VOLCANIC ASH SOILS
CONTENTS PHYSICAL GEOLOGY OF SHALLOW-LEVEL MAGMATIC SYSTEMS—AN INTRODUCTION GEOMETRIC SCALING OF TABULAR IGNEOUS INTRUSIONS: IMPLICATIONS FOR EMPLACEMENT AND GROWTH PLUMBING SYSTEMS OF SHALLOW LEVEL INTRUSIVE COMPLEXES THE VOLCANIC-PLUTONIC CONNECTION STRUCTURES RELATED TO THE EMPLACEMENT OF SHALLOW-LEVEL INTRUSIONS GEOCHEMICAL FINGERPRINTING AND MAGMATIC PLUMBING SYSTEMS GEOPHYSICS AND REMOTE SENSING LABORATORY MODELLING OF VOLCANO PLUMBING SYSTEMS: A REVIEW CATASTROPHIC COLLAPSE FEATURES IN VOLCANIC TERRAINS: STYLES AND LINKS TO SUBVOLCANIC MAGMA SYSTEMS PHYSICAL GEOLOGY OF SHALLOW-LEVEL MAGMATIC SYSTEMS—AN INTRODUCTION THE FATE OF MAGMA IS COMMONLY SEEN AS EITHER ERUPTION FROM VOLCANIC VENTS OR EMPLACEMENT AT DEPTH INTO THE CRUST HOWEVER, MAGMAS OFTEN SOLIDIFY IN THE VERY SHALLOW CRUST (I E LESS THAN CA 3 KM DEEP), AS EITHER SUBHORIZONTAL INTRUSIONS SUCH AS SILLS AND LACCOLITHS, OR AS FROZEN VERTICAL CONDUITS, I E DYKES WHICH OF THESE PROCESSES WILL PREVAIL IS CONTROLLED BY INTRINSIC PARAMETERS LIKE MAGMA DENSITY, VISCOSITY, VOLUME AND ASCENT RATE AMONG EXTERNAL PARAMETERS, FAR ?ELD STRESS, AS WELL AS VARIATIONS OF DENSITY AND STRENGTH IN THE HOST ROCK, ARE SIGNI?CANT WHAT IS A SUBVOLCANIC BODY? A SUBVOLCANIC INTRUSION IS A COOLED MAGMA BODY EMPLACED AT SHALLOW DEPTH INTO THE UPPER CRUST, BETWEEN A FEW TENS OF M AND APPROXIMATELY 3 KM 1 IN THE ABSENCE OF STRATIGRAPHIC AND/OR GEOBAROMETRIC EVIDENCE, IT CAN BE RECOGNIZED BY HAVING EMPLACED BELOW THE EARTH’S SURFACE (E G DISPLAYING NO SCORIA CARAPACE, IN CASE OF A SIO2- POOR BODY) AND NEVERTHELESS SHOWING AN APHA- NITIC GROUNDMASS (FIG 1A 1) AMONG SUBVOLCANIC INTRUSIONS, THOSE WITH TABULAR SHAPES AND ATTITUDES CROSSCUTTING PRE-EXISTING ROCK STRUCTURES (I E MOST COMMONLY A SUBVERTICAL ATTITUDE) ARE CALLED DYKES (FIG 1A 2) FOR SHALLOW-LEVEL INTRUSIONS WITH ATTITUDES MORE OR LESS CONCORDANT WITH PREEXISTING ROCKS (I E MOST COMMONLY A SUBHORIZONTAL ATTITUDE; FIG 1A 2), A LARGE VARIETY OF NAMES WERE PRO- POSED IN THE 19TH AND EARLY 20TH CENTURY (CORRY 1988), AMONG WHICH THE TERMS LACCOLITH, SILL, BYSMALITH, AND LOPOLITH ARE STILL IN USE (JERRAM AND BRYAN THIS VOLUME—CHAP “PLUMBING SYSTEMS OF SHALLOW LEVEL INTRUSIVE COMPLEXES”) SILLS HAVE 13 KM DEPTH HAS BEEN QUOTED AS MAXIMUM EMPLACEMENT DEPTH FOR THE LACCOLITH COMPLEX IN THE HENRY MTNS (HORSMAN ET AL THIS VOLUME—CHAP “PROGRESSIVE CONSTRUCTION OF LACCOLITHIC INTRUSIVE CENTERS: HENRY MOUNTAINS, UTAH, U S A”), AND IT IS THE MAXIMUM VALUE FOR A SUBVOLCANIC COMPLEX PUBLISHED SO FAR HOWEVER, MANY DYKE SYSTEMS MAY HAVE EMPLACED EVEN DEEPER IN THE CRUST