Magnetic striping
Also called: Magnetic anomalies, Normal and reverse polarity · Topic: Continental Drift, Sea-floor Spreading and Plate Tectonics · NCERT: Class 11, Ch 4 "Distribution of Oceans and Continents"
Meaning
Magnetic striping means the parallel bands of ocean-floor rock that run alongside mid-ocean ridges. The bands alternate between normal polarity (magnetised the same way as today's magnetic field) and reversed polarity (magnetised the opposite way). When lava cools at a ridge, its magnetic minerals line up with the earth's field at that time. The earth's field has flipped many times, so each new strip of crust records the field as it was when the strip formed. The pattern on one side of the ridge is a mirror image of the other side. In 1963 Vine, Matthews and Morley explained the stripes as a "tape recorder" of spreading, and this became the deciding proof of sea-floor spreading. The width of the stripes also gives the rate of plate movement.
Example
Vine and Matthews studied the magnetic stripes over the Carlsberg Ridge in the north-western Indian Ocean, south-west of India. The symmetrical bands there helped prove that the sea floor spreads out from the ridge.
Don't confuse with
- Palaeomagnetism: Palaeomagnetism is the general study of magnetism locked in old rocks. It is used, for example, to trace India's past positions from rocks of the Nagpur area. Magnetic striping is one specific pattern of that magnetism, found on the ocean floor.