Major And Minor Elements Flashcards
What is a primary magma? What are some of the criteria for primary magmas in the melt?
After formation by partial melting, hasn’t undergone any changes from fractional crystallization or assimilation.
MgO > 10%
Mg # = 70-74
Cr > 1000ppm
Ni > 400ppm
What are peralkaline and peraluminous rocks? Give examples of some minerals associated.
Peralkaline - excess Na and K (ex: Al and Na pyroxene and Na- amphibole)
Peraluminous- excess alumina (ex: mica, garnet, andalusite, corundum)
What do Harker diagrams show? What do the trend lines on the graphs represent?
Show compositional variations in the rock and show rocks that could be related to fractional crystallization.
Trend lines can represent the liquid line of descent.
What are 4 examples of surface samples that are accepted to be of mantle origin?
- Ophiolites
- Dredge samples from oceanic fracture zones
- Nodules in basalt
- Xenoliths in kimberlites
What is in the residuum when tholeiitic basalts undergoes partial melting?
Turns into lherzolite, Harzburgite and then to dunite as you increase in partial melting
What are the 3 aluminous phases in the mantle?
- Plagioclase
- Spinel
- Garnet
How does raising temperature allow the mantle to melt?
Heating the mantle above the normal geotherm by accumulating heat from decay of radioactive elements or heating from hotspots (conduction)
How can lowering the pressure allow the mantle to melt?
Lowering pressure via adiabatic rise so that the rising rock material would following the adiabat and reach the solidus where melting occurs or reducing pressures at constant temperatures
How can adding volatiles or water help with melting the mantle?
Having the presence of H2O and CO2 in an increasing pressure environment would increase in H2O and CO2 dissolving which would increase melting point
