Review Slides For Midterm 2 Sedimentary And Metamorphic Processes PDF

Midterm 2: Sedimentary and metamorphism November 1 (Friday) in class. Sedimentary process and sedimentary rocks What are the main processes to form sediments? What type of environment produce what type of sediments? What is soil? What process convert sediments into sedimentary rocks? Wha...

Midterm 2: Sedimentary and metamorphism November 1 (Friday) in class. Sedimentary process and sedimentary rocks What are the main processes to form sediments? What type of environment produce what type of sediments? What is soil? What process convert sediments into sedimentary rocks? What are the main types of sedimentary rocks? Some examples? Uplift of land Diagenesis refers to the physical and chemical processes that affect sedimentary materials after deposition and before metamorphism and between deposition and weathering. Lithification, complex process whereby freshly deposited loose grains of sediment are converted into rock. Mechanical/Physical weathering Fragmentation of rock without composition changes. Expansion—Exfoliation Abrasion -- one rock bumps against another rock Wedging -- a pre-existing crack in a rock is made larger by forcing it open, e.g. water/ice, salt, plant and animal activity Chemical weathering Rock changes through chemical reactions, not just in size of pieces, but in composition. Dissolution Hydrolysis Hydration—Dehydration Oxidation polarity of water Erosion Processes that dislodge rock particles produced by weathering and move them away from source area, with moving water, ice, air, gravity. Moving water – a major driver of erosion – involves several processes: Abrasion – scouring of stream bed by transported particles Scouring and lifting – flowing water dislodges and loosens larger rocks Dissolution – stream flows over soluble bedrock Transport and Sorting Currents carry range of particles sizes Variations sort particles according to grain-size and density: Degree of sorting increasing with transport distance Particles transported with bed load (i.e., sand and gravel) undergo extensive abrasion during stream transport: Closer to Source Farther from Source Particle size – diameter decreases as material removed Particle shape – edges become more rounded  Sedimentary Basins Sediment tends to accumulate in depressions in the Earth’s crust. Sedimentary basins are depressions filled with thick accumulations of sediment, receiving dissolved ions and clastic particles produced by weathering. forearc basin foreland basin rift basin trench basin Soil Soil forms an essential interface between the solid Earth (geosphere), biosphere, hydrosphere, and atmosphere. Regolith is the name for the loose, unconsolidated material that covers planetary surface. Soil for the layer of weathered, unconsolidated material that contains organic matter and is capable of supporting plant growth. A mature, fertile soil is the product of centuries of mechanical and chemical weathering of rock, combined with the addition and decay of plant and other organic matter.  Soil Soil is a complex mixture of minerals (~45%), organic matter (~5%), and empty space (~50%, filled to varying degrees with air and water). The mineral content of soil varies, but is dominated by Martian regolith clay minerals and quartz, along with minor amounts of feldspar and small fragments of rock. weathered basalt Sedimentary Structures Sediments and sedimentary rocks are generally characterized by bedding or stratification Range in thickness from < 1 cm to several meters Differentiated by rock or mineral type and particle size Sedimentary Structures Deposition within different sedimentary environments, all kinds of features in sediment formed at the time of deposition. Bedding (stratification) Cross-bedding Ripples Mud cracks Graded bedding Bioturbation structures Graded Bedding Graded bedding is characterized by a change in grain size from bottom to top within a single bed. Most graded beds form in a submarine fan environment, where sediment-rich flows descend periodically from a shallow marine shelf down a slope and onto the deeper sea floor. Bed Younger 2 Clay, Silt Bed Fine sand 1 Older Coarse sand Turbulent cloud Settling Graded Bed Burial Clastic sediments become trapped following deposition in sedimentary basins New layers of sediment accumulate over older layers of sediment Older sediments subjected to: Increasing temperature Increasing pressure Chemical and biological reactions  Lithification: Converting Sediment into Sedimentary Rock Compaction reduces the volume of a deposit by decreasing the amount of pore space as particles fit more closely together deposit settles under its own weight and the weight of any sediment deposited on top of it. Cementation takes place when minerals crystallize in pore spaces and effectively bind the sedimentary particles to one another. Sedimentary Environments Also classified according to sediment type and sediment-forming processes Clastic sedimentary environments Chemical and Biological sedimentary environments Carbonate environments Ca2+(aq) + CO32-(aq) CaCO3(s) Siliceous environments: Silica (SiO2) forms in marine sedimentary environments by Chemical precipitation (Water reaches saturation with Si and O2), and Biomineralization (Diatoms precipitate amorphous silica→diatomite). Evaporite environments The visible unconsolidated materials found on slopes, beneath glaciers, in stream valleys, on beaches, and in deserts are referred to as sediment, and the individual pieces that make it up are called clasts. Clastic Sediments Broken and eroded pieces of rocks and minerals physical and chemical weathering of common silicate-bearing rocks range in size from boulders to sand, silt and clay Chemical and Biogenic Sediments Evaporation: Mineral precipitation due to seawater evaporation forms chemical sediments Dissolved ions accumulate in water due to chemical weathering Chemical and biological reactions precipitate minerals from these dissolved ions Biomineralization Direct mechanism: organisms utilize dissolved ions or molecules to produce shells or skeletons Indirect mechanism: minerals precipitate due to environmental conditions created by organisms Classification of Sedimentary Rocks >85% of all sedimentary rocks are clastic Characterized by grain size Chemical and biological sedimentary rocks account for ~14% Evaporites, cherts and other chemical and biological sedimentary rocks exist in minor amounts Characterized by chemical composition Clastic Sedimentary Rock Types Distinguished by: grain size and shape grain type (mineralogy) texture of the grains, matrix and cements  Easy Minerals Minerals that weather by dissolution (e.g., halite, gypsum, calcite) are the easiest to weather. Silicate minerals with lower silica to oxygen ratios (e.g., silicates made of isolated silica tetrahedra or single chains) are easier to weather than silicate minerals with higher ratios (e.g., those made of silica tetrahedra arranged sheets or frameworks). Minerals that are by-products of chemical weathering are some of the most resistant to further chemical weathering, although they may be more prone to physical weathering (e.g., clay minerals). Hard Mineral (composition) Weathering product dissolved ions halite (NaCl) Na+, Cl– gypsum (CaSO4·2H2O) Ca2+, (SO4)2- calcite (CaCO3) Ca2+, (HCO3)– pyrite (FeS2) hematite Fe2+, (SO4)2- quartz (SiO2) sand grains (SiO4)4- Plagioclase (Ca,Na)AlSi3O8 clay minerals Ca2+, Na+, (SiO4)4- limonite alkali feldspar (KAlSi3O8) clay minerals K+, Na+, (SiO4)4- serpentine, limonite, olivine (Mg, Fe)2SiO4 Mg2+, (SiO4)4- hematite, clay chlorite or smectite, pyroxene (Mg, Fe)SiO3 Ca2+, Mg2+, (SiO4)4- limonite, hematite, clay amphibole limonite, hematite, clay K+, Mg2+, (SiO4)4- Ca2(Fe, Mg)5Si8O22(OH)2 biotite limonite, hematite, clay K+, Mg2+, (SiO4)4- K(Mg, Fe)3AlSI3O10(OH)2 muscovite KAl2(AlSI3O10)(OH)2 clay K+ Types of Sediment Specific combinations of texture and composition for each type Determined by sediment’s history: transport energy and distance, weathering intensity, and composition of source rock. Chemical and Biogenic Rocks Siliceous sediments Lithify to form cherts (flint) Phosphorite sediments Lithified calcium phosphate Iron oxide sediments Indirecty precipitated by microorganisms Lithified after oxygen increased in oceans (i.e., ~3 Ga) Organic sediments Form from accumulation of wetland vegetation Burial and diagenesis converts peat to coal Carbonate Sediments and Rocks Calcium carbonate [CaCO3] formed by direct or indirect precipitation by organisms Limestone forms by accumulation and lithification of CaCO3 Dolomite [CaMg(CO3)2] forms by chemical reaction between CaCO3 and dissolved magnesium. Limestone  Calcium carbonate [CaCO3] Calcite is the most abundant carbonate mineral. Aragonite is a polymorph of calcite, a mineral that has the same chemical composition as calcite, but has a slightly different crystal structure. Aragonite tends to convert to calcite over time. Dolomite is a mineral that most often forms as an alteration of calcite, as magnesium replaces much of the calcium in the crystal structure. The easiest way to distinguish calcite and dolomite is that dolomite will not readily react with dilute acid at room temperature. Hardness: 2.5 to 3.  Evaporites Chemically precipitated from evaporating sea water and (sometimes) lake water Seawater contains dissolved minerals, which are concentrated during evaporation to form: Halite [NaCl] Gypsum [CaSO4 2H2O] Metamorphism Earthquake Mountain building Metamorphic rock Shock metamorphism What are the main processes to form metamorphic rock? What type of environment produce what type of metamorphic rock? What factors play a role? What are the main types of metamorphic rocks? Some examples? Deformation occurs when applied forces exceed the internal strength of rocks, physically changing their shapes. These forces are called stress, and the physical changes they create are called strain. The principle of original horizontality states that sediments accumulate in essentially horizontal layers under the influence of gravity. Subsequent deformation can cause folding or faulting of sedimentary strata. Rock responds to stress differently depending on the pressure and temperature (depth in Earth) and mineralogic composition of the rock. Elastic deformation: Fully reversible: rock returns to original shape Brittle deformation: Stress causes rock to fracture Ductile deformation: Irreversible: rock does not return to original shape non-permanent Increase Temperature More Ductile strain Elastic limit Brittle deformation permanent strain Fracture Stress Increase Strain Rate More Brittle Strain Faults Brittle deformation causes rocks to break, slip on both sides of a fracture Faulting occurs suddenly and produces earthquakes Folds Ductile deformation under directional pressure Develop slowly, common in metamorphic rocks Joints Fractures without faulting Displacement of fracture opening greater than displacement by lateral movement along fracture plane Stress on rock from tectonic forces or thermal contraction squeezing stretching side to side shearing Faults Characterized by rock displacement Caused by different forces: Compression; Tension; Shear Type of fault classified by: Slip direction; Displacement (offset) Associated Plate Associated fault Type of Stress Resulting Strain Boundary type and offset types Tensional Divergent Stretching & Thinning Normal Compressional Convergent Shortening & Thickening Reverse Shear Transform Tearing Strike-slip Faults When rock masses slip past each other parallel to the strike, the movement is known as strike-slip faulting. Movement parallel to the dip is called dip-slip faulting. Oblique-slip faults are defined by combinations of dip-slip and strike- slip displacement.  Elastic rebound theory: When rock experiences large amounts of shear stress and breaks with rapid, brittle deformation, energy is released in the form of seismic waves, commonly known as an earthquake. The point within the Earth where seismic waves first originate is called the focus (or hypocenter ) of the earthquake. This is the center of the earthquake, the point of initial breakage and movement on a fault. Rupture begins at the focus and then spreads rapidly along the fault plane. The point on the Earth’s surface directly above the focus is the epicenter. Elastic rebound theory Seismic waves When a rock breaks, waves of energy are released and sent out through the Earth. These are seismic waves , the waves of energy produced by an earthquake. Two types of seismic waves are generated during earthquakes. Body waves are seismic waves that travel through the Earth’s interior, spreading outward from the focus in all directions. Surface waves are seismic waves that travel on Earth’s surface away from the epicenter, like water waves spreading out from a pebble thrown into a pond. The instrument used to measure seismic waves is a seismometer. Body waves A P wave is a compressional (or longitudinal) wave in which rock vibrates back and forth parallel to the direction of wave propagation. P wave is the fastest and first (or primary ) wave to arrive at a recording station following an earthquake. An S wave ( secondary ) is a slower, transverse wave. The rock vibrates perpendicular to the direction of wave propagation, that is, crosswise to the direction the waves are moving. Both P waves and S waves pass easily through solid rock. A P wave can also pass through a fluid (gas or liquid), but an S wave cannot. Surface waves Surface waves are the slowest waves set off by earthquakes. Surface waves cause more property damage than body waves because surface waves produce more ground movement and travel more slowly, taking longer to pass. Love waves are most like S waves that have no vertical displacement. The ground moves side to side in a horizontal plane that is perpendicular to the direction the wave is traveling or propagating. Rayleigh waves rolls along the ground with a more complex motion than Love waves. Rayleigh waves tend to be incredibly destructive to buildings because they produce more ground movement and take longer to pass. Seismometer Seismographs are instruments used to record the motion of the ground during an earthquake. A seismometer is the internal part of the seismograph The Moment Magnitude(MW) uses seismograms plus what physically occurs during an earthquake, known as the "seismic moment". The seismic moment defines how much force is needed to generate the recorded waves, determined from the strength of the rock, surface area of the rupture, and the amount of rock displacement along the fault.  Hoover Dam, dam in Black Canyon on the Colorado River, at Type of earthquakes the Arizona-Nevada border, U.S. Tectonic Earthquakes Volcanism Impacts from meteoroids Artificial Induction Caused by human activities, including the injection of fluids into deep wells, the detonation of large underground nuclear explosions, the excavation of mines, and the filling of large reservoirs. Reservoir Induction More than 20 significant cases have been documented in which local seismicity has increased following the impounding of water behind high dams. Analyses of seismograms can also indicate at what depth beneath the surface the quake occurred. The maximum depth of focus —the distance between focus and epicenter—for earthquakes is about 670 kilometers. Shallow focus 0–70 kilometers deep, 85% Intermediate focus 70–350 kilometers deep, 12% Deep focus 350–670 kilometers deep, 3% Intermediate and deep focus quakes are rarer because most deep rocks flow in a ductile manner when stressed or deformed; they are unable to store and suddenly release energy as brittle surface rocks do. Types of Plate Boundaries Divergent Convergent 1. Divergent Boundaries a) Oceanic plate separation b) Continental plate separation 2. Convergent Boundaries a) Ocean-ocean convergence b) Ocean-continent convergence c) Continent-continent convergence 3. Transform-Fault Boundaries a) Mid-ocean ridge transform fault Intraplate location Transform margin b) Continental transform fault Divergent Boundaries Shallow earthquakes within ocean basins: Crests of mid-ocean ridges Offsets on transform faults Normal faults also responsible for earthquakes where continental crust undergoes extension Normal East African Rift valley Basin and range province, USA 1959 yellowstone earthquake Largest earthquakes occur at convergent plate boundaries Called megathrust earthquakes Overriding plate thrust upward relative to subducting plate Zone of seismicity along the plane of the subducting plate is called the Wadati-Benioff Zone. Transform boundary A strike-slip fault occurs where plates meet and slide against each other horizontally. Plates move past each other with earthquakes generating close to the surface. Earthquakes are shallow but powerful. Pacific Plate and North American Plate. San Andreas Fault, California North Anatolian Fault, Turkey The San Andreas Fault slashes the desolate Carrizo Plain.Photograph by James P. Blair Hazards and Risks Majority of fatalities due to collapse of buildings and other structures Earthquakes cause damage in several ways: Faulting and shaking – primary hazards Landslides Liquefaction Secondary hazards Fires Tsunamis 2010 Haiti 7.0 MW 2008 Sichuan (China) 7.9 MW Tsunamis (津波 Japanese for harbour wave) Most tsunamis are caused by large earthquakes below or near the ocean floor can also be caused by landslides, volcanic activity, certain types of weather and near earth objects (e.g., asteroids, comets). Not all earthquakes cause tsunamis. Megathrust earthquakes can cause tsunamis. No major earthquake has been predicted. Studying, monitoring and helping to improve the safety of buildings and structures. Creepmeters to check for movement along faults; Tiltmeters to monitor changes in the slope of the land; Seismic Monitor (e.g. IRIS Incorporated Research Institutions for Seismology); Satellites to detect changes in the position of plates. https://ds.iris.edu/seismon/index.phtml  Folds 2cm Original planar structure bent into a curved structure Ductile deformation caused by compressional forces, horizontal or vertical 5c m Anticline: it looks like an “A” or a dome (upward folding orientation of layers). The beds dip away from the axial trace, older going towards the axial trace. Syncline: it looks like a “U” (downward folding orientation of the rock layers). The beds dip towards the axial trace, younger going towards the axial trace. Mountain Building Mountains may be created by volcanism, faulting, and folding. The Stawamus Chief is a granitic mountain at Coast Range of BC. Types of Plate Boundaries 1. Divergent Boundaries a) Oceanic plate separation b) Continental plate separation 2. Convergent Boundaries a) Ocean-ocean convergence b) Ocean-continent convergence c) Continent-continent convergence 3. Transform-Fault Boundaries Mid-ocean ridge transform fault Continental transform fault 1. Divergent Boundaries a) Continental plate separation Extension of boundaries; new lithosphere generated Rift valleys, mountains, volcanoes, and earthquakes b) Oceanic plate separation Extension of boundaries; new lithosphere generated Submarine rift valleys, mountains and volcanoes, and earthquakes E.g. Mid-Atlantic Ridge Mountain Building Along Divergent Margins When continents begin to split apart, normal faults form. This can lead to large blocks of crust that are tilted, raised, or lowered compared to adjacent blocks. Blocks that are elevated compared to adjacent blocks can form another type of mountain, called a fault-block mountain. Yosemite Fault-block mountains = crust is broken into large blocks and lifted above surrounding crust. E.g. Grand Teton Mountains, WY Grabens = long, narrow valleys formed when large blocks of crust have dropped between normal faults E.g. Death Valley, CA Horsts = forms when block of crust is thrust upward between two normal faults E.g. Basin and Range Province of Nevada 2. Convergent Boundaries 2a) Ocean-ocean convergence Oceanic trench, volcanic island arc, and deep earthquakes 2b) Ocean-continent convergence Volcanic mountain chain, folded mountains, and deep earthquakes 2c) Continent-continent convergence Crustal thickening, folded mountains, and earthquakes Mountain Building Along Convergent Margins Mountain building along convergent margins is referred to as orogeny, and the mountains that are built are called orogens. Orogeny creates broad, linear regions of deformation known as orogenic belts Ocean-Continent Collision In ocean-continent collision zones, folding and faulting of rocks combines with volcanism to build mountains. E.g. Sierra Nevada mountain. Mountains form from subduction zone volcanism, and from large sheets of rock that are thrust inland and folded. Materials accumulating on the leading edge of the continent in an accretionary wedge are eventually smashed onto the continent, adding to continental crust. Continent-continent: Fold and Thrust Belts Large compressive stresses are generated in the crust at convergent margins when continental crust collides. Rocks located in the collision zone blocks are folded, faulted, and thrust faulted. Crustal thickening pushes peaks upward and builds deep roots, forming fold-and-thrust mountains. Fold-and-thrust belts form the highest and most structurally complex mountain belts. Rocks are naturally occurring solid aggregates of minerals, or in some cases, non-mineral solid matter. Rocks are grouped based on formation: Igneous, Sedimentary, Metamorphic. Metamorphism Meta- Greek word, meaning Change. Morph is from the Greek morphe meaning shape or form ism- the action or result of… Metamorphic Rock- forms when preexisting rock (parent rock), or protolith undergoes solid state change (recrystallization) in response to the modification of its environment. Metamorphism Driven by four principal factors: Temperature: Increases at a rate of 30°C per km depth Pressure: Increases at a rate of 0.23 kbar per km depth Fluid chemistry: Introduces dissolved minerals Time: Reactions involving silicate minerals are very slow Typically occurs between 200 and 800°C Diagenesis occurs at < 200°C Melting occurs at > 800°C These temperatures are typically encountered at depths of 10–30 km within the crust The Role of Pressure Pressure can also alter the chemical composition, mineralogy and texture of rocks Can control which minerals form and which are stable Minerals formed at higher pressure exhibit higher density Two basic kinds of pressure involved in metamorphism Confining pressure (lithostatic pressure) Directed pressure (differential stress)  Confining Pressure Directed Pressure Force is applied equally in all Force applied in a particular direction directions and increases with depth Recrystallized minerals exhibit in the crust parallel alignment of textural Recrystallized minerals become and structural features reoriented and tightly locked Ductile rocks can be severely distorted Marble Quartzite Directed Pressure Quartz-rich conglomerate as a parent rock. Differential stress has caused quartz pebbles within the rock to become elongated, and it has also caused wings to form around some of the pebbles The Role of Heat Changes in composition, mineralogy and texture due to heat are associated with: Breaking of chemical bonds Changing of crystal structure Recrystallization and stability of minerals are temperature dependent Atoms combine differently at different temperatures Increasing temperature speeds up chemical reactions Geologists can use mineral composition of metamorphic rocks as a geothermometer The Role of Fluids Water and carbon dioxide present in varying amounts: Along grain boundaries mantle In pore spaces peridotite Accelerate chemical reactions: Ions are transported rapidly from one place to another Different sources of fluids: Trapped in sedimentary rocks Released from magmas Breakdown of hydrated minerals Hydrothermal fluids can also transport heat and promote Serpentinite recrystallization Olivine Serpentine Magnetite The Role of Time Most metamorphic reactions in tectonic processes occur very slowly, reach phase equilibrium. New material growth at a rate of approximately 1 mm per million years. Shock metamorphism likely not reaching phase equilibrium. Stable phase and metastable phase observed. Regional metamorphism is the most widespread, forced by high temperature and pressure over large regions usually at plate boundaries. Contact metamorphism is caused by the heat from an igneous intrusion Regional High-pressure Shock metamorphism metamorphism Contact metamorphism metamorphism Oceanic Depth (Km) crust 0 35 75 Oceanic lithosphere Seafloor metamorphism is the result of hot seawater circulating Burial metamorphism is through basalt at mid-ocean caused by deposition of Water ridges. overlying sediment forcing rocks downward. Seafloor metamorphism Burial metamorphism  Limestone forms by accumulation and lithification of CaCO3 Dolomite [CaMg(CO3)2] forms by chemical reaction between CaCO3 and dissolved magnesium. Medium to Fine grained or no coarse grained visible grains Metamorphic Rocks Foliated Non-Foliated Metamorphic Textures Determined by properties of constituent minerals: Size Shape Arrangement Mineral Separated into three general classes: Foliated rocks Non-foliated (granoblastic) rocks Porphyroblasts Foliated Texture Foliation is a term used that describes minerals lined up in planes. Certain minerals, e.g. mica, are mostly thin and planar by default. Other minerals linear like a pencil or a needle, referring as lineation. E.g. hornblende, tourmaline, or stretched quartz grains. Produced by directed stress related to regional metamorphism Non- Foliated Fine grained or Contain crystals with equi- no visible grains dimensional shapes Form due to confining pressure Fine to coarse directed pressure produces grained foliation Often associated with contact metamorphism Regional Metamorphism Contact Metamorphism Contact Metamorphism Zoned Recrystallization Metamorphic Facies and Protolith 43 Chlorite (X,Y)4-6(Si,Al)4O10(OH,O)8 X, Y = Fe+2, Fe+3, Mg+2, Mn+2, Ni+2, Zn+2, Al+3, Li+1, or Ti+4 Biotite K(Mg, Fe)3AlSI3O10(OH)2 Muscovite KAl2(AlSI3O10)(OH)2 Garnet X3Y2(SiO4)3 X= Ca, Mg, Fe2+ or Mn2+ Y= Al, Fe3+, Mn3+, V3+ or Cr3+ Kyanite, Sillimanite Al2SiO5 Shock Metamorphism Hypervelocity impact event Localized metamorphism Shatter cones Planar deformation features, high-pressure polymorphs of quartz Impact melt Manicouagan Crater