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Lecture notes 'Deformation and metamorphosis' UU
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Notes from the second part of the course, the 'metamorphosis' section, deformation and metamorphosis of the bachelor's degree in Earth Sciences at UU.
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Utrecht UniversityAantekeningen Metamorfose
Hoorcolleges
Naam: Sanne Maas
Solis-id: 5133017
Periode 3
Utrecht University
Bachelor Aardwetenschappen
Naam cursus: Deformatie & Metamorfose van de korst
Docent: Dr. H.W. Schrojenstein-Lantman
,Inhoud
Lecture 1 – Metamorphism ..................................................................................................................... 3
Introduction for practicals – How are minerals identified? .................................................................... 9
Lecture 2 – Equilibrium mineral assemblages ....................................................................................... 12
Lecture 3 – Metamorphic rocks and textures ....................................................................................... 19
Optical microscopy for metamorphic rocks .......................................................................................... 27
Lecture 4 – Metamorphic terranes ....................................................................................................... 30
Lecture 5 – Pressure-temperature-time paths...................................................................................... 39
Lecture 6 – Synthesis: the Alps .............................................................................................................. 47
2
,Lecture 1 – Metamorphism
3 main rock types
- Igenous
o At depth or at surface
o Formed by crystallization from melts
- Sedimentary
o Formed from eroded mineral grains cemented
by new mineral growth
- Metamorphic
o Always start with igeneous or sedimentary rock
What is metamorphism?
- Sum of all changes, all changes in a rock when the environment of the rock is changed
o Environment = physical conditions – pressure, temperature and fluid composition
o Changes – minerals, and their grain size and shape
- Occurs by reactions and recrystallization of minerals
Nature of metamorphism
- All 3 rock types in this picture (grey limestone, intruded by a
magma (black igneous rock), at the contact limestone turns white,
locally changed environment by changing its temperature
- Rock changed into white marble
3
, Pressure variation in the crust
- Deeper in the earth, more rock is pressing down (more weight),
so more pressure
- Very simple formula where pressure on a rock is equal to the
density of the overlying rock, the gravitational acceleration and
the depth
- You can also see it as the average of the principle stresses
Temperature variation in the crust
- Residual temperature within the Earth, plus heat generated by
radioactivity
- Temperature at the base of the continental crust is 500-600°C
- Perturbation of system needed for common metamorphic conditions
- Oceanic crust slightly colder
- Stars are two metamorphic conditions that we often find in
metamorphic rocks
→ are not in standard ranges of temperature – something needs to
happen to get this kind of metamorphism
Changing the P-T environment
→ tectonics – subduction
- Deposited sediments are buried when the ocean
gets closed
→ sedimentary rocks are buried to depths of 20-
30km in collision zone
- Pressure increases, because they go deeper, but the T
does not increase as fast, so cold rock
- Normal temp. at 30 km depth is 500°C
→ after burial, sediments are heated for about 30
million years
Metamorphic changes
→ 3 main ways these changes occur
- Polymorphic transformations
- Chemical reactions
- Recrystallization
Polymorphic transformations
- Minerals with same chemical composition, but atoms are arranged
in different structure
- Example – aluminosilicates Al2SiO5
o Kyanite
o Andalusite
o Sillimanite
o Ions arranged in different crystal structures and so different
properties
▪ Density
4
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