Major Elements

Question 1

What are major, minor and trace elements?

Answer 1

Major elements, >1%, SiO2 Al2O3 MgO FeO K2O CaO Na2O H2O, form minerals
Minor Elements 0.1-1%, TiO2 MnO CO2 sometimes form minerals
Trace Elements <0.1% Everything else, rarely form minerals

Question 2

What is the mode of a rock?

Answer 2

Mode is the % volume composition of minerals in a rock, e.g. modal value of plagioclase is 35%

Question 3

What is the norm of a rock?

Answer 3

Norm is the estimates mineral composition of a rock based on its chemistry, no need for microscope and very accurate

Question 4

What is a magma series and list the alkaline, tholetic and calc alkaline

Answer 4

Distinct compositional changes between magmas have different names
Alkaline - Alkali Basalt > Hawaiite > Mugearite > Benmoreite > Trachyte
Tholetic - Tholetic Basalt > Ferrobasalt > Icelandite > Rhyolite
Calc-alkaline - Basalt > Basaltic Andesite > Dacite > Rhyolite

Question 5

What kind of tectonic setting occurs in different magmatic series?

Answer 5

Alkaline magmas can occur in convergent plate boundaries, within a continental plate and oceanic plate - NOT Divergent plate boundaries
Tholetic magmas can occur anywhere
Calc Alkaline magmas can only occur at convergent plate boundaries