Chapter 9 (part I): Metamorphic Rocks Study Help for Chapter 9 Definition of metamorphism, its causes, and the agents of metamorphism. Textures of metamorphic rocks, rock cleavage, foliation. The most common metamorphic rocks and what they are formed from (parent rock). Understand the main types/environments of metamorphism, which are the most/least common, where do they occur? How are they related to plate tectonics? Know the slate  gneiss progression of metamorphism Progressive regional metamorphism and index minerals (Figure Story 9.7)

Chapter 9 (part I): Metamorphic Rocks 1)Introduction 2)Metamorphic environments 3)Agents of metamorphism

Recall:3 fundamental rock types l Igneous l Sedimentary l Metamorphic Example: granite crystallization 1) Introduction

l Igneous l Sedimentary l Metamorphic crystallization Example: Grand Canyon deposition Recall:3 fundamental rock types 1) Introduction

l Igneous l Sedimentary l Metamorphic crystallization deposition today Recall:3 fundamental rock types 1) Introduction

“metamorphism” Lit. “change form” Transform: Igneous Sedimentary Metamorphic into: “process” occurs deep Recall:3 fundamental rock types 1) Introduction

2) Metamorphic environments Contact metamorphism Hydrothermal metamorphism Regional metamorphism rock near or touching magma high temperatures of magma “bake” rock Chemical reactions with ion-rich water Associated with igneous Activity, seafloor spreading centers associated w/ mountain building Large scale deformations, directed forces, high temperatures, (most common), Mostly associated with Convergent plate boundaries Fig. 9.3

3) Agents of metamorphism F Heat F Pressure (stress) F Chemical active fluids

Heat The most important agent Recrystallization results in new, stable minerals Two sources of heat Contact metamorphism – rocks are baked by heat from magma An increase in temperature with depth due to the geothermal gradient (20-30 °C per km in upper crust) 3) Agents of metamorphism See Fig. 9.1

Pressure (stress) Increases with depth ( bar/km) Confining pressure applies forces equally in all directions Rocks may also be subjected to differential stress which is unequal in different directions 3) Agents of metamorphism See Fig. 9.1

Origin of pressure in metamorphism 3) Agents of metamorphism

F Pressure/Stress

3) Agents of metamorphism F Pressure/Stress

3) Agents of metamorphism F Pressure/Stress

3) Agents of metamorphism F Pressure/Stress near surface deformation: brittle fractures shearing force

3) Agents of metamorphism F Pressure/Stress Deep crust/mantle deformation: ductile shearing force (no fractures)

Chemically active fluids = hydrothermal fluids Mainly water with other volatile components Enhances migration of ions Aids in recrystallization of existing minerals Where is the water from from? –Squeezed out of pore spaces of sedimentary rocks –Squeezed out of fractures in igneous rocks –Hydrated minerals such as clays and micas 3) Agents of metamorphism

4) How metamorphism alters rocks F Hydrothermal fluids cause mineralogical changes 3) Agents of metamorphism

The importance of parent rock Most metamorphic rocks have the same overall chemical composition as the parent rock from which they formed Mineral makeup determines, to a large extent, the degree to which each metamorphic agent will cause change e.g., in shale, clays recrystallize to micas, but quartz and feldspars remain largely unaltered 3) Agents of metamorphism

Important: parent rock mineralogy Example: magma intrudes rock host rock alteration quartz sandstone not much limestone lots 3) Agents of metamorphism