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GLE Reviews > Earth Mat Flashcards - Ch 17 > Flashcards

Earth Mat Flashcards - Ch 17

1
Q

equal diameters in all directions and assume forms approximated by spheres or cubes.

A

Equant

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2
Q

one direction in which the grain diameter is not equal to the other grain diameters

A

Inequant

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3
Q

A1 < A2,A3
What shape

A

Tabular

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4
Q

A1 > A2=/A3
What shape

A

Bladed

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5
Q

A1 > A2=A3
What shape

A

Acicular

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6
Q

What divides aphanitic and phaneritic

A

Aphanitic < 1mm > Phaneritic

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7
Q

are large relict grains from the protolith that have experienced deformation but have retained their original composition.

A

Porphyroclasts

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8
Q

In gneiss porhyroclasts, Felds and Qtz are

A

Augen and Flaser

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9
Q

are large grains that have experienced neocrystallization and growth in response to favorable temperature and pressure conditions during metamorphism.

A

Porphyroblasts

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10
Q

no orientation of inequant grain = no foliation

A

Random grain orientation

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11
Q

sub-parrallel inequant grain = foliations and lineations

A

Preferred grain orientation

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12
Q

On the basis of grain orientation, metamorphic rocks can be divided into two major groups:

A

Rocks with non - foliated textures
Rocks with foliated textures

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13
Q

commonly produced by dynamic metamorphism, contact metamorphism or burial metamorphism

A

Non-foliated metamorphic rocks

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14
Q

texture is a fine-grained (<1.0 mm diameter), non-foliated fabric that develops by contact metamorphism, producing a rock called hornfels

A

Hornfelsic

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15
Q

Hornfels develops in

A

metamorphic aureoles, adjacent to igneous intrusions.

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16
Q

textures are characterized by large (> 1.0 mm diameter) equant grains or large inequant crystals that lack preferred orientation

A

Granoblastic

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17
Q

textures occur in granulites, associated with

A

deep burial (high PT)

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18
Q

common rocks with granoblastic textures

A

Metaquartzite, marbles

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19
Q

contain > 90% quartz and are derived from quartz - rich sandstone or chert protoliths

A

Metaquartzites

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20
Q

are granoblastic metamorphic rocks rich in calcite and/or dolomite.

A

Marbles

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21
Q

recrystallization of limestone or dolostone protoliths via

A

dynamothermal, deep burial or contact metamorphism

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22
Q

are granoblastic calc - silicate rocks formed by contact metamorphism of carbonate country rocks such as limestone or dolostone.

A

Skarns , also known as tactites,

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23
Q

Metamorphic rocks with ____________are composed of fractured, angular particles that form in response to the brittle crushing of grains during deformation in upper crustal fault zones

A

cataclastic textures

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24
Q

Cataclastic rocks that lack cohesions are either _____(<2mm) or _____(>2mm)

A

Breccia, Gouge

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25
Q

are derived from metamorphism of sedimentary or igneous breccias

A

Metabreccias

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26
Q

10-50% matrix cataclasite

A

Protocataclasite

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27
Q

50-90% matrix cataclasite

A

Cataclasite

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28
Q

90-100% matrix cataclasite

A

Ultracataclasite

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29
Q

Fault reactivations can be caused by

A

cataclasites rupturing more easily than the host rock

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30
Q

are glassy rocks produced by high strain rates generating localized melting in fault zones

A

Pseudotachylites

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31
Q

are high strain rate cataclastic rocks created by the tremendous short - term stresses associated with extraterrestrial rock bodies impacting Earth

A

Impactites

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32
Q

that form as rocks locally melted from impact and showers down like droplets as it cools

A

Glassy spherules called tektites

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33
Q

that form due to the intense stresses that deform crystal structures

A

Deformation lamellae

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34
Q

Coesite first discovered at

A

Meteor crater, AZ

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35
Q

are non-crystalline, high grade coals that form by heating, compressing and chemically altering bituminous coal.

A

Anthracites

36
Q

are derived from conglomerate protoliths and contain sub - rounded to rounded relict clasts with diameters > 2 mm.

A

Metaconglomerates

37
Q

form by the metamorphism of conglomerates and/or breccias in response to strong non - uniform stress during dynamothermal or dynamic metamorphism.

A

Stretched pebble metaconglomerates

38
Q

Metamophosed pebbles/cobbles are

A

short/flattened at Z strain, elongated at X strain direction

39
Q

are serpentine-rich metamorphic rocks that occur in non - foliated or foliated forms.

A

Serpentinites

40
Q

Serpentinization is the where

A

ol and px are hydrated to form serpentines

41
Q

are fine - grained rocks that form through the alteration of ultrabasic rocks, or magnesium - rich sedimentary rocks such as dolostone, by low temperature and low pressure hydrothermal fluids.

A

Soapstones

42
Q

are green - colored rocks rich in silicate minerals that commonly include chlorite, epidote, prehnite, pumpellyite, talc, serpentine, actinolite and albite.

A

Greenstones

43
Q

Many __________(sodium - rich basalt) and _____________(sodium - rich andesite) occur in greenstones.

A

spilites; keratophyres

44
Q

Greenstone sequence (basal to surface)

A

Metavolcanics (komatiites) and metabasalts
-> inter/silicic metavolcaninc and metavolcaniclastic
-> graywackes and chert.

45
Q

Greenstone belts commonly parallel _____________ containing rocks of granitic to dioritic composition metamorphosed at high temperatures and pressures

A

granulite belts c

46
Q

Greenstone belts; Extensive km wide, Archean and Proterozoic cratons
Ex.

A

Barberton Belt, S. Africa
Eastern Goldfields, W. Aus
Superior & Slave Cratons, NA
Sao Francisco Craton, Brazil

47
Q

Greenstone belt formed by

A

Formed from H2O + CO2 metasomatism of B and UB rocks

48
Q

Why are greenstone belts uncommon in the Phanerozoic Eon?

A

related to lower geothermal gradients in the Phanerozoic as well as changes in plate tectonics
Precambrian metamorphism = high grade in shallow depths; prevention of deep subduction

49
Q

are dark - colored rocks composed largely of amphiboles, such as hornblende, and plagioclase

A

Amphibolites

50
Q

Amphibolite from basic Igni protolith

A

Ortho-Amphibolites

51
Q

Amphibolite from sedimentary protolith

A

Para-amphibolites

52
Q

metamorphism in granulites

A

(>800°C) and high pressure (> 10 kbar; ~ 33 km depth) metamorphism

53
Q

High density of ___________ may drive subduction (slab-pull effect)

A

eclogite

54
Q

are very high pressure, high temperaturerocks that develop principally from basalt/gabbro protoliths.

A

Eclogites

55
Q

are fine - grained, aluminum - rich, pelitic rocks that possess fl at, planar cleavage.

A

Slates

56
Q

________ ° C, slates are transformed to Phyllite

A

250

57
Q

In the case of slates, which minerals are stable in low temps? in high temps

A

kao, smec, zeo;
illite, chl, mica

58
Q

In anoxic envi: oragnics recrystallize to

A

graphite

59
Q

display phyllitic cleavage, characterized by larger crystals and more wavy surfaces than slaty cleavage

A

Phyllites

60
Q

At 250 - 300°C smec and illite transforms to

A

seri, musc, talc, chl

61
Q

_____ phyllites are transformed gradationally into schist

A

~300 ° C,

62
Q

is a very common foliation defined by the sub - parallel arrangement of macroscopic platy minerals such as phyllosilicates in closely spaced metamorphic layers.

A

Schistosity

63
Q

Schists are produced by _metamorphism at convergent plate boundaries with temperatures >300 ° C

A

dynamothermal

64
Q

are characterized by gneissic layering, a foliation characterized by the arrangement of minerals into distinct color bands.

A

Gneisses

65
Q

Gneisses that develop from an igneous protoliths are called

A

orthogneiss

66
Q

gneiss from sedimentary protoliths are called

A

paragneiss

67
Q

which refers to the thin, sill - like intrusion of magma into parallel country rock layers

A

“ Lit par lit intrusion ” ,

68
Q

Gneisses form in dynamothermal settings at temperatures that commonly exceed

A

~ 600 ° C.

69
Q

processes have been suggested for the development of gneissic banding:

A

Originate by layer transposition.
Lit Par Lit
Anatexis

70
Q

Layer transposition process

A

Transposition results from the pulling apart of earlier folded layers resulting in the separation of hinges and limbs
Insoluble phyllosilicates in fold limbs and soluble qts/felds in hinge, tightly compressed forming alternating bands

71
Q

are “ mixed ” rocks that possess textural and structural characteristics of both igneous and metamorphic rocks

A

Migmatites

72
Q

are silica - and iron - rich rocks that formed primarily in the Early Proterozoic and Archean.

A

Ironstones

73
Q

are metaquartzites that contain 20 – 30% iron and are also commonly banded

A

Taconites; found largely in lake superior

74
Q

Metamorphic ______ are pervasively deformed rocks so that their original composition and texture are largely obliterated.

A

tectonites

75
Q

tectonites are Classified by solid state flow fabric from deformation
what are they

A

S tectonites = Foliated
L tectonites = lineation, no foliation
L-S tectonites = Foliation, Lineation

76
Q

are rock structures or textural elements that provide information concerning the relative sense of displacement of rock components within fault zones or shear zone

A

Shear sense indicators

77
Q

indicate the sense of displacement in shear zones and may also provide information on displacement distance.

A

Offset markers

78
Q

allows displacement distance to be measured; intersections by linear features and planar faults/shear zones

A

Piercing Points

79
Q

are asymmetrical porphyroclasts or poryphyroblasts with mineral tails that “ point ” in the direction of shear.

A

Grain tail complexes

80
Q

Mineral tails may form by a combination of:

A

Plastic flattening of pre-existing grains
Pressure soln from grain center
Dynamic. recryst. at the rim of the grain
Neocryst in pressure shadows around grain

81
Q

____________ grain tail complexes consist of wedge - shaped tails that do not cross the reference plane of shear
slow grain rotation; fast tail growth
Tail growth at minimum compressive stress (45° to ref plane) during rotation

A

Sigma (σ)

82
Q

_________ tail complexes are produced by relatively rapid grain rotation relative to tail growth rate
Fast grain rotation = bending of inner portion of the tail, crosses reference plane

A

Delta (δ) grain

83
Q

fractures
oriented at shear direction
<45° inclination from foilation

A

Synthetic Fractures

84
Q

fractures
oriented against shear direction
>45° inclination from foilation

A

Anti-synthetic Fractures

85
Q

develop in mylonitic, schistose and gneissic rocks subjected to ductile shear.

A

S - C foliations

86
Q

in S-C
The letter S represents __________ and the letter C is for ____________, a French term for shear direction, which lies in the C plane

A

Schistosity; cisaillement

GLE Reviews (26 decks)

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