ALBERT

Note: Introduction / Charles E. Chapin and Wolfgang E. Elston References cited Ash-flow magmatism / Robert L. Smith Abstract Introduction Volumes of ash-flow sheets Size of magma chambers Zoned magma chambers Crater Lake, Oregon Bandelier Tuff, New Mexico SiO₂ and phenocryst variation in ash-flow sheets Periodicity-volume-composition relationships Discussion of model Summary and conclusions Acknowledgments References cited Cooling units and composite sheets in relation to caldera structure / Robert L. Christiansen Abstract Introduction Examples of ash-flow-caldera relations Mazama eruption and Crater Lake caldera Bandelier Tuff and Valles-Toledo calderas Thirsty Canyon Tuff and Black Mountain caldera Timber Mountain-Oasis Valley caldera complex Yellowstone Plateau volcanic field General pattern of ash-flow-caldera relations Acknowledgments References cited The Bishop Tuff: Evidence for the origin of compositional zonation in silicic magma chambers / Wes Hildreth Abstract Introduction Eruptive sequence Major units Units of uncertain correlation Summary of eruptive sequence Eruptive temperatures Accuracy and precision of T-fₒ₂ data Mineralogy Fe-Ti oxides Quartz Sanidine Plagioclase Biotite Pyroxenes Allanite Zircon Apatite Pyrrhotite Whole-rock chemistry Major elements Trace elements Compositional gaps Origin of the compositional zonation Crystal settling Assimilation Basaltic underplating Liquid immiscibility Progressive partial melting Trace elements during partial melting Convection-driven thermogravitational diffusion Lines of evidence Concluding remarks Acknowledgments References cited Rare-earth-element content of some highly differentiated ash-flow tuffs and lavas / Donald C. Noble, Ward L. Rigot, and Harry R. Bowman Abstract Introduction Specimens studied and methods of chemical analysis Results and discussion Acknowledgments References cited Geochemistry of the Los Chocoyos Ash, Quezaltenango Valley, Guatemala / William I. Rose, Jr., Norman K. Grant, and John Easter Abstract Introduction Field description Geochemistry Mineralogy and mineral chemistry Sr-isotope data Modeling of crystal fractionation Time required for crystal fractionation Conclusions Acknowledgments Appendix 1. Analytical methods References cited Geochemical correlation of genetically related rhyolitic ash-flow and air-fall ashes, central and western Guatemala and the equatorial Pacific / Gregory A. Hahn, William I. Rose, Jr., and Thomas Meyers Abstract Introduction Previous investigations of chemical fingerprinting The Los Chocoyos Ash and the stratigraphic sequence of the San Cristobal Group Characteristics of the ash-flow member Sample acquisition and preparation Trace-element analyses Chemical correlation Lateral chemical variations Source of the Los Chocoyos Ash Age of the Los Chocoyos Ash Conclusions Acknowledgments References cited Ignimbrites of the Sierra Madre Occidental and their relation to the tectonic history of western Mexico / Fred W. McDowell and Stephen E. Clabaugh Abstract Introduction Volcanic stratigraphy of the Sierra Madre Occidental Pre-Cretaceous volcanic rocks Lower volcanic complex Unconformity between the igneous sequences Upper volcanic supergroup Calderas of the upper volcanic supergroup Structure of the Sierra Madre Occidental Chemistry Tectonic relationships Acknowledgments References cited Emplacement of pyroclastic flows: A review / Michael F. Sheridan Abstract Introduction Eruptions Observed pyroclastic flows Theoretical eruption models Mobility Topographic barriers Energy line Deposits Morphology Depositional sequence Textures Large clasts Deflation Compositional variation Welded peralkaline ignimbrites Emplacement temperatures Models Fluidization Speculation Summary Acknowledgments References cited Primary and secondary flow structures in ash-flow tuffs of the Gribbles Run paleovalley, central Colorado / Charles E. Chapin and Gary R. Lowell Abstract Introduction Paleovalleys and the Wall Mountain Tuff Primary flow structures Gas cavities (lenticules) Lineation Foliation Primary folds Rotated lithic fragments Imbricated crystals Secondary now structures Secondary folds and growth faults Tension cracks Miscellaneous structures Steam spiracles Conclusions Acknowledgments References cited Welded air-fall tuffs / R.S.J. Sparks and J. V. Wright Abstract Introduction Field relationships Santorini, Greece The 1875 Askja welded tuffs, Iceland Other examples Petrology and chemistry Grain-size studies Santorini welded tuffs Askja welded tuff Compaction and welding Strain, bulk density, and porosity measurements Results for Santorini welded tuffs Results for Askja welded tuff Discussion Acknowledgments References cited Globule ignimbrite of Mount Suswa, Kenya / R. L. Hay, W. Hildreth, and R. N. Lambe Abstract Introduction Scope and purpose of study Geologic setting and previous work Description and field relationships Ignimbrite petrography Vitric materials Crystals and rock fragments Devitrification and gas-phase crystallization Low-temperature alteration Nature of lower ignimbrite sheet Nature of the magma Chemical composition Temperature and viscosity Emplacement of ignimbrite and origin of globules Acknowledgments References cited A model of pyroclastic surge / K. H. Wohletz and M. F. Sheridan Abstract Introduction Terminology Objectives and methods of study Deposits Bed forms Locations Results Pyroclastic-surge facies Discussion and conclusions Development of bed forms Reconstruction of the surge cloud A model of pyroclastic surge: Its fluidization and deflation Acknowledgments References cited Significance of the flattening of pumice fragments in ash-flow tuffs / Donald W. Peterson Abstract Introduction Pumice fragments in the Apache Leap Tuff Recognition and description of pumice fragments Flattening of the pumice Applications of the flattening studies Recognition of cooling units Implications of extreme flattening Determination of stratigraphic level and fault displacement Commercial application of flattening ratios Determination of the degree of welding Pumice flattening as a possible guide to relative temperature of emplacement and rate of accumulation Conclusions Acknowledgments References cited Ash-flow sheets and calderas: Their genetic relationship to ore deposits in Nevada / Edwin H. McKee Abstract Introduction Metal deposits in volcanic-tectonic systems Resurgent cauldrons Geologic setting Parameters of study Distribution of mines and ash-flow sheets Distribution of mines and calderas Discussion Acknowledgments References cited

Note: Kartenbeilage (Plate 1) unter dem Titel: Complete Bouguer anomaly map of the Henry Mountains and vicinity, Utah , Kartenbeilage (Plate 2) unter dem Titel: Complete Bouger anomaly map of the Solitario and Vicinity, Texas , Kartenbeilage (Plate 3) unter dem Titel: Complete Bouguer gravity anomaly map of the Sundance 15' quadrangle, Wyoming , Kartenbeilage (Plate 4) unter dem Titel: Complete Bouguer anomaly map of the central part of the Little Belt Mountains, Montana , Kartenbeilage (Plate 5) unter dem Titel: Complete Bouguer anomaly map of the Abajo Mountains and vicinity, Utah , Kartenbeilage (Plate 6) unter dem Titel: Nonlinear finite element models of laccoliths