metamorphic rocks pdfs/chapter 15... · crystals of the metamorphic rock. plagioclase-hornblende...
TRANSCRIPT
![Page 1: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/1.jpg)
Metamorphic Rocks
![Page 2: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/2.jpg)
Reminder notes:
• Metamorphism
• Metasomatism
• Regional metamorphism
• Contact metamorphism
• Protolith
• Prograde
• Retrograde
• Fluids – dewatering and decarbonation – volatile flux
• Chemical change vs textural changes
• Mud to gneiss
![Page 3: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/3.jpg)
Metamorphism – changes in mineralogy
and texture of a rock due to changes in
pressure and temperature. The bulk
chemical composition of the rock doesn’t
change.
Metasomatism – changes in mineralogy and
texture of a rock due to changes in pressure,
temperature, and chemistry. Chemically
active fluids move ions from one place to
another which changes the bulk chemistry of
the rock. These fluids come from the
breakdown of hydrous and carbonate
minerals.
![Page 4: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/4.jpg)
Contact versus Regional metamorphism
![Page 5: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/5.jpg)
Metamorphic Facies
![Page 6: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/6.jpg)
Plotting metamorphic mineral diagrams
![Page 7: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/7.jpg)
![Page 8: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/8.jpg)
Barrovian metamorphic sequences
![Page 9: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/9.jpg)
Thermodynamics and Gibbs free energy
• Reactions take place in a direction that
lowers Gibbs free energy
• Equilibrium is achieved only when Gibbs
free energy reaches a minimum
• At equilibrium, temperature, pressure,
and chemical potentials of all
components must be the same
throughout
• Equilibrium thermodynamics and
kinetics. Thermodynamics tells us what
can happen, kinetics tells us if it does
happen
![Page 10: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/10.jpg)
Petrogenetic Grid
![Page 11: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/11.jpg)
AKFM diagram for pelitic rocks
![Page 12: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/12.jpg)
Petrogenetic grid – reactions in metapelites for greenschist and amphibolite facies
![Page 13: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/13.jpg)
Assemblages in metapelites as a function of metamorphic grade
![Page 14: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/14.jpg)
![Page 15: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/15.jpg)
Role of Fluids in Metamorphism
CaCO3 + SiO2 = CaSiO3 + CO2 (fluid)
![Page 16: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/16.jpg)
Ca2Mg5Si8O22(OH)2 + 3CaCO3 = 4CaMgSi2O6 + CaMg(CO3)2 + H2O + CO2
tremolite calcite diopside dolomite fluid
![Page 17: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/17.jpg)
Metamorphic grade, index minerals, isograds, and metamorphic facies
![Page 18: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/18.jpg)
![Page 19: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/19.jpg)
Textures of metamorphic rocks
• Excess energy present in deformed crystals (elastic), twins, surface free energy
• Growth of new grains leads to decreasing free energy – release elastic energy, reduce
surface to volume ratio (increase grains size, exception occurs in zones of intense shearing
where a number of nuclei are formed).
• Activation energy is provided by heating and deformation.
• Minerals with high surface free energy recrystallize before minerals with lower surface free
energy. This leads to the Crystalloblastic series. Minerals with higher surface free energy
form euhedral crystal faces relative to minerals with lower surface free energy.
Su
rfac
e F
ree
Ener
gy
![Page 20: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/20.jpg)
Textures contact metamorphic rocks - Hornfels
Cordierite and spinel Marble showing 120o grain boundary
junctures
Law of sines γ = surface tension
![Page 21: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/21.jpg)
Deformation and textures of regional metamorphic rocks
Slaty cleavage dips to the left. Bedding near vertical.
![Page 22: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/22.jpg)
Phyllite Schist GneissSlate
![Page 23: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/23.jpg)
Boudinage
![Page 24: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/24.jpg)
Solution cleavage planes in limestone Axial plane solution cleavage in
marble
![Page 25: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/25.jpg)
Development of two cleavage directions
![Page 26: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/26.jpg)
Helicitic texture - bands of
inclusions that indicate original
bedding or schistosity of the parent
rock and cut through later-formed
crystals of the metamorphic rock.
![Page 27: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/27.jpg)
Plagioclase-hornblende mylonite
Black veins of pseudotachylite
![Page 28: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/28.jpg)
Migmatites
Incipient melting of metamorphic rocks. Diagram
below shows melting conditions relative metamorphic
facies. A broad zone of Hbl → pyx + H2O separates
amphibolite and granulite facies and provides the
water for melting
leucosome
melanosome
![Page 29: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/29.jpg)
Geothermometers and Geobarometers
GARB – used to calculate temperature (Exchange reaction)
Fe3Al2Si3O12 + KMg3AlSi3O10(OH)2 ↔ Mg3Al3O12 + KFe3AlSi3O10(OH)2
almandine phlogopite pyrobe annite
52,110 - 19.51*T(K) + 0.238*P(bar) + RT ln K = 0
where K = (XMggar XFe
bio)/(XFegar XMg
bio) which is an exchange reaction
![Page 30: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/30.jpg)
3CaAl2Si2O8 = Ca3Al2Si3O12 + 2Al2SiO5 + SiO2
anorthite = grossular + kyanite + quartz
GASP – used to calculate pressure (Net-transfer reaction)
Net-transfer reactions cause phases to appear or disappear (in this case
anorthotite
-48,357 + 150.66 T(K) -6.608 P (bar) + RT ln K = 0
![Page 31: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/31.jpg)
A Complete Example
Let's suppose you analyze a group of minerals that are in
equilibrium and find the following compositions:
garnet: Ca0.42Mg0.51Fe2.04Mn0.03Al2Si3O12
biotite: KMg1.62Fe1.38AlSi3O10(OH)2
plagioclase:Na0.64Ca0.36Al1.36Si2.64O8
kyanite
quartz
Let's determine the equilibrium P and T.
Determine mole fractions
Xgrs = 0.14
Xprp = 0.17
Xalm = 0.68
Xann = 0.46
Xphl = 0.54
Xan = 0.36
Determine activities, assuming ideal behavior
agrs = 0.143 = 0.0027
aprp = 0.173 = 0.0049
aalm = 0.683 = 0.31
aann = 0.463 = 0.097
aphl = 0.543 = 0.16
aan = 0.36
Calculate equilibrium constants:
KGASP = agrs / aan3 = 0.0025 / 0.363 = 0.054
KGARB = (aprpaann) / (aalmaphl) = (0.0049 * 0.097) / (0.31
* 0.16) = 0.0096
Calculate P and T:
GASP: P (bar) = ( -48,357 + 150.66 *
T(K) + RT ln K ) / 6.608
GARB: P (bar) = ( 52,110 - 19.51 *
T(K) + RT ln K ) / -0.238
Choose T = 873 K:
GASP P = 1.7 kbar
GARB P = -7.7 kbar
Choose T = 1073 K:
GASP P = 13.2 kbar
GARB P = 40.6 kbar These two lines
intersect at ~955K and 10.9 kbar.
![Page 32: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/32.jpg)
![Page 33: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/33.jpg)
Pressure-temperature-time (P-T-t) paths
Radiometric dating – application of different systems to metamorphic rocks.
![Page 34: Metamorphic Rocks Pdfs/Chapter 15... · crystals of the metamorphic rock. Plagioclase-hornblende mylonite Black veins of pseudotachylite. Migmatites Incipient melting of metamorphic](https://reader036.vdocuments.site/reader036/viewer/2022071118/60126f5df28edd7e8128082a/html5/thumbnails/34.jpg)
Summary of Geologic Setting and Metamorphic Facies