Boron recycling in the mantle: Evidence from a global comparison of ocean island basalts

Walowski, K. J.; Kirstein, Linda A.; Hoog, Jan C.M. De; Elliott, Tim; Savov, Ivan P.; Jones, Rebecca; Eimf,

doi:10.1016/j.gca.2021.03.017

Cited by 21 publications

(14 citation statements)

References 80 publications

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“…Understanding the form of boron‐hydrogen in olivine is important for predicting its stability, its effect on properties and also for tracer studies. Boron is an important geochemical tracer due to its two common isotopes which can be used to examine the origin of boron‐containing rocks (e.g., see Cannao, 2020; Clarke et al., 2020; McCaig et al., 2018; Walowski et al., 2021). Understanding the structure of boron in olivine is important for predicting this partitioning with 11 B generally favoring trigonal sites and 10 B generally favoring tetrahedral sites.…”

Section: Introductionmentioning

confidence: 99%

Extremely Stable, Highly Conductive Boron‐Hydrogen Complexes in Forsterite and Olivine

et al. 2022

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Olivine is an important component of Earth's upper mantle and one that controls many of its properties. The presence of extrinsic defects/elements can affect these properties, however, and thus these need to be understood. One element that could be present on defective sites and that could have large effects is boron. The effect of boron on the properties of olivine has been previously ignored due to the fact that boron is largely incompatible in olivine. Most recovered/natural olivine samples have very low concentrations (<0.5 wt ppm) of boron (Kent & Rossman, 2002;Ottolini et al., 2004) and the general boron concentration of the bulk silicate earth (<0.19) and primitive (<0.19 wt. ppm) and depleted mantle (<0.07 wt. ppm) is low (Marschall et al., 2017). Boron partitions heavily from olivine into melts (K ∼ 0.001-0.05) (Ottolini et al., 2009) and so partial melting will deplete olivine of boron. Despite this olivines with very high boron concentrations (23-2,100 wt. ppm) have been found (

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Section: Introductionmentioning

confidence: 99%

Extremely Stable, Highly Conductive Boron‐Hydrogen Complexes in Forsterite and Olivine

et al. 2022

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“…Isotopically light boron signatures in hotspot lavas have been broadly interpreted as sampling crustal boron in their sources (Walowski et al., 2019, 2021). This scenario is consistent with the standard view that (a) OIBs contain materials recycled from the surface of the Earth (Hofmann & White, 1982); (b) boron is exclusively hosted in the crust/seawater (De Hoog & Savov, 2018); and (c) the magnitude of equilibrium isotope fractionation – scaling with T −2 (Schauble, 2004) – is expected to be negligible at high T of the deep Earth.…”

Section: Discussionmentioning

confidence: 99%

“…To explore potential core components in the mantle sources responsible for the isotopically light boron in OIB, we assemble a global set of OIB δ 11 B data (Chaussidon & Marty, 1995;Hartley et al, 2021;Kobayashi et al, 2004;Marschall & Jackson, 2020;Walowski et al, 2021), together with μ 182 W (deviation of 182 W/ 184 W from the terrestrial Alfa Aesar W standard in ppm) data (Jackson et al, 2020;Mundl-Petermeier et al, 2020) from nine volcanic hotspots (Table S8 in Supporting Information S1). Negative μ 182 W anomalies have been traditionally used as fingerprints of the core (e.g., Rizo et al, 2019) and a correlation between δ 11 B and μ 182 W may support the core as a B reservoir.…”

Section: Core Contributions To Anomalous δ 11 B In Oceanic Hotspotsmentioning

confidence: 99%

Possible Control of Earth's Boron Budget by Metallic Iron

Yuan

Steinle‐Neumann

2022

Geophysical Research Letters

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Boron is considered a principal tracer for crustal recycling into the depleted mantle, and high boron anomalies and isotopically light boron ( 10 B) in mantle-derived samples have been interpreted as the result of subduction. Using density functional theory, we predict that boron behavior changes from lithophile to siderophile, with the calculated boron partition coefficients (D m/s ) between liquid metal and silicate ranging from log 10 D m/s ≤ −0.8 at low pressure-temperature conditions (10 GPa, 3000 K) to log 10 D m/s ≥ 3.7 at high pressure and temperature (130 GPa, 5000 K). We further predict that the silicate becomes enriched in the heavier boron isotope ( 11 B) by >1‰ relative to metal at high pressure-temperature. Our results suggest that Earth's core may hold >50% of Earth's boron budget and that a high boron content in deep diamonds and isotopically light boron in ocean islands basalts may reflect contributions from metallic reservoirs, rather than being attributed to crustal subduction and recycling.Plain Language Summary Plate tectonics promotes the transport of surface rocks into the mantle, producing much of its chemical heterogeneity. Boron, a quintessential crustal element, is often used as a proxy for crustal contributions when found in mantle rocks and is, therefore, one of the central tools in geochemistry to trace recycling/mixing in the mantle. Using quantum mechanical calculations, we find that the chemical behavior of boron changes from lithophile (rock-loving) to siderophile (iron-loving) under pressure-temperature conditions relevant to core formation. Thus, much boron may have been transported to the core, and the core may be Earth's largest boron reservoir, rather than the crust. Chemical heterogeneity in the mantle inferred from boron signatures could therefore also result from chemical exchange between the core and mantle or equilibration with metallic iron dispersed throughout the mantle.

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“…By focusing on the most depleted quartile of Icelandic basalts (which have similar La/Yb to MORBs), one can more precisely compare the B characteristics of depleted values by slab-derived fluid or arc melts (Walowski et al, 2021). Finally, the low B/Ce, depleted compositions, and MORB-like δ 11 B values of the melt inclusions may reflect the composition of recycled depleted, and devolatilized slab gabbros (Stracke et al, 2003a).…”

Section: Boron Characteristics Of the Depleted Componentmentioning

confidence: 99%

“…H, O, N, Mg, Cl, Fe, Zn, Tl) (e.g. Blusztajn et al, 2018;Hartley et al, 2021;Walowski et al, 2021Walowski et al, , 2019Wang et al, 2018).…”

Section: Introductionunclassified

Boron isotope evidence for devolatilized and rehydrated recycled materials in the Icelandic mantle source

Marshall¹,

Ranta²,

Halldórsson³

et al. 2022

Preprint

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Enriched mantle heterogeneities are widely considered to be generated through subduction, but the connections between specific subducted materials and the chemical signatures of mantle heterogeneities are not clearly defined. Boron is strongly isotopically fractionated at the surface and traces slab devolatilization, making it a potent tracer of previously subducted and recycled materials. Here, we present high-precision SIMS boron concentrations and isotope ratios on a comprehensive suite of quenched basaltic glasses from all neovolcanic zones in Iceland, two rhyolite glasses, and a set of primitive melt inclusions from central Iceland. Boron isotope ratios (δ11B) in Icelandic basalts and melt inclusions range from -11.6‰ to -1.0‰, averaging -4.9‰, which is higher than mid-ocean ridge basalt (MORB; δ11B = -7.1‰). Because the δ11B value of the Icelandic crust is low, the high δ11B compositions of the Icelandic lavas are not easily explained through crustal assimilation processes. Icelandic basalt glass and melt inclusion B/Ce and δ11B values correlate with trace element ratio indicators of the degree of mantle partial melting and mantle heterogeneity (e.g. Nb/Zr, La/Yb, Sm/Yb), which indicate that the boron systematics of basalts are controlled by mantle heterogeneity. Additionally, basalts with low B/Ce have high 206Pb/204Pb, further indicating mantle source control. These correlations can be used to deduce the boron systematics of the individual Icelandic mantle components. The enriched endmember within the Iceland mantle source has a high δ11B value and low B/Ce, consistent with the composition of “rehydrated” recycled oceanic crust. The depleted endmember comprises multiple distinct components with variable B/Ce, likely consisting of depleted MORB mantle and/or high 3He/4He mantle and two more minor depleted components that are consistent with recycled metasomatized mantle wedge and recycled slab gabbro.The compositions of these components place constraints on the devolatilization history of recycled oceanic crust. The high δ11B value and low B/Ce composition of the enriched component within the Iceland mantle source is inconsistent with a simple devolatilization process and suggests that the recycled oceanic crust component may have been isotopically overprinted by B-rich fluids derived from the underlying hydrated slab lithospheric mantle (i.e. “rehydration”). Further, the B/Ce and δ11B systematics of other OIBs can be used to constrain the devolatilization histories of recycled components on a global scale. Globally, most OIB B/Ce compositions suggest that recycled components have lost >99% of their boron, and their δ11B values suggest that rehydration may be a sporadic process, and not ubiquitous.

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Boron recycling in the mantle: Evidence from a global comparison of ocean island basalts

Cited by 21 publications

References 80 publications

Extremely Stable, Highly Conductive Boron‐Hydrogen Complexes in Forsterite and Olivine

Extremely Stable, Highly Conductive Boron‐Hydrogen Complexes in Forsterite and Olivine

Possible Control of Earth's Boron Budget by Metallic Iron

Boron isotope evidence for devolatilized and rehydrated recycled materials in the Icelandic mantle source

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