EPSC 201 Lecture 4: 4-EPSC-Lecture-Notes
26 Jan 2017
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The sea floor acts like a tape recorder that encodes, by magnetic imprinting, the history of the opening of an ocean basin in terms of the history of the geomagnetic field. Are contours of equivalent age of the sea floor. They show the time that has elapsed and the amount of spreading that has occurred since the magnetized rocks were injected as lava into a mid-ocean rift. Ea(cid:396)th"s oute(cid:396) shell is (cid:271)(cid:396)oke(cid:374) i(cid:374)to (cid:396)igid plates that (cid:373)o(cid:448)e a(cid:374)d i(cid:374)te(cid:396)a(cid:272)t i(cid:374) th(cid:396)ee t(cid:455)pes of plate boundaries. Plate tectonics explains the origin and distribution of earthquakes and volcanoes, mountain belts and seamount chains, mid-ocean ridges and deep ocean trenches and changes in past positions of continents and ocean basins. Where land meets ocean: margin near plate boundaries are active, margins far from plate boundaries are passive, earthquakes common along active margins. Passive-margin continental crust thins seaward: traps eroded sediment, develops into continental shell. Lithosphere is fragmented into around 12 major tectonic plates.
