Hi everyone,
Does anyone have an idea about how do we know the partitioning coeffecient of Ti in rutile equilibrated with felsic melts? This is important for trace element modeling of felsic magma if rutile is stable in the magma source. I saw that Bedard (2006GCA) used a value of 45, but I am not sure if this value is appropriate. How was this determined? Is it too low? Because Ti is the constituent of rutile, obviously we cannot simply use the ratio of Ti in melts and Ti in rutile (0.6) if I understand correctly.
Thanks for your help!
Rongfeng Ge
Hi James,
Thanks for your reply. Your answer makes sense to me. What I more want to know is the Ti partitioning coefficient in rutile used for trace element modelling when rutile is a residual phase in the magma source. I know for a trace element, partitioning coefficient can be determined by partial melting experiment as the ratio of that element in the mineral and melt in equilibrium, but I am not sure if this can be applied to major element like Ti in rutile. I read a few papers about partitioning coefficient of trace elements in rutile like Nb, Ta, Zr, Hf, but none of them mentioned Ti. May be the concept of partitioning coefficient does not apply to a major element?
Cheers,
Rongfeng
It is not properly correct to talk about partition coefficient of Ti in TiO2.
Nobody would describe the Si partition coefficient in quartz or Ca partition coefficient in aragonite.
Partition coefficients are measured for trace element only.
michele
Hi Michele,
I think you are right, that is what confuse me, bacuase in several papers about trace element modeling, Ti in rutile seems to be modeled as a trace element, with a patitioning coefficient of 45. I am not sure if this is correct, and if not, how shoulwe deal with rutile when it is a residual in magma source?
Cheers,
Rongfeng
Perhaps that makes sense. If rutile is present, then the magma is saturated with TiO2 and the concentration of Ti in the magma is fixed (the excess gets precipitated as rutile and other phases such as ilmenite). If this fixed concentration is 45 times less than the Ti content in rutile (in terms of weight percent, approximately 60%, assuming 100% TiO2 and no other components such as iron or Nb/Ta oxides), then there must be 1.33% Ti (or 2.2% TiO2) in the melt.
Iskandar