To the left, I state a conventional definition of the derivative of the function in question. When x is negative as it is on the second line of the derivation, the numerator (|x + dx| - |x|) is -dx because dx is always a positive number. Thus the derivative is -1. On the third line when x is positive, this simplifies to +1.
Plate subduction occurs when two tectonic plates converge and at least one of them is an oceanic plate. Oceanic plates are formed at divergent plate boundaries from dense basaltic magma. This magma originates from the mantle beneath and fills the gap between the spreading plates.
This is a particularly interesting area to study because we can observe two types of plate boundaries (divergent and convergent) and their processes in very close proximity. A divergent boundary occurs when two tectonic plates move away from each other.Along these boundaries, lava spews from long fissures and geysers spurt superheated water. Frequent earthquakes strike along the rift. Beneath the rift, magmaâmolten rockârises from the mantle.here are three kinds of plate tectonic boundaries: divergent, convergent, and transform plate boundaries. This image shows the three main types of plate boundaries: divergent, convergent, and transform. Image courtesy of the U.S. Geological Survey.