Alteration of Feldspathoids Changes pH of Late-Magmatic Fluids: A Case Study from the Lovozero Peralkaline Massif, Russia
The 360-370-Ma-old Lovozero peralkaline massif (NW Russia) is a layered nepheline syenitic–foidolitic pluton. In the rocks of the massif, late-stage (auto)metasomatic alterations of rock-forming minerals are quite intense. We studied the products of the alteration of nepheline and sodalite via micro...
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MDPI AG
2022-12-01
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| Series: | Minerals |
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| author | Julia A. Mikhailova Yakov A. Pakhomovsky Lyudmila M. Lyalina Ekaterina A. Selivanova |
| author_facet | Julia A. Mikhailova Yakov A. Pakhomovsky Lyudmila M. Lyalina Ekaterina A. Selivanova |
| author_sort | Julia A. Mikhailova |
| collection | DOAJ |
| description | The 360-370-Ma-old Lovozero peralkaline massif (NW Russia) is a layered nepheline syenitic–foidolitic pluton. In the rocks of the massif, late-stage (auto)metasomatic alterations of rock-forming minerals are quite intense. We studied the products of the alteration of nepheline and sodalite via microtextural, microprobe, and spectroscopic methods. We found that these minerals are extensively replaced by the association between natrolite + nordstrandite ± böhmite ± paranatrolite in accordance with the following reactions: 3Nph + 4H<sub>2</sub>O → Ntr + Nsd + NaOH; 6Nph + 9H<sub>2</sub>O → Ntr + Pntr + 2Nsd + 2NaOH; Sdl + 4H<sub>2</sub>O → Ntr + Nsd + NaOH + NaCl, where Nph is nepheline, Ntr is natrolite, Nsd is nordstrandite, Pntr is paranatrolite, and Sdl is sodalite. As a result, about one-third of the sodium from nepheline (and sodalite) is set free and passes into the fluid. This leads to an increase in the Na/Cl ratio and, hence, the pH of the fluid. An increase in pH stabilizes hyperagpaitic minerals (e.g., ussingite, villiaumite, thermonatrite, and trona), which can crystallize in close proximity to pseudomorphized nepheline and sodalite. Thus, the alteration of feldspathoids increases the pH of late-magmatic fluids, which in turn can lead to the crystallization of hyperagpaitic minerals. |
| first_indexed | 2024-03-09T11:38:30Z |
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| issn | 2075-163X |
| language | English |
| last_indexed | 2024-03-09T11:38:30Z |
| publishDate | 2022-12-01 |
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| record_format | Article |
| series | Minerals |
| spelling | doaj.art-b923e80da5e94668917283a8ce68b5342023-11-30T23:38:57ZengMDPI AGMinerals2075-163X2022-12-011313910.3390/min13010039Alteration of Feldspathoids Changes pH of Late-Magmatic Fluids: A Case Study from the Lovozero Peralkaline Massif, RussiaJulia A. Mikhailova0Yakov A. Pakhomovsky1Lyudmila M. Lyalina2Ekaterina A. Selivanova3Geological Institute, Kola Science Centre, Russian Academy of Sciences, 184209 Apatity, RussiaGeological Institute, Kola Science Centre, Russian Academy of Sciences, 184209 Apatity, RussiaGeological Institute, Kola Science Centre, Russian Academy of Sciences, 184209 Apatity, RussiaGeological Institute, Kola Science Centre, Russian Academy of Sciences, 184209 Apatity, RussiaThe 360-370-Ma-old Lovozero peralkaline massif (NW Russia) is a layered nepheline syenitic–foidolitic pluton. In the rocks of the massif, late-stage (auto)metasomatic alterations of rock-forming minerals are quite intense. We studied the products of the alteration of nepheline and sodalite via microtextural, microprobe, and spectroscopic methods. We found that these minerals are extensively replaced by the association between natrolite + nordstrandite ± böhmite ± paranatrolite in accordance with the following reactions: 3Nph + 4H<sub>2</sub>O → Ntr + Nsd + NaOH; 6Nph + 9H<sub>2</sub>O → Ntr + Pntr + 2Nsd + 2NaOH; Sdl + 4H<sub>2</sub>O → Ntr + Nsd + NaOH + NaCl, where Nph is nepheline, Ntr is natrolite, Nsd is nordstrandite, Pntr is paranatrolite, and Sdl is sodalite. As a result, about one-third of the sodium from nepheline (and sodalite) is set free and passes into the fluid. This leads to an increase in the Na/Cl ratio and, hence, the pH of the fluid. An increase in pH stabilizes hyperagpaitic minerals (e.g., ussingite, villiaumite, thermonatrite, and trona), which can crystallize in close proximity to pseudomorphized nepheline and sodalite. Thus, the alteration of feldspathoids increases the pH of late-magmatic fluids, which in turn can lead to the crystallization of hyperagpaitic minerals.https://www.mdpi.com/2075-163X/13/1/39feldspathoidssecondary alterationLovozero massifnatrolite |
| spellingShingle | Julia A. Mikhailova Yakov A. Pakhomovsky Lyudmila M. Lyalina Ekaterina A. Selivanova Alteration of Feldspathoids Changes pH of Late-Magmatic Fluids: A Case Study from the Lovozero Peralkaline Massif, Russia Minerals feldspathoids secondary alteration Lovozero massif natrolite |
| title | Alteration of Feldspathoids Changes pH of Late-Magmatic Fluids: A Case Study from the Lovozero Peralkaline Massif, Russia |
| title_full | Alteration of Feldspathoids Changes pH of Late-Magmatic Fluids: A Case Study from the Lovozero Peralkaline Massif, Russia |
| title_fullStr | Alteration of Feldspathoids Changes pH of Late-Magmatic Fluids: A Case Study from the Lovozero Peralkaline Massif, Russia |
| title_full_unstemmed | Alteration of Feldspathoids Changes pH of Late-Magmatic Fluids: A Case Study from the Lovozero Peralkaline Massif, Russia |
| title_short | Alteration of Feldspathoids Changes pH of Late-Magmatic Fluids: A Case Study from the Lovozero Peralkaline Massif, Russia |
| title_sort | alteration of feldspathoids changes ph of late magmatic fluids a case study from the lovozero peralkaline massif russia |
| topic | feldspathoids secondary alteration Lovozero massif natrolite |
| url | https://www.mdpi.com/2075-163X/13/1/39 |
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