Age of the Grenville dyke swarm, Ontario–Quebec: implications for the timing of lapetan rifting

1995 ◽  
Vol 32 (3) ◽  
pp. 273-280 ◽  
Author(s):  
S. L. Kamo ◽  
T. E. Krogh ◽  
P. S. Kumarapeli
Keyword(s):  
Long Range ◽  
Volcanic Rocks ◽  
Canadian Shield ◽  
Dyke Swarm ◽  
Alkaline Complex ◽  
Southeastern Part ◽  
Time Marker ◽  
Continental Breakup ◽  
Iapetus Ocean

U–Pb baddeleyite and zircon ages for three diabase dykes from widely spaced localities within the Grenville dyke swarm indicate a single age of emplacement at [Formula: see text] Ma. The 700 km long Grenville dyke swarm, located in the southeastern part of the Canadian Shield, was emplaced syntectonically with the development of the Ottawa graben. This graben may represent a plume-generated lapetan failed arm that developed at the onset of the breakup of Laurentia. Other precisely dated lapetan rift-related units, such as the Callander Alkaline Complex and the Tibbit Hill Formation volcanic rocks, indicate a protracted 36 Ma period of rifting and magmatism prior to volcanism along this segment of the lapetan margin. The age of the Grenville dykes is the youngest in a progression of precisely dated mafic magmatic events from the 723 Ma Franklin dykes and sills to the 615 Ma Long Range dykes, along the northern and northeastern margins of Laurentia, respectively. Thus, the age for these dykes represents a key time marker for continental breakup that preceded the formation of the Iapetus ocean.

40Ar/39Ar phlogopite and U – Pb perovskite dating of lamprophyre dykes from the eastern Lake Superior region: evidence for a 1.14 Ga magmatic precursor to Midcontinent Rift volcanism

1996 ◽  
Vol 33 (6) ◽  
pp. 958-965 ◽  
Author(s):  
M. Queen ◽  
J. A. Hanes ◽  
D. A. Archibald ◽  
E. Farrar ◽  
L. M. Heaman
Keyword(s):  
Temporal Relationship ◽  
Lake Superior ◽  
Canadian Shield ◽  
Dyke Swarm ◽  
Rift System ◽  
Alkaline Complex ◽  
Complex Activity ◽  
Midcontinent Rift ◽  
Midcontinent Rift System ◽  
The Relationship

Thin lamprophyre dykes are abundant in the vicinity of the ca. 1.1 Ga Midcontinent Rift System and the late Archean – Early Proterozoic Kapuskasing Uplift in the Canadian Shield northeast of Lake Superior. However, the relationship between these dykes and spatially associated alkalic-carbonatite complexes has been unclear. To ascertain the temporal relationship between the two, we have determined, by 40Ar/39Ar and U–Pb dating, precise emplacement ages for six lamprophyre dykes from the region. The [Formula: see text] Ma U–Pb date for perovskite from the western Marathon and Wawa areas is indistinguishable from the 1144 ± 7 Ma 40Ar/39Ar date for phlogopite from the eastern Kapuskasing Uplift, and it is concluded that these dykes are part of a regional 1.14 Ga swarm that extends over 300 km. These dykes were therefore emplaced some 35 Ma prior to the 1109 Ma commencement of Midcontinent Rift volcanism and coeval alkaline-complex activity, but essentially simultaneously with emplacement of the 1141 ± 2 Ma Abitibi diabase dyke swarm. It is suggested that these widespread 1144 Ma lamprophyre dykes and the Abitibi diabase dykes represent the first magmatic response of initiation of the Midcontinent rifting event, and were precursors to the main rift magmatism at 1109 Ma.

Resolving the Richat enigma: Doming and hydrothermal karstification above an alkaline complex

Geology ◽  
2005 ◽  
Vol 33 (8) ◽  
pp. 665-668 ◽  
Author(s):  
Guillaume Matton ◽  
Michel Jébrak ◽  
James K.W. Lee
Keyword(s):  
Volcanic Rocks ◽  
Hydrothermal Fluids ◽  
Alkaline Complex ◽  
Late Proterozoic ◽  
Hydrothermal Origin ◽  
Internal Sediments

Abstract The Richat structure (Sahara, Mauritania) appears as a large dome at least 40 km in diameter within a Late Proterozoic to Ordovician sequence. Erosion has created circular cuestas represented by three nested rings dipping outward from the structure. The center of the structure consists of a limestone-dolomite shelf that encloses a kilometer-scale siliceous breccia and is intruded by basaltic ring dikes, kimberlitic intrusions, and alkaline volcanic rocks. Several hypotheses have been presented to explain the spectacular Richat structure and breccia, but their origin remains enigmatic. The breccia body is lenticular in shape and irregularly thins at its extremities to only a few meters. The breccia was created during karst dissolution and collapse. Internal sediments fill the centimeter- to meter-scale cavities. Alkaline enrichment and the presence of Cretaceous automorphous neoformed K-feldspar demonstrate the hydrothermal origin of these internal sediments and their contemporaneity with magmatism. A model is proposed in which doming and the production of hydrothermal fluids were instrumental in creating a favorable setting for dissolution. The circular Richat structure and its breccia core thus represent the superficial expression of a Cretaceous alkaline complex with an exceptionally well preserved hydrothermal karst infilling at its summit.

PALAEOMAGNETISM OF THE ABITIBI DYKE SWARM

1966 ◽  
Vol 3 (5) ◽  
pp. 671-683 ◽  
Author(s):  
A. Larochelle
Keyword(s):  
Long Range ◽  
Dyke Swarm ◽  
Relative Importance ◽  
Angular Dispersion ◽  
Range Correlation ◽  
Dyke Swarms

Previous data published on the palaeomagnetism of a group of Precambrian diabase dykes, referred to as the Abitibi swarm, were characterized by considerable angular dispersion attributed to a number of possible factors. The relative importance of these factors was investigated in the light of data obtained for an independent suite of samples from the same group of dykes. Most of the previous interpretation is probably no longer valid because the magnetization of the swarm was found to be distributed tightly about three mean directions rather than dispersed widely about one mean direction, as originally thought. It is concluded that the dykes forming the swarm were injected intermittently during several widely distinct periods and that, accordingly, long-range correlation of diabase dyke swarms on the sole basis of their palaeomagnetism may be more hazardous than was realized earlier.

Paleomagnetism of Steel Mountain and Indian Head anorthosites from western Newfoundland

1976 ◽  
Vol 13 (1) ◽  
pp. 75-83 ◽  
Author(s):  
G. S. Murthy ◽  
K. V. Rao
Keyword(s):  
Northern Hemisphere ◽  
Remanent Magnetization ◽  
Canadian Shield ◽  
Relative Rotation ◽  
Southeastern Part ◽  
Lower Paleozoic ◽  
Grenville Province ◽  
Grenville Orogeny ◽  
Paleomagnetic Pole

As part of studies of anorthosites from the northern hemisphere, the paleomagnetism of two anorthosite inliers at Indian Head and Steel Mountain in western Newfoundland is described. The six sites at Indian Head retain a stable remanent magnetization and yield a paleomagnetic pole at 8 °S, 157½° E(δp = 15°, δm = 20°). This is close to poles for anorthositic and other rock units from within the Grenville Province that represent magnetization of age 1000 m. y., suggesting that there is no relative rotation between western Newfoundland and the southeastern part of the Canadian Shield, at least since the time of the Grenville orogeny. The ten sites at Steel Mountain also retain a stable magnetization, which yields a paleomagnetic pole at 22½° S, 41 °W (δp = 8°, δm = 14°). This position is closer to lower Paleozoic poles from Newfoundland and thus probably represents a lower Paleozoic magnetization.

A Cambrian island arc in Iapetus: geochronology and geochemistry of the Lake Ambrose volcanic belt, Newfoundland Appalachians

1991 ◽  
Vol 128 (1) ◽  
pp. 1-17 ◽  
Author(s):  
G. R. Dunning ◽  
H. S. Swinden ◽  
B. F. Kean ◽  
D. T. W. Evans ◽  
G. A. Jenner
Keyword(s):  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Detailed Examination ◽  
Island Arc ◽  
Trace Element Geochemistry ◽  
Geochemical Type ◽  
Element Geochemistry ◽  
South Central ◽  
Iapetus Ocean ◽  
Felsic Volcanic

AbstractThe Lake Ambrose volcanic belt (LAVB) outcrops as a 45 km long northeast-trending belt of mafic and felsic volcanic rocks along the eastern side of the Victoria Lake Group in south-central Newfoundland. It comprises roughly equal proportions of mafic pillow basalt and high silica rhyolite, locally interbedded with epiclastic turbidites. Volcanic rocks have been metamorphosed in the greenschist facies and are extensively carbonatized.U-Pb (zircon) dates from rhyolite at two, widely separated localities give identical ages of 513 ± 2 Ma (Upper Cambrian), and this is interpreted as the eruptive age of the volcanic sequence. Primitive arc and low-K tholeiites can be recognized on the basis of major and trace element geochemistry, ranging from LREE-depleted to LREE-enriched. Geochemical variation between mafic volcanic types is interpreted predominantly to reflect contrasts in source characteristics and degree of partial melting; some variation within each geochemical type attributable to fractional crystallization can be recognized. Detailed examination of some samples indicates that the heavy REE and related elements have locally been mobile, probably as a result of carbonate complexing.The LAVB is the oldest well-dated island arc sequence in Newfoundland, and perhaps in the Appalachian–Caledonian Orogen. Its age requires modification of widely held models for the tectonic history of central Newfoundland. It is older than the oldest known ophiolite, demonstrating that arc volcanism was extant before the generation of the oldest known oceanic crust in this part of Iapetus. It further demonstrates that there was a maximum of approximately 30 Ma between the rift-drift transition which initiated Iapetus, and the initiation of subduction. This suggests that the oceanic sequences preserved in Newfoundland represent a series of arcs and back arc basins marginal to the main Iapetus Ocean, and brings into question whether the Appalachian accreted terranes contain any remnants of normal mid-ocean ridge type Iapetan crust.

scholarly journals Minor intrusions of peralkaline microsyenite in the Ilímaussaq alkaline complex, South Greenland

2001 ◽  
Vol 48 ◽  
pp. 9-29
Author(s):  
J. Rose Hansen ◽  
H. Sørensen
Keyword(s):  
Magma Chamber ◽  
Source Region ◽  
Intermediate Zone ◽  
Dyke Swarm ◽  
Alkaline Complex ◽  
Geometrical Problem ◽  
Incompatible Elements

The agpaitic part of the Ilímaussaq alkaline complex, South Greenland, is made up of a roof zone, an intermediate zone and a floor zone. Dykes and sills of peralkaline microsyenite intersect the rocks of the roof and floor zones, but do not appear to intersect the lujavritic nepheline syenites which make up the intermediate zone. The microsyenites consist of Na-poor microcline, K-poor albite, aegirine and arfvedsonite which are practically identical to those of the agpaitic nepheline syenites of the complex. Neptunite and pectolite are the commonest minor minerals. The microsyenites are silica-saturated, –oversaturated, or, more rarely, undersaturated. The agpaitic part of the Ilímaussaq complex is considered to have been formed in a closed magma chamber; the lujavrites of the intermediate zone representing residual melts left after the consolidation of the roof and floor zones. That the microsyenite intrusions intersect the roof and floor zones but not the youngest lujavrites lying between these zones presents a geometrical problem which is discussed at some length. It is difficult to explain the microsyenites as products of fractionation or contamination of melts within the agpaitic magma chamber. Furthermore, the microsyenites differ mineralogically and chemically from the abundant microsyenitic dykes of the regional Tugtutôq-Ilímaussaq dyke swarm. It is therefore proposed that they originated in the source region which fed the agpaitic melts of the Ilímaussaq complex and that their emplacement in fractures was accompanied by a loss of volatiles and incompatible elements.

scholarly journals The Petrogenesis of Mid-Cretaceous Continental  Intraplate Volcanism in Marlborough, New Zealand,  during the Break-up of Gondwana

2021 ◽  
Author(s):  
◽  
Alexander Joseph McCoy-West
Keyword(s):  
New Zealand ◽  
Lithospheric Mantle ◽  
Volcanic Rocks ◽  
Oceanic Lithosphere ◽  
Small Degree ◽  
Lava Flows ◽  
Dyke Swarm ◽  
Subcontinental Lithospheric Mantle ◽  
Igneous Complex ◽  
Volcanic Material

<p>The Lookout Volcanics are the remnants of an extensive sheet of mid-Cretaceous (ca. 96 Ma) continental intraplate volcanic rocks erupted just prior to the rifting of New Zealand from Gondwana. Preserved in a fault angle depression bounded by the Awatere Fault located in Marlborough, South Island, New Zealand, the volcanic rocks cover an area of ca. 50 km2 with exposed thicknesses up to 1000 m. On the basis of stratigraphic evidence the dominantly terrestrial lavas flows are inferred to have erupted from dykes of a coeval radial dyke swarm. A detailed sampling of the lava flows of the Lookout Volcanics has been undertaken with a ca. 700 m composite stratigraphic section being constructed, largely based on a continuous sequence of lava flows outcropping in Middlehurst Stream. New Rb-Sr age constraints for the Lookout Volcanics (97.6 plus or minus 3.4 Ma) and Blue Mountain Igneous Complex (97.1 plus or minus 0.7 Ma) are consistent with previous radiometric dates of plutonic complexes in the Central Marlborough Igneous Complex, and suggest a rapid accumulation of volcanic material from ca. 98-96 Ma during the initial extension of proto-New Zealand. The predominantly mafic and alkaline samples include basalt, picrobasalt, basanite, trachybasalt and basaltic trachyandesite rock types. No samples represent primary magmas with all samples having undergone fractionation (or accumulation) of olivine plus clinopyroxene plus or minus plagioclase plus or minus Fe-Ti oxides. Initial Sr-Nd-Hf-Pb isotopic variations (87Sr/86Sr = 0.7030-0.7039; 143Nd/144Nd = 0.51272-0.51264; 176Hf/177Hf = 0.28283-0.28278; 206Pb/204Pb = 20.32-18.82) reflect mixing between melts of a HIMUlike mantle component with up to 25-30% of an Early Cretaceous upper crustal component. Oxygen isotope ratios determined by laser fluorination analysis from 6 lava flows yielded delta 18O = 4.7-5.0 per thousand for olivine, 4.8-5.4 per thousand in clinopyroxene cores, 3.9-5.5 per thousand in clinopyroxene rims. Average olivine (4.8 per thousand) and clinopyroxene core (5.1 per thousand) values are 0.4-0.5 per thousand lower than those of average mantle peridotite but comparable to those of HIMU OIB, and are consistent with New Zealand intraplate magmas being generated by a low delta 18O mantle. However, oxygen isotopic disequilibrium between clinopyroxene cores and rims (Delta 18O = -1.4 to +0.3) records the overprinting of this signature by crustal processes. Negative disequilibrium between clinopyroxene rims and cores in primitive samples suggests these phenocrysts grew in a shallow crustal magma chamber with an active meteoric water system. The effects of crustal assimilation can also be observed with clinopyroxene phenocrysts from the most evolved sample exhibiting coupled elevated delta 18O and 87Sr/86Sr. Variations in incompatible trace element ratios are consistent with the Lookout Volcanics being the small degree (2-5%) partial melts of an amphibole-bearing garnet pyroxenite. Furthermore, the elevated NiO contents of olivine phenocrysts are consistent with melting of a pyroxenitic mantle source. The presence of residual amphibole constrains melting to the hydrous subcontinental lithospheric mantle. The Lookout Volcanics and coeval plutonic complexes are the oldest occurrences of HIMU magmatism in Zealandia. This source was generated by small degree silicate melts from recycled oceanic lithosphere that metasomatised the base of the subcontinental lithospheric mantle beneath East Gondwana over 200 Ma ago.</p>

Preservation of primary geochemical signatures in polymetamorphosed tholeiite: The Long Range dyke swarm, Newfoundland, Canada

Lithos ◽  
1989 ◽  
Vol 24 (1) ◽  
pp. 55-64 ◽  
Author(s):  
J.Victor Owen ◽  
John D. Greenough ◽  
Kim A. Bellefontaine
Keyword(s):  
Long Range ◽  
Dyke Swarm

The Dog Bay Line: a major Silurian tectonic boundary in northeast Newfoundland

1993 ◽  
Vol 30 (12) ◽  
pp. 2481-2494 ◽  
Author(s):  
H. Williams ◽  
K. L. Currie ◽  
M. A. J. Piasecki
Keyword(s):  
Volcanic Rocks ◽  
Black Shales ◽  
Ductile Deformation ◽  
Shallow Marine ◽  
Regional Deformation ◽  
Iapetus Ocean ◽  
Tectonic Boundary

The Dog Bay Line separates different Silurian rock groups in northeast Newfoundland. West of the line, terrestrial volcanic rocks and sandstones (Botwood Group) overlie marine greywackes and conglomerates (Badger Group). East of the line, red sandstones overlie shallow marine shales and limestones (Indian Islands Group). Throughout Dog Bay, the line is marked by a disrupted zone of dark grey to black shales, volcanic rocks, and gabbros. Pervasive dextral, transpressive ductile deformation followed by successively more brittle extension with renewed dextral movements mark the northwest side of the line on the coast.The Dog Bay Line is traceable for 100 km and it is open-ended. Dextral offset is deduced to be many tens of kilometres. The line trends northeast, parallel to outcrop belts, and both the line and outcrop belts are curved eastward at the coast. The Mount Peyton Batholith, dated at 420 ± 8 Ma, apparently cuts the line.The Dog Bay Line occurs within the Dunnage Zone whose Cambrian–Ordovician rocks represent vestiges of the Iapetus Ocean. Northwest of the line, the Silurian rocks were deposited on Ordovician rocks already accreted to Laurentia. Southeast of the line, the Silurian rocks were deposited on Ordovician rocks already amalgamated with the continental Gander Zone. Timing of major movement and a Silurian marine to terrestrial depositional change recorded on both sides of the line agree within error with isotopic ages for the onset of plutonism, regional deformation, and metamorphism in central Newfoundland. The Dog Bay Line may mark the terminal Iapetus Ocean.

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