Orogenic Andesites and Plate Tectonics

1 What is "Typical Calcalkaline Andesite"?.- 1.1 Introduction.- 1.2 Definition of Orogenic Andesite.- 1.3 Magma Series Containing Orogenic Andesites.- 1.4 Overview.- 2 The Plate Tectonic Connection.- 2.1 Spatial Distribution of Active Orogenic Andesite Volcanoes.- 2.2 Initiation of Subduction.- 2.3 Cessation of Subduction.- 2.4 Collisions.- 2.5 Reversal of Subduction Polarity.- 2.6 Forearc and Transform Fault Volcanism.- 2.7 Anomalously Wide Volcanic Arcs.- 2.8 Andesites Clearly Not at Convergent Plate Boundaries.- 2.9 Conclusions.- 3 Geophysical Setting of Volcanism at Convergent Plate Boundaries.- 3.1 Topography, Gravity, Heat Flow, and Conductivity.- 3.2 Crustal Thickness, Structure, and Age.- 3.3 Upper Mantle Beneath the Forearc, Volcanic Arc, and Backarc Regions.- 3.4 Dipping Seismic Zones (Benioff-Wadati Zones) and Underthrust Lithosphere.- 3.5 Partial Melting and Magma Ascent Beneath Volcanic Arcs.- 3.6 Magma Chambers Beneath Orogenic Andesite Volcanoes.- 3.7 Conclusions.- 4 Andesite Magmas, Ejecta, Eruptions, and Volcanoes.- 4.1 Characteristics of Andesite Magma.- 4.1.1 Temperature.- 4.1.2 Density.- 4.1.3 Rheology.- 4.1.4 Miscellaneous Properties and Applications.- 4.2 Andesite Rock, Eruption, and Edifice Types.- 4.3 Variations in Magma Composition During and etween Historic Andesite Eruptions.- 4.4 Variations in Rock Composition During Evolution of Stratovolcanoes.- 4.5 Conclusions About Andesite Magma Reservoirs.- 4.6 Stress Fields and Volcano Spacings Within Volcanic Arcs.- 4.7 Relationships Between the Timing of Arc Volcanism and Plate Movements.- 4.8 Magma Eruption Rates at Convergent Plate Boundaries.- 4.9 Relative Proportions of Andesite.- 5 Bulk Chemical Composition of Orogenic Andesites.- 5.1 Rock Analyses: Significance, Averages, and Representative Samples and Suites.- 5.2 Major Elements.- 5.2.1 Silica Contents and Harker Variation Diagrams.- 5.2.2 Alkalies.- 5.2.3 Iron and Magnesium.- 5.2.4 Titanium.- 5.2.5 Aluminum and Calcium.- 5.2.6 Phosphorous.- 5.2.7 CIPW Normative Mineralogy.- 5.3 Volatiles.- 5.3.1 Water.- 5.3.2 Carbon Dioxide.- 5.3.3 Sulfur.- 5.3.4 Halogens.- 5.3.5 Oxygen.- 5.4 Trace Elements.- 5.4.1 The K-Group: Rb, Cs, Ba, and Sr.- 5.4.2 REE Group: Rare Earth Elements Plus Y.- 5.4.3 The Th Group: Th,U, and Pb.- 5.4.4 The Ti Group: Zr, Hf, Nb, and Ta.- 5.4.5 The Compatible Group: Ni, Co, Cr, V, and Sc.- 5.4.6 The Chalcophile Group: Cu, Zn, and Mo.- 5.4.7 Trace Element Systematics.- 5.5 Isotopes.- 5.5.1 Strontium.- 5.5.2 Lead.- 5.5.3 Neodymium.- 5.5.4 Inert Gases.- 5.5.5 U-Disequilibrium.- 5.5.6 Oxygen.- 5.5.7 Synthesis of Isotope Data.- 5.6 Comparison with Andesites Not at Convergent Plate Boundaries.- 5.7 Geochemical Distinctiveness of Volcanism at Convergent Plate Boundaries.- 5.8 Conclusions: Chemical Diversity of Orogenic Andesites.- 6 Mineralogy and Mineral Stabilities.- 6.1 Plagioclase.- 6.2 Pyroxenes.- 6.3 Amphibole.- 6.4 Olivine.- 6.5 Oxides.- 6.6 Garnet.- 6.7 Other Minerals.- 6.8 Inclusions in Orogenic Andesites.- 6.9 Mineral Stabilities in Andesite Magma.- 6.10 Trace Element Equilibria Between Minerals and Melt.- 6.11 Conclusions.- 7 Spatial and Temporal Variations in the Composition of Orogenic Andesites.- 7.1 Variations in Magma Composition Across Volcanic Arcs.- 7.2 Variations in Magma Composition Along Volcanic Arcs.- 7.3 Effects of Plate Convergence Rate on Magma Composition.- 7.4 Relationships Between Compositions of Orogenic Andesites and Adjacent Oceanic Crust.- 7.5 Changes in the Composition of Orogenic Andesites During Earth History.- 8 The Role of Subducted Ocean Crust in the Genesis of Orogenic Andesites.- 8.1 Characteristics of Subducted Ocean Crust Beneath Volcanic Arcs.- 8.2 Circumstantial Evidence of Slab Recycling in Arc Volcanism.- 8.3 Are Orogenic Andesites Primary Melts of Subducted Ocean Floor Basalt? No.- 8.4 The Sediment Solution.- 8.5 IRS Fluids and Maxwell's Demons.- 8.6 Conclusions.- 9 The Role of the Mantle Wedge.- 9.1 Characteristics of the Mantle Wedge.- 9.2 Circumstantial Evidence that Arc Magmas Originate Within the Mantle Wedge.- 9.3 Are Orogenic Andesites Primary Melts of Only the Mantle Wedge? Rarely.- 9.4 Fluid Mixing, Metasomatism, and Demonology in the Mantle Wedge.- 10 The Role of the Crust.- 10.1 Circumstantial Evidence for Crustal Involvement in Orogenic Andesites.- 10.2 Crustal Anatexis.- 10.3 Crustal Assimilation.- 11 The Role of Basalt Differentiation.- 11.1 General Arguments for and Against Differentiation.- 11.2 Roles of Plagioclase, Pyroxenes, and Olivine.- 11.3 Role of Magnetite and the Plagioclase-Orthopyroxene/Olivine-Augite-Magnetite (POAM) Model.- 11.4 Role of Amphibole.- 11.5 Role of Garnet.- 11.6 Role of Accessory Minerals: Apatite, Chromite, Sulfides, Biotite.- 11.7 Role of Magma Mixing.- 11.8 Role of Other Differentiation Mechanisms.- 11.9 Differentiation Processes Leading to Andesites in Anorogenic Environments.- 12 Conclusions.- 12.1 Andesite Genesis by POAM-Fractionation: the Most Frequent Mechanism.- 12.2 Some Outstanding Problems Requiring Clarification.- 12.3 Origin of Tholeiitic Versus Calcalkaline Andesites.- 12.4 Origin of Across-Arc Geochemical Variations.- 12.5 Epilog.- References.