Diffusion of Sr and Ba in plagioclase: Composition and silica activity dependencies, and application to volcanic rocks

IF 4.8 1区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Thomas Grocolas , Elias M. Bloch , Anne-Sophie Bouvier , Othmar Müntener
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In all of the reported experiments, silica activity (<em>a</em>SiO<sub>2</sub>) is buffered by varying stable phase assemblages in the diffusant source powder. The experimental products were analysed by secondary ion mass spectrometry (SIMS) depth profiling and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) line scanning. There is no resolvable dependence of Sr and Ba diffusion in plagioclase upon <em>a</em>SiO<sub>2</sub> or crystal orientation. However, Sr and Ba diffusivities are found to vary as functions of the plagioclase anorthite content. As such, we parameterise the diffusivity of Sr and Ba in plagioclase as a function of temperature and anorthite content as follows:<span><span><span><math><mrow><msub><mi>log</mi><mn>10</mn></msub><msub><mi>D</mi><mtext>Sr</mtext></msub><mspace></mspace><mrow><mo>(</mo><mrow><msup><mrow><mi>m</mi></mrow><mn>2</mn></msup><mspace></mspace><msup><mrow><mi>s</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow><mo>)</mo></mrow><mo>=</mo><mo>−</mo><mn>1.65</mn><mspace></mspace><mrow><mo>(</mo><mrow><mo>±</mo><mn>0.24</mn></mrow><mo>)</mo></mrow><mspace></mspace><msub><mi>X</mi><mtext>An</mtext></msub><mo>−</mo><mn>3.03</mn><mspace></mspace><mrow><mo>(</mo><mrow><mo>±</mo><mn>1.16</mn></mrow><mo>)</mo></mrow><mo>−</mo><mrow><mo>[</mo><mfrac><mrow><mn>368</mn><mo>,</mo><mn>142</mn><mspace></mspace><mo>(</mo><mrow><mo>±</mo><mn>27</mn><mo>,</mo><mn>141</mn></mrow><mo>)</mo></mrow><mrow><mn>2.303</mn><mi>R</mi><mi>T</mi></mrow></mfrac><mo>]</mo></mrow><mo>,</mo></mrow></math></span></span></span><span><span><span><math><mrow><msub><mi>log</mi><mn>10</mn></msub><msub><mi>D</mi><mtext>Ba</mtext></msub><mrow><mo>(</mo><mrow><msup><mrow><mi>m</mi></mrow><mn>2</mn></msup><mspace></mspace><msup><mrow><mi>s</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow><mo>)</mo></mrow><mo>=</mo><mo>−</mo><mn>1.43</mn><mspace></mspace><mrow><mo>(</mo><mrow><mo>±</mo><mn>0.20</mn></mrow><mo>)</mo></mrow><mspace></mspace><msub><mi>X</mi><mtext>An</mtext></msub><mo>−</mo><mn>4.65</mn><mspace></mspace><mrow><mo>(</mo><mrow><mo>±</mo><mn>0.96</mn></mrow><mo>)</mo></mrow><mo>−</mo><mrow><mo>[</mo><mfrac><mrow><mn>337</mn><mo>,</mo><mn>037</mn><mspace></mspace><mo>(</mo><mrow><mo>±</mo><mn>22</mn><mo>,</mo><mn>969</mn></mrow><mo>)</mo></mrow><mrow><mn>2.303</mn><mi>R</mi><mi>T</mi></mrow></mfrac><mo>]</mo></mrow><mo>,</mo></mrow></math></span></span></span>where <em>X</em><sub>An</sub> is the plagioclase anorthite content (mole fraction), <em>T</em> is the temperature (K), and <em>R</em> is the gas constant (J mol<sup>-1</sup> K<sup>-1</sup>). The diffusion rate of Sr in plagioclase determined in this study is ∼1.5–2 orders of magnitude slower than previously determined, whereas Ba diffusion is similar to previous studies. This is most likely due to the Ba-feldspar stability at the experimental conditions employed by previous studies, whereas Sr-feldspar was absent from the source powder assemblage. By applying the diffusivities determined in this study to plagioclase crystals from the Cerro Galán ignimbrite (Argentina) and Santorini caldera (Greece), we find timescales of ∼10<sup>5</sup> years, with a good agreement between results from Sr and Ba diffusion modelling. Therefore, our data reconcile experimental diffusion data with measured Sr and Ba profiles in plagioclase and suggest that, at least regarding the Cerro Galán ignimbrite and Santorini caldera, plagioclase records the time needed to differentiate magma reservoirs and assemble large volumes of eruptible magma.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"651 ","pages":"Article 119141"},"PeriodicalIF":4.8000,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Earth and Planetary Science Letters","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0012821X24005739","RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0

Abstract

Strontium and barium diffusion chronometry in plagioclase is routinely applied to mafic and felsic magmatic systems. This technique can be used to determine the timescales of magma reservoir assembly and the cooling rates of plutons and volcanic rocks, which has emerged as a useful method to assess volcanic hazards. Here we report diffusion experiments that aim to constrain the diffusivities of Sr and Ba in oligoclase and labradorite at 1 atm pressure, between 900 and 1,200 °C, and assessing diffusion in different crystallographic orientations. In all of the reported experiments, silica activity (aSiO2) is buffered by varying stable phase assemblages in the diffusant source powder. The experimental products were analysed by secondary ion mass spectrometry (SIMS) depth profiling and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) line scanning. There is no resolvable dependence of Sr and Ba diffusion in plagioclase upon aSiO2 or crystal orientation. However, Sr and Ba diffusivities are found to vary as functions of the plagioclase anorthite content. As such, we parameterise the diffusivity of Sr and Ba in plagioclase as a function of temperature and anorthite content as follows:log10DSr(m2s1)=1.65(±0.24)XAn3.03(±1.16)[368,142(±27,141)2.303RT],log10DBa(m2s1)=1.43(±0.20)XAn4.65(±0.96)[337,037(±22,969)2.303RT],where XAn is the plagioclase anorthite content (mole fraction), T is the temperature (K), and R is the gas constant (J mol-1 K-1). The diffusion rate of Sr in plagioclase determined in this study is ∼1.5–2 orders of magnitude slower than previously determined, whereas Ba diffusion is similar to previous studies. This is most likely due to the Ba-feldspar stability at the experimental conditions employed by previous studies, whereas Sr-feldspar was absent from the source powder assemblage. By applying the diffusivities determined in this study to plagioclase crystals from the Cerro Galán ignimbrite (Argentina) and Santorini caldera (Greece), we find timescales of ∼105 years, with a good agreement between results from Sr and Ba diffusion modelling. Therefore, our data reconcile experimental diffusion data with measured Sr and Ba profiles in plagioclase and suggest that, at least regarding the Cerro Galán ignimbrite and Santorini caldera, plagioclase records the time needed to differentiate magma reservoirs and assemble large volumes of eruptible magma.
Sr和Ba在斜长石中的扩散:组成和二氧化硅活性依赖关系及其在火山岩中的应用
斜长石中的锶钡扩散计时法通常应用于镁质和长英质岩浆系统。该技术可用于确定岩浆储层组合的时间尺度以及岩体和火山岩的冷却速率,已成为评估火山危险性的一种有用方法。在这里,我们报告了扩散实验,旨在限制Sr和Ba在低晶长石和拉布拉多石中在1atm压力下,900至1200°C之间的扩散,并评估了不同晶体取向的扩散。在所有报道的实验中,二氧化硅活性(aSiO2)被扩散源粉末中不同的稳定相组合所缓冲。采用二次离子质谱(SIMS)深度谱和激光烧蚀电感耦合质谱(LA-ICP-MS)谱线扫描对实验产物进行分析。斜长石中Sr和Ba的扩散与aSiO2或晶体取向没有明显的关系。Sr和Ba扩散系数随斜长石钙长石含量的变化而变化。因此,我们将斜长石中Sr和Ba的扩散系数参数化为温度和钙长石含量的函数如下:log10DSr(m2s−1)=−1.65(±0.24)XAn−3.03(±1.16)−[368,142(±27,141)2.303RT],log10DBa(m2s−1)=−1.43(±0.20)XAn−4.65(±0.96)−[337,037(±22,969)2.303RT],其中XAn为斜长石钙长石含量(摩尔分数),T为温度(K), R为气体常数(J mol-1 K-1)。本研究中测定的Sr在斜长石中的扩散速率比以前测定的慢了~ 1.5-2个数量级,而Ba的扩散与以前的研究相似。这很可能是由于先前研究中采用的实验条件下ba长石的稳定性,而sr长石在源粉组合中缺失。通过将本研究确定的扩散系数应用于Cerro Galán火成岩(阿根廷)和Santorini火山口(希腊)的斜长石晶体,我们发现了~ 105年的时间尺度,Sr和Ba扩散模型的结果非常吻合。因此,我们的数据将实验扩散数据与斜长石中测量的Sr和Ba剖面相一致,并表明,至少对于Cerro Galán火成岩和圣托里尼火山口,斜长石记录了区分岩浆储层和聚集大量可喷发岩浆所需的时间。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Earth and Planetary Science Letters
Earth and Planetary Science Letters 地学-地球化学与地球物理
CiteScore
10.30
自引率
5.70%
发文量
475
审稿时长
2.8 months
期刊介绍: Earth and Planetary Science Letters (EPSL) is a leading journal for researchers across the entire Earth and planetary sciences community. It publishes concise, exciting, high-impact articles ("Letters") of broad interest. Its focus is on physical and chemical processes, the evolution and general properties of the Earth and planets - from their deep interiors to their atmospheres. EPSL also includes a Frontiers section, featuring invited high-profile synthesis articles by leading experts on timely topics to bring cutting-edge research to the wider community.
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