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 Metamorphic rock is formed when existing rocks change due to subjection to pressure and or temperature  Any rock can undergo metamorphism  Metamorphism.

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Presentation on theme: " Metamorphic rock is formed when existing rocks change due to subjection to pressure and or temperature  Any rock can undergo metamorphism  Metamorphism."— Presentation transcript:

1  Metamorphic rock is formed when existing rocks change due to subjection to pressure and or temperature  Any rock can undergo metamorphism  Metamorphism is the process by which heat, pressure, and chemical reactions deep within the earth alter the mineral content and or structure of existing rock without melting it down Chapter 7 Metamorphism and Metamorphic Rocks

2 METAMORPHISM & METAMORPHIC ROCKS NORMAL DEPTHS FOR METAMORPHISM: >10-KM FROM SURFACE (BELOW SEDIMENTARY DEPTHS & ABOVE IGNEOUS DEPTHS) METAMORPHISM: MINERAL CONTENT & STRUCTURE OF SOLID ROCK ALTERED BY HEAT, PRESSURE & CHEMICALLY ACTIVE FLUIDS – DOESN’T MELT CONDITIONS PROMOTING METAMORPHISM: ROCK STABILITY IS RELATED TO FORMATION ENVIRONMENT METAMORPHISM BREAKS SOME BONDS, BUT DOES NOT INCLUDE MELTING `

3 Sedi., meta., igne. rocks

4 Metamorphic Rocks in North America

5 CONDITIONS-CONTD 1) HEAT – MOST IMPORTANT FACTOR GEOTHERMAL GRADIENT (20-30 DEG C/KM-200 DEG C TO METAMORPHOSE ROCKS) SOURCES OF HEAT FOR METAMORPHISM: – CONDUCTION FROM DEEP INTERIOR – RISING MAGMA – RADIOACTIVE ISOTOPES – FRICTION BETWEEN ROCK BODIES PRESSURE

6 Pressure-contd. Lithostatic: Confining pressure in all directions, rock becomes compressed Directed Pressure: Acts in one principal plane Results of Pressure: – Compaction – Smaller & Denser – Ion migration of unbonded ions (recrystallization) – Foliation – Preferred alignment of minerals - Subjected to direct pressure – Units of Pressure: 1 Bar = 1 Atm. Pressure = 1.02 kg/cm 2 = 14.7 lbs/inch 2 = 10 5 Pascal

7 Circulating Fluids Often necessary for chemical reactions (Facilitates movement of ions and atoms) Sources of Water – Surface Infiltration – Pores in Sedimentary Rocks – Cracks on Subducting Plates – Magmas – Decomposing Minerals ALL METAMORPHIC ROCKS ARE CATEGORIZED AS ‘FOLIATED’ OR ‘NON FOLIATED’

8 PARALLEL CLEAVAGE

9 MINERAL GRAINS

10 MINERAL GRAINS-CONTD.

11 Deep burial of rocks

12 What Drives Metamorphism Heat  Accelerate pace of chemical reactions Pressure  Lithostatic (confining)- rock becomes smaller and denser  Directed- minerals become aligned- Foliation Circulating Fluids  Ions in water- change mineral composition Parent Rocks  Original rock’s composition will affect the outcome of metamorphism

13 CONFINING PRESSURE

14 DIRECTED PRESSURE

15 TYPES OF METAMORPHISM Contact  Heat is the dominant factor  Area affected generally smaller than regional metarmorphism Regional are two types with extensive coverage  Burial- occurs in deep sedimentary basins- no plate tectonics involved  Dynamothermal- occurs where converging plates squeeze a rock caught between them Others  Hydrothermal- involves hot water from magma  Fault-zone- rocks grinding past one another  Shock- meteorites strike  Pyrometamorphism- lightning

16 CONTACT METAMORPHISM

17 DYNAMOTHERMAL METAM.

18 HYDROTHER. METAM-CONTD

19 Hydrothermal Metamorphism

20 METAMORPHIC ROCK TYPES Foliated- based on type of foliation  Slate- fine grain  Phyllite- fine grain with sheen  Schist- has ‘split’ appearance  Gneiss- layers/bands of minerals Non-foliated- based on mineral composition  Marble  Quartzite  Hornsfel Mixed Rock  Migmatite- indicates partial melting

21 Quartz-Quartzite

22 Quartz-Sandstone

23 Metamorphism Temperature & Pressure Information about degree to which a metamorphic rock differs from its parent material Metamorphic Grade-  low ( ) slate  high ( ) gneiss Index minerals/metamorphic Zones are used to determine metamorphic condition of temperature and pressure  Chlorite, muscovite-low grade (low P/T)  Garnet, staurolite- intermediate  Sillianite- high grade (high P/T)

24 Common Metamorphic Rocks FOLIATED ROCKS DERIVED FROM SHALE OR MUDSTONES: – SLATE (FINE GRAINED) SLATY CLEVAGE SLATE COLORS (RED: IRON OXIDE; GREEN: CHLORITE; PURPLE: MANGANESE OXIDES; BLACK: CARBON) PHYLLITE: FINE-GRAINED SCHIST: COARSE GRAINED GNEISS: COARSE GRAINED

25 Relationships that produce crystallization

26 Three main metamorphic environments

27 Relationships that produce metamorphic rocks

28 Metamorphic Surface Rocks

29 Rock Slide of 1959

30 St. Francis Dam


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