1. Metamorphic rocks Introduction

2. Today Updates: ? Lecture outline: Basics of metamorphism:
T, P (and stress), fluids

3. Metamorphism

4. Lower limit Low-temperature limit grades into diagenesis
Arbitrary boundary; examples:
Diagenesis/weathering physically similar processes
Metamorphism
begins ~ oC
(unstable protolith)
Some zeolites =
diagenetic, others
metamorphic
Granite
Melts w/
H2O
Diagenesis
Metamorphic rocks

5. Upper limit High-temperature limit grades into melting
While melting solids and liquids coexist
If we heat a metamorphic rock until it melts, when does it become
“igneous”?
Gradational, so
naming =difficult
Granite
Melts w/
H2O
Diagenesis
Metamorphic rocks

6. Metamorphic Agents

7. Temperature

8. Temperature cont’d

9. Pressure

10. P-T example conditions
Fig = estimates of metamorphic temperature-pressure relationships from ancient orogenic belts
Based on P-T estimates for rocks exposed at the surface in these areas along a traverse from lowest to highest metamorphic conditions: metamorphic field gradients – not same as geotherms

11. Estimating P and T

12. How metamorphic?
Granite
Melts w/
H2O
Diagenesis
Metamorphic rocks

13. Stress and pressure

14. Stress and pressure

15. Stress and strain

16. Deviatoric stress

17. Tension
strain ellipsoid
original shape s1 s3

18. Compression s3 s1

19. Result of deviatoric stress

20. Shear s1

21. Fluids
minerals.cr.usgs.gov/gips/images/inclumed.gif

22. Fluids 2
Components: Pfluid = total fluid pressure, = sum of the partial pressures: Pfluid = pH2O + pCO2 + … (or molar: X)
Source of fluids:
Meteoric (rain etc)
Magmatic
Subduction related
Trapped sedimentary
Mantle degassing

23. Fluids 3 (+P&T)