![igneous ternary diagram igneous ternary diagram](https://geea.lyellcollection.org/content/geochem/17/2/63/F17.medium.gif)
talc is stable to much higher temperatures of ~750☌, and breaks down at granulite-facies conditions.tremolite appears at conditions close to where antigorite disappears, and indicates amphibolite facies.
![igneous ternary diagram igneous ternary diagram](https://www.mdpi.com/geosciences/geosciences-10-00340/article_deploy/html/images/geosciences-10-00340-g011.png)
antigorite is stable to ~400☌, and is equivalent to greenschist-facies conditions.Reactions in the CMS(H) system at low pressures-the model system for peridotite If there are 0 degrees of freedom, 0 + P=3 + 2, P=5 there are five phases at an invariant point The four phases create crossing tie linesīulk composition lies within the intersection of the two 3-phase triangles If there is 1 degree of freedom (P or T), 1 + P=3 + 2, P=4 there are four phases along a univariant line-a reaction These three phases define a triangle on the CMS diagramĪ different bulk composition defines a different 3-phase triangle at the same P&T If there are 2 degrees of freedom (P and T), 2 + P=3 + 2, P=3 there are three phases in a divariant field Serpentine (the three polymorphs are chrysotile, lizardite, antigorite) contains (Mg,Fe)SiO(OH) To understand the petrogenesis of ultramafic rocks using the CaO-MgO-SiO system, we plot the phases using molar proportions on a triangle with one component at each apex Which you can see nicely in this closeup: The layering is formed by different proportions of olivine, opx, cpx, and garnet: Here's a famous outcrop at Helgehornvatnet in Norway: In the field, ultramafic rocks are mostly seen in the basal sections of ophiolites and as exhumed pieces of the upper mantle. Peridotites also contain an aluminous phase, either plagioclase, spinel, or garnet. Modeling of meta-lherzolites requires the addition of Ca, which can be done with three components as CaO-MgO-SiO, assuming excess H 2O. Metamorphism of harzburgites can conveniently be modeled using Mg-Si-O-H. Extraction of basalt via melting leads to loss of the cpx and the production of an olivine + opx residuum called harzburgite. Enriched upper mantle is lherzolite: olivine + opx + cpx.
![igneous ternary diagram igneous ternary diagram](https://media.cheggcdn.com/media%2Fe17%2Fe17465cd-2d80-457c-adcd-8412f7f1b9c9%2Fimage.png)
The upper mantle is composed of ultramafic rocks (peridotites), different proportions of olivine (forsterite to fayalite) + orthopyroxene (enstatite to ferrosilite) + clinopyroxene (diopside to hedenbergite). Ultramafic Rocks Read Chapter 29.2 of Igneous and Metamorphic Petrology by John Winter or Chapter 18 of Igneous and Metamorphic Petrology by Philpotts The three-component system CMS (Ca-Mg-Si): Ultramafic Rocks Interaction Between Metamorphism and Deformation Introductory Phase Equilibria and Thermodynamics