In the given ternary (Fo = forsterite; Di = diopside; An = anorthite) eutectic diagram, the point A represents the composition of magma. What will be the sequence of crystallization during cooling of this magma?
The ternary eutectic diagram given is a representation of the crystallization sequence in the system composed of forsterite (Fo), diopside (Di), and anorthite (An). The point A represents the composition of the magma. Let's analyze the crystallization process as the magma cools.
- Initial Crystallization: As the magma starts cooling, the first mineral to crystallize is closest to the liquid composition. In this system, olivine (Fo) will crystallize first because point A is closest to the olivine apex compared to other minerals.
- Formation of Olivine + Pyroxene: As cooling continues, the composition of the remaining liquid moves toward the diopside (Di) apex in the diagram. This results in simultaneous crystallization of olivine and pyroxene.
- Final Crystallization of Olivine, Pyroxene, and Plagioclase: Eventually, the remaining liquid moves towards the eutectic point, where olivine, pyroxene (Di), and plagioclase (An) crystallize together.
Therefore, the sequence of crystallization during cooling of this magma is as follows:
- Olivine
- Olivine + Pyroxene
- Olivine + Pyroxene + Plagioclase
Hence, the correct answer is: Olivine, Olivine + Pyroxene, and Olivine + Pyroxene + Plagioclase.
Important Questions from Igneous Petrology (Binary and Ternary Phase Diagrams)
If 'X' represents the initial composition of a melt, which one of the trends indicated by arrows in the schematic diagram corresponds to the evolution of the residual melt composition during crystallization of diopside?
The diagram given below shows phase relations between components P and Q at 1 bar pressure. If ‘X' represents the initial liquid composition, which of the following statements is/are CORRECT during equilibrium crystallization?
- Choose the CORRECT statement regarding crystallization of a single feldspar of composition $Or_{50}Ab_{50}$ in the Albite-Orthoclase system.
The following diagram shows phase relations in a system consisting of components A and B at 1 bar pressure. If the initial composition of liquid is R, during cooling and crystallization of magma, which of the following statement(s) is/are CORRECT?
The figure below represents an isobaric binary liquidus phase diagram, with the solid phases A, B and C. What are the degrees of freedom associated with equilibrium phase assemblages represented by the bulk compositions w, x, y and z, in the fields indicated in the figure?
