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‰.

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‰.

Rb–Sr geochronology and metamorphic history of Proterozoic to early Archean rocks north of the Cape Smith Fold Belt, Quebec

1987 ◽  
Vol 24 (4) ◽  
pp. 813-825 ◽  
Author(s):  
Ronald Doig
Keyword(s):  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Iron Formation ◽  
Fold Belt ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
The North ◽  
Basement Rocks ◽  
History Of ◽  
Wide Zone

The Churchill Province north of the Proterozoic Cape Smith volcanic fold belt of Quebec may be divided into two parts. The first is a broad antiform of migmatitic gneisses (Deception gneisses) extending north from the fold belt ~50 km to Sugluk Inlet. The second is a 20 km wide zone of high-grade metasedimentary rocks northwest of Sugluk Inlet. The Deception gneisses yield Rb–Sr isochron ages of 2600–2900 Ma and initial ratios of 0.701–0.703, showing that they are Archean basement to the Cape Smith Belt. The evidence that the basement rocks have been isoclinally refolded in the Proterozoic is clear at the contact with the fold belt. However, the gneisses also contain ubiquitous synclinal keels of metasiltstone with minor metapelite and marble that give isochron ages less than 2150 Ma. These ages, combined with low initial ratios of 0.7036, show that they are not part of the basement, as the average 87Sr/86Sr ratio for the basement rocks was about 0.718 at that time.The rocks west of Sugluk Inlet consist mainly of quartzo-feldspathic sediments, quartzites, para-amphibolites, marbles, and some pelite and iron formation. In contrast to the Proterozoic sediments in the Deception gneisses, these rocks yield dates of 3000–3200 Ma, with high initial ratios of 0.707–0.714. These initial ratios point to an age (or a provenance) much greater than that of the Archean Deception gneisses. The rocks of the Sugluk terrain are intruded by highly deformed sills of granitic rocks with ages of about 1830 Ma, demonstrating again the extent and severity of the Proterozoic overprint. The eastern margin of this possibly early Archean Sugluk block is a discontinuity in age, lithology, and geophysical character that could be a suture between two Archean cratons. It is not known if such a suturing event is of Archean age, or if it is related to the deformation of the Cape Smith Fold Belt.Models of evolution incorporating both the Cape Smith Belt and the Archean rocks to the north need to account for the internal structure of the fold belt, the continental affinity of many of the volcanic rocks, the continuity of basement around the eastern end of the belt, and the increase in metamorphism through the northern part of the belt into a broad area to the north. The Cape Smith volcanic rocks may have been extruded along a continental rift, parallel to a continental margin at Sugluk. Continental collison at Sugluk would have thrust the older and higher grade Sugluk rocks over the Deception gneisses, produced the broad Deception antiform, and displaced the Cape Smith rocks to the south in a series of north-dipping thrust slices.

Metallogeny of the Marco zone, Corvet Est, disseminated gold deposit, James Bay, Quebec, Canada

2012 ◽  
Vol 49 (10) ◽  
pp. 1154-1176
Author(s):  
Martin Aucoin ◽  
Georges Beaudoin ◽  
Robert A. Creaser ◽  
Paul Archer
Keyword(s):  
Gold Deposit ◽  
Basaltic Andesite ◽  
Native Gold ◽  
Gold Mineralization ◽  
Isotope Composition ◽  
Hanging Wall ◽  
Volcanic Rocks ◽  
Weighted Average ◽  
James Bay ◽  
Host Rocks

The Corvet Est gold deposit is hosted by Archean rocks of the Superior Province in the James Bay region, northern Quebec, Canada. The Marco zone is hosted by amphibolite-grade, strongly foliated volcanic rocks and consists of disseminated gold, with an apparent thickness ranging from 1.8 to 39.5 m and gold grades up to 23 g·t–1 over 1 m, that is continuous along strike for ∼1.3 km. The lithotectonic sequence comprises footwall basaltic andesite amphibolite overlain by a lenticular unit of metadacite and then by hanging-wall basaltic andesite amphibolite, all intruded by quartz–feldspar porphyry dikes. Dacite, basaltic andesite amphibolite, and quartz–feldspar porphyry show a calc-alkaline to transitional affinity and plot in the plate margin arc basalt field, with typical volcanic arc trace element patterns. Mineralization consists of pyrite, arsenopyrite, pyrrhotite, chalcopyrite, and gold, disseminated in deformed dacite, in andesite amphibolite, and in quartz–feldspar porphyry dikes. Dacite and andesite display weak alteration characterized by silicification. Native gold forms inclusions in metamorphic quartz, garnet, feldspar, arsenopyrite, and pyrite or free grains interstitial to quartz, feldspar, pyrite, chalcopyrite, and arsenopyrite. Free gold in late quartz veins cut the sericitized metamorphic fabric. Inclusion and interstitial native gold within minerals annealed during metamorphism shows that gold mineralization is pre- to syn-metamorphic, with some gold remobilized in later veins. Rhenium–osmium dating of arsenopyrite yields an isochron age of 2663 ± 13 Ma for mineralization and a weighted average model age of 2632 ± 7 Ma for arsenopyrite formed during peak metamorphism. The ∼2663 Ma arsenopyrite has a low initial 187Os/188Os of 0.19 ± 0.10, suggesting a juvenile crust or a mantle Os source. The sulfur isotope composition of Marco zone pyrite and arsenopyrite shows that sulfur could have been leached from its volcanic host rocks or from reduction of Archean seawater. The Corvet Est deposit is interpreted to be an orogenic gold deposit (2663 Ma) deformed and recrystallized during amphibolite-grade metamorphism (2632 Ma).

scholarly journals AN ESTIMATE OF THE COMPOSITION OF PART OF THE CANADIAN SHIELD IN NORTHWESTERN ONTARIO

1967 ◽  
Vol 4 (4) ◽  
pp. 725-739 ◽  
Author(s):  
G. A. Reilly ◽  
D. M. Shaw
Keyword(s):  
Trace Elements ◽  
Significant Variation ◽  
Major Element ◽  
Canadian Shield ◽  
Element Analysis ◽  
Red Lake ◽  
Rock Types ◽  
Northwestern Ontario ◽  
House Area ◽  
Composite Samples

An attempt has been made to estimate the abundance of trace and major constituents in the Precambrian surficial rocks of a large part (43 000 square miles) of the Red Lake–Lansdowne House area in northwestern Ontario. One-hundred and two composite samples were made to represent eight rock types in seven adjacent map-areas of equal size. Major element analysis was carried out on eight composite samples representing rock types for the whole area. Analysis of variance techniques have detected significant regional variations of Cr, Mn, Sr, and Ba. Significant variation exists between rock types for all trace elements analyzed except Cu.

Geological setting of gold, western Wabigoon Subprovince, Canadian Shield: exploration targets in mixed volcanic successions

1988 ◽  
Vol 25 (12) ◽  
pp. 2075-2088 ◽  
Author(s):  
David R. Melling ◽  
Charles E. Blackburn ◽  
David H. Watkinson ◽  
Jack R. Parker
Keyword(s):  
Volcanic Rocks ◽  
Shear Zones ◽  
Canadian Shield ◽  
Field Mapping ◽  
Geological Setting ◽  
Intrusive Rocks ◽  
Volcaniclastic Rocks ◽  
Gold Bearing

The Archean volcanic rocks in the Cameron–Rowan lakes area may be divided into three distinct successions based on field mapping, petrographic studies, and lithogeochemical characteristics. The lowermost Rowan Lake Volcanics are tholeiitic pillowed basalts. These rocks are unconformably overlain by the Cameron Lake Volcanics, a mixed succession of tholeiitic massive and pillowed basalts and intermediate to felsic volcaniclastic rocks. The Brooks Lake Volcanics consist of tholeiitic basalts and represent the youngest volcanic rocks at the top of the preserved succession.Most of the gold concentrations in the Cameron–Rowan lakes area are confined to the mixed Cameron Lake Volcanics. The majority of these, including the Cameron Lake deposit, occur within shear zones near lithologic contacts. In the Eagle–Wabigoon and Manitou lakes areas there are similar stratigraphic subdivisions of the supracrustal rocks and many of the gold concentrations also occur in deformation zones within the mixed volcanic successions. The contrasting competencies among the basalts, the intermediate to felsic volcaniclastic rocks, and the intrusive rocks, which are characteristic of the mixed volcanic successions, localized stress during deformation, forming shear zones into which gold-bearing fluids gained access. The potential for successfully delineating economic gold concentrations appears greatest in the mixed volcanic successions within these areas and elsewhere in the western Wabigoon Subprovince of the Canadian Shield.

U–Pb zircon ages for the Rice Lake area, southeastern Manitoba

1989 ◽  
Vol 26 (1) ◽  
pp. 23-30 ◽  
Author(s):  
A. Turek ◽  
R. Keller ◽  
W. R. Van Schmus ◽  
W. Weber
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Quartz Diorite ◽  
Granitic Rocks ◽  
Lake Area ◽  
The South ◽  
Metasedimentary Rocks ◽  
The North ◽  
Felsic Volcanic ◽  
Felsic Volcanic Rocks

The Archean Rice Lake greenstone belt in southeastern Manitoba is made up of mafic to felsic volcanic rocks and associated intrusive and metasedimentary rocks. The belt is flanked to the north by the Wanipigow River granitic complex and to the south by the Manigotagan gneissic belt. The Ross River quartz diorite pluton is intrusive into the centre of the greenstone belt. U–Pb zircon ages indicate a major volcanic and plutonic event in the area at 2730 Ma. Ages for two volcanic units of the Rice Lake Group are 2731 ± 3 and 2729 ± 3 Ma. The Ross River pluton yields an age of 2728 ± 8 Ma and the Gunnar porphyry gives an age of 2731 ± 13 Ma; both intrude rocks of the Rice Lake Group. Granitic rocks of the Wanipigow River granitic complex give ages of 2731 ± 10 and 2880 ± 9 Ma, while a post-tectonic granite in the Manigotagan gneissic belt has an age of 2663 ± 7 Ma.

U–Pb zircon ages and the evolution of the Michipicoten plutonic–volcanic terrane of the Superior Province, Ontario

1984 ◽  
Vol 21 (4) ◽  
pp. 457-464 ◽  
Author(s):  
A. Turek ◽  
Patrick E. Smith ◽  
W. R. Van Schmus
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Tectonic Activity ◽  
Superior Province ◽  
Zircon Geochronology ◽  
Metasedimentary Rocks ◽  
Metavolcanic Rocks ◽  
Before And After ◽  
Volcanic Cycles

The Archean Michipicoten greenstone belt of the Superior Province in Ontario is made up of supracrustal rocks divided into lower, middle, and upper metavolcanic rocks with associated metasedimentary rocks. The belt has been intruded by granitic rocks and is also surrounded by granitic terranes. Based on U–Pb zircon geochronology it appears that volcanism in the area extended from at least 2749 to 2696 Ma, and plutonism and tectonic activity extended from at least 2888 to 2615 Ma. The various granitic (and also one gabbroic) plutons, both internal and external to the greenstone belt, were emplaced concomitantly with the three volcanic cycles as well as before and after the formation of the volcanic rocks. Zircon ages reported here, together with previously published ages, show that the area evolved in six major volcanic and plutonic events: (I) 2888 Ma—plutonism, (II) 2743 Ma—volcanism and plutonism, (III) 2717 Ma—volcanism and plutonism, (IV) 2696 Ma—volcanism and plutonism, (V) 2668 Ma—plutonism, and (VI) 2615 Ma—plutonism. The oldest rock dated at 2888 ± 2 Ma belongs to the external granitic terrane and may be basement to the supracrustal rocks.

Palaeoproterozoic metasedimentary rocks of the Ji'an Group and their significance for the tectonic evolution of the northern segment of the Jiao–Liao–Ji Belt, North China Craton

2017 ◽  
Vol 155 (1) ◽  
pp. 149-173 ◽  
Author(s):  
EN MENG ◽  
CHAO-YANG WANG ◽  
ZHUANG LI ◽  
YAN-GUANG LI ◽  
HONG YANG ◽  
...  
Keyword(s):  
North China Craton ◽  
North China ◽  
Tectonic Setting ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Geochemical Data ◽  
Metasedimentary Rocks ◽  
The North ◽  
Northern Segment

AbstractIn this paper we present new petrological and whole-rock geochemical data for the Palaeoproterozoic metasedimentary rocks in the upper part of the Ji'an Group within the Jiao–Liao–Ji Belt, China, as well as zircon U–Pb age dates andin situLu–Hf isotope data. The new data improve our understanding of the original nature of the metasedimentary rocks, further providing insights into their tectonic setting and the evolutionary history of the northern segment of the Jiao–Liao–Ji Belt. The zircons can be divided into two groups, viz., one of magmatic origin and the other of metamorphic origin. Zircon U–Pb dating gave mean or statistical peak ages for the magmatic zircons at 2035, 2082, 2178, 2343–2421, 2451–2545, 2643–2814 and 2923–3446 Ma, and mean peak ages for the metamorphic zircons at 1855 and 1912 Ma, which indicate a maximum depositional age of 2.03 Ga and two-stage metamorphic events atc. 1.91 and 1.85 Ga for the metasedimentary rocks. Geochemical data show that (1) the protoliths of these rocks were mainly sandstones, greywackes and claystones, together with some shales; (2) the main sources of the sedimentary material were Palaeoproterozoic granites and acid volcanic rocks, with minor contributions from Archaean granitic rocks; and (3) the sediments were deposited in an active continental margin setting. Moreover, along the northeastern margin of the Eastern Block of the North China Craton there is evidence of ancient crustal materials as old as 3.76 Ga, and multiple crustal growth events at 3.23–3.05, 2.80–2.65, 2.54–2.45 and 2.28–2.08 Ga.

scholarly journals LA-ICP-MS U-Pb apatite dating of Lower Cretaceous rocks from teschenite-picrite association in the Silesian Unit (southern Poland)

2014 ◽  
Vol 65 (4) ◽  
pp. 273-284 ◽  
Author(s):  
Krzysztof Szopa ◽  
Roman Włodyka ◽  
David Chew
Keyword(s):  
Volcanic Activity ◽  
Volcanic Rocks ◽  
Weighted Average ◽  
Magmatic Rocks ◽  
Three Samples ◽  
Icp Ms ◽  
Outer Western Carpathians ◽  
Wide Range ◽  
Igneous Province ◽  
Intrusive Rocks

Abstract The main products of volcanic activity in the teschenite-picrite association (TPA) are shallow, sub-volcanic intrusions, which predominate over extrusive volcanic rocks. They comprise a wide range of intrusive rocks which fall into two main groups: alkaline (teschenite, picrite, syenite, lamprophyre) and subalkaline (dolerite). Previous 40Ar/39Ar and 40K/40Ar dating of these rocks in the Polish Outer Western Carpathians, performed on kaersutite, sub-silicic diopside, phlogopite/biotite as well as on whole rock samples has yielded Early Cretaceous ages. Fluorapatite crystals were dated by the U-Pb LA-ICP-MS method to obtain the age of selected magmatic rocks (teschenite, lamprophyre) from the Cieszyn igneous province. Apatite-bearing samples from Boguszowice, Puńców and Lipowa yield U-Pb ages of 103± 20 Ma, 119.6 ± 3.2 Ma and 126.5 ± 8.8 Ma, respectively. The weighted average age for all three samples is 117.8 ± 7.3 Ma (MSWD = 2.7). The considerably smaller dispersion in the apatite ages compared to the published amphibole and biotite ages is probably caused by the U-Pb system in apatite being less susceptible to the effects of hydrothermal alternation than the 40Ar/39Ar or 40K/40Ar system in amphibole and/or biotite. Available data suggest that volcanic activity in the Silesian Basin took place from 128 to 103 Ma with the the main magmatic phase constrained to 128-120 Ma.

scholarly journals Isotopic age determinations from South Greenland and their geological setting

1965 ◽  
Vol 53 ◽  
pp. 1-56
Author(s):  
D Bridgwater
Keyword(s):  
Biotite Granite ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Isotopic Age ◽  
Fold Belt ◽  
South West ◽  
Intrusive Rocks ◽  
Igneous Activity ◽  
Fold Belts ◽  
Age Determinations

A brief geological review of the area between Sermiligârssuk and Kap Farvel is given using the following five main divisions of the Precambrian of South Greenland: 1) pre-Ketilidian (? 2000-2700 m. y.) 2) Ketilidian (? 1700-2000 m. y.) 3) post-Ketilidian = Kuanitic (? 1650-1700 m. y.) 4) Sanerutian (? 1500-1650 m. y.) 5) Gardar (1020-?1500 m.y.). In the area described these divisions are characterized by: 1) gneisses, 2) geosynclinal sedimentation and lava extrusion, metamorphism and plutonism, 3) basic and intermediate dyking, 4) renewed plutonism, and emplacement of synplutonic basic, intermediate and granitic rocks, 5) post-orogenic sedimentation, lava extrusion and a predominantly alkali suite of intrusive rocks. Isotopic age determinations are available from the two youngest of the above divisions in South Greenland; dates for the three older divisions are suggested by comparison of the development of South Greenland with other fold belts together with sparse data from elsewhere in Greenland. It is suggested that the pre-Ketilidian gneisses represent the remnant of an old fold belt formed approximately 2400-2700 m. y. ago which has been reactivated during the Ketilidian and Sanerutian plutonic episodes in South Greenland. It is further suggested that the Ketilidian, post-Ketilidian and Sanerutian episodes are phases in the evolution of one fold belt which started at approximately 2000 m. y. ago and represents the beginning of the Svecofennid chelogenic cycle in South Greenland. The Gardar magmatism is regarded as a typical post-orogenic alkali suite and it is thought that the Gardar activity at about 1200 m. y. may represent compensatory tensional conditions on the margins of the developing Grenville fold belt which probably passed south of Greenland. Eight K/Ar age determinations (Geochron Laboratories) give the following results: Sanerutian hypersthene gabbro, 1645 m. y. (biotite) and 1700 m. y. (augite); Sanerutian granite, 1620 m. y. (biotite) ; early Gardar dolerite, 1435 m. y. (augite); Gardar syenite, 1128 m. y. (biotite) and 1355 m. y. (augite); inclusion of anorthosite fragment in a Gardar dyke, 1025 m. y. (biotite) and 1075 m. y. (augite). Four Rb/Sr age determinations (Moorbath) give the following results: Ketilidian pegmatite affected by Sanerutian metamorphism, 1630 m. y; Sanerutian granite, 1615 m. y.; Sanerutian granite probably affected by Gardar event, 1220 m. y.; Gardar biotite granite, 1150 m. y. Results from other areas in Greenland are discussed and it is suggested that a large part of the south-west coastal strip is pre-Ketilidian in age and that the Nagssugtoqidian fold belt was formed at approximately the same time as the Ketilidian-Sanerutian fold belt in South Greenland, that is at the beginning of the Svecofennid chelogenic cycle. It is suggested that the main episodes described from South Greenland correspond to events in the Canadian shield as follows: pre-Ketilidian plutonism = Kenoran; Ketilidian-Sanerutian and Nagssugtoqidian = Hudsonian; Gardar = post-Hudsonian, pre-Grenville igneous activity. Tectono-igneous cycles are used in conjunction with basic dykes and age determinations as a method of dividing the Precambrian.

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