Nd- and Sr-isotope systematics for the Kamiskotia–Montcalm area: implications for the formation of late Archean crust in the western Abitibi Subprovince, Canada

1991 ◽  
Vol 28 (1) ◽  
pp. 58-76 ◽  
Author(s):  
C. Tucker Barrie ◽  
Steven B. Shirey
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Isotopic Signatures ◽  
Tectonic Model ◽  
Depleted Mantle ◽  
Lree Enrichment ◽  
Abitibi Subprovince ◽  
Mantle Reservoir ◽  
Element Enrichment

Geochemistry and Nd isotopic compositions are used to characterize mantle and crustal sources and to provide constraints on petrogenetic models for tholeiitic, calc-alkalic, and lamprophyric suites in the Kamiskotia–Montcalm area. The Kamiskotia gabbroic complex (KGC) and cogenetic, bimodal volcanic rocks have εNd(t) = +2.2 to +2.6, consistent with a direct derivation from a long-term, light rare-earth element (LREE)-depleted mantle. The Montcalm gabbroic complex has decreasing εNd(t) upsection from +2.8 to +1.0, consistent with contamination by long-term, LREE-enriched (with respect to the long-term, LREE-depleted Abitibi mantle) crust during fractionation. Two calc-alkalic lamprophyre samples, characterized by large-ion lithophile element (LILE) and LREE enrichment and high MgO, Ni, and Cr contents, have εNd(t) of +2.5 and +2.8, indicating a derivation from a depleted mantle source that had undergone recent trace-element enrichment. A different lamprophyre suite is extremely LILE and LREE enriched and has an εNd(t) of +1.0, indicating a derivation from a slightly different source that had earlier LREE enrichment. Granitoid rocks internal and external to greenstone belt rocks have εNd(t) = +2.5 to +3.8 and +0.6 to −0.4, respectively. The lower values provide additional evidence for the existence of LREE-enriched crust in this area.Considering these data along with other radiogenic isotope studies, a petrogenetic and tectonic model is suggested for the crustal development of the southern Abitibi Subprovince. From >2740 to 2698 Ma—the major period of volcanic activity—komatiitic and tholeiitic suites and one lamprophyre suite were derived from a uniformly LREE-depleted mantle reservoir with εNd(t) = +2 to +3. Calc-alkalic granitoids were emplaced generally after 2700 Ma. Their long-term, LREE-depleted and LREE-enriched Nd isotopic signatures are similar to signatures in continental-arc settings (e.g., the Coastal Batholith of Peru). Form 2690 to 2670 Ma, when transpressional tectonism prevailed, mantle-derived magmatism was represented by long-term, LREE-enriched (εNd(t) = +1 to +2) lamprophyric and alkalic volcanic suites.The Kamiskotia suite has a seven-point, whole-rock – mineral isochron Sm–Nd age of 2710 ± 30 Ma, identical to U–Pb zircon ages for the suite, indicating closed-system behavior. An Rb–Sr mineral – whole-rock isochron age from one KGC sample is 2450 ± 30 Ma, identical to U–Pb ages for the Hearst–Matachewan dike swarm, a prominent feature in the KGC area. Regression of whole-rock and mineral-isotope data for one granitoid sample with a U–Pb zircon age of 2696 ± 1.5 Ma gives identical ages of 2530 ± 30 Ma in the Sm–Nd and Rb–Sr systems. The latter data add to an increasing body of evidence for cryptic, late thermal events after granitoid–greenstone belt development in the southern Abitibi Subprovince.

Geology and geochemistry of an Archean mafic dike complex in the Chan Formation: basis for a revised plate-tectonic model of the Yellowknife greenstone belt

1995 ◽  
Vol 32 (5) ◽  
pp. 614-630 ◽  
Author(s):  
Kate Maclachlan ◽  
Herb Helmstaedt
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Mafic Dike ◽  
Tectonic Model ◽  
Dike Complex ◽  
Metavolcanic Rocks ◽  
Depleted Mantle ◽  
Mid Ocean Ridge ◽  
A Minor ◽  
Ocean Ridge

An Archean mafic dike complex in the Chan Formation at the base of the mafic volcanic section of the Yellowknife greenstone belt consists of multiple metagabbro dikes and sills separated by screens of pillowed mafic volcanic rocks, which are cut by a younger postvolcanic metadiabase dike swarm. Field relationships and geochemical characteristics are compatible with a comagmatic origin for the metagabbro and metavolcanic rocks that were fed through and deposited on an older, rift-related, supracrustal sequence of the Dwyer Group. The synvolcanic metagabbro dikes have extended the strike length of the volcanic section by at least 100%. The mafic rocks of the Chan Formation are geochemically similar to mid-ocean ridge basalt, possibly with a minor subduction-zone component. Preliminary εNd values for metagabbroic rocks are consistent with the derivation of magmas predominantly from a normal, depleted-mantle source. The Chan Formation is interpreted to have formed in a marginal basin-like setting, adjacent to a previously rifted and attenuated protocontinental margin.

Lu–Hf zircon and Sm–Nd whole-rock isotope constraints on the extent of juvenile arc crust in Avalonia: examples from Newfoundland and Nova Scotia, Canada

2015 ◽  
Vol 52 (3) ◽  
pp. 161-181 ◽  
Author(s):  
J.C. Pollock ◽  
P.J. Sylvester ◽  
S.M. Barr
Keyword(s):  
Isotope Composition ◽  
Volcanic Rocks ◽  
Detrital Zircons ◽  
Isotopic Signatures ◽  
Magmatic Arc ◽  
Depleted Mantle ◽  
Felsic Volcanic ◽  
Clastic Sedimentary ◽  
Neoproterozoic Magmatic Arc

Avalonia, the largest accreted crustal block in the Appalachian orogen, consists of Neoproterozoic magmatic arc sequences that represent protracted and episodic subduction-related magmatism before deposition of an Ediacaran–Ordovician cover sequence including siliciclastic rocks. Zircon crystals were obtained from arc-related magmatic rocks and from clastic sedimentary sequences and analyzed in situ for their Hf-isotope composition. The majority of magmatic and detrital zircons are dominated by initial 176Hf/177Hf values that are more radiogenic than chondritic uniform reservoir (CHUR) with calculated crust formation Hf–TDM model ages that range from 0.84 to 1.30 Ga. These results suggest formation by partial melting of juvenile mantle in a Neoproterozoic continental arc. Some zircons have Hf–TDM model ages ca. 1.39–3.09 Ga with εHf values of –33.9 to –0.5 and more clearly indicate involvement of older lithosphere in their petrogenesis. Whole-rock Sm–Nd isotopic compositions from felsic volcanic rocks are characterized by positive initial εNd values with Mesoproterozoic depleted mantle model ages consistent with juvenile extraction. Results suggest a dominant mantle component with long-term light rare earth element (LREE) depletion mixed with an older crustal component with long-term LREE enrichment. The pattern of TDM model ages and variations in Lu–Hf and Sm–Nd isotopic character are compatible with a ca. 1.0–1.2 Ga igneous tectonomagmatic event that formed basement to Neoproterozoic magmatic arcs in Avalonia. The presence of evolved isotopic signatures, however, indicates that significant older Proterozoic crust is present locally beneath Avalonia, suggesting that Avalonia formed in a single Neoproterozoic arc system that generated juvenile mantle-derived crust, coupled with lesser anatectic reworking of significantly older crust.

The tectonic evolution of the Abitibi greenstone belt of Canada

1986 ◽  
Vol 123 (2) ◽  
pp. 153-166 ◽  
Author(s):  
John Ludden ◽  
Claude Hubert ◽  
Clement Gariépy
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Taupo Volcanic Zone ◽  
Rift Basins ◽  
Volcanic Zone ◽  
Tectonic Model ◽  
Abitibi Greenstone Belt ◽  
Southern Volcanic Zone ◽  
The Difference ◽  
Felsic Volcanic

AbstractBased on structural, geochemical, sedimentological and geochronological studies, we have formulated a model for the evolution of the late Archaean Abitibi greenstone belt of the Superior Province of Canada. The southern volcanic zone (SVZ) of the belt is dominated by komatiitic to tholeiitic volcanic plateaux and large, bimodal, mafic-felsic volcanic centres. These volcanic rocks were erupted between approximately 2710 Ma and 2700 Ma in a series of rift basins formed as a result of wrench-fault tectonics.The SVZ superimposes an older volcanic terrane which is characterized in the northern volcanic zone (NVZ) of the Abitibi belt and is approximately 2720 Ma or older. The NVZ comprises basaltic to andesitic and dacitic subaqueous massive volcanics which are cored by comagmatic sill complexes and layered mafic-anorthositic plutonic complexes. These volcanics are overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 ±2 Ma.The tectonic model envisages the SVZ to have formed in a series of rift basins which dissected an earlier formed volcanic arc (the NVZ). Analogous rift environments have been postulated for the Hokuroko basin of Japan, the Taupo volcanic zone of New Zealand and the Sumatra and Nicaragua arcs. The difference between rift related ‘submergent’ volcanism in the SVZ and ‘emergent’ volcanism in the NVZ resulted in the contrasting metallogenic styles, the former being characterized by syngenetic massive sulphide deposits, whilst the latter was dominated by epigenetic ‘porphyry-type’ Cu(Au) deposits.

Geochemistry and isotope studies of the metavolcanic rocks of Shimoga greenstone belt, Western Dharwar craton - an effort to deduce the Petrogenesis.

2020 ◽  
Author(s):  
Anshuman Giri ◽  
Rajagopal Anand
Keyword(s):  
Fractional Crystallization ◽  
Greenstone Belt ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Dharwar Craton ◽  
Metavolcanic Rocks ◽  
Depleted Mantle ◽  
Felsic Volcanic ◽  
Felsic Volcanic Rocks

<p>The archaean greenstone belts, dominated by mafic to felsic volcanic rocks followed by younger granitic intrusions occurs associated with volcano-sedimentary sequences. The Dharwar Super group (2600 to 2900 Ma) of rocks in western Dharwar craton, underlie the older TTG gneisses. The Shimoga greenstone belt (SGB) of WDC constitute the basal polymictic conglomerate along with quartzite, pyroclastic rocks, carbonaceous rocks, greywacke-argillite sequences with a thick pile of mafic and felsic metavolcanic rocks (BADR). These rocks are suffered from greenschist to lower amphibolite grade of metamorphism. The Medur metavolcanic volcanic rocks give an age of 2638 ± 66 Ma (1), whereas the Daginakatte felsic volcanic rocks give an age of 2601 ± 6 Ma (2). The present studied age of 2638 ± 66 Ma, tells about the cessation of mafic magmatism in WDC. The metavolcanic rocks of the Medur formation are tholeiitic to calc-alkaline in nature. These rocks show flat to LREE enriched REE pattern with negative europium anomaly. And also show enrichment in LILE and depletion in HFSE elements with significant Nb-Ta anomaly. The geochemical and the isotope data suggest the involvement of partial melting of the depleted mantle by the slab components and assimilation fractional crystallization (AFC) processes for the magma generation. The SGB metavolcanic rocks have 143Nd/144Nd ratios (0.511150 to .513076) and εNd values of -3.1 to -5.5 and the negative εNd values  for the rocks is due to the crustal contamination of the magma in a shallow marine subduction setting. The parental magmas were derived from melting in the mantle wedge fluxed by slab derived fluids and slab components followed by assimilation fractional crystallization (AFC) processes involving continental crust in an active continental margin.</p><ul><li>(1) Giri et al., 2019. Lithos, <strong>330-331</strong>, 177-193</li> <li>(2) Trendall et al., 1997a. J. Geol. Soc. India, <strong>50</strong>, 25-50.</li> </ul>

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.

Trace element geochemistry of the Meen-Dempster greenstone belt, Uchi subprovince, Superior Province, Canada: back-arc development on the margins of an Archean protocontinent

2000 ◽  
Vol 37 (7) ◽  
pp. 1021-1038 ◽  
Author(s):  
Pete Hollings ◽  
Greg Stott ◽  
Derek Wyman
Keyword(s):  
Trace Element ◽  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Tholeiitic Basalt ◽  
Pyroclastic Flows ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Lree Enrichment ◽  
Compositional Diversity ◽  
Back Arc

Comprehensive trace element analyses of mafic and felsic volcanic rocks from the 2.85-2.74 Ga Meen-Dempster greenstone belt reveal a wide compositional diversity. The ~2.85 Ga Kaminiskag assemblage is dominated by mafic tholeiite characterized by predominantly unfractionated REE (La/Smn = 0.8-1.1). Rare intermediate and felsic pyroclastic flows (SiO2 = 62-74) with moderate to pronounced LREE enrichment are intercalated with the tholeiite. The Kaminiskag assemblage is overlain by the ~2825 Ma Meen assemblage, comprising dominantly dacitic tuffs and pyroclastic breccia, displaying enriched LREE (La/Smn = 3.7-7.2) and moderately fractionated HREE, in conjunction with pronounced negative Nb anomalies. Five distinct suites have been recognized in the ~2740 Ma Confederation assemblage: (1) tholeiitic basalt with flat to smoothly depleted REE, (2) tholeiite with flat to weakly depleted LREE in conjunction with pronounced negative Nb anomalies, (3) Fe-rich basalt with elevated Ti and P contents, LREE enrichment, and fractionated HREE, (4) LREE enriched basalt and andesite with negative Nb anomalies, and (5) dacite and rhyolite with enriched LREE, moderately fractionated HREE, and variable high field strength element anomalies. The geochemistry and geochronology of the Kaminiskag and Meen assemblages are consistent with the formation of an oceanic back arc (Kaminiskag assemblage), which formed the basement for a subduction-related arc complex (Meen assemblage) after a 15 Ma hiatus. The Confederation assemblage is interpreted to represent an Archean back arc, where the complex interplay of mantle sources allows for the eruption of tholeiite, subduction-modified tholeiite, ocean island basalt-like basalt, and subduction-related arc-type volcanic rocks. The recognition of back-arc basins within the Meen-Dempster greenstone belt emphasizes a continuity of crustal growth processes from the Archean to the present day.

Field relations, U-Pb geochronology, and Sm-Nd isotope geochemistry of the Point Lake greenstone belt and adjacent gneisses, central Slave craton, N.W.T., Canada

1999 ◽  
Vol 36 (7) ◽  
pp. 1043-1059 ◽  
Author(s):  
C J Northrup ◽  
C Isachsen ◽  
S A Bowring
Keyword(s):  
Greenstone Belt ◽  
Isotope Geochemistry ◽  
Volcanic Rocks ◽  
Granite Gneiss ◽  
Lake Area ◽  
Slave Craton ◽  
Mafic Dykes ◽  
Depleted Mantle ◽  
Zircon Crystallization ◽  
Back Arc

Data from the Point Lake area, central Slave craton, suggest an intimate tectonic and paleogeographic association between volcano-sedimentary supracrustal rocks and adjacent gneisses. Granite plutons and orthogneisses yield U-Pb zircon crystallization ages ranging from ca. 3230 to 2818 Ma. Numerous mafic dykes cut the gneisses, and two have been dated by U-Pb zircon geochronometry at 2673 ± 3 and 2690 ± 3 Ma, ages similar to those of volcanic rocks in the Point Lake greenstone belt. Although high-strain zones form the greenstone-gneiss in most places, a structural repetition of granite about 4 km east of Keskarrah Bay is cut by numerous mafic dykes and apparently overlain depositionally(?) by pillow basalt. Mafic volcanic and plutonic rocks from Point Lake have initial (2.7 Ga) εNd values ranging from about +2.2 to -6.3, significantly lower than the depleted mantle at that time. The Nd data suggest either derivation from a more isotopically evolved reservoir, or assimilation of crust similar to the granite gneiss at Point Lake. We infer from the presence of mafic dykes of appropriate age in the basement and the low initial εNd values of some pillow basalts that the volcanic sequence developed on the older granitic crust. The supracrustal rocks may have been deposited in a back-arc basin floored at least in part by attenuated continental material. Closure of the basin, bulk east-west shortening, and sinistral oblique or strike-slip faulting then obscured the original relations between the volcanic and gneissic rocks.

scholarly journals Biosignatures of ancient microbial life are present across the igneous crust of the Fennoscandian shield

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Henrik Drake ◽  
Nick M. W. Roberts ◽  
Manuel Reinhardt ◽  
Martin Whitehouse ◽  
Magnus Ivarsson ◽  
...  
Keyword(s):  
Fennoscandian Shield ◽  
Stable Carbon ◽  
Deep Biosphere ◽  
Isotopic Signatures ◽  
Microbial Life ◽  
Carbon Isotopic ◽  
Terrestrial Life ◽  
Vein Mineral ◽  
Methyl Branched Fatty Acids

AbstractEarth’s crust contains a substantial proportion of global biomass, hosting microbial life up to several kilometers depth. Yet, knowledge of the evolution and extent of life in this environment remains elusive and patchy. Here we present isotopic, molecular and morphological signatures for deep ancient life in vein mineral specimens from mines distributed across the Precambrian Fennoscandian shield. Stable carbon isotopic signatures of calcite indicate microbial methanogenesis. In addition, sulfur isotope variability in pyrite, supported by stable carbon isotopic signatures of methyl-branched fatty acids, suggest subsequent bacterial sulfate reduction. Carbonate geochronology constrains the timing of these processes to the Cenozoic. We suggest that signatures of an ancient deep biosphere and long-term microbial activity are present throughout this shield. We suggest that microbes may have been active in the continental igneous crust over geological timescales, and that subsurface investigations may be valuable in the search for extra-terrestrial life.

scholarly journals Oxygen Fugacity and Volatile Content of Syntectonic Magmatism in the Neoarchean Abitibi Greenstone Belt, Superior Province, Canada

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 966
Author(s):  
Baptiste Madon ◽  
Lucie Mathieu ◽  
Jeffrey H. Marsh
Keyword(s):  
Oxygen Fugacity ◽  
Greenstone Belt ◽  
Inductively Coupled Plasma ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Hydrothermal Systems ◽  
Chemical Diversity ◽  
Temporal Association ◽  
Volatile Content ◽  
Abitibi Subprovince

Neoarchean syntectonic intrusions from the Chibougamau area, northeastern Abitibi Subprovince (greenstone belt), may be genetically related to intrusion related gold mineralization. These magmatic-hydrothermal systems share common features with orogenic gold deposits, such as spatial and temporal association with syntectonic magmatism. Genetic association with magmatism, however, remains controversial for many greenstone belt hosted Au deposits. To precisely identify the link between syntectonic magmas and gold mineralization in the Abitibi Subprovince, major and trace-element compositions of whole rock, zircon, apatite, and amphibole grains were measured for five intrusions in the Chibougamau area; the Anville, Saussure, Chevrillon, Opémisca, and Lac Line Plutons. The selected intrusions are representative of the chemical diversity of synvolcanic (TTG suite) and syntectonic (e.g., sanukitoid, alkaline intrusion) magmatism. Chemical data enable calculation of oxygen fugacity and volatile content, and these parameters were interpreted using data collected by electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. The zircon and apatite data and associated oxygen fugacity values in magma indicate that the youngest magmas are the most oxidized. Moreover, similar oxygen fugacity and high volatile content for both the Saussure Pluton and the mineralized Lac Line intrusion may indicate a possible prospective mineralized system associated with the syntectonic Saussure intrusion.

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