Metamorphism influence

It is fairly evident that because of the complex interactions of deposi-tionally influenced and metamorphically influenced properties, the fundamental chemical-structural properties will need to be related to each other in a complex statistical fashion. A multivariate correlation matrix such as that pioneered by Waddell (8) appears to be an absolute requirement. However, characterization parameters far more sophisticated than those employed by Waddell are required. One can hope that, as correlations between parameters become evident, certain key properties will be discovered that will allow coal scientists and technologists to identify and classify vitrinites uniquely. Measurement of reflectance or other optical properties, if carried out properly, possibly on somewhat modified samples, might prove valuable in this respect. It then would not be necessary for every laboratory to have supersophisticated analytical equipment at its disposal in order to classify a coal properly. By properly identifying and classifying the vitrinite in a coal, one then could estimate accurately the many other vitrinite properties available in the multivariate correlation matrix. 

In addition to hydrothermal and volcanic activity, metamorphism may have influenced the CO2 levels of the atmosphere and caused climate changes. Based on a model of the Cenozoic extension in the North American Cordillera, Nesbitt et al. (1995) demonstrated that CO2 generation associated with crustal extension may have been a major contributor to the elevated CO2 levels of the Cenozoic atmosphere and the resulting global warming due to the CO2 greenhouse effect. 

Feldspars are the most abundant minerals of igneous rocks, where their ubiquity and abundance of their components influence normative classifications. They are also abundant in gneisses, and may be observed in several facies of thermal and regional metamorphic regimes. Notwithstanding their alterability, they are ubiquitously present in sedimentary rocks, as authigenic and/or detritic phases. Only in carbonaceous sediments is their presence subordinate. 

Matthews A. (1980). Influences of kinetics and mechanism in metamorphism A study of albite crystallization. Geochim. Cosmochim. Acta, 44 387-402. 

Another proof of the importance of temperature is the fact that there is often a strict relationship between the run of isovols and the run of isotherms in deep profiles, both being influenced no doubt by the varying thermal conductivity of the different rocks. The strong influence of temperature on the rank of coal is obvious in the case of contact-metamorphic coals, whose rank increases distinctly when approaching the intrusive body. Apart from these geological observations, all experiments on artificial coalification have shown that temperature is the decisive factor in the coalification process. Thermodynamic and reaction kinetic considerations (9) also support this opinion. 

Geological investigations have shown that undoubtedly temperature has most influence on geochemical coalification. This is proved by such evidence as contact metamorphism of coals, increase of rank with increasing temperature of the earth s crust with depth, increase of rank of the same seam as magma chambers (batholiths) are approached, and relations between the thermal... 

The word METAMORPHOSIS is derived from the Greek and means adopting a different form . In mineralogy the transitions in the minerals are studied which take place under the influence of pressure (dynamic metamorphosis), temperature (thermic metamorphosis), moisture, etc. Figure 7.4 is an example of a metamorphic process. 

The same phenomenology must be important locally on Earth, too, where thick evaporite deposits of hydrated salts and local thick beds of methane clathrate in permafrost or seafloor sediments should influence the thermal environment of the crust. The predicted control on the crust s thermal state by hydrate deposits should have consequences for the localization of hydrothermal springs around and within evaporite basins, hydrothermal metamorphism... 

More information is needed on carbonate reaction kinetics near equilibrium in complex and high ionic strength solutions, and the influences of temperature and pressure on kinetics to near metamorphic conditions. 

In pro-grade metamorphic reactions, on the other hand, effects of intersite cation ordering at elevated temperatures could influence Fe/Mg ratios of orthopyroxene-olivine assemblages in granulite facies rocks. For the olivine-orthopyroxene exchange reaction... 

In addition to the ideas examined, the viewpoint that unequal pressures in general and lithostatic pressure in particular play an important role in metamorphism is widespread. In theoretical works (Barth, 1956 Sobolev, 1961 Fyfe et al., 1962 Semenenko, 1966) the principle of the shifting of equilibria under the influence of excess loading pressure on the solid phases, with the liberation of HjO or COj in metamorphic reactions, has been examined repeatedly. 

Chamberlain C. P. and Rumble D. (1989) The influence of fluids on the thermal history of a metamorphic terrain New Hampshire, USA. In Evolution of Metamorphic Belts Geological Society Special Publication 43, (eds. J. S. Daly, R. A. Cliff, and B. W. D. Yardley). Blackwell, Oxford, pp. 203-213. 

Thermobarometry, or the calculation oi P-T conditions from mineral compositions, is not based on mineral zoning, nor does it directly inform processes that cause geochemical zoning. Nonetheless, P-T calculations in metamorphic rocks usually require selecting compositions from minerals that are compositionally heterogeneous. How one selects compositions from a zoned mineral can strongly influence retrieved P and T, and that issue is worth discussion. 

England P. C. and Richardson S. W. (1977) The influence of erosion upon the mineral facies of rocks from different metamorphic environments. J. Geol. Soc. London 134, 201-213. 

Thompson A. B. and England P. C. (1984) Pressure-temperature-time paths of regional metamorphism 11. Their influence and interpretation using mineral assemblages in metamorphic rocks. J. Petrol. 25, 929-955. 

Mineral dissolution kinetics influence such phenomena as development of soil fertility, amelioration of the effects of acid rain, formation of karst, acid mine drainage, transport and sequestration of contaminants, sequestration of carbon dioxide at depth in the earth, ore deposition, and metamorphism. On a global basis, mineral weathering kinetics are also involved in the long-term sink for CO2 in the atmosphere ... 

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