Table of Contents - SPE220: Laccoliths; Mechanics of Emplacement and Growth





Definition of laccoliths
Lopoliths: A class of laccoliths
Additional names for laccolithic intrusions
Laccolith group
History of the laccolithic concept
Gilbert's work
Neutrally buoyant elevation
Depth of intrusion versus laccolith diameter
Other early workers
Modern work
Tabulation of known laccoliths: A gazetteer
Statement of problems
Punched and Christmas-tree laccoliths

Genesis of laccoliths

Feeder dikes
Hunt's model. Lateral feeders from a central stock
Feeder dikes below the laccolith
Control of the level of intrusion
Gilbert's hypothesis
Change in magma density as it solidifies
Field evidence
Experimental work
Theoretical work
Neutrally buoyant elevation
Vapor barriers
Stress barriers
Stopping of rising magma at a freely slipping crack

Gravity and magnetic surveys of laccoliths

Testing Gilbert's hypothesis for density control of emplacement level
Use of gravity surveys to determine density contrast
Signal-to-noise ratio
Spatial wavelengths in gravity data
Nyquist sampling theorem
Aeromagnetic surveys of laccoliths
Gravity surveys of felsic laccoliths
Henry Mountains, Utah
Big Bend group, Texas-Mexico
Abajo Mountains, Utah
La Sal Mountains, Utah
Sleeping Ute Mountain, Colorado
Carrizo Mountains, Arizona
Little Belt Mountains, Montana
Black Hills, South Dakota-Wyoming
Bearpaw Mountains, Montana
San Francisco Mountains, Arizona
San Juan Mountains, Colorado
Death Valley, California
Crazy Mountains and Little Rocky Mountains, Montana
Gravity surveys of mafic laccoliths
Exeter pluton, New Hampshire
Mustang Hill laccolith, Texas
Trompsburg lopolith, South Africa
Mara laccolith, Tanzania
Channel Islands, United Kingdom
Joutsenmaki intrusive, Finland
Summary of gravity data

The emplacement of laccoliths

Stage one. The movement of the magma vertically through the lithosphere
Dislocation model
Volumetric calculations for feeder dikes
Pseudo-Archimedian buoyancy
Magma driving pressure
Magma incompressibility
Physical implications of dislocation model
Stage two. Reorientation of the magma from vertical climb to horizontal spreading
Fingered sheet intrusions

The growth of laccoliths

Stage three. Cessation of horizontal spreading and commencement of thickening
Diameter versus depth
Rate of loading
Direct observation of laccolith growth
Pressure gradient in the protolaccolith
Stage four. Large-scale deformation of the overburden by thickening of the intrusion
Punched laccoliths
Field observations
Boundary conditions
Prandtl punch
Limital thickness
Christmas-tree laccoliths
Field observations
Boundary conditions

Continuum solutions for the mechanics of laccolith growth

The finite element method
Material nonlinearity
Geometric nonlinearity
Integration stations Body forces
Configuration of the models
Theoretical models :
Previous model studies
Data display
Punched laccolith models
Model one
Model two
Model three
Model four
Model five
Sill propagation in a brittle regime Model six
Comparison of physical and theoretical models
Christmas-tree laccolith model
Model one Roof deflection
Magma supply

Summary and conclusions


A. Definitions of descriptive terms for laccolithic and associated intrusions
B. A gazetteer of laccoliths
C. Notation used for laccolith models

References cited