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Physical Geology 111 ("Understanding Earth") > Chapter 6: Metamorphism: Alteration of Rocks By Temperature and Pressure > Flashcards

Chapter 6: Metamorphism: Alteration of Rocks By Temperature and Pressure Flashcards

1
Q

What is the parent rock of marble?

A

Limestone

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2
Q

What is the metamorphosed rock from limestone?

A

Marble

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3
Q

What is the parent rock of schist?

A

Shale

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4
Q

What is the metamorphosed rock from shale?

A

Schist

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5
Q

Exhume

A

To transport to the Earth’s surface

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6
Q

3 principal factors of metamorphism

A

Heat, pressure, fluid composition

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7
Q

Average rate that temp increases with depth in the crust

A

30 deg C/km

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8
Q

Geothermal gradient

A

The increase in temp with increasing depth in Earth’s interior

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9
Q

Geothermometer

A

A rock’s mineral composition, which determines the temperature at which the rock formed (because different minerals form at different temperatures).

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10
Q

2 plate tectonic mechanisms that form most metamorphic rocks

A
  • subduction

* continent-continent collisions

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11
Q

2 kinds of pressure (stress) rocks are subjected to

A
  • confining pressure

* directed pressure/differential stress

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12
Q

confining pressure

A

general force applied equally in all directions

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13
Q

directed pressure/differential stress

A

force exerted in a particular direction

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14
Q

Rate that pressure increases with depth in the crust

A

.3 to .4 kbars (kilobars) per km (300-400 bars/km)

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15
Q

geobarometers

A

Mineral assemblages that can be used as pressure gauges, to determine the pressure that the rock formed

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16
Q

metasomatism

A

A change in rock’s composition by fluid transport of chemical substances into or out of it

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17
Q

6 types of metamorphism

A
  • regional
  • contact
  • seafloor
  • high-pressure
  • burial
  • shock
18
Q

regional metamorphism

A
  • takes place where both high temps and pressures are imposed over large parts of the crust
  • characteristic of convergent plate boundaries
  • most widespread type
19
Q

contact metamorphism

A
  • heat from an igneous intrusion metamorphoses the rock immediately surrounding it, normally only affecting a thin zone of country rock
  • heat is from intruding magma
  • pressure only relevant where intrusion is at great depths
20
Q

seafloor metamorphism

A
  • associated with mid-ocean ridges

* hot lava heat sea water which circulates though the new ocean crust by convection; hot temperature alters the basalts

21
Q

burial metamorphism

A
  • affects a smaller amount of rock
  • low-grade metamorphism caused by the progressive increase of pressure and temperature exerted by the growing layers of overlying sediments and rock
  • begins at 6-10 km
22
Q

high-pressure metamorphism

A
  • pressures 8-12 kbars
  • form at very low depths and take a long time to recycle to the surface
  • most form in subduction zones as sediments scraped from oceanic crust and subducted to depths over 30 km
23
Q

shock metamorphism

A
  • occurs when a meteorite collides with Earth

* mass and velocity is transformed into heat and shock waves through the country rock

24
Q

foliation

A
  • a set of flat or wavy parallel cleavage planes produced by deformation of igneous and sedimentary rocks under directed pressure
  • the most prominent textural feature of regionally metamorphosed rocks
25
Q

as the grade of regional metamorphism increases, foliation becomes more or less pronounced

A

more

26
Q

4 main criteria for classifying foliated rocks

A
  • metamorphic grade
  • grain (crystal) size
  • type of foliation
  • banding
27
Q

progression of 5 foliated rocks (lowest grade to highest grade)

A 
1 - slate
2 - phyllite
3 - schist
4 - gneiss
5 - migmatite
28
Q

slate

A
  • lowest grade of foliated metamorphosed rock
  • formed from shales or volcanic ash deposits
  • have strong foliation planes to split the rock
29
Q

phyllite

A
  • foliated rock

* similar in character and origin to slate, but have a more glossy sheen from mica and chlorite

30
Q

schist

A
  • foliated rock
  • characterized by schistosity: coarse, wavy foliation of lighter and darker bands
  • among the most abundant metamorphic rock types
31
Q

gneiss

A
  • foliated rock
  • light colored rock with coarse bands of light and dark minerals throughout
  • gneissic foliation is from segregation of light-colored quartz and feldspar from darker amphiboles and other mafic minerals
  • poor foliation
32
Q

migmatite

A
  • foliated rock
  • mixture of igneous and metamorphic rock
  • higher temperatures begin to melt a part of the country rock, creating the igneous portions
33
Q

granoblastic rocks

A
  • nonfoliated metamorphic rocks that grow in equant shapes like cubes and spheres instead of platy or elongated
  • form where directed pressure is absent, so no foliation occurs
  • defined by mineralogy (because texture is homogeneous and granular)
34
Q

hornfels

A
  • granoblastic rock
  • high-temperature contact metamorphic rock
  • uniform grain size with little or no deformation
  • formed from fine-grained sedimentary and other sliicate rocks
35
Q

quartzite

A
  • granoblastic rock
  • some are homogeneous, some have bands of slate or schist
  • formed from quartz-rich sandstones
36
Q

marbles

A
  • granoblastic rock
  • some are pure white and uniform crystals, some have bands of impurities from silicates and other minerals in the limestone
  • formed from limestone and dolomites
37
Q

greenstones

A
  • granoblastic rock
  • many formed by seafloor metamorphism
  • abundance of chlorite gives the greenish cast
  • formed from volcanic rock
38
Q

amphibolites

A
  • granoblastic rock
  • med- to high-grade metamorphism of mafic volcanic rocks
  • formed from amphibole and plagioclase feldspar
39
Q

granulite (granofels)

A
  • granoblastic rock
  • homogeneous medium- to coarse-grained texture
  • formed from shale, impure sandstone, and many kinds of igneous rock
40
Q

porphyoblasts

A
  • large crystals formed in a much finer-grained matrix of other minerals
  • formed by contact and regional metamorphism
41
Q

zeolite minerals

A
  • form at low temps and pressures

* contain water within crystal structures

42
Q

metamorphic facies

A

grouping of rocks of various mineral compositions formed under different grades of metamorphism from different parent rocks

Physical Geology 111 ("Understanding Earth") (6 decks)

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