Igneous and metamorphic petrology Igneous and metamorphic petrology

1. Fundamentals 2. Classification

3. Thermodynamics and kinetics Igneous

4. Silicate melts and fluids

5. Crystal melt equilibria 6. Chemical dynamics of melts and crystals

7. Magma ascent, emplacement and eruption 8. Generation of magma and differentiation

9. Magmatism and tectonics

Metamorphic 10. Fabric, composition and classification

11. Mineral reactions and equilibria 12. Processes and kinetics

13. P-T-t paths, facies and zones

Lecture part 60% Tests:

1st: Topic 1-3 (20%) 2nd: Topic 4-9 (20%)

3rd: Topic 10-13 (20%)

Final: all

Lab: 1. Identification of rocks

Hand specimen and microscope 2. CIPW norm calculation

3. Thermodynamics problemset

4. Petrological databases 5. MELTS

Lab part 40% Identification: igneous (15%),

metamorphic (9%); exercises

(16%)

Formed by cooling of magma (700-1200oC at the surface)

Concentrated in regions in the Earth

Both igneous and metamorphic processes require thermal energy

Energy: capacity to do work (w), product of force (F) and displacement (d). W=Fd

Work in geological systems related to pressure and volume (PV).

Pressure: force over area P=F/area, volume V=area x d.

PV=Fd=w. Kinetic energy: F=1/2 mv2

Potential energy: related to position. Gravitational potential energy: E=∆mgz Thermal energy: internal, transferred as heat

Magmatic rocks: Magmatic rocks:

Energy transfer and heat Energy transfer and heat

Thermal energy and work (PV) are convertible and transformation is conservative No loss of energy or mass: first law of thermodynamics

Heat flow: quantity of heat (∆q) transferred to a body results in a rise in temperature (∆T): ∆q=cp∆T. cp is heat capacity (J/molK).

Heat can be transferred through:

1. Radiation 2. Advection

3. Conduction 4. Convection

Radiation insignificant for Earth’s heat budget, becauseBB

Advection, where?

Conduction: transfer of kinetic energy by vibrating atoms. No conduction in

perfect vacuum. Difference in T between two locations: thermal gradient

Rate at which heat is conducted from a unit surface area: heat flux or heat flow heatflow= thermal conductivity x thermal gradient

Geothermal gradient or geotherm ∆T/∆z

Cool rocks are opaque

Fluid flow through rocks, cracks. Hydrothermal systems

Geotherm and convection Geotherm and convection

At the surface thermal gradient is 20K/km.

Convecting mantle results in a less steep geotherm with depth

1. Mid-ocean ridge volcanism Three pieces of evidence for convection

and the existence of a viscous mantle:

2. Subducting slabs

3. Mantle plumes

Viscosity: measure of resistance to flow Mantle is 1018 times more viscous than tar

There is a pressure dependence on the viscosity

Igneous activity has petrotectonic association:

Certain rocktypes are found together.

Energy sources: Accretion

Core formation Radioactive decay

Inner core growth

Pressure: Geobaric gradient ∆P/∆z

1bar=105 Pa=0.9896 atm, 1000bar = 1 kbar=0.1 GPa. Lithostatic load is confining pressure P=F/A=mg/A, m is mass and g is acceleration

of gravity or ∆P/∆z= ρg, where ρ is density

Rock forming processes:

Changes in states of a system. System is user defined. State of the system: conditions that define its properties or energy.

Equilibrium, stable-metastable

Rock properties Rock properties 1) Composition

a) -Chemical

b) -Mineralogical c) -Modal

2) Field relation

3) Fabric

What does petrology want to answer What does petrology want to answer

• When and how did a particular magma originate • How was the magma transported from dource to emplacement

• What physical, chemical and thermal processes operated on the system during crystallization

• What was the nature of the rock prior to metamorphism and its history of

deformation and recrystallization • How do petrologic processes control evolution of the crust and relate to global

tectonics • How can the modern petrotectonic associations by used to infer tectonic

regimes in ancient rocks

• How did the planet originate and evolve • What is the effect of petrological processes on society and life

Composition and classification Composition and classification

Analytical procedures: -Sampling controlled by factors like: grainsize, alteration, weathering

-Accuracy and precision. Precision: how well can you reproduce the number

Accuracy: how close to the “true value.

-Modal analysis often done by point counting

-Chemical analyses Major elements content reported

in wt% Trace element content in ppm or

ppb

Instruments: XRF, ICP, electron probe

Volatiles are driven off: Loss On Ignition

Mineral composition Mineral composition

Mineral association: There are a limited number of combinations:

For example: quartz and magnesian olivine do do co-exist Other examples: leucite and orthopyroxene

Major minerals and their composition Major minerals and their composition

Major mineral Simple formula Compatible trace elements Olivine (Mg,Fe)2SiO4 Ni, Cr, Co

Orthopyroxene (Mg,Fe)2Si2O6 Ni, Cr, Co Clinopyroxene Ca(Mg,Fe)(Si,Al)2O6 Cr, Sc

Hornblende (Ca,Na)2-3(Mg,Fe,Al)5 Ni,Cr,Co,Sc

(Si,Al)8O22(OH,F)2

Biotite K2(Mg,Fe,Al,Ti)6 Ni,Cr,Co,Sc,Ba,Rb

(Si,Al)8O20(OH,F)4 Muscovite K2Al4(Si,Al)8O20(OH,F)4 Rb,Ba

Plagioclase (Na,Ca)(Si,Al)4O8 Sr,Eu

K-feldspar KAlSi3O8

Accessory minerals

Magnetite Fe3O4 V,Sc Ilmenite FeTiO3 V,Sc

Sulfides Cu,Au,Ag,Ni,PGE

Zircon ZrSiO4 Hf,U,Th, heavy REE Apatite Ca5(PO4)3(OH,F,Cl) U, middle REE

Allanite Ca2(Fe,Ti,Al)3(O,OH) Light REE, Y, Th, U (Si2O7)(SiO4)

Xenotime YPO4 Heavy REE

Monazite (Ce,La,Th)PO Y, light REE Titanite (Sphene) CaTiSiO5 U,Th,Nb,Ta, middle REE

Chemical composition Chemical composition

Cartesian or triangular variation diagrams Diagrams are designed to highlight process,

Chemical composition II Chemical composition II

Modal composition Sierra Nevada batholith

Classification based on fabric Classification based on fabric Phaneritic: contains grains large enough to identify by eye Aphanitic: grains are too small to be identified by eye

Porphyritic: Large grain size (phenocysts) and small grain size (matric) Aphyric: contains no crystals

Sparsely phyric: contains less then 5% crystals

Phyric: contain more then 5% crystals Holocrystalline: made entirely of crystals

Felsic: contains large amount of feldspars

Mafic: Fe-rich

Ultramafic: Fe and Mg-rich

Granite Aplite

Pegmatite

Mafic and ultramafic Mafic and ultramafic

Apanitic and Glassy Rocks Apanitic and Glassy Rocks

CIPW Normative composition CIPW Normative composition

Hypothetical mineral assembledge based on the whole rock composition

1. Molecular ratio of Fe2O3/FeO=0.15 2. Calculate molar proportions of the oxides

3. Add MnO and NiO to FeO 4. Add SrO and BaO to CaO

5. Normative apatite, Ap, allocate CaO equal

to 3.3 times P2O5 6. Il, allocate FeO equal to the proportion f

TiO2

7. If there is excess TiO2 allocate amount of

CaO equal to the excess TiO2 to make

titanite, but only after An allocation 8. If there is still excess TiO2 allocate it to

rutile 9. Allocate Al2O3 for Or

10. If there is excess K2O make Ks, peralkaline

11. Allocate excess Al2O3 to make provisional Ab,

12. If there is excess Na2O allocate Fe2O3 to make Ac.

CIPW Normative composition cont’d CIPW Normative composition cont’d 13. If there is excess Na2O make Ns.

14. If there is excess Al2O3 make An

15. If there is excess Al2O3 make C.

16. Allocate equal amount of FeO to Fe2O3 to make Mt.

17. If there is excess Fe2O3 make Hm.

18. Calculate FeO/MgO ratio.

19. Allocate (FeO+MgO) equal to CaO with FeO/MgO ratio to Di.

20. If there is excess CaO allocate it to Wo.

21. If there is excess (FeO+MgO) make Hy.

22. Assign SiO2 to the normative minerals.

23. If there is excess SiO2 make Qz.

24. If there is a deficit of SiO2 an additional 10 steps

CIPW Normative composition cont’d CIPW Normative composition cont’d

Why? Silica saturation (Mg,Fe)2SiO4 + SiO2 = 2(Mg,Fe)SiO3 and

NaAlSiO4 + 2SiO2 = NaAlSi3O8

Modest silica deficiencies are shown by normative Ol, while strong

undersaturation is shown by normative Ne and Lc.

Silica oversaturated: Qz; silica saturated: Hy; silica undersaturated: Ol. Different saturation levels lead to different pathways during melting and

crystallization.

Alumina saturation: