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Unformatted text preview: 96NC67: Garnet Core and Rim Thermobarometry Temperature ( o C) Pressure (kbars) 450 550 500 700 650 600 2 4 6 8 10 12 5.0 kbars 640 o C Garnet Core P-T (from pseudosection method) Garnet Rim Equilibria Uncertainty Ellipse Peak Assemblage Garnet P-T Trajectory Pressure- Temperature Pseudosections P-T Path Determination with Pseudosections and Garnet Chemistry P-T pseudosection: A P-T phase diagram portraying the theoretical distribution of equilibrium mineral assemblages in P-T space for a single bulk-rock composition. An important distinction should be made between the concept of a P-T pseudosection and the prominently used P-T projection (petrogenetic grid). Lines on a P-T projection represent possible chemical reactions a particular rock may experience. However, all the reactions on a P-T projection are never experienced by a single bulk rock composition; only a subset of the possible reactions are experienced. In contrast, lines on a P-T pseudosection represent the P-T conditions at which the mode of a particular phase goes to zero for a specified bulk composition, and rarely represent any single reaction which appears on a simplified petrogenetic grid. If the bulk composition of a rock changes, than the positions of mode = 0 lines on a pseudosection will change, but the positions of reactions on a petrogenetic grid will not change. Therefore, pseudosections are a useful tool for showing the on a pseudosection will change, but the positions of reactions on a petrogenetic grid will not change....
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This note was uploaded on 03/19/2012 for the course GEOLOGY 6 taught by Professor Rm during the Spring '12 term at UNAM MX.
- Spring '12