Using PRIMELT2.XLS Warning: Do not use this software on lavas that had fractionated clinopyroxene and/or plagioclase [Herzberg et al., 2007; Herzberg and Asimow, 2008]. It calculates primary magma composition by simulating olivine addition and subtraction, and should be used only on primitive lavas that had fractionated olivine. The primary magma calculations described in this paper are implemented in a publicly available Microsoft Excel workbook called PRIMELT2.XLS, posted as an online supplement to this paper. Please note that this workbook uses Visual Basic for Applications (VBA) macros for several of the iterative calculations. As such, it is incompatible with Microsoft Office 2008 for Macintosh, which does not support VBA macros. There may be other incompatibility issues that we are not aware of, but it has been tested on Microsoft Windows XP 2002 using Microsoft Office 2004 and on MacOS 10.4 and 10.5 using Microsoft Office 2004. Upon opening the workbook you must choose to enable the macros or it will not function. Although PRIMELT1.XLS used iterated circular references, which required a particular setting in the Calculation Preferences control panel, this is no longer needed with PRIMELT2.xls. To use the program, we recommend creating a new worksheet by using the “Move or Copy Worksheet” operation, which can be accessed from the “Edit” menu as well as by a number of mouse and keyboard shortcuts that differ among operating systems. Name your new worksheet according to the sample name of the lava to be studied (by double-clicking on the title tab for this worksheet at the bottom of the window). Enter the oxide weight percent analysis of the sample in cells B4:N4 (yellow cells). Note that cell F4 asks for total Fe as FeOT. The analysis need not be normalized; PRIMELT2.XLS will take care of this. Enter the desired Fe2+/FeT as a mole fraction in cell F5. Alternatively, in order to use the method recommended in the text of adjusting Fe2+/FeT in order to achieve a given Fe2O3/TiO2 ratio, enter the desired Fe2O3/TiO2 ratio in cell L5 and then click the nearby button labeled “Calculate Fe2+/Fe+”, which will update the contents of cell F5 as needed. The only other user inputs are in cells R3:R4, where the FeO and MgO content of the source peridotite may be modified from the default values used in the calibration (KR4003), and in cell R6, where the pressure of the olivine fractionation/addition calculation can be changed (all the calculations in this paper use 1 bar; the program is only set up for isobaric fractionation/accumulation but the melting model is polybaric). Once information is input into these cells, the results appear in the output and warning cells automatically. If the input lava composition fails the peridotite/pyroxenite source test (section 3 above) or the volatile-rich peridotite source test (section 4 above), the text in cell G7 (orange fill) will change from “No Error” to a warning message, but the calculation will still proceed. If the accumulated fractional output primary magma composition fails either the clinopyroxene fractionation or accumulation test (section 5 above), an appropriate warning will appear at cell M13. Instantaneous fractional melts do not always mix to produce an accumulated fractional melt, an issue that was discussed in Herzberg [2007]. These often have unusually low contents of FeO and high MgO, and they plot in the forbidden region below the curve labelled L+Ol in Figure 9a. The calculation will proceed anyway, but the user is alerted with the warning “FeO/MgO forbidden” in the orange-filled cell Q13. This warning will happen whenever the calculated primary magma content has an FeO content with the following characteristics: FeO < 0.577MgO – 0.00026MgO3 + 5.48/MgO (A1) Occasionally, a primitive lava rich in both MgO and Na2O will display F3 < 0 in equation (6) even though SiO2 is not unusually low. These are identified in PRIMELT2 as “negative normative quartz” in cells T9 or T13, and the primary magma solution is considered suspect. When the calculation is finished, the results appear in the green cells. The solution for batch melting appears in A11:W11 and the solution for accumulated fractional melting appears in cells A15:T15. In order from left to right, the meaning of the output cells is: • %ol addition: The mass fraction of olivine added (or, if negative, subtracted) from the input lava composition to find the primary magma solution. • SiO2, TiO2…: The primary magma in oxide weight percent, including Fe2O3/FeO speciation. The MgO value is in boldface. • T: The “primary eruption temperature”, as discussed in Herzberg et al. [2007]. It is the temperature at which the candidate primary magma occurs along the olivine control line at the specified fractionation pressure. • TP or TP_AFM: The mantle potential temperature calculated for the melting region to yield the appropriate primary magma; see Herzberg et al. [2007]. • KD: The Fe/Mg distribution coefficient between olivine and the primary liquid composition, calculated at the primary eruption temperature and the fractionation pressure. See Herzberg et al. [2007] for the choice of KD models. • Xfo: The composition of the liquidus olivine that coexists with the primary liquid at the primary eruption temperature and fractionation pressure. • F (Fe/Mg) or F_AFM: Equation (1) for batch melting; equation (3) for accumulated fractional melting. • Proj F1, F2, F3: Equations (4), (5), and (6). Exactly one of these should equal F(Fe/Mg). If F(Fe/Mg) = F1, the solution is for a harzburgite or dunite residue; if F(Fe/Mg) = F2, the solution is for a spinel lherzolite residue, and if F(Fe/Mg) = F3, then the solution is for a garnet peridotite residue.