Midterm 1 Flashcards
The incompatible elements
Concentrated on last stage differentiations of magmas such as pegmatites and hydrothermal veins
Pragmatite
A course grained igneous rock usually of granite composition
How are minor elements within minerals (4 ways)
1) interstitial lattice positions
2) fluid inclusions
3) exsolved mineral phases
4) ionic substitution
What is the first rule of Goldschmidts substitution
The ions of one element can extensively replace those of another in an ionic crystal if their radii differ by less than 15%
What is the second rule of Goldschmidts substitution
Ions who’s charged differ by one unit substitute readily for one another. If charges differ by more than one unit substitution is slight
What is the third rule of Goldschmidts substitution
When two ions can occupy a particular position in a crystal lattice, the ion with the higher ionic potential forms a stronger bond with the surrounding anions.
What is the forth rule of Goldschmidts substitution
Substitution may be limited even when size and charge criteria are satisfied.
Couples substitution is…
Key to feldspars
Electronegativities
A measure of ionic character in covalent bonds
The distribution of minor elements in minerals depends on… (3 things)
The concentration of ions
The coordination number
The temperature
The coordination number
The number of anions that surrounds a particular cation in an ionic crystal. Can be predicted by radius ratio
Radius ratio
The ratio of radius of cation to that of the anion
Minor elements partitioned between the solid & liquid… (3 ways)
1) camouflage (D=1): occurs when the minor element has the same charge and a similar ionic radius as the major element it is replacing
2) capture (D>1): takes place when a minor element enters a crystal preferentially because it has a higher ionic potential than the ions of the major element
3) admission (D<1): involves the entry of a foreign ion that has a lower ionic potential than the major ion because it has either a lower charge or a larger radius.
Lithophile?
Associated with silicates and concentrated in crust
Chalcophile?
Associated with sufides
Siderophile?
Occurs at the native metal and concentrated in corr
Atmophile?
Occurs as gasses in atmosphere
Internal structure of earth?
Core, mantel, crust
What and where is the crust mantle boundary?
40km under continents
Called Mohorovičić discontinuity “Moho”
What and where is the mantle core boundary?
2883km under continents
Called the wiechert-Gutenberg discontinuity
Pyrolite?
A model of earths mantle composed of peridotite and basalt in 3:1
Made by ringwood (1966)
Undepleted mantle
Estimated using garnet-lherzolite and spinel-lherzolite occurred as demolish and kimberlite
Spinel or garnet lherzolites
Composed of olivine, clinopyroxene, orthopyroxene, garnet, spinel and phlogopite
Depleted mantle rocks
Dunite and harzburgite in ophiolite
