Earth's Changing Face: The Basics of Plate Tectonics (L14) Flashcards
What is the system of rock recycling called?
Rock Cycle
How does an igneous rock become a sedimentary rock?
The igneous rock can be exposed to weathering to produce particles that are eroded, transported, and deposited as sediment. When lithified, it becomes sedimentary rock
How does a sedimentary rock become an igneous rock?
sedimentary rock melted to produce magma, then cooled to produce igneous rock.
Sedimentary rock to Metamorphic rock?
sedimentary rock put under high temperatures and pressures
Metamorphic to Sedimentary Rock?
metamorphic rock can be weathered to produce particles that are eroded, transported, and deposited as sediment
Metamorphic to Igneous?
metamorphic rock can be melted to produce magma that cools to become an igneous rock
Igneous Rock to Metamorphic rock?
igneous rock put under high heat and pressure to become metamorphic rock
What is one of the reasons why movement takes place on the Earth’s surface?
because heat flow within the Earth is not uniform
how does hot material and cold material flow throughout the mantle?
hot material flows upwards, cold material flows downwards
What produces the huge convection currents in the mesosphere
the cells of rising and sinking mantle
what material in the mantle, flows most readily and why?
the Asthenosphere, because it is solid, but in a near-liquid state
what is the boundary between the mantle and crustal part of the lithosphere called?
the Mohorovicic Discontinuity or “Moho” for short
the lithosphere (the brittle outer shell of the Earth, is not a continuous sheet but rather ____
broken into tectonic plates
Explain how the plates of lithosphere actually move
through something called Convection.
Convection currents in the asthensophere drag the pieces of lithospheric plates along on the surface called “Mantle drag”
What happens to the places where the plates were moved apart ?
the asthenosphere fills the cracks and spots where the plates moved apart while the far edges of the plates of lithospheric plates are dragged down by downgoing currents
Where do ridges form?
where the lithospheric plates are being formed as the new lithospheric plates are least dense
What happens when lithospheric plate cools?
it increases greatly in density and sinks and drags the rest of plate along with it
“slab pull”
the movement resulting from the pulling of a plate down a trench by the dense edge of a plate
what does slab pull cause?
causes the old, outer edge of a plate to sink
At the present time, what is thought to create the majority of plate movement?
a combination of slab-pull and convection
what are the 2 Main types of boundaries?
A divergent boundary - the boundary between 2 plates that are moving APART
A convergent boudnary - the boundary between 2 plates that are moving toward one another (Converging)
what are divergent boundaries represented by in the ocean floor?
mid-ocean ridges (e.g., East Pacific Rise, Mid-Atlantic Ridge)
what are convergent boundaries represented by?
Trenches
The 2 types of Crust
Oceanic Crust (mafic crust underlying the oceans) Continental Crust (felsic crust that underlies the continents)
what are the 2 main differing characteristics of an Oceanic and Continental crust and how do they differ?
Density and thickness
continental crust is lighter and thicker than oceanic crust
What is the effect of density on the way oceanic plates and continental plates
oceanic lithosphere floats low on asthenosphere (forming ocean basins)
Continental lithosphere floats high on asthensphere (forming continents)
what is the dependence of the level of floatation on thickness and relative density of the materials called
Isostasy meaning “equal standstill”
why iscontinental lithosphere taller than the oceanic lithosphere?
THICK continental lithosphere, with thick roots, stands higher on the asthenosphere
why does it matter that continental lithosphere is diff from oceanic lithosphere?
oceanic lithosphere is continuously created at oceanic ridges and destroyed at subduction zones (so quite young). However, slabs of continental lithosphere float like rafts as it is buoyant so this is why contients contain such old rocks
How are ocean basins formed?
- in interior of contient, heat can rise from the underlying mantle
- upwards the lithosphere of continent
- cracks develop in this upwarded area, forming rift valleys
- mafic magma generated by decompression melting close to surface
4.b) Magma than cooled at depth to form gabbro of lower crust
- Magma that cools at surface forms basalt
- 2 of the arms continue to spread, forming oceanic lithosphere of an ocean basin, while the remaining failed arm stops spreading and is fillied with sediment
What is the proof that we have that continents have moved around and seas can open and close?
evidnece from Alfred Wegener, who noticed that the contients could be fit together like a puzzle
created the concept of “continental drift”
What was the argument for the concept of “continental drift”
it was that the distribution of certain fossils of land animals and plants could only be explained if all the continents were once together
what are the 3 main types of convergent plate boundaries?
Oceanic-oceanic convergence
Oceanic-continental convergence - (subduction of OL)
Continent-continent collision
What is formed through oceanic-oceanic convergence?
magma generated from hydration melting rises to form an ISLAND ARC
what is formed through Oceanic-continental convergence
molten material from hydration melting rises to form an CONTINENTAL ARC
the process of subduction is indicated by 3 things”
the existence of ocean trenches (deepest area of the ocean)
explosive volcanoes
severe earthquakes
what is a trench?
a trench is the surface expression of a subduction zone where oceanic lithosphere begins its descent
what is an additional consequence of convergence in plate tectonics
the development of clastic wedges which are derived from wearing-down of mountains that were created through the uplifting during the convergence of the plates
what are zones where lithospheric plates move alongside one another called?
transform plate boundaries – basically “offsets” that form within moving plates
