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O. J. Rouxel - One of the best experts on this subject based on the ideXlab platform.
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Depositional setting of the Late Archean Fe oxide- and sulfide-bearing chert and graphitic Argillite in the Shaw Dome, Abitibi greenstone belt, Canada
Precambrian Research, 2018Co-Authors: R. S. Hiebert, A. Bekker, M. G. Houle, O. J. RouxelAbstract:Interbedded chert-rich exhalite and graphitic Argillite are the only sedimentary rocks deposited in deep-water settings during long-lived hiatuses in mafic to ultramafic volcanism within the Hart area of the Shaw Dome in the Late Archean Abitibi greenstone belt in Canada. The Fe oxide- and sulfide-bearing, but predominantly cherty, exhalite lithological unit in the Hart area can be traced laterally to iron formation elsewhere in the Shaw Dome. Whole-rock as well as Fe and S isotope geochemistry suggest that the exhalite unit was formed as a result of direct precipitation from seawater, distally from hydrothermal centres. Fractionation of Fe isotopes through the precipitation of iron oxyhydroxides in a neutrally buoyant hydrothermal plume removed the heavier isotopes of Fe, resulting in the negative delta Fe-56 values observed in the exhalite in the Hart area. Archean seawater is generally considered to be anoxic, but moderate Mn enrichments (up to 1.87 wt% MnO) in exhalite along with negative Fe isotope values resulting from partial Fe(II) oxidation suggest the presence of oxygen in the upper part of the water column along the pathway of hydrothermal plumes from their source to the depositional site in the Abitibi greenstone belt. In contrast, the graphitic Argillite contains abundant pyrite nodules and bands that exhibit systematic negative Fe isotope values, but does not show Mn enrichment. This unit likely formed in a zone of upwelling of nutrient-rich waters from deeper parts of the basin resulting in high organic productivity. Both exhalite and graphitic Argillite have negative Delta S-33 values, suggesting that sulfur was derived from seawater sulfate, which is consistent with an anoxic atmosphere with sulfate aerosols produced by photochemical reactions. Combined, our data indicates disequilibrium between anoxic atmosphere and partially oxygenated upper part of the water column during periods of volcanic quiescence in the similar to 2.7 Ga Abitibi greenstone belt supporting the existence of oxidized oases within the Archean ocean.
R. S. Hiebert - One of the best experts on this subject based on the ideXlab platform.
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Depositional setting of the Late Archean Fe oxide- and sulfide-bearing chert and graphitic Argillite in the Shaw Dome, Abitibi greenstone belt, Canada
Precambrian Research, 2018Co-Authors: R. S. Hiebert, A. Bekker, M. G. Houle, O. J. RouxelAbstract:Interbedded chert-rich exhalite and graphitic Argillite are the only sedimentary rocks deposited in deep-water settings during long-lived hiatuses in mafic to ultramafic volcanism within the Hart area of the Shaw Dome in the Late Archean Abitibi greenstone belt in Canada. The Fe oxide- and sulfide-bearing, but predominantly cherty, exhalite lithological unit in the Hart area can be traced laterally to iron formation elsewhere in the Shaw Dome. Whole-rock as well as Fe and S isotope geochemistry suggest that the exhalite unit was formed as a result of direct precipitation from seawater, distally from hydrothermal centres. Fractionation of Fe isotopes through the precipitation of iron oxyhydroxides in a neutrally buoyant hydrothermal plume removed the heavier isotopes of Fe, resulting in the negative delta Fe-56 values observed in the exhalite in the Hart area. Archean seawater is generally considered to be anoxic, but moderate Mn enrichments (up to 1.87 wt% MnO) in exhalite along with negative Fe isotope values resulting from partial Fe(II) oxidation suggest the presence of oxygen in the upper part of the water column along the pathway of hydrothermal plumes from their source to the depositional site in the Abitibi greenstone belt. In contrast, the graphitic Argillite contains abundant pyrite nodules and bands that exhibit systematic negative Fe isotope values, but does not show Mn enrichment. This unit likely formed in a zone of upwelling of nutrient-rich waters from deeper parts of the basin resulting in high organic productivity. Both exhalite and graphitic Argillite have negative Delta S-33 values, suggesting that sulfur was derived from seawater sulfate, which is consistent with an anoxic atmosphere with sulfate aerosols produced by photochemical reactions. Combined, our data indicates disequilibrium between anoxic atmosphere and partially oxygenated upper part of the water column during periods of volcanic quiescence in the similar to 2.7 Ga Abitibi greenstone belt supporting the existence of oxidized oases within the Archean ocean.
Pierre Maurizot - One of the best experts on this subject based on the ideXlab platform.
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A reappraisal of the Poya Terrane (New Caledonia): Accreted Late Cretaceous-Paleocene marginal basin upper crust, passive margin sediments and Early Eocene E-MORB sill complex.
2017Co-Authors: Dominique Cluzel, Mattew Whitten, Sébastien Meffre, Jonathan C. Aitchison, Pierre MaurizotAbstract:Abstract The Poya Terrane of New Caledonia is a composite lithotectonic unit made of i) Campanian-Paleocene E-MORB and BABB-type basalts and abyssal Argillite (Poya Terrane Basalts); and ii) Coniacian-Santonian sandstone, turbidites and abyssal Argillite (Kone Facies) intruded by Early Eocene E-MORB sills. Remapping reveals that the Kone Facies is more extensive than previously thought. Petrography and detrital zircons provenance show that Kone Facies sediments have the same provenance as coeval autochthonous sediments, albeit with more abundant contemporaneous zircons. They accumulated on the eastern continental slope of the Norfolk Ridge, and eventually mixed with abyssal Argillite. Temporally, sill emplacement is related to subduction inception at ca. 56 Ma. We postulate that either: i) E-MORB intrusion was related to transcurrent thinning of the down going plate; or, ii) the “enriched” (off axis?) partial melt zone of the ancient ridge swept the lower plate, generating E-MORBs in the upper crust, and sills in passive margin sediments before it became extinct. Sliced marginal basin upper crust, and thereafter passive margin sediments and associated dolerites were obliquely accreted to the fore-arc, and partially subducted and recrystallized into the blueschist facies. The Poya Terrane was eventually thrust onto the Norfolk Ridge and its debris fed mid- to Late Eocene syntectonic basins. Meanwhile, mafic portions of the Poya Terrane were subducted and recrystallized into the eclogite facies, mixed with serpentinite to form the Pouebo mélange, and were exhumed in the fore-arc region. Finally, Late Oligocene faulting and hydrothermal events overprinted the NE part of the terrane.
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First sedimentary record of the pre-obduction convergence in New Caledonia: formation of an Early Eocene accretionary complex in the north of Grande Terre and emplacement of the 'Montagnes Blanches' nappe
Bulletin de la Société Géologique de France, 2011Co-Authors: Pierre MaurizotAbstract:New Caledonia lies at the northern tip of the Norfolk ridge, a continental fragment separated from the east Gondwana margin during the Late Cretaceous. Stratigraphic data for constraining the convergence that led to ophiolitic nappes being obducted over Grande Terre during the Eocene are both few and inaccurate. To try and fill this gap and determine the onset of the convergence, we investigated the lithology, sedimentology, biostratigraphy and geodynamic context of the Late Cretaceous - Palaeogene sedimentary cover-rock succession of northern New Caledonia. We were able to establish new stratigraphic correlations between the sedimentary units, which display large southwest-verging overfolds detached along a basal Argillite series, and reinterpret their interrelationships. The sediments from the Cretaceous-Paleocene interval were deposited in a post-rift pelagic environment and are mainly biogenic with minimal terrigenous input. From the base up, they comprise black organic-rich sulphide-bearing Argillite, black chert (silicified equivalent of the Argillite), micritic with chert, and micrite rich in planktonic foraminifera. These passive-margin deposits are found regionally on the Norfolk Ridge down to New Zealand, and on the Lord Howe Rise, and were controlled primarily by regional or global environmental factors. The overlying Eocene deposits mark a change to an active-margin regime with distal calciturbidite and proximal breccia representing the earliest Paleogene flysch-type deposits in New Caledonia. The change from an extensional to a compressive regime marks the beginning of the pre-obduction convergence and can be assigned fairly accurately in the Koumac-Gomen area to the end of the Early Eocene (Late Ypresian, Biozone E7) at c 50 Ma. From this period on, the post-Late Cretaceous cover in northern New Caledonia was caught up and recycled in a southwest-verging accretionary complex ahead of which flysch was deposited in a flexural foreland basin. The system prograded southwards until the Late Eocene collisional stage, when the continental Norfolk ridge entered the convergence zone and blocked it. At this point the autochthonous and parautochthonous sedimentary cover and overlying flysch of northern New Caledonia was thrust over the younger flysch to the south to form a newly defined allochthonous unit, the 'Montagnes Blanches' nappe, that is systematically intercalated between the flysch and the obducted ophiolite units throughout Grande Terre
A. Bekker - One of the best experts on this subject based on the ideXlab platform.
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Depositional setting of the Late Archean Fe oxide- and sulfide-bearing chert and graphitic Argillite in the Shaw Dome, Abitibi greenstone belt, Canada
Precambrian Research, 2018Co-Authors: R. S. Hiebert, A. Bekker, M. G. Houle, O. J. RouxelAbstract:Interbedded chert-rich exhalite and graphitic Argillite are the only sedimentary rocks deposited in deep-water settings during long-lived hiatuses in mafic to ultramafic volcanism within the Hart area of the Shaw Dome in the Late Archean Abitibi greenstone belt in Canada. The Fe oxide- and sulfide-bearing, but predominantly cherty, exhalite lithological unit in the Hart area can be traced laterally to iron formation elsewhere in the Shaw Dome. Whole-rock as well as Fe and S isotope geochemistry suggest that the exhalite unit was formed as a result of direct precipitation from seawater, distally from hydrothermal centres. Fractionation of Fe isotopes through the precipitation of iron oxyhydroxides in a neutrally buoyant hydrothermal plume removed the heavier isotopes of Fe, resulting in the negative delta Fe-56 values observed in the exhalite in the Hart area. Archean seawater is generally considered to be anoxic, but moderate Mn enrichments (up to 1.87 wt% MnO) in exhalite along with negative Fe isotope values resulting from partial Fe(II) oxidation suggest the presence of oxygen in the upper part of the water column along the pathway of hydrothermal plumes from their source to the depositional site in the Abitibi greenstone belt. In contrast, the graphitic Argillite contains abundant pyrite nodules and bands that exhibit systematic negative Fe isotope values, but does not show Mn enrichment. This unit likely formed in a zone of upwelling of nutrient-rich waters from deeper parts of the basin resulting in high organic productivity. Both exhalite and graphitic Argillite have negative Delta S-33 values, suggesting that sulfur was derived from seawater sulfate, which is consistent with an anoxic atmosphere with sulfate aerosols produced by photochemical reactions. Combined, our data indicates disequilibrium between anoxic atmosphere and partially oxygenated upper part of the water column during periods of volcanic quiescence in the similar to 2.7 Ga Abitibi greenstone belt supporting the existence of oxidized oases within the Archean ocean.
M. G. Houle - One of the best experts on this subject based on the ideXlab platform.
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Depositional setting of the Late Archean Fe oxide- and sulfide-bearing chert and graphitic Argillite in the Shaw Dome, Abitibi greenstone belt, Canada
Precambrian Research, 2018Co-Authors: R. S. Hiebert, A. Bekker, M. G. Houle, O. J. RouxelAbstract:Interbedded chert-rich exhalite and graphitic Argillite are the only sedimentary rocks deposited in deep-water settings during long-lived hiatuses in mafic to ultramafic volcanism within the Hart area of the Shaw Dome in the Late Archean Abitibi greenstone belt in Canada. The Fe oxide- and sulfide-bearing, but predominantly cherty, exhalite lithological unit in the Hart area can be traced laterally to iron formation elsewhere in the Shaw Dome. Whole-rock as well as Fe and S isotope geochemistry suggest that the exhalite unit was formed as a result of direct precipitation from seawater, distally from hydrothermal centres. Fractionation of Fe isotopes through the precipitation of iron oxyhydroxides in a neutrally buoyant hydrothermal plume removed the heavier isotopes of Fe, resulting in the negative delta Fe-56 values observed in the exhalite in the Hart area. Archean seawater is generally considered to be anoxic, but moderate Mn enrichments (up to 1.87 wt% MnO) in exhalite along with negative Fe isotope values resulting from partial Fe(II) oxidation suggest the presence of oxygen in the upper part of the water column along the pathway of hydrothermal plumes from their source to the depositional site in the Abitibi greenstone belt. In contrast, the graphitic Argillite contains abundant pyrite nodules and bands that exhibit systematic negative Fe isotope values, but does not show Mn enrichment. This unit likely formed in a zone of upwelling of nutrient-rich waters from deeper parts of the basin resulting in high organic productivity. Both exhalite and graphitic Argillite have negative Delta S-33 values, suggesting that sulfur was derived from seawater sulfate, which is consistent with an anoxic atmosphere with sulfate aerosols produced by photochemical reactions. Combined, our data indicates disequilibrium between anoxic atmosphere and partially oxygenated upper part of the water column during periods of volcanic quiescence in the similar to 2.7 Ga Abitibi greenstone belt supporting the existence of oxidized oases within the Archean ocean.