Geology 111 Lecture 7 metamorphism

What do we need to make metamorphic rocks?

heat, pressure, and or chemical fluids

 What is a protolith? What are some common protoliths?

A protolith is the original rock that undergoes metamorphism. Common protoliths include:

• Shale → Slate, Schist, Gneiss

• Limestone → Marble

• Sandstone → Quartzite

• Basalt → Amphibolite

• Granite → Gneiss

Explain how metamorphic rocks link to plate tectonics

Metamorphism is directly related to plate tectonics because heat, pressure, and stress from tectonic movements drive the transformation of rocks.

• Convergent Boundaries: High pressure and temperature create regional metamorphism (e.g., Himalayas).

• Subduction Zones: High-pressure, low-temperature conditions form blueschist facies.

• Divergent Boundaries: Hydrothermal fluids cause hydrothermal metamorphism (e.g., mid-ocean ridges).

• Mountain Building: Rocks are buried and deformed under extreme conditions, forming foliated metamorphic rocks.

Explain the rock cycle-all of it.

• Igneous Rocks form from the cooling and solidification of magma or lava.

• Weathering & Erosion break down igneous rocks into sediments.

• Sedimentary Rocks form when sediments are compacted and cemented together.

• Metamorphic Rocks form when sedimentary or igneous rocks experience heat and pressure.

• Melting turns metamorphic rocks into magma, restarting the cycle.

What are some of the changes we see to rocks in

metamorphic processes? Can you describe them? Identify them by general diagrams?

• Mineral changes: New minerals form (e.g., clay minerals in shale become mica in schist).

• Texture changes: Grains align, forming foliation in high-pressure conditions.

• Crystal growth: Recrystallization increases grain size.

• Density increase: Minerals become more compact.

How can hydrothermal metamorphism happen?

Hydrothermal metamorphism occurs when hot, mineral-rich fluids circulate through rock, altering its composition. This happens mainly at mid-ocean ridges where seawater interacts with hot basaltic rocks, forming minerals like serpentine.

 What is the difference between stress and pressure?

• Pressure: Equal force applied in all directions (e.g., deep burial in Earth).

• Stress: Unequal force applied in different directions (e.g., tectonic compression causing folding).

What is foliation and nonfoliation?

• Foliation: Minerals align in parallel layers due to pressure (e.g., slate, schist, gneiss).

• Nonfoliation: No layered structure; occurs in uniform pressure conditions (e.g., marble, quartzite).

What are some signs of increasing metamorphism?

• Larger crystal size

• Stronger foliation

• New mineral growth (index minerals like garnet)

• Higher density

• More intense color changes

What are contact, regional, etc. metamorphic areas? Can you explain where those happen in real life?

• Contact Metamorphism: Rock changes due to heat from nearby magma intrusion (e.g., marble forming near an igneous intrusion).

• Regional Metamorphism: Large-scale pressure and heat (e.g., at convergent boundaries, forming schist and gneiss).

• Hydrothermal Metamorphism: Alteration by hot fluids (e.g., mid-ocean ridges).

• Burial Metamorphism: Rocks buried deep under sediments experience increased pressure and temperature.

How do deeper-formed metamorphic rocks get to the

surface?

• Erosion removes overlying material, exposing deeper rocks.

• Uplift & Mountain Building push rocks upward.

• Tectonic Collision forces rocks to rise over time (e.g., ancient metamorphic rocks in mountain ranges).