Chapter 4 - Magma, Igneous Rocks, and Intrusive Activity

Which of the following choices classifies the three listed rocks by composition and texture? -Diorite -Rhyolite -Basalt porphyry

-Diorite is intermediate with a phaneritic texture -Rhyolite is felsic with an aphanitic texture -Basalt porphyry is mafic with a porphyritic texture.

Oldest Event to Youngest Event

-Magma is injected far below Earth's surface, cutting through sedimentary country rocks. -Magma crystallizes and a dike is formed. -Sedimentary country rocks are eroded away. -Humans build a tunnel and road through the resistant igneous rocks.

Which of the following could cause rock to melt? -change in composition -decrease in temperature -increase in pressure -decrease in pressure -increase in temperature

-change in composition -decrease in pressure -increase in temperature

What are the three components of magma?

-the liquid portion (mobile ions of the eight most common minerals found in the Earth's crust) called melt -the solid portion which consists of silicate mineral crystals -the gaseous portion called volatiles

How do the crystallization and settling of the earliest formed minerals affect the composition of the remaining magma?

After the earliest formed minerals have settled, the resulting magma will be more felsic than the original magma.

Extrusive igneous feature associated with felsic, gaseous, material

Composite Volcano

Intrusive igneous feature that crosscuts through country rock

Dike

What is the difference between extrusive igneous rocks and intrusive igneous rocks?

Extrusive igneous rocks cool and solidify on the Earth's surface, whereas intrusive igneous rocks cool and solidify beneath the Earth's surface.

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

Gabbro

Intrusive igneous feature that arches sedimentary rock

Laccolith

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.

Muscovite and pyroxene

First mineral to crystallize, according to Bowen's Reaction Series

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

Extrusive igneous feature not particularly dangerous or explosive

Shield Volcano

Why is decompression melting common at mid-ocean ridges but not at subduction zones?

Tectonic plates are moving apart at mid-ocean ridges, resulting in a lowering of pressure beneath the ridge. Tectonic plates are moving together at subduction zones, resulting in an increase of pressure under new mountains.

Why is water a necessary component of the melting process in subduction zones?

The addition of water lowers the melting temperature of rock.

How does the crystallization of igneous material occur?

The liquid igneous material cools, the ions within slow in their movement, and they pack more closely together. When sufficiently cooled, ions become confined to a crystalline arrangement.

What is the best interpretation for how the porphyritic texture of these rocks formed?

The magma cooled slowly at first, forming large crystals, and then quickly, forming small crystals from the remaining magma.

Which of the following is true based off your observation of intrusive igneous rocks on Earth's surface? -Intrusive igneous rocks were formed from volcanic eruptions. -These rocks were formed from a lava flow that eventually cooled and solidified. -Intrusive igneous rocks are exposed by uplift and deposition. -They are fragments of country rock that have been incorporated into magma. -These rocks have been exposed by uplift and erosion.

These rocks have been exposed by uplift and erosion.

What substance makes ion migration easier in the later stages of magma crystallization, which allows abnormally large mineral crystals to form and create pegmatites?

Water

Where does the water involved in melting at subduction zones come from?

Water contained within minerals in the subducting plate is released during metamorphism.

Which two processes commonly generate magma?

decompression melting and wet melting (the addition of volatiles)

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

greater silica; lower melting temperature

The partial melting of ____ will yield mafic (basaltic) magma.

peridotite

Which group of minerals makes up most igneous rocks?

silicates

The texture of an igneous rock describes

the appearance of a rock based on the size(s), shape(s), and arrangement of the mineral grains it contains.

What factors influence the texture of an igneous rock?

the rate at which the rock cools, the amount of silica that is present in the magma from which it forms, and the amount of dissolved gases present in said magma

What is peridotite?

the rock making up the mantle