SIZE DISTRIBUTIONS OF PLAGIOCLASE CRYSTALS IN LAVA SAMPLES FROM KILAUEA

Crystal size distribution (CSD) is a theory first envisioned by chemical engineers Randolph and Larson in 1971, and brought to igneous petrology by Bruce Marsh in 1988. It is a measure of growth rate and age and generally predicts a log-linear distribution with increasing size. Many researchers have performed CSD studies on a number of different minerals, including garnet, pyroxene and plagioclase. One well published growth rate for plagioclase crystals is 10^-11 cm/s. In this study, I have taken thin sections of 10 samples from Kilauea Volcano, and using an image analysis lab (a microscope with a camera mounted on it, which is connected to a computer), I was able to measure the volumes of the plagioclase crystals, which are needed to calculate the growth rate. The other information needed is the magma residence time, all of which are well known for Kilauea. Thus, using the fundamental CSD equation, I was able to compute the plagioclase growth rate in Hawaiian basalts. My results were consistent with the previously published rate of 10^-11 cm/s.