The mineral assemblage and reaction relationships that you deduced on the previous page are shown again here. Mouseover the T-P diagram on the left to see mineral assemblages on the ternary diagram on the right.
The mineral assemblage that occurs in a rock at equilibrium depends not only on the stable assemblage diagram, but also on the bulk composition of the rock. Click on the "Show BC" button. A red mark will appear on the assemblage diagrams showing a bulk composition that will yield equilibrium assemblages that match almost all of the mineral assemblages observed in the cmSerpentinite samples. Click on the "Show MAD" button. The T-P reaction diagram will be replaced by a T-P "Mineral Assemblage Diagram" (MAD) specific to the red mark bulk composition.
One of the cmSerpentinite rocks has a mineral assemblage that cannot represent equilibrium for a rocks with the red mark bulk composition. Which rock is it? Choose from the pulldown list:
Yes! The assemblage Tr-Tlc-Ath is not shown as an equilibrium triangle around the red mark bulk composition. This mineral assemblage is stable in the same equilibrium mineral assemblage diagram (H.) that contains the assemblage Tr-Ath-Fo, but for a rock with much more silica in the bulk composition.No. Please try again.
If the rocks have equilibrium mineral assemblages, the mineral assemblage of cmSerpentinite_004 is only possible if the pressure is below 0.6 GPa (see the T-P diagram). Conservatively estimating the presure of the contact aureole at 0.4 GPa, and assuming that the mineral assemblages represent equlibrium, what is the minumum temperature needed to form rock cmSerpentinite_007 with the assemblage Tr-Atg-Fo? Choose from the pulldown list:
Yes! The assemblage Tr-Atg-Fo requires a minimum temperature of 500°C at 0.4 GPa. No. Please try again.
At equilibrium, what is the minimum temperature required to form the mineral assemblage of cmSerpentinite_003 with the assemblage Tr-En-Fo at 0.4 GPa? Choose from the pulldown list:
Yes! The assemblage Tr-En-Fo requires a minimum temperature of 700°C at 0.4 GPa. No. Please try again.
A minimum temperature of 680°C is higher than expected for a "simple" contact aureole with "instantaneous" emplacement of an intrusion at a reasonable temperature (1100°C for a basalt) into cold (0°C) rocks. This is important information for understanding the conditions of formation of the contact aureole.
