Behavior of calcium isotopes during continental subduction recorded in meta-basaltic rocks

Lu, Wenning; He, Yongsheng; Wang, Yang; Ke, Shaoyong

doi:10.1016/j.gca.2019.09.027

Cited by 27 publications

(10 citation statements)

References 81 publications

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“…Our results, as described in more detail below, show that seawater and marine carbonates (including SRM915a) have higher ε Ca relative to oceanic basalts and deep-sea hydrothermal fluid. These results contradict those of Caro et al (2010) and confirm earlier inferences that modern seawater Ca is dominated by continental fluxes. − ,, Our results are also in agreement with a number of other studies where ε Ca differences between mantle rocks and carbonate standard SRM915a were noted but not firmly established. − In the remainder of the manuscript, we compare these new data to measurements reported in previous studies and discuss various approaches to estimating Ca fluxes, their uncertainties, and their implications for seawater ε Ca through time.…”

Section: Introductionsupporting

confidence: 86%

Radiogenic ⁴⁰Ca in Seawater: Implications for Modern and Ancient Ca Cycles

Antonelli

DePaolo

Christensen

et al. 2021

ACS Earth Space Chem.

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Radiogenic 40Ca is preferentially concentrated in the continental crust through the decay of radioactive 40K and may have the potential to be used as a tracer for Ca fluxes to the ocean through time. Numerous published flux estimates suggest that rivers are the dominant source of Ca to the oceans. This conflicts, however, with conclusions drawn from previous radiogenic Ca data suggesting that seawater Ca has been dominated by weathering/hydrothermal alteration of oceanic crust throughout Earth history. We attempt to address this discrepancy by carrying out a larger number of radiogenic Ca measurements on materials that represent modern seawater, marine carbonates, and ocean floor basalt. We find that the 40Ca/44Ca composition of the oceanic crust and mantle appear to be different from modern seawater and marine carbonates, such that the latter are measurably enriched in radiogenic 40Ca (εCa = +1.1 ± 0.3, 2SE) relative to basalts and deep-sea hydrothermal fluid. This observation is consistent with most other data available in the literature. The results are also consistent with Sr isotope data and confirm that continental sources of Ca (mainly from rivers and groundwater) dominate the modern seawater budget. We find that off-axis Ca fluxes from the low temperature alteration of the oceanic crust are not large enough to change this balance. The Ca isotope data measured and compiled here also suggest that bulk-silicate earth 40Ca/44Ca is 1.2 ± 0.3 ε-units lower than reference material SRM915a and that variations in seawater εCa in the geologic past are likely too small to be resolved with current analytical techniques.

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Section: Introductionsupporting

confidence: 86%

Radiogenic ⁴⁰Ca in Seawater: Implications for Modern and Ancient Ca Cycles

Antonelli

DePaolo

Christensen

et al. 2021

ACS Earth Space Chem.

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“…While Ca isotopic anomalies in mantle‐derived basalts are often interpreted to be the consequence of recycled sedimentary carbonates (Huang et al., 2011; Liu et al., 2017), the behavior of Ca isotopes during slab dehydration remains poorly constrained. Prograde metamorphism in subduction zones likely fails to induce significant Ca isotopic fractionation (Lu et al., 2019), which contrasts with the results of C‐bearing fluid transfer (John et al., 2012). This difference probably indicates that Ca isotopic fractionation occurs with the transfer of slab fluids.…”

Section: Introductionmentioning

confidence: 99%

Calcium Stable Isotopes of Tonga and Mariana Arc Lavas: Implications for Slab Fluid‐Mediated Carbonate Transfer in Cold Subduction Zones

Wang

Liu

et al. 2021

JGR Solid Earth

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Carbonation of oceanic lithosphere occurs widely during seawater alteration, and subducted carbonated oceanic lithosphere may play a key role in carbon recycling in subduction zones. Here we investigate the Ca isotopic composition of arc lavas from the Tonga rear arc and Mariana arc, western Pacific, to explore the effect of fluid‐mediated carbonate transfer in subduction zones. Fresh basalts (0.84 ± 0.01‰, 2sd, n = 3) and dacites (0.84 ± 0.10‰, 2sd, n = 9) from the Tonga rear arc show indistinguishable δ44/40Ca, reflecting negligible Ca isotopic fractionation during differentiation of hydrous arc magmas. More importantly, arc lavas from both the Tonga rear arc (0.84 ± 0.09‰, 2sd, n = 12) and Mariana arc (0.79 ± 0.12‰, 2sd, n = 9) display MORB‐like δ44/40Ca values. The MORB‐like δ44/40Ca of arc lavas indicates that the carbonates released from altered oceanic lithosphere (AOL) do not significantly modify the Ca isotopic composition of the mantle wedge, although extensive volcanic CO2 degassing at both arcs suggests that slab fluids might introduce abundant carbonate into the depleted mantle wedge. These results could be attributed to a limited Ca budget in the slab fluids added to the mantle wedge and/or homogenization effect of variable δ44/40Ca for the slab fluids. At cold subduction zones, a fraction of carbonates from the AOL may survive during slab dehydration and recycle into the deep mantle.

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“…It thus seems that Ca isotopic fractionation can occur during metamorphism. However, Lu et al (2020) proposed that metamorphic rocks would most likely inherit the isotopic compositions of their protolith, and that prograde metamorphism dehydration cannot significantly fractionate Ca isotopes. To further explore the mechanism of Ca isotopic fractionation during metamorphism, more work needs to be carried out.…”

Section: Calcium Isotopic Ratios Of Metamorphic Rocksmentioning

confidence: 99%

Calcium Isotope Ratios (δ^44/40Ca) of Thirty‐Four Geological Chinese Reference Materials Measured by Thermal Ionisation Mass Spectrometry

Liu

Zhang

et al. 2022

Geostandard Geoanalytic Res

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High-precision calcium isotopic ratios of thirty-four Chinese geological reference materials, including igneous, metamorphic and sedimentary rocks, river/marine sediments and soils, are reported. Measurements were conducted by thermal ionisation mass spectrometry (Triton TIMS) using a 42 Ca-43 Ca double spike. These reference materials cover a wide range of chemical compositions with CaO ranging from 0.10 to 51.1% m/m. The δ 44/40 Ca variation of igneous rocks was up to 0.75‰, ranging from 0.61 AE 0.06‰ to 1.35 AE 0.04‰. Two metamorphic rocks yielded δ 44/40 Ca of 0.39 AE 0.02‰ and 0.86 AE 0.02‰, respectively. δ 44/40 Ca values of sedimentary rocks varied from -0.14 AE 0.09‰ to 0.98 AE 0.12‰, suggesting significant isotopic fractionation during low-temperature processes. Like sedimentary rocks, river/marine sediments and soil displayed large Ca isotopic variations, with δ 44/40 Ca spanning from 0.12 AE 0.06‰ to 0.77 AE 0.03‰ and -0.09 AE 0.11‰ to 0.74 AE 0.08‰, respectively. The comprehensive data set reported in this study serves as a reference for quality assurance and inter-laboratory comparison for high-precision Ca isotopic studies.

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Behavior of calcium isotopes during continental subduction recorded in meta-basaltic rocks

Cited by 27 publications

References 81 publications

Radiogenic ⁴⁰Ca in Seawater: Implications for Modern and Ancient Ca Cycles

Radiogenic ⁴⁰Ca in Seawater: Implications for Modern and Ancient Ca Cycles

Calcium Stable Isotopes of Tonga and Mariana Arc Lavas: Implications for Slab Fluid‐Mediated Carbonate Transfer in Cold Subduction Zones

Calcium Isotope Ratios (δ^44/40Ca) of Thirty‐Four Geological Chinese Reference Materials Measured by Thermal Ionisation Mass Spectrometry

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Behavior of calcium isotopes during continental subduction recorded in meta-basaltic rocks

Cited by 27 publications

References 81 publications

Radiogenic 40Ca in Seawater: Implications for Modern and Ancient Ca Cycles

Radiogenic 40Ca in Seawater: Implications for Modern and Ancient Ca Cycles

Calcium Stable Isotopes of Tonga and Mariana Arc Lavas: Implications for Slab Fluid‐Mediated Carbonate Transfer in Cold Subduction Zones

Calcium Isotope Ratios (δ44/40Ca) of Thirty‐Four Geological Chinese Reference Materials Measured by Thermal Ionisation Mass Spectrometry

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About

Radiogenic ⁴⁰Ca in Seawater: Implications for Modern and Ancient Ca Cycles

Radiogenic ⁴⁰Ca in Seawater: Implications for Modern and Ancient Ca Cycles

Calcium Isotope Ratios (δ^44/40Ca) of Thirty‐Four Geological Chinese Reference Materials Measured by Thermal Ionisation Mass Spectrometry