Tuesday, 7 February 2012

Back to tectonics (FINALLY!!!) - Conservative Margins and Hotspots summary

Hello everyone! I hope the exam went well for you all! We even got mention in the local newspaper - Twin Sails Bridge part of A-level exam - perhaps it would have been interesting to ask students if they would consider visiting Poole before and after studying the bridge for 2 months, then conduct a Mann Whitney U to see if there was a significant difference between number of students inclined to visit the area! Anyway I can now happily say that we will never have to study Poole/Twin Sails Bridge again!!! This means that we can finally get back to good old tectonics.....

Correct me if I am wrong but I think before Christmas I only got as far as outlining the basics of this module, so I have quite a bit to catch up on! I have already lost count of the number of you who have asked very nicely for some case study orientated posts so I will try and find the time over the coming weeks to go over case studies whilst also finding the time to write about Iceland (apologises but I am starting to get a little excited and a condition of me going was that I don't talk about it at home!). For now though I will leave you with a few brief notes on conservative boundaries and hotspots (sorry if the image quality is a bit poor but I gave up trying to find good diagrams online so just photographed my notes) - I am hoping to cover all the volcano stuff this week so I can focus on earthquakes over half term so be warned that a lot of posts may appear over the coming days!

Conservative Margins
These margins are sometimes reffered to as passive or slip margins and occur where two plates meet and the direction of plate motion is either parallel or nearly parallel. No crust is destroyed or created, although these are areas of frequent seismic activity as the build up of friction as the plates pass each other is released by earthquakes. This boundary is not associated with volcanism.
- No subduction or abduction
- Plates try ot move laterally past each other
- Most infamous are the San Andreas Fault in the USA and the North Antolian Fault in Istanbul [both are overdue a huge earthquake!]
- No volcanism
- Generates massive earthquakes

- These are not boundaries, as such, but rather a surface representation of surface plumes
- Plates do not always split above mantle plumes, but as the plate moves over the magma source, it generates a chain of islands
- The oreintation of the island gives an indication of the direction of the plate movement relative to the plume
= Chain of islands, connected to the Emperor Seamount chain (submerged)
= The islands become progressively older to the northwest, indicating the plate is moving in this direction
= This was anticipated before the discovery of continental drift as the islands become shallower in gradient, more advanced vegetation succession and have deeper soils to the northwest.
Other hotspots
- Yellowstone Caldera is probably the niggest and highest risk
- Iceland is unusual being a large plume underneath a divergent boundary
This mantle plume theory is stil hotly debated and poorly understood - it is one of the few remaining mysteries of tectonic theory, which is otherwise now widely accepted.

Divergent and convergent boundary notes are on the way!

No comments:

Post a Comment