ptpath - 1 P-T-time paths Definition A P-T-time path is a...

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1 P-T-time paths Definition: A P-T-time path is a loop or curve connecting all P and T points to which a rock has been subjected from the beginning of its metamorphic history until the time of its exhumation (exposure) at the surface. Each rock or hand sample has a characteristic P-T-time path that sheds some light on the tectonic history of the area. Technically, a P-T-time path can be constructed only if the ages (or at least some age constraints) are known. If such age constraints are lacking, it is better to term the path a "P-T path", even though this path implies a continuum in time. Methods of reconstructing P-T-time paths: (1) Observational method (2) Computational method (3) Geophysical modeling Observational method: This method relies on a careful examination of metamorphic textures, particularly those indicating disequilibrium conditions or reactions. Accordingly, several mineral assemblages believed to have occurred in equilibrium at some time during the rock's history, are identified. This is followed by attempting to determine the prevailing P and T for each one of these "equilibrium assemblages", representing some stages in the rock's history. Two features are particularly useful in this method: inclusions in porphyroblasts and zoning. (i) Inclusions : may be useful in predicting the P-T conditions that prevailed prior to the attainment of peak P or peak T, provided the enclosing poikiloblast crystallized during prograde metamorphism. The process becomes more useful if the inclusions can be used for geothermometry or geobarometry (e.g. inclusions of Cpx in Gt can be used for Gt-Cpx geothermometry, whereas inclusions of plagioclase in Gt can be used for estimating P using the Gt + Ky + Qz = An geobarometer). However, care must be taken
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This note was uploaded on 02/28/2012 for the course GLY 421 taught by Professor Staff during the Fall '11 term at Marshall.

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ptpath - 1 P-T-time paths Definition A P-T-time path is a...

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