Chapter 3: Plate Tectonics

Describe one way to directly measure plate motion

Global Positioning System (GPS) has been the most useful for studying the Earth's crustal movements. By repeatedly measuring distances between specific points, geologists can determine the movement along faults or between plates.

Show on a world relief map the major belts of earthquakes and volcanoes.

Mountain belts next to trenches Oceanic Islands Mid-ocean ridges Island Arcs next to trenches Belts along borders of continents Red Sea and East Africa

Describe the typical rates of relative motion between plates.

plates move 1 to 15 cm/yr.

Discuss how plate tectonics can explain similar continental outlines and geology on opposite sides of an ocean.

theory of plate tectonics: outlines match up continental shelves fill gaps common geologic features- including age and type of rocks and fossils

Sketch, label, and explain an oceanic transform boundary related to seafloor spreading at a mid-ocean ridge.

Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge Most transform boundaries consist of short faults on the seafloor occurring near mid-ocean ridges. Between the spreading segments, the sides of the transform are rubbing together; but as soon as the seafloor spreads beyond the overlap, the two sides stop rubbing and travel abreast. The result is a split in the crust, called a fracture zone, that extends across the seafloor far beyond the small transform that created it.

Sketch, label, and explain the stages of continental rifting, using East Africa and the Red Sea as examples of stages.

(1) The RIFT VALLEY stage involves early graben formation prior to continental splitting. This stage may be associated with domal uplift caused by uprise of hot upper mantle material - but this uplift is not ubiquitous and may be connected with underlying mantle hotspots. Example: African Rift Valley. (2) The YOUTHFUL stage, lasting about 50 my after the onsett of seafloor spreading, while the thermal effects are still dominant. This stage is characterised by rapid regional subsidence of the outer shelf and slope, but some graben formation may persist. Example: Red Sea. (3) The MATURE stage during which more subdued regional subsidence may continue. Example: most of the present Atlantic continental margins. (4) The FRACTURE stage when subduction starts and terminates the history of the continental margin. ex. The continent of Africa is thought to have been split by a series of rift valleys in various states of development. Those in East Africa are still in thick crust. Those in West Africa are associated with thick oil-bearing sediments. In the Red Sea area the rifting has gone so far as to form a narrow ocean. In the south-east Madagascar has been completely separated from Africa by rifting.

Sketch and label the characteristics of a continental rift (i.e., a divergent boundary within a continent).

1) long mountain ranges 2) elevated topography 3) volcanism

Describe observations Wegener used to support continental drift.

1.the continents seemed to fit 2.matching geologic units (rock types, structure) 3.fossil evidence (mesosour, a freshwater reptile) 4.paleoclimatic evidence a)glacial striations b)glacial till Pangaea. Wegener's theory hypothesized that the continents were able to push through the rock of the seafloor to their present positions. As evidence, he noted (as had others before him), of the geographic correlation in coastline perimeters of South America and Africa. This was the feature that led Wegener to investigate other clues. His investigations revealed that mountain ranges in South America and Africa, and strata and composition of coal fields in Europe and North America matched or lined up.

Describe how magnetic reversals help with determining the age of rocks.

A reversal occurs only when the magnetic field orientation changes to the opposite direction. Past reversals of the magnetic field are recorded in the rocks. Many rocks contain iron-bearing minerals that act as tiny magnets. As magma or lava cool, these minerals begin to form.

Describe the characteristics of an island and seamount chain, and how it is interpreted to be related to a hot spot.

Fairly straight lines of oceanic islands and submarine mountains ( seamounts) cross some parts of the ocean floor. These island and seamount chains are different in character and origin from curved island arcs, which are related to subduction. ● At a hot spot, hot mantle rises and melts - forms magma that ascends into the overlying plate. ● If the plate above is moving relative to the hot spot, volcanism constructs a chain of volcanoes - if this grows high enough above seaFoor, it becomes a volcanic island → An area above the plate moves, cools, subsides, and erods. ● If the plate is not moving or is moving very slowly, the hot spot forms a cluster of volcanic islands and seamounts instead of a linear chain

Sketch, label, and explain the features and processes associated with ocean-ocean and ocean-continent convergent boundaries.

If two tectonic plates collide, they form a convergent plate boundary. Usually, one of the converging plates will move beneath the other, which is known as subduction. Deep trenches are often formed where tectonic plates are being subducted and earthquakes are common. As the sinking plate moves deeper into the mantle, fluids are released from the rock causing the overlying mantle to partially melt. The new magma (molten rock) rises and may erupt violently to form volcanoes, often building arcs of islands along the convergent boundary. These island arcs are always landward of the neighboring trenches.

Discuss why the hypothesis was not widely accepted

Lack of evidence for it. scientists could not demonstrate a mechanism that would make the continents move.

Sketch and explain the driving forces of plate tectonics

Slab pull: because oceanic lithosphere is denser than the asthenosphere, the edge of the tectonic plate that contains oceanic lithosphere sinks and pulls the rest of the tectonic plate with it Ridge Push: at mid-ocean ridges, the ocean lithosphere is higher than it is where it sinks into the asthenosphere-because of ridge push, the oceanic lithosphere slides downhill under the force of gravity Convection: Hot rock from deep within the Earth rises, but cooler rock near the surface sinks. Convection causes the oceanic lithosphere to move sideways and awy from the mid-ocean ridge.

Describe plate tectonics and how it explains the distribution of tectonic activity.

The Earth's crust is made up of large, irregularly shaped slabs of rock (tectonic plates) that float atop a subsurface ocean of heated liquid rock called magma. In some regions of the world, particularly on the ocean floor, there are areas where the plates are spreading apart. As they spread, magma bubbles up and hardens, creating new continental crust. In other areas, different tectonic plates are sliding toward each other. The motion of tectonic plates colliding, separating, or just sliding along next to one another is responsible for a range of tectonic activities including earthquakes, volcanoes, and the formation of mountains.

Predict the relative ages of seafloor from place to place using a map of an ocean with a mid-ocean ridge.

a. According to plate tectonics, oceanic crust forms from upwelling magma and spreading at a mid-ocean ridge, then moves away from the ridge with further spreading. *The crust should be youngest near the ridge, where it was just formed, and should be progressively older away from the ridge.

Compare the distributions of earthquakes, volcanoes, and high elevations.

a. Divergent: two plates move apart i. Hurricanes ii. Mid-ocean ridges are divergent plate boundaries iii. Continental rift (East Africa) b. Convergent: Two plates move toward one another, one plates slide under the other i. Volcanoes/Hurricanes ii. Trench iii. Volcanoes form iv. Pacific Ring of Firec. c. Transform: Two plates move horizontally past one another i. Mid-ocean ridges, fracture zones

List some discoveries about the seafloor that brought a renewed interest in the idea of continental drift.

a. Seafloor spreading b. Theory of plate tectonics c. Mid-Atlantic ridged. Magnetism of the sea floor

Identify on a world map the main types of features on the continents and in the oceans.

a. Seamounts b. Island c. Island Arc e. Abyssal plains f. Mid ocean ridges: g. Oceanic Fracture zones h. Oceanic Plateaus j. Plateaus k. Flat coastal planes l. Mountains m. Continental Shelf: submerged benches n. Deep Ocean Trenches

Describe the main characteristics for each type of feature, including whether it occurs in the oceans, on continents, or as islands.

a. Seamounts- mountains on seafloor, some form long belts, and some are isolated or form clusters- ex. Hawaii b. Island- small version of continent ex. New Zealand c. Island Arc: Curving chains of islands cross the seafloor, most are active and dangerous volcanoes, flanked on one side by ocean trench e. Abyssal plains: Ocean floor has a fairly smooth surface, moderately deep- 3 to 5km f. Mid ocean ridges: Broad, symmetrical ridges that cross the ocean basins, 2-3 km higher than average depth of seafloor. ex. middle of Atlantic Ocean g. Oceanic Fracture zones: Cracks and steps across the seafloor, mostly at right angles to the mid-ocean ridges h. Oceanic Plateaus: Broad, elevated regions ex. Kerguelen Plateau near Antarctica i. Ocean trench: follow the edges of continents, or form isolated curving thoughts out in the ocean ex. South America j. Plateaus: broad high regions reach high elevations ex. Tibetan Plateau of south Asia, Mount Everest k. Flat coastal planes l. Mountains- ex. Ural Mtns. m. Continental Shelves-: submerged benches ex. Great Britain n. Deep Ocean Trenches- deepest part of the ocean ex. Pacific Ocean

Describe how Earth's magnetic field is generated

generated by electric currents in the conductive material of its core, created by convection currents due to heat escaping from the core.

Sketch, label, and explain the steps leading to a continental collision (continent-continent convergent boundary).

occurs as two continental tectonic plates run into each other. One of the colliding continental plates will typically dive beneath the other. the other continental plate tends to break and is forced upward & creates some of the world's largest mountains ranges.

Sketch, label, and explain the features and processes of an oceanic divergent boundary.

occurs when two tectonic plates move away from each other. Along these boundaries, lava spews from long fissures and geysers spurt superheated water. Frequent earthquakes strike along the rift. Beneath the rift, magma—molten rock—rises from the mantle. It oozes up into the gap and hardens into solid rock, forming new crust on the torn edges of the plates. Magma from the mantle solidifies into basalt, a dark, dense rock that underlies the ocean floor. Thus at divergent boundaries, oceanic crust, made of basalt, is created.

Sketch, label, and explain the motion of transform faults along the west coast of North America.

zig-zag boundary between the Pacific plate and the small Juan de Fuca plate has 3 transform faults, link three ridge segments that are spreading. Mendocino fracture zone originated as a transform fault, within the Pacific plate no longer active. Oceanic crust--north higher, younger than oceanic in the south. transform fault links with the Cascadia subduction zone and the San Andreas fault. three plate boundaries meet--triple junction. part of California west of the fault is on the Pacific Plate. Transform boundary continues across southern california