GEOG 1290 Lecture Notes - Lecture 28: Mid-Ocean Ridge, Subduction, Asthenosphere
29 Nov 2014
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Document Summary
Oceanic ridges formed by currents of magma rising from mantle; create new crust on ridges. Older crust descends into earth (melted and recycled) Age of ocean floors based on paleomagnetism. Two plates are moving away from each other because of magma welling up from asthenosphere. No volcanoes but there is magma: oceanic rifts (mid-ocean ridges) most common, rift valleys (land, begins on a continent. East african rift valley: grows to become linear sea ( proto-ocean ) Denser plate (oceanic) subducts beneath continent (lighter: ocean to continent, subduction, earthquakes shallow focus <70 km deep. Deep focus up to 600 km deep. Only at subduction zones rocks: destructive (crust being destroyed, e. g. ) Andes mountains and cascade range: magnitude 8. 7-9. 2, jan 26, 1700, date from: Oral tradition: ocean-to-ocean, subduction, destructive, earthquakes shallow and deep, volcanoes yes, subduction trenches in deep ocean, volcanoes yes magma rises, producing extrusive and intrusive igneous.
