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Geochemistry > Final > Flashcards

Final Flashcards

1
Q

batch melting (equilibrium partial melting)

A
  • melt is in EQ w/ the rock and the melt does not leave the system as melting progresses (much more common)
    (melt continually reacts in equilibrium with solid residue at site of melting, until escape as a single batch of magma)
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2
Q

fractional melting

A

melt leaves the system as soon as it is produced by partial melting

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3
Q

partial melting

A

the magma is enriched in SiO2, Na2O, K2O.

  • a low degree of partial melting can produce granitic magma
  • residual rock is enriched in MgO and FeO
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4
Q

fractional crystallization

A

residual magma is enriched in SiO2, Na2, K2O

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5
Q

Equilibrium Crystallization

A

equilibrium between all solids & melt during crystallization

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6
Q

compatible elements

A

preferred to be in the minerals

  • 1st to crystallize into a rock from magma
  • D > 1
  • HREE
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7
Q

incompatible elements

A

preferred to be in the magma

- D

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8
Q

REE Patterns (2)

A

1) total REE will increase with magmatic evolution (if REE were not all equally compatible)
2) REE pattern will be flat (if all REE were equally compatible)

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9
Q

Lanthanide Contraction (3) - REE from La->Lu

A

1) decrease radius La to Lu
2) Increase Ionic Potential
3) Increasing compatibility

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10
Q

Since REE are not all equally incompatible (3)

A

1) total REE will increase with magmatic evolution
2) REE pattern generally inclined to the right
3) there are some anomalies

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11
Q

What is the difference between REE & spider diagrams

A
  • REE diagrams only have REE elements

- Spider diagrams include REE + other elements

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12
Q

Spider Diagrams (3)

A
  • similar to REE diagram but plus other incompatible elements
  • in order of increasing compatibility
  • Normalized to a candidate reservoir (ex: condrites)
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13
Q

What are the 3 sources of magma?

A

1) primitive deep mantle (OIB)
2) depleted upper mantle (MORB)
3) continental crust (CFB) - have more incompatible elements (melt 1st, lighter)

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14
Q

is the crust composed of incompatible or compatible elements?

A

incompatible

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15
Q

is the mantle composed of incompatible or compatible elements?

A

compatible

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16
Q

2 areas of fluid rock interactions

A
  • surface

- burial

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17
Q

Fluid rock interactions - Surface

A
  • weathering of granites/feldspars

- karstification

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18
Q

Fluid Rock Interactions - Burial

A
  • Dolomitization

- Albitization

19
Q

Dolomitization

A
  • most dolomite is from replacement of limestone during diagenesis rather than precipitating from seawater
  • 2CaCO3 + Mg2+ -> CaMg(CO3)2 = Ca2+
20
Q

Albitization

A

Plagioclase + Na+ -> Albite + Ca+

21
Q

Karstification

A

stalagmites, stalactities, CO2 enriched in soil

- when H2O filters into cave its P drops causing CO2 to escape => precipitates of stalagmites/stalactites

22
Q

What are isotopes?

A
  • atoms of the same atomic number but different atomic mass
    -Ex: 12C: 6 protons, 6 neutrons, 6 electrons
    13C: 6 protons, 7 neutrons, 6 electrons
23
Q

Radioactive Decay

A

process in which a radioactive element undergoes constant change in the number of protons and neutrons through emission of alpha, beta, and gamma particles

24
Q

beta decay

A
  • parent -> daughter
  • mass unchanged
  • proton # changed (becomes a different element)
25
Q

alpha decay

A
  • parent -> daughter
  • mass reduced by 4
  • proton number reduced by 2
26
Q

What is a stable isotope?

A

those that do not result from decay of other elements but do not decay to other elements

27
Q

What is the use of Stable Isotopes in geology? (3)

A

1) isotopes of any elements are not equally distributed in different material (rock, fluid, etc.)
2) can be used to trace the source(s) of geologic material (water, CO2)
3) can be used to estimate T b/c their distribution is related to T

28
Q

Isotope Fractionation

A

when 2 substances that contain an element co-exist in equilibrium, the isotopes of the elements is not equally distributed in them, but rather are fractionated

29
Q

General Rule of Isotope Fractionation

A

the heavy isotope goes preferentially to the chemical compound which the element is bound most strongly
- O18 -> water; O16 -> clouds; (some O18 will go to cloud and some O16 will go to water)

30
Q

EQ crystallization

A

minerals being crystallized are in EQ with the melt & do not leave the system

31
Q

fractional crystallization

A

minerals leave the system as soon as crysalized

32
Q

How can granites be formed? (2)

A
  • partial or complete melting of rocks in the crust
  • partial melting of rocks in the mantle
  • can be distinguished by different Sr/Sr initial values
33
Q

What conditions are favorable for carbonate rock formation?

A
  • warm temperatures (Ksp decreases with increase in T)
  • Shallow water is favorable (Ksp decreases w/ decreased P; CO2 is consumed by photosynthesis; CO2 dissolution is low due to low P)
34
Q

What conditions are unfavorable for carbonate rock formation?

A

Deep water is unfavorable

  • Ksp up with T down
  • CO2 is produced by organism decay and CO2 dissolution is high due to High P
35
Q

Precipitation Order of Evaporites

A

Minor Carbonates (50% H2O)
Gypsum (20% H2O)
Halite (10% H2O)
Potash (

36
Q

What is the meaning of metamorphic phase diagrams?

A

each line is a chemical reaction

37
Q

how do we know the P-T-X conditions of metamorphism?

A

geothermometer/geobarameter (ie: garnet/biotite & fluid inclusion)

38
Q

how do we know if an element was gained or lost during metamorphism?

A

construct an isocon and; you can see

39
Q

What is an ore deposit?

A

useful elements are enriched relative to the background to the extent that a profit can be made from extracting them

40
Q

Concentration Factor of an ore deposit

A

minimum expoitable grade/crustal abundance

41
Q

how can ore elements be enriched?

A

mechanical (placer deposits

chemical (most ore deposits)

42
Q

primary halo

A
  • enrichment of elements association with mineralization surrounding a mineral deposit relative to the background
  • concentrations higher than background but lower than the ore bodies
43
Q

primary dispersion

A

the process that forms the primary halo

44
Q

pathfinder elements

A

elements that are associated with ore deposits and that are more mobile than the ore elements on the surface. Thus forming large secondary dispersion that can help to find the primary source

Geochemistry (1 decks)

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