summary 1. the rock cycle 2. formation of igneous rocks 3. classification of igneous rocks

Summary 1. The Rock Cycle 2. Formation of Igneous Rocks 3. Classification of Igneous Rocks

Rock Cycle All rock types can be converted into any other rock type Formation of Sedimentary Rocks (weathering, erosion, deposition, cementation) Formation of Igneous Rocks (subduction, remelting, crystallization) Formation of Metamorphic Rocks (burial, heat and pressure)

Igneous Rocks Formed from magma (liquid rock) Classified in two common ways: 1)Crystal or grain size (relates to crystallization) 2)Chemical Composition (related to colour) Coarse grainedporphyry Fine grained Intermediate Mafic UltramaficFelsic

Grain Size of Igneous Rocks Extrusive (Aphanitic) fine grained Magma is erupted at the surface. (Volcanic) Minerals have little or no time to crystallize Mineral grains are very small (often invisible) Intrusive (Phaneritic) coarse grained Magma cools below the surface. Minerals have time to grow slowly. Mineral grains are larger and are easily visible. In some cases, crystals can grow very large (Pegmatite).

Extrusive (Aphanitic) Rocks Fine grained rock that cooled quickly on the Earths surface. Eruption at the surface causes rapid cooling of lava which does not allow mineral crystals much time to grow. Basalt, the most common extrusive rock, often erupts from the bottom of oceans

Surface Textures of Hawaiian Basalts (Extrusive, Mafic Rocks) Aa (Rubbley) Mostly solid when flowing Pahoehoe (Ropey) mostly liquid when flowing) Hawaiian Volcano eruption http://www.youtube.com/watch? v=WwBVG0Si7rs

Intrusive (Phaneritic) Rocks Course grained rock that cooled slowly under the surface. More time is allowed for crystal growth. Crystals are clearly visible to the eye. This is the most common type of igneous rock. Also described as Plutonic Diapirs a body of magma that rises through another rock (country rock) and then eventually crystallizes as a pluton See Kehew, Fig 3-6

Igneous Rock Textures

Igneous Rock Terminology Intrusive Extrusive Pluton Dike Laccolith Magma Batholith Sill Xenolith Ash Lava volcano

Igneous Intrusions

Igneous Rock Terminology Magma liquid rock that has not solidified or been erupted. Lava recently erupted magma that has yet to solidify Ash fine (often glassy) igneous rock that solidifies rapidly (in the air) during an eruption and is deposited on the surface. Intrusive coarse grained rock not erupted at surface Extrusive - fine grained rock erupted at surface (Volcanic) Pluton A large body of intrusive igneous rock they often form the basis of continental crust.

Igneous Rock Terminology Dike a roughly vertical intrusion of igneous rock that cuts through country rock Laccolith A large igneous body that is intruded horizontally between layers of rock often uplifting the rocks above Batholith A large body of igneous rock Sill A large horizontal intrusion of igneous rock Xenolith a large chunk of country rock that has fallen into a body of magma (often the xenolith undergoes contact metamorphism) Volcano a structure where magma is erupted

Formation of Magma How are rocks melted? 1. Heating Rocks melted in the crust. Rocks carried back into the mantle by subduction or heated from below by a Mantle Plume (Hot Spot) 2. Depressurization Magma requires 10% more volume than the rock. Often rocks remain solid only due to pressure a release in pressure allows rocks to liquify into magma. 3. Partial Melting Only a portion of a pluton is melted, resulting in a magma with a different chemical composition than its parent rock (see Bowens Reaction Series) Types of Volcanism Hawaiian Stratovolcano Intermediate Types of magma? Ultramafic Mafic Intermediate Silicic or Felsic

Chemical Composition of Magma Ultramafic Upper Mantle Less than 45% Silica (SiO 2 ) Very high Mg, Fe (20-30%) olivine and pyroxenes, no Qtz Dark minerals (green, black) Peridotite Mafic Oceanic Crust 45-55% Silica (SiO 2 ) High Mg and Fe (10 - 20%) Dark minerals, no Qtz Basalt, Gabbro Intermediate Cordilleran Mountains (ex Andes, Rockies) 55-63% Silica (SiO 2 ) 5-10% Mg + Fe Mix of light and dark minerals, some Qtz Andesite, Diorite Silicic or Felsic Continental crust Greater than 63% silica 0-5% Mg + Fe High in Group 1 metals (K, Na, Light coloured minerals Orthoclase and abundant Qtz Rhyolite, Granite

Classification of Igneous Rocks Remember that grain size and chemistry are the two main factors when classifying igneous rocks. Grain Size reflects the rate at which magma cools there are two major classifications intrusive and extrusive Chemistry reflects the colour of the minerals and is ultimately related to the geological source of the rocks (oceanic, continental, mix (at subduction zones))

Igneous Rock Classification

Igneous Rock Classification Exercise Materials: 1) Pencil crayons 2 shades of green, white, gray (regular pencil), black, red or pink 2) Igneous rock diagram sheet.

Igneous Rock Classification Intrusive (Plutonic) Extrusive (Volcanic) Mineral Percentage Continental Crust Oceanic Mantle Crust

Igneous Rock Classification Silicic Intermediate Mafic Granite Diorite Gabbro Rhyolite Andesite Basalt (Porphyritic) Intrusive Extrusive

Granite most common intrusive, course-grained Rhyolite rare extrusive, fine-grained rocks Rhyolite Volcanoes very explosive - Yellowstone Park (no cone only a massive 75 km wide caldera) Felsic (a.k.a, silicic) Magmas Cool (

Intrusive Felsic Igneous Rock Granite (Silicic, Phaneritic): Poor in: Fe, Mg, Ca Rich in: Silica (>63%) Rich in: Al, K, Na Light Coloured Coarse Grained Pegmatites show coarse grained crystals Orthoclase, Quartz, Amphibole, Micas http://www.youtube.com/watc h?v=nWNE_f6HqAk

Extrusive Felsic Igneous Rock Rhyolite (Silicic, Aphanitic): Poor in: Fe, Mg, Ca Rich in: Silica (>63%) Rich in: Al, K, Na Light Coloured usually grey Fine Grained Often Ash (Welded Tuff) may contain obsidian Orthoclase, Quartz, Amphibole, Micas http://www.youtube.com/watc h?v=nWNE_f6HqAk

Felsic Volcanism Mantle plumes intrude through the continental crust Magma is very silicic, highly gaseous, low temperature and pressure builds for millenia The volcanism is highly explosive The Yellowstone caldera is 75 km across

Intermediate Rocks Andesite (common) Extrusive, Fine-grained, intermediate rocks are found in subduction zones Diorite Intrusive, Course-grained. If intrusive, Dikes and Sills more common Intermediate Magmas Vary (700 - 1000 o C) Produce lavas and ash and therefore can be unpredictable. Lower temperature magmas are gassy and explosive (ex. Mt. St. Helens and Vesuvius)

Extrusive Intermediate Igneous Rock Andesite (Intermediate, Aphanitic): High in: Ca, Al Rich in: Silica (55-65%) Median amounts of: Al, K, Na, Mg, Fe Colour mixture of light and dark Fine Grained and Porphyritic Orthoclase and Plagioclase, low Quartz, low pyroxene, amphibole, Micas

Intrusive Intermediate Igneous Rock Diorite (Intermediate, Phaneritic): High in: Ca, Al Rich in: Silica (55-65%) Median amounts of: Al, K, Na, Mg, Fe Colour mixture of light and dark Fine Grained - Orthoclase and Plagioclase, low Quartz, Amphibole, low pyroxene, micas

Types of Volcanoes - Intermediate Composite Volcanoes (Stratovolcanoes) - interayered lava flows and pyroclastic deposits - ranges from intermediate to felsic in composition (andesite-dacite-rhyolite) - in volcanic arcs above subduction zones Composite Volcanoes The more felsic these volcanoes, the more explosive. They can be subdivided into: Strombolian Vulcanian Plinian Peleean

Intermediate Volcanism

Stratovolcanoes Pyroclastic flows A mixture of ash, small lava bombs and hot gases that can race down the side of a volcano at speeds of up to 200 km an hour this the biggest killer in most volcanic eruptions. Lahars pyroclastic material melts the glaciers on the sides of mountains forming a rapidly moving mudflow this was the greatest killer in the Cerro Arenal eruption in Columbia. Lava - Slow moving andesitic lava flows.

Mafic Rocks Basalt (very common) Extrusive, Fine-grained, Mafic rock forms oceanic crust, Shield Volcanoes and Basalt Floods Gabbro Intrusive, Course-grained. If intrusive, Dikes and Sills more common Mafic Magmas Hot (>1000 o C) Non-Viscous (runny, flows easily) Dry (no H 2 O or C0 2 ) See Kehew, Fig 3-40

Extrusive Mafic Igneous Rock E.g., Basalt (Mafic, Aphanitic): Poor in: Si(45-55%) Poor in: K, Na Rich in: Mg, Fe, some Ca Rich in: Al, K, Na Dark Coloured Fine Grained Plagioclase, Amphibole or Pyroxene, maybe Olivine, no Quartz, dark mica Pillow Lava

Intrusive Mafic Igneous Rock E.g., Gabbro (Mafic, Phaneritic): Poor in: Si(45-55%) Poor in: K, Na Rich in: Mg, Fe, some Ca Rich in: Al, K, Na Dark Colured Coarse Grained Plagioclase, Amphibole or Pyroxene, maybe Olivine, no Quartz, dark mica

Types of Volcanism Mafic (Basalt) Shield Hawaiian, Iceland Cinder Cones Intermediate (Andesite) Composite Volcanoes (Stratovolcanoes) Vesuvius, Mt. St. Helens, Mt. Fuji Felsic (Rhyolite) Mid-Continent Volcanism - Yellowstone

Types of Volcanism

Types of Volcanoes - Mafic 1) Shield Volcanoes - low viscosity basaltic magmas - lava lakes and flows common - not explosive - flood basalts and submarine pillow lavas are basaltic, too Shield Volcanoes 2) Cinder Cones - variable composition, often basaltic - usually a single batch of magma - steep cones formed by cinders piled around vent at angle of repose associated with shield volcanoes Cinder Cones

Mafic Volcanism, Hawaii Mantle Hot Spot Volcano See Kehew, 3-8

Hawaii 10.3 12.0 20.6 Midway 27.2 19.9 43.4 42.4 48.1 55.2 56.2 59.6 0-5 Current Plate Motion Hawaii A long chain of inactive volcanoes Island ages, millions of years

Shield Volcanoes Mafic Magma Low-viscosity Non-explosive eruptions Gentle slopes Covering large areas

Shield Volcanoes

Another method of classifying volcanos

Types of Eruptions (Mafic Volcanism) Types of Eruptions Lava floods Lava fountains Fissure eruptions Rock Textures (Table 3-1) Aphanitic Porphyritic Vesicular Glassy (Obsidian)

Mafic Sill: Intruded between layers Mafic magma is less viscous and hotter so Does not form plutons but Cuts along layers (Sills) or even across layers (Dikes) Also Baked Zones of adjacent country rock and Chill Zones within the intrusion

Mafic Volcanic Features Columnar Basalt The Giants Causeway (N. Ireland) Lava flows reaching the ocean, Kilauea, Hawaii Pumice basalt with gas bubbles

Types of Volcanoes - Felsic Dome Volcanoes - similar in composition and often related to composite volcanoes - usually more viscous (more silicic) magma type (dacite/rhyolite) - pyroclastic flows abundant - explosive eruptions common Dome Volcanoes Continental Calderas - in continental regions the result of the largest types of volcanic eruptions - large, shallow, silicic magma chambers empty catastrophically with unparalleled violence; roof of magma chamber collapses into emptied portion of magma chamber. The Yellowstone caldera is over 100 km across. Continental Calderas

Types of eruptions Felsic (Silicic) Uncommon usually form at continental hot spots such as Yellowstone. Extraordinarily violent due to the high gas content and low vicosity of the lava. See the videos Yellowstone Supervolcano video http://www.youtube.com/ watch?v=Ap_YUwdiy8I http://www.youtube.com/ watch?v=Ap_YUwdiy8I http://www.youtube.com/ watch?feature=endscreen& v=aVUx1JtT-5I&NR=1 http://www.youtube.com/ watch?feature=endscreen& v=aVUx1JtT-5I&NR=1

Types of Eruptions (Intermediate) Higher gas content due to water content in subducted crust and higher gas content of continental crust Formation of Composite Volcanos (Mt. Fuji, Mt. St. Helens, Etna, Vesuvius) Mt. St. Helens eruption, 1980 http://www.youtube.com/wat ch?v=-H_HZVY1tT4 http://www.youtube.com/wat ch?v=gmwylbF3-CA

10 most active volcanos and dangers related to volcanos 10 most active volcanos: http://www.youtube.com/watch?v=4aYQixhdWY4 http://www.youtube.com/watch?v=4aYQixhdWY4 Lake Nyos Videos (volcanic gas release): http://www.youtube.com/watch?v=eHvPI_pYZBs&list=LPEB BnueOle7g&index=6&feature=plcp http://www.youtube.com/watch?v=eHvPI_pYZBs&list=LPEB BnueOle7g&index=6&feature=plcp http://www.youtube.com/watch?v=pVMcSvG5Mpg Nevada del Ruiz, Columbia (Lahar volcanic mudflow) http://www.youtube.com/watch?v=3XMS-quxdGg Pyroclastic Flow http://www.youtube.com/watch?v=yvG_N7eqMWk

Location of Igneous Rock Production Sea-Floor Spreading Zones Mid-Ocean Ridges Iceland Subduction Zones (Crustal Melting) Cordilleran Mountains (Andes Mtns., Vesuvius) Island Arcs (Japan, Aleutian Islands) Mid-Plate Hot Spots Hawaii (mid-ocean) Yellowstone (mid-continent)

Sea Floor Spreading (Mid-Ocean Ridge) Magma is constantly erupted from the sea floor at mid-ocean ridges. (ex. Mid Atlantic ridge) Mostly intrusive basalt Dark coloured lavas Forms the bulk of oceanic crust which is denser and thinner than continental crust

Subduction Zones Ocean Crust is forced under the continental crust and melts Oceanic crust melts due to heat and release of H 2 O Mafic magma mixes with felsic continental crust to make intermediate rocks Often massive stratovolcanoes are formed

Mantle Plumes or Hot Spots Due to convection in the upper Mantle, plumes of hot mantle rise through the crust and produce a variety of volcanic features: Island Arcs (Hawaiian Islands) with shield volcanoes Continental Flood Basalts (Deccan Traps) Yellowstone style continental Hot Spots

1200 o C 1000 o Bowens Reaction Series Two series of minerals formed during crystallization of magma Intrus. Extrus. Gabbro Basalt Diorite Andesite Granite Rhyolite Low Silica Magma High Silica Magma Frame- Double Single Isolated work Sheet Chain Chain Temperature of Crystallization 750 o

Bowens Reaction Series Illustrates the relationship between the cooling magma and the crystallization of the minerals contained in the rock. Rocks on the right side of this chart are rich in calcium and sodium Rocks on the left side represents iron-rich minerals. They cool and create quartz.

Bowens Dilemma Problem The Mantle is the source of most igneous rocks. So, if the mantle is made of ultramafic rocks how come continental crust is felsic? And how can felsic rocks be produced from an ultramafic source? ANSWER Think of the Bowens Reaction Series

Partial Melting Different minerals melt at different temperatures. As the temperature of a rock rises, minerals melt in the reverse order in which they cooled the Bowens reaction series in reverse! Even if the rock was mafic or ultra mafic, the magma produced can be felsic if the temperatures only rise to 700-800C This explains why continental rocks are felsic they are partially melted oceanic crust

Terminology Felsic or Silicic silicate minerals, magmas and rocks enriched in lighter elements such as oxygen, aluminum, sodium, and silicon.

Terminology Mafic iron and magnesium enriched minerals are found in these rocks. They are dark in colour. Phaneritic Grains in the rock can be seen by the naked eye.

Peridotite Ultrabasic Rare and part of the mantle Course grained Green in colour

Obsidian Glassy (volcanic glass) Glass is produced when any rock is cooled immediately Can be green or black Extrusive Often used by native cultures to produce cutting tools or arrows

Pumice or Scoria Glassy (Frothy) Light (Pumice) to dark (Scoria) in colour depending on its impurities. Solidified foam Extrusive Can float on water

Homework P. 106 #1-3 P. 113 #1-4

Rocks in the Collection 1. Grantie 2. Rhyolite 3. Andesite 4. Obsidian 5. Pumice 6. Basalt 7. Gabbro 8. Anorthosite 9. Diorite 10. Scoria 11. Syenite 12. Peridotite

summary 1. the rock cycle 2. formation of igneous rocks 3. classification of igneous rocks

Documents

rock country rock

igneous rock textures

glassy igneous rock

rock cycle

rock types

layers of rock

common type of igneous

common extrusive rock