Geology 314 Igneous Petrology

Dr. Martin Klausen

Synopsis

Igneous rocks are any rocks that initially crystallized from a magma (= silicate melt + crystals + gases). Magmas form (by melting of a source rock); migrate and ascent towards the surface; evolve (by fractional crystallization, mixing, etc.); emplace, either at the surface (volcanoes) or at depth (plutons); and cool down to crystallize.

This course examines

(1) most important types of igneous rock types (basaltic, gabbroic, ultramafic, andesite-dacite-rhyolites, granitic and alkaline rocks); (2) the tools that geologists use to study igneous rocks (thin-section petrography, major and trace element geochemistry and experimental petrology – phase diagrams); (3) the processes, from partial melting of source rocks, through diversification of primary melts (e.g., fractional crystallization, mixing, etc.), to final cooling and crystallization, that lead to the formation of volcanic as well as intrusive/cumulative igneous rocks; (4) most important associations of igneous rocks (oceanic islands, continental flood basalts, ophiolites and oceanic crust, layered intrusions, island and continental arcs as well as in orogenies, continental rifts), including more unusual igneous rock types from the Archaean.

The curriculum provides a broad and comprehensive knowledge base, but the course also emphasises the scientific approach, whereby field relationships, petrographies and compositions of igneous rocks are first described and processes are subsequently deduced from such facts. The student will therefore, as far as possible, practise his/her skills at reporting such observations, descriptions and interpretations of natural objects both verbally and in writing.

A five day Geology 374 Field Skills trip will be held during the April break to examine and map field relationships amongst gabbros, diorites, granites and possible ignimbrites across the West Coast (mostly on Cape Columbine). This independently marked Field Skills report forms the basis for two subsequent practical assignments on (1) thin section petrography, and (2) bulk rock geochemistry, of samples collected from this study area, compared to available data on other igneous rocks from this approximately 520-560 Ma old Cape Granite Suite.


Goals

  • (1) Understand the tools used to study igneous rocks;

  • (2) Understand the processes leading to the formation, evolution and emplacement of magmas;

  • (3) Obtain general knowledge on the main groups of igneous rocks;

  • (4) Develop an ability to describe and interpret igneous rocks, and present observations and interpretations in a scientific, structured wa


Course outcome

Students should have the following skills at the end of the course

  • General knowledge on the main groups of igneous rocks, their origins and models of formation;

  • Understanding of the main processes that lead to the formation, evolution and emplacement of magmas and accumulating crystals;

  • Understanding of the tools used to study igneous rocks (field observations, optical mineralogy, geochemistry, physical and chemical phase diagrams);

  • Ability to describe igneous rocks at all scales (from outcrop, through thin section petrography to geochemical analysis) and to provide at least some elements of interpretation, using basic tools and concepts;

  • Ability to present the above as a structured, rigorous scientific text, or orally, where factual evidence clearly support interpretations.


Study material and textbooks

In addition to the reference books used for Geology 224 and 254 (that remain useful!), students should use the following book, that is the most recent and applicable for Geol314:

Gill, Robin. Igneous Rocks and Processes. Wiley-Blackwell, 2010.

Lectures and pracs attempt to follow this textbook as stringently as possible and thereby becomes much of the course curriculum that you will be examined in. Lecture and prac slides will be available on SunLearner soon AFTER these have been presented in class. Lecture and prac slides from previous years are also available.


Learning opportunities

My best advice is that every student, as a minimum, reads relevant sections of Gill (2010) BEFORE every lecture and prac. The better prepared you are the more you get out of my classes. Students are also encouraged to consult different text books (e.g., Winter, J.D. An introduction to igneous and metamorphic petrology. Prentice Hall, 2010), web sites, as well as read journal articles. Multiple choice tests will as far as possible be made available every week(end) for the student to test his/her progress, but these are not included in your class mark. Likewise, exercises and questions are provided at the end of Gill’s (2010) chapters as well as supplementary question material from Winter (2010), and these offer an excellent way to train yourself ahead of marked tests and the final exam. After the most important attribute of being prepared, practise makes perfect.