scholarly journals Collection of samples from the Kaminak group for zircon age determination (Kaminak Lake area, District of Keewatin, NTS 55K,55L)

1973 ◽  
Author(s):  
R D Stevens ◽  
R K Wanless
Keyword(s):  
Age Determination ◽  
Lake Area ◽  
Zircon Age

Age of volcanic rocks and syndepositional iron formations, Marquette Range Supergroup: implications for the tectonic setting of Paleoproterozoic iron formations of the Lake Superior region

2002 ◽  
Vol 39 (6) ◽  
pp. 999-1012 ◽  
Author(s):  
D A Schneider ◽  
M E Bickford ◽  
W F Cannon ◽  
K J Schulz ◽  
M A Hamilton
Keyword(s):  
Lake Superior ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Age Determination ◽  
Iron Formation ◽  
Continental Rifting ◽  
The South ◽  
Zircon Age ◽  
Iron Formations ◽  
Northern Michigan

A rhyolite in the Hemlock Formation, a mostly bimodal submarine volcanic deposit that is laterally correlative with the Negaunee Iron-formation, yields a sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon age of 1874 ± 9 Ma, but also contains inherited Archean zircons as old as 3.8 Ga. This precise age determination for the classic Paleoproterozoic stratigraphic sequence of northern Michigan, the Marquette Range Supergroup (MRS), necessitates modification of previous depositional and tectonic models. Our new data indicate that the Menominee Group, previously ascribed to continental rifting during early, pre-collision phases of the Penokean orogenic cycle, is coeval with arc-related volcanic rocks now preserved as accreted terranes immediately to the south and is more aptly interpreted as a foredeep deposit. We interpret these to be second-order basins created by oblique subduction of the continental margin rather than basins formed on a rifting margin. Along with a recently reported age for the Gunflint Formation in Ontario of 1878 ± 2 Ma, our data suggest that an extensive foredeep in the western Lake Superior region was the locus of iron-formation deposition during arc accretion from the south. Further, we interpret the lower MRS (Chocolay Group), a glaciogenic and shallow-marine succession that lies atop Archean basement, to be equivalent to the upper part of the Huronian Supergroup of Ontario and to represent the original continental rifting and passive-margin phase of the Penokean cycle. The upper MRS (Baraga Group) represents deeper marine basins, dominated by turbidites and lesser volcanic rocks, resulting from increased subsidence and continued collision. A stitching pluton, which cuts correlatives of the Hemlock Formation in a thrust sheet, yielded a U–Pb zircon age of 1833 ± 6 Ma, consistent with other post-tectonic plutons in Wisconsin and northern Michigan, indicating that Penokean convergence lasted no longer than ~40 million years.

A U–Pb zircon age from the Kuskanax batholith, southeastern British Columbia

1983 ◽  
Vol 20 (11) ◽  
pp. 1751-1756 ◽  
Author(s):  
Randall R. Parrish ◽  
J. O. Wheeler
Keyword(s):  
British Columbia ◽  
Age Determination ◽  
Border Zone ◽  
Zircon Age

U–Pb dates on three fractions of zircon from the foliated border zone of the southeast part of the Kuskanax batholith are slightly discordant and indicate emplacement of the batholith [Formula: see text] ago, assuming no subsequent zircon Pb loss. The analyses are slightly discordant and reflect the presence of inherited zircon Pb ~2060 ± 300 Ma old. This interpretation of the data is consistent with geological relationships and available K–Ar dates. A geologically derived maximum age for the batholith is about 185 Ma. This age determination has important implications for timing of deformation in the Kootenay Arc.

U–Pb zircon ages in supracrustal and plutonic rocks; North Spirit Lake area, Northwestern Ontario

1986 ◽  
Vol 23 (7) ◽  
pp. 967-977 ◽  
Author(s):  
F. Corfu ◽  
J. Wood
Keyword(s):  
Age Determination ◽  
Quartz Diorite ◽  
Lake Area ◽  
The North ◽  
Northwestern Ontario ◽  
Quartz Arenite ◽  
Two Generations ◽  
Minimum Age ◽  
Mafic Inclusion ◽  
Plutonic Rocks

The North Spirit Lake greenstone belt in the Sachigo Subprovince of the Superior Province comprises parts of three sequences of volcanic and sedimentary rocks; the main (youngest) is separated from the older sequences by an unconformity to disconformity. The belt is bounded by large granitoid batholiths and was metamorphosed under greenschist to, locally, hornblende–cordierite facies. U–Pb zircon dating was performed on volcanic, sedimentary, and plutonic rocks in order to establish an absolute chronology for the evolution of the area.A tuff breccia in the lowermost supracrustal sequence is dated at 3023 ± 2 Ma. Zircons from a tuff in the middle sequence show complex U–Pb relationships; although they do not allow a precise age determination, the data suggest that the tuff formed sometime between 2950 and 2800 Ma ago. Zircons from a quartz arenite, also in the middle sequence, yield a simple data pattern and define an age of [Formula: see text], suggesting derivation of the sediment from a uniform source of this age. A zircon analysis from a tonalitic clast in a conglomerate at the base of the upper sequence yields a minimum age of 2975 Ma. The clast may have had the same origin as the zircons in the quartz arenite. Another tonalitic clast from the same conglomerate yields a slightly older age of 3001 ± 3 Ma. No remnant of these tonalites can be recognized in the field, suggesting that they have been largely removed during subsequent erosional processes.Two subvolcanic intrusions from the upper sequence yield zircon ages of 2743 ± 2 and 2731 ± 2 Ma, respectively. A crystal tuff, also in the upper sequence, contains two generations of zircons: newly formed magmatic zircons, which date the extrusion of the tuff at 2735 ± 10 Ma, and older grains with a minimum age of 2862 Ma, which represent inherited zircons. This tuff was thus generated at least in part by anatectic melting of >2862 Ma crust.A quartz diorite from MacDowell Lake in the adjacent Berens River Subprovince yields an age of 2744 ± 2 Ma. A mafic inclusion in the quartz diorite contains amoeboidal, strongly fractured zircons, which point to an intercept age of about 2727 Ma. This age could either reflect a metamorphic event or represent a geologically meaningless mixed age.

Rubidium–strontium age and origin of uraniferous granite, Molson Lake – Red Sucker Lake area, northwestern Superior Province, Manitoba

1987 ◽  
Vol 24 (3) ◽  
pp. 471-478 ◽  
Author(s):  
G. S. Clark ◽  
W. Weber
Keyword(s):  
Granulite Facies ◽  
Lake Area ◽  
Initial Ratio ◽  
Calc Alkaline ◽  
Small Bodies ◽  
Zircon Age ◽  
Granulite Facies Metamorphism ◽  
The World ◽  
Facies Metamorphism ◽  
Data Points

Late Archean, post-kinematic, uraniferous granite and alaskite occur as several discrete large and small bodies in the 250 km long Molson Lake – Red Sucker Lake batholithic belt, in the western Gods Lake subprovince. Sampled over this length, this unit gave a Rb–Sr whole-rock age of 2495 ± 30 Ma with an initial 87Sr/86Sr ratio of 0.7053 ± 0.0023. The excellent fit of the data points suggest a common, isotopically homogeneous source of magma for the analyzed granite bodies. The initial ratio is consistent with an origin from partial melting of older calc-alkaline rocks, and evidence suggests this event accompanied granulite-facies metamorphism. Based on recent U–Pb zircon ages, this event could have occurred as much as 200 Ma prior to closure of the Rb–Sr isotopic system.An older, monzonite–quartz diorite unit gives a less well-defined age of 2690 Ma, consistent with a U–Pb zircon age from the same unit. This pluton is intrusive into older, tonalitic gneisses and is part of a widespread suite of granitoid plutonic rocks in this subprovince. This pluton gives a low, mantle-like initial ratio, indicating juvenile additions to the crust during this period of batholithic development, consistent with findings for calc-alkaline granitoids in Archean shield areas elsewhere in the world.

Intra-Ordovician deformation in southeast Ireland: evidence from the geological setting, geochemical affinities and U—Pb zircon age of the Croghan Kinshelagh granite

1994 ◽  
Vol 131 (5) ◽  
pp. 669-684 ◽  
Author(s):  
V. Gallagher ◽  
P. J. O'Connor ◽  
M. Aftalion
Keyword(s):  
Subduction Zone ◽  
Hanging Wall ◽  
Volcanic Rocks ◽  
Age Determination ◽  
Volcanic Belt ◽  
Zircon Age ◽  
Regional Deformation ◽  
Iapetus Ocean ◽  
Granite Type

AbstractThe Croghan Kinshelagh alkali granite intrudes a cleaved volcano-sedimentary sequenceon the border of counties Wicklow and Wexford in southeast Ireland. U-Pb dating of zircons fromthe granite indicate a mid-Caradoc emplacement age of 454 ± 1 Ma. The Duncannon Group hostrocks form the southwestern end of the Avoca Volcanic Belt, a Mid-Ordovician (Caradoc) sequenceof acid and intermediate lavas and volcaniclastics. Dolerite dykes intrude the granite; elsewhere in theregion dolerites are generally associated with volcanic rocks. The main, Dl deformation within theDuncannon Group rocks is manifest as a steep Dl cleavage generally regarded as a product of LateCaledonian regional deformation in southeast Ireland. The Croghan Kinshelagh granite showsstrong geochemical coherence with subalkaline varieties of the Caradoc volcanic rocks; relativelyhigh Th, Y, Nb and REE contents set it apart from any other known granite type in southeastIreland. Together with the geochemical evidence, the age determination of 454 Ma indicates that theCroghan Kinshelagh granite was generated and emplaced during Ordovician volcanism in southeastIreland. Volcanism was closely followed by penetrative deformation and emplacement of the granite.The intra-Ordovician deformation may have been a consequence of closure of the Iapetus Ocean ormore localized events such as accretion on the hanging wall of the subduction zone. The age of theCroghan Kinshelagh granite provides an important datum for Ordovician volcanism and subductionin southeast Ireland.

The paleomagnetic significance of new U-Pb age data from the Molson dyke swarm, Cauchon Lake area, Manitoba

2000 ◽  
Vol 37 (6) ◽  
pp. 957-966 ◽  
Author(s):  
Henry C Halls ◽  
Larry M Heaman
Keyword(s):  
Opposite Polarity ◽  
Sensu Stricto ◽  
Dyke Swarm ◽  
Lake Area ◽  
Continental Rifting ◽  
Zircon Age ◽  
Western Margin ◽  
Back Arc ◽  
Superior Craton ◽  
Age Determinations

U-Pb geochronology, paleomagnetism, and petrography indicate that the Molson dyke swarm, along the western margin of the Superior craton, is a composite of at least two ages of intrusion. The more extensive younger dyke set, the Molson swarm sensu stricto, generally has a 030° trend, is mainly pyroxenitic to noritic with subordinate diabase, and has been related to rifting in a back-arc environment during closure of the Manikewan ocean at about 1920-1800 Ma which culminated in the Trans-Hudson Orogen. A U-Pb zircon age from one of these dykes, located at Cauchon Lake, indicates emplacement at 1877+7&#150 4, similar to two previous U-Pb age determinations on Molson dykes. Another dyke from Cauchon Lake yields a baddeleyite-zircon U-Pb date of 2091 ± 2 Ma and appears to be part of an older, mainly diabasic suite of east-northeast-trending dykes that may represent a continental rifting episode that preceded the opening of the Manikewan ocean. The new U-Pb age data require a revision to the interpretation of the A, B, and C paleomagnetic poles previously reported from Molson dykes. The A pole (16.1°N, 96.5°W), initially assigned an age of 1883 Ma, is now considered to be younger and derived from a Paleoproterozoic overprint associated with the Trans-Hudson Orogen at about 1700-1800 Ma. Pole B (27.1°N, 140.8°W) from the Molson swarm sensu stricto is now regarded as primary, and dated at 1880 Ma. Pole C can be subdivided into two poles, one virtually the same as B but of opposite polarity (and therefore about 1880 Ma old) and a new pole (53°N, 180°W) derived from a primary remanence and dated at 2091 Ma. The new paleomagnetic interpretations may have important consequences for tectonic models of the Trans-Hudson Orogen and for Paleoproterozoic continental reconstructions.

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