EXPERIMENTAL STUDY OF THE THERMAL DECOMPOSITION OF LIZARDITE UP TO 973 K

Experimental studies of dehydration reactions responsible for mineral transformations and the production of volatile phases have been limited previously by the time required for thermal equilibration and data collection. Our experimental technique, detailed in Earnest et al. (AGUFM, 2004), allowed for thermal equilibration and data collection in less than seven minutes and did not rely exclusively on quenched run products. This preliminary study focused on the dehydration reactions of a serpentine mineral. The thermal decomposition of lizardite was monitored up to 973 K by using a Bassett-style hydrothermal diamond anvil cell and synchrotron X-ray radiation. The experiments were conducted at the GSECARS 13-BM-D beam line (Advanced Photon Source), using monochromatic X-ray radiation and an online imaging system. The diffraction data were used to monitor the thermal decomposition of lizardite as a function of temperature and time. Experiments at 823 K exhibited a slow breakdown of lizardite with the first noted production of forsterite at 110 minutes. 873 K experiments saw an increased rate of lizardite decomposition and the production of forsterite at approximately 27 minutes. Our highest temperature experiments (973 K) saw the complete thermal decomposition of lizardite within ten minutes along with the production of forsterite and talc within the first minute. Additionally, diffraction peaks attributed to anthophyllite were noted at 22 minutes and grew more intense throughout the experiment. Talc diffraction peaks showed a decrease in intensity after 67 minutes and continued to decrease until the end of the experiment (202 minutes). Forsterite nucleates before more silica-rich phases, at generally lower temperatures and persists throughout the duration of the experiments. These data illustrate an experimental technique that can be used to study the phase equilibria and thermal decomposition kinetics of minerals found in subducting slabs and serpentine mud volcanoes.