Oceanography 2

Plate tectonics
Theory that the outermost portion of Earth is composed of a patchwork of thin, rigid plates that move horizontally with respect to one another, like icebergs floating on water. As a result, the continents are mobile and move about on Earth’s surface, controlled by forces deep within Earth.
Continental drift
Alfred Wegener’s idea that continents were slowly drifting across the globe.
Pangaea
(pan = all, Gaea = Earth) Wegener suggested that during the geologic past, the continents collided to form a large landmass which he named Pangaea.
Mid-Ocean ridge
a continuous underwater mountain range that winds through every ocean basin in the world and resembles the seam on a baseball. It is entirely volcanic in origin, wraps on-and-a-half times around the globe, and rises more than 2.5 km about the surrounding deep-ocean floor.
Oceanic trench
the deepest parts of the ocean floor that resemble a narrow crease of trough. Some of the largest earthquakes in the world occur near these trenches; they are caused by a plate bending downward and slowly plunging back into Earth’s interior.
Subduction
(sub = under, duct = lead) the process of a plate bending downward and slowly plunging back into Earth’s interior.
Subduction zone
The sloping area from the trench along the downward-moving plate.
Paleomagnetism
(paleo = ancient) The study Earth’s ancient magnetic field.
Rift valley
a central downdropped linear depression along the crest of the mid-ocean ridge.
Hot spots
Areas of intense volcanic activity that remain in more or less the same location over long periods of geologic time and are unrelated to plate boundaries.
Tablemounts/Guyots
Volcanic peaks on the ocean floor that are flat on top – unlike anything on land.
Seamounts
Tall volcanic peaks on the ocean floor that are cone shaped, they resemble some volcanoes on land.
Fringing reef
The first of the three stages of development in coral reefs – initially develop along the margin of a landmass, where the temperature, salinity, and turbidity of the ware are suitable for reef-building corals.
Barrier reef
The second of the three stages of development in coral reefs – linear or circular reefs separated from the landmass by a well-developed lagoon.
Atoll
The third of the three stages of development in coral reefs – as a barrier reef around a volcano continues to subside, coral builds up toward the surface. After millions of years, the volcano becomes completely submerged, but the coral reef continues to grow. If the rate of subsidence is slow enough for the coral to keep up, a circular reef called an atoll is formed.
Fracture zone
on the Pacific Ocean sea floor, where scars are less rapidly covered by sediment than in other ocean basins, transform faults are prominently displayed. Here they extend for thousands of km away from the mid-ocean ridge and have widths of up to 200 km. these extensions, however, are not transform faults. Instead they are fracture zones.
Paleogeography
(paleo = ancient, geo = earth, graphy = description of) the study of historical changes of continental shapes and positions.
Alfred Wegener
was the first to advance the idea of mobile continents in 1912. Had the idea of continental drift, he thought the continents were slowly drifting across the globe due to the way the continents seemed to fit together like pieces of a jigsaw puzzle, particularly S. America and Africa.
Harry Hess
was a US Navy captain in WWII, left his depth recorder on at all times, then compiled these and many other depth records to show extensive mountain ridges near the centers of ocean basins and extremely deep, narrow trenches at the edges of ocean basins. He published History of Ocean Basins, which contained the idea of sea floor spreading and the associated circular movement of rock material in the mantle. He indicated the driving mechanism for seafloor spreading was convection cells (circular movement of rock material in the mantle).
Frederick Vine & Drummond Matthews
Compiled the pattern of sea floor spreading to show there was evidence of the Earth’s magnetic polarity changing (the sea floor sediment rests based off of the magnetic pole just like continental rock).
Charles Darwin
he noticed a progression of stages in coral reef development. He hypothesized that the origin of coral reefs depended on the subsidence (sinking) of volcanic islands and published the concept in The Structure and Distribution of Coral Reefs in 1842. His hypothesis was later supported by advances in plate tectonic theory.
Discuss the evidence Wegener used to support continental drift
he initially relied on the fact that the shapes of matching shorelines on different continents supported as evidence for continental drift. Wegener also hypothesized, then evidence should appear in rock sequences that were originally continuous but are now separated by large distances. He noted the similarities in rock sequences on both sides of the Atlantic. He also noticed the occurrence of past glacial activity in areas that are now tropical and suggested that it, too, provided supporting evidence for drifting continents.
paleomagnetism
scientists are able to see the Earth’s magnetic field when the Igneous rocks solidify from molten magma, nearly all igneous rocks contain magnetite which align themselves with the Earth’s magnetic field and then harden. The degree to which a magnetite particle points into Earth is called its magnetic dip, which is directly related to latitude.
Apparent polar wandering
demonstrates that the magnetic pole remained stationary while North America and Eurasia moved.
Seafloor magnetic anomalies
were demonstrated when the US Coast and Geodetic Survey along with Scripps Institution of Oceanography conducted deep-water mapping off of Oregon and Washington in 1955. Using a sensitive instrument called a magnetometer, they found that the entire surveyed area had a pattern of above-average and below-average magnetism and the pattern appeared to be symmetrical with respect to a long mountain range that was fortuitously in the middle of their survey area. These stripes are called “magnetic anomalies”.
the fact that the oceans are 4 billion years old, however the oldest sea floor is only 180 million years old, as well as the age at the mid-ocean ridge is “younger” than the floor on either side, and gets older the further away from the mid-ocean ridge you get.
Divergent
Plates move “apart <- ->” where plates move apart, resulting in upwelling of material from the mantle to create new subfloor.
Convergent
plates move “together -> <-” where plates move together, resulting in the subduction of oceanic lithosphere into the mantle.
When two continental plates collide, a highly elevated mountain is formed.
Transform Plate Boundaries
Plates move “past each other ->/<-? both oceanic and continental crust types. Transform Faulting tectonic process.
Oceanic Rises
exhibit a gently sloping seafloor with a small, indistinct central rift valley that results from relatively fast spreading rates. EXAMPLE: East Pacific Ridge.
Oceanic Ridges
Exhibit a steeper sloping with prominent rift valley that results from slow spreading rates.
Oceanic-Oceanic
Old sea floor is destroyed, subduction tectonic process. Trench; volcanic arc as islands. EXAMPLES: Mariana Trench, Aleutian Islands.
Oceanic-Continental
Old seafloor is destroyed, subduction tectonic process. Trench; volcanic arc on land. EXAMPLES: Peru-Chile Trench, Andes Mountains.
Continental-Continental
Collision tectonic process. Tall mountains. EXAMPLES: Himalaya Mountains, Alps.
Hot Spots
areas of intense volcanic activity that remain in more or less the same location over long periods of geologic time and are unrelated to plate boundaries.
Mantle Plumes
columnar areas of hot molten rock that arise from deep within the mantle.
Seamounts
tall volcanic peaks that resemble some volcanoes on land, they are cone shaped on top like an upside-down ice cream cone. Seamounts do not come out of the water.
Tablemounts
volcanoes that are flat on top, unlike anything on land. The flat spot is created by the oceans waves/current.
Coral Reefs
as the ocean floor resides, the volcanic cone moves into deeper water, when it is shallow the Fringing reef is present, not very thick or well developed because of the volcanic activity that is present (heat). As it moves into deeper water the Barrier reef is present, these are linear or circular reefs separated from the landmass by a well-developed lagoon. Finally, the Atoll is after the barrier reef stage, as the reef around a volcano continues to subside, coral builds up toward the surface, after millions of years, the volcano becomes completely submerged, but the coral reef continues to grow. If the rate of subsidence is slow enough for the coral to keep up, a circular reef called an atoll is formed.
Describe the Wilson cycle
The cyclical opening and closing of ocean basins caused by movement of the Earth’s plates. It begins with a rising plume of magma and the thinning of the overlying crust. As the crust continues to thin due to extensional tectonic forces, an ocean basin forms and sediments accumulate along its margins.