Plate Tectonic Theory Flashcards
What is the mantle made of?
Molten and semi-molten rock containing lighter elements such as silicon and oxygen
What is the crust made of?
Silicon, oxygen, aluminium, potassium and sodium
Describe the; Thickness Age Density Composition Of continental crust
30-70km
Over 1,500 million years old
2.6 (Lighter than oceanic)
Granite (mainly), silicon, aluminium and oxygen
Describe the; Thickness Age Density Composition Of oceanic crust
6-10km
Less than 200 million years old
3.0 (Heavier than continental)
Basalt (mainly), silicon, magnesium and oxygen
Explain Alfred Wegener’s plate tectonic theory
A single continent existed around 3 million years ago - a super continent called Pangea.
Pangea then split into two continents of Laurasia and Gondwanaland
Todays continents were formed from further splitting of these two continents
What is the geological evidence for Alfred Wegener’s plate tectonic theory?
The continental fit of South America and West Africa.
Late carboniferous glaciation deposits found in South America, Antarctica and India.
Rock sequences in Northern Scotland closely agree with those found in Eastern Canada
What is the biological evidence for Alfred Wegener’s plate tectonic theory?
Fossil brachiopods found in Indian limestone are comparable with ones found in Australia.
Fossil remains of Mesosaurus found in both South America and Southern Africa
Fossil remains of a plant that existed when coal was formed, only located in India and Antarctica
Explain further development of Alfred Wegener’s plate tectonic theory - sea floor spreading.
Iron particles in oceanic crust shows alternating polarity (the paleomagnatism).
Shows that the earths polarity reverses every 400,000 years
This implies that the plates must be being destroyed through subduction at a subductive plate margin - causing oceanic trenches and then remade at hotspots, where convection currents in the mantle cause magma to rise to the crust.
What are ocean ridges?
Form when plates move apart in oceanic areas. The space between the plates are filled with basaltic lava from below to form a ridge.
What are rift valleys?
Form when plates move apart on continental areas. The brittle crust fractures as sections move apart. This crust drops down between parallel faults to form the valley. The area between the two rift valleys forms an upstanding block known as a horst.
What are deep sea trenches?
Where oceanic and continental plates meet, denser oceanic plate is forced under the lighter continental plate, forming a deep trench in the ocean.
What are island arcs?
During subduction, the descending plate encounters hotter surroundings, along with the heat from friction, the plate melts. This material then rises to the surface as magma and when they reach the surface they form complex, composite and explosive volcanoes.
What are young fold mountains?
The plates forming continental crust have a lower density than the underlying layers, so there is not much subduction when these plates meet. As the plates move towards each other the sediments are forced up into fold mountains.
