Lecture 9: Metamorphic Rocks Flashcards
Metamorphism
A process by which: Temperature Pressure & Chemical Reactions alters: Mineral content & Structure Of pre-existing rock(without melting and solid state only)
Metamorphic rocks are produced from:
Potential protoliths:
Igneous rocks
Sedimentary rocks &
Other metamorphic rocks
What type of changes do protoliths undergo?
They undergo changes in texture and mineralogy due to variations in temperature, pressure, tectonic stress, and the amount of reactive water.
What is the example of metamorphosis?
Limestone metamorphosizes into marble
Slide
6,7,8
Foliation
A planar fabric that cuts through the rock and is defined by the alignment of platy minerals or creation of alternating light and dark bands.
A set of flat or wavy parallel planes produced by directed pressure/deformation.
Provide an example of platy minerals
Mica
Metamorphosis often imparts ________ upon new rocks
Foliation
What is the most common textural feature of metamorphic rocks?
Foliation
Foliation vs lineation
Slide 10
Metamorphic processes:
- Recrystallization:
- Neo-crystallization:
- Pressure Solution:
- Plastic Deformation: (no squiggly lines or sharp edges nothing was dissolve or deposited elsewhere)
- Overprinting:
Which parameters control metamorphism?
Temperature
Pressure
Hydrothermal fluids
Describe the control of temperature on metamorphism.
The change in temperature is what is key to look at not absolute. Temperature ranges from 250 to 850 degrees Celsius which varies with tectonic setting. The sources of heat are from geothermal gradients, magnetic intrusions, or tectonic compression.
Slide 16
Describe the metamorphic process: recrystallization provide an example.
the minerals change size and shape through dissolution and growth of crystals. The composition of the minerals does not change, however. Example: limestone has tiny clasts (protolith) → marble has large, new grains (metamorphic rock)
Solid solution vs polymorphs **MIDTERM**
Exam question slides: 18
Polymorphs
Slide 18
Pressure in metamorphism
Pressure:
- lithostatic or confining: pressure pushes rock equally from all directions to become more dense and retain same shape
- directed: pressure is greatest in one specific direction resulting in a change in shape and the new mineral growth aligns perpendicular to pressure equal to folation
Stress in metamorphism
Slides:20-29
Hydrothermal fluid in metamorphism
Hydrothermal fluid (hot water with dissolved ions and volatiles) accelerates metamorphism. Hydrothermal fluids speed up chemical reactions which add or subtract elements. Hydrothermal alteration is called metasomatism.
Is metamorphosis isochemical? What is its non-isochemical name?
Yes; metasomatism
Metasomatism
Hydrothermal alteration from accelerated metamorphism by hydrothermal fluid
Classifications of metamorphic rocks
Foliated rocks:
Granoblastic rocks:
Slide 31
Foliated Metamorphic Rocks increasing by temp.
(200-300): Slate (300-400): Phyllite Metaconglomerate: metamorphosed conglomerate (400-600): Schist (>650): Gneiss (>750): Migmatites
Non foliated rocks are called
Granoblastic rocks
Non foliated rock types
Quartzite, and marble
Metamorphic grade
A measure of the intensity of temp and pressure conditions that lead to alteration of metamorphic rocks from pelitic (clay-rich) protolith
The metamorphic grade displays that different temperature and pressure conditions occur in different ___
Geological settings
Slides
49-53
Geothermal gradient in metamorphism
Occurs in different settings that have different characteristics of :
- heat flow
- differential stress &
- hydrothermal fluid interaction.
Slides
55
Types of metamorphism
1. Thermal: heating by a plutonic intrusion 2. Burial: deep burial in a basin 3. Dynamic: shearing in a fault zone 4. Regional: P and T change due to orogenesis 5. Hydrothermal: alteration by hot water leaching 6. Subduction: high P and low T alteration • 7. Shock: extreme high P from a bolide impact
Types of geological settings in metamorphism
- Contact metamorphism
- Dynamic metamorphism
- Regional metamorphism
- Burial metamorphism
- Hydrothermal metamorphism
- Subduction metamorphism