Transcript Bergarter - Royal Institute of Technology

Rock types
Igneous
Sedimentary
Metamorphic
Differences in the rock
textures
• Igneous – isometric
Differences in the rock
textures
• Sedimentary rocks have layers,
bedding, strata
Differences in the rock
textures
• Metamorphic rocks – are banded, and
foliated
metamorphic rocks
• Re crystallization of sedimentary or
igneous rocks or even other
metamorphic rocks
• In solid state (not liquid)
Metamorphism
• Due to:
– High pressure
– High temperature
– Liquid in pores
Metamorphic temperatures
• Lower boundary – ca 150 Celcius
• Upper boundary – ca 1200 Celcius – Above this
temperature the rock mass will melt and form
igneous rocks
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
?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
high pressure
Thin section of mica schist
Types of metamorphic rocks
• Regionala metamorphism - high
pressure
• Contact metamorphism – high
temperature due to igneous intrusion
Regionala metamorphism
Contact metamorf
Contact metamorphism
Textur
• Foliated –
preferred direction of
minerals or banding
• Non foliated –
no preferred direction
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
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
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
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
Preferred directions
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
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
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
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
Most common metamorphic
rock types
ROCK
NAME
TYPE
PARENT
ROCK
CHARACTERISTICS
SLATE
foliated
shales and
muds
prominant splitting surfaces
SCHIST
foliated
fine grained
rocks
mica minerals, often crinkled or wavy
GNEISS
foliated
coarse grained
rocks
dark and light bands or layers of aligned
minerals
QUARTZITE
nonfoliated
sandstone
interlocking almost fused quartz grains,
little or no porosity
MARBLE
nonfoliated
limestone
interlocking, often coarse, calcite crystals,
little or no porosity
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
Indication minerals
Mineral associations - facies
mineral changes
rock names –
bergarts namn –
illite to muscovite
chlorite enlarged
calcite with the clay to epidote
muscovi te and chlorite to
biotite
biotite to garnet or sillimanite
starting with shales and
mudstones
börja med lerskiffer
slate
phyllite
mica schi st
gneiss
starting with ultra basi c
rock s
skiffer (no difference)
fyllit
glimmerskiffer
gneiss
igneous basi ska
bergarter
green schi st
garnet schi st
amphibolite
volcanic rock s
grönski ffer
grantskiffer
amfibolit
volcani ska bergarter
metavolcanics
greenstone
limestone
leptit, hälleflinta
grönsten
kalksten
marble
calc-schi st
skarn
marmor
kalkskiffer
skarn
clorite and epidote common
epidote and chlorite common
dolomite to calcite and brucite,
tremolite
wollastonite
garnet
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
joints
• sets of 4 or more are common
• joints coated with clay or silt
• intersections isolate potentially
removable blocks (fig 8.12)
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
Engineering and
metamorphic rocks
Exploration
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irregular extent
recognition of rock types
foliation directions important
weathering zones detection
geophysical methods
drilling (difficult in quartzite)
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
surface
excavation
•
•
•
•
blasting often required
landslide risk – block theory
slab slides
toppling
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
Case histories
• Several in the book
• Read – do you understand the
descriptions of the rock and their
physical nature?