Chapter 11

Question 1

Rock Cycle

Answer 1

Igneous —> Sedimentary —> Metamorphic

Question 2

Igneous Rock

Answer 2

Rock that has solidified from magma.

Ex: Basalt

Question 3

Contact

Answer 3

A surface seperating different rock types.

Question 4

Country Rock

Answer 4

An accepted term for any older rock into which an igneous body intruded.

Question 5

Chill Zones

Answer 5

Finer-grained rocks that indicate magma solidified more quickly here because of the rapid loss of heat to cooler rock.

Question 6

Plutonic Rocks

Answer 6

Igneous rocks that are formed at considerable depth(more than several km).

Coarse-grained(grains>5cm), reflecting the slow cooling and solidification of magma.

Question 7

Porphrytic Rocks

Answer 7

Large crystals are enclosed in a groundmass of finer crystals or glass.

Ex: appearance of milk chocolate bar containing whole almonds.

Question 8

Gabbro

Answer 8

Formed of course-grained ferromagnesian minerals and gray, plagioclase feldspar.

Question 9

Basalt

Answer 9

Gabbro’s fine-grained counterpart, also composed of ferromagnesian minerals and plagioclase.

Question 10

Xenoliths

Answer 10

Fragments of rock that are distinct from the body of igneous rocks in which they are enclosed.

Question 11

Rhyolite

Answer 11

Fine-grained Composed predominantly of feldspars (pink and white) and quartz.

Granite (course-grained counterpart).

Question 12

Diorite and Andesite

Answer 12

Composed of feldspars and significant amounts of ferromagnesian minerals (30-50%).

Diorite is course grained
Andesite is fine grained(grey-green)

Question 13

Mafic Rocks

Answer 13

Igneous Rocks with silica content close to 50% by weight are considered silica-poor, despite being the most abundant component. But have relatively high content of Mg, Fe, and Ca.

Ex: basalt, gabbro

Tend to be darker in color due to high presence of Fe, Mg minerals.

Question 14

Felsic Rocks

Answer 14

Rocks that are (Silicic) silica-rich (65% or more SiO2) and very small amounts of oxides, Ca, Fe, Mg…

Ex: Rhyolite, granite.

Tend to be lighter in color due to lack of Fe, Mg minerals.

Question 15

Intermediate Rocks

Answer 15

Rocks with chemical content between that of felsic and mafic.

Ex: andesite

Color is also mid range such as grey, green..

Question 16

Ultramafic Rocks

Answer 16

Composed entirely of ferromagnesian minerals. No feldspars present, or quartz.

Ex: Peridotite (course, pyroxene and olivine), contains less than 45% SiO2

Question 17

Intrusive bodies

Answer 17

Intrusive rock whose names are based on size and shape and relation to surrounding rocks.

Question 18

Volcanic Neck

Answer 18

A shallow intrusive structure formed from magma that solidified within the throat of a volcano.

Question 19

Dikes and Sills

Answer 19

Shallow intrusive structures.

Dike: tabular, discordant(body not parallel to any layering in country rock).

Sill: tabular, concordant(are parallel to any planes or layering in the country rock).

Question 20

Intrusives that Crystallize at Depth

Answer 20

Pluton: Body of magma or igneous rock that crystallized at considerable depth within the crust.

Stock: small, discordant pluton (less than 100km square).

Batholith: large pluton (greater than 100 sq km)- predominantly granite.

Diapirs: large blobs of magma worked upward through the lower crust and collected, and solidified 5-30kms below surface.

Question 21

Geothermal Gradient

Answer 21

The rate at which temperature increases with increasing depth beneath the surface.

On average: 3 deg Celcius for each 100m of depth in the upper crust decreasing in the mantle.

Question 22

Decompression Melting

Answer 22

Takes place when a body of hot mantle rock moves upward and the pressure is reduced.

Question 23

Bowen’s Reaction Series

Answer 23

Series of experiments that determined the sequence in which minerals crystallize in a cooling magma.

Can be used to show differentiation and partial melting- two processes that create/modify magma.

(1) A mafic magma will crystallize into pyroxene and calcium rich plagioclase(basalt or gabbro) if the early formed crystals are not removed from the remaining magma.
(2) if minerals are separated from the magma, the remaining magma is more slilicic than the original magma.
(3) if you heat a rock, the minerals will melt in reverse order.

Question 24

Differentiation

Answer 24

The process by which different ingredients separate from an originally homogenous mixture.

Ex: separating whole milk into cream and nonfat milk.

Takes place mainly through Crystal settling.

Question 25

Crystal Settling

Answer 25

The downward movement of minerals that are denser than the magma from which they crystallized.

Process of differentiation.

Platinum ores form this way.

Question 26

Partial Melting

Answer 26

Progressing upward through Bowen’s series(cool-hot) gives us the sequence in which minerals melt…

First to melt form liquid composed of quartz, K feldspar.

Partial melting of lower crust produces silicic magma. Rises and eventually solids at a higher level of the crust into granite or rhyolite.

Question 27

Divergent Boundary

Answer 27

Plate tectonic setting where oceanic crust is created.

Intraplate -plateau basalt. - volcanic island chains

Original magma and Final mamga are mafic

(Basalt and Gabbro)

Question 28

Convergent Boundary

Answer 28

Plate-tectonic setting

Intraplate - over mantle plume
Where partial melting of lower crust, the original and final magmas are silicic..(Granite and Rhyolite)

Where partial melting of mantle, the original magma is mafic usually and the final magma is intermediate.

Question 29

Mantle Plumes

Answer 29

Narrow upwellings of hot material within the mantle.

Igneous activity within a plate, a long distance from the boundary is unusual because of these hot spots.