This paper presents a table of abundances of the elements in the various major units of the Earth's lithic crust with a documentation of the sources and a discussion of the choice of units and data.

Distribution of the Elements in Some Major Units of the Earth's Crust

MOST volcanic rocks in modern island and continental arcs are probably derived from melting of the mantle wedge, induced by hydrous fluids released during dehydration reactions in the subducted lithosphere1. Arc tholeiitic and calc-alkaline basaltic magmas are produced by partial melting of the mantle, and then evolve by crystal fractionation (with or without assimilation and magma mixing) to more silicic magmas2—basalt, andesite, dacite and rhyolite suites. Although most arc magmas are generated by these petrogenetic processes, rocks with the geochemical characteristics of melts derived directly from the subducted lithosphere are present in some modern arcs where relatively young and hot lithosphere is being subducted. These andesites, dacites and sodic rhyolites (dacites seem to be the most common products) or their intrusive equivalents (tonalites and trondhjemites) are usually not associated with parental basaltic magmas3. Here we show that the trace-element geochemistry of these magmas (termed 'adakites') is consistent with a derivation by partial melting of the subducted slab, and in particular that subducting lithosphere younger than 25 Myr seems to be required for slab melting to occur.

Derivation of some modern arc magmas by melting of young subducted lithosphere

The velocity of compressional waves has been determined by measurement of travel time of pulses in specimens of rock at pressures to 10 kilobars and room temperature. Most of the samples, mainly igneous and metamorphic rocks, furnished three specimens oriented at right angles to one another. The present paper gives experimental details, modal analyses, and numerical tables of velocity as function of direction of propagation, initial density, and pressure. Discussion of various aspects of the measurements is reserved for part 2.

The velocity of compressional waves in rocks to 10 kilobars: 1.

Every large eruption of nonbasaltic magma taps a magma reservoir that is thermally and compositionally zoned. Most small eruptions also tap parts of heterogeneous and evolving magmatic systems. Several kinds of compositionally zoned ash flow tuffs provide examples of preemptive gradients in T and ƒO2, in chemical and isotopic composition, and in the variety, abundance, and composition of phenocrysts. Such gradients help to constrain the mechanisms of magmatic differentiation operating in each system. Roofward decreases in both T and phenocryst content suggest water concentration gradients in magma chambers. Wide compositional gaps are common features of large eruptions, proving the existence of such gaps in a variety of magmatic systems. Nearly all magmatic systems are ‘fundamentally basaltic’ in the sense that mantle-derived magmas supply heat and mass to crustal systems that evolve a variety of compositional ranges. Feedback between crustal melting and interception of basaltic intrusions focuses and amplifies magmatic anomalies, suppresses basaltic volcanism, produces and sustains crustal magma chambers, and sometimes culminates in large-scale diapirism. Degassing of basalt crystallizing in the roots of these systems provides a flux of He, CO2, S, halogens, and other components, some of which may influence chemical transport in the overlying, more silicic zones. Basaltic magmas become andesitic by concurrent fractionation and assimilation of partial melts over a large depth range during protracted upward percolation in a plexus of crustal conduits. Zonation in the andesitic-dacitic compositional range develops subsequently within magma chambers, primarily by crystal fractionation. Some dacitic and rhyolitic liquids may separate from less-silicic parents by means of ascending boundary layers along the walls of convecting magma chambers. Many rhyolites, however, are direct partial melts of crustal rocks, and still others fractionate from crystal-rich intermediate parents. The zoning of rhyolitic magma is accomplished predominantly by liquid state thermodiffusion and volatile complexing; liquid structural gradients may be important, and thermal gradients across magma chamber boundary layers are critical. Intracontinental silicic batholiths form where extensional tectonism favors coalescence of crustal partial melts instead of hybridization with the intrusive basaltic magma. Cordilleran batholiths, however, result from prolonged diffuse injection of the crust by basalt that hybridizes, fractionates, and preheats the crust with pervasive mafic to intermediate forerunners, culminating in large-scale diapiric mobilization of partially molten zones from which granodioritic magmas separate. Much of the variability among magmatic systems probably reflects the depth variation of relative rates of transport of magma, heat, and volatile components, as controlled in turn by the orientation and relative magnitudes of principal stresses in the lithosphere, the thickness and composition of the affected crust, and variations in the rate and longevity of basaltic magma supply. Extension of the lithosphere may reduce the susceptibility of basaltic magmas to hybridization in the crust, but it can also enhance the role of mantle-derived volatiles in chemical transport.

Gradients in silicic magma chambers: Implications for lithospheric magmatism

A review on the adsorption of heavy metals by clay minerals, with special focus on the past decade

------------------------------------------------1 Recognition of ash-flow tuffs—Continued Introduction ------------------------------------------------1 Microscopic characteristics Pyroclastic character------------------------------- 31 32 Acknowledgments 2 Pumice fragments ---------------------------------33 Welding, distortion, and stretching-------------33 Nomenclature ------------------------------------------- 2 Phenocrysts and foreign materials -------------35 Glossary of terms ---------------------------------3 Devitrification ----------------------------------36 Development of concepts 8 Physical chemistry 38 Heat -------------------------------------------------------39 Historic eruptions of ash-flow tuffs---------------------- 15 Viscosity -------------------------------------------40 Pelee 15 Volatile components--------------------------------40 Valley of Ten Thousand Smokes-------------------- 16 Welding ----------- 41 Cotopaxi -------------------------------------------------16 Devitrification 44 Source vents for ash-flow tuffs -------------------------16 Physical properties 45 Recognition of ash-flow tuffs-----------------------18 Indices of refraction . ____________ 45 Field characteristics ----------------------------------18 Specific gravity 46 Pyroclastic character---------------------------18 Porosity ------ 46 Degree of sorting ------------------------------19 Thickness ---- 20 Ash-flow materials of intermediate composition 47 Layering -----------------------------------20 Andesitic ash flows of Costa Rica 48 Areal extent ---------------------------------- 22 Distribution in time 48 Gentle dips ------------------------------------23 Mesozoic 49 Welding and deformation of pumice ----------24 Paleozoic --- 49 Fused tuffs contrasted with welded tuffs -----26 Precambrian ---------------------------------------------49 Devitrification and vapor-phase minerals ----26 Jointing ------------------------------------------28 Selected references-------------------------------------50 Erosion forms------------------------------------29 Fossil fumaroles---------------------------------30 Index ------------------ 79

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Ash-flow tuffs: Their origin, geologic relations, and identification

Origin of dunites and of olivine-rich inclusions in basaltic rocks

Geologic map of the Jemez Mountains, New Mexico

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Clarence S. Ross

Papers

Ash-flow tuffs: Their origin, geologic relations, and identification

Origin of dunites and of olivine-rich inclusions in basaltic rocks

Geologic map of the Jemez Mountains, New Mexico

Minerals of the montmorillonite group, their origin and relation to soils and clays

Water and other volatiles in volcanic glasses