In-situ observation of the crystallization kinetics and texture evolution of basalts
Final Report Abstract
The crystallization kinetics of different basaltic melts (K-rich basalt, MORB, alkali basalt) was studied by in-situ observation in a moissanite cell at 1 bar. Main observations made in all systems are: (1) Nucleation of new phases (e.g. olivine, clinopyroxene) always occurs only in short events; (2) growth rates of crystals are size-dependent (proportionate growth); (3) Ostwald ripening removes small crystal fractions. Overall, these observations show that the interpretation of igneous textures by conventional CSD (crystal size distribution) theory is severely flawed and needs revision. In the course of this study, it was observed that the moissanite cell is very well suited for observing processes of bubble nucleation and growth in silicate melts. Therefore, these processes were studied in a range of rhyolitic to basaltic systems, first at 1 bar with the conventional moissanite cell; later, a new “hydrothermal” moissanite cell was developed, which allows precise control of pressure and temperature. With this new cell, a number of novel experiments were carried out that allowed the direct observation of the behavior of bubbles both during periodic (sinusoidal) pressure fluctuations and during decompression. The experiments suggest that bubble nucleation in silicate melts requires less supersaturation than previously thought. The importance of Ostwald ripening for the evolution of bubble size distributions was directly demonstrated.
Publications
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(2014) In situ observation of crystal growth in a basalt melt and the development of crystal size distribution in igneous rocks. Contrib Mineral Petrol 167: Article Number: 1003
Ni H, Keppler H, Walte N, Schiavi F, Chen Y, Masotta M, Li ZJ
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(2014) In situ observations of bubble growth in basaltic, andesitic and rhyodacitic melts. Contrib Mineral Petrol 167: Article Number: 976
Masotta M, Ni H, Keppler H
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(2017) A new hydrothermal moissanite cell apparatus for optical in-situ observations at high pressure and high temperature, with applications to bubble nucleation in silicate melts. Am Mineral 102: 2022–2031
Masotta M, Keppler H
