Kimberlite genesis from a common carbonate-rich primary melt modified by lithospheric mantle assimilation

Giuliani, Andrea; Pearson, D. Graham; Soltys, Ashton; Dalton, Hayden; Phillips, David; Foley, Stephen F.; Lim, Emilie; Goemann, Karsten; Griffin, William L.; Mitchell, Roger H.

doi:10.1126/sciadv.aaz0424

Cited by 92 publications

(39 citation statements)

References 50 publications

(119 reference statements)

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“…The recent experimental work of Chowdury and Dasgupta 61 on the concentration of S at sulfide saturation in carbonate-rich silicate melts provides a potential theoretical framework in support of our hypothesis. Assimilation of silicate mantle wall rocks ubiquitously affect CO 2 -rich silicate magmas during their ascent through the lithospheric mantle 62 , 63 . This process results in an increase of SiO 2 contents in alkaline mafic/ultramafic magmas and, therefore, lowers the solubility of CO 2 , which is inversely related to SiO 2 concentrations 60 .…”

Section: Discussionmentioning

confidence: 99%

Fluxing of mantle carbon as a physical agent for metallogenic fertilization of the crust

et al. 2020

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Magmatic systems play a crucial role in enriching the crust with volatiles and elements that reside primarily within the Earth's mantle, including economically important metals like nickel, copper and platinum-group elements. However, transport of these metals within silicate magmas primarily occurs within dense sulfide liquids, which tend to coalesce, settle and not be efficiently transported in ascending magmas. Here we show textural observations, backed up with carbon and oxygen isotope data, which indicate an intimate association between mantle-derived carbonates and sulfides in some mafic-ultramafic magmatic systems emplaced at the base of the continental crust. We propose that carbon, as a buoyant supercritical CO 2 fluid, might be a covert agent aiding and promoting the physical transport of sulfides across the mantle-crust transition. This may be a common but cryptic mechanism that facilitates cycling of volatiles and metals from the mantle to the lower-to-mid continental crust, which leaves little footprint behind by the time magmas reach the Earth's surface.

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Section: Discussionmentioning

confidence: 99%

Fluxing of mantle carbon as a physical agent for metallogenic fertilization of the crust

et al. 2020

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“…To understand if primitive mantle is preserved in the deep Earth and sampled by kimberlites (19) and constrain its relationship to the LLSVPs, here we interrogate an Sr-Nd-Hf isotope compilation of kimberlites and closely related magmatic rocks named ultramafic lamprophyres, which were emplaced in the upper crust since 2.06 Ga. These carbonate-rich, silica-poor magmas are generated by low-degree partial melting of the sublithospheric (i.e., convecting) mantle beneath thick continental regions (cratons and surrounding belts) (23)(24)(25). Crustal assimilation in these magmas is limited by their rapid ascent, lack of processing in magma chambers, and high mantle-incompatible trace element concentrations.…”

Section: Significancementioning

confidence: 99%

Remnants of early Earth differentiation in the deepest mantle-derived lavas

Giuliani

Jackson

Dalton

2020

Proc. Natl. Acad. Sci. U.S.A.

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The noble gas isotope systematics of ocean island basalts suggest the existence of primordial mantle signatures in the deep mantle. Yet, the isotopic compositions of lithophile elements (Sr, Nd, Hf) in these lavas require derivation from a mantle source that is geochemically depleted by melt extraction rather than primitive. Here, this apparent contradiction is resolved by employing a compilation of the Sr, Nd, and Hf isotope composition of kimberlites—volcanic rocks that originate at great depth beneath continents. This compilation includes kimberlites as old as 2.06 billion years and shows that kimberlites do not derive from a primitive mantle source but sample the same geochemically depleted component (where geochemical depletion refers to ancient melt extraction) common to most oceanic island basalts, previously called PREMA (prevalent mantle) or FOZO (focal zone). Extrapolation of the Nd and Hf isotopic compositions of the kimberlite source to the age of Earth formation yields a143Nd/144Nd-176Hf/177Hf composition within error of chondrite meteorites, which include the likely parent bodies of Earth. This supports a hypothesis where the source of kimberlites and ocean island basalts contains a long-lived component that formed by melt extraction from a domain with chondritic143Nd/144Nd and176Hf/177Hf shortly after Earth accretion. The geographic distribution of kimberlites containing the PREMA component suggests that these remnants of early Earth differentiation are located in large seismically anomalous regions corresponding to thermochemical piles above the core–mantle boundary. PREMA could have been stored in these structures for most of Earth’s history, partially shielded from convective homogenization.

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“…Assimilation of lithospheric mantle material, which is ubiquitous in kimberlites (e.g., ref. 31), can be ruled out because the lithospheric mantle traversed and entrained by kimberlites is highly refractory (32) and, hence, highly depleted in W. This contrasts with the W-rich nature inferred for the kimberlitic parental melts. Further, no evidence currently indicates that lithospheric mantle is characterized by negative μ 182 W values.…”

Section: Discussionmentioning

confidence: 94%

Tungsten-182 evidence for an ancient kimberlite source

Nakanishi

Giuliani

Carlson

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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Globally distributed kimberlites with broadly chondritic initial 143Nd-176Hf isotopic systematics may be derived from a chemically homogenous, relatively primitive mantle source that remained isolated from the convecting mantle for much of the Earth’s history. To assess whether this putative reservoir may have preserved remnants of an early Earth process, we report 182W/184W and 142Nd/144Nd data for “primitive” kimberlites from 10 localities worldwide, ranging in age from 1,153 to 89 Ma. Most are characterized by homogeneous μ182W and μ142Nd values averaging −5.9 ± 3.6 ppm (2SD, n = 13) and +2.7 ± 2.9 ppm (2SD, n = 6), respectively. The remarkably uniform yet modestly negative μ182W values, coupled with chondritic to slightly suprachondritic initial 143Nd/144Nd and 176Hf/177Hf ratios over a span of nearly 1,000 Mya, provides permissive evidence that these kimberlites were derived from one or more long-lived, early formed mantle reservoirs. Possible causes for negative μ182W values among these kimberlites include the transfer of W with low μ182W from the core to the mantle source reservoir(s), creation of the source reservoir(s) as a result of early silicate fractionation, or an overabundance of late-accreted materials in the source reservoir(s). By contrast, two younger kimberlites emplaced at 72 and 52 Ma and characterized by distinctly subchondritic initial 176Hf/177Hf and 143Nd/144Nd have μ182W values consistent with the modern upper mantle. These isotopic compositions may reflect contamination of the ancient kimberlite source by recycled crustal components with μ182W ≥ 0.

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Kimberlite genesis from a common carbonate-rich primary melt modified by lithospheric mantle assimilation

Cited by 92 publications

References 50 publications

Fluxing of mantle carbon as a physical agent for metallogenic fertilization of the crust

Fluxing of mantle carbon as a physical agent for metallogenic fertilization of the crust

Remnants of early Earth differentiation in the deepest mantle-derived lavas

Tungsten-182 evidence for an ancient kimberlite source

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