Maaloe S. Principles of Igneous Petrology

Springer, 1985. — 388 p. — ISBN: 978-3-642-49356-0.Igneous petrology was to some extent essentially a descriptive science until about 1960. The results were mainly obtained from field work, major element analyses, and microscopical studies. During the 1960's two simultaneous developments took place, plate tectonics became generally accepted, and the generation of magmas could now be related to the geodynamic features like convection cells and subduction zones. The other new feature was the development of new analytical apparatus which allowed high accuracy analyses of trace elements and isotopes. In addition it became possible to do experimental studies at pressures up to 100 kbar. During the 1970's a large amount of analytical data was obtained and it became evident that the igneous processes that control the compositions of magmas are not that simple to determine. The composition of a magma is controlled by the compositions of its source, the degree of partial melting, and the degree of fractionation. In order to understand the significance of these various processes the relationship between the physical processes and their geochemical consequences should be known. Presently there are several theories that attempt to explain the origin of the various magma types, and these theories can only be evaluated by turning the different ideas into quantitative models. We will so to speak have to do some book keeping for the various theories in order to see which ones are valid. the present book is intended as an introduction to the more fundamental aspects of quantitative igneous petrology.
Apart from using quantitative analysis as an evaluation of ideas, the application of physicochemical equations has a much more significant potential. Many if not most igneous processes can not be observed, and will never be observed. Processes like convection in the mantle and magma chambers, dyke propagation, and magma accumulation in the mantle can not be observed directly. These and other processes can only be understood by developing quantitative models. Hence, the application of physical and chemical principles, by using equations and various constants, is mandatory for the understanding of the generation of magmas.
The attempt to convert an idea into equations is frequently a difficult task, and this represents a real challenge for the present generation of the students of igneous petrology. It is hoped that the present book will assist the graduate students to a quantitative treatment of petrology, although the present book only represents a beginning.
Clearly in order to bring further development to igneous petrology it is nescessary to apply physicochemical principles. However, the new ideas, the creative insight, is hardly attained by reading text books on physics. There is still a lot left for the individual petrologist to discover without the direct aid of the exact sciences, but some training in these will no doubt prove most useful.