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Geology AS > AS Igneous Processes > Flashcards

AS Igneous Processes Flashcards

1
Q

Adiabatic process

A

a thermodynamic process in which no heat enters or leaves the system during expansion or compression.

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2
Q

Adiabatic cooling

A

occurs when crust or mantle material rises, undergoes expansion and the temperature falls; with no loss or gain of thermal energy.

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3
Q

Adiabatic heating

A

occurs when crust or mantle material descends and temperature rises as it contracts; with no loss or gain of thermal energy.

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4
Q

Divergent plate margins

A

occur where two plates are moving apart and magma is riding up between them.

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5
Q

Partial melting

A

occurs where some of the minerals in a rock melt to form a magma.

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6
Q

Hot spots

A

are formed by a fixed mantle plume bringing magma to the surface.

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7
Q

Convergent plate margins

A

are where two plates are colliding and magma is formed above a subduction zone or deep in the crust.

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8
Q

Batholith

A

a very large igneous intrusion, with an undefined depth, in the Earth’s crust.

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9
Q

Decompression melting

A

accounts for most volcanism, including mid-ocean ridges and hot spots. Decompression of the ultramafic peridotite causes partial melting and produces mafic magmas by decompression melting.

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10
Q

Concordant intrusions

A

are parallel to the existing beds.

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11
Q

Discordant intrusions

A

cut across the existing beds.

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12
Q

Country rock

A

any rock into which an igneous rock intrudes.

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13
Q

Dyke

A

a discordant, sheet-like intrusion.

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14
Q

Minor intrusions

A

cool at hypabyssal depth below the surface and include sills and dykes.

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15
Q

Sill

A

a concordant, sheet-like intrusion.

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16
Q

Diapir

A

a body of relatively low density material that pierces and rises up through overlying material of a higher density.

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17
Q

Contact

A

where the igneous rock meets with country rock.

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18
Q

Baked margin

A

in the country rock where it was heated by the intrusion and altered.

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19
Q

Chilled margin

A

where the igneous rock has cooled rapidly so it has fine crystals.

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20
Q

Major intrusions

A

are plutonic and cool deep below the surface and include batholiths.

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21
Q

Plutons

A

large igneous intrusive bodies. If they are greater than 100 km² then they are called batholiths, usually made of several plutons.

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22
Q

Batholith

A

a large igneous intrusion which may be an aggregate of plutons.

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23
Q

Metamorphic aureole

A

a large area around a batholith where the rocks have been metamorphosed.

24
Q

Contact

A

where the igneous rock meets the country rock.

25
Q

Partial melting

A

occurs when only a portion of a rock is melted. When a rock is heated, those minerals with lower melting temperatures will melt. Those with higher melting temperatures will remain solid.

26
Q

Stoping

A

the process that accommodates the magma, as it moves upwards into the country rock, by the mechanical fracturing of the surrounding country rock.

27
Q

Xenoliths

A

clasts or blocks of pre-existing rock contained within an igneous rock.

28
Q

Assimilation

A

the melting process that incorporates blocks of country rock, freed by stoping, into the magma.

29
Q

Tiltmeters

A

designed to measure very small changes in vertical level.

30
Q

GPS

A

stands for Global Positioning System and is the radio navigation system that allows the determination of an exact position.

31
Q

Fumaroles

A

openings in or near a volcano, through which hot gases emerge.

32
Q

Cumulate

A

an igneous rock produced by gravity settling of crystals in a magma body.

33
Q

Chilled margin

A

where the igneous rock has cooled rapidly so it has fine crystals.

34
Q

Baked margin

A

in the country rock where it was heated by the intrusion and altered.

35
Q

Palaeosol

A

a soil horizon that was formed in a past geological age.

36
Q

Melt

A

the name given to magma or lava, in the liquid phase.

37
Q

Aa

A

lava flows that have a rough, blocky, jagged surface.

38
Q

Pahoehoe

A

lava flows that have a smooth or ropy surface.

39
Q

Scoria

A

a volcanic rock that is usually mafic but can be intermediate in composition.

40
Q

Pyroclast

A

an individual fragment ejected during an eruption. Pyroclastic describes all the fragmental materials formed by explosive eruptions, including bombs, blocks, lapilli and ash.

41
Q

Nuée ardente

A

(French, ‘burning cloud’) is an incandescent, gaseous, pyroclastic cloud of magma droplets and ash. When cooled and solidified the deposit is called an ignimbrite.

42
Q

Pyroclastic flow

A

is a hot mixture of pyroclastic material and gas. A nuée ardente is a type of pyroclastic flow.

43
Q

Volcanoes

A

vents at the surface of the Earth through which magma and other volcanic materials are ejected.

44
Q

Low viscosity

A

where magma or lava are fluid and flow freely.

45
Q

Shield volcanoes

A

have gentle slopes of less than 10 degrees and a roughly circular shape around a central vent.

46
Q

Fissure eruptions

A

where magma reaches the surface along long, linear cracks or fissures.

47
Q

Submarine eruptions

A

where magma comes from a vent or fissure on the sea floor.

48
Q

Composite volcanoes

A

tall, conical shaped and are composed of alternate layers of lava and ash.

49
Q

Caldera

A

a large volcanic crater that has undergone collapse, following an eruption.

50
Q

Effusive

A

the term used to describe the fluid, non-explosive, basalt lava.

51
Q

Volcanic Explosivity Index (VEI)

A

a measure of the explosiveness of volcanic eruptions, allowing them to be compared. It is a 0 to 8 index of increasing explosivity.

52
Q

Hawaiian eruptions

A

have large amounts of very fluid basaltic magma from which gases escape, but few pyroclasts.

53
Q

Strombolian eruptions

A

are more explosive with less fluid basalt and andesite lava. They have regular explosions of gas and pyroclastic material.

54
Q

Vulcanian eruptions

A

violent with viscous andesitic lava and large quantities of pyroclastic material from large explosions.

55
Q

Plinian eruptions

A

extremely explosive with viscous gas-filled andesitic and rhyolitic lava and tremendous volumes of pyroclastic material blasted out.

56
Q

Isopachyte

A

a line joining points of equal thickness of a deposit such as ash. The maps may be called isopach maps.

Geology AS (10 decks)

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