Exploring Geochemistry in the Classroom Using MELTS Computational Tools

Access the Program from the MELTS Homepage
This webpage was created for SERC by Heather Rissler and Aleshia Mueller in consultation with Mark Ghiorso, V.P., OFM Research Inc.

The Tool

MELTS is a software package designed to facilitate thermodynamic modeling of phase equilibria in magmatic systems. Users can compute equilibrium phase relations for igneous systems over the temperature range 500-2000 °C and the pressure range 0-2 GPa.

Use and Relevance

Pillow Basalts from the south Pacific seafloor; Image from NOAA.
Examining the structure of the solid Earth is important for understanding phenomena such as electromagnetic fields and plate tectonics. MELTS computational tools allow scientists to model igneous processes using data in a way that would not normally be accessible by direct inspection of the raw data. The data that scientitsts typically examine using melts include compositions of liquids and solids that are coexisting under known expermimental conditions of temperature, pressure, and oxidation states. Scientists use MELTS tools to examine questions such as how the Earth melt along a pressure-temperature path defined by an adiabatic temperature gradient (where the total heat content of the system remains the same as the material moves up through the Earth's changing pressure). MELTS can be used to test diverse scenarios ranging from examining how much sulfur a volcanoes gives off, which has implications to climate change, to understanding and predicting how the Earth melts.

Use in Teaching

This tool can be used to teach the following topics and skills in petrology and geochemistry:
AFM graph showing equilibrium crystallization of Mid-Ocean Ridge Basalt at a constant pressure over a temperature range of 50 degrees; from MELTS manual.

Topics

Skills

Exploring the Data with the Tool

Obtaining and accessing the tool

MELTS can be accessed as a web applet by choosing the 'run applet' option. Alternatively, Mac OS X and Unix versions can be downloaded for standalone use.

Obtaining input data required for working with the tool

Several databases are available that provide rock and mineral composition data, including an experimental database at MELTS. Users can input these compositions into the MELTS program to perform computer experiments. Two other available databases are the Petrological Database of the Ocean Floor (PETDB) and EarthChem.

Using the tool and interpreting output results

The MELTS Manual provides information about testing, graphs, output format, display elements, menus, and common problems. It also provides examples of MELTS experiments. This simple example is a good way to test newly downloaded MELTS software and begin to familiarize yourself with the program. For more advanced users, try using the Phase Properties Calculator Form or the Phase Properties Calculator Applet to compute thermodynamic properties of mineral-solid solutions that occur in nature with variable compositions. MELTS outputs files in comprehensive and tabular formats.

Manipulating data and creating visualizations

Data can be displayed as graphs, tables, or phase diagrams.

About the tool

How the tool works

The MELTS program is based on a model that describes the geometry of the energy surface for a multi-dimensional system of up to 16 chemical components. The model predicts compositional changes by determining the minimal energy for the system under the user defined parameters (including initial composition, temperature, pressure, and oxidation state of the system).

Limitations and sources of error

MELTS is intended for modeling magmatic phase relations at low pressure (< 2 GPa). It is better calibrated in mafic systems and should work especially well for MORBs and alkalic mafic magmas. Phase equilibria involving hornblende and biotite are not modeled well by the MELTS package and consequently simulating the evolution of intermediate to silica-rich calc-alkaline systems is not recommended. MELTS results are only as good as the underlying experimental data source so make sure you are working from a reliable dataset.

References and resources

Scientific references that use this tool

Discusses the errors associated with forward modeling of mantle melting:

Education resources that use this tool

Examples
Tutorial

Other related scientific references

Citing use of the tool

Related links