Chapter four: Up from the Inferno, Magma and Igneous rocks

What are lava flows?

Extrusive, above ground

What occurs when lava erupts as a fountain from a volcanic vent of Hawaii?

Flows downslope, at a distance from the vent (the lava has completely crusted over with new rock, but the interior of the flow remains molten) eventually, the flow cooled completely and becomes a layer of new rock

Where is lava found? What is the extrusive realm?

Earth's surface, above the ground (fine grained, basalt)

Where is magma found? What is the intrusive realm?

Beneath earth's surface, below the ground (coarse grained, gabbro)

What do extrusive deposits involve?

Lava flows and pyroplastic deposits

What do intrusive rocks form?

Below ground

What is decompression melting?

Pressure decreases but T remains constant, creating a melt. A hot rock at a high pressure moves to a shallower crustal level/lower pressure, causing the rock to melt

What are geologic environments where decompression melting can occur?

Mantle plumes, continental rifts, divergent plate boundaries

What is flux melting?

When volatiles help break chemical bonds, creating a melt. In a subduction zone, volatiles such as water and carbon dioxide are driven from the oceanic crust into the asthenosphere creating a melt above the subducting plate

What are intermediate rocks?

felsic and mayfic rocks, or when magma mixes with felsic continental crust

What is heat transfer?

When heat from magma melts adjacent rocks, rocks surrounding magma chambers can be melted through heat transfer

What type of rock melts at the lowest temperature?

Continental felsic rocks

What is melting a rock due to a decrease in pressure called?

Decompression melting

Igneous rocks are formed from?

Magma that originates in asthenosphere

What are the different types of melts based on silica content?

Felsic melts, intermediate melts, mafic melts, ultramafic melts

What are felsic melts?

Have a relatively high proportion of silica relative to magnesium oxide and iron oxide, the coolest melt. (quartz, feldspar)

What are intermediate melts?

Their composition lies part way between those of mafic and felsic melts

What are mafic melts?

Contain a relatively high proporiton of magnesium oxide and iron oxide relative to silica, the hottest melt, (olivine and perxoine)

ultramafic melts?

have an even higher proportion of magnesium oxide and iron oxide relative to silica

What is the technical term for a resistance to flow?

The viscosity of a liquid, affects the speed at which the liquid moves

What does the viscosity of molten rock depend on?

Depends on its temperature, volatile content and silica content

A hotter melt?

Tends to be less viscous than cooler melt

How does volatiles relate to viscosity?

A melt containing more volatiles has lower viscosity than does a dry (volatile-free) melt

What is the viscosity of a mafic melt in relation to felsic melts?

less viscous, because relatively more silicon-oxygen tetrahedra occur in felsic melt (if something has lots of bubbles, it has too much content because the liquid and bubbles have to be pushed)

What does the silica content of a melt determine?

A melt's viscosity and the name given to a particular melt

What does partial melting of a rock do?

Makes the melt silica enriched because felsic minerals melt first

What is assimilation?

As a melt rises, it assimilated the wall rock, changing the composition of the melt (ice cubes in coke water down and change the composition of cola)

If a melt has lower viscosity, what properties does it have?

Hotter, Mafic, less volatiles

If a melt has higher viscosity, what properties does it have ?

Cooler, felsic, more volatiles

When does volcanic precipitation occur?

When melts solidify or freeze, shallow flows (that are small or thin) cool quickly, large blobs (plutons) take a long time to cool

What are the cooling rates specific melts?

spherical cool slowly, tabular cools faster (circulating groundwater removes heat)

What is the fractional crystallization for mafic and felsic minerals?

Mafic crystallize first, Felsic crystallize last (the original melt is primarily mafic, as the mafic minerals settle out the magma becomes more felsic)

What is Bowen's reaction series?

It indicates the succession of crystallization in cooling magmas (with decreasing temperature, fractional crystallization begins and the composition of the remaining magma becomes more felsic)

What are pyroclastic flows?

Deadly, fast-moving avalanches of superheated volcanic ash and debris (mt. Vesuvius, mt. St Helens, Yellowstone)

What do explosive volcanoes erupt?

Various sizes of debris, like microscopic ash or large pumice (made up of obsidian extrusives)

What is a dike?

A tabular intrusion that run vertically, cut across rock layers and can occur in swarms, can result in spreading the rock sideways

What is a sill?

A tabular intrusion that run horizontally, are parallel to rock layers. Typically close to the surface and result in a change in the elevation of the land surface

What is a laccolith?

A tabular intrusion similar to a sill that cannot spread laterally and accumulates into a blister-shaped intrusion

What are plutons?

Blob-shaped intrusions that solidify from magma chambers

What is a batholith?

A group of plutons that covers a large area

What occurs with rising magma?

Magma moves upward by percolating between grains, wedging open cracks, melting and breaking off blocks of the wall rock

What are xenoliths?

Chunks of wall rock incorporated into the magma (something stays and gets trapped, foreign)

What to textures reveal about igneous rocks?

Reveal something about the history of how the melt cooled

What is crystalline texture in igneous rocks?

Crystals fit together like jigsaw puzzle pieces

What is fragmental texture in igneous rocks?

igneous chunks and shards welded together

What is glassy texture in igneous rocks?

Solid glass or glass shards

What are the different types of glassy and fragmented igneous rocks?

Pumice, scoria, tuff, obsidian

What is pumice?

Felsic rock full of vesicles, extremely light it floats

What is scoria?

Vesicular and glassy mafic rock

What is tuff?

fragmented rock composed of ash

What is obsidian?

glassy, felsic rock with no vesicles

What is a subduction zone?

Many volcanoes are part of subduction zone volcanism (intermediate, pyroclastic and dangerous)

What is a mid ocean ridge?

Most igneous activity occurs along the mid-ocean ridge (most activity occurs below sea level)

What is continental rift?

Rift-lithospheric thinning causes decompressional melting of the asthenosphere (Heat transfer melts crust, creating felsic magmas)

What are hot-spots?

Mantle plume hot-spots generate igneous activity independent of tectonic plate boundaries (can track plate movement)

What are large igneous provinces?

Large areas of mafic melt that appear periodically over geologic time (result from mantle plumes at the base of the lithosphere that create huge volumes of low-viscosity mafic magmas. Lava flows cover large areas and can accumulate in thick piles.)