Geology 107: Homework #4

Batholiths are known to form the cores of mountain ranges such as the Sierra Nevada. What is the implication of this observation?

Because batholiths form deep within Earth, the occurrence of one at the surface implies that it has since been uplifted and/or the rocks above have been removed.

Which of the following terms is best described as a massive pluton?

batholith

While working in the field, you find a dike cutting across some sedimentary rocks. What grain size would you expect to find in this pluton?

fine-grained

Igneous rocks of felsic composition have __________ and __________ relative to mafic igneous rocks.

greater silica; lower melting temperature

What is an accessory mineral?

A mineral that makes up a relatively small portion of the total rock composition

What is the rock name of an intermediate rock with two distinct grain sizes?

Andesite porphyry

How is basaltic magma transformed into felsic magma?

Basaltic magma partially melts the continental crust, which is more felsic in composition.

What causes an elevated geothermal gradient in a divergent plate setting?

Decompression melting of the mantle

The more silica in magma, the lower the viscosity.

False

Once a source rock partially melts, what does it produce?

Felsic magma and mafic residue

You have found a mafic rock with a phaneritic texture. What is a potential rock name?

Gabbro

Which of the following best describes the difference between granite and rhyolite?

Granite is phaneritic and rhyolite is aphanitic.

Why does magma have a tendency to rise after its formation?

It is less dense than the surrounding rock.

Which of the following is true about mafic igneous rocks?

Mafic igneous rocks are rich in Fe, Mg, and Ca.

Based on the diagram shown in the video, name two minerals that are unlikely to coexist in the same igneous rock.

Quartz and muscovite Muscovite and pyroxene**** Na-plagioclase and amphiboles Quartz and feldspar Pyroxene and olivine

Based on what you learned in this video, what minerals make up rhyolite?

Quartz, K-feldspar, and plagioclase feldspars, with relatively fewer biotite and amphiboles

What do pumice and scoria have in common?

They both exhibit a vesicular texture.

Most igneous rocks never reach the surface. However, igneous rocks other than those formed in volcanoes are found exposed on many parts of Earth. How do you account for this phenomenon?

They formed at depth and have been exposed by uplift and erosion.

Pyroclastic debris from a volcanic eruption can include _____.

ash and cinders

What is the term for a tabular igneous pluton that occurs in an orientation that is discordant with the bedding surfaces of adjacent sedimentary rocks?

dike

When lava erupts at Earth's surface, what type of rock is produced?

extrusive

Ultramafic rocks contain __________ and are commonly found in __________.

olivine; mantle

According to Bowen's Reaction Series, __________ is one of the first minerals to melt, but last to crystallize.

quartz

What is the term for a tabular igneous pluton that occurs in an orientation that is concordant with the bedding surfaces of adjacent sedimentary rocks?

sill

As a result of partial melting, magma originates in __________.

the mantle and crust

In a subduction zone, water driven from subducted oceanic crust causes __________.

the melting temperature of mantle rocks to decrease