* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Midterm Review 1
Survey
Document related concepts
Ore genesis wikipedia , lookup
Future of Earth wikipedia , lookup
History of geology wikipedia , lookup
Geology of Great Britain wikipedia , lookup
Sedimentary rock wikipedia , lookup
Large igneous province wikipedia , lookup
Age of the Earth wikipedia , lookup
Late Heavy Bombardment wikipedia , lookup
Algoman orogeny wikipedia , lookup
Tectonic–climatic interaction wikipedia , lookup
Transcript
Where did we come from and how did we get here? The Universe formed about 14 billion years ago The Solar System and Earth formed about 4.6 billion years ago We are a planet, revolving around a star that is one of about four hundred billion stars in a galaxy (The Milky Way), that is one of more than 80 billion galaxies in the observable Universe. Our Star, the Sun, like most stars is composed of mostly Hydrogen, with some Helium The outer planets (Jupiter, Saturn, Neptune and Uranus) are gas giants (H and He) The Earth is one of four ‘terrestrial’ planets (Mercury, Venus, Earth and Mars) in the inner Solar System, and like those planets, is composed largely of a silicate (SiO2) and Iron (Fe) Unlike most of the other ‘terrestrial’ planets, the Earth is a dynamic planet, with a constantly changing lithosphere (rocks), atmosphere (wind), hydrosphere (water), and biosphere (life). That is why the surface of the Earth is largely free of meteorite impact craters. Much of this dynamism is due to heat-driven convection ~14 GA (GigaAnnum, i.e, Billion Years) But first things first today Typical spiral galaxy. Similar to ‘our’ Milk Way Galaxy’ We are not alone. About 80 billion galaxies in the observable universe. About 400 billion stars in the Milky Way galaxy (but that may be a bit larger than average) Many (most?) of those probably have planets. How many of those planets are terrestrial (Earth-like?) How many have life? The Crab Nebula in Lyra Remnants of a supernova The Surface of our Sun ( a very close star) SUN Hydrogen (74%), some helium (24%) Rocky inner planets Silicates with Iron/Nickel cores The giant Gas planets of the outer solar system Hydrogen, Helium, methane, water, ammonia plus small icy planets like Titan Gaseous Outer Giant ‘terrestrial planets’ Mars ‘terrestrial planets’ The surface of Mars – close up ‘terrestrial planets’ The surface of Idaho – close up Earth Our moon: Luna Close up of Tycho Earth’s Outermost Layers • The most dynamic portion of the Earth – Atmosphere • Thin gaseous envelope surrounding Earth – Hydrosphere • Water layer dominated by the oceans – Biosphere • All living things on the planet – Lithosphere • Rocky outer shell Heat driven convection 1. Bottom water is warmed 2. It expands an is therefore less dense 3. It rises to the surface and then spreads out 4. Cooler water at the sides descends to fill the void A convective thunderstorm Atoms and Minerals What are we (the Earth) made of? All matter is composed of atoms, which consist of a nucleus with protons and neutrons, and electrons which ‘orbit’ the nucleus Bonds are formed between the valence electrons of atoms to form molecules Minerals are ‘naturally occurring inorganic solid that has an exact (or clearly defined range) chemical composition with an orderly internal arrangement of atoms generally formed by inorganic processes’. The nature of the bonds results in the physical properties of minerals, including crystal form, cleavage, fracture, hardness, density, color, luster, streak, etc. Rocks are formed of minerals The rock-forming minerals include silicates, carbonates, evaporites and secondary minerals such as clays Rocks are formed of minerals Most rocks are silicates and are composed of cations linked by silicate tetrahedra, chains, sheets and solids Matter • Atoms – The smallest unit of an element that retain its properties • Molecules - a small orderly group of atoms that possess specific properties - H2O – Small nucleus surrounded by a cloud of electrons – The nucleus contains protons and neutrons Bonding • Atoms are stable when their outmost electron shell is filled – Atoms lose, gain or share electrons to achieve a noble gas structure • Types or bonds – Ionic Covalent Metallic The Nature of Minerals • Mineral – A naturally occurring inorganic solid that has an exact (or clearly defined range) chemical composition with an orderly internal arrangement of atoms generally formed by inorganic processes. Physical Properties Crystal Form Cleavage and Fracture Hardness Density Color Luster: Metallic vs Non-metallic Streak Taste, magnetism, etc. Rock-Forming Minerals • About 20 common minerals make up most rocks – Silicates dominate – Quartz, Feldspars, Mica, Amphiboles, Pyroxenes – Carbonates are common – Evaporite minerals – Secondary minerals formed during weathering Silicate Minerals • Silica tetrahedron may polymerize to form a variety of geometric structures, alone or in combination with other cations • Isolated tetrahedron • Single chains • Double chains • 2-D sheet • 3-D frameworks Silica Tetrahedron Silicate Structures Isolated Single chain Double chain Sheet Solid Nonsilicate Minerals – Carbonates (biologic) • Calcite - Ca CO3 • Dolomite - CaMg(CO3)2 – Evaporite Minerals (seawater evaporation) • Gypsum - CaSO4-2H2O • Halite – NaCl – Clays and Oxides (rust and weathering) • Hematite • Bentonite, Kaolinite Rocks Imagine the first rock and the cycles that it has been through. Igneous Rocks Igneous Rocks • Form from Magma (hot, liquid rock) • Cool and solidify underground (plutonic) or as lavas above ground (volcanic) • Most properties are controlled by silica (SiO2) content: classification, melting point, minerals, appearance, etc. • Viscosity of magma is controlled by temperature, silica content, and to a lesser extent, water. • Silica-rich magmas are more likely to erupt explosively than are mafic magmas, which are runny • Texture (size and shape of xtals) is controlled by the rate cooling history of the rock. Igneous Rocks (cont) • Faster cooling results in finer-grained crystals • Common textures include aphanitic (fine-grained), phaneritic (coarse-grained), porphyritic (big xtals in a fine-grained matrix), pyroclastic (explosive) and glassy • The kind of volcanism depends upon the viscosity of magma • Plutonic bodies include plutons, batholiths, sills, dikes etc. • Magmas originate in the upper Mantle • Magmas differentiate (change composition) through mixing, melting of country rock, and partial melting • The Bowen’s Reaction series describes the order in which silicate minerals solidify in a magma Mafic (Fe,Mg –rich) Magmas • Silica content of ~ 50% • High concentrations of Fe, Mg and Ca • High temperature of molten magma – 1000o to 1200oC • Major minerals – Olivine – Pyroxene - Ca-rich Plagioclase Felsic (Si,Al-rich) Magma • Silica content of 65-77% • High concentrations of Al, Na and K • Lower temperature magmas – Less than 850oC • Major minerals – Feldspars – Quartz - Micas Magma Viscosity • Controlled by silica temperature • As magma cools, silica tetrahedron form links – Similar to polymers - e.g., nylon • Increasing linkages – Higher silica & lower temp • Linkages increase viscosity Note: this is just like oils, fats and other organic compounds used in the household Igneous Textures • Texture - the size, shape and relationship of mineral crystals in the rock • Reflects cooling history of the magma or lava Big crystals • Slow cooling rate >> • Fast cooling rate • Very fast cooling rate >> Small crystals >> glass Glassy texture in obsidian Aphanitic Texture • Fine grained texture • Few crystals visible in hand specimen • Relatively rapid rate of cooling Aphanitic texture in rhyolite Phaneritic Texture • • • • • Coarse grained texture Relatively slow rate of cooling Equigranular, interlocking crystals Slow cooling = crystallization at depth Pegmatites - very coarse grained texture Phaneritic texture in granite Porphyritic Texture • Well formed crystals (phenocrysts) • Fine grained matrix (groundmass) • Complex cooling history – Initial stage of slow cooling • Large, well formed crystals form – Later stage of rapid cooling • Remaining magma crystallizes more rapidly Porphyritic igneous rock: Big xtals in a fine grain matrix Pyroclastic Texture • Produced by explosive volcanic eruptions • May appear porphyritic with visible crystals – Crystals show breakage or distortion • Matrix may be dominated by glassy fragments – Fragments also show distortion – Hot fragments may “weld” together Concept Art, p. 105 Fine grained Coarse grained Classification of common igneous rocks Volcanic Eruptions • Basaltic eruptions are runny • Low Silica + High T = Low Viscosity • Produce – Lava Flows - Pahoehoe or Aa – Flood basalts – Shield Volcanoes – Pillow lavas Fig. 4-1, p. 102 Flood basalts with several thick and thin layers. Each layer represents a separate eruption. Fig. 5-12d, p. 145 Intermediate & Silicic Eruptions • Higher Silica + Lower T = Higher Viscosity – Composite or Stratovolcanos – Lava Domes – Ash Flow Calderas Concept Art, p. 155 Mt Fuji: Stratovolcano Caldera Explosions: Super volcanoes Fig. 5-9b, p. 142 Fig. 5-9c, p. 142 Fig. 5-9d, p. 142 Fig. 5-9e, p. 142 Basalt River Gravels Rhyolite Basalt Fig. 5-21c, p. 157 Concept Art, p. 104 Plutonic Rocks • Less dense magmas rise through the crust • Intrusions form as magma solidifies beneath the surface Figure 4.18. Types of magmatic intrusions Half Dome; part of the Sierra Nevada batholith Sill; parallels layers in the country rock Dike; cuts across layers in the country rock Origin of Magmas • Solid rock is at equilibrium with its surrounding • Changes in the surroundings may cause solid rock magma – Raising T – Lowering P – Changing composition Magma Differentiation • Magmas, and the resulting igneous rocks, show a wide range of compositions • Source Rock – variations cause major and minor variations in the magma • Magma Mixing • Assimilation Bowen’s Reaction Series Metamorphic Rocks • • • • • • • • • • Rocks can be metamorphosed (changed) into other rocks when subjected to high temperatures and pressures. The presence of fluids increases the rate of metamorphism Metamorphic changes occur in the solid state The three kinds of metamorphism are Regional, Contact and Hydrothermal Regional metamorphism involves large scale pressures and temperatures caused by collision of plates in subduction zones or continental collisions Contact metamorphism involves baking of adjacent rocks by hot magma intrusions Hydrothermal alteration involves alteration of minerals through percolation of hot, mineral-rich fluids through the rock The ‘Parent’ rock is an important control on the type of metamorphic rock formed Index minerals form at specific temperatures and pressures and thus record the T and P ‘experienced’ by the rock Metamorphic rock textures are either foliated (layered due to directional pressure) or non-foliated Metamorphic Rocks • The transformation of rock by temperature and pressure • Alters igneous, sedimentary and even other metamorphic rocks What causes metamorphism? • Heat • Most important agent • Heat drives recrystallization - creates new, stable minerals • Pressure (stress) • Increases with depth • Pressure can be applied equally in all directions or differentially, i.e. directed • Fluids • The flow of hot mineral-rich water through the rock can have a big impact on metamorphism • Referred to as hydrothermal alteration and creates specific easily identified minerals Main factor affecting metamorphism • Parent rock • Metamorphic rocks typically have the same chemical composition as the parent rock. • They contain different minerals, but the same chemicals; just rearranged. • Exception: at sometimes gases like carbon dioxide (CO2) and water (H2O) are released • Examples: – Quartz SandstoneQuartzite – ShaleSlate Schist Gneiss – GraniteGranite, though minerals might align Source of Heat Source of Fluids Ocean-Continent convergence Regional Metamorphism: Subduction zones ….. High T Low P High T High P High P Low T Why it is called regional Colors represent Fig. 6.15. levels of different Temperature and Regional Pressure as recorded in Metamorphic the minerals. Gradients This regional pattern was caused by the collision of two continents Other minerals behave similarly Metamorphic Index Minerals Index Minerals in metamorphic rocks Each of these minerals is an index of T and P Metamorphic textures • Foliation • Foliation can form in various ways: – Rotation of platy or elongated minerals – Recrystallization of minerals in a preferred orientation – Changing the shape of equidimensional grains into elongated and aligned shapes Development of foliation due to directed pressure Change in metamorphic grade with depth Progressive metamorphism of a shale Shale Progressive metamorphism of a shale Schist Progressive metamorphism of a shale Gneiss Common metamorphic rocks • Nonfoliated rocks • Quartzite – Formed from a parent rock of quartz-rich sandstone – Quartz grains are fused together – Forms in intermediate T, P conditions Sample of quartzite Thin section of quartzite Marble (Random fabric = annealing; nonfoliated)