SiO2 48.21 TiO2 1.70 Al2O3 15.23 FeO(T) 10.00 MgO 8.72 CaO 11.51 Na2O 2.29 K2O 0.20 H2O 8.00This is done by clicking in the white box to the right of SiO2 (use the left mouse button to select the box) and typing the weight % value: . The delete key, arrow keys and mouse may be used to edit the ty ped value.
Typing a return advances the text entry cursor to the next oxide. Continue entering the composition until the liquid composition display panel looks like:
The water content in the above is purposely input as larger than the expected saturation value. We will determine the saturation condition by (1) specifying T and P, (2) supressing crystallization of the solid phases and (3) exolving water as a separate phase until the system comes to equilibrium.
The starting and stopping temperatures are both set to the temperature at which we want to determine the water saturation state. The temperature increment is zero (as the temperature will not change in this model) and may be left blank. The starting and stopping pressures are set equal to the system pressure. The pressure increment and dP/dT gradient are zero and may be left blank.
To impose an oxygen fugacity equivalent to the Quartz-Fayalite-Magnetite buffer at the starting temperature and pressure, select the f O2 Constraint entry of the Intensive Variables menu and while depressing the left mouse button, slide the mouse to the right and down and release on the Q-Fa-Mt constraint buffer entry.
Next, go to the Composition menu and select the Compute Redox State entry. The Fe2O3 and FeO quantities displayed in the liquid composition panel should change to reflect a ferric/ferrous ratio appropriate to the QFM buffer for a hypothetical liquid of the bulk composition displayed at the starting T and P entered above.
Finally, turn off the f O2 constraint by selecting the absent option item of the f O2 Constraint entry of the Intensive Variables menu.
By default all solid phases are allowed to crystallize. This is indicated by a filled or highlighted diamond symbol to the left of the indicated phase. Supressed phases are labeled by an unfilled diamond. (Phases to be made available in a later MELTS release are inactive and toggled permanently off.) Turn off all of the solid phases by clicking on the diamond symbol or the phase name using the mouse pointer and the left mouse button. Leave wat er checked on.
The model may be halted at any time by invoking the Execute/Halt entry of the Commands menu. The user may change bulk composition or model constraints and restart the calculation using the same menu entry.
A manual page describes many common numerical problems that may occur when the program is running.
MELTS has determined that at 1200 C and 500 bars, the saturation state of water is 1.81 wt % in the liquid. The remaining water in the system should be listed as a separate phase in the phase display panel.