Archean mafic dyke swarms near the Cameron River and Beaulieu River volcanic belts and their implications for tectonic modelling of the Slave Province, Northwest Territories

1992 ◽  
Vol 29 (10) ◽  
pp. 2226-2248 ◽  
Author(s):  
M. B. Lambert ◽  
R. E. Ernst ◽  
F. Ö. L. Dudás
Keyword(s):  
Isotope Geochemistry ◽  
Flood Basalts ◽  
Nd Isotope ◽  
Slave Province ◽  
Depleted Mantle ◽  
Magmatic Underplating ◽  
Basaltic Magmas ◽  
Dyke Swarms ◽  
Volcanic Belts ◽  
Extensive Involvement

Three dense swarms of Archean mafic dykes, which intrude the Beaulieu River and Cameron River volcanic belts and adjacent granitoid terranes of the Sleepy Dragon Complex and Meander Lake complex in the southern Slave Province, all contain clusters of multiple, parallel-sided "sheeted" dykes. None of the swarms can be convincingly modelled as being part of an ophiolite assemblage. The 3 km by 20+ km Step'nduck dyke complex, comprising about 350 mainly metabasaltic to meta-gabbroic dykes separated by screens of granitoid gneiss (>2750 Ma), represents profuse mafic magmatism in the Meander Lake complex. Dense dyke swarms within the Cameron River belt fed the lavas and are an integral part of the volcanic stratigraphy.All basaltic magmas represented by the volcanic belts, and the dyke sets, are predominantly mantle-derived, fractionated, tholeiites. Nd-isotope geochemistry indicates that they were all contaminated by Archean sialic material. Isotopic systematics are satisfied by mixing of depleted mantle and varying proportions of Sleepy Dragon-type crust.The dyke swarms in the Sleepy Dragon Complex and the Step'nduck swarm record extensional events in Archean continental crust. Possibly they are subsurface equivalents of now-eroded flood basalts that signalled the activity of mantle plumes during Archean times. This hypothesis is consistent with magmatic underplating of continental lithosphere and with extensive involvement of continental material.

New approaches to crustal evolution studies and the origin of granitic rocks: what can the Lu-Hf and Re-Os isotope systems tell us?

1996 ◽  
Vol 87 (1-2) ◽  
pp. 339-352 ◽  
Author(s):  
Clark M. Johnson ◽  
Steven B. Shirey ◽  
Karin M. Barovich
Keyword(s):  
Continental Crust ◽  
Isotope Ratios ◽  
Granitic Rocks ◽  
Nd Isotope ◽  
Volcanic Arcs ◽  
Depleted Mantle ◽  
Os Isotopes ◽  
Isotope System ◽  
Os Isotope

ABSTRACT:The Lu-Hf and Re-Os isotope systems have been applied sparsely to elucidate the origin of granites, intracrustal processes and the evolution of the continental crust. The presence or absence of garnet as a residual phase during partial melting will strongly influence Lu/Hf partitioning, making the Lu–Hf isotope system exceptionally sensitive to evaluating the role of garnet during intracrustal differentiation processes. Mid-Proterozoic (1·1–1·5Ga ) ‘anorogenic’ granites from the western U.S.A. appear to have anomalously high εHf values, relative to their εNd values, compared with Precambrian orogenic granites from several continents. The Hf-Nd isotope variations for Precambrian orogenic granites are well explained by melting processes that are ultimately tied to garnet-bearing sources in the mantle or crust. Residual, garnet-bearing lower and middle crust will evolve to anomalously high εHf values over time and may be the most likely source for later ‘anorogenic’ magmas. When crustal and mantle rocks are viewed together in terms of Hf and Nd isotope compositions, a remarkable mass balance is apparent for at least the outer silicate earth where Precambrian orogenic continental crust is the balance to the high-εHf depleted mantle, and enriched lithospheric mantle is the balance to the low-εHf depleted mantle.Although the continental crust has been envisioned to have exceptionally high Re/Os ratios and very radiogenic Os isotope compositions, new data obtained on magnetite mineral separates suggest that some parts of the Precambrian continental crust are relatively Os-rich and non-radiogenic. It remains unclear how continental crust may obtain non-radiogenic Os isotope ratios, and these results have important implications for Re-Os isotope evolution models. In contrast, Phanerozoic batholiths and volcanic arcs that are built on young mafic lower crust may have exceptionally radiogenic Os isotope ratios. These results highlight the unique ability of Os isotopes to identify young mafic crustal components in orogenic magmas that are essentially undetectable using other isotope systems such as O, Sr, Nd and Pb.

scholarly journals Ore and Geochemical Specialization and Substance Sources of the Ural and Timan Carbonatite Complexes (Russia): Insights from Trace Element, Rb–Sr, and Sm–Nd Isotope Data

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 711
Author(s):  
Irina Nedosekova ◽  
Nikolay Vladykin ◽  
Oksana Udoratina ◽  
Boris Belyatsky
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Crustal Evolution ◽  
Trace Element Data ◽  
The Urals ◽  
Nd Isotope ◽  
Enriched Mantle ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
Geochemical Specialization

The Ilmeno–Vishnevogorsk (IVC), Buldym, and Chetlassky carbonatite complexes are localized in the folded regions of the Urals and Timan. These complexes differ in geochemical signatures and ore specialization: Nb-deposits of pyrochlore carbonatites are associated with the IVC, while Nb–REE-deposits with the Buldym complex and REE-deposits of bastnäsite carbonatites with the Chetlassky complex. A comparative study of these carbonatite complexes has been conducted in order to establish the reasons for their ore specialization and their sources. The IVC is characterized by low 87Sr/86Sri (0.70336–0.70399) and εNd (+2 to +6), suggesting a single moderately depleted mantle source for rocks and pyrochlore mineralization. The Buldym complex has a higher 87Sr/86Sri (0.70440–0.70513) with negative εNd (−0.2 to −3), which corresponds to enriched mantle source EMI-type. The REE carbonatites of the Chetlassky сomplex show low 87Sr/86Sri (0.70336–0.70369) and a high εNd (+5–+6), which is close to the DM mantle source with ~5% marine sedimentary component. Based on Sr–Nd isotope signatures, major, and trace element data, we assume that the different ore specialization of Urals and Timan carbonatites may be caused not only by crustal evolution of alkaline-carbonatite magmas, but also by the heterogeneity of their mantle sources associated with different degrees of enrichment in recycled components.

TRACE ELEMENT AND Sr-Nd ISOTOPE GEOCHEMISTRY OF FLUORITE FROM THE XIANGSHAN URANIUM DEPOSIT, SOUTHEAST CHINA

2006 ◽  
Vol 101 (8) ◽  
pp. 1613-1622 ◽  
Author(s):  
Y.-h. Jiang ◽  
H.-f. Ling ◽  
S.-y. Jiang ◽  
W.-z. Shen ◽  
H.-h. Fan ◽  
...  
Keyword(s):  
Trace Element ◽  
Uranium Deposit ◽  
Isotope Geochemistry ◽  
Nd Isotope ◽  
Southeast China

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.

Re--Os and Sm--Nd Isotope Geochemistry of the Stillwater Complex, Montana: Implications for the Petrogenesis of the J-M Reef

1994 ◽  
Vol 35 (6) ◽  
pp. 1717-1753 ◽  
Author(s):  
D. D. LAMBERT ◽  
R. J. WALKER ◽  
J. W. MORGAN ◽  
S. B. SHIREY ◽  
R. W. CARLSON ◽  
...  
Keyword(s):  
Isotope Geochemistry ◽  
Stillwater Complex ◽  
Nd Isotope

Sr–Nd isotope geochemistry and petrogenesis of the Chah-Shaljami granitoids (Lut Block, Eastern Iran)

2011 ◽  
Vol 41 (3) ◽  
pp. 283-296 ◽  
Author(s):  
R. Arjmandzadeh ◽  
M.H. Karimpour ◽  
S.A. Mazaheri ◽  
J.F. Santos ◽  
J.M. Medina ◽  
...  
Keyword(s):  
Isotope Geochemistry ◽  
Nd Isotope ◽  
Lut Block ◽  
Eastern Iran

Early Tertiary basalts from the Labrador Sea floor and Davis Strait region

1989 ◽  
Vol 26 (5) ◽  
pp. 956-968 ◽  
Author(s):  
D. B. Clarke ◽  
B. I. Cameron ◽  
G. K. Muecke ◽  
J. L. Bates
Keyword(s):  
Volcanic Rocks ◽  
Labrador Sea ◽  
Baffin Island ◽  
Nd Isotope ◽  
Sea Floor ◽  
West Greenland ◽  
Depleted Mantle ◽  
Davis Strait ◽  
Isotope Systematics ◽  
Seawater Exchange

Fine- to medium-grained, phyric and aphyric basalt samples from ODP Leg 105, site 647A, in the Labrador Sea show little evidence of alteration. Chemically, these rocks are low-potassium (0.01–0.09 wt.% K2O), olivine- to quartz-normative tholeiites that compare closely with the very depleted terrestrial Paleocene volcanic rocks in the Davis Strait region of Baffin Island and West Greenland. However, differences exist in the Sr–Nd isotope systematics of the two suites; the Labrador Sea samples have ε Nd values (+9.3) indicative of a more depleted source, and are higher in 87Sr/86Sr (0.7040), relative to the Davis Strait basalts (ε Nd +2.54 to +8.97; mean 87Sr/86Sr 0.7034). The higher 87Sr/86Sr in the Labrador Sea samples may reflect seawater exchange despite no petrographic evidence for significant alteration. The Labrador Sea and early Davis Strait basalts may have been derived from a similar depleted mantle source composition; however, the later Davis Strait magmas were generated from a different mantle. None of the Baffin Island, West Greenland, or Labrador Sea samples show unequivocal geochemical evidence for contamination with continental crust.

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