Rock types

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Rock types

• Igneous
• Sedimentary
• Metamorphic

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Differences in the rock textures

• Igneous isometric

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Differences in the rock textures

• Sedimentary rocks have layers, bedding, strata

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Differences in the rock textures

• Metamorphic rocks are banded, and foliated

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metamorphic rocks

• Re crystallization of sedimentary or igneous
  rocks or even other metamorphic rocks
• In solid state (not liquid)

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Metamorphism

• Due to
• High pressure
• High temperature
• Liquid in pores

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Metamorphic temperatures

• Lower boundary ca 150 Celcius
• Upper boundary ca 1200 Celcius Above this
  temperature the rock mass will melt and form
  igneous rocks

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Result of metamorphism

• new minerals grow
• minerals deform and rotate
• re crystallization of course minerals
• rocks become either
• stronger but more brittle
• or
• weaker and anisotropic

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?What is the difference between metamorphism,
diagenesis and chemical weathering?

•  metamorphism entails high temperature and high
  pressure
• diagenesis entails a bonding and hardening of a
  sediment relatively near the earths surface
• weathering entails the disruption and
  alteration of a solid rock at or near the earth
  surface

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high pressure
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Thin section of mica schist
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Types of metamorphic rocks

• Regionala metamorphism - high pressure
• Contact metamorphism high temperature due to
  igneous intrusion

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Regionala metamorphism
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Contact metamorf
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Contact metamorphism
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Textur

• Foliated preferred direction of minerals or
  banding
• Non foliated no preferred direction

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metamorphic textures

• mosaic texture interlocking equigranular grains
  (fig 8.1)
• porphoblstic texture larger minerals in a fine
  matrix (fig 8.2)

• folitation anisotropy, strong directional
  structure which effects the properties of the
  rock so they are different in different directions

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Foliation types

• fracture cleavage strong rock between
  fractures, evenly spaced, low grade metamorphism
• slaty cleavage parallel to mineral plates,
  often mica
• bedding cleavage when slaty cleavage coincides
  with bedding
• schistosity is foliation developed by
  non-random orientation of macroscopic minerals
• lepidoblastic schistosity flat mineral plates
  parallel to on another
• nemotablastic schistosity elongate minerals in
  one plane but not parallel to one another in the
  plane

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Foliation types

• fracture cleavage strong rock between
  fractures, evenly spaced, low grade metamorphism
• slaty cleavage parallel to mineral plates,
  often mica
• bedding cleavage when slaty cleavage coincides
  with bedding
• schistosity is foliation developed by
  non-random orientation of macroscopic minerals
• lepidoblastic schistosity flat mineral plates
  parallel to on another
• nemotablastic schistosity elongate minerals in
  one plane but not parallel to one another in the
  plane

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Foliation types

• fracture cleavage strong rock between
  fractures, evenly spaced, low grade metamorphism
• slaty cleavage parallel to mineral plates,
  often mica
• bedding cleavage when slaty cleavage coincides
  with bedding
• schistosity is foliation developed by
  non-random orientation of macroscopic minerals
• lepidoblastic schistosity flat mineral plates
  parallel to on another
• nemotablastic schistosity elongate minerals in
  one plane but not parallel to one another in the
  plane

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Preferred directions
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banding and other structures

• bands segregation of different minerals in
  distinct bands
• augen german for eye refers to the growth
  porphyroblasts, large crystals, in the otherwise
  finer matrix around which the banding is bent so
  an eye shape is formed
• boudinage French for sausage is a term for a
  structure where one layer, which is more brittle
  than the surrounding layers, is broken into
  segments around which the other more plastic rock
  fill in the voids. This forms a series of boudin.
  (fig 8.4)
• lineations a linear structure, deferrers from
  foliation in that it is a sub texture of the main
  metamorphic texture. All linear structure are
  oriented parallel

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banding and other structures

• bands segregation of different minerals in
  distinct bands
• augen german for eye refers to the growth
  porphyroblasts, large crystals, in the otherwise
  finer matrix around which the banding is bent so
  an eye shape is formed
• boudinage French for sausage is a term for a
  structure where one layer, which is more brittle
  than the surrounding layers, is broken into
  segments around which the other more plastic rock
  fill in the voids. This forms a series of boudin.
  (fig 8.4)
• lineations a linear structure, deferrers from
  foliation in that it is a sub texture of the main
  metamorphic texture. All linear structure are
  oriented parallel

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banding and other structures

• bands segregation of different minerals in
  distinct bands
• augen german for eye refers to the growth
  porphyroblasts, large crystals, in the otherwise
  finer matrix around which the banding is bent so
  an eye shape is formed
• boudinage French for sausage is a term for a
  structure where one layer, which is more brittle
  than the surrounding layers, is broken into
  segments around which the other more plastic rock
  fill in the voids. This forms a series of boudin.
  (fig 8.4)
• lineations a linear structure, deferrers from
  foliation in that it is a sub texture of the main
  metamorphic texture. All linear structure are
  oriented parallel

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banding and other structures

• bands segregation of different minerals in
  distinct bands
• augen german for eye refers to the growth
  porphyroblasts, large crystals, in the otherwise
  finer matrix around which the banding is bent so
  an eye shape is formed
• boudinage French for sausage is a term for a
  structure where one layer, which is more brittle
  than the surrounding layers, is broken into
  segments around which the other more plastic rock
  fill in the voids. This forms a series of boudin.
  (fig 8.4)
• lineations a linear structure, deferrers from
  foliation in that it is a sub texture of the main
  metamorphic texture. All linear structure are
  oriented parallel

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Most common metamorphic rock types
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Metamorphic grade

• Pressure and temperature together results in
  changes such as the growth of minerals and
  textures
• Indicator minerals show which temperature and
  pressure the rock has undergone

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Indication minerals
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Mineral associations - facies
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Weathering of metamorphic rocks

• Wide range of weathering products
• gneiss, granulites and other quartz rich rocks
  sandy residual soils smilar to granitic soils
• slate and phyllite miaceous, silty residual
  soils
• marble red clay
• foliation bladed outcrops tombstone rock head
  separated by completely decomposed material
• banded banded saprolite with clay between bands
• weathering depth dependent upon spacing of
  fractures, typical 6 to 24 m depth

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joints

• sets of 4 or more are common
• joints coated with clay or silt
• intersections isolate potentially removable
  blocks (fig 8.12)

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foliation shears

• persistent shear zones parallel to the plane of
  foliation, cm to m in size
• tensile and shear strengths are considerably less
  than in all other directions, strength anisotropy
• characterized by finely fractured or crushed rock
• two end members
• impervious - plastic clay seam common, alteration
  to chlorite or kaolinite replacing feldspars and
  biotite
• pervious - shear zone of crushed rock

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Engineering and metamorphic rocks
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Exploration

• irregular extent
• recognition of rock types
• foliation directions important
• weathering zones detection
• geophysical methods
• drilling (difficult in quartzite)

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slope stability

• Landslides
• common due to extremely weak shear strengths of
  platy minerals
• valley form asymetrical
• gentle - dip slip slopes slab slide
• steep slopes with creep, toppling, landslides

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surface excavation

• blasting often required
• landslide risk block theory
• slab slides
• toppling

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foundations

• fresh rock usually good
• weathered rock
• compressible sandy silty soil
• pile difficult
• saprolite protect from drying loose of fabric
• slope failures common along the plain of
  foliation

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Case histories

• Several in the book
• Read do you understand the descriptions of the
  rock and their physical nature?