Gem Elbaite as a Recorder of Pegmatite Evolution: In Situ Major, Trace Elements and Boron Isotope Analysis of a Colour-Zoning Tourmaline Crystal
Few studies have focused on gem-quality tourmaline acting as a petrogenetic recorder, and the colour genesis of pink elbaite is still controversial. We carry out in situ major, trace element and boron isotope composition analyses on a single tourmaline crystal. This crystal is characterized by sudde...
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| Autores principales: | , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
MDPI AG
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/2a87756dca924462965d8b853916a457 |
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| Sumario: | Few studies have focused on gem-quality tourmaline acting as a petrogenetic recorder, and the colour genesis of pink elbaite is still controversial. We carry out in situ major, trace element and boron isotope composition analyses on a single tourmaline crystal. This crystal is characterized by sudden transformation from colourless to pink, which can represent full pegmatite magma evolution. According to the analysis results, all spots are divided into alkali groups according to X-site occupancy and subdivided into elbaite series. The pink part accommodates higher concentrations of volatile and incompatible elements. The result is most consistent with successive pegmatite evolution in which the colourless part crystallized from the early stage, while the pink part crystallized from the late stage. The relatively consistent δ<sup>11</sup>B value between the colourless and the pink part suggests no fluid exsolution occurred during pegmatite evolution. The slight increase of δ<sup>11</sup>B values within the pink part and the colourless part may be due to mica crystallization. The combination of (Li<sup>+</sup>+Mn<sup>2+</sup>) (Al<sup>3+</sup>+X<sub>vac</sub>)-<sub>1</sub> and the exclusive positive linear relationship of Mn<sup>2+</sup> vs. Ti<sup>4+</sup> indicate that Mn<sup>2+</sup> is the main cause of pink, while Mn<sup>2+</sup>-Ti<sup>4+</sup> intervalence charge transfer also plays an important role. |
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