Relaxation of concentration variance: A new tool to measure chemical element mobility during mixing of magmas
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| Title: | Relaxation of concentration variance: A new tool to measure chemical element mobility during mixing of magmas |
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| Authors: | Perugini, D.1,2 diegop@unipg.it, De Campos, C.P.2, Dingwell, D.B.2, Dorfman, A.2 |
| Source: | Chemical Geology. Jan2013, Vol. 335, p8-23. 16p. |
| Subjects: | Analysis of variance, Variances, Chemical elements, Magmas, Silicate minerals, Phase transitions, Crystal growth |
| Abstract: | Abstract: The ability of chemical elements to diffuse in silicate melts is central to igneous processes. It controls the rates of phase transitions such as crystal growth and dissolution kinetics, the rate of homogenization of compositional gradients generated by fractional crystallization and assimilation of country rocks as well as one of the most intriguing processes of all, magma mixing. A very useful measure, commonly used to quantify the rate of homogenization of chemical elements in silicate melts, is the diffusion coefficient. It is widely approximated to be of a constant value (at a fixed pressure and temperature) for a melt with a given composition and rheology. When dealing with magma mixing processes, melts with different initial compositions and rheological properties (e.g. basalt and rhyolite) coexist in the same system. Under such circumstances, the compositional and rheological dependence of diffusion coefficients must be considered, leading to a considerable increase of complexity in the modeling of magma mixing. Yet, an additional and even more dramatic increase in complexity is due to the fact that the mixing of magmas is undoubtedly a very dynamic process. Scale-invariant distributions of filaments of different melts are generated by stretching and folding dynamics. This has a dual effect on the mobility of chemical elements. On the one hand their mobility increases because of an exponential increase of contact area. On the other hand, mobility can be buffered by the different diffusivities in the melts (larger in the low-viscosity than in the high-viscosity melt). Uphill diffusion of chemical elements is likely to develop at the interface between interacting magmas, further increasing the complexity of the process. Here we aim to understand chemical element mobility during melt homogenization in a magma mixing event under dynamic conditions. We have performed experiments by mixing phonolitic and alkali-basaltic melts. The mixing process was induced using a high-temperature centrifuge apparatus. The rotating speed and acceleration during all experiments were 1850rpm and 1000g, respectively. Experiments were performed for 5, 20 and 120min. Samples were arranged in a buoyantly unstable geometry, with the denser material placed at the inner side of the rotating circle, resulting in injection of the mafic melt into the felsic melt during rotation. The temperature during experimental runs was 1200 (±1)°C. From the resultant glasses, vortex-like structures generated by repeated stretching and folding dynamics were observed at the interface between the two melts. The concentrations of major and trace elements were then measured along interfaces by electron microprobe and LA-ICP-MS. The mobility of each element was next quantified by calculating the decrease (or relaxation) of concentration variance with time. The first notable result is that for major and trace elements, concentrations variance decays exponentially. The exponent of the exponential function is then chosen as a measure of element mobility. Our results show clearly that different chemical elements homogenize in the melt at differing rates. Amongst the major elements Na is the fastest element followed by Al, Mg, Ca, K and Si. The trace elements, Ba, Rb, Sr, Nb and Zr exhibit similar mobilities. The REE display the lowest mobility and they show a systematic decrease from light to heavy. The results from this study indicate that the decay of concentration variance is a robust tool for obtaining new insights into chemical exchanges during the mixing of silicate melts. Concentration variance includes in a single measure an expression of the influence of all possible factors (e.g. viscosity, composition, fluid-dynamic regime) controlling the mobility of chemical elements during the mixing of two liquids. A new parameter, the Relaxation of Concentration Variance (RCV), is proposed as an effective tool for quantifying the homogenization of chemical elements during the mixing of silicate melts. [Copyright &y& Elsevier] |
| Copyright of Chemical Geology is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | Engineering Source |
| FullText | Text: Availability: 0 |
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| Header | DbId: egs DbLabel: Engineering Source An: 84597920 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: Relaxation of concentration variance: A new tool to measure chemical element mobility during mixing of magmas – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Perugini%2C+D%2E%22">Perugini, D.</searchLink><relatesTo>1,2</relatesTo><i> diegop@unipg.it</i><br /><searchLink fieldCode="AR" term="%22De+Campos%2C+C%2EP%2E%22">De Campos, C.P.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Dingwell%2C+D%2EB%2E%22">Dingwell, D.B.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Dorfman%2C+A%2E%22">Dorfman, A.</searchLink><relatesTo>2</relatesTo> – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Chemical+Geology%22">Chemical Geology</searchLink>. Jan2013, Vol. 335, p8-23. 16p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Analysis+of+variance%22">Analysis of variance</searchLink><br /><searchLink fieldCode="DE" term="%22Variances%22">Variances</searchLink><br /><searchLink fieldCode="DE" term="%22Chemical+elements%22">Chemical elements</searchLink><br /><searchLink fieldCode="DE" term="%22Magmas%22">Magmas</searchLink><br /><searchLink fieldCode="DE" term="%22Silicate+minerals%22">Silicate minerals</searchLink><br /><searchLink fieldCode="DE" term="%22Phase+transitions%22">Phase transitions</searchLink><br /><searchLink fieldCode="DE" term="%22Crystal+growth%22">Crystal growth</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: Abstract: The ability of chemical elements to diffuse in silicate melts is central to igneous processes. It controls the rates of phase transitions such as crystal growth and dissolution kinetics, the rate of homogenization of compositional gradients generated by fractional crystallization and assimilation of country rocks as well as one of the most intriguing processes of all, magma mixing. A very useful measure, commonly used to quantify the rate of homogenization of chemical elements in silicate melts, is the diffusion coefficient. It is widely approximated to be of a constant value (at a fixed pressure and temperature) for a melt with a given composition and rheology. When dealing with magma mixing processes, melts with different initial compositions and rheological properties (e.g. basalt and rhyolite) coexist in the same system. Under such circumstances, the compositional and rheological dependence of diffusion coefficients must be considered, leading to a considerable increase of complexity in the modeling of magma mixing. Yet, an additional and even more dramatic increase in complexity is due to the fact that the mixing of magmas is undoubtedly a very dynamic process. Scale-invariant distributions of filaments of different melts are generated by stretching and folding dynamics. This has a dual effect on the mobility of chemical elements. On the one hand their mobility increases because of an exponential increase of contact area. On the other hand, mobility can be buffered by the different diffusivities in the melts (larger in the low-viscosity than in the high-viscosity melt). Uphill diffusion of chemical elements is likely to develop at the interface between interacting magmas, further increasing the complexity of the process. Here we aim to understand chemical element mobility during melt homogenization in a magma mixing event under dynamic conditions. We have performed experiments by mixing phonolitic and alkali-basaltic melts. The mixing process was induced using a high-temperature centrifuge apparatus. The rotating speed and acceleration during all experiments were 1850rpm and 1000g, respectively. Experiments were performed for 5, 20 and 120min. Samples were arranged in a buoyantly unstable geometry, with the denser material placed at the inner side of the rotating circle, resulting in injection of the mafic melt into the felsic melt during rotation. The temperature during experimental runs was 1200 (±1)°C. From the resultant glasses, vortex-like structures generated by repeated stretching and folding dynamics were observed at the interface between the two melts. The concentrations of major and trace elements were then measured along interfaces by electron microprobe and LA-ICP-MS. The mobility of each element was next quantified by calculating the decrease (or relaxation) of concentration variance with time. The first notable result is that for major and trace elements, concentrations variance decays exponentially. The exponent of the exponential function is then chosen as a measure of element mobility. Our results show clearly that different chemical elements homogenize in the melt at differing rates. Amongst the major elements Na is the fastest element followed by Al, Mg, Ca, K and Si. The trace elements, Ba, Rb, Sr, Nb and Zr exhibit similar mobilities. The REE display the lowest mobility and they show a systematic decrease from light to heavy. The results from this study indicate that the decay of concentration variance is a robust tool for obtaining new insights into chemical exchanges during the mixing of silicate melts. Concentration variance includes in a single measure an expression of the influence of all possible factors (e.g. viscosity, composition, fluid-dynamic regime) controlling the mobility of chemical elements during the mixing of two liquids. A new parameter, the Relaxation of Concentration Variance (RCV), is proposed as an effective tool for quantifying the homogenization of chemical elements during the mixing of silicate melts. [Copyright &y& Elsevier] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Chemical Geology is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1016/j.chemgeo.2012.10.050 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 16 StartPage: 8 Subjects: – SubjectFull: Analysis of variance Type: general – SubjectFull: Variances Type: general – SubjectFull: Chemical elements Type: general – SubjectFull: Magmas Type: general – SubjectFull: Silicate minerals Type: general – SubjectFull: Phase transitions Type: general – SubjectFull: Crystal growth Type: general Titles: – TitleFull: Relaxation of concentration variance: A new tool to measure chemical element mobility during mixing of magmas Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Perugini, D. – PersonEntity: Name: NameFull: De Campos, C.P. – PersonEntity: Name: NameFull: Dingwell, D.B. – PersonEntity: Name: NameFull: Dorfman, A. IsPartOfRelationships: – BibEntity: Dates: – D: 06 M: 01 Text: Jan2013 Type: published Y: 2013 Identifiers: – Type: issn-print Value: 00092541 Numbering: – Type: volume Value: 335 Titles: – TitleFull: Chemical Geology Type: main |
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