Major elements: usually greater than 1%

Major elements: usually greater than 1%

• Major elements: usually greater than 1%

• SiO2 Al2O3 FeO* MgO CaO Na2O K2O H2O

• Minor elements: usually 0.1 - 1%

• TiO2 MnO P2O5 CO2

• Trace elements: usually < 0.1%

• everything else

Mode is the volume % of minerals seen

• Mode is the volume % of minerals seen

• Norm is a calculated “idealized” mineralogy

Example: AFM diagram

• Example: AFM diagram

• (alkalis-FeO*-MgO)

Harker diagram

• Harker diagram

• Smooth trends
• Model with 3 assumptions:
• 1 Rocks are related by FX
• 2 Trends = liquid line of descent
• 3 The basalt is the parent magma from which the others are derived

Extrapolate BA  B and further to low SiO2

• Extrapolate BA  B and further to low SiO2

• K2O is first element to  0 (at SiO2 = 46.5)

Can chemistry be used to distinguish families of magma types?

• Can chemistry be used to distinguish families of magma types?

Early on it was recognized that some chemical parameters were very useful in regard to distinguishing magmatic groups

• Early on it was recognized that some chemical parameters were very useful in regard to distinguishing magmatic groups

• Total Alkalis (Na2O + K2O)
• Silica (SiO2) and silica saturation
• Alumina (Al2O3)