1. Convergent Plate Margins
May also be called destructive plate margins.
What makes them converge?
Downwelling convection cell
SLAB PULL
There are 3 types margins depending on what types of plate are involved:
Oceanic v oceanic
Oceanic v continental
Continental v continental
Each will produce different hazards and rocks.

2.
The movements of Earth’s tectonic plates shape the face of our planet. The sinking of one plate beneath another, known as subduction, causes volcanism and earthquakes. Subduction zones lie, for example, off the coast of Indonesia, Chile and Japan. But how exactly did this process begin? As part of the International Ocean Discovery Program, an international science team was able to drill and investigate the origin of a subduction zone for the first time in The team is now publishing its data in the international scientific journal Earth and Planetary Science Letters.
About 2000 kilometers east of the Philippine Islands lies one of the most famous topographical peculiarities of the oceans: the Mariana trench. Reaching depths of up to 11,000 meters below sea level, it holds the record as the deepest point of the world’s ocean. This 4000-kilometer-long trench extends from the Mariana Islands in the south through the Izu-Bonin Islands to Japan in the north. Here, the Pacific Plate is subducted beneath the Philippine Sea Plate, resulting in intense volcanic activity and a high number of earthquakes. The entire area is part of the “Pacific Ring of Fire.”
But when and how exactly did the subduction of the Pacific Plate begin? This is a controversial topic among scientists. An international team led by the GEOMAR Helmholtz Center for Ocean Research Kiel, the Japan Agency for Marine Earth Science and Technology (JAMSTEC) and the Australian National University investigated this early phase of subduction along the Izu-Bonin-Mariana trench, with findings published in the March edition of the scientific journal Earth and Planetary Science Letters.
The study is based on a drill core that was obtained by the International Ocean Discovery Program (IODP) in 2014 with the US research drilling vessel JOIDES RESOLUTION some 600 kilometers west of the current Izu-Bonin Trench. “For the first time, we were able to obtain samples of rocks that originate from the first stages of subduction,” says Dr. Philipp Brandl from GEOMAR, first author of the study. “It is known that the active subduction zone has been moving eastwards throughout its history and has left important geological traces on the seabed during its migration. We have now drilled where the process has begun.”
The team of the JOIDES RESOLUTION was able to drill more than 1600 meters deep on the seabed, starting at a water depth of around 4700 meters below sea level. “This is already at the limit of the technically feasible”, emphasizes Dr. Brandl. Based on analysis of this drill core, the researchers were able to trace the history of the subduction zone layer by layer up to the approximately 50 million year-old rocks at the bottom of the core, which are typical for the birth of a subduction zone. “There has not been such a complete overview yet,” says Dr. Brandl.
Brandl and his colleagues were now able to acquire and analyze microscopic inclusions of cooled magma from the rocks. The data obtained provide the scientists with insights into the history of volcanic activity at the Pacific Ring of Fire million years ago. The researchers found evidence that volcanism was only beginning to gain momentum. The volcanic activity intensified with the rollback of the subduction zone towards the east and the huge explosive stratovolcanoes formed, similar to those present nowadays, for example along the western rim of the Pacific Ring of Fire.
However, further drilling is necessary to test the validity of these observations. “The more drill cores we can gain from such old strata, the better we learn to understand our own planet,” Dr. Brandl says. The question of how subduction zones develop is not only interesting to understand the history of the earth. Subduction zones are the drivers for the chemical exchange between the earth’s surface and the earth’s interior. “The dynamics of a subduction zone can thus also influence the speed of global elemental cycles”, summarizes Dr. Brandl.
Reference: Philipp A. Brandl, Morihisa Hamada, Richard J. Arculus, Kyle Johnson, Kathleen M. Marsaglia, Ivan P. Savov, Osamu Ishizuka, He Li. The arc arises: The links between volcanic output, arc evolution and melt composition. Earth and Planetary Science Letters, 2017; 461: 73 DOI: /j.epsl
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3. Oceanic v Oceanic collision
The features/landforms:
Subduction zone: describes the whole area where subduction is taking place.
Ocean Trench: is the deep valley formed in the ocean floor as the subducted plate bends.
Benioff zone: zone of earthquakes set off by the solid lithospheric plate forcing it’s way through the mantle.
Island Arc: An arc of islands running parallel to the trench/subduction zone created by volcanic activity fed by magma from the melting subducted plate.

4. Oceanic v Oceanic collision
DRAW ONE ON THE BOARD – FULLY LABEL UP

5. Oceanic v Oceanic 2 The processes: Subduction:
Occurs where a piece of oceanic lithosphere bends and sinks beneath another plate.
Why do oceanic plates subduct?
Because subducting slab is COLDER than the overriding slab
SLAB PULL theory – it is dragged down

6. Oceanic v Oceanic 3 Seismic activity:
As the cold/solid oceanic plate sinks through the mantle there is frictional resistance.
When the resistance is overcome and the plate moves the energy is released as seismic waves = earthquake.
This is the Benioff zone.

7. Oceanic v Oceanic 4 Melting:
As mentioned earlier there are 3 reasons why crust may melt.
Which is occurring in this situation?
Increased T as the plate sinks deeper.
Also the plate is saturated in water.
The melting oceanic crust is basic so what kind of magma will form when it melts?
More SiO2 rich and so will move towards being intermediate.
But there is also a production of basalt because the bit of the mantle above the subducted plate also melts.
This magma will move upwards through the overlying mantle and thin crust to the surface.

8. Oceanic v Oceanic 5 Explosive volcanic activity.
Intermediate magma will be fairly violent. Because it is thicker and stickier and traps gases.
Enough volcanic activity will occur to build volcanic islands above sea level in an arc parallel to the plate margin (island arc).

9. Oceanic v Oceanic examples
Montserrat/Caribbean arc: Soufriere Hills.
Aleutian islands.
Indonesia: Krakatoa
Philippines: Pinatubo
Kamchatka.

10. Oceanic v Continental Crust collision
The features/landforms:
Many are the same:
Trench.
Subduction zone.
Benioff zone
Continent based volcanoes.
Fold mountains.

11. Oceanic v Continental Crust collision
CARTOON DIAGRAM ON BOARD

12. Oceanic v Continental Crust collision
CARTOON DIAGRAM ON BOARD

13. Oceanic v Continental The processes: Subduction:
Occurs where a piece of oceanic lithosphere bends and sinks beneath another plate.
Why do oceanic plates subduct?
Because oceanic crust is denser (3.0). Than continental crust (2.7)
SLAB PULL

14. Oceanic v Continental Crust 2
The processes.
Again very similar to ocean v ocean with a subtle difference.
Subduction (but only the oceanic crust will subduct).
Seismic activity.
Melting:
Mountain building (orogenesis)

15. Oceanic v Continental Crust 3
What happens to the melt as it enters the continental crust?
Remember that the magma is now intermediate.
It travels up through the continental crust that has what composition?
Silicic.
The hot magma melts the continental crust and adds SiO2 rich crust to the intermediate magma to make magma that is very intermediate or silicic.

16. Oceanic v Continental Crust 4
Silicic magma will produce what kind of volcanic activity?
Very explosive and dangerous.
Mountain building (orogenesis).
This involves crust being compressed and either folding or faulting.
Fault movement sets off earthquakes.
There will therefore be earthquakes linked to both the Benioff zone and orogenesis.

17. Oceanic v Continental Examples
Volcanoes along the Andes:
Popacatapetl (Mexico)
Nevada del Ruiz (Columbia)
The Rockies/Cordillera:
Mt. St. Helens

18. Continental v Continental Crust
The features/landforms.
Mountain ranges
The processes:
Mountain building (orogenesis).
No subduction because continental crust will not subduct because the rocks are not as dense.

19. http://www. geologypage. com/2014/08/collision-mountain-ranges-video

20. https://mail.google.com/mail/u/0/#inbox/15c3c548d0483fd6?projector=1

21. Continental v Continental Crust
Will there be volcanoes?
The crust is up to 90 km thick and so is hot enough at it’s base to melt.
However, the melt produced is so viscous and the distance to the surface so far that magma will not make it to the surface.
Therefore NO VOLCANOES.

22. Continental v Continental Crust
Will there be earthquakes?
Orogenesis is still taking place.
All the energy is being put into deforming the rocks.
So YES there will be many large earthquakes.

23. Continental v Continental Crust examples
Himalayas

24. Check wall charts in CG07 for examples and their locations

25. Conservative Plate Margins
This is where 2 plates are sliding past each other horizontally but are not being created or destroyed.
There is only one really good example in the world, where is it:
California, San Andreas Fault.

26. Conservative Plate Margins
Seismic activity
Lots!
Many faults
San Andreas Fault ZONE
Note movement arrows of plate

27. Conservative Plate Margin
What kind of volcanic activity will there be?
None.
Why not?
Nothing is melting.
Will there be any earthquakes?
Yes and very large.

28. Passive Plate Margins Nothing is happening.
2 pieces of crust are fused together.
Like the N. American continental plate and the Atlantic oceanic plate.
However, in time the margin may become active.
It is already starting to subduct in the Caribbean arc region (Montserrat).

29. Check wall charts in CG07 for examples and their locations

30. What have you learned so far? 1 minute review!

31. Review: Construct a graphic organiser ….
There are going to be 3 types of collision
And for each we will look at
features/landforms
Processes
Seismics
Melting
Explosivity
Examples
feature
process EQ
melt
explosion
Ocean:Ocean
Ocean: continent
Continent: continent