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Recent posts
#81
The MELTS family of algorithms, and scientific discussion / Re: Determining Fe2O3 content ...
Last post by Sati - November 11, 2022, 03:11:09 AMThanks Paul for your reply! :)
When I see the change in Fe2O3 behaviour is indeed at the temperature of cpx precipitation in the residue...Thanks!
Sati
When I see the change in Fe2O3 behaviour is indeed at the temperature of cpx precipitation in the residue...Thanks!
Sati
#82
The MELTS family of algorithms, and scientific discussion / Re: Determining Fe2O3 content ...
Last post by asimow - November 08, 2022, 04:26:05 PMDear Sati,
What you are doing sounds correct. The reason the behavior you are seeing is unexpected is that the bulk system Fe2O3 is a combination of two effects: the varying Fe2O3/FeO of the melt (which is what Kress and Carmichael describe) and the varying melt fraction and mineralogy as you crystallize the system. The superposition of these two effects indeed gives a minimum in bulk system Fe2O3, I think at the temperature where clinopyroxene joins the residue.
-- Paul
What you are doing sounds correct. The reason the behavior you are seeing is unexpected is that the bulk system Fe2O3 is a combination of two effects: the varying Fe2O3/FeO of the melt (which is what Kress and Carmichael describe) and the varying melt fraction and mineralogy as you crystallize the system. The superposition of these two effects indeed gives a minimum in bulk system Fe2O3, I think at the temperature where clinopyroxene joins the residue.
-- Paul
#83
The MELTS family of algorithms, and scientific discussion / Determining Fe2O3 content by s...
Last post by Sati - November 08, 2022, 05:54:43 AMHi everyone! I'm a new user and I'm trying to model the variation in Fe2O3 content as a function of fO2 at given P-T conditions, but I have few things that I'm unsure of...
First of all I'm using pMELT at 1GPa and 1600ºC, the process I'm using is to set an fO2, then computing redox state and then execute, and read directly the Fe2O3 content in the Bulk system window, is this the right approach?
What is the meaning of the bulk system composition with respect to the Fe2O3 content? does it indicate the overall Fe2O3 content of melt+solid system? by selecting "phase: liquid-00" this should give the fO2 of the melt produced in this system?
When I decrease the temperature at fixed fO2 and 1GPa, the bulk system Fe2O3 diminishes from 1600 to 1400C but then it rises from 1400 to 1200C, from my understanding there should be a direct relationship between T and Fe2O3 (e.g., Kress and Carmichael 91) which seems to not being followed here when the temperature goes below 1400 C (?)
Sorry for the very basic questions, I'm not yet familiar with the software ::)
Thanks!
First of all I'm using pMELT at 1GPa and 1600ºC, the process I'm using is to set an fO2, then computing redox state and then execute, and read directly the Fe2O3 content in the Bulk system window, is this the right approach?
What is the meaning of the bulk system composition with respect to the Fe2O3 content? does it indicate the overall Fe2O3 content of melt+solid system? by selecting "phase: liquid-00" this should give the fO2 of the melt produced in this system?
When I decrease the temperature at fixed fO2 and 1GPa, the bulk system Fe2O3 diminishes from 1600 to 1400C but then it rises from 1400 to 1200C, from my understanding there should be a direct relationship between T and Fe2O3 (e.g., Kress and Carmichael 91) which seems to not being followed here when the temperature goes below 1400 C (?)
Sorry for the very basic questions, I'm not yet familiar with the software ::)
Thanks!
#84
alphaMELTS 2 text-menu interface / Re: Fractionating water as a f...
Last post by giosp86 - November 03, 2022, 11:17:56 AMPaula, I thank you so much for the very enlightening explanation!!!
Best regards,
Giovanna
Best regards,
Giovanna
#85
alphaMELTS 2 text-menu interface / Re: Fractionating water as a f...
Last post by Paula - October 31, 2022, 01:56:45 PMSee the MELTS decision tree:
https://melts.ofm-research.org/MELTS-decision-tree.html
Generally, you should run 1.2.0 if possible if you have H2O and/or CO2 present.
The exception is if you are trying to model the granite ternary minimum. For that specific case then you should run 1.1.0 if you have CO2. If you don't have CO2 then 1.1.0 and 1.0.2 amount to essentially the same thing.
https://melts.ofm-research.org/MELTS-decision-tree.html
Generally, you should run 1.2.0 if possible if you have H2O and/or CO2 present.
The exception is if you are trying to model the granite ternary minimum. For that specific case then you should run 1.1.0 if you have CO2. If you don't have CO2 then 1.1.0 and 1.0.2 amount to essentially the same thing.
#86
alphaMELTS 2 text-menu interface / Re: Fractionating water as a f...
Last post by giosp86 - October 31, 2022, 07:29:10 AMDear Paula,
Thank you very much for your reply. Actually I'm using the version rhyolite- MELTS 1.1.0 in alphaMELTS 2. I didn't quite understand, but should I use version 1.1.0 only when I have the CO2 content data or can I run it only with the H2O content? Thanks for the clarification regarding the "Mode: fractionate fluids" variable.
Best regards,
Giovanna
Thank you very much for your reply. Actually I'm using the version rhyolite- MELTS 1.1.0 in alphaMELTS 2. I didn't quite understand, but should I use version 1.1.0 only when I have the CO2 content data or can I run it only with the H2O content? Thanks for the clarification regarding the "Mode: fractionate fluids" variable.
Best regards,
Giovanna
#87
alphaMELTS 2 text-menu interface / Re: Fractionating water as a f...
Last post by Paula - October 25, 2022, 02:17:46 PMHi Giovanna,
I'm am sorry for the delay in replying. I had just got back from traveling and your post got buried in trying to catch up.
I'm assuming you mean you are using the rhyolite-MELTS model version 1.1.0. There's not much point using 1.1.0 without CO2. 1.1.0 uses the old water model, same as 1.0.2 (except that it in 1.0.2 it is called 'water' and 1.1.0 it is called 'fluid').
Which version of alphaMELTS 2 are you using? It should say at the top when you run it. The menu options, including those for solids and liquids have been gradually overhauled so it's possible that's why it's not working. Were you typing 'water' or 'fluid' at the menu?
You can also turn on fluid fractionation with a "Mode: fractionate fluids" line in the .melts file.
Best wishes,
Paula
I'm am sorry for the delay in replying. I had just got back from traveling and your post got buried in trying to catch up.
I'm assuming you mean you are using the rhyolite-MELTS model version 1.1.0. There's not much point using 1.1.0 without CO2. 1.1.0 uses the old water model, same as 1.0.2 (except that it in 1.0.2 it is called 'water' and 1.1.0 it is called 'fluid').
Which version of alphaMELTS 2 are you using? It should say at the top when you run it. The menu options, including those for solids and liquids have been gradually overhauled so it's possible that's why it's not working. Were you typing 'water' or 'fluid' at the menu?
You can also turn on fluid fractionation with a "Mode: fractionate fluids" line in the .melts file.
Best wishes,
Paula
#88
General usage / Re: Isentropic fractional crys...
Last post by Paula - October 25, 2022, 01:52:34 PMHi Ri,
I split your posts, as there are six different topics covered and it's difficult to find the original advice posted for the FAQ about quadratic minimization failure.
I'm not quite sure from the information you've given, but if you are using the OFM version of the graphical user interface then there is a bug that can mean that isenthalpic / isentropic calculations get into an infinite loop. See this similar issue:
https://magmasource.caltech.edu/forum/index.php/topic,900.msg1331.html#msg1331
There are Mac and Linux builds that fix this problem on the alphaMELTS links page:
https://magmasource.caltech.edu/alphamelts/links.php?software=gui
The Mac version was built on Mojave, so your mileage may vary now that it is four macOS releases behind the current one. It has become too cumbersome to keep building the old GUI, so if it doesn't work I recommend trying easyMelts instead:
https://magmasource.caltech.edu/alphamelts/links.php
eayMelts doesn't suffer from the bug mentioned above because you always input the number of steps you want it to take.
Paula
I split your posts, as there are six different topics covered and it's difficult to find the original advice posted for the FAQ about quadratic minimization failure.
I'm not quite sure from the information you've given, but if you are using the OFM version of the graphical user interface then there is a bug that can mean that isenthalpic / isentropic calculations get into an infinite loop. See this similar issue:
https://magmasource.caltech.edu/forum/index.php/topic,900.msg1331.html#msg1331
There are Mac and Linux builds that fix this problem on the alphaMELTS links page:
https://magmasource.caltech.edu/alphamelts/links.php?software=gui
The Mac version was built on Mojave, so your mileage may vary now that it is four macOS releases behind the current one. It has become too cumbersome to keep building the old GUI, so if it doesn't work I recommend trying easyMelts instead:
https://magmasource.caltech.edu/alphamelts/links.php
eayMelts doesn't suffer from the bug mentioned above because you always input the number of steps you want it to take.
Paula
#89
The MELTS family of algorithms, and scientific discussion / Re: Melting peridotite under c...
Last post by Paula - October 25, 2022, 11:28:02 AMHi Liz,
Sorry for the late response. A couple of thoughts...
(a) If you think that the starting conditions are going to be above the solidus and you have a fO2 buffer turned on then putting separate FeO and Fe2O3 is redundant but will do no harm. If the starting conditions are subsolidus then you should definitely input separate FeO and Fe2O3, even if you have a buffer imposed (the distribution of FeO and Fe2O3 doesn't have to be all that close to the buffer but not as extreme as all Fe as FeO!) The reason is that the subsolidus start calculated using the norm routine may be far from equilibrium, and the subsolidus fO2 buffer can fail. Hence, the program may turn the buffer off temporarily to get closer to equilibrium, before trying to impose it properly.
(b) I'm not sure which MELTS manual you are looking at but it sounds like it might be out of date. You can run isentropic calculations with an fO2 buffer in more recent versions. In alphaMELTS 1.X you needed set an environment variable (ALPHAMELTS_IMPOSE_FO2) but the rhyolite-MELTS graphical user interface and alphaMELTS 2 both automatically switch between isentropic steps that equilibrate the system with no buffer and isothermal steps that reimpose the buffer. The main differences are that the GUI doesn't have a subsolidus start option, and that alphaMELTS 2 always ends with an equilibration step, rather than a buffering step (GUI is other way round).
(c) I agree with what Paul is implying that you should turn off fractional melting, at least for a start. Maybe explore the space just above the solidus with the fO2 buffer on and look at the resulting residue compositions.
(d) I don't know exactly what steps Paul used. My hunch is that if you avoid turning on the buffer and the liquid in the same step that it should work better. The equivalent of ALPHAMELTS_ALTERNATIVE_FO2 is also implemented inside alphaMELTS 2 - I just need to hook it up to the menu / code that reads the input file. I'll try to get that in the next release, which may help here too.
Cheers,
Paula
Sorry for the late response. A couple of thoughts...
(a) If you think that the starting conditions are going to be above the solidus and you have a fO2 buffer turned on then putting separate FeO and Fe2O3 is redundant but will do no harm. If the starting conditions are subsolidus then you should definitely input separate FeO and Fe2O3, even if you have a buffer imposed (the distribution of FeO and Fe2O3 doesn't have to be all that close to the buffer but not as extreme as all Fe as FeO!) The reason is that the subsolidus start calculated using the norm routine may be far from equilibrium, and the subsolidus fO2 buffer can fail. Hence, the program may turn the buffer off temporarily to get closer to equilibrium, before trying to impose it properly.
(b) I'm not sure which MELTS manual you are looking at but it sounds like it might be out of date. You can run isentropic calculations with an fO2 buffer in more recent versions. In alphaMELTS 1.X you needed set an environment variable (ALPHAMELTS_IMPOSE_FO2) but the rhyolite-MELTS graphical user interface and alphaMELTS 2 both automatically switch between isentropic steps that equilibrate the system with no buffer and isothermal steps that reimpose the buffer. The main differences are that the GUI doesn't have a subsolidus start option, and that alphaMELTS 2 always ends with an equilibration step, rather than a buffering step (GUI is other way round).
(c) I agree with what Paul is implying that you should turn off fractional melting, at least for a start. Maybe explore the space just above the solidus with the fO2 buffer on and look at the resulting residue compositions.
(d) I don't know exactly what steps Paul used. My hunch is that if you avoid turning on the buffer and the liquid in the same step that it should work better. The equivalent of ALPHAMELTS_ALTERNATIVE_FO2 is also implemented inside alphaMELTS 2 - I just need to hook it up to the menu / code that reads the input file. I'll try to get that in the next release, which may help here too.
Cheers,
Paula
#90
The MELTS family of algorithms, and scientific discussion / Re: Melting peridotite under c...
Last post by elipes - October 14, 2022, 11:43:54 AMHi Paul,
Thanks for your feedback! I really appreciate your getting back to me.
a) The composition I have explicitly reports only FeO total—I've attempted to recalculate this into FeO and Fe2O3. If AlphaMELTS 2 allows a user to report only the original FeO total in the MELTS file for the calculation, then impose an FMQ buffer and have the program redistribute and output the total Fe to both FeO and Fe2O3 quantities while melting proceeds, this is definitely preferable.
b) I turned the melt on and off because I was following the steps in a tutorial (https://magmasource.caltech.edu/gitlist/Workshops.git/tree/main/workshop_files/isentropic_melting/alphaMELTS2/) for melting a Workman & Hart depleted upper mantle composition, and attempting to adapt the steps toward my problem. Any unusual sounding decisions on my part are due to unfamiliarity with the program. If I could execute different calculations that follow different melting modes, i.e. melting the composition as a pure fractional melt, and then at a later time melt the composition as a pure batch melt, that would be great however I'm unsure how to accomplish that.
c) I have some melt depleted natural samples (residues) reported in previous literature that recovered from a mid-continental zone, and I need to come up with a melting curve (I'm making a chart that plots Fe isotopic composition against Mg# where I measured the isotopes) that account for them. I'm not exactly sure of the P/T conditions needed to do this, but I have kept increased the temperature and pressure to cause a great enough degree of melting to produce residue with high Mg#s. The composition I want to melt starts with an Mg# of 89.4, and the most depleted literature sample I have has an Mg# of about 92. I want to melt my starting composition to the extent I could plausibly produce a highly depleted residue that looks like my depleted literature samples. Melting the starting composition isentropically at a very high P/T seems to do the trick but I don't think this matches conditions under the continent, my feeling is the P should be much lower. And thus far the program has been unhappy when I've tried to impose an fO2 buffer.
d) Would you mind telling me explicitly what steps you've used within your command/terminal window to execute this composition with the buffer, please? An example of this would be super helpful for me now and in the future.
Thank you again and please let me know if you need more details about what I'm trying to do here!
Cheers, Liz
Thanks for your feedback! I really appreciate your getting back to me.
a) The composition I have explicitly reports only FeO total—I've attempted to recalculate this into FeO and Fe2O3. If AlphaMELTS 2 allows a user to report only the original FeO total in the MELTS file for the calculation, then impose an FMQ buffer and have the program redistribute and output the total Fe to both FeO and Fe2O3 quantities while melting proceeds, this is definitely preferable.
b) I turned the melt on and off because I was following the steps in a tutorial (https://magmasource.caltech.edu/gitlist/Workshops.git/tree/main/workshop_files/isentropic_melting/alphaMELTS2/) for melting a Workman & Hart depleted upper mantle composition, and attempting to adapt the steps toward my problem. Any unusual sounding decisions on my part are due to unfamiliarity with the program. If I could execute different calculations that follow different melting modes, i.e. melting the composition as a pure fractional melt, and then at a later time melt the composition as a pure batch melt, that would be great however I'm unsure how to accomplish that.
c) I have some melt depleted natural samples (residues) reported in previous literature that recovered from a mid-continental zone, and I need to come up with a melting curve (I'm making a chart that plots Fe isotopic composition against Mg# where I measured the isotopes) that account for them. I'm not exactly sure of the P/T conditions needed to do this, but I have kept increased the temperature and pressure to cause a great enough degree of melting to produce residue with high Mg#s. The composition I want to melt starts with an Mg# of 89.4, and the most depleted literature sample I have has an Mg# of about 92. I want to melt my starting composition to the extent I could plausibly produce a highly depleted residue that looks like my depleted literature samples. Melting the starting composition isentropically at a very high P/T seems to do the trick but I don't think this matches conditions under the continent, my feeling is the P should be much lower. And thus far the program has been unhappy when I've tried to impose an fO2 buffer.
d) Would you mind telling me explicitly what steps you've used within your command/terminal window to execute this composition with the buffer, please? An example of this would be super helpful for me now and in the future.
Thank you again and please let me know if you need more details about what I'm trying to do here!
Cheers, Liz