Tectonics Topic 1.3 (magnetic stripping)

magnetic striping

Magnetic striping → zebra like pattern where there are strips of normal polarity rocks alternating alongside strips of reversed polarity rocks on the seafloor 

• Symmetrical or both sides of the mid ocean ridge

• Magnetic stripping occurs as : 

• Basaltic rocks from the oceanic crust are volcanic rocks formed from iron-rich lava

• Contain magnetic materials

• When the iron rich lava erupts, it cools and solidifies

• Its magnetic materials point towards earth’s magnetic north, recording evidence of earth’s polarity at that time

normal vs reverse polarity

• Earth has a geographic north and a geographic south + magnetic north and magnetic south 

• Geographic north and south do not change

• Magnetic north and south can shift, and they have reversed multiple times over geological time 

• Normal polarity → magnetic north points towards geographic north, magnetic south points towards geographic south

• Reverse polarity → magnetic north points towards geographic south, magnetic south points towards geographic north

evidence of magnetic stripping which supports plate tectonic theory

Zebra like pattern is symmetrical on either side of mid-ocean ridges, showing that it is not a random or isolated occurrence

zebra like pattern provides evidence that …

• Oceanic plates move away from each other

• Iron-rich lava erupts from the centre of the ridge

• Lava cools, solidifies and forms new oceanic crust

• Crust is then pushed in both directions away from the ridge when new lava erupts and solidifies as plates move apart

• When earth’s polarity reverses, the rocks record the reversals

• Over time, as more lava moves away from the ridge due to plate divergence, a symmetrical zebra-like pattern forms