VOLCANOES PLUTONS AND IGNEOUS
ROCKS UPDATED ACTUAL EXAM
QUESTIONS AND CORRECT ANSWERS
●● Magma forms
Answer: three tectonic environments: spreading centers, mantle plumes,
and subduction zones
●● Pressure-release melting
Answer: Melting caused by a decrease in pressure, expansion of rock
volume, and melting. Usually occurs in the asthenosphere
●● Magma production in a spreading center(mid-oceanic ridge)
Answer: as lithospheric plates separate at a spreading center, hot, plastic
astenosphere oozes upward to fill the gap
●● Magma production in a mantle plume
Answer: mantle plume is rising column of hot, plastic rock that
originates with the mantle
●● Magma production in a subduction zone
Answer: the addition of water, decreasing pressure, and heat from
friction all combine to form huge quantites of magma
, ●● Basalt
Answer: - Partial melting of asthenosphere (peridotite)
- Peridotite to basalt (20% richer in silica)
●● Granite
Answer: - Lower melt point
- Granitic magma rises to form plutonic rocks
Granite contains more silica than basalt and therefore melts at a lower
temperature between 700c-900c.
●● When did continents form?
Answer: - 3.96 billion-year-old Acasta gneiss - oldest
known rocks on Earth
- 4.2 billion-year-old zircon crystals from
●● Continents Australia
Answer: Indicate that granite-like rocks (and thus the continental crust)
formed around 4 bya
• Earliest crust likely mantle-like (komatiite)
• Partial melting
- Increases silica content
- Partial melting of basalts forms granite
ROCKS UPDATED ACTUAL EXAM
QUESTIONS AND CORRECT ANSWERS
●● Magma forms
Answer: three tectonic environments: spreading centers, mantle plumes,
and subduction zones
●● Pressure-release melting
Answer: Melting caused by a decrease in pressure, expansion of rock
volume, and melting. Usually occurs in the asthenosphere
●● Magma production in a spreading center(mid-oceanic ridge)
Answer: as lithospheric plates separate at a spreading center, hot, plastic
astenosphere oozes upward to fill the gap
●● Magma production in a mantle plume
Answer: mantle plume is rising column of hot, plastic rock that
originates with the mantle
●● Magma production in a subduction zone
Answer: the addition of water, decreasing pressure, and heat from
friction all combine to form huge quantites of magma
, ●● Basalt
Answer: - Partial melting of asthenosphere (peridotite)
- Peridotite to basalt (20% richer in silica)
●● Granite
Answer: - Lower melt point
- Granitic magma rises to form plutonic rocks
Granite contains more silica than basalt and therefore melts at a lower
temperature between 700c-900c.
●● When did continents form?
Answer: - 3.96 billion-year-old Acasta gneiss - oldest
known rocks on Earth
- 4.2 billion-year-old zircon crystals from
●● Continents Australia
Answer: Indicate that granite-like rocks (and thus the continental crust)
formed around 4 bya
• Earliest crust likely mantle-like (komatiite)
• Partial melting
- Increases silica content
- Partial melting of basalts forms granite
