High gradient metamorphism

The relevance of the remarks on sulfur content is that, for reasons explained above, it is usually a valid index of the salinity of the environments of deposition. It was remarked earlier that the Eastern and Interior provinces have experienced different temperature/pressure/time histories. It should be added that coals of the Rocky Mountain, Pacific and Alaskan provinces most probably experienced yet further sets of conditions of metamorphism a locally increased geothermal gradient that produced relatively high temperatures at relatively low depths of burial and hence at relatively low pressures of overburden. 

Hodges K. V., Hames W. E., and Bowring S. A. (1994) Ari Ar age gradients in micas from a high-temperature-low-pressure metamorphic terrain evidence for very slow cooling and implications for the interpretation of age spectra. Geology 22(1), 55-58. 

Snow is a porous medium formed of air, ice crystals and small amounts of chemical impurities. Because ice has a high vapor pressure (165 Pa at -15°C, 610 Pa at 0°C), the vertical temperature gradient that is almost always present within the snowpack generates sublimation and condensation of water vapor that change the size and shape of snow crystals. This results in changes in physical variables such as density, albedo, heat conductivity, permeability and hardness. These physical changes have formed the basis for the definition of snow metamorphism. ... 

In this study, to clarify the effect of water vapor, we chose a wide temperature range (-65 °C to -12 °C), for which the water vapor concentrations differed by a factor 1000 between the lowest and highest temperatures, and carried out snow metamorphism experiment under high temperature gradient in a cold room. The density change with water vapor was measured and the effects of water vapor transport on crystal growth, and on density change were examined experimentally. 

Snow metamorphism under high temperature gradient... 

Low groundwater velocities are most common in highly impermeable, low K rocks, and deep systems with near-zero hydraulic gradients. Example rocks are unfractured metamorphic and ig-... 

Figure 18. The results of calcite-graphite isotope thermometry (filled symbols) and calcite-dolomite solvus thermometry (open symbols) plotted against distance to the Tndor Gabbro contact, Ontario. The solvns thermometiy is reset by regional metamorphism at 490°C while the isotope thermometry preserves high temperatures due to earlier contact metamorphism. The sohd cnrved line is the predicted thermal gradient for contact metamorphism (from Dnim and Valley 1992).

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