The geochronology of the granitic rocks along the Bear–Slave Structural Province boundary, northwest Canadian Shield

1977 ◽  
Vol 14 (6) ◽  
pp. 1356-1373 ◽  
Author(s):  
Rosaline Frith ◽  
R. A. Frith ◽  
R. Doig
Keyword(s):  
Age Groups ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Thermal Event ◽  
Slave Province ◽  
Fault Block ◽  
Granitic Intrusions ◽  
Main Period ◽  
Archean Crust ◽  
Archean Basement

Archean granitic rocks along the southern Bear–Slave boundary fall into three age groups: the oldest are 3000 Ma old intrusive tonalites and granodiorites that form the basement to the Yellowknife Supergroup; the second are syn-volcanic granitic intrusions of ~ 2700 Ma; and the youngest are ~ 2560 Ma granitic and migmatitic diapirs formed in part from supracrustal and granitic rocks. Two Proterozoic thermal events are recognized within the Slave Province. A ~ 2300 Ma event may be related to early rift breakup of the Archean crust and is recorded in Rb–Sr whole-rock and K–Ar mineral systems. A ~ 1970 Ma event was less intense but may be related to further rifting of the Archean and to fault-block depression of the Indin Lake supracrustal basin, the intrusion of a group of granodioritic stocks, and the formation or granitic pegmatite.Within the Bear Province, evidence of a ~ 2700 Ma intrusive event and a ~ 2300 Ma thermal event are preserved in Rb–Sr whole rock systems. Practically all the granitic rocks of the Bear Province, including the Hepburn batholitic rocks, are thought to have been derived wholly or partly from Archean rocks. The main period of Hudsonian deformation and metamorphism was accompanied by a diapiric remobilization of the Archean basement about 1800 Ma ago. Twelve Rb–Sr isochrons, as well as other published geochronologic data from the region, support these conclusions.

Isotopic data bearing on the origin of Mesozoic and Tertiary granitic rocks in the western United States

1984 ◽  
Vol 310 (1514) ◽  
pp. 743-753 ◽  
Keyword(s):  
Granitic Rocks ◽  
Precambrian Basement ◽  
Regional Survey ◽  
Regional Patterns ◽  
Peraluminous Granite ◽  
Isotopic Compositions ◽  
Geographic Coverage ◽  
Magma Flux ◽  
Archean Basement ◽  
Mantle Magma

A regional survey of initial Nd and Sr isotopic compositions has been done on Mesozoic and Tertiary granitic rocks from a 500 000 km 2 area in California, Nevada, Utah, Arizona, and Colorado. The plutons, which range in composition from quartz diorite to monzogranite, are intruded into accreted oceanic geosynclmal terrains in the west and north and into Precambrian basement in the east. Broad geographic coverage allows the data to be interpreted in the context of the regional pre-Mesozoic crustal structure. Initial Nd isotopic compositions exhibit a huge range, encompassing values typical of oceanic magmatic arcs and Archean basement. The sources of the magmas can be inferred from the systematic geographic variability of Nd isotopic compositions. The plutons in the accreted terrains represent mantle-derived magma that assimilated crust while differentiating at deep levels. Those emplaced into Precambrian basement are mainly derived from the crust. The regional patterns can be understood in terms of: (1) the flux of mantle magma entering the crust; (2) crustal thickness; and (3) crustal age. The mantle magma flux apparently decreased inland; in the main batholith belts purely crustal granitic rocks are not observed because the flux was too large. Inland, crustal granite is common because mantle magma was scarce and the crust was thick, and hot enough to melt. The values of peraluminous granite formed by melting of the Precambrian basement depend on the age of the local basement source.

Rubidium and Strontium age determination of some Pre-Cambrian granitic rocks, S.E. Uganda

1971 ◽  
Vol 108 (5) ◽  
pp. 353-360 ◽  
Author(s):  
R. A. Old ◽  
D. C. Rex
Keyword(s):  
Age Groups ◽  
Age Determination ◽  
Granitic Rocks ◽  
Age Limit ◽  
Age Determinations

SummaryWhole rock rubidium-strontium age determinations on granitic bodies in S.E. Uganda give ages of 2930 m.y. for the Masaba Granite and 2430 m.y. for the Buteba Granite and granitic gneisses. The former age is considered to represent the upper age limit of the post-Nyanzian orogeny, and 2430 m.y. the upper age limit of the post-Kavirondian orogeny. A second isochron age of 2100 m.y. for the Masaba Granite may reflect a second intrusion, or remobilization of part of the original granite associated with the Buganda–Toro orogeny. Tentative correlations are suggested between these age groups and others within the Tanzanian Shield and beyond.

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‰.

Petrology and geochronology of Paleoproterozoic intrusive rocks, Kiggavik uranium camp, Nunavut

2015 ◽  
Vol 52 (7) ◽  
pp. 495-518 ◽  
Author(s):  
J.M.J. Scott ◽  
T.D. Peterson ◽  
W.J. Davis ◽  
C.W. Jefferson ◽  
B.L. Cousens
Keyword(s):  
Granitic Rocks ◽  
Uranium Deposits ◽  
Zircon Age ◽  
Core Samples ◽  
Thelon Basin ◽  
Intrusive Rocks ◽  
Uranium Exploration ◽  
Melt Infiltration ◽  
Granitic Intrusions ◽  
Baker Lake

We investigated the age and petrology of Paleoproterozoic granitic intrusions in the area of the Kiggavik uranium exploration camp, near the southeast margin of the Aberdeen subbasin of the Thelon Basin. A subset of these intrusions (e.g., the Lone Gull stock) is spatially associated with and mineralized by basement hosted, unconformity-related uranium deposits. Surface (outcrop) samples have field relations, textures, and compositions consistent with Hudson Suite granitoids and mixtures of monzogranite with minette. We obtained U–Pb (zircon) ages ranging from ca. 1818 to 1840 Ma, within the known range of the Hudson Suite and cogenetic minettes of the Baker Lake Group (1.80–1.84 Ga). Core samples of granitic rocks adjacent to mineralized zones are more complex and indicate an influence from the younger Nueltin Granite (Kivalliq Igneous Suite, ca. 1.77–1.73 Ga). One sample from the Lone Gull stock contains two zircon populations in texturally distinctive domains, one at 1806 ± 41 Ma and the other at 1748 ± 9.4 Ma. A porphyritic hypabyssal syenite below the Bong deposit yielded a U–Pb zircon age of 1837.8 ± 7.7 Ma and a U–Pb titanite age of 1758.5 ± 44 Ma. We recognize a Kivalliq-age overprint in the form of metasomatism and partial remelting or melt infiltration in the drill core samples, which is not evident at the surface and is consistent with the presence of a Nueltin Granite intrusive complex at depth. The geochemistry and primary igneous textures of the Bong syenite, including its euhedral zircons, resemble those of lava flows near the base of the Baker Lake Group, and we recognize a mixed magma (i.e., Martell Syenite) continuum between intrusive Hudson granitoids and minette with extrusive equivalents in the lower felsic minette member of the Christopher Island Formation.

Striding-Athabasca mylonite zone: implications for the Archean and Early Proterozoic tectonics of the western Canadian Shield

1995 ◽  
Vol 32 (2) ◽  
pp. 178-196 ◽  
Author(s):  
Simon Hanmer ◽  
Michael Williams ◽  
Chris Kopf
Keyword(s):  
Continental Margin ◽  
Canadian Shield ◽  
Magmatic Evolution ◽  
Tectonic Zone ◽  
Early Proterozoic ◽  
Plate Margin ◽  
Mylonite Zone ◽  
Northern Saskatchewan ◽  
Archean Crust ◽  
Rifted Margin

Study of the northern Saskatchewan–District of Mackenzie segment of the Snowbird tectonic zone suggests that fragments of relatively stiff mid-Archean crust, possibly arc related, have controlled the localization, shape, and complex kinematics of the multistage Striding–Athabasca mylonite zone during the Archean, as well as the geometry of the Early Proterozoic rifted margin of the western Churchill continent. By the late Archean, the Striding–Athabasca mylonite zone was located in the interior of the western Churchill continent, well removed from the contemporaneous plate margins. Except for the Alberta segment, the Snowbird tectonic zone was not the site of an Early Proterozoic plate margin. We suggest that the geometry of the Archean–Early Proterozoic boundary in the western Canadian Shield represents a jagged continental margin, composed of a pair of reentrants defined by rifted and transform segments. These segments were inherited from Early Proterozoic breakup and controlled by the Archean structure of the interior of the western Churchill continent. The geometry of this margin appears to have strongly influenced the Early Proterozoic tectono-magmatic evolution of the western Canadian Shield.

Nd evidence for extensive Archean basement in the western Churchill Province, Canada

1986 ◽  
Vol 23 (9) ◽  
pp. 1433-1437 ◽  
Author(s):  
C. D. Frost ◽  
R. A. Burwash
Keyword(s):  
Drill Hole ◽  
Crust Formation ◽  
Southern Alberta ◽  
Northern Saskatchewan ◽  
Archean Crust ◽  
Northeastern Alberta ◽  
Archean Basement

To determine the extent of reworked Archean crust in the western Churchill Province, we have examined Sm–Nd crustal residence ages of basement cores in southern Alberta and southwestern Saskatchewan along with crustal residence ages calculated for other Sm–Nd data available from the Churchill Province. The deep drill hole samples from the Interior Platform give Sm–Nd crustal residence ages that average 2.8 Ga. Granulites from northeastern Alberta and composite gneisses from northern Saskatchewan also provide Archean crustal residence ages. These data demonstrate that the presence of reworked Archean crust in the western Churchill Province is more widespread than has been confirmed previously. We suggest that Sm–Nd crustal residence ages are valuable estimates of crust formation times, especially in orogenic areas where other isotope systems have been disturbed.

Geophysical characteristics of the continental crust along the Lithoprobe Eastern Canadian Shield Onshore–Offshore Transect (ECSOOT): a review

2002 ◽  
Vol 39 (5) ◽  
pp. 569-587 ◽  
Author(s):  
Jeremy Hall ◽  
Keith E Louden ◽  
Thomas Funck ◽  
Sharon Deemer
Keyword(s):  
Normal Incidence ◽  
Shear Zones ◽  
Canadian Shield ◽  
P Wave ◽  
Seismic Profiles ◽  
Grenville Province ◽  
Core Zone ◽  
The Core ◽  
Geodynamic Processes ◽  
Archean Crust

The Eastern Canadian Shield Onshore–Offshore Transect (ECSOOT) of the Lithoprobe program included 1200 km of normal-incidence seismic profiles and seven wide-angle seismic profiles across Archean and Proterozoic rocks of Labrador, northern Quebec, and the surrounding marine areas. Archean crust is 33–44 km thick. P-wave velocity increases downwards from 6.0 to 6.9 km/s. There is moderate crustal reflectivity, but the reflection Moho is unclear. Archean crust that stabilized in the Proterozoic is similar except for greater reflectivity and a well-defined Moho. Proterozoic crust has similar or greater thickness, variable lower crustal velocities, and strong crustal reflectivity. Geodynamic processes of Paleoproterozoic growth of the Canadian Shield are similar to those observed in modern collisional orogens. The suturing of the Archean Core Zone and Superior provinces involved whole-crustal shearing (top to west) in the Core Zone, linked to thin-skinned deformation in the New Quebec Orogen. The Torngat Orogen sutures the Nain Province to the Core Zone and reveals a crustal root, in which Moho descends to 55 km. It formed by transpression and survived because of the lack of postorogenic heating. Accretion of the Makkovik Province to the Nain Province involves delamination at the Moho and distributed strain in the juvenile arcs. Delamination within the lower crust characterizes the accretion of Labradorian crust in the southeastern Grenville Province. Thinning of the crust northwards across the Grenville Front is accentuated by Mesozoic extension that reactivates Proterozoic shear zones. The intrusion of the Mesoproterozoic Nain Plutonic Suite is attributed to a mantle plume ponding at the base of the crust.

scholarly journals Instability of the southern Canadian Shield during the late Proterozoic

2018 ◽  
Author(s):  
Kalin T. McDannell ◽  
Peter K. Zeitler ◽  
David A. Schneider
Keyword(s):  
Elevated Temperatures ◽  
Geothermal Gradient ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Deep Time ◽  
Magmatic Underplating ◽  
Thermal Histories ◽  
Lower Temperature ◽  
The Stability ◽  
Uplift And Erosion

Cratons are generally considered to comprise lithosphere that has remained tectonically quiescent for billions of years. Direct evidence for stability is mainly founded in the Phanerozoic sedimentary record and low-temperature thermochronology, but for extensive parts of Canada, earlier stability has been inferred due to the lack of an extensive rock record in both time and space. We used 40Ar/39Ar multi-diffusion domain (MDD) analysis of K-feldspar to constrain cratonic thermal histories across an intermediate (~150-350°C) temperature range in an attempt to link published high-temperature geochronology that resolves the timing of orogenesis and metamorphism with lower-temperature data suited for upper-crustal burial and unroofing histories. This work is focused on understanding the transition from Archean-Paleoproterozoic crustal growth to later intervals of stability, and how uninterrupted that record is throughout Earth’s Proterozoic “Middle Age.” Intermediate-temperature thermal histories of cratonic rocks at well-constrained localities within the southern Canadian Shield of North America challenge the stability worldview because our data indicate that these rocks were at elevated temperatures in the Proterozoic. Feldspars from granitic rocks collected at the surface cooled at rates of <0.5°C/Ma subsequent to orogenesis, seemingly characteristic of cratonic lithosphere, but modeled thermal histories suggest that at ca. 1.1-1.0 Ga these rocks were still near ~200°C – signaling either reheating, or prolonged residence at mid-crustal depths assuming a normal cratonic geothermal gradient. After 1.0 Ga, the regions we sampled then underwent further cooling such that they were at or near the surface (<< 60°C) in the early Paleozoic. Explaining mid-crustal residence at 1.0 Ga is challenging. A widespread, prolonged reheating history via burial is not supported by stratigraphic information, however assuming a purely monotonic cooling history requires at the very least 5 km of exhumation beginning at ca. 1.0 Ga. A possible explanation may be found in evidence of magmatic underplating that thickened the crust, driving uplift and erosion. The timing of this underplating coincides with Mid-Continent extension, Grenville orogenesis, and assembly of the supercontinent Rodinia. 40Ar/39Ar MDD data demonstrate that this technique can be successfully applied to older rocks and fill in a large observational gap. These data also raise questions about the evolution of cratons during the Proterozoic and the nature of cratonic stability across deep time.

Sign in / Sign up

Export Citation Format

Share Document