Continental plates move when olivine from upper mantle comes through basalt crack {rift}|, pushing plates apart. Pushed plates move one inch per year. Atlantic-Ocean middle has rift north to south that rises above sea level at Iceland, Azores, and Ascension Islands. Southeast South Pacific Ocean and central Indian Ocean have rifts.
Old rift valleys can fill with sediment {aulacogens}.
Along rift, lava makes mountain ridge, with valley down middle {sea floor spreading}|.
Continent granite {shield, continent}| can be at surface.
5-Earth Science-Planet-Plate Tectonics
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Date Modified: 2022.0225