Ig/met Exam 2

Front 1

What is the chemical formula for kyanite?

Back 1

Al2SiO5

Front 2

What is the chemical formula for albite?

Back 2

NaAlSi3O8

Front 3

What is the chemical formula for almadine?

Back 3

Fe3Al2Si3O12

Front 4

What is the chemical formula for muscovite?

Back 4

KAl2AlSi3O10(OH)2

Front 5

What is the chemical formula for biotite?

Back 5

K(Mg,Fe)3AlSi3O10(OH)2

Front 6

What determines the ability of a trace element to substitute for an essential structural constituent of a particular mineral phase? Give an example of a trace element and the element that it substitutes for in a.) plagioclase b.) olivine

Back 6

1. Must have similar valence
2. Must have similar ionic radius

a. Sr for Ca in plagioclase
b. Ni for Fe in Olivine

Front 7

With respect to trace elements, define distribution coefficient, compatible, and incompatible

Back 7

Distribution Coefficient- Kd = Cxtl/Cliq; determines elements ability to substitute in given mineral

Compatible- kd>1; trace element is able to substitute

incompatible- kd<1; trace element is not able to substitute

Front 8

For a basalt lava flow, which trace element ration in the lava will most closely compare to ("fingerprint") the mantle source of the basalt magma?

Back 8

Zr/Nb

Front 9

Why are element concentrations normalized to those in chondrite meteorites in plotting Rare Earth Element (REE) data?

Back 9

Chondrite meteorites represent primordial unfractionated earth and the atomic number trace elements create a saw tooth pattern otherwise that is difficult to analyse.

Front 10

In rare earth element patterns, What is the Eu anomaly and how is it produced?

Back 10

The anomaly is when Eu is greater(+) or less (-) in abundance when compared to other elements. This is due to Eu 2+ ability to substitute for Ca in plagioclase.

Front 11

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Front 12

Explain in terms of partitioning of the REE minerals and magma, why the cumulate and differentiated magma have the REE patterns that they do.

Back 12

LREE becomes enriched in the melt (differentiate magma) and the remaining cumulate show a LREE depletion. Due to LREE being more incompatible meaning kd<1 so Cliq>Cxtl. Also the slope of REE decreases and there is a observable Eu anomaly due to the crystallization of plagioclase.

Front 13

The radioactive decay of Sm to Nd takes place by?

Back 13

alpha decay

Front 14

What are the two important caveats for age dating a suite of rock samples?(geochronology)

Back 14

1. Rock samples are comagmatic
2. Rock samples must have remained in a closed system

Front 15

The slope of the isochron yields the age of a rock suite. What is the slope of the isochron equal to?

Back 15

e^(gamma*t) - 1

Front 16

A suite of metavolcanic rocks define a 147Sm/144Nd vs.
143Nd/144Nd isochron with a slope of .01984. What is the Sm-Nd age of these rocks?
(gamma=6.54*10^-12 year)

Back 16

0.01948= e^((6.54*10^12)t) -1
ln 1.01948 = 6.54*10^-12 t
t=2.95 Ga

Front 17

For one of the whole rock samples in the suite referred to in the previous question, analysis of the spearated constituent mineral phase gave 87Rb/86Sr vs 87Sr/86Sr isochron with a slop of .04278. What is the Rb-Sr age of this mineral(internal) isochron? (gamma = 1.42*10^-11 year) What is the geological signifance of this mineral age compared to the whole rock age?

Back 17

.04278 = e^(1.42*10^-11)t - 1
ln 1.04278 = 1.42 *10^-11 t
t = 2.95 Ga
This is significant because it means it melted shortly after the protolith.

Front 18

For what reasons is zircon a useful mineral for geochronology using the U-Th-Pb system?

Back 18

1. Concentrates U and Th but excludes Pb
2. Resistant to chemical and mechanical weathering with harness of 7.5
3.It is a common assesory in igneos and metamorphic rocks
4. Has concordia for age dating
5. Zoned growth is inherited in crustal melting
6. It is refractory

Front 19

Back 19

Front 20

Typical, "normal", mid-ocean ridge basalt (N-MORB) is?

Back 20

Low-K olivine tholeiite

Front 21

MORB magma most likely is produced by partial melting of?

Back 21

Spinel peridotite

Front 22

Back 22

Front 23

What are the important mineralogical and chemical consequences of hydrothermal alteration of the oceanic crust?

Back 23

Cold water penetrates the crust and deposits LILE's and REE. It forms zeolites, amphiboles, and chlorites. Also the Sr87/Sr86 ratio above normal water is mineralized by leaching metals and can escape back into the ocean through black smokers.

Front 24

What is the relationship of the arch trench gap and the angle of subdunction in subduction zones?

Back 24

The angle of subduction determines the beginning of the volcanic front. Subducting plate subduct to 100-150 km before front can be created. Old colder-denser plates subduct at a steeper angle and therefor you have a shorter arch trench gap.

Front 25

What is the K-h relationship in subduction zones?

Back 25

The further away the volcanic front is the more high K it becomes. h controls this distance based on subducting plate x.

Front 26

Briefly explain the important processes involved in the generation of magma in subduction zones.

Back 26

It begins with hydrothermal circulation at the mid ocean ridge. This process makes oceanic crust hydrous and not pristine. As this plate is the subducted it will increasingly become anhydrous by losing H2O(ie from amphiboles, etc). This water seeps into the mantle wedge and enables a lowering of the peridodite solidus. Melting peridotite solidus creating a volcanic arc. You get a hydrous magma with LILE spider diagram that is sawtooth, typical of IATs

Front 27

Contamination of subduction zone magmas with sediment and/or continental crust changes the Sr, Nd, and Pb isotope compositions of the magmas. What are the changes?

Back 27

Epislon Sr increases and Nd decreases moving towards the enrichment quadrant.
Pb isotope increases
sediment and continental crust is typically enriched which causes these isotopic changes.

Front 28

What isotope characteristics distinguish the three different OIB types - HIMU, EMI, and EMII from each other and from N-MORB?

Back 28

HIMU- recycled ocean crust, high Pb, depleted pattern, it is epsilon Nd positive and epsilon Sr negative.

EMI and EMII are both enriched, however EMII has a stronger enriched pattern Sr
EMI has low Pb and EMII has high Pb
OIB is epsilon Sr positive and epsilon Nd negative
N-MORB is epsilon Nd positive and epsilon Sr negative

Front 29

What is the best model for growth in volume of the continental crust over the age of the Earth? Has crustal growth been continous or episodic (cite evidence)?

Back 29

Taylor-McLennon- growth has been episodic, histograms of varying crust show exponential growth in some eras and with almost complete lack of growth in others. Histograms created from archaen rocks support this, showing 75% growth at 2.5 Ga and slowing since.

Front 30

Compared to terrestrial basalt compositions (MORB, IAT, OIB), lunar basalt compostions characteristically are?

Back 30

Lower in Al2O3 and Na2O and higher in MgO

Front 31

The meteorites that represent the crust and mantle of differentiated planetismals are what kind of meteroites?

Back 31

stone

Front 32

Use chemical formulae for the minerals to balance the metamorphic equation which states: enstatite + anorthite = pyrope + diopside + quartz

Back 32

2 Mg2 Si3 O6 + CaAl2Si2O8 = Mg3Al2Si3O12 + CaMgSi2O6 + SiO2

Front 33

Metamorphism typically is considered to be an isochemical process.In this context, explain "isochemical"

Back 33

The rocks bulk composition will not change. Cations and anions will move withing the structure and new growth will occur but the bulk composition will remain constant throughout metamorphism. Except with volatiles.

Front 34

On the P-T diagram below, draw the P-T path followed by a rock that underwent prograde metamorphism during burial and retrograde metamorphis during uplift. Explain why the P-T path looks like this, and why high P-T minerals survive metastably to surface conditions.

Back 34

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Front 38

Describe the lunar history to 3.2 Ga in terms of crystallization of the magma ocean and the subsequent melting events that produce various lunar mare lava types. Relate the REE patterns A and B to the lunar evolution you have described.

Back 38

As the magma ocean crystalized plagioclase was less dense and floated towards the top creating the lunar highlands composed of almost pure anorthite. The remaining mafic minerals sank (ol + px) and created mare. Pattern B is the anorthosite, the positive Eu anomaly shows the rock had sufficient plagioclase, due to Eu ca replacement also its LREE enriched. Pattern A is the mafic rocks of the mare, the negative Eu anomaly shows the rock did not have much plag. It is slight LREE depleted

Front 39

Heat transfer through the asthenosphere and mesosphere occurs mainly by what process?

Back 39

Convection

Front 40

heat transfer through the lithosphere occurs mainly by what process?

Back 40

conduction

Front 41

What are the most important radioactive heat producing elements in the earth?

Back 41

Thorium and Uranium

Front 42

Radioactive heat production is lowest in what rock type?

Back 42

peridotite

Front 43

In which environment is heat flow lowest?

Back 43

old mountain belts

Front 44

During partial melting of garnet peridotites which minerals are, relative to their initial proportions preferentially extracted into the melt?

Back 44

clinopyroxene and garnet

Front 45

A moderate degree of partial melting of peridotite leaves a residual bimeralic rock name what?

Back 45

harzburgite

Front 46

A high degree of partial melting of peridotite leaves a residual monomineralic rock named what?

Back 46

lherzolite

Front 47

During partial melting elements X and Y are both incompaitble but element X has a higher bulk distribution coefficient than element Y. Therefore, compared to the X/Y ratio of the mantle source, the magma produced by melting this source will have a X/Y ratio that is what?

Back 47

lower

Front 48

The radioactive decay of Rb87 to Sr87 takes place by what decay?

Back 48

beta decay

Front 49

A suite of comagmatic metavolcanic rocks define a Sm147/Nd144 vs Nd143/Nd144 isochron with a slope of .015673. What is the age of these rocks. Gamma = 6.54 * 10^-12

Back 49

t=2.38 Ga

Front 50

What does it mean when the Rb-Sr and Sm-Nd ages turn out the same?

Back 50

Possibly the age of metamorphism.

Front 51

In the U-Th-Pb system, what is the order of incompatibility from most incompatible to least incompatible?

Back 51

Th>U>Pb

Front 52

In the Pb isotope system mu is ration U238/Pb204. Mu for the earth is?

Back 52

8

Front 53

The ocean crust has a layered structure which, from top to bottom is?

Back 53

lava flows, dykes, gabbro

Front 54

Typical normal, mid-ocean ridge basalt (N-MORB) is?

Back 54

low-K olivine tholeiite

Front 55

The mg number and Ni abundance of typical N-MORB indicates that the magma?

Back 55

underwent significant crystal fractionation prior to eruption.

Front 56

MORB magma most likely is produced by partial melting of what?

Back 56

spinel peridotite

Front 57

Subduction-related magmas with high K2O with relatively low SiO2. What is the magma series?

Back 57

shoshonitic

Front 58

What is the moons bulk density like compared to the earth?

Back 58

The moon has a lower bulk density then the earth

Front 59

The bulk density of the moon compared to the earth implies what?

Back 59

The moon has a higher proportion of mantle relative to core than the Earth.

Front 60

What is the crust like on the moon compared to the earth?

Back 60

The moon has a thicker crust and a thicker lithosphere

Front 61

Compared to the lunar mare, the lunar highlands are?

Back 61

more densley cretered therefor are older

Front 62

Which mineral is not found in lunar rocks?

Back 62

amphibole

Front 63

The mineral armalcolite was first described from lunar basalt samples? Armalcolite is a what?

Back 63

Fe-Ti oxide

Front 64

Lunar high-Ti basalt magma was produced by melting of what kind of mantle?

Back 64

Clinopyroxene and ilmenite rich

Front 65

Compared to terrestrial basalt compositions (MORB, IAT, OIB), lunar basalt compositions characteristically are?

Back 65

lower in Al2O3 and Na2O and higher in MgO

Front 66

What is the difference in compositional spectrum of lavas erupted from continental volcanic arcs compared to oceanic volcanic arcs? Why is there this difference?

Back 66

Continental volcanic arcs are high-K and andesite rich, while oceanic volcanic arcs are basalt with lower k values. This is because of the contamination from the continental crust and the fact that more crystal fractionation takes place in continental volcanic arcs because of the thick overlying layer of crust it must travel through before reaching the surface. Oceanic crust is much thinner and therefor doesnt have a problem.

Front 67

Which hotspot lava series represents the highest degree of silica undersaturation?

Back 67

basanite to phonolite

Front 68

The REE patterns of ocean island basalt rocks characteristically are what?

Back 68

strongly LREE enriched

Front 69

Compare to N-MORB, the abundances of incompatible trace elements in OIB are what?

Back 69

Much higher

Front 70

Compared to N-MORB, the isotopic characteristics of OIB are that they have what?

Back 70

Higher Sr87/Sr86 and lower Nd143/Nd144

Front 71

Of the three different varieties of OIB, which of them is distinctive in having very radiogenic Pb isotopic ratios?

Back 71

HIMU

Front 72

According to the Taylor-McLennan model for crustal growth, how much of the present volume of the continental crust was in existence in the Archaen eon?

Back 72

75 percent

Front 73

The meteorites that represent primitive, chemically unfractionated solar system material are what?

Back 73

chondrite

Front 74

We know that SNC meterorites came from mars using what evidence?

Back 74

They contain the same gases with the same composition as the martian atmosphere

Front 75

What are LILE?

Back 75

Large Ion Lithophiles Elements, Cs Rb K Ba Pb Sr Na

Front 76

What are HFSE?

Back 76

High Field Strendth elements Th U Ce Pb Zr Hf Ti Nb U