Why 13N in the Atlantic?

Why 13N in the Atlantic? That is a good question.

The central Atlantic marks one of the places on the Earth’s surface where there is a boundary between two tectonic plates that comprise the hard outer shell of the Earth. In the Atlantic, two plates are separating and new oceanic crust is being created in the gap in-between. Also, the Earth is sphere-like and so such boundaries between plates are broken up into segments which slide past each other along large-scale faults called fracture zones. The seabed is very deep indeed within a fracture zone and so their location is very easy to spot simply by measuring seabed depth.

 

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In this map of seabed depth, covering the region 12 deg 30 min N to 15 deg 20 min N and 44 deg W to 45 deg 50 min W, the east-west trending fracture zones that mark the ends of the 13N Mid-Atlantic Ridge segment are clearly shown by the deep water areas coloured in blue. The place where the two plates are separating, trending north-south, is also relatively deeper than the surrounding seabed, and is bound to either side by a series of parallel fault scarps. These fault terraces give the seabed its north-south stripy appearance.

What makes 13N special are the features located on the Mid-Atlantic Ridge at 13 deg 20N and 13 deg 30N – the yellow-coloured E-W trending lumps in the map above. These have been sampled and the rocks recovered are of the type that we would normally expect to find deep within the oceanic crust some 6 to 8 km below the seabed. What are these rocks doing at the surface? How did they get there?

Our mission is to image what lies beneath and between these two features which are called oceanic core complexes and we will deploy a grid of instruments onto the seabed covering these features and then make sound waves to do the imaging. Our plan of attack is shown below and it will take us, working 24 hrs a day in shifts, about 2.5 days to deploy these instruments, about 4 days to make the number of necessary sound sources along the survey profiles, and about 4 days to recover all the instruments.

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If all of the instruments work correctly we will record of the order of 1 Tbyte of data. We will, of course, also record any local and global earthquakes that happen while we are doing our own imaging, to add to the data set.

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