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Rocks Tell Stories Records of Geologic Past Rock Classification – 3 major groups based on their methods of formation or origin 1. Igneous rocks … from cooling and solidification of lava or magma 2. Sedimentary rocks … from compacted and cemented sediments, or chemical precipitates or evaporites 3. Metamorphic rocks … meta (change) morphic (form) … rocks changed by heat and pressure – but remain solid IGNEOUS ROCKS MAGMA VS. LAVA Magma – molten material BELOW the surface of the Earth Lava – molten material AT OR ABOVE earth’s surface ENVIRONMENT OF FORMATION COOLING HISTORY MAGMA LAVA Intrusive – below the surface Extrusive - above the surface A pluton is a body or chamber of magma deep inside the crust. Ejected from volcano Rocks formed when magma Rocks formed when lava cools and solidifies are called cools and solidifies are called INTRUSIVE (PLUTONIC) EXTRUSIVE (VOLCANIC) EXTRUSIVE FEATURES VOLCANO - landforms generated when lava is released from the Earth’s interior through openings. Magma Intrusive Features - Plutonic IGNEOUS ROCKS ARE CLASSIFIED BASED ON 2 MAIN CHARACTERISTICS • TEXTURE – MINERAL GRAIN SIZE • MINERAL COMPOSITION Classification of Igneous Rocks by Texture • WHAT IS TEXTURE? It is not how it feels SIZE OF MINERAL CRYSTALS What controls texture? How fast an igneous rock cools. What controls how fast an igneous rock cools? Where the rock is formed. slower cooling coarser crystals deep in ground Classification of Igneous Rocks – Texture or Grain Size Extrusive Extrusive Intrusive Intrusive Volcanic LAVA VolcanicLAVA Plutonic MAGMA Plutonic MAGMA Extremely fast cooling Fast Cooling Slow Cooling Extremely slow cooling NonFine-grained crystalline Glassy vesicular (gas pockets) Coarsegrained Very Coarsegrained EXTRUSIVE – VOLCANIC - LAVA • When lava cools extremely fast crystals have no time to form – JUST FROZEN IN PLACE RANDOMLY WHEN LAVA ENTERS ATMOSPHERE OR WATER • GLASSY – NON-CRYSTALLINE Non-vesicular Vesicular gas pockets EXTRUSIVE – VOLCANIC - LAVA Lava that cools fast at or near the Earth’s surface Produces small crystals FINE-GRAINED TEXTURE not easily seen with the naked eye. INTRUSIVE – PLUTONIC - MAGMA Magma that cools slowly deep underground produces large crystals COARSE-GRAINED TEXTURE easily seen with the naked eye. INTRUSIVE – PLUTONIC - MAGMA EXTREMELY SLOW COOLING HAS ABNORMALLY LARGE CRYSTALS AND IS VERY COARSE. IGNEOUS ROCK MANTRA • INTERGROWN CRYSTALS IN A RANDOM PATTERN FOR ALL ROCKS EXCEPT: NO CRYSTALS • OBSIDIAN – GLASSY • PUMICE, SCORIA, VESICULAR BASALT – GAS POCKETS OR VESICULAR IGNEOUS ROCK COMPOSITION CONTINENTAL CRUST GRANITE – coarse-grained (continental crust) RHYOLITE – fine-grained OBSIDIAN - glassy and PUMICE - porous (vesicular). PEGMATITE - very coarse-grained IGNEOUS ROCK COMPOSITION MAFIC ROCKS –OCEANIC CRUST GABBRO – coarse-grained BASALT – fine-grained (ocean crust) SCORIA – vesicular (gas pockets) VESICULAR BASALT – vesicular INTRUSIVE EXTRUSIVE Granite Rhyolite Figure 4.7 A MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE Intrusive vs. Extrusive INTRUSIVE EXTRUSIVE MINERAL COMPOSITION THE SAME ---- TEXTURE ONLY DIFFERENCE Andesite Diorite Intrusive vs. Extrusive INTRUSIVE Gabbro EXTRUSIVE Basalt MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE Intrusive vs. Extrusive WHAT GRAPH BELOW SHOWS AS TIME INCREASES THE CRYSTAL SIZE INCREASES? A B VOLCANISM Has produced most of the water on Earth. Has vastly modified the Earth’s atmosphere. Has created new land. Produces fertile agricultural land. Provides a source of geothermal energy in Iceland and California. Presents significant natural hazard. VOLCANOES AND VOLCANISM The Nature and Status of Volcanoes EXTINCT - has not erupted in very long time, generally > 10,000 years. Shiprock, New Mexico VOLCANOES AND VOLCANISM The Nature and Status of Volcanoes DORMANT - has not erupted in past 2000-3000 years, but has potential to erupt. Mt. Baker, WA Chiliques volcano in Chile. VOLCANOES AND VOLCANISM The Nature and Status of Volcanoes ACTIVE - currently erupting volcano or one that has erupted recently. Mt. Lassen, CA Kilauea, HI Explosive vs Non-explosive VOLCANOES AND VOLCANISM Mt. St. Helens, WA 17 May 1980 VOLCANOES AND VOLCANISM Mt. St. Helens, WA 18 May 1980 VOLCANOES AND VOLCANISM Mt. St. Helens, WA 19 May 1982 SEDIMENTARY ROCKS Sedimentary Rocks • 80 % of Earth’s surface is covered with sediments and Sedimentary Rocks What is sediment???? Broken pieces of rocks called CLASTS Chemical precipitates ( dissolved solids come out of solution) Organic fragments – shells, decayed plant matter – this is called BIOCLASTIC Source of Sediment When Igneous, Metamorphic Rocks, and Sedimentary Rocks are uncovered and exposed to the atmosphere and hydrosphere they start to break down Weathering is the general term for all actions that break down or wear away rock Erosion is the carrying away of the sediment Sedimentary Rocks form when sediments/clasts are transported to large bodies of water and are … Deposited in horizontal layers called beds or strata Buried Compacted – particles forced extremely close together because of the pressure of the overlying layers and water Cemented – glued together Sedimentary Rocks Sediments that are eroded settle to the bottom of the rivers, lakes, and oceans Layer after layer of eroded earth is deposited on top of each other Cementing Material (Glue) • Minerals precipitate out of solution to cement particles together. Cementing material is often quartz, calcite, and hematite Most Sedimentary Rocks form under large bodies of water, such as lakes, seas, and oceans Horizontal layers deposited under water E D C B A Future index fossil! According to the law of Super position which layer is the oldest? Classification of Sedimentary Rocks • We classify sedimentary rocks depending whether the sediments are LAND DERIVED (came from) CHEMICALLY - ORGANICALLY DERIVED INORGANIC LAND DERIVED Main source of clasts are from pre- existing igneous, metamorphic or other sedimentary rocks that have been weathered. Sand Composition Varies BUT TO BE CONSIDERED SAND THE GRAIN SIZE IS BETWEEN 0.2 -0.006 CM. Sediments are pebbles, cobbles, and boulders rounded Breccia angular Silt (0.006 to 0.0004 cms. SILTSTONE Sand (0.2 to 0.006 cms.) SANDSTONE Clay (less than 0.0004 cms.) SHALE CHEMICAL Sedimentary Rocks Sediment From Solution All liquid water contains dissolved minerals. These minerals precipitate (dissolved solids come out of solution/water) Usually happens because of evaporation Characteristics of Chemically Formed Sedimentary Rocks They are monominerallic – consisting of intergrown crystals of just 1 mineral. Form in shallow seas ROCK SALT Intergrown crystals of just 1 mineral DOLOSTONE ROCK GYPSUM ORGANIC Sedimentary Rocks Bioclastic Sediment LIMESTONE AND CORALS • Dissolved minerals (CaCO3) taken out of solution by marine organisms for their hard parts (shells) pile up on the seafloor when they die. • These fossil remains accumulate into a thick enough layer to form an “organic” sedimentary rock • Cement is commonly calcite ( Test = bubbles with acid) COAL • Decayed plant remains • Peat-> • Lignite-> • Bituminous-> • Anthracite-> • Crude Oil-> • Natural gas BIOCLASTIC LIMESTONE COAL (Bituminous) CHEMICALLY PRECIPITATED LIMESTONE LIMESTONE forming THE SIZE OF THE GRAIN IS DETERMINED BY THE ENVIRONMENT OF FORMATION HIGH ENERGY ENVIRONMENT Large particles Fast moving water – rivers, ocean waves LOW ENERGY ENVIRONMENT Small particles Slow moving water – lake, bay, swamp SEDIMENTARY ROCK WHERE IT WAS PUT TOGETHER CONGLOMERATE BRECCIA HIGH ENERGY SANDSTONE MEDIUM ENERGY SILSTONE LOW ENERGY SHALE VERY LOW ENERGY Environment of Formation Ocean Derived Sedimentary Rocks Sedimentary Rocks help us understand our past geologic history There is evidence of climate change as well as lost species of plants and animals in Sedimentary Rocks During the Cretaceous Period (about 120 mya) a shallow inland sea split North America. We know this by the Sedimentary Rocks deposited in the former shallow sea Cretaceous Limestone Deposits in Kansas HORIZONTAL LAYERS MUDCRACKS ALTERNATING WET AND DRY CONDITIONS Limestone - FOSSILS SEDIMENTARY ROCK MANTRA 1.COMPACTED AND CEMENTED SEDIMENTS FOSSILS RIPPLE MARKS MUDCRACKS METAMORPHIC ROCKS METAMORPHIC ROCKS META = CHANGE Called MORPH = FORM the “Cinderella Rock” Start with pre-existing rock and change to another rock – but these changes occur in the SOLID STATE METAMORPHISM Process by which igneous, sedimentary, or another metamorphic rock called the “parent rock” undergoes changes in minerals and texture METAMORPHISM Occurs in rocks due to the effects of • High temperature • High pressure HEAT EFFECTS Temperature increases with depth or contact with magma Recrystallization – a process that forms new mineral crystals because the mineral is no longer stable at the new temperature • Changes to a new (high temperature) mineral PRESSURE EFFECTS Pressure increases with depth – weight of overlying rock Mineral crystals grow larger Mineral crystals are more dense Mineral crystals grow perpendicular to pressure Mineral crystals are arranged in parallel layers – PRODUCES FOLIATION FOLIATION Pressure actually rearranges the minerals into parallel layers. More pressure – minerals grow larger and recrystallize and separate into layers Even more pressure – alternating layers of light and dark minerals called Banding Random arrangement of minerals Organized arrangement of minerals - banding METAMORPHIC ROCK MANTRA • INTERGROWN CRYSTALS IN AN ORGANIZED PATTERN Granite Intergrown crystals random pattern Gneiss Intergrown crystals Organized Pattern 2 Types of Metamorphism 1. Regional Metamorphism – Occurs over large areas where there is active mountain building a) Convergent plate boundaries 2. Contact Metamorphism – areas in contact with magma intrusions and/or lava extrusions MOUNTAIN BUILDING GRADES OF METAMORPHISM LOW GRADE – LESS HEAT AND PRESSURE – SLATE HIGH GRADE – MORE HEAT AND PRESSURE - GNEISS FOLIATED METAMORPHIC ROCKS METAMORPHIC ROCKS WILL OFTEN BE DEFORMED BECAUSE OF INTENSE HEAT AND PRESSURE LOOK AT ROCK SYMBOL FOR GNEISS DEFORMED GNEISS A metamorphic rock exposed to too much heat will melt and become ??? MAGMA CONTACT METAMORPHISM Contact Metamorphic • Metamorphism means "changed form". • The Changes occur because of: • Heat from magma intruding on the surrounding rock • Very little pressure Near magma chambers (plutons) Rocks in “contact” with the magma are baked New minerals are formed – recrystallization Transition zone of contact metamorphism is usually relatively narrow baking the adjacent rocks Contact Metamorphism – Baking the adjacent rocks Symbol for Contact Metamorphism is a line with tick marks When limestone undergoes contact metamorphism what rock will it metamorphose into? Marble! PARENT ROCK IN THE COMMENTS LIMESTONE METAMORPHOSES INTO MARBLE SANDSTONE METAMORPHOSES INTO QUARTZITE