Week 5 Flashcards
Decompression melting
Melting that occurs as rock ascends due to a drop in confining pressure
Addition of volatiles
Lowers melting temperature
Increased temperature
Causes melting
Bowen’s reaction series
A concept by Bowen that illustrates the relationships between magma and the minerals crystallizing from it during the formation of igneous rocks
Magmatic differentiation
The process of generating more than one rock type from a single magma
Crystal setting
A process that occurs during the crystallization of magma in which earlier formed minerals are denser than the liquid portion and settle to the bottom of the magma chamber
Dike
A tabular shaped intrusive igneous figure that cuts through the surrounding rock
Sill
Intrusive deposit. A tabular igneous body that was intruded parallel to the layering of preexisting rock
Pluton
Magma displaces rock, the solidified magma structures that result from this are intrusions (plutons)
Batholith
Extrusive, a large mass of igneous rock that formed when magma was emplaced at depth, crystallized, and subsequently exposed by erosion
Explain the process of decompression melting
As hot mantle rock goes up, it moves into zones of lower pressure. The drop in pressure initiates decompression melting.
What role does water and other volatiles play in the formation of magma
They act as salt does to melt ice. Water causes rock to melt at lower temperatures. This happens mainly at convergent plate boundaries( cool oceanic lithosphere sink, heat and pressure drive water from it and brings it to the wedge of the mantle, making it hotter and leads to melting
What 3 locations (in class) that magma will form
Midocean ridge
Subduction zones
Mantle plumes
Describe the process of crystal settling
Earlier formed minerals are denser than the liquid portion and sink to the bottom of the magma chamber(makes the result richer in sodium potassium and silica
Process of magmatic differentiation
When the remaining melt solidifies, if it migrates into surrounding rock it will form a rock with mineral composition
Process of assimilation
Rocks get into the magma and their composition does as well
Process of magma mixing
2 chemically different magma bodies are going up and the more buoyant may rise faster. They eventually join and mix and the two masses blend
3 ways magma will form
- Decrease in pressure (no increase in temp)-decompression
- adding water
- Heating is crustal rocks above melting temp
Viscosity
Fluids resistance to flow
Volatile
Gaseous components of magma dissolved in the melt. Ready to vaporize at surface pressures
Aa
Lava flow that has a jagged blocky surface
Pahoehoe
Lava flow with a smooth to ropy surface
Block lavas
Lava that has a surface of angular blocks associated with material having andesitic and rhyolitic composition
Pyroclastic materials
Volcanic rock ejected during an eruption. Includes ash bombs and blocks
Fissure
A crack in a rock along which there is a distinct separation
Vent
Surface opening at a conduit or pipe
Summit and flank
I
Crater
The depression at the summit of a volcano or a depression that is produced by a meteorite impact
Shield volcano
BASALTIC. Starts on the ocean floor Broad gently sloping volcano built from fluid basaltic lavas. Tend to form at hot spots. Decompression melting, increased temperatures
Composite cone volcano
Erupts big Volcano composed of both lava flows and pyroclastic material
Cinder cone
ANDESITIC. Rather small volcano built primarily of ejected lava fragments that consider mostly pea to walnut sized lapili,
Pyroclastic flow
Highly heated mixture, largely of ash and pumice fragments that travels down the flanks of a volcano or along the surface of the ground
Lahar
Debris flow on the slopes of a volcano that results when unstable layers of ash and debris become saturated and flow downslope, usually following steam channels
Tsunami
Japanese word for seismic air wave
Caldera
Large depression typically caused by collapse or ejection of the summit area of a volcano
Flood basalt
Flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thickness of hundreds of meters
Define viscosity and 3 factors that influence it
Resistance to flow
- temperature (lower temp)
- composition (more silica)
- Dissolved gasses (less gas)
List the 3 magmas basaltic andesitic and rhyolitic in order most to least silica
Rhyolitic -most (felsic) 70
Andesitic-middle
Basaltic- least (mafic) 50
Compare and contrast aa and pahoehoe
Aa: rough jagged sharp, hard to cross
Pahoehoe: smooth, twisted braid, means “one can walk
List main gases released during a volcanic eruption. What role do they play in the eruption?
70% water vapor 15 carbon dioxide 5 nitrogen (Contribute to the atmosphere) Gas rich magma produces ash, causes it to be explosive like a wine bottle
What are pyroclastic materials: 3 examples
Pulverized rock, lava, and glass fragments from eruptions
- ash:
- Lapili:
- Volcanic bombs
Crater vs caldera
Crater is a funnel shaped depression (bowl)
Caldera is a large circular depression
Distinguish conduit and vent
The circular path that the magma makes is a condiut, it goes into a surface opening called a vent
Describe composition and viscosity of shield volcano lava
Basaltic, low viscosity
Where do most shield volcanoes form?
Ocean floor
Composition of a cinder cone
Made up entirely of pyroclastic material/ fragments, often basaltic
How does size and steepness of a cinder cone compare with a shield volcano
Cinder cones are much steeper
Where do most composite cone volcanos form
Ring of fire (Pacific Ocean)
What kind of pyroclastic material result from composite cone eruption
Materials with a felsic composition , High viscosity
What is the difference between a lahar and a pyroclastic flow
Pyroclastic:Hot glowing ash and large lava fragments,
Lahar: cooled at surface, a fluid mud flow when debris becomes saturated with water
3 ways magma will evolve
Crystal settling
Assimilation
Magma mixing
Magma always starts as ____
Mafic
Mafic/ felsic high or low viscosity
Mafic low
Felsic high
What texture is basalt
Aphanitic
Where do basaltic plateaus form
Continental rift zones
