Unit 3 Rock Types Metamorphic Rocks Basic Rock

Unit 3 - Rock Types Metamorphic Rocks

Basic Rock Classifications ● Igneous ● Sedimentary ● Metamorphic

Metamorphic Rocks Pages 193 - 198 • Metamorphism means to “change form” and take thousands to millions of years to complete. • During this change, minerals in the rocks“flow in solid state” (i. e. NO MELTING) and can change on the atomic scale. • Three metamorphic agents cause rocks to change, which include: 1) increased heat (i. e. temperature) 2) increased pressure 3) chemically active fluids (e. g. water)

3 Agents Causing Metamorphism pg. 193 1. Heat - drives chemical reactions that transform minerals into new forms - can be supplied by lava, magma or by radioactive decay of isotopes at great depth - main agent responsible for contact metamorphism

3 Agents Causing Metamorphism pg. 193 2. Pressure/stress - The weight of the material around the rock, causes compressional forces - reduces porosity (spaces) and volume of the rock - occurs mainly during regional metamorphism

3 Agents Causing Metamorphism pg. 193 3. Chemically Active Fluids • mainly water which dissolves ions • allows movement of mineral grains allowing the rock to recrystallize • produces new minerals in the rock. • Needed in both contact and regional metamorphism

Metamorphic Textures The degree (Amount) of metamorphism is reflected in the rocks’ texture and mineralogy. Two textures are formed as a result of metamorphism, which include: 1) Foliated Texture 2) Non-foliated Texture

Metamorphic Textures 1) Foliated Texture When the minerals in the rock form a banded or layered appearance. Results when the minerals of a rock are brought into parallel alignment during recrystallization. • Examples: slate, phyllite, schist, and gneiss

Foliated Texture Process: • Unequal pressure results in the distortion of rock • The orientation of these minerals is usually perpendicular to the compressional forces. • This gives the resulting metamorphic rock a layered or banded (foliated) appearance.

Metamorphic Textures 2) Non - Foliated Texture • These metamorphic rocks are harder, denser, more crystalline, have new minerals but are very similar to parent rock • Rocks have uniform sized crystals with no visible foliation.

Non - Foliated Texture Process: • Pressure is in all directions and forms larger, more dense crystals. • the pressure pushes the minerals into smallest volume with no change in shape • The minerals formed are uniform sized crystals with

Types and grades of Metamorphism There can be different grades of metamorphism depending on the amount of change due to the metamorphic agents. 1) Low-grade Metamorphism Rocks are subjected to small changes in temperatures and pressures, which result in slight changes to the rock. Example: Shale changes to form slate.

Shale →Slate

Types and grades of Metamorphism 2) High-Grade Metamorphism When rocks are subjected to extreme temperatures and pressures, which result in large changes to the rock. i. e. close to where the rocks melt; however, there is no melting, Example: Shale to Gneiss, and Granite to Gneiss.

Slate →Phylite

Phylite →Shist

Shist → Gneiss

Granite → Gneiss

Two types of Metamorphism 1) mountain building: regional metamorphism 2) The intrusion of molten material: contact metamorphism

1. Contact Metamorphism - changes in rock caused by heat from a nearby magma body - rocks immediately surrounding an igneous body are cooked and altered from their original state. - Found below lava, near magma bodies, dykes and sills Examples rocks: include marble and quartzite

Limestone → Marble

Sandstone → Quartzite

Buried lava flow or intrusive bed? We can tell by the location of contact metamorphism

2. Regional Metamorphism pg. 201 - Occurs with large scale mountain building. - Occurs over a large geographical area due to massive plate collisions deforming the land. - the crust is squeezed horizontally creating stress - happens with: – increased temperature – increased pressure (mainly) - Example: Shale to Gneiss

Core Lab 3 – Metamorphic Rocks ⦿ Concept ⦿ Unit Map for rocks 3 Test ● Minerals ● Igneous ● Sedimentary ● Metamorphic