![polymath software multiple reactions polymath software multiple reactions](http://websites.umich.edu/~elements/5e/software/polymath/images/linresults.gif)
Repeat, but add the script justrelu (“just relative uncertainties”) to the scriptfile in each case, check that this produces similar P to before, and record the sd( P) values (ignore the horrifying sigfit values).Do avP on each sample in each case, check that the sigfit value is okay, and if so, record the value of avP.Much smaller uncertainties are involved in estimating this difference than in estimating absolute values, because many of the uncertainties affect both calculations in the same way, and can therefore be ignored. ∆P, ∆T and ∆PT (Worley & Powell, 2000) can be applied where one wants to find the difference in P (or T) for two (or more) samples with the same assemblage. Never use results that are calculated with an incomplete set of reactions!.You may want to try to improve your results by, for example, excluding phases that seem to be causing problems – is this telling you that they are not part of the equilibrium assemblage? Or, you might want to remove, say, ferric end-members that have particularly uncertain activities.There is an on-screen explanation of the statistical parameters involved, but for more help, see the references in the Documentation section below, especially Optimal geothermometry and geobarometry.
![polymath software multiple reactions polymath software multiple reactions](https://s3.studylib.net/store/data/008234675_1-d48c5be55bf2e3dbe9ab3718e6945a8b.png)
THERMOCALC provides a lot of output related to the statistics of this process, and it’s important to analyse it carefully in order to gain geological insight.adjusts the positions and slopes of the reactions, respecting the uncertainties and correlations, until all of the reactions coincided at an “average pressure”.supposedly independent uncertainties in the activities of the end-members, derived from uncertainties in the x-eos and in the compositional analysis.the correlated uncertainties in the enthalpies of the end-members, obtained from fitting the Holland & Powell dataset,.considers the correlated uncertainties on the positions and slopes of each reaction, which are derived from.uses each of those reactions separately to calculate a value for P at the specified T.assembles an independent set of reactions among end-members in the various model phases.Using avP mode as an example, THERMOCALC:.There may not be much pressure or temperature information present, as a result of weaknesses in the x-eos, a shortage of the necessary information in the compositional data, or both. The question is, can the compositional data actually contain enough information to constrain both P and T uniquely, even if the x-eos were perfect? So we suggest calculating avP at multiple temperatures, choosing the temperature at you get the best sigfit/smallest uncertainty, or alternatively calculating avT at multiple pressures. You will be given a choice between avP, avT and avPT modes.You should exclude any ordered end-members in your phases – see the headers to the x-eos in axfiles or -it files. THERMOCALC will ask you if you want to exclude any end-members.You will need to provide your analysed mineral compositions to THERMOCALC, which will then convert them to activities of end-members.The prompts will guide you through the process. As usual, you will need a prefs file, scriptfile, and the axfile containing your chosen HP x-eos set.The user has to run these procedures manually.ĪvP, avT and avPT (Powell & Holland, 1994) are used for estimating absolute values of pressure, temperature or both. average temperature (avT): calculate at multiple temperatures and find the best fit to estimate P.Īnother possibility is ∆P or ∆T – relative pressures and temperatures.average pressure (avP): calculate at multiple temperatures and find the best fit to estimate T.THERMOCALC 3.50 offers two types of multiple-reaction thermobarometry calculation: Using some assumptions about the uncertainties involved and how they are correlated, THERMOCALC infers one optimal estimate of pressure and/or temperature from the set of constraints, along with an uncertainty, a goodness-of-fit value and other diagnostic parameters. Each of these constraints acts as an independent estimate of pressure or temperature.
![polymath software multiple reactions polymath software multiple reactions](https://dev2u.net/static/2021/01/10/055638449/pg_xxiv-01.jpg)
The analysed compositions are given to THERMOCALC, which converts them to activities using the HP x-eos, and incorporates them into a set of thermodynamic equilibrium constraints. In multiple-reaction thermobarometry mode, the user must have mineral analyses for an assemblage that is believed to represent the equilibrium assemblage, or a subset of the equilibrium assemblage.