GEO 1111 Lecture Notes - Lecture 11: Oceanic Crust, Geothermal Gradient, Protolith

• School: University of Ottawa
• Department: Geology
• Course: GEO 1111
• Professor: Donald Cummings

Document Summary

Magma : hot, liquid rock with crystals, fragments of rock, and gas that exists below the earth surface. Lava : hot, liquid rock with crystals, fragments of rock and gas that exist at the earth surface. Geothermal gradient insufficient to instigate partial melting of rocks. Temp increases with depth in the earth, along the geothermal gradient. Magmas and igneous rocks are generated : hotspots, spreading ridges, subduction zones. Magmas are generated by the partial melting of pre-existing source rocks (mantle, crust) Partial melting instigated in three ways : temp increase (ex, hotspots) 2. pressure decrease - decompression melting (ex. mid-oceanic ridges) 3. flux melting -introduction of volatiles (water) which act like road salt on ice to depress the rock"s melting point (ex. subduction zones) When it reaches the surface, it erupts : lava. Lava crystallizes to form extrusive rocks (volcanic rocks) Most magmas crystallize before they reach the surface - generate intrusive (plutonic) rocks.