Chapter 2: Ocean Basins and Plate Tectonics

Describe the general origins of igneous, sedimentary, and metamorphic rock. Which type of rock composes most of Earth's crust?

-Igneous rock is produced by the cooling and crystallization of magma (or lava). | *Most composes Earth's crust -Sedimentary rock may be composed of rock and mineral fragments, partially decomposed remains of dead organisms, and minerals precipitated from solution. -Metamorphic rocks form when igneous or sedimentary rocks are exposed to high pressure, intense heat, and chemically active fluids.

Cycles of ocean basin spreading and closing are known as Wilson Cycles and each cycle has a period of about _______ million years.

500-600

What % of Earths surface is covered by ocean water? In which hemisphere is most land located?

71% , Northern Hemisphere.

Explain why a hydrothermal vent community may have a limited life expectancy (10 to 100 years or so).

A hydrothermal vent may go through frequent periods of geologic activity when new lava destroys the habitats of vent communities.

Describe 2 different types of tectonic plate interactions that a subduction zone.

A subduction zone forms where two oceanic plates converge or where an oceanic plate and a continental plate converge. In a subduction zone, the denser oceanic plate slips under the other plate and descends into the mantle. An ocean trench is formed through a collision between two oceanic plates.

Describe a transform plate boundary and give an example of this type of boundary.

A transform plate boundary occurs where adjacent plates slide laterally past one another. Crust is neither created nor destroyed at this boundary, but earthquakes may occur. An example is the boundary between the Pacific plate and the North American plate, where the San Andreas Fault is located.

Describe the general relationship between continental shelf width and tectonic activity in the continental margin.

As a general rule, the continental shelf is widest where the continental margin is passive, such as along North America's East Coast. The continental shelf is narrowest where the margin is tectonically active, such as along North America's West Coast.

How might investigating ultraslow divergent plate boundaries benefit our understanding if Earth history?

At ultraslow divergent plate boundaries, huge slabs of mantle rock rise to the seafloor through fractures in the ocean crust. Analysis of samples of mantle rock provides us with insights on the structure and origins of Planet Earth

Compare and contrast oceanic and continental crust. Which type of crust typically comprises the continental origin?

Continental crust is mostly granite, a coarse-grained igneous rock, and oceanic crust is mostly basalt, a fine-grained igneous rock. Granite is rich in minerals containing silica and aluminum and basalt is rich in minerals containing iron and magnesium. Continental crust is thicker and less dense than oceanic crust. The continental margin is mostly a submerged portion of the continental crust.

How does land subsidence influence mean sea level in coastal areas.

In coastal areas as land subsides, sea level rises and ocean water may inundate the land.

Describe the origin of most submarine canyons.

Most submarine canyons are produced through erosion by turbidity currents. A turbidity current is a down-slope flow of water heavily laden with suspended sediment and denser than normal seawater. Turbidity currents scour the ocean bottom and carve out submarine canyons.

Most land is located in the _______ Hemisphere.

Northern

Explain why oceanic crust becomes older with increasing distance from the mid ocean ridge system

Oceanic crust originates from the cooling and crystallization of magma emanating from Earth's mantle and surfacing (as lava) at divergent plate boundaries that mark the mid-oceanic ridges. New oceanic crust slowly moves away from the ridge system and hence, is progressively older with distance from the ridge.

Name the 5 ocean basins?

Pacific(largest), Atlantic, Indian, Arctic, and Southern Oceans

Define sea floor spreading and its significance for oceanic crust.

Sea-floor spreading involves divergence of adjacent tectonic plates on the ocean bottom caused by convection currents in the mantle. New oceanic crust forms from cooling and crystallization of lava that flows out of this divergent plate boundary from Earth's interior.

The waters located between 60 degrees S and the Antarctic continent are known as the _______ Ocean.

Southern

Compare and contrast the geological characteristics of the continental margins of the west and east coast of North America.

The continental margin of the North American west coast is geologically active with a relatively narrow continental shelf, volcanic and seismic activity, and offshore trenches. On the other hand, the continental margin of the North American east coast is geologically passive with a broader continental shelf, substantial sediment deposition and broad abyssal plains, no volcanic activity, and infrequent seismic events.

What are some implications of the slow pace of the geological processes involved in the rock cycle?

The geological processes involved in the transformation of rock types as part of the rock cycle is so slow (measured in human terms) that the supply of rock, mineral, and fuel resources is essentially fixed.

How does the lithosphere and the deep ocean basins differ from the lithosphere of the continents?

The lithosphere of the deep-ocean basin is thinner and denser than the lithosphere of the continents. Much of the deep-ocean lithosphere is composed of basalt, rock rich in ferromagnesian silicate minerals whereas much of the continental lithosphere is composed of granite, rock rich in non-ferromagnesian silicate minerals.

Summarize the key evidence in support of the theory of plate tectonics

The theory of plate tectonics is grounded in several observations including: the close fit between continents on either side of the Atlantic (like giant pieces of a puzzle); similar geological structures and rock types on either side of the Atlantic; symmetrical pattern of magnetic anomalies on either side of the mid-ocean ridge system; increase in age of oceanic crust and thickness of the overlying sediment with distance from the mid-ocean ridge system.

How do turbidity currents help maintain submarine canyons?

Turbidity currents periodically scour accumulated sediment from the floors of submarine canyons. Much of this sediment was delivered to the head of a canyon by rivers and streams flowing into the ocean.

What conditions are required for violent volcanic eruptions in the continental margins.

Violent eruptions occur where the magma feeding a volcano is rich in silica (SiO2) and volatiles (gases). Such magmas are relatively viscous and may block volcanic vents. Pressure produced by the volatile components beneath the block increases and eventually the volcano explodes. This is most likely to happen where oceanic crust subducts under continental crust

What are wilson cycles? What is the approximate period of each cycle?

Wilson cycles are sequences of ocean basin spreading and closing. Each cycle has a period of about 500-600 million years.

Near hydrothermal vents, bacteria that form the base of food chains derive energy through

chemosynthesis.

A subduction zone forms where two oceanic plates or an oceanic plate and a continental plate

converge.

Most hydrothermal vents occur near or along

deep-ocean trenches.

New oceanic lithosphere is generated via cooling and solidification of lava along _______ plate boundaries.

divergent

Most of the rock composing Earth's crust is

igneous

The age of the ocean crust _______ with increasing distance from the mid-ocean ridge.

increases

The bedrock of the continental margin is _______ the continental crust.

markedly different from

As a general rule, the continental shelf is widest where the continental margin is _______ such as along North America's East Coast

passive

A deep-ocean trench is produced by

plate subd uction.

Divergence of adjacent plates on the ocean bottom is known as

sea floor spreading

Adjacent plates slide laterally past one another along a _______ plate boundary.

transform

Most submarine canyons were produced through erosion by

turbidity currents