TIMING OF METAMORPHISM AND DEFORMATION IN THE FOOTWALL OF THE MAIN MANTLE THRUST, SWAT VALLEY, PAKISTAN
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1964)
Rocks of the Franciscan formation suffered a type of glaucophanitic regional metamorphism, being widely exposed in the Coast Ranges in California. The geological and petrological characters of the Franciscan metamorphism are outlined.
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Abstract The metamorphism of Pre-Cambrian dolerites in the Northwest Highlands is described and compared with that of basic rocks in the Southwest Highlands, Banffshire and other regions. The first products of metamorphism are not the same in every area. It is suggested that the trend of regional metamorphism differs according to the environment in which it took place, and that a sequence of changes established in one area cannot be used as a standard by which to judge the changes in other areas. In particular, rocks of high metamorphic grade have not invariably passed through stages characterized by low-grade minerals.
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1967)
Three stages metamorphism of the Tanzawa metamorphic rocks are discriminated from the data of the field and microscopic observations, regional metamorphism, contact metamorphism, and hydrothermal metamorphism. The geologic relationships among these different stages of metamorphism are obtained by examining the structure of original rocks and their metamorphism. The conclusions are as follows. 1) Regional metamorphism of the first stage was not followed immediately by the contact metamorphism of the second stage, and the meta-morphosed areas of the two stages do not coinside to each other. The plutonic mass of this district is a composite mass composed of acidic and basic facies, of which the basic plutonic rock is closely related to the regional metamorphism, while the acidic plutonic rock is related to the contact metamorphism. 2) Hydrothermal metamorphism of the third stage gave an effect over-lappling with the effects due to the metamorphism during the preceeding stages. 3) Original rocks are divided into two groupes, i.e., the rocks of the inner zone and the rocks of the outer zone. The metamorphosed area of the first stage coincide to the rocks of the inner zone, while the metamorphosed area of the second stage do not coincide to that and moreover seem to extend to the rocks of the outer zone. 4) Judging from the presence of debris of plutonic rocks in the lower part of the rocks of the outer zone, it is suggested that there might have been some geologic gap between the rocks of the outer zone and those of the inner zone. The gap is compared to that between the two stages of metamorphism, i.e. the first regional metamorphism and the second contact metamorphism.
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The recent metamorphic geological studies had revealed that not all metamorphic rocks are formed under the conditions of conventional pTrange of the Earth's crust.There are a series of metamorphic rocks formed under extreme metamorphic conditions,which includes ultrahigh-pressure metamorphism,ultrahightemperature metamorphism,migmatization,very low grade metamorphism and impact metamorphism.The ultrahigh-pressure metamorphism refers to the metamorphic process under pressures larger than 2.5GPa and with a very low p/Tgradient of less than 10 ℃/km;the ultrahigh-temperature metamorphism refers to the metamorphic process happened under temperatures larger than 900 ℃;the migmatization refers to the transformation of felsic rock partly into melts as a result of anatexis;the very-low grade metamorphism refers to those low temperature transformation from diagenesis to epizone;while the impact metamorphism refers to those metamorphic processes that were caused by the transient high temperature and dynamic high pressure induced by the impact of extra-terrestrial bodies.The study of these metamorphism under extreme conditions is crucial for the development of geodynamics.Recently a series of research results on these types of metamorphism have been made both in China and abroad The present paper deals with the categories and criteria of these types of metamorphism and aims at a general review on these geodynamic processes and their contribution to the further development of geodynamics.
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