Geology Chapter 3: Plate Tectonics

continental shelves

Areas where continental surfaces extend under the shallow ocean water around the continents

Paleomagnetism

The study of the alignment of magnetic minerals in rock,specifically as it relates to the reversal of Earth's magnetic poles; also the magnetic properties that rock requires during formation

mountains and oceans

what forms islands such as Hawaii

ridge push

when the force of gravity moves a plate downward and away from a ridge

convergent boundaries

where are oceanic trenches, island arcs, and Earths largest mountain belts formed

Rate of spreading equation

width of stripe / time duration

Gondwana

Supercontinent that existed before Pangea, more than 500 million years ago.

convergent boundary

-A tectonic plate boundary where two plates collide, come together, or crash into each other (a typical result is that one plate slides under the other) -can involve two oceanic plates, oceanic and continental, or two continental

ocean continent convergence boundary

-along this boundary the denser oceanic plate subducts beneath the more buoyant continental plate -volcanoes form on the surface of the overriding continental plate in the same way the volcanoes form in an ocean ocean convergence boundary

fracture zone

-an area of irregular, seismically inactive topography, marking the position of once active transform faults -opposite sides of the zone have different elevations because they formed by seafloor spreading at different times

when oceanic plates converge

1. convergence 2. oceanic trench and accretionary prism form 3. as plate subducts, temperature increases which causes melting 4. some magma erupts and with continued activity it can construct a curving belt of islands in an island arc

Earth's Magentic Field

1. inner core transfers hear and less dense material to the liquid outer core which causes liquid in the outer core to rise, forming convection currents 2. movement of the molten iron is affected by forces associated with Earths rotation, the resulting movement of liquid iron and electrical currents generates the magnetic field 3. currently flows from south to north causing magnetic ends of a compass needle point toward the north (this is called normal polarity)

Alfred Wegener

A German scientist who proposed the theory of continental drift in the 1900s

triple junction

A point where three lithosphere plate boundaries intersect (ex: Mendocino _____ ______ is the )

Seamounts

An underwater mountain rising from the ocean floor and having a peaked or flat-topped summit below the surface of the sea.

Mesosaurus

Animal whose fossil, a small reptile who was freshwater and could not have swam across the ocean, was found both on the continents of Africa and South America

driving force, resisting force

for plates to move, an object must be subjected to a _______ ______. This must exceed the _______ _______

negative magnetic anomaly

Less than average strength of Earth's magnetic field.

Hess and Dietz

Sea floor spreading hypothesis

geomagnetic polarity timescale

The Earth's magnetism has changed polarity at irregular intervals of several million years or less. The ages of each polarity reversal form a sequence of dates which defines the ________ _____ ________ which then serves as a reference to compare against other sequences of rocks

transform boundary

The boundary between tectonic plates that are sliding past each other horizontally

divergent boundary

The boundary between two tectonic plates that are moving away from each other (in most cases, magma fills the space between the plates)

tectonic activity

The movement of plates within the earth's crust against each other, contributing to volcanic eruptions and massive earthquakes.

Subduction, subduction zone

The process of one plate going under another is _______... the zone around the downward moving plate is the _______ _______ (many large earthquakes happen here)

oceanic trench, accretionary prism

_____ ______ forms as the subducting plate bends down... sediment and slices of oceanic crust collect in the trench, forming a wedge called a _______ _______

Iceland

______ is a large volcanic island

continental crust

_______ ______ is not strong enough to survive the forces needed to move a large mass across such a great distance while pushing aside oceanic crust

island and seamount chains

_________ and _________ ________ have two key things in common 1. they were formed by volcanism 2. they are near sites that geologists interpret to be above unusually high-temperature regions in the deep crust and upper mantle (geologists refer to these regions as hot spots)

earthquakes

_________ are not distributed uniformly across the planet. Most are concentrated in discrete belts, such as one that runs along the western coasts of North and South America

island arcs

a curved chain of volcanic islands located at a tectonic plate margin, typically with a deep ocean trench on the convex side.

Glossopteris

a genus of fossilized woody plants/ferns found as fossils that have been dated to roughly 300 to 200 million years. The fossils currently exist on five continents. The distribution of this plant was among the first evidence for continental drift.

slab pull

a mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and "pulls" the trailing lithosphere along

positive magnetic anomaly

a reading of magnetic field strength that is higher than the regional average

mantle convection

a recurring current in the mantle that occurs when hotter, less dense material rises, cools, and then sinks again. This current is believed to be one of the driving forces behind tectonic plate movement.

magnetic time scale

a scale that shows the ages of magnetic reversals and is based on the polarity of lava flows of various ages

abyssal plains

a smooth, nearly flat region of the deep ocean floor

older

age determinations from fossils in the sediment and from underlying volcanic rocks show that oceanic crust gets systematically ______ away from mid-ocean ridges

age and distance

ages of volcanic rocks in the islands and seamount chain increase systematically to the northwest. When we plot the ages of these rocks as a function of distance from Kilauea (the active volcano on the Big island), there is a clear relationship between _____ and _____

hot spot

an area where hot mantle rises and melts, forming magma that ascends into the overlying plate. If the plate above the ____ ____ is moving relative to the hot spot, volcanism constructs a chain of volcanoes

active tectonics

areas of yellow and orange on the map show areas of ______ ________

seamounts

as an area on the plate moves beyond the hot spot, it cools subsides, and erodes, so volcanoes that start out as islands may sink beneath the sea to become __________

transform faults

at transform boundaries, plates slip horizontally past each other along _______ ________. These are associated with mid ocean ridges

mid ocean ridges

broad symmetrical ridges that cross ocean basins are called

oceanic fracture zone

continuing outward from most transform faults is an ______ _____ _____, which is a step in the elevation of the seafloor

mid-ocean ridge

divergent plate boundaries where new oceanic lithosphere forms as two oceanic plates move apart... these boundaries are also known as spreading centers

continents and mid ocean ridges

earthquakes are more common along the edges of _________ and _____ ______ ________

Lithosphere

earths strong upper layer...broken into a dozen or so fairly rigid pieces called tectonic plates

plate boundaries

generally, most tectonic activity occurs near ______ _______ (earthquakes are the best example of this)

3-5 km

how deep is most of the ocean floor?

cluster

if a plate is not moving or is moving very slowly, the hot spot forms a ________ of volcanic islands and seamounts instead of a linear chain (ex: Galapagos islands)

change

nearly all plate boundaries contain curves or abrupt bends, so most boundaries _______ type as they cross Earths surface

earthquakes

ocean trenches and associated island arcs have numerous _________

1-15

plates move about ___ to ___ cm per year (about as fast as fingernails grow)

Pacific Ring of Fire

region around the Pacific Ocean where most of the volcanoes and earthquakes on Earth occur regularly

Glaciers

scientists have been confused to find evidence of ancient _______ in places near the equator

continental rifting

splitting of a continent at a divergent plate boundary 1.magma rises through crust 2.stretching of the crust (basins may form resulting in lakes) 3. if this continues, the continent will split into two pieces and a narrow ocean basin forms as seafloor spreading takes place 4. with continuing seafloor spreading the ocean basin can become a full ocean such as the Atlantic

outer core

the layer of earth that behaves as a dynamo (electrical generator) producing the magnetic field, is the _______ ______

boundaries

the location of earthquakes is a better guide to plate _______ than the location of volcanoes

plate tectonics

the process of _____ ______ circulates material back and forth between the asthenosphere and the lithosphere... this process is the major way that Earth transports heat to the surface

zigzag pattern of mid ocean ridges

the spreading direction must be parallel to the transform faults and perpendicular to the spreading segments, so this pattern is required to allow a plate boundary to be curved

continent-continent convergent boundary

this type of boundary is commonly called a continental collision, and it produces huge mountain ranges (ex: Himalaya and and Tibetan plateau of Southern Asia)