SEA FLOOR SPREADING
What is Sea floor spreading?
The process where the oceanic ridges spreads and moves away from the ridge axis with a motion like that of a conveyor belt as new lithosphere is created and it is filled up by the resulting gap is known as seafloor spreading.
Oceanic lithosphere is consumed in the aesthenosphere in the subduction zone and that accommodate the newly created lithosphere. This area of the earth is unaltered linear magnetic anomalies characterized by the seafloor spreading.
Alternative stripe for positive and negative anomalies were caused by bands of basaltic rocks in layer of the oceanic rock crust that were alternate magnetize in normal and reverse direction of the earth magnetic field.
It is propose that the new lithosphere is formed alternate by convective upward current beneath oceanic by migmatic processes.
As magmas in place in the axis rift zone cools through the curie temperature of magnetic mineral they acquire a magnetization in the direction of the existing earth magnetic field.
The newly magnetized crust then splits and is forced apart to make room for fresh injection for magma. The absence of deep sea sediments older than Jurassic is explained by the fact that current sea floor spreading rate of a few centimeters per year indicate that the ocean floor should be completely renewed every (200-300 million years ago).
Importance of seafloor spreading.
Seafloor spreading helps geologists/scientists to explain continental drift in the theory of plate tectonics. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere.
The required force for seafloor spreading ridges is tectonic plate pull rather than magma pressure, although there is typically significant magma activity at spreading ridges.
At the spreading center, basaltic magma from the crust rises up the fractures/faults and cools/crystalized on the ocean floor to form new seabed/crust.
In additionally spreading rates help in the determination, if the ridge is a fast, intermediate, or slow. As a general rule, fast ridges have spreading (opening) rates of more than 9 cm/year. Intermediate ridges have a spreading rate of 5–9 cm/year while slow spreading ridges have a rate less than 5 cm/year link
References
• Link
• Oxford dictionary of geology and earths science