Failed to Find Isograd Solution!

[thahn1]

Hello,

I am trying to run some simple equilibrium and fractional crystallization models using alphamelts 1.5.    I am rather new to MELTs, although I have successfully ran similar models in the past on different bulk composition.  When running the script I can't seem to get past a single bath calculation before executing the program.  My problem seems to be from Cr2O3, which is affecting the spinel stability.  The program fails to find an isograd solution and either crashes or suggests twiddling the starting temperatures.  I have tried to mess with the temperatures but can't seem to fix it.  The only thing that seems to get me past the single batch step is to do a monotonic search but I not sure if this is actually fixing the problem!  I have copied my settings and MELTs files below.  Can someone please help?!

SETTINGS FILE
! *************************************
!  Equilibrium Crystallization Vesta
! *************************************

! this variable chooses MELTS or pMELTS; for low-pressure use MELTS
ALPHAMELTS_VERSION         MELTS

! use the spinel volume model from Java MELTS
!ALPHAMELTS_OLD_SPINEL   true

! don't use this unless fO2 anomalies at the solidus are a problem
!ALPHAMELTS_ALTERNATIVE_FO2   true

! use this if you want to buffer fO2 for isentropic, isenthalpic or isochoric mode
! e.g. if you are doing isenthalpic AFC
!ALPHAMELTS_IMPOSE_FO2   true

! use if you want assimilation and fractional crystallization (AFC)
!ALPHAMELTS_ASSIMILATE   true

! isothermal, isobaric, isentropic, isenthalpic, isochoric, geothermal or PTPath
ALPHAMELTS_MODE             isobaric
!ALPHAMELTS_PTPATH_FILE   ptpath.txt

! need to set DELTAP for polybaric paths; DELTAT for isobaric paths
ALPHAMELTS_DELTAP        0
ALPHAMELTS_DELTAT        -1
ALPHAMELTS_MAXP          30000
ALPHAMELTS_MINP          1
ALPHAMELTS_MAXT          2400
ALPHAMELTS_MINT          500

ALPHAMELTS_CELSIUS_OUTPUT true

! this one turns on fractional crystallization for all solids
! use 'Fractionate:' in the melts file instead for selective fractionation
!ALPHAMELTS_FRACTIONATE_SOLIDS   true
!ALPHAMELTS_MASSIN         0.001

! free water is unlikely but can be extracted
!ALPHAMELTS_FRACTIONATE_WATER   true
!ALPHAMELTS_MINW                  0.005

! the next six options refer to the trace element engine
!ALPHAMELTS_DO_TRACE              true
!ALPHAMELTS_TRACE_DEFAULT_DPTX  true
!ALPHAMELTS_TRACE_NORMALIZATION 2
!ALPHAMELTS_TRACE_INPUT_FILE    yourtraceinfile.txt
!ALPHAMELTS_TRACE_USELIQFEMG    true

! the next one gives an output file that is always updated, even for single calculations
!ALPHAMELTS_SAVE_ALL       true
!ALPHAMELTS_SKIP_FAILURE   true

! this information overwrites stuff in the initial melts file
! a new melts file is created if this information is different
!Initial Temperature: 1400
!Initial Pressure: 500
!Log fO2 Path: FMQ


MELTS FILE
Title: Juvinas Kitts and Lodders (1998)
Initial Composition: SiO2 49.1
Initial Composition: TiO2 0.6
Initial Composition: Al2O3 13.1
Initial Composition: Fe2O3
Initial Composition: Cr2O3 0.3
Initial Composition: FeO 17.9
Initial Composition: MgO 7.0
Initial Composition: CaO 10.7
Initial Composition: Na2O 0.4
Initial Composition: K2O 0.0
Initial Composition: P2O5 0.1
Initial Composition: H2O
Initial Temperature: 1250
Final Temperature: 600
Increment Temperature: 3.00
Initial Pressure: 200
Final Pressure: 200
Increment Pressure: 0.00
dp/dt: 0.00
log fo2 Path: IW




Tim

[Paula]

Hi Tim,

Sorry for the delayed response. I assume you mean you are locating the liquidus? It does seem that you need the "special monotonic search for troublesome phases" for this particular bulk composition and low fO2. That monotonic option is perfectly valid - it's just slower, and often not required.

Paula