MacArgon

MacArgon allows simulation of argon retention in minerals and rocks, and modelling and simulation of the results of argon geochronology. Arbitrary pressure-temperature-time paths can be input, and calculations are performed as how the diffusion of argon would take place from the mineral grains in question. 

Argon accumulates through radiogenic decay but is lost by diffusion, or as the result of microstructural events such as recrystallisation or diffusion domain reduction at individual control points along the pressure-temperature-time path.

Parametric inversion considers the variation obtained in families of pressure-temperature-time paths. Manual inversion takes advantage of the highly interactive nature of the graphical user interface. Monte Carlo inversion allows comparison with control points selected by the user from an observed age spectrum input in a standard XML format. 

Both Parametric Inversion and Monte Carlo simulations attempt to match the simulated spectrum with selected steps in a reference age spectrum. A sensitivity analysis can then be performed for individual simulations. A "MacArgon document" is used to store data in XML format, allowing later retrieval and FAIR data use.

Different types of parametric inversion are facilitated by inclusion of options for flash heating or analytical solutions for cooling near igneous bodies. The temperature history above and below a compressional thrust or an extensional detachment can also be simulated prior to being applied to a mineral to generate an apparent age spectrum. 

The program allows distributions of diffusion domain size and volume that allow replication of data obtained from temperature-controlled furnace-step-heating experiments in an ultra-high-vacuum mass spectrometer designed to measure the concentration of the isotopes of argon. By considering bulk fusion the program also replicates the answers likely to be obtained using laser-spot analysis, or laser-step-heating by pulse-heating the crystals.

The contribution of individual components of the microstructural model can now be indicated in the morphology of the age spectrum. 

Information can be saved about the magic markers that map the microstructural events at different pressure-temperature-time points onto the different computational domains throughout the simulations. The mapping of events onto computational domains is also preserved, as well as the mapping of events onto individual points in the Pit path. 

Version §8 allows quantitative modelling of the effect of microstructural change, including recrystallisation and grain growth, mineral shredding during mylonitisation, and regrowth during thermal and metasomatic fluid alteration events. This version allows parametric inversion of P-T-t-Δ paths, inversion of functional P-T-t-Δ paths, and inversion of P-T-t-Δ paths using Monte Carlo processes. temperature constraints to be independently placed on growth events. This might be necessary if independent information from metamorphic petrology provides an additional constraint outside of the constraints handled internally by MacArgon itself. During Monte Carlo inversion, the defined regions act as attractors, to encourage the choice of compliant Δ-T-t paths.

Version §8.6 introduced constraints that draw the pressure-temperature-time (P-T-t) path towards defined stability fields for growth of individual phases when simulating the effect of microstructural events during the geological history. These growth fields can be explicitly defined, with given time ranges and/or preferred temperature ranges. The option is given to allow the Magic Marker defining the growth event to be drawn towards these limit fields as the Monte Carlo produces attempts to achieve a better fit.