ESS 101 Lecture Notes - Lecture 8: Asthenosphere, Yellowstone Caldera, Continental Crust
27 Feb 2017
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Granitic magma forms from a partial melt of continental crust, which contains dissolved water. As granitic magma rises, it solidifies as its melting temperature increases while the geothermal gradient (actual temperature) decreases. Granitic composition magmas rarely reach the surface as volcanic rhyolite flows because of the high water content and corresponding increase in melting temperature as it rises towards the surface. Granitic composition magma is produced at continental collision margins. As the continental crust thickens, it begins to partially melt at depth. Igneous intrusions (plutons) form below the mountain belts. Volcanism is rare in continental collision boundaries. As collisional tectonic mountain ranges are uplifted, the overlying marine sedimentary and metamorphic rocs are eroded, exposing the underlying granitic plutons. The granitic rocks of new hampshire and vermont represent old granitic plutons that were intruded when the appalachian mountains formed 300mya as the north american continent collided with the proto-european continent.
