METAMORPHISM / EARTH AND LIFE SCIENCE / SCIENCE 11 - MELC 8

Summary

This educational video delves into metamorphism, the process by which rocks are transformed due to changes in pressure and temperature. It explains the concept of metamorphism, the role of pressure and temperature in rock transformation, and the types of metamorphic rocks, including foliated and non-foliated textures. The script also distinguishes between regional and contact metamorphism, highlighting the geological processes that lead to these changes and the resulting rock characteristics.

Takeaways

• 📚 Metamorphism is the process by which rocks change due to heat, pressure, and chemically active fluids, maintaining the same chemical composition as the parent rock.
• 🔍 The term 'metamorphism' comes from the Greek words 'meta' for change and 'morphe' for form, indicating an isochemical transformation.
• 🌡️ Pressure and temperature are key factors in metamorphism, with pressure increasing with depth and temperature rising due to the geothermal gradient.
• 💧 Types of pressure include pore pressure from trapped fluids, load pressure from overlying rocks, and tectonic pressure from folding.
• ♨️ Metamorphic reactions accelerate with increasing temperature, which also affects the stability of minerals under new conditions.
• 🌀 Chemically active fluids, primarily water with dissolved ions, facilitate reactions by transporting ions and speeding up the alteration of minerals.
• 🏞️ Metamorphic grade describes the temperature and pressure conditions under which metamorphic rocks form, with low, medium, and high grades corresponding to different temperatures and pressures.
• 🗻 Low-grade metamorphism occurs at lower temperatures and pressures, producing hydrous minerals like clay and serpentine.
• 🌋 Medium-grade metamorphism happens at moderate temperatures and pressures, resulting in minerals such as muscovite, biotite, and garnet.
• 🏜️ High-grade metamorphism takes place at high temperatures above 450 degrees Celsius, leading to the formation of non-hydrous minerals like pyroxene.
• 📈 The degree of metamorphism increases with the grade, affecting how rocks such as shale transform into slate or granite into gneiss.
• 📏 Foliated metamorphic rocks display a layered or banded appearance due to directional pressure, while non-foliated rocks lack this planar fabric and have a granular appearance.
• 🏔️ Regional metamorphism is caused by large-scale geological processes like mountain building, often associated with convergent plate boundaries.
• 🔥 Contact metamorphism occurs when magma contacts existing rock, causing temperature rise and fluid penetration, typically resulting in non-foliated rocks.

Q & A

What is metamorphism?

Metamorphism is an isochemical process by which rocks are changed by heat and pressure, or some chemically active fluids, without changing the overall chemical composition of the parent rock.

What is the origin of the term 'metamorphism'?

The term 'metamorphism' comes from ancient Greek words 'meta' meaning change, and 'morphed' meaning form, referring to the transformation of rocks under new conditions.

How does pressure affect metamorphism?

Pressure applied to rocks can cause metamorphism. It increases with depth and is applied in three ways: pore pressure from trapped fluids, load pressure from the weight of overlying rocks, and tectonic pressure from folding due to high pressures over short periods.

How does temperature influence the rate of metamorphic reactions?

As temperature increases, the rate of metamorphic reactions also increases. Temperature rises with depth due to the geothermal gradient, affecting how rocks are transformed.

What role do chemically active fluids play in metamorphism?

Chemically active fluids, mostly water with dissolved ions, can speed up chemical reactions that alter solid minerals into new solid minerals by transporting dissolved ions, often occurring in subduction zones.

What is the concept of metamorphic grade?

Metamorphic grade is a term used to describe the relative temperature and pressure conditions under which metamorphic rocks form. It increases as temperature and pressure on a rock body increase.

What are the characteristics of low-grade metamorphism?

Low-grade metamorphism occurs at temperatures between 200 to 320 degrees Celsius and relatively low pressure, characterized by an abundance of hydrous minerals like clay minerals, serpentine, and chlorite.

What types of rocks are formed during high-grade metamorphism?

High-grade metamorphism, occurring at temperatures above 450 degrees Celsius, forms non-hydrous minerals such as pyroxene and magmatic rocks.

What distinguishes foliated from non-foliated metamorphic rocks?

Foliated metamorphic rocks have a layered or banded appearance due to exposure to heat and directed pressure, while non-foliated rocks lack a planar fabric or foliation, crystallizing under conditions with no differential stress.

What are the two types of metamorphism mentioned in the script?

The two types of metamorphism are regional metamorphism, which is caused by large geologic processes like mountain building, and contact metamorphism, which occurs when magma comes in contact with an existing rock body.

What are some examples of non-foliated metamorphic rocks?

Examples of non-foliated metamorphic rocks include quartzite, marble, and anthracite, which have a granular appearance and are formed under conditions without directed pressure.