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)