Phosphorus and aluminum zoning in olivine: contrasting behavior of two nominally incompatible trace elements

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Publicado en:Contributions to Mineralogy and Petrology vol. 174, no. 10 (Oct 2019), p. 1
Autor principal: Shea, Thomas
Otros Autores: Hammer, Julia E, Hellebrand, Eric, Mourey, Adrien J, Costa, Fidel, First, Emily C, Lynn, Kendra J, Melnik, Oleg
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Springer Nature B.V.
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100 1 |a Shea, Thomas  |u Department of Earth Sciences, SOEST, University of Hawaii at Mānoa, Honolulu, USA 
245 1 |a Phosphorus and aluminum zoning in olivine: contrasting behavior of two nominally incompatible trace elements 
260 |b Springer Nature B.V.  |c Oct 2019 
513 |a Journal Article 
520 3 |a Phosphorus zoning in olivine is receiving considerable attention for its capacity to preserve key information about rates and mechanisms of crystal growth. Its concentration can vary significantly over sub-micron spatial scales and form intricate, snowflake-like patterns that are generally attributed to fast crystal growth. Ostensibly similar aluminum enrichment patterns have also been observed, suggesting comparable incorporation and partitioning behavior for both elements. We perform 1-atm crystallization experiments on a primitive Kīlauea basalt to examine the formation of P and Al zoning as a function of undercooling − ΔT (− ΔT = Tliquidus − Tcrystallization) during olivine growth. After 24 h spent at Tinitial = 1290 °C (10 °C above olivine stability), charges are rapidly cooled to final temperatures Tfinal = 1220–1270 °C, corresponding to undercoolings − ΔT  = 10–60 °C (with Tliquidus = 1280 °C). Compositional X-ray maps of experimental olivine reveal that only a small undercooling (≤ 25 °C) is required to produce the fine-scale enrichments in P and Al associated with skeletal growth. Concentration profiles indicate that despite qualitatively similar enrichment patterns in olivine, P and Al have contrasting apparent crystal/melt mass distribution coefficients of \[K_{\text{P}}^{{{\text{ol}}/{\text{melt}}}}\] = 0.01‒1 and \[K_{\text{P}}^{{{\text{ol}}/{\text{melt}}}}\] = 0.002‒0.006. Phosphorus can be enriched by a factor > 40-fold in the same crystal, whereas Al enrichment never exceed factors of 2. Glass in the vicinity of synthetic and natural olivine is usually enriched in Al, but, within analytical uncertainty, not in P. Thus, we find no direct evidence for a compositional boundary layer enriched in P that would suffice to produce P enrichments in natural and synthetic olivine. Numerical models combining growth and diffusion resolve the conditions at which Al-rich boundary layers produce the observed enrichment patterns in olivine. In contrast, the same models fail to reproduce the observed P enrichments, consistent with our observation that P-rich boundary layers are insignificant. If instead, P olivine/melt partitioning is made to depend on growth rate, models adequately reproduce our observations of 40-fold enrichment without boundary layer formation. We surmise that near-partitionless behavior (\[K_{\text{P}}^{{{\text{ol}}/{\text{melt}}}}\] close to 1) of P is related to the olivine lattice being perhaps less stiff in accommodating P during rapid crystallization, and/or to enhanced formation of vacancy defects during fast growth. Our results confirm that P is a robust marker of initial rapid growth, but reveal that the undercooling necessary to induce these enrichments is not particularly large. The near-ubiquitous process of magma mixing under volcanoes, for instance, is likely sufficient to induce low-to-moderate degrees of undercooling required for skeletal growth. 
653 |a Zoning 
653 |a Trace elements 
653 |a Boundary layers 
653 |a Crystallization 
653 |a Phosphorus 
653 |a Aluminum 
653 |a Growth rate 
653 |a Uncertainty analysis 
653 |a Partitioning 
653 |a Basalt 
653 |a Stability 
653 |a Crystal growth 
653 |a Mass distribution 
653 |a Crystal defects 
653 |a Diffusion layers 
653 |a Aluminium 
653 |a Robustness (mathematics) 
653 |a Magma 
653 |a Defects 
653 |a Lava 
653 |a Olivine 
653 |a Lattice vacancies 
653 |a Maps 
653 |a Volcanoes 
653 |a Enrichment 
653 |a Profiles 
653 |a Coefficients 
653 |a Numerical models 
653 |a Mathematical models 
653 |a Supercooling 
653 |a Mineralogy 
653 |a Petrology 
653 |a Environmental 
700 1 |a Hammer, Julia E  |u Department of Earth Sciences, SOEST, University of Hawaii at Mānoa, Honolulu, USA 
700 1 |a Hellebrand, Eric  |u Department of Earth Sciences, SOEST, University of Hawaii at Mānoa, Honolulu, USA; Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands 
700 1 |a Mourey, Adrien J  |u Department of Earth Sciences, SOEST, University of Hawaii at Mānoa, Honolulu, USA 
700 1 |a Costa, Fidel  |u Earth Observatory of Singapore, Nanyang Technological University, Singapore, Singapore 
700 1 |a First, Emily C  |u Brown University, DEEPS, Providence, USA 
700 1 |a Lynn, Kendra J  |u Department of Geological Sciences, University of Delaware, Newark, USA 
700 1 |a Melnik, Oleg  |u Institute of Mechanics, Moscow State University, Moscow, Russia 
773 0 |t Contributions to Mineralogy and Petrology  |g vol. 174, no. 10 (Oct 2019), p. 1 
786 0 |d ProQuest  |t Science Database 
856 4 1 |3 Citation/Abstract  |u https://www.proquest.com/docview/2300521653/abstract/embedded/7BTGNMKEMPT1V9Z2?source=fedsrch 
856 4 0 |3 Full Text - PDF  |u https://www.proquest.com/docview/2300521653/fulltextPDF/embedded/7BTGNMKEMPT1V9Z2?source=fedsrch