What are the imp considerations in terms of equilibrium assemblage, that i should keep in mind while plotting spots for thermobarometry using EPMA? Especially the Textural Criteria
The following systems i have planned to employ are :-
1.Garnet-Hornblende
2.Hornblende-Plagioclase
3.Qtz-in-Garnet
4.Qtz-in-Epidote
5.Ti-in-K-feldspar
6.Ti-in-Qtz
Tehmina Khan
Equilibrium Assemblage Stability:Ensure that the minerals in your chosen assemblage are stable under the specific pressure and temperature conditions you are investigating. Mineral Zoning:Check for zoning within the minerals (e.g., garnet, hornblende, epidote). Zoning can provide insights into the pressure-temperature history of the rock. Inclusion Relationships:Pay attention to inclusion relationships, as they can indicate the sequence of mineral growth or reaction history. Mineral Associations:Evaluate the association of minerals within the rock. Ensure that the selected minerals coexist in equilibrium and are representative of the geological conditions. Chemical Homogeneity:Confirm that the selected minerals are chemically homogeneous within the analyzed spots to avoid complications in interpretation. Microtextural Relationships:Examine microtextural relationships between minerals. Certain textures (e.g., symplectites, reaction rims) can provide insights into the metamorphic history. Crystallographic Orientation:Consider the crystallographic orientation of minerals, as it can influence the accuracy of thermobarometric calculations. Sample Representativity:Ensure that your selected spots are representative of the overall rock composition and are not biased by specific mineral segregations. Calibration and Standardization:Regularly calibrate and standardize the EPMA to ensure accurate and reproducible results. Check for Common Path Elements:Be aware of common path elements that may affect mineral compositions and potentially influence thermobarometric calculations.
When plotting spots for thermobarometry using EPMA (Electron Probe MicroAnalyzer), especially for the listed equilibrium assemblages, consider the following textural criteria:
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