magma generation

Question 1

how is magma generated

Answer 1

most by partial melting of solid mantle rock (peridotite) typically in upper mantle

less common in lower crust by partial melting

Question 2

what is the silica content of mantle rocks

Answer 2

ultramafic (peridotite)

Question 3

what is the silica content of partially melted mantle rock (peridotite)

Answer 3

basic (basaltic) (mafic)

Question 4

geotherm

Answer 4

normal increase of temperature with depth

Question 5

4 main minerals of peridotite

Answer 5

olivine ~Fo90 mg rich

orthopyroxene ~En90 mg rich

clinopyroxene Cr rich

al-bearing minerals
* Plagioclase (<50km)
* (50-80km)
* Garnet (80->400km)

Question 6

how is magma generation initiated

Answer 6

increasing t

lowering p
-causes an adiabatic rise (rise without losing to much temperature)

volatiles
-Gaseous components, such as:
o Water vapor
o Carbon dioxide
o Sulphur
o Chlorine

lowers melting point of mantle rock

Question 7

what is partial melting

Answer 7

mixture of melted and not melted material

Question 8

what is practical melting of lower crust called

Answer 8

anatexis

Question 9

where does magma form

Answer 9

plate boundaries

Question 10

primary basaltic magmas

Answer 10

tholeiitic basalts (alkaline rocks)

calc-alkaline basalts (alkaline rocks)

alkaline basalts (subalkaline rocks)

Question 11

what are silica oversaturated rocks called

Answer 11

subalkaline rocks

Question 12

what are silica undersaturated rocks called

Answer 12

alkaline rocks