Comment: 09:29 - 10:36 (01:07)
Source: Annenberg/CPB Resources - Earth Revealed - 7. Mountain Building
Keywords: sediment, orogeny, lithosphere, continent, "convergent plate", pressure, subduction, volcano, "island arc", "continental margin", trench, uplift, heat, melting, "metamorphic rock", crust, "igneous rock", granite
Our transcription: Because of differences in density and makeup of continental and oceanic lithosphere, the edge of a continent is a likely place for a convergent plate boundary to form.
If enough pressure is applied, the lithosphere splits.
Heavier than continental lithosphere, the oceanic lithosphere begins sinking or subducting beneath the adjacent continent as the new plates are pushed together.
An orogeny begins as volcanoes form an island arc or belt along the continental margin.
Sea floor sediment between the trench and shore is caught in the squeeze, crumpled up and uplifted.
Ultimately, so much pressure and heat may accumulate that the soft sediment recrystallizes into durable metamorphic rock, the very rock that makes up vast areas of older continental crust.
At high enough temperatures the sediment will even melt, eventually forming igneous rocks such as granite.
Geology School Keywords