Andesites: Orogenic Andesites and Related Rocks

The orogenic andesite association is the basalt-andesite-dacite-rhyolite association characteristic of island ares, active continental margins, and continental collision zones. This book is intended as a reference text for under graduate, postgraduate, and research workers who wish to gain an insight into the orogenic andesite association. It contains invited contributions covering the geology, volcanology, petrology, and geochemistry of orogenic andesites and related rocks, the role of such rocks through geological time, and the wider implications of andesite volcanism such as continental growth and the formation of economic mineral deposits. There were several reasons for producing such a volume. These include the abundance and importance of orogenic andesite volcanism in continental areas, and the important advances in our understanding of such volcanism achieved since the development of pi ate tectonics in the late 1960s. Noting the existence of several volumes devoted to the rarer alkaline rocks, it was felt that it would be valuable to produce a volume devoted entirely to the orogenic andesite association. The volume is divided into 10 sections, chosen to cover all aspects of the association. Section I is a brief introduction to the setting of orogenic andesite volcanism and how the problems posed by these volcanic rocks have evolved during the last few decades. Section II is a general account of the terminology and classification of orogenic volcanic rocks, with a review of the petrology and mineralogy. In Section III, the characteristics of each of the major orogenic volcanic provinces are reviewed and Section IV outlines the evolution of volcanism through time in relation to plate tectonic activity in contrasted provinces. The later sections of the book outline the characteristics of andesite volcanoes and their products (Section V), the relationship of andesitic volcanism to intrusive activity (Section VI), and experimental, chemical, and isotopic characteristics of andesites and related orogenic volcanic rocks (Sections VII and VIII). Some characteristics of andesite volcanism throughout geological time are explained by reference to Archaean volcanic rocks and to Upper Proterozoic volcanism in north-eastern Africa and Arabia and Lower Palaeozoic volcanism in the Caledonian orogenic belt of Britain (Section IX). In conclusion, Section X emphasizes the importance of andesitic volcanism by examining the role of such volcanism in continental growth, in large-scale geochemical cycles, in the eruption of volcanic gases, and in the formation of mineral deposits.