Geology 1010 FINAL EXAM
What conditions favor fossil preservation?
- Low oxygen environment (prevents decay) - Rapid burial (prevent destruction by scavengers) - Presence of hard parts (bones, teeth, shells, preserve better than soft tissue)
Hydraulic Conductivity
A measure of how fluid flows in porous material
Vadose zone
A zone above the water table and below the land surface that is not saturated with water
What is a metamorphic aureole?
An area that surrounds rock that has been changed and undergone Metamorphosis
Where are conglomerates found?
Close to the sediment source
How many mass extinctions have there been?
Five
Chemical Sedimentary Rock
Minerals precipitated directly from water solutions
How much would sea level rise if all mountain glaciers melt? Greenland Ice Sheets? Antarctic ice sheets?
Mountain glaciers: 0.7 meters Greenland ice: 7 meters Arctic ice: 70 meters
What are surface features of sedimentary structures?
Mudcracks and ripple marks
Are earthquakes predictable?
No
Is the current rate of sea level rise unprecedented?
No, it is not unprecedented
Is the Earth a perfect sphere?
No. Spinning had caused the Earth to "bulge" around the Equator (This is due the fact that the Earth is comprised of many different chemicals)
What are the four kinds of seismic waves?
P-waves S-Waves Love Waves Rayleigh Waves
How does sorting affect primary porosity?
Poorly sorted = low porosity well sorted = high porosity
Equation to calculate porosity
Porosity = volume of voids/total volume
How does porosity vary with grain size, sorting, and packing?
Porosity goes up as grain size goes down
Porosity
Porosity is spaces in sediment
What are the 3 main minerals found in felsic magmas?
Potassium Feldspar, Quartz, Plagioclase
What is an extrusive igneous rock?
Rocks that are formed when lava hardens above the Earth's surface
What is an intrusive igneous rock?
Rocks that are formed when magma hardens beneath Earth's surface
Angular unconformity
Rocks underneath horizontally layered sediments are tilted or folded.
Aquifer
Rocks with high permeability containing groundwater
Rayleigh Waves
Rolls in wave motion, surface waves
What kind of rocks are fossils found in?
Sedimentary rocks
Types of Foliated Rock
Shale Slate, Phyllite, Schist, Gneiss Sharks Sometimes Play with Scientists and Grandmas
Compare groundwater flow through shale and sandstone
Shale: K= 10 to the -6- m/day, Q= 1 mL/day (¼ teaspoon/day) Sandstone: K= 1m/day, 1 m to the 3/day, (about 6 barrels)
How deep in Earth do earthquakes occur in divergent boundaries?
Shallow
How deep in Earth do earthquakes occur in convergent boundaries?
Shallow-Deep
How deep in Earth do earthquakes occur in collision zones?
Shallow-Intermediate
How does sorting vary with energy or transport distance?
Sorting will increase with more transport distance and lower energy
Volcanic Arcs
Subaerial eruptions at convergent margins, andesitic to rhyolitic magma
Where do subducted slabs go?
Subducted slabs sink, ultimately reaching the core-mantle boundary
What are the 3 types of differential stress we considered?
Tensional Compressional Shear
How many ice sheets are on Earth at present?
Three
Love Waves
Undulates laterally, surface waves
What is Colorado's state rock?
Yule marble
Strike-Slip Fault
birds eye view, forward and backward motion
What are the two kinds of crust?
oceanic and continental
What is the Moho?
the boundary between the crust and the mantle. Where seismic velocity increases abruptly.
How do magnetic anomalies (magnetic stripes) on the seafloor prove seafloor spreading?
• Stripes parallel to mid-ocean ridge. • Stripes are symmetric about the Ridge. • Stripes are due to orientation of magnetic minerals in sea floor rocks
What are the 4 processes involved in metamorphism?
-Heat -Pressure -Shear (pressure/force with direction) -Hydrothermal fluids
Stratovolcanoes
-High silica content -High viscosity -Andesitic-granitic composition -Explosive eruptions -Steep sided
Unconformity
-Long period of time of non-deposition -Gaps (we have no rock left in that time interval; maybe eroded?) in geologic record
What are the basic features of the seafloor spreading hypothesis?
1) Basalt magma rising at mid-ocean ridges makes new crust 2) Crust moves away from the ridge as new eruptions occur Accumulates sediment 3) Crust must sink into mantle somewhere--- this occurs at oceanic trenches
What conditions affect the deformation behavior of rock?
1) Temperature- warmer temps are more likely to have plastic behaviors 2) Pressure- higher pressure likely to have plastic behavior 3) Deformation rate- slower deformation favors plastic behavior 4) Composition of rock- softer rock types are more likely to have plastic behavior
Within a convergent boundary, where would these metamorphic environments be found, and what rocks would be produced?
1) low-temperature, high-pressure 2) high-temperature, low-pressure 3) high-temperature, high-pressure
What pressure/temperature conditions and metamorphic rock types are associated with the following:
1) regional metamorphism in a mountain belt 2) contact metamorphism around a magma chamber 3) subduction zone metamorphism
What does water table topography look like?
1. Vadose zone (unsaturated) 2. Water table boundary 3. Groundwater (saturated)
What is 1 mm in microns?
1000 microns
How long ago was the big bang?
13.7 Ga
How long did Big Bang nucleosynthesis go on, and which elements were made?
3 minutes Hydrogen and Helium
What causes sea level rise?
30% of sea level rise is from thermal expansion of the ocean 55% glaciers/ice sheets 25% other causes
Grain size of Silt
4-62 microns (gritty)
What is the circumference of the Earth?
40,000 km
What is the density of the Earth?
5.5 g/cm³
Grain size of Sand
62 microns - 2 mm (sandy)
What is the radius of the Earth?
6370 km
What fraction of geologic time is represented by the Precambrian Eon?
90%
What fraction of the Solar System mass is in the Sun?
99.9%
Grain size of Clay
< 4 microns (creamy)
Grain size of Pebbles
> 2 mm
What does Ga stand for?
A Billion Years
What does Ma stand for?
A Million Years
What is a glacier?
A body of ice that flows
What is a fault?
A break in the earth's crust
What is a nebula
A cloud of gas and dust containing the remnants of stars
What is a trench?
A deep canyon in the ocean floor
What is a rift valley?
A deep valley that forms where two plates move apart
Non-Foliated Rocks
A metamorphic rock that does not have parallel layers of mineral grains
What is the definition of rock?
A naturally occurring solid composed of minerals or glass or organic matter. Usually a mixture.
How does particle shape vary with energy or transport distance?
A particle becomes more round with more transport distance
Uniformitarianism
A principle that explain how geologic processes that occurred in the past can be explained by current geologic processes.
What is a mineral?
A pure substance Naturally-occurring Inorganic solid with a specific internal structure (crystal structure) A definable chemical composition
What is metamorphic grade?
A scale denoting the level of pressure and temperature involved in forming a particular metamorphic rock
What is the (current record) oldest rock on Earth?
Acasta Gneiss. 4.03 billion years old.
Glacial Accumulation
All forms of delivery of snow or ice to glacier (Snowfall, windblown, avalanche)
Where are the volcanoes found in a convergent boundary?
Along the volcanic arc
What is a silica tetrahedron?
An Anion containing 4 oxygen atoms and 1 silicon atom; can directly bond to others by sharing oxygen atoms.
What is a seamount?
An active volcano that occurs along the crest of the mid-ocean ridge. HOT SPOT!
What are magnetic declination?
Angle of offset between magnetic pole (where your compass needle points) and geographic pole
Where would the oldest rocks be found in a dome?
Anticline = Oldest rocks in the middle
What kind of fold is a dome?
Anticline with center point
What is apparent polar wander?
Apparent polar wander paths measured on different continents don't line up. Therefore, continents move!
What defines the beginning of the Phanerozoic Eon
Appearance of "visible life"
How does melt viscosity vary with composition? How does this affect the volcanic eruption style?
As you increase the silica content, magma becomes more viscous.
Felsic Eruption Style
Ash, lapilli, bombs, tephra, pyroclastic flow, lahars Caldera
What is partial melting?
At conditions between the solidus and the liquidus, the rock undergoes partial melting
What are the layers of the Earth, defined by chemical composition?
Atmosphere Crust Mantle Core
What are isotopes?
Atoms of the same element with different numbers of neutrons
What are the physical properties of oceanic crust?
Basalt Composition Fe + Mg Dense Really thin (5-7 km)
What are three extrusive igneous rocks?
Basalt: low Si, mafic (Mg + Fe) Andesite: intermediate Si Rhyolite: high Si, felsic
Where is Sandstone found?
Beach Shore
What is a hanging wall?
Block above the fault
Contact
Boundary between formations
Water table
Boundary between unsaturated and fully saturated zones Rule of thumb: water table is subdued version of the surface topography
What chemical is Limestone made of?
Calcium Carbonate
Biochemical Sedimentary Rock
Cemented shells of organisms
What are the time spans of the Phanerozoic period
Cenozoic 0-66Ma Mesozoic 66-252Ma Paleozoic 252-541Ma
Name the Eras in the Phanerozoic Eon
Cenozoic, Mesozoic, Paleozoic
Where is Earth's magnetic field generated?
Circulating liquid iron in the outer core generates the magnetic field
What was dated to determine the age of the Earth?
Claire Patterson used uranium-lead to determine the age of the Earth in a meteorite.
What defines glacier ice?
Coarse grains and contains air bubbles
How does composition of the Earth compare to composition of the Sun?
Composition of Earth is similar to the Sun, except for low H and He Volatiles lost in solar system formation
What does differentiated mean, with respect to a planet?
Comprised of layers that differ in chemical composition and in physical properties
Clastic Sedimentary Rocks
Conglomerate Breccia Sandstone Siltstone Shale Mudstone Can Bees Save Silver Sharks' Mouths
What evidence compelled Alfred Wegener to propose the continental drift theory in early 20th century?
Continental shift theory, archean rock assemblages match, ancient mountain ranges line opposite sides of the Atlantic, Fossils of extinct organisms found on different continents.
Why does the lithosphere thicken and the ocean deepen with distance away from a mid-ocean ridge axis?
Cooler and thicker lithosphere sinks into the asthenosphere
What is the Core's composition and density?
Core • Fe • Iron (Fe) alloy (mixture with a little nickel (Ni) and other elements) • Super dense: 10-13.5 g/cm3
What can we do to protect ourselves from earthquake hazards?
Create buildings with reinforced corners
What are internal features of sedimentary structures?
Cross-bedding indicates deposited in flowing water or air in dunes or ripples Also... fossils
What is the Crust's composition and density?
Crust • O + Si • Light silicate minerals • Density 2.6-3.2 g/cm3 • Thin: 8-75 km
What is fractional crystallization?
Crystallization of part of a magma, leaving behind melted rock with a different composition from the original magma
Where is Mudstone found?
Deep Marine
Where is Shale found?
Deep Marine
What does the moment depend upon?
Depends on energy released which depends on length and distance of rupture
How does the energy release of a Mw 7 compare with the energy release in a Mw 6 Earthquake?
Difference in 1 unit = 31 x more energy
How does the energy release of a Mw 7 compare with the energy release in a Mw 5 Earthquake?
Difference in 2 units = 1000 x more energy
How do we identify the location of an earthquake?
Difference in P Wave and S Wave arrival times at 3 different sources
Where is there a better potential for geothermal energy?
Differences in tectonic settings Plate boundary on the west, but the east coast is passive margin
What are the 3 deformation styles that occur in response to differential stress?
Displacement Change in orientation (rotation) Change in shape (distortion)
Index Fossils
Distinctive fossils used to establish and compare the relative ages of rock layers and the fossils they contain. These are useful because of their... - Widespread geographic distribution - Existence for a limited period of time (then went extinct) - Easily preserved in sedimentary rock
What is a strain?
Distortion or the response to stress
What kind of fold is a syncline?
Down Fold, limbs dip toward the hinge
In general, where do earthquakes occur within the Earth? Where do the deepest earthquakes occur? Why?
Earthquake belts are wide at convergent margins. Deepest earthquakes occur in the Wadati-Benioff zone (earthquake belt along the subducting slab)
What are tectonic plates, and what is a good way to identify their edges?
Earthquake epicenter maps do good job outlining plate boundaries.
What is the moment (M0) of an earthquake?
Energy released
How are metamorphic rocks from deep in the crust ever exposed on the surface?
Exhumation - from collision or erosion
Where is the High Plains Aquifer?
Extends across 7 states
Where is it fatter—around the equator or the poles?
Fatter around the equator Reference spheroid has radius 6378 km around equator and 6357 km around poles
What are the four categories of magma, and what wt% silica define them?
Felsic 66-76 wt% Intermediate 52-66 wt% Mafic 45-52 wt% Ultramafic 38-45 wt%
What causes changes in water table level?
Fluctuations in the water table level are caused by changes in precipitation between seasons and years.
What are 3 ways to melt rock?
Flux melting, decompression, application of heat
How much does lithostatic pressure increase with depth?
For every ~3km in depth, pressure increases by ~1 kbar
Lateral continuity
Formations are still continuous even in eroded area spans
What is an metamorphic rock?
Formed by recrystallization of other rocks under heat and pressure
What is an sedimentary rock?
Formed from fragments of other rocks
What is the principle of fossil succession?
Fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content.
How is magma composition affected by partial melting or fractional crystallization?
Fractional crystallization and partial melting changes magma from being mafic to felsic.
What component of the cryosphere is the most extensive?
Frozen ground
What are three intrusive igneous rocks?
Gabbro: low Si, mafic (Mg + Fe) Diorite: intermediate Si Granite: high Si, felsic
What is the eruption style of a volcano that is located on a hotspot?
Gentle, effusive eruption style
Glacial positive balance
Glacier advances, sea level falls
What control's a glacier's speed?
Glacier mass balance
Glacial negative balance
Glacier retreats, sea level rises
What are the two largest freshwater reservoirs on Earth?
Glaciers and polar ice
What are the components of the cryosphere?
Glaciers, permafrost, and sea ice
What variables determine hydraulic conductivity?
Grain size, grain shape and, fluid viscosity
What are the physical properties of continental crust?
Granitic Composition Less dense Thicker (35-40 km)
Why does subduction occur?
Gravity causes older, denser oceanic crust to sink beneath less dense continental crust
How common are great earthquakes (Mw > 8)? How frequent are lower magnitude Earthquakes?
Great ones aren't so common, lower magnitude EQs are EXTREMELY common
What are some hazards from earthquakes?
Ground shaking- building damage Landslides and rockfall Sediment Liquefaction: Fire Tsunamis
Normal fault (What is the definition and stress regime?)
Hanging wall moves down (below) relative to the footwall Stress regime: Extension (lengthened/expanded by movement of the fault)
Reverse fault
Hanging wall moves up (above) relative to footwall Stress regime: Compression (shortened/narrowed by movement of fault)
What are the 3 main causes (drivers) of metamorphism
Heat, Pressure, and Hydrothermal fluids
What does felsic mean?
High silica and light coloration
Volcanic domes or plugs
High viscosity, small, steep
Pore connectivity
Higher connectivity, higher permeability
We can assess hazard from
History of earthquakes Monitoring of earthquakes Monitoring plate motion Understanding plate tectonics context and subsurface structure
Types of Non-Foliated Rock
Hornfels (silicates) Quartzite (quartz) Marble (calcium carbonate)
Where are hot spots relative to tectonic plates?
Hot spots are fixed relative to plates moving around on the surface
Hydrothermal Fluids
Hot water with dissolved ions and volatiles
What differs between the inner planets and the outer planets of the Solar System?
Hotter (inner) region where "refractory" materials dominate (solidify at high temperatures), while the Frost Line separates Colder (outer) region where volatiles (gases and ices) dominate
What were the objections to Wegener's continental drift theory?
How do continents move? Why do continents move? Coastal erosion by waves should erode coastline shapes
How is radioactivity used as a clock to date rocks?
If we know the half-lives of both the parent and the daughter atoms, we can determine the age of a rock by looking at the ratio of parent to daughter atoms. This picture should help.
Oxidation/hydration cracking
In biotite tetrahedral sheets Iron oxidises and biotite expands
What is the ratio of accumulation area to total glacier area for a stable glacier?
In stable glacier, accumulation at least 60% of glacier area
What is the moment magnitude (Mw) of an earthquake?
Index is called Moment Magnitude Mw Reported on logarithmic scale
What is an example of an active collision zone on Earth now?
Indian subplate combining with Eurasian plate
Formation
Interval of sedimentary strata composed of a specific rock type or group of rock types that can be traced over a wide area
What are the 3 main minerals found in mafic magmas?
Iodine, Pyroxene, Plagioclase
Oxidation
Iron reacts with water to make iron oxides
What are the three most abundant elements in Earth (by mass)?
Iron, Silicon, Oxygen
Confined Aquifer
Isolated from the Earth's surface. An aquifer surrounded by a layer of impermeable rock or clay that impedes water flow
Why is the High Plains Aquifer important to the U.S.?
It makes up 30% of groundwater irrigation
Who wrote "we find no vestige of a beginning, no prospect of an end", and what were they talking about?
James Hutton; geologic time and the principle of uniformitarianism
What is a supercontinent?
Jigsaw puzzle-like fit of continents together
What causes sediments to mobilize?
Landslides, rock fall, debris flows and creep
What is a shield?
Large area of exposed Precambrian crystalline igneous High-grade metamorphic rocks that form tectonically stable areas.
Breccia
Large clasts compiled together (Angular)
Conglomerate
Large grains compiled together (Rounded)
Pore Size
Large pores, higher permeability
What kind of lava is associated with volcanoes located on hotspots?
Lava is basaltic, mafic, low silica content, low viscosity
What is foliation?
Layers (visible in gneiss or schist) or alignment in rock form by a preferred orientation (in metamorphic rocks) Alignment of platy minerals (alternating light and dark minerals)
Exfoliation jointing
Like an onion skin, joints are fracture planes. Unloading is erosion taking load off rock. Created by erosion unloading; only found in strong, otherwise flawless rock.
Biochemical Sedimentary Rocks
Limestone and chert
Pattern of sedimentary bedding that shows transgression?
Limestone, Shale, Sandstone
How does the mobility (viscosity) of lava vary with silica content?
Low silica = low viscosity (runny and thin) High silica = high viscosity (thick)
What does mafic mean?
Low silica and dark/colored coloration
Shield volcanoes
Low silica content, low viscosity, gentle slopes
What is the "cone of depression"?
Lowered water table around a well
Organic Sedimentary Rock
Made of carbon-rich relics of plants or other organics
Clastic Sedimentary Rock
Made of particles from other rocks
How does magma differ from lava?
Magma is molten rock beneath Earth's surface; lava is molten rock at Earth's surface.
What is magnetic inclination?
Magnetic reversals recorded in the rocks. The field lines dip
What is the Mantle's composition and density?
Mantle • O + Si + Mg • 2/3 of the mass of Earth • Dense silicate minerals • Density: 3.3 to 5.4 g/cm3 • Extends to 2900 km depth
Where are transform boundaries found?
Many transform boundaries are found on the seafloor, where they connect segments of diverging mid-ocean ridges.
Nonconformity
Metamorphic or igneous rocks in contact with sedimentary strata
Metamorphic Rock
Metamorphic rock is rock formed from pre-existing rock (the protolith), by solid state change (no melting), in response to changes in its environment.
Where are metamorphic rocks generally found?
Metamorphic rocks are formed mainly in the lithosphere, wherever there is high pressure and high temperature. ... Metamorphic rocks are most abundant at convergent plate boundaries, but can occur in other areas where there are increased pressures and/or temperatures
What is a Mid-Ocean Ridge?
Mid-ocean ridges form long chains of mountains that rise up from the ocean floor.
Dissolutions
Minerals dissolve in water producing salt solutions and often clay minerals.
What are the main steps of formation of our Solar System?
Nebula Protoplanetary Disk Rings of Planetesimals The Eight Planets
What are the consequences of negative or positive mass balance?
Negative mass balance over many years leads to glacier retreat, while a positive balance over many years will advance.
Where would the oldest rocks be found relative to the fold axis in a Syncline?
Oldest on the limbs, youngest on the axis
Where would the oldest rocks be found relative to the fold axis in an anticline?
Oldest rocks on the axis, youngest on the limbs
In short, why do earthquakes occur repeatedly on the same failure surface?
Once a failure has occurred, that location is a plane weakness, makes it more likely for another failure to occur there, easiest place for a slip to be accommodated
What does "protolith" mean?
Original rock before change in property occurred
Products of Chemical Weathering
Oxide minerals & Clay minerals
What does it mean when rocks are red?
Oxidizing, most likely on land
What are the three most abundant elements in Earth's crust (by mass)?
Oxygen, Silicon, Aluminum
Which is the faster of the two body waves?
P waves are faster than S waves
Basalt Eruption Style
Pahoehoe, a'a, pillow lava
What is the Wadati-Benioff zone?
Pattern of shallow-deep EQs map the subducting slab
What is permafrost?
Perennially (2 or more years) frozen ( below 0 degrees celsius) ground
What is Peridotite, and where is it the dominant mineral?
Peridotite is a super ultramafic mineral that is predominantly located in the mantle
Disconformity
Periods of non-deposition and erosion, without tilting or folding of the rocks, produce a disconformity. Sedimentary layers above and below the disconformity are parallel.
Permeability
Permeability describes the ease of fluid movement or flow in a rock
Why are planets spherical, rather than potato or snowman shaped?
Planets must have enough mass and be made up of a material that is able to deform under the influence of gravity.
How does glacier ice form?
Plastic deformation
What is the asthenosphere and what are its physical properties?
Plastic layer Warmer (temperature >1280°C)
Differentiate plastic deformation and brittle deformation
Plastic: Recoverable deformation Brittle: Unrecoverable deformation
How do plates differ from continents?
Plates are bigger than continents
What are divergent plates?
Plates move apart Hot mantle (asthenosphere) rises, melts to form magma Magma rises Forms new crust with characteristic layering Bottom: Gabbro Middle: Basalt dikes Top: Pillow basalt Cooler and thicker lithosphere sinks into the asthenosphere
What are convergent plates?
Plates move toward each other Old oceanic plates are denser than the asthenosphere Plate bends, and sinks down into the mantle Earthquakes (breaking rock on faults) occur along the subducting slab (plate)
What are transform plates?
Plates slide past each other Earthquakes are generated No volcanic activity
What is the hypocenter (or focus) of an earthquake?
Point underground where earthquake occurred
What are the names of the 5 mass extinctions?
Present Cenozoic - Age of mammals 65.5 MYA - mass extinction (meteorite impact) Mesozoic - Age of dinosaurs (Reptiles) 251 MYA - mass extinction (volcanism) Paleozoic - Age of Marine Organisms 542 MYA - Cambrian explosion (dramatic increase in abundance, complexity, diversity of life)' Precambrian Late - age of soft-bodied life Early - age of single-celled life
Lithification
Process of sediments compacting under pressure.
What is groundwater recharge?
Process of water going through the soil and back to the aquifer
Glacial Ablation
Processes that remove ice (Melting, evaporation, removal by wind, calving/splitting of icebergs)
Darcy's Law
Q = -K * i * A K is hydraulic conductivity I is delta h/L (head difference and length, basically slope) A is cross section area of tube
Unconfined Aquifer
Reaches the Earth's surface. An aquifer made of porous rock covered by soil out of which water can easily flow
Thrust Fault (What is the definition and stress regime?)
Reverse fault w low angle (less than 30º) Stress regime: Compressive (shortening/narrowed by movement of fault)
What is the lithosphere and what are its physical properties?
Rigid layer 100-150 km thick Cooler (temperature <1280°C)
Foliated Rocks
Rock that contains parallel layers of flat and elongated minerals
Inclusions
Rock that formed before is engulfed in the intruding rock
What is an igneous rock?
Rocks formed from magma (molten rock)
Sedimentary Rock
Rocks made of fragments of other rocks cemented together. Minerals precipitated from water solutions at Earth's surface.
What is the typical organization of sedimentary units from shoreline beaches to deep ocean?
Sandstone Siltstone Shale Mudstone
Pattern of sedimentary bedding that shows regression?
Sandstone, Shale, Limestone
How are sedimentary rocks formed?
Sediment undergoes lithification
Original horizontality
Sedimentary rocks (and sedimentary rocks only) are formed in roughly horizontal layers
What is the Frost Line?
Separates Colder (outer) region where volatiles (gases and ices) dominate.
How deep in Earth do earthquakes occur in transform boundaries?
Shallow
Where is Limestone found?
Shallow Marine
Where is Siltstone found?
Shallow Marine
What is the geoid?
Shape the earth's surface would have if only gravity and rotation were involved, and other forces were absent
What kind of volcanoes are located on hotspots?
Shield volcanoes: low slopes and lava flows
What are the limbs of a fold?
Sides or flanks of folds
What chemical composition does chert have?
Silica
What is Granite?
Silica Content: Felsic/High Texture: Course Freezing Temp: Low (900-600C) Density: 2.5 g/cm³
What is Rhyolite?
Silica Content: Felsic/High Texture: Fine Freezing Temp: Low (900-600C) Density: 2.5 g/cm³
What is Diorite?
Silica Content: Intermediate Texture: Coarse Freezing Temp: Medium/Low (1000-900C) Density: 2.8 g/cm³
What is Andesite?
Silica Content: Intermediate Texture: Fine Freezing Temp: Medium/Low (1000-900C) Density: 2.8 g/cm³
What is Gabbro?
Silica Content: Low/Mafic Texture: Coarse Freezing Temp: High (1100-1200) Density: 3.0 g/cm³
What is Basalt?
Silica Content: Mafic/Low Texture: Fine Freezing Temp: High (1100-1200C) Density: 3.0 g/cm³
What are Feldspars?
Silicate Mineral Family Silica Content: High Mg-Fe Content: Low-Felsic Color: Light Density: 2.6 g/cm³ Melting Point: High -> 1000-1200C
What are Pyroxenes?
Silicate Mineral Family Silica Content: Low Mg-Fe Content: High-Mafic Color: Dark Density: 3.2 g/cm³ Melting Point: High -> 1000-1200C
What are Amphiboles?
Silicate Mineral Family Silica Content: Low-Medium Mg-Fe Content: High-Mafic Color: Dark Density: 3.2 g/cm³ Melting Point: High -> 1000-1200C
What are Olivines?
Silicate Mineral Family Silica Content: Lowest Mg-Fe Content: Very High-Ultra mafic Color: Green Density: 3.3 g/cm³ Melting Point: High -> 1000-1200C
What are Micas?
Silicate Mineral Family Silica Content: Medium Mg-Fe Content: High-Mafic Color: Dark or Light Density: 2.8 g/cm³ Melting Point: High -> 1000-1200C
What is Quartz?
Silicate Mineral Family Silica Content: Very High Mg-Fe Content: No Cations Color: Light Density: 2.65 g/cm³ Melting Point: Lower -> 650-900 C
What are the most abundant class of minerals in the Earth's crust and mantle?
Silicate minerals make up 95% of the crust and mantle, and of these, feldspars and quartz make up 75% of the crust
What kind of fold is a monocline?
Simple bend makes it not horizontal Only one limb Product of a reverse fault that occurred deep in the crust
How does grain size vary with energy or transport distance?
Size decreases with more transport distance and lower energy
How does ice flow?
Sliding
What do we mean by geologic structure?
Small scale deformation of earth's crust
Thermal expansion cracking
Spikes in surface temperature cause rock to expand (caused by fire, solar radiation, air temp)
What is the epicenter of an earthquake?
Spot above hypocenter above ground
How fast do plates move, and how do we know?
Spreading centers: 3-15 cm/yr Absolute rates measured directly from GPS receivers
What type of volcanoes are located on a convergent margin/subduction zone?
Stratovolcanoes
What is stress, and how does it differ from force?
Stress = Force acting over an area
What happens in collision zones?
Subduction zone is closed up Subducted slab (oceanic lithosphere) detaches Slab sinks into mantle Continental crust collides, thickens, fractures, forming Collisional mountain belt
Mid ocean ridges (In terms of volcanoes)
Submarine eruptions, basaltic lava types. In middle of rift---> not much volcanic edifice
Where would the oldest rocks be found in a bowl?
Syncline = Oldest rocks on the outside
What kind of fold is a bowl?
Syncline with center point
How is it possible to accumulate thousands of meters of sediments in an area?
Tectonic shifts that cause rifts, basins, and any other thinning of the crust tend to shift some of the mantle out of the way, creating space for sedimentation
What does dip measure?
The acute angle that a rock surface makes with a horizontal plane.
Relative Age
The age of a rock compared to the ages of rock layers
Absolute Age
The age of a rock given as the number of years since the rock formed.
How does the age of the ocean change with distance away from the mid-ocean ridge axis?
The age of the ocean increases the further it gets away from the MOR
Saturated zone
The area of permeable rock or soil in which the cracks and pores are totally filled with water.
Why doesn't the low spot fill with sediment?
The asthenosphere that is below the sediment, deforms from the weight of the sediments above.
How does the density of the Earth compare to the density of a typical rock?
The average density of a rock is ~2.7 g/cm³ while the density of the Earth as a whole is 5.5 g/cm³
What is a footwall?
The block of rock that forms the lower half of a fault
How do we know about the Cretaceous Interior Seaway?
The bottom of the seaway had very little oxygen, which meant that any of the unique sea creatures that died were fossilized
How does the depth of the ocean change with distance away from the mid-ocean ridge axis?
The depth of the ocean increases the further it gets away from the MOR
What does strike measure?
The direction of the line formed by the intersection of a rock surface with a horizontal plane
What is the axis of a fold?
The intersection of the axial plane with one of the strata of which the fold is composed
Why is the magnetic field important for life on Earth?
The magnetic field protects the Earth and the living creatures on the planet from solar wind.
What is radioactive decay?
The process in which unstable isotopes decay into other elements and emit radiation as they attempt to become more stable
Stellar Nucleosynthesis
The production of new, larger atoms by fusion reactions in stars created atoms Li -> Fe
Supernova Nucleosynthesis
The production of new, larger atoms by supernovae. Created atoms larger than Fe
What are fossils?
The remains or traces of organisms preserved in rocks
What is non-permanent deformation of rocks/surfaces?
The rock can return to its original shape when the stress is removed
What is permanent brittle deformation?
The rock cannot return to its original shape when the stress is removed
What is elastic deformation?
The rock returns to its original shape when the stress is removed
What kinds of igneous rocks are associated with convergent boundaries?
The rocks are mostly mafic
What kinds of igneous rocks are associated with divergent boundaries?
The rocks are mostly mafic
What do we mean by "geologic history"
The sequence of events recorded in rocks and cross-cutting relationships
Primary porosity
The space that remains between solid grains or crystals immediately after sediment accumulates or rock forms.
What is paleomagnetism?
The study of the magnetic properties of rocks. Features of the magnetic field are preserved in volcanic rocks (and some sedimentary rocks)
How does thickness of lithosphere change with distance away from the mid-ocean ridge axis?
The thickness of lithosphere increases the further it gets away from the MOR
How does thickness of sediment change with distance away from the mid-ocean ridge axis?
The thickness of sediment thins the further it gets away from the MOR
What is the half-life?
The time it takes for half of a group of a radioactive element's isotopes to decay
What is drainable water in storage?
The total amount of water that can be withdrawn in an aquifer.
What is an earthquake?
The vibration of Earth produced by the rapid release of energy
What is specific yield (with respect to groundwater)?
The volume of water released per volume of aquifer
What feeds springs and most flow in rivers (especially that between storms and snowmelt)?
The water flow from recharge areas to discharge areas, or where the water table intersects the ground surface
What are the two largest uses of water in the US?
Thermal electric power and irrigation
What does it mean when rocks are black/blue?
They are organic rich with little to no oxygen
Glacial total net balance
Total net balance = accumulation - ablation
Biological processes
Tree roots, fungal hyphae growing towards and through minerals.
What is the current rate of sea level rise?
Trend is 3.1 mm/year in sea level rise
What kind of fold is an anticline?
Up Fold, limbs dip away from the hinge
Tectonic Jointing
Uplift and displacement of the crust breaks rock, forming faults and pervasive sets of fractures called joints.
How are major time period boundaries defined?
Using fossils and the principle of superposition
What composition do volcanoes on a convergent margin/subduction zone have?
Volcanic arc has intermediate silica content, viscous magma where bubbles cannot escape easily
Why are volcanoes and trenches both associated with convergent boundaries?
Volcanic arcs parallel the trench, sit on the over-riding plate
What is the difference between a continental volcanic arc and an island arc?
Volcanic island arc forms on the overriding plate, while Continental volcanic arc forms on the continental overriding plate
Frost-cracking
Water in cracks might not freeze at exactly 0º C Water can migrate through porous material to freezing area.
What is a marine regression?
Water levels fall away from the shore
What is a marine transgression?
Water levels rise towards the shore
What are parent and daughter atoms?
We can measure the ratio of parent and daughter atoms to determine the geologic age. Parent atoms are the original isotopes, whereas daughter atoms are the newer isotopes.
Sediment Liquefaction
When pressure in the water in the pores push sediment grains apart so that they become surrounded by water and no longer rest against each other, and the sediment becomes able to flow like a liquid
What is the hinge line of a fold?
Where the limbs of the fold meet
How did post-WWII research lead to development of the theory of seafloor spreading?
World War II development of sonar led to mapping and revealed seafloor topography
Cross-cutting relationships
Younger features cut across older ones
Superposition
Youngest sedimentary rocks on top
What is a volcanic arc?
a row of volcanoes that forms on the overriding plate near a subduction zone
What does crystal structure mean?
atoms are arranged in a repeated, orderly pattern
S-Waves
back and forth, body waves, secondary waves, slower than p-waves
Types of sedimentary rocks
clastic, chemical, organic and biochemical
Oblique slip fault
combination of strike-slip and dip-slip
What are the three types of plate boundaries?
divergent, convergent, transform
What is the eruption style of a volcano that is located on a convergent margin/subduction zone?
explosive eruption: tephra (ash+lapilli+bombs)
What is an accretionary prism?
faulted sediments scraped up by subduction
What does geothermal gradient mean, and what is a typical geothermal gradient?
geothermal gradient = change in temperature with depth dt/dz (t is temp in C, z is depth in km) Usually about 25 C/km, but it varies from place to place Typically, west US has higher geothermal gradients
What is an abyssal plain?
large flat areas on the ocean floor
Intraplate Volcanism
mantle plume (hotspot), volcanic ocean islands
Left Lateral Fault
straddle fault→ Left foot comes towards you
Right Lateral Fault
straddle fault→ Right foot comes towards you
P-Waves
up and down, body waves, primary wave, travels through all layers of earth
What are the categories of organization of silica tetrahedra that define the 6 silicate mineral families?
• Silica content • Organization of silica tetrahedra • Types of cations present • Density