Part 1- Intro Flashcards
What do ppm and ppb mean in terms of trace elements?
- Ppm = 1 micro g in 1g of rock
* Ppb = 1ng in 1g of rock
What are trace element abundances usually quoted in?
Ppm or ppb
What do major elements govern in rocks?
The mineralogy
What do trace elements do in a rock?
Substitute into mineral phases
What is a lithophile element?
- “rock-loving”
* partition into silicate phases
What is a siderophile element?
- “metal-loving”
* Partition into metallic liquids
What is a chalcophile element?
- “Sulphur-loving”
* Partition into sulphide liquids
What is an atmosphile elements?
- Highly-volatile
* Form gases or liquids at Earth’s surface
Which two groups of elements bond together with which type of bonding to form oxide silicate minerals?
Therefore what classification do they belong to?
- Low and high electronegativity elements forming iconic bonds
- lithophile
What electronegativities do siderophile and chalcophile elements have? What bonding do they prefer?
- Intermediate
* Covalent and metallic
What type of sulphide liquids does the term chalcophile include?
Magmatic NOT AQUEOUS
What does HSE stand for?
Highly Siderophile Elements
Give an example of an element that exhibits more than one type of Goldschmidt’s behaviour…
Nickel- is siderophile therefore concentrates in the core.
Behaves as lithophile in the mantle and substitutes for Mg in olivine
How does ionic radius vary across a period?
Decreases
How does ionic radius vary down a group?
Increases
How much can the ionic radii of ions vary for them to be able to substitute?
Up to 15%
How much can an ions charge vary by before it isn’t substituted?
One unit
Are elements with a higher or lower ionic potential preferred for substitution?
Higher because they form stronger bonds
When size and charge of the substituting ions are similar what else can stop substitution occurring? (2)
- Different electronegativities
* Form bonds of different ionic character
What is the camouflage principle?
Give an example.
When two ions have virtually the same charge, ionic radii and electronegativity.
E.g.
Zr and Hf in Zircon
What is the capture principle?
When a trace is used in a mineral over a major because the trace has a higher ionic potential
What is the admission principle?
When ions are incorporated that have a lower ionic potential than the major
What essential does a partition/distribution (KD) coefficient mean?
How well a trace element partitions in a mineral from a melt
What KD value do compatible elements have?
Do they prefer solid or melt
KD > 1
Prefer solid phase
What KD value do incompatible elements have?
What phase do they prefer?
KD < 1
Prefer Liquid
What is the bulk partition coefficient (D)?
The sum of the individual partition coefficients weighed according to the relative proportions (mass fraction) of the mineral phases present
How can elements be deemed compatible in the mantle?
If they can substitute for the major cations that exist there
What does PGE stand for?
Are they compatible in the mantle?
Platinum Group Elements
Yes- partition strongly into mantle sulphides
What elements do the HSE include?
PGE and Re
Give an example of 2 elements that are incompatible in the mantle and thus where are they enriched?
Which of the 2 is more incompatible.
Rubidium (Rb) and Strontium (Sr)
Enriched in melt phases.
Rb is more incompatible.
What does LILE stand for
Large Ion Lithophile Elements
E.g. Rb, Sr, Cs, Ba
What is the only type of mineral in which Sr is compatible?
Where are the most dramatic Rb/Sr fractionations due to this?
- Feldspars
* Continental crust
What does REE stand for?
Rare Earth Elements (lanthanides)
Which of the REEs are most compatible?
The “heavy” REEs
Which is the most important mantle phase for REE fractionation?
Garnet
- heavy REEs are significantly more compatible (KD = 5) than LREE (KD = 0.02)
