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EAS 201 > Igneous Rocks > Flashcards

Igneous Rocks Flashcards

1
Q

Igneous rock

A

Formed through the melting of rocks in the hot, deep crust and upper mantle. The rocks are formed through a process of crystallization from the solidification of magma or lava.

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2
Q

Extrusive Igneous rock

A

Igneous rocks cool rapidly on the earth’s surface and are fine-grained.

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3
Q

Intrusive Igneous rocks

A

Igneous rocks cool slowly in the earth’s interior, allowing large, coarse crystals to form.

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4
Q

Mafic Igneous rocks

A

containing magnesium and iron

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5
Q

Felsic igneous rocks

A

containing aluminum and silica

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6
Q

Plutonic rocks

A

also called intrusive rock

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7
Q

Phenocrysts

A

Crystallization which occurs below the surface slowly over thousands of years allows for grains to grow into larger sizes called phenocrysts.

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8
Q

Porphyritic crystals

A

Crystals start to grow beneath the earth’s surface. Some crystals grow large, but the remaining melt cools faster, forming smaller crystals, either because it erupts to the surface or because it is intruded close to the earth’s surface.

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9
Q

Country rock

A

Rock that exists before an igneous intrusion occurs

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10
Q

Stock

A

An intrusion of lava (dike) that makes it from beneath the earth to the surface

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11
Q

Pluton

A

An individual magma under the surface (lump of rock-forming)

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12
Q

Batholith

A

The large size of magma/intrusive rock beneath the surface. Often, made up of many plutons/

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13
Q

Difference between Still and Dike

A

A still runs parallel to country-rock layers, while a dike cuts across layers.

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14
Q

Still

A

A tubular, sheet-like body formed by the injection of magma between parallel layers of pre-existing sedimentary rock.

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15
Q

Dike

A

Cross-cutting bedding of rocks, and are formed when magma forces its way through open fractures.

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16
Q

Veins

A

Deposits of minerals are found within a rock fracture.

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17
Q

Lava

A

Magma that flows quickly to the earth’s surface is still partially or wholly molten. This cools relatively quickly so that there is less time for crystallization making fine-grained crystals.

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18
Q

Obsidian

A

A rock formed from very quickly cooling lava, such that it does not have time to form crystals and looks glassy.

19
Q

Pyroclasts

A

Rocks that eventually fall and are lithified together upon cooling, forming rocks known as tephra or smaller rocks called volcanic tuffs. Larger rocks are called volcanic breccias.

20
Q

Porphyry

A

Occurs when a melt begins to crystalize slowly at depth, growing large crystals. When it is subject to rapid cooling following a volcanic eruption, it results in a fine-grained groundmass with a course-grained rock embedded into it.

21
Q

Two examples of Felsic igneous rocks

A

Granites (intrusive)

Rhyolites (extrusive)

22
Q

Two examples of Mafic igneous rocks

A

Basalt (extrusive)

Gabbro (intrusive)

23
Q

The higher the silica content and the lower the lava temperature, the ____ viscous the lava is and the ___ it flows.

A

more

slower

24
Q

The more gas that lava contains, the more _____ an eruption is.

A

violent

25
Q

The lower the silica content and the higher the lava temperature, the ____ viscous and ____ it flows.

A

less

Faster

26
Q

Four categories of silica content in ingeous rocks

A

Felsic, intermediate, mafic, and ultramafic

27
Q

Two examples of intermediate igneous rocks

A

dacite, andesite

28
Q

Example of ultramafic igneous rocks

A

peridotite

29
Q

Composition of intrusive igneous rocks

A

coarse-grained

30
Q

Composition of extrusive igneous rocks

A

fine-grained

31
Q

Basaltic (mafic) lavas

A
  • contain high Fe/Mg and low silica content
  • dark in color
  • erupt at 1000-1200 Celcius
  • highly fluid (can travel at speeds of 100 km/hr)
32
Q

Intermediate (andesitic) lavas

A
  • have an intermediate composition between basalt and rhyolite
  • intrusions of intermediate magma form diorite
33
Q

Rhyolitic (felsic) lavals

A
  • low Fe/Mg and high silica content
  • erupt at 800-1000 Celcius
  • highly viscous (travel 10 times slower than basalt)
  • because of it’s viscosity, it resists flow and builds up as thick, bulbous deposits
  • the vesicular variety of rhyolite is called “pumice”
34
Q

The higher the water content in rock, the ___ the melting point

A

lower

35
Q

The composition of the melt (magma) will be determined by the minerals with the ____ melting points.

A

lowest

36
Q

How magmas from underwater

A
  1. subducting ocean crust carries sediment with it and trapping water between sediment grains.
  2. Trapped water is released as temperature increases
  3. Sedimentary rocks melt at a lower temperature
  4. Water and molten sediments move upward and meet parts of the overlying plate
  5. This magma accumulates in magma chambers
  6. Magma erupts and forms volcanoes
37
Q

Two ways to change the composition of magma

A
  1. subduct sediment on top of the magma

2. Magma moves through sediment of different composition absorbing it

38
Q

Magma chambers

A

Partial melts rise upward through pores, along grain boundaries, and through cracks in overlaying rocks. As the molten material rises, it mixes with other liquids forming large pools called magma chambers.

39
Q

Xenoliths

A

Blocks of country rock that break off and melt into magma, changing the overall melt composition.

40
Q

Decompression melting

A

This produces the greatest volume of molten rock.

Example: mid-ocean ridge

Mantle material rises as pressure decreases below the critical point resulting in solid rock melting without any increase in temperatures.

41
Q

Magmatic Differentiation

A

This process occurs when different materials crystalize when different minerals crystalize at different temperatures. During the crystallization process, the composition of the parent magma changes from its initial ultramafic composition as it becomes depleted of the chemical elements that compromise the crystals. The first minerals to crystalize from a cooling magma are the last to melt.

42
Q

Bowen’s Reaction Series

A
  1. As magma temperatures decrease
  2. Olivine and other materials crystalize in an ordered series
  3. Simultaneously, plagioclase feldspar crystallized, from a calcium-rich form to a sodium-rich form
  4. the composition of magma changes from ultramafic to andesitic (intermediate silica)
43
Q

Bowen’s Reaction Series summary

A

Mafic crystalizes first and then magma changes to intermediate rocks as silica forms

EAS 201 (12 decks)

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