Adsorption- and desorption-controlled magnesium isotope fractionation during extreme weathering of basalt in Hainan Island, China

Huang, Kangjun; Teng, Fang‐Zhen; Wei, Gangjian; Ma, Jinlong; Bao, Zhengyu

doi:10.1016/j.epsl.2012.10.007

Cited by 167 publications

(85 citation statements)

References 82 publications

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“…5). These changes are fairly large, varying between −3 and +0.5 ‰, which is approximately the modern range of rivers Tipper et al, 2006bTipper et al, , 2008Tipper et al, , 2012de Villiers et al, 2005;Huang et al, 2012;Wimpenny et al, 2011). However, given that the dominant control over the δ 26 Mg of rivers is the lithology undergoing weathering (isotopically light carbonates, and heavy silicates), this would require that during most of the Oligocene and late Miocene rivers, were dominated by carbonate weathering, Figure 5.…”

Section: A Cenozoic Seawater Reconstruction Based On Foraminiferal Camentioning

confidence: 99%

“…The flux-weighted mean riverine input has a δ 26 Mg (‰ deviation of the sample 26 Mg / 24 Mg ratio from the standard DSM-3) of −1.09 ± 0.05 ‰ that is intermediate between that of silicate and carbonate sources. Additional fractionation is caused by Mg uptake into plants, or into secondary minerals formed during weathering (Tipper et al, 2010(Tipper et al, , 2006a(Tipper et al, , b, 2008Pogge von Strandmann et al, 2008Teng et al, 2010a, b;Huang et al, 2012;Black et al, 2006;Bolou-Bi et al, 2012. Modern oceans, which are isotopically uniform (Foster et al, 2010;Young and Galy, 2004), have an isotope ratio (−0.83 ± 0.01 ‰) close to the riverine input.…”

Section: Introductionmentioning

confidence: 99%

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Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

2014

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Abstract. Magnesium is an element critically involved in the carbon cycle, because weathering of Ca-Mg silicates removes atmospheric CO 2 into rivers, and formation of Ca-Mg carbonates in the oceans removes carbon from the oceanatmosphere system. Hence the Mg cycle holds the potential to provide valuable insights into Cenozoic climate-system history, and the shift during this time from a greenhouse to icehouse state. We present Mg isotope ratios for the past 40 Myr using planktic foraminifers as an archive. Modern foraminifera, which discriminate against elemental and isotopically heavy Mg during calcification, show no correlation between the Mg isotope composition (δ 26 Mg, relative to DSM-3) and temperature, Mg / Ca or other parameters such as carbonate saturation ( CO 3 ). However, inter-species isotopic differences imply that only well-calibrated single species should be used for reconstruction of past seawater. Seawater δ 26 Mg inferred from the foraminiferal record decreased from ∼ 0 ‰ at 15 Ma, to −0.83 ‰ at the present day, which coincides with increases in seawater lithium and oxygen isotope ratios. It strongly suggests that neither Mg concentrations nor isotope ratios are at steady state in modern oceans, given its ∼ 10 Myr residence time. From these data, we have developed a dynamic box model to understand and constrain changes in Mg sources to the oceans (rivers) and Mg sinks (dolomitisation and hydrothermal alteration). Our estimates of seawater Mg concentrations through time are similar to those independently determined by pore waters and fluid inclusions. Modelling suggests that dolomite formation and the riverine Mg flux are the primary controls on the δ 26 Mg of seawater, while hydrothermal Mg removal and the δ 26 Mg of rivers are more minor controls. Using Mg riverine flux and isotope ratios inferred from the 87 Sr / 86 Sr record, the modelled Mg removal by dolomite formation shows minima in the Oligocene and at the present day (with decreasing trends from 15 Ma), both coinciding with rapid decreases in global temperatures.

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Section: A Cenozoic Seawater Reconstruction Based On Foraminiferal Camentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

2014

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“…4), but the general trend in  Huang et al, 2012;Liu et al, 2014;Teng et al, 2010;Tipper et al, 2010 (Wimpenny et al, 2014).…”

Section: Fractionating Geochemical Reactions Within the Regolithmentioning

confidence: 99%

The influence of critical zone processes on the Mg isotope budget in a tropical, highly weathered andesitic catchment

Lara

Buss

Strandmann

et al. 2017

Geochimica et Cosmochimica Acta

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In order to assess the effects of critical zone processes on Mg concentrations and isotopic signatures of tropical streams, we studied a well constrained, highly weathered andesitic volcaniclastic catchment in the Luquillo Critical Zone Observatory, Puerto Rico. Our results indicate that dissolved Mg concentrations and isotope ratios in the regolith pore water are mainly controlled by rain input, with weathering inputs being more important at sites with thinner regolith (2.7 to 0.9 m deep) and at

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“…It is well known that the variation of Mg isotope compositions is limited during high-temperature geological processes (Teng et al 2007(Teng et al , 2010aHandler et al 2009;Yang et al 2009;Bourdon et al 2010;Dauphas et al 2010;Pogge von Strandmann et al 2011;Xiao et al 2013), but is quite large during low-temperature processes (Pogge von Strandmann et al 2008;Teng et al 2010b;Tipper et al 2010;Huang et al 2012;Liu et al 2014). Just like other fluid-mobile elements, Mg displays a highly variable and remarkably discrepant isotope composition in the upper continental crust (Shen et al 2009;Huang et al 2013) and the hydrosphere (Tipper et al 2006;Foster et al 2010;Ling et al 2011) when compared with the relatively homogeneous mantle (d 26 Mg = -0.25 ± 0.07‰, Teng et al 2010a).…”

mentioning

confidence: 99%

“…Just like other fluid-mobile elements, Mg displays a highly variable and remarkably discrepant isotope composition in the upper continental crust (Shen et al 2009;Huang et al 2013) and the hydrosphere (Tipper et al 2006;Foster et al 2010;Ling et al 2011) when compared with the relatively homogeneous mantle (d 26 Mg = -0.25 ± 0.07‰, Teng et al 2010a). The main processes responsible for such large isotopic variation are continental weathering and/or carbonate deposition that occurred among sedimentary systems/ upper continental crust and hydrosphere (Pogge von Strandmann et al 2008;Teng et al 2010b;Tipper et al 2010;Huang et al 2012;Liu et al 2014). During continental weathering, light Mg isotopes favor the hydrosphere to weathered residue, whereas during carbonate deposition, light Mg isotopes prefer carbonate minerals to the hydrosphere.…”

mentioning

confidence: 99%

The deep continental crust has a larger Mg isotopic variation than previously thought

Zhang

2016

American Mineralogist

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Magnesium isotope compositions of the bulk continental crust is a key to understand Mg isotope behaviors during crustal processes, and is the prerequisite to study mantle-crust material exchange/reaction by Mg isotopes. However, thus far, little is known about Mg isotopic compositions of the middle and lower continental crust. In the article by Yang et al. in this issue entitled "Magnesium isotopic composition of the deep continental crust," the authors present high-precision Mg isotopic analyses of highgrade metamorphic terrane samples and granulite xenoliths from China, which represent the middle and lower continental crust, respectively. Large Mg isotopic variation is observed in the deep continental crust, reflecting the combination of several processes, such as continental weathering, involvement of supracrustal materials, and fluid metasomatism. In addition, this article also provides an average Mg isotope composition of the bulk continental crust, which is crucial to future applications of Mg isotopes.

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Adsorption- and desorption-controlled magnesium isotope fractionation during extreme weathering of basalt in Hainan Island, China

Cited by 167 publications

References 82 publications

Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

The influence of critical zone processes on the Mg isotope budget in a tropical, highly weathered andesitic catchment

The deep continental crust has a larger Mg isotopic variation than previously thought

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