U–Pb ages constraining structural development of an Archean terrane boundary in the Lake of the Woods area, western Superior Province, Canada

2006 ◽  
Vol 43 (7) ◽  
pp. 967-993 ◽  
Author(s):  
M Melnyk ◽  
D W Davis ◽  
A R Cruden ◽  
R A Stern
Keyword(s):  
Greenstone Belt ◽  
Thermal Ionization Mass Spectrometry ◽  
Magmatic Zircon ◽  
Ionization Mass ◽  
Structural Development ◽  
Ion Microprobe ◽  
Widespread Occurrence ◽  
Lake Of The Woods ◽  
Second Stage ◽  
Winnipeg River

Layered gneisses in the Winnipeg River subprovince contain magmatic zircon with U–Pb ages of 3317 ± 9 and 3055 ± 4 Ma at Tannis Lake, and ~3170 and 3255 ± 5 Ma at Cedar Lake, indicating widespread occurrence of Mesoarchean crust. This is in contrast to the well-documented Neoarchean age of the western Wabigoon subprovince. Further geochronology using both SHRIMP (sensitive high resolution ion microprobe) and ID-TIMS (isotope dilution thermal ionization mass spectrometry), combined with structural observations, in the Kenora area and Lake of the Woods greenstone belt show the effects of juxtaposition of these two terranes. Isoclinally folded gneiss north of the subprovince boundary zone near Kenora gives a magmatic age of 2882 ± 2 Ma with 3051 ± 6 Ma inheritance. Ages of syntectonic dykes show that asymmetric refolding of these gneisses occurred between 2717 ± 2 and about 2713 ± 1 Ma. Subsequent regional vertical flattening and horizontal extension are dated at 2708 ± 2 Ma by syntectonic tonalite sheets. These events are broadly coeval with deposition of orogenic sediments in the Warclub Group and a first stage of regional folding (age brackets of 2716–2709 Ma) in the Lake of the Woods greenstone belt to the south. A second stage of folding and regional faulting in the greenstone belt occurred about 2695 ± 4 Ma and is approximately coeval with open upright folding in the Winnipeg River subprovince. These observations are consistent with overthrusting and collapse of a Mesoarchean continental terrane by a juvenile Neoarchean arc terrane over the time span 2717–2695 Ma.

Nd and Pb isotopes from the Lake of the Woods greenstone belt, northwestern Ontario: implications for mantle evolution and the formation of crust in the southern Superior Province

2000 ◽  
Vol 37 (12) ◽  
pp. 1677-1689 ◽  
Author(s):  
John A Ayer ◽  
Jaroslav Dostal
Keyword(s):  
Greenstone Belt ◽  
Crustal Contamination ◽  
Pb Isotopes ◽  
Superior Province ◽  
Elevated Concentration ◽  
Lake Of The Woods ◽  
Metavolcanic Rocks ◽  
Depleted Mantle ◽  
Winnipeg River ◽  
Mantle Reservoir

Nd and Pb isotopes from the Lake of the Woods greenstone belt indicate the presence of three distinct reservoir sources: old enriched crust (>3.0 Ga); pre-2.7 Ga, homogeneous depleted mantle; and post-2.70 Ga heterogeneous mantle. EpsilonNd values of +1.1 to +2.3 for ultramafic to felsic metavolcanic rocks (2.74–2.72 Ga) indicate derivation from depleted mantle. The εNd value of –0.9 for younger turbidite (2.71 Ga), in conjunction with detrital zircon ages ranging from 2.72 to 3.0 Ga, indicates detritus from local greenstone belt sources (depleted mantle) mixed with an older crustal source. Post-2.70 Ga heterogeneity is demonstrated by εNd values ranging from –0.4 to +0.4 in shoshonitic to calc-alkaline metavolcanic rocks and +2.1 in a coeval ultrapotassic pluton. Pb isotopes from the pluton indicate derivation from a depleted mantle reservoir with an initial 207Pb/204Pb of 14.52, an initial 206Pb/204Pb of 13.29, and µ1 of 7.86. Isotopic comparison with post-2.70 Ga potassic suites from across the Superior Province indicates widespread mixing between depleted mantle and enriched end members. The enriched end member has isotopic characteristics of rocks derived from old crustal terrains, such as the Winnipeg River and Opatica subprovinces. This type of isotopic heterogeneity could be the result of crustal contamination or derivation from metasomatized mantle. Contamination of the mantle wedge by influx of fluids derived from partial melting of isotopically evolved, subducted sediments is favoured for the Superior Province potassic suite, because elevated concentration of Sr, Nd, and Pb in conjunction with primitive Mg#s suggest only limited crustal contamination has occurred.

scholarly journals The geology, petrology, and geochronology of the Archean Côté Gold large-tonnage, low-grade intrusion-related Au(–Cu) deposit, Swayze greenstone belt, Ontario, Canada

2017 ◽  
Vol 54 (2) ◽  
pp. 173-202 ◽  
Author(s):  
Laura R. Katz ◽  
Daniel J. Kontak ◽  
Benoît Dubé ◽  
Vicki McNicoll
Keyword(s):  
Greenstone Belt ◽  
Thermal Ionization Mass Spectrometry ◽  
Ionization Mass ◽  
Low Grade ◽  
Metavolcanic Rocks ◽  
Volcanogenic Massive Sulphide ◽  
Abitibi Subprovince ◽  
Back Arc ◽  
Miarolitic Cavities ◽  
Subvolcanic Intrusion

The Archean Côté Gold Au(–Cu) deposit is the first large gold deposit discovered in the Swayze greenstone belt of the Abitibi Subprovince. The deposit is a low-grade, large-tonnage type with a combined indicated and inferred resource of 8.65 M oz Au (245.2 t Au). The deposit is hosted by the Chester intrusive complex (CIC), a multiphase, subvolcanic intrusion composed of low-Al tonalite, diorite, and quartz diorite, plus magmatic and hydrothermal breccia bodies. The age of the tonalite and dioritic phases is constrained at 2741–2739 ± 1 Ma using high-precision isotope dilution – thermal ionization mass spectrometry (ID–TIMS) U–Pb zircon geochronology. Although these phases are co-temporal and co-spatial, they appear to be petrogenetically unrelated. The CIC was emplaced into mafic metavolcanic rocks of the Arbutus Formation whose geochemistry reflects a back-arc environment. The tonalite of the CIC is coeval and co-genetic with the felsic to intermediate metavolcanic rocks of the Yeo Formation. Emplacement of the CIC into a shallow crustal level is inferred based on the incorporation of screens and inclusions of the Yeo Formation and is supported by the presence of textures in tonalite and dioritic rocks (e.g., granophyres, miarolitic cavities, and pegmatites), as well as Al-in-hornblende geobarometry results of ≤1.3 ± 0.6 kbars (1 kbar = 100 MPa). The CIC is petrologically similar to other subvolcanic, low-Al tonalite–trondhjemite–diorite intrusions that underlie volcanogenic massive sulphide (VMS)-type deposits and which themselves may contain syn-intrusion mineralization. Several geochemically unrelated dykes and deformation events crosscut and postdate the CIC.

Tectonic implications of new SHRIMP and TIMS U–Pb geochronology of rocks from the Sask Craton, Peter Lake Domain, and Hearne margin, Trans-Hudson Orogen, Saskatchewan

2005 ◽  
Vol 42 (4) ◽  
pp. 635-657 ◽  
Author(s):  
N M Rayner ◽  
R A Stern ◽  
M E Bickford
Keyword(s):  
Thermal Ionization Mass Spectrometry ◽  
Ionization Mass ◽  
Ion Microprobe ◽  
Geochronological Data ◽  
Zircon Growth ◽  
Precursor Material ◽  
Three Samples ◽  
Limited Support ◽  
Age Range ◽  
Superior Craton

This study reports new sensitive high-resolution ion microprobe (SHRIMP) and thermal ionization mass spectrometry (TIMS) U–Pb geochronological data for thirteen rocks from the Archean to Paleoproterozic Sask Craton, the Peter Lake Domain and Hearne margin, Saskatchewan. Seven samples from the exposed Sask Craton in both the Glennie Domain and Pelican Window record zircon growth between 2425 and 2525 Ma and at ~1800 Ma. Older precursor material has been identified, most notably a refined crystallization age of 3117 Ma for a sample of quartzofeldspatic gneiss ("Q-gneiss") in the Pelican Window, which also experienced ca. 2450 Ma zircon growth. Three samples from the Peter Lake Domain and a sample from the Linn Island inlier of the Wollaston Domain yield ages of ~2575 Ma. One sample from the Peter Lake Domain is distinctly older, yielding an age of 2640 Ma, but also displays zircon growth at 2575 Ma. The simplest interpretation of these data is that the Peter Lake Domain is likely a part of the Hearne margin, although the significance and distribution of 2575 Ma ages within the larger Hearne craton is unclear. Conversely, the age range of most samples from the Sask Craton is distinctly younger than those of the Peter Lake and Hearne margin rocks. We suggest that 2.45 Ga was a major episode of magmatic reworking of older material within the Sask Craton, which includes, but is not restricted to, 3.1 Ga precursors. These ages do not coincide with typical ages reported from the Superior craton and thus the data, although limited, support an exotic origin for the Sask Craton.

Mineralogical, geochronological, and geochemical characterization of Early Devonian aquamarine-bearing dykes of the Zealand Station beryl and molybdenite deposit, west central New Brunswick

2010 ◽  
Vol 47 (6) ◽  
pp. 859-874 ◽  
Author(s):  
Kristy-Lee Beal ◽  
David R. Lentz ◽  
Douglas C. Hall ◽  
Gregory Dunning
Keyword(s):  
New Brunswick ◽  
Thermal Ionization Mass Spectrometry ◽  
Magmatic Zircon ◽  
Ionization Mass ◽  
Nd Isotope ◽  
Early Devonian ◽  
Geochemical Characterization ◽  
Source Characteristics ◽  
High Level

The Zealand Station beryl (aquamarine) and molybdenite deposit is located 25 km northwest of Fredericton, New Brunswick, along the northeastern cusp of the Hawkshaw Granite, previously dated at 411 ± 1 Ma (U–Pb titanite), of the multiphase Devonian Pokiok Batholith. A late-stage, southeast-trending, pegmatite–aplite dyke has abundant aquamarine associated with pegmatitic sections. An exposure of a pegmatitic dyke is predominantly quartz and K-feldspar that exhibits a border, intermediate, and core zone. The main pegmatite–aplite dyke has been dated at 400.5 ± 1.2 Ma using U–Pb thermal ionization mass spectrometry on magmatic zircon. This is consistent with the 404 ± 8 Ma age using the chemical U–Th – total Pb isochron method from the pegmatitic beryl-rich section. These ages link these pegmatitic to aplitic dykes to the Allandale Granite, which is the youngest (402 ± 1 Ma by U–Pb on monazite) and most evolved phase of the Pokiok Batholith. The granitic aplite and pegmatite dyke samples are predominantly magnesian with one pegmatite sample being ferroan (FeOt/(FeOt +MgO) = 0.64–0.94); the samples are slightly potassic and calc-alkaline with strong peraluminosity (A/CNK = 1.23–4.76). The various phases of dykes were derived from magma with crustal A-type source characteristics similar to the Allandale Granite. The Sm–Nd isotope values for the aplite dyke (εNd(400) = –2.15) and the Allandale Granite (εNd(400) = –1.6) reflect some assimilation of metasediments relative to other phases of the Pokiok Batholith. The pegmatite and aplite dykes are high-level, rare-earth element pegmatite phases (Nb–Y–F-type) with some Li–Cs–Ta-type characteristics.

U–Pb geochronology of Cretaceous magmatism on Svalbard and Franz Josef Land, Barents Sea Large Igneous Province

2013 ◽  
Vol 150 (6) ◽  
pp. 1127-1135 ◽  
Author(s):  
FERNANDO CORFU ◽  
STÉPHANE POLTEAU ◽  
SVERRE PLANKE ◽  
JAN INGE FALEIDE ◽  
HENRIK SVENSEN ◽  
...  
Keyword(s):  
Thermal Ionization Mass Spectrometry ◽  
Barents Sea ◽  
Large Igneous Province ◽  
The Arctic ◽  
Ionization Mass ◽  
Franz Josef Land ◽  
Igneous Province ◽  
Stratigraphic Record ◽  
Single Grain ◽  
Cretaceous Magmatism

AbstractThe opening of the Arctic oceanic basins in the Mesozoic and Cenozoic proceeded in steps, with episodes of magmatism and sedimentation marking specific stages in this development. In addition to the stratigraphic record provided by sediments and fossils, the intrusive and extrusive rocks yield important information on this evolution. This study has determined the ages of mafic sills and a felsic tuff in Svalbard and Franz Josef Land using the isotope dilution thermal ionization mass spectrometry (ID-TIMS) U–Pb method on zircon, baddeleyite, titanite and rutile. The results indicate crystallization of the Diabasodden sill at 124.5 ± 0.2 Ma and the Linnévatn sill at 124.7 ± 0.3 Ma, the latter also containing slightly younger secondary titanite with an age of 123.9 ± 0.3 Ma. A bentonite in the Helvetiafjellet Formation, also on Svalbard, has an age of 123.3 ± 0.2 Ma. Zircon in mafic sills intersected by drill cores in Franz Josef Land indicate an age of 122.7 Ma for a thick sill on Severnaya Island and a single grain age of ≥122.2 ± 1.1 Ma for a thinner sill on Nagurskaya Island. These data emphasize the importance and relatively short-lived nature of the Cretaceous magmatic event in the region.

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