Continental crust strength

Question 3

What is the motivation for quantifying past processes in mountain belts?

Answer 3

To understand and quantify past processes using isotope geochemistry

Question 4

What are the main topics covered in the lecture on geochronology and isotope geochemistry?

Answer 4

• Radiometric dating
• Isotope fractionation
• Case study on the Western Alps

Question 5

What was Lord Kelvin’s calculation regarding the age of the Earth?

Answer 5

100 million years based on size and thermal gradients

Question 6

Who discovered radioactivity and in what years?

Answer 6

Henri Becquerel and Marie & Pierre Curie between 1896-1898

Question 7

What is an isotope?

Answer 7

Different varieties of the same element that differ in the number of neutrons

Question 8

What is the significance of the half-life in radiogenic dating?

Answer 8

It allows the determination of the age of a rock based on the decay of radioactive isotopes

Question 9

What is the current estimated age of the Earth?

Answer 9

4.54±0.05 billion years

Question 10

What are common types of radiation emitted during radioactive decay?

Answer 10

• Alpha particles
• Beta particles
• Gamma radiation

Question 11

What is the decay constant in radiometric dating?

Answer 11

A value that depends on what can be measured and the initial concentrations of parent and daughter isotopes

Question 12

Fill in the blank: The temperature at which isotopes are retained in minerals is called the _______.

Answer 12

closure temperature

Question 13

What is the main challenge in applying geochronology to metamorphic rocks?

Answer 13

Relating dated minerals to geology and ensuring undisturbed parent and daughter concentrations

Question 14

What are some commonly used radiogenic isotopes in geology?

Answer 14

• 40K-40Ar
• 87Rb-87Sr
• 147Sm-143Nd
• 238U-206Pb

Question 15

What does the term ‘crystallisation age’ refer to?

Answer 15

The age at which minerals crystallize from a melt or solution

Question 16

What is the purpose of using isochrons in radiometric dating?

Answer 16

To calculate a model age from different fractions of the same sample with different isotope ratios

Question 17

True or False: Most natural isotopes are radioactive.

Answer 17

False

Question 18

What is significant about zircon in U-Pb dating?

Answer 18

Zircon crystallizes with significant concentrations of U and Th but not Pb, making it ideal for dating

Question 19

What is a key factor in the accuracy of radiometric dating?

Answer 19

The retention of parent and daughter isotopes in the mineral during geological processes

Question 20

What geological feature was studied in the case study on the Zermatt Ophiolite?

Answer 20

The prograde path of metamorphism

Question 21

What is the relationship between the closure temperature and the timing of mineral growth?

Answer 21

Closure temperature determines when isotopes are retained, affecting age calculations

Question 22

What does the term ‘peak metamorphism’ refer to?

Answer 22

The highest temperature and pressure conditions experienced by a rock during metamorphism

Question 23

Fill in the blank: The isotopic ratios used in isochron dating must come from the same _______.

Answer 23

age population

Question 24

What mineral is associated with a closure temperature of >750°C?

Answer 24

Zircon

Question 25

What does the term 'retrogade path' refer to in metamorphic processes?

Answer 25

The path of cooling and decreasing pressure after peak metamorphism

Question 26

What was a significant finding in the Zermatt Ophiolite case study?

Answer 26

Different ages may represent peak metamorphism or different stages of the prograde path

Question 27

What is the importance of understanding PT history in metamorphic rocks?

Answer 27

To determine the pressure and temperature conditions during the rock's formation

Question 28

Fill in the blank: The oldest rocks are the Jack Hills zircons, dated at _______.

Answer 28

4.4 billion years

Question 29

What does the term 'diffusion' refer to in the context of mineral dating?

Answer 29

The movement of atoms within a mineral, which can affect isotopic ratios

Question 30

What is a major challenge in interpreting whole rock analyses in geochronology?

Answer 30

Minerals may incorporate different amounts of parent isotopes, complicating age calculations

Question 31

What is the significance of closure temperatures in radiometric dating?

Answer 31

They define the conditions under which isotopes are retained in minerals

Question 32

What is the relationship between mineral growth rates and age calculations?

Answer 32

Different growth rates can lead to varying ages from the same sample

Question 33

What does microstructural evolution refer to?

Answer 33

The crystallisation ages from major minerals depending on temperature and isotopic equilibration among minerals. ## Footnote Isotopic equilibration can affect how we date minerals and their thermal history.

Question 34

What hypothesis is used to date thermal history of minerals?

Answer 34

Closure temperature hypothesis. ## Footnote This hypothesis raises questions about the influence of non-thermal factors on mineral systems.

Question 35

Who authored the reference chapter on Isotope Geochemistry?

Answer 35

Krauskopf & Bird. ## Footnote This chapter is found in the book 'Introduction to Geochemistry'.

Question 36

In what century did Rev. James Ussher calculate the age of the Earth?

Answer 36

1600’s. ## Footnote Ussher's calculation placed the creation of Earth at 4004 BC.

Question 37

What significant idea did James Hutton propose in the 1700’s?

Answer 37

Uniformitarianism. ## Footnote This idea suggests that the Earth's processes are consistent over time.

Question 38

What did James Hutton conclude about the age of the Earth?

Answer 38

The Earth must be significantly older than 4004 BC. ## Footnote Hutton's observations led to the conclusion that there is 'no vestige of a beginning,–no prospect of an end'.

Question 39

Name two locations where Hutton made geological observations.

Answer 39

* Siccar Point * Arthur’s Seat ## Footnote These locations were critical in forming Hutton's ideas about Earth's age.

Question 40

Who developed Hutton’s ideas further?

Answer 40

* William Smith * John Phillips * Charles Lyell ## Footnote These geologists contributed to the understanding of Earth's geological history.

Question 41

What age did Charles Lyell suggest for the Earth?

Answer 41

More than 300 million years. ## Footnote Lyell's suggestion was a significant advancement in geological thought.

Question 42

Fill in the blank: The age of the Earth was initially calculated by Rev. James Ussher as _______.

Answer 42

4004 BC.

Question 43

True or False: James Hutton's ideas were based solely on religious texts.

Answer 43

False. ## Footnote Hutton's ideas were based on geological observations, not religious texts.