Tectonic significance and redox state of Paleoproterozoic eclogite and pyroxenite components in the Slave cratonic mantle lithosphere, Voyageur kimberlite, Arctic Canada

Smart, Katie A.; Tappe, Sebastian; Simonetti, Antonio; Simonetti, Stefanie S.; Woodland, Alan B.; Harris, Chris

doi:10.1016/j.chemgeo.2016.10.014

Cited by 35 publications

(14 citation statements)

References 142 publications

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“…These new data are combined with published studies on mantle eclogites and pyroxenites from Voyageur in the northern Slave craton, which are coeval with their ca. 2 Ga central Slave counterparts 11 , as well as from the Lace kimberlite in the Kaapvaal craton with ca. 3 Ga old protoliths 12 .…”

Section: Samples and Eclogite Petrogenesismentioning

confidence: 99%

“…In contrast, there is recent evidence for a subtle but significant terrestrial mantle redox evolution between 3.5 and 1.9 Ga based on the behaviour of V 8–10 . Moreover, recent studies reveal that garnet in mantle eclogites has low Fe 3+ /ΣFe, typically ≪ 0.10 11–13 , which may be related either to Fe 3+ loss during partial melting in subduction zones or to an intrinsically more reducing convecting mantle source to the eclogites’ mafic protoliths 8,12,13 .…”

Section: Introductionmentioning

confidence: 99%

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Evidence for a dominantly reducing Archaean ambient mantle from two redox proxies, and low oxygen fugacity of deeply subducted oceanic crust

Aulbach

Woodland

Stern

et al. 2019

Sci Rep

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Oxygen fugacity (ƒO2) is an intensive variable implicated in a range of processes that have shaped the Earth system, but there is controversy on the timing and rate of oxidation of the uppermost convecting mantle to its present ƒO2 around the fayalite-magnetite-quartz oxygen buffer. Here, we report Fe3+/ΣFe and ƒO2 for ancient eclogite xenoliths with oceanic crustal protoliths that sampled the coeval ambient convecting mantle. Using new and published data, we demonstrate that in these eclogites, two redox proxies, V/Sc and Fe3+/ΣFe, behave sympathetically, despite different responses of their protoliths to differentiation and post-formation degassing, seawater alteration, devolatilisation and partial melting, testifying to an unexpected robustness of Fe3+/ΣFe. Therefore, these processes, while causing significant scatter, did not completely obliterate the underlying convecting mantle signal. Considering only unmetasomatised samples with non-cumulate and little-differentiated protoliths, V/Sc and Fe3+/ΣFe in two Archaean eclogite suites are significantly lower than those of modern mid-ocean ridge basalts (MORB), while a third suite has ratios similar to modern MORB, indicating redox heterogeneity. Another major finding is the predominantly low though variable estimated ƒO2 of eclogite at mantle depths, which does not permit stabilisation of CO2-dominated fluids or pure carbonatite melts. Conversely, low-ƒO2 eclogite may have caused efficient reduction of CO2 in fluids and melts generated in other portions of ancient subducting slabs, consistent with eclogitic diamond formation ages, the disproportionate frequency of eclogitic diamonds relative to the subordinate abundance of eclogite in the mantle lithosphere and the general absence of carbonate in mantle eclogite. This indicates carbon recycling at least to depths of diamond stability and may have represented a significant pathway for carbon ingassing through time.

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Section: Samples and Eclogite Petrogenesismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evidence for a dominantly reducing Archaean ambient mantle from two redox proxies, and low oxygen fugacity of deeply subducted oceanic crust

Aulbach

Woodland

Stern

et al. 2019

Sci Rep

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“…This constitutes an efficient process to achieve high diamond modes, aided by the high volume of carbonaceous fluids and melts present in this tectonic setting (e.g., Poli, 2015; Tumiati et al, 2017). Moreover, the low oxygen fugacity of eclogitized oceanic crust (Smart et al, 2017; Aulbach, Woodland, et al, 2017; Aulbach, Woodland, et al, 2019) may cause CO 2 in the auto‐metasomatic fluid to be reduced to diamond.…”

Section: Discussionmentioning

confidence: 99%

“…(b) Total HREE content (ΣHREE, summing abundances from Tb to Lu in ppm) as a function of Eu/Eu* (chondrite‐normalized Eu/(Sm*Gd)^0.5; chondrite of Sun & McDonough, 1989) in garnet, separating gabbroic from non‐gabbroic eclogites and (c) Ca# (molar Ca/(Ca + Mg + Fe + Mn)) as a function of Mg#, classifying non‐gabbroic eclogites into high‐Mg, low‐Mg, and high‐Ca classes. Samples are from the northern Slave craton (Jericho, Muskox, Voyageur; Smart et al, 2009, 2014, 2017), central Slave craton (Diavik; Schmidberger et al, 2007; this study), West African craton (Koidu; Barth et al, 2001, 2002; Aulbach, Höfer, & Gerdes, 2019), Zimbabwe craton (Orapa; Viljoen et al, 1996; Aulbach et al, 2016; this study), and the Kaapvaal craton (Kimberley, Jacob et al, 2009, and Lace, Aulbach & Viljoen, 2015; Aulbach et al, 2016).…”

Section: Sample Classification and Databasementioning

confidence: 99%

Ultramafic Carbonated Melt‐ and Auto‐Metasomatism in Mantle Eclogites: Compositional Effects and Geophysical Consequences

Aulbach

Massuyeau

Garber

et al. 2020

Geochem Geophys Geosyst

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The mineralogy, chemical composition, and physical properties of cratonic mantle eclogites with oceanic crustal protoliths can be modified by secondary processes involving interaction with fluids and melts, generated in various slab lithologies upon subduction (auto-metasomatism) or mantle metasomatism after emplacement into the cratonic lithosphere. Here we combine new and published data to isolate these signatures and evaluate their effects on the chemical and physical properties of eclogite. Mantle metasomatism involving kimberlite-like, ultramafic carbonated melts (UM carbonated melts) is ubiquitous though not pervasive, and affected between~20% and 40% of the eclogite population at the various localities investigated here, predominantly at~60-150 km depth, overlapping cratonic midlithospheric seismic discontinuities. Its hallmarks include lower jadeite component in clinopyroxene and grossular component in garnet, an increase in bulk-rock MgO ± SiO 2 , and decrease in FeO and Al 2 O 3 contents, and LREE-enrichment accompanied by higher Sr, Pb, Th, U, and in part Zr and Nb, as well as lower Li, Cu ± Zn. This is mediated by addition of a high-temperature pyroxene from a UM carbonated melt, followed by redistribution of this component into garnet and clinopyroxene. As clinopyroxene-garnet trace-element distribution coefficients increase with decreasing garnet grossular component, clinopyroxene is the main carrier of the metasomatic signatures. UM carbonated melt-metasomatism at >130-150 km has destroyed the diamond inventory at some localities. These mineralogical and chemical changes contribute to low densities, with implications for eclogite gravitational stability, but negligible changes in shear-wave velocities, and, if accompanied by H 2 O-enrichment, will enhance electrical conductivities compared to unenriched eclogites. Plain Language SummaryOceanic crust formed at spreading ridges is recycled in subduction zones and undergoes metamorphism to eclogite. Some of this material is captured in the overlying lithospheric mantle, where it is exhumed by passing magmas. Having formed in spreading ridges, these eclogites have proven invaluable archives for the onset of plate tectonics, for the construction of cratons during subduction/collision, as probes of the convecting mantle from which their precursors formed, and as generators of heterogeneity upon recycling into Earth's convecting mantle. During subduction and until exhumation, interaction with fluids and melts (called metasomatism) can change the mineralogy, chemical composition, and physical properties of mantle eclogites, complicating their interpretation, but a comprehensive study of these effects is lacking so far. We investigated mantle eclogites from ancient continents (cratons) around the globe in order to define hallmarks of metasomatism by subduction-related fluids and small-volume ultramafic carbonated mantle melts. We find that the latter is pervasive and occurs predominantly at midlithospheric depths where seismic discontinuities are detected, ...

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“…Oceanic crust that has been subducted and metamorphosed to the eclogite facies and beyond (e.g., Han et al, 2015) is available for direct study in two geodynamic settings: (1) as xenoliths in kimberlite magmas that sample the subcontinental lithospheric mantle (SCLM) and (2) as eclogites and amphibolites in the world's orogenic belts (the OEAs). Although some researchers have had success using the geochemistry of kimberlite eclogite xenoliths to understand the geochemistry of subducted oceanic crust, it is generally recognized that a variety of processes operating with the SCLM itself alter the xenoliths' chemical composition and mineralogy (e.g., Aulbach et al, 2007;Smit et al, 2014;Smart et al, 2017). In considering that most kimberlite eclogite xenoliths are inferred to have resided in the SCLM over billion-year time scales, it is very difficult to understand which aspects of the eclogites reflect the chemical signature imparted by subduction versus those that have been acquired from the SCLM.…”

Section: Rationale: Justification For the Use Of Orogenic Eclogite Anmentioning

confidence: 99%

Lu-Hf and Sm-Nd geochronological constraints on the influence of subduction metamorphism in controlling the Hf-Nd terrestrial array: Evidence from the world’s orogenic belts

Zirakparvar

2019

Geosphere

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To create a better understanding of the influence of subduction metamorphism on the Hf-Nd terrestrial array, this study examines all of the available Lu-Hf and Sm-Nd garnet isochron ages from the world's orogenic eclogites and amphi bolites. The garnet isochron y-intercept values provide a record of each sample's epsilon Hf (ε Hf) and Nd (ε Nd) at the age recorded by the isochron, which in the case of most orogenic eclogites and amphibolites is the time of prograde metamorphism during subduction. It is further possible to assess the extent to which each sample's Lu-Hf and Sm-Nd isotope systematics have remained undisturbed since the date recorded by the isochron by comparison of the bulk-rock isotope systematics with the isochron initial value. This approach provides a means of understanding the Lu-Hf and Sm-Nd systematics of post-subduction metamorphic oceanic crust. On a global scale, the coupled Lu-Hf and Sm-Nd isotope systematics of this crust closely align with the Hf-Nd terrestrial array and have average 176 Lu/ 177 Hf and 147 Sm/ 144 Nd ratios within error of the chondritic uniform reservoir values. This is an important finding because it suggests that a reservoir of deeply subducted oceanic crust, possibly residing at the core-mantle boundary, is unlikely to be significantly fractionated from the Hf-Nd terrestrial array. In contrast to the samples of subduction-metamorphosed oceanic crust, metamorphic rocks with a continental crustal protolith demonstrate garnet isochron initial values and bulkrock Lu-Hf and Sm-Nd isotope systematics indicating significant decoupling from the Hf-Nd terrestrial array. However, because this material is not readily subducted, this strongly decoupled signature is unlikely to be transferred into deep Earth. Mixing calculations aimed at developing a clearer understanding of what factors control decoupling of a sample's Lu-Hf and Sm-Nd systematics from the Hf-Nd terrestrial array highlight the complexity of mass-transfer regimes operating in the subduction environment.

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Tectonic significance and redox state of Paleoproterozoic eclogite and pyroxenite components in the Slave cratonic mantle lithosphere, Voyageur kimberlite, Arctic Canada

Cited by 35 publications

References 142 publications

Evidence for a dominantly reducing Archaean ambient mantle from two redox proxies, and low oxygen fugacity of deeply subducted oceanic crust

Evidence for a dominantly reducing Archaean ambient mantle from two redox proxies, and low oxygen fugacity of deeply subducted oceanic crust

Ultramafic Carbonated Melt‐ and Auto‐Metasomatism in Mantle Eclogites: Compositional Effects and Geophysical Consequences

Lu-Hf and Sm-Nd geochronological constraints on the influence of subduction metamorphism in controlling the Hf-Nd terrestrial array: Evidence from the world’s orogenic belts

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