Part 4 Flashcards
What are ocean floor rocks mainly composed of ?
A composition known as basalt
Is oceanic crust or continental crust less variable in composition?
Ocean crust is much less variable than the continents and has a simpler structure
Is oceanic crust older or younger than continental crust,
It is much younger than the average age of continental crust
Describe the pattern of ocean crust age in the Atlantic Ocean in the way it corresponds to the depth of the ocean floor . What is the oldest crust mapped in the Atlantic Ocean and where does it occur? Are there any features where the relationship between age and depth does not hold.
The youngest ocean crust <2 million years old is the red line snaking down the middle of the Atlantic Ocean
This corresponds very well with the shallowest (palest blue) zone forming down the middle of the ocean.
The oldest crust is immediately east of North America and immediately west of west Africa dates at up to 180 million years ago
In the south Atlantic there is an irregular ridge linking it to continental shelves of South America and Africa
What importance does the asthenosphere have in allowing lithospheric plates to move?
It is weak, and deforms plastically allowing the lithosphere to slide across it
How did the age of the continental crust make continental drift more of a reality?
The discovery that the crust at mid ocean ridges is young and that the age of the ocean floor becomes older symmetrically on either side led to the acceptance of continental drift.
What type of rock is basalt?
An igneous rock low in silica,
It was erupted as molten lava quickly cooled and solidified
What is radiometric dating?
It is the measuring of products of radioactive decay within rocks and minerals
When igneous rocks cool down from a molten state what happens to the in terms of magnetisation?
They inherit magnetisation from the earths magnetic field
Rocks today are magnetised in the current magnetic field
The earths magnetic field has flipped many times in the past
The rocks formed at these different times were formed when the field was in the opposite direction are magnetised in the reverse direction
This is called paleomagnetism
It allowed the ocean floors to be ages without drilling
When the lava came out because it was in the same field it split in the opposite direction at the oceanic crust and widens
What is sea floor spreading?
It is the break of the lithosphere between continents that widens due to the magnetism of the igneous rock
This allows continents to move further apart
Where do most mid ocean ridges usually occur?
Midway between the continents on either side of the ocean
They are made of the youngest oceanic crust
They are added to by sea floor spreading
When the ocean crust cools what does it inherit?
Magnetisation that records the direction of the earths magnetic field at the time
