MELTS Software Users

Hi Paula,

I have a question about the integrated output option of alphaMELTS...

Specifically -- how does the program determine the bounds of the 2D melting/extraction windows? Does it just use values of initial pressure of melting and pressure at the base of the crust, and a thermal profile to determine F laterally away from the ridge axis? If I understand correctly from the literature, Spiegelman and McKenzie defined streamlines for the melt extraction window, which Asimow and Stolper approximate the 2D window with a 1D column using focusing factors. Does the 2D integration simply assume all melt produced makes it to the base of the crust, or if some is trapped off-axis? Lastly, how does the program actually define the "base of crust?"

I apologize if this is a simple question that I may have overlooked in the literature and/or documentation of alphaMELTS.

Any help would be greatly appreciated,
Brandon

Hi Brandon,

The base (P_o) is the initial pressure of melting and the top is the pressure at the base of the crust (P_c). The 1-D columns are for a column and the 2-D for a triangular melting regime, from which it is assumed that all the melt is extracted. The matrix streamlines are simplified (borrowing this image from an old post so ignore the coloured lines) and the melt ones aren't considered:


F_B is the mean extent of melting, where melting stops at P_c. The routine solves for P_c so that the pressure due to the overlying crust (assumed to have a density of 2.62 g.cm^-3) is P_c and the amount of extracted melt corresponds to F_B. See Asimow et al. (2001) (https://doi.org/10.1093/petrology/42.5.963) for more details, including equations.

Hope that helps. Sorry for delay.

Paula