plate tectonics pt.2 Flashcards
what are triple junctions
Places where 3 plate boundaries coincide – they migrate and change across time
how do volcanos form
hot spots
- Volcanic plumes originate independently of tectonic plates
- as the plate moves, volcanoes drift off the plume and become inactive
- Extinct volcanoes erode over time + subsidence turns them into seamounts or guyots
- This process supports sea-floor spreading
- mafic magmas feed the volcanoes
how can we tell the direction of plate motion
Seamounts and islands age as they move away from the hot spot so can tell by their arrangement
whats continental rifting and how does it happen
process where a continent stretches and splits apart forming 2 separate landmasses e.g. Red Sea
- Continental lithosphere can stretch and break apart
- Upper crust fractures, forming normal faults
- Lower crust stretches and thins
- Asthenosphere melts, triggering volcanic activity.
- Rift valleys form, often with lakes.
- Continued widening leads to the formation of a new ocean basin.
- Eventually, a mid-ocean ridge develops, separating the land into two continents
what marks remnants of ancient oceanic crust
Ophiolites (including pillow basalts)
old theory for Driving Mechanisms of Plate Tectonics
Plates were thought to be dragged by mantle convection
recent theory for Driving Mechanisms of Plate Tectonics
Plate motion is driven by multiple forces:
- Ridge-Push: Elevated mid-ocean ridges push lithosphere away
- Slab-Pull: Gravity pulls subducting plates downward
- Mantle Convection: Flow in the asthenosphere assists or resists plate movement
how to calculate velocity / rate
distance (cm) / time (year)
how to measure absolute and relative plate velocity
- Absolute Plate Velocity: Measured relative to a fixed point in the mantle.
- Relative Plate Velocity: Measured relative to another moving plate
**Oceanic crust gets older as it moves away from mid-ocean ridges
