Some notes by Dr. Nielsen follow:
MIXNFRAC.DAT must be edited to change input parameters. The first line is the title of the run; it is followed by the number of elements to be modeled. The current number is 42, and is best left alone. If you do not have information on some of the trace elements, simply enter 0.
The next section is the major element input data. The name of each major component is followed by it concentration in ppm. Data on each element, including partition coefficients, are kept in file NEWDS3.DAT.
The next input is the composition of the assimilant. Each element name is followed by the concentration of that element, wt% for the majors and ppm for Cr, Ni, and other trace elements in the same order as the starting composition was given.
The following eight entries are the fractionation factors for each mineral. A value of zero represents equilibrium crystallization, 1 is fractional crystallization. The recharge, assimilation and eruption factors are described in detail in Nielsen (1988, GCA) and in comment statements.
Output results in intervals of % crystallization. This requires an additional input line for that parameter. An interval of 2% is appropriate for simple fractionation; 10-50% for open system cases.
The next four numbers are, in order, the number of log units above or below QFM the oxygen fugacity is to be set, the periodic mixing percentage (set to 0 for continuous mixing), the output interval (in %), and the crystallization increment (in %).
The final group of numbers are the indicators for the randomization of the sampling interval, periodicity of mixing, and the amount of recharge, assimilation and eruption. A value of 1 will cause these parameters to be randomized, and any other value will bypass the randomization. The randomization seed sets your initial position within the table of random numbers loaded from RANDOM.DAT.
BLF outputs after each increment of solidification zone magma is mixed into the magma chamber. In addition there are two inputs needed to tell the computer the size of the solidification zone (5-90%). If these values are set to 0.99 and 99 respectively, the program will calculate a simple homogeneous fractional crystallization line of descent.
Some notes on operation:
1. Input Fe+2/Fe+3 should be close to the appropriate value for the T and the fO2 of the run. This is due to the sensitivity of the spinel calculations. An unrealistic +3/+2 ratio will cause the program either to calculate the wrong spinel or to crash.
2. The program will not run without values for Mg, Al, Si, Ca, Ti, Fe+2, and Fe+3. All other values may be zero.
3. Cr values above 400 ppm at fO2 near QFM may cause problems in the calculation of a spinel because of the extremely high D for Cr in spinel.
4. The range of applicable compositions include alkali basalts, tholeiitic basalts, andesites, and dacites with less than 65% SiO2. The calculations have not been tested for extremely undersaturated basalts such as olivine mellilite nephelinites.
5. Olivine and pyroxene calculations are the most stable, followed by ilmenite, plagioclase and spinel. Plagioclase calculations give unrealistically high temperatures for liquids with Al2O3 > 20 wt.%.
6. The range of fO2 is from +2 to -4 log units relative to the QFM buffer.
7. REE may be entered either as ppm or as chondrite normalized values.
8. The periodic mixing option will be enabled if the value of the % crystallization between periodic mixing events, is greater than zero. For example, if it is 5, the system will crystallize for 5 percent, then recharge, and mixing of the assimilant and eruption will take place. In continuous mixing, recharge, assimilation, and eruption are modeled to occur as each increment of liquidus material is removed.
9. The size of the crystallization increment depends on the type of system being simulated. An increment which is too large will over-fractionate the compatible elements. In addition, because crystallization is modeled by oscillating down the cotectic, a large increment will cause unstable oscillations when equilibrium crystallization is being modeled. There is no fixed method for the selection of a crystallization increment. Some testing should be made using several values. However, for simulations involving fractional crystallization of a closed system, the recommended crystallization increment is 0.2%. For recharge models, a value of 0.05-0.01% will produce the best results.
10. At the end of each liquidus temperature calculation section, calculated mineral liquidus temperatures are output to the screen. This is useful for the monitoring of the approach of minerals to the liquidus as differentiation proceeds. In addition, if can signal the approach (or arrival) of problems with an individual mineral calculation.
11. Do not print the output files until you have determined their length. Many runs can result in output running into the 100-200 page range.
12. The phase compositions, proportions, and temperature are output to file BLF.OUT or MIXNFRAC.OUT. A run title, percent fractionation, temperature and liquid composition are output to BLFPLOT or MIXPLOT. This file is tab delimited and can be entered directly into a spreadsheet.