geology chapter 13

An ________ is a remnant of oceanic lithosphere scraped onto an active continental margin during subduction

"ophiolite"

what is the oceanic lithosphere composed of

Oceanic Lithosphere is oceanic crust + upper mantle.

what are active continental margins usually associated with?

Often associated with deep-ocean trenches

what are continental margins?

Outer margins of the continents and the transition to oceanic crust

how many seamounts exist?

Over a million seamounts exist

what are ocean ridges?

A broad, linear swell at a divergent plate boundary

what is the most continuous landscape on earth?

Abyssal Plains

what is an active continental margin?

Where the oceanic lithosphere is being subducted beneath the continent

what is the width of the oceanic ridge?

Width varies from 1000 to 4000 km

what is a continental shelf?

a gently sloping, flooded portion of the continent

what is a continental slope?

a steep structure that marks the boundary between the continental and oceanic crust (Inclination varies but on average is 5 degrees, in some areas 25 degrees)

what is a continental rise?

a thick accumulation of sediment from the continent, continental shelf, and continental slope

what are the three main areas of the ocean floor?

continental margins, deep ocean basins, ocean ridges

A ______ _____ (a deep, down-faulted structure) exists on the axis of most ridges

rift valley

how are the sediments from a continental rise carried?

sediments are typically carried by turbidity currents (mixtures of sediment and water) down submarine canyons

how many layers does the oceanic lithosphere have

5 compositional layers

anatomy of the ocean ridge

An oceanic ridge, or mid-ocean ridge, or rise is a broad, linear swell along a divergent plate boundary (Occupy elevated positions)

what is a deep ocean trench usually associated with?

Associated with volcanic activity (Volcanic island arcs and Continental volcanic arcs)

Subduction Zone Earthquakes

Benioff Zone

what are deep ocean basins?

Between the continental margins and the oceanic ridge

what is the deepest point in the ocean?

Challenger Deep, in Mariana trench, is the deepest spot in the ocean (10,994 meters below sea level)

what are examples of seamounts growing into islands?

Easter Island, Tahiti, Bora Bora, the Galapagos Islands, and Hawaii

what is the Abyssal Plains

Flat features of the ocean floor (Likely the most level places on Earth)

where are seamounts found?

Found in all ocean floors but most common in the Pacific

where are passive continental margins found?

Found on continental plates trailing from spreading centers

where are active continental margins found?

Located primarily around the Pacific Ocean

what is a deep ocean trench?

Long narrow creases that represent the deepest part of the seafloor Surface expression of a subduction zone

where do seamounts form?

Many form near oceanic ridges or over a hot spot

what are the two types of continental margins?

Passive Continental Margins and Active Continental Margins

what is the size of a rift valley?

Range in width from 30 to 50 km and can have walls towering 500-2500 m above the valley floor

abyssal plains continued

Sites of thick accumulations of sediment • Fine sediments from turbidity currents • Minerals precipitated from seawater • Shells of marine plankton

what are seamounts?

Submarine volcanoes

what are passive continental margins?

Tectonically inactive regions (not associated with plate boundaries) Experience little volcanism and few earthquakes

When a turbidity current emerges onto the relatively flat ocean floor, the sediments spread out in a fan shape called a ________-____ ____

deep-sea fan (The continental rise is composed of multiple deep-sea fans)

Oceanic Crust is mostly ________ rock (Gabbro through basalt)

igneous

layers of the oceanic lithosphere are related to each other through ______ ___________ we have discussed previously

igneous processes

where are the Abyssal Plains found?

in all oceans

what is the longest topographic feature on Earth?

oceanic ridge

segments are offset by _______ _______

transform faults

A seamount may grow large enough to emerge as a __________ __________

volcanic island

continental shelf continued

•Varies greatly in width • Gently sloping (average one-tenth of a degree slope) • Contains important mineral and oil deposits • Were exposed during the last glacial maximum • Some areas contain submarine canyons (which were river valleys during the last glacial maximum)