Silicon isotope homogeneity in the mantle

Savage, Paul S.; Georg, R. Bastian; Armytage, R. M. G.; Williams, Helen M.; Halliday, Alex N.

doi:10.1016/j.epsl.2010.03.035

Cited by 146 publications

(173 citation statements)

References 40 publications

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“…1; Savage et al, 2010) and studies show that mafic and ultramafic igneous rocks appear to show little variation from this value (e.g. Fitoussi et al, 2009;Zambardi et al, 2009;Savage et al, 2010;Armytage et al, 2011). Despite this, and in contrast to many stable isotope systems that show little resolvable isotope fractionation as a result of high-temperature igneous processes, i.e.…”

Section: Introductionmentioning

confidence: 94%

“…The d 30 Si value (using NBS28 as the bracketing standard; see Section 3.2 for definition) of Bulk Silicate Earth (BSE) is À0.29 ± 0.08& ( Fig. 1; Savage et al, 2010) and studies show that mafic and ultramafic igneous rocks appear to show little variation from this value (e.g. Fitoussi et al, 2009;Zambardi et al, 2009;Savage et al, 2010;Armytage et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

“…Magmatic differentiation enriches more silica-rich samples in the heavier isotopes. Also shown is the Si isotope value for Bulk Silicate Earth (BSE, square symbol, Savage et al, 2010). Georg et al (2009); granitic protolith data are taken from Ziegler et al (2005b).…”

Section: Introductionmentioning

confidence: 99%

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The silicon isotope composition of granites

Savage

Georg

Williams

et al. 2012

Geochimica et Cosmochimica Acta

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Because weathering results in preferential incorporation of the lighter Si isotopes into clay minerals, the Si in magmas derived from (meta)sedimentary lithologies enriched in such phases should also be isotopically light, relative to melts derived from igneous sources. With the advent of new high precision techniques it should therefore be possible to resolve such differences. Hence, Si isotopes have to potential to distinguish between, and characterise, different magmatic source regions.To explore this, here we report the Si isotopic compositions of a suite of Phanerozoic I-, S-and A-type granites and mineral separates, as well as samples of associated country rock. The whole-rock data fall between δ30Si = −0.40 and −0.11 ± 0.04‰ (95% s.e.). This range is more limited than that defined by previous low precision measurements of granites, but is significantly broader than that displayed by more recent, high precision, measurements of high-Si extrusive igneous rocks. As predicted, S-type granites are, on average, isotopically lighter than I-and A-type samples, and negative correlations with alumina saturation index (ASI) values and initial 87Sr/86Sr provide evidence that Si isotope variations in granites can be explained by variable incorporation of an enriched sedimentary component. However, the relatively small isotopic perturbations and apparent degree of overlap between granite affinities suggest that Si isotopes are not as sensitive to sedimentary input, relative to more established proxies such as, for example, O isotopes. The average Si isotope value of all granites analysed in this study is δ30Si = −0.23 ± 0.15‰ (2 s.d.), which is entirely consistent with a recently published estimate for the continental crust, based on an andesitic bulk composition and the well defined relationship between Si isotopes and magmatic fractionation. AbstractBecause weathering results in preferential incorporation of the lighter Si isotopes into clay minerals, the Si in magmas derived from (meta)sedimentary lithologies enriched in such phases should also be isotopically light, relative to melts derived from igneous sources. With the advent of new high precision techniques it should therefore be possible to resolve such differences. Hence, Si isotopes have to potential to distinguish between, and characterise, different magmatic source regions.To explore this, here we report the Si isotopic compositions of a suite of Phanerozoic I-, S-and A-type granites and mineral separates, as well as samples of associated country rock. The whole-rock data fall between d 30 Si = À0.40 and À0.11 ± 0.04& (95% s.e.). This range is more limited than that defined by previous low precision measurements of granites, but is significantly broader than that displayed by more recent, high precision, measurements of high-Si extrusive igneous rocks. As predicted, Stype granites are, on average, isotopically lighter than I-and A-type samples, and negative correlations with alumina saturation index (ASI) values and initial 87 Sr/ 86 Sr provide e...

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Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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The silicon isotope composition of granites

Savage

Georg

Williams

et al. 2012

Geochimica et Cosmochimica Acta

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“…While pristine (unweathered) silicate rocks usually display uniform Si isotopic compositions on continents (d 30 Si $ À0.3 ± 0.2‰; e.g. Savage et al, 2010Savage et al, , 2012), their alteration leads to weathering products having very distinctive Si isotopic ratios: a dissolved pool characterized by positive d 30 Si values (up to $+4.7‰; e.g. De la https://doi.org/10.1016/j.gca.2018.03.015 0016-7037/Ó 2018 Elsevier Ltd. All rights reserved.…”

Section: Introductionmentioning

confidence: 99%

The silicon isotopic composition of fine-grained river sediments and its relation to climate and lithology

Bayon

Delvigne

Ponzevera

et al. 2018

Geochimica et Cosmochimica Acta

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The d 30 Si stable isotopic composition of silicon in soils and fine-grained sediments can provide insights into weathering processes on continents, with important implications on the Si budget of modern and past oceans. To further constrain the factors controlling the distribution of Si isotopes in sediments, we have analysed a large number (n = 50) of separate size-fractions of sediments and suspended particulate materials collected near the mouth of rivers worldwide. This includes some of the world's largest rivers (e.g. Amazon, Congo, Mackenzie, Mississippi, Murray-Darling, Nile, Yangtze) and rivers from the case study areas of the Congo River Basin and Northern Ireland. Silt-size fractions exhibit a mean Si isotopic composition (d 30 Si = À0.21 ± 0.19‰; 2 s.d.) similar to that previously inferred for the upper continental crust. In contrast, clay-size fractions display a much larger range of d 30 Si values from À0.11‰ to À2.16‰, which yield a global d 30 Si clay of À0.57 ± 0.60‰ (2 s.d.) representative of the mean composition of the average weathered continental crust. Overall, these new data show that the Si isotopic signature transported by river clays is controlled by the degree of chemical weathering, as inferred from strong relationships with Al/Si ratios. At a global scale, the clay-bound Si isotopic composition of the world's largest river systems demonstrates a link with climate, defining a general correlation with mean annual temperature (MAT) in corresponding drainage basins. While the distribution of Si isotopes in river sediments also appears to be influenced by the tectonic setting, lithological effects and sediment recycling from former sedimentary cycles, our results pave the way for their use as paleo-weathering and paleo-climate proxies in the sedimentary record.

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“…4 (Georg et al, 2007;Fitoussi et al, 2009;Ziegler et al, 2010;Chakrabarti & Jacobsen, 2010;Armytage et al, 2011Armytage et al, , 2012Savage & Moynier, 2013; see recent compilation by Savage et al, 2014). The average δ 30 Si isotopic signature of terrestrial mantle rocks is estimated to be -0.29‰ ± 0.07‰, 2 SD (Douthitt, 1982;Georg et al 2007;Fitoussi et al, 2009;Ziegler et al, 2010;Savage et al, 2010;Chakrabarti & Jacobsen, 2010;Armytage et al, 2011Armytage et al, , 2012Savage & Moynier, 2013;Savage et al, 2014;see Fig. 4).…”

Section: The Role Of Si Stable Isotopesmentioning

confidence: 99%

Silicon stable isotope fractionation between metal and silicate at high-pressure, high-temperature conditions as a tracer of planetary core formation

Kempl

Vroon

Wagt

et al. 2016

Netherlands Journal of Geosciences

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The largest differentiation event in Earth and other terrestrial planets was the high-pressure, high-temperature process of metal core segregation from a silicate mantle. The abundant element silicon (Si) can be partially sequestered into the metallic core during metal-silicate differentiation, depending on pressure, temperature and planetary oxidation state. Knowledge of the Si content of a planet's core can constrain the conditions of core formation, but in the absence of direct samples from planetary cores, quantifying core Si content is challenging. One relatively new tool to study core formation in terrestrial planets is based on combining measurements of the Si stable isotopic composition of planetary crust and mantle samples with measurements of the Si stable isotope fractionation between metal and silicate at high-temperature and high-pressure conditions. In this study we present the results of a small set of high-pressure, high-temperature (HPT) experiments and combine these with a review of literature data to investigate how the Si isotope fractionation behaviour between metal and silicate varies as a function specifically of experimental run time and temperature. We show that although there is no debate about the sign of fractionation, absolute values for Si isotope fractionation between metal and silicate are difficult to constrain because the experimental database remains incomplete, and because Si isotopic measurements of metals in particular suffer from the absence of a true inter-laboratory comparison. We conclude that in order to derive accurate quantitative estimates of the Si content of the core of the Earth or other planets a wide range of additional experiments will be required.

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Silicon isotope homogeneity in the mantle

Cited by 146 publications

References 40 publications

The silicon isotope composition of granites

The silicon isotope composition of granites

The silicon isotopic composition of fine-grained river sediments and its relation to climate and lithology

Silicon stable isotope fractionation between metal and silicate at high-pressure, high-temperature conditions as a tracer of planetary core formation

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