Integrated degree of melting for 2-D

[jakemoore]

Paula,

To get to the point, is there a way to see the mean extent of melting for 2-D when the calculation does not reach the base of the crust?


In some of my runs with isentropic continuous melting I get to the upper limit of pressure for pMELTS (10 kbars) before melting ceases, and when I try option 12 I am prompted with this dialogue:

WARNING: calculation did not get to base of crust (2-D)
Writing final aggregate composition instead

and the integrated output file (major or trace) has a 0 for FBbase (table 3), the mean extent of melting for 2-D.  I'd like to know and use the mean extent of melting. 

Secondly, am I correct in my understanding from the documentation that I can't really make a plot of F vs. SiO2_2D (for example) because the SiO2_2D is integrated for the triangular 2-D region and F (table 4) is the 1-D integrated value?  Perhaps I'm explaining poorly.

Cheers,
Jacob

[Paula]

Hi Jake,

Calculating the mean extent of melting for a 2-D melting regime requires the pressure at the base of the crust (Pc), even if melting stops (or, in this case, pMELTS reaches the limit of its calibration range) before reaching this.  Basically, the top of the triangular region is cut-off so the melting zone you are interested in is a trapezoid.  But the melt extracted from below does not contain any information about how wide the trapezoid it.  For a more detailed discussion see the Asimow et al, 2001, paper (JPet, v42, p963-998) - in particular equations 6 and 7.  So you either need to run the calculation to the base of the crust or otherwise estimate the pressure at the base of the crust.

Similarly if you want to plot the 2-D mean extent of melting up to a given depth versus SiO2_2D (e.g. if you are interested melt mixing and extraction processes) you will need Pc.  Then you can calculate the 2-D F in Excel or the like using equation 7 of Asimow et al.

Hope that helps.
Paula