- Pressure increases with depth - Melting occurs at higher temp with depth due to higher confining pressure - Confining pressure drops = decompression melting

- Water and others cause rock to melt at lower temps. - Generate magma where oceanic lithosphere descends into the mantle - When mafic magma forms, it rises toward the surface. - Mafic pooling melts crusts and forms silica rich felsic magma

- Cooling magma results in systematic arrangement of ions into crystal structures - Silicon and oxygen atoms link to form silicate minerals - Minerals formed first tend to have better developed crystal faces

Lecture 3 Flashcards by Édouard Ungur

Most common phaneritic igneous rock ?

Granite

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How Igneous rocks forms ?

Form as molten rock cools and solidifies

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Parent material igneous rock ?

Magma

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Extrusive igneous rocks ?

Form when magma solidifies at surface,
can be called volcanic rocks

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Intrusive igneous rocks ?

Form at depth from magma that crystallizes slowly,
can be called plutonic rocks, where a body is called pluton

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Role of heat ? (IMPORTANT)

Geothermal gradient : Change in temperature with depth.
Rocks in lower curst and upper mantle are near their melting points
Bulk of magma forms without additional heat
Melting begins if confining pressure drops or if volatiles (fluids, gases) are introduced

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Role of pressure ?

Pressure increases with depth
Melting occurs at higher temp with depth due to higher confining pressure
Confining pressure drops = decompression melting

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Decompression melting ?

It moves into zones of lower pressure. This can trigger melting, even without additionnal heat.

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Role of volatiles ?

Water and others cause rock to melt at lower temps.
Generate magma where oceanic lithosphere descends into the mantle
When mafic magma forms, it rises toward the surface.
Mafic pooling melts crusts and forms silica rich felsic magma

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How magma can be generated ? (IMPORTANT)

Addition of heat,
Decrease in pressure, causing decompression melting,
Introduction of volatiles, which lowers the melting temp.

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What are the 3 distinct components ?

Liquid portion, composed of mobile ions
Solids, silicate minerals that have already crystallized from the melt
Volatiles : H2O, CO2, SO2

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Crystallization ?

Cooling magma results in systematic arrangement of ions into crystal structures
Silicon and oxygen atoms link to form silicate minerals
Minerals formed first tend to have better developed crystal faces

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Bowen’s reaction series ?

One volcano can have lavas with different compositions
Magma cools, minerals crystallize in a systematic fashion based on melting points
During crystallization, composition of liquid portion of magma changes

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Magmatic differentiation ?

Formation of 1 or more secondary magmas from a single parent magma

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Assimilation ?

Changing of magma’s composition by incorporation of foreign matter into magma

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Magma mixing ?

Occurs when magma body intrudes another

Partial melting and magma formation ?

Incomplete melting of rocks is known as partial melting

Formation of a mafic (basaltic) magma ?

Partial melting of peridotite in the mantle.

Primary magmas ?

Mafic magmas that originate from direct melting of mantle rock, and have not yet evolved.

Formation of Andesitic magma ?

Found in continental margins
Generated by interactions between mantle mafic magma and silica-rich crust
Intermediate composition = andesite

Secondary magmas ?

Enriched silica magmas

Formation of Felsic magma ?

Higher in silica and therefore more viscous (thicker) than other magmas
Form at lower temp. than mafic magmas
Produce large plutonic structures

Composition of igneous rocks ?

Dark silicates and light
Determined by composition of magma

Dark (ferroamagnesian) silicates ?
(OPABm)

Olivine
Pyroxene
Amphibole
Biotite mica

Light (non-ferromagnesian) silicates ?

- Quartz - Muscovite mica - Feldspars

Felsic composition ?

- Granite composition - Composed of light-cloured silicates - Rich in silica, SiO2 (70%) - Major constituents of continental crust

Mafic composition ?

- Basaltic composition - Composed of dark silicates - More dense than granitic rocks - Comprise the oecan floor,volcanic islands

Intermediate rocks ?

- Andesitic composition - Contains at least 25% dark silicate minerals - Associated with volcanic activity on continental margins

Ultramafic composition ?

- Peridotite - Rare, composed only of ferromagnesian silicates

Texture ?

- Describe overall appearance of igneous rock based on size, shape, arrangement of interlocking crystals. - Envionment in which the rock was formed

3 Factors affecting crystal size ? (IMPORTANT)

- Rate of cooling : Slow rate promotes the growth of fewer but larger crystals, fast rat forms many small crystals, very fast rate forms glass - Amount of silica present - Amount of volatiles

Type of igneous textures ?

- Aphanitic texture - Phaneritic texture (coarse-grained) - Porphyritic texture - Glassy texture - Pyroclastic texture (fragmental)

Naming of igneous rocks ?

- Classified by their texture and mineral composition - Can have similar compositions but different textures = different names

Granite ?

- Phaneriti - Composed of about 20% quartz and 65% feldspar - Exhibit a porphyritic tex

Rhyolite ?

- Extrusive equivalent of granite, - Aphanitic texture, - May contain glass fragments and vesicles - Less common and less voluminous than granite

Andesite ?

- Volcanic origin - Medium gray colour, fine-grained, - Commonly exhibits porphyritic texture - May resemble rhyolite

Diorite ?

- Plutonic equivalent of andesite, - Coarse-gained, - Intrusive - Composed mainly of intermediate feldspar and amphibole

Basalt ?

- Volcanic origin - Dark green to black in colour - Composed mainly of pyroxene and calcium-rich plagioclase feldspar - Most common extrusive igneous rock

Gabbro ?

- Intrusive equivalent of basalt - Dark green to black in colour - Composed primarily of pyroxene and calcium-rich plagioclase - Makes up a significant percentage of the oceanic crust