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Lec 05

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University of Toronto Scarborough
Environmental Science
Nick Eyles

Lec 05 thMonday February 6 2012 y Pacific ocean closing surrounding continents coming together y Pacific rim most dangerous place on the planet y Volcanoes steep sided volcanoes o Magma has silica in them and stiffens them so gases cant come out o Sudden release of gas which is propelling o Pyroclastic fire to break magma o These volcanoes produce a lot of ash y The pacific rim of fire o Trenches mark where the floor of the pacific ocean is being pushed down underneath surrounding land masses o Trenches underlying subduction zones o This is how earth recycles ancient crust o Canada is also pacific rim country Vancouver threatened by major earthquake o Continents that surround the rim are growing at the expense of the oceans o Magma erupt along continents and become part of the continents y Dying oceans make bigger continents o Oceanic crust subducted o Blue and yellow stars epicenters o Descending plate will start to melt and magma will rise to surface BUTTTTT the magma is moving up the continental crust and gets contaminated picks up silica o Continents grow as a result o See sediments sea floor sediments being scraped off the descending plateso Sediments being added to the continents o Adding to the continents and recycling to oceanic crust y Subduction II o Density the older thicker plate o The older heavier one going down o Important process volcanic island arc Japan is island arc all volcanoes joined together o What are we creating Creating embryonic continents o Prolly how the firs continents started o Cant subduct the continental crust because of the density o This process of subduction is important o Glimpse of conditions on early earth o 4 billion years ago o Earth consisted a magma ocean before o Next stage was formation of oceans ocean water came out through mantle dewatering of minerals deep in the mantle this is what was thought before o Cools the magma and begins thesubduction
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