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Geology > Mama and igenous rocks > Flashcards

Mama and igenous rocks Flashcards

1
Q

What is a volcano?

A

vent where molten rock comes out of Earth

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2
Q

how are igneous rocks formed?

A

by cooling from a melt. they start to crystallize at high temps

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3
Q

what is the difference between magma and lava?

A

magma = molten rock below ground
lava = molten rock above surface

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4
Q

what is the difference between intrusive and extrusive rocks?

A

extrusive: quickly cools at the surface
Intrusive: cool underground and much slower

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5
Q

name three elements that are part of the extrusive igneous rock formation

A

lava flows (streams or mounds of cooled melt)
pyroclastic flow and fall (fragmented magma)
volcanic ash (fine particles of volcanic glass)

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6
Q

where does magma form?

A

not everywhere. only in special tectonic conditions. partial melting occur in crust and upper mantle

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7
Q

what is melting of magma caused by?

A

pressure release, volatile addition, heat transfer

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8
Q

what is decompression?

A

magma ascent that leads to pressure release. at base of crust, T is hot enough to melt rock but due to high P, it doesn’t. if P is decreased (shallower), rock can melt and become magma

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9
Q

what is addition of volatiles?

A

flux melting. volatiles lower melting T of hot rock. H2O and CO2. subduction carries hydrous minerals into mantle and they break down to release H2O which causes partial melting of overlying mantle.

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10
Q

what is heat transfer melting?

A

rising magma carries mantle heat with it. raises T in nearby crustal rock which then melts.

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11
Q

what are the 3 components of magma?

A

solid: solidified mineral crystals
liquid: ions in the melt itself
gas: dissolved gas in magma

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12
Q

why is dry and wet magna>

A

dry: scarce variables
wet: up to 15% volatiles

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13
Q

what are the 4 major types of magma?

A

felsic, intermediate, mafic, ultramafic (decreasing silica_

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14
Q

what kinds of magma come from the mantle vs the crust?

A

mantle: ultra-mafic and mafic
crust: mafic, intermediate, felsic

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15
Q

why does partial melting occur?

A

rocks rarely melt uniformly, only a portion of the rock melts. it yields a silica rich magma

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16
Q

does si-poor or si-rich melt first?

A

si-rich minerals melt first

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17
Q

what is assimilation?

A

the process whereby solid or fluid foreign material is incorporated into magma

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18
Q

what is a xenolith?

A

a piece of rock trapped in another type of rock. rock embedded in magma while the magma was cooling

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19
Q

what is a pluton?

A

a large igneous rock body that forms when magma cools and solidifies underground

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20
Q

how does magma move?

A

it is buoyant, tends to rise upward. can move upward in the crust and may breach the surface VOLCANO. transfers mass from deep to shallow parts of Earth

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21
Q

why does magma rise?

A

less dense than surrounding rocks. more buoyant thus lifted upward. weight of overlying rock creates pressure and it squeezes magma upward

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22
Q

what is lower viscosity generated by?

A

low silica
higher T
higher volatile content
More silica means more tetrahedra and they get linked up and become more viscous

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23
Q

how fast does magma cool?

A

depends on depth. deep magma takes longer to cool than shallow magma. spherical bodies cool slowly, tabular faster.

24
Q

what is fractional crystallization?

A

removal of early formed crystals from an originally homogeneous magma (for example, by gravity settling) so that these crystals are prevented from further reaction with the residual mel

25
Q

what does bowen’s reaction series state?

A

low temp, more felsic = last to crystallize
high temp, ultramafic = first silicate minerals to crystallize

26
Q

what are the crystal sizes based on cooling rate?

A

intrusive = lose heat slowly = large crystals
extrusive = cool rapidly = no time to grow big crystals

27
Q

name if felsic or mafic:
basalt, olivine, quartz, feldspar

A

mafic, ultra-mafic, most felsic, felsic

28
Q

what are two types of extrusive volcano eruption?

A

lava effusion: low viscosity lava flows and spreads outwards
explosive eruptions: high viscosity (felsic) magma erupts explosively

29
Q

how does magma invade preexisting wall rock?

A

fracturing and partial melting of host tock. forcing open cracks. high heat (baked zone, chill margin)

30
Q

what is stoping

A

process by which local rock is broken up and removed by the upward movement of magma.

31
Q

smaller intrusions tend to form shallowly, larger = deeper

A
32
Q

what are tabular intrusions?

A

uniform thickness
can be traced laterally
sill: parallel to rock layering
dike: cut across rock layering

33
Q

how do dikes intrude?

A

cut across preexisting layers. spread rocks sideways

34
Q

how do sills intrude?

A

injected parallel to preexisting layering. intruded close to surface. cause uplift

35
Q

igneous intrusion -> pluton -> batholith

A

batholiths form above subduction zones and mark former subduction

36
Q

what do magma chambers do?

A

feed overlying volacnoes
can cool to become plutons

37
Q

how is a pluton exposed?

A

continued uplift and erosion. intrusive rocks are more resistant to erosion so they stand high on the landscape.

38
Q

what is unroofing?

A

erosion of covering geological units. what exposes a pluton

39
Q

what are the different arranements of minerals in igneous rocks?

A

crystalline: crystals fit like jigsaw puzzle
fragmental: pieces of shattered preexisting rocks
vitric/glassy: solid glass or glass shards

40
Q

what are the two types of igneous textures and their characteristics?

A

fine grained: rapid cooling, extrusive, no time to grow
coarse-grained: slow cooling, intrusive

41
Q

what is porphyritic texture?

A

mixture of coarse and fine crystals. two-stage cooling history. slow cooling (large phenocrysts) eruption cools remaining magma rapidly

42
Q

how are glassy textures formed?

A

extremely rapid cooling of lava. solid mass of glass or crystals surrounded by glass

43
Q

name felsic vesicular rocks

A

pumice and scoria
obisidian is felsic but not vesicular

44
Q

name pyroclastic rocks. what are they?

A

fragments of violent eruptions
tuff - from volcanic ash
breccia - larger volcanic fragments cemented together

45
Q

what is partial melting?

A

rock is subjected to temperatures high enough to cause certain minerals to melt, but not all of them

46
Q

partial melting and fractional crystallization

A

they are inverse processes. felsic minerals crystallize last and thus melt first. thus, felsic magma has lower temp than mafic magma

47
Q

where does igneous activity occur? 4

A

isolated hot spots
volcanic arcs bordering trenches
MORs
continental rifts

48
Q

describe mid-ocean ridges

A

rifting spreads plates leading to decompression melting
basaltic magma wells up and created magma chambers
solidifies as gabro
moves upward to form dikes or extrude
MAFIC MAFIC

49
Q

what is decompression melting?

A

When rock rises up in order to melt because deeper in there is too much pressure. Decompression allows it to lower pressure in order to melt and turn into magma

50
Q

where are volcanic arcs formed?

A

When oceanic plates collide, subduction occurs, where one plate slides beneath the other. Typically, the older, denser, colder plate will subduct, and the younger, warmer, more buoyant plate will override it. It is at these subduction boundaries where volcanic island arcs form.

51
Q

why are volcanic arcs formed?

A

subduction adds volatiles (water)
rocks of asthenosphere partially melt
magma rises and creates volcanoes on overriding plate

52
Q

continental rifts

A

places where cont. lithosphere is being stretched. rifting thins the lithosphere. causes decompressional melting of mafic rock and heat transfer melts crust creating felsic magmas
east african rift valley!

53
Q

what are hot spots

A

independent of tectonic plate boundaries. erupt through oceanic (mafic) or cont. (mafic and felsic) crust. burn volcano chain through overriding tectonic plate. creates track HAWAII

54
Q

large igneous provinces

A

extremely large accumulation of igneous rocks, including intrusive and extrusive, arising when magma travels through the crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate tectonics.

55
Q

LLLM

A

low silica
low viscosity
liquidy
mafic

Geology (19 decks)

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