Evidence from aeromagnetics on the configuration of Matachewan dykes and the tectonic evolution of the Kapuskasing Structural Zone, Ontario, Canada

1991 ◽  
Vol 28 (11) ◽  
pp. 1797-1811 ◽  
Author(s):  
Gordon F. West ◽  
Richard E. Ernst
Keyword(s):  
Dyke Swarm ◽  
Aeromagnetic Survey ◽  
Plausible Assumption ◽  
South Central ◽  
Southeastern Margin ◽  
Major Fault ◽  
Horizontal Strain ◽  
Transcurrent Deformation ◽  
Dyke Injection ◽  
Differential Uplift

By digital image processing of federal–provincial aeromagnetic survey data for the south-central Superior Province, we have obtained an improved picture of the distribution of dykes in the huge Matachewan mafic dyke swarm (2454 Ma). We deduce from it a picture of post-emplacement deformation in the vicinity of the uplifted granulite gneisses of the Kapuskasing Structural Zone (KSZ). Matachewan dykes are emplaced in three subswarms. The two easterly subswarms are clearly truncated by the KSZ's eastern boundary faults. The western subswarm shows an open Z-bend as it crosses the KSZ, but it does not reveal any major fault offset. On the plausible assumption (supported by paleomagnetic data) that the subswarms were originally intruded radially, the horizontal strain suffered by the KSZ since emplacement of the dykes is mainly a northeast–southwest-trending band of dextral transcurrent deformation, which in the northeast is discontinuous and concentrated in a fault (horizontal offset 60–80 km) and in the southwest widens through a series of horsetail splays into an ~80 km wide zone of distributed strain. The KSZ is believed to have formed by a major, crustal-scale, thrust uplift along the KSZ's southeastern margin. Some thrusting is recorded by the dyke pattern, but this can account for only part of the ~20 km of differential uplift seen in the KSZ. Most likely, the mainly transcurrent deformation recorded by the dykes is a secondary event, and the primary period of thrust uplift predated dyke injection.

scholarly journals Potassium-argon ages from Phanerozoic basic dykes in South-East Greenland

1978 ◽  
Vol 90 ◽  
pp. 141-146
Author(s):  
J.G Mitchell
Keyword(s):  
North Atlantic ◽  
East Coast ◽  
Dyke Swarm ◽  
The South ◽  
East Greenland ◽  
Break Up ◽  
Dyke Injection ◽  
General Period

Nine basaltic dykes were sampled by coring during geological reconnaissance of the south-east coast of Greenland (Bridgwater et al., 1977) between Angmagssalik (65°40') and Nordfjord (fig. 49). The samples were initially collected for palaeomagnetic investigations (Beckmann,1977). In the field it was assumed that all the fresh basic dykes in the region were Tertiary in age and represented a southern continuation of the coastal dyke swarm described by Wager & Deer (1938). The timing of dyke injection is very important as a possibie indication of the initial break-up of the original North Atlantic mass. Furthermore, it was assumed that the major coast-parallel dyke swarm (for example site 26 & 28, see fig. 49) was the continuation of the more intense Tertiary dyke swarm reported by Wager & Deer (1938) further north, while the more sporadic dykes with other trends were presumed also to belong to the same general period of injection. The preliminary palaeomagnetic studies by Beckmann (1977) showed no consistent differences between dykes grouped according to their trends.

Amphibole and plagioclase chemistry in two Proterozoic dyke swarms and its relation to the uplift history of the Kapuskasing Structural Zone

1992 ◽  
Vol 29 (8) ◽  
pp. 1791-1801 ◽  
Author(s):  
H. C. Palmer ◽  
R. L. Barnett
Keyword(s):  
Country Rock ◽  
Magnetic Polarity ◽  
Dyke Swarm ◽  
Limited Data ◽  
History Of ◽  
Magnetite Particles ◽  
Differential Uplift ◽  
Highly Correlated ◽  
Dyke Swarms ◽  
Lower Crustal

The gneisses of the Chapleau portion of the Kapuskasing Structural Zone (KSZ) and of the Wawa Gneiss Terrane (WGT) can be partitioned into subregions on the basis of magnetic polarity of 2.45 Ga Matachewan diabase dykes emplaced within them. West of the Ivanhoe Lake fault zone (ILFZ) the polarity sequence across the trend of the dyke swarm is normal–reverse–normal (N–R–N) over a traverse distance >100 km. Highly correlated with dyke N polarity is the presence of tea-coloured groundmass plagioclase and hornblende with high Al, Na, and Ti content. Reversely magnetized dykes within the WGT and in dykes of either polarity in regions far removed from the KSZ have groundmass plagioclase with hydrous alteration and relatively Al-poor amphiboles. Although N and R magnetized dykes have groundmass plagioclase with comparable Fe contents, the plagioclase of N dykes and Kapuskasing dykes in the highest grade country rock contain discrete, micrometre-sized, Ti-poor magnetite particles. The mineralogical variations are independent of whole-rock bulk chemistry and are ascribed to greater crystallization depth for N magnetized dykes. The magnitude of the amphibole compositional change in dykes at the western N–R boundary within the WGT is comparable to that across the ILFZ. The western N–R boundary is wholly within the WGT, whereas the ILFZ juxtaposes upper and lower crustal levels. As a consequence, only some of the differential uplift between the KSZ and the Abitibi belt can be accounted for in post-Matachewan dyke time. Limited data from the amphiboles in the 2.04 Ga east-northeast-trending Kapuskasing dykes suggest that this phase of faulting along these block boundaries postdates Kapuskasing dyke emplacement.

Geology, geochronology, and geochemistry of Archean rocks in the Eqe Bay area, north-central Baffin Island, Canada: constraints on the depositional and tectonic history of the Mary River Group of northeastern Rae Province

2003 ◽  
Vol 40 (8) ◽  
pp. 1137-1167 ◽  
Author(s):  
K M Bethune ◽  
R J Scammell
Keyword(s):  
Hanging Wall ◽  
Volcanic Rocks ◽  
Dyke Swarm ◽  
Baffin Island ◽  
Calc Alkaline ◽  
North Central ◽  
Bay Area ◽  
Gneiss Complex ◽  
Southeastern Margin ◽  
Greenstone Belts

Results of stratigraphic, U–Pb geochronological, and geochemical study are reported for rocks in a 2800 km2 area along the southeastern margin of the Archean Rae Province on north-central Baffin Island. Archean rocks include a gneiss complex, two greenstone belts of the Mary River Group, and various younger plutonic rocks. The 3000–2800 Ma gneiss complex contains intrusions of orthogneiss, dated at 2780–2770 Ma. Intermediate-felsic volcanism in overlying greenstone belts occurred at 2740–2725 Ma and was accompanied and outlasted by calc-alkaline plutonism (2730–2715 Ma). Peraluminous plutonism at ca. 2700 Ma, possibly associated with low- to medium-pressure metamorphism, represents the culmination of the Archean tectonic cycle. Dating of metamorphic zircon and titanite in Archean gneissic rocks indicates that overprinting, high-grade metamorphism in the northwest part of the area (footwall of the Isortoq fault zone) is Paleoproterozoic (ca. 1820 Ma). A weaker, somewhat older thermal disturbance (ca. 1850–1840 Ma with large errors) is recorded in the hanging wall of this zone. Additional tectonothermal events at ca. 1500–1400 Ma and ca. 700 Ma may, respectively, correlate with Mesoproterozoic faulting and emplacement of the Franklin dyke swarm. Unlike their age-correlative counterparts in the Mary River area and on the mainland to the southwest, the greenstone belts at Eqe Bay lack abundant orthoquartzite and komatiitic volcanic rocks: calc-alkaline volcanic rocks predominate, suggesting a fundamentally different tectonic environment. Striking similarities, both in lithology and age, to greenstone belts of the Minto block of the Superior Province raises the question of Rae–Superior correlation.

A Discussion on volcanism and the structure of the Earth - Structure of the Icelandic basalt plateau and the process of drift

1972 ◽  
Vol 271 (1213) ◽  
pp. 141-150 ◽  
Keyword(s):  
Sea Level ◽  
Flood Basalt ◽  
Dyke Swarm ◽  
Seismic Velocities ◽  
Fissure Zone ◽  
Layer 2 ◽  
Dyke Injection ◽  
The Individual ◽  
Basalt Plateau ◽  
Seismic Discontinuity

Conventional stratigraphic mapping of parts of the Icelandic flood basalt succession and regional studies of the palaeomagnetic stratigraphy suggest that in at least two areas the basalt pile is composed of large lenticular shield-like lava units. Each unit is related spatially to its own feeding dyke swarm and is the result of a protracted period of dominantly fissure volcanism from a single fissure zone. The geophysical evidence suggests that the most important seismic discontinuity is the boundary between layers 2 and 3: P seismic velocities 5.1 and 6.3 km/s respectively. This seismic discontinuity has been mapped over large areas of Iceland by Palmason who has shown that it is generally at a depth of between 2 and 5 km below sea level. In eastern Iceland the discontinuity is approximately horizontal and markedly discordant with the observed dip of the individual lavas at sea level. It is suggested that, under Iceland, layer 3 is composed of intrusive dykes and gabbroic masses, whereas layer 2 is made up of extrusives cut by dykes and smaller intrusions. The observed relationships of the lava lenses constituting layer 2 are compatible with a crustal spreading model. The drift away from the axial zone, largely accommodated by dyke injection, appears to be at about 1 cm/year, a rate comparable to that observed on the adjacent Reykjanes Ridge.

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