Inside the Subduction Factory

Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 138. Subduction zones helped nucleate and grow the continents, they fertilize and lubricate the earth's interior, they are the site of most subaerial volcanism and many major earthquakes, and they yield a large fraction of the earth's precious metals. They are obvious targets for study—almost anything you learn is likely to impact important problems—yet arriving at a general understanding is notoriously difficult: Each subduction zone is distinct, differing in some important aspect from other subduction zones; fundamental aspects of their mechanics and igneous processes differ from those in other, relatively well-understood parts of the earth; and there are few direct samples of some of their most important metamorphic and metasomatic processes. As a result, even first-order features of subduction zones have generated conflict and apparent paradox. A central question about convergent margins, for instance—how vigorous magmatism can occur where plates sink and the mantle cools—has a host of mutually inconsistent answers: Early suggestions that magmatism resulted from melting subducted crust have been emphatically disproved and recently just as emphatically revived; the idea that melting is fluxed by fluid released from subducted crust is widely held but cannot explain the temperatures and volatile contents of many arc magmas; generations of kinematic and dynamic models have told us the mantle sinks at convergent margins, yet strong evidence suggests that melting there is often driven by upwelling. In contrast, our understanding ofwhy volcanoes appear at ocean ridges and "hotspots"—although still presenting their own chestnuts—are fundamentally solved problems.

Preface vii Introduction: Inside the Subduction Factory John M. Eiler 1 Section I: The Subducted Slab Thermal Structure and Metamorphic Evolution of Subducting Slabs Simon M. Peacock 7 Tracers of the Slab Tim Elliott 23 Basic Principles of Electromagnetic and Seismological Investigation of Shallow Subduction Zone Structure George Helffrich 47 Section II: The Mantle Wedge Seismological Constraints on Structure and Flow Patterns Within the Mantle Wedge Douglas A. Wiens and Gideon P. Smith 59 Rheology of the Upper Mantle and the Mantle Wedge: A View From the Experimentalists Greg Hirth and David Kohlstedf 83 Experimental Constraints on Melt Generation in the Mantle Wedge Glen A. Gaetani and Timothy L Grove 107 Mapping Water Content in Upper Mantle Shun-ichiro Karato 135 Section III: Focus Regions Volcanism and Geochemistry in Central America: Progress and Problems M. J. Carr, M. D. Feigenson, L C. Patino, and J. A. Walker 153 n Overview of the Izu-Bonin-Mariana Subduction Factory Robert J. Stern, Matthew J. Fouch, and Simon L Klemperer 175 Along-strike Variation in Lavas of the Aleutian Island Arc: Genesis of High Mg# Andesite and Implications for Continental Crust Peter B. Kelemen, Gene M. Yogodzinski, and David W. Scholl 223 Section IV: Synthesis Some Constraints on Arc Magma Genesis Yoshiyuki Tatsumi 277 Thermal Structure due to Solid-State Flow in the Mantle Wedge Beneath Arcs Peter B. Kelemen, Jennifer L. Rilling, E. M. Parmentier, Luc Mehl, and Bradley R. Hacker 293