Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization

摘要: Crystal size distributions (CSDs) measured in metamorphic rocks yield quantitative information about crystal nucleation and growth rates, times, the degree of overstepping (ΔT) reactions during metamorphism. CSDs are described through use a population density function n=dN/dL, where N is cumulative number crystals per unit volume L linear size. Plots ln (n) vs. for olivine+pyroxene magnetite high-temperature (1000° C) basalt hornfelses from Isle Skye define arrays, indicating continuous Using slope intercept these plots conjunction with rate estimates we infer minimum mineral times less than 100 years at ΔT<10° C, rates between 10−4 10−1/cm3/s. Garnet regionally metamorphosed pelitic schists south-central Maine have which bell-shaped. We interpret this form to be result two processes: 1) initial crystals, 2) later loss small due annealing. The large regional retain original frequency distribution may used obtain on conditions growth. extent annealing increases increasing grade could estimate duration if value constant were known. Finally, different forms directly reflect differences thermal histories contact rocks: because metamorphism involves high temperatures short durations, resulting unaffected by annealing, similar those produced crystallization melt; prolonged cooling temperatures, primary modified bell shapes.