Chapter 4: Earth's Structure and Plate Tectonics

Question 1

Stress is responsible for these three deformation processes. What are they?

Answer 1

1. Compression
2. Tension
3. Shear

Question 2

Definition of Deformation

Answer 2

a process of physically compressing rock sequences to cause them to slide up and over adjacent cratons (overthrusting) or to exert a compressing force that reduces the width of a mobile belt, producing steeply dipping, folded sequences by flattening and elongating the rocks sequence perpendicular to the stress.

Question 3

What is compression?

Answer 3

pushes on rocks from opposite directions which
causes rocks to be shortened parallel to the stress applied.

Question 4

What is Tension?

Answer 4

pulls rocks from opposite directions, resulting it to
become stretched/lengthened.

Question 5

What is Shear?

Answer 5

occurs when rocks are being pushed in an uneven
manner, causing the rocks to be skewed such that different sides of a rock body slide or move in opposite directions.

Question 6

True or False. Rocks on the surface of the Earth are elastic.

Answer 6

True

Question 7

What is Elasticity?

The elastic force developed in an elastic object is directly proportion. As you stretch or compress an elastic material like a bungee cord, it resists the change in shape. It exerts a counter force in the opposite direction. This force is called elastic force.

Answer 7

is the ability of a material to return to its original shape after being stretched or compressed.

Question 8

When all elastic materials reach this point, deformation becomes permanent and they no longer behave elastically.

Answer 8

Elastic limit

Question 9

This type of deformation is permanent by flowing plastically.

In physics, a plastic flow (sometimes written as plastic flows) refers to any fluid flow in which the rate of motion is proportional to the force that is being applied (above the yield value). (geology) Any deformation that is induced by a force that acts continuously.

Answer 9

Ductile Material

Question 10

This type of deformation is permanent by fracture.

A fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane.

Answer 10

Brittle Materials

Question 11

What happens to rocks near surface when buried?

Answer 11

Since they are typically brittle and will fracture, high temperatures and pressures will cause them to become ductile and deform plastically.

Question 12

When rocks deform, they often slide past one another along a fracture plane, this point of fracture is called ______.

All faults involve some type of slippage movement, whereas fractures do not.

Answer 12

Fault

A fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements.

Question 13

How do waves travel when seismic waves generated by earthquakes and human-made explosions encounter a low density layer?

Answer 13

Reflective

Question 14

How do waves travel when seismic waves generated by earthquakes and human-made explosions encounter a high density layer?

Answer 14

Refracted

Question 15

It is the transition zone between SIAL and SIMA. Found between upper and lower crust.

Answer 15

Conrad Discontinuity

A boundary within the Earth’s continental crust that can be detected seismically at about 10–12 km depth, although exploratory deep drilling has failed to locate it. The boundary separates the crust into a lower, basic layer and an upper, granitic layer.

Question 16

Found between lower crust and upper mantle. This boundary is located approximately 24 miles below the earth’s surface and 6 miles below the oceanic floor, a distance which varies from place to place.

Answer 16

Mohorovicic Discontinuity

Question 17

Divides mantle in upper and lower, it is approximately between 660 and 700 km deep. Passing through this discontinuity, seismic waves increase it’s speed. As explained in post about tectonic plates, lower mantle is hotter and liquefied while upper is cooler and pasty.

Answer 17

Repetti Discontinuity

Question 18

This is the transition zone between the lower mantle and the outer core.

Answer 18

Gutenberg Discontinuity

Question 19

This is the layer separating the outer core from the inner core.

Answer 19

Lehmann Discontinuity

Question 20

In geology, this term is used for a surface at which seismic waves change velocity.

Answer 20

Discontinuity

Question 21

Thickness of the Crust (low density rock)

Answer 21

7-70 km thick

Question 22

Physical property of the outer core

Answer 22

liquid

Question 23

Physical property of the inner core

Answer 23

solid

Question 24

Chemical composition of the core

Answer 24

Iron and nickel

Question 25

Composed largely of **dark-colored**, **mafic rocks** enriched in oxides of **magnesium**, **iron** and **calcium** (MgO, FeO, and Cao) relative to average crust.

Answer 25

Oceanic Crust ## Footnote Depth of oceanic crust to the Moho averages 5-7km. However, under some oceanic islands, its thickness reaches 18km

Question 26

The Oceanic Crust consists principally of which rocks?

Answer 26

**Basalt** and **Gabbro**

Question 27

May be slices of ocean crust thrust onto continental margins.

Answer 27

Ophiolites ## Footnote A section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks.

Question 28

One of the most studied upper mantle-crust sequence in the Philippines, had most of the studies concentrated on the northern portion (Masinloc Massif) of the ophiolite.

Answer 28

The Zambales Ophiolite Complex (ZOC) ## Footnote The ZOC is made up of three massifs, Masinloc, Cabangan and San Antonio as one goes from north to south.

Question 29

Oceanic Crust Ophiolite Model

Answer 29

1. Sediment 2. Pillow Lava 3. Sheeted Dykes 4. Gabbro 5. Layered Gabbro 6. Layered peridotite 7. Upper Mantle

Question 30

Generalized as "**granitic**" in composition, enriched in **K2O, Na2O, and SiO2** relative to average crust. **Thicker** than oceanic crust.

Answer 30

Continental Crust

Question 31

This is the **oldest** well-documented continental crust (Stern & Bleeker, 1998).

Answer 31

**4.03 Ga** rocks from the Northwest Territories of Canada

Question 32

The reason why some continent crust result into great age

Answer 32

Relative Buoyancy

Question 33

Thickness of mantle relative to the radius of the Earth (~6370km)

Answer 33

~2900 km

Question 34

The mantle constitutes how many percentage of Earth's total volume?

Answer 34

~83%

Question 35

Composition of Mantle

Answer 35

Ultrabasic composition ## Footnote contains average of approximately 40-45% SiO2

Question 36

It is the uppermost part of the mantle and the crust together constitute this relative rigid which is strong enough to rupture in response to stress.

Answer 36

Lithosphere

Question 37

Occurs within the upper mantle at depths of ~100-250 km below the surface. The top of this zone marks the contract between the strong lithosphere and the weak asthenosphere.

Answer 37

**discrete low velocity zone (LVZ)**

Question 38

Is more plastic and flows slowly, rather than rupturing, when subjected to stress.

Answer 38

Asthenosphere

Question 39

Mineral found at 410 km depth

Answer 39

Wadleysite/Beta Spinel (Mg2SiO4)

Question 40

Minerals at the Transition Zone

Answer 40

1. Ringwoodite (Mg2SiO4) 2. Garnet (Mg2SiO4)

Question 41

Minerals at 60 km depth

Answer 41

1. Perovskite [(Mg,Fe,Al)SiO3] 2. Periclase (MgO)

Question 42

Proposed by Williams and Garnero (1996) that may be related tot he formation of deep mantle plumes within the lower mantle.

Answer 42

**ultra-low velocity zones (ULVZ)**

Question 43

This discontinuity ranges from ~130 to 340 km above the **core -mantle** bounary.

Answer 43

**D" layer** (discontinuity)

Question 44

Density of outer core

Answer 44

10-12 g/cm^3

Question 45

Density of inner core

Answer 45

~13g/cm^3

Question 46

Seismic studies have shown that the inner core is seismically _________.

Answer 46

Anisotropic

Question 47

How did the magnetic field formed?

Answer 47

results of the planet's rotation causing metallic ions inthe outer core to circulate.

Question 48

How can magnetic field help the Earth from hazards?

Answer 48

It helps shield the Earth from harmful radiation streaming from the Sun, hence it is important to the biosphere.

Question 49

Heat sources in the Earth

Answer 49

1. Heat from when the planet formed and accretted which has not yet been lost. 2. Frictional heating, caused by denser core material sinking to the center of the planet. 3. Heat from the decay of Naturally Occuring Radioactive Elements/Nuclides

Question 50

It is a mantle convection model which suggests that cold oceanic lithosphere sinks to great depths and stirs the entire mantle; the ultimate burial ground for subducting slabs is the core-mantle boundary. This downward flow is balanced by bouyantly rising mantle plumes that transport hot material toward the surface.

Answer 50

Whole-Mantle Convection Model

Question 51

Has two largely disconnected convective layers. A dynamic upper layer driven by descending slabs of a cold oceanic lithosphere and a sluggish lower layer that carries heat upward without appreciably mixing with the layer above.

Answer 51

Layer Cake Model

Question 52

The lithosphere is broken along major fault systems into large pieces called "plates", moving on top of a plastic asthenosphere, that move relative to one another.

Answer 52

Fundamental tenet of plate tectonics (Isacks et al., 1968; Le Pichon 1968)

Question 53

Three major types of plate boundary segments

Answer 53

1. Divergent 2. Convergent 3. Transform

Question 54

Describes one of the earliest ways geologists thought continents moved over time. This map displays an early "supercontinent," Gondwana, which eventually moved to form the continents we know today. Fossils of similar organisms across widely disparate continents encouraged this revolutionary theory

Answer 54

Continental Drift

Question 55

Matching of coastlines on different continents i.e., the South American and African continents seem to fit together.

Answer 55

Continental Fit

Question 56

This evidence shows organisms that were restricted in geographical distribution but appeared in 2 or more areas that are presently separated by major barriers.

Answer 56

Fosil Evidence

Question 57

Aquatic reptile with fossils limited to eastern South America and Southern Africa. It lived during the early Permian period (286 to 258 million years ago).

Answer 57

Mesosaurus

Question 58

A mammal-like reptile that existed during the Triassic Period (250-240 mya). Its fossils are found only in South Africa and South America.

Answer 58

Cynognathus

Question 59

Thought to have been a herbivore with a stout build like a pig. Relatively dominant on land during the early Triassic period (250 mya). Lystrosaurus fossils are only found in Antarctica, India, and South Africa.

Answer 59

Lystrosaurus

Question 60

known as woody, sead bearing tree, the Glossopteris is named after the Greek description for tongue due to its tongue shaped leaves and is the largest genus of the extinct descendant of seed ferns. The Glossopteris fossil is found in Australia, Antarctica, India, South Africa, and South America- all the southern continents.

Answer 60

Glossopteris

Question 61

Evidence of mountain belts such as the Appalachians in eastern US and British Isles and Scandinavia have comparable age & structure

Answer 61

Rock Type and Structural Similarities

Question 62

Glacial deposit evidence. At the end of the Paleozoic era (220-300 mya), ice shets covered extensive areas of the Southern Hemisphere; at present these areas are in the subtropics to tropics.

Answer 62

Paleoclimatic Evidence

Question 63

Records the orientation of the magnetic field at the time the rocks formed.

Answer 63

Magnetite-rich rocks

Question 64

How to determine the paleolatitude?

Answer 64

1. steep inclination of "fossil magnets" indicates formation of the rock at high latitude. 2. Very low angle = near the equator

Question 65

What is magnetite's Curie Temperature?

Answer 65

580 degrees Celsius (?)

Question 66

Are volcanic locales thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle.

Answer 66

Hotspot

Question 67

It is a Hawaiian Island northwest of Molokai with an age rank of 2.2 to 3.3 MA

Answer 67

Oahu

Question 68

-dating of the ocean floor using **fossils** -age of sediment increases with distance from the ridge

Answer 68

Evidence from Ocean Drilling

Question 69

Depth of the seafloor ________ away from the ridge

Answer 69

decreases

Question 70

the outer rigid lithosphere consist of rigid segments

Answer 70

plate

Question 71

Oceanic crust is ____ than continental crust

Answer 71

thinner

Question 72

hotter and weaker zone; facilitates motion of teh earth's rigid outer shell

Answer 72

asthenosphere

Question 73

two places on the same plate do not move relativee to each other

Answer 73

rigid plates

Question 74

Where do all major interaction between plates take place?

Answer 74

along plate boundaries

Question 75

This drives mantle convection which results into plate motions, plumes, volcanoes, earthquakes, mountain ranges, mineral deposits, etc.

Answer 75

Earth's internal heat

Question 76

Areas where divergent plate boundaries occur (where to plates are moving apart relative to their boundary).

Answer 76

Areas characterized by horizontal extension and vertical thinning of lithosphere

Question 77

marked by continental rift systems and in oceanic lithosphere by the oceanic ridge system.

Answer 77

horizontal extension in continental lithosphere

Question 78

form where horizontal extension occurs in continental lithosphere. In such regions, the lithosphere is progressively stretched and thinned, like a candy bar being stretched in two. This stretching occurs by brittle, normal faulting near the cooler surface and by ductile flow at deeper, warmer levels.

Answer 78

Continental Rift Systems

Question 79

Modern examples of continental rift valleys

Answer 79

East african rift, the Rio Grande Rift in the United States, and Dead Sea rift in the Middle East

Question 80

the process by which supercontinents such as Pangea and Rodinia were broken into smaller continents such as those we see on Earth's surface at present.

Answer 80

Complete continental rifting

Question 81

When continental rifting happens, a new and growing ocean basin begins to form between the two continents by this process

Answer 81

Sea Floor Spreading