Igneous petrogenesis. A global tectonic approach

My main objective in writing this book has been to review the processes involved in present-day magma generation and their relationship to global tectonic processes. Clearly, these are fundamental to our understanding of the petrogenesis of ancient volcanic and plutonic sequences, the original tectonic setting of which may have been obscured by subsequent deformation and metamorphism.

Until fairly recently, undergraduate courses in igneous petrology tended to follow rather classical lines, based on the classification of igneous rocks, descriptive petrography, volcanic landforms, types of igneous intrusions and regional petrology. However, the geologist of the late 1980s requires, in addition, an insight into the fundamental processes which operate within the Earth, and are responsible for the diversity of igneous rocks presently exposed. Unfortunately, attempts to make petrology

courses more petrogenesis-orientated are immediately confronted with a basic problem; the average student does not have a strong enough background in geochemistry to understand the finer points of most of the relevant publications in scientific journals. It is virtually impossible to find suitable reading material for such students, as most authors of igneous petrology textbooks have deliberately steered clear of potentially controversial petrogenetic models. Even the most recent texts place very little emphasis on the geochemistry of magmas erupted in different tectonic settings, despite extensive discussions of the processes responsible for the chemical diversity of magmas. Perhaps even more surprisingly, few texts have attempted to relate igneous activity to global tectonic processes, except at the most elementary levels.