rexn - 1 METAMORPHIC REACTIONS Since we have decided to use...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
1 METAMORPHIC REACTIONS Since we have decided to use an equilibrium approach for studying metamorphic rocks, the law of mass action can be applied to any metamorphic reaction. This means that every metamorphic reaction will have “an equilibrium constant”. Types of Metamorphic reactions: On the basis of applying the phase rule, any metamorphic reaction will belong to one of two types: (a) Discontinuous reactions : are those which are univariant on P-T diagrams in the "model" system considered. A discontinuous reaction takes place between phases of fixed chemical composition, and will always occur at the same P-T conditions for the compositions defined. (b) Continuous reactions : are those which take place over a range of P and T as a result of solid solution in one or more of the phases involved. Accordingly, in the model system, such reactions are characterized by assemblages that are at least divariant. Unlike discontinuous reactions, reactants and products can coexist over an range of P and T, but where at least one of the phases constantly changes its composition. The flow chart provided presents a more detailed classification, where reactions are divided into two main groups on the basis of the type of phases involved; homogeneous equilibria are those that take place between similar phases (i.e. solids because of our interest in metamorphic rocks), and heterogeneous equilibria, those involving a fluid phase (in addition of course to the solids). I- Homogeneous Equilibria: A- Solid - solid reactions: Characteristics: 1- All phases taking part in the reaction are condensed phases (i.e. solids). 2- For the most part, they exhibit very little curvature if any, when plotted on P-T diagrams. (Curvature usually arising from ordering of one of the phases). 3- They tend to have shallow slopes in P-T space, and are therefore more sensitive to changes in P rather than T. This property makes many such reactions good geobarometers. Types (1) Polymorphic transitions : e.g. Ky Sill, Calcite Aragonite, Graphite Diamond, α -quartz β -quartz.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/28/2012 for the course GLY 421 taught by Professor Staff during the Fall '11 term at Marshall.

Page1 / 5

rexn - 1 METAMORPHIC REACTIONS Since we have decided to use...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online