Lecture 24
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What is the world’s largest mountain range?
The mid-oceanic ridge
What is the mid-oceanic ridge?
A giant chain of mountains running along the middle of the ocean
Due to the link between the topography of the ocean floor and heat flux, what was found?
Bands of high heat flux were found located on ridges in the middle of the ocean, leading to the idea of sea-floor spreading
Sea-floor spreading is?
mid-oceanic ridges represent places where two oceanic plates are moving apart and new oceanic crust is forming from volcanic eruptions
How is new crust formed at mid-oceanic ridges?
Through volcanic eruptions that exist on the boundary of two plates that move farther apart, expanding the size of the ocean basin overtime
What support is there for sea-floor spreading?
Linear bands of rocks that were magnetized in alternatively reversed and normal polarities, and the magnetic bands were symmetrical on opposite sides of the ridge
What did Alfred Wegener discover and when?
In the early 1900s, he proposed the idea of continental drift based on the apparent fit of the continents and other evidence, such as fossils
Why was Wegener ignored and what do we now know?
His idea was ignored due to lack of a plausible driving force, but we now know it is right due to sea-floor spreading theory to explain continental drift
What is plate tectonic theory?
A unifying theory showing how a large number of diverse, seemingly-unrelated geological facts are interrelated. The theory was the linkage of two ideas: Continental Drift and Sea Floor Spreading.
What does Plate tectonic theory involve?
A number of large plates plus numerous small plates composed of crust and upper mantle that move slowly, change size, and shape overtime.
What is a plate?
A massive, irregularly shaped slab of solid rock
How much do plates move by and how?
Plates are moving 1-10 cm/yr, caused by the convection flow of the lower mantle
What are plates?
The outermost 100km of Earth, composed of the crust plus the uppermost part of the mantle
How are plates organized?
They are broken into about 12 plates that slowly move laterally over the lower mantle, they behave in a rigid manner, and their boundaries are where active geological processes are
What are the 3 kinds of plate boundaries?
divergent, convergent, and transform
What is a divergent plate boundary?
Where two plates are pushing AWAY from each other, resulting in rising magma to rise up and push older crust away and form new crust
What is an example of a divergent plate boundary?
The mid ocean ridge
What makes Iceland special?
You can see the two plates (North America and Eurasian) on both sides of the divergent plate boundary
The age of the ocean floor ____ with distance from the MOR in both directions
increases
Why is there no oceanic crust older than 280 million years old?
Because when the oceanic crust gets older, it cools and gets dense and starts to dive into the Earth (subduction)
What happens at an oceanic-oceanic convergent plate boundary?
The older crust subducts under the younger crust and melts
What is a subduction zone?
A site where old (and thus dense) oceanic plates sink and move down another plate, either oceanic or continental plate
What is a trench?
A linear trough in the ocean floor that runs along the convergent plate boundary, it is the site of the greatest water depths
A trench is a ____
topographic depression on the sea-floor, that is narrow and long and parallel to the convergent plate boundary.