lecture 3: rocks and minerals references: principles and applications of geochemistry (ch. 7 &...
TRANSCRIPT
![Page 1: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/1.jpg)
Lecture 3: Rocks and Minerals
References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)
![Page 3: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/3.jpg)
Granite: intrusive igneous rock
quartz hornblende feldspar
![Page 4: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/4.jpg)
What defines a mineral?
• Naturally Occurring• Inorganic• Solid• Specific composition (e.g., Gold - Au, Salt -
NaCl, quartz - SiO2)
• Definite crystalline structure – atoms are arranged in a specific pattern
![Page 5: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/5.jpg)
Mineral Identification• Colour: caused by trace elements or impurities within a mineral• Lustre: how a mineral surface reflects light• Texture: how the mineral feels to the touch• Streak: the colour of a mineral when it is scratched on a streak plate
(i.e., colour when broken up)• Hardness (Moh’s scale: 1-10 – diamond is 10, talc is 1)• Cleavage: how a mineral breaks (typically along planes of weakness
– related to bonding• Fracture: splitting with no orientation• Density• Flame: colour under a flame• Special properties like double refraction, radioactivity,
taste, pleochroism, fluorescence
![Page 6: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/6.jpg)
Mineral groups1) Silicates (SiO4) – make up 96% of minerals, e.g., olivine
2) Carbonates (CO3): e.g, calcite CaCO3
3) Oxides: metal and oxygen (e.g., hematite, magnetite)
4) Sulfides: element + S2 (pyrite – FeS)
5) Sulfates: element + SO4 (gypsum – CaSO4nH2O)
6) Halides: element + halide (salt - NaCl)
7) Native elements: e.g., Cu, Au, Agpyrite
gypsum
![Page 7: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/7.jpg)
Crystal Habit
• appearance – shape and size of crystals
Botryoidal: grape-like
Bladed
Dendritic: tree-like
stibnite
hematite
![Page 8: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/8.jpg)
Crystal Form Any grouping of crystal faces or facets that are arranged in the same symmetry is referred to as a crystal's "form." There are approximately 48 unique crystal forms.
![Page 9: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/9.jpg)
Atomic structure of crystals
The relative size of ions determine how atoms pack and which ions can serve as substitutes.
![Page 10: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/10.jpg)
Crystal structure:
• determined by radius size…
![Page 11: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/11.jpg)
Silicates
Silicate tetrahedron olivine, quartz
Single chain structure pyroxene
Double chain structure hornblende
Sheet silicate structure micas
Framework silicate structure Feldspars
O2-
O2- O2-O2-
Si4+
SiO44-: although it is
geometrically balanced, it is not charge balanced – needs ions or other tetrahedra to balance charge
![Page 12: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/12.jpg)
How are minerals formed?
1) Solution: if a solution is supersaturated, minerals will precipitate
2) Magma: minerals form during cooling of a magma – the slower a magma cools, the larger the crystals
Intrusive: cools slowly beneath Earth’s surface (e.g., basalt)Extrusive: cools rapidly at Earth’s surface (e.g., granite)Metamorphism
3) Metamorphism: transformation due to changes in pressure and temperature
![Page 13: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/13.jpg)
![Page 14: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/14.jpg)
Phase DiagramsA phase diagram is common way to represent the various phases of a substance and the conditions under which each phase exists.A phase diagram is a plot of pressure (P ) vs temperature (T). Lines on the diagram represent conditions (T,P) under which a phase change is at equilibrium. That is, at a point on a line, it is possible for two (or three) phases to coexist at equilibrium. In other regions of the plot, only one phase exists at equilibrium.
Phase diagram for water
Triple point: where 3 phases coexist
![Page 15: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/15.jpg)
Binary phase diagram for a solid solution of Olivine
Solidus: the temperature below which the substance is stable in the solid state
Liquidus: the temperature above which the substance is stable in the liquid state
Lever Rule: to determine quantitatively the relative composition of a mixture in a two-phase region in a phase diagram
fliqfsolid
Fayallite (Fa) Forsterite (Fo)% Fo (Mg2SiO4)
![Page 16: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/16.jpg)
Magma: mixture of molten rock, gases and mineral phases, produced by mantle melting
Mantle melts between ~800-1250ºC due to:
1) Increase in temperature
2) Decrease in pressure
3) Addition of volatile phases
Upwelling mantle plumes – hotspots
Hawaii, Icelandgeothermsolidus
liquidus
![Page 17: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/17.jpg)
Magma: mixture of molten rock, gases and mineral phases, produced by mantle melting
Mantle melts between ~800-1250ºC due to:
1) Increase in temperature
2) Decrease in pressure
3) Addition of volatile phases
Adiabatic rise of mantle material with no heat loss – decompression melting
Mid-Ocean Ridges
Partial melting
![Page 18: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/18.jpg)
Magma: mixture of molten rock, gases and mineral phases, produced by mantle melting
Mantle melts between ~800-1250ºC due to:
1) Increase in temperature
2) Decrease in pressure
3) Addition of volatile phases (e.g., water)
Mantle solidus is depressed by addition of water
Subduction zone settings
Wet mantle plumes
0
200
100
150
50
Dep
th (
km)
![Page 19: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/19.jpg)
Mantle melting: endmember modelsBatch melting: Melt remains in contact with residual crystals at all times, so
the bulk composition remains constant
Fractional melting: Melt leaves the system as soon as it is formed, so the bulk composition of the residual solid changes continuously.
• Incompatible elements: preferentially partition into the melt phase (D<1)
• Compatible elements: preferentially partition into the solid phase (D>1)
• Partition or distribution coefficient (D) = Csolid/Cliquid
Spider diagram showing depleted MORB vs. enriched OIB sources
Most incompatible Less incompatible
Concentrations normalized to bulk earth, C1 chondrites, or primitive mantle
![Page 20: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/20.jpg)
Relating trace element concentrations to melt fraction (F)
Batch melting equation: Cliq/Csol = 1/(F+D(1-F))
Fractional melting equation: Cliq/Csol = (1/D)*(1-F)(1/D-1)
E. Klein, “The Crust”, T.I.G series
![Page 21: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/21.jpg)
Spider diagram of crust vs mantle
Workman and Hart, 2005
![Page 22: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/22.jpg)
Rare Earth Element diagrams
• REE are a group of 15 elements with atomic numbers ranging from 57 (La) to 71 (Lu) – LREE vs. HREE
• Although they are geochemically similar, they have different partition coefficients so are sensitive tracers of source enrichment, the degree of melting and/or fractional crystallization
Shaw et al., 2009
![Page 23: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/23.jpg)
Samples of the mantle
1) Ophiolites– Slabs of oceanic crust and upper mantle– Thrust at subduction zones onto edge of
continent2) Dredge samples from oceanic fracture zones3) Nodules and xenoliths in basalts4) Kimberlites
– Diamond-bearing pipes blasted up from the mantle carrying xenoliths from depth
Hacker
Oman ophiolite
![Page 24: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/24.jpg)
Mafic Rocks – Magnesium, Iron rich, usually dark coloured
![Page 25: Lecture 3: Rocks and Minerals References: Principles and applications of Geochemistry (Ch. 7 & 8) Igneous Petrogenesis (Ch. 2)](https://reader036.vdocument.in/reader036/viewer/2022062409/56649cbb5503460f949833b1/html5/thumbnails/25.jpg)
Felsic or SiAlic Rocks – Silicon, Aluminum rich, usually light coloured