The Lithosphere and Tectonic System

Question 1

he theory describing the changing configuration of the continents through time is called

Answer 1

plate tectonics

Question 2

________________y maintains that the Earth’s outermost solid layer consists of huge, rigid plates that float on a layer of plastic rock. These plates are in slow, constant motion, powered by energy sources deep within the planet. When two plates come together, one may be forced under the other in a process calle________________

Answer 2

plate tectonic theory – subduction

Question 3

The Earth is an almost spherical body, approximately ___ in radius

Answer 3

6,400 km

Question 4

The centre of the Earth is occupied by the ___, which is about 3,500 km in radius (two zones: the outer core which has the properties of a liquid; the inner core is solid

Answer 4

core

Question 5

Even though temperature _____toward the Earth’s centre, the inner core remains solid because ____

Answer 5

increases —— it is under very high pressure

Question 6

Enclosing the metallic core is the ______, a rock shell about 2,900 km thick, which accounts for about 50 percent of the Earth’s mass. Seismic data indicate that mantle rock is composed of magnesium and iron silicates similar to the ultramaficigneous rock peridotite. Temperatures in the mantle range from about 2,800 °C near the core to about 1,800 °C near the crust, and are maintained by the release of energy through radioactive decay of uranium, thorium, and potassium isotopes.

Answer 6

mantle

Question 7

The outermost and thinnest of the Earth’s layers is the

Answer 7

crust. It is formed mainly of igneous rock, but also contains substantial proportions of metamorphic rock and a comparatively thin upper layer of sedimentary rock.

Question 8

Two crustal types are distinguished:

Answer 8

Oceanic crust, which accounts for about 0.1 percent of Earth’s mass, can be up to 10 km thick under the oceans, but is absent beneath the continents. Continental crustaccounts for about 0.4 percent of Earth’s mass and is present only in continental areas where it is generally 30 to 40 km in thickness

Question 9

lithosphere

Answer 9

a zone of rigid, brittle rock, includes not only the crust, but also the cooler, upper part of the mantle (ranges in thickness from 60 to 150 km, and is thickest under the continents – consisting of lithospheric plates)

Question 10

athenosphere

Answer 10

Deep within the Earth, the brittle condition of the lithospheric rock gives way gradually to a plastic layer named the asthenosphere, where temperatures reach 1,400 °C (density increases from 3.7 to 5.5 gcm-3 with depth).

Question 11

The solid Earth originated some 4,600 million years ago. This long period of time can be considered in two different ways from a geological perspective.

Answer 11

he chronostraticapproach to geological time is based on the relative age of rock types and events, and uses fossil assemblages and an idealized set of sedimentary rock strata as its reference. The chronometric approach establishes the absolute age of earth materials from radiometric and other dating methods

Question 12

Continents can be subdivided into two basic region

active belts where mountain-building processes are still occurring and shield areas composed of old, stable rock. The mountain ranges in the active belts grow either through volcanism or by tectonic activity.

Answer 12

Volcanism can result in massive accumulations of volcanic rock by extrusion of magma, as seen in the Cascade Mountains of western North America. Tectonic activityinvolves the breaking, bending, and upthrusting of the Earth’s crust due to internal forces associated with the collision of the lithosphericplates.

Question 13

Continental shields

Answer 13

are low-lying continental surfaces, beneath which are complex arrangements of ancient igneous and metamorphic rocks. Some core areas of the shields are composed of rocks dating back to the Archean Eon, 2,500 to 3,800 million years ago

Question 14

The deepest parts of ocean basins are the_______

Answer 14

e ocean trenches that mark the positions of subduction arcs where oceanic crust is being forced down into the mantle. Of the 22 ocean trenches that have been located, 18 are in the Pacific Ocean, three are in the Atlantic Ocean, and one is in the Indian Ocean. The deepest is the Mariana Trench in the Pacific Ocean, about midway between Indonesia and Japan; it is 2,540 km in length, descends to 11,033 m, and is 69 km in width

Question 15

The major relief feature of ocean basins is a central ridge, which in the case of the Atlantic Ocean divides the basin approximately in hal

Answer 15

his mid-oceanic ridge consists of submarine hills that rise gradually to a rugged central zone. In the centre of the ridge is a narrow, elongated depression known as the axial rift. The location and form of the axial rift suggest that this is a region where the crust is being pulled apart (the age of the rocks on both sides of the ridge increases symmetrically with distance from the rift).

Question 16

Continental Margins The continental margin

Answer 16

is the narrow zone where oceanic lithosphere is in contact with continental lithosphere

Question 17

As the ______ is approached from the deep ocean, the ocean floor begins to slope gradually upward, forming the continental rise, then becomes much steeper on the _____

Answer 17

continental rise, continental slope

The top of this slope marks the edge of the continental shelf, a gently sloping platform with vertical relief of less than 20 m. The average width of the continental shelves is about 80 km, but this is quite variable.

Question 18

The Earth’s crust consists of distinctive lithosphericplates of various sizes; seven of these are considered to be major or primary plates. ______ is the largest primary plate and covers about 103.3 million km2; the smallest is the South American Plate, covering 43.6 million km2.

Answer 18

The Pacific Plate

Question 19

he motion of lithospheric plates and how they interact at their boundaries is collectively calle

Answer 19

plate tectonics

Question 20

The process in which one plate is carried beneath another is called

Answer 20

subduction; the descending slab is heated and softened, and is eventually incorporated into the mantle.

Question 21

zone of seperation, or ____, between the lithospheric plates along the axis of a mid-oceanic ridge is called a ____ or ______

Answer 21

rife, divergent or spreading boundary.

Question 22

Prominent mountain masses and mountain chains can also be elevated by one of two basic tectonic processes

Answer 22

extension and compression. Extensional tectonic activity occurs where oceanic plates pull apart or where a continental plate undergoes breakup

Compressional tectonic activity occurs at converging plate boundaries. The result is often an alpine mountain chain consisting of intensely deformed rock strata (folds). The entire deformed rock mass produced by compression is called an orogen, and the event that produced it is an orogeny.

Question 23

old Belts The wavelike shapes imposed on the strata consist of alternating arch-like ______ called anticlines, and trough-like downfolds, called _____

Answer 23

anticlines, synclines

Question 24

One common type of fault associated with crustal rifting is the _____ in which the plane of slippage, or fault plane, is steeply inclined, and the rocks on one side are displaced relative to the othe

Answer 24

normal fault

his may arise either through the land on one side being lowered, or downthrown, or because movement has occurred on both sides of the fault.

Question 25

If the land is raised, or upthrown, the process is referred to as a _____ (thrust sheet or nappe).

Answer 25

reverse fault

Question 26

Normal faults commonly occur in multiple arrangements, often as intersecting sets of parallel faults, where land may drop down to form a _____or rise as a _____

Answer 26

graben, horst

Question 27

A mass of metamorphic rock is formed between the joined continental plates, welding them together and terminating further tectonic activity along that collision zone

Answer 27

continental suture

Question 28

• starts when the crust is lifted and fractured, creating a region of upthrown block mountains and intervening basins (long narrow rift valleys).

Answer 28

continental rupture

As separation continues, the rift valley widens and opens to the ocean to form a narrow sea with a spreading plate boundary running down its centre. Continued widening of the basin results in a large ocean with the continental lithosphere moved far apart.

Question 29

Geologic evidence suggests a supercontinent, known as Rodinia, was fully formed about 700 million years ago. Rodinia broke apart and its fragments were carried away in different directions. Later these ancient continents converged toward a common centre, where they collided and joined to form a more recent supercontinent, called Pangaea, about 200 million years ago. Assuming that similar supercontinent cycles began 3 billion years ago (Middle Archean time), it is feasible that six to ten such events could have occurred (Wilson Cycle).

Answer 29

qqq

Question 30

Credit for the first full-scale scientific hypothesis of the breakup of a single large continent belongs

Answer 30

alfred wegener