2Rock of Ages granite quarry, Barre, Vermont What important natural resources are found in igneous rock?
3Stawamus Chief, Squamish BC Mafic dyke (~5 m across)Massive graniteSteven Earle
4Igneous RockIgneous rock is formed when molten, or partially molten, rock solidifies.
5Igneous Rocks (two types) ExtrusiveLava and Pyroclastic DebrisExtruded at surface or at veryshallow levels and cooled quicklyIntrusiveMagma crystallized slowly within the crust.No exposure to the cool atmosphere.Plutonic – intrusive igneous rock cooled slowly at great depth within crust or mantle.Basalt is ExtrusiveGranite is IntrusiveWhat is the key textural difference between these two rocks?
6Why Study Igneous Rocks? All rocks on Earth have evolved from the first igneous rocks through Igneous EvolutionProvide information about the composition of the mantleAbsolute age can be obtained through Radiometric DatingFeatures are characteristic of a specific tectonic environmentHost important mineral deposits (metal ores)Numerous other critical economic usesMillions of people are endangered by volcanoes
7Decompression melting Convection brings hot rock to shallower depthsRifting lowers pressureLower pressure causes a lower melting pointIgneous rock is formed through a process of crystallization and magma differentiationWhy does a lower pressure lower the melting point?
8Partial Melting Partial Melting Magma Differentiation Silica-rich compounds melt before other compounds.Magma DifferentiationFour types:Magma mixingCrystal settlingWall-rock assimilationMagma migration
9Bowen’s Reaction Series Describes the order and process of magma crystallizationBowen’s Reaction Series Animation
10How Are Igneous Rocks Named? TextureTexture depends on crystal sizePhaneritic:Slow cooling (or in the presence of water), larger crystalsCoarse textureIntrusive or PlutonicAphanitic:Rapid cooling , smaller crystalsFiner textureExtrusive or VolcanicOther textures are Glassy, Pyroclastic, Vesicular, and PorphyriticCompositionMinerals at the top of Bowen’sDark in colorMafic to UltramaficIron and Magnesium are dark.Minerals at the bottom of Bowen’sLight in colorFelsicSodium plagioclase, potassium plagioclase, and quartz are lightIntermediate composition between these
11How is Texture Estimated? Texture is estimated using visual grain size(depends on crystallization history)What has to happen for a porphyritic texture to form in an igneous rock?
12How is Composition Estimated? Composition is estimated using visual colorCan be misleading
13Mafic vs. FelsicMafic minerals crystallize early and felsic minerals crystallize late in magmaMinerals at the top of Bowen’s Reaction Series:Dark in colorMafic to ultramaficIron- and magnesium-rich and relatively heavyMinerals at the bottom of Bowen’s Reaction Series:Light in colorIntermediate to FelsicIron- and magnesium-poor and relatively light in weight
14Bowen’s Reaction Series What does olivine react with to produce pyroxene?What is the significance of the word “reaction” in the Bowen Reaction Series?
15Igneous Rock NamingIgneous rocks are named on the basis of their texture and composition
16Igneous Rock Naming (continued) The igneous rock diagram shows the range of mineral proportions of the various types of igneous rocksWhat are the approximate mineral proportions (in %) of the rocks indicated by the two dashed lines?
17Classification System for Igneous Rocks The classification system for igneous rocks is based on the following:Intrusive and extrusive igneous rocks with the same chemical composition contain the same mineralsSilica content decreases as iron and magnesium content increasesPotassium and sodium content decreases as silica content decreases
18Seven Common Types of Igneous Rock Felsic Composition1) Graniteintrusive2) Rhyoliteextrusive
19Seven Common Types of Igneous Rock Intermediate Composition3) Dioriteintrusive4) Andesiteextrusive
20Seven Common Types of Igneous Rock Mafic Composition5) Gabbrointrusive6) Basaltextrusive
21Seven Common Types of Igneous Rock Ultramafic Composition7) Peridotiteintrusive
22Igneous EvolutionAll rocks on Earth have evolved from the first igneous rocksAll Igneous Rocks Result from Magma Differentiation
23Tectonic ProcessesIgneous rock evolves as a product of tectonic processes and is a major component of Earth’s crustWhat is the mechanism that leads to partial melting above a subduction zone?
24Identify the magma source for each type of volcano Identify the magma source for each type of volcano. How is the magma source responsible for the rock composition?
25Basalt Formation (Spreading Centers) High heat flow creates Hydrothermal (hot water) Vents (black smokers)Oceanic crust consists of layers of igneous rockGabbro crystallizes at the baseSheeted dikes of basalt extend above the gabbroPillow basalt, glassy fragments and metallic sulfide deposits (at black smokers) form at the sea floor
26Basalt Formation (Hot Spots) Intraplate sites of active Plutonism and VolcanismLarge Igneous Provinces of Flood Basalts form above mantle hot spotsPlumes of anomalously hot mantle rock underly active hot spots. Mantle plumes, which are solid rock, not magma, rise slowly through the mantle (but faster than the rate of mantle convection) due to their positive buoyancy with respect to the surrounding rock.Basalt is also present at many subduction-related volcanoes, but typically only in minor amounts.
27Modern sea-floor pillow basalt 40 mya pillow basalt on Vancouver IslandSteven Earle
28Igneous IntrusionsIgneous intrusions occur in a variety of sizes and shapes.
29Subduction Zones and Spreading Centre Subduction zones and spreading centers are areas in which magma is formed as a result of partial melting, plutonism, and volcanism.What igneous environment is not represented in this image?