Here is an explanation of how plate tectonics in a spreading zone, moves…. using a slab of chocolate…. as you do…. and a bit of imagination.
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The choc’ based explanation, may help visualise how the spreading process works and could help understand what can be seen on the geological map, shown below.
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A brief on plate tectonics general:
Plate tectonics is the name given to a process that takes place all over the Earth’s surface crust. The entire crust comprises, not one continuous crust, but a crust that has broken up into pieces (plates). Each plate is being shoved around by huge forces below it, from moving molten magma.
Three main consequences occur at plate edge zones/margins, depending on the direction, relative to each other, that they are being shoved.
1. Both plate edges spread apart from each other (Spreading)
2. One plate edge is shoved under the edge of the other plate (Subduction)
3. Both plate edges collide and are often together, thrust upwards (Collision)
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This article explains an example of 1. A Spreading Zone / Margin..
This choc’ based explanation below, should help understand what can be seen on the geological map, shown here:
Image depicting: Atlantic Ocean with Mid Atlantic Ridge (Spreading Zone) revealed
Image courtesy of The Open University**
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Earth has a thin rock crust all over… Made mainly of two sorts… Continental Crust (the bit we jump around on and grey in the map picture)… and Oceanic Crust (the bit that is between the chunks of Continental Crust and is red/yellow/green in the map pic).
This whole crust is broken into variously sized, solid pieces (plates)
There are many spreading zones between the plates and here we focus on one… The Atlantic Ocean Mid Atlantic Ridge.
You can learn how the spreading zone works, using a slab of chocolate and a bit of imagination:
Take slab of choc… this is your Continental Crust.
Before the Atlantic Ocean existed, South America used to be connected to Africa… It used to be ‘one land’… as is our slab of choc.
You can demo how the ‘one land’, separated to form what is seen in the map, as it is today… using the choc slab (plus imagination)
Place choc on table and snap it in two… keep both bits together… this represents the long ago ‘one land’… take a look at the map… we will now create the Atlantic Ocean area and separate South America from Africa.
Look at your snapped choc slab… imagine a flow of smooth melt choc comes out of the table below (all along the snap line)… Then, as it flows up… move the snapped choc slab slowly apart so the flow spreads thinly out on the table and you keep pulling the choc slabs further apart as the melt flows out… STOP… let melt choc ‘sea floor’ harden (all this held in your mind)
You should have:
1. A centre line where the melt always flowed out from
2. An area of melt flow on either side of the centre line
3. Two slabs of choc, now separated by 1 & 2 above
That is what is seen on the map pic:
1 = spreading mid-ocean ridge (reddish line all up the mid-ocean)
2 = Oceanic Crust (red yellow green areas, both sides of 1.)
3 = Continental Crust… (grey chunks)
This shifting apart of the tectonic plates at a spreading zone, moves the ‘choc slab’ (Continental Crusts) apart… causing continental drift. The melt choc is molten magma, pouring out, all along the centre-line of the Mid-Atlantic Ridge.
The Mid-Atlantic Ridge is a huge long, still active volcano. This ridge is still spreading today. The Atlantic spreads further apart each year, by several centimetres.
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That’s it… You may now eat your chocolate.
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** The Open University… Oceanography (paid study course) S330… LINK HERE
** The Open University… Nature & Environment (free study courses)… LINK HERE
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