Lecture 5: Igneous Processes Flashcards
completely/partially molten rock beneath the earth’s surface composed of:
s -
l -
g -
magma
solid: minerals, unmelted rock fragment
liquid: melt, ions of (Mg, Ca, Al, Na, K, O, Si, Fe
gas: volatiles (H2O, CO2, SO2)
Types of Magma
felsic, intermediate, mafic, ultramafic
granitic, andesitic, basaltic, picritic
Based on SiO2 and Fe, Mg content Felsic Intermediate Mafic Ultramafic
Felsic highest SiO2 content (>63%), lowest Fe, Mg content (~2%)
Ultramafic lowest SiO2 content (<45%), highest Fe, Mg content (>8-32%)
Based on Temperature and Viscosity Felsic Intermediate Mafic Ultramafic
Felsic - lowest temperature, high viscosity
Ultramafic - highest temperature, low viscosity
Felsic - high
Intermediate - intermediate
Mafic - low
Ultramafic - low to very low
Based on eruptive behavior and where it is commonly found Felsic Intermediate Mafic Ultramafic
Felsic : explosive, continental crust
Intermediate: explosive, continental crust
Mafic: gentle, oceanic crust
Ultramafic: gentle, upper mantle
How to melt rocks? (generate magma)
- Increase temperature (hot spots)
- Decrease pressure (rift zones)
- Addition of volatiles (subduction zones)
Temperature is * proportional to viscosity
inversely
decrease in pressure with no heat transfer
Adiabatic decompression
‘any process which cause magma composition to change’
Magmatic Differentiation: (How magma evolves)
Magmatic DIfferentiation
- Assimilation of host rock
- Magma mixing
- Fractional crystallization
Explain:
- Assimilation of host rock
- Magma mixing
- Fractional crystallization
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phenomenon by which magma is erupted to the surface through volcanoes as lava
Volcanism
Geomorphic (landform) feature where magma is exhumed to the surface (not always conical)
Volcanoe
Why do volcanoes erupt?
- Influx of new magma
2. Degassing magma
What is VEI
Volcano Explosivity Index
Relative measure of explosiveness of volcanic eruptions based on volume of products, height of eruption cloud, frequency
Volcano Explosivity Index
VEI is based on
volume of products, height of eruption cloud, frequency
Parts of a volcano
Conduit (pipe), vent, crater, parasitic cone, lava, bombs, pyroclastic material
VEI of Mt. Pinatubo
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degassed form of magma
Lava flows
aa vs pahoehoe
- Aa – more viscous, composed of clinker (broken lava)
* Pahoehoe – smooth, billowy, undulating, ropy surface
Columnal joints/basalts
Lava flow:
cooling joints refecting the high temperature during its emplacement
- Fragmented crystals or rocks that are either from the crystallizing magma or from the volcano edifice itself
Pyroclasts
Pyroclasts examples
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Volcanic Gases
SO2, CO2, CO, H2O
Form of Volcanic gas (type)
juvenile (from magma), heated meteoric (ground or surface)
Types of Volcanic Eruptions based on degree of explosivity
a. Explosive – pyroclastic rocks, ash fall, pyroclastic flows, debris avalanches, pyroclastic surges
b. Non-explosive/Effusive – lava flows, lava fountains
Types of Volcanic Eruptions based on Type of Material
- Magmatic (magma)
- Phreatomagmatic (magma + H2O)
- Phreatic (mostly gaseous)
Magmatic volcanic eruptions
- Hawaiian and Kelandic type
- Vulcanism type
- Strombolian type
- Palean type
- Plinian type
Phreatomagnetic volcanic eruptions
- Surtseyan
2. Subglacial
Phreatic volcanic eruptions
Geysers and fumaroles
*highly viscous lava
*volcanic bombs and blocks
MVE
Vulcanism
- short-lived eruptions of lavas; lava fountains
Strombolian
- creates large eruptive columns
* glowing gases
Palean type
pumice, pyroclastic flows, calderagenic collapse
Plinian type
Gentle, very little amount of ash (gentle/effusive)
Hawaiian and Icelandic Type
Hawaiian
vent
Icelandic
(more linear or fissure)
involves basaltic magma interacting with water in a shallow sea or lake
PmER
Surtseyan
involves basaltic magma interacting with ice
PmER
Subglacial
Erupts steam or hot fluids (no magma)
Geysers and Fumaroles
Types of Volcanoes (Age of Activity)
- Active
- Erupted for last 10,000 years
- Erupted with historical times (human record within 600 years) - Potentially Active
- Volcanic activity between 1.65 Ma to Ka - Inactive
- No historical records of eruption (morphologically young-looking)
Types of Volcanoes (Architecture)
- Shield
- Composite/Stratovolcano
- Pyroclastic cones
- Caldera
- Plug domes
- Composed mostly of fluid lava flows
- Resembles warrior shield
Shield volcano
- Alternating layers of lava flows and pyroclastic deposit
- Steep; periodic, explosive eruptions
- Composite/Stratovolcano
- Short lived explosive activity
- Collection of airborne ash, lapilli and blocks as they fall around a central vent
- Pyroclastic cones
- Mound-shaped protrusion resulting from slow extrusion of viscous lava from a volcano
- Plug domes
Types of pyroclastic cones
Scoria cone, Maar, Tuff ring, Tuff cone
Caldera formation process
Plinian eruption - faulting - collapse
melt field and start of crystallization; demarcates the start of crystallization
Liquidus
complete solidification (melt + crystals) boundary
Solidus
temperature gradient of Earth with depth
geotherm
