The influence of the low-high quartz transformation on recrystallization and grain growth during contact metamorphism (Traversella intrusion, North Italy) |
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| Authors: | R Wirth |
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| Abstract: | Recrystallization and grain growth of quartz occur only within 35 m of the contact. This limit of recrystallization and grain growth coincides with an inferred maximum temperature of 620 ± 20°C, which at about 6–7 km is the temperature for the low-high quartz transformation. The remarkable coincidence of the temperature of about 620°C for the beginning of recrystallization and grain growth with the transformation temperature of quartz is explained by the atomic displacement mechanism of the low-high quartz transformation. The already disordered structure of the grain boundary becomes even more distorted by the fluctuations of the SiO4 tetrahedra during the low-high quartz transformation. This results in an increase of the number of atoms which are transferred from one grain into the grain boundary, and from the grain boundary to the other grain. A lowering of the activation energy for grain boundary migration results such that grain boundary migration becomes the most important process for recrystallization and grain growth. |
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