The kinetic control of crystal growth in geological reactions: An example of olivine–ilmenite assemblage

doi:10.3390/min15060569

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DOI Доступ к ресурсу на сайте издателя			10.3390/min15060569

Title: The kinetic control of crystal growth in geological reactions: An example of olivine–ilmenite assemblage
Creator: Borisova, Anastassia Y.
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Lozovoy, Kirill A.
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Pugliara, Alessandro
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Hungria, Teresa
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Josse, Claudie
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Parseval, Philippe de
Date: 2025
DOI: 10.3390/min15060569
Description: The main constituent of the planetary lithosphere is the dominant silicate mineral, olivine α-(Mg,Fe)2SiO4, which, along with associated minerals and the olivine-hosted inclusions, records the physical–chemical conditions during the crystal growth and transport to the planetary surface. However, there is a lack of physical–chemical information regarding the kinetic factors that regulate crystal growth during melt–rock, fluid–rock, and magma–rock interactions. Here, we conducted an experimental reaction between hydrated peridotite rock and basaltic melt and coupled this with a structural and elemental analysis of the quenched products by high-resolution transmission electron microscopy. The quenched products revealed crystallographically oriented oxide nanocrystals of ilmenite (Fe,Mg)(Ti,Si)O3 that grew over the newly formed olivine in the boundary layer melt of the reaction zone. We established that the growth mechanism is epitaxial and is common to both experimental and natural systems. The kinetic model developed for shallow (<1 GPa) crystal growth requires open system conditions and the presence of melt or fluid. It implies that the current geodynamic models that consider natural ilmenite–olivine assemblage as a proxy for deep to ultra-deep (>>1 GPa) conditions should be revised. The resulting kinetic model has a wide range of geological implications—from disequilibrium mineral growth and olivine-hosted inclusion production to mantle metasomatism—and helps to clarify how geological reactions proceed at depth.