MAGMA PROPERTIES + SHAPES AND EMPLACEMENT OF IGNEOUS BODIES
Magma Properties
Si-Al-O Polymerization – function of SiO2 Concentration and Temperature
Si-Al-O structures mimic minerals
Viscosity - Large range, affected by crystals and concentration of gases
- increases as you get closer to crystallization of magma / lava
Yield strength – stationary magma/lava has bonding that must be overcome to make it move
Extrusive bodies – Central Vent Landforms
shield volcano (convex up, 2 to 10° slope, up to 200 km across + 9 km high)
stratovolcano (composite volcano, slightly concave-up, slope <36°, < 2 km high)
Pyroclastic volcano (cinder or scoria cones, 2 km across and < 0.3 km high)
volcanic complex
Dome
lava flow
ash-flow tuff (ignimbrite)
flood basalt
caldera
Extrusive bodies – Fissure Landforms
Feeder dikes (regional extension - MOR)
Flood basalts
Extrusive bodies – Pyroclastic Landforms
Pyroclastic Deposits include
– volcaniclastic – formed by volcano (process irrelevant)
- pyroclastic – formed from magma/lava aerially expelled from vent
- lahar – volcanic debris mixed with water/melting ice or snow
Pyroclastic Fall Deposits – material falls from vertical eruption, well sorted, blankets everything,
very extensive distribution, voluminous eruptions
Pyroclastic Flow Deposits – 400-800°C, 50 to 200km/hr, unsorted deposits, dense flows that fill
valleys, often welded (fiamme), contains trapped gases, small extent
Pyroclastic Surge Deposits –stratified with dunes/antidunes, fills valleys and covers some hills
because of turbulent, high speed flow of this less dense material.
Intrusive bodies
stock - any small plutonic body
batholith - large, usually >100 km2 plutonic body, often consisting of multiple plutons
laccolith
lopolith
dike
sill
ring dike / cone sheets
Mechanisms of magma movement through the crust
dikes - driven by density difference and magma pressure
diapirs - a controversial mechanism.
Mechanisms of emplacement
displacement of overlying and surrounding rocks
stoping