Geometry of isograds in metamorphic terrains |
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| Authors: | DS Bhattacharyya |
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| Institution: | Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, West BengalIndia |
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| Abstract: | A simple mathematical relation among the dip of isograd surface (θ), dip of isotherm surface (α), temperature gradient (Tg), pressure gradient (Pg) and δT/gdP of reaction is given by: Pg is taken to be constant at 0.3 kb/km. Four major theoretical models for shapes and orientations of isograds are formulated on the basis of the parameters α, Tg and δT/δP. This offers a rational basis for studying the geometry of isograds, normal/reverse metamorphism and determination of temperature gradient. Two examples have been studied in the light of these models; in one case the domed shape of the isograd is best explained by a downwardly directed Tg; in the other case, reverse metamorphism is best explained as the result of a horizontal Tg of 18°C/km. |
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