Synthetic polycrystalline aragonite to calcite transformation kinetics: experiments at pressures close to the equilibrium boundary |
| |
| Authors: | W-L Huang |
| |
| Institution: | (1) Department of Geosciences, National Taiwan University, Taiwan, R.O.C., CN |
| |
| Abstract: | Summary ¶This study experimentally investigated the transformation kinetics of synthetic polycrystalline aragonite to calcite at four temperature/pressure conditions (330 °C/200MPa, 380°C/325MPa, 430°C/580MPa, and 480°C/875MPa), close to the calcite-aragonite equilibrium phase boundary. The extents of transformation measured as a function of time in a synthetic system, using in-situ annealed, high purity samples, are consistent with the kinetic model for grain-boundary nucleation and interface-controlled growth. The growth rates are slightly lower than those previously determined for a natural polycrystalline sample at 330 and 380°C. The activation energy (158kJ/mol) for calcite growth from synthetic samples is lower than that (247kJ/mol) from natural samples, but is close to the previously reported value (163kJ/mol) from a single crystal aragonite. The extrapolation of our experimental data to natural conditions reveals unusually fast transformation rates, in contrast to those of natural samples. The presence of deformational strain, fractures, defects or impurities in natural samples, and other factors may account for the discrepancy. This study suggests that the retrograde metamorphism of aragonite to calcite may proceed in a wide range of rates also depending on other geological factors than temperature and pressure.Received July 15, 2002; revised version accepted May 15, 2003 |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
