Question

question 45
2 pts
which of the following igneous rock textures indicates the slowest cooling rate?
pyroclastic
porphyritic
glassy
phaneritic
aphanitic
question 46
2 pts
which of the following describes the formation of the oceanic lithospheric mantle?
sediment scraped from subducting oceanic lithosphere accumulates in the accretionary prism.
decompression melting of ultramafic asthenosphere produces mafic magma which cools to form mafic rocks.
flux melting in the asthenosphere produces magmas which cool at the base of the crust.
gradual cooling of the uppermost mantle beneath oceanic crust.

Explanation:

• For Question 45: Phaneritic igneous rocks have large - sized crystals which form when magma cools slowly deep within the Earth's crust, allowing enough time for the crystals to grow.
• For Question 46: The oceanic lithospheric mantle is formed by the decompression melting of ultramafic asthenosphere which produces mafic magma that cools to form mafic rocks.

Answer:

Question 45: Phaneritic
Question 46: Decompression melting of ultramafic asthenosphere produces mafic magma which cools to form mafic rocks.