Magnetic Striping: Why Do We Care?
As magma rises out of the Earth’s mantle, materials that compose it assume the polarity of the Earth’s current geomagnetic field before it then solidifies into oceanic crust. This creation of new oceanic crust by volcanic activity is known as seafloor spreading, and occurs at mid-ocean ridges.
A spreading centre is the location where new ocean crust forms. Outwards from spreading centres, the crust can be seen to have separated into parallel strips of rock that form as a result of waves of newly arising magma. When the geomagnetic or magnetic field of the Earth reverses, the polarity change can be seen in the solidified magma therefore creating a pattern of stripes with alternating magnetism.
These stripes are formed from molten basalt (an igneous rock, low is silica and rich in iron + magnesium) which captures the magnetic orientation at the time acting like a kind of magnetic tape.
In order to determine the location of a virtual magnetic pole relative to the location of the magnetic stripe, researchers consider two factors through investigation.
Firstly, if the rock is formed at the magnetic equator it contains the horizontal magnetisation in the rock, however if the rock stripes are formed at higher ‘magnetic latitudes’ contain a field that points up or down at an inclination.
Secondly, looking at declining gradients reveals the direction of the magnetic pole at the time of rock formation and magnetisation.
The Earth’s Magnetic Field:
The magnetic field is dipolar, meaning that it has two poles these being the north and south magnetic poles. The further away from the surface the more warped the dipole.
"...when the geomagnetic or magnetic field of the Earth reverses, the polarity change can be seen in the solidified magma..."