EES 1030 Lecture 11: 11
11 May 2017
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Continents show a marked range of different topographies: there are flat shields and flat platforms, but also mountains, which can be young or old. Oceanic crust is ___________________ dense that continental crust. Mountains form where crust is ___________________________ and they are higher than surrounding crust due to ___________________________. How continents work: we have remnants of crust that are ____________________ of years old preserved at a few locations on earth. These silica-rich rocks are too buoyant to subduct into the denser mantle, and have been cruising around as a result of plate tectonics since their formation. The east coast of the united states is an example of a ____________________ continental margin: over the past 250 million years, it has not accreted anything. Continental crust grades into oceanic crust, which extends out to the mid ocean ridge. These boundaries have no volcanoes and rare earthquakes. In contrast, we make mountains through orogenic processes at ______________________ continental margins.
