Metamorphism
This presentation is the property of its rightful owner.
Sponsored Links
1 / 47

Metamorphism PowerPoint PPT Presentation


  • 112 Views
  • Uploaded on
  • Presentation posted in: General

Metamorphism. The transformation of rock by temperature and pressure Metamorphic rocks are produced by transformation of: Igneous, sedimentary and igneous rxs. Thanks to CU Boulder Geology Dept for use of some of these slides. Metamorphism.

Download Presentation

Metamorphism

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Metamorphism

Metamorphism

  • The transformation of rock by temperature and pressure

  • Metamorphic rocks are produced by transformation of:

    • Igneous, sedimentary and igneous rxs

Thanks to CU Boulder Geology Dept for use of some of these slides


Metamorphism1

Metamorphism

  • Metamorphism progresses from low to high grades

  • Rocks remain solid during metamorphism


Metamorphism

What causes metamorphism?

  • Heat

    • Most important agent

    • Heat drives recrystallization - creates new, stable minerals

  • Pressure (stress)

    • Increases with depth

    • Pressure can be applied equally in all directions or differentially


Metamorphism

Origin of pressure in metamorphism

Confining or hydrostatic pressure: equal in all directions

Directed pressure: largely in one direction or along a particular axis


Main factor affecting metamorphism

Main factor affecting metamorphism

  • Parent rock

    • Metamorphic rocks typically have the same chemical composition as the rock they were formed from

    • Different minerals, but made of the same stuff.

    • Exception: gases (carbon dioxide, CO2) and water (H2O) may be released


Metamorphism

Progressive metamorphism of a shale

Shale


Metamorphism

Progressive metamorphism of a shale

Slate


Metamorphism

Progressive metamorphism of a shale

Phyllite


Metamorphism

Progressive metamorphism of a shale

Schist


Metamorphism

Progressive metamorphism of a shale

Gneiss


Metamorphism2

Metamorphism

  • Three types of metamorphic settings:

    • Contact metamorphism– from a rise in temperature within host rock

    • Hydrothermal metamorphism– chemical alterations from hot, ion-rich water

    • Regional metamorphism -- Occurs in the cores of mountain belts and makes great volumes of metamorphic rock


Contact metamorphism

Contact metamorphism

Produced mostly by local heat source


Metamorphism

Hydrothermal metamorphism

Requires hot circulation of fluids


Metamorphism

Regional metamorphismin Mountain Belts

Requires crustal thickening and shortening


Metamorphism and plate tectonics

Metamorphism and plate tectonics

  • Most regional metamorphism occurs along convergent plate boundaries

    • Compressional stresses deform plate edge

    • Occurs in major mountain belts: Alps, Himalayas, and Appalachians

    • Not necessarily in all mountains, depends on orogenic forces, i.e., uplift versus compression


Metamorphism and plate tectonics1

Metamorphism and plate tectonics

  • Metamorphism at subduction zones

    • Cores of subduction zones contain linear belts ofmetamorphic rocks

      • High-P, low-T zones near trench

      • High-T, low-P zones in region of igneous activity (arc)


Metamorphism

Location of metamorphic zones

in a subduction zone


Metamorphic environments

Metamorphic Environments

  • Index minerals and metamorphic grade

    • Certain minerals, called index minerals, are good indicators of the metamorphic conditions in which they form


Metamorphism

Index Minerals in metamorphic rocks


Metamorphic environments1

Metamorphic Environments

  • Metamorphic grade

    • A group of minerals that form in a particular P-T environment

Zeolite (really low T,P; <200C)

Greenschist (low T, P; 200-450C, 10-15 km)

Blueschist (low T, high P - subduction zones)

Amphibolite (high T, P; 450-650C, 15-20 km)

Granulite (super high T, P; >700C, >25km)


Metamorphism

Metamorphic Environments in Subduction Zones


Metamorphism

Greenschist Hand Sample

Greenschist Thin Section


Metamorphism

Mica

Schist


Metamorphism

Blueschist

Amphibolite


Common metamorphic rocks

Common metamorphic rocks

  • Nonfoliated rocks

    • Quartzite

      • Formed from a parent rock of quartz-rich sandstone

      • Quartz grains are fused together

      • Forms in intermediate T, P conditions


Metamorphism

Sample of

quartzite

Thin section

of quartzite


Metamorphism

Flattening of quartz grains in quartzite


Common metamorphic rocks1

Common metamorphic rocks

  • Nonfoliated rocks

    • Marble

      • Coarse, crystalline

      • Parent rock usually limestone

      • Composed of calcite crystals

      • Fabric can be random or oriented


Metamorphism

Marble (Random fabric = annealing; nonfoliated)


Metamorphism

Change in metamorphic grade with depth


Common metamorphic rocks2

Common metamorphic rocks

  • Foliated rocks

    • Slate

      • Very fine-grained

      • Excellent rock cleavage

      • Made by low-grade metamorphism of shale


Metamorphism

Example of slate


Metamorphism

Slate roof


Common metamorphic rocks3

Common metamorphic rocks

  • Foliated rocks

    • Phyllite

      • Grade of metamorphism between slate and schist

      • Made of small platy minerals

      • Glossy sheen with rock cleavage

      • Composed mainly of muscovite and/or chlorite


Phyllite left and slate right lack visible mineral grains

Phyllite (left) and Slate (right) lack visible mineral grains


Common metamorphic rocks4

Common metamorphic rocks

  • Foliated rocks

    • Schist

      • Medium- to coarse-grained

      • Comprised of platy minerals (micas)

      • The term schist describes the texture

      • To indicate composition, mineral names are used (such as mica schist)


Metamorphism

Mica Schist - note well developed foliation


A mica garnet schist

A mica garnet schist


Common metamorphic rocks5

Common metamorphic rocks

  • Foliated rocks

    • Gneiss

      • Medium- to coarse-grained

      • Banded appearance

      • High-grade metamorphism

      • Composed of light-colored feldspar layers with bands of dark mafic minerals


Gneiss displays bands of light and dark minerals

Gneiss displays bands of light and dark minerals


Metamorphism

Diorite to Gneiss Morph

(orthogneiss - from igneous protolith)


What are metamorphic textures

What are metamorphic textures?

  • Texture refers to the size, shape, and arrangement of mineral grains within a rock

  • Foliation – planar arrangement of mineral grains within a rock


Metamorphism

Outcrop of foliated gneiss


Metamorphic textures

Metamorphic textures

  • Foliation

    • Foliation can form in various ways:

      • Rotation of platy or elongated minerals

      • Recrystallization of minerals in a preferred orientation

      • Changing the shape of equidimensional grains into elongated and aligned shapes


Metamorphism

Flattened Pebble Conglomerate = flattening


Development of foliation due to directed pressure

Development of foliation due to directed pressure


  • Login