Geology 407a Petrology

Exam 1 Study Guide

(be sure to review web page notes)


Earth structure

General plate tectonics

Review Bowen's reaction series

Know what is meant by magma differentiation

***Know what elements occur in the following minerals: quartz, muscovite, K-feldspar, plagioclase feldspar (anorthite to albite), nepheline, leucite, hornblende, clinopyroxene (diopside, augite), orthopyroxene (enstatite, hypersthene), olivine (forsterite to fayalite), biotite.


Physical properties of magmas

What is a silicate liquid?

Concept of a silicate network - network formers and modifiers

Magma viscosity & relationship to network

Magma temperatures

Magma viscosity

Magma density & relationship to ascent from the mantle and crystal settling issues

Magmatic volatiles - what species are present , how does solubility of H2O depend on T & P


Rock classification

Major oxides that make up magmas

Normative classification scheme. How is it done? What is assumed? Why is it useful?

Modal classification - IUGS. Make sure you know how to use all the triangles! Bring your plastic triangle to the exam.

Textural terms: phaneritic, aphanitic, holocrystalline, hypocrystalline, holohyaline, euhedral, subhedral, anhedral, idiomorphic, hypidiomorphic, allotriomorphic, granular, foliated, lineated, porphyritic

Chemical classification of volcanic rocks: alkaline and subalkaline series, calcalkaline versus tholeiitic (and their relationship to plate tectonic setting)


Unary and Binary phase diagrams

Purpose of phase diagrams

Terminology: phase, system, intensive and extensive parameters, component, equilibrium

The phase rule, calculate degrees of freedom

Invariant, univariant, and divariant fields on phase diagrams. What do they mean?

Be able to determine the number of components versus the number of phases in a system

Terminology: liquidus, solidus, eutectic, peritectic

Know how to read these temperature versus composition diagrams - be able to determine composition of liquid, composition of solid phases, eutectic proportions

What is physically happening at the eutectic. Why can't temperature drop?

Simple two component binary diagrams with 2 endmember phases

Binary diagrams with intermediate compounds:

Solid solution diagrams - know process

Simple ternary diagrams - know how they are put together


Magma differentiation and layered intrusions

Mechanisms for magma differentiation

How do we chart compositional changes? (Harker diagrams, etc)

What are parental magmas? Primary magmas?

How do layered intrusions help us to understand magma differentiation processes?

What are some typical characteristics of layered intrusions?

Understand how a sequence of rock such as dunite overlain by harzburgite overlain by pyroxenite is formed (i.e., using a relevant phase diagram)


Basalts (MORBs and ophiolites)

What is a MORB?

MORB: magma generation in light of plate tectonics, magma chambers (slow vs fast spreading)

What is an ophiolite?


OIBs and CFBs

Where do we find OIBs?

What are their characteristics? what types of fractionation trends do we find?

Hawaiian islands as model

Eruptive histories: pre-shield, shield-building stage, caldera-filling stage, post-erosional stage

Origin of OIBs