Exam 1: Geology
What are the different types of sandstones?
-Four groups: Arkose: feldspar-rich Quartz arenite: quartz-rich Lithic: particles of other rocks, rather than minerals Graywacke: a sandstone cemented with clay mineral matrix (kaolinite)
What are the active volcanoes in the US?
-Hawaii South-central Alaska and Aleutian Island chain -Cascade Range Washington, Oregon, northern CA, southwestern Canada -Yellowstone Supervolcano Wyoming, Montana
What is limestone and how would you identify it?
-Biological sedimentary rocks -Limestone (calcite-based) -Composed of biologically precipitated carbonate mineral calcite CaCO3. Types: Fossiliferous limestone: visible fossils Reef limestone: visible coral reef fossils Coquina: broken fragments of shell pieces Oolitic limestone: pearl-like grains (ooids) Chalk: fine-grained calcite -Chert (silica-based) Microfossils from silica-fixing lifeforms, rather than calcite -Organic (organic carbon-based) Phosphorite (phosphate-based
What sediment sizes would you expect at low, medium, and high-energy depositional locations?
-Continental (on land) Higher-energy transport Coarser grain sizes deposited -Shoreline (where land meets water) Medium-energy transport Medium grain sizes deposited -Marine (sea/ocean) Lower-energy transport Finer grain sizes deposited
What does transport affect sediment size, sorting, roundness, and mineral composition?
-Distance of transport affects: Size of particles More distance = smaller Rounding of particles More distance = more rounded Mineral composition of particles More = less variety Sorting of particles More distance = well sorted -Well-sorted sediment refers to sediments with similar size, shape, and mineral composition -Poorly-sorted will be different sizes, shapes, and compositions
What are the linkages between igneous groups and tectonic plate boundaries?
-Divergent plate boundaries Oceanic-oceanic: mafic, ultramafic Continental-continental: felsic, then intermediate, then mafic -Convergent plate boundaries Oceanic-oceanic: mafic Oceanic-continental: intermediate to felsic -Continental-continental: felsic -Hot spots Under oceanic crust: mafic Under continental crust: intermediate to felsic
Divergent plate boundaries and volcanoes
-Fissures at seafloor spreading ridges -Most voluminous volcanic activity -30,000 miles of ridges on earth -Mostly under oceans - except Iceland -Magma typically melted asthenosphere material rich in ultramafic rock (periodite) -Basalt emplaced as new seafloor at spreading ridge or rift -Oceanic-oceanic: mafic -Conitnental-continental: felsic and intermediate compositions -Fissures at continental rifts -Magma melts overlying continental crust, may produce andesite or rhyolite lavas in addition to basaltic Ex. East African Rift
What are hot spots, and what do they tell us about plate movement?
-Hot spots: areas of upwelling magma located in the interior of a plate, not at the plate boundary -Position of volcanic island groups (like Hawaii) trace the direction and speed of the plates over fixed hot spots in the mantle -The Pacific plate has moved northwest over the Hawaiian hot spot, resulting in a chain of volcanic islands -The ages of the volcanoes are consistent with plate movement of about 100 mm/year
Convergent plate boundaries and volcanoes
-If oceanic-continental convergence, lavas are most often andesitic Fluid-induced melting Intermediate compositions Rhyolitic can occur under specific conditions -If oceanic-oceanic convergence, lavas are most often basaltic No continental crust in fluid-induced melting
Convergent
-Lithospheric plates move toward each other -Continental-oceanic Ex. Oregon/Washington, Andes Mountains (west coast South America) -Oceanic-oceanic Ex. Japan; southern coast of Alaska -Continental-continental Ex. Himalaya Mountains (between India and China) -Nothing subducts which is what creates the mountains -Lower density plate overrides higher density plate and causes subduction: the plunging down of the denser plate into the mantle. If the density is equal, mountain ranges form -Crust created at divergent plate boundaries is destroyed at subduction zones
Transform
-Plates slide past each other, side by side -Can offset oceanic ridges, breaking ridges up into short segments -Separate continental plates Ex. San Andreas Fault, California and Mexico -San Andreas Fault: Transform boundary between Pacific plate and North American plate (California, Mexico); continental-continental -Oceanic-oceanic transform boundary between Pacific plate and Juan de Fuca Plate (off coast of Oregon, Washington) -Also note oceanic-continental convergence of Juan de Fuca plate and North American plate
How do location and speed of magma cooling affect igneous rock textures?
-Plutonic/Intrusive: magma cools within the crust and does not make it to surface; cooling is slow -Volcanic/Extrusive: magma reaches the Earth's surface as lava flows or explodes as pyroclastic fragments; cooling is fast Texture: size of mineral crystals 1. Phaneritic: coarse/large (slow cooling) 2. Aphanitic: fine/small (fast cooling) 3. Porphyritic: mix of large and small (fast for some minerals, slow for others) 4. Glassy: no crystals (super fast cooling) Two types: frothy and compact
What is planetary differentiation?
-Process by which heavier (denser) metals (Fe, Ni, Mg) sank deeper into the Earth while lighter metals (Si, K, Ca, Na) concentrated at the surface -Created the layering of the Earth -During gravitational differentiation, iron sank to the center and lighter material floated upward to give us Earth as a layered planet
What clastic sediments become what clastic sedimentary rocks?
-Siliciclastic sediments are classified by particle size (clay, silt, sand, gravel) -Siliciclastic sedimentary rocks are classified by particle size (texture) and mineral composition Main siliciclastic rocks based on texture: -Clay becomes shale or claystone -Clay + silt becomes mudstone -Silt becomes siltstone Sand becomes sandstone -Gravel becomes conglomerate or breccia
What is viscosity, and how does that change between lava types?
-The resistance of a fluid to flow High viscosity: more resistance to flow -Flows more slowly; thicker Ex. Ketchup Low viscosity: less resistant to flow -Flows more easily, faster Ex. Water
What are silicate minerals? What are the two main types?
-Variety of compounds based on silicon and oxygen -Mafic silicates are Ferromagnesian: higher in Fe and Mg; lower in Si) Olivine Pyroxene Amphiboles Biotite mica -Felsic silicates are Non-Ferromagnesian: lower in Fe and Mg; higher in Si Quartz Orthoclase feldspar Plagioclase feldspar Muscovite mica
What is the link between volcanism and climate?
-Volcanism and the atmosphere -Ash and gas entering atmosphere can cause climate changes Short-term example: Mt. Pinatubo eruption in 1991 The eruption ejected so much ash into the atmosphere (blocking the sun's rays) that it dropped Earth's temperature for over a year Long-term example: Siberian traps 251-250 mya In the Permian, large, frequent volcanism over 300,000 years emitted enough greenhouse gasses into atmosphere to increase global temperatures, may have caused Permian Mass Extinction
What happens to iron minerals at divergent plate boundaries, and what does this tell us about plate movement?
-When magnetic iron emerges from the mantle at diverging plates, it aligns with Earth's magnetic field before solidifying into rock -As the plates spread, rocks move away in both directions -A symmetric pattern occurs on both sides of the boundary, showing magnetic orientation through time -These continuous movements along plate boundaries show the movement of the continents from Pangea to their current positions and indicates what occurred prior to Pangea (topic for another day)
What is a covalent bond?
-bond with electrons shared -atoms share valence (outermost) electrons -by sharing, each atom then has stable number of electrons -stronger than ionic bond, makes minerals harder
Divergent
-plates move apart -Lithospheric plates move apart -Form rift zones (continental-continental divergence) -Ex. East Africa -Form oceanic ridges (oceanic-oceanic divergence) -Mid-Atlantic Ridge -Upwelling of asthenosphere (under lithosphere) at plate boundary injects molten mantle material to the surface, forming new oceanic crust -When new crust forms, it forces plates apart -Seafloor spreading: separation of lithospheric plates and mid ocean ridges -Plates must be destroyed at the edge by subduction and convergent plate boundaries to balance out the creation of new oceanic crust -Magma: molten mantle material Process: -Continental rift valley -Water fills in rift valley and forms narrow seas/lakes -Larger seas begin to form and new oceanic crust begins to form -What started as continental divergence is now oceanic divergence
What observations led to Continental Drift Hypothesis?
-postulated that a supercontinent called Pangea began breaking into smaller continents about 200 million years ago -These smaller continental fragments drifted to their present day positions Based observations between continents: -"Jigsaw puzzle" fit -Rock sequences -Fossil assemblages -Glacial evidence
What are pyroclasts?
-solid fragments extruded from volcanic eruption; cause pyroclastic texture -Include ash, pumice, fine solidified magma combined into a rock Volcanic ash: smallest pyroclastic fragments; form tufts and weld together breccias
What is the principle of uniformitarianism?
-the fundamental principle of geology -Geological processes presently occurring on Earth are the same processes that operated throughout Earth's history. So, the past can be understood by modern observations -"The present is the key to the past" -Studying how rivers transport and deposit sediment today help interpret how rivers deposited sediment in the past -Earth's natural history can be understood by examining rocks -Geology is studied in the outdoors, in the lab, or through use of remote sensing
What is fractional crystallization and why does it occur?
-the process by which the crystals are formed in a cooling magma and are segregated from the remaining liquid -Temperature-dependent; the first minerals to crystallize from a cooling magma are the ones that are the last to melt -Bowen's reaction series explains the sequence of fractional crystallization
What are the three main Earth systems?
1. The plate tectonic system -involves interactions among the lithosphere, asthenosphere, and deep mantle 2. The climate system -involves interactions among the atmosphere, hydrosphere, biosphere, cryosphere, and lithosphere 3. The geodynamo system -involves interaction between the inner and outer cores Only the climate system is energized by the sun. The rest are energized by the Earth itself
What are the different lava types?
Basaltic lavas -Highest temperature (1000-1200 degrees celsius) -Lowest viscosity -Form basalt igneous rock (mafic) Types: Aa More viscous, sharp, jagged Pahoehoe Less viscous, "ropey" Pillow -Form on seafloor -Lowest silica content, lowest viscosity -Common at hot spots and mid-ocean ridges Andesitic lavas: -Intermediate viscosity and silica content, temperature -Form andesite igneous rock (intermediate) -Common at subduction zones Rhyolitic lavas: -Lower temperature (600-800 degrees celsius) -Highest viscosity and silica content -Form rhyolite igneous rock (felsic) -Common where magma melts large quantities of continental crust
What are the different types of sedimentary structures?
Bedding: -Formation of parallel layers of sediment as particles are deposited Bedding plane: the surface separating one bedding layer from another Bedding sequences: vertically stacked bedding with different types of sedimentary rocks and/or structures in each layer -Analyzing bedding sequences inform geologists the history of sedimentation in that location Cross-bedding: -Bedding on an angle to the main bedding plane Graded-bedding: Gradual change of one sediment size into another; coarser/heavier sediments are deposited first Ripples: -Wave-shaped features showing direction of movement Bioturbation structures/ trace fossils: -Evidence that living organisms were present without any remains of the organism Mudcracks: -Clayey desiccation features indicating water was evaporated from a lake bed
What are carbonates? What are their main diagnostic properties?
Carbonates: cation + CO3 Ex. Calcite CaCO3 -rhombohedral cleavage, react with acid
What is coal and how is it formed?
Coal: -Organic carbon-rich plant remains are buried relatively fast Bituminous (~80% carbon) Anthracite (~98% carbon; actually a metamorphic rock)
What physical properties do we use to identify minerals?
Color: -Color of a mineral as viewed by the naked eye -Additional information usually needed -Single minerals may have a variety of colors -Different minerals may have same color -Color variety related to impurities from other trace elements Luster: -Appearance of mineral in reflected light -Two categories: Metallic: strong light reflection; looks like a metal Nonmetallic: weak/no light reflection; does not look like a metal -Several sub adjectives Streak: -The color of the powder residue after rubbing the mineral against a porcelain tile -Minerals will have a diagnostic streak color, primarily for metallic lusters -Minerals of the same color can have different color streaks -A mineral exhibiting multiple colors will always have the same color streak (hematite) Crystal Form: -The growth shape of a mineral; based on arrangement of atoms -Slight formation variations may cause variations of crystal structure for same mineral -Massive: the appearance of a large mass; no obvious appearance of crystal form at macroscale Cleavage: -The tendency of a crystal to break along planar surfaces -Bonding forces between atoms not equal in all directions, which creates planes of weakness along which the mineral tends to break -Minerals strongly bonded in all directions such as quartz and garnet have no cleavage -Weak bonds = good cleavage -Classified according to number of cleavage planes and pattern -Perpendicular or non-perpendicular Hardness: -The ease at which a mineral can be scratched -Higher hardness = less easily scratched -Measured by Moh's Hardness Scale -Depends on: Size: smaller atoms have larger electrostatic attraction = harder -Charge: larger charges have larger electrostatic attraction = harder -Packing: small distances between atoms have larger electrostatic attraction = harder
What are the differences between P-waves and S-waves?
Compression (P) waves: -push-pull motion -Travel through both solids and liquids -Faster velocity -P-wave velocity increases with density -P-waves indicate two types of crust Shear (S) waves: -side to motion -Travel only through solids -Slower velocity -S-waves indicate multiple zones within the mantle based on effects of temperature and pressure on peridotite, a rock with very low Si, high Fe and Mg -Unlike P-waves, these velocity changes are NOT caused by changes in chemical composition
What are the differences between continental crust and oceanic crust?
Continental: high silica = low density = slower P-values (~6 km/s) Oceanic: low silica (Si) = high density = faster P-waves (~7 km/s)
What is convection and how does it affect the Earth's magnetic field?
Convection: hotter, less dense material rises, while cooler, denser material sinks, then the pattern continues -The Earth's outer core is in a state of turbulent convection as the result of radioactive heating and chemical differentiation. This sets up a process that is a bit like a naturally occurring electrical generator, where the convective kinetic energy is converted to electrical and magnetic energy. -Without convection, there is no magnetic field, and radiation from Sun would strip away the atmosphere
How is convection related to plate tectonics?
Convection: upwells heat and magma from mantle to surface at divergent plate boundaries -New oceanic crust formed as old crust pushed away from spreading centers -Hot matter from the mantle rises, sinks, warms, and rises again -We can reconstruct the rates on history of plate motion based on: Hot spots Orientation of magnetic minerals
What two ways turn sediments into sedimentary rocks?
Diagenesis/Lithification first requires: Compaction: removal of air and water between particles and/or Cementation: addition of minerals into the void space
What are the main types of plate boundaries and what features would be found at each?
Divergent, convergent, and transform
How does mineral composition affect igneous rock classifications?
Four total compositional groups, based on chemistry of the source magma (mainly silica content): 1. Felsic igneous rocks (high silica) 2. Intermediate igneous rocks (medium silica) 3. Mafic igneous igneous rocks (low silica) 4. Ultramafic igneous rocks (very low silica)
What are the main sediment sizes?
From largest to smallest: gravel, sand, silt, clay
What is the difference between a hypothesis and a theory?
Hypothesis -formed to explain the observations of data -conceptual framework or model is developed -multiple explanations or equations developed -must be testable and test must be reproducible -proof of a hypothesis is sought as well as evidence to disprove it -test the hypothesis repeatedly and systematically -make set of predictions and perform series of experiments Theory -formed as accepted explanation for an observation or set of data -Hypothesis becomes a theory only after extensive testing of the hypothesis
What is an ionic bond? Cations? Anions?
Ionic bond: electrons are transferred -formation caused by an electrical attraction of + to - Cations: atom that is positively charged -have fewer electrons relative to the number of protons (element lost an electron) Anions: atom that is negatively charged -have more electrons relative to the number of protons (element gained an electron)
What is the difference between the lithosphere and asthenosphere?
Lithosphere: hard, brittle (rigid) solid made of crust and uppermost portion of mantle Asthenosphere: soft, ductile (plastic) solid below the lithosphere
What is the compositional difference between the mantle and the core?
Mantle: a semi-solid magma layer consisting of iron, magnesium, and silicon. Core: centrally located solid mass of metal (inner core) and a liquid mass of iron and nickel (outer core).
What makes a mineral a mineral?
Mineral composition (laboratory-technology based), crystal structure and symmetry (laboratory-technology based), and observing physical and chemical properties (easy for trained humans to see, feel, taste, smell, and recognize
What are the differences between protons, neutrons, and electrons? Which defines an element?
Protons: positively charged -dictates the chemical element Neutrons: neutral Electrons: negatively charged -determined by the number of positively charged protons -fill up energy levels surrounding the nucleus
What is shale and how does it appearance identify shale?
Shale/Claystone: -Sedimentary rocks formed from clay -Cannot see particles with naked eye -Generally deposited in quiet waters -Lakes, lagoons, swamps, or deep ocean -If black, less oxygen in water -If red, more oxygen in water -Shale breaks along bedding planes; claystone does not
What are the volcano types and how are they linked to tectonic plate boundaries and igneous rock types?
Shield volcanoes: -Large, flat shield-shape -Larger area relative to height -Form basalt lava; thin basalt flows build up over time -Most common at hot spots -Relatively predictable and "quiet" eruptions Ex. Hawaiian Islands (Kilauea; Mauna Loa) Stratovolcanoes / composite volcanoes: -Built up layers of lava and pyroclasts -Andesitic lavas plus pyroclastic layers form a tall volcano -Usually associated with subduction zones -Tend to be violent and explosive eruptions Ex. Mount St. Helens (WA); Cascade Range (WA/OR); Mt. Shasta (CA); Fujiyama, Japan Cinder cones: -Minor explosive volcano -Mostly pyroclastic discharges of varying sizes -Pyroclastics build up around the vent creating cones Ex. Paricutin, Mexico; Cerro Negro, Nicaragua Volcanic Domes: -Composed of rhyolite, but can cause andesite lavas as well -Too viscous to flow - material oozes out to surface from a tube close to the vent -May explode as nuee ardente: a cloud of gas and ash -Commonly occur at subduction zones after stratovolcano eruptions, hot spots under continents, and continental rifts -Vary in size
What are oxides? Sulfides? Native elements?
Sulfates: cation + SO4 Ex. Gypsum CaSO4 Sulfides: cation + sulfur (S) Ex. Pyrite FeS2 Oxides: cation + oxygen Ex. Hematite Fe2O3 Native elements: mineral composed of single element -Carbon as diamond and graphite -Copper, gold, silver, platinum -Sulfur
What are sills and dikes?
Types of plutons (Any magma that has intruded and solidified into rock at depth): Sill: intrusion parallel to the layering of country rock "with the grain" Dike: intrusion cross (not parallel to) the country rock layers "against the grain"
How do seismic wave velocities tell us about the layering of the Earth?
When an earthquake occurs the seismic waves (P and S waves) spread out in all directions through the Earth's interior. Seismic stations located at increasing distances from the earthquake epicenter will record seismic waves that have traveled through increasing depths in the Earth. Seismic velocities depend on the material properties such as composition, mineral phase and packing structure, temperature, and pressure of the media through which seismic waves pass. Seismic waves travel more quickly through denser materials and therefore generally travel more quickly with depth. Anomalously hot areas slow down seismic waves. Seismic waves move more slowly through a liquid than a solid. Molten areas within the Earth slow down P waves and stop S waves because their shearing motion cannot be transmitted through a liquid. Partially molten areas may slow down the P waves and attenuate or weaken S waves. When seismic waves pass between geologic layers with contrasting seismic velocities (when any wave passes through media with distinctly differing velocities) reflections, refraction (bending), and the production of new wave phases (e.g., an S wave produced from a P wave) often result. Sudden jumps in seismic velocities across a boundary are known as seismic discontinuities.
