Effect of chromium on phase relations in the join forsterite-anorthite-diopside in air at 1 Atm
✍ Scribed by Kosuke Onuma; Tatsuhide Tohara
- Publisher
- Springer
- Year
- 1983
- Tongue
- English
- Weight
- 720 KB
- Volume
- 84
- Category
- Article
- ISSN
- 0010-7999
No coin nor oath required. For personal study only.
✦ Synopsis
The effect of Cr on the silicate system has been studied in air at I arm by adding a small amount of MgCr204 (0.2-0.5 wt.%) to the join Mg2SiO 4 (forsterite) -CaA12Si208 (anorthite) -CaMgSi206 (diopside), which has been considered to form a thermal divide in the system CaO-MgO-A1203 -SiO 2. The spinel primary field is enlarged compared with that in the Cr-free join at the expense of the anorthite primary field. The piercing points forsterite + anorthite + diopside +liquid and forsterite + anorthite + spinel + liquid approach each other with increasing MgCr204, meet at the join with 0.25wt.% MgCr204 (0.20 wt.% Cr203) to form the 'isobaric quaternary invariant point' forsterite + anorthite + diopside + spinel + liquid, and then separate again as new 'piercing points' of diopside + spinel + anorthite + liquid and forsterite + diopside + spinel+liquid. This process indicates that the join Mg2SiO4-CaA12Si20 s-CaMgSi206 containing more than 0.2 wt.% Cr203 cannot be a thermal divide in the basalt tetrahedron. The results of the present study show that the presence of a minor amount of Cr causes a significant effect on the phase relations and therefore, the role of Cr must be taken into account in the formulation of a petrologic model.