MINERALOGY BASIC CONCEPTS (ISOTOPES) Flashcards by Sean Levi Abiera

Technique used to determine Isotope Ratios

Mass Spectrometry

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Application of Isotope Studies

1) Source of Rock Studies
2) Origin of Water
3) Source Rocks for PetGeol
4) Changes in Ocean water Temp, Biological productivity and circulation
5) History of ice age glacial expansions and Contractions
6) Timing of Orogenies involving intrusions and metamorphisms

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Contain nuclei that do not tend to change spontaneously and their nuclear configurations remain constant over time

Stable Isotopes

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What are the stable isotopes of Oxygen?

Oxygen-18, Oxygen-17, Oxygen-16

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What is the atomic number of Oxygen?

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Relative proportion of Oxygen Isotopes on Earth

O16 99.7%
O18 0.2%
O17 Rare

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What oxygen isotope ratio gives info on earth’s history

O18/O16

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What is the isotopic signature of the atmosphere during evaporation

enriched with O16 (low O18/O16 ratio)

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What is the isotopic signature of seawater during evaporation

enriched with O18 (High O18/O16 ratio)

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Why?

MAS PREFERENTIALLY NAGEEVAPORATE SI O16 since it is lighter

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What is the implication of GLACIAL EXPANSION in O18 and O16?

O16 which has more affinity to the atmosphere will be trapped in Glacial Ice and thus making Sea water saturated with O18

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Whats the working principle on Glaciation and Oxygen Isotope?

MAXIMUM GLACIAL PERIOD = PEAKS of O18 in Marine Sediments

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Unit of O18/O16 ratio

part per thousands (mils)

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A period where there was an unusually warm period and unusually high evaporation leading to high O18/O16 ratio on marine seds

Cretaceous

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The standard in for Carbon Isotope study

Cretaceous Pee Dee Belemnite

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Naturally Occuring Isotopes of Carbon

Carbon-12, Carbon-13, Carbon-14 (Radioactive)

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Atomic Number of Carbon

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Relative abundance of Carbon Isotopes on Earth

Carbon-12 98.9%
Carbon-13 1.1%

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What carbon isotoped is preferentially utilized by orgamism to synthesize organic molecules?

C12 (low C13/C12)

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What carbon isotope is preferentially concentrated in the water column

C13 (High C13/C12)

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When sediments have enriched with C13/C12 is implies that the water column is enriched with C13

Stagnant Circulation in the Oceans

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Information or application of C13/C12

Global Ocean Circulation
Eveolution of New Group and Extinction of Old Groups

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A period of warming that exist in the boundary of Paleocene and Eocene

Paleocene-Eocene Thermal Maximum

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What happens during PETM

emergence and rapid radiation of mamals
extinciton of deep sea benthic forams

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What may have caused PETM

Melting of clathrates - Frozen water which contain methane, methano and another trapped organic carbon molecule

Isotopes with unstable nuclei whose nuclear configuration tends to be spontaneously transformed

Radioactive Isotopes

Spontaneous transformation of Nuclear Configuration of an isotope

Radioactive Decay

The Isotope with unstable nucleus

Parent Isotope

Product of spontaneous transformation

Daugther Isotope

Ejection of alpha particle plus gamma rays from the nucleus

Alpha Decay

Equivalent Proton and neutron of Alpha Particle

2 neutron 2 proton

What will be the resulting daughter nuclear configuration?

Daughter isotope AN -2 AM -4 (2N+2P)

Example of Alpha decay

U238 to Th234

Ejection of Beta Particles plus heat from the nucleus

Beta Decay

A high speed electron

Beta Particle

What happens when a beta particle is emitted

A neutron is converted to proton (n - e = p)

Resulting daughter isotope will have a nuclear configuration of?

AN +1 AM is conserved since loss of neutron is compensated by addition of proton

Example of Beta Decay

Rb87 St87

Addition of a high speed electron to the nucleus w/ release of heat in the form of gamma rays

Electron Capture

Resulting nuclear configuration of the daughter isotope?

AN - 1 Am conserved loss of proton is compensated by addition of Neutron (p+e=n)

Example of Electron Capture

KAr40

The time required for one half of the radioactive isotope to be converted to the daugther isotope

Half life

The stable isotope of U238

Lead 206

How many steps will it take for U238 to be converted to Lead 206?

14 steps

What is the primary use of U238 Pb206 Isotope?

the ratio of it Determines crystallization ages for minerals especially those formed in precambrian

Process which convert Radioactive isotopes to Nuclear Enegry?

Nuclear Fission (I for energy)

Uranium isotope which causes lung cancer

radon 222

If radon is diluted in water, it will form

Radium

The proportion of radioactive atoms that will decay per unit of time

Decay Constant (Lambda) unit is /year

Relation formula of half life and decay constant

Half Life = ln2/ decay constant (Lambda)

Formula for remaining Radioactive Isotope

Nremaining = Noriginal x e^-lambda*lapse time since formation Nremaining = Noriginal x (1/2)^lapse time since formation / half life

Formula for age of sample

Age = (1/lambda) ln (D/P +1)

2 radioactive isotopes of Uranium

238 and 235

Dating of Zircon, Titanite and Monazite

238U 206Pb

Pb pair of U235

207 Pb

Pair of Pb 208

232Th

Half life of U238 to Pb 206

4.47 Ga

Half life of R87 Sr 87

48.8 Ga

Rb: K substitute = Sr:

Ca Substitute

Line of constant age

Isochron

Use of Initial 87Sr/86Sr

Identification of source regions from which magmas are derived

The temperature below which a crystal lattice traps radioactive daughter products

Blocking or Closing temp

Most reliable technique for rocks with ages exceeding 10Ma

U-Pb (4.47 Ga)

Minerals which can be analyzed for U-PB

Zircon, Titane and Monazite

What rocks are analyzed for Monazite and Sphene

Met Rocks

ZrO2 minerals

Baddeleyite or Zirconia

Upper curve of concordia represents

Age of orig magma or Inherted zrcons

Lowe curve represents

Met age

If points do not plot close to the statistically dertemined line

Mixing line/Scatterchron line

87Sr/86Sr ratio of Middle to upper continental crust

>0.706

Useful in detremining source of magmas for plutons ad volcanic rocks and to reconstruct ancient continental margins

Rb-Sr (48.8 Ga)

Usefuk for determination of uplift of a rock mass and determination of age of fine grained met rocks

K-Ar (1.2 Ga)

Best used to dertermine ages of basaltic rocks and is most commonly employed to provide a model age for the time of separation of a magma from parent mantle and sea water contamination

Sm-Nd (106 Ga))