ENVIRON 222 Lecture Notes - Lecture 6: Accretionary Wedge, Volcanic Arc, Convergent Boundary
Document Summary
At mid-ocean ridges, new crust is formed by process of plate separation and upwelling of hot, lower density asthenosphere (seafloor spreading) At a divergent plate boundary, two plates separate from each other. At a convergent plate boundary, two plates come together. Divergent plate boundaries are often associated with material upwelling from below. Location where 2 plates slide past one another horizontally. Fracture zones are a dominant feature of the seafloor. Heating and release of gases at depth causes melting of basalt and granite, creating intermediation composition rocks (andesite) High volatile content of andesitic magmas makes them explosive. Volcanoes form linear, arc-like shapes along continent, reflect position of subducting slab. Lithosphere cools as it moves away from ridge. Becomes more dense than underlying asthenosphere and sinks at subduction zones. Sinking lithosphere provides tensional stress (pull) on plate. Fastest plate movements is in the pacific, which is lined by subduction zones. Atlantic is getting larger (no subduction, just mid-ocean ridges)
