Seafloor Spreading and Plate Boundary Movements Flashcards
endogenic processes
earthquakes, diastrophism/deformation, magmatism, metamorphism
exogenic processes
weathering, erosion, deposition, sedimentation
how does endogenic processes go
internal heat - mantle convection current - plate movement - endogenic processes
what is the driving force of endogenic
earth’s internal heat
theories about plate movement
continental drift, seafloor spreading, tectonic plates
A theory stating that the Earth’s continents have been joined together and have moved away from each other at different times in the Earth’s history.
- developed the new continents we have today
continental drift theory
who proposed the continental drift theory and when
German Meteorologist Alfred
Wegener (1915)
a supercontinent that existed during the late Paleozoic and early Mesozoic eras.
- single landmass
Pangaea
After many years Pangaea split into ________ and _________
Gondwanaland and Laurasia
Evidence of Continental Drift Theory
- Fit of Continental Shorelines
- Rock Distribution
- Glacial Sediments
- Paleoclimate
- Fossil Distribution
Evidence of Continental Drift Theory
Explain shoreline fit and rock distribution
- Continent’s shape looks like puzzle pieces
- Same rocks and landforms are found on the shore of continents
(e.g. North America, Africa, South America)
Evidence of Continental Drift Theory
Explain glacial sediments
Glacial deposits from South America, Africa, India, and Australia are similar to Antarctica
Evidence of Continental Drift Theory
Explain paleoclimate
- Tropical Plant Fossils in Antarctica
- Coal Deposit in Northern/Eastern
Europe
coal and these plants thrive in tropical environments. hence, this suggests that these continents once had a tropical climate.
Evidence of Continental Drift Theory
Explain fossil distribution
Fossils of a shallow-water reptile, Mesosaurus, were found in both Africa and South America even though they could not swim across the Atlantic Ocean. Fossils of a family of seed ferns, Glossopteris, were found in Africa, South America, India, and Antarctica. These and a number of other fossil groups had identical populations separated by thousands of kilometers of ocean. Paleontologists called on implausible land bridges connecting the continents. But Wegener argued that rising and falling land bridges in the oceans were not likely considering the observation that the ocean crust was made of denser (basaltic) rock than the continents. He argued that this denser oceanic crust could not rise up above sea level. Likewise, if the land bridge was less dense (granitic) continental rock it would be too light to sink into the denser rock below.
despite the pieces of evidence, why was the continental drift theory not accepted?
unclear mechanism of the plate movement
- Wegener thought that the Earth’s spin caused the movement, (spin theory) but geologists knew that the continents were far too heavy to be moved by Earth’s rotation
- argued that the world we see is the result of extreme events like worldwide floods and volcanoes. All the world’s continents wrenching themselves apart from a single landmass would certainly qualify as a catastrophe. (catastrophic theory)
the mechanism by which new oceanic lithosphere is created at and moves away from divergent plate boundaries.
- New oceanic crust is formed due to the rising of hot, less dense material on the ocean floor
seafloor spreading theory
who proposed the seafloor spreading theory
Using data from SONAR-equipped vessels, oceanic cartographer Marie Tharp was able to create maps of the ocean floor that revealed the presence of underwater mountain ranges.
- proposed by the American geophysicist Harry H. Hess in 1960 based on Tharp’s discovery
Observations that support the Seafloor Spreading
- Increasing distance between continents
- Age of rocks in oceanic ridges
- Thickness of rocks along oceanic ridges
- Deposition of sediments away from the ridge
- Magnetic Anomalies
Observations that support the Seafloor Spreading
explain the increasing distance between continents
e.g. The North American and Eurasian tectonic plates are moving away from each other at
the rate of about 2.5 centimeters (1 inch) per year
Observations that support the Seafloor Spreading
explain the age of rocks in oceanic ridges
- younger/newer rocks are found at the ridge
- the age of the seafloor is progressively older away from midocean ridges
Observations that support the Seafloor Spreading
Explain the Thickness of rocks along oceanic ridges
- Along with the seafloor rock, scientists also hypothesized and proved that sediment accumulation must be thicker the farther away from the ridge they are. This is due to older rocks having more time to accumulate sediments than newly-formed rocks.
- ( the elevation of the seafloor is progressively lower away from midocean ridges but the crust tends to bulk up and gets thicker as they get compressed with other rocks)
Observations that support the Seafloor Spreading
Explain the deposition of sediments away from the ridge
- older parts of the seafloor have the greatest potential to have accumulated sediments over
the longest time - sedimentary rocks are found further from the ridge
Observations that support the Seafloor Spreading
Explain magnetic anomalies
- the magnetic history of the seafloor bears the striped-pattern of the Earth’s magnetic reversals
Periodically, the magnetic poles of the Earth flip, north and south becoming reversed. This phenomenon is then recorded in the magma that forms in ridges, having the minerals in the rock to match the polarity of the Earth when it was formed. These create bands of varying polarity and when observed using a magnetometer, the patterns created are mirrored on both sides of the ridge.
example of landforms produced by seafloor spreading
- Atlantic mid-ocean ridges
- east pacific rise (pacific ocean)
why does seafloor spreading occur
because of mantle convection
Unifies the concepts of continental drift, seafloor spreading, magnetic field reversal, and other geological and geophysical discoveries.
* States that lithosphere is not a continuous layer but consists of several-irregularly shaped pieces
called Tectonic Plates.
* Plates move and interact in Plate Boundaries
- bc of mantle convection
plate tectonic theory
if some plates diverge/move away from each other, why does the earth not expand?
because of convergent boundaries/subduction caused also by mantle convection
plate boundary movements
convergence, divergence, transform
the motion/stress of convergent plate boundary
subduction/compressional
is there volcanic activity in a convergent plate boundary
yes
land formation of convergent boundaries
oceanic to continental (oceanic subducts)
- cascades volcano/volcanic arcs (through flux melting, sa continental)
- trenches
oceanic to oceanic (older denser oceanic subducts)
- trenches
- volcanic arc/islands (through flux melting)
continental to continental
- geologic folds - ductile deformation due to compressional stress
- mountains/mountain ranges
a fold that is arched upward to form a ridge
anticline
a fold that arches downward to form a trough
syncline
step-like fold in rock strata consisting of a zone of steeper dip within an otherwise horizontal or gently-dipping sequence. (forms a plateau)
monocline
-Happens when one fold is pushed over the other limb due to increasing compression. -Both limbs are sloping in the same direction.
overturned fold
the motion/stress of divergent plate boundary
spreading/tensional
the effect of divergent plate boundary
constructive (oceanic lithosphere is created)
is there volcanic activity in a convergent plate boundary
yes
land formation of divergent boundaries
continental to continental
- Joints- brittle deformation in surface rocks due to tensional stress.
- fissure volcanoes (Icelandic)
- rift valleys
oceanic to oceanic
- oceanic ridges (seafloor spreading, decompression melting)
the motion/stress of transform plate boundary
lateral sliding/shearing
the effect of transform plate boundary
conservative (lithosphere is neither created or destroyed)
is there volcanic activity in a transform plate boundary
no
land formations of transform plate boundary
none, except faults (brittle deformation and may vary
based on plate movement)
there are earthquakes
the san Andreas fault is a combination of what plate boundary movement
transform and convergent
what fault does convergent plate boundary produce
- hanging wall pushed up despite gravity
reverse fault
what fault does divergent plate boundary produce
- lower hanging wall (because of gravity)
normal fault
what fault does the transform plate boundary produce
strike-slip fault
the rock above the fault zone
- acute
hanging wall
he rock below the fault zone
foot wall
Do all plate boundary movements produce faults?
In order to produce faults, the rocks along these boundaries must obtain their fracture stage. Hence, not all plate boundary movements produce faults.
