Earthquakes 1EarthquakesJessica SvorinichAxia College University of Phoenix2EarthquakesThe Red Sea is an example of Divergent Margins. Divergent margins are a result of twolithospheric plates that move apart. These Divergent Margins can occur either in continental or oceanic crust.Schematic diagram of plate divergence. U.S. Geological Survey image.A divergent zone happens when the plates are pulled apart, not pushed apart. The circumstances that cause a divergent zone is " "slab pull" that arises where plates sink into the mantle under their own weight." This process is known as subduction. The divergent zone pulling motion can uncover the deep mantle rock of the asthenosphere. "As the pressure eases on the deep rocks, they begin to partially melt even though their temperature may fall. (This is called adiabatic melting.) The melted portion expands (as melted solids generally do) and rises, having nowhere else it can go. This magma then freezes onto the trailing edges of the diverging plates, and so the plates grow."http://geology.about.com/library/bl/blnutshell_divergence.htm Says "Lithospheric Plates diverge at a wide range of speeds, giving rise to differences in spreading ridges. Slow-spreading ridges like the Mid-Atlantic Ridge have steeper-sloping sides because it takes less distance for their new lithosphere to cool. They have relatively little magma production so that the ridge crest can develop a deep dropped-down block, a rift valley, at its center. Fast-spreading ridges like the East Pacific Rise make more magma and lack rift valleys.One fact not widely appreciated is that divergent margins move sideways just like the plates themselves do.Divergent margins are passive windows into the asthenosphere, releasing magmas from below wherever they happen to wander. While textbooks often say that plate tectonics is part of a convection cycle in the mantle, that notion cannot be true in the ordinary sense. Mantle rock is lifted to the crust, carried around, and subducted somewhere else, but not in a closed circle."3The text states "Convergent margins occur when two plates move toward each other. This leads to different types of margins, depending on whether the boundary is between two oceanic plates, two continental plates, or one of each.
When one continent meets another continent along a convergent margin, they crumple upwards and downwards as the lithosphere thickens, in a collision zone." Prof. Stephen A. Nelson says. "The convergent plate margins are the most intense areas of active magmatism above sea level at the present time. Most of world's violent volcanic activity occurs along these zones. In addition, much magmatism also has resulted (and probably is resulting at present) in significant additions to the crust in the form of plutonic igneous rocks."The texts also say that another kind of convergent margin occurs when one or both plates are oceanic. "In this case, one...