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Lecture 4

5 Pages

Environmental Science
Course Code
Nick Eyles

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Lecture 4 EESA06 Topics for lecture 4 and for quiz 3 on Thursday Feb 10 Introduction to mid-ocean ridges: modern and ancient fossil MORs (called ophiolites) Why are MORs fractured? The role of transform faults Iceland: walking over a mid-ocean ridge Magnetic stripes recorded in ocean floor crust and the age of ocean floors Basalt lava flows: fissure eruptions Volcanic activity under glaciers: jokulhlaups! o Jokulh- mountain o Laup- leap Geothermal energy Red Sea Embryonic ocean Continues to widen, one day will grow up into a mature, wide ocean like the Atlantic In Iceland is where the mid-ocean ridge come up to sea level Oceans only widen to a certain wide Stages of Rift figure 2.19 As you move away from mid-ocean ridge, thickness of oceanic crust is thickens because it is cooling, as you go away from ridge from either side When you have thick slab of oceanic crust, it wants to sink back to mantle Young oceanic crust- thin, ocean depth is not that deep History of continent dictated by history of the ocean Earth history is really controlled by ocean history Like an accordion- opens and closes Introduction to mid-ocean ridges: modern and ancient fossil MORs (called ophiolites) Oceans closed and they push up on land- ancient pieces of ocean crust- ophiolites Important because they contain minerals Figure 2.8 Mid-ocean ridge, are literally underwater volcano, active all the time If we add new volcanic material, pushing apart something Iceland sitting right astride mid-ocean ridge, it is an island The mid-ocean ridge is not strictly continuous, there are cracks running along ridges, called fractures o Enable ocean floor spreading on the curved earth surface How oceans widen- rocks and a bike picture Continuous intrusion of dikes at MORs Orange strips on rocks- dikes o Result of hot magma intruding onto older rocks along fractures o The rocks are being extended to accommodate the dikes o Older crust that is cooled earlier is being pushed apart- concept of plate movement Result of continuous feeding of magma o Many dikes are called sheeted dikes Magma chamber o Top of magma chamber are sheeted dikes o When magma reaches ocean floor, it cools and find pillow magma, basalt magma was cooled very quickly o Gabbro: chemically the equivalent of basalt, only difference is that it has larger crystals within because it is cooling slowly Igneous rocks cooling slowly
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