Early and Middle Proterozoic evolution of Yukon, Canada

2005 ◽  
Vol 42 (6) ◽  
pp. 1045-1071 ◽  
Author(s):  
Derek J Thorkelson ◽  
J Grant Abbott ◽  
James K Mortensen ◽  
Robert A Creaser ◽  
Michael E Villeneuve ◽  
...  
Keyword(s):  
Hydrothermal Activity ◽  
Igneous Rocks ◽  
Isotopic Data ◽  
Zircon Age ◽  
Depleted Mantle ◽  
Windermere Supergroup ◽  
Bear River ◽  
Mackenzie Mountains ◽  
Hydrothermal Event ◽  
Middle Proterozoic

This paper provides a comprehensive synthesis of virtually all units and events of Early and Middle Proterozoic age in the Yukon, spanning ~1 Ga. Early and Middle Proterozoic time was dominated by a series of extensional-basin-forming events punctuated by orogenesis, magmatism, and hydrothermal activity. Basinal deposits include the Wernecke Supergroup (>1.71 Ga), Pinguicula Group (~1.38 Ga), and Mackenzie Mountains Supergroup (1.00–0.78 Ga). Igneous rocks include the Bonnet Plume River Intrusions (1.71 Ga), Slab volcanics (≥1.6 Ga), Hart River sills and volcanics (1.38 Ga), and Bear River (Mackenzie) dykes (1.27 Ga). A voluminous hydrothermal event generated the widespread Wernecke breccias at 1.60 Ga. The Racklan orogeny deformed the Wernecke Supergroup prior to emplacement of the Wernecke Breccia. The Corn Creek orogeny deformed Mackenzie Mountains Supergroup and older rocks prior to deposition of the Windermere Supergroup (<0.78 Ga). Long intervals with scanty rock records extended for as much as 300 Ma and appear to represent periods of crustal stability and subaerial conditions. By the time of Windermere rifting (<0.78 Ga), the supracrust of northwestern Laurentia was a mature, largely denuded orogenic belt with a composite sedimentary–metamorphic–igneous character. New isotopic data include Nd depleted mantle model ages for the Wernecke Supergroup (2.28–2.69 Ga) and Wernecke Breccia (2.36–2.96 Ga), a U–Pb zircon age for a Hart River sill 1381.9+5.3-3.7 (Ma), detrital U–Pb zircon ages from the basal Pinguicula Group (1841–3078 Ma), detrital muscovite ages from the Mackenzie Mountains Supergroup (1037–2473 Ma), and muscovite 40Ar/39Ar cooling ages from the Wernecke Supergroup (788 ± 8 and 980 ± 4 Ma).

Nd isotopic compositions of felsic igneous rocks in Cape Breton Island, Nova Scotia

1992 ◽  
Vol 29 (4) ◽  
pp. 650-657 ◽  
Author(s):  
Sandra M. Barr ◽  
Ernst Hegner
Keyword(s):  
New Brunswick ◽  
Small Variation ◽  
Igneous Rocks ◽  
Northwestern Part ◽  
Isotopic Data ◽  
Cape Breton Island ◽  
Late Precambrian ◽  
Cape Breton ◽  
Depleted Mantle ◽  
Juvenile Crust

Nd isotopic data from 18 felsic plutonic and volcanic units in Cape Breton Island show variations consistent with other geological and geophysical evidence for at least three distinct terranes. A ca. 1.2 Ga syenite considered to be part of Grenvilleage basement exposed in the northwestern part of the island yields an initial εNd value of +0.4 and a depleted-mantle model age (TDM) of 1.66 Ga, suggesting substantial involvement of older (Archean or Early Proterozoic) crust in its petrogenesis. A TDM of 1.38 Ga indicated by Nd isotopic data for a Devonian granite spatially associated with the syenite is also consistent with the presence of older crust in that part of Cape Breton Island. In contrast, Silurian rhyolite and Devonian granites from the Aspy terrane have TDM ranging from 0.7 to 1.1 Ga and initial εNd between +2.8 and −1.2, and overlap in isotopic characteristics with late Precambrian and Early Ordovician plutons in the Bras d'Or terrane that yield TDM of 0.9–1.1 Ga and initial εNd of +1.4 to −1.8. The relatively small variation in εNd and TDM in these terranes suggests that old crust like that under the Blair River Complex may not be present. Granitic plutons and rhyolite in the Mira terrane of southeastern Cape Breton Island have a range in TDM (0.8–1.2 Ga) similar to that of the Aspy and Bras d'Or terranes, but initial εNd values ranging from +0.8 to +5.0 indicate more juvenile crust. This juvenile crust also appears to be present under southern New Brunswick and eastern Newfoundland and may be characteristic of the Avalon terrane.

Episodic tectono-thermal activity in the southern part of the East Greenland Caledonides

2000 ◽  
pp. 42-49 ◽  
Author(s):  
A. Graham Leslie ◽  
Allen P. Nutman
Keyword(s):  
Thermal Activity ◽  
Isotopic Data ◽  
Zircon Age ◽  
East Greenland ◽  
Original Series ◽  
Age Determinations

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Leslie, A. G., & Nutman, A. P. (2000). Episodic tectono-thermal activity in the southern part of the East Greenland Caledonides. Geology of Greenland Survey Bulletin, 186, 42-49. https://doi.org/10.34194/ggub.v186.5214 _______________ Isotopic data from the Renland augen granites of the Scoresby Sund region (Figs 1, 2) provided some of the first convincing support for relicts of potentially Grenvillian tectono-thermal activity within the East Greenland Caledonides. In Renland, Chadwick (1975) showed the presence of major bodies of augen granite (Fig. 2) interpreted by Steiger et al. (1979), on the basis of Rb–Sr whole rock and U–Pb zircon age determinations, to have been emplaced about 1000 Ma ago.

Long-term Aptian marine osmium isotopic record of Ontong Java Nui activity

Geology ◽  
2021 ◽  
Author(s):  
Hironao Matsumoto ◽  
Rodolfo Coccioni ◽  
Fabrizio Frontalini ◽  
Kotaro Shirai ◽  
Luigi Jovane ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Volcanic Eruptions ◽  
Hydrothermal Activity ◽  
Published Data ◽  
Isotopic Data ◽  
Oceanic Plateaus ◽  
Carbon Burial ◽  
Organic Carbon Burial ◽  
Isotopic Records

The early to mid-Aptian was punctuated by episodic phases of organic-carbon burial in various oceanographic settings, which are possibly related to massive volcanism associated with the emplacement of the Ontong Java, Manihiki, and Hikurangi oceanic plateaus in the southwestern Pacific Ocean, inferred to have formed a single plateau called Ontong Java Nui. Sedimentary osmium (Os) isotopic compositions are one of the best proxies for determining the timing of voluminous submarine volcanic episodes. However, available Os isotopic records during the age are limited to a narrow interval in the earliest Aptian, which is insufficient for the reconstruction of long-term hydrothermal activity. We document the early to mid-Aptian Os isotopic record using pelagic Tethyan sediments deposited in the Poggio le Guaine (Umbria-Marche Basin, Italy) to precisely constrain the timing of massive volcanic episodes and to assess their impact on the marine environment. Our new Os isotopic data reveal three shifts to unradiogenic values, two of which correspond to black shale horizons in the lower to mid-Aptian, namely the Wezel (herein named) and Fallot Levels. These Os isotopic excursions are ascribed to massive inputs of unradiogenic Os to the ocean through hydrothermal activity. Combining the new Os isotopic record with published data from the lowermost Aptian organic-rich interval in the Gorgo a Cerbara section of the Umbria-Marche Basin, it can be inferred that Ontong Java Nui volcanic eruptions persisted for ~5 m.y. during the early to mid-Aptian.

scholarly journals Nd-Hf isotope geochemistry and lithogeochemistry of the Rambler Rhyolite, Ming VMS deposit, Baie Verte Peninsula, Newfoundland: evidence for slab melting and implications for VMS localization

2021 ◽  
Author(s):  
S J Piercey ◽  
J -L Pilote
Keyword(s):  
Rare Earth ◽  
Trace Element ◽  
Isotope Geochemistry ◽  
Primitive Mantle ◽  
Isotopic Data ◽  
Depleted Mantle ◽  
Element Enrichment ◽  
Felsic Volcanic ◽  
Magmatic History ◽  
Felsic Rocks

New high precision lithogeochemistry and Nd and Hf isotopic data were collected on felsic rocks of the Rambler Rhyolite formation from the Ming volcanogenic massive sulphide (VMS) deposit, Baie Verte Peninsula, Newfoundland. The Rambler Rhyolite formation consists of intermediate to felsic volcanic and volcaniclastic rocks with U-shaped primitive mantle normalized trace element patterns with negative Nb anomalies, light rare earth element-enrichment (high La/Sm), and distinctively positive Zr and Hf anomalies relative to surrounding middle rare earth elements (high Zr-Hf/Sm). The Rambler Rhyolite samples have epsilon-Ndt = -2.5 to -1.1 and epsilon-Hft = +3.6 to +6.6; depleted mantle model ages are TDM(Nd) = 1.3-1.5 Ga and TDM(Hf) = 0.9-1.1Ga. The decoupling of the Nd and Hf isotopic data is reflected in epsilon-Hft isotopic data that lies above the mantle array in epsilon-Ndt -epsilon-Hft space with positive ?epsilon-Hft values (+2.3 to +6.2). These Hf-Nd isotopic attributes, and high Zr-Hf/Sm and U-shaped trace element patterns, are consistent with these rocks having formed as slab melts, consistent with previous studies. The association of these slab melt rocks with Au-bearing VMS mineralization, and their FI-FII trace element signatures that are similar to rhyolites in Au-rich VMS deposits in other belts (e.g., Abitibi), suggests that assuming that FI-FII felsic rocks are less prospective is invalid and highlights the importance of having an integrated, full understanding of the tectono-magmatic history of a given belt before assigning whether or not it is prospective for VMS mineralization.

scholarly journals 207Pb-206Pb dating of magnetite, monazite and allanite in the central and northern Nagssugtoqidian orogen, West Greenland

2006 ◽  
Vol 11 ◽  
pp. 101-114 ◽  
Author(s):  
Henrik Stendal ◽  
Karsten Secher ◽  
Robert Frei
Keyword(s):  
Hydrothermal Activity ◽  
Alkaline Magmatism ◽  
Calc Alkaline ◽  
Isotopic Data ◽  
Sulphide Deposit ◽  
Late Archaean ◽  
West Greenland ◽  
Isotopic Signatures ◽  
Source Characteristics ◽  
Isotopic Measurements

Pb-isotopic data for magnetite from amphibolites in the Nagssugtoqidian orogen, central West Greenland, have been used to trace their source characteristics and the timing of metamorphism. Analyses of the magnetite define a Pb-Pb isochron age of 1726 ± 7 Ma. The magnetite is metamorphic in origin, and the 1726 Ma age is interpreted as a cooling age through the closing temperature of magnetite at ~600°C. Some of the amphibolites in this study come from the Naternaq supracrustal rocks in the northern Nagssugtoqidian orogen, which host the Naternaq sulphide deposit and may be part of the Nordre Strømfjord supracrustal suite, which was deposited at around 1950 Ma ago. Pb-isotopic signatures of magnetite from the Arfersiorfik quartz diorite in the central Nagssugtoqidian orogen are compatible with published whole-rock Pb-isotopic data from this suite; previous work has shown that it is a product of subduction-related calc-alkaline magmatism between 1920 and 1870 Ma. Intrusion of pegmatites occurred at around 1800 Ma in both the central and the northern parts of the orogen. Pegmatite ages have been determined by Pb stepwise leaching analyses of allanite and monazite, and source characteristics of Pb point to an origin of the pegmatites by melting of the surrounding late Archaean and Palaeoproterozoic country rocks. Hydrothermal activity took place after pegmatite emplacement and continued below the closure temperature of magnetite at 1800– 1650 Ma. Because of the relatively inert and refractory nature of magnetite, Pb-isotopic measurements from this mineral may be of help to understand the metamorphic evolution of geologically complex terrains.

Paleomagnetic evidence for late Cenozoic glaciations in the Mackenzie Mountains of the Northwest Territories, Canada

1996 ◽  
Vol 33 (6) ◽  
pp. 896-903 ◽  
Author(s):  
R. W. Barendregt ◽  
R. J. Enkin ◽  
J. Baker ◽  
A. Duk-Rodkin
Keyword(s):  
Large Scale ◽  
Magnetic Measurements ◽  
Laurentide Ice Sheet ◽  
Paleoenvironmental Reconstruction ◽  
Pleistocene Glaciations ◽  
Late Cenozoic ◽  
Last Glaciation ◽  
Stratigraphic Record ◽  
Bear River ◽  
Mackenzie Mountains

The Mackenzie Mountains were affected by montane valley glaciers during the Pleistocene and peripherally by the Laurentide Ice Sheet during the last glaciation. In this paper we report on magnetostratigraphic dating and correlation of three sections recording Late Pliocene to Late Pleistocene glaciations: Katherine Creek, Little Bear River, and Inlin Brook (located around 65°N, 127°W). Each section consists of a colluvial unit overlying a Pliocene pediment surface cut into Proterozoic or Paleozoic bedrock, or Tertiary gravel, which is in turn overlain by a stack of five, and in places six, montane tills, usually with soils developed at their surfaces, and capped by a Laurentide till. Normal and reversed magnetizations were recognized with single-domain magnetite as a dominant remanence carrier. The Katherine Creek section has a normally magnetized colluvium at its base, which is overlain by two reversed tills, succeeded by three normal tills. We interpret the top two tills to be of Brunhes age (< 780 ka) but argue that the lowermost normal till is of probable Olduvai age (ca. 1.8 Ma). The two underlying tills are of Matuyama age (2.6 Ma to 780 ka), and the colluvial base is assigned to the Gauss (3.5–2.6 Ma). The Little Bear River section exposes a stratigraphic record similar to that found at Katherine Creek. Only four units could be assigned a paleomagnetic polarity, the others yielding incoherent results. Paleosols on the first and second till units were reversed and normal, respectively, and the top till was normal. Thus there is clear evidence of an older (reversed) Pleistocene glaciation and a magnetostratigraphic record compatible with that found at Katherine Creek. Magnetic measurements from Inlin Brook gave largely incoherent results, with the exception of the surface (Laurentide) till, which is normal. The glacial history recorded in the Mackenzie Mountains correlates well with other studies carried out in the Cordillera. The large-scale changes in climate revealed in these terrestrial records provide baseline data for paleoenvironmental reconstruction.

scholarly journals Sr–Nd–Pb–Hf Isotopic Constraints on the Mantle Heterogeneities beneath the South Mid-Atlantic Ridge at 18–21°S

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1010
Author(s):  
Yun Zhong ◽  
Xu Zhang ◽  
Zhilei Sun ◽  
Jinnan Liu ◽  
Wei Li ◽  
...  
Keyword(s):  
Isotopic Data ◽  
The South ◽  
Mantle Heterogeneities ◽  
Depleted Mantle ◽  
Mid Ocean Ridge ◽  
Trace Elemental ◽  
Heterogeneous Mantle ◽  
Mid Atlantic Ridge ◽  
St Helena ◽  
Ocean Ridge

In an attempt to investigate the nature and origin of mantle heterogeneities beneath the South Mid-Atlantic Ridge (SMAR), we report new whole-rock Sr, Nd, Pb, and Hf isotopic data from eight basalt samples at four dredge stations along the SMAR between 18°S and 21°S. Sr, Nd, and Pb isotopic data from SMAR mid-ocean ridge basalts (MORBs) at 18–21°S published by other researchers were also utilized in this study. The SMAR MORBs at 18–21°S feature the following ratio ranges: 87Sr/86Sr = 0.70212 to 0.70410, 143Nd/144Nd = 0.512893 to 0.513177, 206Pb/204Pb = 18.05 to 19.50, 207Pb/204Pb = 15.47 to 15.71, 208Pb/204Pb = 37.87 to 38.64, and 176Hf/177Hf = 0.283001 to 0.283175. The 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, and 176Hf/177Hf ratios of these MORBs varied considerably along the SMAR axis. The variable compositions of the Sr–Nd–Pb–Hf isotopes, combined with the corresponding whole-rock major and trace elemental abundances reported in previous studies, suggest that the SMAR MORBs at 18–21°S were probably derived from a heterogeneous mantle substrate related to a mixture of depleted mantle (DM) materials with a small amount (but variable input) of HIMU (high-μ, where μ = 238U/204Pb)- and enriched (EMII)-type materials. The HIMU-type materials likely originated from the proximal St. Helena plume and may have been transported through “pipe-like inclined sublithospheric channels” into the SMAR axial zone. The EMII-type materials possibly originated from a recycled metasomatized oceanic crust that may have been derived from the early dispersion of other plume heads into the subcontinental asthenosphere prior to the opening of the South Atlantic Ocean. In addition, the contributions of subducted sediments, continental crust, and subcontinental lithospheric mantle components to the formation of the SMAR MORBs at 18–21°S may be nonexistent or negligible.

Serpentinization at the Rainbow and Saldanha sites, Mid-Atlantic Ridge: Mineralogical, geochemical, and isotopic features

2019 ◽  
Vol 57 (5) ◽  
pp. 677-706
Author(s):  
Isabel Ribeiro da Costa ◽  
Frederick Joseph Wicks ◽  
Fernando J.A.S. Barriga
Keyword(s):  
Upper Mantle ◽  
Hydrothermal Activity ◽  
Isotopic Data ◽  
Geochemical Characterization ◽  
Textural Evolution ◽  
Mantle Peridotites ◽  
Carbonate Deposition ◽  
Mid Atlantic Ridge ◽  
Ree Patterns

Abstract The Rainbow hydrothermal field (36°14′N) and the Saldanha seamount (36°34′N), in the Mid-Atlantic Ridge (MAR), are tectonic exposures of serpentinized upper mantle peridotites, both associated with significant hydrothermal activity. On the basis of detailed mineralogical and geochemical characterization of serpentinites from both sites, several serpentinization-related issues are discussed in the present work. As expected in oceanic environments, most of the sampled rocks are lizardite-chrysotile serpentinites exhibiting a variety of pseudomorphic through non-pseudomorphic textures, such textural evolution probably being related to changing water/rock ratios during this retrograde process. Oxygen isotope temperatures indicate that the serpentinization took place at 300–200 °C; on the other hand, isotopic data suggest that replacement of early pseudomorphic lizardite by lizardite ± chrysotile non-pseudomorphic textures requires that temperatures and/or water/rock ratios are high enough to promote the necessary dissolution–recrystallization processes. Mass-balance calculations for olivine-serpentine and orthopyroxene-serpentine pairs provided a basis for establishing serpentinization reactions likely to have produced the present rocks. Moreover, these calculations also showed that, notwithstanding some noticeable loss of MgO from olivine and of SiO2 from orthopyroxene, serpentinization of both minerals implies volume increases on the order of 26–27%, therefore potentially promoting the overall expansion of the rock. The geochemical and isotopic features of the studied rocks indicate that unmodified seawater was responsible for the serpentinization of the MAR peridotites. However, the mineralogy and REE patterns of some of these serpentinites indicate occasional subsequent interaction of the serpentinized rocks with seawater at much lower temperatures (seafloor alteration, characterized by carbonate deposition and negative Ce anomalies), or with high-temperature ore-forming hydrothermal fluids (ore-forming alteration, characterized by sulfide precipitation and steep positive Eu anomalies).

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