Doing the sort of modelling metamorphic petrologists do can be compared to various skill levels in cooking. Some people “cook” by opening a box or a can and following the instructions printed on the label to heat the contents. Others “cook” by looking at a recipe and faithfully performing every step of the instructions in the sequence suggested, with no real understanding why the author of the cookbook wanted them to do step A before step B; but by correctly following the instructions they obtain a result which they are happy to eat. Still others of us decide what we are hungry for, rummage around in the pantry and throw together delicious food that brings us joy to eat, instinctively doing some tasks before others because we understand the manner in which the tasks coordinate to create a perfect dish. We do things differently every time, never fearing to improvise because we understand *why* things work in the kitchen and what things may be changed and what rules are iron-clad.
As a petrologist I’m slowly working my way from the one end of that spectrum towards the other. The first time I attempted to use Perple_X to calculate what phases should be present in my rocks I had no idea what I was doing, or why. My advisor had pointed out a recently published paper which used that tool for calculations on a similar rock type to my own, so I downloaded the supplemental data set, used the “in” file provided, and ran the program using the settings their paper reported them to have used. Low and behold, the program generated a diagram which looked just like the one they had published (open box, remove plastic from tray, put trya in oven at 350 F for 35 minutes).
Thus encouraged, I edited their in file to show the composition of my sample instead of theirs, and ran it again, getting a very different diagram. This marked my first baby step in moving away from heating packaged food to something about on the level of complexity of using a packaged cake mix (just add water, eggs, and oil). Some months passed while I used this technique for a variety of different samples. Then, one day I realized that I needed to generate a different type of diagram, so I began to learn what changes are necessary to do so. This required much reading of the tutorials accompany the program. Not unlike learning to follow a recipe (cream butter and sugar together, beat in eggs and vanilla, add flour mixture alternatively with milk…).
I find that the more papers I read on this topic, the more I understand about the many, many options for calculations available in programs such as this one (there are others out there I should like to try as well, if I can only make the time to do so). It is my hope that, eventually, I will join the ranks of those who understand a-X models and will be able to reach the same stage of confidence in using these as I enjoy each time I enter the kitchen to cook or bake myself something yummy.