I Igneous rocks II Earth s Heat Magma Igneous Rocks a Melt freezes at about 650oC to 1000oC b Most abundant a Meteorite collisions b Gravitational compression c Sinking heavy elements d Radioactive decay e Earth cooled which led to i Thin skin of igneous rock ii Solidification of mantle f Magma melt underground g Lava melt at surface h Extrusive rocks i At surface 1 Lava flows 2 Pyroclastic debris a Ash bombs cinders i Intrusive rocks i III Magma Formation Inside the earth a Decrease in pressure b Addition of volatiles c Heat transfer IV Magma Composition i Moves to shallower depths i H2O CO2 i Melts surrounding rock a All contain Si O tetrahedron i Al Ca Na K Fe Mg i Up to 15 volatiles Wet magmas b 1 H2O CO2 N2 H2 SO2 2 Vented at volcanoes V Magma Types Intermediate 52 66 silica content a Based on Composition b Felsic 66 76 silica content c d Mafic 45 52 silica content e Ultramafic 38 45 silica content f The higher the silica the lower the melt temperature g Why different magma compositions i Source rock composition ii Partial melting VI Magma Contamination a Assimilation i Rock falls into magma and dissolves b Fractional crystallization i Minerals crystallize ii Precipitate c Magma mixing VII Bowen s Reaction Series a Mafic minerals first b Minerals crystallize at different temperatures in a discontinous series VIII Magma Lava Movement a Tends to move upward i Buoyant 1 Less dense than rock ii Pressure of overlying rock b Raw materials for i New rocks ii Atmosphere iii Oceans i Determines speed magma or lava travels IX Viscosity b Low viscosities flow easier c Viscosity depends on i Temperature ii Volatiles iii Silica d Cooling rate factors Intrusion depth i ii Shape size iii Groundwater X Extrusive Environments a Mafic lavas b Felsic lavas i Low viscosity i High viscosity XI Intrusive Environments a Magma freezes underground b Stoping c Types of intrusions i Baked contact i Tabular or sheet like ii Dikes iii Sills iv Laccoliths v Plutons vi Batholith 1 10s m to 10s km 1 10s 100s of km a Controlled by cooling rate b Interlocking XII Textures c Glassy d Fragmental e Types i Aphanitic fine grained ii Phaneritic coarse grained XIII Classifying Crystalline Igneous Rocks a Light colored minerals rich in silica b Dark colored minerals rich in iron low in silica c Chemically identical rocks i Rhyolite granite ii Andesite diorite iii Basalt gabbro iv Komatiite peridotite XIV Distribution of Igneous Rocks a Four settings i Volcanic arcs 1 Continental vs oceanic island arcs 2 Subducting slab sinks 150 km 3 Volatiles are driven off 4 Erupts as basalt andesite or rhyolite 5 Magma pools at continental crust mantle boundary a Partial melting of peridotite a Forms plutons batholiths ii Hot spots 1 Hot solid rock rises from core mantle boundary 2 Decompression causes partial melting 3 Mafic magma pools in crust 4 Oceanic settings only mafic magma 5 Continental settings mafic and silicic magma 1 Lithosphere thins basaltic magma rises into crust iii Rifts a May follow fractures b Erupts as basalt a Produces rhyolite 2 Partial melting of continental crust iv Flood Basalts v Mid Ocean Ridges 1 Form when hotspots underlie rift zones 2 Large amounts of basaltic material erupts 1 Largest amount of igneous rocks form here 2 Magma forms due to decompression 3 Process of sea floor spreading produces gabbro basalt and or pillow basalts