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GLE Reviews > Earth Mat Flashcards - Ch 18 > Flashcards

Earth Mat Flashcards - Ch 18

1
Q

Subdivisions on metamorphic pressures

A

low pressure (0 – 2 kbar ≈ 0 – 6 km depth),
moderate pressure (2 – 6 kbar) or high
pressure ( > 6 kbar ≈ > 20 km depth).

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2
Q

provide critical information because they effectively indicate the temperature/pressure conditions of metamorphism.

A

index minerals,

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3
Q

are lines drawn on geological maps that mark the first appearance of a particular index mineral.

A

Isograds

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4
Q

consists of the regionbounded by two isograd lines.

A

A metamorphic zone

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5
Q

bounded by the chlorite and biotite isograds

A

Chlorite Zone

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6
Q

The six metamorphic zones based on the six index mineral isograds are called

A

Barrovian zones.

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7
Q

occurs between the biotite isograd—marking the first appearance of biotite—and the almandine (garnet) isograd.

A

The biotite zone

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8
Q

Almandine forms through the chemical transformation of

A

chlorite and magnetite.

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9
Q

is bounded by the almandine garnet isograd—marking the first appearance of almandine garnet—and the staurolite isograd.

A

The almandine zone

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10
Q

lies between the staurolite isograd—marking the first appearance of the higher temperature mineral staurolite—and the kyanite isograd.

A

The staurolite zone

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11
Q

Kyanite forms through

A

dehydration reactions of
staurolite [Fe2+2Al9Si4O23(OH)] or
pyrophyllite [Al2Si4O10(OH)2]

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12
Q

occurs inside the sillimanite isograd and marks the highest temperature zone defined by Barrow and Tilley

A

The sillimanite zone

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13
Q

Limitations of barrovian zones and isograds

A

not useful for non-pelitic rocks, subduction zones or contact metamorphism

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14
Q

Sillimanite and potassium feldspar can also develop by

A

dehydration of muscovite in the presence of quartz,

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15
Q

introduced the concept of metamorphic facies—a more comprehensive approach to assessing the conditions recorded by metamorphic rocks.

A

Eskola

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16
Q

are distinctive mineral assemblages in metamorphic rocks that form in response to a particular range of temperature and/or pressure conditions.

A

Metamorphic facies

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17
Q

Introduced the zeolite facies; the prenite-pumpellyite facies

A

Turner; Coombs

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18
Q
  • include non-foliated, fine-grained hornfels rocks and coarser-grained rocks with granoblastic textures.
  • form by heat-induced metamorphism in aureoles surrounding igneous intrusions.
A

Hornfels facies

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19
Q

is the low-temperature hornfels facies, with temperatures generally < 450 °C and pressures < 2 kbar (depth < 6 km).

A

The albite-epidote hornfels facies

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20
Q

The albite-epidote hornfels facies is roughly the low-pressure equivalent

A

greenschist facies

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21
Q

compose the bulk of many metamorphic aureoles, forming at temperatures generally between 450 and 600 °C and at pressures. <2.5 kbar (<8km)

A

Hornblende hornfels facies rocks

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22
Q

The Hb-Hornfels is the low pressure equivalent of

A

amphibolite

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23
Q
  • facies develop at temperatures of 600–800 °C and at pressures < 2.5 kbar (< 8 km)
A

Px-Hornfels

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24
Q

are very rare, forming in very high temperature (> 800 °C) and low pressure (< 2.5 kbar ≈ < 8 km) conditions in association with basic and ultrabasic intrusions

A

Sanidinite hornfels facies

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25
Q

the dehydration rxn of phlogophite to sanidinte and enstatite is associated with what facies

A

Sanidinite hornfels facies

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26
Q

a low-grade metamorphic facies produced by temperatures between ∼150 and 300 °C and pressures less than 5 kbar (∼15 km depth).

A

Zeolite

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27
Q

are a hydrous sodium and calcium aluminum tectosilicate mineral group formed by diagenetic or low-temperature metamorphic reactions.

A

Zeolites

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28
Q

Critical zeolite facies minerals, which commonly coexist with quartz, include

A

analcime, laumontite, heulandite, and wairakite.

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29
Q

Zeolite facies minerals originate from

A

the hydrothermal alteration of volcanic protoliths
the devitrification of basaltic glass and tuff,
reaction of pelites and graywackes with saline waters.

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30
Q

Transition of zeolite minerals as PT conditions increase

A

Stillbte -> Heulandite -> Laumontite -> Waikarite

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31
Q

facies minerals are produced by hydrothermal alteration and burial metamorphism at temperatures and pressures that exceed zeolite facies conditions.

A

Prehnite-pumpellyite
(250–350 °C) (< 6 kbar, ∼20 km depth)

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32
Q

minerals found in the prehnite pumpellyite series

A

albite, chlorite, muscovite, illite, phengite, smectite

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33
Q

Higher temperature alteration of prehnite and pumpellyite results in _______________, two minerals that mark the transition to the higher grade albite-epidote hornfels facies and the greenschist facies

A

the neocrystallization of actinolite and epidote

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34
Q

The higher temperature assemblage containing pumpellyite and actinolite has been called the

A

transitional pumpellyite-actinolite facies

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35
Q

generally form under medium temperature (350–550 °C) and pressure (3–10 kbar ≈ 10–30 km depth) conditions associated with dynamothermal metamorphism at convergent plate boundaries.

A

Greenschist facies rocks

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36
Q

Where metapelites occur, the greenschist facies can be subdivided into three Barrovian zones

A
  • The chlorite zone corresponds to lower greenschist facies conditions with minerals such as chlorite, dolomite, stilpnomelane, and calcite.
  • The biotite zone corresponds to upper greenschist facies conditions and contains biotite and tremolite.
  • The lower part of the almandine garnet zone corresponds to the uppermost greenschist to epidote-amphibolite facies.
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37
Q

form at high temperatures (∼550–750 °C) and moderate to high pressures (4–12 kbar ≈ 12–40 km depth) in regional orogenic belts at convergent margins.

A

Amphibolite facies rocks

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38
Q

The transition from greenschist to amphibolite facies is marked by

A

an increase in hornblende, garnet, and anthophyllite
Plagioclase minerals become less sodic and more calcic during this transition.
appearance of staurolite in pelitic rocks
transformation from kyanite to sillimanite in pelitic rocks,

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39
Q

The amphibolite facies encompasses several different Barrovian zones (see Figure 18.3) that include:

A

The upper part of the almandine zone
All of the staurolite zone
The lower part of the sillimanite zone

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40
Q

The low-temperature part of the amphibolite facies corresponding with the almandine zone is also known as the

A

epidote-amphibolite facies

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41
Q

consists of high-temperature (∼700–900 °C) and moderate to high-pressure (3–15 kbar ≈ 10–50 km depth) mineral assemblages.

A

The granulite facies

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42
Q

Difference betweeen the lower granulite (I) and upper granulite (II) facies

A

Hydrous minerals like hornblende and biotite can occur in the lower part of the granulite facies (granulite I), while the upper part (granulite II) is characterized entirely by anhydrous minerals.

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43
Q

Common minerals in granulite facies include ________in pelitic and quartz-feldspathic rocks. Calcareous rocks are characterized by the

A

quartz and orthoclase;
appearance of wollastonite and the absence of hydrous minerals like phlogopite.

44
Q

are hypersthene-bearing granitic gneisses.
found in granulite facies

A

Charnockites

45
Q

Granulite facies metamorphism occurs in the highest temperature dynamothermal metamorphism regions at:

A

Convergent plate boundaries
The base of thick continental crust
The uppermost part of the mantle

46
Q

The granulite facies corresponds with which zones

A

the upper parts of the Barrovian sillimanite zone and, at even higher temperatures, the cordierite-garnet zone.

47
Q

consists of moderate to high pressure (4–20 kbar ≈ 13–66 km depth) and low temperature (150–500 °C) mineral assemblages.

A

The blueschist facies

48
Q

The blue amphibole mineral glaucophane gives this facies its distinctive color. Other common minerals in the blueschist facies include:

A

Magnesio-riebeckite
Lawsonite
Jadeite pyroxene
Aegirine
Crossite
Kyanite

49
Q

The eclogite facies (see Figure 18.2) typically develops at

A

high temperatures (400 – 900 °C) and very high pressures (12 – 25 kbar ≈ 40 – 82 km).

50
Q

Eclogite facies rocks occur in three major environments:

A

In the lower continental crust and mantle (> 40 km depth) and later exposed on Earth’s surface in deeply eroded fold and thrust belts.
At convergent margins in ophiolite complexes and subduction zone mélanges.
As xenoliths in diamond-bearing kimberlite pipes.

51
Q

occur within the eclogite facies (Figure 18.5) at pressures > 25 kbar (> 80 km depth) and temperatures > 600 °C.

A

Ultra-high pressure (UHP) minerals

52
Q

UHP conditions are indicated by critical minerals such as:

A

Coesite, a high pressure polymorph of silica.
Diamond, the high pressure polymorph of carbon.
Majorite, a high pressure mineral (Mg₂Al₃Si₂O₁₂ – MgSiO₃).

53
Q

Coesite was first observed in a laboratory, where it was synthetically created by

A

Loring Coes, Jr., in 1953.

54
Q

Naturally occurring coesite was first noted at

A

Meteor (Barringer) Crater, Arizona

55
Q

discovered the first dynamothermally produced coesite in Alpine rocks.

A

Christian Chopin (1984)

56
Q

is a sequence of facies that occurs across a metamorphic terrane due to differences in pressure and temperature (P/T) conditions.

A

A metamorphic facies series

57
Q

Low P/T series group: two low pressure and high temperature facies series are recognized:

A

(1) the very low P/T contact facies series, and (2) the somewhat higher P/T Buchan facies

58
Q

Moderate P/T series group:

A

Barrovian facies series,

59
Q

High P/T series group

A

Sanbagawa facies series and Franciscan facies series,

60
Q

The geothermal gradient for the contact facies series is_implying a significantly higher than average heat input due to magmatic activity.

A

> 80 °/km,

61
Q

Low pressure contact metamorphism produces what textures

A

hornfelsic and/or granoblastic

62
Q

With increasing temperature, the contact facies series progresses through the sequence:

A

Zeo - AbEp - HbHf - PxHf - SnHf

63
Q

The Buchan facies series records high geothermal gradients ranging

A

from 40 to 80 °C/km.

64
Q

The Buchan facies series is also known as the

A

Abukuma facies series,

65
Q

The Buchan facies series progresses, with increasing temperature and pressure, through:

A

Zeo - PP - Grn - Amp - Gra

66
Q

Buchan facies series metamorphism reflects

A

higher temperatures, but only moderate increases in pressure.

67
Q

Buchan facies series develop by
How about non foliated?

A

regional metamorphism and magmatic arc activity at convergent margins;
crustal thinning and heating

68
Q

The Barrovian facies series develops in response to geothermal gradients of

A

∼ 20 – 40 °C/km,

69
Q

With increasing temperature, the Barrovian facies series progresses through the same facies sequence as the Buchan facies series, from:

A

Zeo - PP - Grn - Amp - Gra

70
Q

Hows does buchan differ from barrovian series

A

Higher P/T ratio
Kya in Buchan

71
Q

Tectonic affinity of Barrovian facies

A

thickening orogenic belts at convergent plate boundaries, especially collisional orogens.

72
Q

The Sanbagawa facies series are produced under geothermal gradients in the range of

A

10 to 20 °C/km.

73
Q

The Sanbagawa facies series progression includes:

A

Zeolite,
Prehnite-pumpellyite,
Blueschist facies, followed in some cases by
Greenschist, and/or
Amphibolite facies.

74
Q

Sanbagawa facies series is characterized by slightly higher temperatures.
This may result from

A

Slower subduction giving the rocks more time to heat up as pressures increase, or
Higher geothermal gradients during subduction

75
Q

The Franciscan facies series develop where geothermal gradients are

A

< 10 °C/km.

76
Q

The Franciscan facies series progresses from:

A

Zeolite,
Prehnite-pumpellyite,
Blueschist, possibly to
The eclogite facies

77
Q

Franciscan series metamorphism reflects

A

the progressive rapid increase in pressure relative to slow increases in temperature during regional metamorphism as rocks are rapidly dragged downward in subduction zones.

78
Q

Occur when chemical reactions have reached completion, resulting in no further net changes.

A

Equilibrium Condition

79
Q

Disequilibrium Indicators:

A

Reaction rims on minerals.
Coexisting minerals that cannot exist in equilibrium.
Incomplete replacement of minerals.

80
Q

Equilibrium Indicators:

A

Absence of disequilibrium features.
Planar grain contacts between mineral crystals.

81
Q

Equilibrium mineral reaction and assemblage diagrams are known as

A

petrogenetic or paragenetic grids.

82
Q

Petrogenetic vs Paragenetic

A

Petrogenetic refers to the conditions under which the rock originated, while
Paragenesis refers to the formation sequence of equilibrium minerals.

83
Q

Components of ACF ternary diagram

A

A = (Al2O3 + Fe2O3) − (Na2O + K2O)
C = (CaO – 3.33 P2O5)
F = FeO + MgO + MnO.

84
Q

particularly useful for displaying common equilibrium mineral assemblages that occur in rocks derived from the quartzo-feldspathic, basic, calcareous, and pelitic protoliths

A

ACF diagram

85
Q

proposed by Eskola (1915), is used to discriminate equilibrium mineral assemblages derived from pelitic and quartzo-feldspathic protoliths with excess Al2O3 and SiO2

A

The A′KF diagram

86
Q

particularly useful in discriminating mineral compositions in ferromagnesian-rich basic and ultrabasic rocks as well as many pelitic rocks.

A

The AFM diagram

87
Q

diagrams have also been developed for calcareous rocks as illustrated in which the three components are CaO, MgO, and SiO2.

A

CMS ternary

88
Q

Regional metamorphism, which produces the vast majority of metamorphic rocks, occurs primarily at:

A

Divergent plate boundaries, associated with continental and oceanic rifts and sea floor spreading, where hydrothermal processes dominate.
Convergent plate boundaries, associated with subduction, magmatic arcs, and continental collisions, where dynamothermal metamorphic processes dominate.

89
Q

Continental rift basin metamorphism can occur by a number of processes:

A

Contact metamorphism from the intrusion of shallow dikes, sills, and flood basalts.
Hydrothermal alteration associated with hot magmatic and wall rock volatile fluids.
Dynamic metamorphism due to brittle extensional faulting in the upper crust and ductile shearing in the lower crust.
Burial metamorphism producing zeolite and prehnite-pumpellyite facies assemblages due to the deposition of thick, non-marine detrital sediment sequences in rift basins.

90
Q

extensive hydrothermal metamorphism of basalt, gabbro, and peridotite occurs at ocean ridges, resulting

A

albite-epidote hornfels, zeolite, and prehnite-pumpellyite

91
Q

At deeper levels within the oceanic crust and upper mantle, gabbro and peridotite are altered to higher temperature

A

hornblende hornfels facies assemblages

92
Q

The paired metamorphic belts encircling the Pacific Ocean were recognized as

A

subduction zone (outer metamorphic belt) and magmatic arc (inner metamorphic belt) assemblages,

93
Q

The outer metamorphic belt consists of what series

A

Sanbagawa or Franciscan

94
Q

The inner metamorphic belt consists of what series

A

Buchan or Barrovian

95
Q

characteristic of Phanerozoic subduction zones,

A

Blueschist facies mineral assemblages

96
Q

Forearc basins consists of what facies

A

zeolite to prehnite-pumpellyite

97
Q

the metamorphic grade of accretionary prism, metamorphic belts

A

High; Low

98
Q

the forearc basement can have what kind of metamorphism

A

Dynamothermal metamorphism can also produce either high P/T facies associated with the underlying subduction zone or moderate P/T due to the adjacent magmatic arc.

99
Q

facies associated with magmatic arc complexes

A

Contact, Buchan, and Barrovian

100
Q

The metamorphic facies commonly found in pull-apart basins include

A

zeolite and prehnite-pumpellyite facies.
(sub-greenschist conditions)

101
Q

are among the most distal tectonic features created in the overlying plates of many convergent margins.

A

Fold and thrust belts and foreland basins

102
Q

The horizontal shortening is accommodated by folds and thrust faults that result in the

A

telescoping or “piggybacking” of thrust slices.

103
Q

facies assemblages in fold and thrust belts.

A

assemblages in fold and thrust belts.

104
Q

In the adjoining foreland basin, an initially deep basin fills with marine deposits producing alternating shale, sandstone, chert, and carbonate layers producing what is referred to as

A

flysch deposits.

105
Q

With continued thrusting and infilling in foreland basins, fine-grained marine rocks are succeeded by sandstones and conglomerates in what are referred to as

A

molasse deposits.

106
Q

facies to be expected in a Continent – continent collision

A

Barrovian facies series

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