Equilibrium Thermodynamics in Petrology
Date: 15 April 2011, 23:48
|
Geological materials are not the result of well controlled chemical experi- ments. For example, during the metamorphism of a pelite, the original clay or silt follows some temperature-pressure (P- T) path through time (r) as a result of burial and heating followed by uplift and cooling. Can we talk about equilibrium in the metamorphic process? This will depend almost completely on the rate at which equilibrium is attained along the P-T-t path. If the rate of equilibration is fast compared to the rate at which P and T are changing with time, then the rock will maintain equilibrium throughout its P-T path and would reach the Earth's surface as some low temperature assemblage of clay minerals, etc. This does not usually happen, the rock reaches the Earth's surface with a high P-T assemblage. A reasonable interpretation is that the rate of attainment of equilibrium became much slower than the rate of change of P-T with time during cooling, so that the mineralogy of the rock records some high P-T equilibrium attained before substantial cooling and uplift took place.The equilibrium represented in the mineralogy has been frozen in. Metamorphic rocks are often more complicated, for example, the miner- als may be zoned, the rock may have been metamorphosed several times, or late-stage alteration minerals may be developed. Zoning can be interpreted in several ways, but primarily it indicates that the rate of formation of unzoned grains was slower than the rate of change of P-T with time. For example, a zoned garnet in a metapelite may have formed as the result of growth of the garnet over a section of the P-T-t path, with each new zone of garnet attaining equilibrium with the rest of the minerals while the rate of change of composition of previously-formed zones in the garnet was insufficient to form homogeneous grains. The presence of late-stage alteration minerals suggests that the high P-T assemblage attempted to equilibrate at new lower P-T conditions under certain favourable circumstances. In general this book is tailor made for the newcomers in the realm of thermodynamics with applications in petrology.
|
DISCLAIMER:
This site does not store Equilibrium Thermodynamics in Petrology on its server. We only index and link to Equilibrium Thermodynamics in Petrology provided by other sites. Please contact the content providers to delete Equilibrium Thermodynamics in Petrology if any and email us, we'll remove relevant links or contents immediately.