Regional Dynamothermal Metamorphism
Unlike contact metamorphism, regional metamorphism is no localized phenomenon. It takes place at deeper regions of the crust and is, as the name already signifies, of regional extent. The different types of regional dynamothermal metamorphism are confined to areas of mountain building, so that metamorphism as well as orogenesis ought to be regarded as due to “one and the same process”. 1) The factor bringing about both of them can be viewed only in an additional supply of thermal energy at specific regions of the earth, the causes of which may be presumed at great depths, namely within the mantle. Based on his detailed investigations of plagoiclases as index minerals of metamorphism in the central Alps, E. WENK (1962) pictures the presence of “thermal domes” during the metamorphism within the belt of orogenesis. “We cannot regard these thermal highs as independent phenomena, they are genetically connected to orogenesis. ” It is therefore “the thermal energy surging from the depths, that imparts to the rock masses their special character, ” i. e. brings about rock metamorphism. In principle however, regional metamorphism, in course of which rather high temperatures may have been attained, is hardly anything different from contact metamorphism, both of them requiring supply of thermal energy. In case of contact metamorphism the original source of heat is small and now exposed as a plutonic mass, whereas with the regional metamorphism it is essentially larger, more deep-seated and not visible.
KeywordsClay Quartz Silicate Geochemistry Shale
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