I have some diabase samples (SiO2=47-53 wt. %, MgO=6-10 wt. % and TiO2=0.7-1.2 wt. %), which consist of mainly clinopyroxene and plagioclase. There is no olivine and orthopyroxene appeared in the thin section. How could I calculate the melting temperature and pressure of the diabase samples?
Thanks for your help!
With best regards
Dear Feng Huang,
You can use the algorithm given in Thomas (1990) for a first estimation of the formation temperature. Further information, here in English, you can get from Thomas (1988).
Best regards,
Rainer Thomas
Dear feng
to have a temperature estimation (but always make attention to the results that you get) you can use these two geothermometers:
- Putirka, K., 2008. Thermometers and Barometers for Volcanic Systems. In: Putirka, K., Tepley, F. (eds.). Minerals, Inclusions and Volcanic Processes: Reviews in Mineralogy and Geochemistry. Mineralogical Society of America, 69, 61-120.
- Thy, P., Lesher, C.E., Tegner, C., 2013. Further work on experimental plagioclase equilibria and the Skaergaard liquidus temperature. American Mineralogist, 98, 1360-1367.
The first one is a book where you can find, among the other, a geothermometer based on the cpx-liquid equilibrium. Prof. Putirka in his personal website provides the excel file with the algorithms (http://www.fresnostate.edu/csm/ees/faculty-staff/putirka.html).
The second geothermometer works using the equilibrium plagioclase-liquid
as you can imagine from the title of the paper.
Cheers, Fabio
Dear Feng Huang
I'm very interested in these gabbroic rocks.
As FAbio suggests, there are two thermobarometric models that can be used for your purpose Cpx-melt and Pl-melt.
I usually do this in my works: constraining magma using inverse modelling.
If you are interested we can collaborate to solve the problem.
Ciao
Federico
Dear Rainer Thomas,
Thanks for your suggestion. I have read the references. However, the algorithm you suggested is based on empirical explanation. So I doubt whether I can obtain the reasonable melting temperature and pressure.
Best regards,
Feng Huang
Dear Fabio Carmine Mazzeo,
Thank you. I'm reading the articles you suggested. I still have another question. If the diabase samples crystallization at different depths, could I get different melting temperature and pressure using the two geothermometers?
Best regards,
Feng Huang
Dear Federico Lucci,
Thank you. I recent start to consider the melting temperature and pressure of the mafic magmatism. If there are no phenocryst minerals in the rocks, how could I get the reasonable P-T condition of the melts?
Could I add the olivine step by step into the composition of the melts, until I get the primary magma composition?And then calculate the melting temperature and pressure based on the primary magma?
Best regards,
Feng Huang
Dear Feng
it is of course possible that you get different values of T using different algorithms even if the crystallization pressure is constant during the ascent of magmas.
For example, in trachytic systems, from the results of many experimental works it is now clear that the liquidus appearance of the feldspar, holding P constant, varies from 700 to almost 1000 ° C, depending on the water and/or CO2 precence/absence in the system.
This is to say that the estimate of P and T should be assessed time to time. This is the beautiful and the ugly of natural systems.
If you have not already done, calculate the stoichiometric content Al4 and Al 6 of cpx. This way you can get a qualitative idea of the crystallization P of these cpx (low P/high P).
Cheers, Fabio