Paleoproterozoic pole from the Slave Province and, hence, the first Paleoproterozoic Slave pole suitable for reconstructing paleocontinents. Although a direct comparison is not available with precisely dated paleopoles of identical age from other Archean cratons, a comparison is made with a sequence of precisely dated poles from Superior Province dyke swarms, including those 40–50 million years older and 25 million years younger. It yields two options depending on the relative magnetic polarity assumed for data from the two cratons. The two cratons were either at similar latitudes, but not in their present relative orientations, when the swarms were emplaced, or separated in latitude by ∼40°–60°. In either case, they may have drifted separately or formed part of a single (super)continent that subsequently broke up with the two cratons drifting separately to attain their present configuration. Additional key paleopoles are required to distinguish between these interpretations.

Trace and Major Element Geochemistry of Basalts from Leg 81

1984 ◽  
Author(s):  
C. Richardson ◽  
P.J. Oakley ◽  
J.R. Cann
Keyword(s):  
Major Element ◽  
Element Geochemistry

Data Report: Major element geochemistry of the sediments from Site 997, Blake Ridge, Western Atlantic

2000 ◽  
Author(s):  
H. Lu ◽  
R. Matsumoto ◽  
Y. Watanabe
Keyword(s):  
Major Element ◽  
Element Geochemistry ◽  
Western Atlantic ◽  
Blake Ridge

Characterization and dispersal of indicator minerals associated with the Pine Point Mississippi Valley-type (MVT) district, Northwest Territories, Canada

2015 ◽  
Vol 52 (9) ◽  
pp. 776-794 ◽  
Author(s):  
N.M. Oviatt ◽  
S.A. Gleeson ◽  
R.C. Paulen ◽  
M.B. McClenaghan ◽  
S. Paradis
Keyword(s):  
Northwest Territories ◽  
Major Element ◽  
Bimodal Distribution ◽  
Mississippi Valley ◽  
Element Geochemistry ◽  
Element Concentrations ◽  
Pine Point ◽  
Indicator Minerals ◽  
Mississippi Valley Type ◽  
Valley Type

A glacial dispersal study was conducted around a subcropping Pb–Zn deposit (O28) in the Pine Point Mississippi Valley-type (MVT) district, Northwest Territories, Canada, with the intent of characterizing and documenting the indicator minerals and their dispersal from a known orebody. Mapping of striations adjacent to deposit O28, and throughout the Pine Point district, along with observed glacial stratigraphy, indicate that there are three phases of ice flow that have affected the Pine Point district. Sphalerite, galena, and pyrite were identified in mineralized bedrock samples at deposit O28, and sphalerite and galena were recovered from the sand fraction of till samples up to 500 m from the mineralized subcrop. The majority of sphalerite and galena grains recovered from till samples down-ice of deposit O28 were 0.25–0.5 mm in size. Size and morphology of sphalerite grains in till demonstrate relative proximity to their bedrock source, with the largest and more angular grains being closer to the ore zone (<50 m) whereas smaller and more rounded grains occur further down-ice (∼250 m). The paragenesis, textures, major-element concentrations, and S and Pb isotopic compositions of bedrock samples from deposit O28 and from newly drilled core from four other deposits were characterized. Concentrations of Zn in bedrock sphalerite grains range from 43.95 to 67.48 wt.%, concentrations of S range from 32.03 to 34.01 wt.%, and concentrations of Fe range from 0.02 to 16.94 wt.%. The Fe concentration in bedrock sphalerite decreases from east to west across the district. Concentrations of S in galena grains in bedrock range from 12.50 to 14.00 wt.% and have a bimodal distribution. Generally, the geochemistry of sphalerite grains recovered from till were statistically similar to bedrock grains recovered from deposits O28 and L65. Major-element concentrations were statistically the same between the sphalerite grains recovered from till and the honey-brown and cleiophane varieties in the bedrock samples. Galena grains recovered from till samples were similar to the cubic and fracture-fill varieties of grains recovered from bedrock in the R190 and M67 deposits. Sulphur isotopic values for sphalerite grains from bedrock range from 20.6‰ to 24.2‰, while those from till samples range from −5.3‰ to 24.4‰. Lead isotopic ratios for galena grains from bedrock and till samples had very little variation, which is a characteristic of the Pine Point district. The S and Pb isotopic studies as well as major-element geochemistry suggest that indicator minerals derived from Pine Point-type mineralization can be distinguished from those sourced from other types of carbonate-hosted mineralized systems (e.g., Cordilleran zinc–lead deposits) and that the methods here can be used as exploration tools for identifying MVT deposit provenance or potential. The results of this study present criteria and highlights additional methods for exploration of MVT deposits in glaciated terrain.

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