The oxygen isotope composition of the surface crystalline rocks of the Canadian Shield

1978 ◽  
Vol 15 (11) ◽  
pp. 1773-1782 ◽  
Author(s):  
Yuch-Ning Shieh ◽  
Henry P. Schwarcz
Keyword(s):  
Isotope Composition ◽  
Crystalline Rocks ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Baffin Island ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Rock Types ◽  
Northern District ◽  
Basic Rocks

The average 18O/16O ratios of the major rock types of the surface crystalline rocks in different parts of the Canadian Precambrian Shield have been determined, using 47 composite samples prepared from 2221 individual rock specimens. The sampling areas include Baffin Island, northern and southwestern Quebec, Battle Harbour – Cartwright, northern District of Keewatin, Fort Enterprise, Snowbird Lake, Kasmere Lake, and Saskatchewan, covering approximately 1 400 000 km2. The granitic rocks from the Superior, Slave, and Churchill Provinces vary only slightly from region to region (δ18O = 6.9–8.4‰) and are significantly lower in 18O than similar rock types from the younger Grenville Province (δ = 9.2–10.0‰). The sedimentary and metasedimentary rocks have δ18O = 9.0–11.7‰ and hence are considerably lower than their Phanerozoic equivalents, possibly reflecting the presence of a high percentage of little-altered igneous rock detritus in the original sediments. The basic rocks in most regions fall within a δ18O range of 6.8–7.6‰, except in northern and southwestern Quebec where the δ-values are abnormally high (8.5–8.9‰). The overall average 18O/16O ratio of the surface crystalline rocks of the Canadian Shield is estimated to be 8.0‰, which represents an enrichment with respect to probable mantle derived starting materials by about 2‰.

An estimate of the oxygen isotope composition of a large segment of the Canadian Shield in northwestern Ontario

1977 ◽  
Vol 14 (5) ◽  
pp. 927-931 ◽  
Author(s):  
Yuch-Ning Shieh ◽  
Henry P. Schwarcz
Keyword(s):  
Isotope Composition ◽  
Volcanic Rocks ◽  
Weighted Average ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Large Segment ◽  
Metasedimentary Rocks ◽  
Northwestern Ontario ◽  
Intrusive Rocks ◽  
Composite Samples

The O18/O16 ratios of the plutonic and supracrustal rocks from a large segment of the Superior province of the Canadian Precambrian Shield in Ontario (total area 111 000 km2) have been determined, using 8 composite samples prepared from 8076 individual specimens. The δO18 values (in ‰) relative to SMOW are: granitic rocks, 7.6–8.6; basic intrusive rocks, 7.2; metasedimentary rocks, 9.2; and volcanic rocks, 7.6. The composites from the granitic, basic intrusive, and volcanic rocks display δ values very similar to their contemporary or younger equivalents reported in the literature. The metasedimentary composite shows significantly lower δO18 than most Phanerozoic and Proterozoic metasediments of comparable metamorphic grades, possibly reflecting the presence of a high percentage of little-altered igneous rock detritus in the Archean sediments. The weighted average δ value (according to percent outcrop of each rock type) of this part of the Canadian Shield is estimated to be 8.1‰.

Determination of the characteristics of crystalline rocks by field experiments: a review

1986 ◽  
Vol 319 (1545) ◽  
pp. 139-156 ◽  
Keyword(s):  
Radioactive Waste ◽  
Field Experiments ◽  
The United States ◽  
Crystalline Rocks ◽  
Granitic Rocks ◽  
Rock Types ◽  
Basement Rocks ◽  
Deep Boreholes ◽  
High Level ◽  
Underground Research Laboratory

Crystalline rocks, particularly granitic rocks and basalts, are one of the principal rock types under consideration as a potential host rock for a high-level radioactive waste repository. Permeability in such rocks is related to discontinuities of various scales, and the quantification and prediction of groundwater flow within both the fractures and the intact rock between the fractures is the major goal of field experiments. The Canadian Underground Research Laboratory is unique in that the hydrogeological conditions within a large volume of rock surrounding the experimental shaft are being monitored before, during and after excavation and the results compared with model predictions. In Switzerland twelve deep boreholes are being drilled to over 1000 m to investigate crystalline basement rocks beneath a cover of sediments. The Stripa Mine in Sweden has hosted a major experimental programme including heater tests to stimulate the thermal effect of radioactive waste and hydrogeological tests at various scales down to individual fractures. The United States of America, the United Kingdom, France and Finland have also embarked on major experimental programmes. Continuing research is needed, with an emphasis on field experiments and research in underground rooms, to provide the data on which detailed risk assessments can be based.

A Discussion on global tectonics in Proterozoic times - The Grenville Province in Helikian times: a possible model of evolution

1976 ◽  
Vol 280 (1298) ◽  
pp. 499-515 ◽  
Keyword(s):  
Continental Crust ◽  
Granulite Facies ◽  
Continental Collision ◽  
Canadian Shield ◽  
Grenville Province ◽  
East Central ◽  
Metasedimentary Rocks ◽  
Grenvillian Orogeny ◽  
Triangular Area ◽  
Global Tectonics

It is suggested that the Helikian (1650-1000 million years (Ma) ago) evolution of the Grenville Province in the Canadian Shield was marked by three events: emplacement of anorthosites around 1450-1500 Ma ago, rifting associated with opening of a proto-Atlantic ocean between 1200 and 1300 Ma ago, and continental collision responsible for the Grenvillian ‘orogeny’ about 1100-1000 Ma ago. Emplacement of rocks of the anorthosite suite (anorthosites and adamellites or mangerites) into continental crust was accompanied by formation of aureoles in the granulite facies. The Grenville Group was deposited in the southern part of the Province between 1300 and 1200 Ma ago and comprises marbles, clastic metasedimentary rocks and volcanics. It occupies a roughly triangular area limited on the northwest by the Bancroft—Renfrew lineament and on the southeast by the Chibougamau—Gatineau lineament. It is thought to have been accumulated in an aulacogen that would have developed along a fracture zone separating two basement blocks. The Grenvillian thermotectonic event may represent a Tibetan continental collision in the sense of Burke & Dewey. The suture zone would now be hidden under the Appalachians. Collision would cause reactivation of continental crust and renewed movement on pre-existing lineaments. The east—central part of the Grenville Province appears to have been more intensively reactivated than the western part.

Geology and Ages of Buried Precambrian Basement Rocks, Manitoulin Island, Ontario

1975 ◽  
Vol 12 (7) ◽  
pp. 1175-1189 ◽  
Author(s):  
W. R. Van Schmus ◽  
K. D. Card ◽  
K. L. Harrower
Keyword(s):  
Granitic Rocks ◽  
Precambrian Basement ◽  
Aeromagnetic Data ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Basement Rocks ◽  
Metavolcanic Rocks ◽  
Northern Half ◽  
East End ◽  
Archean Basement

The geology of the buried Precambrian basement under Manitoulin Island in northern Lake Huron, Ontario, has been re-evaluated on the basis of aeromagnetic data, well cuttings, core samples, and rubidium–strontium and uranium–lead geochronologic data on some of the subsurface samples. We conclude that the northern half of the island is underlain in part by Huronian metasedimentary rocks, but that these are absent from the southern part of the island, which is underlain by granitic, gneissic, and metavolcanic rocks. Granitic and gneissic rocks are also present under the northern half of the island.Geochronologic data show that rocks underlying major positive aeromagnetic anomalies are quartz-monzonitic composite plutons which are about 1500 ± 20 m.y. old. Surrounding metasedimentary. gneissic, and granitic rocks are at least 1700 m.y. old. No evidence was found for extrapolation of the pre-Huroman Archean basement beneath Manitoulin Island; if it is present it has been affected by younger metamorphic overprinting.The south west ward extension of the boundary zone between the Grenville Province and rocks to the west can he traced along the east end of Manitoulin Island on the basis of aeromagnetic data.

scholarly journals The crystalline rocks of western and southern Dove Bugt, North-East Greenland

1990 ◽  
Vol 148 ◽  
pp. 127-132
Author(s):  
B Chadwick ◽  
C.R.L Friend ◽  
A.K Higgins
Keyword(s):  
Crystalline Rocks ◽  
Fold Belt ◽  
Deformation History ◽  
Isotopic Data ◽  
East Greenland ◽  
Metasedimentary Rocks ◽  
North East ◽  
Rock Types ◽  
Different Types ◽  
History Of

The land areas around Dove Bugt are dominated by quartzo-feldspathic orthogneisses with a complex history of emplacement and deformation. The oldest rocks recognised are supracrustal units, mainly marbles and rusty-weathering metasedimentary rocks. Locally gabbro-anorthosite units are associated with the supracrustal rocks. These rock units are cut by different phases of the gneisses, of which the most abundant are grey banded orthogneisses. Two different varieties of pink orthogneiss are also recognised. Different types of tabular amphibolitic bodies, relicts of dykes or sills, cut most rock types. The area lies within the East Greenland Caledonian fold belt, but available isotopic data suggest that the crystalline rocks include Archaean and early Proterozoic suites which have undergone uncertain degrees of Caledonian reworking. It is not clear at present how much of the deformation history of at least four periods of deformation and associated mylonitisation is Caledonian, and how much pre-Caledonian.

Zonal structure of the Perth Road monzonite, Grenville Province, Ontario

1970 ◽  
Vol 7 (2) ◽  
pp. 414-434 ◽  
Author(s):  
I. F. Ermanovics
Keyword(s):  
Rock Type ◽  
Maximum Velocity ◽  
Alkali Feldspar ◽  
Granulite Facies ◽  
The Body ◽  
Grenville Province ◽  
Flow Models ◽  
Metasedimentary Rocks ◽  
Rock Types ◽  
Quartz Monzonite

The Perth Road pluton is a lenticular, grossly conformable body emplaced in metasedimentary rocks of the Grenville series during a period in which the enclosing gneisses deformed by plastic flow. The body is zoned and from the center outward comprises gabbro, diorite, monzonite (the dominant rock-type), quartz monzonite, and granite. The change from one rock-type to the next is gradual and the progressive acidification toward all the contacts, without regard to the type of enclosing gneiss, is taken as an indication of cogenesis of the plutonic assemblage; modal mineral variations of quartz, alkali-feldspar, plagioclase, and color index demonstrate this mineral progression.The enclosing crystalline metasedimentary rocks have been metamorphosed to the hornblende granulite facies, and although recrystallization has kept pace with deformation some cataclasis pervades all rocks. The pluton occupies a flattened crestal position of a doubly plunging fold, and all folds show a combination of fold-styles depending on the relative competence of the various rock-types. Flow models demonstrate that the early magmatic precipitates collected in regions of maximum velocity of the magma during folding of the enclosing envelope of gneisses and that syntectonic differentiation in this manner obtains for the Perth Road and other plutons in the area.

Geology and age of the Precambrian basement in the Windsor, Chatham, and Sarnia area, southwestern Ontario

1982 ◽  
Vol 19 (8) ◽  
pp. 1627-1634 ◽  
Author(s):  
A. Turek ◽  
R. N. Robinson
Keyword(s):  
Oil And Gas ◽  
Precambrian Basement ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Gas Drilling ◽  
Arch System ◽  
Grenvillian Orogeny ◽  
Anomaly Map ◽  
Paleozoic Rocks ◽  
Basement Surface

Precambrian basement in the Windsor–Chatham–Sarnia area is covered by Paleozoic rocks that are up to 1300 m thick. The basement surface is characterized by a northeast–southwest arch system with a relief of about 350 m. Extensive oil and gas drilling has penetrated and sampled this basement, and an examination of core and chip samples from 133 holes and an assessment of the magnetic anomaly map of the area have been used to produce a lithologic map of the Precambrian basement. The predominant rocks are granite gneisses and syenite gneisses but also significant are gabbros, granodiorite gneisses, and metasedimentary rocks. The average foliation dips 50° and is inferred to have a northeasterly trend. The Precambrian basement has been regarded as part of the Grenville Province. An apparent Rb–Sr whole rock isochron, for predominantly meta-igneous rocks, yields an age of 1560 ± 140 Ma. This we interpret as pre-Grenvillian, surviving the later imprint of the Grenvillian Orogeny. Points excluded from the isochron register ages of 1830, 915, and 670 Ma, and can be interpreted as geologically meaningful.

Layered Granitic Rocks at Chebucto Head, Halifax County, Nova Scotia

1975 ◽  
Vol 12 (3) ◽  
pp. 456-463 ◽  
Author(s):  
T. E. Smith
Keyword(s):  
Grain Size ◽  
Nova Scotia ◽  
Granitic Rocks ◽  
Textural Characteristics ◽  
Rock Types ◽  
Flow Sorting

Structural, mineralogical and textural characteristics of some layered granitic rocks are described. The layers result from the segregation of minerals into bands and lenses of contrasting color and grain size. They were formed near the roof of the pluton prior to final crystallization by flow sorting during episodic shearing generated during intrusion. Comparison of the mineralogy and textures of the layered rocks with those of the main rock types of the pluton shows that the differentiation of the pluton as a whole took place after the formation of the layers by interaction of felsic components concentrated in residual liquids with earlier formed crystals.

Chapter 4 The Loch Maree Group

2002 ◽  
Vol 26 (1) ◽  
pp. 29-44
Keyword(s):  
Cross Section ◽  
Detrital Zircon ◽  
Main Part ◽  
Close Association ◽  
Volcanic Origin ◽  
Metasedimentary Rocks ◽  
Rock Types ◽  
Depositional Age ◽  
Nd Model Age ◽  
Narrow Bands

The supracrustal rocks of the Loch Maree Group (LMG) consist of a variety of metasedimentary rocks interbanded with amphibolites considered to be of volcanic origin. The metasedimentary rocks fall into two distinct categories: a) schistose semipelites, which form the main part of the outcrop; and b) narrow bands of different rock types, including siliceous, carbonate-bearing and graphitic rocks, occurring in close association with the metavolcanic amphibolites. Both the compositional banding and the dominant foliation throughout the LMG outcrop are steeply dipping and trend uniformly NW-SE.The sequence of lithotectonic rock units from SW to NE (structurally upwards) is shown in the cross-section (Fig. 4.1) and briefly described in Table 4.1. The original names of the lithotectonic units (Park 1964) are retained for convenience. The depositional age of the LMG is presumed to be around 2.0 Ga, based on a Sm-Nd model age (O'Nions et al. 1983) and detrital zircon dates (Whitehouse et al. 1991 a, 2001) (see below).Semipelites form several distinct NW-trending belts separated by amphibolite sheets. The most prominent belt comprises the Flowerdale schist unit (see map) which occupies a broad belt about 700 m in width, extending in a northwesterly direction across the Gairloch district, but ending north of the mapped area, where the two amphibolites from either side converge, 3.5 km north of the Gairloch-Poolewe road. This belt is offset in the centre of the area by the Flowerdale fault, and has a total exposed length of about 15 km. Southwest of this belt is the

scholarly journals Gold-hosting supracrustal rocks on Storø, southern West Greenland: lithologies and geological environment

2007 ◽  
Vol 13 ◽  
pp. 41-44 ◽  
Author(s):  
Christian Knudsen ◽  
Jeroen A.M. Van Gool ◽  
Claus Østergaard ◽  
Julie A. Hollis ◽  
Matilde Rink-Jørgensen ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
West Greenland ◽  
Metasedimentary Rocks ◽  
Quartz Veins ◽  
Rock Types ◽  
Minimum Age ◽  
Arc Setting ◽  
Basic Volcanic ◽  
Back Arc ◽  
Different Sources

A gold prospect on central Storø in the Nuuk region of southern West Greenland is hosted by a sequence of intensely deformed, amphibolite facies supracrustal rocks of late Mesoto Neoarchaean age. The prospect is at present being explored by the Greenlandic mining company NunaMinerals A/S. Amphibolites likely to be derived from basaltic volcanic rocks dominate, and ultrabasic to intermediate rocks are also interpreted to be derived from volcanic rocks. The sequence also contains metasedimentary rocks including quartzites and cordierite-, sillimanite-, garnet- and biotite-bearing aluminous gneisses. The metasediments contain detrital zircon from different sources indicating a maximum age of the mineralisation of c. 2.8 Ga. The original deposition of the various rock types is believed to have taken place in a back-arc setting. Gold is mainly hosted in garnet- and biotite-rich zones in amphibolites often associated with quartz veins. Gold has been found within garnets indicating that the mineralisation is pre-metamorphic, which points to a minimum age of the mineralisation of c. 2.6 Ga. The geochemistry of the goldbearing zones indicates that the initial gold mineralisation is tied to fluid-induced sericitisation of a basic volcanic protolith. The hosting rocks and the mineralisation are affected by several generations of folding.

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