Materials of the Earth GEO01 - Earth Science PDF

Official Business Materials of the Earth Course Outcome 2 GEO01 – Earth Science Materials Prepared by: Ryo Jerome C. Tuzon, LPT Video Lecture Prepared by: Perseval S. Pin...

Official Business Materials of the Earth Course Outcome 2 GEO01 – Earth Science Materials Prepared by: Ryo Jerome C. Tuzon, LPT Video Lecture Prepared by: Perseval S. Pineda, LPT Official Business Igneous Rocks, Intrusive Activity, and the Origin of Igneous Rocks Official Business The Rock Cycle Rock – a naturally formed, consolidated material usually composed of grains of one or more minerals. Rock cycle – shows how one type of rocky material gets transformed into another. Representation of how rocks are formed, broken down, and processed in response to changing conditions. Processes may involve interactions of geosphere with hydrosphere, atmosphere and/or biosphere. Arrows indicate possible process paths within the cycle.  The Rock Cycle and Plate Official Business Tectonics Convergent Boundary – magma is created by melting of rock at a convergent boundary/subduction zone. Less dense magma rises and cools to form igneous rock. Igneous rock exposed at surface gets weathered into sediment. Sediments transported to low – lying areas, buried and hardened into sedimentary rock. Sedimentary rock heated and squeezed at depth to form metamorphic rock. Convergent plate boundary Metamorphic rock may heat up and melt at depth to form magma. Official Business Igneous Rocks Igneous rocks form when magma cools and solidifies. Intrusive igneous rocks form when magma solidifies underground. Extrusive igneous rocks form when magma solidifies at the Earth’s surface (lava). Official Business Classification of Igneous Rocks Igneous rock are classified based on their texture and chemical composition Texture – the rock’s appearance with respect to the size, shape and arrangement of grains or other constituents. Crystal size is determined by the rate of cooling of the magma. Intrusive – formed deep underground and typically cools slowly. Extrusive – formed at or near the Earth’s surface and cools quickly. Chemical Composition – mineral content indicates origin and evolution of the magma. Official Business Aphanitic and Phaneritic Textures Crystalline Textures Fine Grained or Aphanitic – crystals are too small to see easily with the naked eye. Magma cooled quickly at or near the surface. Coarse Grained or Phaneritic – crystals are large enough to see with the naked eye. Magma cooled slowly. Fine – grained (Aphanitic) igneous rock Coarse – grained (Phaneritic) igneous rock Official Business Pegmatitic and Porphyritic Textures Pegmatitic – extremely coarse–grained (most crystals >5 cm), formed when magma cools very slowly at depth. Porphyritic – includes two distinct crystal sizes, with the larger phenocrysts having formed first during slow cooling underground and the smaller groundmass forming during more rapid cooling at the Earth’s surface. Pegmatitic Texture Porphyritic Texture Official Business Glassy Textures Glassy – contains no crystals at all and is formed by extremely rapid cooling of the magma. Vesicular – contains cavities (vesicles) in extrusive rocks resulting from gas bubbles that were in the lava. Scoria and pumice are examples. Obsidian – Pumice – Glassy Vesicular Texture Texture Official Business Fragmental Texture Pyroclastic – consolidated pyroclastic debris such as ash, pumice or crystalline rock. Tuff and Volcanic Breccia are examples. Tuff – Pyroclastic Texture Official Business Chemistry of Igneous Rocks Rock chemistry, particularly silica (S i O2) content, determines mineral content and general color. Felsic rocks – >65% silica by weight, and contain light- colored minerals that are abundant in silica, aluminum, sodium and potassium. Rhyolite and Granite are examples. Intermediate rocks – silica contents between 55% and 65% by weight. Diorite and Andesite are examples. Mafic rocks – silica content between 45% and 55% by weight, contain dark-colored minerals that are abundant in iron, magnesium and calcium. Gabbro and Basalt are examples. Ultramafic rocks – 256 mm. Cobble – 64 to 256 mm. Pebble – 2 to 64 mm. Sand – 1/16 to 2 mm. Silt – 1/256 to 1/16 mm. Clay – 90% quartz grains. Arkose – mostly feldspar and quartz grains. Graywacke – sand grains surrounded by dark, fine-grained matrix, often clay – rich.  Detrital Rocks Official Business The Fine-Grained Rocks Shale – fine-grained clastic sedimentary rock; fissile (splits into thin layers) Silt – and clay-sized grains. Sediment deposited in lake bottoms, river deltas, floodplains, and on deep ocean floor. Siltstone – slightly coarser-grained than shale; non-fissile Claystone – predominantly clay – sized grains; non-fissile Mudstone – silt – and clay – sized grains; massive/blocky Official Business Chemical Sedimentary Rocks Carbonate Rocks Contain C O3 as part of their chemical composition. Most are biochemical, but can be inorganic. often contain easily recognizable fossils. Limestone is composed mainly of Bioclastic limestones calcite, Susceptible to recrystallization. Dolomite chemical alteration of limestone in Mg-rich water solutions can produce dolomite. Official Business Chemical Sedimentary Rocks Chert Hard, compact, fine-grained, formed almost entirely of silica. Can occur as layers or as lumpy nodules within other sedimentary rocks, especially limestone. Bedded Chert  Chemical Official Business Sedimentary Rocks Evaporites Form from evaporating saline waters (lake, ocean). Common examples are rock gypsum, rock salt.  Organic Official Business Sedimentary Rocks Coal – sedimentary rock forming from compaction of partially decayed plant material Organic material deposited in water with low oxygen content (that is, stagnant). Coal Bed Official Business Diatoms The Origin of Oil and Gas Oil and natural gas Originate from organic matter in marine sediment Diatoms and single – celled algae settle to sea floor Oxygen poor waters preserve the organic material Higher temperatures convert organics to oil and gas Accumulates in porous overlying rocks Single-Celled Algae Official Business Sedimentary Structures Features within sedimentary rocks produced during or just after sediment deposition Provide clues to how and where deposition of sediments occurred. Bedding Series of visible layers within a rock. Most common sedimentary structure. Official Business Bedding in sandstone and shale  Sedimentary Official Business Structures: Cross-bedding Cross - bedding Series of thin, inclined layers within a horizontal bed of rock. Common in sandstones. Indicative of deposition in ripples, bars, dunes, deltas. Cross - bedded sandstone  Sedimentary Official Business Structures: Ripples Marks Ripple marks Small ridges formed on surface of sediment layer by moving wind or water. Official Business Sedimentary Structures: Graded Bedding Graded bedding Progressive change in grain size from bottom to top of a bed. Official Business Sedimentary Structures: Mud Cracks and Fossils Mud cracks Polygonal cracks formed in drying mud. Fossils Traces of plants or animals preserved in rock. Hard parts (shells, bones) more easily preserved as fossils. Official Business Formations Formation – A rock body of considerable thickness that is large enough to be mapped. Often based on rock type. Must have a visible characteristic that makes it a recognizable unit. Given proper names such as the Anastasia Formation or Ocala Limestone. Contact – a boundary surface between two different rock types or ages of rock. Official Business Formation contacts in the Grand Canyon Official Business Interpretation of Sedimentary Rocks Sedimentary rocks give important clues to the geologic history of an area Source area Locality that eroded and provided sediment. Sediment composition, shape, size and sorting are indicators of source rock type and relative location. Environment of Depositional – location where sediment came to rest Sediment characteristics and sedimentary structures (including fossils) are indicators. Glacial Environments, Alluvial Fans, River Channels, Floodplains, Lakes, Deltas, Beaches, Lagoon, Shallow Marine Shelves, Reefs, Deep Marine. Official Business Sea Level Changes Transgression and Regression Records the rising and falling of sea level. Transgression – sea level rises and marine sedimentary deposits will migrate onto the subsided land areas. Regression – sea level falls and the sedimentary deposits will migrate away from the land areas. Official Business Tectonic Setting of Sedimentary Rocks Plate movement is responsible for the distribution of many Convergent Boundary sedimentary rocks Sedimentary rock distribution often provides information that helps geologists reconstruct tectonic events erosion rates and depositional characteristics give clues to each type of tectonic plate boundary Divergent Boundary Official Business Metamorphism and Metamorphic Rocks Official Business Metamorphism Metamorphism refers to solid- state changes to rocks in Earth’s interior Produced by increased heat, pressure, or the action of hot, reactive fluids. Old minerals, unstable under new conditions, recrystallize into stable ones. Rocks produced from pre-existing or parent rocks in this way are called metamorphic rocks Metamorphic rocks common in the old, stable cores of continents, known as cratons Official Business Metamorphic Rocks Texture and mineral content of metamorphic rocks depend on: Parent rock composition. Temperature and pressure during metamorphism. Effects of tectonic forces. Effects of fluids, such as water. Parent rock composition Usually no new material is added to rock during metamorphism. Resulting metamorphic rock will have similar composition to parent rock. Official Business Temperature The heat for metamorphism comes from Earth’s deep interior All minerals stable over finite temperature range, if range exceeded, new minerals result. If temperature gets high enough, melting will occur. Official Business Pressure Confining pressure applied equally in all directions. Pressure proportional to depth within the Earth. High-pressure minerals more compact/dense. Differential Stress – created by forces that are not equal in all directions. Compressive stress causes flattening perpendicular to stress. Shearing causes flattening by sliding parallel to stress. Official Business Foliation Planar rock texture of aligned minerals produced by differential stress Formed by differential stress. Official Business Fluids and Time Fluids Hot water (as vapor) is most important. Rising temperature causes water to be released from unstable minerals. Hot water very reactive; acts as rapid transport agent for mobile ions. Time Metamorphism, particularly from high pressures, may take millions of years. Longer times allow newly stable minerals to grow larger and increase foliation. Official Business Nonfoliated Metamorphic Rocks Nonfoliated rocks are named based on composition Marble – coarse grained rock composed of interlocking calcite crystals. Quartzite – produced when grains of quartz sandstone are welded together. Hornfels – fine grained rock typically composed of microscopically visible micas formed from the clay particle in shale. Marble Quartzite Official Business Foliated Metamorphic Rocks Foliated rocks are named based on the type of foliation (slaty, schistose, gneissic) Slate Phyllite Schist Gneiss  Contact Official Business Metamorphism Contact Metamorphism occurs when a body of magma comes in contact with relatively cool country rock High temperature is dominant factor. Produces non-foliated rocks. Occurs in narrow zone (~1- 100 m wide) known as contact aureole. Rocks may be fine- (for example, hornfels) or coarse-grained (for example, marble, quartzite).  Hydrothermal Official Business Metamorphism Hydrothermal Metamorphism – rocks precipitated from or altered by hot water Common at divergent plate boundaries. Hydrothermal processes: Metamorphism. Metasomatism. Hydrothermal Processes and Ore Deposits Water passes through rocks and precipitates new minerals on walls of cracks and in pore spaces. Metallic ore deposits often form this way (veins). Metallic Ore Vein deposit  Regional Official Business Metamorphism Regional metamorphism occurs over wide areas and deep in the crust High pressure is dominant factor. Results in rocks with foliated textures. Prevalent in intensely deformed mountain ranges. May occur over wide temperature range.  Shock Official Business Metamorphism Shock metamorphism is produced by rapid application of extreme pressure Meteor impacts produce this. Shocked rocks are found around and beneath impact craters. Official Business Metamorphic Grade Minerals present in a metamorphic rock indicate its metamorphic grade. Prograde Metamorphism – as a rock is buried to greater depths it is subject to greater temperatures and pressures causing recrystallization into higher grade rocks. Slate → Phyllite → Schist → Gneiss → Lower Grade → Higher Grade Migmatites (partial melting) exhibit both intrusive igneous and foliated metamorphic textures Pressure and Temperature Paths in Time Index minerals can be used to approximate temperature and pressure Migmatite conditions Official Business Index Minerals Index minerals can be used to approximate temperature and pressure conditions Official Business Foliation and Plate Tectonics Regional metamorphism associated with convergent plate boundaries Differential stress. Gravitational collapse and spreading. Source: W.G. Ernst, Metamorphism and Plate Tectonics Regimes. Stradsburg, PA: Dowden, Hutchinson & Ross, 1975, p.425. Official Business Pressure – Temperature Regimes Temperature varies laterally at convergent boundaries Isotherms bow down in sinking oceanic plate and bow up where magma rises. Wide variety of metamorphic facies. Official Business Hydrothermal Metamorphism and Plate Tectonics Particularly important at mid –oceanic ridges as seas water moves downward into cracks in the sea floor Hydrothermal vents such as “black smokers” occur as the water returns to the ocean Dissolved metals and sulfur precipitate to create mounds around the vents. Source: Courtesy of New Zealand American Ring of Fire 2007 Exploration, N OAA Vents Program Official Business Reference: Official Business