ESCI 1001 REVIEW
What is the mineral group in which the silicate tetrahedra form sheets?
Micas and clays
Intrusive rocks and their different shapes?
Minor intrusions and plutons: -Dikes -Sills -Laccoliths -Volcanic pipes and necks Major plutons -Batholiths -Stocks
P-Waves
Primary waves: -Compression and expand through material -Fastest -Temperature changes density -Can travel through solids, liquids, and gases -Parallels the direction of the seismic wave -PROPAGATE IN LIQUIDS BUT SLOW DOWN
Driving Force Pressure
Pressure -Confining Pressure (for sedimentary rocks): Forces are applied equally in all directions. Causes the spaces between mineral grains to close. Deeper, Pressure increases -Directed Pressure (pushing one side): Change in mineral orientation(re-alignment/reorientation), composition, and texture ---confining pressure (related to depth), change in confining pressure--> change in minerals ---application of directed pressure--> change in mineral orientation
What is the nucleus of an atom made of?
Protons (+ charge) and neutrons (no charge) **Nucleus is positively charged **Protein gives atomic number
What is the mineral group in which the silicate tetrahedra form single chains?
Pyroxenes
What is the mineral group in which the silicate tetrahedra form a 3D framework?
Quartz and Feldspar
Why does the density of olivine ((Fe1Mg)2SiO4) vary whereas the density of quartz (SiO2) remain constant?
Quartz remains constant because it can't move. The density is not changing from being in Earth's surface. Olivine changes density due to high pressure and high temperature
Where does metamorphism occur? (what tectonic settings?)
Regional: Characterized by scale or geological setting -Convergent Margins: arcs(batholiths form in crust), collisions -Divergent Margins: ocean ridges Contact: Characterized by local, scale of meters -Hydrothermal (geo): Hot fluids, heat from earth -Fault Zone: Earthquakes can happen from rupture. Changing pressure and temperature. (super hot, cool quickly can form gas. sill is parallel to sedimentary rocks below). Continental Subduction Zones -Increase in pressure and temperature -Pressure increases more (HIGH P) -lowest temperature at highest depth (cold) Divergent Plate Boundaries (rocks near by) -Decrease in pressure and temperature stays the same (HIGH T) -highest temperature at lowest depth (hot) Continental-Continental Convergent -Increase in temperature and pressure (HIGH T AND HIGH P) -(moderately hot/cold)
What is erosion?
Removal of weathered material (sediments) from landscape
Radiometric Dating
a method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope
Granite (protolith to metamorphic)
-Igneous -Protolith: Granite -Metamorphic: Metagranite -High SiO2
M-Discontinuity
(Moho) discontinuity at the base of the crust. Marks the break from the crust to the mantle
Methods for determining Absolute Age
- Rates of erosion - Rates of deposition - Varves
What TWO pieces of information/data do you need to know in order to be able to calculate the age of crystallization of a rock or mineral using radiometric (isotopic) methods?
-Half-life of isotopic system (=rate of decay of parent to daughter) -Different types of isotopes (parent and daughter)
Under what set of circumstances would a thick layer of weathered rock/soil be produced? What combo of variables would produce thin/no soil?
-High temperature and water -Combo of variables: --Any temperature with no water or low temperature with water
Why is it difficult/impossible to get an absolute date from a very young rock using an isotope system with a very long half-life (for example, a half-life in the billions of years)?
-Absolute age dating is based upon the decay of radioactive (unstable) isotopes. -Not enough parent will have decayed for daughter concentrations to be reliably measured.
What type of metamorphic rock forms only in subduction zones? Give a rock name and describe the combination of pressure and temperature conditions of metamorphism. Why are these rocks not formed elsewhere in the Earth?
-Basalts- Blueschist -High pressure, low temperature -The cold water from the subduction zone best explains why there would be low temperature while there's high pressure.
What are the 3 compositional types of magma? What is the main difference in their composition?
-Based on silica content: --Basalt --Andesite --Rhyolite -Main difference is the amount of gas inside ----Determines their explosiveness
Why is frost wedging more efficient in a place like MN or CO than in the Arctic?
-Because MN and CO have a variety of temperatures. It freezes and thaws every night in colder months (more action) rather than just once a year like the Arctic
Why do basaltic volcanoes erupt non-explosively but si-rich volcanoes erupt explosively?
-Because basaltic volcanoes have less gas and SiO2 content, making it less explosive from low pressure -Si-rich volcanoes have probably rhyolite which is high in SiO2 and has more gas, making it more explosive from high pressure -Rhyolite magma is vicious and clogs volcano, building up the pressure
Why does Yellowstone National Park have geysers and hot springs?
-Because geo-thermal energy is near the surface and theres lots of water and strong rock
Why are high SiO2 intrusive rocks (granite) common, but low SiO2 intrusive rocks (gabbros) relatively rare?
-Because high SiO2 intrusive rocks like granite take a hotter temperature to melt. Whereas low SiO2 intrusive rocks like gabbro probably already melted and conjoined with another igneous rock in the magma
Why are the volcanoes on the big island of Hawaii shield volcanoes?
-Because they're gently sloping mountains produced from a large number of generally very fluid lava flows -Known as "quiet" volcanism -Lava flows long distances from fissures
Why do elements combine? For example, hydrogen and oxygen to form water?
-Both want to have 8 electrons and become stable
How can we determine the protolith (parent rock) of a metamorphic rock? (What characteristic of a rock does not change during metamorphism?)
-By looking at the original texture or when replaced with metamorphic texture, look at the bulk chemical composition of the rock -the chemical composition does not change
Limestone (protolith to metamorphic)
-Chemical sedimentary -Protolith: limestone -Metamorphic: marble -No SiO2 -Super fine grained
Shale (protolith to metamorphic) Know the progression of rocks that form during metamorphism of a shale, from low to high grade
-Clastic sedimentary -Protolith: mudstone (shale) -Metamorphic: look down (: -High SiO2 and other minerals low to high grade: -(Mudstone) Shale --Fine grained *Shale+Heat+Pressure=Slate -Slate (low) --Super fine grained --Low temperature forms --Used for roofs, tile, walkways *Slate+Heat+Pressure=Schist -Schist (medium) --Minerals/Crystals grown larger --Tiny micas (if grows can see sheets) --Clay transformed --Garnets --Texture develops in metamorphic rocks that can align themselves (foliation) --Barely can see in slate *Schist+Heat+Pressure=Gneiss -Gneiss (high) --Foliation stronger/stronger texture increases from increase in temperature and pressure, realigning minerals under metamorphism --Directional (alignment of layers) --Static (just grow) --Dark and light layers (Biotite and Amphibole, Quartz and Feldspar Plagioclase) --Separation of minerals *Gneiss---> Migmatite -Migmatite (partially melted rock. Crossed over to igneous processes here) --Felsic bits melt before mafic rocks --Granite: high felsic --Really common at convergent and continental-continental boundaries
How do calderas (big craters) form?
-Collapse triggered by emptying magma chamber beneath the volcano
Composition of Earth
-Core: Iron (Fe) and Nickel (Ni) and rest of Earth is silicate minerals (SiO2) -Upper part of mantle: silicate olivine -Continental crust: Feldspar and Quartz -Mantle and deep crust: Garnet, Pyroxene, Olivine -Mantle and minor crust: Amphibole -Crust: silicon and oxygen elements
Shadow Zones
-Direct arrivals of waves -S-Waves can't pass because shear -P-Waves change direction and that's why they go in other directions after going through the core
Why is an element positively or negatively charged?
-Elements normally have a neutral (no) charge atom, but the addition or removal of electrons cause the atom to become an ion (charged atom). -If electrons are transferred= ionic bonding -If electrons are shared= covalent bonding -Adding electrons= (Non-metals) "-" charge (anion) -Removing electrons= (Metals) "+" charge (cation)
Rhyolite
-Extrusive -Fine grained -High in SiO2 content
Andesite
-Extrusive -Fine grained -Intermediate in SiO2 content
Basalt
-Extrusive -Fine grained -Low in SiO2 content
What are the main controls on the rate and extent of chemical weathering?
-Global temperature and global precipitation
Basalt (protolith to metamorphic)
-Igneous -Protolith: basalt -Metamorphic: metabasalt -Low SiO2 -Divergent/convergent -Basalt and gabbro=oceanic crust -Eclogite --moderately low T and high P -Blueschist= basalt metamorphosed in a subduction zone --high T and low P
What is obsidian? Is it associated with Si-rich or Si-poor volcanoes?
-Igneous rock formed from cooled lava (volcanic, on surface) -Si-rich volcanoes
Compare brittle and ductile deformation of rocks: where does each type of deformation generally occur in the Earth?
-In ductile deformation, a gradually increasing force will cause the rock to undergo smooth and continuous plastic deformation. The rock will contort and change shape without fracturing -Mantle, depth of about 40km -In brittle deformation, a continuous, force is applied to a rock. As the force is gradually increased, little change occurs in the rock until suddenly it fractures -Crust, depth of about 15km
Peridotite
-Intrusive -Coarse-grained -<50% SiO2 (low SiO2 content) -Dark color
Granite
-Intrusive -Coarse-grained -High in SiO2 content
Diorite
-Intrusive -Coarse-grained -Intermediate in SiO2 content
Gabbro
-Intrusive -Coarse-grained -Low in SiO2 content
Importance of carbonate?
-It occurs near earth's surface and participates in the composition of the atmosphere by either removing or adding CO2 with implications for climate evolution
Why does granite appear much less weathered than limestone?
-Limestone was affected are because of its mineral property (calcite) Which is weaker than granite and the minerals its made up is quartz, feldspar, mica)
How do sediments become sedimentary rocks?
-Lithification ---Compaction and cementation of particles. Then cementation occurs
Does lithosphere thicken or thin as it moves away from mid-ocean ridges? Why?
-Lithosphere thickens because asthenosphere solidifies on to the underside of the plate as the plate cools -Ocean lithosphere becomes more dense than asthenosphere beneath, thus old oceanic lithosphere will sink into the asthenosphere if it gets the chance
What happens to plates at mid-ocean ridges?
-Magma is created from convection currents rising in the mantle beneath oceanic crust where two tectonic plates meet at a divergent boundary -Ridge-Push: --Weight of the ridge pushes the plate away towards a subduction zone -Slab-Pull: --At subduction zone, weight of plate is being subjected (pulled) below the overlying plate. Drags the rest of plate behind it
What is metamorphism?
-Means to "change form" -Transition of one rock into another by temperature and or pressure -Changes in mineralogy, texture, and sometimes chemical composition -Has a parent rock
How do metamorphic rocks relate to igneous and sedimentary rocks? (in other words: where does metamorphism fit into the rock cycle?)
-Metamorphic rocks form when sedimentary, igneous, or other metamorphic rocks are subjected to heat and pressure from burial or contact with intrusive or extrusive igneous rocks. -Most of the crust has been metamorphosed -Helps us understand tectonic processes and has an important role in global geochemical cycles (adds fluids releases CO2)
What does cross-bedding tell you about how a sediment was deposited?s
-Motion of dunes via wind or water
The generation of magma involves partial melting of rocks. Why do rocks only partially melt rather than completely melt?
-Partially melt due to rocks being made of different mineral species, each mineral has its own properties, varying what temperature that it melts
How can physical and chemical weathering work differently
-Physical weather breaks up rock into smaller pieces, creating more surface -Chemical weathering creates area of weakness that may help the physical weathering process
What drives metamorphism in a subduction zone?
-Pressure -Sediments and oceanic crust are subducted fast enough that pressure increases rapidly while the rocks stay at relatively low temperature -High pressure metamorphism
Principles of Seismology
-Rocks break--> Has earthquake--> energy is released-->creates seismic wave -Uncovered two types of layering in earth: ---Compositional (core, mantle crust) ---Rheological (lithosphere, asthenosphere)
How do pyroclastic rocks form?
-Rocks formed from fragments blown out of a volcano during an explosion that were then packed or welded together
What are the mineral classes?
-Silicates -Oxides -Sulfates -Sulfides -Carbonates -Native Elements -Halides
What drives metamorphism next to igneous intrusions?
-Temperature -Crystallizes rock in magma -Magma intruded environment by increasing temperature of rock
What are some of the driving forces of plate tectonics?
-Temperature- heat rising from core causing plates to move -Friction -Gravity -Tides
Which is more important in affecting what minerals are stable in a rock: confining pressure (pressure related to the depth of a rock) or directed pressure? Which is more important in determining the texture (for example, orientation of minerals)? Explain.
-Texture=more alignment of mineral -Stable in a rock: --Confining pressure, the change in confining pressure increase in pressure and temperature will cause a change in minerals -Texture/Orientation: --Directed Pressure, the orientation of the minerals will be re-aligned/re-oriented. The texture will also change.
If you found a shale containing delicate leaf fossils, what can you conclude about the environment of deposition? Describe the environment in general terms (low/high energy, water/no water) and then name some possible settings
-The environment would be relatively deep calm water -Must be low energy in order to preserve the fine sediments -Maybe occurred at continental shelves at sea edges or near the shores of a large lake could be possible settings
If you saw a big crack in a rock, how would you determine if it were a fault or just an open fracture?
-The movement is often evident in a fault because a displacement of strata can be seen. Or sometimes scratch marks can be found on the fault plane indicating both a movement and direction. -Fracture is confined to one rock formation whereas a fault is not
What types of materials can be dated by numerical methods involving counting physical features?
-Tree Ring Dating (Great Basin Bristlecone Pine)- based on annual growth rings produced by trees. -Fission Track Dating - based on counting scars left by nuclear decay products in minerals -The Magnetic time scale, based on reversals of the Earth's magnetic field.
What happens to plates at subduction zones?
-Two plates collide, one bends and slides underneath the other, curving down into the mantle. Earthquakes and volcanoes can occur
Describe the type of volcano that erupts pyroclastic rocks?
-Unconsolidated tephra or consolidated agglomerate project lava in the atmosphere violently
Radiocarbon Dating
-Used to find the age of once living materials between 100 and 50,000 years old. -Useful for determining age of human fossils and habitation sites -Carbon12, Carbon13, Carbon14
Seismic wave velocity
-Wave velocity increases as depth increases -Velocity of wave changes every time a layer is hit
How does temperature change with increasing depth?
-When depth increases, temperature increases from pressure increasing -Temperature rises in the oceanic lithosphere, asthenosphere, and mesosphere
What drives metamorphism at divergent zones (seafloor metamorphism)?
-hot fluid, cold sea water, hot magma -Cold seawater descends -Heated water rises as steam -Serpentinization of oceanic basalt - form of metasomatism occurring at mid-ocean ridges - seawater infiltrates hot basaltic lava, is heated, circulates through the newly forming oceanic crust by convection, and reacts with and alters the chemical composition of the basalt
3 main general agents of erosion?
-wind -ice -water (driven by slope/gravity)
What are the three types of rocks? Process in the rock cycle?***********************
1. Igneous 2. Sedimentary 3. Metamorphic
What are the 3 types of chemical weathering?
1. Oxidation: iron rich minerals (rusting) 2. Dissolution: carbonate minerals 3. Hydrolysis: silicate minerals (dominate process because it effects feldspar which is what most of the crust is made of)
What are the main factors (driving forces, variables) in metamorphism?
1. Parent rock (protolith) 2. Driving force: Temperature, pressure, and fluids 3. Peridotite (mantle rock): driving force is fluid and heat
What methods are used for determining relative ages of geologic events?
1. Superposition: oldest at bottom, youngest rock at top -Unconformity: missing sedimentary rock ----break between two rocks ----missing time 2. Original Horizontality: sedimentary layers are deposited horizontally -tilting younger than rock -folded sedimentary layers 3. Cross Cutting: cutting -rocks have to been there first to cut them (ex. faults) -cross-cutting feature is younger than rocks they cross-cut -Igneous intrusions ---Igneous dike is youngest 4. Inclusions: older, rocks had to exist before taken by magma -Always older 5. Faunal Succession: -Sense of where we are relative on time scale -Handy when geologist want to correlate rocks from other different rocks -Index fossils: ----restricted occurrences in time
Varies
A banded layer of sand and silt that is deposited annually in a lake. Coarse summer layers and an overlaying fine layer.
Why do igneous rocks that crystallized above ground tend to be fine-grained and those that crystallize at depth tend to be coarse-grained?
At depth- cools slowly and grains in the magma have time to grow At surface- cools very fast and grains don't have time to grow
Radioactive Isotopes
Atoms that are unstable, meaning they decay, or break down, to form stable atoms of a different element. Emit energy and particles
List the primary hazards of basaltic (shield) and stratovolcano (Si-rich) eruptions
Basaltic Shield: -Thin lava flows built up over a central vent -Low viscosity -Gentle upper slope, steeper lower slope -Little pyroclastic -Si-low Stratovolcano Composite: -Steeper slope -High viscosity -Lots of pyroclastic materials -More explosive -Long times of inactivity -Si-high
Why are high SiO2 volcanic rocks (rhyolite) relatively rare but low SiO2 volcanic rocks (basalts) are common?
Basalts have a low silica content which means they have a low viscosity. It's most common because lava can quickly and easily flow whereas rhyolite is the opposite
Why does peridotite melt at the seafloor spreading center?
Because peridotites rise too fast to cool, the decrease in pressure at the sea floor spreading center melts a large fraction of the mineral.
Rates of deposition
By studying rates of deposition, scientists can estimate absolute age. Not always accurate because rates changes over time or within depositional events
What is the fundamental layering of the Earth - chemical layers/mechanical (rheological) layers?
Chemical Layers: -Crust -Mantle -Core Mechanical (rheological) Layers: -Lithosphere -Asthenosphere -Mesosphere -Outer Core -Inner Core
What are the typical thicknesses of continental crust, oceanic crust, and lithosphere?
Continental crust: 5-70km Oceanic crust: 5-6km Lithosphere: 100km
Think about the three types of plate boundary (divergent, convergent, and transform). What is the dominant stress at each boundary and what type of fault is associated with each?
Divergent -Normal Faults ---Horst (footwall-ranges) and Graben (hanging wall-basin) -Tensile Stress (tension) -Dip slip fault (vertical motion) Convergent -Reverse Faults -Thrust Faults -Compressive stress -Dip slip fault (vertical motion) Transform -Strike slip fault (horizontal motion) -Shear stress
What are the general characteristics of divergent, convergent, and transform boundaries?
Divergent: -Two plates move away from each other -Mountain chains w/ fissures -Volcanic -Shallow earthquakes in a narrow line Convergent: -Two plates collide-can create a subduction or continent collision zone -Subduction Zones: --Trenches --Mountain ranges --Volcanic --Shallow earthquakes at trench, deep below mountains, and in wide line -Continent Collision Zones: --Mountains --Not volcanic --Scattered earthquakes and at random depths Transform: -Two plates slide past each other -Creates a linear fault valley or undersea canyon from rocks breaking from the plates grinding along one another -Earthquakes in a wide boundary zone -Not volcanic -Crust is cracked and broken at transform margins but not created or destroyed
Why does granite that is exposed at the earth's surface have characteristic curving fractures?
Double action of mechanical and chemical weathering. Surface areas increase dramatically
What is the difference between elastic, brittle, and plastic deformation? Which are recorded in deformed rocks? In other words, which are permanent?
Elastic Deformation -Rocks abruptly shift along a fault, snap back to their original shape, releasing the energy stored during their elastic deformation as an earthquake -Shaking of ground from elastic -Reversible: object will return to its original shape and size when applied stress is removed Plastic Deformation -Under high stress and temperature dominating asthenosphere and lower mantle -Dominates as rock warms and is under more pressure from past stresses. Also when elastic strength of the solid is exceeded -Non-reversible -Takes place by brittle or ductile processes -Past stresses used to interpret an area's past plate tectonic history. Brittle Deformation -Rocks break/fracture under stress -If broken in pieces but don't move, called joints. Joints don't reveal anything about past plate motion but are crucial in groundwater flow and waterfall retreat -If broken pieces move relative to one another, called faults. Faults have different stresses that create different types of faults that can interpret a region's tectonic history -Form of plastic deformation, also non-reversible. Occurs when rocks strength is exceeded Recorded in deformed rocks or are permanent: -Plastic deformation and brittle deformation because non-reversible
How do we know about the Earth's interior?
Experimental Petrology -Combining data with seismology (study of seismic waves and their passage through Earth) and data from igneous rocks and meteorites
What is the difference between a fracture and a fault?
Faults require a break in the rock to move whereas fractures do not
What clastic sedimentary rock is composed of fine particles? Which is composed of medium-sized particles? Which is composed of large particles?
Fine: Shale Medium: Sandstone, siltstone Large: Conglomerate
Driving Force Fluids
Fluid composition (move elements) -becomes more soluble from cool fluid, cools down, everything precipitates out -Chemically active fluids: enhance migration of ion and aids in recrystallization of existing minerals. In some environments, fluids can transport mineral matter over considerable distances.
Glacial sediments and fluvial sediments
Glacial: -Called glacial till "tillite" is the rock Fluvial: -Conglomerate, sandstone, organic matter (plant debris, etc.)
Why do shales experience dramatic changes in minerals and textures during metamorphism, but granites subjected to the same metamorphic conditions do not change as much?
Granites are igneous rocks whereas shales are clastic sedimentary rocks.
Where in/on the earth do sedimentary rocks form?
Gravel---> Conglomerate Sand---> Sandstone Silt---> Siltstone Clay ---> Shale
What can we learn from sedimentary rocks?
Help us learn/better understand the history of an area
What are some high energy sedimentary systems? What are some low energy sedimentary systems?
High: -Nearshore, shelf, pluvials (rivers), aeolian (wind), desert, overbook, flooding deposits Low: -Deep offshore, lacustrine (lake), over bank flooding, lagoon deposits
What are the tectonic environments in which the different rocks form?
Igneous: -melted, then cooled. Found where plates diverge and converge. Near volcanoes Metamorphic: -lithosphere with high temperature and high pressure. If pressure and temperature too high, will melt to magma. Mostly found at convergent Sedimentary: -surface on earth. By clastic-pieces of other rocks cemented together or by chemical (precipitation/evaporation). All plate boundaries. Thickest at convergent
Why is weathering important? What effect does it have on the physical environment?
Important because it makes: -Soil: breaks down rocks and mineral to form soil -Life: releases elements from minerals, provides nutrients -Climate: Co2 removed rom the atmosphere -Landscape: Shapes earth's surface -Connects all of earth's systems **Rocks break down into smaller pieces -Rock takes on CO2 sot, the more weathering the less CO2 you have in abundance
What are the cations that hold the silicate tetrahedra together in the mineral olivine?
Iron (Fe) and Magnesium (Mg)
What is the mineral group in which the silicate tetrahedra form double chains?
Iron (Fe), Magnesium (Mg) and Calcium (Ca)
What are the cations that hold the silicate tetrahedra together in the mineral pyroxene?
Iron (Fe), Magnesium (Mg), Sodium (Na), and Calcium (Ca)
LVZ
Low Velocity Zone -In between lithosphere and asthenosphere, seismic waves are slowed down because the top 100km of Earth form a set of rigid plates that move over a softer material
Numerical (absolute) date
Measure parent/daughter ratio --Material must contain both parent and daughter elements --Material can't be too old or too young compared to the half-life of the system NO ALTERATION AFTER FORMATION OF MINERAL
Why are sedimentary rocks commonly layered? (layering=bedding)
New layer indicated a a new condition so rocks are commonly layered because their conditions are changing
3 Major types of sedimentary rocks? Example?
Non-Clastic: limestone --Chemical: precipitated from solution (usually water) --Biogenic: produced by biological activity Clastic: Quartz
How is magma generated at subduction zones?
OCCURS WITHOUT ADDITION OF HEAT!! MELTING OCCURS WITHOUT HEATING -Basaltic and andesitic composition -When plate is subjected under the other plate, rocks undergo new conditions of temperature (decrease temp) and pressure, and melts forming magma. Magma then rises to form magmatic and volcanic arcs *Crust is thickened and heated up at zones of continental collision, results in magma of rhyolitic composition
How is magma generated at divergent zones?
OCCURS WITHOUT ADDITION OF HEAT!! MELTING OCCURS WITHOUT HEATING. -Basaltic composition -Plates move apart, mantle rises and has less pressure on piece of mantle from overlying rock. This causes mantle rocks to move upward, resulting in decreasing pressure, which leads to DECOMPRESSION melting.
What is the mineral group in which the silicate tetrahedra are independent?
Olivine or Garnet
Rates of erosion
One way to estimate absolute age; practical only for geological features that formed within the past 10,000 to 20,000 years. (less reliable because rates may vary greatly over millions of years)
Parent and Daughter isotope
Parent-Original radioactive isotope Daughter- The stable isotope produced by the radioactive decay of the parent isotope. Has a more stable half-life.
What is partial melting? A magma? Igneous rock?
Partial Melting: -melting of a rock starts with melting at the margin of 2 or more types of minerals resulting in a melt fraction and an unmelted fraction Magma: -not completely melting the (parent) silicate rock. Less dense than a parent rock Igneous: -melting of a magma forms igneous rocks when solidifies --Intrusive/Plutonic: forms when magma solidifies deep underground --Extrusive/Volcanic: at earth's surface as lava
What does basaltic lava look like when it has flowed into water (ex. ocean)?
Pillow structure
SiO2 content of igneous rocks affect: color?
Rocks that are high in silica are light whereas low silica means dark colors
S-Waves
Secondary waves: -Changes the shape of the material as they pass -No change in density -Perpendicular to the seismic wave's direction -Shear wave -Can't pass across through liquids or gases -DO NOT PROPAGATE IN LIQUIDS
Why is it possible to obtain an absolute age for the crystallization of volcanic rocks but not for deposition of clastic sedimentary rocks (such as sandstone or conglomerate)?
Sedimentary rocks can best be measured by the dating of volcanic ash. But can't be measured due to the grains being mixed with different ages and significance, as well as their alteration of minerals.
What is the charge of silicon? Oxygen? Silicate tetrahedron?
Silicon: -4 or +4 Oxygen: -2 Silicate tetrahedra: +4
What do sorting and grain shape tell you about the transport history of a sediment or sedimentary rock?
Tell where the rocks were when they were deposited
Driving Force Temperature
Temperature- -Geothermal Gradient: an increase in temperature with depth -Contact Metamorphism: rising mantle plumes, also caused from heating next to an igneous intrusion
List at least 3 variables that affect the deformation of rocks and describe the effects of each.
Temperature: -At high temperature molecules and their bonds can stretch and move, thus materials will behave in more ductile manner. At low Temperature, materials are brittle. Confining Pressure -At high confining pressure materials are less likely to fracture because the pressure of the surroundings tends to hinder the formation of fractures. At low confining stress, material will be brittle and tend to fracture sooner. Strain rate -At high strain rates material tends to fracture. At low strain rates more time is available for individual atoms to move and therefore ductile behavior is favored. Composition -Some minerals, like quartz, olivine, and feldspars are very brittle. Others, like clay minerals, micas, and calcite are more ductile This is due to the chemical bond types that hold them together. Thus, the mineralogical composition of the rock will be a factor in determining the deformational behavior of the rock -Presence or absence of water. Water appears to weaken the chemical bonds and forms films around mineral grains along which slippage can take place. Thus wet rock tends to behave in ductile manner, while dry rocks tend to behave in brittle manner.
Why is there only one Hawaiian Island with active volcanoes and all the other islands are made of extinct volcanoes?
The active volcano is a submarine volcano, below sea level. The other volcanoes are now extinct because they're above sea level and its continually being moved. The active volcano is under a hot spot
Which sedimentary structures form at the top of a sedimentary layer?
The finest layers are at the top, large coarse layers are at the bottom (graded bedding)
Kyanite, Andalisute, and Sillimanite all have the same chemical composition (Al2SiO5), why are these considered different minerals?
They differ in crystal structure, each mineral is stable over a particular range of temperature *Depends on pressure and temperature in which the minerals (polymorphs) were formed
What methods are used for determining relative ages of geologic events?
Uniformitarianism - "present is the key to the past" --Observation -----Relative: observations -----Absolute: tells how much (number/age) Catastrophism -Sudden, violent events that account for much of what we see in the geological record
How does magma viscosity relate to SiO2 content?
Viscosity is the ability to resist flow -In magma, building block silica tetrahedra links together. So more siO2 content, the less runny it is and doesn't flow well. Low SiO2 content has low viscosity and flows High T Low V High SiO2 High V
If you wanted to determine the age of a piece of wood that was thousands of years old, what absolute dating technique would you use? If you wanted to determine the age of a tree that was still growing, what absolute dating technique would you use?
Wood: -Radiocarbon Dating -Short half-life -measurement of the beta decay activity of a buried piece of wood provides a measurement of the time elapsed since it was living and in equilibrium with the atmosphere -Carbon 14 dating (parent) Nitrogen (daughter)- occurs with a constant ratio Growing Tree: -Tree Ring Dating
Isotope
atoms of the same element that have different numbers of neutrons
Disconformity
boundary between horizontal layers of old sed. rock and younger sed. rocks. The layers above disconformity are deposited on an eroded surface.
Angular Unconformity
boundary between tilted layers and horizontal layers.
Old rock dating
isotopes with a long half-life
Young rock dating
isotopes with a short half-life
What is sorting?
size of grains
Non-comformity
stratified rock is on unstratified rock
Half-life
the period of time in which half of a radioactive substance decays to form a daughter isotope.
