Chapter 2 oceanography

What is the difference between an atoll and a guyot?

An atoll top is at sea level but a guyot top is below sea level

How does an ocean basin form?

A continental plate is pulled apart and seafloor spreading creates ocean lithosphere in the gap left between the pieces

You are exploring an ocean basin and trying to determine whether it formed by seafloor spreading. Which of the following evidence would you NOT expect to find in an actively spreading ocean?

Dredging of the mid-ocean ridge would yield granite

wilson cycle

John Tuzo Wilson -achieved worldwide acclaim for his contributions to the theory of plate tectonics. plate tectonics model shows life cycle of ocean basin (formation, growth, destruction) The cyclical opening and closing of ocean basins caused by movement of the Earth's plates. The Wilson cycle begins with a rising plume of magma and the thinning of the overlying crust.

Why are oceanic ridges different from oceanic rises?

Oceanic rises spread quickly and produce vast amounts of rock while oceanic ridges spread slowly and accumulate steeply

plate tectonics

alfred wegener first proposed in 1912 and called it "continental drift" describing the large-scale motion of seven large plates and the movements of a larger number of smaller plates of the Earth's lithosphere, over the last hundreds of millions of years. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century.

frederick vine and drummond matthews (1963)

analysis of igneous rock stripes around mid ocean ridge (stripes record earths magnetic polarity) sea floor spreading evidence When material from the mantle rises up through mid ocean ridges and cools, it preserves a record of the polarity of the Earth's magnetic field. This is because magnetite in the basalts is strongly magnetic, and aligns with the field when it cools. either side of the oceanic ridge

when do transform faults occur

between mid ocean ridge segments

continental accretion

continental material added to edges of continents through plate motion

what can subduction generate

deep ocean trenches

ultra slow

deep rift valley widely scattered volcanoes arctic and southwest india

oceanic oceanic convergence

denser plate is subducted (light goes up) deep trenches created volcanic island arcs are generated An ocean trench marks the location where the plate is pushed down into the mantle. In this case, the line of volcanoes that grows on the upper oceanic plate is an island arc.

sea floor spreading

depth recordings show sea floor features mantle convection cells as driving mechanisms mid-ocean ridge (site of new ocean crust) subduction zones (oceanic trench site of crust destruction) (harry hess)

fringing reef

develop along margin of landmass

what are the three types of plate boundaries

divergent convergent transform

Evidence of plate tectonics

earths magnetic field and paleomagnetism earth has magnetic polarity (north and south) apparent polar wondering location of north pole changed over time magnetic dip data

continental transform fault

extends from mid ocean ridge and cuts across continent (san andres fault) (all transform faults occur between mid ocean ridge segments) The fracture zone that forms a transform plate boundary is known as a transform fault. Most transform faults are found in the ocean basin and connect offsets in the mid-ocean ridges.

oceanic rise

fast spreading gentle slopes east pacific

Magnetic polarity reversals

polarity reverses over time 176 reversals in the past 76 million years unpredictable pattern recorded in ancient rocks

what does the plate tectonics model describe

features and processes on earth

table mounts or guyots

flattened tops an isolated underwater volcanic mountain (seamount), with a flat top over 200 m (660 ft) below the surface of the sea.

coral reef development

fringing reef barrier reef atolls

what does plate tectonics explain?

global distribution of volcanoes, earthquakes, faults, mountain belts, features of seafloor evolution of continents and seafloor

Heat flow

heat from earths interior release to surface very high at mid ocean ridges low at subduction zones (evidence of sea floor spreading) is higher in areas with either high radioactivity or where the Earth's crust is thinner, such as the mid-oceanic ridges or the Basin and Range Province of the Western United States

nematath

hotspot track hawaiian island- emperor seamount;Chains of extinct volcanoes that are progressively older as one travels away from a hotspot A submarine ridge across an Atlantic-type ocean basin which is not an orogenic structure, but which is composed of otherwise undeformed continental crust

mantle plumes and hotspots

intraplate features- volcanic islands within a plate, island chain MP- is an upwelling of abnormally hot rock within the Earth's mantle. As the heads of mantle plumes can partly melt when they reach shallow depths, they are thought to be the cause of volcanic centers known as hotspots and probably also to have caused flood basalts. H- volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. They may be on, near to, or far from tectonic plate boundaries.

earthquakes as evidence

large earthquakes occur at subduction zones earthquake activity mirrors tectonic plate boundaries

plate tectonic theory

lithosphere plates "float" and move around the atmosphere large scale geologic features occur at plate boundaries

Paleomagnetism and the ocean floor

magnetic anomalies (regular pattern of north-south magnetism "stripes") stripes were symmetrical about long underwater mountain range 1955 deep water rock mapping

applications of plate tectonics

mantle plumes and hotspots record ancient plate motions nematath

what is the evidence for continental drift?

matching sequences of rocks and mountain chains glacial ages and other climate evidence direction of glacial flow and rock scouring distribution of fossil organisms polar plant fossils found in tropics today

divergent plate boundary features

move in opposite directions of each other mid ocean ridge (rift valley) new ocean floor is created shallow focus earthquakes boundaries are underwater (Iceland is an exception) and form submarine mountain ranges called oceanic spreading ridges. While the process is volcanic, volcanoes and earthquakes along oceanic spreading ridges are not as violent as they are at convergent plate boundaries

continental continental convergence

no subduction (both sides go up) tall mountains uplifted himalayas from india- asia collision

oceanic transform fault

ocean floor only (all transform faults occur between mid ocean ridge segments)

Oceanic continental convergence

ocean plate subducted continental arcs generated explosive andesitic volcanic eruptions

what are the three types of convergent boundaries?

oceanic continental convergence oceanic oceanic convergence continental continental convergence

what are types of spreading centers

oceanic rise oceanic ridge ultra slow

subduction zones

oceanic trench site of crust destruction region of the Earth's crust where tectonic plates meet. Tectonic plates are massive pieces of the Earth's crust that interact with each other. The places where these plates meet are called plate boundaries. takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced or sinks due to gravity into the mantle

Transform boundary features

offsets oriented perpendicular to mid ocean ridge (slide past each other) offsets permit mid ocean ridge to move apart at different rates shallow but strong earthquakes oceanic tranform fault continental transform fault

what is pangaea

one large continent existed over 200 million years ago

what is panthalassa

one large ocean (included the tethys sea)

convergent boundary features

plates move toward each other oceanic crust destroyed (oceanic trench, volcanic arc) deep focus earthquakes (great forces involved, mineral structure changes associated)

alfred wegener

proposed one large continent (1912) and broke up 200 million years ago

age of ocean floor

radiometric dating of ocean rocks symmetric pattern of age distribution about mid ocean ridges oldest ocean floor only 180 million years old late 1960s deep sea drilling

atolls

reefs continue to grow after volcanoes are submerged The coral of the atoll often sits atop the rim of an extinct seamount or volcano which has eroded or subsided partially beneath the wate

seamounts

rounded tops submarine mountain is a mountain rising from the ocean seafloor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor

plate tectonics and intraplate features

seamounts table mounts or guyots subsidence of flanks of mid ocean ridge waves erosion may flatten seamount coral reefs associated with subsiding seafloor

what is earthquake intensity measured with ?

seismic moment magnetude

barrier reef

separated from landmass by lagoon

what are the two major tectonic forces

slab pull slab suction

oceanic ridge

slow spreading steep slopes mid-atlantic any section of the narrow, largely continuous range of submarine mountains that extends into all the major oceans and at which new oceanic lithosphere is created by the rise of magma from the earth's interior

mid ocean ridge

spreading center

paleography

study of ancient continents continental accretion continental separation or rifting pangaea

what is paleomagnetism

study of earths ancient magnetic field interprets where rocks first formed magnetic dip

lithosphere

tectonic plates that float in ductile asthenosphere consist of crust and upper mantle

harry hess

ww2 submarine cant and geologist He is best known for his theories on sea floor spreading, specifically work on relationships between island arcs, Earth's crust moved laterally away from long, volcanically active oceanic ridges. He only understood his ocean floor profiles across the North Pacific Ocean